GB2178181A - Contact printing - Google Patents

Abstract

A contact printer comprises a printing table 4 for supporting a photosensitive material, and a hinged cover including a light-transmitting plate 10 through which the photosensitive material is exposed to a light source 8. A conveyor belt 6 is provided for moving an original over the photosensitive material on table 4 to a desired position and nozzles (15, Fig. 1) are positioned to blow air between the original and photosensitive material during movement of the original. Air cylinders 30, 32 are provided for moving the cover between a fully opened position and a fully closed position, and are also arranged to hold the cover in an intermediate slightly open position during positioning of the original on the photosensitive material in order to prevent damage to the photosensitive material and ensure accurate positioning of the original. Belt 6 is moved in the Y-direction by a screw and in the X-direction by rotation of pulleys and is moved under the control of a microcomputer or numerical control device. The photosensitive material is positioned with the aid of register pins, which are then removed. Before printing, air is exhausted through ports (25, Fig. 3) in table 4. <IMAGE>

Description

SPECIFICATION A contact photocopying apparatus This invention relates to a contact printer in which an original, such as an image-bearing film, contacts a photosensitive material such as film, presensitized plate, etc., and the photosensitive material is exposed to copy the image on the original onto the photosensitive material, and more particularly to a contact printer for multi-duplication in which an image on the original is repeatedly copied onto the photosensitive material.

The applicant has already disclosed a printer for multi-duplication in Japanese laid-open Patent Publication (unexamined) Sho 60-10253, in which an end of an original is fixed to a belt and moved in mutually perpendicular X and Y-directions to a desired position with respect to a photosensitive material by movement of the belt with the original held suspended on an air cushion formed by blowing air along the original.

According to this prior contact printer, multi-duplication can be accurately performed in spite of the contact nature of the process, even in the case of an original of large size or a non-standard original with one dimension elongated.

A problem exists, however, in that when using the aforesaid printer for an original with having an extraordinary length compared to its width, the original cannot be satisfactorily held in the air and one end of the original contacts the surface of the photosensitive material unless the pressure and flow rate of the air blown along the original are high. If the belt is moved under such conditions of contact between the original and the photosensitive material, the original may drag to the extent of damaging a film surface of the photosensitive material, so that accuracy in positioning the original is affected.

According to the present invention, there is provided a contact printer comprising a printing table for supporting a photosensitive material, a cover including a light-transmitting plate through which the photosensitive material is exposed to a light source, the cover being supported for movement relative to the printing table between an open first position and a closed second position, a packing carried by the cover outside an effective printing area thereof for forming an airtight space between the printing table and the lighttransmitting plate in the second position of the cover, conveying means for moving an original to be reproduced over the surface of the photosensitive material, pressurised air means for blowing air between the original and the photosensitive material during move ment of the original to a desired position, and drive means for moving the cover between the open and closed positions, in which printer the drive means is arranged to hold the cover in an intermediate third position between the first and second positions during movement of the original to its desired position.

Since the air blown out of the nozzles flows in the form of a laminar flow through a space formed between the printing table mounting on the photosensitive material thereon and the cover, there is an action tending to enlarge the space between the original and the photosensitive material and accordingly the original can be held in the air by a smaller quantity of air when moving the original without damaging the photosensitive material and affecting the accuracy of the positioning of the orginal. Furthermore, a contact printer embodying this invention may also provide the following advantages: (1) Since the cover is not completely open when moving the original, such disadvantages as hitting the cover against an operator when the cover is opened and closed, the introduction of a part of the operator's body between the printing table and the cover, etc. are considerably decreased.

(2) Since the cover is not completely open when moving the original, the time necessary for completion of one cycle of multi-duplication is reduced by no less than 5-10%.

In order that the invention may be readily understood, an embodiment thereof will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a contact printer embodying the invention with a side plate and light source removed; Figure 2 is a perspective view of the contact printer; Figure 3 is a plan view showing a printing table area of the contact printer; Figure 4 is a front view of the printing table area shown in Fig. 3; Figure 5 is a sectional view of a hinge mechanism of the contact printer; and Figure 6 is a circuit diagram of an air pres sure control circuit for opening and closing the cover.

Referring firstly to Figs. 1 to 4, a contact printer embodying this invention comprises a printer body 2, a light source 8 and a hinged cover 10 including a light-transmitting plate 12 such as a glass plate in the centre thereof. A packing 14 is disposed on the lower side of the cover 10 surrounding the light-transmitting plate 12. Although not illustrated in the draw ings, a masking device is disposed on the upper part of the light-transmitting plate 12 to mask areas to remain unexposed.

