Method for feeding a piece of material into a machining zone of a machine tool - Patent Application 20070122997

Abstract

The present invention relates to a method for feeding a workpiece into a processing zone of a punching press, the workpiece being clamped between a pair of feed rollers and intermittently fed by intermittently rotating the feed rollers, and after each feeding of the workpiece and before the next feeding of the workpiece, feeding is interrupted so that the workpiece is stationary and clamped between the feed rollers, and the method comprises the steps of: a) holding the workpiece by fixing the feed rollers with a specific holding torque; b) temporarily reducing or canceling the holding torque of the feed rollers; c) temporarily reducing or canceling the holding torque of one or more pilot rollers; a) positioning the piece of material with the holding torque of the feed rollers reduced or removed by inserting a pilot pin into an associated pilot opening of the piece of material, wherein the piece of material is displaced by the pilot pin(s) and the feed rollers are rotated as the piece of material is displaced by clamping the piece therebetween, optionally by overcoming the reduced holding torque; and b) re-ejecting the pilot pin(s) from the pilot opening of the piece of material. The method of the present invention allows for high precision feeding of the piece of material without complex intermediate lift mechanisms.

Description

[Technical Field]

[0001] The present invention relates to a method for feeding workpieces into a machining zone of a machine tool, a feeding device for use when performing said method, and a machine tool equipped with said feeding device, according to the preambles of the independent patent claims. [Background technology]

[0002] In the case of machine tools in which a material strip is machined in several steps, it is often necessary to precisely maintain a specific feed speed. In particular in the case of automatic punching machines in which products are punched out of the material strip in a subsequent cutting process, very small tolerances are required, which can no longer be ensured via control of the feed rollers of the feed device used.

[0003] To allow the necessary tolerances to be maintained, the clamping of the piece of material between the feed rolls is temporarily released, allowing the piece of material to move freely. This process is also known as "intermediate lifting." In this free-moving state, pilot pins are then inserted into the assigned pilot openings of the piece of material, which precisely positions the piece of material. Before the pilot pins exit the pilot openings, the piece of material is clamped again between the feed rolls, thereby fixing it in a precisely aligned state.

[0004] Although this known process allows for highly accurate piece processing with regard to feed dimensions, it has the disadvantage that the feed devices required for this purpose are mechanically very complex and correspondingly expensive and difficult to maintain. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, the problem here is to provide a technical solution that does not have or at least partially avoids the above-mentioned disadvantages of the prior art. [Means for solving the problem]

[0006] This problem is solved by the subject matter of the independent patent claims.

[0007] Thereby, a first aspect of the invention relates to a method for feeding a piece of material into a machining zone of a machine tool, preferably an automatic punching machine.

[0008] The strip is permanently clamped between at least one pair of feed rollers and advanced by intermittently rotating the feed rollers. Thus, there is no intermediate lift of the feed rolls. After each advancement of the strip, the following steps occur in the feed interruption until the next advancement of the strip: a) Holding the piece of material by fixing the feed roller with a certain holding torque. b) temporarily reducing or removing the holding torque of the feed roller; c) positioning the piece of material with the holding torque of the feed rollers reduced or cancelled by inserting one or more pilot pins into the assigned pilot openings of the piece of material, if the piece of material deviates from the nominal position or the pilot pins and pilot openings do not match, the piece of material is displaced by the pilot pin(s) and the feed rolls are rotated as the piece of material is displaced by clamping the piece between them, if necessary by overriding the reduced holding torque. d) Re-ejecting the pilot pin(s) through the pilot holes in the material belt.

[0009] The method according to the invention makes it possible to achieve a fairly accurate piece feeding even without the use of complex intermediate lift mechanisms.

[0010] If the holding torque is temporarily reduced to a certain value greater than zero in step b) of the process, the material piece can only move by overcoming the reduced holding torque. If the holding torque is temporarily removed, the material belt is free to move in the feed direction and against the feed direction.

