Power supply control device and electrical discharge machining system

Abstract

The power control device (50) includes a high-frequency pulse power supply (1) that applies a high-frequency pulse voltage between the electrodes and the workpiece, an inductance (3) that generates a voltage at both ends that is proportional to the time change of the inter-electrode current, which is the current flowing between the electrodes, and a discharge pulse cutoff device (2) that monitors the voltage across the inductance, which is the potential difference across the inductance (3), and cuts off the application of the high-frequency pulse voltage to the electrodes formed between the electrodes and the workpiece based on the change in the voltage across the inductance.

Description

Technical Field

[0001] The present disclosure relates to a power control device for applying a power supply voltage for electric discharge machining and an electric discharge machining system.

Background Art

[0002] Electric discharge machining is a method of machining a workpiece by applying a pulsed voltage to the space between an electrode and the workpiece, bringing the electrode and the workpiece close to each other to generate an electric discharge, and using the heat generated by the electric discharge. Hereinafter, the space between the electrode and the workpiece is referred to as "inter-electrode gap", the current flowing through the inter-electrode gap is referred to as "inter-electrode current", and the voltage between the electrodes is referred to as "inter-electrode voltage".

[0003] The machining modes of an electric discharge machine are roughly classified into two types: "rough machining" for roughly machining a workpiece and "finish machining" for approaching the dimensions of a drawing. By performing machining step by step in multiple times from rough machining to finish machining, the workpiece is machined into an arbitrary machining shape.

[0004] Examples of workpieces of an electric discharge machine include members such as molds, automotive parts, and aerospace parts where friction occurs on the surface during use. However, if the surfaces of these workpieces are not smooth, problems such as shortening of the life of the mold or deterioration of the performance of the parts may occur due to the metal surface being shaved by the friction generated during use. Therefore, when evaluating the performance of an electric discharge machine, an index called "surface roughness", which indicates the degree of unevenness of the surface of the machined workpiece after machining, is highly regarded.

[0005] Generally, the surface roughness of the machined surface of a workpiece of an electric discharge machine depends on the integrated value of the inter-electrode current flowing during electric discharge. The smaller the integrated value of the inter-electrode current, the finer the surface roughness obtained. Therefore, in order to obtain a fine surface roughness in electric discharge machining, it is necessary to set the peak value and pulse width of the inter-electrode current small.

[0006] The peak value of the inter-pole current can be adjusted by the voltage applied between the poles from the power supply control device, or by the value of the current-limiting resistor installed on the output side of the power supply control device. Furthermore, the pulse width of the inter-pole current can be adjusted by performing high-frequency switching in the power supply control device. However, there is a problem in that the pulse width of the inter-pole current is limited by the performance of the switching elements, which are components of the power supply control device.

[0007] One solution to this problem is to interrupt the discharge pulse during the discharge after detecting the discharge. In the electrical discharge machining machine disclosed in Patent Document 1, when the peak value of the inter-electrode current flowing through a detection resistor provided between the negative electrode of the power supply that applies voltage between the electrodes and the workpiece is detected to reach a set value, a switching element provided between the positive electrode of the power supply and the electrode is turned off, thereby achieving a pulse width of 1 μsec or less and obtaining a fine surface roughness. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 55-96230 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the inter-electrode current waveform fluctuates due to parasitic components resulting from the mechanical structure of the electrical discharge machining machine, such as the casing and wiring, as well as the power supply voltage. Therefore, the method disclosed in Patent Document 1 requires setting the peak value of the inter-electrode current each time the electrical discharge machining machine is changed or the machining conditions are changed. In addition, machining debris or bubbles generated during electrical discharge machining may accumulate between the electrodes, and if the condition between the electrodes changes, the discharge energy used for electrical discharge machining will also change. For this reason, even if the peak value is set based on the parasitic components of the electrical discharge machining machine and the power supply voltage, the peak value of the inter-electrode current will not be the same each time. In the method disclosed in Patent Document 1, if the peak value cannot be set correctly, the switching element cannot be turned off at the appropriate timing, and the desired pulse width cannot be obtained. For this reason, the electrical discharge machining machine disclosed in Patent Document 1 may result in insufficient discharge energy input or inability to interrupt the discharge.

[0010] This disclosure has been made in view of the above, and aims to provide a power supply control device that can shorten discharge pulses regardless of variations in parasitic components caused by the mechanical structure of the electrical discharge machining machine and the machining conditions. [Means for solving the problem]

[0011] To solve the above-mentioned problems and achieve the objective, the power control device according to this disclosure comprises a high-frequency pulse power supply that applies a high-frequency pulse voltage between electrodes formed by an electrode and a workpiece, and an inductor that generates a voltage at both ends that is proportional to the time change of the inter-electrode current, which is the current flowing between the electrodes. The power control device also comprises a discharge pulse cutoff device that monitors the voltage across the inductance, which is the potential difference across the inductance, and cuts off the application of the high-frequency pulse voltage to the electrodes based on the change in the voltage across the inductance. [Effects of the Invention]

[0012] The power control device described herein has the effect of shortening the discharge pulse regardless of variations in parasitic components caused by the mechanical structure of the electrical discharge machine and the processing conditions. [Brief explanation of the drawing]

[0013] [Figure 1] Figure showing the configuration of the electric discharge machining system according to Embodiment 1 [Figure 2] Timing chart showing the operation of the power supply control device according to Embodiment 1 [Figure 3] Figure showing the first configuration example of the discharge pulse cutoff device of the power supply control device according to Embodiment 1 [Figure 4] Figure showing the second configuration example of the discharge pulse cutoff device of the power supply control device according to Embodiment 1 [Figure 5] Figure showing the third configuration example of the discharge pulse cutoff device of the power supply control device according to Embodiment 1 [Figure 6] Figure showing the configuration of the electric discharge machining system according to Embodiment 2 [Figure 7] Timing chart showing the operation of the power supply control device according to Embodiment 2 [Figure 8] Figure showing the first configuration example of the discharge pulse cutoff device of the power supply control device according to Embodiment 2 [Figure 9] Figure showing the second configuration example of the discharge pulse cutoff device of the power supply control device according to Embodiment 2 [Figure 10] Figure showing the configuration of the electric discharge machining system according to Embodiment 3 [Figure 11] Timing chart showing the operation of the power supply control device according to Embodiment 3 [Figure 12] Figure showing the configuration of the electric discharge machining system according to Embodiment 4 [Figure 13] Figure showing the configuration of the electric discharge machining system according to Embodiment 5 [Figure 14] Figure showing the configuration of the power supply control device according to Embodiment 6 [Figure 15] Figure showing the inter - electrode current and the voltage across the inductor at the time of discharge cutoff in the power supply control device of the electric discharge machining system according to Embodiment 1 [Figure 16] Timing chart of the power supply control device according to Embodiment 6 [Figure 17] Figure showing the configuration of the power supply control device according to Embodiment 7 [Figure 18] Figure showing the configuration of the power control device according to Embodiment 8

