JPS5937302A - Speed control method of cylinder in hydraulic system - Google Patents

Abstract

PURPOSE:To ensure quick response, stable and accurate control by means of a simple control system where the speed of a hydraulic cylinder is controlled to be varied suddenly to a large extent by performing open loop control in the transient condition immediately after a set value is modified and then shifting the control to feedback control when a controlled object comes into an approximately normal condition. CONSTITUTION:Based on a speed setting signal from a program setter 13 which sequentially switches and generates a speed setting value preset in accordance with variation of a cylinder stroke signal from a position detector 12, open loop control and feedback control are switched and a speed-pulse number conversion circuit 21 calcurates a pulse number which corresponds to the preset value. The number is then converted into a pulse signal in a pulse generating circuit 22 and fed via a driving device 15 and a pulse motor 10 to control an opening of a flow rate regulting valve 11. Said pulse signals are generated at the maximum rate which a cylinder speed can follow and at a rate which causes no overshoot. When the speed of the hydraulic cylinder 1 comes almost into the normal condition, the open loop control is switched to the feedback control loop.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the speed of a cylinder in a fluid pressure system.

Conventionally, for example, in devices such as die-casting machines and injection molding machines that change the injection speed during the injection process, the speed control method of the injection cylinder can be roughly divided into open-loop and There are methods of control and closed-loop control.

Conventionally, when performing open loop control using an electromagnetic 9J replacement valve, for example, a device as shown in FIG. 1 has been used.

In FIG. 1, 1 is a hydraulic cylinder for injection.

2 is a hydraulic pump, and Ro is a low-fire 11i 111 electromagnetic switching valve.

4 is an electromagnetic 1JJ replacement plate ρ for high-speed injection, 5i (J low-speed n,
Flow rate adjustment valve for J output, 6J flow t7J adjustment valve for high-speed side output, 7 is a relief valve, 8i1: tank, 9iJ: high-speed switching position command device such as a limit switch, and the limit switch during low-speed injection. 9 is negative, high speed firing 111
It is now switched to .

Only 1～. In this case r1. If the oil 1-F piping becomes complicated, or surge pressure is generated when switching the solenoid switching valve 4, or if the electrical 41" Fi switching valve 4 is switched in steps, the electromagnetic switching valve Immediately after switching to 4.

There were drawbacks such as an overshoot in which the injection speed temporarily exceeded the high-speed injection speed of 191 degrees, and the inability to control temperature changes.

Unfortunately, a device like the one shown in Figure 2 was used in open loop control using a pulse motor.

In FIG. 2, a flow rate switching valve 11 whose opening degree can be controlled by the operation of a pulse motor 10 is provided in the piping between the hydraulic pump 2 and the hydraulic cylinder 10. 12 is a position detector that detects the moving position of the piston rod 1a of the hydraulic cylinder 1;

Injection speed program setter 13. An instruction is given to the pulse motor 10 via the pulse generator 14 and the drive device 15, and the flow rate adjustment valve is controlled based on the output signal from the 1-position detector 12 and the injection speed program set in advance by the injection speed program setting device 13. The opening degree of 11 can be controlled.

However, the viscosity of hydraulic oil 1 changes with changes in oil temperature, and the flow state changes, so the moving speed of hydraulic cylinder 1 naturally changes depending on changes in the ml vortex. However, the speed of the hydraulic cylinder also changes due to changes in the cylinder load acting on the piston rod 1a ('5). 11 river fi 1
At 11.

Corrections for deviations from the set value according to this further example are performed by Jl-.

Also, in feedback control, a device as shown in Fig. 1 is used.

Figure 3 (r), oil 1-1-bo/pu 2 and hydraulic
V in the piping between the cylinder 1 and the electromagnetic proportional flow control valve 1.
A piston rod detector 17 of the hydraulic cylinder 1 is provided, and a speed detector 17 detects C-
1. The piston rod signal [,'' is output, and the input buffer 18 converts this 71Σ signal into the original signal into the corresponding voltage signal 1 or 'r. On the other hand, the position detector 12 and the injection The setting value of the moving speed is set based on the action of the speed programmer and setting device 1.
1. signal and output at 17 J'1, both voltage signals are momentarily IIs + Ii & S, 11, injection; moderate block '1 If the output from the 1 crumb setter 1 is higher than the output from the input buffer 18, there is a positive deviation Borrowing is noito back control (
4) sent to device 19; The flow rate regulating valve 16 is then controlled to a predetermined opening degree via the amplifier 2o.

In this type of feedback control, the transfer function of the system combining the flow control valve 16 and the injection cylinder is:

Must have resonant second-order delay characteristics that include an integral element.

Because the response of the flow rate control valve 16 is slow, the initial deviation becomes large when the set speed is changed in a stepwise manner, and at the same time, the transient deviation becomes zero under normal feedback control.
This had the disadvantage of worsening stability and causing open neatness and undershoot. And this open NEET.

If the effectiveness of the feedbank control is reduced in order to prevent undersheeting, there is a drawback that the responsiveness, that is, the followability becomes poor.

The present invention aims to eliminate the drawbacks of such step-like setting value changes, and is designed to provide quick response speed and easy stable and accurate control when controlling the speed of a hydraulic cylinder to be changed greatly and suddenly. It is designed to be obtained in a control system, and for that purpose.

In the present invention, when controlling the speed of a cylinder in a fluid pressure system. Open-loop control is performed in a transient state immediately after changing the set value, and then when the controlled object reaches a substantially steady state, open-loop control is switched to feedback control.

Combining open-loop control and feedback control compensates for the shortcomings of both.

Try to make the most of your strengths.

Next, the present invention will be explained in more detail with reference to an embodiment shown in the drawings.

In addition, in FIG. 4 showing one embodiment of the present invention, the first
6 to 6. Components that are the same as those shown in FIG.

In the device shown in Fig. 4, d,,' is a program controller that sequentially switches and outputs preset speed settings according to changes in the cylinder stroke signal from the position detector 12, and speed settings from the setting device 1B. Open loop fltll Ill and feedback control are performed by the signal. When the speed setting signal from the program controller 13 is switched, the speed-to-pulse number conversion circuit 21 operates to calculate the number of pulses corresponding to the set value.

The calculated number of pulses is transmitted to the pulse generation circuit 22.
+, , converted into a pulse signal by the pulse generation circuit 22,
Output. In this case, the number of pulses and pulse intervals of the output pulse signal, which is a command pulse, and the setting change timing signal are controlled based on the settings of the program setter 13.

Based on experimental results, the pulse signal is set to be output at the maximum speed that the cylinder speed can follow, and at a speed that does not cause overburn-1. And drive device 15. The valve opening degree of the flow rate regulating valve 11 is controlled via the pulse motor 10 . For example, when one pulse is output, the pulse motor 10 rotates by a predetermined step angle, and the valve opening degree changes accordingly. However, in this case, one flow rate adjustment valve 11 is used to control the injection speed.

When the output of the pulse signal is completed, the change in the valve opening degree is also completed, and in the experiments conducted by the inventors, the speed of the hydraulic cylinder 1 is almost in a steady state at this time, so a feedback control loop is established. (7) Enable.

V''1 in the feedback control loop. The cylinder speed from the speed detector 17 is received by the innoput controller 718, and the deviation from the programmer/setter 1 is calculated 1-7. Performs feedback control. Feet
・Operations D'j'rtan, l' from the Tsuku control device 19,
+ is converted into a pulse signal and output from the pulse generation circuit 23 to the drive device 15 via the changeover switch 24.

Note that the setting change timing signal d1. Output when changing the setting signal output from the program setting device 13,
Speed-pulse number conversion circuit 21. The setting change is transmitted to the pulse generation circuit 22.

This is a timing signal for starting calculations for both circuits, and is generated by inputting all predetermined command pulses 11j in the pulse generation circuit 22.
l: Transmitted to the U change switch 24.

While the hydraulic cylinder is moving forward at low speed, the injection speed suddenly changes greatly and in the transient state region where it changes to high-speed injection, if feedback control is performed here, the deviation between the set value (8) and the detected value is large, so There will be more output signals, resulting in an attempt to over-correct. Therefore, when changing this setting, open loop control should be used instead of feedback control. However, when the speed is changed by open loop control and the detected value based on it approaches the set value and becomes constant, the deviation becomes small, so even if feed control is used, control will be effective. . Therefore, here, the speed of the hydraulic cylinder, which tends to change slightly depending on the fluid temperature, cylinder load, etc., is controlled by feedback control.

In this way, in the present invention, open-loop control is performed in a transient state immediately after a large step change in the set value, and feedback control is performed when the controlled object reaches a substantially steady state. The following effects can be obtained, and effective and reliable speed control can be easily performed.

The cylinder speed control is highly accurate (i, I stable 1/1 is 1 (I et al, l 4゜ilr
Since then, the injection speed control system for die casting 77 has undergone a difficult step-like speed setting change.

Most are open loop! Although fli is controlled only by fu control, if it has a significant impact on plunger speed accuracy, stability, or product quality, apply one noste l from -1-.
: There is a large merino I.

4 Sections of the drawings; Figures 1 to 6 V1 Similar to the present invention/ζ Carrying out the conventional method/Each of the different apparatuses 71-)/Oil showing this example 11- Circuit diagram and block diagram, Figure 4 is a block diagram of one embodiment of a device implementing the present invention. ... Oil 11 Bonzo, 10
...Pulse motor, 5, 6, 11.16...Flow rate adjustment valve, 12...Position detector, 1ro...Program setting device, 15...Drive device 117...Speed detector.

18... Input buffer, 19... Feedback control device, 22.23 - Pulse generation circuit Patent applicant Ube Industries, Ltd. 1 Figure 3 Figure 2 Figure 4 Sen

Claims (2)

[Claims] (1) When controlling the speed of a cylinder in a fluid pressure system, open-loop control is performed in a transient state immediately after changing the set value, and then, when the controlled object becomes approximately steady, open-loop control is changed to feedback control. A cylinder speed control method in a fluid pressure system that switches to (2) When detecting that the controlled object is in a substantially steady state by changing the set value, the detection is performed at the time when the change in the output of the operation signal to the operation unit is completed. A method of controlling cylinder speed in a fluid pressure system.