Hydraulic control device

Abstract

To suppress noise during pressure holding without modifying an interface of a host control device and a hydraulic control device.SOLUTION: This hydraulic control device 14 is provided with a hydraulic pump 9 for supplying hydraulic pressure to a hydraulic circuit, a motor 7 for driving the hydraulic pump 9, a pressure sensor 11 for detecting the pressure of the hydraulic circuit for connecting the hydraulic pump 9 and a load 10, and a detector 8 for detecting the rotation speed of the motor 7, and controls the hydraulic unit for driving the load 10 by using the hydraulic pressure supplied from the hydraulic pump 9, and is provided with a speed command arithmetic unit 15 for calculating a rotation speed command value Vc of the motor 7 based on a difference between a pressure command value Pc and a pressure detection value Pd, and a pressure holding determination part 17 for determining whether or not the load 10 is in a pressure holding state where it is not operated based on at least one of the difference between the pressure command value Pc and the pressure detection value Pd and the rotation speed detection value Vd of the motor 7 detected by the detector 8.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydraulic control device for a hydraulic unit that drives a hydraulic pump with a motor, and more particularly to a hydraulic control device that controls hydraulic pressure by controlling the drive of the motor. [Background technology]

[0002] In industrial equipment such as machine tools, hydraulic units are used to control pressure by driving hydraulic pumps with motors as the power source for actuators such as cylinders. These motors may be inverter-driven for the purpose of saving energy.

[0003] When controlling a hydraulic unit using a motor driven by an inverter in this way, the control response differs when the actuator is operating and when it is not operating, so a method is known in which the control gain is changed depending on the operation of the actuator (see, for example, Patent Document 1).

[0004] Furthermore, in the axis operation of a machine tool, a method is known in which the gain is changed in accordance with the position error when performing position control (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-106403 A [Patent Document 2] Japanese Patent Application Publication No. 01-194884 Summary of the Invention [Problem to be solved by the invention]

[0006] Figure 5 is a block diagram of a conventional hydraulic control device 13 that controls a hydraulic unit that drives a hydraulic pump 9 with a motor 7 driven by an inverter. The hydraulic pump 9 and a load 10 such as an actuator are connected by a hydraulic circuit, and a pressure sensor 11 is attached to the hydraulic circuit. An NC (Numerical Control) control device, which is the upper control device 1, outputs a pressure command value Pc to the hydraulic control device 13, and the hydraulic control device 13 applies a voltage to the motor 7 to drive the hydraulic pump 9 connected to the motor 7 and control the pressure in the hydraulic circuit.

[0007] The hydraulic control device 13 includes a speed command calculator 3, a torque command calculator 5, and a current control unit 6. The speed command calculator 3 receives a pressure error, which is the difference between a pressure detection value Pd detected by a pressure sensor 11 and a pressure command value Pc output by the higher-level control device 1, calculates a rotational speed command value Vc by proportional-integral control or the like, and outputs the rotational speed command value Vc. The torque command calculator 5 receives a speed error, which is the difference between a rotational speed detection value Vd, obtained by differentiating a position detection value detected by a detector 8 attached to the motor 7 using a differentiator 12, and the rotational speed command value Vc output by the speed command calculator 3, and outputs a torque command value Tc. Then, based on the torque command value Tc, the current control unit 6, which includes an inverter, supplies current to the motor 7 to control the motor 7.

[0008] When a load 10 such as an actuator operates, oil flows into the hydraulic cylinder, etc., causing the pressure in the hydraulic circuit to drop. The hydraulic control device 13 detects this drop in pressure in the hydraulic circuit and drives the hydraulic pump 9 to restore the pressure in the hydraulic circuit.

[0009] However, if the control gain of the speed command calculator 3 is low, the rise of the rotation speed command value Vc will be slow, which may slow down the drive of the hydraulic pump 9 and cause a drop in pressure in the hydraulic circuit, slowing down the operation of the load 10 such as an actuator. Therefore, it is necessary to set the control gain of the speed command calculator 3 high.

