Technical Field

This invention relates to electrically controlled devices of the kind including an electri¬ cally operated mechanism, scanning means adapted to sense indicia of alignment of said mechanism, and an electrically conductive lead adapted to carry signals for operating said mechanism. The invention has a particular application where the controlled device is a printer such as a high-speed dot matrix printer having an electrically operated print head which is movable relative to record media on which printing is to occur, and a scanner for sensing indicia of alignment or position of the print head relative to the record media.

Background Art

An electrically controlled device such as a high-speed line printer of the dot-matrix type, for example, typically includes a print head which is movable across a paper document in a reciprocating manner for serial printing of selected dot positions in a dot column or row. The print head may be moved by cable and pulley arrangement, a lead screw, or a cam drive or like drive mechanism. A typical print head is mounted for movement on a carriage, and has one or more electrically operated print elements which are actuated or energized at high speed to cause printing of dots by jet-like ejection of ink droplets or movement of print wires attached to solenoids for impact against the paper. In the case of a thermal printer, the print elements are actuated to provide highly localized sources of heat for thermal printing of dots on record media which is heat-sensitive.

The print elements may be arranged in a row for printing a single horizontal line of dots at a time so that a line of printed characters is completed by plural horizontal passes of the print head across the record media. Alternatively, the print elements may be arranged in one or more vertically oriented groups of elements for printing a line of dot-matrix characters with a single print head pass.

When printing begins, the print head is normally moved to the lefthand margin position on the paper document and the print head is then moved from left to right across the document at a substantially constant speed while successively printing dots at selected positions until reaching the righthand margin of the paper to complete a line of print. The print head may then be moved in the reverse direction, that is from right to left, back to the lefthand document margin whereupon the paper document will be advanced in readiness for printing of the next line. In the case of a bi-directional printer, the document is advanced at the conclusion of each print line and printing occurs in both directions of print head movement.

An electrically controlled device of the kind specified, which is embodied as an impact type dot matrix printer is known from U.S. Patent Specification No. 3,970,183. According to the known device a scan¬ ning device in the form of a light source and photo- transistor assembly moving with the print head cooper- ates with a fixed timing strip mounted on the printer body and having slits formed therein to define timing instants for dot printing. The known device has the disadvantage of a relatively complex and hence expen¬ sive construction resulting from the provision of a separate timing strip and separate timing strip mount¬ ing means.

Disclosure of the Invention

It is an object of the present invention to provide an electrically controlled device of the kind specified wherein the aforementioned disadvantage is alleviated.

Therefore, according to the present inven¬ tion, there is provided an electrically controlled device of the kind specified characterized in that said electrically conductive lead is employed to provide said indicia of alignment.

It will be appreciated that in a device according to the invention, an economy of construction is achieved in that the electrically conductive lead is additionally employed to provide the indicia of alignment.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 shows a configuration for a carriage position sensing system in use with a thermal-type print head in accordance with this invention;

Fig. 2A shows a schematic for a trans issive type optical scanner circuit which may be used with the sensing system shown in Fig. 1;

Fig. 2B shows a typical output signal of the circuit shown in Fig. 2A on scanning of an electrical conductor comprised of parallel copper runs separated by transparent Kapton type plastic; Figs. 3A and 3B respectively illustrate exemplary outputs of the circuit shown in Fig. 2A when used for scanning a conventional type timing strip (Fig. 3A) , and for scanning a special electrical conductor type timing strip (Fig. 3B) of the type shown in Fig. 1;

Fig. 4 shows a thermal-type print head connected with a special electrical conductor by which timing indicia are provided by parallel copper runs with one run being widened to represent a print head home position;

Fig. 5 illustrates a section of special electrical conductor which, in accordance with this invention, provides indicia for printing of ten-dot wide dot matrix characters; Fig. 6 illustrates a means for mounting a transmissive type optical scanner for use in conjunc¬ tion with a thermal print head and electrical conduc¬ tor as shown in Figs. 1 and 4;

Fig. 7 illustrates a variation of an electrical conductor and scanner configuration which may be used in accordance with this invention;

Fig. 8 illustrates an embodiment of the invention in which an optical scanner may be mounted for movement with the print head in a high-speed printer device.

