JPS6113244B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electric/hydraulic conversion device using an electric/hydraulic proportional valve as a control element, and more specifically, the present invention relates to an electric/hydraulic conversion device that uses an electric/hydraulic proportional valve as a control element. The present invention aims to provide an electro-hydraulic conversion device that can produce a constant dither effect.

(Prior art) Electric/hydraulic proportional valves, which can obtain pressure or flow rate proportional to the value of the current applied to the solenoid of a pilot solenoid valve, are often used in hydraulic automatic control equipment because they have high controllability. However, this type of electric/hydraulic proportional valve does not apply a smooth DC voltage in order to eliminate the fluid sticking phenomenon, increase resolution, and improve hysteresis characteristics.
A dither effect is created by applying a pulsed DC power source.

In order to effectively demonstrate current control performance while producing such a dither effect, conventional electric/hydraulic proportional valves change the average voltage by changing the pulse width of the pulsed DC voltage waveform applied to the solenoid.
Means to control the average current were widely employed.

For example, after full-wave rectification of an AC power supply using a rectifier, a pulsating DC current is passed through a circuit made up of a solenoid of an electromagnetic proportional valve and a transistor amplifier connected in series, and current control is performed while slightly vibrating a spool valve. A typical example is a device that allows

In this case, in order to change the average value of the current, the desired truncated pulsating flow shape is obtained by cutting the wave height portion above the set level from the maximum current value of the full-wave rectified direct current (pulsating current). Current control is performed within a range of values, and the control is normally performed steplessly using an appropriate current adjustment circuit.

(Problem to be Solved by the Invention) However, in such a control system, the pulse width of the pulsed voltage waveform sheared becomes narrower (the pulse width becomes wider) in the maximum range of average current, and conversely, in the minimum range However, the problem has been that the sheared pulse width of the pulsed voltage waveform becomes wider (the pulse width becomes narrower), the dither becomes less effective, and the hysteresis characteristic of the spool valve also deteriorates.

This is not desirable because it means that a uniform and safe dither effect cannot be expected over the entire range of the solenoid current.

The present invention addresses these facts and has led to the invention of a new electro-hydraulic conversion device that can eliminate the above-mentioned conventional defects. By adjusting the width of the DC voltage pulse as well as the oscillation frequency of the pulse in the current range and large current range, an effective dither effect can be produced, and it can be applied throughout the wide current control range. The main purpose is to eliminate the fluid sticking phenomenon.

(Means for Solving the Problems) The present invention provides an electric command signal having high and low levels according to a set current value and a dither variable circuit 5.
The output side of a transistor amplifier 2, which operates in response to a dither oscillation output inputted with a variable frequency output generated by
The dither variable circuit 5 is connected to a constant voltage DC power supply 3 having a DC voltage higher than the rated voltage of the solenoid, and the dither variable circuit 5 is configured such that the average value of the current flowing through the solenoid 1 falls within each of a plurality of current bands. The dither oscillation circuit 4 is formed into a circuit that generates a stepped frequency output whose frequency is higher in the medium current band than in other current bands.
is a square wave pulse having a constant peak value and a stepped frequency of high and low according to the output of the variable dither circuit 5, and whose pulse width ratio is proportionally controlled in magnitude according to the electric command signal. This is an electric/hydraulic conversion device formed in a circuit that emits .

(Function) When the current applied to the solenoid 1 is small, the present invention can enhance the dither effect by reducing the pulse width ratio of the square wave voltage pulse without changing the peak value and lowering the frequency of the voltage pulse.

Further, even when the current is large, the dither effect can be similarly enhanced by increasing the pulse width ratio without changing the peak value and lowering the frequency of the voltage pulse.

In other words, in the case of a small current range, the pulse width is substantially widened without changing the pulse width ratio, while in the case of a large current range, the no-voltage width between pulses is also widened. The effect is fully realized.