[0010] However, if a high control gain is used during pressure maintenance when the load 10, such as an actuator, is not operating, the motor 7 may react too sensitively to noise in the pressure detection value or pressure fluctuations caused by the rotation of the hydraulic pump 9, resulting in unpleasant operating sounds (noise).Noise is unpleasant for factory workers, so it should be suppressed as much as possible from the perspective of safety and health.

[0011] As with the technology disclosed in Patent Document 1, if a hydraulic control device can detect in advance that a load such as an actuator will be operating, it is possible to select the optimal control gain for each operation and appropriately set the control gain when the load such as an actuator is not operating. However, the technology disclosed in Patent Document 1 requires information communication between a host control device such as an NC control device and the hydraulic control device. This information communication cannot be realized unless the host control device and the hydraulic control device are equipped with an interface for sending and receiving actuator operation signals. Therefore, if there is no interface for sending and receiving actuator operation signals between the host control device and the hydraulic control device, it is necessary to incur costs for interface modification work.

[0012] Therefore, an object of the present invention is to provide a hydraulic control device that can suppress noise during pressure maintenance without modifying the interface between the host control device and the hydraulic control device. [Means for solving the problem]

[0013] The hydraulic control device according to the present invention is a hydraulic control device comprising: a hydraulic pump that supplies hydraulic pressure to a hydraulic circuit; a motor that drives the hydraulic pump; a pressure sensor that detects the pressure in the hydraulic circuit that connects the hydraulic pump to a load; and a detector that detects the rotational speed of the motor, and controls a hydraulic unit that drives the load using the hydraulic pressure supplied from the hydraulic pump, and is characterized by comprising: a speed command calculator that calculates a rotational speed command value for the motor based on the difference between a pressure command value sent from a higher-level control device and a pressure detection value detected by the pressure sensor; and a pressure holding determination unit that determines whether a pressure holding state is present based on at least one of the difference between the pressure command value and the pressure detection value and the rotational speed detection value of the motor detected by the detector.

[0014] In one aspect of the hydraulic control device according to the present invention, a control gain of the speed command calculator may be changed based on a determination result of the pressure maintenance determination unit.

[0015] According to this aspect, by calculating the speed command value using a low control gain during pressure maintenance, the motor can rotate the hydraulic pump without overreacting to pressure detection noise or pressure fluctuations due to the rotation of the hydraulic pump during pressure maintenance, thereby suppressing noise during pressure maintenance.

[0016] In one aspect of the hydraulic control device according to the present invention, a variable filter may be provided that performs a filtering process on the pressure detection value, and a filter coefficient of the variable filter may be changed based on the determination result of the pressure maintenance determination unit.

[0017] According to this aspect, by using the variable filter to reduce noise in the pressure detection value during pressure maintenance, the motor will no longer react to noise in the pressure detection value during pressure maintenance, thereby suppressing noise during pressure maintenance. [Effects of the Invention]

[0018] The hydraulic control device according to the present invention can determine whether the pressure is being maintained even if a signal indicating whether a load such as an actuator is operating or not is not received from a host control device, and can smoothly drive the hydraulic pump during pressure maintenance by switching the control gain etc. of the speed command calculator between when a load such as an actuator is operating and when a load such as an actuator is not operating and maintaining pressure. Therefore, the hydraulic control device according to the present invention can suppress noise during pressure maintenance without modifying the interfaces between the host control device and the hydraulic control device. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a block diagram of a hydraulic control device according to a first embodiment. [Figure 2] 10A and 10B are diagrams illustrating a method by which a pressure-maintaining determination unit determines whether a pressure-maintaining state is in which a load such as an actuator is not operating. [Figure 3] FIG. 4 is a block diagram of a hydraulic control device according to a second embodiment. [Figure 4] FIG. 10 is a block diagram of a hydraulic control device according to a third embodiment. [Figure 5] FIG. 1 is a block diagram of a conventional hydraulic control device. DETAILED DESCRIPTION OF THE INVENTION

[0020] First Embodiment A hydraulic control device 14 according to a first embodiment will be described below with reference to FIGS. 1 and 2. FIG. 1 is a block diagram of the hydraulic control device 14 according to the first embodiment. As shown in FIG. 1, the hydraulic unit controlled by the hydraulic control device 14 includes a hydraulic pump 9 that supplies hydraulic pressure to a hydraulic circuit, a motor 7 that drives the hydraulic pump 9, a pressure sensor 11 that detects the pressure in a hydraulic circuit that connects the hydraulic pump 9 with a load 10 such as an actuator, and a detector 8a that detects the rotational speed of the motor 7, and drives the load 10 such as an actuator using the hydraulic pressure supplied from the hydraulic pump 9. The detector 8a may be, for example, a combination of an encoder that detects the rotational position of the motor 7 and a differentiator that differentiates the position detection value detected by the encoder.

