JP2006300187A - Hydraulic servo device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydraulic servo device applicable to various industrial hydraulic machines including a machine tool such as a press, and to accurately control a stroke position of a hydraulic cylinder regardless of the kind of a workpiece. <P>SOLUTION: A cylinder 11 is vertically arranged, and pressure on a tube side generated by the own weight of a cylinder rod 21 is guided to a hydraulic pump 13. Pilot pressure is used for switching the capacity of the hydraulic pump 13. Higher pressure between the pressure on tube side of the cylinder 11 and the pressure on the rod side is used for pressure for switching the capacity of the hydraulic pump 13. The pilot pressure is obtained by switching an electromagnetic selector valve 16. The switching of the electromagnetic selector valve 16 follows a stroke of the cylinder rod 21. The stroke of the cylinder rod 21 is detected by a position sensor 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydraulic servo apparatus applied to various industrial hydraulic machines and the like in addition to machine tools such as a press machine.

  In a plastic working apparatus (press machine) using a hydraulic cylinder, the following hydraulic servo apparatus is employed to control the operation thereof.

  FIG. 2 shows an example of a hydraulic servo device employed in a press machine (see, for example, Patent Document 1). In this hydraulic servo apparatus, when the servo motor 1 rotates and the two-way discharge type hydraulic pump 2 is driven, pressure oil is supplied to the tube side port 4 of the hydraulic cylinder 3 and the cylinder rod 5 is moved to a predetermined initial position. Extends to the bottom dead center position. As a result, the die 6 is lowered to a predetermined pressing position, and the work 7 is pressed. Thereafter, the servo motor 1 rotates in reverse to shorten the cylinder rod 5 from the bottom dead center position to the initial position. Note that the rotation of the servo motor 1 is controlled by a predetermined control device.

  In such a press machine or the like, it is necessary to accurately control the operation of the hydraulic cylinder 3 (stroke of the cylinder rod 5) in order to perform high-precision pressing. That is, the cylinder rod 5 quickly extends from the initial position to a position where the die 6 comes into contact with the workpiece 7, and at the press stage, the die 6 becomes the predetermined dead position at the bottom dead center position of the cylinder rod 5. It is necessary to precisely match the position. In addition, it is necessary to quickly return from the bottom dead center position to the initial position.

  In order to perform such control, a variable displacement hydraulic pump 2 as shown in the figure is employed, and the cylinder rod 5 is extended at a high speed by increasing the discharge amount until the die 6 contacts the workpiece 7. After that, until the bottom dead center position, the discharge amount is reduced and the stroke speed of the cylinder rod 5 is lowered to precisely control the position. When returning from the press position to the initial position, the discharge amount is increased again to return at a high speed.

The hydraulic pump 2 is of a pilot-type variable displacement type, and the tube side pressure of the hydraulic cylinder 3 is guided to the hydraulic pump 2 as a pilot pressure, and the discharge amount is set to decrease as the pilot pressure increases. Yes.
Japanese Patent Laid-Open No. 10-166199 (FIG. 9)

  However, since the switching of the capacity of the hydraulic pump 2 (switching of the tilt amount) depends on the tube side pressure of the hydraulic cylinder 3, there are the following problems.

  That is, when a large pressing force is not required for plastic processing of the workpiece 7 or when it is desired to slightly increase or decrease with no load when not being processed (no load operation), the tube side pressure of the hydraulic cylinder 3 Therefore, the capacity of the hydraulic pump 2 cannot be switched. As a result, there is a problem that the bottom dead center position of the cylinder rod 5 cannot be precisely matched to the press position of the die 6.

  Accordingly, an object of the present invention is to provide a hydraulic servo apparatus capable of controlling the stroke position of a hydraulic cylinder with high accuracy regardless of the type of workpiece.

  (1) Since the inventor of the present application can control the stroke position of the hydraulic cylinder with high accuracy if the displacement of the hydraulic pump can be reliably performed, the displacement of the hydraulic pump can be switched with the pressure of the hydraulic cylinder as in the past. It was considered that the above object could be achieved by directly detecting the stroke of the hydraulic cylinder and forcibly switching the capacity of the hydraulic pump based on this, instead of detecting and performing indirectly.

