JPH0442561Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a positioning control circuit for a piston cylinder device, and particularly to a positioning control circuit that has high positioning accuracy in a piston cylinder device that can hold a piston in an intermediate position. be.

[Prior Art] Conventionally, as a piston cylinder device that has a neutral point of the piston at the center position of the cylinder and can hold the piston at an arbitrary center position, there is a fifth piston cylinder device.
It was as shown in FIG. 6 or 7. The piston cylinder device shown in Fig. 5 was published in Japanese Patent Application Laid-open No. 57.
-Disclosed in No. 9306. In each figure, 10
1,102 is a piston cylinder device; 10
3 is a cylinder, 104 is a piston, 105, 10
Reference numeral 6 denotes springs provided in the left and right oil chambers of the cylinder 103 for setting the piston to a neutral position. Each piston 104 is equipped with a feedback sensor 4 via a piston rod. The piston cylinder device 101, 102
is provided with a hydraulic circuit that communicates with the left and right oil chambers in the cylinder 103 and controls the position of the piston 104.
07 is a hydraulic pump, 108 is a hydraulic tank, 109
-113 are electromagnetic switching valves. Each electromagnetic switching valve 10
9 to 113 are each 2 required for a predetermined action.
an electromagnetic coil 114 for changing the flow path configuration on the hydraulic circuit of these valves;
Spring 11 for restoring the flow path configuration to its original state
5.

Further, 116 shown in FIG. 6 is a one-way valve.

[Problems to be solved by the invention] In the hydraulic circuits that control the piston cylinder devices 101 and 102 shown in FIGS. 5 and 6, in order to ensure safety, each hydraulic circuit is By turning off all the electromagnetic switching valves, the springs 105, 10
6, the piston 104 returns to the neutral position within the cylinder 103. Therefore,
On the other hand, when positioning the piston 104, it is necessary to turn on any electromagnetic switching valve, and therefore the accuracy of piston positioning depends on the ON delay time that occurs when turning on the electromagnetic switching valve. It turns out. This ON delay time is affected by the inductance of the electromagnetic coil 114, so it becomes a larger value compared to the OFF delay time that occurs when piston positioning is performed by turning off the electromagnetic switching valve. Piston positioning by turning on has a problem in that the positioning accuracy is worse than piston positioning by turning off.

The above problems will be explained in more detail.

The flow path configuration of the electromagnetic switching valve used to position the piston changes when the attraction force of the electromagnetic coil becomes stronger than the spring force of the return spring in pressure-balanced switching valves. be. In the case of a switching valve that is not a pressure balance type, this occurs when the attraction force of the electromagnetic coil becomes stronger than the force calculated by the product of the cross-sectional area of the seat surface and the pressure.

Generally, the attractive force of an electromagnetic coil is inversely proportional to the square of the gap length between the fixed core and the movable core. Therefore, as shown in Fig. 8, the current value at which the movable core starts to move in the attracting direction by energizing the electromagnetic coil when both cores are separated, and the current value to the electromagnetic coil when both cores are attracted, are By gradually lowering the amount of current, the current value becomes different from the current value at which the movable iron core begins to move in the direction of releasing the adsorption.

Also, as shown in FIG. 8, even when a voltage is applied to the electromagnetic coil, the current does not flow rapidly due to its inductance, and a certain delay time occurs.
Expressing this delay time mathematically, for example, when a solenoid switching valve is changed from an on state to an off state, electricity is applied at the same time to change it from an off state to an on state, and a flywheel diode is used as a protection element for the switching element. The delay time tf in the case is tf=-(L/R)1og _e [{1-(I2/Im)
}/{1-(I1/Im)}] Here, R: Resistance value of the electromagnetic coil L: Inductance of the electromagnetic coil I1: Coil current value when the electromagnetic switching valve switches from the on state to the off state I2: The current value when the current switching valve switches from the off state to the on state Coil current value Im: Current value when the coil current is saturated.

Further, the delay time tz when a varistor or Zener diode is used as a protection element is expressed by the following formula: tz=-(L/R)1og _e {1-(I2/Im)}.

The on-delay times tf and tz as described above have a magnitude of about τ/2 to τ, where the time constant τ of the electromagnetic coil is L/R. Therefore, even if it is a solenoid switching valve with a relatively small time constant, the on-delay time will be 5 to 5.
It will be about 10msec. Because such an ON delay time exists, in a hydraulic circuit in which the electromagnetic switching valves 112 and 113 on both sides are normally in the on state as shown in FIG. 6, when the electromagnetic switching valve on one side is turned off and the piston 10 Even if an attempt is made to move the piston 104 and hold the piston 104 at another position by turning on both electromagnetic switching valves when the target position is reached, an overtravel amount es occurs. This overshoot amount es is expressed as es=vs×tf, where vs is the cylinder speed.

