JP2012166323A - Electric discharge machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric discharge machining device that can prevent electric discharge from becoming uneven, can achieve stable machining and has an increased machining speed even in a group pulse application method using a finish machining power supply.SOLUTION: The electric discharge machining device for applying a group pulse between a machining electrode and an object to be machined to thereby machine the object to be machined includes: an inter-electrode state detector for detecting an inter-electrode state between the machining electrode and the object to be machined after the group pulse has been applied therebetween; and a controller for controlling an application pattern of the group pulse based on the inter-electrode state detected by the inter-electrode state detector.

Description

  The present invention relates to an electric discharge machining apparatus for machining a workpiece by electric discharge, and particularly to a wire electric discharge machining apparatus.

  The electric discharge machining apparatus is an apparatus for machining a workpiece by generating an arc discharge between the machining electrode and the workpiece. The electric discharge machining apparatus requires a power source (machining power source) for generating arc discharge. Conventionally, there are various types of processing power supply configurations.

  For example, electric discharge machining configured with two power supply units including a roughing power supply unit, a full bridge circuit including four switching elements, and a finishing power supply unit provided with a current limiting resistor for limiting the discharge current Power supply devices exist (for example, Patent Documents 1 and 2).

  This patent document 1 discloses a finishing method using only a finishing power supply unit. Briefly, a group pulse generated by intermittently turning on and off two switching elements forming a diagonal arm of a full bridge circuit is applied to an electrode gap formed by a workpiece and a machining electrode. Then, the voltage between the electrodes gradually rises, and when the discharge start voltage is exceeded, dielectric breakdown occurs and arc discharge occurs. As a result of the discharge, a discharge current flows through the electrode gap and the voltage between the electrodes decreases. This discharge current is defined by the ON width of the switching element at the maximum, and the discharge stops when the switching element is turned OFF. Thereafter, when the switching element is turned on, charging of the electrode gap is resumed and the above operation is repeated. After the switching element is intermittently turned on / off for an arbitrary time, the switching element is switched to two switching elements forming the other diagonal arm, and the same ON / OFF action is intermittently performed. When water is used as the working fluid, it is necessary to keep the average interelectrode voltage at zero V in order to prevent electrolysis. Therefore, it is common to alternately switch the diagonal arms in this way, invert the polarity, and control the average interelectrode voltage to zero V.

  Further, in Patent Document 2, as in Patent Document 1, two power sources, that is, a power supply unit for finishing and a power source unit for roughing are used, and a method for improving variation (unevenness) in discharge particularly during roughing is disclosed. is doing.

  On the other hand, as a method for keeping the distance between the electrodes constant, it is common to use an “average voltage servo” that controls the traveling speed of the shaft so that the average value of the voltage between the electrodes is approximately constant. In this method, there is a large gap between the time variation of the voltage necessary for the axis control and the time variation of the voltage generated as a machining phenomenon. Therefore, even if the average voltage is the same, uneven discharge (variation) ) Occurs. When the discharge is concentrated in time, the wire breakage is caused, so that it is necessary to reduce the variation in the discharge. Therefore, the rest time is provided so that the number of discharges per unit time becomes a constant value.

  First, a rectangular voltage pulse is applied from the finishing power supply unit. The occurrence of discharge is detected by monitoring the interelectrode voltage with a comparator. When the voltage between the electrodes decreases due to the discharge, it is considered that a discharge has occurred, and the pulse application of the finishing power supply unit is stopped and switched to the roughing power supply unit to supply a machining current between the electrodes. After applying a pulse current having an arbitrary pulse width, the rough machining power supply is stopped. After providing an arbitrary pause time, a rectangular voltage pulse is applied again from the power supply unit for finishing, and the above operation is repeated.

  The time from when a voltage is applied across the electrodes from the finishing power supply to when the discharge occurs is called no-load time. Discharge variation is evaluated by measuring the no-load time per unit time. When the no-load time is shortened on average, it is determined that the discharge density has increased, and the pause time is set longer, and the number of discharges per unit time is controlled to be constant. As a result, uneven discharge can be reduced and stable machining can be performed.

International Publication No. 2009/096025 JP 2001-113419 A

  In particular, in an electric discharge machining apparatus that uses oil as a machining fluid, non-uniformity of electric discharge as disclosed in Patent Document 2 is likely to occur. That is, the wire electric discharge machining apparatus has a problem that the wire is easily broken. In addition, if the wire electrode is a thin wire region of φ0.05 or less, processing may be performed using only the finishing power supply unit as roughing processing, so there is uneven discharge when applying group pulses with the finishing power supply. Improvement is indispensable for improving machining performance. In this regard, the prior art has the following problems.

