Cross-Reference to Related Applications

This application is related to the subject matter disclosed in the following United States Patent Applications which are incorporated herein by reference. Serial No. Filing Date

055,523 09 July 1979

056.129 09 July 1979

056.130 09 July 1979 075,980 17 September 1979 076,310 17 September 1979 086,749 22 October 1979^ 115,715 - 28 January 1980 109,393 03 January 1980 123,389 21 February 1980 056,128 09 July 1979 162,500 24 June 1980

Background of the Invention

Photocopying apparatus employing liquid development have been in use for many years. The first photocopying apparatus employing liquid development in connection with a reusable photoconductor was commer¬ cially available in or about 1975-1976. These apparatus are marketed today by such companies as Ricoh K.K. and Caron K.K. , both Japanese manufacturers, and others. Over the past five years, for the most part, the basic liquid copier system has remained substantially about the same and as a result the quality and reliability of the systems has been similarly unchanged.

In general operation, copiers using liquid developers employ the standard operating elements of most photocopying apparatus employing a dry developer. The copiers have (a) a charging station whereat the reusable photoconductor is charged to a high sensitizing potential; (b) an exposure station whereat the charged photoconductor is exposed to a pattern of radiation, to which it is sensitive, to selectively discharge the pho¬ toconductor surface; (c) a liquid development station for developing the latent image, wherein a liquid deve¬ loper (generally consisting of an insulating liquid in which finely divided particles of toner are admixed), is brought into contact, under the influence of a develop¬ ment electrode, with the selectively charged latent image on the photoconductor; the development station further has a fluid level control element to control the thickness of the developer liquid remaining on the pho¬ toconductor surface as the photoconductor surface leaves the development station; a transfer station for trans¬ ferring the now developed latent image from the photo¬ conductor to a sheet or web of copy material; and a cleaning station whereat residual toner material, left on the photoconductor surface after transfer, is removed or cleaned from the photoconductor surface to present a clean surface to the charging station for the next copying cycle. The now cleaned photoconductor generally has a non-uniform charge pattern undesireably remaining thereon and this charge pattern is neutralized, for example by passing the photoconductor in operative proximity to an AC corona prior to application of the sensitizing DC charge. The copy material, when it is in sheet form, is directed by a sheet feeding system toward the transfer station from a removable cassette or a fixed stack and is removed or picked off the photocon¬ ductor by a sheet pick-off system.

Photocopiers of this construction, employing liquid development have a short paper path and a relati¬ vely small development station volume which both contri¬ bute to a small sized copier system and hence one having a generally lower manufacturing cost when compared to comparable dry copier systems.

On the other hand, in many areas, the liquid copier technology has remained substantially unchanged during the five years in which liquid copiers of this type have been commercially available. For example, commercially available liquid copier systems have suf¬ fered a phenomenon known as "edge deletion" wherein a marginal portion of the copy sheet, for the full length of the sheet, is unable to contact the photosensitive surface and therefore to accept or receive a developed image. This occurs because of the particular methods by which the sheet is pulled off of the photoconductor. Another area wherein improvement is desirable is, for example, the automatic bias system. In most commercial liquid copiers, the bias system measures the charge remaining on the drum after exposure through the liquid developer, and often is ineffective between maintainance calls when developer dries on the charge sensing ele¬ ments. In another area of the present commercial liquid copiers, the liquid level after development is fixed by a roller spaced apart from the drum. The gapping bet¬ ween the roller and drum is set by rotating bearing wheels on the ends of the central roller. These wheels can bind and present a wearing surface to the drum. This causes the gap between the control roller surface and the photoconductor surface to change, unusually quickly, leading to a higher frequency of maintenance calls.

It is therefore a principle object of this invention to provide an improved liquid developer copier apparatus which has lower maintenance requirements and improved copy quality. Another object of the invention is an improved liquid developer apparatus having reduced edge deletion, improved reliability, better controlled operating parameters, and improved bias stability and operation. Other objects of the invention are to pro¬ vide an improved liquid copier apparatus while main¬ taining ease of manufacture, low manufacturing costs, and the high quality of the liquid copier apparatus.

Summary of the Invention

The invention relates to an improved photo¬ copying apparatus wherein many of the operating stations positioned around the rotating drum of the illustrated embodiments have been mutually improved to provide a higher reliability and better output quality liquid copying machine. There is disclosed in this application details of many of the conceptual features which enable this copier to provide improved copy quality. The details of the features disclosed herein are the subject of separate patent applications. The detailed structure disclosed herein is representative of apparatus which enable the several concepts to be advantageously com¬ bined to provide the improved copier of this invention.

In particular, the invention relates to a pho¬ tocopier apparatus having an assembly for scanning an original and forming a latent electrostatic image on a photosensitive surface of a rotating drum. A develop¬ ment station is provided for developing the latent electrostatic image using a liquid developer; a transfer station is provided for transferring the developed latent image to a transfer material; and a cleaning sta-

tion is provided for cleaning the photosensitive surface for reuse. The transfer station has elements for con¬ veying a sheet of transfer material into contact with the photosensitive surface at the transfer station for transferring a developed image from the surface of the drum to the sheet, portions of the sheet successively contacting the surface.

In one aspect, the invention features a transfer station having a sheet stripping apparatus for removing sheet material from the photosensitive surface of the drum and a sheet hold-down assembly working in connection with the sheet stripping assembly for pro¬ viding an advantageous transfer station pick-off with improved copy quality.

The sheet stripping apparatus features a guide member having a sheet contacting blade portion, moveable between a first position in which the sheet contacting portion overlays a marginal portion of the surface at the transfer station for engaging a corner of a leading edge of the sheet conveyed to the transfer station and guiding the leading edge to a transport means. The guide member further moves between a second position in which the sheet contacting portion is removed from its overlaying position with respect to the surface whereby the sheet can, at least at the transfer station, contact the surface at the marginal portion. An assembly is also provided for moving the guide member between the first and second positions.

The sheet hold-down assembly has a support member extending substantially normal to the direction of movement of the photosensitive surface and a sheet hold-down member is supported by the support member.

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The sheet hold-down member extends from the support member to the photosensitive surface at a position adja¬ cent an edge of the blade portion, and the sheet hold- down member terminates adjacent the photosensitive surface for holding down the sheet conveyed to the drum surface. Thereby sheet portions adjacent the drum edge are urged into contact with the photosensitive surface.

In combination with the sheet pick-off and hold-down members, there can advantageously be employed a cleaning blade according to the invention having at least one elastic material for providing a cleaning edge with a primary blade axis effective modulus of elasti¬ city and a transverse blade axis effective modulus of elasticity; and the primary blade axis effective modulus of elasticity is less than the transverse blade axis effective modulus of elasticity.

The reliability of the apparatus is further improved by employing in connection with the wiper blade, a jam detection apparatus wherein an assembly is provided for detecting a transfer sheet which remains on the photosensitive surface after the transfer station. The jam apparatus has an energy transmitting and receiving assembly, elements for supporting the assembly between the transfer station and the cleaning station, and electrical circuitry responsive to a signal output for indicating the presence of the sheet material on the photosensitive surface between the two stations. There is further provided a delay circuit responsive to the assembly output signal for providing a delayed output signal and the electrical circuit includes elements responsive to the delay output signal for terminating movement of the photosensitive surface at a time which is sufficient to enable at least the leading edge of the

sheet material to contact the wiper blade prior to ter¬ mination of the movement of the photosensitive surface. Thereby a buckle is created which facilitates removal of the sheet material from the copier.

A yet further assembly which contributes to improved copy quality is an apparatus for generating and applying an electrical potential to a development electrode at the development station. This apparatus has a detector disposed to sense unfocused light energy reflected from the document, a circuit assembly for determining when the respective light energy corresponds to scanning a central portion of the document, and a signal generating element responsive to the detector and circuit assembly for generating an electrical output potential which is applied to the development electrode. This assembly can also effect accurate registration of a sheet fed from, for example, a cassette, when a special initial reflective strip is employed in connection with the original document scanning.

At the development station, copy quality is further improved by an assembly for controlling the minimum distance between a metering roll and the photosensitive surface. This assembly provides for biasing the metering roll toward the photosensitive surface and thereby controlling the thickness of liquid toner remaining on the drum just prior to the transfer station. The controlling assembly has a positionally fixable element, a member for securing the element in operative fixed position between the drum and the metering roll, and the fixable element, when it is in its operative position, having a first sur¬ face against which a drum marginal edge can rotate in sliding frictional contact therewith and a second sur¬ face against which the metering roll can rotate in

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sliding frictional contact so that the distance between the first and second surfaces thereby controls the mini¬ mum distance between the roll and the drum photosen¬ sitive surface.

In yet another aspect of the copier, there is provided advantageous circuitry for maintaining a reliable cleaning station. Elements are provided for supplying liquid developer to the cleaning station only when the blade and roller are in their operative posi¬ tion in contact with the photosensitive surface. This is preferably performed by contacting the photosensitive surface with the roller and blade at a predetermined time after initial rotation of the photoconductive drum so that the blade and roller contact the drum at a pre¬ viously wetted portion thereof.

The improved copier of the invention thus com¬ bines these and other features to provide a reliable and effective copying apparatus.

Brief Description of the Drawings

Other objects, features, and advantages of the invention will appear from the following description of preferred embodiments taken together with the drawings in which:

Figure 1 is a schematic front elevation view of a photocopier according to the invention;

Figure 2 is a perspective view of a portion of the photocopier drum, pickoff blade, and sheet hold-down apparatus;

Figure 3 is a front elevation view of a por¬ tion of the drum and sheet stripping apparatus;

Figure 3A is a detailed sectional view of the drum, pickoff blade, and sheet hold-down apparatus.

along the lines 3A-3A of Figure 3;

Figure 4 is a plan view of the sheet stripping apparatus shown in Figure 3 , showing particularly the linkage between the scanner of the photocopier and the apparatus shown in Figure 3;

Figure 5 is an elevation view of the linkage shown in Figure 4 in a position in which the scanner is at the start of its path of travel;

Figure 6 is a similar view to that of Figure 5 in which the scanner is at an intermediate point in its path of travel;

Figure 7 is a view similar to that of Figure 6 in which the scanner has gone further in its path of travel;

Figure 8 is a perspective view like that of Figure 2 showing the front edge of a transfer sheet' being conveyed to the drum surface;

Figure 9 is a plan view of a sheet holding tray for use with the photocopier;

Figure 10 is a side elevational view of the tray of Figure 9;

Figure 11 is a rear elevational view of a tray receiver assembly;

Figure 12 is a plan view of the tray receiver assembly of Figure 11;

Figure 13 is a plan view of the shaft sub- assembly of the tray receiver assembly of Figure 11;

Figure 13A is a cross-sectional view along lines 13A-13A of Figure 13;

Figure 14 is a side elevational view of the tray receiver assembly of Figures 11 and 12, along lines 14-14 of Figure 12, showing particularly the locking handle and lever arm without the tray of Figure 9 inserted;

Figure 14A is a view along lines 14A-14A of

Figure 12, partially in section, of the portion of the tray receiver assembly including the lift member and locking device, in positions corresponding to those in Figure 14;

Figure 15 is a view like that of Figure 9 wherein the tray is inserted and engaged in the tray receiver assembly;

Figure 15A is a view like that of Figure 14A, corresponding to the position of the elements in Figure 15;

Figure 16 is a perspective view of the rear portion of the ramp plate and adjacent portions of the tray when it is inserted and engaged in the tray receiver assembly;

Figure 17 is a sectional view along lines 17-17 of Figure 9, of the rear guide portion of the - tray, showing particularly the pivot rod;

Figure 18 is a plan view of an alternate embodiment of the photocopier tray cassette;

Figure 19 is a side elevation view of the tray cassette of Figure 18;

Figure 20 is a side sectional view of the latching apparatus of the tray cassette before the lift plate is locked;

Figure 21 is a view like that of Figure 20 in which the lift plate is locked;

Figure 22 is a view like that of Figure 20 in which the lift plate is released from its locked position;

Figure 23 is a cross-sectional view of one embodiment of the preferred cleaning blade;

Figure 24 is a cross-sectional view of a second embodiment of the cleaning blade;

Figure 25 is a cross-sectional view of another embodiment of the cleaning blade;

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Figure 26 is a cross-sectional view of a still further embodiment of the cleaning blade showing also the cleaning roller;

Figure 27 is a schematic elevation view of a photocopy machine showing details of the cleaning and developer systems;

Figure 28 is an electrical schematic diagram of the timing circuit which controls the drum cleaning apparatus;

Figure 29 is a simplified schematic front ele¬ vation view of the photocopier in which the bias and registration system is detailed;