The printer has a printing table 4 on which a photosensitive material 3, such as a presen sitized plate (PS Plate), is positioned by regis ter pins 23. Exhaust ports 25 connected to a vacuum pump (not shown) are formed at two location of an end portion of the table. Fur ther, the printing table 4 is so arranged as to be lowered to a point indicated by the dot and chain line in Fig. 4 during movement of an original 5.

A belt 6 serves for positioning the original 5 and is composed of a metal band of no more than 0.2 mm in thickness stretched around pulleys 17 and 19. The belt 6 is moved in the Y-direction in Fig. 3 by a drive mechanism such as a screw (not shown) in the stretched state, and in the X-direction by rotation of the pulleys 17 and 19. In the printing process, a guide film 7 on which the original is taped with a tape 9 is positioned by register pins 21 and taped on the belt 6 with a tape 11.

A tubular member 13 has a plurality of nozzles 15 for blowing air to the lower side of the belt 6 with the original 5 thereon and is connected to an air compressor 40 in Fig.

6.

The foregoing arrangement is almost the same as the disclosure of aforementioned Japanese laid-open Patent Publication (unexamined) Sho 60-10253 and detailed description thereof is therefore omitted herein.

A rear side of the cover 10 is supported by hinge mechanisms 16 and the mid points of the adjacent lateral side are supported by air cylinders 18 and 20 and springs 34 received on the cylinder rods 30 and 32 of the air cylinders, so that opening and closing of the cover is performed between a first position A, a second position B and third position C, by operating the air cylinders 18 and 20. The first position A is an open position in which the cover 10 is completely open, the second position B is a closed position in which the cover 10 is completely closed to the extent that an airtight space is formed between the printing table 4, the light-transmitting plate 12 and the packing 14, and the third position is an intermediate position in which the cover is partly open.If the movement of the cover 10 between the third and second positions C, B is a vertical movement, it is preferable that the distance between the lower surface of the cover 10 and the upper surface of the belt 6 in the third position C is 0.5-10 cm. The distance between the lower surface of the belt 6 and the upper surface of the printing table 4 when carrying the original is also preferable 0.5-10 cm.

Fig. 5 shows a sectional view of the hinge mechanism 16 in which a hinge 22 fixed to the cover 10 is connected to a shaft 26 so to be movable in vertical direction through a spherical bearing 24, and is resiliently supported by a spring 28 received on the shaft 26.

Fig. 6 is a circuit diagram of an air pressure control circuit for opening and closing the cover 10, which circuit includes an air compressor 40, electromagnetic valves 42 and 44, and a flow regulating valve 46. A pressure regulating valve 50 is arranged to supply first chambers 18-1, 20-1 of the air cylinders 18, 20 with air from the compressor 40 at the pressure necessary for opening the cover 10 to the first position A, and the pressure is set to 6 kg/cm2, for example. A pressure regulating valve 52 is arranged to supply second chambers 18-2, 20-2 of the air cylinders 18, 20 with the air pressure necessary to lower the cover 10 from the third position C to the second position B and to form the airtight space surrounded by the packing 14 between the light transmitting plate 12 and the printing table 4, and the air pressure is set to 1.5 kg/cm2, for example.A pressure regulating valve 54, is arranged to supply the first chambers 18-1, 20-1 of the air cylinders 18, 20 with air at a pressure which is a little lower than the pressure balanced to the weight of the cover at the time of closing it, and the pressure is set to 1.5 kg/cm2, for example, according to the weight of the cover 10.

The printer described above operates as follows.

Air pressure of 6 kg/cm2 is fed to the first chambers 18-1, 20-1 of the air cylinders 18, 20 by switching the electro-magnetic valve 42 to the state shown in Fig. 6, so as to open the cover 10 to the first position A. The photosensitive material 3 is mounted on the printing table 4 using the register pins 23 to locate the material 3, while the original 5 is mounted on the belt 6 through the guide film 7 and using the register pins 21. After completing the positioning, the pins 21 and 23 are removed.

When the air pressure in the first chambers 18-1, 20-1 of the air cylinders 18, 20 is reduced to 1.5 kg/cm2 by switching the electro-magnetic valve 42, the cover 10 begins gradually to close as a result of the difference between the downward force due to the weight of the cover 10 and the upward force due to the actuation by the air cylinders 18, 20. When the cover 10 is closed as far as the third position C, the downard force due to the weight of the cover 10 balances the sum of the upward forces due to the air cylinders 18, 20 and the upward force due to the springs 28, 34, and accordingly the cover 10 does not stop in a horizontal position but stops in an intermediate slightly inclined position with its front side a little higher than the rear side as shown in Fig. 1.

