BREAKTHROUGH BUFFER FOR PRESSES AND CONTROL METHOD THEREFOR

Abstract: A breakthrough buffer for presses, for reducing noise or vibration occuring during blanking using a mechanical press, and a control method therefor. The apparatus is provided with a buffer body (20) disposed below the punch (3) of a press (1) and cushioning the punch during the breakthrough of the press, a timing regulator (40) connected to the buffer body and regulating the timing of the same during the breakthrough of the press, and a controller (60) adapted to send out a command for a regulating position to this regulator. The noise or vibration occuring during the breakthrough of the press is detected, and a command signal is sent out from the controller (60) to the timing regulator (40) to regulate the timing of the buffer body (20), whereby noise or vibration occuring during the breakthrough of the press is minimized.

Description: TECHNICAL FIELD The present invention relates to a breakthrough buffer for presses and a control method therefor, for reducing noise occurring during blanking, as known from DE-C-3 734 701. BACKGROUND ART Buffers according to the prior art are disclosed, for example, in Japanese Patent Publication No. 60-21832 and Japanese Patent Application Laid-open No. 52-19376. These buffers have a rod, a piston, a cylinder, a throttle valve and the like, and utilizes as a buffering force a flowing resistance which occurs when oil flowing out from a cylinder chamber passes through the throttle valve, thereby reducing the breakthrough of a press. However, in order to effectively reduce noise by buffering the breakthrough of the press, it is necessary to finely regulate the timing of buffering against the timing of blanking. A spacer is attached to the rod or the like for this regulation. Since an optimum timing varies depending on blanking conditions such as a plate thickness, shape and size of a punch, material of a plate, temperature and the like, this method requires a worker to find out an optimum timing by trial and error each time blanking conditions change, and to set the timing accordingly. Even when the optimum timing is set, a change of conditions (temperature, etc.) during blanking will cause the timing to deviate, with a resultant occurrence of a problem in actual use. Another problem is that utilizing a flowing resistance induced by throttling requires a slide to lower against the flowing resistance after the breakthrough of the press, thus causing the press to do excess work. Fig. 15A shows the load of a press in a conventional blanking state, i.e. a load exerted on the press at blanking. Fig. 15B shows an oil pressure in a buffer cylinder in the conventional blanking state, indicating that the pressure remains unchanged. Fig. 15C shows the displacement of a slide in the conventional blanking state. Fig. 15D shows the sound pressure of noise in the conventional blanking state, indicating that a noise level is higher. Fig. 16A shows the load of a press when buffering is performed using conventional throttling, indicating that the press does an excess work represented with W after the breakthrough of the press. Fig. 16B shows an oil pressure occurring in the buffer cylinder when buffering is performed using conventional throttling. From DE-C-3 734 701 (closest prior art) a control method is known for a breakthrough buffer for presses for buffering the breakthrough of a press ram occurring during blanking in a mechanical press in which noise or the vibration of a slide occurring during the breakthrough of a press is detected, and a controller sends out a command signal to a position regulator for regulating the position of the piston of a buffer body, thereby exercising control for minimising noise or the vibration of the slide during the breakthrough of the punch. SUMMARY OF THE INVENTION In view of the foregoing conventional problems, it is an object of the present invention to provide a breakthrough buffer for presses for buffering the breakthrough of a punch occurring during blanking in a mechanical press, comprising more than one buffer body disposed below a punch plate of the press and cushioning the punch plate during a breakthrough of the punch, a timing regulator connected to the buffer bodies and regulating the position of a buffer piston of each of the buffer bodies before the breakthrough, and a controller adapted to send out a command for a regulating position to the timing regulator before the breakthrough, wherein pipings are connected with said buffer bodies and said timing regulator. According to the invention a breakthrough buffer according to the pre-characterising part of claim 1 is characterised in that either two or four buffer cylinders are provided and that a ratio between the diameter of a buffer cylinder and the diameter of each of said pipings is so selected as to minimize a noise level at the ratio 10:1 in case of two buffer