Figures 30-32 are schematic views similar to Figure 29 showing the relative positions of the illumi¬ nation source and mirrors during operation of the photocopier;

Figure 33 is a fragmentary detailed view of the photodetector and lens-mirror as positioned within the photocopier;

Figure 34 is a schematic diagram of the bias and control circuit;

Figure 35 is a diagram showing the temporal relationship of the various timing pulses generated by the bias and control circuit;

Figure 36 is a diagram showing the rela¬ tionship between the reflectivity of the document being copied and the development electrode bias for the illustrated copier;

Figure 37 is a perspective view of the drum and a metering roll apparatus according to the preferred embodiment of the invention;

Figure 38 is a detailed elevational, sectional view of one end of the metering roll apparatus shown in Figure 37;

Figure 39 is a sectional view along lines 39-

39 of the apparatus shown in Figure 38;

Figure 40 is a perspective view, in cutaway, of the photosensitive drum and the internal support structure therefor during normal copier operating conditions;

Figure 41 is an exploded detailed view of an extender guide, depicting the structure by which it is mounted to the support member;

Figure 42 is a detailed view of an extender guide in the operative position;

Figure 43 is a side elevation view, in cutaway, of the drum showing its interrelationship with the extender guides during.a typical drum removal procedure;

Figure 44 is a fragmentary detailed view of the beveled end of an extender guide according to a pre¬ ferred embodiment of the invention;

Figure 45 is a schematic representation of a liquid toner transfer copier system showing typical place¬ ment of the jam detection sheet detector assembly;

Figure 46 is a side elevation view of the detector assembly in position adjacent the photosen¬ sitive surface;

Figure 47 is an enlarged fragmentary view of the transmitting and receiving assembly showing the placement of the infrared transducer; and

Figure 48 is a preferred embodiment of the electrical circuit for the jam detection system.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to Fig. 1, a photocopier 12 has a photosensitive drum 14, preferably one having a photo¬ sensitive selenium layer deposited on an aluminum substrate, rotating in the counterclockwise direction as indicated by arrow 14a. A charge corona 14b charges the

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drum photosensitive surface 15, preferably to about +1000 volts D.C. The charged drum is exposed to an image 16 through a lens 18 at an exposure station 20. The image is focused on the drum photosensitive surface and thereupon the charge on the drum surface is selec¬ tively discharged to form thereon an electrostatic latent image having a pattern of electrical charges. In the illustrated embodiment, the lens 18 receives the image through an arrangement of mirrors, not shown, from a scanner 24 operated by an arrangement of pulleys 26 and cables 28. The electrostatic latent image on the drum surface is brought to a development station 30 at which a liquid developer 32 having a negatively charged toner contacts the electrostatic image to develop the image. The development station includes a developer tank 34 and a development electrode 36. The liquid- developer is directed between the development electrode and the drum surface to develop the latent electrostatic image. The drum surface, now wetted and carrying the developed image, travels past a metering roll 38, which controls and limits the thickness of the liquid on the drum surface. A wiper 39 engages a central metering portion 723 (Fig. 37) of the metering roll 38, and removes the excess liquid that accumulates on the metering roll. A copy material 40 is directed to the drum surface at a transfer station 42 through feed rollers 44. A positive charge from a transfer corona 46 is applied to the back side of the coy material 40, causing the transfer of toner particles from the developed image on the drum's surface to the copy material. The copy material is then removed or "stripped" fom the drum surface at 47 and follows a path 48 through rollers 50 and 52 and guide 54. The photoconductor surface, still having residual toner thereon, then passes to a cleaning station 55 having a cleaning roller 56 and a cleaning blade 58.

The now cleaned photosensitive surface is now passed beneath an AC corona 60 whereby the residual surface charge, if any, is neutralized. The photosensitive sur¬ face is now ready to produce a new copy.

Having described the basic structure of a liquid developer photocopying apparatus-according to the claimed invention, several operating stations and auxi¬ liary maintainance and service functions of the cooperating apparatus components will be described in more detail. The stations and apparatus not described in further detail are well known in the art and are well within the skill of one practiced in the art.

The Transfer Station-Paper Pickoff

The copy material 40, which is preferably _. a sheet material, is fed to the drum surface 15 at the transfer station 42. The sheet 40 is conveyed to the surface by the sheet registration rollers 44 from a cassette (Fig. 9). The sheet 40 contacts the drum sur¬ face 15, and as noted above, a positive charge from the transfer corona 46 is applied to the back side of the copy material sheet 40, causing the transfer of toner particles from the developed image on the drum's surface 15 to the copy sheet 40. An edge portion 40D (Fig. 3A) of the front of the sheet 40 is maintained in a spaced apart relationship with respect to the drum surface by a pick-off blade 48 that directs the sheet 40 to the feed- away roller 50 and paper guide 52. The sheet is fed along a path to other rollers 54 that transport the sheet to an exterior receiving tray (not shown) of the photocopier 12.

When the sheet 40 of transfer material, usually paper, is brought to the transfer station 42,

the sheet contacts the drum surface 15 in successive portions. Referring to Fig. 1, for example, it can be seen that a leading portion 40A of the sheet is between rollers 54 for transport away from the drum surface. An intermediate portion 40B of the sheet is in contact with the drum surface 15 at the transfer station 42, where image transfer occurs. A trailing portion 40C of the sheet is being conveyed to the transfer station 42.

Figs. 2, 3, and 3A show in greater detail portions of the drum 14, the pick-off blade 48, and a sheet hold-down apparatus 61, and, just above the pick- off blade 48, a sheet transport assembly 62 that inclu¬ des the feed-away roller 50 and the paper guide 52 of Fig. 1. The feed-away roller 50 is mounted for free rotation on a shaft 64. Shaft 64 in turn is posi- tionally fixed adjacent the drum by the paper handling portion of the photocopier frame. The roller preferably has a metal body 66 with a surface layer 68 of rubber.

The rest of the illustrated sheet transport assembly 62 is supported adjacent the roller 50 by the paper handling frame section and includes a vertically oriented base plate 70 with a shim plate 71 secured to it by screws 72. The shim plate, made for example from a plastic material such as that sold under the trademark, Mylar, has a lower edge 73 shaped to conform to a portion of the circumference of the feed-away roller 50 so that a paper sheet 40 carried around the roller is guided by the edge. The base plate 70 is pivotally secured to a stud 74 mounted on the photocopier frame. Plate 70 carries a cylindrical collar 76 projecting from the back of the base plate which mates with stud 74. A locking latch 78 is pivotally mounted on the face of the assembly to engage

a groove in the stud 74 to lock the assembly into position. The assembly further has a lower knurled wheel 82 and a upper knurled wheel 84 secured to and mounted for free rotation on shafts 86, 88 respectively. Shafts 86, 88 project rearwardly from the base plate 70. When the assembly 70 is locked into position, the knurled wheels 82, 84 ride along the feed-away roller 50 to grip and transport the image carrying "wet" side of sheets 40 around the roller 50, guided by the edge 73 of the shim plate 71.

As shown in Fig. 2 , the photosensitive layer 15 extends over the aluminum substrate 16, typically leaving an edge of the substrate 16 not covered by sele¬ nium. The pick-off blade 48 is located below the transport assembly 62 adjacent the marginal edge of~.the drum photosensitive surface 15. The blade 48 is curved and conforms generally to the circumference of the drum 14. The illustrated blade is pivotally mounted for quick release at its lower end 48A by a spring loaded stud member 92 extending from a bracket 94 secured to the photocopier rear panel (not shown) and the blade 48 is movable between the positions shown in Fig. 2 by dashed and solid line representations of the blade. Preferably, the blade is spaced from the drum surface 15 so that its movement will not create wear on the sur¬ face.

In a first position of the blade 48, which, is shown by the dashed line representation in Fig. 2, the blade 48 partially overlays the marginal edge of the photosensitive surface 15 of the drum. With the blade 48 in this position, a side edge portion 40D of the sheet 40, directed to the drum 14 by the sheet registra¬ tion rolls 44, will slide along the interposed blade

rather than contact the photosensitive surface 15 of the rotating drum 14. An upper end 48B of the blade has a tang 96 projecting away from the drum and toward the sheet transport assembly 62, particularly to the nip 98 formed between the feed-away roller 50 and the lower knurled wheel 82, so that the leading edge 40A of a sheet 40, sliding along the blade 48, is eventually engaged by the roller 50 and wheel 82 of the assembly.

The illustrated sheet hold-down assembly 61 includes a flat, resilient support plate 101 made, for example, of 0.012 inch stainless shim stock. The sup¬ port plate 101 is fixed at one end, here by two screws 103, to the bracket 94 on which the blade 48 is pivo- tally mounted. The support plate 101 extends over the blade 48, parallel to the drum axis, that is, normal to the direction of movement of the photosensitive surface. A sheet hold-down member 105 extends downwardly toward the drum from the end of the support plate 101 opposite that fixed to the bracket 94. The illustrated hold-down member 105 is a longitudinal rod about 0.096 inch in diameter, extending about 0.15 inch below the support plate 101. The hold-down member 105 is mounted in the support plate 101 by passing through a hole 107 in a press fit; and the member 105 includes a head 105A, slightly larger in diameter than the hole 107.

The hold-down member 105 is made preferably of a polyolefin, such as that sold by Dixon Corporation, of Bristol, Rhode Island under the trademark "Pennlon". It extends substantially normal to the drum photosensitive surface 15, and terminates in a rounded surface 105B touching the drum surface 15 at substantially a point contact. Rounded surface 105B in combination with the drum surface define an entrance "throat region" 111 into

which the copy material is directed. The hold-down member 105 extends to the surface 15 of the drum just adjacent the inner edge 48C of the blade 48 when it is in the first position overlaying a marginal portion of the drum photosensitive surface 15 (as shown by the dotted representation in Fig. 2) . At this position, the hold-down member 105 can hold down a part of the sheet edge portion 40D close to the photosensitive surface 15 of the drum where it will pick up the developed image on the surface, a part that would ordinarily not be close to the surface 15 because it is in a transition zone between the sheet portion on the drum surface 15 and the sheet portion on the blade 48. The dashed represen¬ tation in Fig. 3A shows the position that this part of the sheet would take in the absence of the hold-down member 105. Thereby the area of image deletion at the leading corner of the copy is minimized.

Relative to the length of the pick-off blade 48, the sheet hold-down assembly 61 is located preferably near the pivotal end 48A, near where the transfer sheet 40 first approaches the drum photosensitive surface 15. Its preferred position near the pivotal end of the pick-off blade places it at the edge of the field of charge of the transfer corona 46, assuring that no arcing occurs. Moreover, the assembly 61 appears to have no appreciable effect on the charge applied by the transfer corona 46 even if it is posi¬ tioned beneath the corona.

The upper end 48B of the blade includes a forked portion 99 over which the split end 100 of a laterally movable actuator rod 102 passes. A pin 104 through the split end 100 of the rod passes between the teeth of forked portion 99 of the blade so that lateral

movement of the actuator rod 102 will pivot the blade 48 about its pivot screw 92. In the second position of the blade 48, shown by the solid line representation in Fig. 2, the illustrated blade no longer overlays any portion of the photosensitive drum surface 15, so that successive portions of the sheet 40 brought to the drum 14 will contact the photosensitive drum surface 15 fully, from one side edge of the sheet to the other.

Fig. 4 shows the relation between the actuator rod 102 and the other elements of the photocopier apparatus. The figure also shows the lateral positions of the roller 50, lower and upper knurled wheels 8_ and 84, and paper guide shim plate 71 of the sheet transport assembly 62 relative to the pick-off blade 48. It also shows the relative position of a side edge portion 40D of a sheet of paper 40 in the apparatus.

The actuator rod 102 for pivoting the blade 48 passes through a rear panel 106 of the photocopier and is connected to an actuator pivot 108 pivotally mounted on a pin 109 in a bracket 110 secured to the rear panel 106. The actuator pivot 108 has an arm 112 with a forked end 114 that engages a pin 116 extending through the actuator rod, so that lateral rearward movement of the actuator pivot arm 112 moves the actuator rod 102 rearward (in the direction of the arrow 118) . The actuator rod 102 is connected by a spring 120 (see Figs. 5-7) to the rear panel 106, so that it is constantly biased to move forward.

The actuator pivot 108 is operated by a pin 122 extending down from a slide 124 to engage a gap 125 in a forward extension of the actuator pivot arm 112. The slide 124 is secured to the rear panel 106 by studs

126 passing through horizontal slots 128 in the slide 124, so that the slide can move horizontally. Two brackets mounted on the scanner 24, a slide release bracket 130 and a trigger bracket 132, actuate movement of the slide 124. The different positions of the scanner 24 during operation of the photocopier, and the effect on the slide 124 and the actuator rod 102 can be seen by also referring to Figs. 5-7.

