TECHNICAL FIELD

This invention concerns the printing of documents. More particularly, it concerns a supporting arrangement for documents which are to be printed. It is particularly applicable, ^• but is not restricted to, supporting arrangements for pre-assembled booklets of a standard size (such as passports, savings bank pass books, multi-page driving licences, and the like) upon which information-containing indicia have to be printed in precise locations. BACKGROUND ART

When a passport is issued, details about the person receiving the passport have to be entered into the booklet that constitutes the passport. When a savings bank issues a pass book to a customer or client, details of the savings account and the customer or client have to be entered into the pass book. There are many instances of a similar situation arising. The required information is applied to the relevant page or pages of the pre-assembled booklet in one of the following ways: a) the information is handwritten; b) the booklet is inserted into a typewriter and the information is typed; c) • the information is handwritten or typed on to a sheet which is stuck on to the page or pages.

While these techniques have been generally adequate in the past, they are. slow, and the final product is often aesthetically unpleasing. With the introduction of machine-readable characters, these techniques are inadequate. The equipment which performs the machine-

reading requires the indicia to be accurately positioned and formed to very close tolerances which cannot be achieved with these techniques. Thus, when machine- readable characters are required to be applied to a passport, pass book or the like, the only current satisfactory way of applying the characters is to print them in the relevant locations on pages before the booklet is assembled. This approach, however, is expensive because the economics of assembling a large number of booklets in an automatic or semi-automatic procedure are not available.

The need for accurate application of machine-readable characters to documents which are single sheets, to identification cards and to credit cards and the like, has meant that existing printing equipment can be operated only slowly, and with careful attention to the accurate placement of the document in the equipment. DISCLOSURE OF THE PRESENT INVENTION It is an object of the present invention to provide equipment which will facilitate the accurate application of indicia to pre-assembled booklets and other documents.

This objective is achieved by providing a supporting arrangement for the document which can be used to position the document accurately in a required location relative to a printing head. The supporting arrangement consists of a flat plate which is positioned in a supporting framework or carriage and which can be moved relative to the framework or carriage in a direction perpendicular to the plane of the plate. The position of the framework relative to the head of a fixed head printer (for example, a dot matrix printing head) can be

O FI ■*

WHO ι_Vi

controlled using suitable -.drive mechanisms. Thus, when a document is laid against the flat plate, the document can be precisely positioned at any required height relative to the printing head. 5 According to the present invention, there is provided a document supporting plate arrangement for a document printer comprising a) a rectangular thick plate having a flat front surface and a rear surface; 10 b) a rectangular plate supporting carriage, said carriage having an upper frame member and a lower frame member, a pair of side members and a planar back member; said frame members extending across the carriage, said ^" 15 planar back member being connected to said frame members and said side members; the dimensions of the thick plate being such that the thick plate is a close but sliding fit between said frame members and the thick 20 plate covers at least part of each said side member; c) a plurality of shafts extending from the back of said thick plate in a direction perpendicular to the plane of said flat

25 front surface, each said shaft being positioned within respective guide means mounted on said planar back member; d) biasing means acting on the rear surface "of said thick plate to bias the thick plate

30 towards the planar back member; and e) means for applying a force to said thick plate in a direction away from said planar back member.

Conveniently, the biasing means is a plurality of tension springs connected to both the planar back member and the rear surface of the thick plate, the means for applying a force to the thick plate is a solenoid-controlled piston, and the guide means are linear bearings.

In a normal printer, (i) the lower frame member will extend further from the planar back member than the upper frame member (to provide a ledge upon which a document can be supported), (ii) the flat front surface of the thick plate will be coated with rubber or a similar composition, (iii) the carriage will be provided with at least one vertically-extending rack, so that it can be positioned relative to the printer head using a motor-driven pinion in co-operation with the or each rack, and (iv) a pair of flat, elongate plates will be fixedly located above and below the printing head, to hold the document being printed at precisely the required distance from the front of the printing head. These and other features of embodiments of the present invention will become more apparent from the following description of a preferred embodiment of the invention. In this description, reference will be made to the following drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective sketch, partly schematic, showing the thick plate and its supporting carriage, with the thick plate removed from the carriage, and an optical sensing arrangement. Figure 2 is a side view, partly schematic, of the document supporting arrangement and the printing head of a document printer.

