JPH03239801A - Electric hydraulic servo device - Google Patents

Abstract

PURPOSE:To control a position with high accuracy and a simple structure by introducing pressure oil from respective hydraulic pumps to two supply/discharge ports for driving a piston of an actuator, and controlling the set pressure of relief valves. CONSTITUTION:A position detector 2 is provided on a controlled object 1, while pressure oil in a double hydraulic pump 6 driven by a motor 7 is introduced to respective pressure oil supply/discharge ports of a driving hydraulic cylinder 4 through set pressure variable relief valves 11, 12. Signals from the position detector 2 are input to a controller 3 an with comparison to a targent value, a signal for driving a flow rate control valve 10 is output. Thus, the set pressure of the relief valves 11, 12 is controlled. The position of the controlled object 1 is regulated with accuracy, accordingly.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a control device for a hydraulic actuator, and in particular, it is possible to control a hydraulic actuator by controlling the set pressure of a relief valve provided in a pressure oil and a pressure oil line. The present invention relates to an electro-hydraulic servo device for controlling.

[Prior Art] When position control is performed using a hydraulic actuator such as a hydraulic cylinder or a hydraulic motor, it is common to use an electromagnetic switching valve or control the rotation of a hydraulic pump. 6th
The figure is a block diagram showing position control using an electromagnetic switching valve. In FIG. 6, the position of the controlled object 1 is detected by the position detector 2.
The control unit 3 outputs a control signal based on the difference between the target value and the detected position. The hydraulic cylinder 4 gives a reciprocating motion to the controlled object 1 to move its position. The electromagnetic switching valve 5 excites a solenoid in response to a control signal output from the control unit 3 and switches the pressure oil hydraulic line to the hydraulic cylinder 4 . A fixed amount of pressure oil is transferred to the electromagnetic switching valve 5 in a fixed direction from the hydraulic pump 6, and when the position of the controlled object 1 is maintained, the pressure oil is not sent to the hydraulic cylinder 4, but is transferred from the relief valve 8. returned to the tank. The hydraulic pump 6 is rotationally driven by a squirrel cage electric motor 7 that rotates in a constant direction at a constant speed.
The valve 8 is provided to protect the wave pressure system. 7th
The figure is a block diagram when position control is performed by controlling the rotation of a hydraulic pump. The same symbols as in FIG. 6 represent the same functions, and differences will be explained.

The hydraulic motor 6 sends out an amount of oil according to the rotational speed, and controls the moving speed and direction of the hydraulic cylinder 4 by rotating forward and backward. The electric motor @7 outputs a rotation direction and a rotation speed according to a control signal from the control section 3, and rotationally drives the hydraulic motor 6. An induction motor is used as such a motor, and its control method is PWM (Pulse Width
Modulation) A speed control method using an inverter is often used.

In FIG. 8, the electromagnetic switching valve 5 in FIG. 6 is replaced with a servo valve 30. The moving coil 28 is excited by an electric signal from the control section 3. A permanent magnet 29 provided movably within the moving coil reciprocates a spool 31 within the servo valve 30 in response to the excitation direction and strength of the moving coil, thereby operating the servo valve 30.

Pressure oil from the hydraulic pump is switched by a servo valve 30 to operate the cylinder 4.

[Problems that the invention aims to solve]

However, in the case of a control method using an electromagnetic switching valve, the hydraulic pump 6 and electric @1 structure are simple and inexpensive, but the position control of the controlled workpiece is controlled by the electromagnetic switching valve on and off, resulting in poor accuracy. It is difficult to perform position control that requires In addition, in the method of controlling the rotation of the hydraulic pump 6, in order to accurately control the position, the electric motor is frequently rotated in forward and reverse directions, which puts a burden on the electric motor, and furthermore, the control device for the hydraulic pump and the electric motor becomes complicated and expensive. There are many cases. Further, since the hydraulic pump 6 rotates forward and backward, a backing is required to seal against forward and reverse rotation, and the hydraulic pump 6 usually needs to be installed in oil. Further, in the case of the servo valve 30 shown in FIG. 8, the size of the servo valve 30 is large, requiring a large installation space and being expensive.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electro-hydraulic servo device that performs position control with high accuracy using a hydraulic pump and electric motor with a simple structure.