Embodiments for Carrying out the Invention

[0014] Hereinafter, the power control device and the electrical discharge machining system according to the embodiments will be described in detail based on the drawings.

[0015] Embodiment 1. FIG. 1 is a diagram showing the configuration of the electrical discharge machining system according to Embodiment 1. The electrical discharge machining system 100 according to Embodiment 1 includes an electrical discharge machine 30 and a numerical control (NC) device 80. The electrical discharge machine 30 includes a power control device 50 for electrical discharge machining and a machining unit 70. The machining unit 70 includes an electrode E. In FIG. 1, the electrode E and the workpiece W are schematically shown as triangular and rectangular figures, but the shapes of the electrode E and the workpiece W are not limited. When the electrical discharge machining system 100 is a wire electrical discharge machine, the electrode E is a wire. When the electrical discharge machining system 100 is a micro-hole electrical discharge machine and a die-sinking electrical discharge machine, the electrode E is a shaped electrode.

[0016] The power control device 50 is a power supply device that applies a pulsed voltage for electrical discharge machining to the gap formed between the electrode E and the workpiece W.

[0017] The machining unit 70 is a part of the electrical discharge machining system 100 where the electrode E and the workpiece W are relatively moved to perform electrical discharge machining, and has a shaft drive unit for relatively moving the electrode E and the workpiece W. The shaft drive unit is composed of a motor, a servo amplifier, etc. In FIG. 1, the illustration of the shaft drive unit is omitted.

[0018] The power control device 50 comprises a high-frequency pulse power supply 1, a discharge pulse interruption device 2, and an inductance 3. The high-frequency pulse power supply 1 is a power supply that applies a positively polarized pulse voltage and has two terminals, terminal A and terminal B. Terminal A of the high-frequency pulse power supply 1 is connected to one end of the inductance 3, and terminal B is connected to the workpiece W. The high-frequency pulse power supply 1 outputs a positive voltage between the terminals from terminal A with reference to terminal B. The discharge pulse interruption device 2 comprises a switching element 4, a comparator 5, and a gate driver 6. The comparator 5 detects the voltage applied to the inductance 3.

[0019] The switching element 4 has an input terminal and an output terminal. The input terminal of the switching element 4 is connected to the other end of the inductance 3, and the output terminal of the switching element 4 is connected to electrode E.

[0020] Inductor 3 is connected between terminal A of the high-frequency pulse power supply 1 and the input terminal of the switching element 4. Inductor 3 generates a voltage across its ends that is proportional to the time change of the inter-electrode current, which is the current flowing between the electrodes.

[0021] The comparator 5 of the discharge pulse interruption device 2 monitors the inductance voltage, which is the voltage difference across the inductance 3, and sends a signal to the gate driver 6 to turn off the switching element 4 when the inductance voltage becomes negative.

[0022] An example of a switching element 4 is a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), but it is not limited to this. The switching element 4 can be any element whose conduction state can be controlled by the gate driver 6, and may be an IGBT (Insulated Gate Bipolar Transistor) or a transistor element other than an IGBT.

[0023] Figure 2 is a timing chart showing the operation of the power control device according to Embodiment 1. Note that the voltage across the inductance actually has a waveform that rises sharply, but Figure 2 schematically represents the waveform of the voltage across the inductance. The NC device 80 transmits a command signal to the high-frequency pulse power supply 1 that includes parameters such as the timing of applying the high-frequency voltage between the poles, the on time, off time, number of pulses, voltage value, and polarity of the high-frequency pulse voltage.

[0024] Furthermore, the NC device 80 transmits a command signal to the machining unit 70 to control the positional relationship between the electrode E and the workpiece W.

[0025] The initial state of the power control device 50 is that no voltage is applied between the electrodes, the voltage output of the high-frequency pulse power supply 1 is off, and the switching element 4 of the discharge pulse interruption device 2 is on.

[0026] The output start command to initiate the voltage output of the high-frequency pulse power supply 1 is sent from the NC device 80.

[0027] If the voltage output of the high-frequency pulse power supply 1 does not start, the initial state is maintained. On the other hand, when the output of the high-frequency pulse power supply 1 starts, the high-frequency pulse power supply 1 changes from the off state to the on state, and a voltage is applied between the electrodes.

[0028] When a discharge occurs, the voltage across the electrodes drops to an arc voltage, and an inter-electrode current begins to flow between the electrodes. This inter-electrode current also flows through the inductance 3, and when the inter-electrode current increases, the voltage across the inductance becomes positive, relative to electrode E. Conversely, when the inter-electrode current decreases, the voltage across the inductance becomes negative. Therefore, when the inter-electrode current reaches its peak and begins to decrease, the voltage across the inductance changes from a positive voltage to a negative voltage. The comparator 5 detects the voltage across the inductance 3. At this time, the comparator 5 detects that the voltage across the inductance has become negative and outputs a discharge interruption signal to the gate driver 6. The gate driver 6 supplies a switching element control signal to the switching element 4 based on the discharge interruption signal input from the comparator 5. As a result, the drain-source voltage, which is the voltage between the drain and source of the switching element 4, changes, and the discharge pulse is interrupted by the switching operation.

[0029] Furthermore, delay time a shown in Figure 2 is the propagation delay time from when the comparator 5 detects that the voltage across the inductance has become negative until it outputs a discharge cutoff signal, or the propagation delay time from when the comparator 5 detects that the voltage across the inductance has become 0V until it stops outputting the discharge cutoff signal. Delay time b is the propagation delay time from when the discharge cutoff signal output by the comparator 5 is input to the gate driver 6 until the gate driver 6 outputs a switching element control signal to turn off the switching element 4, or the propagation delay time from when the comparator 5 stops outputting the discharge cutoff signal until the gate driver 6 outputs a switching element control signal to turn on the switching element 4. Delay time c is the turn-off time from when the switching element control signal to turn off the switching element 4 is input from the gate driver 6 to the switching element 4 until the drain-source voltage of the switching element 4 rises and the switching element 4 actually turns off. The delay time d is the turn-on time from when the switching element control signal that turns on the switching element 4 is input from the gate driver 6 to the switching element 4 until the drain-source voltage of the switching element 4 decreases and the switching element 4 actually turns on.

[0030] After the discharge pulse is cut off, when the current between the poles stops flowing, no current flows through the inductance 3, and the voltage across the inductance becomes 0V. The comparator 5 outputs a discharge cutoff signal to the gate driver 6 so that the switching element 4 turns off when the voltage across the inductance is negative. Therefore, when the voltage across the inductance is 0V, the comparator 5 stops outputting the discharge cutoff signal to the gate driver 6 so that the switching element 4 turns on. As a result, when the current between the poles stops flowing, the switching element 4 automatically turns on, and a voltage is applied between the poles from the high-frequency pulse power supply 1.

[0031] When a discharge pulse is interrupted, the negative value that becomes the comparison voltage in comparator 5 is, for example, a voltage value that takes into account the input offset voltage of comparator 5. The input offset voltage of comparator 5 is the small voltage difference that occurs between the input terminals of comparator 5. If the input offset voltage is not taken into consideration, the voltage will be compared with a voltage value that is shifted by the input offset voltage from the set comparison voltage. Therefore, if the input offset voltage is not taken into consideration, the discharge may not be interrupted as designed, or the discharge may be interrupted under unintended conditions. In order to prevent malfunction of the discharge pulse interruption device 2, it is important to set the comparison voltage to a voltage value that has a margin of the input offset voltage. When setting the comparison voltage, the wider the margin of the input offset voltage, the better the malfunction can be prevented, but if the margin of the input offset voltage is wide, the time from when the inter-electrode current reaches its peak until interruption will be longer. For this reason, it is preferable to set the comparison voltage in comparator 5 while considering the margin at which malfunctions do not occur and the time until the discharge pulse is interrupted.

[0032] The method for obtaining the reference potential of the comparator 5 and the gate driver 6 will be explained. Figure 3 is a diagram showing a first configuration example of the discharge pulse interruption device of the power control device according to Embodiment 1. Figure 3 shows the configuration of the discharge pulse interruption device 2 using a non-isolated gate driver 61 as the gate driver 6. In the example shown in Figure 3, a MOSFET is used for the switching element 4. The discharge pulse interruption device 2 shown in Figure 3 is equipped with a power supply 7 for driving the gate driver, a power supply 8 for driving the comparator, and a power supply 9 for the comparison voltage of the comparator 5. In the first configuration example of the discharge pulse interruption device 2 of the power control device 50 according to Embodiment 1, the comparator 5 detects the voltage applied to the series circuit between the switching element 4 and the inductance 3 adjacent to the switching element 4, and outputs a discharge interruption signal to the gate driver 6 when it detects that the polarity of the voltage applied to the series circuit between the switching element 4 and the inductance 3 adjacent to the switching element 4 has changed.

[0033] When a non-isolated gate driver 61 is used for the gate driver 6, the reference potential of the non-isolated gate driver 61 and the reference potential of the comparator 5 are set to be the same as the potential at the connection point between the output terminal of the switching element 4 and electrode E. In this case, the potential between the connection point of terminal A of the high-frequency pulse power supply 1 and the inductance 3 is input to the inverting input terminal of the comparator 5, and a negative voltage calculated from the reference potential of the comparator 5, taking into account the input offset voltage, is input from the comparison voltage power supply 9 to the non-inverting input terminal. Note that a dual-power supply driven comparator 5 is used.

[0034] Figure 4 shows a second configuration example of the discharge pulse interruption device of the power control device according to Embodiment 1. Figure 4 shows the configuration of a discharge pulse interruption device 2 using an isolated gate driver 62 as the gate driver 6. In the example shown in Figure 4, the potential of the connection point between terminal A of the high-frequency pulse power supply 1 and the inductance 3 is input to the inverting input terminal of the comparator 5. The reference potential on the secondary side of the isolated gate driver 62 is the same as the potential of the connection point between the output terminal of the switching element 4 and electrode E. The reference potential on the primary side of the isolated gate driver 62 and the reference potential of the comparator 5 are the same as the potential of the connection point between the input terminal of the switching element 4 and the inductance 3. At this time, the potential of the connection point between terminal A of the high-frequency pulse power supply 1 and the inductance 3 is input to the inverting input terminal of the comparator 5, and a negative voltage considering the input offset voltage from the reference potential of the comparator 5 is input from the comparison voltage power supply 9 to the non-inverting input terminal. Note that a dual-power supply driven comparator 5 is used.

[0035] Figure 5 shows a third configuration example of the discharge pulse interruption device of the power control device according to Embodiment 1. Figure 5 shows the configuration of a discharge pulse interruption device 2 using an isolated gate driver 62 as the gate driver 6. In the example shown in Figure 5, the potential of the connection point between terminal A of the high-frequency pulse power supply 1 and the inductance 3 is input to the non-inverting input terminal of the comparator 5. The reference potential on the secondary side of the isolated gate driver 62 is the same as the potential of the connection point between the output terminal of the switching element 4 and electrode E. The reference potential on the primary side of the isolated gate driver 62 and the reference potential of the comparator 5 are the same as the potential of the connection point between the input terminal of the switching element 4 and the inductance 3. At this time, the potential of the connection point between terminal A of the high-frequency pulse power supply 1 and the inductance 3 is input to the non-inverting input terminal of the comparator 5, and a positive voltage considering the input offset voltage from the reference potential of the comparator 5 is input from the comparison voltage power supply 9 to the inverting input terminal. The comparator 5 may be driven by a single power supply or by a dual power supply.