  (2) Therefore, the hydraulic servo device according to the present application is arranged such that the capacity is changed by the pilot pressure for capacity switching and the cylinder rod is expanded and contracted along the vertical direction. A hydraulic cylinder in which the two discharge ports of the pump are hydraulically connected to the tube side port and the cylinder rod side port, respectively, and a position where a stroke signal is detected and detected when the cylinder rod makes a predetermined stroke A sensor, a pilot line that guides at least the cylinder rod side port pressure to the hydraulic pump as the capacity switching pilot pressure, an electromagnetic switching valve that opens and closes the pilot line, and an electromagnetic switching valve that receives the stroke signal based on the pilot signal And a control device for transmitting a signal for opening the screen.

  In a press machine or the like, the hydraulic cylinder is usually arranged in the vertical direction, so that even if the load is light or no load, a constant pressure is applied to the cylinder rod side port due to the weight of the cylinder rod, die and mold. appear. This pressure is guided to the hydraulic pump by the pilot line, but since the pilot line is opened and closed by the electromagnetic switching valve, the cylinder rod side port pressure is not guided to the hydraulic pump when the electromagnetic switching valve is closed, but is introduced in the open state. It is burned. That is, by switching the electromagnetic switching valve, the capacity switching pilot pressure can be reliably guided to the hydraulic pump.

  Here, the switching timing of the electromagnetic switching valve is performed based on the detection signal (stroke signal) at that time when the stroke of the cylinder rod is detected by the position sensor. That is, a required stroke of the cylinder rod is set in advance according to the application / function of a machine tool such as a press machine to which the hydraulic servo device is applied, and the stroke is detected by the position sensor. And the said stroke signal is received by the control apparatus, and a control apparatus transmits a signal based on this. The electromagnetic switching valve opens the pilot line based on this signal.

  (3) In the pilot line, either the pressure of the discharge port connected to the tube side port of the hydraulic pump or the pressure of the cylinder rod side port is led to the hydraulic pump as the capacity switching pilot pressure. A high pressure selection valve can be provided. This has the advantage that the pilot pressure for switching the capacity of the hydraulic pump can be obtained more reliably.

  A counter balance valve can also be provided at the cylinder rod side port of the hydraulic cylinder. Accordingly, the cylinder rod can be extended with the brake applied as necessary, and the stroke can be controlled so that the cylinder rod accurately stops at the preset bottom dead center position.

  As described above, according to the present invention, by detecting the stroke of the cylinder rod by the position sensor, the electromagnetic switching valve is operated to the open position, and the pressure generated by the cylinder rod's own weight causes the hydraulic pump to pass through the pilot line. Therefore, the capacity of the hydraulic pump can be switched reliably when necessary. Therefore, the stroke position of the hydraulic cylinder can be controlled with high accuracy regardless of the type of workpiece (invention according to claim 1).

  In addition, by introducing one of the high pressure side of the pressure of the discharge port connected to the tube side port of the hydraulic pump and the pressure of the cylinder rod side port to the pilot line as the pilot pressure for switching capacity to the hydraulic pump. Therefore, the pilot pressure for switching the capacity of the hydraulic pump can be obtained more reliably, and the stroke position of the hydraulic cylinder can be controlled reliably and with high accuracy regardless of the type of workpiece (the invention according to claim 2). ).

  In particular, by providing a counter balance valve at the cylinder rod side port of the hydraulic cylinder, so-called cylinder overshoot can be prevented and the stroke position of the hydraulic cylinder can be controlled more reliably and with high accuracy. Further, it is also effective as a safety measure means for preventing the cylinder rod and the die from dropping at the time of failure of the control device or power failure (invention according to claim 3).

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a system diagram showing a configuration of a hydraulic servo apparatus according to an embodiment of the present invention. In the present embodiment, the hydraulic servo apparatus 10 is applied to a press machine that plastically processes a workpiece, and the stroke of a press hydraulic cylinder (hereinafter simply referred to as “cylinder”) 11 is used to perform precise pressing. Control precisely. The hydraulic servo apparatus 10 is not limited to a press machine, and can be applied to general industrial machines and the like in addition to various machine tools.

  The configuration of the hydraulic servo apparatus 10 will be described. The hydraulic servo apparatus 10 includes a two-way discharge variable displacement hydraulic pump (hereinafter simply referred to as “hydraulic pump”) 13 driven by a servo motor 12 and a cylinder 11 that operates by receiving supply of pressure oil from the hydraulic pump 13. A position sensor 14 for monitoring the stroke of the cylinder 11, a pilot line 15 for guiding a pilot pressure for switching the capacity of the hydraulic pump 13 to the hydraulic pump 13, and an electromagnetic switching valve 16 for opening and closing the pilot line 15. And a control device 17 for controlling the operation of the entire hydraulic servo device 10 in addition to the operation of the electromagnetic switching valve 16.