[Means to solve the problem]

In order to achieve the above object, the electro-hydraulic servo device of the present invention controls the pressure oil and the set pressure of the relief valve provided in the pressure oil line, and the electro-hydraulic servo device of the present invention is designed to control the pressure oil and the set pressure of the relief valve provided in the pressure oil line. a hydraulic actuator operated by input pressure oil; a first relief valve with variable setting pressure connected to the first pressure oil supply/discharge port; and a second relief valve with variable setting pressure connected to the second pressure oil supply/discharge port. a valve, a first hydraulic pump that supplies pressure oil to the first pressure oil supply/discharge port, a second hydraulic pump that supplies pressure oil to the second pressure oil supply/discharge port, the first hydraulic pump, and the The present invention is characterized in that it includes a motor that drives a second hydraulic pump, and a pressure setting section that controls set pressures of the first relief valve and the second relief valve. Further, it is preferable that the pressure setting section is capable of setting a difference in set pressure between the first relief valve and the second relief valve so that a gain characteristic curve having a desired shape is obtained. Further, it is preferable that the pressure setting section drives a piezoelectric element using an electric signal and expands the displacement of the piezoelectric element to control the set pressures of the first relief valve and the second relief valve. Further, a first check valve is provided in a first hydraulic line connected to the first pressure oil supply/discharge port, a second check valve is provided in a second hydraulic line connected to the second pressure oil supply/discharge port, and the Preferably, the second check valve is operated by the hydraulic pressure in the first hydraulic line, and the first check valve is operated by the hydraulic pressure in the second hydraulic line. Furthermore, the first hydraulic line between the first pressure oil supply/discharge port and the first check valve;
A relief valve may be provided in at least one of the second hydraulic lines between the pressure oil supply and discharge port and the second check valve.

(Function) With the above configuration, the first relief valve and the second relief valve are connected to each other in the pressure setting section.
If the set pressure is the same as that of the relief valve, the hydraulic cylinder does not move in any direction and maintains its position. When the set pressure of the first relief valve is set higher than that of the second 'J relief valve, the second relief valve operates and pressure oil is supplied from the first pressure oil supply and discharge port, and pressure oil is supplied from the second pressure oil supply and discharge port. As it is discharged, the hydraulic cylinder moves in a certain direction, for example to the right. When the set pressure of the second relief valve is made higher than the set pressure of the first relief valve, the first relief valve operates, pressure oil is supplied from the second pressure oil supply and discharge port, and pressure oil is supplied from the first pressure oil supply and discharge port. is discharged and the hydraulic cylinder moves to the left. The force and moving speed generated by the hydraulic cylinder have values that correspond to the difference between the set pressures of the first relief valve and the second relief valve, so highly accurate position control can be achieved by changing this set pressure. Further, if the difference in set pressure can be set so as to form a gain characteristic curve of a desired shape, accuracy and operability will be improved. For example, if the controlled object driven by a hydraulic actuator is far away from the target position, a large gain is used, a gradual gain is applied when it approaches, and a large gain is applied when the target is close to the target in order to respond to even the slightest deviation. do. Further, since a large displacement is not required to set the pressure of the relief valve, the displacement of the piezoelectric element can be expanded. In addition, since each of the first and second hydraulic lines is equipped with a check valve that is operated by the hydraulic pressure of the other hydraulic line, even if the hydraulic actuator is loaded with the hydraulic pump stopped, the position of the control target can be held in the position when the hydraulic pump is stopped. Furthermore, the relief valve provided in at least one of the first hydraulic line and the second hydraulic line makes it possible to ensure the safety of the hydraulic system by operating the relief valve even if the temperature change in the hydraulic circuit becomes large.

(Example) Hereinafter, an example of the present invention will be described using FIGS. 1 to 5.

FIG. 1 shows a hydraulic circuit and control block showing the configuration of a first embodiment of the present invention. In FIG. 1, this embodiment includes a controlled object l, a position detecting section 2 that detects the moving position of this controlled object 1, and a difference value between the detected position of this position detecting section 2 and a specified target value. a control unit 3 that outputs a control signal from;
Flow rate control valve 10 that outputs a set pressure based on this control signal
, a hydraulic cylinder 4 that reciprocates the controlled object 1, a dual pump 6 consisting of two pumps having the same rotating shaft that supplies pressure oil to each pressure oil supply and discharge port of the hydraulic cylinder 4, and A squirrel cage electric motor 7 that rotates the dual pump 6 in one direction at a constant rotation speed, and variable set pressure relief valves 11 and 12 provided in hydraulic lines respectively connected to two pressure oil supply and discharge ports of the hydraulic cylinder 4. The main components are:

The operation of the first embodiment configured as above will be explained. The position detection unit 2 detects the position of the controlled object l and outputs it to the control unit 3. The control unit 3 calculates a difference value between the target value inputted in advance and the detected position, and outputs a control signal to reduce the difference value according to the magnitude and sign of this difference value. The details of this control signal will be explained using FIG. 4. In FIG. 4, the horizontal axis represents the difference value as input, and the vertical axis represents the gain as output. In order to overcome the dead zone of the relief valves 11 and 12, a large gain is set so that the human power responds to even a slight difference between -Vl and +v1 near the zero point, and the input is from ■ to Vt (-
If the input is between v2 and -Vz), the gain should be gentle to ensure stable control.
For large values such as those below, a large gain is required because a sharp response is required. Each of these gains has a slope at the zero point, the first point (V, point, -V, point), and the second point (V2 point, -92 point), as shown in the fan shape in Figure 4, according to the controlled object. can be set in advance.

