Plate clamping device of printing press

Abstract: In a plate clamping device of a printing press for clamping a plate (3) by a bottom clamping rail (2) and a pressure plate (5), chips (10a,10b) hardened to form serrations inclined in the lateral direction of a plate clamp so as to bite the plate in the direction of slipping-off of the plate are embedded in the clamp surfaces of the bottom clamping rail and the pressure plate such that the serrations on the bottom clamping rail side and the pressure plate side are inclined in opposite directions. Thus, the plate can be held with sufficient force without plastic deformation of the end of the plate, and the plate can be reused.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a plate clamping device of an intaglio printing press or a sheet-fed offset printing press. Such a plate clamping device is known e.g. from DE-A-2 702 393. 2. Description of the Related Art A plate cylinder of an intaglio printing press is equipped with a plate clamping device for pulling and locking the ends of a plate wound round the peripheral surface of the plate cylinder. A conventional plate clamping device is exemplified in FIG. 10. This plate clamping device comprises a combination of a bottom clamping rail 2 slidable in the peripheral direction of a plate cylinder 1; a pressure plate 5 for tightening and locking the end of a plate 3 onto the bottom clamping rail 2 by means of a set bolt 4; and a plate tension bolt 6 screwed into the bottom clamping rail 2. This combination at the leading edge of the plate 3 and the same combination at the trailing edge of the plate 3 are provided adjacently and symmetrically on a part of the peripheral surface of the plate cylinder 1. The respective plate tension bolts 6 are screwed into the bottom clamping rails 2 to slide the bottom clamping rails 2 in the direction of plate tension, thereby making the plate 3 spread tensely on the peripheral surface of the plate cylinder 1. With a conventional plate clamping device, the clamp surfaces of the bottom clamping rail 2 and the pressure plate 5 are formed in the shape of big waves to cause wavy plastic deformation to the end of the plate 3 when clamping the plate 3. Thus, the plate 3 that has been mounted is plastically deformed. When this plate 3 is dismounted and then mounted again, the positioning of the plate 3 while aligning the wavy form of the bottom clamping rai! 2 and the pressure plate 5 with the wavy form of the plate 3 is very difficult. This is because tightening holes 3b for the set bolts 4 formed in the plate 3, and reference pin holes 3a of the plate 3 are each deformed in the shape of an elongated hole. Actually, the plate 3 cannot be positioned using reference pins, so that the reuse of the plate 3 and the use of reference pins are impossible. A solution to this problem may be to make the wavy form of each of the bottom clamping rail 2 and the pressure plate 5 a small wavy form which will not cause the plastic deformation of the plate 3. This method may cause displacement or slipping-off of the plate pulled with a strong force during clamping. SUMMARY OF THE INVENTION It is an object of the present invention to provide a plate clamping device of a printing press which holds a plate with sufficient force without causing plastic deformation of the end of the plate and which permits reuse of the plate. To attain this object, the present invention claims a plate clamping device according to claim 1. This configuration imparts sufficient clamping force without causing plastic deformation of the plate. Since the serrations are inclined, components of force parallel to the serrations are counteracted to obtain a stable clamp force in the lateral direction of the clamp. Since the serrations head in different directions at a plurality of sites in the lateral direction of the clamp, respective forces in the lateral direction of the clamp are balanced. If the serrated portion is formed at the surface of the chip embedded in the clamp surface, its formation is easy and leads to reduced costs. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the following detailed description in conjunction with the accompanying drawings which are given for the purpose of illustration only, and thus are not limitative, and wherein: FIG. 1 is a sectional view of an essential part of a plate clamping device concerned with an embodiment of the present invention; FIG. 2 is an explanatory view of a chip on the bottom clamping rail of the plate clamping device; FIG. 3 is an explanatory view of a chip on the pressure plate of the plate clamping device; FIG. 4 is a plan view of the entire plate clamping device; FIG. 5 is an explanatory view of a plate on the plate clamping device; FIG. 6 is an explanatory view showing an example of the arrangement of the chips; FIG. 7 is a sectional view of an essential part showing another embodiment of the present invention, (a) showing chips provided only on the pressure plate side, and (b) showing chips provided, only on the bottom clamping rail side; FIG. 8 is a sectional view of an essential part showing still another embodiment of the present