  Further, in this embodiment, the hydraulic pump 13 is of a two-way discharge type, and the hydraulic oil on the cylinder tube side and the cylinder rod side is circulated when the cylinder 11 is operated. Is provided with a hydraulic oil adjustment circuit 18.

  Hereinafter, each part will be described in detail.

(1) Hydraulic pump The hydraulic pump 13 is a swash plate pump that can be switched between a large capacity and a small capacity. In the hydraulic pump 13, the capacity is switched by changing the tilt angle of the swash plate by the external pilot pressure. The hydraulic pump 13 includes an adjuster 29 for capacity control, and the adjuster 29 includes a pilot port 19 and a set pressure adjusting spring 20. By adjusting the spring force of the spring 20, the set pressure for switching the capacity of the hydraulic pump 13 can be changed. Further, the spring constant of the spring 20 can be made smaller than that of the prior art corresponding to the cylinder rod side port pressure, and the capacity switching can be made extremely responsive. The operation of the servo motor 12 for driving the hydraulic pump 13 is controlled by the control device 17.

  When the main shaft of the hydraulic pump 13 is rotated forward, hydraulic oil is absorbed from the cylinder rod side and pressure oil is supplied to the cylinder tube side. When the main shaft is reversed, the hydraulic oil is absorbed from the cylinder tube side and the pressure oil is supplied to the cylinder rod side. Such a hydraulic circuit connecting the hydraulic pump 13 and the cylinder 11 is theoretically closed, but in actuality, some hydraulic oil leaks inside. The leaked hydraulic oil is drained by a drain circuit (not shown), but in some cases, the amount of hydraulic oil in the hydraulic circuit is insufficient and cavitation may occur. Further, since the cylinder 11 is a single rod double acting type, the amount of hydraulic oil flowing on the cylinder tube 22 side and the amount of hydraulic oil flowing on the cylinder rod 21 side during the stroke of the cylinder rod 21 are different. On the other hand, the oil absorption amount and the discharge amount of the hydraulic pump 13 are equal. Therefore, when the cylinder rod 21 is extended, the amount of hydraulic oil in the hydraulic circuit is insufficient, and when the cylinder rod 21 is contracted, the amount of hydraulic oil on the cylinder rod side is excessive, which may cause abnormal pressure.

(2) Hydraulic oil adjustment circuit The hydraulic oil adjustment circuit 18 described above is provided to avoid such inconvenience. Specifically, a check valve 23a and a pilot check valve 23b are arranged inside, and the check valve 23a and the pilot check valve 23b are connected to an oil tank 24 provided in the press machine.

  According to this hydraulic oil adjustment circuit 18, when the hydraulic pump 13 rotates forward and hydraulic oil is absorbed from the cylinder rod 21 side and supplied to the cylinder tube 22 side, the electromagnetic switching valve 35 is excited. The amount of oil shortage in the hydraulic circuit is replenished from the tank 24 through the pilot check valve 23b. When the electromagnetic switching valve 35 is not excited, the pressure on the cylinder tube side is increased by the counter balance valve 27, so that the pilot check valve 23b is closed. Therefore, the amount of oil shortage is sucked from the check valve 23a and replenished. As a result, even if the amount of hydraulic oil in the hydraulic circuit is insufficient, the hydraulic oil is sucked up from the oil tank 24 to compensate for the shortage.

  On the other hand, when the hydraulic pump 13 rotates in the reverse direction and hydraulic oil is absorbed from the cylinder tube 22 side and supplied to the cylinder rod 21 side, the pressure on the cylinder rod 21 side first increases similarly, and thereby the pilot check valve 23b. Opens. As a result, even if the amount of hydraulic oil in the hydraulic circuit becomes excessive, it can be returned to the oil tank 24. The hydraulic oil adjustment circuit 18 is not limited to the one using the check valve 23a and the pilot check valve 23b, and may adopt other known structures.

(3) Cylinder and position sensor The cylinder 11 is a single rod double acting type including the cylinder tube 22 and the cylinder rod 21 as described above. When the hydraulic servo apparatus 10 according to the present embodiment is employed in a press machine, the cylinder 11 is arranged along the vertical direction. Further, the cylinder 11 includes a die 25 at the tip of the cylinder rod 21, and a counter balance valve 27 is disposed at the cylinder rod side port 26.

  The die 25 is for pressing the workpiece 28 and has an outer shape necessary for plastic working the workpiece 28 into a required shape. In addition, by providing the counter balance valve 27, when the cylinder rod 21 extends, a brake is applied to prevent rapid expansion (falling).