[0021] The hydraulic control device 14 includes a subtractor 2, a speed command calculator 15, a subtractor 4, a torque command calculator 5, and a current control unit 6. The subtractor 2 calculates the difference between a pressure command value Pc output from the higher-level control device 1 and a pressure detection value Pd detected by the pressure sensor 11. The speed command calculator 15 includes a proportional calculator 18 and an integrator 19, and calculates a rotational speed command value Vc for the motor 7 based on the difference between the pressure command value Pc and the pressure detection value Pd, and outputs the rotational speed command value Vc. The subtractor 4 calculates the difference between the rotational speed command value Vc and the rotational speed detection value Vd detected by the detector 8a. The torque command calculator 5 calculates a torque command value Tc for the motor 7 based on the difference between the rotational speed command value Vc and the rotational speed detection value Vd, and outputs the torque command value Tc. Then, based on the torque command value Tc, the current control unit 6, which includes an inverter, supplies current to the motor 7 to control the motor 7.

[0022] The hydraulic control device 14 further includes a subtractor 16 and a pressure-maintaining determination unit 17. The subtractor 16 calculates the difference between the pressure command value Pc output from the higher-level control device 1 and the pressure detection value Pd detected by the pressure sensor 11. At least one of a pressure error Pe, which is the difference between the pressure command value Pc and the pressure detection value Pd, and a rotational speed detection value Vd is input to the pressure-maintaining determination unit 17. Then, the pressure-maintaining determination unit 17 determines whether or not a pressure-maintaining state in which a load 10 such as an actuator is not operating is in effect, based on at least one of the pressure error Pe and the rotational speed detection value Vd, and outputs a pressure-maintaining state signal to a proportionalizer 18 and an integrator 19 when it determines that a pressure-maintaining state is in effect.

[0023] FIG. 2 illustrates how the pressure-maintaining determination unit 17 determines whether the load 10, such as an actuator, is in a pressure-maintaining state when the load 10, such as an actuator, is not operating. FIG. 2 shows an example of fluctuations in the pressure error Pe, the rotational speed detection value Vd of the motor 7, and the pressure-maintaining state signal when the load 10, such as an actuator, transitions from an operating state to a pressure-maintaining state. As shown in FIG. 2, the pressure error Pe fluctuates when the load 10, such as an actuator, is operating, but the pressure error Pe stabilizes in the pressure-maintaining state. When determining whether the pressure-maintaining state is determined based on the pressure error Pe, the pressure-maintaining determination unit 17 determines that the pressure is maintained and outputs a pressure-maintaining state signal after the pressure error Pe falls within the pressure-maintaining determination threshold range and the time set by the pressure-maintaining state confirmation timer has elapsed. Also, as shown in FIG. 2, the rotational speed detection value Vd fluctuates when the load 10, such as an actuator, is operating, but the rotational speed detection value Vd decreases and stabilizes in the pressure-maintaining state. When determining whether the pressure is maintained based on the rotation speed detection value Vd, the pressure maintaining determination unit 17 determines that the pressure is maintained and outputs a pressure maintaining state signal after the rotation speed detection value Vd becomes equal to or less than the pressure maintaining reference speed and the time on the pressure maintaining state confirmation timer has elapsed. In this way, the hydraulic control device 14 can determine whether the pressure is maintained using the pressure maintaining determination unit 17 even if it does not receive a signal from the upper control device 1 indicating whether the load 10, such as an actuator, is operating.