(Example) Hereinafter, one example of the present invention will be described in detail based on the accompanying drawings.

In FIGS. 1 and 2, 1 is a solenoid of an electric/hydraulic proportional valve (hereinafter referred to as a current proportional valve) related to an electric/hydraulic converter, and the solenoid 1 is connected in series to the output side of a transistor amplifier 2. 1st
The illustrated device is connected to a constant voltage DC power source 3 via a resistor 12 in series.

A signal processing device including a dither oscillation circuit 4 and a dither variable circuit 5 is disposed on an input setting line connected to the input side of the transistor amplifier 2.

Of the control devices shown in the above figures, the one shown in the first figure is a closed loop type control device, which smooths the voltage appearing across the resistor 12 in proportion to the value of the current flowing through the solenoid 1. After being smoothed by a circuit 6 and extracted as a signal corresponding to the average current, this signal is configured to be inputted as a feedback signal to a dither oscillation circuit 4 via a dither variable circuit 5.

On the other hand, the one shown in FIG. 2 is basically an open-loop type control device, in which the set signal level for controlling the current proportional valve is determined by the dither variable circuit 5, and a control signal is sent to the dither oscillation circuit 4. It is configured so that it can be input as .

The device shown in FIG. 2 includes a comparator 7 connected in series with the input side of the variable dither circuit 5.
are being set up.

Therefore, the dither oscillation circuit 4 is
As shown in the block diagram of the main components, it consists of a sawtooth wave generation circuit 8 and a switching circuit 9. The output current can be converted into a square wave with a constant peak value and then input to the transistor amplifier 2. In this case, the output current can be adjusted by changing the operating level of the switching circuit 9 using the setting input S. ,
By changing the on/off time ratio of an on/off signal with a predetermined frequency and appropriately changing the pulse width ratio of the square wave, a circuit is formed in which the peak value is constant and the average value can be changed from 0 to the maximum value. There is.

On the other hand, the dither variable circuit 5 has a sawtooth wave switching circuit 11 as an element, and is configured to generate an output that converts the base frequency of the sawtooth wave generation circuit 8 from high to low when a signal is input.

To explain each device having the above-mentioned basic configuration sequentially starting from FIG. The dither effect of the current flowing through the solenoid 1 is controlled by changing the pulse width ratio of the output voltage waveform of the transistor amplifier 2.

At this time, a command is sent to the dither oscillation circuit 4 through the dither variable circuit 5 according to the average current value of the solenoid 1 to modify the frequency of the dither wave to be lower in the small current region and large current region than in the medium current region. will be accomplished.

In this way, a dither effect adapted to the natural vibration characteristics of the valve can be automatically obtained over the entire range from the minimum current range to the maximum current range.

The reason why the dither effect is effectively applied is explained below. In the conventional variable pulse width method with a predetermined frequency, when the current value is low and when the current value becomes high, the solenoid current at the falling point of the voltage pulse However, the extent to which the voltage attenuates (width of current fluctuation) until the rise of the next applied voltage pulse becomes smaller, and the width of the current oscillation that causes the dither effect becomes smaller, making it impossible to obtain a sufficient dither effect. On the other hand, the control method according to the present invention changes the frequency according to the current value, so that when the current amplitude becomes small, the dither frequency is lowered and the current decay time is increased while maintaining the same average current value. Since sufficient current attenuation is obtained, it is possible to increase the current amplitude and effectively exhibit the dither effect.

By the way, since a continuously variable configuration involves a complicated circuit, it is preferable to achieve an effect substantially equivalent to such a dither effect, and in this case, a circuit as shown in FIG. It can be configured by

That is, in FIG. 3, the dither variable circuit 5 has:
In addition to the sawtooth wave switching circuit 11, a Schmitt trigger circuit 10 is provided, and the Schmitt trigger circuit 10 is interposed between the input side of the sawtooth wave switching circuit 11 and the smoothing circuit 6.

