Punch press machine and method of repositioning the workpiece on the table of such machine

Abstract: To enable a press machine to reliably reposition a workpiece without causing it to become offset. A press machine 1 includes a punch tool for punching a workpiece and a workpiece gripping section 23 for gripping and moving a workpiece on a table . A workpiece gripping section 23 repositions the workpiece. A control means 35 stops the punch tool while it is penetrating the workpiece during a punching operation. In this stop condition, the control means causes the workpiece gripping section 23 to perform a repositioning operation. During the repositioning operation, the control means 35 selects a punch tool with a shape other than a perfect circle to fix the workpiece.

Description: Field of the Invention The present invention relates to a press machine such as a turret punch press machine and a method of re-positioning a workpiece. Background of the Invention In conventional turret punch press machines, a workpiece feeding apparatus for feeding a plate workpiece on a table to a punching position includes a workpiece holder that is moved while gripping a workpiece. A condition such as the size of a workpiece or a punching position on the workpiece may require the workpiece feeding apparatus to perform a repositioning operation for repositioning the workpiece to change the gripping position of the workpiece holder. During such repositioning operation, since the workpiece may become offset if it is simply released from the workpiece holder, a pair of friction pads that can be elevated and lowered by an elevating cylinder are provided and used to press the workpiece against the table to prevent such offset. When the frictional force of the friction pads is used to fix the workpiece against the table as described above, the workpiece is not properly fixed and can get offset while being re-gripped by the workpiece holder. Document US-A-4602541 discloses a method and apparatus according to the preambles of independent claims 1 and 4. This invention is designed to provide a press machine capable of reliably repositioning the workpiece without causing it to be offset. Summary of the Invention A press machine according to this invention is defined in claim 1. This configuration allows the workpiece gripping section to reposition the workpiece while the punch tool is penetrating the workpiece during a punching operation, the punch tool acts as a means for restricting the position of the workpiece in order to prevent it from becoming offset during a repositioning operation. In addition, the need to provide a position restricting member such as pads is eliminated to ensure a simpler configuration. During a repositioning operation, the control means may select a punch tool with a shape other than a perfect circle to fix the workpiece. This configuration restricts not only the horizontal offset of the workpiece but also its rotational offset around the punch tool, thereby more reliably preventing the workpiece from becoming offset during a repositioning operation. In this configuration, friction pads for pressing the workpiece against the table may be provided so that the workpiece is fixed using the punch tool penetrating the workpiece and the friction pads. This configuration allows not only the punch tool penetrating the workpiece but also the friction pads to restrict the position of the workpiece, thereby more reliably preventing the workpiece from becoming offset during a repositioning operation. In this case, the rotational offset of the workpiece around the punch tool can also be prevented by the friction pads by using a punch tool shaped like a perfect circle to fix the workpiece. The invention also relates to a method, as defined in claim 4. Brief Description of the Drawing Figure 1 is a conceptual drawing of a press machine according to one embodiment of this invention. Figure 2 is a plan view of the press machine. Figure 3 is a perspective view of the press machine. Figure 4 is a cross sectional view of a workpiece holder in the press machine. Figure 5 is a vertical cross sectional view showing a punch driving device installation portion of the press machine. Figure 6 is a front view of a conversion mechanism in the punch driving device. Figure 7A is a plan view showing the workpiece repositioning operation, and Figure 7B is a vertical cross sectional view showing this operation. Figure 8 is a control flow chart of the workpiece repositioning operation. Figure 9 is a conceptual drawing of a press machine according to another embodiment. Figure 10 is a plan view of the press machine. Figure 11 is a perspective view of the press machine. Figure 12 is a side view showing a presser device installation portion of the press machine. Figure 13A is a plan view showing the workpiece repositioning operation and Figure 13B is a vertical cross sectional view showing this operation. Figure 14 is a plan view showing another example of the workpiece repositioning operation. Figure 15 is a conceptual drawing of a press machine according to yet another embodiment. Figure 16 is a cross sectional view of an upper and lower friction pad installation portion in still another embodiment. Detailed Description of the preferred Embodiments One embodiment of this invention is described with reference to Figures 1 to 8. Figure 1 is a conceptual drawing showing a press machine according to this embodiment. Figure 2 is a plan view of this press machine and Figure 3 is a perspective view of this press machine. A press machine 1 is a turret punch press machine of which a frame 2 comprises an upper frame section 2A, a lower frame section 2B and a pillar section 2C each having a cross section like a box and that has a C-shaped side shape. An upper and a lower turrets 3A and 3B are disposed in the space between the upper and the lower frame sections 2A and 2B