JP5313736B2 - Surge pressure prevention device for hydraulic cushion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surge pressure prevention device for an oil pressure cushion which can prevent the generation of surge pressure with a simple constitution. <P>SOLUTION: In the surge pressure prevention device for an oil pressure cushion including: an oil pressure cylinder 17 for a cushion mounted on a press machine; a feed oil path 72 for feeding oil pressure from an oil pressure feed means 71 to an oil chamber 22 for a cushion of the oil pressure cylinder 17 for a cushion; a relief oil path 73 for relieving the oil pressure of the oil chamber 22 for a cushion upon a cushion operation; and a relief valve 91 mounted to the relief oil path 73, before the start of the cushioning operation of the oil pressure cylinder 17, relief valve operating means 74, 97 operating the relief valve 91 from the point of time at which the slide of the press machine reaches the set position between the top dead center and the bottom dead center are provided. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a surge pressure preventing device for a hydraulic cushion, and more particularly to a surge pressure preventing device for preventing surge pressure generated in a hydraulic cushion including a cushion hydraulic cylinder equipped in a press machine.

  Conventionally, a hydraulic cylinder for holding and knocking out a printed circuit board (cushion hydraulic cylinder) is also incorporated in a printed circuit board punching device for punching a large number of pin holes in a printed circuit board for mounting an electronic device and forming an electric circuit. ing. Further, various die forming apparatuses for producing a molded product by forming a metal plate (work) with a press machine are equipped with a hydraulic die cushion device (hydraulic cushion).

  As described in Patent Documents 1 and 2, generally, a printed circuit board punching apparatus includes a knockout device attached to a lower end of a slide of a press machine, and an upper die for punching attached to a lower end of the knockout device. A unit and a lower die unit for punching that is mounted on a base (bolster) of a press machine so as to face the upper die unit are provided.

  The knockout device is provided in the main body member fixed to the lower end of the slide, a receiving hole recessed in the lower portion of the main body member, a movable pad mounted to be raised and lowered in the receiving hole, and an upper side of the movable pad. And a hydraulic cylinder for holding and knocking out (corresponding to a hydraulic cylinder for cushion) formed on the movable pad and a hydraulic pressure supply means for supplying hydraulic pressure to the hydraulic cylinder. The upper die unit is a presser plate that can be raised and lowered to hold the upper surface of the printed circuit board, a number of punching pins and pin holding plates that are inserted through the presser plate, and a pressure transmission mechanism that transmits the pressing force from the movable pad to the presser plate. And a pressing force transmission mechanism for transmitting the pressing force from the main body member to the pin holding plate.

  When a printed circuit board is punched by this printed circuit board punching device, the slide is lowered with hydraulic pressure supplied to the hydraulic cylinder and the movable pad at the lower limit position. Immediately thereafter, the printed circuit board is punched by a large number of punching pins that are driven downward by the slide at the bottom dead center of the slide.

  By the way, at the time of punching, the printed board is punched with a punching pin when the slide is lowered to the bottom dead center while maintaining the hold state where the printed board is pressed by the holding plate pressed by the hydraulic cylinder for holding and knocking out. . At this time, the hydraulic pressure of the hydraulic cylinder is relieved from a relief oil passage provided with a balance piston type relief valve.

  On the other hand, the die cushion device described in Patent Document 3 is equipped with a bolster of a press machine, and a plurality of pressure equalizing cushion pins that support a blank holder, and a plurality of hydraulic cylinders that support lower portions of these cushion pins, A die cushion device including a die cushion pad and a cushion air cylinder is provided. The oil chambers of the plurality of hydraulic cylinders are connected by a pipe and connected to a hydraulic pressure supply source.

  A high primary peak pressure (surge pressure) is generated in the hydraulic pressure of the plurality of hydraulic cylinders at the moment when the slide moves down to just before the bottom dead center and the upper die contacts the workpiece. Therefore, in order to limit the primary peak pressure below a certain level, a balance piston type relief valve is connected to the oil passage connected to the plurality of hydraulic cylinders, and this relief valve can adjust the relief pressure. It is configured.

Japanese Utility Model Publication No. 2-118623 Japanese Utility Model Publication No. 3-76622 Japanese Patent Laying-Open No. 2005-297021

  Recently, there is a tendency to mount a large number of miniaturized electronic components on a printed circuit board at a high density, the pin holes and pin hole intervals of the printed circuit board are reduced, the number of pin holes is increased, the printed circuit board is thinner, Since there is a tendency to increase the number of layers, a higher level of punching performance is required.