  First, an adverse effect of applying the control method disclosed in Patent Document 2 to the processing method disclosed in Patent Document 1 will be described by comparing the configurations of Patent Document 2 and Patent Document 1. In Patent Document 2, a rectangular voltage pulse is applied from the finishing power supply unit, and once the pulse is applied, basically, the switching element continues to be turned on until discharge occurs. When a pulse is applied and the voltage between the electrodes rises and becomes higher than the reference voltage (discharge detection voltage) of the comparator, measurement of the no-load time is started. Thereafter, when the voltage between the electrodes decreases due to the occurrence of discharge and becomes lower than the reference voltage of the comparator, it is regarded as the occurrence of discharge, the pulse application from the finishing power supply unit is stopped, and the measurement of the no-load time is ended. On the other hand, in Patent Document 1, a simple group pulse is applied between electrodes regardless of discharge / non-discharge. In a no-load state (also referred to as an open state), the interelectrode voltage gradually increases with the application of the group pulse. However, since the discharge start voltage changes in accordance with the distance between the electrodes and the state between the electrodes, the voltage level at which the discharge is performed cannot be determined by the comparator of Patent Document 2. That is, since discharge timing and no-load time cannot be measured accurately, discharge unevenness cannot be eliminated.

  Even if the no-load time can be detected by a method other than that disclosed in Patent Document 2, the meaning of the no-load time is different between Patent Document 1 and Patent Document 2, so the same control is simply performed. The method cannot be taken. In Patent Document 2, since a constant voltage value (power supply voltage) is applied between the electrodes in the open state, it is only necessary to measure the no-load time at that time. However, in Patent Document 1, both the no-load time and the interelectrode voltage change in an open state, particularly when voltage application starts. Since a simple group pulse is applied between the electrodes, the voltage between the electrodes rises with a certain time constant. For example, if the voltage between the electrodes is sufficiently lower than the power supply voltage and close to zero V, the voltage that rises by one pulse application becomes high, but if the voltage between the electrodes approaches the power supply voltage, it rises by one pulse application. The voltage to be reduced. For this reason, the interval between discharges and the discharge unevenness cannot be managed correctly only by measuring the no-load time.

  In Patent Document 2, a voltage pulse in an open state is applied by a finishing power supply unit, and a current pulse necessary for machining is supplied by a rough machining power supply unit. In this way, the pulse for starting discharge and the pulse for machining are separated, but in Patent Document 1, these functions are combined. The machining current in the group pulse is mainly provided by the electric charge stored in the interelectrode stray capacitance, and depends on the interelectrode voltage when discharged. Since the voltage between the electrodes rises with a time constant determined by the duty ratio between the ON width and OFF width of the pulse, the discharge energy cannot be controlled depending on the time from discharge to the next discharge. Processing energy corresponding to the determined inter-electrode voltage is input. For this reason, optimal processing is not performed, which may cause a reduction in processing speed and instability of processing.

  The present invention has been made in view of the above, and even with a group pulse application method using a finishing machining power supply, an electrical discharge machining apparatus that prevents uneven discharge, stabilizes machining, and improves machining speed is obtained. For the purpose.

  In order to solve the above-described problems and achieve the object, the present invention provides an electrical discharge machining apparatus that performs machining by applying a group pulse between a machining electrode and a workpiece, by applying the group pulse. In order to detect the state between the electrodes between the machining electrode and the workpiece, the voltage between the electrodes for machining and the workpiece is detected, and the change in the detected voltage between the workpieces is detected. It is characterized by comprising an inter-electrode state detecting means for calculating, and a control means for controlling an application pattern of the group pulse based on a change in the inter-electrode voltage.

  According to the present invention, even in the group pulse application method using the finishing power source, the group pulse application pattern can be set according to the gap state between the non-discharge state and the discharge state. Therefore, it is possible to prevent uneven discharge, stabilize the machining, and improve the machining speed.

FIG. 1 is a block diagram showing a configuration of an electric discharge machining apparatus according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a configuration example of the discharge state detection circuit shown in FIG. FIG. 3 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining a basic discharge control operation. FIG. 4 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the first embodiment. FIG. 5 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the second embodiment. FIG. 6 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the third embodiment. FIG. 7 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the fourth embodiment. FIG. 8 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the fifth embodiment.