In the position shown in Fig. 5, the scanner 24 has not yet begun to scan the original, and the scanner brackets 130, 132 are located over the left portion of the slide 124. A slide lock 134, pivotable about a pin 136, is in an unlocked position. The slide 124 is biased to the left by a spring 138 extending from a rearwardly projecting tab 140 at the end of the slide to a fastener 142 secured to rear panel 106. In this position of the slide 124, the actuator pivot arm 112 is not urging the actuator rod pin 116 rearward, and, the actuator rod 102, reacting to the bias exerted by the actuator spring 120, extends forwardly (as shown by the dashed representation in Fig. 4') . When the actuator rod 102 is in this position, the pick-off blade 48 is in the position in which it overlays the marginal edge of the drum photosensitive surface 15 (as shown by the dashed line representation in Figs. 2 and 4).

In a second position of the apparatus, shown in Fig. 6, the scanner 24 has moved to the right, and the trigger bracket 132 is shown in a position in which a tab 144 extending rearwardly from the bottom of the bracket 132 engages a slide positioner 146. The slide positioner 146 is a flat, elongate element that extends between the slide 124 and the rear panel 106. The positioner 146 is pivotally mounted on a pin 148 and

biased by a spring 150 to maintain an upright position. When the trigger bracket 132 is moving to the right, as shown in Fig. 6, the trigger bracket tab 144 engages the slide positioner 146 which in turn engages a forwardly extending tab 152 at the right end of the slide 124, moving the slide to the right. When the slide 124 moves to the right, the actuator pivot arm 112 swings rearwardly because of the movement of the slider pin 122, the actuator rod pin 116 is urged rearward by the actuator arm 112, and the rearward movement of the actuator rod 102 moves the pick-off blade 48 to its second position (as shown by the solid line representation of the elements in Figs. 2 and 4), clear of the drum photosensitive surface. When the slide 124 moves further to the right, the pivotable lock 134 at its left end, biased by a spring 154 to pivot clockwise, does so, and a slide locking surface 156 (Fig. 5) is moved into position against the end of the slide 124, . blocking leftward movement of the slide.

In a third position of the scanner 24, illustrated in Fig. 7, the scanner 24 has moved further to the right, but no change is effected in the position of the slide 124, which remains locked in place. The scanner 24 can move further and further to the right without effecting any change in the position of slide 124.

When the scanner 24 returns to its original position, a slide release tab 158, extending rearwardly from the slide release bracket 130, engages an upward extension 160 of the slide lock 134, pivoting it counterclockwise to release the slide 124, which then moves leftward in response to the bias force of spring 138. Slide 124 moves leftward until it engages the

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studs 126 and the entire assembly is restored to the first position, shown in Fig. 5. The pick-off blade 48 is accordingly also restored to its first position (the dashed line representation of Fig. 2) .

During operation of the photocopier 12, a sheet 40 is conveyed to the drum photosensitive surface 15 after the scanner 24 has begun to scan the original (see Fig. 8). As the first portion of the developed image on the drum surface 15 approaches the transfer station 42 the leading portion 40A of the transfer sheet 40 is brought to the drum surface 15 by the registration rollers 44 in the direction shown by the arrow 162. At this time the pick-off blade 48 is in its first position, as shown in Fig. 8, corresponding to the dashed line representation in Fig. 2. As the leading portion 40A of the transfer sheet comes into contact with the drum surface 15, the side edge portion 40D slides along the pick-off blade 48. The leading portion 40A of the sheet enters the throat area 111 and is caught under the hold-down member 105. The portion of the sheet edge portion 40D just next to the edge 48C of the pick-off blade 48 is pressed to the surface 15 of the drum by the hold-down member 105 (see Fig. 3A), so that it can pick up developed image toner there.

The leading edge corner of the sheet 40 is subsequently brought by the tang 96 of the pick-off blade 48 into engagement with the nip 98 of the roller 50 and lower knurled wheel 82 of the sheet transport assembly 62. The alignment of the brackets 130, 132 on the scanner 24 is selected so that after this engagement of the paper, the slide 124 is brought to the position shown in Fig. 6, and the pick-off blade 48 is pivoted away from its first position to its second position,

clear of the drum photosensitive surface 15. The blade remains in this second position at least until after the sheet 40 has left contact with the drum surface 15 and the transfer process is completed. The return of the scanner 24 to its original position restores the blade 48 to its position, overlaying the drum surface 15.

Thus it can be seen that successive portions of the transfer sheet after the leading portion 40A contact the photosensitive drum surface 15 completely, from one side edge of the sheet to the other. At the conclusion of the transfer process the scanner 24 returns to its original starting position and returns the pick-off blade 48 to its original starting position. The pick-off blade 48 overlays the photosensitive sur¬ face 15 for a period only long enough to allow the - leading corner of the transfer sheet 40 to be engaged by the sheet transport assembly 62. As soon as that goal is accomplished, the pick-off blade 48 is moved away from its overlying position and the transfer sheet 40 can contact the drum surface fully. Only a small corner of the transfer sheet 40 is not available for copying purposes. The amount of the corner not available for copying purposes is advantageously reduced by the action of the hold-down member 105 of the hold-down assembly 61.

The Transfer Station - Paper Feeding

The source of the copy material directed to the transfer station 42 can be either a stack of sheet or a. continuous roll. When sheet material is used, it is convenient to use portable cassettes which can be loaded external of the copier and then placed into the paper feed position. According to the preferred embodi¬ ment of the invention, a tray 210, suitable for use in

storing a stack of sheets of copy material 40, typically paper, and for insertion into the photocopier, is shown in Figs. 9 and 10. The tray 210 has a bottom 212, a front wall 214, side walls 216, and a back wall 218. The interior of the tray 210 includes raised stack sup¬ port portions 220 and 222. It also includes a side guide 224 and a rear guide 226. The side guide 224 includes a horizontal metal sleeve 228 with downwardly projecting fasteners 230 with nuts 232 cooperating with a slot 234 in a plastic slide 236 on which the metal sleeve 228 is slidable. The side guide 224 includes a vertical wall 238 for adjusting the width of the sheet stack area in the tray 210. The rear guide 226 simi¬ larly includes a horizontal metal sleeve 240 with faste¬ ners 242 and nuts 244 cooperating with a slot 246 in a rear plastic slide 248. The rear guide 226 has a ver¬ tical wall 250 for adjusting the length of the sheet stack area of the tray 210.

The vertical wall 238 of _, the side guide 224 includes at its forward end (shown near a front corner of the tray 210) a corner separator member 252, engageable with sheets stacked in the tray 210 when the wall 238 is brought up against the side of the stack by sliding the sleeve 228 on the slide 236. Another corner separator member 254 is mounted at the other front corner on the tray front wall 214 near the side wall 216.

A ramp plate 256 has a front edge 258 near the tray front wall 214. A rear edge 260 of the ramp plate has downwardly extending tabs 262 resting in slots 264 in the stack support portions 220, 222 so that the ramp plate 256 is pivotable about its rear edge 260. The illustrated tray bottom 212 has a rectangular opening

266 through which a bottom surface 268 of the ramp plate 256 can be engaged to lift the plate 256. Thereby sheets stacked in the tray are brought into a feed position to be fed from the tray into the photocopier when the tray is inserted and "armed" as described in detail below.

A tray receiver assembly 270, as shown in Figs. 11 and 12, is mounted in the photocopier in a conventional manner not shown here. The assembly 270 includes side walls 272 and 273, a horizontal upper stay 274 joining the side walls 272, and a bottom plate 276 with an opening 278 (Fig. 12) aligned with the opening 266 in the bottom 212 of the tray 210 when the tray is fully inserted into the photocopier. A shaft 280 extends beneath the bottom plate 276 through a pillow block 282 (Fig. 13) in one side wall 273 and through another pillow block 284 in the other side wall 272. The shaft 280 is rotatable in the pillow blocks 282, 284. One end 286 of the shaft 280 extends beyond the side wall pillow block 284.

When the tray is inserted into the tray receiver assembly opening 287, it is aligned laterally by plastic alignment bumpers 287a, 287b, and is inserted into the receiver assembly until it engages forward stops (not shown) in the machine frame.

As shown particularly in Fig. 13, mounted on shaft 280, for movement through the bottom plate opening 278, is a paper lift member, here a roller 288. The paper lift roller 288 is rotatably mounted on a roller shaft 290 secured to the arms 292 of a paper lift fork 294. The arms 292 of the paper lift fork 294 terminate in a base 296 attached rigidly to the shaft 280 by

fasteners 297, so that as the shaft 280 rotates, the paper lift roller 288 rotates or pivots upwardly through the bottom plate opening 278.

A locking bracket 298 is also mounted on and supported by the shaft 280, by way of bushings 300, so that the locking bracket 298 is rotatable with respect to the shaft 280. The locking bracket 298 has a central plate 302 located beneath the paper lift roller 288, and two upwardly rising side walls 304 located outwardly of the lift roller 288. A locking bracket spring 306 is coiled around the shaft 280. One end 308 of the spring 206 is secured to the locking bracket 298 by extending into a hole 310 in a bracket side wall 304. The other end 312 of the spring is extended and meets the bottom plate 276 of the tray receiver assembly 270. The spring 306 biases the locking bracket 298 upward. When bracket 298 is allowed to rotate upward in response to the bias of the spring 306, tab 313, extending from the front of the bracket central plate 302, prevents the plate 302 from passing through the opening 278 in the bottom plate 276 although the upwardly rising side walls 304 of the bracket do extend through the opening 278 when the tab 313 meets the bottom plate 276 of the assembly 270.

Referring now to Fig. 14, it can be seen that end 286 of the shaft 280 extending through the assembly side wall 272 is secured to a ramp arm 314. The ramp arm 314 extends horizontally forward to an end 316 secured to one end of a spring 318. The other end of the spring 318 is secured to a spring post 320 (see Fig. 11) that is fastened to the frame of the photocopier, not shown. A contact arm 322 extends downwardly from pivotal attachment via a fastener 324 to the assembly side wall 272, and includes at its lower end 326 a rota-

table wheel 328 that allows the arm 322 to slide easily along an upper surface 330 of the ramp arm 314. Rigidly secured to an intermediate portion of the contact arm 322 is a rearwardly horizontally extending locking handle 332.

The arrangement of the ramp arm 314, contact arm 322 and locking handle 332 shown in Fig. 14 corresponds to a position of the tray receiver assembly in which a tray 210 can be safely inserted or removed from the photocopier. With the locking handle 332 down, as shown in Fig. 6, the ramp arm 314 is in a stable down position. The shaft 280 secured to the ramp arm 314 then corresponds to a position in which the lift roller 288 mounted on the shaft 280 is kept below the plane of opening 278 in the assembly bottom plate 276. As shown in Fig. 14A, the lift roller 288 in such a position engages and maintains the locking bracket 298 in a downward position, so that the side walls 304 of the bracket are also below the plane of opening 278.

After the tray 210 is inserted into the tray receiver assembly 270, the locking handle 332 can be manually moved upwardly. Moving the handle 332, moves the contact arm lower end 326 rearward. After a certain amount of rearward rotation by the contact arm 322, the bias of the spring 318 urges further rearward movement, positively urging the contact arm 322 and locking handle 332 to the position shown in Fig. 15. The rotation of the shaft 280 caused by this rearrangement results in the positions of the paper lift roller 288 and the locking bracket 298 shown in Fig. 14A. The paper lift roller 298 is pivotally moved through the assembly bot¬ tom plate opening 278 and through the aligned opening 266 of the tray bottom 212, to engage the bottom sur-

face 268 of the ramp plate 256 in the tray 210. The ramp plate 256 accordingly pivots about its rear edge 260 in the tray to lift upwardly the stack of sheets on it to a suitable feed position for engagement by the feed rollers of the photocopier. The locking bracket 298, freed by the upward movement of the paper lift roller 288, responds to the bias of its spring 206 to move upwardly. The tab 313 limits upward movement of the locking bracket 298 but allow the side walls 304 of the bracket to extend above the assembly bottom plate opening 278. In this position, the side walls 304 extend up through the tray bottom opening 266. There the side walls 304 prevent any rearward movement of the tray 210, as for example, in response to an attempt to remove the tray 210 while the paper lift roller 288 is engaging the ramp plate 256 in the tray 210.

