GB2219866A - A contact printer - Google Patents

Abstract

A contact printer comprising a rotatable spring roller (32) with a flexible, airtight sheet (33) wound round said spring roller, where the free end of the sheet is held by belt (34) so that the roller and the sheet can be rolled out across transparent plate (12), a squeeze roller (30) which rolls together with the spring roller on the sheet so as to squeeze air out between the plate (12) and the sheet (33), the rollers being carried by bars (25) with the lower ends coupled to endless chains (20) via pins (26) the front portion of the printer is provided with a step (15) and the rollers are raised from this step by circular, translatory movement caused by the pins in the endless chain rotating round a sprocket (42) of a relatively large diameter compared with the depth of the step; sprocket (42) replacing sprockets (18a, 18b) of Fig 3 which cause rollers to move vertically from step 15 to plate 12. <IMAGE>

Description

A CONTACT PRINTER The invention relates to a contact printer comprising a spring roller adapted to rotate on its own axis and to roll over a transparent plate and with a flexible, airtight sheet wound round said spring roller, where the free end of the spring roller is connected to the front rim of the plate In such a manner that the sheet can be rolled out on the plate by rolling off the spring roller, said printer further comprising a pair of endless chains extending on both sides of the frame member above the chain wheel in such a manner that they extend horizontally below the plate, and a squeeze roller adapted to be rolled off together with the spring roller on the sheet so as to squeeze air out of the space between the plate and the sheet, as well as vertical support means supporting the spring roller and the squeeze roller and with the lower end coupled to at least one of the endless chains, whereby the front portion of the frame member is provided with a step, and whereby a pair of vertically situated bars are provided so as to allow the support means to be moved by means of guides.

A contact printer of this type is known from German Offenlegungsschrift No. 3,234,515, where the support means of the spring roller and the squeeze roller are adapted to follow a vertical movement in the area of the step.

According to the invention the support means is adapted to follow a substantially circular, translatory movement in the area of the step, e.g. by the endless chain being provided with a sprocket wheel of a relatively large diameter in the area of said step. As a result, a smooth movement is achieved, and the printer is inexpensive because one of the sprocket wheels can be omitted.

In the accompanying drawings: Figure 1 is a sectional view of the known contact printer, Figure 2 is a sectional view taken along the line III-III of the printer of Figure 1, Figure 3 illustrates the printer of Figure 1 immediately after the starting position, Figures 4 and 5 illustrate two different positions of the contact printer according to the invention, and Figure 6 is a side end view of the moving portion of the printer.

The known contact printer of Figure 1 comprises a frame member 11. A plate 12 of transparent material is situated on the top side of the frame member 11. A portion of the plate 12 is provided with suction holes communicating with a vacuum pump (not shown). A light source 14 is situated in the lower portion of the printer.

The plate 12 and the upper portion of the front wall of the frame member 11 are provided with a step 15. A slot is situated in the area of the left and the right side rim of the top wall lia, said slot extending rearwardly.

Partitions lic and side walls llb are situated in the interior of the frame member 11, the above slot extending parallel to said side walls. A guide rail 17 extends horizontally at the outer surfaces of the partitions llc at a predetermined distance from the outer side of the partition lic in question.

As illustrated in Figure 1 and 2 a pair of upper and a pair of lower idler sprockets 18a, 18b are provided. Furthermore, a driving chain sprocket 19 is provided, which is pivotally mounted in the outer side of the partition 11 by means of a horizontal shaft below the rearward end portion of a guide. An endless chain 20 extends around the chain sprockets.

In this embodiment the upper portion of the rearmost chain sprocket is situated below the lower area of a front chain sprocket. The vertical running of the endless chain 20 is carried downwards. A chain guide 21 is secured to the partition llc, and the endless chain 20 is situated immediately below as well as parallel and close to the upper vertical running.

A moving member 22 of a rectangular form is provided on the guide 17, said moving member comprising four pivotally mounted rollers 23. The upper rollers 23 can roll on the upper rims, while the lower rollers 23 can roll on the lower rims of the guide. Furthermore, some relatively small rollers 24 appear, said rollers being pivotally arranged at the upper and lower portions of the moving member. The latter rollers 24 support a vertical support bar 25. The lower end of the support bar 25 is pivotally mounted to the endless chain 20 by means of a horizontal pin 26. The upper end of the support bar 25 projects upwards through a slit. As illustrated in the Figure, some oblong bearing members 27 are interconnected via a coupling bar 28.

The endless chain 20 is driven by a motor (not shown) in such a manner that the pins 26, the endless chain 20 and the vertical support bars 25 are interconnected between the front portion of the lower front chain sprocket, and just before the rear chain sprocket 19 said parts can be moved through the upper front chain sprocket.

By moving the endless chain 20, the support bars 25, which are supported by the moving member 22, are moved along the rails 17 when the pins 26 are moved between the lower front chain sprocket and the upper front chain sprocket, and the upper front chain sprocket and the rear chain sprocket. Each oblong bearing member 27 is provided wlth a slot 29 extending vertically in the front lower portion, cf.

Figure 3. Furthermore, a shaft of a squeeze roller 30 is fitted in the slot 29 by the right and the left bearing member. A fixed shaft 31 is mounted between the bearing members 27 and the rear upper portion. A biased roller 32 is pivotally mounted on the fixed shaft 31 by means of a spring (not shown). In this manner the helical spring, the biased roller 32-, and the fixed shaft 31 are pressed downwards.

