JPH04251306A - Method for controlling position of hydraulic cylinder - Google Patents

Abstract

PURPOSE:To highly precisely control the position of a hydraulic cylinder with a simple device. CONSTITUTION:This method for controlling the position of a hydraulic cylinder 1 which controls the stroke of the cylinder 1 to an aimed value in such a way that a stroke detecting section 7 detects the actual stroke of the cylinder 1 and a control section 6 intermittently supplies hydraulic oil to the cylinder 1 so as to eliminate the difference between the actual stroke of the cylinder 1 detected by the section 7 and the aimed value by giving drive signals to the driving sections of the 1st and 2nd solenoid valves 51 and 52 for individually and periodically turning on and off the valves 51 and 52 changes the duty ratio between the drive signals of the valves 51 and 52 in accordance with the difference. In addition, the control section 6 learns the relation between the turning on/off periods of the drive signals of the valves 51 and 52 and the stroke changing speed on the basis of the information regarding the turning on/off periods of the valves 51 and 52 and regarding the stroke detected by the section 7 and controls the turning on/off periods on the basis of the learnt relation.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention supplies hydraulic oil intermittently to a hydraulic cylinder by periodically turning on and off a driving part of a solenoid valve. The present invention relates to a hydraulic cylinder position control method for controlling the stroke of a hydraulic cylinder to a target value. 2. Description of the Related Art A continuous casting apparatus is equipped with a hydraulic cylinder for correcting the taper of the short side of a mold. Such a hydraulic cylinder is adapted to push and pull the short side of the mold by reciprocating the piston rod, thereby correcting the taper of the short side of the mold. Methods for controlling the position of the piston rod of a hydraulic cylinder include a hydraulic servo control system that combines a servo valve and a hydraulic cylinder, a direct-acting cylinder control system that uses a stepping cylinder, or a solenoid valve that performs on/off control. Generally, the position of the hydraulic cylinder is controlled using an on/off control system that combines a hydraulic cylinder and a hydraulic cylinder. [0004] In the hydraulic servo control system, a servo valve switches the direction of supply of hydraulic oil to the hydraulic cylinder and adjusts the amount of supply, thereby controlling the position of the piston rod in feedback. The linear cylinder control system includes a ball screw whose axis is rotated by a pulse motor;
The nut of the ball screw is built into the hydraulic cylinder and includes a switching valve that moves in the axial direction of the ball screw by rotation of the axis of the ball screw to switch the flow direction of the hydraulic oil and adjust the flow rate of the hydraulic oil. , the position of the piston rod is feedback-controlled by operating the piston rod based on pressure fluctuations inside the cylinder due to movement of the switching valve. In the on-off control system, a solenoid valve is turned on and off to switch the direction of supply of hydraulic oil to the hydraulic cylinder and adjust the amount of supply, thereby controlling the position of the piston rod. [0005] However, in the method of controlling the position of the piston rod of a hydraulic cylinder using a hydraulic servo system as described above, the device is complicated, and there is There was a problem in that position control accuracy was poor due to operation delays due to compression of hydraulic oil in the piping. In addition, in the method of position control using a stepping cylinder as described above, since a pulse motor is attached to the hydraulic cylinder, the stepping cylinder cannot be used in a hot and humid environment such as inside a mold cover. There was a problem in that there were many restrictions on installation as the cylinder became larger. Furthermore, in the above-mentioned method of controlling the position by turning the solenoid valve on and off using the on-off control system, hunting (limit cycle) is likely to occur, and the position control is affected by the delay in the operation of the solenoid valve and the variation in the flow rate characteristics of the solenoid valve. There was a problem with poor accuracy. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for controlling the position of a hydraulic cylinder that is executable with a simple device and has high accuracy. Means for Solving the Problems [0008] A first method for controlling the position of a hydraulic cylinder according to the present invention detects the stroke of a hydraulic cylinder and eliminates the deviation between the detected stroke and its target value. , a hydraulic cylinder that intermittently supplies hydraulic oil to the hydraulic cylinder by applying a drive signal to the drive unit to periodically turn on and off the drive unit of the electromagnetic valve, and controls the stroke of the hydraulic cylinder to a target value. The position control method is characterized in that a duty ratio of a drive signal for the electromagnetic valve is changed depending on the deviation. A second hydraulic cylinder position control method according to the present invention adjusts the on/off cycle of the drive signal and the stroke of the hydraulic cylinder based on information about the on/off cycle of the drive signal of the electromagnetic valve and the detected stroke. The present invention is characterized by learning the relationship with the rate of change and correcting the on-off cycle based on the learned relationship. [Operation] In the first hydraulic cylinder position control method according to the present invention, the duty ratio of the solenoid valve drive signal is changed depending on the deviation between the detected stroke and its target value. If the duty ratio is made smaller as the deviation becomes smaller, the ON time of each drive signal becomes shorter, which slows down the rate of change in the stroke of the hydraulic cylinder, so that the stroke relative