Best Mode for Carrying Out the Invention

The presently preferred embodiments of this invention relate to printer devices, particularly high speed dot matrix type printer devices, such as thermal printers, ink jet printers and dot matrix impact type printers. Fig. 1 illustrates a presently-preferred embodiment of this invention in the form of an assem¬ bly 10 which is part of a thermal type printer device. The assembly 10 comprises a thermal print head 12 which is in the form of a printed circuit board mounted to a movable carriage assembly 14. The carriage assembly 14 has a pair of guide holes 16 for movement along a pair of rails (not shown) or the like in the directions 18 illustrated in Fig. 1. The print head 12 and the carriage assembly 14 are thus movable relative to record media on which printing is to

occur. The print head 12 has a total of ten print elements, the electrical connections 20 for which are shown on the backside of the circuit board 10 in Fig. 1. The ten print elements are laid out in a horizon- tal row and spaced apart so that the print head 12 may be used, for example, to print a 40 character long line of dot matrix characters, with each print element printing four such characters in a line of print.

The electrically operated print head 12 is connected to an electrically conductive lead 22 re¬ ferred to for brevity hereinafter as an electrical conductor 22 in the form of a ribbon-like cable or circuit which carries the signals by which the print head 12 is operated. The conductor 22 has connections soldered to the print head 12 in a conventional man¬ ner, and is further secured to the print head 12 by means of a clamping bracket 24 fastened to the print head 12 by screws or other means.

The electrical conductor 22 comprises eleven individual electrical conductors 26 referred to for brevity hereinafter as electrically conductive runs 26 inclusive of an input lead for energizing each of the ten print elements and an eleventh conductive run 26 which leads to ground. Over a distance 28, represent- ing a scanner sensing area, each of the runs 26 is arranged adjacent one another in parallel spaced apart coplanar relationship supported by an electrically insulative material 30 which is essentially optically transparent. The conductive runs 26 are essentially optically opaque, and are preferably made of copper or copper alloy or equivalent conductive material. The essentially transparent insulative material 30 is preferably made of a flexible heat-resistant plastic, such as a Mylar or Kapton type of plastic, so that the electrical conductor 22 is in effect a flexible cir¬ cuit. Such flexible circuits are well-known and are used to accommodate relative movement between a mova-

ble print head and stationary control electronics (not shown) which are interconnected by the flexible cir¬ cuit.

As shown in Fig. 1, the assembly 10 includes a scanner which is in the form of a transmissive type optical scanner 32 comprising a light emitting diode or LED 33A and a phototransistor 33B (shown only in Fig. 2A) disposed respectively on opposite sides of the electrical conductor 22. The scanner 32 is thus mounted to sense the alternating clear and opaque spaces which are defined by optical contrast between the electrical runs 26 and the insulative material 30. These alternating spaces provide indicia of alignment or position of the print head 12, to represent the position of the print head 12 over the constant veloc¬ ity area of movement of the carriage 14 with respect to the record media (not shown) . The scanner 32 is mounted to sense the indicia of alignment provided by the electrical conductor 22 and to feedback related signals representing the location of the print head 12 to conventional control electronics (not shown) .

When the printer device is operated, the conductive runs 26 interrupt the light emissions of the scanner 22 diode, whereas the clear spaces formed by the insulative material 30 will allow the photo- transistor of the scanner 32 to detect the light which such diode emits. In other words, the scanner 32, being fixed with respect to the printer frame (not shown) , senses alternating light beam interruptions caused by the conductive runs 22 as the print head 12 is shuttled horizontally while printing upon a paper document. For the assembly illustrated in Fig. 1, it may be expedient to anchor or clamp the electrical conductor 22 to the thermal print head 12 at points on both sides of the scanner sensing area 28 to ensure that the electrical conductor 22 moves with the print head and does not buckle or twist in the area 28.