As a result of the above, for example, a stroke of 8mm is 0.2sec.
In a piston-cylinder device with a piston that moves at
An overshoot of mm occurs, and as a result, the range of ±0.4 mm with respect to the target value becomes an uncontrollable value. As described above, positioning by turning on the electromagnetic switching valve has poor accuracy.

In order to solve the above-mentioned problem of positioning accuracy, a method called a pulse width control method has conventionally existed. In this method, in the hydraulic circuit configuration shown in Fig. 7, the piston is moved to the target position by applying a pulse having a target value and a width proportional to the current position of the piston to the electromagnetic switching valve. The power to the electromagnetic switching valve is stopped before the target position is reached, thereby compensating for the off delay time of the electromagnetic switching valve and the phase delay time of the feedback signal, and creating a half-open state in the electromagnetic switching valve to move the piston near the target position. This reduces the speed and improves positioning accuracy.

However, according to the above method, the electromagnetic switching valve is constantly turned on and off by the applied pulse voltage, which has the disadvantage that the piston vibrates slightly. Therefore, when the above method is applied to the electromagnetic switching valve shown in FIGS. 5 and 6, it is impossible to achieve the original purpose of holding the piston in an intermediate position and eliminating minute vibrations.

The purpose of this invention is to be able to hold the piston in an intermediate position without causing slight vibrations, and to
It is an object of the present invention to provide a positioning control circuit for a piston cylinder device that improves responsiveness and has high positioning accuracy by compensating for delay time.

[Means for Solving the Problems] In the present invention, the above object is to energize at least two electromagnetic switching valves provided in the piston cylinder device and for changing the flow path of the hydraulic circuit, and to switch the electromagnetic switching valves. A positioning control circuit for a piston cylinder device capable of maintaining a piston in an intermediate state by turning on a valve, comprising: a command device for instructing the position of the piston; a feedback sensor for detecting the position of the piston; a deviation detection circuit that detects a difference between a command signal from a command device and a feedback signal from the feedback sensor; and a deviation detection circuit that detects a difference between a command signal from a command device and a feedback signal from the feedback sensor, and a control device that determines whether to continue holding the piston or move it in any direction based on the output signal of the deviation detection circuit. and a dither signal addition means for adding a dither signal to either the reference voltage of the window comparator circuit with hysteresis or the input voltage of the window comparator circuit with hysteresis. It is achieved by doing so.

[Function] In the positioning control device for a piston cylinder device according to the present invention, the comparator circuit that inputs the deviation signal between the command signal and the feedback signal is a window comparator circuit with hysteresis, and the reference voltage of the window comparator circuit with hysteresis and its By adding a dither signal to either input voltage, the output voltage from the hysteretic window comparator circuit becomes an on/off pulse waveform that ensures a predetermined off time proportional to the deviation when the pulse voltage turns off. Therefore, even though an off pulse is applied to the electromagnetic switching valve, the range of deviation in which the piston does not move due to the delay time when the electromagnetic switching valve is turned off and the off pulse continues to be applied is reduced. As a result, even if an off pulse is output, within a small deviation range, it is possible to change the output pulse from off to on at a time interval of 1/2 period or less of the dither signal and stop the piston. As an effect similar to width control, it is possible to obtain an effect of compensating for the ON delay time of the electromagnetic switching valve and the phase delay of the feedback signal. As described above, the responsiveness of the electromagnetic switching valve is improved and the positioning accuracy of the piston is increased.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of a positioning control circuit according to the present invention, and this control circuit is configured to add a dither voltage to a reference voltage of a window comparator circuit. This control circuit is applied to the hydraulic circuit shown in FIG. It can also be applied to the hydraulic circuit of FIG. 5 by adding an electrical logic circuit.

In FIG. 1, reference numeral 1 denotes a differential transformer that functions as a feedback position sensor shown as a feedback sensor in FIG. 6, and the differential transformer 1 detects the position of a piston. The output of the differential transformer 1 is converted by a detection circuit 2 into a DC voltage proportional to the stroke of the piston, and is input to a deviation detection circuit 3 at the next stage. Further, the command voltage given by the joystick 4 is also input to the deviation detection circuit 3. The deviation detection circuit 3 outputs the difference between the command voltage from the joystick 4 and the feedback voltage from the differential transformer 1. The deviation detection circuit 3 actually outputs the sum of both voltages, but since the feedback voltage is obtained by inverting the output voltage, the deviation is obtained by the addition circuit.