cylinders and 3:1 in case of four buffer cylinders. Further developments are disclosed in the subclaims. In addition, in the control method for the breakthrough buffer for presses, as set out in claim 4, noise or the vibration of a slide occurring during the breakthrough of the press is detected, and a command is sent out from the controller to the timing regulator to regulate the timing of the buffer body, whereby noise or the vibration of the slide is minimized. In a preferred embodiment, to regulate the timing of buffering, noise or the vibration of the slide correlating highly with noise is detected at each blanking, and the controller averages a set of measurements to obtain a minimum average, and then outputs a command signal to the timing regulator. In response to the command signal, the timing regulator sets upper and lower positions for a buffer piston. By utilizing an action of hydraulic shock through an appropriate selection of a buffer piston diameter and the diameter of piping for connection with a tank, a load exerted on the press after the breakthrough of the press is reduced more and thus the power is saved more as compared with the conventional buffer utilizing a flowing resistance. This is because a hydraulic shock occurs in response to a quick movement like the breakthrough of the press and hardly occurs when the slide lowers at a lower speed after the breakthrough of the press. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front view which illustrates a press equipped with a breakthrough buffer according to a first embodiment of the present invention; Fig. 2 is a side view of Fig. 1; Fig. 3 is a conceptual diagram which illustrates the breakthrough buffer and controller according to the first embodiment; Fig. 4 is a front view which illustrates a timing regulator according to the first embodiment; Fig. 5 is a plan view which illustrates the timing regulator according to the first embodiment; Fig. 6 is a cross-sectional view along the line Z-Z of Fig. 1; Fig. 7 is a flow chart which illustrates a control method according to the present invention; Fig. 8 is a graph which illustrates the relationship between the timing of buffering and noise level; Fig. 9 is a front view which illustrates a further timing regulator, which is useful for understanding the invention, but does not fall under the scope of the claims; Fig. 10 is a conceptual diagram which illustrates a timing regulator according to a second embodiment; Fig. 11 is front view which illustrates an applied example of a press equipped with the breakthrough buffer; Fig. 12 is a front view which illustrates another applied example of a press equipped with the breakthrough buffer; Fig. 13 is a graph which illustrates the relationship between the ratio of a buffer cylinder diameter to a piping diameter and noise level; Figs. 14A-14D are graphs which illustrate effects of the present embodiment; Figs. 15A-15D are graphs which illustrate effects of the prior art; and Figs. 16A-16B are graphs which illustrate other effects of the prior art. BEST MODE FOR CARRYING OUT THE INVENTION A breakthrough buffer for presses and a control method therefor according to a first embodiment of the present invention will now be described in detail with reference to the drawings. In a mechanical press 1 shown in Figs. 1 and 2, a punch plate 3 is fixed on a slide 2 whose rising and lowering motions are driven by a driving mechanism (not shown) comprising a crank, a connecting rod and the like. A punch 4 is attached to the punch plate 3, and also guide posts 5 are fixed to the same. A die block 6 opposed to the punch plate 3 is attached to a press frame 7 through a bolster 8. A die 9 is attached to the die block 6. A buffer body 20 cushioning the punch plate 3 during the breakthrough of the press is disposed in the die block 6 of the mechanical press 1, opposed to the guide post 5 fixed to the punch plate 3. A timing regulator 40, for regulating the timing of the buffer body 20 during the breakthrough of the press, is connected to the buffer body 20 through a piping 30. As shown in Fig. 3, a controller 60 sends out a control signal to the timing regulator 40 for regulating a timing position during the breakthrough of the press. The buffer body 20 comprises a buffer cylinder 21 and a buffer piston 22. A plurality of buffer bodies 20 are disposed below the punch plate 3 and in the die block 6. Figs. 4 and 5 show the timing regulator 40 in detail. The timing regulator 40 comprises a stepping motor 41 which runs under a command from the controller 60, a worm gear 42 which is supported by bearings 41a at both ends and rotated by the stepping motor 41, a worm wheel 44 which rotates a nut 45 held rotatably by a bearing 43 at one end and engages with the worm gear 42, a guide 46 with external threads 46a which engages with internal threads 45a of the rotating nut 45 and moves upward/downward through rotations of the