[0011] In a preferred variant of the process, the pilot pin(s) move out of the pilot opening for the piece again while the holding moment of the feed roller is temporarily reduced or cancelled. This prevents the pilot pin(s) from getting stuck if the feed roller rotates when the holding moment is reduced or cancelled again. Furthermore, it is also possible to release the reduction or cancellation of the holding torque by driving the feed roller with a specific drive torque for feeding the piece, without having to previously restore the original holding torque when the machine is stopped.

[0012] In a preferred variant of the process, the temporary reduction or cancellation of the holding torque of the feed roller is released again before the pilot pin(s) re-exit the pilot opening in the piece of material, preferably by restoring the original holding torque, whereby the feed roll can be prevented from moving when the reduction or cancellation of the holding torque is resumed.

[0013] In a further preferred embodiment of the process, the piece of material is displaced in the feed direction during positioning with the pilot pin(s), which is particularly advantageous when very thin pieces of material are processed and a reduced holding torque is used, since in this way buckling of the piece of material can be avoided.

[0014] The feed rolls are preferably driven by one or more servo motors, which are particularly suitable for this purpose since they can be precisely controlled not only in terms of their rotational position but also in terms of their drive and holding torque.

[0015] The servo motor(s), and thus the feed rollers driven by the servo motors, are preferably controlled by a control system for each feed interval according to predefined target movement and stop profiles.

[0016] The actual movement and stop profile of the servo motor(s) or feed roller is monitored, and the target movement and stop profile of the subsequent feeding interval, in particular the next feeding interval, is shifted, with the target position of the servo motor(s) or feed roller at the start of this shifted target movement and stop profile being particularly advantageously shifted to correspond to the actual position of the servo motor(s) or feed roller after positioning the piece of material using the pilot pin(s). In this way, setpoint tracking is then performed after each feeding interval, which prevents accumulation of setpoint deviations over several feeding intervals.

[0017] Advantageously, the machine tool is a punch press, whereby the nominal movement and stopping profile of the servo motor(s) or feed roller is synchronized with the movement profile of the press ram.

[0018] Said synchronization is preferably carried out as a so-called relative synchronization, in which the executed part of the target movement and stop profile of the servo motor(s) always coincides, in relative terms, with the executed part of the movement profile of the press ram. When the press is in a feed process and the feed is synchronized in this way, the servo motor(s) continue in the correct position of the nominal movement and stop profile, i.e. are advanced by the "remaining length". The "remaining length" is moved synchronously with the movement profile of the press ram. The servo motors or feed rollers can therefore be started and stopped as required in the nominal movement and stop profile.

[0019] In another preferred embodiment of the method, the feed roll is monitored for any rotational movement after the pilot pin(s) exit the pilot opening in the material belt and while the reduction in the holding torque of the feed roll is being canceled. If setpoint tracking is performed as described above, where the setpoint movement and stop profile for the next feeding interval is shifted, and the setpoint position of the servo motor(s) or feed roller at the start of this shifted setpoint movement and stop profile is shifted to correspond to the actual position of the servo motor(s) or feed roller after positioning the material piece with the pilot pin(s), monitoring preferably begins with the start of setpoint tracking and ends after the reduction or cancellation of the holding torque is completed, i.e., after a return to normal holding torque. If an exceedance of a certain maximum allowable twist angle is detected, the press is automatically stopped, and advantageously the detected twist angle that led to the press stop is communicated to the press operator via the press control system, thereby enabling the operator to perform a specific fault analysis.

[0020] A second aspect of the present invention relates to a feeding device for use in carrying out the method according to the first aspect of the present invention. The feeding device comprises at least one pair of feed rollers, between which a piece of material can be clamped. The at least one pair of feed rollers can be intermittently fed by intermittently rotating the feed rollers, and the feed rollers can be fixed with a certain holding torque so that the piece of material can be held stationary and clamped between the feed rollers during a feeding interruption. The feeding device is designed so that, during a feeding interruption, when the piece of material is stationary and clamped between the feed rollers, the holding torque of the feed rollers can be temporarily reduced or canceled while holding the piece of material, so that the piece of material can be displaced by a force acting on the piece of material, and the feed rollers clamping the piece of material are rotated by the piece of material clamped between them.