A flexible airtight sheet 33 is wound round the spring roller 32. A steel belt 34 engages the lower free end of the airtight sheet 33. A cover 35 covering the squeeze roller 30 and the biased roller 32 is secured at the upper end of the vertical support bar 25. Furthermore, a U-shaped hook 36 is secured to the ends of the cover 35.

When the horizontal pins 26 connected to the lower end of the vertical support bar 25 are positioned at the front rim of the front chain sprocket, the squeeze roller 30 and the biased roller 32 are in the lower step 15 of the frame member. In this position the steel belt 34 engages the hook, said steel belt 34 being secured to the free end of the airtight sheet. The squeeze roller 30 pushes the free end of the airtight sheet 33 downwards towards the lower step by its own weight and is maintained in this position. The airtight sheet 33 is wound round the biased roller 32 and is positioned at a predetermined distance from the top side of the lower step 15. The airtight sheet is thereby contacted by the lower step at a certain angle. Subsequently, the endless chains 20 are moved rearwards from the position illustrated in Figure 1, and both the squeeze roller 30 and the biased roller 32 are moved upwards together with the vertical support bars 25 until the horizontal pins 26 reach the front end of the upper front chain sprocket, and they are moved until the horizontal pins arrive at the top portion of the upper front chain wheels indicated by dotted lines in Figure 1.

When the endless chains are moved further rearwards, the vertical support bars 25 are also moved rearwards along the rails 17. The squeeze roller 30 and the biased roller 32 roll over the transparent plate 12. As illustrated in Figure 3, the steel belt 34 is kept in position by the front end of the transparent plate 12, and the airtight sheet 33 is extended to cover an original plate and a sheet of photosensitive material laid one upon another on the transparent plate, while the squeeze roller 30 squeezes the air out of the space between the transparent plate 12 and the airtight sheet 33 by its own weight.

As illustrated in Figure 3, the airtight- sheet 33 wound round the biased roller 32 is moved rearwards, whereby its diameter is gradually reduced. As described above, the endless chain is slightly inclined in the rear direction to compensate such a reduction of the diameter of the roller with the airtight sheet 33. The biased roller 32 is gradually lowered while rolling rearwards, so that the distance between the transparent plate 12 and the point of contact of the flexible airtight sheet 33 is kept at a fixed value. In this manner the inclined contact angle of the airtight sheet 33 relative to the transparent plate 12 between the squeeze roller 30 and the biased roller 32 is kept at a fixed value. At the same time the squeeze roller 30 rolls on the airtight sheet 33 at a proper pressure and regardless of the position of the biased roller 32 and the vertical support bar 25.

When the endless chain is moved in the opposite direction, the airtight sheet 33 on the transparent plate 12 is wound round the biased roller 32. When the biased roller 32 reaches the front end of the transparent plate, the biased roller scoops up the steel belt 34 and is then lowered downwards onto the lower step 15.

According to a particularly advantageous embodiment, the two chain sprockets causing a vertical movement of the transversely moving member 43 have been replaced by a chain sprocket 42 of a relatively large diameter on each side of the frame member. In the area of the step, the moving member 43 is thereby able to carry out a substantially circular, translatory movement. In this manner a smooth movement is allowed with a low risk of errors. Furthermore, an inexpensive structure is obtained. The only provision is that a chain bolt 41, cf. Figure 4, is provided in connection with the chain. The diameter of the chain sprocket 42 corresponds to almost twice the depth of the step.

Figures 4 and 5 show the moving member 43 over the plate and in the starting position in the step.

Figure 6 shows the guiding of the roller mechanism. The roller mechanism comprises four wheels 45 and can be moved forwards and backwards on a horizontal rail, said wheels resting on the rail. A spring 46 between the shafts of the two lower wheels ensures that all four wheels 45 engage the rail continuously, said shafts-of each of the two lower wheels being situated at the end of- a pivotal pin 47. The pin 47. can rotate about the location 49 and carry out a circular movement in such a manner that the lower wheels are always pressed upwards against the rail. The spring 46 ensures furthermore that the wheels absorb shocks, if any.

The wheels 45 can also be pushed to the sides, cf. the right side of the Figure. In addition, a plastic box is provided in which the vertical bar can move up and downwards. In front of the plastic box a brass plate is provided, said plate ensuring that the vertical bar is kept in its position.

According to a particularly advantageous embodiment the squeeze roller is made of a flexible material. In this embodiment the squeeze roller is fixedly mounted.

Claims (4)

1. A contact printer comprising a spring roller adapted to rotate on its own axis and to roll over a transparent plate and with a flexible, airtight sheet wound round said spring roller, where the free end of the spring roller is connected to the front rim of the plate in such a manner that the sheet can be rolled out on the plate by rolling off the spring roller, said printer further comprising a pair of endless chains extending on both sides of the frame member above the chain wheel in such a manner that they extend horizontally below the plate, and a squeeze roller adapted to be rolled off together with the spring roller on the sheet so as to squeeze air out of the space between the plate and the sheet, as well as vertical support means supporting the spring roller and the squeeze roller and with the lower end coupled to at least one of the endless chains, whereby the front portion of the frame member is provided with a step, and whereby a pair of vertically situated bars are provided so as to allow the support means to be moved by means of guides, characterised in that in the area of the step the support means is adapted to follow a substantially circular, translatory movement.

2. A contact printer as claimed in claim 1, characterised in that the substantially circular, translatory movement is caused by the endless chain engaging a sprocket wheel of a relatively large diameter in the area of the step.

3. A contact printer as claimed in claim 1 or 2, characterised in that the squeeze roller is fixedly mounted and made of a flexible material.

4. A contact printer substantially as described above with reference to the accompanying drawings.