JP4070910B2 - EDM machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a discharge additive.ConstructionMore specifically, the electric discharge machining that can accurately give the required electric discharge machining energy to the electric discharge machining gap.ConstructionIs related to the position.
[0002]
[Prior art]
In electrical discharge machining equipment such as engraving and wire cutting, a machining pulse voltage is repeatedly supplied to the electrical discharge machining gap formed between the machining electrode and the workpiece, and electrical discharge machining is performed by applying each machining pulse voltage. The workpiece is processed by the discharge current generated in the gap. Here, the machining pulse energy to be supplied to the electric discharge machining gap is set according to the discharge time and the discharge current value. In actual machining, a machining pulse voltage is applied to the electric discharge machining gap. Even if it is applied, the discharge does not start immediately, and in most cases, the discharge starts with a slight time delay from the application of the machining pulse voltage. Since the delay time at the start of discharge greatly depends on the value of the machining pulse voltage or the current state of the electrical discharge machining gap, it is not constant and is therefore supplied to the electrical discharge machining gap every time the machining pulse voltage is applied. Some device is required to set the processing pulse energy to a required value.
[0003]
Therefore, in order to control the discharge current to flow through the electric discharge machining gap for a required time from when the electric discharge is actually started, conventionally, after applying the machining pulse voltage to the electric discharge machining gap, A configuration is known in which the timing at which discharge is started is electrically detected and application of the machining pulse voltage to the discharge machining gap is stopped when a predetermined time has elapsed from the discharge start timing.
[0004]
FIG. 5 is a block diagram of the electric discharge machining apparatus configured as described above. In the electric discharge machining apparatus 100 shown in FIG. 5, reference numeral 101 denotes a DC power source that can output a DC voltage E of 60 V to 150 V. The DC voltage E is for machining via a diode 102, a current limiting resistor 103, and a switching transistor 104. An electric discharge machining gap G formed between the electrode 105 and the workpiece 106 is applied. Here, what is indicated by a symbol L is a line-to-line inductance of the wiring provided between the DC power supply 101 and the electric discharge machining gap G.
[0005]
The gate electrode 104G of the switching transistor 104 is supplied with a gate pulse signal GATE from a gate control circuit (not shown). When the level of the gate pulse signal GATE becomes a high level state, the switching transistor 104 is turned on, and the DC voltage E is used to apply a machining pulse voltage to the electrical discharge machining gap G.
[0006]
In order to detect the timing at which discharge is started in the electric discharge machining gap G, a discharge start detection circuit 110 is connected to the electric discharge machining gap G. In the discharge start detection circuit 110, a series circuit of a bias power source 111 and resistors 112 and 113 is connected in parallel with the electric discharge machining gap G, and the machining gap at that time is determined from the connection point between the resistor 112 and the resistor 113. The detection voltage Vf indicating the level of the voltage Vg is taken out, and the detection voltage Vf is level-compared with the reference voltage Vs in the comparator 114.
[0007]
If the voltage of the bias power supply 111 is Vcc, the value of the detection voltage Vf is Vf = Vcc− (Vcc−Vg) × R1 × (R1 + R2)^-1Indicated by Here, R1 is the resistance value of the resistor 112, and R2 is the resistance value of the resistor 113.
[0008]
According to this configuration, when the level of the gate pulse signal GATE changes from a low level to a high level at a given timing, and thus the switching transistor 104 is turned on, the DC voltage E is applied to the electric discharge machining gap G as a machining pulse voltage. Applied. Until the discharge current starts to flow in the electric discharge machining gap G, the value of the machining gap voltage Vg is substantially equal to the value of the DC voltage E, and the value of the detection voltage Vf is lower than the reference voltage Vs, and therefore from the output of the comparator 114. The level of the discharge start signal SK is high. When electric discharge is started in the electric discharge machining gap G and the level of the machining gap voltage Vg is lowered to a predetermined low voltage level during discharge, for example, about 25 V, Vf ≧ Vs, and the level of the discharge start signal SK is lowered.
[0009]
The discharge start signal SK is sent to a gate control circuit (not shown). Here, when a preset discharge current supply period elapses from the detection of the discharge start, the level of the gate pulse signal GATE is lowered to turn off the switching transistor 104. Control is performed.
[0010]
As a result, the switching transistor 104 is turned on for a predetermined set time for supplying the discharge current from the detection of the discharge start, and the electric discharge machining current flows in the electric discharge machining gap G only while the switching transistor 104 is turned on. The required machining energy can be supplied to the gap G.
[0011]
[Problems to be solved by the invention]
By the way, since the time until the machining gap voltage Vg reaches the reference voltage Vs after the start of discharge greatly depends on the set value of the electrical machining conditions, even if the DC voltage E is constant at 150 V, for example, after the discharge starts. The state of reduction of the machining gap voltage Vg that occurs is a transient state according to the setting conditions at that time.
[0012]
However, according to the configuration shown in FIG. 5 in which the value of the detection voltage Vf is compared with a given constant level reference voltage Vs and the discharge start timing is determined based on the comparison result, the discharge is actually started. Since the fluctuation of the detection time delay until the start of discharge is detected by the discharge start detection circuit 110 is not considered, the electric discharge machining energy supplied to the electric discharge machining gap G cannot be accurately controlled to a desired value. . As a result, the machining current energization time per pulse of the machining pulse voltage is not necessarily a required value, and machining different from the desired machining characteristics is performed, and electrode wear characteristics are deteriorated and surface roughness is reduced. Will cause problems.
[0013]
An object of the present invention is to provide an electric discharge machining method and apparatus capable of accurately giving a required amount of electric discharge machining energy to an electric discharge machining gap every time a pulse voltage for machining is applied even if electric machining conditions are changed. It is to provide.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, according to the present invention,The output voltage can be switched according to the machining condition input settings to the NC unit.From DC power supplyON / OFF controlled by gate control circuitThe machining pulse voltage taken out using the switch means is applied to the electric discharge machining gap formed between the workpiece and the machining electrode via a current limiting resistor circuit whose resistance value is determined according to the set machining current value. Electrical discharge machining in which an electrical discharge machining current is caused to flow through the electrical discharge machining gap to intermittently repeatedly apply the workpiece to the workpiece.apparatusIn
A gap detection circuit in which a DC bias power supply is connected in series to two series voltage dividing resistors is connected in parallel to the electric discharge machining gap, and the detection voltage of the gap detection circuit is compared with a reference voltage to control the discharge start detection signal. A discharge start detection circuit to be supplied to the circuit, and the reference voltage is calculated by the following equation (1) according to the output voltage value of the DC power supply according to the power supply voltage command output from the machining condition setting unit.It is output from the quasi-voltage generator,MoreON control time of the switching means according to the set machining current valueAnd a calculation unit that performs correction calculation and outputs to the gate control circuit,
According to the gate control circuit outputThe level of the machining gap voltage generated in the EDM gap due to the ON operation of the switching means is set in advance.Base outputSaid gap caused by the occurrence of discharge by comparing with quasi-voltage leveldetectionDetect voltage drop timing of voltageDischarge start detection circuitWhen,
From the detected voltage drop timingCorrection calculationWhen the on-control time has elapsed, the switching means is turned off to stop applying the machining pulse voltage to the electrical discharge machining gap.The above gate control circuit has the function.I got
Formula (1) Vs = (E-25V (discharge voltage)) * 0.75 + 25V
      Where E is the command output voltage value of the DC power supply.
DischargeEngineering equipmentProposed.
[0015]
When the switching means is turned on, a machining pulse voltage is applied to the electric discharge machining gap, and when the electric discharge starts in the electric discharge machining gap, the machining gap voltage starts to decrease. The rate of this reduction greatly depends on the time constant determined by the resistance value of the current limiting resistor circuit and the line inductance value of the wiring from the DC power supply to the electric discharge machining gap, and the level of the machining gap voltage follows this time constant. It will decrease along the characteristic curve. Here, the line inductance value is a parameter that does not change every time the machining condition is set, but the resistance value of the current limiting resistance circuit is a parameter that changes according to the setting of the machining current value. Therefore, Discharge start detectionOutIn circuitThe detected voltage drop timing is delayed from the timing at which discharge is actually started in the electrical discharge machining gap, and this detection delay time is a value corresponding to the resistance value of the current limiting resistor circuit.
[0016]
on the other hand,Correction of on-control time for gate control circuitIsIn calculationThe on-control time having a length corresponding to the set machining current value at that time is calculated. That is, the ON control time is short when the set machining current value is such that the detection delay time is large, whereas the ON control time is long when the set machining current value is such that the detection delay time is small. Thus, the ON control time is calculated. The off control of the electric discharge machining current to the electric discharge machining gap is performed so that the switching means is turned off when the on control time has elapsed from the voltage drop timing detected in the detection step. As a result, the discharge current energization time per pulse of the machining pulse voltage can be set to a required value regardless of the set machining current value.
[0017]
Moreover, according to the present invention,The electric discharge machining apparatus,In an electric discharge machining apparatus configured to perform electric discharge machining on the workpiece by intermittently passing an electric discharge current through an electric discharge machining gap formed between the workpiece and a machining electrode, a direct current power source and machining condition setting ON / OFF control of the switching means for intermittently repeatedly applying the machining pulse voltage to the electric discharge machining gap, and switching means provided between the DC power source and the electric discharge machining gap A gate control circuit for setting a level of the discharge current set to a resistance value corresponding to a set machining current value set by the machining condition setting means provided in series with the electric discharge machining gap; Given a current limiting resistance circuit and a level of machining gap voltage generated in the electric discharge machining gap by the ON operation of the switching means.Calculated based on the set DC voltage EThe voltage drop timing of the machining gap voltage caused by the occurrence of discharge is detected by comparing with the quasi-voltage level.Discharge start detectionBased on the set machining current value, the output circuit means and the on-control time from the voltage drop timing to turning off the switching meansCorrectionAn electric discharge machining apparatus comprising: an on-control time calculation unit for calculating, wherein the gate control circuit turns off the switching means when the on-control time has elapsed from the voltage drop timing. The
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0019]
FIG. 1 is a block diagram showing an example of an embodiment of an electric discharge machining apparatus according to the present invention. The electric discharge machining apparatus 1 intermittently repeatedly applies a DC voltage E from a DC power source 4 as a machining pulse voltage to an electric discharge machining gap G formed by the machining electrode 2 and the workpiece 3, thereby performing electric discharge machining. This is an apparatus for electric discharge machining the workpiece 3 by the electric discharge current generated in the gap G. In the illustrated embodiment, an example of an electric discharge machining apparatus is shown. However, it does not mean that the present invention is applied only to the sculpting electric discharge machining apparatus, and the present invention can be applied to other types of electric discharge machining apparatuses, for example, wire cut electric discharge machining apparatuses.
[0020]
The DC power supply 4 has a configuration in which the value of the output DC voltage E can be set stepwise in the range of 60V to 150V, and the DC power supply 4 is controlled in accordance with the power supply voltage command signal SE output from the numerical control device (NC device) 5. The value of voltage E is set. In the present embodiment, the DC voltage E can be switched in four stages of 60V, 90V, 120V, and 150V.
[0021]
The negative electrode of the DC power supply 4 is connected to the workpiece 3. On the other hand, the positive electrode of the DC power supply 4 is connected to the grounded processing electrode 2 via a diode 6, a current limiting resistor circuit 7 and a source-drain circuit of a switching field effect transistor 8. In FIG. 1, a coil indicated by a symbol L between the field effect transistor 8 and the machining electrode 2 is a wiring (not shown) that electrically connects the DC power supply 4 and the electric discharge machining gap G. The line-to-line inductance is shown. Thus, an inductance component exists between the DC power supply 4 and the electric discharge machining gap G in addition to the resistance component by the current limiting resistor circuit 7.
[0022]
The gate pulse signal SG is given to the gate electrode 8G of the field effect transistor 8 from the gate control circuit 9, and when the level of the gate pulse signal SG becomes a high level state, the field effect transistor 8 is turned on, and the gate When the level of the pulse signal SG becomes a low level state, the field effect transistor 8 is turned off. As described above, the field effect transistor 8 is ON / OFF controlled by the gate pulse signal SG, whereby the machining pulse voltage is intermittently and repeatedly applied to the electric discharge machining gap G.
[0023]
The current limiting resistor circuit 7 is a circuit provided for setting the level of the electric discharge machining current flowing through the electric discharge machining gap G via the field effect transistor 8. The resistance value in the current limiting resistor circuit 7 is as follows: This is a known configuration that is set to a value according to a machining current setting signal SI indicating a machining current value set in a machining condition setting unit 5A provided in the numerical control device (NC device) 5. Accordingly, in FIG. 1, the current limiting resistor circuit 7 is represented as a resistor, and the detailed circuit configuration is not shown and described.
[0024]
Therefore, when the field effect transistor 8 is switched from OFF to ON, a DC voltage E having a value set in accordance with the power supply voltage command signal SE is first applied to the electric discharge machining gap G as a machining pulse voltage, whereby electric discharge machining is performed. When a discharge occurs in the gap G, a level of electric discharge machining according to the resistance value set in the current limiting resistor circuit 7 can be passed through the electric discharge machining gap G.
[0025]
In order to electrically detect that electric discharge has occurred in the electric discharge machining gap G from a voltage drop phenomenon of the machining gap voltage Vg generated when electric discharge is started in the electric discharge machining gap G, a discharge detection circuit 10 is provided.
[0026]
In the discharge detection circuit 10, a series circuit of a DC bias power source 11 and resistors 12 and 13 is connected in parallel to the electric discharge machining gap G as shown in the figure. From the connection point between the resistor 12 and the resistor 13, The detection voltage Vf of a level corresponding to the level of the machining gap voltage Vg is obtained.
[0027]
The detection voltage Vf is applied to the negative input terminal of the voltage comparator 14, and the reference voltage Vs output from the reference voltage generator 15 and applied to the positive input terminal of the voltage comparator 14 in the voltage comparator 14. The level is compared with the detection voltage Vf. ReleaseElectricity start inspectionThe output circuit 10 is configured to detect a voltage drop timing of the machining gap voltage Vg indicating that an electric discharge has occurred in the electric discharge machining gap G by this level comparison.
[0028]
The reference voltage generating unit 15 includes a microprocessor (CPU) 16, a memory 17, and a digital-analog converter (D / A) 18 that are connected as illustrated, and the CPU 16 receives a power supply voltage command from the NC device 5. Signal SE and machining current setting signal SIIn response, the value of the reference voltage Vs most suitable for the value of the DC voltage E set at that time is calculated. In the present embodiment, a value obtained by adding 25 V to 75% of a value obtained by subtracting 25 V as the discharge voltage from the value of the DC voltage E set at that time is calculated, and this is used as the value of the reference voltage Vs. The memory 17 stores a program and data necessary for this calculation, and the CPU 16 outputs calculation output data DVs indicating the reference voltage value at that time and sends it to the D / A 18. The D / A 18 converts the arithmetic output data DVs that is digital data sent from the CPU 16 into a corresponding analog voltage signal, and this analog voltage signal is applied to the + input terminal of the voltage comparator 14 as the reference voltage Vs. .
[0029]
Therefore, when no electric discharge occurs in the electric discharge machining gap G, Vf ≦ Vs and the output level of the voltage comparator 14 is in a high level state. On the other hand, when discharge starts in the electric discharge machining gap G, the level of the detection voltage Vf increases, and when Vf ≧ Vs, the output level of the voltage comparator 14 becomes a low level state. That is, when the output of the voltage comparator 14 is in a low level state, this indicates that electric discharge is generated in the electric discharge machining gap G.
[0030]
Next, discharge generation detection by level comparison operation of the detection voltage Vf and the reference voltage Vs using the voltage comparator 14 will be described with reference to FIGS.
[0031]
FIG. 2 shows the state of the level drop due to the discharge of the machining gap voltage Vg when the resistance value of the current limiting resistor circuit 7 is 1 ohm, in each case where the DC voltage E is 150V, 120V, 90V, and 60V.simulationIt is what was done. FIG. 3 shows how the level of the machining gap voltage Vg is reduced when the resistance value of the current limiting resistor circuit 7 is 10 ohms, and the DC voltage E is 150V, 120V, 90V, and 60V.simulationIt is what was done. The level of the reference voltage Vs is set to a value obtained by adding 25 V to 75% of a value obtained by subtracting 25 V as a discharge voltage from the DC voltage E, and thus becomes 120 V, 97.5 V, 75 V, and 52.5 V, respectively. . Here, the reason for changing the level of the reference voltage Vs according to the DC voltage E is that if a voltage drop is detected at one reference voltage Vs level, for example, 52.5 V, the DC voltage E is different as shown in FIG. YoAs the DC voltage E increasesThis is to cause a long detection delay.Therefore, for example, if the DC voltage E is 150 V and the voltage drop detection level (reference voltage Vs for detecting the start of discharge) is 52.5 V, 5 μs or less.Since it is difficult to accurately set the lower discharge time, the level of the reference voltage Vs is calculated and set according to the value of the DC voltage E as described above in order to advance the detection time.
[0032]
As can be seen from FIG. 2, when detected at the level of the reference voltage Vs corresponding to the value of the DC voltage E, even if the value of the DC voltage E changes, the value of the machining gap voltage Vg is 75% of the value due to the start of discharge. The time to decrease to 0.6 is 0.6 μsec. Similarly, in the case of FIG. 3, all become 0.08 microseconds.
[0033]
That is,Electricity start inspectionWhen an attempt is made to detect the occurrence of discharge using the output circuit 10, there is always a time between the time when the discharge is actually generated in the electric discharge machining gap G and the time when the output level of the voltage comparator 14 changes from the high level to the low level. Although a delay occurs, it can be seen that this detection delay time DT is closely related not to the level of the DC voltage E but to the resistance value of the current limiting resistor circuit 7.
[0034]
The present invention utilizes this knowledge to accurately control the energization time of the discharge current flowing in the electric discharge machining gap G.
[0035]
That is, if the resistance value of the current limiting resistor circuit 7 is determined, that is, if the content of the machining current setting signal SI from the machining condition setting unit 5A is determined, the value of the detection delay time DT is also determined accordingly. . Therefore, if the discharge current energization time ST is set in the machining condition setting unit 5A, the time of ST-DT is from the voltage drop timing at which the output level of the voltage comparator 14 changes from the high level to the low level. If the field-effect transistor 8 is turned off by the gate control circuit 9 after a lapse of time, the energization time ST of the discharge current flowing in the electric discharge machining gap G is released.Electricity start inspectionIn spite of the detection delay in the output circuit 10, it will be as set.
[0036]
For this reason, the electric discharge machining apparatus 1 shown in FIG. 1 is provided with a calculation unit 19 for calculating the ST-DT value.
[0037]
The arithmetic unit 19 receives the machining current setting signal SI and the set value of the energization time ST from the numerical control device (NC device) 5 and responds to the set machining current value at that time, that is, the resistance value of the current limiting resistor circuit 7. The time delay DT is called from the memory of the arithmetic unit 19 (not shown) as the number of clock pulses, and the subtraction is performed from the number of pulses converted from the set value of the energization time ST to the number of clock pulses. The value of ST-DT as the number of clock pulses is the on-control time of the field-effect transistor 8 after discharge detection set as the count value of the on-time counter of the gate control circuit 9, and an operation indicating this on-control time The output 19A is sent to the gate control circuit 9.