By using an amplifier having such a plurality of broken line characteristics, it becomes possible to smoothly move the controlled object 1 to the target position. The flow control valve 10 adjusts the set pressure of the relief valve LL12 in response to this control signal. At this time, the electric motor [7] rotates the dual pumps in a fixed direction at a constant speed, and sends out pressure oil from the dual pumps 6, respectively.

The hydraulic pressure applied to each pump 6 is controlled by a relief valve 11.1.
2, and more pressure oil is returned to the tank from the relief valve 11 or 12 with the lower set pressure.

Depending on the sign of the difference value between the detected position of the controlled object 1 and the target value, it is determined which relief valve 11.12 should have a higher setting pressure, and the relief valve 11.1 is set higher depending on the magnitude of the difference value.
2 set pressure difference is determined. As a result, if the controlled object l goes too far over the target position, it is controlled to return, and if it does not reach the target position, it is controlled to advance, and if the difference value between the target position and the detected position is large, the moving speed becomes faster. This means that if the set pressures of both relief valves 1112 are the same, both relief valves 1112
From 1.12, the amount of oil that returns to the tank remains the same and the movement of the hydraulic cylinder 4 stops, but as the set pressure difference is gradually increased, more hydraulic oil returns to the tank from the relief valve with the smaller set pressure. Therefore, the speed of the hydraulic cylinder 4 becomes faster.

However, since the hydraulic pump 6 is of a constant discharge flow rate type, when the difference exceeds a certain value, the speed of the hydraulic cylinder 4 becomes a constant speed determined by the discharge amount of the hydraulic pump 6. As described above, according to this embodiment, the movement of the hydraulic cylinder 4 can be controlled in accordance with the sign and magnitude of the difference between the detected position of the controlled object 1 and the target value, so that accurate control can be performed.

Next, a second embodiment will be explained with reference to FIG. In the second embodiment, each hydraulic line between the relief valve ILI2 and the hydraulic cylinder 4 of the first embodiment is connected to a pyro 7 valve 13.
．． 14 and relief valves 15 and 16.

The pilot check valves 13 and 14 each function to open the valves by the hydraulic pressure of the opposing hydraulic line. Therefore, when the hydraulic pump 6 is operating, the relief valve 11
．． The pilot check valves 13 and 14 do not block the flow of hydraulic oil because the pressure oil at the set pressure of 12 is in the hydraulic line, but when the hydraulic pump 6 stops, both check valves 1314 stop the flow of hydraulic oil. Due to this action, even if the hydraulic pump 6 is stopped while a load is applied to the hydraulic cylinder 4, the piston position of the hydraulic cylinder 4 is maintained when the hydraulic pump 6 was stopped.This allows long-term control. When the object 1 is stopped at a fixed position, the electric motor 7 can be stopped.In addition, by providing the relief valve 15.16, even if the temperature rises and the hydraulic oil expands, the relief valve 15.16 does not work. This protects the hydraulic system.

Next, a third embodiment will be explained with reference to FIG. Figure 3 shows
Only the changed parts in FIG. 2 are shown, and the rest is the same as FIG. 2. In FIG. 3, the operating pressure setter 17, 18 consists of a piezoelectric element and an expansion mechanism that magnifies the displacement of this FE element. The displacement of the piezoelectric element is normally several tens of microns, and since several displacements are required to set the pressure of the relief valves 11 and 12, the magnification of the magnification mechanism is about 100 times.

FIG. 4 shows a fourth embodiment. FIG. 4 shows the working pressure setting device 17, 18 shown in FIG. 3 as an electro-hydraulic conversion mechanism. In FIG. 4, a indicates the position a in FIG. 3, that is, the vent circuit of the relief valves 11, 12. The Ghent circuit a is connected to the pilot room 19. Pilot room 1
9 is provided with a nozzle 20, and a flapper 21 is provided opposite to the nozzle 20, and the surface on which the flapper 21 and nozzle 20 are provided is surrounded by a hollows 22 to form a space. A drain will be installed in this space to return the oil to the oil tank.

