JPH0289802A - Control device for fluid actuator - Google Patents

Abstract

PURPOSE:To prevent the abnormal increase of a working pressure and a speed by a method wherein during control of a speed (pressure), a command signal is compared with a detecting signal by a pressure (speed) signal comparing means, and when the latter is higher than the former, switching to the pressure (speed) control side is effected by a switch means. CONSTITUTION:A pressure sensor 5 is situated between a hydraulic cylinder 2 provided with a speed sensor 10 and a servo valve 4 to control the hydraulic cylinder. A difference between detecting and command signals Ps, Pr : Vs, Vr is determined by means of pressure and speed subtractors 6 and 8. The difference is guided as a pressure and speed control signal to a control change- over switch 11 by means of pressure and speed compensating circuits 7 and 9. A control signal selected by the change-over switch is fed to the solenoid of a servo valve 4 to perform feedback control. The control change-over switch 11 is changed over by pressure signal comparators 12 and 13 according to formulas of Ps>Pr and Vs>Vr, and during control of a pressure, switching to speed control is effected or the above is reversed. This constitution enables prevention of the abnormal increase of a pressure during control of a speed and the abnormal increase of a working speed during control of a pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a fluid actuator control device that switches and controls the operating speed and operating pressure of a fluid actuator using one control valve and two feedback control loops.

<Conventional technology> Conventionally, as a control device for this type of fluid actuator,
For example, the one shown in FIG. 3 is known. This control device connects a hydraulic power source 1 to a hydraulic cylinder 2 of an injection molding machine, etc.
A servo valve 4 and a pressure sensor 5 are interposed in the pressure line 3 leading to the pressure line 3, and a pressure subtractor 6 calculates the difference between the pressure command signal and the pressure detection signal from the pressure sensor 5, and the difference signal is used to calculate the pressure. The compensation circuit 7 performs compensation to obtain a pressure control signal, while the speed subtracter 8 calculates the difference between the speed command signal and the speed detection signal from the speed sensor 10 provided in the hydraulic cylinder 2, and generates this deviation signal. A speed compensation circuit 9 performs compensation on the signal to obtain a speed control signal. When injecting molten resin (negative g2+) into a mold (not shown), the control changeover switch 22 is switched to the speed compensation circuit 9 side by a limit switch or timer that operates at a specific position of the hydraulic cylinder, and the speed command signal is Solenoid 4 of servo valve 4
a to control the injection speed, while at the time of resin solidification after injection, the control changeover switch 22 is switched to the pressure compensation circuit 7 side, and the injection pressure is similarly controlled using the pressure command signal.

<Problems to be Solved by the Invention> However, the conventional hydraulic cylinder control device described above selects either the speed control signal or the pressure control signal with the control changeover switch 22 and outputs it to the servo valve 4. Since it controls the speed or pressure of the hydraulic cylinder 2, the pressure increases while the controlled amount is the speed (on the contrary, the speed cannot be controlled while the controlled amount is the pressure. Therefore, the molten resin during speed control If the piston rod accidentally collides with an obstacle such as a mold during injection, there is a problem in that the pressure control does not work and the suppressing force increases rapidly, damaging the mold and the piston rod. Furthermore, if the load on the resin is light during resin solidification during pressure control, the piston rod may run out of control because the speed control does not work, causing defects such as cracks in the molded product or damaging the molding machine.

Therefore, an object of the present invention is to convert the pressure detection signal during speed control into
It is an object of the present invention to provide a fluid actuator control device capable of preventing abnormal increases in the operating pressure and operating speed of a fluid actuator and eliminating damage to the fluid actuator by monitoring a speed detection signal during pressure control. .

Means for Solving the Problems> In order to achieve the above object, the fluid actuator control device of the present invention, as illustrated in FIG. While the detection signal Vs is subtracted from the speed command signal Vr to output a speed control signal, the pressure detection signal Ps from the pressure detector 5 of the fluid actuator 2 is detected by the comparison means 6.
is subtracted from the pressure command signal Pr to output a pressure control signal, and one of the two control signals is selected by the switch means 11 and output to the control valve 4 interposed in the pressure line 3 of the fluid actuator 2. When the speed control signal is selected, the pressure command signal P
When the pressure detection signal Ps is larger than the pressure command signal P, the switch means 1
1 to the pressure control signal side
During pressure control when the pressure control signal is selected, the speed command signal Vr and the speed detection signal Vs are compared, and when the speed detection signal Vs is larger than the speed command signal V', the switch means 11 is controlled to speed. The present invention is characterized in that it includes at least one of the speed signal comparison means 12 that switches to the signal side.