to the target value becomes smaller. Excess amount of is suppressed. Further, in the second hydraulic cylinder position control method according to the present invention, the on-off cycle and the hydraulic cylinder position are determined based on information about the on-off cycle of the drive signal of the solenoid valve and the detected stroke. Since the relationship with the stroke change speed is learned, when the on-off cycle is corrected based on the learned relationship, the stroke change speed is adjusted to an appropriate value. [Embodiments] The present invention will be specifically explained below based on drawings showing embodiments thereof. FIG. 1 is a schematic block diagram showing the configuration of a position control device to which a method for controlling the position of a hydraulic cylinder according to the present invention is applied. In the figure, numeral 1 indicates a hydraulic cylinder, and the hydraulic cylinder 1 is of a double-acting, single-rod type. The piston rod 10 moves back and forth a pressing part 2 attached to its tip by its double action, thereby pressing a short side mold (not shown) of the continuous casting apparatus. The hydraulic cylinder 1 has a piston rod 10
It has a first oil chamber 11 on one side and a second oil chamber 12 on the opposite side. A hydraulic pump 3, which is a hydraulic pressure generation source, supplies hydraulic oil in a tank T to a first oil chamber 11 and an inlet of a first valve 51, which is a two-port electromagnetic valve, through a check valve 4. The hydraulic oil sent out from the hydraulic pump 3 is supplied to the first oil chamber 11 and the first valve 51 via the check valve 4. Furthermore, the outlet of the first valve 51 is connected to the inlet of a second valve 52, which is a two-port solenoid valve, and the second oil chamber 12, and the outlet of the second valve 52 is connected to the tank T. There is. Therefore, the hydraulic oil flowing out from the first valve 51 flows into the second oil chamber 12 and the second valve 52, and the hydraulic oil flowing out from the second oil chamber 12 flows into the second valve 52. . The hydraulic oil flowing out from the second valve 52 is returned to the tank T. The first valve 51 and the second valve 52 are individually turned on and off by on/off control signals given from the control section 6. These first valves 51
The and second valves 52 each operate to allow hydraulic oil to flow in one direction when turned on, and to cut off the flow of hydraulic oil when turned off. Further, a stroke detection section 7 consisting of a differential transformer for detecting the stroke of the piston rod 10 is attached to the hydraulic cylinder 1, and a detection signal from the stroke detection section 7 is sent to the control section 6. It has become. The control unit 6 performs on/off control of the first valve 51 and the second valve 52 based on the detection signal of the stroke detection unit 7, and adjusts the stroke of the piston rod 10. In the position control device configured as above,
When both the first valve 51 and the second valve 52 are off, no hydraulic oil flows through them, so the piston rod 10 is in a stopped state. Further, when the first valve 51 is on and the second valve 52 is off, hydraulic oil flows into both the first oil chamber 11 and the second oil chamber 12, but the first oil chamber 11 is in the second oil chamber. Since the pressure receiving area is smaller than that of 12 by the cross-sectional area of the piston rod 10, the second
The acting force on the oil chamber 12 side becomes larger than the acting force on the first oil chamber 11 side, and the piston rod 10 moves in the direction of protruding outward. On the contrary, when the first valve 51 is off and the second valve 52 is on, the hydraulic oil flows only into the first oil chamber 11, and the acting force on the first oil chamber 11 side causes the hydraulic oil to flow into the first oil chamber 11. Since the hydraulic oil in the second oil chamber 12 flows out through the second valve 52, the piston rod 10 moves inwardly. Next, the configuration of the aforementioned control section 6 will be explained. FIG. 2 is a schematic block diagram showing the configuration of the control section 6 to which the first hydraulic cylinder position control method of the present invention is applied. The control section 6 includes a subtraction section 61 and a frequency function section 6.
2 and a signal oscillation section 64. The subtraction unit 61 includes:
A stroke target value is supplied from an input section 8 that inputs a target value of the stroke of the piston rod 10, and a stroke detection signal is supplied from a stroke detection section 7. The subtraction section 61 subtracts the detected stroke value from the stroke target value to obtain the stroke deviation ε, and provides data of the obtained stroke deviation ε to the frequency function section 62. The frequency function section 62 calculates the on/off frequency of the first valve 51 or the second valve 52 from the stroke deviation ε using a function to be described later, and uses the data of the calculated frequency and
The data on the stroke deviation ε is provided to the signal oscillation section 64. The signal oscillation unit 64 determines whether the stroke deviation ε given from the frequency function unit 62 is positive or negative, determines the direction in which the stroke deviation ε becomes zero as the direction in which the piston rod 10 is to be moved, and moves the piston in that direction. rod 1
0, an on/off signal of the frequency specified by the frequency data is given to the first valve 51 or the second valve 52. In this case, the magnitude of the stroke deviation ε is determined, and a characteristic is given to the on-off signal such that the duty ratio of the on-off signal becomes smaller as the stroke deviation ε becomes smaller. Next, the function of the frequency function section 62 will be explained. FIG. 3 is a graph showing the function of the frequency function section 62, and shows the relationship between the on-off frequency f of the first valve 51 or the second valve 52 on the vertical axis and the stroke deviation ε on the horizontal axis. In FIG. 3, the on-off frequency has a characteristic that it increases as the stroke deviation ε increases toward the positive and negative sides.
When the absolute value of f becomes equal to or greater than a predetermined value, the on-off frequency f saturates to a constant value. In a function with such characteristics, the on-off frequency f decreases as the absolute value of the stroke deviation ε becomes smaller, so when the stroke deviation ε is small, that is, the closer the detected stroke is to the stroke target value, the control period becomes shorter. The longer the time, the less responsive it becomes. To prevent this, a lower limit of the on/off frequency f is set, and thereafter the duty ratio of the on/off signal is adjusted. The on-off signal given such a frequency is given the characteristic that the duty ratio of the on-off signal becomes smaller as the stroke deviation ε becomes smaller, as described above, so by changing the duty ratio, , in the first valve 51 or the second valve 52 to which the on-off signal is applied, the closer the detected stroke is to the stroke target value, the shorter the ON time each time is, and thereby the rate of change in the stroke of the hydraulic cylinder is reduced. Since the stroke becomes slower, the amount of stroke that exceeds the stroke target value can be suppressed. FIG. 4 is a schematic block diagram showing the configuration of the control section 6 to which the second hydraulic cylinder position control method of the present invention is applied, and the same parts as in FIG. omitted. Reference numeral 63 in the figure is a learning control section that performs learning control of the on/off frequency.
The on-time and off-time data of the on-off signal oscillated from the oscillator are given. Learning control unit 6
3, learns the operating characteristics of the hydraulic cylinder 1 with respect to a predetermined on-off frequency f based on the stroke detection data and on-time and off-time data,
Based on this learning result, a correction coefficient for the on/off frequency f is determined, and the data of the determined correction coefficient is sent to the frequency function section 62.
It is designed to be given to Next, the learning control method in the learning control section 63 will be described in detail. First, in the cold state, the on-time T
ON and OFF time TOFF and one ON/OFF period (
Based on the stroke LA of the hydraulic cylinder 1 operated during TON+TOFF), the stroke change speed VF of the hydraulic cylinder 1 is determined using the following equation (1). [0030]VF=LA/(TON+TOFF)
...(1) [0031] Then, during actual position control in hot conditions, the obtained on-time TON and off-time TOFF and one on-off period (TON+T
Stroke L of hydraulic cylinder 1 operated during OFF )
Based on B, the stroke change speed V of the hydraulic cylinder 1 is determined using the following equation (2). [0032]V=LB/(TON+TOFF)
...(2) When the stroke change speed V is determined, a correction coefficient r is calculated to correct the on-off frequency f by dividing the stroke change speed VF by the stroke change speed V.
is determined, and the determined correction coefficient r is provided to the frequency function section 62. The frequency function section 62 multiplies the on-off frequency f obtained from the above-mentioned function by the correction coefficient r as shown in equation (3) below to obtain an on-off frequency correction value f1, and then calculates the on-off frequency correction value f1. The signal is given to the signal oscillation section 64. [0034] f1 = r・f (3) 00
35] The on-off frequency correction value f1 obtained in this way is corrected to be lower as the stroke change speed V becomes faster than the stroke change speed VF under the same on-off frequency condition, and the stroke change speed V becomes faster than the stroke change speed VF. It is set to be revised higher as it becomes slower than the above. The signal oscillator 64 provides the first valve 51 or the second valve 52 with an on/off signal having a frequency of the on/off frequency correction value f1. By performing such learning control, even if the operating characteristics of the solenoid valve change over time, it is possible to perform on-off control of the solenoid valve at a constant stroke change rate at an on-off frequency that compensates for the change over time. . Furthermore, some solenoid valves such as the first valve 51 and the second valve 52 described above have a large delay in operation with respect to on/off signals, but in such solenoid valves, the absolute value of the stroke deviation ε is small. If the on/off frequency is set high, hunting tends to occur due to the operation delay. Such hunting can be eliminated by giving the on/off signal a characteristic that turns off earlier by the amount of operation delay when the absolute value of the stroke deviation ε is small. [0038] As described in detail above, in the hydraulic cylinder position control method according to the present invention, the duty ratio of the drive signal of the electromagnetic valve is changed in accordance with the deviation between the detected stroke and its target value. However, if the duty ratio is made smaller as the deviation becomes smaller, the ON time of each drive signal becomes shorter, which slows down the rate of change in the stroke of the hydraulic cylinder. The amount of excessive stroke can be suppressed, and
The relationship between the on-off cycle of the solenoid valve and the rate of change in the stroke of the hydraulic cylinder is learned based on the information on the on-off cycle of the solenoid valve and the detected stroke, but the on-off cycle is corrected based on the learned relationship. , it is possible to perform highly accurate control such as adjusting the rate of stroke change to an appropriate value, and it is also possible to use commonly used solenoid valves, so it can be done with a simple device. The present invention has excellent effects such as being able to perform control.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the configuration of a position control device to which a hydraulic cylinder position control method according to the present invention is applied.