[0024] The pressure-maintaining determination unit 17 stores the pressure-maintaining determination threshold, pressure-maintaining reference speed, and pressure-maintaining state confirmation timer time. By setting the pressure-maintaining determination threshold to a value greater than the amplitude of detection noise superimposed on the pressure detection value Pd during pressure maintenance, it is possible to prevent the pressure-maintaining state from being mistakenly determined to be not being maintained even when it is. Furthermore, the pressure-maintaining reference speed is a reference speed for preventing the pressure-maintaining determination unit 17 from mistakenly determining that the pressure is maintained when the load 10, such as an actuator, is operating. Therefore, the pressure-maintaining reference speed must be set to be greater than the rotation speed during pressure maintenance and smaller than the rotation speed during operation of the load 10, such as an actuator. The pressure-maintaining determination unit 17 can determine whether the pressure is maintained using either the pressure-maintaining determination threshold or the pressure-maintaining reference speed, but using both of them in combination can further improve the reliability of the determination.

[0025] A pressure error Pe, which is the difference between a pressure command value Pc and a detected pressure value Pd, is input to the speed command calculator 15, which calculates a rotation speed command value Vc by proportional-integral control. A normal proportional gain and a proportional gain for holding pressure that is lower than the normal proportional gain are stored in the proportional calculator 18. The proportional calculator 18 uses the normal proportional gain when no holding pressure state signal is input, and uses the proportional gain for holding pressure when a holding pressure state signal is input. Similarly, the integrator 19 stores a normal integral gain and an integral gain for holding pressure that is lower than the normal integral gain. The integrator 19 uses the normal integral gain when no holding pressure state signal is input, and uses the integral gain for holding pressure when a holding pressure state signal is input.

[0026] The hydraulic control device 14 of the first embodiment can determine whether the pressure is maintained even if there is no signal from the host control device 1 indicating whether the load 10, such as an actuator, is operating, and can switch the control gain of the speed command calculator 15 between when the load 10, such as an actuator, is operating and when the pressure is maintained. The hydraulic control device 14 calculates the rotation speed command value Vc using a low control gain when the pressure is maintained, thereby allowing the hydraulic pump 9 to rotate without overreacting to noise in the pressure detection value Pd or pressure fluctuations due to the rotation of the hydraulic pump 9 when the pressure is maintained. Therefore, the hydraulic control device 14 can suppress noise when the pressure is maintained without modifying the interface between the host control device 1 and the hydraulic control device 14.

[0027] <Second embodiment> Next, a hydraulic control device 21 of a second embodiment will be described with reference to Fig. 3. The hydraulic control device 21 of the second embodiment has the same configuration as the hydraulic control device 14 of the first embodiment, except that it includes a variable filter 22 and changes the filter coefficient of the variable filter 22 based on the determination result of the pressure maintenance determination unit 17, rather than changing the control gain of the speed command calculator 3 based on the determination result of the pressure maintenance determination unit 17. Therefore, differences from the hydraulic control device 14 of the first embodiment will be described below, and parts common to the hydraulic control device 14 of the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

[0028] 3 is a block diagram of a hydraulic control device 21 according to a second embodiment. As shown in FIG. 3, the hydraulic control device 21 includes a subtractor 2, a speed command calculator 3, a subtractor 4, a torque command calculator 5, a current control unit 6, a subtractor 16, a pressure holding determination unit 17, and a variable filter 22.

[0029] At least one of a pressure error Pe, which is the difference between a pressure command value Pc and a pressure detection value Pd, and a rotation speed detection value Vd is input to the pressure maintaining determination unit 17. Then, the pressure maintaining determination unit 17 determines whether or not the pressure is maintained from at least one of the pressure error Pe and the rotation speed detection value Vd, and outputs a pressure maintaining state signal to the variable filter 22 when it determines that the pressure is maintained.

[0030] The variable filter 22 is configured with a low-pass filter or the like that removes high-frequency components. The variable filter 22 can switch its filter coefficient so that it uses either a normal filter coefficient or a filter coefficient for pressure holding. When the filter coefficient for pressure holding is used, the variable filter 22 has a lower cutoff frequency than when the normal filter coefficient is used. The variable filter 22 converts the pressure detection value Pd using the normal filter coefficient when no pressure holding state signal is input, and using the filter coefficient for pressure holding when a pressure holding state signal is input. The speed command calculator 3 then receives the difference between the pressure detection value Pd filtered by the variable filter 22 and the pressure command value Pc, and calculates the rotational speed command value Vc. Unlike the hydraulic control device 14 of the first embodiment, the hydraulic control device 21 of the second embodiment does not switch the proportional gain and integral gain of the speed command calculator 3.