During speed control, the comparison means 8 compares the speed command signal Vr.
A speed control signal obtained by subtracting the speed detection signal Vs from the speed detection signal Vs is outputted to the control valve 4 via the switch means ti, thereby controlling the speed of the fluid actuator 2. At this time, the pressure signal comparison means 13 compares the pressure command signal Pr and the pressure detection signal Ps, and if the pressure detection signal Ps becomes larger than the pressure command signal P', the switch means 11
Switch to the pressure control signal side. Then, the fluid actuator 2 comes to be pressure-controlled, and its pressure is suppressed below the pressure value represented by the pressure command signal Pr.

Conversely, during pressure control, the pressure control signal is sent to the switch means 1.
1 to the control valve 4, and the fluid actuator 2
pressure is controlled. At this time, the speed signal comparison means 12
compares the speed command signal Vr and the speed detection signal v8, and when the speed detection signal Vs becomes larger than the speed command signal Vr, switches the switch means 11 to the speed control signal side. Then, the fluid actuator 2 comes to be speed-controlled, and its speed is suppressed below the speed value represented by the speed command signal Vr.

<Example> Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 shows an example of a control device for a fluid actuator, and this control device includes a servo valve 4 serving as a control valve and a pressure sensor 5 connected to a pressure line 3 extending from a hydraulic source 1 to a hydraulic cylinder 2 of an injection molding machine or the like. In addition, a pressure subtracter 6 takes the difference between the pressure command signal Pr and the pressure detection signal Ps from the pressure sensor 5, and a pressure compensation circuit 7 compensates this pressure deviation signal to calculate the pressure. On the other hand, a speed subtractor 8 calculates the difference between the speed command signal Vr and the speed detection signal Vs from the speed sensor 10 provided in the hydraulic cylinder 2, and the speed deviation signal is used as a speed compensation circuit 9. Compensation is applied to the speed control signal. Each of the following constituent elements has exactly the same structure and operation as the conventional constituent elements already described in FIG. 3, and the same elements are given the same numbers.

The output side of both compensation circuits 7.9 is connected to a limit switch that operates at a specific position of the hydraulic cylinder 2, a timer, or a manual switch, and is also switched by a switching signal to be described later, and is connected to the pressure control signal or speed control signal. A control changeover switch 11 is provided to select one of the two and send it to the solenoid of the servo valve 4. Also, on the pressure control loop side, the pressure command signal Pr and the pressure detection signal Ps from the pressure sensor 5 are constantly compared, and when the pressure detection signal Ps is larger than the pressure command signal Pr (Ps>Pr), the above control switching is performed. A pressure signal comparator I3 is provided to output a switching signal for switching the switch 11 to the pressure horn control signal side, and a speed command signal Vr and a speed sensor 10 are provided on the speed control loop side.
When the speed detection signal Vs is larger than the speed command signal Vr (Vs>Vr
), a speed signal comparator 12 is provided which outputs a switching signal for switching the control changeover switch 11 to the speed control signal side. In addition, the control changeover switch 11 is switched to the pressure and speed control signal side, respectively, in response to the forced changeover signal PcVc, in order to initial reset the injection molding cycle, etc., with priority over the above changeover signals, and maintains this switching state for a predetermined period of time. It looks like this.

The operation of the hydraulic cylinder control device configured as described above will now be described with reference to FIG.

Now, during speed control when the control changeover switch 11 is switched as shown in FIG. 4 solenoid 4a,
The speed of the hydraulic cylinder 2 is feedback controlled. Then, in step S1 of FIG. 2, it is determined that the pressure signal comparator 13 is positive, and in step S2, the pressure signal comparator 13 compares the pressure command signal Pr and the pressure detection signal Ps, and the pressure detection signal Ps
becomes larger than the pressure command signal Pr (Ps>Pr)
, R, and proceeds to step S3.
A switching signal is output for switching the control changeover switch 11 from the speed control signal side to the pressure control signal side. Then, the hydraulic cylinder
is now controlled by the servo valve 4 operated by the pressure control signal passed through the switched control changeover switch 11, and thereafter the pressure is controlled so as to follow the pressure command signal Pr. Therefore, even if the piston rod of the hydraulic cylinder 1 collides with an obstacle such as a mold and the pressing force exceeds the upper limit value indicated by the pressure command signal P'' during speed control such as when injecting molten resin, the piston rod of the hydraulic cylinder 1 will immediately Pressure feedback works to suppress the pressing force to below the above upper limit value, preventing damage to the mold or piston rod due to excessive pressing force.In addition, the pressure command signal Pr is set to a high pressure higher than the capacity of the hydraulic source l. If the pressure signal comparator 13 is set to , the pressure signal comparator 13 will not work, so that only the conventional speed control can be performed.It should be noted that if the determination in step S2 is negative, the process returns to step S+. Not even.