nut 45, a buffering timing regulating piston 48 which has an end piece 48a abutting on the guide 46 at one end and a piston 47 at the other end, and a tank 49 which houses the buffering timing regulating piston 48, maintains an air pressure in an air chamber 49a located on one side of the buffering timing regulating piston 48, and contains oil in an oil chamber 49b located on the other side. A piping 51 leading to an air source (not shown) is connected to the tank 49 at one end, and a piping 30 leading to the buffer body 20 is connected at the other end. The guide 46 is provided with a locking mechanism to restrain trailing whirl. As exemplified in Fig. 3, two buffer bodies 20 are disposed in the die block 6, opposed to the guide posts 5. The pipings 30 from the buffer cylinders 21 of the buffer bodies 20 are independently connected to the tank 49. Pipings from the buffer bodies 20 may be integrated into one piping before the timing regulator 40 and connected to the tank 49. The buffer body 20 may be disposed in the bolster 8 At this time, when the buffer cylinder 21 and the tank 49 are connected through the piping 30 and when two buffer cylinders 21, i.e. 21a and 21b are used, the ratio of buffer cylinder dia. : piping dia. is set substantially at 10:1 for a reason described later. When four buffer cylinders 21, i.e. 21a, 21b, 21c and 21d are used, the ratio of buffer cylinder dia. : piping dia. is set substantially at 3:1. The controller 60, as shown in Fig. 3, comprises a noise meter 61 to measure noise occurring during the breakthrough of the press, an angle detector 62 to detect the rotation angle of a crank, and a controller 63 which regulates the timing of the buffer body 20 based on signals from these meters 61, 62 and sends out a next command to the stepping motor 41 of the timing regulator 40 for minimizing noise. The controller 63 is disposed on the press frame 7. Noise occurring during the breakthrough of the press is measured here, but the vibration of the slide or the like may be measured with an accelerometer 65 for exercising control so as to reduce vibration. Regulating operations of the timing regulator 40 will now be described. As shown in Figs. 4 and 5, in the timing regulator 40, when the stepping motor 41 receives a command signal from the controller 63 and rotates by a certain angle, the worm gear 42 rotates. Accordingly, the worm wheel 44 and the nut 45 rotate about the shaft of the regulating piston 48 by a fixed angle according to the gear ratio between the worm gear 42 and the worm wheel 44. As a result, as the nut 45 with internally incised threads 45a rotates, the guide 46 with the external threads 46a engaged with the threads 45a moves upward/downward by a certain fixed distance. As the guide 46 moves upward/downward, the end piece 48a abutting thereon moves upward/downward. At this time, the air chamber 49a of the tank 49 always maintains an air pressure of about 5 kg/cm 2 , and hence the regulating piston 48 is normally pressed downward. Thus, the top face of the guide 46 serves as a stopper against the end piece 48a of the regulating piston 48, thereby determining the lower limit position of the regulating piston 48. Accordingly, oil in the oil chamber 49b of the tank 49 moves to the buffer cylinder 21 through the piping 30, thereby determining the upper limit position of the buffer piston 22. Thus, the upper limit position of the buffer piston 22 for maintaining an optimum state with a minimum noise at all times can be set automatically without manual operations. A method of issuing a command of a setting position in the first embodiment will now be described with reference to a flow chart in Fig. 7. First, at step 1, when operation starts, the controller 63 enters an active state. At step 2, the controller 63 receives a signal indicative of the angle of a crank from the angle detector 62 of the press. At step 3, noise or vibration ai is measured at each blanking using the angle signal as a trigger. At step 4, the controller 63 calculates an average of values measured at N times of blanking ( An = 1/N x Σai ). At steps 5 and 6, noise ai is measured at each subsequent blanking in the same manner until the blanking count reaches N. The controller 63 calculates an average of thus measured values ( An+1 = 1/N x Σai ). At step 7, the difference Δ between the average value An+1 and the preceding average value An is obtained. At step 8, if the difference Δ is within a tolerance, the controller 63 goes to step 12 without sending out a command signal to the timing regulator 40. If the difference Δ does not fall within the tolerance at step 8, the controller 63 goes to step 9 and determines, from a magnitude or a plus/minus sign of the difference Δ, a command signal to be sent out to the timing regulator 40. If the difference Δ is smaller than zero, at step 10, the controller 63 outputs to the timing regulator 40 a command to act in