[0021] With the feeding device according to the invention, it is possible to achieve high precision one-sided feeding even without using a complex intermediate lift mechanism.

[0022] In a preferred embodiment, the feeder is designed in such a way that the holding torque can be temporarily reduced to a certain value greater than zero, which means that the piece of material can only be moved by overcoming the reduced holding torque.

[0023] In an alternative preferred embodiment, the feeding device is designed so that the holding torque can be temporarily cancelled.

[0024] Depending on the machining process and operating conditions, one or other alternative may be more preferable.

[0025] The feed rollers of the feed device are advantageously driven by one or more servo motors, which are particularly suitable for this purpose since they can be precisely controlled not only with regard to their rotational position but also with regard to their drive and holding torque.

[0026] The servo motor(s) and the feed rollers driven by the servo motors can preferably be controlled via a control system for each feed interval according to predefined target movement and stop profiles.

[0027] A third aspect of the invention relates to a machine tool, preferably for carrying out the method according to the first aspect of the invention, comprising a feeding device according to the second aspect of the invention, the machine tool comprising a control unit by means of which the servo motor(s) or the feeding roller can be controlled for each feeding interval according to a predetermined desired movement and stopping profile.

[0028] Preferably, the machine tool or a tool associated with the machine has one or more pilot pins for insertion into associated pilot openings in the piece of material to position the piece of material when the holding torque is temporarily reduced or removed.

[0029] The control is designed to monitor the actual movement and stop profile of the servo motor or feed roller of the feeding device, and can shift the target movement and stop profile of a subsequent feeding interval of the feeding device, preferably the next feeding interval, so that the target position of the servo motor or feed roller at the start of this shifted target movement and stop profile corresponds to the actual position of the servo motor or feed roller after positioning the material piece using the pilot pin(s).

[0030] In this way, set point tracking can be performed after each delivery interval, which prevents accumulation of set point deviations over several delivery intervals.

[0031] In a particularly preferred embodiment, the machine tool is a punch press, whereby the target motion and stopping profile of the servo motor or feed roller can be synchronized with the motion profile of its press ram.

[0032] The synchronization is preferably performed as a so-called relative synchronization, in which the executed parts of the target movement and stop profile of the servo motor(s) always coincide with the executed parts of the movement profile of the press slide when compared to each other. When the press is in a feed process and the feed is synchronized in this way, it continues at the correct point of the nominal movement and stop profile of the servo motor(s), i.e., it is advanced by the "remaining length". The "remaining length" is moved synchronously with the movement profile of the press ram. The servo motor or the feed roller can therefore be started and stopped as required in the target movement and stop profile.

[0033] In yet another preferred embodiment, the machine tool is designed so that after the pilot pin(s) exit the pilot opening in the workpiece and during the release of the reduction in the holding torque of the feed roller of the feeder device, the feed roller can be monitored for any rotational movement, whereby the press can be automatically stopped if it is determined that a certain maximum allowable rotation angle has been exceeded, and advantageously the rotation angle determined to have led to the stop of the press can be communicated to the press operator via the press control system, thereby enabling the operator to perform specific fault analysis.

[0034] When set point tracking is performed as described above, where the set point movement and stop profile for the next feeding interval is shifted, but the set point position of the servo motor(s) or feed roller at the start of this shifted set point movement and stop profile is shifted to correspond to the actual position of the servo motor(s) or feed roller after positioning the material piece using the pilot pin(s), it is preferable that monitoring begins with the start of set point tracking and ends after the holding torque is reduced or canceled, i.e., after the normal holding torque is restored.

