JPH1030608A - Speed and pressure control circuit for hydraulic actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform control of a pressure having smooth speed response and high response. SOLUTION: A proportional and integral compensator 13 for speed control, a proportional and integral compensator 13 for pressure control and a proportional and integral compensator 15 for pressure control, and a circuit to store a control value Sa by the proportional and integral compensator 13 for speed control during control of a speed at a proportional and integral compensator 15 for pressure control are arranged in a closed loop control circuit to effect speed control, through which the drive speed of a hydraulic actuator 17 is controlled, and pressure control to control a drive pressure by a single three-way control valve 16. Further, a rise and fall delay circuit 14 to regulate a delay in rise and a fall is arranged in an input signal line to input a command value of the speed and the pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single three-way control valve for speed control for controlling the drive speed (flow rate of hydraulic oil) and pressure control for controlling the drive pressure (pressure of hydraulic oil) of a hydraulic actuator. The present invention relates to a speed / pressure control circuit of a hydraulic actuator composed of a closed loop control circuit performed by using a speed control.

[0002]

2. Description of the Related Art In a speed / pressure control circuit of a hydraulic actuator, in order to remove an unstable element of open loop control which does not have a function of detecting a control state, it is impossible only by a simple program control. There is a need for closed-loop control that constantly monitors set conditions and corrects the results to obtain extremely high-precision reproducibility.

Conventionally, as a speed / pressure control circuit of this type of hydraulic actuator, there is, for example, a circuit shown in a block diagram in FIG. FIG. 11 is a schematic configuration diagram of a hydraulic system using the same, and FIG. 12 is a hydraulic symbol diagram showing a configuration of a three-way control valve used therein.

A speed / pressure control circuit shown in FIG. 10 is a closed loop control circuit using proportional integral (PI) compensation. For example, in a hydraulic system in which a heating cylinder 20 of a plastic molding machine is driven by a hydraulic actuator 17, It is used for controlling the speed at the time of injection for injecting and filling a resin material as a molding material into a mold cavity and for controlling the pressure holding after filling the resin material. Therefore, the servo controller 40 can switch between the two circuits for speed control and pressure control by a switching signal from the outside.

In the speed control state, the switching signals SWA, / S
WB is high, SWB and / SWA are low, the first, third, and fifth analog switches 7, 9, and 11 in the servo controller 40 are on, and the second, fourth, and sixth analog switches 8, 10 and 12 are each in an off state. Note that "/" before the switching signals SWA and SWB means inversion, and is shown with an overline in the figure.

Therefore, in this state, the input signal Vi
And a speed feedback signal Vs obtained by detecting the drive speed of the hydraulic actuator 17 by the speed sensor 18;
The difference is input to the subtractor 2 and the difference is calculated. The difference is passed through the subtractor 3 (in this case, the analog switch 8 is turned off, so that the difference is passed), and the first proportional / integral compensator 13 which is a speed control compensation circuit. Proportional and integral compensation. The control value Sa
Becomes a control signal of the three-way control valve 16 via the adder 4 to control the drive of the three-way control valve 16 to control the flow rate of hydraulic oil to the hydraulic actuator 17. Thereby,
The speed at which the hydraulic actuator 17 drives the heating cylinder 20 is controlled so that the input signal Vi matches the speed feedback signal Vs.

At this time, the control value Sa output from the proportional / integral compensator 13 is input to the subtractor 6 through the signal line L and stored in the second proportional / integral compensator 15 which is a pressure control compensation circuit. Is done. In this state, the control value Sb output from the proportional / integral compensator 15 becomes a negative input of the subtractor 6 through the analog switch 11, and the difference from the positive input control value Sa is input to the proportional / integral compensator 15. ,
Since the operation is performed so that the difference becomes 0, Sb = Sa.

On the other hand, in the pressure control state, the switching signal SW
A, / SWB is low, SWB, / SWA is high, the first, third, and fifth analog switches 7, 9, and 11 in the servo controller 40 are off, and the second, fourth, and sixth analog switches 8, 10, and 12 are on.

