JPH07293506A - Pressure control device of hydraulic device - Google Patents

Abstract

PURPOSE:To carry out a pressure control at a high accuracy and a high responsiveness while preventing a hunting. CONSTITUTION:A hydraulic device to drive a load; a pressure detecting means 51 to detect the loading pressure Ps of the hydraulic device; an electromagnetic control valve 52 to control the feeding pressure to the hydraulic device; a deflection operating means 53 to operate the deflection from the difference between an instruction value P1 and the detected value Ps; a sampling means 54 to sample the deflection at a specific cycle; a compensating means 55 to operate the compensating value according to the amount and the cycle of the sampled deflection; and an adding means 56 to output a control signal Pc adding the output of the compensating means and the instruction value P1 to the electromagnetic control valve 52; are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a pressure control device for a hydraulic device which controls the drive of a hydraulic actuator by a closed loop or feedback of pressure.

[0002]

2. Description of the Related Art In a hydraulic actuator including a non-linear element such as a sliding resistance or a hydraulic device using a highly viscous fluid as a working fluid, it is disclosed in Japanese Patent Laid-Open No. 3-255205 which controls pressure with high accuracy. It has been known.

To explain this, referring to FIG.
In the hydraulic system in which the pressure generated by the pump 1 is supplied to the cylinder 5 after the direction is selected by the switching valve 94 and the load 6 is driven, based on the deviation between the detected value of the pressure sensor 7 and the command value P _1. The electromagnetic relief valve 93 is driven.

The output of the pressure sensor 7 is input to the characteristic converter 92 and the PID compensator 91, respectively, and the detected pressure is shown in FIG.
If it is in the shaded area shown in Fig. 1, the first switches 97a and 97b are closed to perform closed loop control, while if not, the second switch
The switches 98a and 98b are closed to perform open loop control.

When the deviation is small, the PID compensator 91 compensates for the offset (steady deviation) by automatically switching between the closed loop control and the open loop control according to the magnitude of the deviation, while the deviation is large. In that case, the response characteristic is improved by the open loop control.

[0006]

By the way, the magnitude and polarity of the compensation amount during feedback control depend on the constants of the control circuit. By increasing these constants, the response characteristics and the offset (steady deviation) can be improved. However, if there are non-linear elements in the control system (relief valve response characteristics, actuator sliding resistance, etc.), the control system will not be able to follow the changes in the magnitude and polarity of the compensation amount, and the change in the compensation amount will further increase. It may become violent and cause hunting or oscillation, and in order to suppress such hunting, the control constant must be reduced and the response characteristics and offset may not be sufficiently improved.

Further, although the pressure characteristic of the electromagnetic relief valve 93 can secure the linearity in the high pressure region, it becomes non-linear in the low pressure region. Therefore, in the conventional pressure control device, the closed loop is changed to the open loop. In the case of switching the control, or vice versa, in order to suppress the disturbance of the control pressure at the time of switching, it is necessary to set the response characteristic in the closed loop control low for the above reasons.

However, when the response characteristic of the closed loop is set low, the pressure fluctuates within the closed loop control region, and when the fluctuation period exceeds the closed loop response period, it takes time for the control pressure to stabilize. If the control gain is set low and the control system has a non-linear element due to the sliding resistance of the cylinder 5 or the like, the cylinder 5
If the deviation due to an unexpected disturbance added to the constant pressure continues for a certain period of time, the integral compensation amount suddenly increases and decreases, so that the control pressure becomes unstable and hunting may occur.

Therefore, the present invention has been made in view of the above problems, and provides a pressure control device for a hydraulic device that suppresses hunting even when an unexpected disturbance is applied and has high response characteristics and accuracy. The purpose is to do.

[0010]

The first invention, as shown in FIG. 1, is a hydraulic device for driving a load, a pressure detecting means 51 for detecting a load pressure P _S of the hydraulic device, and a hydraulic pressure. An electromagnetic control valve 52 for controlling the supply pressure to the device, and a means for feedback controlling the electromagnetic control valve 52 so that the detection value P _S of the pressure detection means 51 matches the command value P _{1 of the} pressure are provided. In the pressure control device, a deviation calculating means 53 for calculating a deviation from the difference between the command value P ₁ and the detected value P _S , a sampling means 54 for sampling the deviation at a predetermined cycle, the sampled deviation and the cycle Compensation means 55 for calculating a compensation value according to the above, and addition means 5 for adding the output of the compensation means and the command value and outputting the result to the electromagnetic control valve.
6 and 6.