This device smoothes the pulsed voltage appearing across a resistor 12 and corresponding to the load current using a smoothing circuit 6, and when the voltage reaches a set voltage value, activates a Schmitt trigger circuit 10 to activate a sawtooth wave switching circuit 11. It operates to convert the base frequency of the sawtooth wave generating circuit 8 as described above.

By operating in this way, the current flowing through the solenoid 1 is distinguished into three current bands, for example, large, medium, and small, and the maximum current of the solenoid 1 is determined.
If it is 700mA, the range from 0 to 700mA is the small current range (0 to below 250mA) and the medium current range (over 250mA).
The dither frequency is reduced to 80 Hz in the small current area and large current area, and to 100 Hz in the other areas. It is possible to perform stepwise conversion, and thus it is possible to provide an effective dither output similar to that in the medium current range in a small current range with a small pulse width ratio and in a large current range with a large pulse width ratio. .

Next, the device shown in the second figure is a stepwise frequency variable type device, and when the setting input S is applied to the comparator 7 along with the generation of a sawtooth wave by the sawtooth wave generation circuit 8, the comparator 7 compares it with the reference value. If it deviates from the reference value, a frequency conversion command is input to the dither oscillation circuit 4 via the sawtooth wave switching circuit 11 (see FIG. 4).

In this way, stepwise frequency conversion control is performed in the same way as in the device whose operation was explained based on FIG. 3.

(Effects of the Invention) As described above, the present invention is capable of controlling the pulse DC voltage applied to the solenoid 1 of an electric/hydraulic proportional valve in a stepwise manner by controlling the dither frequency stepwise according to the magnitude of the average current value. Since the dither frequency in specific current ranges, such as the small current range and large current range, which are less effective, is set to an appropriately low frequency that can produce a dither effect compared to the normal current range, the dither frequency can be effectively reduced over the entire usage range. It is possible to produce a constant dither effect, and the resolution and hysteresis characteristics are demonstrated stably and with high precision over the entire current range.

In particular, in conventional control systems for proportional throttle switching valves whose spool symbol is an all-port block, the fluid sticking phenomenon is overcome when adjusting the valve opening from a no-applied state to achieve normal valve adjustment. However, since the present invention can sufficiently exhibit effective dither characteristics even in the low current range, the control performance has been greatly improved, and the reliability and responsiveness have been excellent. Furthermore, since this feature is fully automatic, it has great practical value as a control device, and is an outstanding electro-hydraulic conversion device that contributes to this field.

[Brief explanation of the drawing]

1 and 2 are basic block circuit diagrams of each example of the device of the present invention, and FIGS.
FIG. 3 is a block circuit diagram further functionally illustrating each device in FIG. 3 and FIG. 2; 1... Solenoid, 2... Transistor amplifier, 3... Constant voltage DC power supply, 4... Dither oscillation circuit, 5... Dither variable circuit.

Claims (1)

[Claims] 1. The output side of the transistor amplifier 2 that operates in response to the oscillation output of the dither oscillation circuit 4 to which the electric command signal having high and low levels according to the set current value and the variable frequency output generated by the dither variable circuit 5 are input. , and a solenoid 1 of an electric/hydraulic proportional valve are connected in series, and this series circuit is connected to a constant voltage DC power supply 3 having a DC voltage higher than the rated voltage of the solenoid 1, and the dither variable circuit 5
determines which of the plurality of current bands the average value of the current flowing through the solenoid 1 falls in, and determines that the frequency is higher in the middle current band than in the other current bands. The dither oscillation circuit 4 is formed into a circuit that emits a stepped frequency output.
is a square wave pulse having a constant peak value and a stepped frequency of high and low according to the output of the variable dither circuit 5, and whose pulse width ratio is proportionally controlled in magnitude according to the electric command signal. An electric/hydraulic conversion device characterized in that it is formed in a circuit that emits .