Fig. 8 shows the rear portion of the ramp plate 256 in the tray 210, with the tray inserted in the tray receiver assembly 270 and with the front portion of the plate 256 in a lifted or raised condition. In the illustrated embodiment, the ramp plate 256 pivots about its rear edge 260 in response to the upward movement of the front of the ramp plate, and paper stacked on it (not shown in the drawing) is raised to a feed position for engagement by feed rollers (also not shown) . The feed rollers are arranged on a shaft generally parallel to the front edge 258 and rear edge 260 of the ramp plate 256.

The ramp rear edge 260 rests on a pivot rod 334 on top of the rear guide metal sleeve 240. As can be seen in Fig. 9, the illustrated pivot rod 334 has a semicircular cross section with its convex surface 336 facing upwardly. The elongate rod 334 extends in a

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direction transverse to the rear edge 260 of the ramp plate 256, and is secured to the metal sleeve 240 for example with an adhesive. The illustrated rod 334 extends from near the rear guide wall 250 forward and beyond the sleeve 240, so that the ramp plate rear edge 260 rests upon some part of the pivot rod 334 whatever the relative position of the metal sleeve 240 of the rear guide 226. Thus different paper sizes have no effect upon the ramp pivot function.

The rod 334 extends substantially beneath the central portion of the ramp plate rear edge 260, so that the ramp plate 256 can pivot about the contact point of the rear edge 260 with the top of the curved surface 336 of the rod 334. The ramp plate 256 will pivot in response to the pressure of the feed rollers on the stack of sheets supported by the ramp plate 256 to automatically align itself with the feed rollers.

In operation, then, when the locking handle 332 is in the lower position, as shown in Fig. 14, the paper lift roller 288 and the locking bracket 298 are in a position below the opening 278 of the tray receiver bottom plate 276, as shown in Fig. 14A, and the tray 210 may be inserted into, or withdrawn from, the tray receiver assembly 270. When the tray 210 is inserted into the assembly 270 the opening 266 in the tray bottom 212 becomes aligned with the opening 278 in the assembly bottom plate 276. The locking handle 332 can be brought to an upward position, as shown in Fig. 15. The shaft 280 rotates in response to the movement of the ramp arm 314 to which the shaft end 286 is secured. This causes the paper lift roller 288 to pivot upwardly through the opening 278, as shown in Fig. 14A, and engage the ramp plate bottom surface 268 through the tray bottom opening

266. Meanwhile, and simultaneously, the locking bracket 298 is released by the movement of the paper lift roller 288 upward from the position in which it had restrained the upward movement of the bracket. The bracket 298 therefore responds to the force of the spring 306 and moves upward. The tab 313 on the end of the bracket 298 meets the bottom plate 276, preventing movement of the bracket beyond that point, but the upwardly rising side walls 304 of the bracket do extend through the bottom plate opening 278 and through the aligned tray bottom opening 266. Accordingly the bracket side walls 304 in this position prevent removal of the tray 210 because of their positive interference with the edges of the tray bottom opening 266.

The lift given the ramp plate 256 by the paper lift roller 288 positions the ramp plate for engagement with the feed rollers, which can descend to meet the stack, or which can be fixed in position above the stack. By virtue of the free pivotal movement of the ramp plate rear edge 260 about the extended pivot rod 334 alignment between the stack and the feed wheels is assured.

The embodiment just described is for a feed system in which the feed rollers are fixed and the ramp plate is selectively lifted to an operative position, adjacent the rollers. In another particular embodiment of the invention, the feed rollers are moved into and out of position adjacent a cassette in which the range plate is internally spring loaded. In this particular embodiment of the invention, the lift plate 256 has a front edge 258 near the tray front wall 214. The rear edge 260 of the lift plate 256 has downwardly extending tabs 262 resting in slots 264 in the stack support por-

tions 220, 222 so that the lift plate 256 is, as before, pivotable about its rear edge 260. The rear edge 260 of the lift plate 256 includes the a centrally positioned, rounded projecting portion 266, which rests on the upper surface of the metal sleeve 240 of the rear guide 226. Two lift plate springs 368 are located between the lift plate 256 and the tray bottom 212. They are located generally near the forward corners of the tray bottom 212 to provide an upward bias to the lift plate 256 so that the top of a sheet stack on the lift plate 256 will be positioned against the bottom surfaces of separators 252, 254, where it can be engaged by the feeding appara¬ tus of the photocopier.

A latching apparatus 370 for locking the lift plate 256 in a downward position against the bias of the springs 368 is shown in the forward part of the tray 210 in Figs. 18 and 19, and is shown in greater detail in Figs. 20-22.

The illustrated latching apparatus 370 includes a lower latch member 372 contained in a latch housing 374 attached to the tray bottom 212 underneath a front central portion of the lift plate 256. The lower latch member 372 includes a head 376 from which extend front 378 and rear 380 rods slidable through front 382 and rear 384 walls, respectively, of the latch housing 374. The front rod 378 has a vertical stop rod 386 inserted therethrough, between the front wall 382 and head 376, to prevent passage of the front rod 378 in a forward direction beyond the- portion at which stop rod 386 meets the front wall 382. A compression spring 388 is wound around the rear rod 380 inside the housing 374, biasing the latch member head 376 forward toward wall 382.

The latch head 376 has a downwardly sloping front upper camming surface 390 terminating in a forward nose portion 392 having a horizontal under latch surface 394. The illustrated latch head 376 is movable in the horizontal direction between front and rear positions, and is biased toward the front position by the compression spring 388. The front rod 378 of the latching apparatus 370 extends through the latch housing front wall 382 through an opening 396 in the front wall 214 of the tray 210. The front rod 378 projects beyond wall 314 to where its front surface 398 can meet a portion 400 of the photocopier frame 402 when it is inserted into the receiving opening 404 of the photocopier frame after being stacked with paper.

In the illustrated embodiment, the front portion of the lift plate 256 forms the upper latch member of the latching apparatus 370. The lift plate 256 has an aperture 406 in its front portion just over the lower latch member 372. The lift plate 256 includes a downwardly extending tab 408 terminating in a generally horizontal, rearwardly extending upper latch surface 410.

In operation of the photocopier, the tray 210 must be removed from the photocopier frame 402 and reloaded by stacking paper 412 on the lift plate 256. When the tray 210 is removed from the photocopier, the positions of the lift plate 256 and the latching apparatus 370 are generally as shown in Fig. 20. The lower latch member head 376 is biased in the forward position because of the compression spring 388. The lift plate tab 408 is out of contact with the lower latch member head 376 because of the upward bias of the lift plate springs 368 on plate 256.

Placing downward pressure on the front portion of the lift plate 256 (as indicated by the words 414 printed on the lift plate) in the direction shown by the arrow 416 causes the lift plate tab 408 to slide down the front upper surface 390 of the lower latch head 376 in a camming action that forces the lower latch head 376 rearwardly (in the direction shown by the arrow 418) against the bias of the compression spring 388. After sliding completely down the latch head upper surface 390, the upper surface of tab 408 is engaged by the lower horizontal under surface 394 of the lower latch head 376 (as head 376 becomes free to move forward toward wall 214) , and the lift plate 256 is locked in a lowered position against the bias of the lift plate springs 368 (see Fig. 21).

The tray 210 may be stacked with sheets 412 conveniently while the lift plate 256 is locked in this lowered position. After the stack 412 is loaded, the tray 210 is inserted into the receiving opening 404 of the photocopier frame 402. When this is done, the front rod 378 of the latch assembly 370, projecting forwardly of the tray front wall 414, meets the portion 400 of the photocopier frame 402 defining the end of the receiving opening 404. Insertion of the tray 210 into the opening 404 (in the direction of the arrow 420 (Fig. 21)) causes the rod' s front surface 398 to engage the frame portion 400 and move the latch head 376 rearwardly (in the direction of the arrows 422 (Fig. 22)). As the latch head 376 moves in the direction of arrows 422, the under surface 394 of the latch head 376 disengages from the lift plate tab 408 and the lift plate 256 moves upwardly (in the direction of the arrow 424) until the corners of the top sheet of paper engage corner separators 252, 254. As seen from Fig. 22, the lift plate 256 is now in

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a position to respond, unimpeded by the latch head, to the lift plate springs 368.

The Cleaning Station

Referring to Fig. 23, the blade 58 of the drum cleaning assembly is depicted in exaggerated detail. The rotating drum photosensitive surface 15 is in contact with a trailing cleaning blade 58 so that as a photosensitive surface 15 rotates, any residual toner particles remaining on the surface after the transfer operation are wiped from the surface. Cleaning blade 58 is attached to a bracket 427, for example, by a plura¬ lity of screws spaced along its length parallel to the drum axis, and bracket 427 in turn is attached to a pivotable member 428. The member 428 is adapted to fit on a shaft (not shown) at a hole 429 which allows the blade assembly to pivot toward and away from photosen¬ sitive surface 15. An edge 430 of blade 58 contacts the photosensitive surface 15 and wipes residual developer therefrom. The blade assembly is located so that the edge 430 contacts photosensitive surface 15 at an angle * past the top position of photosensitive surface 15. A suitable value for the angle βr is 24°.

In this embodiment, the illustrated blade 58 has a metal support surface M, such as aluminum, and three resilient layers: a soft layer (that is, a layer of a material having a relatively lower modulus of elasticity) S flanked by two layers HI and H2 of a relatively harder material; Suitable materials for the layers S, HI and H2 are elastic synthetic resins and rubbers which will not "poison" or be degraded by the developer solution. Typical materials can be composed of teflon, silicon rubber, polyester, polyethylene, polyurethane, etc. It is preferred that layers HI and

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H2 be made of polyurethane having a hardness of 75-80 Durometer (Shore A) and that layer S be made of closed cell medium neoprene. A suitable material for layer HI is Elastacast® polyurethane available from Acushnet Company. The bracket 427 can be made of chromic acid anodized or clear anodized aluminum. Blade 58 also has, at either end, vertical side members (not shown) which extend in a radial direction outside and below the sur¬ face of the drum. The side members can wipe against the drum edges for preventing liquid developer in front of the trailing blade from moving around the blade to the back side of the blade.

Before the layers are assembled to create blade 58, the layer HI polyurethane is treated with Eccoprime. The layers are then bonded to one another and, in the illustrated embodiment, to metal layer M using semi—rigid formula Eccobond 45 (clear) adhesive and Catalyst-15 (clear) . A suitable composition is one part adhesive to two parts catalyst by weight. These materials are available from Emerson and Cuming, Inc. of Canton, Massachusetts. The adhesive composition is cured for approximately forty-five minutes at a temperature of 160°F (71°C). In the embodiment of Fig. 1, layer HI is approximately 3/8" thick, layer S, 3/16" thick, and layer H2, 1/8" thick. The width of blade 58, that is, the dimension in the direction perpen¬ dicular to a primary blade axis 431, i.e., a transverse blade axis 432, is approximately 0.5".

The blade structure described above resists transverse blade axis deformations relatively more than deformations along the longitudinal blade axis 431. The relatively high transverse stiffness of the blade 58 enhances its toner removal capability, while at the same

time the relative deformability along primary blade axis 431 prevents toner particles from becoming wedged in the space between the blade 58 and photosensitive surface 15, thereby reducing the likelihood that photosensitive surface 15 will be scratched by toner or other par¬ ticles. Illustrated blade 58 can also be reversed, in the preferred embodiment, so that blade edge 433 can also be used as a blade wiping edge in contact with the photosensitive surface.

The illustrated blade 58 is oriented with respect to photosensitive surface 15 so that it is a trailing blade, that is, the angle O subtended by a tangent to the photosensitive surface 15 at the line of contact between the surface 15 and the blade 58 and the primary blade axis 431 is less that 90° The preferred value for the angle O is approximately 56°. Still referring to Fig. 23, the bracket 427, in addition to supporting the blade 58, can limit the amount of trans¬ verse deflection of the blade 58 to a predetermined maximum amount, for example, 1/16".

Now referring to Fig. 24, a second illustrated embodiment of the invention, the trailing cleaning blade 58 is made of a relatively hard elastic material such as a hard polyurethane and has a cavity 434 created within the blade either in the forming process or by removing some of the blade material after the complete solid blade is formed. In this embodiment blade 58 is adhesi¬ vely bonded to supporting bracket 427. The resulting blade, having thin side walls 435 of a hard, elastic material and defining in part the cavity 434 results in blade having relatively high transverse stiffness for efficient cleaning with relatively low stiffness along the primary blade axis 431 to prevent drum surface scratching and the trapping of solid particulate.