  Here, during punching, when the slide is lowered and the presser plate comes into contact with the printed circuit board, the balance piston type relief valve has a relief action due to a delay in response due to the inertia of the relief valve body, etc. High surge pressure is generated in the hydraulic pressure of the knockout hydraulic cylinder. Excessive pressing force acts on the printed circuit board due to the surge pressure generated in the hydraulic cylinder, so the punching performance is degraded, the printed circuit board is damaged, the punching quality is degraded, and burrs are generated at the edge of the pin hole. Or

  The technique described in Patent Document 3 is intended to suppress the primary peak pressure (surge pressure) to a relief set pressure or less by a balance piston type relief valve, but the inertia of the relief valve body of the relief valve, etc. Since the response delay due to, cannot be eliminated, the generation of surge pressure cannot be avoided.

  An object of the present invention is to provide a surge pressure preventing device for a hydraulic cushion that can reliably prevent the generation of surge pressure with a simple configuration.

  According to a first aspect of the present invention, there is provided a hydraulic cushion surge pressure preventing device comprising: a hydraulic cylinder for cushion provided in a press machine; and a hydraulic pressure supply passage for supplying hydraulic pressure from a hydraulic pressure supply means to a cushion oil chamber of the hydraulic cylinder for cushion. In the surge pressure prevention device for a hydraulic cushion having a relief oil passage for relieving the oil pressure of the oil chamber for cushioning during a cushion operation and a relief valve interposed in the relief oil passage, the cushion operation of the hydraulic cylinder is started. Relief valve actuating means for actuating the relief valve from the point in time when the slide of the press machine reaches the set position between the top dead center and the bottom dead center is provided.

  The relief valve actuating means operates the relief valve from the time when the slide of the press machine reaches a set position between the top dead center and the bottom dead center before the hydraulic cylinder cushioning operation is started. When starting the cushion operation just before reaching the dead center, the relief valve is in the relief operation, and the relief valve response delay is not caused by the stationary inertia of the relief valve body. The surge pressure that is generated is not generated in the oil pressure in the cushion oil chamber.

  According to a second aspect of the invention, there is provided the hydraulic cushion surge pressure preventing device according to the first aspect, wherein the relief valve actuating means has one end connected to the hydraulic pressure supplying means and the other end connected to the cushion oil chamber. A hydraulic pressure supply path, a variable throttle valve interposed in the auxiliary hydraulic pressure supply path, an electromagnetic on-off valve connected in series with the variable throttle valve in the auxiliary hydraulic pressure supply path, and a phase related to the lift position of the slide And a control means for controlling the electromagnetic on-off valve in response to a signal.

  According to a third aspect of the present invention, in the invention according to the second aspect, the control means is configured so that the control means has a period of time from when the slide reaches the set position until the slide reaches at least bottom dead center. The electromagnetic on-off valve is controlled to be opened.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the hydraulic cushion is a hydraulic cushion provided in a knockout device of a printed circuit board punching apparatus. It is characterized by that.

  According to the first aspect of the present invention, the relief valve is operated so that the relief valve is operated from the time when the slide of the press machine reaches the set position between the top dead center and the bottom dead center before the cushion hydraulic cylinder starts the cushion operation. Because the means is provided, when the slide reaches the bottom dead center and starts the cushion operation, the relief valve is in the relief operation, and there is no response delay of the relief valve due to the stationary inertia of the valve body of the relief valve. Surge pressure generated due to the response delay does not occur in the hydraulic pressure of the cushion oil chamber. Therefore, it is possible to prevent the cushion performance from being lowered, mechanical vibration and noise are reduced, and the durability of the apparatus is improved.

  According to a second aspect of the present invention, the relief valve operating means includes a sub hydraulic pressure supply path having one end connected to the hydraulic pressure supply means and the other end connected to the cushion oil chamber, and the sub hydraulic pressure supply path. An intervening variable throttle valve, an electromagnetic on-off valve connected in series to the sub-hydraulic supply passage in series with the variable throttle valve, and a phase signal related to the lift position of the slide are controlled to control the electromagnetic on-off valve Therefore, when operating the relief valve, the relief valve is opened and the relief oil is supplied by supplying a small amount of hydraulic pressure throttled by the variable throttle valve from the auxiliary hydraulic pressure supply path to the oil chamber for cushioning. The valve can be relieved.