By lowering the printing table 4 under these conditions to the position indicated by dotchain line in Fig. 4 and blowing air beneath the original 5, the original 5 is kept raised in the air with its front end supported on the belt 6. Then, when the belt 6 is moved in the X and Y directions according to the commands of a microcomputer or numerical control (NC) device, the original 5 is positioned at the first printing position on the photosensitive material 3.In this case, since the cover 10 is closed to a position not affecting the position ing of the original 5 and the air blown out of the nozzles 15 flows in the form of laminar flow through the space between the glass plate 12 supported by the cover 10 and the printing table 4 lowered to the position indicated by the dot-chain line in Fig. 4, the original 5 can be held suspended in the air with a relatively small rate of air flow, and there is no possibility of the end of the original 5 dragging across and scratching the surface of the photosensitive material 3.

When completing the positioning of the original 5 in relation to the photosensitive material 3, the air flow from the nozzles 15 is stopped and the printing table 4 is raised to the position indicated by solid lines in Fig. 4.

When the electro-magnetic valve 44 is switched from the position of Fig. 6 to supply the second chambers 18-2, 20-2 of the air cylinders 18, 20 with air at a pressure of 4 kg/cm2, the cover 10 lowers from the third position C to the second position B against the force of the springs 28 and 34 due to the difference in pressure between the first and second chambers 18-1, 20-1 and 18-2, 20-2 and brings the packing 14 into contact with the printing table 4.

The air in the airtight space formed by the glass plate 12, the printing table 4 and the packing 14 is then exhausted through the exhaust ports 25 so as to bring the glass plate 12 into contact with the printing table 4 as well as the original 5 with the photosensitive material 3, both put therebetween. At the same time, portions not required to be exposed other than the original 5 are shaped by masking means (not illustrated). After attaining complete contact between the original 5 and the photosensitive material 3, the light source 8 is lit and printing is performed.

After completing the printing, the cover 10 is lifted to the third position C, the printing table 4 is lowered to the position indicated by the dot-chain line in Fig. 4, and air is blown out of the nozzles 15 to hold the original 5 on the air again. The original 5 is carried to the next printing position by driving the conveyor belt 6, and the aforesaid operations are repeated for multi-duplication. After completing the scheduled multi-duplication, the electromagnetic valves 42, 44 are switched to the position shown in Fig. 6 to open the cover 10 up to the first position A, and the original 5 and the photosensitive material 3 are removed.

In the foregoing embodiment, the opening and closing of the cover 10 between the first position A and the third position C is a turning movement around the hinge mechanism 16, while the open and close operation between the third position C and the second position B is a vertical movement, but it is also possible to make these two movements either by the turning movement or by the vertical movement only.

If the cover 10 is moved by a turning movement between the third position C and the second position B, the angle made by the cover 10 with the horizontal in the third position is preferably 1-10", although it depends on the size of the cover 10. If the cover 10 is moved by both turning and vertical movements, the angle of opening of the cover 10 at the third position C and the distance between the lower side of the cover 10 and the upper side of the belt 6 can be adequately established based on aforesaid range considering the extent of the vertical ,movement of the cover 10.

Claims (7)

1. A contact printer comprising a printing table for supporting a photosensitive material, a cover including a light-transmitting plate through which the photosensitive material is exposed to a light source, the cover being supported for movement relative to the printing table between an open first position and a closed second position, a packing carried by the cover outside an effective printing area thereof for forming an airtight space between the printing table and the light-transmitting plate in the second position of the cover, conveying means for moving an original to be reproduced over the surface of the photosensitive material, pressurised air means for blowing air between the original and the photosensitive material during movement of the original to a desired position, and drive means for moving the cover between the open and closed positions, in which printer the drive means is arranged to hold the cover in an intermediate third position between the first and second positions during movement of the original to its desired position.

2. A contact printer according to claim 1, in which the conveying means comprises a belt to which the original is attached and which is movable lengthwise and transversely of its length to position the original.

3. A contact printer according to claim 1 or 2, in which the pressurised air means comprises a plurality of nozzles.

4. A contact printer according to any one of claims 1 to 3, in which the cover is supported by hinge means permitting turning and vertical movements of the cover.

5. A contact printer according to any preceding claim, in which the drive means comprises air cylinder means connected between the cover and a body of the printer and resilient means acting between the cylinder means and the cover.

6. A contact printer substantially as hereinbefore described with reference to the accompanying drawings.

7. Any novel feature or combination of features described herein.