Yet another embodiment of the invention is shown in Fig. 25. Here, the illustrated trailing cleaning blade 58 is made of a relatively hard elastic material which has a cavity filled with a relatively softer elastic material 435. The cavity can be created in the forming process, for example, or by removing material from the blade. As with the other embodiments described above, this arrangement of a relatively softer material embedded within a relatively harder material results in the blade 58 having relatively high stiffness transversely and relatively less stiffness along the primary blade axis 431.

Referring now to Fig. 26, according to yet another embodiment of the invention, the trailing blade 58 is supported, for example, by an adhesive bond, by a pivoting bracket 441 arranged to pivot about a pivot line 442. A slot 443 in bracket 441 rides on a guiding pin 444 secured to the frame of the photocopying appara¬ tus (not shown) . The blade 58 of this embodiment, is similar to the blade illustrated in Fig. 23, that is, the blade which is composed of three resilient layers: two hard layers H3 and H4 flanking a softer layer SI. It is to be understood that the blades described in Figs. 24 and 25 are also suitable for use in this embo¬ diment.

Bracket 441 pivotably supports a lubricant dispensing assembly 445 including a perforated tube 446. By conventional means (not shown) , lubricating liquid, preferably developer liquid, is pumped into the tube or nozzle 446. The tube 446 extends the full length of drum 14. The fluid then travels through perforations 447 onto the surface of a cleaning roller 448. These perforations are preferably spaced apart along the

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length of the tube 446. The cleaning roller 56 rotates in the same sense as photosensitive drum 14 so that the surface of roller 56 and photosensitive surface 15 are moving in opposite directions at their area of contact. Because the surfaces are moving in opposite directions, some of the lubricating fluid from the perforations 447 is squeezed from the roller 56 and flows by gravity and friction to the position where the blade 58 contacts the photosensitive surface 15. Such lubrication makes less likely the marring of the photosensitive surface 15 because of toner particles trapped between the photosen¬ sitive surface 15 and the blade 58. A bracket 449 is positioned to limit transverse deflection of the blade 58,

Referring now to Fig. 27, the cleaning station of Fig. 26 operates as follows. As soon as the drive ^~ . power is applied to the photocopying machine 12, a pump 540 begins to pump the liquid developer 32 both to the electrode 36 and through a conduit 541. At the same time, the main drive motor 541a begins to rotate the drum 14 in the direction of the arrow 14a. At this time, the cleaning roller 56 and the cleaning blade 58 are in their inoperative position spaced apart from the rotating drum surface 15. The inoperative position of both the cleaning roller 56 and the cleaning blade 58 are shown in phantom.

As the drum 14 begins to rotate, it contacts liquid developer in the vicinity of the electrode 36, thereby wetting the photosensitive surface 15 with the liquid developer 32. The drum 15 continues to rotate for approximately three-fourths of a revolution carrying the wetted photosensitive surface 15 past a cleaning station 55. At this time, solenoids 542 and 543 are activated by a timing circuit which will be described in

detail in conjunction with Fig. 28. When the solenoids 542 and 543 are activated, their respective plungers 544 and 545 are pulled into the solenoids causing the cleaning blade 58 and the cleaning roll 56 to pivot into contact with the photosensitive surface 15. Thus, at the time that the cleaning roller 56 and the cleaning blade 58 move into their operative position in contact with the photosensitive surface 15, the surface 15 has been wetted with the liquid developer 32 carried to the cleaning station 55 from the vicinity of the electrode 36.

All the while, the pump 540 has been pumping the liquid developer 32 through the conduit 541 toward the cleaning station 55. Disposed between sections of the conduit 541 is an accumulator 547 of increased - cross-sectional area, as compared to the conduit 541. The accumulator 547 must fill up with developer fluid 32 before any of the fluid is delivered to the cleaning station 55. The delay resulting from the filling of the accumulator 547 prevents the delivery through the nozzle 446 of the liquid developer 32 until after the cleaning roller 56 and the cleaning blade 58 are in their opera¬ tive position in contact with the photosensitive surface 15. This delay prevents the developer 32 from splashing underneath the roller 56 and the blade 58 which would be the case if the developer liquid 32 were delivered before the roller 56 and the blade 58 were moved into their operative positions.

After the cleaning roller 56 and the cleaning blade 58 have moved into the operative position when the photocopier is first turned on, they remain there as the drum 14 rotates for a period of time sufficient to clean the drum surface 15. A typical time period is from 3-35

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seconds. The cleaning roller 56 is driven (by means not shown) to rotate in the same sense as the drum 14; so that at their area, of contact, the surface 15 and the surface of the roller 56 are moving opposite directions, thereby to provide good cleaning action to loosen any toner which may have become dried onto the photosen¬ sitive surface 15. After the cleaning roller 56 has dislodged the toner particles, the surface 15 is wiped clean by the cleaning blade 58. After the photosen¬ sitive surface 15 has been cleaned, after the photo¬ copier is first turned on or after a copy cycle, the solenoids 542 and 543 are deactivated causing the cleaning roller 56 and the cleaning blade 58 to return to their inoperative positions spaced away from the pho¬ tosensitive surface 512. At the same time, the pump 540 is turned off, allowing the developer fluid 32 to flow by gravity out of the accumulator 547 back into the developer reservoir 549. Thus, after the end of the cleaning cycle, the cleaning roller 56 and the cleaning blade 58 are both in their inoperative position and the accumulator 547 has emptied into the reservoir 549.

Referring to Fig. 28, the timing circuit which delays the movement of the illustrated cleaning roller 56 and the cleaning blade 58 from the inoperative to the operative position has twenty-four volts applied across a first portion 549a, when the main power is turned on and 115 volts A. C. applied across a second portion 549b of the circuit. Note that the 115 volts A.C. imme¬ diately appears across the pump 540 which begins to pump the liquid developer 32. As soon as the 24 volts D.C. appears, a capacitor Cl begins to charge. Initially, the voltage at a noninverting input 550 to an opera¬ tional amplifier 551 is higher than that at an inverting input 552. This causes the output voltage of the opera-

tional amplifier 551 to be high which causes a relay 553 to be in its off state. When the capacitor Cl has become charged so that the voltage at the input 552 is greater than the voltage at the input 550, the output of the operational amplifier 551 becomes low, which turns on the relay 553. The time interval before the relay 553 is turned on is determined by the relative values of the resistors Rl, R2, R3 and the capacity of the capaci¬ tor Cl. A typical delay period is approximately one second which is enough time, in the illustrated embodi¬ ment, for the rotating drum to complete approximately three-fourths of a revolution. Thus, the cleaning blade and roller, when they move to their operative position, contact a wet photosensitive surface.

When the relay 553 is turned on, 115 volts A.C. is applied across the solenoids 542 and 543, causing their plungers to be pulled in, thereby moving the cleaning roller and cleaning blade to their operative positions as described hereinbefore.

Thus the illustrated cleaning apparatus pre¬ vents damage to the photosensitive surface and to the cleaning roller and cleaning blade by moving the photo¬ sensitive surface before moving the cleaning roller and cleaning, blade from their inoperative positions to operative positions in contact with the photosensitive surface. In addition, the delivery of developer fluid to the cleaning station near the cleaning roller and cleaning blade is delayed until the cleaning roller and cleaning blade are moved into their operative position, thereby preventing the splashing of fluid beneath the roller and the blade.

Development Electrode Bias

As noted above, at the development station, there is provided a development electrode 36 in opposed juxtaposition to the rotating xerographic drum. In order to reduce background, a bias voltage is applied to the development electrode. The bias voltage may be either fixed, or variable to take into account changes for example in the paper background color. In the pre¬ ferred embodiment of the invention, the bias voltage is variable, and is generated by examining the document during a beginning portion of the scanning thereof. The resulting voltage is then applied as a bias to the electrode structure.

Referring to Figure 29, in which the elements of the bias system are particularly shown, the bias, signal is generated by a bias control circuit 641. Advantageously, circuit 641 also controls the feeding (or registration) of sheet material at the transfer sta¬ tion 42. Thus, the surface 15, bearing the developed image, advances to the transfer station 42 where the image is transferred to a copy material 40. The copy material is advanced toward the drum surface at the appropriate time and speed so that the leading edge of the material will coincide with the leading edge of the developed image on the drum. A feed mechanism for the copy material, typically clutch controlled registration rollers 44, is initiated by energizing a registration clutch solenoid 645. The solenoid 645 is controlled by the bias and control circuit 641 in response to the receipt of a selected predetermined input from a photo- detector 629.

Referring to FIG. 30, a light source 619 and the mirrors 625, 627 are shown in their initial

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positions prior to initiation of a typical copying cycle. The light source is disposed directly below a bracket 647 painted flat-black so that it is essentially non-reflective. Thus no light from the light source 619 is reflected by the mirrors 625 and 627 to the photodetector 629. This positioning is desirable to prevent premature activation of the bias and control circuit by stray light impinging on the photodetector 629.

Upon initiation of a copying cycle by an operator, the light source 619 and the first mirror 625 will begin to move (by a mechanism not shown) to the left in a direction parallel to the document support plate 621 and the document 623. The light source and mirror 625 move at the same speed as the photoconductive surface of the drum, in the case of a 1:1 reproduction, although the speed relationships will be different for the case of either a reduced or an enlarged reproduc¬ tion. The second mirror 627 also will move to the left, but at only one-half the speed of the light source and the first mirror so that the total distance travelled by light reflected from the surface of the document 623 to the lens-mirror 631 (see FIG. 19) will remain constant, thereby keeping the image of the document 623 in proper focus at the drum surface. As seen in FIG. 21 the first reflection of light from the light source 619 will occur when the light source becomes positioned beneath a highly-reflective strip 649 which is placed just before a leading edge 651 of the document 623 and is coexten¬ sive with its width. This reflective strip preferably has a titanium-white surface possessing exceptionally high reflectivity in the visible spectrum, higher than the expected reflectivity of white areas on typical documents. A portion of the light reflected from the

highly-reflective strip 649 is directed by the mirrors 625 and 627 onto the photodetector 629. The excep¬ tionally high detected intensity of this light produces a correspondingly high level signal output from the pho¬ todetector, and this high level signal will exceed a preset threshold level within the bias and control cir¬ cuit 641 (as hereinafter discussed with reference to FIG. 34) to initiate the generation of the development electrode potential and the registration solenoid energizing signal as described in detail hereinbelow.

Referring to FIG. 32, the light source 619 has continued its movement to a position beneath the docu¬ ment 623, about one-third of the way from the leading edge 651, and is iluminating a thin strip 652 of the document. The mirrors 625 and 627 have moved accorr dingly. As described above, with reference to FIG. 29, the light energy is reflected onto the surface 15 of the drum 14, and as the light source 619 and the mirror 625 proceed along the face of the document at the same speed as the photoconductive surface is moving (for 1:1 reproduction) , the image of the entire document will be reproduced in continuous fashion on the surface 15. Simultaneously, a portion of the light being reflected from the document (FIG. 32) is incident on the photode¬ tector 629 and conveys information about the reflec¬ tivity of this particular document which will determine the magnitude of the development electrode biasing potential generated by the bias and control circuit 641.

In FIG. 33, the photodetector 629 is mounted on a chassis 653 in proximity with the lens-mirror combination 631, and is directed toward the incoming light reflected from the document via the mirrors 625, 627 (see FIG. 32). Since the photodetector is

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intercepting unfocused reflected light, the incident light contains components emanating from all areas within the particular strip 652 of the document being illuminated at any particular instant of time, rather than from merely an isolated area along this strip. This insures that the light information received by this single photodetector is a reliable indicator of the average reflectivity of the document. In the illustrated embodiment, a tube 655 approximately one inch long, and attached to the photodetector, has an opaque sidewall 655a which restricts the field of view of the photodetector*s light sensitive surface (not shown), so that only light coming from the second mirror 627 (see FIG. 29) and not stray light, affects the output of the photodetector 629. A filter 657 can be, and in the preferred embodiment is, mounted over the entrance to the tube 655 to equalize the light response of the photodetector over the spectral range of interest, in case it should be objectionably sensitive to one or more specific colors or wavelengths. Otherwise if the document being copied used paper, type or indicia of those colors, the photodetector would produce an inordinately high output, possibly resulting in an inadequate development electrode bias potential and a copy with too dark a background.