Figure 3 is a vertical sectional view through the centre of the thick plate and its supporting carriage, when positioned ready for printing a document.

Figure 4 is a perspective view showing the bottom 5 edge and the underside of the thick plate featured in Figures 1 and 3. DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The embodiment illustrated in the accompanying drawings has been built specifically for the printing of 0 information on pages of passports. As shown in the drawings, there are two major components of this apparatus, namely a thick plate 10 and its supporting carriage 20.

The plate 10 is approximately 6.5 mm thick, and is made of aluminium. Other plate thicknesses can be used, and the plate can be fabricated from other materials.

The important factor is the ability of the plate to withstand, without distortion, an impact from a printing head that is applying characters to a document held against the front face 11 of the plate. For accurate work, with a dot matrix printer, the front face of the plate must be flat to within about 0.05 mm. To prevent the possibility of a document sliding on the front face

11 of the plate 10, a thin coating.12 of rubber has been vulcanised on to the front face. This coating could not be formed by gluing a rubber sheet on to the front surface 11 as any ripples in the sheet formed by this process, or an uneven application of an adhesive, would have destroyed the required flatness of the surface. The supporting carriage 20 has an upper frame member

^• 21, a lower frame member 22 and side members 23. The frame members 21 and 22 and the side members 23 were machined from a single piece of aluminium, although they

OMPI

VA IPO * " PWλrAATT'l nO« ^" 8

could have been produced separately and connected together in the illustrated configuration. A planar back member of the carriage, in the form of a steel plate 24, is rigidly attached to the frame members and to the side members.

Affixed to the steel plate 24 are three guides 25, which receive correspondingly located shafts 15 affixed to the rear face of the thick plate 10. The shafts 15 and guides 25 in the apparatus constructed by the present inventors are linear bearings. These linear bearings ensure that movement of the plate 10 away from the carriage can only occur in a direction that is perpendicular to the plane of plate 24 (and also perpendicular to the plane of the front surface 11 of plate 10) .

Such movement of plate 10 is effected by a piston 30 which is located within an aperture 26 in plate 24. When piston 30 is moved towards plate 10, the front surface of piston 30 bears against the inside surface of a dished member 16 mounted on the rear of plate 10, to apply a force to move plate 10 away from the carriage 20. Movement of the plate is constrained by a pair of tension springs 27 which are connected to both the rear of plate 10 and the front of plate 24. In the absence of the application of a force upon plate 10 by piston 30, the tension springs 27 bias the plate 10 into a position where the side regions of the rear of plate 10 are held in contact with the front surfaces of the side -members

23 of carriage 20, as shown in Figure 2. Other means to bias the plate 10 towards the plate

24 can be used instead of tension springs 27.

The tension springs 27 are connected to the plate 10 by being affixed to spring mounting points 14 at each end of a support plate 17 that is held firmly against the rear surface 13 of plate 10 by the dished member 16

5 (see Figure 4). In the embodiment constructed by the present inventors, the piston 30 had a diameter of about

8 mm and the dished member 16 was formed by machining a dish shape into the head of a stud or bolt. The threaded shaft of the stud or bolt was then passed through an

10 aperture in support plate 17 and screwed into a threaded hole drilled into the rear of plate 10, to hold plate 17 firmly against the rear surface of plate 10. It will be readily appreciated, however, that other constructions may be used to provide both an equivalent to the dished

' 15 member 16 and a means for connecting the tension springs to the rear face of plate 10.

In the equipment constructed by the inventors, the movement of piston 30 is controlled by a solenoid which is mounted in a solenoid housing 31, which is positioned 20 above the upper frame member 21 of carriage 20. A linkage 36 connects the solenoid to piston 30. The linkage 36 may be any one of many alternative suitable forms of linkage known to practising engineers.

Alternatives to a solenoid-controlled piston may be

25 used to apply a force to the rear surface 13 of plate

10. Such alternatives include hydraulically-controlled pistons and direct mechanical linkages to the rear of plate 10.

It will be noted that the upper frame member 21

30 extends forward a distance d_ from plate 24, the side members 23 each extend forward a distance d,, the lower frame member 22 extends forward a distance -, and plate

10 has a thickness d.. The distance d., is greater than

d ₂ , and the sum of distances d, and d. is approximately equal to the distance d~. Distance d ₃ is greater than distance d ₂ to provide a ledge 28 to support a document to be printed. The forward-most edge of frame member 22 is turned up to provide a lip 29 (shown exaggerated in the drawings) which prevents a document 33 from slipping off ledge 28 before or after the document has been printed.