  The position sensor 14 is installed along the vertical direction (that is, the expansion / contraction direction of the cylinder rod 21), and can detect the stroke of the cylinder rod 21 by outputting a signal S1 corresponding to the position.

(4) Pilot line and electromagnetic switching valve The pilot line 15 is used to guide the higher one of the pressure at the cylinder tube side port 31 or the pressure at the cylinder rod side port 26 to the pilot port 19 of the hydraulic pump 13 as a pilot pressure. is there. For this reason, the pilot line 15 is provided with a high pressure selection valve 32, and both ports of the high pressure selection valve 32 are connected to the cylinder tube side port 31 and the cylinder rod side port 26, respectively.

  Further, an electromagnetic switching valve 16 is provided in the middle of the pilot line 15, and the pilot line 15 is opened and closed by switching. That is, the electromagnetic switching valve 16 is normally set to the closed position (state shown in the figure), and the pilot pressure is not led to the pilot port 19 of the hydraulic pump 13, but the electromagnetic switching valve 16 is electrically connected. By setting the switching open position, the pilot line 15 communicates with the pilot port 19 and the pilot pressure is guided to the pilot port 19 of the hydraulic pump 13. The switching timing of the electromagnetic switching valve 16 is based on a command from the control device 17.

(5) Control Device The control device 17 includes a memory 34 and a CPU 33. The memory 34 stores a program for controlling the servo motor 12 at a preset speed, rotation direction, and the like. And according to it, CPU33 outputs the signal (deviation signal of command signal S4 and detection signal S1 of position sensor 14) S2 which operates servomotor 12. FIG.

  The memory 34 stores two predetermined positions of the cylinder rod 21 to be detected by the position sensor 14 as signals. One is a position corresponding to the timing at which the electromagnetic switching valve 16 is switched, and specifically, a position at which the die 25 provided on the cylinder rod 21 starts to contact and press the workpiece 28. The other is the position where the die 25 has completely pressed the workpiece 28, and it is important to accurately detect this position in order to perform a highly accurate pressing operation.

  The CPU 33 receives the detection signal S1 output from the position sensor 14, compares the detection signal S1 with the first predetermined position signal stored above, and turns the solenoid of the electromagnetic switching valve 16 on if they match. The driving signal S3 is output, and the electromagnetic switching valve 16 switches the pilot line to an open state. If the detection signal S1 matches the second predetermined position signal stored, the servo motor 12 stops and the cylinder rod stops at the predetermined position.

(6) Operation of Hydraulic Servo Device Next, the operation of the press machine according to this embodiment will be described together with the effects of the hydraulic servo device 10.

  The greatest merit by adopting the hydraulic servo device 10 described above is accurate even when a thin steel plate or the like is processed by a press machine, that is, even in the case of a light load that does not generate high pressure in the cylinder 11. It is a point which can perform press work.

  More specifically, first, the hydraulic pump 13 is set to a large capacity in a normal state. When the hydraulic pump 13 is rotated forward, a large amount of hydraulic oil is supplied to the cylinder tube 22 side, and the cylinder rod 22 is rapidly lowered.

  The stroke of the cylinder rod 21 is monitored by the position sensor 14, and when the cylinder rod 21 extends and the die 25 starts to press the workpiece 28, the position sensor 14 and the control device 17 detect this and a signal S3 is transmitted. Is done. Based on this signal, the electromagnetic switching valve 16 is switched and the pilot line 15 is opened.

  At this time, even if the cylinder 11 is lightly loaded or unloaded, a constant pressure is generated on the cylinder rod 21 side due to the weight of the cylinder rod 21 and the die 25. This pressure is guided to the high pressure selection valve 32. On the other hand, when the cylinder 11 is lightly loaded or unloaded, almost no pressure is generated on the cylinder tube 22 side. For this reason, the pilot line 15 guides the pressure on the cylinder rod 21 side to the pilot port 19 of the hydraulic pump 13 as a pilot pressure. With this pressure, the capacity of the hydraulic pump 13 is switched to a small capacity. As a result, the cylinder 11 is driven at a low speed, and the stroke of the cylinder rod 21 can be controlled with high accuracy. The preset bottom dead center position of the cylinder rod 21, that is, the die 25 completely moves the workpiece 28. The pressed position can be accurately detected.

  As described above, in the present embodiment, the pressure generated by the dead weight of the cylinder rod 21 and the like is introduced as the pilot pressure of the regulator 29 for controlling the capacity of the hydraulic pump 13, so regardless of the type of the workpiece 28 (load of the cylinder 11 Regardless of the size of the cylinder 11), the stroke control of the cylinder 11 can be performed precisely and a highly accurate press operation can be performed.