The electronics of the bias and control cir¬ cuit 641 generate the development electrode potential and the registration solenoid energizing signal. Referring to FIG. 34, the electrical circuit, prior to initiation of a copy cycle, is in a "passive" condition. The photodetector 629, here an FTP 400 Darlington pho- totransistor, manufactured by Fairchild Semiconductor Co. located in Sunnyvale, California, has a collector- emitter current which is directly proportional to the

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a ount of light incident upon its photosensitive sur¬ face. When no light is incident on the photodetector, as for example when the light source is in the initial position as depicted in FIG. 30, the photodetector will not conduct. However when there is sufficient light to cause the photodetector to conduct, a voltage developed across resistors 659 and 660 will appear at pin B of a comparator 661. A preset voltage determined by a voltage Vp-Q and resistors 662 and 663 exists at pin A of the comparator, and as long as the voltage at pin B does not exceed the voltage at pin A, the output of the com¬ parator 661 at pin C will be OV and the circuit remains in its "passive" state. The preset voltage is suf¬ ficiently high so that only an amount of light energy corresponding to that reflected from the titanium-white highly-reflective strip (see FIG. 31) will be adequate to generate the minimum required collector current through the photodetector. When the light from the highly- reflective strip impinges on the photodetector, and the voltage at pin B exceeds that at pin A, the output of the comparator 661 will switch from OV to +23V and the circuit thereby enters an "active" operating condition.

The +23V signal turns on a onostable multivibrator or "one-shot" 664, which in turn generates a pulse approximately 0.8 second long, a sufficient time duration to insure that it stays on and is not multiply-pulsed during the brief time period that the photodetector is being illuminated by light from the reflective strip. The leading edge of the pulse from the one-shot 664 produces additional timing pulses of 0.4, 0.7 and 0.25 second from respectively one-shots 665, 666 and 667 (see also FIG. 35). The trailing edge of the pulse from the one-shot 666 activates still another one-shot 668 which turns on transistors 669 and

670, for approximately 0.5 second. This delivers a +24V energizing signal to the registration solenoid 645 for the duration of the pulse from the one-shot 668. As discussed above, energizing the registration solenoid starts the copy paper feed mechanism to insure arrival of the copy paper at the drum surface at the appropriate time to produce registration with the developed image thereon.

When the one-shot 667 has completed its pulse, it then, triggers a one-shot 671 which in turn pulses for approximately 1.5 seconds to cause transistors 672 and 673 simultaneously to energize a relay 674 and de-energize a relay 675, which closes a contact 674a and opens a contact 675a. This disconnects the development electrode from a -430 Volt "cleaning" potential, supplied on a line 676, and connects it to a nominal bias potential, between 150V and 330V, supplied on a line 677. This nominal potential is determined by the residual voltage left on a capacitor 678 from the previous copying cycle, which voltage biases a shunt voltage regulator 679, and the potential will be adjusted either up or down to the final bias potential by the regulator 679, as follows.

Shortly after the photodetector 629 has been illuminated by the light from the reflective strip, it will be illuminated by lower intensity light reflected from the document, at an area about one-third of the way in from its leading edge 651 (see FIG. 32). This light level will produce a corresponding voltage at the collector of the photodetector 629 which voltage will be imposed through a transistor 680 onto a _r source S of a field-effect transistor, or FET, 681. At the completion of the 0.4 second pulse from the one-shot 665,

transistors 682 and 683 generate a positive signal pulse to a gate G of the FET 681, thereby turning on the FET long enough for the capacitor 678 to be charged to the level of the voltage appearing at the source S of the FET 681. This new voltage level on the capacitor 678 provides an input to a pin D of an operational amplifier 684 of the shunt voltage regulator 679. The regulator 679, in accordance with the voltage on the capacitor 678, determines the final positive bias voltage to be applied to the development electrode 36 for the present copying cycle and adjusts the nominal voltage accordingly. The higher the voltage on the capacitor 678, the higher the positive bias voltage. The upper and lower limits of this bias voltage are fixed by varistors 684 and 685 respectively. In the present embodiment the upper limit is set at 330 V (varistor 684) and the lower limit at 150 V (varistor 685).

At the completion of the pulse from the one-shot 671, the relays 674 and 675 will be de-energized and energized respectively, thereby opening the contact 674a and closing the contact 675a and reconnecting the development electrode 36 to the -430 V cleaning potential on the line 676. The bias and control circuit thus returns to its "passive" state and is ready for the next copying cycle. FIG. 35 illustrates the timing sequence of the various pulses and the operations described above.

The magnitude of the development electrode bias being generated in response to the light received by the photodetector is predicated on some assumptions and experimentally verified operating parameters based thereon. One assumption is that the majority of documents likely to be copied are typewritten letters on

white bond with double spacing between lines. Therefore a sheet of white bond typing paper having a 25% cotton fiber content (such as Trojan Bond - Radiant White, made by Eagle Papers Division of the Brown Company, Holyoke, Massachusetts) was selected to serve as a "standard white background" document, and typing double-spaced thereon with an IBM "Prestige PICA 72 (Legal)" font and an IBM High Yield Correctable Ribbon provided a "standard document".

In the body of such a document, approximately 4% of the unit surface area will be covered by typed characters. For ease of consideration, a measure of the reflection of a document, termed "utilization" will be introduced. The utilization factor of a document equals (R _Q -RJ/R _Q where _Q is the reflectivity of a blank document having a standard white background and R is the reflectivity (in the same units as R _Q ) of an unknown document. Thus, a "standard document" has about a "4% utilization" corresponding to black print over about 4% of its surface. Referring to Fig. 36, test results based on the reflectivity of a "standard document" have shown that a development electrode bias of approximately 180 volts will yield optimum clarity and contrast in the resulting copy.

Clearly, different documents have different average reflectivities because of, for example, a difference in the background paper color, density of the typed lettering in the background, or even the color of the ink. Thus, for a single-spaced, typewritten document having a standard white background there is approximately twice as much loss of the reflected light when compared to the "standard document"; and this corresponds to an 8% utilization. Referring to Fig. 36,

a bias of 240 volts is thus provided for this single-spaced document. Correspondingly, for a smaller utilization factor corresponding to a document having a higher average reflectivity than the "standard document", a bias swing in the direction of potentials less than 180 volts will be called for. In the preferred embodiment the allowable range of bias is from 150 to 330 volts.

Thus, a particular utilization factor can be obtained from a combination of many parameters and corresponds to the total average reflectivity from the particular document. Thus, a 4% utilization, which corresponds to a "standard document", can be produced by a document having a less densely spaced type on a lower reflectivity background, for example colored paper, or a document having more densely spaced type on a higher reflectivity background, for example a super-white background.

Thus, the photoelectric detector, which responds solely to the average amount of light being reflected from the document, regardless of the source of the reflection, and the connected circuitry provide, for each value of average reflectivity, a corresponding electrode bias. The term "utilization" is therefore a convenient way to label the reflectivity which generates a predetermined bias on the electrode. Generally, the relectivity for the class of documents being copied will be more affected by the background reflectivity of the document than the density of information on the document; and hence, it is the background of the document which primarily determines the electrode bias.

Development Station-Metering Roll

After the drum surface passes the surface area defined by the development electrode 36, it has on its surface the developed image plus an excess or extra quantity of liquid developer. If the transfer material 40 were brought into contact with the drum when it had the excess developer, the transfer sheet, if it were for example paper, would be excessively wetted and would be difficult to properly dry. In addition, the resolution of the transferred image could be reduced by an excessive amount of liquid on the drum. According to the preferred embodiment, the metering roll 38 is pro¬ vided.

Referring to Fig. 37, wherein elements not needed to understand the structure of the metering roll assembly have been removed for clarity, the structural relationship of the drum 14, the metering roll 38, and sliders 741, separating the drum and the roll, is shown. Other elements of the photocopier 12 have been omitted for the sake of clarity in Figures 37-39. And the rela¬ tive spacing and sizes of the metering roll 38 and the sliders 741 have been exaggerated to enable a clearer understanding of the structure.

The drum 14 is mounted on a shaft 742 about which it is rotated in the direction shown by the arrow 14a. The metering roll 38 is mounted by shaft members 744 extending from the central portion 723 about whose axes it is rotated in the direction shown by an arrow 745. The photosensitive surface 15 of the drum 14 and the surface 748 of the metering roll 38, accordingly, are moving in opposite directions at the location of their closest approach. The surfaces 15 and 748 are separated from each other by a gap 760, however, because of the presence of the sliders 741.

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The metering roll 38 has the central metering portion 723 and shaft members 744, which, in the illustrated embodiment, are different portions of a single cylinder of circular cross section, preferably made of aluminum and having an anodized surface to pro¬ vide a hard durable surface. The metering roll shaft 744 extends through spring biased bushings or bearings 770. The bushings or bearings 770 are connected by respective springs 772 to support mountings 774 secured to the frame (not shown) of the photocopier apparatus. The springs 772 urge the metering roll 38 toward the drum 14. The illustrated metering roll shaft'744 has a drive gear 776 attached thereto. Gear 776 is driven by a chain 778 connected to a drive gear 780 mounted on the drum shaft 742. This drive structure causes metering roll 38 to rotate whenever the drum 14 is rotating, and in the same angular direction as the drum (compare arrows 14a and 745).

The surface of the drum 14 in the illustrated embodiment has a substrate 782 of aluminum which is uncovered and visible at each edge 783 of the peripheral surface for a distance of about 0.5 inch. The central, photosensitive, portion 15 of the drum surface has a layer of photosensitive selenium approximately .0015 inch thick on the aluminum substrate. A typical width for the central portion 784 would be 8.5 inches.

In the embodiment illustrated, the slider spacer 741 has a shoe-like rigid body. The slider includes an exterior arcuate drum contact surface 790 substantially conforming to an arc of the drum edge 783, for sliding, frictional contact with the drum. edge sur¬ face. The drum contact surface 790 is designed to have a radius of curvature no greater than that of the drum

surface it contacts. Consequently, it has edges 794 and 795 always in firm contact with the surface of the drum edge 783, providing a contact position that is always stable.

The slider element 741 also includes an interior surface 792 defining a hole 793 through which the stepped down shaft 744 of the metering roll 38 extends, so that the shaft is in a sliding relationship with that surface 792 of the slider 741. The slider element 741 also has a surface forming a notch 797 on its side opposite the drum 14. A stop rod 798 is shown near the notch 797 directly in the path the slider ele¬ ment 741 will take as the roller 38 is pivoted away from the drum 14, as is done when the drum must be removed for cleaning or maintenance. The rod 798 is attached to the frame of the photocopier in a conventional manner not shown in the drawing.

The sliders 741 are preferably formed from a polyolefin such as the one sold under the trademark "Pennlon" by Dixon Corporation, Bristol, Rhode Island. However other materials such as Teflon, vinyl acetals, olefins, Rulon, etc., that have the necessary lubricity and wear characteristics can also be employed. In par¬ ticular, the material comprising the surfaces of the strips 741 should be self-lubricating to reduce sliding friction with drum 14, and roll 38, and should be hard and tough to provide long life.

In operation, the metering roll 38 removes the excess liquid remaining on the photosensitive drum sur¬ face portion 15 after it passes the development station, that is, the step of contacting liquid developer to the drum at the development electrode. The gap 760 between

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the metering portion 723 and the drum surface is one of the parameters, as is well known in the art, which sets the thickness of the liquid developer presented to the transfer station 42.

Thus, according to the invention, the metering roll 38, driven by the drum shaft 742, rotates in the same angular direction as the drum so that its surface 748 is moving opposite the drum surface 15 at the gap 760. In the illustrated embodiment, the drum 14 can rotate, for example, at 34 rpm and the metering roll 38 can rotate, for example, at 396 rpm.

During this operation of the photocopier, the arcuate surface 790 of the shoe-like slider 741 is in sliding contact with the surface of the drum edge 783, and the shaft 744 of the metering roll 38 is in sliding, rotational contact with the surface 792 of the spacer that defines the hole 793 through which the shaft extends. The diameter of the hole 793 is slightly greater than that of the shaft 744. The diameter of the shaft, for example, in the illustrated embodiment is 0.754 inch, and the diameter of the hole 793 is .004 inch larger. The gap 760 between the photosensitive surface 15 of the drum 14 and the surface 748 of the metering roll 38 is controlled by the shortest distance between the slider surface 792 of the hole 793 and the drum contacting slider surface 790. The dimension of this distance in the embodiment, shown by the line designated 799 in Fig. 38, is .175 inch. Since the slider surface 790 slides on the aluminum substrate edge 783, and the selenium surface 15 is about .0015 inch in height, with a metering roll central portion 723 of diameter of 1.098 inch, the gap 760 between surfaces 15 and 748 would be .0015 inch.

When the metering roll 38 is pivoted away from the drum 14, the notch 797 meets the stop rod 798 mounted on the photocopier frame. The spacer 41 is therefore prevented from rotating around the roller shaft 744 and interfering with removal or insertion of the drum 14.