  Embodiments of an electric discharge machining apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a block diagram showing a configuration of an electric discharge machining apparatus according to an embodiment of the present invention. In FIG. 1, the electric discharge machining apparatus 1 includes a power supply unit, an electric discharge machining unit 3, and a control unit 4.

  In the power supply unit and the electric discharge machining unit 3, the workpiece 11 and the machining electrode 12 arranged opposite to each other are the electric discharge machining unit, and the switching elements SW1 to SW4 and the current limiting resistor 13 arranged around the workpiece 11 are finished. It corresponds to the machining power supply. The workpiece 11 is grounded to the ground. In this configuration, the inter-electrode state detection circuit 16 is arranged in the present embodiment.

  The four switching elements SW1 to SW4 are connected in a full bridge to form a full bridge circuit. Switching elements SW1 and SW4 and switching elements SW2 and SW3 are switching elements that constitute a diagonal arm.

  In this full bridge circuit, a terminal D1 to which one end of the switching element SW1 and one end of the switching element SW3 are connected, and a terminal D2 to which one end of the switching element SW2 and one end of the switching element SW4 are connected are a pair of direct currents. Configure the terminal. A terminal D3 to which the other end of the switching element SW1 and the other end of the switching element SW2 are connected and a terminal D4 to which the other end of the switching element SW3 and the other end of the switching element SW4 are connected are a pair of alternating currents. Configure the terminal.

  In the full bridge circuit configured as described above, the positive terminal of the DC power source 10 is connected to one terminal D1 of the pair of DC terminals, and the negative terminal of the DC power source 10 is connected to the other terminal D2. Further, the workpiece 11 is connected to one terminal D3 of the pair of AC terminals via the current limiting resistor 13, and the processing electrode 12 is directly connected to the other terminal D4.

  1 shows the case where the current limiting resistor 13 is connected to the workpiece 11 side, it may be connected to the processing electrode 12 side. The configuration of FIG. 1 is a circuit configuration for performing AC driving particularly when water is used as the machining fluid. If oil is used as the working fluid, it may be configured with only one arm. For example, a configuration in which the switching elements SW2 and SW3 are removed may be used.

  Further, as indicated by a broken line, between the workpiece 11 and the processing electrode 12, the shape and size of the workpiece 11 and the processing electrode 12, or between the workpiece 11 and the processing electrode 12. There is a stray capacitance component 14 that is determined by the distance between the electrodes (distance between the poles), and at the same time, there is a stray resistance component 15 that is determined by the type of the processing liquid, the material of the workpiece 11, and the like. There are two types of processing fluids, water and oil. The specific resistance value of water is lower than that of oil, and the current flows easily. That is, the value of the floating resistance component 15 is lower in water than in oil.

  An inter-electrode state detection circuit 16 is provided to detect an inter-electrode state between the workpiece 11 and the processing electrode 12, and the detected inter-electrode state is input to the control unit 4.

  The contents of electric discharge machining performed by the electric discharge machining apparatus 1 are controlled by the host controller 5. The host controller 5 includes a storage unit 6 in which machining parameters are stored and an operation identification processing unit 7. The machining parameters stored in the storage unit 6 include information indicating machining operations and machining conditions. The operation identification processing unit 7 identifies control information (hereinafter referred to as “machining information”) necessary for performing electrical discharge machining based on the machining parameter information read from the storage unit 6 and transmits the control information to the control unit 4. Here, the control information includes, for example, information on which of processing speed, surface roughness, electrode wear, and straightness is important.

  The control unit 4 determines the voltage to be applied between the workpiece 11 and the processing electrode 12 (hereinafter referred to as “interelectrode applied voltage”) using the processing information output from the motion identification processing unit 7. Based on the detection signal output from the inter-pole state detection circuit 16, the pulse width (pulse application time), pulse pause width (pulse pause time), pulse period (pulse duration) in the pulse signal for switching control of the switching elements SW1 to SW4 ( The ratio of the pulse width to the pulse width + pulse period width (duty ratio), the length of the group pulse, the pause time of the group pulse and the group pulse, and the like are determined. The switching elements SW <b> 1 to SW <b> 4 are controlled based on a switching signal output from the control unit 4 and generate a group pulse to be applied to the workpiece 11 and the processing electrode 12. As a result, a desired inter-electrode applied voltage is supplied between the workpiece 11 and the processing electrode 12. When a discharge is generated by a group pulse between the workpiece 11 and the processing electrode 12, the discharge state is detected one by one by the inter-electrode state detection circuit 16 and notified to the control unit 4.

