JPH10288203A - Control method for hydraulic drive system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically regulate an offset quantity by setting an offset quantity against an electromagnetic proportional valve, providing an offset regulating means changing the offset quantity and outputting on the input side of the electromagnetic proportional valve, and changing over the offset quantity according to increase or decrease of a flow command value. SOLUTION: An offset quantity regulating part 11 automatically measures and memorizes the offset quantities A, B peculiar to an electromagnetic proportional valve, and changes over the offset quantity A or B according to increase or decrease of a flow command value given to a control device 10. Automatic measurement of the offset quantities A, B is periodically carried out. In the case of increase of the flow command value, the offset quantity regulating part 11 selects the offset quantity A and gives it to the electromagnetic proportional valve 23, and in the case of decrease of the flow command value, the offset quantity regulating part 11 selects the offset quantity B and gives it to the electromagnetic proportional valve 23. Hereby, the offset quantity can be automatically regulated, and the labor for the regulating operation can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control system for a hydraulic drive system, and more particularly to a control system suitable for controlling an injection speed in an injection cylinder of an injection molding machine.

[0002]

2. Description of the Related Art A conventional injection speed control method for an injection molding machine will be described with reference to FIG. 4, an injection speed control system includes a swash plate type variable displacement pump 21 for supplying hydraulic oil to an injection cylinder 20 and a variable displacement pump 2.
Drive piston 22 for displacing the position of the swash plate 1
And an electromagnetic proportional valve 23 for driving the drive piston 22
And a position detector 24 for detecting the position of the swash plate. Further, the detection value from the position detector 24 is fed back to the control device 26 to detect the difference from the flow command value by the subtracter 27, and this difference is given to the electromagnetic proportional valve 23 via the amplifier 28, The position of the swash plate is displaced by the electromagnetic proportional valve 23 to control the flow rate of hydraulic oil.

The operating oil from the variable displacement pump 21 is supplied to the injection cylinder 20 by switching the switching valves 29 and 30 or returned to the tank 31. The drive piston 22 and the proportional solenoid valve 23 are driven by hydraulic oil from a constant-pressure hydraulic source 32, and the return oil is returned to the tank 31. The variable displacement pump 21 is driven by a motor 33, and this return oil is also returned to the tank 31.

[0004]

As for the characteristics of the proportional solenoid valve, it is desirable that the input command value is proportional to the moving speed of the swash plate. However, in actuality, as shown in FIG. 5, the solenoid proportional valve has a swash plate between a direction in which the swash plate moves in a direction in which the flow rate increases and a direction in which the swash plate moves in a direction in which the flow rate decreases. There is an area that does not move, this is called the dead zone. In addition, the dead zone differs for each solenoid proportional valve, and there is a large difference between devices. This means that the speed control characteristics of the injection speed control system differ for each electromagnetic proportional valve used therein.

For this reason, conventionally, a fixed offset amount is added to the input of the proportional solenoid valve to allow for machine differences, or an operator manually adjusts the control system with time while operating the control system. Was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control system of a hydraulic drive system which can measure a dead zone inherent to an electromagnetic proportional valve and can automatically adjust an offset amount for correcting the dead zone. .

[0007]

According to the present invention, a swash plate type variable displacement pump for supplying hydraulic oil to a hydraulic cylinder, and a drive piston for displacing the position of the swash plate of the variable displacement pump are provided. An electromagnetic proportional valve for driving the drive piston, and a position detector for detecting the position of the swash plate, wherein the electromagnetic proportional valve based on a flow rate command value and a detection value from the position detector. In the hydraulic drive system that controls the flow rate of the hydraulic oil, at least two predetermined offset amounts are set for the electromagnetic proportional valve, and the at least two offset amounts are switched and output. Offset adjusting means is provided on the input side of the electromagnetic proportional valve, and the offset adjusting means switches the offset amount according to an increase or decrease of the flow rate command value. Hydraulic drive system control method according to claim bets is provided.

The offset adjusting means has a means for measuring and storing a flow command value to the electromagnetic proportional valve.
It is preferable that the offset amount is a command value of the solenoid proportional valve when the swash plate starts moving in the flow increasing direction or the flow decreasing direction in a state where the change of the flow command value is sufficiently gradual. This is because, when the swash plate is moved at a sufficiently low speed, the command value almost coincides with the command value when the swash plate starts to move as shown in FIG.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an example in which the present invention is applied to an injection speed control method of an injection molding machine similar to FIG. Therefore, the same parts as those in FIG. This embodiment uses the electromagnetic proportional valve 23
Is characterized in that the control device 10 includes an offset amount adjusting unit 11. The offset amount adjusting unit 11 automatically measures and stores the offset amounts A and B unique to the electromagnetic proportional valve as shown in FIG.
The switching of the offset amounts A and B is performed in accordance with the increase or decrease of the flow command value given to. Although the offset amount adjustment unit 11 for performing such an operation is illustrated in a simplified manner for convenience, it is actually realized by an electronic circuit having a storage device. Note that the offset amount A,
The automatic measurement of B is periodically performed when the injection molding machine is started.

FIG. 2 is a diagram for explaining the principle of the automatic measurement of the offset amounts A and B. The automatic measurement is performed by the steps shown in FIG.