Developer Composition

The apparatus of the present invention employs a developer composition which in use has improved deple¬ tion characteristics and produces copies of high image density. Use of the developer allows upwards of 20,000 copies of high image density to be made before the deve- loper must be replaced. These properties of the deve¬ loper may be traced to the inclusion in the composition of a "gelatex". As used herein, the term "gelatex" ~ refers to a mixture of vinyl polymers which together function both as a dispersant and a fixitive, that is, a mixture of a first polymer component on the borderline of solubility in the carrier or sparingly soluble in the carrier (gel component) and a second, carrier-insoluble component (latex). Accordingly, the gelatex consists essentially of a covalently cross-linked, vinyl polymer comprising a three dimensional multiply-branched molecu¬ lar framework in the form of a gel, and a carrier inso¬ luble vinyl polymeric latex physically entrapped and/or entangled within the three dimensional molecular frame¬ work.

In use, the components of developer compositions containing the gelatex are depleted at a substantially uniform rate. Thus, the image density of successively produced copies remains at a desired high level, but the number of copies that can be made per unit volume of toner is essentially identical to prior

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art toners. Piecemeal additions of toner added to the working developer as it is used upgrade the developer so that copies having an image density quite close to that of fresh developer are possible. Also, less settling of toner components occurs during the useful life of the developer.

The developer compositions advantageously employed in the photocopier described herein, in addi¬ tion to the gelatex, include an organic liquid carrier having a resistivity greater than 10 ⁹ ohm-cm and a dielectric constant less than 3, a charge control agent, and a pigment or pigments system. Desirably, a wood rosin and wax, preferably paraffin wax, are also included. While various conventional charge control agents can be used to impart either a positive or nega¬ tive polarity to the composition, carrier insoluble charge control agents which have an affinity for the gelatex are preferred. The preferred charge control agent in the manufacture of negative developer com¬ positions made in accordance with the invention is a copolymer of 10-50 parts of a lower alkyl (C2-Cg) vinyl ether and 50-90 parts of a vinyl chloride. Optionally the charge control agent may contain trace amounts of covalently bonded anionic surfactant molecules such as ^c 10~ ^c 40 aliphatic hydrocarbons (petroleum fractions) multiply substituted with alkali metal sulfonate groups.

The compositions which are used are prepared by synthesizing a covalently cross-linked, three- dimensional and multiply-branched vinyl polymeric gel and thereafter synthesizing a carrier insoluble vinyl polymeric latex in the presence of the gel. The reac¬ tions are conducted under an inert atmosphere with the aid of a free radical initiator type catalyst such as

benzoyl peroxide or azobisisobutyro nitrile. Trace amounts, generally within the range of 0.1-1.2% by weight, of monomer units having 2-5 vinyl moieties attached by covalent bonds are included in the prepara¬ tion of the gel polymer to obtain the cross-linked, multiply-branched three-dimensional network. Physical entanglement or entrapment of the insoluble latex com¬ ponent is promoted by synthesizing the latex within the formed gel structure. The gelatex is then mixed with the other components of the developer and ball milled in the carrier for a suf icient amount of time to intima¬ tely associate all ingredients and to reduce the parti¬ cular size to the submicron range.

In the preferred embodiments, the gel polymer comprises a major amount of monomer units selected-from the group consisting of:

X CH ₂ - c-3- c=o

O-Y where X is H or CH3 and Y is C _n H2 _n +ι where 8 _< n <_ 20 and a trace amount of monomer units having 2-5 vinyl moieties attached by covalent bonds, preferably ethylene dimethacrylate. The carrier insoluble latex component of the gelatex is preferably synthesized from a major amount of monomer units selected from the group consisting of:

X

-E^H ₂ - c-3-

1 c=o

1 o-z where X is H or CH3 and Z is C _n H2 _n +ι where 1 < _^ n _< 6. Synthesis of these types of polymers may also be accomplished using other monomers. Copolymers of the

above-mentioned acrylic and methacrylic acid esters with other vinyl monomers may also be used. The guiding principle in selecting particular polymer systems is that the matrix-like branched component must be on the borderline of solubility in the carrier and the latex component substantially insoluble. Preferably, the respective polymers will also be oxidation resistant and have sufficient structural similarity such that they have an affinity for one another.

The carriers useful in the preferred developer composition are nonpolar solvents or solvent systems of the type conventionally used in liquid developers. The carrier will have a resistivity greater than about 10^ ohm-cm and a dielectric constant less than about 3. As known to those skilled in the art, it will be charac¬ terized by an evaporation rate suitable for rapid, e.g., two second, evaporations from the substrate to be deve¬ loped when exposed to temperatures below which paper is charred. It will preferably be free of aromatic liquids and other excessively toxic or corrosive components. Also, as is known, it should have a viscosity low enough to permit rapid migration of particles which are attracted to the electrostatically charged image to be developed. Typically, the viscosity of the vehicle may range between about 0.5 and 2.5 centipoise at room tem¬ perature.

Examples of suitable carriers include petro¬ leum fractions which are substantially odorless, relati¬ vely inexpensive, and commercially available such as those sold by Humble Oil and Refining Company under the trademarks ISOPAR G, ISOPAR H, ISOPAR K, and ISOPAR L. These materials comprise various mixtures of about Cg - ^c 16 hydrocarbons.

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The pigment or pigment system employed in the developer composition is also conventional. The pre¬ ferred method of imparting color to the toner particles is to use a fine solid particulate pigment in com¬ bination with one or more dyes which associate with the composition's resinous components. Carbon black par¬ ticles in the submicron range are preferred, but powdered metals and metal oxides may also be used. Various dyes of recognized utility in imparting color to vinyl resins may be used in combination with the par¬ ticulate pigment. The presently preferred pigment system for use in the composition comprises Printex 140u, a carbon black sold by Degussa Inc. having a mean particle size of 0.029 microns, plus alkali blue (BASF Wyandotte) and phthalo green (Herculese Inc.).

Vehicle-soluble or vehicle-insoluble charge control agents of known utility which impart either a positive or negative polarity to the developer composition may be used. Examples of such materials include cobalt naphthanate, a carrier-soluble material which imparts a positive charge to the developer, dode- cyl benzene alkali metal sulfonate, which is sparingly soluble in organic carriers of the type described above and imparts a negative charge to the developer, and various homopolymers or multipolymers of alkali metal salts of acrylic or methacrylic acid which may be engi¬ neered to be either soluble or insoluble in the carrier, depending on the concentration and identity of the corn- monomers (if any) included in their structure, and which impart a negative charge to the developer.

However, the preferred charge control agent for use in the composition comprises a copolymer of 10 to 50 parts of a lower alkyl (C2 - Cg) vinyl ether and

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50 to 90 parts vinyl chloride. It is believed that the chlorinated component of the copolymer is responsible for its ability to impart negative charge to the toner; the lower alkyl group attached to the polymer chain via an ether linkage is believed to be responsible for imparting to the polymer an ability to remain in intimate association with the insoluble resinous components. Generally, as the molecular weight of the alkoxy side chain in the copolymer increases, its affinity for the carrier increases and its affinity for the insoluble resinous components correspondingly decreases. This charge control agent is therefore substantially insoluble in the carrier and remains in intimate association with the resinous components. This property, in combination with its outstanding ability to impart a negative charge to the resinous components of the developer composition, is believed to contribute to the improved depletion properties, to the uniformly high image density and lower rate of image density decrease characteristic of compositions employed herein, and to the high optical density of the copies it produces. In general, the greater the length of the alkoxy side chain within the range specified, the smaller is the fraction of vinyl ether that must be included in the copolymer. The charge control agent is preferably included in the developer such that it constitutes between about 4% and 10% of the total weight of the composition, excluding the carrier.

The currently preferred charge control agent comprises a copolymer of 25 parts isobutyl vinyl ether and 75 parts vinyl chloride. This copolymer is available commercially from BASF Wyandotte Corporation under the trademark LAROFLEX-MP 35. LAROFLEX-MP 35 is synthesized from isobutyl vinyl ether and

monochloroethane employing an interfacial polymerization which results in the formation of a latex which is spray dried. The copolymerization is conducted in the presence of anionic surfactants which become mixed with the resin. Attempts to remove the surfactants have led to the conclusion that at least a fraction of the surfactant content is covalently bonded to the copolymer. Typically, the surfactant used is a mixture of saturated and unsaturated aliphatic hydrocarbon chains containing 10-40 carbon atoms multiply substituted with sulfonate groups. These alkali metal petroleum sulfonates are present only in trace quantities and do not adversely affect the properties of the charge control agent. In fact, it is believed that the presence of the anionic surfactants mixed with or covalently bonded to the polymer may enhance its ability to impart a negative charge.

At the heart of the composition is the gelatex which comprises a mixture of two or more polymers or copolymers which are designed to act in tandem to provide both a fixative and a dispersant function and to intimately associate with the pigment system and charge control agent. The gelatex fits the definition of a mixture since its gel and carrier-insoluble components remain unconnected by chemical bonds. However, the components of the gelatex do not depend solely on second order forces for association. Rather, the gel component comprises a covalently cross-linked, multiply-branched, three-dimensional vinyl polymer having a void volume which holds the carrier-insoluble latex component as well as other insoluble components as an inclusion complex or clatherate-like compound by physical entanglement or entrapment. Thus, as toner is removed from the developer in use, there is a marked tendency

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for all components to deplete at a uniform rate. Developer components thus have a reduced tendency to settle out, and the dispersion exhibits outstanding stability.

Broadly, the gelatex is made by reacting a major amount of monovinyl monomers which, when polymerized, result in a substance on the borderline of solubility in the carrier, together with monomers having 2-5 vinyl moieties attached by covalent bonds. As the number of vinyl moieties in the cross-linker increases, the reaction becomes increasing difficult to control. Di-vinyl compounds are preferred in admixture with Cg - C20 alkyl esters of acrylic or methacrylic acids. Outstanding results have been achieved with lauryl methacrylate and ethylene dimethacrylate, but other cross-linkers and other monovinyl monomers may be used. Nonlimiting examples of useful cross-linkers include ethylene glycol dimethacrylate, tri-ethyleneglycol diacrylate, divinyl benzene, pentaerythritol triacrylate, neopentylglycol diacrylate, and 1, 6 hexane diol diacrylate. As will be apparent to those skilled in the liquid developer art, vinyl monomers other than the preferred Cg-C20 alkyl acrylic or methacrylic acid esters may be used as the monomer used to form the gel. Carrier-insoluble monovinyl monomers may also be included within the gel polymer provided that the resulting branched copolymer nevertheless exhibits the appropriate solubility. The preferred Cg-C20 alkyl acrylic or methacrylic acid esters may be copolymerized with, for example, glycidyl methacrylate or acrylate, crotonic, aleic, atropic, fumaric, itaconic, and citraconic acids, acrylic, methacrylic, and maleic, anhydrides and acids, acrylonitrile, methacrylonitrile, acrylamide, hydroxy ethyl methacrylate and acrylate,

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hydroxy propyl methacrylate and acrylate, dimethyl amino methyl methacrylate and acrylate, allyl alcohol, cinnamic acid, ethallyl alcohol, propargyl alcohol, mono and dimethyl maleate and fumarate, vinyl pyrrolidone, and others. The important properties of this component of the gelatex are its carrier solubility properties and its highly branched structure. The gel in its reaction medium has the appearance of a translucent, viscous liquid.

Synthesis is conducted using conventional techniques. Thus, the monomer or monomers to be polymerized are added to a suitable vehicle together with about 0.1%-1.2% by weight cross-linker and a free radical initiator type catalyst. Under an inert atmosphere, the reaction is continued, typically for 4-6 hours, at temperatures in the 80 ^β C range until the reaction rate approaches zero. The fraction of divinyl monomer or other multifunctional cross-linker employed in the reaction medium may be varied as a function of the relative reactivities of the particular divinyl and monovinyl compound employed. Increased concentrations of catalyst result in lower molecular weight copolymers.

The latex component of the gelatex is most preferably polymerized in the presence of the soluble component after production as set forth above. This technique promotes entrapment and/or entanglement of the latex within the gel matrix. Thus one or a combination of vinyl monomers which will result in a polymer which is substantially insoluble in the carrier are added, to the product described above together with fresh catalyst and optionally a small amount of cross-linker (e.g. less than about 0.5% by weight). The reaction results in the formation of insoluble polymer chains of widely varying

molecular weight formed within and about the gel structure. Again, those skilled in the art will be able to select various vinyl monomers which will result in a polymer of the desired solubility properties. Some unreacted carrier-soluble monomer will often remain after completion of the first reaction stage, and this can be incorporated as copolymer units in the carrier-insoluble latex. Minor amounts of other carrier-soluble monomers may be included as long as the resulting polymer remains substantially insoluble. The ratio of gel polymer to carrier-insoluble polymer in the gelatex can vary generally within the range of 2:1 to 1:2. For the preferred system, the ratio is about 1:1.1. Optionally, the foregoing reactions may be conducted in the presence of the charge control agent and other developer components such as wax. This technique promotes intimate admixture of all components, and some covalent bonds between the gelatex polymers and the wax and/or charge control agent are formed which promote uniform depletion.