Reference numeral 5 denotes a window comparator circuit with hysteresis, which includes two comparators 6a and 6b, each of which is provided with positive feedback resistors 7, 8, 9, and 10, respectively. The output of the deviation detection circuit 3 is input to each of the negative input terminal of one comparator 6a and the positive input terminal of the other comparator 6b.

Reference numeral 11 denotes a dither voltage generation circuit, specifically a triangular wave generation circuit composed of an integrating circuit and a comparator with positive feedback. The triangular wave generated by this triangular wave generating circuit is used as a dither voltage. In this embodiment, a triangular wave is used as the dither, but other voltage waveforms such as a sawtooth wave or a voltage waveform obtained by passing a repetitive square wave through a first-order delay circuit may also be used.

12 is a resistance circuit including six resistors, and each comparator 6 in the window comparator circuit 5
It has the function of producing reference voltages for comparison of a and 6b, and adding the dither voltage given from the dither voltage generation circuit 11 to each reference voltage.

Reference numeral 13 denotes a drive circuit, in which two stages of transistors 14 and 15 having the same circuit configuration are provided for each of the two outputs of the window comparator circuit 5.
A light emitting element 16 is disposed between the two transistors 14 and 15 to indicate the energized state. 1
7 and 18 are the electromagnetic switching valves 1 shown in Fig. 3, respectively.
This corresponds to 12,113. Drive circuit 1
3 amplifies the output of the window comparator circuit 5 so that the electromagnetic switching valves 17 and 18 can be turned on and off sufficiently. In the drive circuit 13, 19 is an element for protecting the power transistor 15 from back electromotive force generated when the electromagnetic switching valves 17 and 18 are turned on and off.

Next, the operation of the piston positioning control circuit having the above configuration will be explained.

FIG. 2 shows the output states of the comparators 6a and 6b of the window comparator circuit 5 when there is no dither addition. In the figure, the horizontal axis shows positive and negative deviations, and the vertical axis shows voltage. Further, 20 is the output of the comparator 6a,
That is, the operating state of the electromagnetic switching valve 17 is shown, and 21
indicates the output of the comparator 6b, that is, the operating state of the electromagnetic switching valve 18. When the deviation is around 0, comparator 6
The outputs of a and 6b are both 1, so both electromagnetic switching valves 17 and 18 are in the on state. When the deviation increases in the positive direction, the electromagnetic switching valve 17
is turned off, and when the deviation increases in the negative direction, the electromagnetic switching valve 18 is turned off. Each comparator 6a, 6b has hysteresis due to positive feedback, so it has a characteristic that the deviation when changing from on to off is larger than the deviation when changing from off to on. However, in the circuit configuration described above, since the dither voltage is added to each reference voltage of the window comparator circuit 5, each comparator 6
The deviation when a and 6b change from off to on and the deviation when they change from on to off change as time passes. The state of this change is shown in FIG.

In FIG. 3, 22 is a reference voltage that changes from on to off, 23 is a reference voltage that changes from off to on, and a gently rising curve 24
indicates the change in deviation value. In addition, the lower part of FIG. 3 shows the on/off operation of the electromagnetic switching valve when the curve 24 shows two changes 24a and 24b, and 25 corresponds to 24a and 2
6 corresponds to 24b.

If there is no deviation, the electromagnetic switching valve is kept in the on state, as indicated by 25 and 26. When the deviation value increases gradually by operating the joystick 4, the curve 24 first intersects the reference voltage 23. Here, the output to the electromagnetic switching valve does not change. Thereafter, the reference voltage 22 intersects at the valley part where it changes from on to off, and at this time, the electromagnetic switching valve is in the off state, and the piston moves so as to reduce the deviation, drawing a trajectory 24b. and,
When the reference voltage that changes from off to on is crossed, the electromagnetic switching valve changes from off to on and stops the movement of the piston.

If the piston does not move even though the electromagnetic switching valve is turned off, or if the deviation does not decrease at all due to a phase delay in the feedback signal, etc., as shown at 24a in FIG. The output state of the electromagnetic switching valve changes from the OFF state to the ON state at a time interval of 1/2 period or less of the dither voltage waveform. For this reason, it is recommended that the 1/2 period of the dither voltage waveform be turned on during a period that allows the electromagnetic switching valve to remain half-open or while the back electromotive force of the electromagnetic coil is effective. often,
It will be about 1 to 2 msec.

In addition, the voltage value of the valley of the reference voltage 22 and the reference voltage 2
It is preferable to set the voltage value so that it overlaps with the voltage value of the peak 3.