invention; FIG. 9 is a sectional view of an essential part showing a further embodiment of the present invention; and FIG. 10 is a sectional view of an essential part of a conventional plate clamping device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a plate clamping device of a printing press concerned with the present invention will be described by reference to FIG. 1 to FIG. 6, in which the same members as in FIG. 10 are assigned the same numerals, and overlapping explanations are omitted. As shown in FIG. 1 and FIG. 4, a bottom clamping rail 2 slidable in the peripheral direction of a plate cylinder 1; a pressure plate 5 for tightening and locking the end of a plate 3 onto the bottom clamping rail 2 by means of a plurality of set bolts 4; and a plurality of plate tension bolts 6 screwed into the bottom clamping rail 2 form a combination. This combination at the leading edge of the plate 3 and the same combination at the trailing edge of the plate 3 are provided adjacently and symmetrically on a part of the peripheral surface of the plate cylinder 1. A plurality of (ten in the drawings) chips 10a, 10b are embedded in flat clamp surfaces of the bottom clamping rail 2 and the pressure plate 5 with predetermined spacing in the lateral direction of the clamp. That surface of the chip 10a on the bottom clamping rail 2 side which contacts the plate 3 is processed by hardening to form serrations 11 0.2 to 0.3 mm deep and inclined at a predetermined angle (about 20 to 30.) with a pitch of 1 to 1.5 mm so as to engage the plate 3 in the direction of slipping-off of the plate 3 (see the direction of an effective impression area shown by an arrow), as illustrated in FIG. 2. Tooth spaces 12 are similarly formed with a pitch of 1 to 1.75 mm by hardening such that the tooth spaces 12 are 0.2 to 0.3 mm deep and inclined in a direction opposite to the direction of the serrations 11. The numeral 13 denotes a mounting hole for mounting by a bolt or the like. The surface of the chip 10b on the pressure plate 5 side is also processed by hardening to form serrations 11 and tooth spaces 12 of the same design as for the chip 10a on the bottom clamping rail 2 side, as shown in FIG. 3. The chip 10a on the bottom clamping rail 2 side and the chip 10b on the pressure plate 5 side are mounted such that the serrations 11 and tooth spaces 12 of the chip 10a and those of the chip 10b intersect (are inclined in opposite directions). Because of this configuration, the plate 3 bent as shown in FIG. 5 by a plate bender has its leading edge positioned by fitting two reference pin holes 3a, formed at the leading edge, over two reference pins 7 (see FIG.. 4) on the bottom clamping rail 2. Then, the pressure plate 5 is placed, and the leading edge of the plate 3 is clamped onto the bottom clamping rail 2 by means of the set bolts 4. Likewise, the trailing edge of the plate 3 is clamped, and tension is applied by the plate tension bolts 6, whereby the plate 3 is intimately contacted with the surface of the plate cylinder 1. At this time, the serrations 11 of the above-mentioned chips 10a, 10b enable a low clamping force to impart a sufficient tension which will bring the plate 3 into intimate contact with the surface of the plate cylinder 1 without the plate 3 slipping. The inclination of the serrations 11 increases the area of engagement with the plate 3 to give a sufficient force for holding the plate 3. Moreover, the serrations 11 of the chips 10a and 10b intersect each other. Thus, components of force parallel to the serrations 11 during pulling of the plate are counteracted, so that the plate 3 does not move in the right-and-left direction (in the lateral direction of the clamp). Hence, a stable pulling force can be generated. The tooth spaces 12 are effective in uniformizing the contact of the plate 3 during clamping, and facilitating the removal of the plate during opening. However, the tooth spaces 12 may be omitted. With a conventional plate clamping device, the end of the plate 3 was plastically deformed in wavy form by a clamping force of the set bolt 4 to secure a plate holding force. In this case, since the plate 3 remounted was sure to move during clamping, the reference pins 7 as used in the instant embodiment were not usable. Thus, the positioning of the plate 3 was very difficult, and plate alignment with a triple- or quadruple-sized plate, in particular, took time, resulting in low productivity. In the instant embodiment, by contrast, the plate 3 is not plastically deformed, and the plate 3 dose not move during clamping. Thus, the reference pins 7 are used to position the plate 3 promptly and easily, increasing productivity. With a conventional plate clamping device, furthermore, the end of the plate 3 is plastically deformed in wavy form. Thus, the tightening holes 3b are deformed in the shape of elongated holes, and bite into the set bolts 4, making plate removal difficult, and posing difficulty in plate mounting for reuse of the plate. In the instant embodiment, on the other hand, the tightening holes 3b are free from deformation, markedly facilitating the removal of the plate 3 and the mounting of the