the same direction as the preceding command. On the other hand, if the difference Δ is greater than zero, at step 11, the controller 63 outputs to the timing regulator 40 a command signal to act in the reverse direction to the preceding command signal. Then, the controller 63 repeats the operation of step 10 or 11 and outputs to the timing regulator 40 a command signal indicative of the timing of buffering when the difference Δ has become zero, i.e. when noise has been minimized (step 12). For example, as shown in Fig. 8, suppose that obtaining measurement data on point No. 1, the controller 63 has outputted to the timing regulator 40 a next command to delay the timing of buffering and thus has caused the buffer piston 22 to move slower, and then has obtained next data on point No. 2. In this case, since the difference between noise levels No. 1 and No. 2 is smaller than zero, the next command is to act in the same direction as the preceding command, i.e. in such a direction as to delay the timing of buffering. Likewise, suppose that a noise level at this time has been measured and noise level No. 3 lower than noise level No. 2 has been obtained. This operation continues until the noise level is inverted, i.e. until the difference between the currently measured noise level and the previously measured noise level exceeds zero. Noise level No. 4 is inverted, indicating that noise level No. 3 is a minimum value. Hence, the controller 63 outputs to the timing regulator 40 such a command as to set the timing of buffering to the one corresponding to noise level No. 3, i.e. Tr, thereby regulating the position of the buffer piston 22 accordingly. As a result, the minimum noise level is obtained. A further breakthrough buffer, which does not fall under the scope of the claims, will now be described with reference to Fig. 9. The same features as in the first embodiment are denoted by common reference numerals, and their description is omitted. The timing regulator 70 abuts on the buffer piston 22 of the buffer body 20 and is disposed on the top face of the die block. In details, externally incised threads 71a of a guide 71 engage with internal threads 45a of the nut 45 fixed to the worm wheel 44. As the nut 45 rotates, the guide 71 moves upward/downward with its bottom face 71c abutting on the buffer piston 22. A hole 71b is cut in the guide 71 at its central portion to allow the guide post 5 to pass therethrough. When in operation, the end portion of the guide post 5 abuts on the buffer piston 22. The guide 71 is provided with a keyway-like locking mechanism 73 to restrain the guide 71 from rotating with respect to a case 72, thereby allowing the guide 71 to slide only in the vertical direction. The bearing 43 is fixed to the timing regulator 70, and a guide member 74 for guiding the guide post 5 is attached to the case 72 at its top end. The bottom end of the case 72 is attached to the top face of the die block 6. In such a construction, the guide 71 of the timing regulator 70 determines directly the position of the buffer piston 22 of the buffer body 20 in the vertical direction. In other words, the buffer piston 22 is pushed up by air having a pressure of about 5 kg/cm 2 and supplied from a tank (not shown) through a piping 52. The bottom face 71c of the guide 71 abutting on the buffer piston 22 serves as a stopper to determine the upper limit position of the buffer piston 22. A required stroke of the buffer piston 22 is about 10 mm. A second embodiment of the present invention will now be described with reference to Fig. 10. The same features as in the first embodiment are denoted by common reference numerals, and their description is omitted. A buffer body 80 to cushion the punch plate 3 during the breakthrough of the press is disposed on the die block 6, opposed to the guide post 5. A timing regulator 90 to regulate the timing of the buffer body 80 at the breakthrough of the press is connected to the buffer body 80 through the piping 30. The controller 60 sends out a control command to the timing regulator 90, thereby exercising control. The buffer body 80 comprises a buffer cylinder 81, a buffer piston 82, a spring 83 to press the buffer piston 82, and a case 84 to accommodate the spring 83. A plurality of buffer bodies 80 are disposed in the die block 6. A hole 84b is cut in the case 84 at its central portion to allow the guide post 5 to pass therethrough. When in operation, the end portion of the guide post 5 abuts on the buffer piston 82. The timing regulator 90 comprises an electromagnetic proportional selector valve 91 which operates under a command from the controller 60 and an air-oil actuator 93 which receives an air pressure from a pump 92 through the electromagnetic selector valve 91 and sends pressure oil to the buffer body 80. A piston 94 is disposed in the air-oil actuator 93. Air is contained in an air chamber 93a on one side of the piston 94, and