of said frame 2 and rotatably supported by the upper and the lower frame sections 2A and 2B, respectively. A plurality of press molds 4 constituting a punch tool are installed on the circumference of the upper turret 3A, while a plurality of die molds 5 are installed on the circumference of the lower turret 3B (Figure 5). The upper and the lower turrets 3A and 3B are indexed and rotated by a turret driving device (not shown in the drawings) on the frame 2. A punch driving device 6 for the punch tool 4 is composed of a servo motor 7 installed on the upper frame section 2A and a conversion mechanism 8 for converting the rotation of the servo motor 7 into linear reciprocating motion in the vertical direction, as shown in the vertical cross sectional view in Figure 5. The servo motor 7 has a built-in speed reducer 9 at one end and is accommodated in the upper frame 2A along longitudinal direction Y. The conversion mechanism 8 consists of an eccentric cam mechanism and an eccentric cam 10 is rotatably supported by a pair of bearings 11 and 12 at one end of the upper frame section 2A on the same rotational center O as a motor shaft 7a of the servo motor 7, as shown in the front view in Figure 6. The eccentric cam 10 and the motor shaft 7a of the servo motor 7 are connected together via a rotating shaft 13. The eccentric cam 10 has its eccentric shaft section 10a rotatably fitted via a bearing (not shown in the drawings) in a hole at the upper end of a crank arm 14. A ram 16 is coupled to the lower end of the crank arm 14 via a pin 15 and supported by a ram guide 17 provided at one end of the upper frame section 2A on its bottom surface so that it can be elevated and lowered. A T-shaped head coupling section that is coupled to the head of the press mold 4 held in the upper turret 3A is provided at one end of the ram 16. A table device 18 is provided in front of the frame 2. The table device 18 comprises a workpiece table 20 consisting of a middle fixed table 20a provided on a bed 19 and a movable table 20b disposed on both sides of the fixed table 20a, and the movable table 20b is moved back and forth (in direction Y) on a rail 21 on the bed 19 along with a carriage 22. The carriage 22 has a cross slide 24 having a workpiece holder 23 and installed so as to be moved laterally (in direction X). A plate workpiece W gripped by the workpiece holder 23 is fed in direction X, Y relative to the position P of the ram when the carriage 22 and the cross slide 24 are moved. The lateral movement of the cross slide 24 is driven via a feed screw 26 and a ball nut 27 by the servo motor 25 provided in the carriage 22 (Figure 3). As shown in Figure 4, the workpiece holder 23 comprises an upper movable jaw 29 coupled to a lower fixed jaw 28 in such a way that the upper movable jaw 29 can be rotatably opened and closed around a supporting shaft 30. The plate workpiece W is gripped by the ends of both jaws 28 and 29. The upper movable jaw 29 is opened and closed by an air cylinder 31 mounted on its proximal end. The workpiece holder 23 is supported on the cross slide 24 to enable lateral movement when a groove 32 formed in its rear surface engages with a mounting rail 33 on the front surface of the cross slide 24, and the workpiece holder 23 is fixed in an arbitrary position by a tightening device 34. A control means 35 (Figure 1) controls the entire operation of the press machine 1. The control means 35 also controls a repositioning operation in which the workpiece holder 23 acting as a workpiece gripping section repositions the plate workpiece W on the workpiece table 20. Figure 8 shows a flow chart describing the control of the repositioning operation. The repositioning operation controlled by the control means 35 is described with reference to Figure 8. Prior to the repositioning operation, a punch tool 4 with a horizontal cross sectional shape of a rectangle or the like other than a perfect circuit is indexed as the press molds 4 (step S1) and the punch driving device 6 is driven to punch the plate workpiece W (step S2). The punching operation can be used not only as part of the processing of the workpiece W but also solely for a repositioning operation where in processing is not required. Next, once the ram 16 has reached a bottom dead center and the punch tool 4 has penetrated the plate workpiece W, the driving by the punch driving device 6 is stopped (step S3). In this case, since the driving source of the punch driving device 6 consists of the servo motor 7, such control as the punch driving device 6 is stopped with the punch tool 4 penetrating the plate workpiece W can be easily provided. In this condition, even when the plate workpiece W is released from the workpiece holder 23, the punch tool 4 penetrating the plate workpiece W acts as a position retraining member to restrict the plate workpiece W without horizontal or rotational offset. In this condition, after the plate workpiece W has been released from the workpiece holder 23 (step S4), the cross slide 24 is moved laterally as shown by the dotted line in Figure 7A (step S5) and the plate workpiece W is then gripped again by the workpiece holder 23 (step S6). The press tool 4 is subsequently elevated (step S7). This workpiece repositioning apparatus therefore allows the workpiece holder 23 to reposition the plate workpiece W without the use of position restricting members such as pads, which press the plate workpiece W against the workpiece table 20, and without causing the plate workpiece W to become offset. This enables simple application to existing press machines. Figure 9 is a conceptual drawing of a press machine according to another embodiment. Figure 10 is a plan view of the press machine. Figure 11 is a perspective view of the press machine. This embodiment includes in the front of the upper frame section 2A of the press machine 1, a presser device 36 that presses the plate