plate 3 for its reuse. In the foregoing embodiment, the serrations 11 and the tooth spaces 12 are formed in the chips 10a, 10b, but may be directly formed in the bottom clamping rail 2 and the pressure plate 5. Alternatively, as shown in FIG. 6, the chips 10b (and 10a) of the pressure plate 5 (and the bottom clamping rail 2) may be arranged such that their serrations 11 are inclined either alternately differently (FIG. 6(a)), or symmetrically with respect to the center (FIG. 6(b)), to keep a balance of force in the right-and-left direction (in the lateral direction of the clamp). In this case, the chips 10b (10a) are balanced in terms of force in the right-and-left direction (in the lateral direction of the clamp). Thus, there is no need to provide the chips 10b (10a) in both of the bottom clamping rail 2 and the pressure plate 5 as shown in the aforementioned embodiment. As illustrated in FIG. 7, the chips 10b (10a) may be provided on the pressure plate 5 side only, and the bottom clamping rail 2 side may be formed in a flat shape [FIG. 7(a)]. Alternatively, the chips 10a (10b) may be provided on the bottom clamping rail 2 side only, and the pressure plate 5 side may be formed in a flat shape [FIG. 7(b)]. By so doing, a comparable holding force to the aforementioned embodiment can be obtained. The instant embodiment has been described using the set bolts 4 to clamp the plate 3. However, the present invention can be applied to an embodiment using an air cylinder 15A or 15B as shown in FIG. 8 and FIG. 9, or to an embodiment in which the pressure plate is opened and closed by a cam mechanism. In FIG. 8, when a plate 3 is to be inserted, the air cylinder 15A is extended toturn a pressure plate 5 about a support shaft 16. When the plate 3 is to be clamped, the air cylinder 15A is contracted to turn the pressure plate 5 in the clamping direction by the spring force of a compressed coiled spring 17. In FIG. 9, when the plate 3 is to be inserted, the air cylinder 15B is extended, whereupon a bolt 18 locked to the front end of a piston rod pushes a pressure plate 5 upward to allow the insertion of the plate 3. When the plate 3 is to be clamped, the air cylinder 15B is contracted, whereby the pressure plate 5 goes down to clamp the plate 3 onto a bottom clamping rail 2. As described so far, according to the present invention, at least one of the clamp surfaces of the bottom clamping rail and the pressure plate is provided with a serrated portion biting in to the plate in a direction in which the plate slips off. Thus, the plate is held with sufficient force without causing plastic deformation to the end of the plate, so that printing quality and productivity are improved. Also, reuse of the plate is possible, and the efficiency of mounting and dismounting is increased. In addition, the plate does not slip off even when the clamping force is relatively low. Thus, small set bolts suffice, making the plate clamping device compact. Since the serrations are inclined, components of force parallel to the serrations are counteracted to obtain a stable clamp force in the lateral direction of the clamp. Since the serrations head in varying directions at a plurality of sites in the lateral direction of the clamp, respective forces in the lateral direction of the clamp are balanced. If the serrated portion is formed at the surface of the chip embedded in the clamp surface, its formation is easy and leads to reduced costs. While the present invention has been described in the foregoing fashion, it is to be understood that the invention is not limited thereby, but may be varied in many other ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims: A plate clamping device of a printing press, adapted to clamp a plate by means of a bottom clamping rail (2) and a pressure plate (5), wherein at least one of the clamp surfaces of the bottom clamping rail (2) and the pressure plate (5) is provided with a serrated portion biting into the plate in a direction in which the plate slips off, serrations (11) of the serrated portion are inclined with respect to the lateral direction, wherein a plurality of the serrated portions are provided in the lateral direction, and the serrations (11) of some of the plurality of the serrated portions point in a direction different from a direction in which the serrations of the other serrated portions point. The plate clamping device of claim 1, wherein the serrated portion is formed at the surface of a chip (10) embedded in the clamp surface. The plate clamping device of claim 1, wherein the serrated portion is provided at each of the clamp surfaces of the bottom clamping rail (2) and the pressure plate (5), and the serrations (11) of the serrated portion of the bottom clamping rail (2) point in a direction different from a direction in which the serrations (11) of the serrated portion of the pressure plate (5) point.

Inventors: ENDO YUTAKA, TOYODA HIDEAKI, ENDO, YUTAKA, TOYODA, HIDEAKI, Endo, Yutaka, c/o Komori Corp., Toyoda, Hideaki, c/o Komori Corp.
Applicants: KOMORI PRINTING MACH, KOMORI CORPORATION
Application year: 1996
Main classification: B41F27
IPC codes: B41F27, B41L29