The gelatex is then ball milled in the carrier together with the charge control agent, the pigment system, and preferably rosin and wax, for a sufficient amount of time, typically 20-40 hours, to produce a homogeneous, blend of all components having a mean particle size in the 0.2-0.3 micron range with particle distribution in the range of about 0.1-1.5 microns. Detailed examples indicating preferred ratios of ingredients are provided in U.S. application Serial No. 109,393 filed January 3, 1980.

Machine Maintenance Improvements - Drum Removal

The congested condition, due in part to the array of those components described above which are clo-

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sely situated to the drum, makes removal of the drum for maintainence, repair, or replacement a potentially dif¬ ficult mechanical operation. Any inadvertent movement of the drum in a direction radial to its axis of rota¬ tion may cause contact with one of the closely situated components and either damage the components themselves or permanently mar the fragile photoconductive surface.

Referring to Fig. 40, apparatus for sup¬ porting the drum, while it is being removed from its operative position, will now be described. The central shaft 742 extends along the entire length of drum 14, protrudes through both ends thereof, and is supported at opposite ends by brackets 836 and 837, which brackets are mounted to the main housing of the copier. A central hub 838 encircles shaft 742 and is able to _ rotate about said shaft by means of bearings 839 and 841. Extending outwardly from hub 838 are three support members 843, which are of essentially the same length as hub 838. The illustrated support members 843 are spaced equidistantly around the circumference of hub 838 but this spacing, although preferred, is not required for the proper operation of the present invention, nor is the limitation to only three such members. Each support member includes a planar portion 845 (see also Fig. 41) and an integrally formed tubular portion 347, the tubu¬ lar portion 847 having a threaded inner bore 849 at each end thereof and a smooth, straight outermost surface 851, which surface is generally parallel to shaft 742. The entire assembly consisting of hub 838, planar por¬ tions 845 and tubular portions 847 can be formed from a single casting or extrusion, or can be assembled by rigidly bonding together the component elements. Drum 14 and support members 843 are held in a fixed spatial relationship by end covers 853 and 855. Covers 853 and

855 tightly engage the openings at either end of the drum and are rigidly attached to support members 843 by screws 857 which engage the threaded bores 849 of tubu¬ lar portions 847. With the covers properly in place, as shown in Fig. 40, a clearance of several thousandths of an inch is maintained between the outer surfaces 851 of tubular portions 847 and the inner surface 858 of the drum. Thus the drum is not directly resting on any por¬ tion of the support members 843 during normal operation of the copier.

Slidably mounted on each planar portion 845 of a support member 843 is an extender guide 859. As shown more clearly in Fig. 41, each guide is.shaped to conform generally to the contour of the underlying support member 843 so that an outer segment 860a slides directly against tubular portion 847 while an inner segment 860b slides against a thin spacer 861 intermediate the guide 859 and planar portion 845. Each guide has a generally straight outer edge 863 and a longitudinal slot 865 parallel to edge 863, the slot extending along almost the entire length of guide 859. Each guide 859 is held in slidable contact against a corresponding tubular portion 847 and spacer 861 by flanged sleeves 867a and 867b which protrude through longitudinal slot 865 and which are themselves held in place by screws 869 and 871, the screws passing through spacer 861 and being anchored in planar portion 845. Sleeves 867a and 867b, through their engagement with slot 865, serve as guides for directing the movement of guides 859, and as stops for limiting the extent of movement of the guides. Sleeves 867a and 867b are positioned such that edge 863 of the guide will be aligned radially with outer surface 851, and will remain aligned as the guide is slid in the direction parallel to the drum axis. The phrase

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"aligned radially" signifies that along the entire length of the edge 863, this straight edge is lined up with the straight outer surface 851 and neither extends radially beyond surface 851 toward drum inner surface

858 (see also Fig. 40), nor stops short of reaching surface 851. A spring 873 connects between screw 869 and the end of guide 859, and urges guide 859 toward the left. This corresponds to the direction of drum removal. Referring to Fig. 42, guide 859, in the absence of a physical restraint, moves as far as possible to the left, sufficient to protrude beyond the end of the drum, until stopped by sleeve 867b. In the illustrated embodiment (Fig. 40), end cover 853 provides this physical restraint, so that during normal operation of the copier, extender guides 859 are held or maintained in an inoperative position within the "- interior of drum 13.

Fig. 43 shows how the extender guides aid in removal of drum 14. The end covers and shaft support bracket 836 (see Fig. 40) have been removed, and guides

859 are fully extended. The drum 14 has been moved axially a considerable distance from its original position to the right and rides on the surface 851 of tubular portion 847 and the radially aligned edge 863 of guide 859. Since in the operative position of the drum there was only several thousandths of an inch clearance between the drum interior and surfaces 851 of the circumferentially arranged support members, there is no appreciable radial movement of the drum during the drum removal process. In the absence of guide 859, in the removal position depicted in Fig. 43, the trailing edge 875 of the drum would be encompassing only the axially . outermost ends of support members 843 and the drum would be able to pivot about its axis and in the radial

direction. Since the drum would not yet have advanced to a point where it was clear of all potentially damaging interference, any radial movement still could mar the drum surface. Instead however, according to the invention, guides 859 have effectively extended the drum support to minimize damaging radial movement until the drum is clear of the drum cavity.

The guides are equally helpful in reinstalling the drum. To facilitate engagement of the guides with the only fractionally larger drum opening, the edges of the guides are, in the illustrated embodiment, beveled (Fig. 44) . The reduced height of the guides at edge 877 makes it easier for the drum to encompass the ends of the guides, and the gradually sloping surface 879 will direct the drum into full contact with surface 863 of the guide. The drum can thereby be safely returned to its operative position.

Jam Detection

Referring to Fig. 45, which is similar to Fig. 1 except that sheet pick-off has not been effected and components pertinent to "jam detection" are shown thereon, if the copy sheet 40 is not properly "picked- off" from the photosensitive surface 15, it is detected as the copy sheet leading edge 22a passes beneath a sheet detection assembly 930 positioned between the transfer station and the cleaning station. The sheet detection assembly 930 provides an output signal over its output lines 932 to electrical circuitry 934, which in one state indicates the undesired presence of the sheet 40. In response to this one state of the signal on lines 932, the electrical circuitry 934 terminates rotation of the drum 14 by stopping the drive motor 541a, and renders the electrostatic copier inoperative

for making further copies until the missed sheet is removed and the copier is reset.

The cleaning station 55 includes the cleaning blade 48 and a cleaning roller 56. The cleaning blade contacts the photosensitive surface 15 across its width, in a direction normal to its surface, and applies a pressure against the surface. According to the inven¬ tion, after the detection of the undesired sheet 40 on the photosensitive surface 15 by the sheet detection assembly 930, a predetermined delay is provided so that the leading edge 922a can contact the blade 48 whereby the sheet leading edge is stopped and a buckle 946 is formed in the sheet material at a position between the cleaning blade 48 and the transfer station 42. This buckle is spaced away from the photosensitive surface 15 and is made accessible to the operator upon the opening of a top panel (not shown) of the copier, so that the "jammed" sheet can be easily removed thereby. For faci¬ litating removal of the sheet material, the sheet detec¬ tion assembly 930 is mounted for pivotable movement in an upward direction to an inoperative position whereby it will neither interfere with the removal of the sheet nor be damaged thereby.

Referring to Figure 46, the sheet detection assembly 930 has a transducer 948 having, in the illustrated embodiment, individual transmitting and receiving elements 949, 950 respectively (see FIG. 47) attached to, and extending downwardly from, a sup¬ port arm 952. The support arm 952 is pivotably fastened by a pin 953 to a bracket 954 which in turn attaches to a convenient location on the copier chassis. In this operative position the illustrated transducer typically is spaced 3/4 inch away from the photosensitive surface

15. ^' An adjustment screw 955 whose bottom end protrudes through the support arm 952 and bears against the bracket 954, can be adjusted to vary the distance bet¬ ween the transducer 948 and the photosensitive surface 15 to optimize the operation of the transducer. In the illustrated embodiment, the support arm 952 pivots about an axis 953 which is parallel to a line tangent to the photosensitive surface 15 at a position directly beneath the transducer 948. The bracket 954 provides a stop portion 957 against which the pivoting support arm 952 rests when it is in the upward inoperative position (shown in phantom lines at 930a). A torsion spring 958 urges the support arm toward the operative position.

The transducer 948 is directed downwardly at the photosensitive surface 15 of the drum 14 and is „con- nected through wires 932 to the electrical circuitry 934 (see FIG. 48). Preferably, the transducer 948 is an infrared device which transmits an infrared energy signal through a transmitting element 949 toward the photosensitive surface and receives the reflected signal through the receiving element 950. When there is no paper on the photosensitive surface beneath the trans¬ ducer, the signal reflected from the surface is exceed¬ ingly small because of the infrared-absorbing characteristic of the selenium surface. However, when a sheet of copy material is beneath the transducer, the amount of reflection increases significantly and the large signal received by element 950, as described below, is reflected in the electrical signal level to the circuitry 934.

The necessary close proximity of the transducer assembly to the photosensitive surface causes the transmitting and receiving elements to be

susceptible to having liquid toner splashed onto their optical surfaces from the photosensitive surface which is rotating in the direction of an arrow 960. Referring to FIG. 47, it can be seen that an end shield 961 and a side shield 961a are provided on the support arm 952. These shields, when the detector assembly is in the operative position (see FIG. 46), extend down toward the photosensitive surface, beyond the bottom surface of the transducer, and deflect toner from the photosensitive surface away from the transducer optics. Shields 961 and 961a also serve a secondary purpose, that is, restricting the field of view of the transducer, so that the receiving element 950 is less likely to receive spurious signals reflected from areas other than the portion of the photosensitive surface being monitored.

Referring now to Figure 48, the illustrated infrared transmitting element 949 is an infrared light-emitting diode (LED) , and the receiving element 950 is an infrared-sensitive photo-Darlington transistor. The amount of collector-to-emitter current flowing through the photo-Darlington is directly related to the intensity of infrared light incident on its light-sensitive surface. This collector-to-emitter current produces a voltage drop across a resistor 962, and both the magnitude and duration of .this voltage drop determine the width of an output pulse produced by an amplifier 964 in response thereto. Thus the width of this output pulse ultimately depends on the intensity and duration of the reflected infrared signal.

The output pulse from the amplifier 964 is an input to a second amplifier 966 via a filter circuit 968. The values of a resistor 968a and a capacitor 968b within the filter circuit are selected so that only a

pulse whose width extends a predetermined threshold value can generate an output change from the amplifier 966. The threshold value can be exceeded only by pulses produced in response to the relatively large amount of light reflected from a sheet of copy material, and this insures that a noise burst or another extraneous, short-lived signal will not actuate the amplifier 966.

Once the amplifier 66 is "triggered", it switches from a normally grounded output ^' state to a high output level to drive a relay 970 through a coil 972. The relay 970 has a normally open contact 974 and a normally closed contact 976. When the coil 972 is energized, a motor control line 978 which communicates with the drive motor 541a (see Figure 45) is discon¬ nected and as a result the rotation of the drum ceases. In addition, a lamp control line 980 is connected to a' voltage source 981, in this instance 24 volts, and a lamp indicator (not shown) is lit.

The values of the resistor 968a and the capacitor 968b also provide the required RC time-constant to delay "triggering" of the amplifier 966 until the leading edge of the sheet of copy material reaches the cleaning blade (see FIG. 45). The amount of time delay depends on several factors including, for example, the rate of rotation of the photosensitive surface, and the response time of the photo-Darlington transistor.

It should also be noted that in this configuration, the relay 972 is self-latching. That is, when the normally open contact 974 is connected to the voltage source, a loop is completed whereby the relay coil 972 is energized by the voltage source 981 via a

diode 990 and remains energized even after the output of the amplifier 966 stops. The self-latching provision is removed when the paper jam is cleared and a pushbutton 992 (normally closed) is depressed, thereby disconnecting the relay coil from the voltage source 981 and returning the relay to its normally open configuration.

Additions, subtractions, deletions and other modifications of the disclosed preferred embodiment of the invention will be obvious to those practiced in the art and are within the scope of the following claims.

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