[0035] Further preferred embodiments of the invention are set forth in the dependent claims and in the following description based on the drawings. [Brief explanation of the drawings]

[0036] [Figure 1] 1A) to 1G) show curves of various operating parameters of a punching press with a crank drive and a pilot pin over the crank angle of the press during application of various methods according to the invention for feeding a workpiece into the processing zone of the punching press. [Figure 2] 2A) to 2G) show curves of various operating parameters of a punching press with a crank drive and a pilot pin over the crank angle of the press during application of various methods according to the invention for feeding a workpiece into the processing zone of the punching press. [Figure 3]3A) to 3F) show curves of various operating parameters of a punching press with a crank drive and a pilot pin over the crank angle of the press during application of various methods according to the invention for feeding a workpiece into the processing zone of the punching press. DETAILED DESCRIPTION OF THE INVENTION

[0037] The partial diagrams marked A) to G) show the curves of the following operating parameters in each case over the crank angle: A) Pressing process B) Actual motion and stop profile of the feed roll C) Target motion and stop profile of the feed roll D) Position pilot pin E) Feeder roll holding or driving torque F) Set Point Tracking G) Process Monitoring

[0038] 1A) to 1G) show curves of various operating parameters of a punch press over the crank angle of the press in the application of a first method according to the invention for feeding a workpiece into a processing zone of the punch press over two crankshaft revolutions, i.e. a crank angle X of 720°C.

[0039] As can be seen from FIG. 1A), which shows the press stroke or ram position between top dead center OT and bottom dead center UT over a crank angle X, the press ram passes bottom dead center UT at 180° and 540° and passes top dead center OT at 360° and 720°.

[0040] As can be seen from Fig. 1B) and Fig. 1C) which show the actual movement and stop profile of the feed roll (Fig. 1B)) and the target movement and stop profile of the feed roll (Fig. 1C)) in circumferential rotation of the feed roll (in millimeters) and therefore in feeding movement of the material band (in millimeters): The actual displacement of the material band due to the rotation of the feed roll as shown in Figure 1B) occurs during the passage from top dead center OT to approximately 90° after OT, according to a specific target movement and stop profile in Figure 1C), from approximately 90° after OT, an interruption in the feed begins, which lasts until approximately 270° after OT or 90° after UT.

[0041] 1D) and 1E), which show the position of the pilot pin about to be inserted into the pilot opening of the material belt (FIG. 1D)) between the fully retracted position 0 and the fully inserted position 1 in the pilot opening, and the course of the holding or driving torque (Nm) of the feed roller (FIG. 1E)), the movement of the pilot pin into the pilot opening begins during the feeding interruption, just before 135° after OT or just before 45° before UT. While the pilot pin is inserted, the holding or driving torque of the feed roll, preset to a constant 1 Nm, is reduced to a reduced holding torque of 0.1 Nm. Both processes, i.e., the insertion of the pilot pin into the pilot opening of the material band and the reduction of the holding torque, are completed at 135° after OT.

[0042] As can be seen from the progression offset marked Y in FIG. 1B), which is shown enlarged for better clarity, when the pilot pin enters the pilot opening of the material piece, during which the material piece is brought to its final processing position, the material piece is pushed back against the feed direction and the feed roller rotates backward accordingly, while the target movement and stop profile of the feed roller remains unchanged, as shown in FIG. 1C).

[0043] The piece is then punched near bottom dead center UT with the pilot pin fully inserted into the pilot hole in the piece and the holding torque of the feed roll reduced.

[0044] As can be seen from FIG. 1F), which shows the state of set point tracking of the press control between "off" 0 and "on" 1, set point tracking is activated at approximately 200° after OT or approximately 20° after UT, which ends at approximately 215° after OT or 35° after UT, and then deactivated again.

[0045] As can be seen from the progression offsets marked Z in FIG. 1C, which is shown enlarged for better understanding, when setpoint tracking is activated, the target move and stop profile of the immediately following feed interval is shifted so that the target position of the feed roller at the start of this shifted target move and stop profile corresponds to the actual position of the feed roller after positioning the material strip with the pilot pin, which is fully inserted into the pilot opening of the material strip and the feed roll is held with a reduced holding torque.

[0046] As can be seen from Figures 1D) and 1E), the pilot pin is retracted after the set point correction at approximately 220° after OT or 40° after UT, and during the pilot pin retraction the holding torque of the feed roll is increased again to its original value of 1 Nm. Both processes, i.e., pilot pin retraction from the pilot opening in the material belt and reapplication of the holding torque, are completed at 225° after OT or 45° after UT.