Therefore, in this state, the input signal Vi
And a pressure feedback signal Vp obtained by detecting the pressure (corresponding to the driving pressure) of the hydraulic oil supplied to the hydraulic actuator 17 by the pressure sensor 19, is input to the subtractor 5, and the difference is obtained. Through the subtractor 6 (in this case, since the analog switch 11 is off, it passes through)
Second proportional / integral compensator 15 which is a compensation circuit for pressure control
Proportional and integral compensation.

The control value Sb becomes a control signal for the three-way control valve 16 via the adder 4 and drives and controls the three-way control valve 16 to control the pressure of the hydraulic oil to the hydraulic actuator 17. Accordingly, the pressure at which the hydraulic actuator 17 drives the heating cylinder 20 is controlled so that the input signal Vi matches the pressure feedback signal Vp.

The operation of speed / pressure control by the three-way control valve 16 will be briefly described with reference to FIGS. FIG. 11 shows an example of a hydraulic system in which a heating cylinder of an injection molding machine is driven by a hydraulic actuator. In FIG. 11, reference numeral 40 denotes the above-described servo controller, and 16 denotes a drive controlled by the servo controller.
The directional control valve has a variable throttle function for adjusting the flow rate and pressure of the hydraulic oil flowing into the hydraulic actuator (in this example, the injection cylinder) 17. Actually, as shown in FIG. The control valve has four ports of T (B port is always closed), and the spool 16a is slid by the torque motor 16b to take four positions.

The hydraulic actuator 17 is provided in the cylinder chamber 1
7a, piston 17 of both rods sliding in A and B directions
b, a forward extending rod 17 c is connected to the screw 20 a of the heating cylinder 20, and a rearward extending rod 17 d is connected to the hydraulic motor 21. Reference numeral 24 denotes a mold, which includes a fixed mold 24a and a movable mold 24b which are opened and closed by a mold clamping mechanism (not shown). The fixed mold 24a has an injection hole at a position corresponding to the nozzle 20b at the tip of the heating cylinder 20. Then, a mold chamber (cavity) 24c corresponding to the shape of the molded product is formed inside.

A speed sensor 18 for detecting the moving speed of the rod 17c of the hydraulic actuator 17 in the direction of arrow B is provided, and the detection signal is fed back to the servo controller 40 as a speed feedback signal Vs. The speed sensor 18 includes, for example, an encoder and a frequency / voltage converter (F / V converter).
Further, a pressure sensor 19 for detecting the oil pressure of hydraulic oil in a pipe line 25 connecting the A port of the three-way control valve 16 and the cylinder chamber 17a of the hydraulic actuator 17 is provided. The controller 40 is fed back.

In this hydraulic system, prior to the injection filling step, the three-way control valve 16 is switched so that the cylinder chamber 17a of the hydraulic actuator 17 communicates with the tank side, and the hydraulic motor 21 is rotated to rotate the piston 17b.
Is rotated in the direction indicated by the arrow A, and the heating cylinder 20 is rotated.
The resin material 23 is supplied from the hopper 22 and the required amount is measured by the screw 20a. This weighing is performed for each shot.

When the resin material 23 is measured, the heating cylinder 2
By heating with 0 and shearing with the screw 20a, it is heated and in a molten state. In the injection step, pressure oil is supplied to the cylinder chamber 17a of the hydraulic actuator 17 via the three-way control valve 16 to cause the piston 17b to move to the left.
a also moves to the left, and the molten resin is injected from the nozzle portion 20b into the mold chamber 24c of the mold 24, and is filled therein. When the mold chamber 24c of the mold 24 is filled with the molten resin, the process enters a pressure holding step of maintaining the pressure at a predetermined value.

In the injection step, an output signal of the speed sensor 18 for detecting the operating speed of the hydraulic actuator 17 is input to the servo controller 40 as a speed feedback signal Vs together with an input signal Vi serving as a speed command value. In order to control the supply flow rate of the hydraulic oil by the three-way control valve 16, the above-described speed control is performed.

