JPS5813296B2 - Hoden Kakousouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In electric discharge machining, when the feed speed changes during machining, the machining expansion allowance for each part in the depth direction of the machined hole is not constant, and therefore machining accuracy deteriorates.

The present invention has been proposed to eliminate this drawback.
The following description will be given with reference to an embodiment of the drawings. Reference numeral 1 denotes a processing electrode, and 2 a workpiece, which face each other to form a processing gap.

3 is a voltage source for machining, and 4 is a voltage source for turning on transistors, thyristors, etc. A voltage source 3 is connected in parallel to the machining gap via this switch 4 in series with an off-switching element to supply machining pulses.

Reference numeral 5 denotes a detection power supply for detecting the state of the machining gap, which is connected in parallel to the gap via a detection resistor 6, so that changing current is detected in an analog manner as the resistance of the gap changes.

7 is a conversion circuit that converts the analog signal of the voltage detected from the resistor 6 into a pulse with a frequency corresponding to the magnitude of the voltage; 8
is a circuit that generates a gate pulse by shaping the waveform using a counter that counts the output pulse, a timer, and other circuits, and this output is applied to switch 4 to turn it on. Apply machining pulses to the gap with off-switching control.

9 is a servo motor that provides servo feed to the processing electrode 1;
10 is a discrimination circuit for discriminating the voltage of the machining gap; 11 is a pulse circuit for generating a servo signal based on the discrimination output thereof; these constitute a servo device.

12 is a count signal generation circuit according to the output of the discrimination circuit 10; 13 is a counter; when a predetermined count is reached, a pulse for reciprocating the electrode is generated from the next pulse circuit 14, and a reciprocating signal is sent to the servo motor 9; Add.

15 is an encoder connected to the rotating shaft of the servo motor 9 and generates pulses according to the number of rotations; 16 is a pulse detection circuit of the encoder; 16 is an encoder that stops counting by the next counter 18 when the reciprocating signal from the counter 13 is output. 19 is an oscillation circuit that generates clock pulses, and 20 is an arithmetic circuit that divides the count number of the counter 18 by the clock signal from the oscillation circuit 19. Through this operation, the amount of feed within a unit time, that is, the feed rate. A signal is output.

21 is a comparison circuit such as a comparator, and external terminal 22
Compare the preset signal with the feed rate signal, and if both signals match, output a signal and add it to the circuit 23;
A conversion circuit 70 that converts the frequency of an analog signal outputs a control signal that changes and controls the conversion frequency by changing the level.

That is, the comparison circuit 21, the control signal generation circuit 23, the level changeover switch of the conversion circuit 7 (not shown), etc. constitute an automatic level change control device.

In the machining gap between the electrode 1 and the workpiece 2, the switch 4 is turned on.
When turned off, the machining power source 3 is supplied with pulses, which causes intermittent discharge to occur in the gap and machining is performed.

The state of the machining gap is determined by a detection power source 5 that is always connected to the gap, a detection current that changes depending on the resistance of the gap is detected by a series resistor 6, and an analog signal of this detection voltage is applied to a conversion circuit 7 to convert it into an analog voltage. This pulse-converted digital signal is applied to the next gate pulse generation circuit 8, and is counted by, for example, a counter that constitutes the circuit 8, and the counter output sets or resets a flip-flop, etc. By doing so, a gate pulse is generated, and in addition to the switch 4, pulse control is performed.

Here, in the frequency conversion by the conversion circuit 7, the frequency of the conversion pulse increases in proportion to the voltage of the human power signal, so the detection signal of the resistor 6 increases during normal machining when the discharge in the machining gap is stably repeated. , the frequency of the output digital pulse of the conversion circuit 7 increases, and a high-frequency pulse signal is added to the gate pulse generation circuit 8, which outputs a proportionally high-frequency gate pulse, but on the other hand, it becomes unstable due to the machining gap. When processing is performed, the detection signal of the resistor 6 decreases,
The output pulse frequency of the conversion circuit 7 is lowered, and the gate pulse applied from the circuit 8 to the switch 4 is also lowered in frequency to reduce the number of repeated discharges and perform optimal control according to the state of the gap. You will be able to do it.

Of course, to detect the state of the machining gap, the machining current from the power source 3 may be used directly without providing a special power source 5 for detection as shown in the figure, or the voltage of the machining gap may be used as a signal. .

Next, since the machining gap changes as machining progresses, it is necessary to control the gap length to always be constant by servo-feeding the electrode that forms the gap (in some cases, the workpiece) in accordance with the progress of machining.

If the machining gap widens beyond a predetermined value, the voltage increases, and if it narrows, the voltage decreases. Therefore, the analog value of this gap voltage is discriminated by the discrimination circuit 10, and when the voltage is equal to or higher than the discrimination reference voltage from the control pulse generation circuit 11, the voltage is increased. Conversely, if the detection signal is lower than the standard value, a separation control signal is generated and applied to the servo motor 9 to apply servo feed to the electrode 1, controlling so that a constant gap is always maintained.