  Furthermore, the pilot pressure for switching the capacity can be set to a low pressure by operating the set pressure adjusting spring 20 of the hydraulic pump 13. As a result, there is an advantage that the switching of the capacity of the hydraulic pump 13 can be extremely responsive.

  When the position sensor 14 detects the bottom dead center position of the cylinder rod 21, a signal S2 is output from the control device 17, and the servo motor 12 is rotated in the reverse direction. It is also possible to output a signal for closing the pilot line by switching the electromagnetic switching valve 16 again together with the output of the signal S2. In this way, the capacity of the hydraulic pump 13 can be increased and the cylinder 11 can be shortened at high speed.

  In particular, in the present embodiment, since the pilot line 15 is provided with the high pressure selection valve 32, either the high pressure side of the pressure generated on the cylinder tube 22 side or the pressure generated on the cylinder rod 21 side is switched to the capacity. Can be derived as a pilot pressure. As a result, the pilot pressure for switching the capacity of the hydraulic pump 13 can be more reliably obtained regardless of the load of the cylinder 11.

  Moreover, in the present embodiment, the counter balance valve 27 is provided in the cylinder 11. When the workpiece 28 is pressed, the electromagnetic switching valve 35 is excited to cause the counter balance valve 27 to function, and the cylinder 11 is braked. Thereby, the overshoot of the cylinder 11 can be surely avoided, and a press operation with higher accuracy becomes possible.

  In the present embodiment, as described above, the pressure on the cylinder rod 21 side is guided as the pilot pressure on the basis of the stroke of the cylinder 11, but at the same time, the pressure on the cylinder tube 22 side is used as a reference. It is also possible to have a conventional structure for guiding the pressure as a pilot pressure.

  That is, for example, when a high pressure is generated in the cylinder 11 as in processing a thick steel plate or the like, the cylinder rod 21 is extended by the pressure generated in the cylinder tube side port 31, and the die 25 is moved to the workpiece 25. It is possible to detect the position where the pressure 28 is started to be pressed. Therefore, the pressure on the cylinder tube 22 side at that time is detected by a required pressure sensor, and the electromagnetic switching valve 16 is switched based on the detection signal. As a result, the hydraulic pump 13 has a small capacity, the cylinder 11 is driven at a low speed, and the accuracy of the preset bottom dead center position of the cylinder rod 21 (that is, the position where the die 25 completely presses the workpiece 28) is improved. It becomes possible.

  Regardless of the type of workpiece, it can be applied to applications where it is essential to control the stroke position of the hydraulic cylinder with high accuracy.

1 is a system diagram showing a configuration of a hydraulic servo apparatus according to an embodiment of the present invention. It is the figure which showed typically the structure of the hydraulic servo apparatus employ | adopted as the conventional press machine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hydraulic servo apparatus 11 Cylinder 12 Servo motor 13 Hydraulic pump 14 Position sensor 15 Pilot line 16 Electromagnetic switching valve 17 Control apparatus 19 Pilot port 21 Cylinder rod 22 Cylinder tube 26 Cylinder rod side port 27 Counter balance valve 28 Work 31 Cylinder tube side port 32 High pressure selection valve 35 Electromagnetic switching valve

Claims (3)

A two-way discharge type hydraulic pump capable of changing the capacity by the pilot pressure for capacity switching;
A hydraulic cylinder in which the cylinder rod is arranged to extend and contract along the vertical direction, and two discharge ports of the hydraulic pump are hydraulically connected to the tube side port and the cylinder rod side port, respectively;
A position sensor that detects when the cylinder rod makes a predetermined stroke and transmits a stroke signal;
A pilot line that leads at least the pressure of the cylinder rod side port to the hydraulic pump as the above-mentioned pilot pressure for capacity switching;
An electromagnetic switching valve that opens and closes the pilot line;
A hydraulic servo device comprising: a control device that receives the stroke signal and transmits a signal for opening an electromagnetic switching valve based on the stroke signal. The hydraulic servo device according to claim 1,
The pilot line is a high pressure selection for leading either the pressure of the discharge port connected to the tube side port of the hydraulic pump or the pressure of the cylinder rod side port to the hydraulic pump as a high pressure side as the displacement switching pilot pressure. A hydraulic servo device comprising a valve. The hydraulic servo device according to claim 1 or 2,
A hydraulic servo device comprising a counter balance valve at a cylinder rod side port of a hydraulic cylinder.

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