In a second aspect based on the first aspect, the compensating means generates a compensation value based on a ramp function according to the magnitude of the deviation.

In a third aspect based on the second aspect, the compensating means generates a compensation value with a ramp function according to the magnitude of deviation until a predetermined time period according to the sampling period, This compensation value is held until the above cycle.

The fourth invention is the first to third inventions.
In any one of the inventions, the sampling means sets the cycle according to the response characteristics of the hydraulic device.

[0014]

Therefore, according to the first aspect of the present invention, the compensating means calculates the compensation value according to the magnitude of the deviation calculated by the deviation calculating means based on the load pressure and the command value and the sampling period. Is added by an adder and output to the electromagnetic control valve. It becomes possible to correct the command value with the compensation value calculated for each sampling cycle and perform open loop control,
It is possible to perform accurate pressure control while suppressing a sudden change in the command value and suppressing hunting.

In a second aspect based on the first aspect, the compensating means generates a compensation value based on a ramp function according to the magnitude of the deviation, and suppresses a sudden change in the command value for control. It is possible to suppress hunting of the system and accurately control the pressure.

According to a third aspect of the present invention, in the second aspect, the compensating means generates a compensation value based on a ramp function according to the deviation until a predetermined time according to the sampling period, and then the compensation value is generated. Is held up to the above cycle and the control signal is held at a constant value after a lapse of a predetermined time. Therefore, even if the response speed of the control system is slow, hunting can be suppressed and highly accurate pressure control can be performed.

The fourth invention is the first to third inventions.
In any one of the inventions described above, when the response characteristic of the hydraulic device is low, the sampling cycle is shortened, while when the response characteristic of the hydraulic device is high, the sampling cycle is extended to increase the hydraulic pressure. Stable pressure control can be performed according to the response characteristics of the device.

[0018]

2 to 3 show an embodiment of the present invention.

In FIG. 2, the hydraulic pressure generated by the pump 1 is supplied to the cylinder 5 after the direction is selected by the switching valve 4 and drives the load 6.

The pressure applied to the cylinder 5 is adjusted by returning a part of the working fluid from the pump 1 to the tank 2 via the proportional electromagnetic relief valve 3 as an electromagnetic control valve, and is detected by the pressure sensor 7. Cylinder 5 load pressure P _S
Based on the above, the controller 8 as the pressure control device drives the proportional electromagnetic relief valve 3 to control the pressure.

The controller 8 detects the pressure P _S is the command value P ₁ of the pressure sensor 7 based on the command value P ₁ of the input pressure
A control signal P _C that satisfies the above condition is output to the proportional electromagnetic relief valve 3.

As shown in FIG. 3, from the command value P ₁ input to the controller 8 and the detected pressure P _S fed back, the adder 12 as the deviation calculating means calculates the deviation Δe from the command value P ₁ .

The deviation Δe is read by the sampler 11 as sampling means at every predetermined sampling period T, and the read deviation Δe is inputted to the ramp function generator 10 as compensating means.

The ramp function generator 10 generates a compensation value Δp according to the magnitude of the read deviation Δe and the cycle T, and as shown in FIG. 4, up to a predetermined time of T / 2. Deviation of compensation value Δp from 0 by Δe (or −Δ
This value (Δp = Δe) is held until the cycle T after increasing or decreasing to e), and the compensation value Δp gradually changes until the time T / 2, and then the deviation Δe ( Alternatively, it is held at a constant value of −Δe).

Compensation value Δ generated by the ramp function generator 10
p is converted by the converter 9b into a command value of pressure according to the control system, that is, according to the characteristics of the proportional electromagnetic relief valve 3 and the cylinder 5.

On the other hand, the command value P ₁ input to the controller 8 is similarly converted into a pressure value by the converter 9a, and the converted command value P ₁ 'and the compensation amount ΔP' are added by the adder 13. , Proportional solenoid relief valve 3 as control signal P _C
Is output to.

In the pressure control device configured as described above, when the detected pressure P _S deviates from the command value P ₁ and the deviation Δe is read by the sampler 11, the ramp function generator 1
The compensation value Δp from 0 is held at a constant value Δe after changing until time T / 2, and open loop control is performed based on the deviation Δe sampled at each cycle T.

