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(11) | EP 0 528 049 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | PAPER CLAMP FOR PRINTER |
| (57) A paper clamp for printer having a satisfactory clamping force which does not decrease
even if dusts such as paper powder stick to it and being able to position paper with
high reproducibility. The clamp is provided with pressing surfaces for clamping the
paper at ends on one side of upper and lower clamp members, ends on the other side
of which are rotatably supported independently of each other, wherein either one of
the paper pressing surfaces is formed of an elastic pressing member and the other
of the paper pressing surfaces is formed of a hard, highly frictional member such
as ceramics, thus increasing the paper clamping force. |
Technical Field
[0001] The present invention relates to a sheet clamping device for holding a sheet at one end when the sheet is being printed in a printer.
Technical Background
[0002] Fig. 3 is a side view of a sheet clamping device constructed in accordance with the prior art and disclosed in Japanese Patent Laid-Open No. Hei 2-132471. The clamping device 1 conveys a sheet 2 by moving in a direction shown by arrow 14 in Fig. 3 while holding the sheet 2 at one end. The sheet clamping device 1 comprises upper and lower clamp members 4, 5 which are adapted to grasp the sheet 2. The upper clamp member 4 is pivotally supported at one end on a support shaft 3, with the other end of the upper clamp member being adapted to engage the sheet 2. The engaging end of the upper clamp member 4 is biased against the lower clamp member 5 under the influence of a spring 7. On the other hand, the engaging end of the lower clamp member 5 includes a friction plate 6 of resilient material secured thereto. The sheet 2 will be held between the friction plate 6 on the lower clamp member 5 and the upper clamp member 4 biased against the lower clamp member 5 under the biasing force of the spring 7.
[0003] The right-hand portion of the Fig. 3 schematically shows a printing mechanism including a thermal head 8. On printing, the sheet 2 is grasped, together with an ink sheet 11, between a platen roller 9 and the thermal head 8. When the sheet clamping device 1 is moved in the direction of arrow 14, the sheet is also fed in the same direction. At the same time, the respective heat emitting elements in the thermal head 8 are energized by image signals. The heat fuses the ink on the ink sheet 11 and the fused ink is transferred to the sheet 2 for printing.
[0004] As the sheet 2 is being moved, the ink sheet 11 is also moved from an ink sheet supply roller 13 to an ink sheet take-up roller 12. In the illustrated device, a pinch roller 10 is provided to stabilize the sheet 2 on the platen roller 9.
[0005] In the aforementioned arrangement, the coefficient of friction at the friction plate 6 is insufficient to clamp the sheet 2. If any dirt or dust is deposited on the friction plate 6, the clamping force is further reduced, resulting in slippage of the sheet 2 into misalignment. This will raise various problems such as printing shear, jamming and others.
[0006] Particularly when it is desired to make a color print, a color shift may be produced due to the printing shear since a plurality of printing operations are carried out onto the same sheet.
Disclosure of Invention
[0007] In order to overcome the aforementioned problems in the prior art, an object of the present invention is to provide a sheet clamping device in a printer, which will not reduce the clamping force even if any dirt or dust is deposited therein and which can provide an improved reproducibility with respect to the sheet position.
[0008] To this end, the present invention provides a sheet clamping device in a printer, comprising a lower clamp member, a support shaft disposed thereon at one end, and an upper clamp member pivotally supported on the support shaft. One of the upper and lower clamp members includes a sheet contacting surface of hard, high-friction material while the sheet contacting surface of the other clamp member includes a resilient urging member applied thereto. The hard, high-friction material may be a bonded body of ceramic particles or sand paper.
[0009] In such an arrangement, a printing sheet can be reliably clamped and grasped between one sheet contacting surface of hard, high-friction material and another sheet contacting surface of resilient urging member. Even if any dust becomes deposited on the hard, high-friction layer, they can be absorbed by the resilient urging member without reduction of the clamping force. Therefore, the position of sheet can be repro duced with an increased accuracy.
Brief Description of the Drawings
[0010] Fig. 1 is a side view of one embodiment of a sheet clamping device constructed in accordance with the present invention.
[0012] Fig. 3 is a side view of a sheet clamping device constructed in accordance with the prior art.
[0013] In the drawings: reference numeral 15 denotes an upper clamp member; 16 a hard, high-friction material; 17 a lower clamp member; and 18 a resilient urging member.
Best Mode for Carrying out the Invention
[0014] Referring to Fig. 1, there is shown one embodiment of a sheet clamping device constructed in accordance with the present invention which comprises parts 2, 3 and 7-13 similar to those of the prior art device shown in Fig. 3 and which will not be further described herein.