[0036] As described above, the power control device 50 according to Embodiment 1 can shorten the pulse width because it interrupts the discharge when a discharge occurs and the inter-electrode current reaches its peak and begins to decrease. Therefore, the power control device 50 according to Embodiment 1 can reduce the processing energy for each discharge, and thus can contribute to improving the surface roughness performance of the electrical discharge machining system 100.

[0037] Furthermore, in the power control device 50 according to Embodiment 1, it is only necessary to detect the timing when the voltage across the inductance becomes a negative value or 0V, taking into account the input offset voltage of the comparator 5, so there is no need to set the peak value. For this reason, the power control device 50 according to Embodiment 1 can shorten the discharge pulse regardless of the variation in parasitic components caused by the mechanical structure of the electrical discharge machine 30 and the processing conditions.

[0038] Furthermore, the power control device 50 according to Embodiment 1 has a control circuit for interrupting discharge composed of a comparator 5 and a gate driver 6, eliminating the need for complex control elements such as FPGAs (Field Programmable Gate Arrays) and ASICs (Application Specific Integrated Circuits) that have computational functions. Therefore, the power control device 50 according to Embodiment 1 does not experience delays in interrupting discharge pulses due to computation time and delay time occurring within FPGAs and ASICs, enabling high-speed interruption of discharge pulses.

[0039] Embodiment 2. Figure 6 shows the configuration of the electrical discharge machining system according to Embodiment 2. The electrical discharge machining system 100 according to Embodiment 2 differs from the electrical discharge machining system 100 according to Embodiment 1 in that the high-frequency pulse power supply 1 applies a pulse voltage of negative polarity.

[0040] In the electrical discharge machining system 100 according to Embodiment 2, the high-frequency pulse power supply 1 is a power supply that applies a negative polarity pulse voltage. Terminal A of the high-frequency pulse power supply 1 is connected to one end of the inductance 3, and terminal B is connected to the workpiece W. The high-frequency pulse power supply 1 outputs a negative voltage between terminals from terminal A with reference to terminal B.

[0041] The discharge pulse interruption device 2 comprises a switching element 4, a comparator 5, and a gate driver 6. The input terminal of the switching element 4 is connected to electrode E, and the output terminal of the switching element 4 is connected to the other end of the inductance 3.

[0042] The inductor 3 is connected between terminal A of the high-frequency pulse power supply 1 and the output terminal of the switching element 4.

[0043] The comparator 5 of the discharge pulse interrupter 2 detects the voltage across the inductance and sends a signal to the gate driver 6 to turn off the switching element 4 when the voltage across the inductance becomes positive.

[0044] Figure 7 is a timing chart showing the operation of the power control device according to Embodiment 2. When the output of the high-frequency pulse power supply 1 is started, the high-frequency pulse power supply 1 changes from the off state to the on state, and a voltage is applied across the electrodes. When discharge occurs, the voltage across the electrodes decreases to the arc voltage, and an inter-electrode current begins to flow between the electrodes. The inter-electrode current also flows through the inductance 3, and when the inter-electrode current flowing in the negative direction increases, the voltage across the inductance becomes a negative value with respect to electrode E. Conversely, when the inter-electrode current flowing in the negative direction decreases, the voltage across the inductance becomes a positive value. Therefore, when the inter-electrode current flowing in the negative direction reaches its peak and begins to decrease, the voltage across the inductance changes from a negative voltage to a positive voltage. The comparator 5 detects the voltage applied to the inductance 3. At this time, the comparator 5 detects that the voltage across the inductance has become a positive value and outputs a discharge cutoff signal to the gate driver 6. The gate driver 6 supplies the voltage signal necessary to control the switching element 4 based on the discharge cutoff signal input from the comparator 5. As a result, the gate driver 6 outputs a switching element control signal that turns off the switching element 4, thereby interrupting the discharge pulse. Delay time a is the propagation delay time from when the comparator 5 detects that the voltage across the inductance has become positive until it outputs the discharge interruption signal, or the propagation delay time from when the comparator 5 detects that the voltage across the inductance has become 0V until it stops outputting the discharge interruption signal. Delay times b, c, and d are the same as those for the power control device 50 according to Embodiment 1.

[0045] Thus, the power control device 50 according to Embodiment 2 can block negative polarity discharge by changing the direction of the switching element 4 and the signal output method of the comparator 5 from those of the power control device 50 according to Embodiment 1.

[0046] Here, we will explain how to obtain the reference potentials for the comparator 5 and the gate driver 6. Figure 8 is a diagram showing a first configuration example of a discharge pulse interruption device of a power control device according to Embodiment 2. Figure 8 shows the configuration of a discharge pulse interruption device 2 using a non-isolated gate driver 61 as the gate driver 6. In the example shown in Figure 8, a MOSFET is used for the switching element 4. The discharge pulse interruption device 2 shown in Figure 8 is equipped with a power supply 7 for driving the gate driver, a power supply 8 for driving the comparator, and a power supply 9 for the comparison voltage of the comparator 5.

[0047] In the first configuration example of the discharge pulse interruption device 2 of the power control device 50 according to Embodiment 2, the reference potential of the non-isolated gate driver 61 and the reference potential of the comparator 5 are set to be the same as the potential at the connection point between the output terminal of the switching element 4 and the inductance 3. A negative voltage is input to the non-inverting input terminal of the comparator 5, taking into account the input offset voltage from the reference potential of the comparator 5. A dual-power supply driven type comparator 5 is used.

[0048] Figure 9 shows a second example configuration of the discharge pulse interruption device of the power control device according to Embodiment 2. Figure 9 shows the configuration of the discharge pulse interruption device 2 using a non-isolated gate driver 61 as the gate driver 6. In the example shown in Figure 9, the potential of the connection point between terminal A of the high-frequency pulse power supply 1 and the inductance 3 is input to the non-inverting input terminal of the comparator 5. In the example shown in Figure 9, a MOSFET is used as the switching element 4. The discharge pulse interruption device 2 shown in Figure 9 is equipped with a gate driver drive power supply 7, a comparator drive power supply 8, and a comparison voltage power supply 9 for the comparator 5.