In the pressure holding step after the resin is filled in the mold chamber 24c of the mold 24, a pressure detection signal in the pipe 25 by the pressure sensor 19 is sent to the servo controller 40 as a pressure feedback signal Vp. Input together with an input signal Vi that is a command value, and
In order to control the hydraulic pressure of the hydraulic oil by the three-way control valve 16,
The pressure control described above is performed.

FIG. 13 shows a specific circuit example of the subtractor 6 and the second proportional / integral compensator 15 for pressure control in FIG. The proportional / integral compensator 15 includes a proportional circuit 151 using an operational amplifier, an integrating circuit 152, and an inverting / adding circuit 153. The output of the subtractor 6 is input. The proportional value based on the ratio is output by the integrating circuit 152 as an integrated value based on the integration constant of the resistor R3 and the capacitor C0, and is added and inverted by the inverting / adding circuit 153, and is output as the control value Sb through the analog switch 12. .

The subtractor 6 also forms an inverting / adding circuit using an operational amplifier. The control value Sb output from the second proportional / integral compensator 15 is inverted three times for the input signal. Therefore, during speed control, it is input to the subtractor 6 via the analog switch 11 and added to the control value Sa input from the first proportional / integral compensator 13 for speed control. The difference Sa-S
b is inverted and input to the proportional / integral compensator 15. Then, since control is performed so that Sa−Sb = 0 (Sb = Sa), the control value Sa is stored in the integration capacitor C0 of the integration circuit 152.

At the time of pressure control, the analog switch 11 is turned off, and the analog switch 12 and the analog switch 10 shown in FIG. 10 are turned on. Therefore, the difference Vi-Vp between the input signal Vi and the pressure feedback signal Vp is input to the subtractor 6. Since the analog switch 9 is also turned off, the control value Sa is not input. The proportional / integral compensator 15
Then, the pressure control is started from a state in which the control value Sa of the speed control immediately before the switching is stored.

[0021]

However, in such a conventional speed / pressure control circuit of a hydraulic actuator, a hydraulic supply source such as a hydraulic system using an accumulator is extremely required. Good control is possible when it is stable, but stable control cannot be obtained due to the influence of the pressure fluctuation when the hydraulic supply source fluctuates like a variable displacement pump. There are cases.

That is, when the flow rate and pressure are supplied to a hydraulic actuator such as a cylinder using a variable displacement pump in order to save energy in the hydraulic system, the above-described problem may occur.

In such a case, when the closed loop control of the cylinder speed is performed by the control valve, the speed control is performed according to the command value to the control valve. For example, if the control valve is suddenly opened when increasing the cylinder speed, the flow rate of the pump increases after the control valve is opened, and a smooth speed response waveform cannot be obtained. Results. In the pressure control state, overshoot and undershoot occur, and it becomes difficult to perform high-response pressure control. The present invention has been made in view of the above points, and has as its object to enable smooth speed response and high response pressure control.

[0024]

SUMMARY OF THE INVENTION According to the present invention, a closed three-way control valve is used to perform speed control for controlling the drive speed of the hydraulic actuator and pressure control for controlling the drive pressure as described above. In order to achieve the above object, in a speed / pressure control circuit of a hydraulic actuator comprising a loop control circuit, in the closed loop control circuit, a compensation circuit and a pressure control for speed control having proportional and integral compensation as main compensation elements, respectively. And a circuit for storing a control value of the speed control compensation circuit during speed control in the pressure control compensation circuit, and an input signal line for inputting speed and pressure command values. A speed / pressure control circuit for a hydraulic actuator, comprising a rise / fall delay circuit capable of adjusting a fall delay. .

It is preferable to provide a means for preventing the rise / fall delay circuit from functioning when shifting from speed control to pressure control. Further, a differential compensator may be provided in the compensation circuit for pressure control, and the differential compensator may be made to function for a set time when shifting from speed control to pressure control.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Parts corresponding to those shown in FIG. FIG.
FIG. 1 is a block diagram showing a first embodiment of the present invention.

