JPS6362330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electric machining device for machining the workpiece by arranging a machining electrode and a workpiece to face each other with a machining gap therebetween, interposing a machining liquid in the machining gap, and energizing the workpiece. It is about improvement.

A conventional device of this type is shown in FIG. In Figure 1, 1 is an electrode for machining, 2 is a workpiece, 3 is a power source for machining, 4 is a hydraulic cylinder for feeding the electrode, 5A and 5B are resistors that divide the voltage in the machining gap, and 6 is a variable resistor. 7 is a control coil for the servo valve, 8 is a potentiometer, 9 is a + side power supply, 10 is a - side power supply, 11 is a bias coil for the servo valve, 12 is a resistor, 13 is a potentiometer, and the machining gap is In this embodiment, a voltage obtained by dividing the voltage of the machining gap by resistors 5A and 5B is used as the evaluation function. potentiometer 8
The + side power supply 9 is voltage-divided so that an arbitrary voltage can be set, and this voltage becomes the control target value, that is, the reference signal. In this case, a current flows through the control coil 7 due to the potential difference between the voltage across the resistor 5B and the set voltage of the potentiometer 8, and the value of the current is adjusted by the variable resistor 6. On the other hand, the current flowing through the bias coil 11 is supplied to the limiting resistor 1 from the potentiometer 13 provided between the + side power supply 9 and the - side power supply 10.
2. Flows through the bias coil 11 to the OV line. Generally, this current value is set so that the current flowing through the control coil 7 becomes zero and the electrode 1 driven by the cylinder 4 almost stops. The moving speed of the cylinder 4 changes depending on the sum of the current values flowing through the control coil 7 and bias coil 11 of the servo valve.

In the above circuit example, if the voltage across the resistor 5B is higher than the reference signal set by the potentiometer 8, the machining gap should be made smaller, and if it is lower, the machining gap should be made larger. If selected to operate, the machining gap is controlled so that its feedback signal is equal to the reference signal. Potentiometer 1 is a drawback of the above circuit.
Even if the current value flowing through the bias coil 11, which was set in step 3, is kept constant, due to the following fluctuation factors,
This is because the operating neutral point of the servo valve changes.

(A); The mechanical neutral point of the servo valve changes due to fluctuations in the servo valve's hydraulic oil temperature.

(B); When the amount of workpiece 2 to be machined is large, the electrode 1 moves in the direction of machining progress in order to maintain an appropriate machining gap. At this time, since a current flows through the control coil 7 in the direction of reducing the machining gap, the average voltage across the resistor 5B differs from the reference signal.

(C): When the weight of the electrode is large, force is applied in the direction that the machining gap becomes smaller, and conversely, when pressure is applied to the machining gap, force is applied in the direction that the machining gap becomes larger. In this case, in order to support this force, the servo valve uses the control coil 7 or bias coil 11 only by the current value determined by the pressure gain characteristics.
It is necessary to correct the value of the current flowing through the

Due to the fluctuation factors described in (A) to (C) above, a reference signal corresponding to the target machining gap is set with the potentiometer 8, and a voltage of the same magnitude as the set voltage is on average applied to the resistor 5B. There is a problem in that once the bias current is fixed so that it occurs at both ends, an error occurs in the voltage across the resistor 5B. An object of the present invention is to solve the above problem by controlling the voltage across the resistor 5B so that it is always the same as the reference signal.

The above fluctuation factors occur when a servo valve and cylinder are used as converters, but similar problems occur when a servo motor or the like is used. When the operating neutral point of the hobo valve fluctuates due to the above-mentioned fluctuation factors, in the conventional circuit, in order to maintain an appropriate machining gap, the operator must adjust the potentiometer while monitoring the average voltage across the resistor 5B to keep it constant. It is necessary to adjust the meter 8 or 13, and if this operation is neglected, there is a risk that the state of the machining gap will deviate from its target optimum value, resulting in the occurrence of a steady arc or a decrease in the machining speed.

The present invention has been made in view of these points, and an object of the present invention is to provide an electric machining device that can perform optimal machining simply by setting a target value for the machining gap.