[0031] The hydraulic control device 21 of the second embodiment can determine whether the pressure is maintained even without a signal from the host control device 1 indicating whether the load 10, such as an actuator, is operating, and can switch the filter coefficient of the variable filter 22 between when the load 10, such as an actuator, is operating and when the pressure is maintained. The hydraulic control device 21 reduces noise in the detected pressure value Pd by using a filter coefficient for the variable filter 22 that has a lower cutoff frequency than the normal filter coefficient, thereby allowing the hydraulic pump 9 to rotate without overreacting to noise in the detected pressure value Pd when the pressure is maintained. Therefore, the hydraulic control device 21 can suppress noise when the pressure is maintained without modifying the interface between the host control device 1 and the hydraulic control device 21. The hydraulic control device 21 is advantageous over the hydraulic control device 14 of the first embodiment when used in a hydraulic unit in which the pressure sensor 11 has poor observation noise characteristics.

[0032] <Third embodiment> Next, a hydraulic control device 23 of a third embodiment will be described with reference to Fig. 4. The hydraulic control device 23 of the third embodiment has the same configuration as the hydraulic control device 14 of the first embodiment, except that it includes a variable filter 22 and changes not only the control gain of the speed command calculator 15 but also the filter coefficient of the variable filter 22 based on the determination result of the pressure maintenance determination unit 17. Therefore, differences from the hydraulic control device 14 of the first embodiment will be described below, and parts common to the hydraulic control device 14 of the first embodiment will be assigned the same reference numerals and description thereof will be omitted.

[0033] Fig. 4 is a block diagram of a hydraulic control device 23 according to a third embodiment. As shown in Fig. 4, the hydraulic control device 23 includes a subtractor 2, a speed command calculator 15, a subtractor 4, a torque command calculator 5, a current control unit 6, a subtractor 16, a pressure maintenance determination unit 17, and a variable filter 22. The speed command calculator 15 includes a proportional unit 18 and an integrator 19.

[0034] At least one of a pressure error Pe, which is the difference between a pressure command value Pc and a pressure detection value Pd, and a rotation speed detection value Vd is input to the pressure maintaining determination unit 17. Then, the pressure maintaining determination unit 17 determines whether the pressure is maintaining, in which the load 10, such as an actuator, is not operating, based on at least one of the pressure error Pe and the rotation speed detection value Vd, and outputs a pressure maintaining state signal to the proportional unit 18, the integrator 19, and the variable filter 22 when it determines that the pressure is maintaining.

[0035] The variable filter 22 is composed of a low-pass filter or the like that removes high-frequency components. The variable filter 22 can switch its filter coefficient so that it uses either a normal filter coefficient or a filter coefficient for maintaining pressure. When the filter coefficient for maintaining pressure is used, the variable filter 22 has a lower cutoff frequency than when the normal filter coefficient is used. The variable filter 22 converts the pressure detection value Pd using the normal filter coefficient when no maintaining pressure state signal is input, and using the filter coefficient for maintaining pressure when a maintaining pressure state signal is input.

[0036] A pressure error Pe, which is the difference between the pressure command value Pc and the filtered pressure detection value Pd obtained by variable filter 22, is input to speed command calculator 15, which calculates a rotation speed command value Vc by proportional-integral control. A normal proportional gain and a proportional gain for maintaining pressure that is lower than the normal proportional gain are stored in proportional calculator 18. Proportional calculator 18 uses the normal proportional gain when no pressure-maintaining state signal is input, and uses the proportional gain for maintaining pressure when a pressure-maintaining state signal is input. Similarly, integrator 19 stores a normal integral gain and an integral gain for maintaining pressure that is lower than the normal integral gain. Integrator 19 uses the normal integral gain when no pressure-maintaining state signal is input, and uses the integral gain for maintaining pressure when a pressure-maintaining state signal is input.

[0037] The hydraulic control device 23 of the third embodiment can determine whether the pressure is maintained or not, even if there is no signal from the host control device 1 indicating whether the load 10, such as an actuator, is operating, and can switch the filter coefficient of the variable filter 22 and the proportional gain and integral gain of the speed command calculator 15. Then, during pressure maintenance when the load 10, such as an actuator, is not operating, the hydraulic control device 23 uses a filter coefficient for pressure maintenance, which has a low cutoff frequency, for the variable filter 22, and calculates the rotational speed command value Vc using a low control gain for the speed command calculator 15, thereby allowing the hydraulic pump 9 to rotate during pressure maintenance without overreacting to noise in the pressure detection value Pd or pressure fluctuations due to the rotation of the hydraulic pump 9. Therefore, the hydraulic control device 23 can suppress noise during pressure maintenance without modifying the interface between the host control device 1 and the hydraulic control device 23.

[0038] Furthermore, the hydraulic control device 23 of the third embodiment switches the proportional gain and integral gain of the speed command calculator 15 and the filter coefficient of the variable filter 22 in accordance with the determination result of the pressure maintenance determination unit 17, and therefore can achieve appropriate disturbance suppression performance against pressure fluctuations and appropriate observation noise resistance performance by taking into account the respective influences of pressure fluctuations due to the rotation of the hydraulic pump 9 and the observation noise characteristics of the pressure sensor 11. While the hydraulic control device 14 of the first embodiment cannot design the disturbance suppression performance against pressure fluctuations and the observation noise resistance performance independently, the hydraulic control device 23 of the third embodiment can design the disturbance suppression performance against pressure fluctuations and the observation noise resistance performance independently.

[0039] <Supplementary information on the embodiment> The hydraulic control device of the present disclosure is not limited to the above-described embodiment and can be implemented in various forms within the scope of the present disclosure. For example, the speed command calculator may be configured with only a proportional unit, rather than a proportional integrator. Furthermore, the variable filter may be configured with a notch filter that blocks only specific frequencies, a bandpass filter that passes only specific frequencies, or a combination of these, rather than a lowpass filter.

[0040] Furthermore, the configuration of the hydraulic control device may be realized by a CPU included in the hydraulic control device executing various software stored in a storage device, or may be realized by a configuration mainly using hardware such as an FPGA (Field Programmable Gate Array). A program for executing a control method corresponding to the above-described processing content executed by the hydraulic control device of the first to third embodiments can be recorded on various computer-readable recording media (for example, a ROM, a semiconductor memory such as a flash memory, a magnetic recording medium, or an optical disk such as a CD-ROM or a DVD-ROM). [Explanation of symbols]

[0041] 1 Upper control device, 2, 4, 16 subtractor, 3, 15 speed command calculator, 5 torque command calculator, 6 current control section, 7 motor, 8, 8a detector, 9 hydraulic pump, 10 load, 11 pressure sensor, 12 differentiator, 13, 14, 21, 23 hydraulic control device, 17 pressure holding determination section, 18 proportional controller, 19 integrator, 22 variable filter.

Claims

1. A hydraulic control device comprising: a hydraulic pump that supplies hydraulic pressure to a hydraulic circuit; a motor that drives the hydraulic pump; a pressure sensor that detects the pressure in the hydraulic circuit that connects the hydraulic pump and a load; and a detector that detects the rotational speed of the motor, the hydraulic control device controlling a hydraulic unit that drives the load using hydraulic pressure supplied from the hydraulic pump, a speed command calculator that calculates a rotation speed command value of the motor based on the difference between a pressure command value sent from a host control device and a pressure detection value detected by the pressure sensor; a pressure-maintaining determination unit that determines whether the load is in a pressure-maintaining state where it is not operating, based on at least one of a difference between the pressure command value and the pressure detection value and a rotational speed detection value of the motor detected by the detector; A hydraulic control device comprising:

2. 2. The hydraulic control device according to claim 1, A hydraulic control device characterized in that a control gain of the speed command calculator is changed based on a determination result of the pressure maintenance determination unit.

3. The hydraulic control device according to claim 1 or 2, A hydraulic control device comprising: a variable filter that performs filtering on the pressure detection value; and a filter coefficient of the variable filter that is changed based on the determination result of the pressure maintenance determination unit.

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