workpiece W against the workpiece table 20 and that can be elevated and lowered. The presser device 36 consists of an elevating cylinder 37 that is a driving source and friction pads 38 provided at one end of an elevating rod, as shown in Figure 12. When the control means 35 controls the repositioning operation, the friction pads 38 are lowered to press the plate workpiece W against the workpiece table 20 while the press molds 4 penetrate the plate workpiece W. It is recommendable that friction pads 40, located under the friction pads 38 so as to oppose them, are preferably provided on the workpiece table 20 or the frame 2 to allow the upper and lower friction pads 38 and 40 to hold the plate workpiece W. The lower friction pads 40 may be fixed or may be elevated and lowered by a driving source such as the elevating cylinder 41, as shown in Figure 16. The remaining part of the configuration of the embodiment in Figures 9 and 16 is the same as in the first embodiment. Since, in this embodiment, not only the punch tool 4 penetrating the plate workpiece W, but also the friction pads 38 that press it against the workpiece table 20 operate as position restricting members for the plate workpiece W, the plate workpiece W is more reliably prevented from becoming offset when it is released from the workpiece holder 23. After the repositioning operation, the friction pads 38 are elevated and saved as the press molds 4 are elevated. In this embodiment, which includes the friction pads 38 as an additional workpiece position restricting member, the punch tool 4 is not limited to one having a horizontal cross section other than a perfect circle, but may have a perfectly circular horizontal cross section as shown in Figure 14. In this case, the punch tool 4 and the friction pads 31 can also reliably prevent the plate workpiece W from becoming horizontally and rotationally offset. Since the punch tool 4 with a horizontal cross section other than a perfect circle need not be indexed for a repositioning operation as described above, currently indexed punch tool 4 can be used to perform a repositioning operation, thereby preventing unnecessary increases in the cycle time. Although each of the above embodiments has been described in conjunction with the press machine 1 that uses the servo motor 7 as the driving source of the punch driving device 6, any punch driving device that enables the ram to be stopped at an arbitrary position may be used. For example, this invention is applicable to a press machine 1 that uses a hydraulic cylinder 39 as the driving source of the punch driving device 6, as shown in Figure 15. In addition, the punch driving device may be a combination of a driving source such as a servo motor and a toggle mechanism. Since, even in such configurations, the punch driving device 6 can be stopped easily while the punch tool 4 is penetrating the plate workpiece W, the offset of the plate workpiece W can be reliably restricted to allow the workpiece holder 24 to perform a repositioning operation. The press machine according to this invention comprises the combination of features of claim 1. This configuration can reliably prevent the workpiece from becoming offset during a repositioning operation. In addition, position restricting members such as pads need not be provided, ensuring a simpler configuration. According to further development of the invention set forth in Claim 2, during a repositioning operation, the control means may select a punch tool with a shape other than a perfect circle to fix the workpiece. This configuration restricts not only the horizontal offset of the workpiece, but also its rotational offset around the punch tool, thereby more reliably preventing the workpiece from becoming offset during a repositioning operation. According to Claim 3, the apparatus includes friction pads for pressing the workpiece against the table, and the workpiece is fixed using the punch tool that penetrates the workpiece and the friction pads. This configuration allows not only the punch tool to penetrate the workpiece, but also the friction pads to restrict the position of the workpiece, thereby more reliably preventing the workpiece from becoming offset during a repositioning operation.

Claims: A press machine (1) comprising a workpiece gripping section (23) for gripping and moving a workpiece on a table (20), the workpiece gripping section (23) being capable of a repositioning operation in which the workpiece is repositioned; a punch tool (4) for punching a hole in the workpiece characterised by control means (35) which control the press machine such as to stop said punch tool (4) while it is penetrating the workpiece during a punching operation and then cause said workpiece gripping means to perform a repositioning operation in this stop condition. A press machine according to Claim 1 wherein during said repositioning operation, said control means (35) selects a punch tool (4) with a shape other than a perfect circle to fix a workpiece. A press machine according to Claim 1 including friction pads (38) for pressing said workpiece against the table (20), wherein said workpiece is fixed using the punch tool (4) penetrating the workpiece and said friction pads (38). Method for repositioning a workpiece on the table of a press machine which has a gripping section (23) characterised by stopping the punching movement while penetrating the workpiece by a punch tool (4), loosening the gripping of the workpiece by the gripping section (23), repositioning of the gripping section (23) with respect to the workpiece, gripping the workpiece by the gripping section (23), and continuing of the punching movement.

Inventors: AIZAWA HIDETO, AIZAWA, HIDETO, Aizawa, Hideto, Murata Kikai Inuyamaryo B4-502,
Applicants: MURATA MACHINERY LTD, MURATA KIKAI KABUSHIKI KAISHA
Application year: 1997
Main classification: B21D43
IPC codes: B21D28, B21D43