The speed / pressure control circuit of this hydraulic actuator constitutes the same closed-loop control circuit as that of the conventional example shown in FIG. 10, and an input signal Vi for inputting an input signal Vi which is a command value of the speed and pressure. The line is provided with a rise / fall delay circuit 14. And
When a variable displacement pump is used as the hydraulic pressure source, its response characteristics differ depending on the rise and fall. Therefore, the rise and fall delay characteristics of the rise and fall delay circuit 14 are independent of each other. To make adjustments. Other configurations are the same as those in FIG.

As shown in FIG. 5, for example, as shown in FIG. 5, a rise / fall delay circuit 14 compares an input with an output, and inverts the difference in accordance with the magnitude relation, outputs an increase / decrease detection circuit A1 using an operational amplifier, a resistor R and a capacitor. An operational amplifier A2 for obtaining an output by forming an integrating circuit together with C, and an increase / decrease detecting circuit A
1 and a series circuit of a diode D1 and a variable resistor VR1, and a series circuit of a diode D2 and a variable resistor VR2, which are provided in parallel between the output terminal 1 and the input terminal of the resistor R.

The series circuit of the diode D1 and the variable resistor VR1 is a rise delay adjusting circuit, and the series circuit of the diode D2 and the variable resistor VR2 is a fall delay adjusting circuit.
That is, the rising delay characteristic when the input signal Vi increases can be adjusted by the variable resistor VR1, and the variable resistor VR1
2, the fall delay characteristic when the input signal Vi decreases can be adjusted.

With such a circuit configuration, in a hydraulic system in which a variable displacement pump or the like is used as a hydraulic supply source, for example, in the case of speed control, a rise / fall delay circuit 14 causes a speed command value by an input signal Vi. Is increased or decreased at a constant acceleration that the variable displacement pump can follow, so that the variable resistances VR1 and VR shown in FIG.
By adjusting the rise delay characteristic and the fall delay characteristic by the method 2, a smooth speed response waveform can be obtained.

Further, in the pressure control, it is possible to cover the disturbance caused by the variable displacement pump and to perform a very smooth pressure closed loop control without overshoot or undershoot. In the rise and fall delay circuit 14 shown in FIG. 5, the delay waveforms of the rise and fall are integrated waveforms, but the same effect can be obtained by using a first-order delay waveform.

FIGS. 6A and 6B are waveform diagrams showing the relationship between an input waveform, an integral waveform, and a first-order lag waveform. FIG. 6A shows a rectangular input waveform, FIG. 6B shows its integral waveform, and FIG. 6C shows a first-order lag waveform. ing. tu is a rise delay time, and td is a fall delay time. Both the integral waveform and the first-order lag waveform are effective for slowly switching signals.

FIG. 7 shows an example of a circuit for forming a first-order lag waveform used as the rising / falling delay circuit 14.
The operational amplifier A1a and the diode Da perform a diode function without a voltage drop for rising, and the operational amplifier A
1b and the diode Db perform a diode function without a falling voltage drop. VRa is a volume for adjusting the rise delay time, and VRb is a volume for adjusting the fall delay time. C is a capacitor for storing voltage, A
Reference numeral 2 denotes an operational amplifier that forms an impedance conversion circuit.

FIG. 2 is a block diagram showing a second embodiment of the present invention. The difference from the embodiment shown in FIG. 1 is that the rising / falling delay circuit 14 'uses a rising / falling circuit in FIG. The only difference from the falling delay circuit 14 is that the operation is controlled by a timer circuit 50.

The timer circuit 50 starts the timer operation from the time when the switching signal SWB changes from low to high at the time of transition from speed control to pressure control, and sets the timer for a predetermined time (10 to 100
ms), the pulse-like switching signal St is generated. Then, the switching signal St is supplied to the rising and falling delay circuit 1.
4 ', the function is stopped only during the period when the switching signal St is generated, and the input signal Vi is output as it is.

The rising / falling delay circuit 14 'is shown in FIG.
Is provided with a bypass circuit connecting the output terminal of the increase / decrease detection circuit A1 of the rise / fall delay circuit 14 and the inverting input terminal of the operational amplifier A2 with a resistor having a very small resistance value, and only when the switching signal St is high. By connecting a bypass circuit, the output can be immediately made the same as the input signal Vi. This makes it possible to cause the pressure control value to quickly follow the target pressure by the input signal Vi without delay.