FIG. 2 is a schematic block diagram showing the configuration of a control section to which the first hydraulic cylinder position control method of the present invention is applied.

FIG. 3 is a graph showing a function of a frequency function part.

FIG. 4 is a schematic block diagram showing the configuration of a control section to which a second hydraulic cylinder position control method of the present invention is applied.

[Explanation of symbols]

1 Hydraulic cylinder 6 Control section 7 Stroke detection section 51 First valve 52 Second valve 63 Learning control section

Claims (2)

[Claims] [Claim 1] Detecting the stroke of a hydraulic cylinder,
intermittently feeding hydraulic oil to the hydraulic cylinder by applying a drive signal to the drive unit to periodically turn on and off the drive unit of the electromagnetic valve in order to eliminate the deviation between the detected stroke and its target value; A hydraulic cylinder position control method for controlling the stroke of the hydraulic cylinder to a target value, characterized in that a duty ratio of a drive signal for the electromagnetic valve is changed in accordance with the deviation. [Claim 2] An on/off cycle of a drive signal of a solenoid valve,
A claim characterized in that the relationship between the on-off cycle of the drive signal and the rate of change of the stroke of the hydraulic cylinder is learned based on information regarding the detected stroke, and the on-off cycle is corrected based on the learned relationship. 1. The method for controlling the position of a hydraulic cylinder according to 1.