Next, during pressure control when the control changeover switch 11 is switched in the opposite direction to that shown in FIG. 1, a pressure control signal is output to the servo valve 4, and the pressure in the hydraulic cylinder 2 is feedback-controlled. Then, in step S1 of FIG. 2, it is determined that the answer is NO.
In step S4, the speed signal comparator I2 compares the speed command signal Vr and the speed detection signal Vs, and if Vs>Vr, it is determined to be positive, and the process proceeds to step S5.
The control changeover switch 11 is switched from the pressure control signal side to the speed control signal side. Then, the hydraulic cylinder l is thereafter controlled by the servo valve 4 which is operated by the speed control signal, and its speed is controlled so as to follow the speed command signal V. Therefore, during pressure control during resin solidification, etc. Even if the piston rod tries to run out of control due to a light load on the resin, speed feedback is activated immediately to suppress the runaway and prevent molded products from bursting or damage to the molding machine due to the runaway.In addition, the speed command signal V If " is set to a high speed higher than the capacity of the hydraulic power source 1, only conventional pressure control can be performed.

In the above embodiment, since both the speed signal comparator 12 and the pressure signal comparator 13 are provided, there is an advantage that abnormal increases in both the speed and pressure of the hydraulic cylinder can be prevented. However, it is not necessary to provide only one of them. Of course, it is also possible. Also,
In order to easily determine whether speed control or pressure control is in operation, a light emitting diode or the like may be connected to the control changeover switch 11, and the determination can also be made remotely based on the output signal of an interlocking transistor. Furthermore, the speed and pressure signal comparison means of the present invention is not limited to the comparators 12 and 13 which are hardware in the embodiment, but may be software such as a microprocessor program.

Furthermore, it goes without saying that the present invention is applicable not only to the hydraulic cylinder of the illustrated injection molding machine but also to fluid actuators in general.

<Effects of the Invention> As is clear from the above description, the fluid actuator control device of the present invention subtracts the speed control signal obtained by subtracting the speed detection signal from the speed command signal and the pressure detection signal from the pressure command signal. In a device that controls the speed or pressure of a fluid actuator by outputting either one of the pressure control signals obtained by the control valve to the control valve via a switch means, the pressure signal comparison means compares the pressure command signal and the pressure detection signal during speed control. and when the latter is large, the switch means is automatically switched to the pressure control side, or when the latter is large, the speed signal comparison means is used to compare the speed command signal and the speed detection signal, and when the latter is large. - Since the switch means is automatically switched to the speed control side, the command signal can be changed to the speed control side.

By setting the pressure to the upper limit value, it is possible to prevent an abnormal increase in the operating pressure during speed control or an abnormal increase in the operating speed during pressure control, and it is possible to eliminate problems that occur in the fluid actuator etc. due to these abnormal increases.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the fluid actuator control device of the present invention, FIG. 2 is a flowchart showing the operation of the above embodiment, and FIG. 3 is a diagram showing a conventional hydraulic cylinder control device. 2... Hydraulic cylinder, 4... Servo valve, 5... Pressure sensor, 6... Pressure subtractor, 7... Pressure compensation circuit,
.. Subtractor for speed, 9.. Compensation circuit for speed, 10.
...Speed sensor, 11...Control changeover switch, 12.
...Speed signal comparator, ]3...Pressure signal comparator.

Claims (1)

[Claims] (1) Fluid actuator (2) by comparing means (8)
) is subtracted from the speed command signal (Vr) to output a speed control signal, while the pressure of the fluid actuator (2) is detected by the comparison means (6). Pressure detection signal (P
s) from the pressure command signal (Pr) to output a pressure control signal, and one of the two control signals is selected by the switch means (11) to control the pressure line (3) of the fluid actuator (2). In a control device for a fluid actuator that outputs to a control valve (4) installed in ,
pressure signal comparison means (13) for switching the switch means (11) to the pressure control signal side when the pressure detection signal (Ps) is larger than the pressure command signal (Pr); , the above speed command signal (V
speed signal comparison means (12) for comparing the speed detection signal (Vs) with the speed detection signal (Vs) and switching the switch means (11) to the speed control signal side when the speed detection signal (Vs) is larger than the speed command signal (Vr); ) A fluid actuator control device comprising at least one of the following.