FIG. 3 is a block diagram showing a third embodiment of the present invention. This corresponds to the second embodiment of the present invention shown in FIG.
In addition to the circuit of the embodiment, as a compensation circuit for pressure control,
A differential compensator 30 is provided in parallel with the second proportional / integral compensator 15, and its output is supplied to the second
Is a negative input of a subtractor provided on the output side of the proportional / integral compensator 15.

At the time of transition from speed control to pressure control, the switching signal St output from the timer circuit 50 is also used as a control signal for the analog switch 32. 32
Is turned on, and the value obtained by subtracting the output of the differential compensator 30 from the output of the second proportional / integral compensator 15 is used as a control value S for pressure control.
b. In this manner, when the speed control is shifted to the pressure control, not only does the rise / fall delay circuit 14 'not function, but also the differential compensator 30 functions, so that the pressure control value can be extremely quickly changed to the input signal Vi. Can follow the target pressure.

FIG. 4 is a block diagram showing a fourth embodiment of the present invention. Instead of rising and falling delay circuit 14 shown in FIG. 1, a rising and falling delay is applied to an input signal line for inputting input signal Vi. The circuit 54 is provided. The rising / falling delay circuit 54 is a rising / falling delay adjusting circuit 54 for speed control as shown in FIG.
A and rise / fall delay adjustment circuit 54B for pressure control
Are provided separately and independently so that the optimum delay time in the speed control and the optimum delay time in the pressure control can be adjusted independently.

In FIG. 8, parts corresponding to those in FIG. 5 are denoted by the same reference numerals. The series circuit of the diode D11 and the variable resistor VR11, and the series circuit of the diode D12 and the variable resistor VR12 constitute a rise delay adjustment circuit and a fall delay adjustment circuit for speed control, respectively. The series circuit and the series circuit of the diode D22 and the variable resistor VR22 form a rise delay adjustment circuit and a fall delay adjustment circuit for pressure control, respectively. 55 and 56 are analog switches interposed between these adjustment circuits and the output terminal of the increase / decrease detection circuit A1.

Since the switching signal SWA is high and the switching signal SWB is low during speed control, the analog switch 55 is turned on and the analog switch 56 is turned off, and only the rising / falling delay adjusting circuit 54A for speed control is effectively enabled. Become. During pressure control, since the switching signal SWA is low and the switching signal SWB is high, the analog switch 56
Is turned on, the analog switch 55 is turned off, and only the rise / fall delay adjustment circuit 54B for pressure control is enabled. This makes it possible to independently adjust the optimal rise and fall delay times in the speed control and the optimal rise and fall delay times in the pressure control, thereby enabling optimal control corresponding to the characteristics of the hydraulic system. Become.

Further, instead of the rising and falling delay circuit 54 in FIG. 4, the output terminal of the increase / decrease detection circuit A1 of the rising and falling delay circuit 54 shown in FIG. 8 and the operational amplifier A2 of the integration circuit as shown in FIG. And a rising / falling delay circuit 54 'provided with a bypass circuit for connecting an inverting input terminal to an inverting input terminal via an analog switch by a resistor R0 having an extremely small resistance value, as well as the circuits shown in FIGS. May be provided with a switching circuit St which is output for a set time when the timer circuit 50 shifts from speed control to pressure control, and the analog switch 57 of FIG. 9 may be turned on.

In this manner, at the time of transition from speed control to pressure control, the delay function of the rise / fall delay circuit 54 'is stopped for the set time of the timer circuit 50 in which the switching signal St is generated. , The change in the input signal Vi is immediately output, and the pressure control value can quickly follow the target pressure by the input signal Vi without delay. In this case, even if the rising and falling delay adjusting circuits 54A and 54B of FIG. 9 remain connected, the resistance value of the resistor R0 of the bypass circuit is smaller than the resistance value of the series circuit of each variable resistor and the resistor R. This is not a problem because the value is extremely small.