[0038]
In addition to the arithmetic output 19A, the gate control circuit 9 has a free output.Electricity start inspectionThe output signal Ss of the voltage comparator 14 is input from the output circuit 10. The gate pulse control circuit 9 includes a 10 MHz clock pulse generator, an on counter that counts clock pulses and sets an on time, an off time counter that counts clock pulses and sets a discharge pause time, and the like. The number of on-clock pulses of the on-control time indicated by the arithmetic output 19A is set as the count number of the on-counter, and starts counting clock pulses at the voltage rise timing that is the level change timing of the output signal Ss from high to low. When the count reaches the set value, that is, when the time (ST-DT) has elapsed, the on-count is terminated and the off-time counter starts counting clock pulses. Then, a gate control operation is performed in which the field effect transistor 8 is turned off until the count number of the off counter reaches a predetermined set number sent from the processing condition setting unit 5A. Further, a gate pulse signal for turning on the field drop transistor 8 again when the count number of the off-time counter reaches a predetermined number.SGIs output, and the above operation is repeated by the output signal Ss.
[0039]
As a result, the field effect transistor 8 has passed the energization time ST from the timing at which the electric discharge actually starts in the electric discharge machining gap G.BeforeAs a result, the energization time S set in the machining condition setting unit 5A is set.T-DTAn electric discharge current can be passed through the electric discharge machining gap G for machining the workpiece 3.
[0040]
The gate control circuit 9ControlledThisTaThe timing at which the gate pulse signal SG is repeatedly output in the period and the level of the output signal Ss of the voltage comparator 14 changes from the high level to the low level.PredeterminedAfter the elapse of time, the output of the gate pulse signal SG is stopped.Control settingsSpecified energization time ST-DTIn this configuration, an electric discharge machining current can flow through the gap E. This energization time ST is preset in the numerical control device (NC device) 5 as a discharge current energization period according to the required processing purpose, and an operator sets and inputs the value from an input device (not shown). It has a configuration that can.
[0041]
Next, the operation of the gate control circuit 9 will be described with reference to FIG. First off-count at time TAClock pulse byWhen the count value reaches the set value, the level of the gate pulse signal SG is switched from the low level to the high level, the field effect transistor 8 is turned on, and the machining gap voltage Vg generated at both ends of the electric discharge machining gap G rises. At TB, the level of the machining gap voltage Vg becomes substantially equal to the level of the DC voltage E. At this time, the level of the detection voltage Vf was kept at zero during the period of time TA to TB for the DC bias power supply 11.Rising rapidly from theAt the timing of the time point TB, the level of the detection voltage Vf becomes a level corresponding to the value of the machining gap voltage Vg.
[0042]
When electric discharge is started in the electric discharge machining gap G at the time point TC, the discharge current Ig starts to flow in the electric discharge machining gap G, and thereby the level of the machining gap voltage Vg starts to decrease. Then, when Vf ≧ Vs at time TD, the level of the output signal Ss changes from the high level to the low level. That is, when electric discharge is actually started at the electric discharge machining gap G at the time point TC, this can be electrically detected at the time point TD with a time delay corresponding to the time delay DT.
[0043]
As the level of the output signal Ss changes from the high level to the low level, the clock pulse CP from the clock pulse generator (not shown) in the gate control circuit 9 starts to be counted, and the clock set by the arithmetic output 19A At the time point TE when the number of pulses CP is counted, the level of the gate pulse signal SG is lowered and the field effect transistor 8 is turned off. As a result, the machining gap voltage Vg and the discharge current Ig are both zero. Since the discharge current Ig becomes zero, the level of the output signal SsIs lowBellRatakaReturn to Bell. In this way, the electric discharge machining gap G has a predetermined length from the time point TD to the time point TE at which the start of discharge is detected.timeThe on-time of the field effect transistor 8 is controlled only during this period. In general, if the level of the gate pulse signal SG is changed from a high level to a low level when the Nth clock pulse CP is output according to the set number of calculation outputs 19A calculated by the calculation unit, N pieces The discharge current can be set to flow through the electric discharge machining gap G for a time corresponding to the minute clock pulse CP.