When configured as schematically shown in Fig. 2A, the scanner 32 will produce a signal similar to that shown in Fig. 2B. In a manner which is well known, this signal can be converted to an analog voltage signal and then amplified and digitized to produce a digital signal for conventional use by control electronics. Through the control electronics, the digital signal input can be used to control motor speed for horizontal shuttling of the print head and to energize the print elements of the print head at the proper time for accurate printing of the dot matrix characters.

Using a scanner circuit as shown in Fig. 2A, the waveforms shown in Figs. 3A and 3B were produced to compare the scanner output for a conventional type timing strip (Fig. 3A) to the output for a Kapton (polyimide) type plastic flexible circuit used as a timing strip (Fig. 3B) . The conventional type timing strip was a plastic type provided with alternating dark (black) and clear spaces each 0.18 mm in width. The Kapton plastic flexible circuit was of a type having 0.51 mm wide copper runs, each spaced 0.13 mm apart by the clear Kapton plastic.

Fig. 4 shows a thermal print head assembly 10A which is similar to that shown in Fig. 1. The assembly 10A shown in Fig. 4 has a thermal print head 12A for which ten connections 20A for respective print elements and related electrical conductive runs 34A are shown. Also shown in Fig. 4 is a flexible circuit 22A having electrical conductive runs 26A with widened ends 36A to facilitate connection to control elec¬ tronics. It will be seen in Fig. 4 that one of the electrical runs 26A has an expanded area 38A within the scanner sensing area 28A. The expanded area 38A is in this case intended to be the last area of opti¬ cal contrast to be sensed by the scanner, and is accordingly of different width compared with the other

areas of optical contrast provided by electrical runs 26A relative to the insulative material 30A within the scanner sensing area 28A. The expanded area 38 may thus be used to provide indicia representing the right hand margin home position for the print head 12A. In other words, the expanded area 38A will be used to indicate the right hand "turn-around" area for the print head 12A over which the print head 12A velocity will decrease from a constant velocity from left to right to a zero velocity, at which point the print head 12A will subsequently have its speed increased to a constant velocity in the right to left direction. While not shown, one of the other electrical runs 26A may be provided with an expanded area 38A in a similar fashion, so that the first area of optical contrast to be sensed by the scanner will be of different width compared with that of the other runs 26A, to provide indicia for representing the left hand margin home position for the print head 12A. By fixing the number of electrical runs 26A and their spacing, the electrical conductor 22A may be employed to provide indicia of alignment of the print head 12A to signal any combination of positions for characters, dots and half-dots in printing of dot matrix characters. As is well known in the art, bidirectional printing is facilitated by providing a timing strip with alternating opaque and transparent areas of equal width.

Fig. 5 shows a section of electrical conductor 22B adapted for sensing of full dot and half-dot positions for a bidirectional printer device for printing dot matrix characters. (Reference to full dot and half dot positions for character printing is well-known, with a half dot position indicating the position between two full dot positions. Dots may be printed at either half dot or full dot positions.) Fig. 5 shows a conductive run 26B with its leading

edge 40 representing the location of the first full dot position for the first matrix character to be printed. That electrical run 26B has at its center line a cut-out portion defined by edges 42B and 44B which is filled in by the essentially transparent insulative material 30B, so that there are four opti¬ cally contrasting transitions between the run 26B and the insulative material 30B to define indicia repre¬ senting dot and half-dot positions. Each of the other electrical runs 26B illustrated in Fig. 5 similarly have cut-out portions within the scanner sensing area 28B. Edge 42B represents the location of the first half-dot position for the first dot matrix character and edge 44B thus represents the location of the second full dot position for that same character.

Referring to the scale 46B shown at the bottom of Fig. 5, the width 48B represents the distance between adja¬ cent full dot positions and the distance 50B repre¬ sents the width of the dot matrix characters where two half dot positions and one full dot position will represent the spacing between characters. The illus¬ trated configuration for the electrical conductor 22B can be used for printing a ten dot wide character matrix, for which there are five full dot locations and five half-dot locations and only the first four full dot locations are to be printed.