To position the carriage 20 at a required height relative to a printer head 40, a pair of racks 34 are mounted, one at each side, on the rear of steel plate 24. Each rack 34 has an associated pinion 35. The pinions 35 are mounted coaxially and are driven by a common electric motor (not shown). Limit switches, actuated by the upper and lower frame members 21 and 22, ensure that the movement of the carriage 20 is such that the pinions 35 do not reach the end of the racks 34. Guides ensure that the movement of carriage 20 is vertical. These control mechanisms- are standard engineering practice.

When the printer is to be used to perform printing, sequentially, in a number of locations on a standard document (which is the usual situation with passports and printed certificates), the electric motor driving the pinions may.be controlled by a microprocessor which is programmed so that once a new document has been positioned on ledge 28, the height of the carriage is adjusted so that each printing location becomes adjacent the printing head in turn. In this way, the required printing can be rapidly effected, and a large number of the documents can be printed upon in a short time period.

With a view to such volume printing of documents, the thick plate 10 of the unit produced by the present inventors is provided with a pair of grooves 18 in its lower edge and a pair of slots 19 are milled into the upper surface of lower frame member 22. The grooves 18 and the slots 19 are in corresponding positions on the plate 10 and frame member 22, respectively. Two generally U-shaped brackets 50 are provided, each with an optical source 51 mounted on the top of one vertical arm of the bracket and an optical sensor 52 mounted on the other vertical arm of the bracket. In the equipment produced by the present inventors, the optical source 51 was an off-the-shelf infra-red emitter having a generally cylindrical form, being about 6 mm tall and about 3 mm in diameter, and the optical sensor 52 was an infra-red sensor having similar shape and dimensions, which was also purchased as an off-the-shelf item. The connecting (lower) arm 53 of each bracket 50 was dimensioned to fit within a slot 19 with the optical source 51 adjacent to, but spaced from, the steel plate

24, and with the sensor 52 in front of the carriage 20.

With this arrangement, with plate 10 in position, an optical signal from each source 51 passes through the respective groove 18 and (in the absence of a document on ledge 28) is detected by the associated sensor 52.

When a document is placed on the ledge 28, it interrupts the optical signals. This interruption could be used to initiate the step operation of the electric motor. Removal of the document after the printing is completed restores the optical signals to the sensors. The signals from the sensors upon receipt of the restored optical signal would. then cause the microprocessor program to be reset.

fτj∑_πt ₍

The optical source need not be an infra-red source, and the sensor 52 may be any suitable photo-sensitive detector for use with the selected optical source.

As shown in Figure 3, when a document 33 is positioned on ledge 28 (having been inserted through the gap 38 between the upper frame member 21 and the housing 42 above the printing head 40) and the carriage has been moved to the correct height for printing on the document, the piston 33 is moved forward to cause the plate 10 ^* to move towards the printing head 40. This movement continues -until the document 33 comes into contact with a pair of horizontal, elongate plates 41, mounted above and below the printing head 40. The document is then spaced from the printing head a distance which is the required distance for performing the printing on the document. That printing is then effected (the printing head moves laterally between plates 41). When the printing at this location is completed, the piston is retracted, and either the document 33 is removed or the carriage is re-positioned for printing at a different location on the document.

Engineers will appreciate that although a specific embodiment of the present invention has been described in detail above, variations in the construction of this embodiment of the present invention (some of which have been indicated in the above description) may be made without departing from the present inventive concept.

Also, it will be appreciated that although, in the above description, the front face of plate 10 is stated to be vertical, this is the situation when the equipment is used in the manner envisaged by the present inventors. The equipment can be used at any suitable angle relative to vertical (even with back plate 24 and

plate 10 each in a horizontal plane) provided the document feed to the equipment operates satisfactorily at the selected orientation of the equipment. INDUSTRIAL APPLICABILITY

The present invention is adapted for the printing of any type of document. It is particularly useful (as noted already) for the printing of machine-readable characters on documents such as passports, savings pass books, and identity cards.

OMH _