Since the compensation value Δp changes gently until time T / 2, a non-linear element (the response characteristic of the proportional electromagnetic relief valve 3 or the sliding of the cylinder 5 is added to the control system including the proportional electromagnetic relief valve 3 and the cylinder 5). (Such as resistance) or when an unexpected disturbance is applied to the cylinder 5, a rapid change in the control signal P _C is suppressed, so that hunting of the control system is prevented and stable control is performed. In addition, the pressure control accuracy is not affected by the response characteristics of the proportional electromagnetic relief valve 3,
Highly accurate pressure control can be performed.

The deviation Δe sampled in the cycle T
Since the periodic open loop control is performed based on the above, the hunting due to the change of the load condition can be prevented to cope with a wide range of load conditions like the closed loop control in the conventional example, and the ramp function generator 10 can Since the compensation value Δp is held at a constant value every T / 2, it is possible to prevent hunting and perform highly accurate pressure control even when the response speed of the control system is low.

Here, the sampling cycle T is appropriately set in accordance with the load condition. For example, when the response characteristic of the cylinder 5 is low, the cycle T is reduced, while when the response characteristic is also high. By increasing the cycle T, stable control can be performed according to the load condition.

FIG. 5 shows another embodiment, showing an example of control in the case where the controller 8 in the first embodiment is constituted by a microcomputer, and other configurations are the same as those in the first embodiment. is there.

The flowchart of FIG. 5 is executed every predetermined time Δt of the counter t, and will be described in detail below with reference to this figure.

In step S1, the deviation Δe is calculated from the input command value P ₁ and the detected pressure P _S read from the pressure sensor 7, and in step S2 it is determined whether the value of the counter t is equal to or greater than the cycle T. If the counter t is equal to or longer than the cycle T, the counter t is reset and the next cycle is started (step S3).

In step S4, the counter t and the cycle T / 2 are set.
When the counter t is less than T / 2, the process proceeds to step S5, while if not, step S6.
Go to processing.

In step S5, the compensation value Δp is calculated based on the ramp corresponding to the magnitude of the deviation Δe, like the ramp function generator 10 shown in the first embodiment. The compensation value Δp is the deviation Δe. Is defined in advance as a function of the counter t using the parameter as a parameter, and the compensation value Δp gradually changes to the deviation Δe or −Δe while the counter t is up to T / 2.

On the other hand, in step S6, the counter t is T /
If it is 2 or more, the compensation value Δp becomes the deviation Δe calculated in step S1, and in these steps S5 and S6, the compensation value Δp is calculated based on the ramp function similar to FIG. 4 of the first embodiment.

A value obtained by adding the converted pressure command value P ₁ 'to the compensation amount ΔP' thus calculated is calculated as a control signal P _C (step S7), and based on the control signal P _C in step S8. After the proportional electromagnetic relief valve 3 is driven, a predetermined time Δt is added to the counter t in step S9 to prepare for the next process.

By repeating the above steps S1 to S9, the compensation value Δ is adjusted by the ramp according to the magnitude of the deviation Δe sampled for each cycle T as in the first embodiment.
By gradually changing p, open-loop control can be performed, hunting can be prevented during transient response or when disturbance is received, and high-precision control can be performed while ensuring high response characteristics. is there.

FIG. 6 shows still another embodiment, in which the first
The load 6 in the embodiment is replaced with a cylinder 60 used in an injection molding machine or the like, and a pressure sensor 7 is arranged in the cylinder 60 to directly detect the pressure applied to the load. This is similar to the first embodiment.

Since the closed loop control for changing the command value of the pressure is performed based on the directly detected load pressure, it is high even when the sliding resistance of the cylinder 5 and the control characteristic of the proportional electromagnetic relief valve 3 include a non-linear element. It is possible to control with high accuracy and high response characteristics.

Although the proportional electromagnetic relief valve 3 is disclosed as an electromagnetic control valve in the above embodiment, it is not shown in the drawings, but it is not disclosed in JP-A-2-72201 and JP-A-4-210.
A control valve as disclosed in Japanese Patent Application Publication No. 180 or Japanese Patent Application Laid-Open No. Hei 5-141572 can be adopted. In this case, since it has a pressure override characteristic superior in linearity as compared with the above-mentioned embodiment, it affects the flow rate. It is possible to perform highly accurate pressure control in proportion to the command value P ₁ without receiving the pressure change, and the converter 9 in the first embodiment.
The control system can be easily changed by changing the set values of a and 9b, that is, the proportional electromagnetic relief valve 3 and the cylinder 5
Can be changed to other elements.