  According to the invention of claim 3, the control means controls the electromagnetic on-off valve to an open state from the time when the slide reaches the set position until the slide reaches at least a bottom dead center. The relief valve can be operated by supplying a small amount of hydraulic pressure throttled by the variable throttle valve from the auxiliary hydraulic pressure supply path to the cushion oil chamber.

  According to the invention of claim 4, since the hydraulic cushion is a hydraulic cushion provided in the knockout device of the printed circuit board punching apparatus, surge pressure is generated in the cushion oil chamber.

It is sectional drawing of the printed circuit board punching processing apparatus which concerns on the Example of this invention. It is sectional drawing of a knockout apparatus. It is a perspective view of a movable pad and a spring mechanism of the knockout device. It is principal part sectional drawing which expanded the bearing. It is a hydraulic circuit diagram of a drive unit. It is a time chart which shows opening and closing of an electromagnetic direction switching valve. The printed circuit board punching performance can be improved.

  Hereinafter, modes for carrying out the present invention will be described with reference to examples.

  The printed circuit board punching apparatus 1 is for punching a large number of pin holes in the printed circuit board P. As shown in FIG. 1, a printed circuit board punching device 1 includes a knockout device 10 attached to the lower end of a slide 2 of a crank press machine, an upper mold unit 30 attached to the lower end of the knockout device 10, The lower die unit 50 mounted on the upper surface of the base 3 (bolster) of the press machine so as to face the lower side of the die unit 30 and the drive unit 70 for supplying hydraulic pressure to the holding and knockout hydraulic cylinder 17 of the knockout device 10. It has.

First, the knockout device 10 will be described.
As shown in FIG. 1, the knockout device 10 has a rectangular thick plate-like main body member 11 fixed to the lower end surface of the slide 2 with a plurality of bolts, etc., and a lower end opened recessed at the center of the lower portion of the main body member 11. -Shaped circular accommodation hole 12, an annular member 13 that is fitted in the accommodation hole 12 in a fitting manner and is fixed to the main body member 11 with a plurality of bolts (not shown), and an upright formed in the annular member 13 A movable pad 16 mounted in a cylindrical guide hole 14 via a bearing 15 so as to be movable up and down, and a hydraulic cylinder 17 (provided in the hydraulic cylinder for cushion) provided in the central portion of the movable pad 16 to apply hydraulic pressure to the movable pad 16. 6 pairs of spring mechanisms 18 (see FIGS. 2 and 3) for elastically supporting the movable pad 16 with the elastic force of the compression coil spring.

  The hydraulic cylinder 17 includes a cylinder hole 19 formed at the center of the movable pad 16 and a piston member 20 fixed to the main body member 11 with four bolts 21 and inserted into the cylinder hole 19. An oil chamber 22 (corresponding to a cushion oil chamber) of the hydraulic cylinder 17 is formed by the movable pad 16 and the piston member 20, and a seal 23 is attached to the outer peripheral portion of the cylinder hole 19. An oil passage 24 for supplying hydraulic pressure to the oil chamber 22 of the hydraulic cylinder 17 is formed in the piston member 20 and the main body member 11, and this oil passage 24 is connected to a drive unit 70 as a hydraulic pressure supply source described later (FIG. 5). reference). As shown in FIG. 4, the bearing 15 is mainly composed of a number of steel balls 15 a mounted so as to cover most of the outer peripheral surface of the movable pad 16.

  As shown in FIG. 2, the spring mechanism 18 is fixed to the main body member 11 and inserted into the guide hole 25 of the movable pad 16 and a hooked case 26 having a cross-sectional hat shape, and the spring mechanism 18 is arranged at the center of the case 26. A bolt 27 and a spacer 28 that are provided and pass through the bottom wall of the case 26 and are fixed to the movable pad 16, and are mounted so as to surround the bolt 27 and the spacer 28 in the case 26, and the movable pad 16 is interposed via the bolt 27. And a compression spring 29 for urging the upper side of the upper side. In a state where the hydraulic pressure of the hydraulic cylinder 17 is released, the movable pad 16 is returned to the upper limit position by the six sets of spring mechanisms 18.