Fig. 6 illustrates an assembly 10C for a high speed thermal dot matrix type printer similar to the designs previously described. The assembly 10C shown in Fig. 6 comprises a thermal print head 12C, a flex¬ ible circuit 22C and a transmissive optical interrupt type of scanner 32C similar to the assembly 10 shown in Fig. 1. The flexible circuit 22C with its electri¬ cal conductor runs 26C and the optically transparent material 30C is mounted for use as a character posi¬ tion sensor strip in a moving print head type thermal printer. Having the flexible circuit 22C act as the

character position sensor strip eliminates the need for a separate sensor strip and associated holder and mounting means. The assembly IOC shown in Fig. 6 uses an interrupt type scanner 32C, shown mounted to the stationary printer frame 52C, although other types of scanners might be employed.

In the design of an electrical conductor for use in a printer device, the electrical conductor may comprise a plurality of electrically conductive runs to be sensed as indicia of character position (as opposed to dot position) , for example, with each of the runs being spaced according to the character spacing desired. Thus, for a 20 print element print head, indicia representing two character positions could be used for printing a 40 character line of print. Alternatively, the runs may be configured for sensing of dot positions to be printed for printing of dot matrix type characters. Indicia representing 50 full dot positions and 50 half-dot positions could be used for printing a 40 character line of print with a four element print head bidirectionally printing 10 x 7 dot matrix characters.

Fig. 7 illustrates an assembly 10D for a high-speed thermal type dot matrix printer, wherein the electrical conductor, in the form of a flexible circuit 22D, is provided with an extended area 54D with alternating runs 56D of copper or copper alloy spaced apart by essentially transparent plastic insu¬ lative material 30D. The runs 56D may be electrically a part of the conductive runs 26D which are connected to operate the print head 12D, or they may be sepa¬ rate. The design illustrated in Fig. 7 lends itself for use with a scanner 32D of a type with a light transmissive sensing slot 58D oriented parallel to the bracket leg 60D of the scanner 32D as depicted.

Fig. 8 shows an assembly 10E for a high-speed impact type dot matrix printer having a print head 12E

mounted for shuttle type movement on a carriage 14E along rail 62E by means of an endless toothed belt 64E connected to a controlled motor drive (not shown) . The assembly 10E shown in Fig. 8 has an electrical conductor 22E connected to the print head 12E at one end, to carry signals to operate the electrically operated print head 12E, by supply of signals to energize solenoids 66E which drive print wires for impact against the record media (not shown) for print- ing of dots forming dot matrix characters. At one end 68E, the electrical conductor 22E is fixed relative to the printer frame (not shown) for interface with the control electronics (not shown) .

The assembly 10E shown in Fig. 8 is configured such that the scanner, in the form of a reflective type optical scanner 32E, is mounted to the carriage 14E in a position which is fixed relative to the print head 12E. As illustrated in Fig. 8, the electrical conductor 22E is provided along a substan- tial portion of its length with indicia of alignment which are in the form of a line of bar code 70E which are oriented transversely to the length of the elec¬ trical conductor 22E. The bar code 70E may be provid¬ ed on the electrical conductor 22E by any expedient means, such as by means of a stick-on label. In the illustrated configuration, the electrical conductor 22E is mounted so that when sensed by the optical scanner 32E the bar code 70E have positions which are fixed relative to the record media (not shown) during printing of a line of print. During printing, the record media or paper document is supported by a platen (not shown) or the like to support an area of the document for printing thereon. The impact print head 12E is electrically operated for impact printing on the area of the document supported by the platen, with the print head 12E being horizontally movable with respect to the platen in the directions shown by 18E in Fig. 8 for printing a line of print.

Although the described embodiments utilize an optical reader it will be appreciated that a magnetic reader could alternatively be utilized to sense indi¬ cia which are magnetically readable.