Further, although the ramp function shown in FIG. 4 is shown as a linear function, it can be replaced with a curve or the like as appropriate in accordance with the characteristics of the control system although not shown, and the maximum compensation value Δp is similarly obtained. The value can also be obtained by multiplying the deviation Δe by a predetermined constant according to the response characteristic of the control system.

[0043]

As described above, the first aspect of the present invention controls the hydraulic device for driving the load, the pressure detecting means for detecting the load pressure P _S of the hydraulic device, and the supply pressure to the hydraulic device. In a pressure control device comprising an electromagnetic control valve and means for feedback controlling the electromagnetic control valve so that the detection value P _S of the pressure detecting means matches the command value P ₁ of pressure, the command value P ₁ Deviation calculating means for calculating a deviation from a difference from the detected value P _s , sampling means for sampling the deviation at a predetermined cycle, compensating means for calculating a compensation value according to the sampled deviation and the cycle, It is possible to perform an open loop control by adding an output of a compensating unit and an adding unit for adding the command value to the electromagnetic control valve and correcting the command value with the compensation value calculated for each sampling period. It becomes possible, with the magnitude of the deviation Since the compensation value is prevented from changing abruptly according to the cycle, it is possible to perform high-precision pressure control while preventing hunting even when the hydraulic device has a non-linear element such as sliding resistance. Since there is no switching from the open loop to the closed loop as in the prior art, it is possible to prevent disturbance of the control system and obtain smooth control characteristics.

In a second aspect based on the first aspect, the compensating means generates a compensation value based on a ramp corresponding to the magnitude of the deviation, and a rapid change in the command value is suppressed. The response characteristics can be secured while preventing hunting of the control system, and stable control characteristics can be obtained.

In a third aspect based on the second aspect, the compensating means generates a compensation value with a ramp according to the magnitude of the deviation until a predetermined time period according to the sampling period, and then the compensation is performed. Since the value is held up to the above cycle and the control signal is held at a constant value after a lapse of a predetermined time, it is possible to follow up while suppressing hunting even in a control system with a slow response speed, which makes it possible to achieve high accuracy. Pressure control can be performed.

Further, a fourth invention is the above-mentioned first to third inventions.
In any one aspect of the present invention, the sampling means can perform pressure control according to the response characteristic of the load by setting the cycle according to the response characteristic of the load, and can cope with a wide range of load conditions. it can.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is a block diagram of a hydraulic device showing an embodiment of the present invention.

FIG. 3 is a block diagram showing a controller.

FIG. 4 is a characteristic diagram of a ramp function generator.

FIG. 5 is a flowchart of control showing another embodiment.

FIG. 6 is a block diagram showing another embodiment.

FIG. 7 is a block diagram showing a conventional example.

FIG. 8 is a graph similarly showing control characteristics.

[Explanation of symbols]

 3 Proportional Electromagnetic Relief Valve 5 Cylinder 7 Pressure Sensor 8 Controller 10 Ramp Function Generator 11 Sampler 12 Subtractor 13 Adder 51 Pressure Detection Means 52 Electromagnetic Control Valve 53 Deviation Calculation Means 54 Sampling Means 55 Compensation Means 56 Addition Means

Claims (4)

[Claims] 1. A hydraulic device for driving a load, a pressure detecting means for detecting a load pressure of the hydraulic device, an electromagnetic control valve for controlling a supply pressure to the hydraulic device, and a detecting means for detecting the pressure. In a pressure control device comprising means for feedback controlling an electromagnetic control valve so that the value matches a pressure command value, a deviation calculation means for calculating a deviation from a difference between the command value and a detected value, and a predetermined cycle And sampling means for sampling the deviation, compensating means for calculating a compensation value according to the sampled deviation and cycle, and output of the compensating means and the command value are added and output to the electromagnetic control valve. A pressure control device for a hydraulic device, comprising: an adding means. 2. The pressure control device for a hydraulic device according to claim 1, wherein the compensation means generates a compensation value based on a ramp function corresponding to the magnitude of the deviation. 3. The compensating means generates a compensation value by a ramp function according to the magnitude of deviation until a predetermined time according to the sampling cycle, and then holds the compensation value up to the cycle. The pressure control device for a hydraulic device according to claim 2. 4. The pressure control device for a hydraulic device according to claim 1, wherein the sampling means sets the cycle in accordance with a response characteristic of the hydraulic device. .