oil is contained in an oil chamber 93b on the other side. The air chamber 93a is connected to the electromagnetic proportional selector valve 91 through a piping 95, and the oil chamber 93b is connected to the buffer cylinder 81 through the piping 30. In such a construction, an oil pressure and a spring force exerted on the buffer piston 82 determines the position of the buffer piston 82 in the vertical direction. In other words, the electromagnetic proportional selector valve 91 is controlled by a command from the controller 60 to bring the air pressure of the air chamber 93a to Pa. At this time, with the pressure exerted area of the air chamber 93a taken as Sa and the pressure exerted area of the oil chamber 93b as Sh, oil pressure Ph of the oil chamber 93b is expressed by Ph = Pa x Sa/Sh This oil pressure Ph acts on the bottom face of the buffer piston 82. With the spring constant of a spring 83 acting on the buffer piston 82 taken as K, a deflection from a free length as y, and the pressure exerted area of the buffer piston 82 as Sp, the deflection y of the spring 83 is expressed by y = -Ph x Sp/K An equilibrium state is established at a predetermined position. Hence, by controlling the air pressure Pa with the electromagnetic proportional selector valve 91, the deflection y of the spring 83 is controlled, and thus the position of the buffer piston 82 can be controlled. In the above description, an air pressure is used at one end, but it may be replaced with an oil pressure. Also, the air pressure at one end is controlled with the electromagnetic proportional selector valve 91, but with the air pressure at one end enclosed, an oil pressure at the other end may be controlled with the electromagnetic proportional selector valve 91. Moreover, the electromagnetic proportional selector valve 91 is used, but it may be replaced with an electromagnetic proportional pressure control valve. In the above description, the buffer bodies 20, 80 are placed in the die block 6, but it is not necessary for them to be placed in the die block 6. As shown in Fig. 11, the buffer body 20 may be placed between the punch plate 3 and the die block 6. Alternatively, not shown, but the buffer body 20 may be placed between the slider 2 and the bolster 8. Also, as shown in Fig. 12, the buffer body 20 may be placed in the bolster 8. The ratio between the bore diameter D of the buffer cylinder 21 and the diameter d of the piping 30 connecting the buffer cylinder 21 and the tank 49 will now be described. As a result of conducting a study at various ratios between the bore diameter D of the buffer cylinder 21 and the diameter d of the piping 30, data as shown in Fig. 13 was obtained. It was found that a noise level was minimized at a ratio of about 10:1, as represented with curve Y, when two buffer cylinders 21 were used and that a noise level was minimized at a ratio of about 3:1, as represented with curve Z, when four buffer cylinders 21 were used. Also, the load of the press 1, an oil pressure in the buffer cylinder 21, the displacement of the slide 2, and noise were measured. Fig. 14A shows the load of the press 1 along the elapse of time or a change of the angle of press). Fig. 14B shows the oil pressure in the buffer cylinder 21. Fig. 14C shows the displacement of the slide 2. Fig. 14D shows the sound pressure of a noise level. As seen from the above figures, a sound pressure level having a lower amplitude is obtained as compared with the sound pressure of the prior art as shown in Fig. 15D and described before. Also, as compared with a load exerted on a press reducing noise by conventional throttling as shown in Fig. 16A and described before, an excess load represented by shaded portion W does not exist, and thus the load of the press can be reduced after the breakthrough of the punch. According to the present embodiment, by utilizing the action of hydraulic shock instead of throttling and by selecting as appropriate the bore diameter D of the buffer cylinder 21 and the diameter d of the piping 30 connecting the buffer cylinder 21 and the tank 49, the hydraulic shock can be used effectively. Moreover, since the hydraulic shock occurs in response to a quick movement, the hydraulic shock occurs only during the breakthrough of the punch and hardly occurs at a subsequent stage where the slide lowers at a lower speed. Hence, the load of the press after the breakthrough of the punch can be reduced, and power can be saved. INDUSTRIAL APPLICABILITY The present invention is effective to serve as a breakthrough buffer for presses and a control method therefor capable of automatically obtaining a low noise level, capable of further reducing the low noise level by selecting as appropriate the diameter of a buffer piston and the diameter of piping connecting the buffer piston and a tank, and capable of reducing the load of a press after the breakthrough of the press and thus saving power.