[0049] In the second configuration example of the discharge pulse interruption device 2 of the power control device 50 according to Embodiment 2, the reference potential of the comparator 5 and the reference potential of the non-isolated gate driver 61 are set to be the same as the potential at the connection point between the output terminal of the switching element 4 and the inductance 3. A positive voltage is input to the inverting input terminal of the comparator 5, taking into account the input offset voltage from the reference potential of the comparator 5. The comparator 5 may be driven by a single power supply or by a dual power supply.

[0050] The electrical discharge machining system 100 according to Embodiment 2 can shorten the pulse width of the negative polarity discharge pulse. Therefore, the power control device 50 according to Embodiment 2 can reduce the machining energy for each discharge, which can contribute to improving the surface roughness performance of the electrical discharge machining system 100.

[0051] Embodiment 3. Figure 10 shows the configuration of the electrical discharge machining system according to Embodiment 3. The electrical discharge machining system 100 according to Embodiment 3 differs from the electrical discharge machining system 100 according to Embodiment 1 in that the high-frequency pulse power supply 1 applies bipolar pulses between the electrodes. The high-frequency pulse power supply 1 is a power supply that applies bipolar pulse voltages between the electrodes, and an example is a full-bridge inverter. The high-frequency pulse power supply 1 can output only positive-polarity pulse voltages or negative-polarity pulse voltages continuously, or it can output positive-polarity pulse voltages and negative-polarity pulse voltages alternately.

[0052] In the power control device 50 of the electrical discharge machining system 100 shown in Embodiments 1 and 2, if the switching element 4 is an element capable of reverse conduction, such as a MOSFET, it can interrupt current in one direction, but it cannot interrupt current flowing in the reverse direction. Therefore, in the power control device 50 of the electrical discharge machining system 100 according to Embodiment 3, as shown in Figure 10, a switching element 4a for interrupting positive pulses and a switching element 4b for interrupting negative pulses are connected in parallel and in opposite directions between the electrode E and the inductance 3. Furthermore, a polarity switching switch 10 is connected between the switching elements 4a, 4b and the inductance 3 to switch which of the switching elements 4a and 4b is connected to the inductance 3. An example of a polarity switching switch 10 is an SPDT (Single-Pole Double-Throw) switch. The polarity switching switch 10 switches which of the switching elements 4a and 4b is connected to the inductance 3 according to a polarity switching signal transmitted from the NC device 80. In Embodiment 3, a polarity switching flag indicating the polarity of the high-frequency pulse voltage is included as a parameter.

[0053] When a positive pulse voltage is applied from the high-frequency pulse power supply 1, the NC device 80 sends a command to the polarity switching switch 10 that includes a polarity switching flag as a parameter indicating the application of a positive pulse voltage. This causes the polarity switching switch 10 to operate in such a way that the switching element 4a, which has its input terminal connected to the output terminal OUT1 and its output terminal connected to electrode E, conducts with the inductance 3. The comparator 5a of the discharge pulse interruption device 2 then detects the voltage across the inductance and sends a positive pulse interruption discharge interruption signal to the gate driver 6a to turn off the switching element 4a when the voltage across the inductance becomes negative.

[0054] On the other hand, when a negative polarity pulse voltage is applied from the high-frequency pulse power supply 1, the NC device 80 sends a command to the polarity switching switch 10 that includes a polarity switching flag as a parameter indicating that a negative polarity pulse voltage is to be applied. This causes the polarity switching switch 10 to operate in such a way that the switching element 4b, which has its output terminal connected to the output terminal OUT2 of the polarity switching switch 10 and its input terminal connected to electrode E, conducts with the inductance 3. The comparator 5b of the discharge pulse interruption device 2 then detects the voltage across the inductance and sends a negative polarity pulse interruption discharge interruption signal to the gate driver 6b that turns off the switching element 4b when the voltage across the inductance becomes a positive value.

[0055] Figure 11 is a timing chart showing the operation of the power control device according to Embodiment 3. When the output of the high-frequency pulse power supply 1 is started, the high-frequency pulse power supply 1 changes from the off state to the on state, and a voltage is applied between the electrodes. When discharge occurs, the voltage between the electrodes decreases to the arc voltage, and an inter-electrode current begins to flow between the electrodes. The inter-electrode current also flows through the inductance 3, and when a positive polarity pulse is applied between the electrodes, the voltage across the inductance becomes a positive value with respect to electrode E as the inter-electrode current increases.

[0056] On the other hand, when the inter-electrode current decreases, the voltage across the inductance becomes negative. Therefore, when the inter-electrode current reaches its peak and begins to decrease, the voltage across the inductance changes from a positive voltage to a negative voltage. Comparator 5 detects the voltage across inductance 3. At this time, comparator 5a detects that the voltage across the inductance has become negative, and outputs a discharge interruption signal for positive polarity pulse interruption to gate driver 6a.

[0057] The gate driver 6a supplies a positive pulse interruption switching element control signal to the switching element 4a based on the signal input from the comparator 5a. At this time, the polarity switching signal transmitted from the NC device 80 to switch the polarity switching switch 10 includes a polarity switching flag as a parameter indicating that a positive pulse voltage should be applied. As a result, the positive pulse interruption switching element 4a and the inductor 3 are connected, while the negative pulse interruption switching element 4b and the inductor 3 are not connected, so no current flows. Consequently, the gate driver 6a outputs a positive pulse interruption switching element control signal that turns off the switching element 4a, thereby interrupting the discharge pulse.

[0058] When a negative polarity pulse is applied between the electrodes, the voltage across the inductance becomes negative when the inter-electrode current flowing in the negative direction increases, relative to electrode E. On the other hand, when the inter-electrode current flowing in the negative direction decreases, the voltage across the inductance becomes positive. Therefore, when the inter-electrode current flowing in the negative direction reaches its peak and begins to decrease, the voltage across the inductance changes from a negative voltage to a positive voltage. Comparator 5 detects the voltage across inductance 3. At this time, comparator 5b detects that the voltage across the inductance has become positive, and comparator 5b outputs a discharge interruption signal for negative polarity pulse interruption to gate driver 6b.