[0047] As can be seen from Figure 1G), which shows the state of the process monitoring with respect to the unintentional rotation of the feed roll between "off" 0 and "on" 1, this process monitoring is activated when the setpoint tracking is activated, i.e., at approximately 200° after OT or 20° after UT, and is deactivated after the pilot pin has fully exited the pilot opening in the workpiece and the holding torque has returned to 1 Nm, i.e., at 225° after OT or 45° after UT.

[0048] If rotation of the feed roll beyond a certain maximum allowable rotation angle is detected, the press is automatically stopped and the operator is informed of the detected angle of rotation via the press control.

[0049] At approximately 270° after OT or 90° after UT, the feed interruption ends and the material piece is advanced by the rotation of the feed roll while the press ram moves upwards towards top dead centre OT, which is reached at 360° after OT or 180° after UT, after which the process described above starts again from the beginning.

[0050] 2A) to 2G) show curves of various operating parameters of a punch press over the crank angle of the press when using a second method according to the invention for feeding a workpiece into the processing zone of the punch press over two crankshaft revolutions, i.e. a crank angle X of 720°.

[0051] The method according to Figures 2A) to 2G) differs from the method according to Figures 1A) to 1G) only in that when the pilot pin moves into the pilot opening of the material piece, during which time the material piece is brought to its final processing position, the material belt is pulled or pushed forward in the feed direction and the feed roller is correspondingly rotated forward.

[0052] 3A) to 3F) show curves of various operating parameters of a stamping press over the crank angle of the press when using a third method according to the invention for feeding a workpiece into the processing zone of the stamping press over two crankshaft revolutions, i.e. a crank angle X of 720°.

[0053] The process according to Figures 3A-F differs from the process according to Figures 1A-G in that the setpoint tracking is activated after the pilot pin is fully retracted and the holding torque of the feed roll is increased again to its original value of 1 Nm, which in this process is approximately 225° after OT or 45° after UT. In this embodiment, the process monitoring according to Figure 1G is also omitted.

[0054] Although preferred embodiments of the present invention have been described in this application, it is expressly noted that the invention is not limited thereto and may be practiced in other ways within the scope of the following claims.

Claims

1. 1. A method of feeding a piece of material into a machining zone of a machine tool, comprising: the piece of material is clamped between at least one pair of feed rollers and intermittently advanced by intermittently rotating the feed rollers; After each advancement of the piece of material and before the next advancement of the piece of material, advancement is interrupted so that the piece of material is stationary and clamped between the feed rollers, the steps of: a) holding the piece of material by fixing the feed roller with a certain holding torque; b) temporarily reducing or canceling the holding torque of the feed roller; c) positioning the piece of material with the holding torque of the feed roller reduced or removed by inserting one or more pilot pins into pilot openings in the piece of material, the piece of material being displaced by the pilot pin(s) and the feed rollers being rotated by the piece of material clamped therebetween by overcoming the reduced holding torque if the holding torque has been reduced but not removed, as the piece of material is displaced; and d) retracting the pilot pin(s) from the pilot opening in the piece of material; was carried out, The feed roller is driven by a servo motor, the servo motor or the feed roller is controlled using a control system according to a predetermined target movement and stopping profile for each feeding interval; an actual movement and stop profile of the servo motor or the feed roller is monitored, and the target movement and stop profile for a subsequent feed interval is shifted such that a target position of the servo motor or the feed roller at the start of the shifted target movement and stop profile corresponds to an actual position of the servo motor or the feed roller after positioning the piece of material using the pilot pin(s); the machine tool is a punch press; The method, wherein the target movement and stopping profile of the servo motor or the feed roller is synchronized with the motion profile of a press ram of the punch press.

2. The method of claim 1 , wherein the subsequent delivery interval is a next delivery interval.

3. 3. The method of claim 1 or 2, wherein retraction of the pilot pin(s) from the pilot opening in the piece of material occurs while the holding torque of the feed roller is temporarily reduced or canceled.

4. 3. The method of claim 1, wherein the temporary reduction or cancellation of the holding torque of the feed roller is released again before the pilot pin(s) retract from the pilot opening of the piece of material.