Claims: A breakthrough buffer for presses for buffering the breakthrough of a punch (4) occurring during blanking in a mechanical press, comprising more than one buffer body (20) disposed below a punch plate (3) of the press and cushioning the punch plate during a breakthrough of the punch, a timing regulator (40) connected to the buffer bodies and regulating the position of a buffer piston (22) of each of the buffer bodies before the breakthrough, and a controller (60) adapted to send out a command for a regulating position to the timing regulator before the breakthrough, wherein pipings (30) are connected with said buffer bodies and said timing regulator, characterized in that either two or four buffer cylinders are provided and that a ratio between the diameter of a buffer cylinder (21) and the diameter of each of said pipings (30) is so selected as to minimize a noise level at the ratio 10:1 in case of two buffer cylinders and 3:1 in case of four buffer cylinders. A breakthrough buffer for presses according to Claim 1, wherein said timing regulator (40) comprises a guide (71) which has a hole at its central portion to allow the guide post (5) of said press to pass therethrough and which moves in the vertical direction with its bottom face abutting on a buffer piston (22) of said buffer body (20), a worm wheel (44) and a nut (45) for driving the guide, a locking mechanism (73) for restraining a trailing whirl of the guide, and a case (72) for housing then and the upper limit position of the buffer piston of said buffer body is determined by the bottom face of the guide. A breakthrough buffer for presses according to Claim 1, wherein said buffer body (20) comprises a buffer cylinder (81), a buffer piston (82), a spring (83) for pressing the buffer piston, and a case (84) which accommdates the spring and has a hole (84b.) at its central Portion to allow the guide Post (5) of said press to mve in the vertical direction with its end Portion abutting on the buffer piston, and the Position of the buffer piston of saId buffer body in the vertical direction is determined by a pressure exerted on the buffer piston and a spring force acting against the pressure. A control method for a breakthrough buffer for presses for buffering the breakthrough of a punch (4) occurring during blanking in a mechanical press, comprising detecting a noise level or the vibration of a slide (2) occurring during the breakthrough of a punch (3), and sending out a command signal from a controller (60) to a timing regulator (40) for regulating the position of a buffer piston (22) of each of buffer bodies (20) before the breakthrough, characterized in that either two or four buffer cylinders are provided and that there is controlling to minimize the noise level or the vibration of the slide by selecting a ratio between the diameter of a buffer cylinder (21) of each of the buffer bodies and the diameter of each of pipings (30) connecting with the buffer bodies and the timing regulator, wherein the ratio is 10:1 in case of two buffer cylinders and 3:1 in case of four buffer cylinders

Inventors: EJIMA KIKUO, IMAMURA KAZUYA, IWASAKI SHIGEKI, NISHIKAWA KENJI, SUWA TATSUNORI, SUZUKI KAZUHISA, EJIMA, KIKUO, IMAMURA, KAZUYA, IWASAKI, SHIGEKI, NISHIKAWA, KENJI, SUWA, TATSUNORI, SUZUKI, KAZUHISA
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1993
Main classification: B30B15
IPC codes: B21D28, B30B15