[0015] The sheet clamping device comprises upper and lower clamp members 15, 17. The upper clamp member 15 is pivotally supported on a support shaft 3 for rotational movement relative to the lower clamp member 17. The other end of each of the upper and lower clamp members 15, 17 includes a pressure sheet contacting surface formed therein. One of the pressure sheet contacting surfaces (the upper clamp surface) is formed of a hard, high-friction material 16 in the form of a bonded body of ceramic particles while the other pressure sheet contacting surface (the lower clamp surface) is formed of a resilient urging member 18 applied thereto, such as a rubber plate, a synthetic resin elastomer plate or the like.
[0016] In operation, the upper clamp member 15 is pivoted about the support shaft 3 to provide an opening between the upper and lower clamp members 15, 17. The sheet 2 is then inserted into the opening. Thereafter, the opening is closed to hold the sheet 2 between the hard, high-friction material 16 of the upper clamp member 15 and the resilient urging member 18 of the lower clamp member 17. The upper clamp member 15 is loaded by the spring 7. Thus, the sheet 2 can be reliably clamped between the upper and lower clamp members 15, 17. On printing, the thermal head 8 is brought into pressure contact with the platen roller 9. While the sheet clamping device is being moved in a direction of arrow 19, the thermal head 8 is energized by image signals to heat the head 8. The heat fuses the ink in the ink sheet 11 with the fused ink being transferred to the sheet 2. During this operation, the sheet 2 is subjected to an increased tension. However, the sheet 2 will be undesirably shifted since it is firmly clamped between the upper and lower clamp members 15, 17.
[0017] Although the hard, high-friction material 16 is formed of ceramic particles, the combination of such a material 16 with the resilient urging member prevents the frictional force therebetween from being reduced. Even if any dust is, present on the hard, high-friction material 16, they can be absorbed by the resilient urging member to provide a stabilized clamping force for a prolonged period without reduction of the frictional force. Consequently, the sheet 2 can be reliably held in place to provide a high-quality print with a substantial reduction in undesirable shift in printing.
[0018] Although the embodiment of the present invention has been described as to the ceramic particles used in the hard, high-friction material 16, the present invention is not limited to such a configuration and may be similarly applied to a hard, high-friction material of sand paper.
[0019] As shown in Fig. 2, the pressure sheet contacting surface of an upper clamp member 25 may include a resilient urging member 28 while the pressure sheet contacting surface of a lower clamp member 27 may include a hard, high-friction material 26. This can provide the same advantages as in the first embodiment.
[0020] Since the sheet clamping device of the present invention comprises one of two clamp members which includes its pressure sheet contacting surface of hard, high-friction material, with the other clamp member including its pressure sheet contacting surface of resilient material, the sheet can be reliably urged against the hard and high-friction member to increase the area of contact for holding the sheet. Further, any dust on the hard, high-friction member can be absorbed by the resilient urging member to prevent the frictional force from being reduced. Consequently, the sheet clamping device can provide a reduced shift of the sheet away from the desired position.
Field of Industrial Application
1. A sheet clamping device in a printer for conveying a printing sheet while holding
said sheet at one end: said device comprising:
(a) a lower clamp member including a pressure sheet contacting surface of hard, high-friction material;
(b) an upper clamp member pivotally supported on a support shaft, said support shaft being fixedly mounted relative to said lower clamp member; and
(c) a resilient urging member applied to the pressure sheet contacting surface of said upper clamp member.
2. A sheet clamping device as defined in claim 1 wherein said hard, high-friction material
comprises a bonded body of ceramic particles.
3. A sheet clamping device as defined in claim 1 wherein said hard, high-friction material
comprises sand paper.
4. A sheet clamping device as defined in any one of claims 1, 2 and 3 wherein said upper
clamp member is supported at one end on said support shaft, the other end of said
upper clamp member including the pressure sheet contacting surface disposed thereon.
5. A sheet clamping device as defined in any one of claims 1, 2 and 3 wherein a force
holding the sheet is provided under the biasing force of a spring.
6. A sheet clamping device in a printer for conveying a printing sheet while holding
said sheet at one end: said device comprising:
(a) a lower clamp member;
(b) an upper clamp member pivotally supported on a support shaft fixedly mounted on said lower clamp member, said upper clamp member including a pressure sheet contacting surface of hard, high-friction material; and
(c) a resilient urging member applied to the pressure sheet contacting surface of said lower clamp member.
7. A sheet clamping device as defined in claim 6 wherein said hard, high-friction material
comprises a bonded body of ceramic particles.
8. A sheet clamping device as defined in claim 6 wherein said hard, high-friction material
comprises sand paper.
9. A sheet clamping device as defined in any one of claims 6, 7 and 8 wherein said upper
clamp member is supported at one end on said support shaft, the other end of said
upper clamp member including the pressure sheet contacting surface disposed thereon.
10. A sheet clamping device as defined in any one of claims 6, 7 and 8 wherein a force
holding the sheet is provided under the biasing force of a spring.