Of course, this servo feed control is not limited to control using differential digital signals, but may also be analog continuous control based on the difference between the gap voltage and a constant reference voltage, and the drive device may be configured with a hydraulic cylinder, magnet, etc. alone or in combination as appropriate. used.

, on the other hand, the discrimination output from the discrimination circuit 10 is the next counter 13
is also counted.

For example, the count signal generation circuit 1 selects only the separation control signal when the machining gap becomes too narrow among the discrimination outputs.
In addition to 2, if the count number of the counter 13 is increased by one each time the separation control signal is output, and when the count number reaches a predetermined value, a reciprocating signal is output.
Every time the counter 13 performs a predetermined count, a reciprocating signal is output to activate the circuit 14, and a control signal is applied to the servo motor 9, causing the electrode 1 to perform a rapid reciprocating motion of approaching and separating. Eliminate and clean the estimated processing waste, and control the processing waste concentration.

This reciprocating motion is not limited to one reciprocating motion when the reciprocating signal is output, but may be repeated several times by the control signal generation circuit 14, but it is also possible to repeat the reciprocating motion several times when the reciprocating signal is output. The count number of the counter 13, the control signal generation circuit 14, and the servo motor 9 are set so that stable and normal machining can be continued.
The reciprocating stroke, number of repetitions, etc. are set optimally.

Of course, the counter 13 that outputs this reciprocating signal distinguishes whether each discharge repeated in the machining gap is normal or abnormal based on its voltage, current, etc., and determines whether only normal discharge or only abnormal discharge is present.
Alternatively, the difference may be counted and a reciprocating signal may be output when the count value reaches a set value.
Further, the reciprocating drive can be configured to be performed by a device provided separately from the servo motor 9.

Thus, the servo feed amount for electrode tracking by the servo motor 9 is detected by an encoder 15 coupled to the motor shaft.

That is, the encoder 15 generates an electric pulse signal proportional to the rotation of the shaft, which is detected by the detection circuit 16.

Pulse detection by this detection circuit 16 is carried out by selectively detecting only the pulse signals in the direction in which the servo motor 9 is used to feed the electrode 1 close to the workpiece 2, and not detecting the distant pulse signals in the opposite direction. do.

Therefore, by counting these detection pulses with a counter, the electrode feeding distance can be easily detected, but before applying the detection pulse signal to the counter 18, the lock circuit 1
7 is provided, and controls not to apply pulse signals to the counter 18 during reciprocating motion, so that only processing feed pulses are accurately detected and counted.

On the other hand, the oscillation circuit 19 outputs a clock pulse at predetermined set time intervals and applies a signal to the arithmetic circuit 20.
It compares and calculates the count signal added from 8, that is, the feed amount signal, and outputs a signal corresponding to the feed speed obtained by dividing the feed distance by a predetermined time.

This feed rate outputted from the arithmetic circuit 20, that is, an output signal corresponding to the feed amount per unit time, is then applied to a comparator circuit 21, where it is compared with the signal reset at X, and if they match, a signal is output.

A plurality of stages of preset signals are input in advance to the comparator circuit 21 from an external terminal 22, and each time the feed speed signal from the arithmetic circuit 20 matches this preset signal, a signal is output and the circuit 23 is activated. The conversion level of the frequency conversion circuit 7 is changed.

For example, if the feed rate decreases even though stable addition is being performed, this is when the machining area increases as the machining depth increases, and in such a case, switch 4 Turn on. The switching control of the conversion frequency of the conversion circuit 7 is performed so as to increase the number of repetitions of the electric discharge generated in the machining gap when the electric discharge is turned off.

The feed rate signal from the arithmetic circuit 20 decreases and the comparator circuit 2
1, the conversion frequency of the conversion circuit 7 is automatically switched to a higher level when it matches the preset value one level lower than the preset value from the terminal 22 of 1, which increases the number of discharge repetitions and increases the amount of machining per unit time. Although the machining speed is increased, if the machining feed rate still decreases, it is compared with a preset lower setting value in the comparator circuit 21, and if they match, a terminal is set in the converter circuit 70 so that the frequency is switched to an even higher level. It is preset to 22.

In this way, even when machining a shape in which the machining area increases as the depth of the hole increases, the amount of machining per unit time increases by increasing the repetition of electrical discharge as the area increases. , it is possible to proceed with machining at a substantially constant feed rate without reducing the feed rate, and to perform highly efficient machining.

In addition, by automatically controlling the number of discharge repetitions using the feed rate as a signal, the feed rate can be kept almost constant even if the machining area changes slightly, and therefore machining can be expanded at various parts in the depth direction of the machined hole. This has the effect of making it possible to perform machining with high precision by keeping the distance etc. constant.

[Brief explanation of drawings]

The drawing is a circuit diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1 Electrical discharge machining equipped with a pulse power source that supplies machining pulses to a machining gap where a machining electrode and a workpiece face each other, and a servo device that provides follow-up control servo feed to the electrode or workpiece according to the progress of machining. The apparatus is provided with a calculation device that detects the amount of feed per unit time by the servo device, that is, the feed speed, and a control device that automatically changes and controls the frequency level of the pulse power source based on the feed speed signal of the detection calculation device. Electrical discharge machining equipment featuring: