JPH07104728B2 - Servo valve neutral compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a servo for applying an offset voltage of a servo valve so that a fluid to an actuator is shut off when a deviation between a target set value and a feedback amount is zero. The present invention relates to a valve neutral compensation circuit.

B. Conventional Technology For example, an electro-hydraulic material testing machine has an actuator such as a hydraulic cylinder that applies a test load to a specimen, and the actuator is controlled by a servo valve. This servo valve functions as a so-called proportional control valve that is controlled to open and close by a current according to the deviation between the target set value and the feedback amount, and is configured to obtain a flow rate corresponding to this current value. For example, when the current i is (+), the control amount is insufficient with respect to the set value and the deviation is (+), so oil is flown in the (+) direction, and when the current is (-), the set value is On the other hand, the control amount is higher,
Since the deviation is (-), the oil flows in the (-) direction, and when the current is zero, the current control amount is equal to the set value and the deviation is zero. There is no such thing.

However, even if the servo valve current indicates the valve neutral position due to the condition of hydraulic pressure or oil temperature or the change over time of the servo valve, the oil may actually flow in either direction. Electric current
Only when i ₀ is supplied, the actuator is held, that is, held in that state. In other words, the actuator is held while the deviation between the target set value and the feedback amount is not zero, which adversely affects the accuracy of feedback control.

As will be described in detail with reference to FIG. 2, in FIG. 2, the displacement of the actuator 26 acting on the specimen 28 is detected by a piston displacement meter 29, and this displacement is fed back via a stroke amplifier 27. In the figure, when the current supplied to the servo valve 25 is zero in the figure, the deviation ε ₁ between the set value and the feedback amount at the addition point 21 is zero, and therefore it is originally The actuator 26 is held in its current position. However, if the servo valve is not in the true neutral position where it completely shuts off fluid such as oil even when the input current is zero due to the influence of changes in hydraulic pressure and oil temperature and the change with time of the servo valve as described above. While the current i ₀ is supplied to the servo valve 25, the servo valve 25 becomes the true neutral position and the actuator 26 is held.

Therefore, conventionally, in order to prevent such an error in the feedback control, the neutral adjustment trimmer 28a is provided in the preceding stage of the servo amplifier 24, and the servo valve 25 operates when the deviation ε ₁ and the output voltage E _{1 of the} amplifier 22 are zero. Offset voltage is added to the mating point 23 to achieve the true neutral position.
The correction current i ₀ is obtained by giving E ₂ . In FIG. 2, − represents an electric signal line, Is the hydraulic circuit Indicates a rigid body. Further, 30 is a load cell.

C. Problems to be Solved by the Invention However, since the current i ₀ changes with the conditions of hydraulic pressure and oil temperature or the change over time of the servo valve, the offset current E ₂ for flowing this current i ₀ is not constant. Absent. For this reason,
The operator had to manually operate the neutral adjustment trimmer 28 to give a predetermined offset voltage E ₂ each time the test was performed, which was extremely complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a neutral compensating circuit for a servo valve in which an offset voltage for compensating the servo valve to a neutral position can be set only by opening / closing a switch in order to solve the above problems.

D. Means for Solving Problems The present invention is provided in a feedback control system that controls an actuator by a servo valve that is opened / closed according to a deviation between a target set value and a feedback amount. In the neutral compensation circuit of the servo valve for applying the offset voltage to the servo valve so that the actuator is held at the target setting value when the actuator is held in the state where the deviation signal of Of the clock pulse from the clock oscillator while outputting a signal indicating that the deviation signal is larger than the reference value from the comparator when the comparator has a switching means and the switching means is on. Up-count, the comparator The up-down counter that down-counts the clock pulse from the clock oscillator while outputting the signal indicating that the deviation signal is smaller than the reference value, and the output signal of the up-down counter is input to the servo valve as the offset voltage. And a digital-to-analog converter.

E. Action When the switching means is operated, the comparator compares the deviation signal between the target set value and the feedback amount with the reference value, and indicates that the deviation signal is greater than the reference value zero (“H” level signal). , Or a signal indicating that the deviation signal is smaller than the reference value (“L” level signal ”is output. While the comparator outputs the signal indicating that the deviation signal is larger than the reference value zero, the up / down counter The clock pulse from the clock oscillator is up-counted, and the clock pulse from the clock oscillator is down-counted while the comparator outputs the deviation signal or the signal indicating that it is smaller than the reference value. Offset voltage is input to servo valve.

F. Example One example of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a feedback control system using the present invention. In FIG. 1, 11 is a summing point of a target set value of displacement of an actuator and the feedback amount, and 12 is a deviation ε from the summing point 11. An amplifier for amplifying ₁ is shown.
A servo amplifier 14 and a servo valve 15 are sequentially connected to the output side of the amplifier 12 through an addition point 13, and the oil whose flow rate is controlled by the servo valve 15 is supplied to an actuator 16 which drives a test piece 18. It has become so. The displacement of the actuator 16 is applied to the stroke amplifier 17 via the piston displacement gauge 19, and the output terminal of the stroke amplifier 17 is connected to the addition point 11 to form a known feedback loop.

Therefore, the valve neutral circuit according to the present invention is provided between the amplifier 12 and the addition point 13, and includes the comparator 1, the clock oscillator 2, the AND gates 3 to 6, the battery back-up up / down counter 7, the digital counter. -Analog converter (hereinafter, DA converter) 8
And a valve neutral switch 9 as a switching means. That is, the output terminal of the amplifier 12 is connected to the non-inverting input terminal of the comparator 1,
The inverting input terminal of the comparator 1 is grounded, and its output terminal is connected to one input terminal of the AND gate 3 and the inverting input terminal of the AND gate 4, respectively. The clock pulses from the clock oscillator 2 are input to the other input terminals of the AND gates 3 and 4, and these output terminals are connected to the input terminals of the AND gates 5 and 6, respectively. . The other input terminal of each of the AND gates 5 and 6 is grounded via the valve neutral switch 9.

Further, the output terminal of the AND gate 5 is connected to the up count terminal of the up / down counter 7, and the output terminal of the AND gate 6 is connected to the down count terminal of the up / down counter 7. The output terminal of the up / down counter 7 is connected to the DA converter 8, and the output terminal thereof is connected to the addition point 13. It should be noted that as the D-A converter 8, a converter that can take both positive and negative values for its output is used.

To explain this operation, assuming that the output voltage E ₁ of the amplifier 2 is (+) in the state where the valve neutral switch 9 is turned on at the stage of performing the feedback control while keeping the target set value constant, assuming that the output voltage E ₁ of the amplifier 2 is (+). Since the output signal is at "H" level, the clock pulse from the clock oscillator 2 is input to the up-count terminal of the up-down counter 7 via the AND gates 3 and 5. As a result, the up / down counter 7 counts up and D
The offset voltage E ₂ is increased to the (+) side via the −A converter 8. Therefore, the output signal ε ₀ of the addition point 13
And the correction current i ₀ also increases to the (+) side, and by driving the servo valve 15 to the (+) side, the displacement of the actuator 16 can be increased to the (+) side. That is,
Since the feedback amount increases to the (+) side, the deviations ε ₁ and E ₁ approach zero as the operation of the entire control system.

When E ₁ is (-), the output signal of the comparator 1 becomes "L" level, and the clock pulse is AND gate 4,
It is input to the down count terminal of the up / down counter 7 via 6 and the offset voltage E ₂ is increased to the (−) side via the DA converter 8. Therefore, ε ₁ and E ₁ approach zero due to the opposite operation.

At this time, the absolute value of the offset voltage E _{2 is} the number of up-count pulses or down-count pulses counted by the up-down counter 7, in other words, the comparator 1
The longer the period E ₁ that is the input of E is positive or negative, the larger. That is, the servo valve at zero input current
As the position of 15 (apparent neutral position) is farther from the true neutral position, the above period is longer, and the offset voltage E _2, that is, the magnitude of the correction current i ₀ , is the difference between the apparent neutral position and the true neutral position. The optimum value is automatically taken according to the difference, and the servo valve 15 is always kept accurately and in the true neutral position.

Thus, if the valve neutral switch 9 is turned off when ε ₁ and E ₁ are sufficiently zero, the valve neutral operation is automatically completed.

In this embodiment, if the up / down counter 7 and the AND gates 5 and 6 are backed up by the battery, the offset voltage E ₂ can be held even after the valve neutral switch 9 is turned off, and the test is interrupted or the set value is set. Even if is changed, the valve neutral operation can be performed without adjustment.

Further, although the above-mentioned embodiment is the case where the present invention is applied to the displacement feedback control system, it goes without saying that the present invention can also be applied to the load feedback control system. Further, the present invention is not limited to the material testing machine, but can be applied to the feedback control system of other devices and equipment. Furthermore, the present invention can be applied to a device using an electro-pneumatic servo valve.

G. Effect of the Invention Since the present invention is configured as described above, the servo valve can be controlled to the true neutral position only by operating the switching means, and the conventional complicated neutral position adjustment is unnecessary.

Further, if the switching means of the present invention is always operated at the start of the test by a command from a control circuit such as a personal computer, the neutral position compensation of the servo valve can be completely automated.

[Brief description of drawings]

FIG. 1 is a block diagram of a feedback control system of an electrohydraulic material testing machine using the present invention, and FIG. 2 is a block diagram of a feedback control system of a conventional electrohydraulic material testing machine having a valve neutral circuit. . 1 ... Comparator, 2 ... Clock oscillator 3-6 ... AND gate 7 ... Up / down counter 8 ... DA converter 9 ... Valve neutral switch 11, 13 ... Addition point, 12 ... Amplifier 14 …… Servo amplifier, 15 …… Servo valve 16 …… Actuator, 17 …… Stroke amplifier 18 …… Sample, 19 …… Displacement meter

Claims (1)

[Claims] 1. A feedback control system for controlling an actuator by a servo valve that is controlled to open and close according to a deviation between a target set value and a feedback amount, and a deviation signal between the target set value and the feedback amount is not zero. In the neutral compensation circuit of the servo valve that applies an offset voltage to the servo valve so that the actuator is held at the target set value when the actuator is held, a comparator that compares the deviation signal with the reference value is provided. When the switching means is on, the clock pulse from the clock oscillator is up-counted while the signal indicating that the deviation signal is larger than the reference value is output from the comparator, and the deviation signal is output from the comparator. Is smaller than the standard value An up-down counter that down-counts the clock pulse from the clock oscillator while outputting a signal indicating that the output signal is not present, and a digital-analog converter that inputs the output signal of the up-down counter to the servo valve as the offset voltage. A neutral compensation circuit for a servo valve, which is characterized by being provided.