JPS6334302A - Pressure control device for hydraulic cylinder - Google Patents

Abstract

PURPOSE:To improve the responsiveness, stability and accuracy, by carrying out open loop control by a feedforward signal in consideration of the characteristics of a proportional electromagnetic pressure valve, and carrying out feedback control for the excess and deficiency only. CONSTITUTION:An output from an injection pressure commander 16 is input to a feedforward compensator 20 for generating a feedforward signal ef according to a polygonal line function considering input/output characteristics of a proportional electromagnetic pressure valve 23. The output from the commander 16 is also input to a controller 19 for carrying out feedback control by a deviation signal between a command signal and an output signal from a pressure detector 17. Accordingly, open loop control is carried out by the feedforward signal from the feedforward compensator 20, and a reduction in control performance is improved by the feedback control, thus improving the responsiveness, stability and accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pressure control device for a hydraulic cylinder used in an injection device of an injection molding machine or a construction machine.

(Prior Art) Now, taking a conventional injection molding machine as an example, we will discuss the pressure (hereinafter referred to as injection pressure) control of the hydraulic cylinder that drives the screw. There are two types of methods for this control:

One of them is the open loop injection pressure filJ? using a proportional solenoid pressure valve as shown in Figure 3. il, and the other method is the fourth
This is closed-loop injection pressure control using a servo valve as shown in the figure.

By the way, in recent years, synthetic resins have come to be used in a wide variety of fields, including materials and parts, and as the proportion of plastics has increased, there has been a strong demand for greater versatility and greater density of injection molded products. In order to achieve this, various injection process controls are being carried out. In this injection process control, the injection speed in the filling process and the injection pressure in the pressure holding process are program-controlled based on functions of the screw position or time, respectively.

The injection pressure in the pressure holding process determines the shrinkage rate when the molten resin cools and solidifies, and when the injection pressure fluctuates,
Molding defects such as cracks, short circuits, and poor dimensional accuracy occur.

Therefore, as one way to reduce these molding defects and to improve the precision of molded products, it has become necessary to improve the reproducibility of the injection pressure from cycle to cycle, in which the injection pressure does not fluctuate from cycle to cycle. ing.

From this point of view, when considering the conventional control methods described above, we first look at the open-loop control of the proportional electromagnetic pressure valve shown in FIG. 3. This control has the following three problems.

In other words, the first point is that the input current/output pressure characteristics vary greatly from valve to valve, and there are large individual differences from machine to machine.The second point is that the hysteresis width of the input current/output pressure characteristics is large, and the injection pressure The accuracy is poor (particularly the effect on the low pressure region is large).The third point is that due to aging of the proportional electromagnetic pressure valve, the actual value will fluctuate even if the settings are the same.

Next, looking at the closed loop control using the conventional servo valve shown in Fig. 4, it is effective in terms of compensating for the fluctuations mentioned above, but it is expensive compared to the proportional electromagnetic pressure valve, and furthermore, the hydraulic contamination
The problem is that it is weak. Therefore, in order to solve these problems, it may be possible to adopt a closed loop control system using a proportional electromagnetic pressure valve.

-For boat fishing, it is possible to use proportional solenoid pressure valves used for open loop control in place of servo valves for closed loop control, but when using proportional solenoid pressure valves for closed loop control, there are problems with coordination and stability. In addition, it is not sufficient in terms of steady-state characteristics. For example, if the controller is configured with a proportional controller in order to quickly match the injection command pressure and the injection pressure, the responsiveness of the proportional solenoid pressure valve will be poor, so if you try to improve controllability by increasing the gain. , these control systems easily oscillate and become unstable. On the other hand, if the gain is lowered to stabilize this control system, a very large offset (steady-state deviation) will occur. As a countermeasure to this problem, it has been considered to eliminate the offset by using a proportional-integral type controller, for example.
In this controller, for example, if the time constant of integration is made small in order to obtain continuity, the injection pressure command a
However, there is a drawback that vibrations with poor damping occur due to the injection pressure, and good control effects cannot be obtained.