[0059] The gate driver 6b supplies a negative polarity pulse interruption switching element control signal to the switching element 4b based on the negative polarity pulse interruption discharge interruption signal input from the comparator 5b. At this time, the polarity switching signal transmitted from the NC device 80 to switch the polarity switching switch 10 includes a polarity switching flag indicating that a negative polarity pulse voltage is to be applied. Therefore, the switching element 4b for negative polarity pulse interruption and the inductor 3 are connected, while the switching element 4a for positive polarity pulse interruption and the inductor 3 are not connected, and no current flows. As a result, the gate driver 6b outputs a negative polarity pulse interruption switching element control signal that turns off the switching element 4b, thereby interrupting the discharge pulse.

[0060] Thus, the power control device 50 of the electrical discharge machining system 100 according to Embodiment 3 can switch the switching elements 4a and 4b that conduct for each polarity, and can shut off the conducting switching elements 4a and 4b by fluctuations in the voltage across the inductance. The delay times a, b, c, and d are the same as those of the power control device 50 according to Embodiment 1.

[0061] Embodiment 4. Figure 12 shows the configuration of the electrical discharge machining system according to Embodiment 4. The electrical discharge machining system 100 according to Embodiment 4 differs from the electrical discharge machining system 100 according to Embodiment 1 in that the positions of the inductance 3 and the switching element 4 are different. In the electrical discharge machining system 100 according to Embodiment 4, the input terminal of the switching element 4 is connected to terminal A of the high-frequency pulse power supply 1, one end of the inductance 3 is connected to electrode E, and the other end of the inductance 3 is connected to the output terminal of the switching element 4.

[0062] In the power control device 50 of the electrical discharge machining system 100 according to Embodiment 4, the discharge can be interrupted in the same way as in the power control device 50 of the electrical discharge machining system 100 according to Embodiment 1.

[0063] Similarly, when a negative-polarity pulse voltage is applied between the poles, as in Embodiment 2, it is possible to swap the positions of the switching element 4 and the inductance 3.

[0064] Embodiment 5. Figure 13 shows the configuration of the electrical discharge machining system according to Embodiment 5. The electrical discharge machining system 100 according to Embodiment 5 differs from the electrical discharge machining system 100 according to Embodiment 1 in that a discharge pulse interrupter 2e and an inductance 3e are installed between terminal B of the high-frequency pulse power supply 1 and the workpiece W. A parasitic capacitance 12 exists between the housing of the electrical discharge machining machine 30 and the ground.

[0065] Since current flows from terminal B of the high-frequency pulse power supply 1 to the workpiece W, the input terminal of the switching element 4e is connected to the inductance 3e and the output terminal is connected to the workpiece W. When the current due to the parasitic capacitance 12 begins to flow through the inductance 3e and starts to increase, the voltage across the inductance, which is the potential difference across the inductance 3e with respect to the workpiece W, is a positive voltage. When the current starts to decrease, the voltage across the inductance 3e changes from a positive voltage to a negative voltage. The comparator 5 detects the voltage across the inductance 3. Therefore, when the comparator 5e detects that the voltage across the inductance 3e has become negative, the discharge pulse interruption device 2e outputs a discharge interruption signal to the gate driver 6e and interrupts the discharge pulse. For this reason, the electrical discharge machining system 100 according to embodiment 6 can also interrupt the current flowing between the electrodes from the parasitic capacitance 12 present between the housing of the electrical discharge machining machine 30 and the ground.

[0066] Furthermore, if the switching element 4e is capable of reverse conduction, even if the switching element 4e is turned off, the discharge of the positive pulse voltage will not be interrupted by the switching element 4e.

[0067] In the electrical discharge machining system 100 according to Embodiments 1 to 4, since one discharge pulse interrupter 2 is installed between terminal A of the high-frequency pulse power supply 1 and electrode E, if a parasitic capacitance 12 between the housing of the electrical discharge machining machine 30 and ground exists on the terminal B side of the high-frequency pulse power supply 1, the current flowing due to the charge stored in the parasitic capacitance 12 flowing between the electrodes cannot be interrupted. In the electrical discharge machining system 100 according to Embodiment 5, since a discharge pulse interrupter 2e is also installed between terminal B of the high-frequency pulse power supply 1 and workpiece W, the current flowing due to the parasitic capacitance 12 existing between the housing of the electrical discharge machining machine 30 and ground can be interrupted.

[0068] Embodiment 6. Figure 14 shows the configuration of the power control device according to Embodiment 6. The power control device 50 according to Embodiment 6 differs from the power control device 50 of the electrical discharge machining system 100 according to Embodiment 1 in that it includes a diode 13. The diode 13 has its anode side connected to the input terminal of the switching element 4 and its cathode side connected to terminal A of the high-frequency pulse power supply 1, and is connected in parallel with the inductance 3.

[0069] Here, the effects of the power control device 50 according to Embodiment 7 will be explained by comparing it with the power control device 50 of the electrical discharge machining system 100 according to Embodiment 1. Figure 15 is a diagram showing the inter-pole current and the voltage across the inductance when the discharge is interrupted in the power control device of the electrical discharge machining system according to Embodiment 1. When the discharge is interrupted during discharge, the inter-pole current changes instantaneously to zero amperes, so the slope of the inter-pole current waveform, di / dt, becomes steep. At this time, the voltage across the inductance also increases according to the formula L × di / dt for the voltage across the inductance, which may cause peripheral components to fail because it exceeds the input voltage range of the comparator 5. Specifically, assuming that the current decreases from 10A to 0A in 20nsec with a constant slope, di / dt is -500Meg. Therefore, if the inductance value of the inductance 3 through which this current flows is 10nH, a voltage fluctuation of -5V occurs, and if the inductance value is 100nH, a voltage fluctuation of -50V occurs.

[0070] For simplicity, the slope of the current waveform was assumed to be constant in this explanation. However, since the slope di / dt of the current waveform is not constant, the range of variation may be larger.