A moving coil 23 is provided on the flapper 21 and moves in the vertical direction. A permanent magnet 24 is arranged around the moving coil. Hula 7pa 21 is held by a horizontal leaf spring 25 on the upper side by a vertical axis, and a leaf spring 26 bent at about 135 degrees is overlapped to adjust this leaf spring 25, and this leaf spring 26 is pushed horizontally to push the leaf spring 25. The attachment is provided with an adjustment screw 27 for adjusting the force.

Next, I will explain the operation. First, the adjustment screw 27 is turned to adjust the zero point of force when pressing the leaf spring 25. The pressure oil flowing from the Ghent circuit a enters the pilot chamber 19 and is ejected from the nozzle 20, hits the flapper 21 and receives resistance, thereby determining the pressure of the pressure oil in the pilot chamber 19. Since the value of this pressure is determined by the distance between the nozzle 20 and the flapper 21, by controlling the amount of excitation of the moving coil 23 using an electric signal, the oil pressure in the pilot chamber, that is, the oil pressure in the Ghent circuit a can be controlled.

As described above in the first to fourth embodiments, the method of controlling the hydraulic actuator by controlling the set pressure of the pilot relief valve has the following advantages.

■ Since the capacity of the pilot signal circuit of the pilot relief valve is small, the control signal is generated by converting a small capacity battery.
Large volumes of hydraulic oil are controlled by the amount of unload from the relief valve. This makes it possible to downsize the electro-hydraulic converter.

■ Pressure oil supply is not required to the electro-hydraulic converter to be controlled.

■ When controlling the controlled object so that it does not deviate from the target position, the control amount is usually small. In such a case, by changing the differential pressure between the two relief valves as in this embodiment, smooth and accurate control becomes possible.

(Effects of the Invention) As is clear from the above description, the present invention connects relief valves with variable set pressures to the two oil supply and drain ports of a hydraulic actuator, and controls the set pressures of the control target. Position can be controlled with high precision.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of the invention, FIG. 2 is a diagram showing the configuration of a second embodiment of the invention, and FIG. 3 is a diagram showing the configuration of a third embodiment of the invention. , FIG. 4 is a diagram showing a fourth embodiment of the present invention, FIG. 5 is a diagram showing characteristics of an amplifier having a plurality of polygonal gain characteristics, and FIG. 6 is a diagram of a device for position control using an electromagnetic switching valve. FIG. 7 is a diagram of a device for controlling the position by controlling the rotation of a hydraulic pump, and FIG. 8 is a diagram of a device for controlling the position by a servo valve. 1-m-Controlled object 2-m-Position detecting section 3--Control section 4---Hydraulic cylinder 6--Hydraulic pump 7--Electric motor 10--Pressure setting section 1L12--General constant pressure variable relief Valves 13, 14---Pilot check valve 15, 16---
-Relief valve 17.18---Operating pressure setting device

Claims (5)

[Claims] (1) A hydraulic actuator operated by pressure oil flowing in and out from the first and second pressure oil supply/discharge ports, a first relief valve with variable set pressure connected to the first pressure oil supply/discharge ports, and the second pressure oil supply/discharge port.
a second relief valve with variable setting pressure connected to the pressure oil supply and discharge port;
a first hydraulic pump that supplies pressure oil to the first pressure oil supply/discharge port; a second hydraulic pump that supplies pressure oil to the second pressure oil supply/discharge port; the first hydraulic pump and the second hydraulic pressure; An electrohydraulic servo device comprising: a motor that drives a pump; and a pressure setting section that controls set pressures of the first relief valve and the second relief valve. (2) The pressure setting section is connected to the first relief valve and the second relief valve.
2. The electrohydraulic servo device according to claim 1, wherein the difference in set pressure with the relief valve can be set to provide a gain characteristic curve of a desired shape. (3) the pressure setting section drives a piezoelectric element with an electric signal;
3. The electrohydraulic servo device according to claim 1, wherein the set pressures of the first relief valve and the second relief valve are controlled by expanding the displacement of the piezoelectric element. (4) providing a first check valve in a first hydraulic line connected to the first pressure oil supply/discharge port, and a second check valve in a second hydraulic line connected to the second pressure oil supply/discharge port; Claim 1, wherein the second check valve is operated by the hydraulic pressure in the first hydraulic line, and the first check valve is operated by the hydraulic pressure in the second hydraulic line.
4. The electrohydraulic servo device according to any one of . (5) At least the first hydraulic line between the first pressure oil supply/discharge port and the first check valve, and the second hydraulic line between the second pressure oil supply/discharge port and the second check valve. 5. The electro-hydraulic servo device according to claim 4, further comprising a relief valve.