First, automatic measurement of the offset amount will be described. The switching valve 29 is closed and the switching valve 30 is opened. At this time, the hydraulic oil discharged from the variable displacement pump 21 returns to the tank 31. In this state, the flow command value is gradually increased and decreased (step S1 in FIG. 3). Since the detection value of the position detector 24 is fed back, the swash plate position of the variable displacement pump 21 changes according to the flow rate command value, and the flow rate is controlled (step S2 in FIG. 3). During this time, the command to the electromagnetic proportional valve 23 is measured by the offset amount adjusting unit 11 (Step S3 in FIG. 3).

The relationship between the command value to the proportional solenoid valve 23 and the moving speed of the swash plate of the variable displacement pump 21 is as shown in FIG. 5, and if the change in the flow rate command value is sufficiently gentle, the swash plate is changed. The command value to the electromagnetic proportional valve 23 when the swash plate moves backward (flow rate decrease) and the command value to the electromagnetic proportional valve 23 when the swash plate moves backward (flow rate decrease) respectively correspond to both ends of the dead zone in FIG. I do. That is, when the swash plate is moved at a sufficiently low speed, the offset amount substantially coincides with the command value when the swash plate starts to move as shown in FIG. Offset amount adjustment unit 11
Stores the command values to the electromagnetic proportional valve 23 at this time as offset amounts A and B (step S4 in FIG. 3). The offset amounts A and B are values specific to the electromagnetic proportional valve.

Next, the flow rate control of the hydraulic oil based on the offset amount measured as described above will be described. In order to control the injection speed by the injection cylinder 20, the switching valve 29 is opened and the switching valve 30 is closed. The measured offset amounts A and B are switched by the offset amount adjusting unit 11 in accordance with the increase or decrease of the flow command value. That is, when the flow rate command value increases, the offset amount adjustment unit 11 selects the offset amount A and supplies it to the electromagnetic proportional valve 23. When the flow rate command value decreases, the offset amount adjustment unit 11 selects the offset amount A. B is selected and given to the electromagnetic proportional valve 23.

As described above, since the offset amount is switched in accordance with the increase or decrease of the flow command value, the characteristics of the electromagnetic proportional valve are automatically corrected, and the characteristic is uniform without being affected by the offset amount inherent to the electromagnetic proportional valve. Speed control characteristics can be obtained. This means that good speed control characteristics can be obtained even when an inexpensive electromagnetic proportional valve having a large machine difference is used.

Although the above embodiment has been described by applying the present invention to the hydraulic control system of the injection cylinder for controlling the injection speed of the injection molding machine, the present invention is not limited to this, and the present invention is not limited to this. The present invention can be applied to all hydraulic drive systems in which hydraulic control is performed by a variable displacement pump having.

[0016]

According to the present invention, in a hydraulic drive system in which hydraulic control is performed by a variable displacement pump having a swash plate controlled by an electromagnetic proportional valve, the offset amount inherent to the electromagnetic proportional valve is not affected. A control system of a hydraulic drive system having improved control characteristics can be provided. Since the adjustment of the offset amount is automatically performed, labor for the adjustment operation can be saved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration when the present invention is applied to an injection speed control system of an injection molding machine.

FIG. 2 is a view for explaining the principle of automatically measuring a dead zone of an electromagnetic proportional valve in the present invention.

FIG. 3 is a flowchart showing a procedure for automatically measuring an offset amount for compensating for a dead zone of an electromagnetic proportional valve according to the present invention.

FIG. 4 is a diagram showing a configuration of an injection speed control system of a conventional injection molding machine.

FIG. 5 is a diagram for explaining a dead zone of an electromagnetic proportional valve.

[Explanation of symbols]

 10, 26 Control device 11 Offset amount adjustment unit 20 Injection cylinder 21 Variable displacement pump 22 Drive piston 23 Electromagnetic proportional valve 24 Position detector 29, 30 Switching valve 31 Tank 32 Constant pressure hydraulic pressure source 33 Motor

Claims (2)

[Claims] 1. A swash plate type variable displacement pump for supplying hydraulic oil to a hydraulic cylinder, a driving piston for displacing a position of a swash plate of the variable displacement pump, and an electromagnetic for driving the driving piston. Proportional valve, including a position detector for detecting the position of the swash plate, controlling the electromagnetic proportional valve by a flow command value and a detection value from the position detector to control the flow rate of the hydraulic oil. In the hydraulic drive system, the offset adjusting means for setting at least two predetermined offset amounts with respect to the electromagnetic proportional valve, and switching and outputting the at least two offset amounts, comprises: The hydraulic drive system is provided on the input side, wherein the offset adjusting means switches the offset amount in accordance with an increase or decrease of the flow command value. Method. 2. The control method according to claim 1, wherein said offset adjusting means has means for measuring and storing a flow command value to said electromagnetic proportional valve, and wherein said at least two offset amounts are equal to said flow command. A control method for a hydraulic drive system, wherein the control value is a command value of an electromagnetic proportional valve when the swash plate starts moving in a flow increasing direction or a flow decreasing direction in a state where the value change is sufficiently gradual.