[0044]
The operation for one pulse of the gate pulse signal SG has been described above.Is output when the off-clock set in the off-counter is counted after the above-mentioned on-counter finishes counting the off-clock.Each time, the above-described control operation is repeated, the machining energy scheduled for each output of the gate pulse signal SG is supplied to the electric discharge machining gap G, and the workpiece 3 is subjected to electric discharge machining.
[0045]
As described above, when the electric discharge is actually started in the electric discharge machining gap GControl-compensated ST-DTIt becomes possible to allow the discharge current to flow through the electric discharge machining gap G only during the interval, and the variation from the set value of the energization time of the machining current becomes small. For this reason, the malfunction that an electrode consumption characteristic falls or a processing surface becomes rough is improved remarkably.
[0046]
【The invention's effect】
According to the present invention, the time per discharge current flowing in the electric discharge machining gap can be made substantially equal to the set value regardless of the value of the machining pulse voltage applied to the electric discharge machining gap and the value of the current limiting resistance. As a result, variations in the machining current energization time are reduced. As a result, it is possible to perform processing with desired processing characteristics, and the problem that the electrode wear characteristics are deteriorated and the processing surface is roughened is remarkably improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of an embodiment of an electric discharge machining apparatus according to the present invention.
FIG. 2 is a graph for explaining discharge detection in the discharge detection circuit shown in FIG. 1;
FIG. 3 is a graph for explaining discharge detection in the discharge detection circuit shown in FIG. 1;
FIG. 4 is a waveform diagram of each part for explaining the operation of the electric discharge machining apparatus of FIG. 1;
FIG. 5 is a block diagram showing an example of a conventional electric discharge machining apparatus.
[Explanation of symbols]
1 EDM
2 Processing electrode
3 Workpiece
4 DC power supply
5 Numerical control device (NC device)
5A Machining condition setting section
8 Field effect transistors
9 Gate control circuit
10 Discharge start detection circuit
15 Reference voltage generator
19 Calculation unit
E DC voltage
G EDM gap
L Line inductance
SE Power supply voltage command signal
SI machining current setting signal
Ss output signal
Vg Machining gap voltage
Vf detection voltage
Vs reference voltage

Claims (1)

The machining pulse voltage taken out from the DC power supply that can be set to change the output voltage according to the machining condition input setting to the NC device using the switch means that is controlled on and off by the gate control circuit, The electric discharge machining current is applied to the electric discharge machining gap by intermittently and repeatedly applying the electric discharge machining gap formed between the workpiece and the machining electrode through a current limiting resistance circuit whose resistance value is determined according to the value. In an electric discharge machining apparatus in which the workpiece is subjected to electric discharge machining,
A gap detection circuit in which a DC bias power supply is connected in series to two series voltage dividing resistors is connected in parallel to the electric discharge machining gap, and the detection voltage of the gap detection circuit is compared with a reference voltage to control the discharge start detection signal. comprising a discharge start detecting circuit for supplying the circuit, the reference voltage group reference voltage generated by computing the following formula (1) in accordance with the output voltage value of the DC power supply by the power supply voltage command output from the machining condition setting section is what is output from the section, and an arithmetic unit for outputting the gate control circuit and the correction operation more on-control time of said switching means in accordance with the set machining current value,
The gap caused by the generation of the discharge by comparing the gate control circuit output by said switching means on operation by the electric discharge machining gap resulting machining gap voltage level before Symbol operation to output the criteria voltage level a discharge start detecting circuit for detecting the voltage drop timing of the detection voltage,
The gate control circuit has a function of turning off the switching means in order to stop the application of the machining pulse voltage to the electric discharge machining gap when the correction calculation ON control time has elapsed from the detected voltage drop timing. An electrical discharge machining apparatus characterized by
Formula (1) Vs = (E-25V (discharge voltage)) * 0.75 + 25V
Where E is the command output voltage value of the DC power supply.

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