(Problem to be Solved by the Invention) In this way, if it were possible to control the pressure of conventional hydraulic cylinders, it would be possible to use proportional It has been considered desirable to use electromagnetic pressure valves for closed-loop control with high control stability. There is a problem that variations occur in the set value and the actual value due to changes, and as a result, there are problems in control coordination, stability, and steady-state characteristics, making it difficult to implement. It was something that existed.

The present invention aims to solve these problems.
The objective is to take advantage of the advantages of conventional proportional electromagnetic pressure valves and closed-loop control, compensate for their disadvantages, and provide a hydraulic cylinder pressure control device that is fully satisfactory in terms of speed response, stability, and accuracy. be.

(Means for Solving the Problems) Therefore, the present invention provides a feedforward compensator that outputs a feedforward signal in response to a command signal from a pressure command device, and a deviation between the command signal and the output signal of a pressure detector. A hydraulic cylinder comprising: an iB controller that performs feedback control based on a signal; and a proportional electromagnetic pressure valve that adjusts the pressure of the hydraulic cylinder based on the feedforward signal and the output signal from the controller. The pressure control device is configured as a means for solving the above-mentioned problems.

(Function) Open-loop control is performed using the feedforward signal of the feedforward compensator that takes into account the characteristics of the proportional solenoid pressure valve, and at the same time, feedback control improves control performance deterioration due to individual differences, hysteresis, aging, etc. of the pressure valve. do.

(Example) Hereinafter, an example in which the present invention is applied to an injection molding machine will be described based on the drawings.

FIG. 1 shows an example in which a control device according to an embodiment of the present invention is incorporated into an injection section of a general injection molding machine.

In the figure, the screw 1 is connected to the rod 6,
The inside of the screw cylinder 2 can be moved in the axial direction via the piston 4 by the pressure oil of the hydraulic cylinder 5, and the molten resin IO
can be injected into a cavity 9 of a mold 8 through a nozzle 3.

Further, the screw 1 is rotationally driven by a hydraulic motor 12 via a spline shaft 11. The granular or powdered raw material resin supplied from the hopper 13 into the screw cylinder 2 is
As the screw l rotates, it is sent forward (leftward in the figure), melted, and pushed out to the tip of the screw l. The molten resin pushed out to the tip pushes the screw l back (to the right in the figure) and stops at a predetermined metering completion position.

On the other hand, a member 14 is attached to a part of the screw 1 or the rod 6, and is connected to a screw position detector 15.

In the pressure control device according to the present embodiment shown in FIG. 1, the screw position detector 15 detects the position of the screw 1 during injection, and when the screw 1 reaches the preset pressure holding switching position, the injection pressure A signal is output to the command unit 16,
The injection pressure command device 16 issues an injection pressure command signal e set that is a time function.

On the other hand, the pressure inside the hydraulic cylinder 5 is constantly detected by a pressure detector 17, and the detection signal is sent to a comparator 18. The comparator 18 sends the output signal of the pressure detector 17 to the injection pressure command The deviation e1 is calculated by subtracting the command signal e from the command signal e set. The controller 19 controls the deviation e1
As input, PIDM? 1l (P--proportional, I-integral, D--differential).

Further, the command signal e set output from the injection pressure command device 16 is input to a feedforward compensator 20 that outputs a feedforward signal e, according to a predetermined function, and the output signal from the controller 19 and the feedforward signal e Forward signal e.

are added by an adder 21, and the output from the adder 21 is controlled by an amplifier 22 and input to a proportional electromagnetic pressure valve 23. This proportional electromagnetic pressure valve 23 adjusts the pressure of the hydraulic cylinder 5 approximately in proportion to the input. Pressure oil is supplied from the hydraulic source 24 to the hydraulic cylinder 5.

Here, the feedforward compensator 20 in the present invention receives a command signal e3 from the injection pressure command unit 16, for example.
．． ．． A feedforward signal e is output in accordance with the number of broken lines in consideration of the input/output characteristics of the proportional electromagnetic pressure valve 23. In other words, the input current/output pressure characteristics of the proportional electromagnetic pressure valve 23 form a curve as shown in FIG. If it is approximated by the so-called number of broken lines that changes, the command signal e sat and the feedforward signal e that become the target pressure.

The number of line intervals is obtained between

When the command signal e_set is outputted from the command unit 16 in this manner, the feedforward compensator 20 outputs a feedforward signal 6.set according to the number between the broken lines. Calculate and output.

However, if this feedforward signal et is input directly to the proportional electromagnetic pressure valve via an amplifier, it will be affected by changes in oil temperature as mentioned above, and the disadvantages of proportional electromagnetic pressure valves are ■ Variations due to individual differences and aging ■ Variations due to hysteresis still occur, and a difference occurs between the pressure command value e ssL and the actual pressure in the feedforward signal e. When this difference occurs, the comparator 18
A deviation e occurs in the output of the controller 19, which is compensated for by the control operation of the controller 19, and then added to the adder 21 to generate the feedforward signal e.

is corrected. Therefore, the above system? Is the feedback system so that the injection pressure matches the command injection pressure by the action of the IL device 19, that is, so that the deviation eb becomes zero? 11.

According to the present invention, since feedback control is performed only for the excess or deficiency of these feedforward amounts, the offset can be considerably small even if the controller 19 is proportionally controlled, for example. However, since the offset is small, the control gain can be lowered, thereby improving the stability.

In addition, although the present invention is applied to a pressure control device for a hydraulic cylinder used in an injection molding machine as an embodiment of the present invention, the present invention is not limited to the above embodiment. Of course, the present invention can also be applied to, for example, a pressure side jTj device of a hydraulic cylinder in a hydraulic system such as a construction machine.

(Effects of the Invention) As described above in detail, the present invention provides the following effects.

(1) Feedforward compensation is performed using a feedforward signal that takes into account the characteristics of the proportional solenoid pressure valve, and feedback control is added only for the excess and deficiency, thereby eliminating individual differences and hysteresis, which are the shortcomings of proportional solenoid pressure valves. , it is possible to compensate for control fluctuations due to aging.

(2) Even though an inexpensive proportional solenoid pressure valve is used instead of an expensive servo valve, high-precision pressure control is now possible, so the advantages of the proportional solenoid pressure valve over the servo valve are utilized. This leads to improved reliability due to low cost and resistance to contamination of hydraulic fluid.

[Brief explanation of drawings]

Fig. 1 is a system diagram in which a control device according to an embodiment of the present invention is incorporated into an injection molding machine, Fig. 2 is an input/output characteristic diagram of a proportional electromagnetic pressure valve used in the present invention and conventionally used, and Fig. 3 4 and 4 are block diagrams of different conventional pressure control devices,
FIG. 5 is an explanatory diagram showing response characteristics to a pressure command when closed loop control is performed using a proportional electromagnetic pressure valve. Explanation of main parts of the diagram 16 - (injection pressure) command unit 17 - pressure detector 18 - comparator 19 - controller 20 - feedforward compensator 21 - adder 23 - proportional electromagnetic pressure valve Patent application People Mitsubishi Heavy Industries, Ltd. Figure 2 Figure 5 Time

Claims (1)

[Claims] a feedforward compensator that outputs a feedforward signal in response to a command signal from a pressure command device; a controller that performs feedback control based on a deviation signal between the command signal and the output signal of the pressure detector; 1. A pressure control device for a hydraulic cylinder, comprising a proportional electromagnetic pressure valve that adjusts the pressure in the hydraulic cylinder based on an output signal from a controller.