[0044]

As described above, the speed / pressure control circuit of the hydraulic actuator according to the present invention has the following effects. In the invention according to claim 1,
Even in a hydraulic system having a large pressure fluctuation such as a variable displacement pump system as a hydraulic supply source, the delay characteristics of the rise and fall of the input signal can be appropriately adjusted, so that a smooth speed response is obtained in the speed control. In the pressure control, a pressure step response without overshoot or undershoot can be obtained.

According to the second aspect of the present invention, the rise and fall delay circuits are not operated at the time of transition from speed control to pressure control. At times, the target pressure can be quickly followed, and a quick transition from speed control to pressure control becomes possible.

Further, in the invention according to claim 3,
When shifting from speed control to pressure control, the rise and fall delay circuits are disabled, and the differential compensator is enabled to follow the target pressure more quickly. An even faster transition is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram of a speed / pressure control circuit of a hydraulic actuator according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a speed / pressure control circuit of a hydraulic actuator showing a second embodiment of the present invention.

FIG. 3 is a block diagram of a speed / pressure control circuit of a hydraulic actuator showing a third embodiment of the present invention.

FIG. 4 is a block diagram of a speed / pressure control circuit of a hydraulic actuator showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a specific circuit example of a rise fall delay circuit 14 in FIG. 1;

FIG. 6 is a waveform diagram showing a relationship between an input waveform, its integral waveform, and a first-order lag waveform.

FIG. 7 is a circuit diagram showing a specific example of a circuit for forming a first-order lag waveform used as a rise / fall lag circuit 14;

8 is a circuit diagram showing a specific example of a rising and falling delay circuit 54 in FIG.

9 is a circuit diagram of a rising / falling delay circuit 54 'in which a bypass circuit is provided in the rising / falling delay circuit 54 of FIG. 8;

FIG. 10 is a block diagram showing an example of a conventional speed / pressure control circuit of a hydraulic actuator.

FIG. 11 is a configuration diagram showing an example of a hydraulic system in which a heating cylinder of an injection molding machine is driven by a hydraulic actuator.

FIG. 12 is a hydraulic symbol diagram of the three-way control valve 16 in FIG.

FIG. 13 is a circuit diagram showing a specific circuit example of the subtractor 6 and the second proportional / integral compensator 15 in FIG.

[Explanation of symbols]

2, 3, 5, 6, 31: subtractor 4: adder 7 to 12, 32, 55, 56, 57: analog switch 13: first proportional / integral compensator 14, 14 ', 54, 54': Rise / fall delay circuit 15: Second proportional / integral compensator 16: Three-way control valve 17: Hydraulic actuator 18: Speed sensor 19: Pressure sensor 20: Heating cylinder 21: Hydraulic motor 30: Differential compensator 40: Servo controller 50: Timer circuit Vi: Input signal Vs: Speed feedback signal Vp: Pressure feedback signal Sa: Control value of speed control Sb: Control value of pressure control SWA, / SWA, SWB, / SWB: Switching signal St: Timer circuit output Switching signal

Claims (3)

[Claims] 1. A speed / pressure control of a hydraulic actuator comprising a closed loop control circuit for performing a speed control for controlling a driving speed of a hydraulic actuator and a pressure control for controlling a driving pressure by using a single three-way control valve. In the circuit, in the closed loop control circuit, the compensation value of the speed control and the compensation circuit of the pressure control with proportional and integral compensation as the main compensation elements, and the control value by the compensation circuit of the speed control at the time of the speed control, A compensation circuit for pressure control is provided, and a rise / fall delay circuit capable of adjusting rise and fall delays is provided on an input signal line for inputting a speed and pressure command value. Speed and pressure control circuit for hydraulic actuators. 2. The speed / pressure control circuit for a hydraulic actuator according to claim 1, further comprising means for preventing the rise / fall delay circuit from functioning when shifting from speed control to pressure control. Speed / pressure control circuit of hydraulic actuator. 3. The speed / pressure control circuit of a hydraulic actuator according to claim 2, wherein a differential compensator is provided in the pressure control compensating circuit, and the differential compensator functions only for a set time at the time of shifting from speed control to pressure control. A speed / pressure control circuit for a hydraulic actuator, wherein the speed and pressure are controlled by a hydraulic actuator.