As explained above, in this embodiment, the comparator circuit that inputs the deviation signal between the command voltage and the feedback voltage is configured to have hysteresis.
It consists of two comparators 6a and 6b, and the dither voltage is added to the reference voltage of the comparator, so the comparator 6a and 6b
The on/off pulse waveforms output from a and 6b are waveforms that ensure a predetermined off time proportional to the deviation when the pulse voltage turns off, as shown in Figure 3, and give an off pulse to the electromagnetic switching valve. Despite this, the range of deviation in which the piston does not move due to the delay time when the electromagnetic switching valve is turned off and continues to give an off pulse indefinitely is reduced. As a result, even if an off-pulse is output, the output pulse will turn on at a time interval of 1/2 period or less of the dither signal in a small deviation range and stop the piston, so the electromagnetic The effect of compensating for the ON delay time of the switching valve and the phase delay of the feedback signal can be obtained. As described above, the responsiveness of the electromagnetic switching valve is improved and the positioning accuracy of the piston is increased.

FIG. 4 shows a second embodiment of the piston positioning control circuit according to the present invention. This control circuit is configured to add a dither voltage to the deviation between the input command voltage and the feedback voltage.
In FIG. 4, 27 is an adder circuit, which includes the deviation output from the deviation detection circuit 3 and the dither voltage generation circuit 11.
The dither voltage is inputted, and the deviation output and the dither voltage are added. The rest of the structure is almost the same as that shown in FIG. 1, and the same elements are given the same reference numerals. However, resistance circuit 2
8 has only the function of creating a reference voltage for each comparator of the window comparator circuit 4. The operation of the control circuit is also basically the same as that of the control circuit according to the first embodiment.

The deviation detection circuit 3 has a linear characteristic, and the dither output from the dither voltage generation circuit 11 can also be added to the command voltage or the feedback voltage.

[Effects of the invention] As is clear from the above explanation, according to the invention, by using dither, it is possible to control the dither voltage waveform at 1/2 period or less regardless of the operation of the electromagnetic switching valve or the movement state of the piston. Since the electromagnetic switching valve is turned on in time, the electromagnetic switching valve is not completely off when the on signal is applied, and responsiveness can be improved. In addition, since the time for the off state is inversely proportional to the moving speed of the piston, the effect of pulse width control is produced, and the positioning control is reduced from the conventional 0.5mm
It can be increased from about 0.05 to 0.1 mm.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a positioning control circuit for a piston-cylinder device according to the first embodiment of the present invention, FIG. 2 is a characteristic diagram of a window comparator circuit without dither addition, and FIG. 3 is a characteristic diagram with dither addition. FIG. 4 is a time chart showing the relationship between the output state of the window comparator circuit and the on/off operation of the electromagnetic switching valve when Fig. 5 is a schematic diagram showing a conventional piston cylinder device and its hydraulic circuit, Fig. 6 is a schematic diagram showing another conventional piston cylinder device and its hydraulic circuit, and Fig. 7 is a schematic diagram showing another conventional piston cylinder device and its hydraulic circuit. A schematic diagram showing the hydraulic circuit, and FIG. 8 is a waveform diagram showing the relationship between the coil voltage and coil current of the electromagnetic switching valve. In the figure, numerals 1... operating transformer (feedback sensor), 2... detection circuit, 3... deviation detection circuit, 4... joystick (command device), 5...
Window comparator circuit with hysteresis, 6
a, 6b...Comparator, 11...Dither voltage generation circuit, 12...Resistance circuit, 13...Drive circuit, 1
7, 18... Solenoid switching valve.

Claims (1)

[Claims for Utility Model Registration] (1) At least two electromagnetic switching valves provided in the piston cylinder device for changing the flow path of the hydraulic circuit are energized and these electromagnetic switching valves are turned on. A positioning control circuit for a piston cylinder device capable of maintaining a piston in an intermediate state by: a command device for instructing the position of the piston; a feedback sensor for detecting the position of the piston; a command signal from the command device; a deviation detection circuit that detects a difference from the feedback signal from the feedback sensor; and a hysteresis device that determines whether to continue holding the piston or to move it based on the output signal of the deviation detection circuit. A piston cylinder device comprising: a window comparator circuit; and dither signal addition means for adding a dither signal to either the reference voltage of the window comparator circuit with hysteresis or the input voltage of the window comparator circuit with hysteresis. Positioning control circuit. (2) The piston cylinder according to claim 1, wherein the dither signal addition means adds the dither signal to each of a plurality of reference voltages included in the window comparator circuit with hysteresis. Device positioning control circuit. (3) The positioning control circuit for a piston cylinder device according to claim 1, wherein the dither signal addition means adds the dither signal to the command signal. (4) The positioning control circuit for a piston cylinder device according to claim 1, wherein the dither signal addition means adds the dither signal to the feedback signal. (5) The positioning control circuit for a piston cylinder device according to claim 1, wherein the dither signal addition means adds a dither signal to the output signal of the deviation detection circuit.