[0071] Figure 16 is a timing chart of the power control device according to Embodiment 6. Figure 16 shows an example where a positive high-frequency pulse is applied between the electrodes. In the power control device 50 according to Embodiment 6, when the discharge is interrupted, the current that was flowing between the electrodes flows back through the diode 13, and the current flowing through the inductance 3 is not instantaneously interrupted. In contrast, in the power control device 50 of the electrical discharge machining system 100 according to Embodiment 1, the current flowing through the inductance 3 is the same as the current flowing between the electrodes, so when the discharge is interrupted, the current flowing through the inductance 3 is also instantaneously interrupted.

[0072] Therefore, in the power control device 50 according to Embodiment 6, the di / dt, which is the slope of the current waveform when the discharge is interrupted, is smaller compared to the power control device 50 of the electrical discharge machining system 100 according to Embodiment 1, and the fluctuation of the voltage across the inductance is also smaller.

[0073] As described above, the power control device 50 according to Embodiment 7 prevents the current flowing through the inductance 3 from being instantaneously interrupted when discharge is interrupted, and prevents large fluctuations in the voltage across the inductance. This prevents the voltage across the inductance from exceeding the input voltage range of the comparator 5 and other input devices, thereby preventing failure of peripheral components.

[0074] In some cases, depending on the inductance value of inductance 3 and the amount of current flowing through inductance 3, the voltage across the inductance may exceed the input voltage of comparator 5. In such cases, a voltage divider circuit may be connected across inductance 3, and the voltage reduced by the voltage divider circuit may be input to comparator 5.

[0075] Embodiment 7. Figure 17 shows the configuration of the power control device according to Embodiment 7. The power control device 50 according to Embodiment 7 differs from the power control device 50 according to Embodiment 6 in that it applies a negative polarity pulse between the electrodes. In the power control device 50 according to Embodiment 7, which applies a negative polarity pulse between the electrodes, the current between the electrodes during discharge flows in the opposite direction to that in the case of positive polarity, so the switching element 4 has its input terminal connected to electrode E and its output terminal connected to inductance 3.

[0076] Since the orientation of the diode 13 must be reversed to match the direction of the inter-electrode current, in the power control device 50 according to Embodiment 8, the diode 13 is connected in parallel with the inductance 3, with its cathode side connected to the output terminal of the switching element 4 and its anode side connected to terminal A of the high-frequency pulse power supply 1.

[0077] The power control device 50 according to Embodiment 7 can prevent large fluctuations in the voltage across the inductance when a negative polarity pulse is applied between the electrodes.

[0078] Embodiment 8. Figure 18 shows the configuration of the power control device according to Embodiment 8. The power control device 50 according to Embodiment 8 differs from the power control device 50 according to Embodiment 1 in that it includes a coil 14 that is electromagnetically coupled to the inductance 3. The comparator 5 receives the voltage across the coil 14 that is electromagnetically coupled to the inductance 3 as input.

[0079] In the power control device 50 according to Embodiment 1, the voltage across the inductance was directly input to the comparator 5. At this time, the parasitic components present in the power control device 50 increase due to the capacitance between the terminals of the comparator 5 and the parasitic inductance component of the wiring connecting the ends of the inductance 3 to the comparator 5. In actual electrical discharge machining, in addition to the current flowing from the power supply to the electrodes, current due to the energy stored in the parasitic components also flows to the electrodes. Therefore, the more the parasitic components increase, the longer the discharge pulse width becomes.

[0080] In the power control device 50 according to Embodiment 8, the comparator 5 detects both ends of the coil 14 which is electromagnetically coupled to the inductance 3, thus physically separating the inductance 3 and the comparator 5. As a result, the power control device 50 according to Embodiment 8 can suppress the influence of parasitic components and maintain a short high-frequency pulse applied from the high-frequency pulse power supply 1.

[0081] Embodiment 9. The power control device 50 according to Embodiment 9 differs from the power control device 50 of the electrical discharge machining system 100 according to Embodiment 1 in that a wide bandgap power semiconductor is used for the switching element 4.

[0082] Wide-bandgap power semiconductors are power devices formed from wide-bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), or diamond. Compared to silicon power semiconductors, wide-bandgap power semiconductors have a shorter delay time between the input of a control signal and the switching element 4 becoming on or off.

[0083] The power control device 50 according to Embodiment 9, which uses a wide-bandgap power semiconductor for the switching element 4, is able to shorten the delay time c shown in Figure 2, and as a result, the width of the discharge pulse can be made shorter, making it possible to obtain a finer machined surface roughness.

[0084] However, because wide-bandgap power semiconductors switch faster than silicon power semiconductors, common-mode noise tends to increase. If this common-mode noise is superimposed on the terminal voltage of comparator 5, comparator 5 may malfunction. For this reason, a filter for common-mode noise suppression may be implemented at the input of comparator 5 to reduce common-mode noise.

[0085] The configurations shown in the above embodiments are merely examples of the content, and can be combined with other known technologies. It is also possible to omit or modify parts of the configuration without departing from the gist of the invention. [Explanation of Symbols]

[0086] 1 High-frequency pulse power supply, 2,2e Discharge pulse interrupter, 3,3e Inductance, 4,4a,4b,4e Switching element, 5,5a,5b,5e Comparator, 6,6a,6b,6e Gate driver, 7 Power supply for gate driver drive, 8 Power supply for comparator drive, 9 Power supply for comparison voltage, 10 Polarity change switch, 12 Parasitic capacitance, 13 Diode, 14 Coil, 30 Electrical discharge machining machine, 50 Power supply control device, 61 Non-isolated gate driver, 62 Isolated gate driver, 70 Machining section, 80 NC device, 100 Electrical discharge machining system.

Claims

1. A high-frequency pulse power supply that applies a high-frequency pulse voltage between the electrode and the workpiece, An inductor is provided at both ends to generate a voltage proportional to the time change of the inter-electrode current, which is the current flowing between the electrodes, A power control device comprising a discharge pulse interruption device that monitors the voltage across the inductance, which is the potential difference across the inductance, and interrupts the application of the high-frequency pulse voltage to the electrodes based on the change in the voltage across the inductance.

2. The power control device according to claim 1, characterized in that the discharge pulse interruption device interrupts the application of the high-frequency pulse voltage to the electrodes when it detects that the polarity of the voltage across the inductance has changed.