  The upper die unit 30 is fixed to the lower surface of the main body member 11 by a plurality (e.g., eight) of hydraulic clamping devices 31, but a T for attaching the hydraulic clamping device 31 to the lower surface portion of the main body member 11. Grooves are formed.

Next, the upper mold unit 30 will be described.
As shown in FIG. 1, the upper mold unit 30 includes a base plate 32, a frame member 33, a movable plate 34 that can be moved up and down, a pin holding upper plate 35 and a pin holding lower plate 36, a frame-shaped die 37, and an inside thereof. The presser plate 38 can be moved up and down, fixed to the plurality of movable first rods 39, the plurality of movable second rods 40, the plurality of third rods 41, the pin holding upper plate 35 and the pin holding lower plate 36. A plurality of clamping devices 31 for fixing a large number of punching pins 43, four connecting bolts 44, and base plate 32 inserted into the numerous pin guide holes 42 of 38 to the main body member 11 of the knockout device 10. Etc.

  A first transmission system that transmits a pressing force acting on the movable pad 16 from the hydraulic cylinder 17 to the presser plate 38 includes a plurality of first rods 39, a movable plate 34, and a plurality of second rods 40. The second transmission system that transmits the downward driving force of the slide 2 and the main body member 11 to a large number of punching pins 43 includes a base plate 32, a plurality of third rods 41, and a pin holding upper plate 35.

Next, the lower mold unit 50 will be described.
As shown in FIG. 1, the lower mold unit 50 includes a base plate 52, a large number of die holes 53 corresponding to a large number of pins 43, and cooperates with the frame-shaped dice 37 to form an outer peripheral residual portion Pb of the printed circuit board P. A lower die main body 54 that functions as a punch plate for punching, a frame-shaped receiving plate 55 that is externally fitted to the lower die main body 54 so as to be movable up and down, four guide rods 56 that guide the frame-shaped receiving plate 55, and guide rods 56 A rubber member 57 or a coil spring that is externally fitted to the frame-shaped receiving plate 55 and elastically supports the frame-shaped receiving plate 55 so as to be movable up and down, four connecting bolts 58 that connect the lower die body 54 to the base plate 52, and the base plate 52 as the base of the press 3 has a plurality of clamping devices 51 and the like for fixing to the upper surface of the three.

Next, the drive unit 70 of the knockout device 10 will be described.
As shown in FIG. 5, the drive unit 70 supplies hydraulic pressure to the oil chamber 22 (corresponding to a cushion oil chamber) of the hydraulic cylinder 17 and relieves the hydraulic pressure of the oil chamber 22. . The drive unit 70 is connected to a hydraulic pressure supply section 71 (corresponding to a hydraulic pressure supply means), a hydraulic pressure supply path 72 extending from the hydraulic pressure supply section 71 to the oil chamber 22 of the hydraulic cylinder 17, and the oil chamber 22 of the hydraulic cylinder 17. A relief oil path 73 and a relief valve operating circuit 74 connected in parallel to the hydraulic pressure supply path 72 are provided.

  The hydraulic pressure supply unit 71 includes an oil tank 75, a swash plate hydraulic pump 77 driven by an electric motor 76, a cooler 78 that cools the oil returned from the hydraulic cylinder 17, and a cooling device for cooling the cooler 78. A fan 79 driven by a motor 76, a check valve 80, and the like are provided.

  In the hydraulic pressure supply path 72, a pressure gauge 81, a check valve 82, a pressure reducing valve 83, an accumulator 84 for storing the hydraulic pressure of a knockout pressure, which will be described later, a pressure gauge 85, and an electromagnetic direction switch are sequentially provided from the hydraulic pressure supply section 71 side. A valve 86 is provided. The electromagnetic direction switching valve 86 includes a closing position for closing the oil passage, a supply position for supplying hydraulic pressure from the hydraulic pressure supply unit 71 to the oil chamber 22, and an oil tank for supplying the oil pressure of the oil chamber 22 via a discharge oil passage 97 described later. It can be switched to a discharge position for discharging to 75.

  One end of the relief oil path 73 is connected to the oil chamber 22 of the hydraulic cylinder 17 via the hydraulic pressure supply path 72, and the other end of the relief oil path 73 is connected to the oil tank 75. In the relief oil passage 73, a pressure gauge 90, a balance piston type relief valve 91, a buffer tank 92, and a cooling cooler 93 are provided in this order from the oil chamber 22 side.

  The relief valve operating circuit 74 is connected in series to the auxiliary hydraulic pressure supply path 94, an electromagnetic direction switching valve 95 (corresponding to an electromagnetic opening / closing valve) provided in the auxiliary hydraulic pressure supply path 94, and the electromagnetic direction switching valve 95. And a variable throttle valve 96 provided in the auxiliary hydraulic pressure supply path 94. A discharge oil passage 97 is connected to the electromagnetic direction switching valves 86 and 95.

  One end of the sub hydraulic pressure supply path 94 is connected to the oil chamber 22 of the hydraulic cylinder 17 via the hydraulic pressure supply path 72, and the other end of the sub hydraulic pressure supply path 94 supplies hydraulic pressure between the pressure gauge 81 and the check valve 82. It is connected to the path 72. The electromagnetic direction switching valve 95 is connected to a portion of the auxiliary hydraulic pressure supply path 94 closer to the hydraulic cylinder 17 than the variable throttle valve 96.

  One end side of the discharge oil passage 97 is connected to the electromagnetic direction switching valves 86 and 95, and the other end is connected to the oil tank 75. The electromagnetic direction switching valve 95 closes the sub-supply path 94, supplies a position for supplying hydraulic pressure to the oil chamber 22, and supplies the oil pressure in the oil chamber 22 and the supply oil path 72 to the oil tank 75 via the discharge oil path 97. It is possible to switch to a discharge position for discharging to.

The control device 98 receives the phase signal PS related to the lift position of the slide 2 from a control unit (not shown) that controls the press machine, and controls the electromagnetic direction switching valves 86 and 95.
As shown in FIG. 6, for example, the electromagnetic direction switching valve 86 is opened to the supply position so that the slide 2 knocks out the printed circuit board P at a predetermined time immediately before the top dead center, and is hydraulically supplied to the oil chamber 22. And the slide 2 is switched to the valve-closed state immediately after passing through the top dead center.

The electromagnetic direction switching valve 95 is opened to the supply position in order to perform the relief operation of the relief valve 91 when the slide 2 is set at a position between the top dead center and the bottom dead center (for example, a crank angle position of 90 degrees). When 2 reaches bottom dead center, the valve is switched to the closed state. The above-mentioned setting position of the crank angle of 90 degrees is an example, and may be a position smaller than 90 degrees. Although the position may be larger than 90 degrees, it is necessary that the timing is earlier than the timing when the pressing plate 38 contacts the printed board P.
The relief valve actuation circuit 74 and the control device 98 correspond to “relief valve actuation means”. The relief oil passage 73 and the relief valve 91, the relief valve actuation circuit 74, and the control device 98 provide “hydraulic cushion surge”. A "pressure prevention device" is configured.

Next, the operation and effect of the surge pressure preventing device for preventing the surge pressure generated in the hydraulic pressure of the printed circuit board punching device 1 and the hydraulic cylinder 17 will be described.
When the slide 2 is lowered to just before the bottom dead center in a state where the hydraulic pressure is supplied to the hydraulic cylinder 17, the presser plate 38 contacts and presses the printed board P. When the slide 2 reaches the set position between the top dead center and the bottom dead center, the electromagnetic direction switching valve 95 is opened to the supply position, so that a high pressure (this is not reduced by the pressure reducing valve 83 from that time) Is higher than the relief operating pressure of the relief valve 91) is supplied to the supply oil passage 72 and the oil chamber 22 of the hydraulic cylinder 17 at a small flow rate throttled by the variable throttle valve 96. Starts the relief operation and enters a relief state in which relief is performed in small flow rates.

  Thus, after the relief valve 91 starts the relief operation, the slide 2 descends to just before the bottom dead center, and the presser plate 38 presses the printed board P. Immediately after that, when the slide 2 reaches the bottom dead center, the relief valve 91 is fully relieved and the movable pad 16 moves to the upper limit position relative to the annular member 13, while the downward driving force of the slide 2 is reached. Is transmitted from the base plate 32, the third rod 41, and the pin holding upper plate 35 to a large number of punching pins 43, and the printed board P is punched out.

  In this way, when the slide 2 reaches the set position between the top dead center and the bottom dead center, the electromagnetic direction switching valve 95 is switched to the supply position and the relief operation of the relief valve 91 is started. There is no response delay in the relief operation due to the stationary inertia of the relief valve element (not shown). Therefore, when the movable pad 16 comes into contact with the printed circuit board P, a surge pressure is not generated in the oil pressure of the oil chamber 22 of the hydraulic cylinder 17 due to a response delay of the relief valve 91, and the hydraulic cylinder 17 is good. Soft cushioning performance can be secured, punching performance can be improved, and mechanical vibration and noise generation can be reduced.

  Thereafter, when the electromagnetic directional control valve 86 is opened to the supply position by the control device 97 when the slide 2 reaches a predetermined position immediately before the top dead center, the movable pad 16 is driven to descend strongly, and the printed circuit board P is moved. A number of punching pins 43 are knocked out by the presser plate 38 and dropped onto a chute (not shown) inserted below the upper die unit 30 and taken out to the outside. In parallel with this, a printed board material (not shown) is put on the lower mold unit 50 and the chute is retracted, and the punching process similar to the above is repeatedly executed.

  The surge pressure generated in the oil chamber 22 of the hydraulic cylinder 17 can be prevented by the relief valve operating circuit 74 and the control device 98 having a simple configuration, so that the surge pressure can be easily implemented at low cost and has excellent practicality. A prevention device can be realized.

Here, the example which changes the said Example partially is demonstrated.
1] Instead of connecting one end of the auxiliary supply oil passage 94 on the oil chamber 22 side to the supply oil passage 72, it may be connected to the bypass portion of the relief valve 91 so that the relief valve 91 is directly operated for relief. Good.

2] Instead of the balance piston type relief valve 91, a differential type relief valve or a hydro cushion type relief valve may be adopted.
3] Although the example in which the bearing 15 having a large number of steel balls is incorporated in the outer peripheral portion of the movable pad 16 is described, the bearing 15 is not essential, the bearing 15 is omitted, and the movable pad 16 is made by metal touch. It is also possible to adopt a structure that slides.

  4] The surge pressure suppressor for the hydraulic cushion of the present application can be applied to a hydraulic cylinder for cushions of various die cushion devices in addition to the printed circuit board punching device 1. In addition, those skilled in the art can implement the present invention by adding various modifications to the above-described embodiments, and the present invention includes such modifications.

  The present invention can be used as a surge pressure prevention device for a hydraulic cushion equipped in various mechanical devices such as press machines.

1 Printed circuit board punching device 2 Slide 17 Hydraulic cylinder (hydraulic cylinder for cushion)
22 Oil chamber (oil chamber for cushion)
71 Hydraulic supply section 72 Supply oil path 73 Relief oil path 74 Relief valve operation circuit 91 Relief valve 94 Sub hydraulic pressure supply path 95 Electromagnetic direction switching valve 96 Variable throttle valve 98 Control device

Claims (4)

  Cushion hydraulic cylinder equipped in the press machine, a hydraulic supply path for supplying hydraulic pressure from the hydraulic supply means to the cushion hydraulic chamber of the cushion hydraulic cylinder, and relief of the hydraulic pressure of the cushion hydraulic chamber during cushion operation In the surge pressure preventive device for a hydraulic cushion having a relief oil passage and a relief valve interposed in the relief oil passage, the slide of the press machine before the start of the cushion operation of the hydraulic cylinder A surge pressure preventing device for a hydraulic cushion, comprising a relief valve actuating means for actuating the relief valve from the time when a set position between bottom dead centers is reached.   The relief valve actuating means includes a sub hydraulic pressure supply path having one end connected to the hydraulic pressure supply means and the other end connected to the cushion oil chamber, and a variable throttle valve interposed in the sub hydraulic pressure supply path, An electromagnetic on-off valve connected in series with the variable throttle valve in the auxiliary hydraulic pressure supply path, and a control means for controlling the electromagnetic on-off valve in response to a phase signal related to the lift position of the slide. The surge pressure preventing device for a hydraulic cushion according to claim 1.   The said control means controls the said electromagnetic opening-and-closing valve to an open state from the time of the said slide reaching the said setting position until the said slide reaches a bottom dead center at least. Surge pressure prevention device for hydraulic cushion.   The surge pressure preventing device for a hydraulic cushion according to any one of claims 1 to 3, wherein the hydraulic cushion is a hydraulic cushion provided in a knockout device of a printed circuit board punching device.