An embodiment of the present invention will be described in detail below. FIG. 2 shows the basic configuration of the present invention, and in FIG. 2, the same reference numerals as in FIG. 1 indicate the same or corresponding parts. 14 is an amplifier;
A reference signal V _S set by the potentiometer 8 is input to the non-inverting input terminal of the amplifier 14.
In addition, the voltage across the voltage dividing resistor 5B is applied to the inverting input terminal.
V _F is connected through resistor 17 and switch 16 . Further, a capacitor 18 and a resistor 19 are connected between the inverting input terminal of the amplifier 14.

In this circuit configuration, when the switch 16 is open, the output terminal voltage V _O of the amplifier 14 is V _O
=V _S and the same operation as the circuit shown in Figure 1 is performed.
Next, when the switch 16 is closed, the amplifier 14 amplifies the potential difference between the reference signal V _S and the feedback signal V _F by the amplification factor A = -1 x resistor 19/resistor 17.
Since the capacitor 18 is connected in parallel to the capacitor 9, the circuit operates as a first-order lag circuit with time constant T ₁ =resistance 19×capacitor 18. Therefore, the output voltage V _O of the amplifier 14 where the difference voltage between the reference signal V _S and the feedback signal V _F is amplified is V _O = V _S + A (V _F - V _S ) x (1
--t/eT ₁ ). The feedback signal V _F constantly fluctuates as the machining gap changes, but
so that it is longer than the response period of the follow-up servo device.
If T ₁ /|A|, that is, a time constant expressed by resistor 17×capacitor 18, is selected, the output voltage V _O can be regarded as a DC voltage sufficient for the response frequency of the servo. Therefore, this output voltage V _O can be regarded as a reference signal automatically corrected for fluctuations in the operating neutral point of the servo valve. The switch 16 is connected to the amplifier 14 by maintaining the open-circuit voltage before starting energization.
In order to prevent the output voltage V _O from deviating significantly from the appropriate value, it is necessary to close the machining gap when it reaches a level where current can be passed. Further, the resistor 19 is necessary to keep the output voltage V _O equal to the reference voltage V _S when the switch 16 is opened, and there is no problem in terms of control function even if the resistor 19 is removed. In this case, the amplifier 14 operates as an integrator, and the output voltage V _O =V _S -1/T∫(V _F -V _S )dt is expressed as T=resistance 17×capacitor 18. Like T ₁ /|A|, the integral time constant T also needs to be longer than the response period of the servo device.
In the embodiment shown in FIG. 2, the neutral point of operation of the servo valve is changed and controlled by correcting the _current on the control coil side of the servo valve. Naturally, the same effect can be obtained even if the current is corrected. Also, in this embodiment, the output voltage V _O is used directly, but a device that responds to this output voltage V _O , for example, divides the voltage range of the output voltage V _O into multiple parts, and uses the divided voltage ranges. It is also possible to control the system indirectly by interposing a device that outputs a signal corresponding to the system.

Next, other embodiments of the invention will be described.
Further consideration of the operability of the configuration example shown in FIG. 2 described above reveals the following problems.

(D); When a signal to forcibly widen the machining gap is given to the servo device during energized machining, the amplifier 14 is activated during the period when the machining gap is widened and when the machining gap once expanded returns to the normal machining gap. Output voltage V _O
fluctuates widely, and when the machining gap returns to its original performance, the value of _VO will be different from the value before widening the machining gap.

(E); When interrupting electrical machining and restarting machining,
In order for the operating neutral point of the transducer that was corrected during the previous machining to be reset, time is required to reach the optimal operating center point again.

A description will be given of FIG. 3, which shows an embodiment of the present invention that can solve the problems (D) and (E) above. In FIG. 3, the same reference numerals as in FIG. 2 indicate the same or corresponding parts. A switch 20 is provided to forcibly widen the machining gap. While this switch 20 is pressed, one end of the variable resistor 6 is disconnected from the feedback signal and connected to the OV side, thereby increasing the machining gap by controlling the control coil 7 of the servo valve. The other contact circuit, which operates in conjunction with the flow of current to expand the NAND gate 22, is also connected to the OV side.
The flip-flop composed of A and 22B
The output of the NAND gate 22A is set to a low level (hereinafter abbreviated as "L"). The voltage comparator 21 compares the voltage V _F across the resistor 5B with the reference voltage V _S set by the potentiometer 8, and calculates V _F
<When V _S is detected, it outputs an “L” output, resets the flip-flop, and sets the output of the NAND gate 22A to a high level (hereinafter abbreviated as “H”).
The period during which the output of the NAND gate 22A is "L" corresponds to the period during which the machining gap is forcibly expanded and the subsequent period until the machining gap returns to its normal state. While the flip-flop is set, the relay coil 23 is energized and its contact 24 is closed. The resistor 25 and the capacitor 26 constitute a first-order delay circuit, the time constant of which is given by τ ₂ =resistance 25×capacitor 26. Reference numerals 27 and 28 are voltage comparators, and 27 outputs an "H" output when the voltage across the capacitor 26 is higher than a predetermined value compared to the reference signal V _S . On the other hand, the voltage comparator 28 outputs "H" when the voltage across the capacitor 26 is lower than a predetermined value compared to the reference signal V _S . 30 is a pulse generator, and the generation cycle of its generated pulses is selected to be longer than the time constant τ ₂ of the first-order lag circuit. The NAND gate 29A receives the output of the NAND gate 22A, the voltage comparator 27 output, and the pulse generator output. On the other hand, the NAND gate 29B receives the NAND gate 22A output, the voltage comparator 28 output, and the pulse generator output. Therefore, when the voltage of the capacitor 26 is higher than the reference signal _VS , the NAND gate 29A sets its output to "L" in synchronization with the pulse generated by the pulse generator, thereby exciting the stepping relay coil 31A. On the other hand, NAND gate 29B, contrary to 29A, excites stepping relay coil 31B when the voltage of capacitor 26 is lower than reference signal _VS.
Since the output of the flip-flop 22a is "L" while the machining gap is widened as described above, it is prohibited to excite both the stepping relay coils 31A and 32A, and the input of the first-order delay circuit is connected to the relay contact 24. Disconnected capacitor 2
6 is prevented from being charged with abnormal voltage. Since the voltage of the capacitor 26 has a time constant τ ₂ selected to be longer than the response period of the servo device, it can be considered as a DC voltage sufficient to withstand fluctuations in the voltage across the machining gap. The contact 32 of the stepping relay moves one step to the side connected to the resistor 33A each time the excitation coil 31A is excited, and conversely, when the excitation coil 31B is excited, the contact 32 moves to the side connected to the resistor 33E. Move in the same way to the side where it is being played. The bias coil 11 of the servo valve is connected to the common terminal of the contact 32 of the stepping relay, and a resistor is attached to each step of the selected side contact of the stepping relay contact 32. Its resistance value is 33A<3
3B<33C<33D<33E, and when connected to 33A, the neutral point of the servo valve is set to the side that narrows the machining gap, and vice versa.
When connected to E, the current of the bias coil 11 changes to the side where the machining gap is widest. Through the above circuit operation, the feedback signal V _F is controlled in the direction of becoming equal to the reference signal V _S.
If the above circuit is used, even if the machining gap is forcibly expanded during machining, the above-mentioned problem (D) will be solved because a flip-flop is provided that responds to the change in the machining gap. Furthermore, the same effect can be obtained in the example of FIG. 2 by replacing the switch 16 provided in the basic example of FIG. 2 with the relay contact 24 responsive to the flip-flop shown in FIG. In the embodiment shown in FIG. 3, a method of detecting the voltage of the machining gap using the voltage comparator 21 is used as a method of detecting that the machining gap has been once widened and recovered again, but a method of detecting the position or moving speed of the electrode is used. It goes without saying that you can also use .
On the other hand, the stepping relay contact 32 does not change its selected position unless its excitation coils 31A and 32A are excited, which poses a problem when machining is interrupted.
(E) is also solved at the same time. In this embodiment, a stepping relay is used as a device for storing the neutral point of the variable device of the servo device, but the number of steps may be any number as long as it is two or more. Also, instead of using a mechanical storage device, NAND gates 29A and 29B
It is also possible to count and store each output in a reversible counter circuit. It is also possible to A/D convert the output voltage V _O of the amplifier 14 in the example of FIG. 2 and store it as a digital value.

In both the basic example shown in Fig. 2 and the embodiment shown in Fig. 3, a servo valve and cylinder are used as a converter to convert the difference between the reference signal and the feedback signal into displacement or moving speed. The apparatus can also be easily constructed by referring to the above embodiments. In addition, the voltage of the machining gap is used as the evaluation function of the machining gap, but
In an electric discharge machining device that supplies machining pulses to a machining gap, an evaluation function that detects a delay time until the start of electric discharge and uses that delay time as a variable can also be used.

As described above, according to the present invention, in an electric machining apparatus in which machining fluid is interposed in the machining gap facing each other between a machining electrode and a workpiece, and electricity is supplied,
Adjustment of the operating neutral point of the converter that converts the electric signal into displacement or speed used in the servo device that controls the machining gap, changes over time in the operating neutral point, load fluctuations such as the weight of the machining electrode, etc. There are advantages such as automation being possible because the value is always corrected to an appropriate value regardless of fluctuations in the machining progress speed.

In addition, even if an operation is performed to forcibly widen the machining gap during energized machining or if machining is interrupted, the operating neutral point of the converter will be adjusted to an appropriate value when machining is resumed. be.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional device, FIG. 2 is a circuit diagram showing one embodiment of the invention, and FIG. 3 is a circuit diagram showing another embodiment of the invention. In the figure, 5A, 5B, 17, 19 are resistors, 7 is a control coil, 8, 13 are potentiometers, 9, 10 are power supplies, 11 is a bias coil, 1
4 is an amplifier, 16 is a switch, 18 is a capacitor, and 21 is a voltage comparator. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. The state of the machining gap between the machining electrode and the workpiece is converted into an electrical signal as its evaluation function, and the value of the evaluation function corresponding to the target machining gap is controlled as a reference signal. In an electric machining device using a follow-up servo system that has a converter that converts the difference between the feedback signal and the reference signal into position or velocity, the response of the follow-up servo system is A delay circuit having a time constant longer than the cycle and into which the feedback signal is input, and a detection circuit for detecting the difference between the output of the delay circuit and the reference signal, and The reference signal is corrected or the bias adjustment circuit of the follow-up servo system is corrected so as to reduce the difference between the average value of the feedback signal and the reference signal, and the operating neutral point of the converter is controlled. The detection circuit includes a detector that detects that the machining gap is larger than a predetermined value, and during a period when the detector detects that the machining gap is larger than the predetermined value, the converter is An electrical processing device configured to interrupt the function of changing and controlling the neutral point of operation. 2 The state of the machining gap between the machining electrode and the workpiece is converted into an electrical signal as its evaluation function, and the feedback of the machining gap condition is controlled using the value of the above evaluation function corresponding to the target machining gap as a reference signal. In an electrical processing device using a follow-up servo system that has a converter that converts the feedback signal into position or speed in response to the difference between the feedback signal and the reference signal, the time constant is longer than the response period of the follow-up servo system. a delay circuit into which the feedback signal is input, and a detection circuit that detects the difference between the output of the delay circuit and the reference signal, and determines the average value of the feedback signal based on the output signal of the detection circuit. The reference signal is corrected or the bias adjustment circuit of the follow-up servo system is corrected so as to reduce the difference between and the reference signal, and the operating neutral point of the converter is controlled. The converter has a storage device that stores a state in which the change in the operating neutral point of the converter is controlled, and the converter is brought into the stored change controlled state in the operating neutral point of the converter at the time of re-processing after interruption of processing. An electrical processing device configured to reproduce the neutral point of operation.