3. The aforementioned high-frequency pulse power supply is The power control device according to claim 1, characterized in that it applies the high-frequency pulse voltage generated based on parameters relating to the output characteristics of the high-frequency pulse voltage between the electrodes.

4. The power control device according to claim 3, characterized in that the parameter is at least one of the following: the timing for applying the high-frequency pulse voltage between the poles, the on time, off time, number of pulses, voltage value, and polarity switching flag indicating the polarity of the high-frequency pulse voltage.

5. The aforementioned parameter includes the polarity switching flag, When the polarity switching flag indicates the application of a positive polarity high-frequency pulse voltage, the high-frequency pulse power supply applies the positive polarity high-frequency pulse voltage between the electrodes, and when the discharge pulse interruption device detects that the polarity of the voltage across the inductance has changed from positive to negative, it interrupts the application of the high-frequency pulse voltage between the electrodes. The power supply control device according to claim 4, characterized in that when the polarity switching flag indicates the application of the negative polarity high-frequency pulse voltage, the high-frequency pulse power supply applies the negative polarity high-frequency pulse voltage between the electrodes, and when the discharge pulse interruption device detects that the polarity of the voltage across the inductance has changed from a negative to a positive value, it interrupts the application of the high-frequency pulse voltage between the electrodes.

6. The aforementioned discharge pulse interruption device, The system comprises a switching element that turns on and off the application of a high-frequency pulse voltage between the poles, a comparator that detects the voltage across the inductance, and a gate driver that outputs a switching element control signal for turning the switching element on and off. When the comparator detects that the polarity of the voltage across the inductance has changed, it outputs a discharge interruption signal to the gate driver. The power control device according to claim 1, characterized in that when the gate driver detects the discharge interruption signal, it outputs a switching element control signal that turns off the switching element.

7. The discharge pulse interruption device comprises a switching element that turns on and off the application of a high-frequency pulse voltage to the electrodes, a comparator that detects the voltage applied to the series circuit between the switching element and an inductor adjacent to the switching element, and a gate driver that outputs a switching element control signal for turning the switching element on and off. When the comparator detects that the polarity of the voltage applied to the series circuit between the switching element and the inductance adjacent to the switching element has changed, it outputs a discharge interruption signal to the gate driver. The power control device according to claim 1, characterized in that the gate driver turns off the switching element control signal when it detects the discharge interruption signal.

8. The diode element is connected in parallel with the inductance, The power control device according to claim 6, characterized in that the anode side of the diode element is connected to the low-potential side of the inductance, and the cathode side of the diode element is connected to the high-potential side of the inductance.

9. The system includes a coil for non-contact detection of the voltage across the inductance, The power control device according to claim 6, characterized in that the output voltage of the coil is input to the comparator, and the comparator outputs the discharge interruption signal to the gate driver.

10. The power supply control device according to claim 6, characterized in that a wide-bandgap power semiconductor is applied to the switching element.

11. The aforementioned discharge pulse interruption device, The system comprises a switching element that turns on and off the application of a high-frequency pulse voltage between the poles, a comparator that detects the voltage across the inductance, and a gate driver that outputs a switching element control signal for turning the switching element on and off. When the comparator detects that the polarity of the voltage across the inductance has changed, it outputs a discharge interruption signal to the gate driver. The power control device according to claim 3, characterized in that when the gate driver detects the discharge interruption signal, it outputs a switching element control signal that turns off the switching element.

12. The aforementioned discharge pulse interruption device, The system comprises a switching element that turns on and off the application of a high-frequency pulse voltage between the poles, a comparator that detects the voltage across the inductance, and a gate driver that outputs a switching element control signal for turning the switching element on and off. When the comparator detects that the polarity of the voltage across the inductance has changed, it outputs a discharge interruption signal to the gate driver. The power control device according to claim 5, characterized in that when the gate driver detects the discharge interruption signal, it outputs a switching element control signal that turns off the switching element.

13. The switching element includes a positive polarity switching element that blocks positive polarity pulses, It has a negative polarity switching element that blocks negative polarity pulses, The system includes a polarity switching switch that, based on the polarity switching flag, switches whether to connect the inductance to the positive polarity switching element or the negative polarity switching element, The power control device according to claim 12, characterized in that the polarity switching switch connects the positive polarity switching element to the inductance when the polarity switching flag indicates that a positive polarity pulse voltage is to be applied, and connects the negative polarity switching element to the inductance when the polarity switching flag indicates that a negative polarity pulse voltage is to be applied.

14. The discharge pulse interruption device comprises a switching element that turns on and off the application of a high-frequency pulse voltage to the electrodes, a comparator that detects the voltage applied to the series circuit between the switching element and an inductor adjacent to the switching element, and a gate driver that outputs a switching element control signal for turning the switching element on and off. When the comparator detects that the polarity of the voltage applied to the series circuit between the switching element and the inductance adjacent to the switching element has changed, it outputs a discharge interruption signal to the gate driver. The power control device according to claim 3, characterized in that the gate driver turns off the switching element control signal when it detects the discharge interruption signal.

15. The diode element is connected in parallel with the inductance, The power control device according to claim 11, characterized in that the anode side of the diode element is connected to the low-potential side of the inductance, and the cathode side of the diode element is connected to the high-potential side of the inductance.

16. The system includes a coil for non-contact detection of the voltage across the inductance, The power control device according to claim 11, characterized in that the output voltage of the coil is input to the comparator, and the comparator outputs the discharge interruption signal to the gate driver.

17. The power supply control device according to claim 11, characterized in that a wide-bandgap power semiconductor is applied to the switching element.

18. A power control device according to any one of claims 1, 2, 6 to 10, A machining unit that performs electrical discharge machining by moving the electrode and the workpiece relative to each other, The power control device and the numerical control device that outputs command signals to control the processing unit to the power control device and the processing unit, An electrical discharge machining system characterized by comprising the following features.

19. A power control device according to any one of claims 3 to 5 or 11 to 17, A machining unit that performs electrical discharge machining by moving the electrode and the workpiece relative to each other, The power control device and the numerical control device that outputs command signals to control the processing unit to the power control device and the processing unit, An electrical discharge machining system characterized by comprising the following features.

20. The electrical discharge machining system according to claim 19, characterized in that the command signal is a command including the parameters.

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