5. The method according to any one of claims 1 to 4, wherein the piece of material is displaced in the feed direction during positioning with the pilot pin(s).

6. 6. The method of claim 1, wherein the synchronization is performed such that the servo motor or the feed roller can be started and stopped as desired in the target movement and stopping profile of the servo motor or the feed roller.

7. 7. The method of claim 1, wherein after the pilot pin(s) exit the pilot opening in the piece and while the reduction in the holding torque of the feed roller is released, the feed roller is monitored for any rotational movement, and if the detected rotation angle of the feed roller exceeds a certain maximum allowable rotation angle, the punch press is automatically stopped.

8. 8. The method of claim 7, wherein the punch press is automatically stopped upon indication of the detected rotation angle via the control system.

9. 9. The method according to claim 7 or 8, wherein the monitoring starts with the start of the next shift of the feeding interval and ends at the end of the reduction or cancellation of the holding torque.

10. A machine tool comprising: A feeding device comprising at least one pair of feed rollers, capable of clamping a piece of material between the at least one pair of feed rollers, wherein the at least one pair of feed rollers allows the piece of material to be intermittently fed by intermittently rotating the feed rollers driven by a servo motor, and the piece of material can be held stationary and clamped between the feed rollers by fixing the feed rollers with a specific holding torque during a feeding interruption; the feeding device is designed such that, in the interruption of feeding, when the piece of material is stationary and clamped between the feeding rollers, the holding torque of the feeding rollers can be temporarily reduced or canceled, so that the piece of material can be displaced by a force acting on it, and the feeding rollers clamping the piece of material are rotated by the piece of material clamped between them; one or more pilot pins that enter into associated pilot openings in the piece of material to position the piece at a temporarily reduced or canceled holding torque; and the machine tool comprises a control system capable of controlling the servo motor or the feed roller for each feed interval according to a predetermined target movement and stop profile; The control system is designed to monitor the actual movement and stopping profile of the servo motor or the feed roller, and can shift the target movement and stopping profile for a subsequent feeding interval such that the target position of the servo motor or the feed roller at the start of the shifted target movement and stopping profile is the actual position of the servo motor or the feed roller after positioning the piece of material using the pilot pin(s).

11. The machine tool according to claim 10, wherein the machine tool is a machine tool for carrying out the method according to any one of claims 1 to 9.

12. A machine tool according to claim 10 or 11, wherein the subsequent feeding interval is the next feeding interval.

13. A machine tool according to any one of claims 10 to 12, wherein the feeding device is designed to be able to temporarily reduce the holding torque to a certain value that is greater than zero.

14. The machine tool according to any one of claims 10 to 13, wherein the feeding device is configured to be able to temporarily cancel the holding torque.

15. 15. A machine tool according to claim 13 or 14, wherein the feeding device comprises a servo motor that drives the feeding roller.

16. 16. The machine tool of claim 15, wherein the servo motor or the feed roller can be controlled for each feed interval using a control system according to a predetermined target move and stop profile.

17. 17. The machine tool according to any one of claims 10 to 16, wherein the machine tool is a punch press, and the target movement and stopping profile of the servo motor or the feed roller can be synchronized with a movement profile of a press ram of the punch press.

18. 18. The machine tool of claim 17, wherein the synchronization is performed such that the servo motor or the feed roller can be started and stopped as desired in the target move and stop profile of the servo motor or the feed roller.

19. 19. The machine tool of claim 17 or 18, wherein the machine tool is equipped to monitor the feed roller for any rotational movement after the pilot pin(s) exit the pilot opening in the piece and while the reduction in the holding torque of the feed roller is released, and to automatically stop the punch press if the detected rotation angle of the feed roller exceeds a certain maximum allowable rotation angle.

20. 20. The machine tool of claim 19, wherein the punch press is automatically stopped, if the detected rotation angle of the feed roller exceeds a certain maximum allowable rotation angle, with visualization of the detected rotation angle via the control system.

21. 21. The machine tool according to claim 19 or 20, wherein the machine tool is designed such that the monitoring starts with the start of the displacement of the next feeding interval and ends when the reduction or cancellation of the holding torque is lifted.

Images