  FIG. 2 is a circuit diagram showing a configuration example of the inter-pole state detection circuit 16. In FIG. 2, the inter-electrode state detection circuit 16 includes a voltage dividing resistor 21 for dividing the inter-electrode voltage, a differentiation circuit unit 22 for detecting a change point when the inter-electrode voltage changes, and a differential waveform. A polarity extracting unit 23 for extracting only the plus side and the minus side, and an A / D conversion unit 24 for digitizing and outputting the plus side voltage and the minus side voltage of the extracted differential waveform to the control unit 4. I have. However, depending on the voltage between the electrodes, it is not necessary to provide the voltage dividing resistor 21 in particular.

<Basic discharge control operation>
FIG. 3 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining a basic discharge control operation. 3, FIG. 3A shows a switching signal applied to the switching elements SW1 and SW4, and FIG. 3B shows a switching signal applied to the switching elements SW2 and SW3.

  As shown in FIGS. 4A and 4B, in the present embodiment, the switching elements SW1 and SW4 are subjected to switching control so as to repeat ON (conductive state) and OFF (non-conductive state). The switching elements SW2 and SW3 are controlled so as to be always OFF without performing the switching operation. That is, the full bridge circuit in the present embodiment performs a unipolar operation for generating a group pulse so that the workpiece 11 is at the ground potential and the machining electrode 12 is at a negative voltage.

  FIG. 6C shows an inter-electrode voltage waveform between the workpiece 11 and the machining electrode 12 generated by the switching signals shown in FIGS. FIG. 4D shows an output waveform of the differentiation circuit unit 22 of the inter-electrode state detection circuit 16. In the present embodiment, a description will be given using a driving waveform particularly when oil is used as a machining fluid. That is, there is no need to apply an AC waveform like water, and a unipolar waveform is simply applied.

  Further, FIG. 3 shows a state in which the stray capacitance 14 between the electrodes is charged from the timing (1) to the timing (2) and from the timing (3) to the timing (4). It shows that discharge occurs at the moment of timing (4).

  The charging waveform is determined by the time constant determined by the current limiting resistor 13 and the stray capacitance 14, and the duty ratio of the ON time and OFF time of the switching elements SW1 and SW4. The larger the difference between the interelectrode voltage and the power supply voltage, The slope of the voltage waveform increases and the output value of the differentiation circuit unit 22 also increases. Discharge occurs at an arbitrary timing, and the interelectrode voltage drops to the arc voltage. At this time, it should be noted that the direction in which the interelectrode voltage is increased by charging is different from the direction in which the interelectrode voltage is decreased by discharging. That is, if the inter-electrode state detection circuit 16 has the configuration shown in FIG. 2, the polarity extracting unit 23 extracts only the positive polarity shown in FIG. A signal will be sent.

  The discharge current flowing between the electrodes is divided into a current flowing from the power source through the current limiting resistor 13 and a current flowing through the stray capacitance 14. Although depending on the resistance value of the current limiting resistor 13, generally, the closer to the finishing condition, the weaker the processing energy is, so the resistance value of the current limiting resistor 13 becomes larger and the influence of the stray capacitance 14. Becomes dominant. That is, the discharge current depends on the voltage between the electrodes at the start of discharge, and the magnitude of the output waveform from the differentiating circuit unit 22 is an index of machining energy. The A / D converter 24 digitally reads this value and outputs the frequency and intensity of discharge to the controller 4.

  The basic signal flow in the inter-pole state detection circuit 16 is as shown in FIG. 2, but it is necessary to incorporate peripheral circuits depending on the operating frequency and environment. For example, either the polarity extraction unit 23 or the A / D conversion unit 24 may have a sample and hold function, and may be operated so as to be reset in synchronization with the rising edge of the signal input, or a filter may be used to increase noise resistance. It may be inserted.

  The control unit 4 determines a group pulse generation pattern according to the control algorithm based on the inter-pole state detected by the inter-pole state detection circuit 16, and causes the full bridge circuit to perform the above-described unipolar operation based on the determination. That is, the group pulse generation pattern shown in FIG. 3 is that when the control unit 4 does not detect the occurrence of discharge. For example, it may be considered that a simple group pulse generation pattern when the control is not performed without using the inter-electrode state detection circuit 16 is shown. Hereinafter, as an embodiment, the pulse pause time or group pulse pause of the group pulse performed when the controller 4 determines whether the gap state detected by the gap state detection circuit 16 is a non-discharge state or a discharge state. A control example such as time will be described.

<Example 1>
FIG. 4 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the first embodiment. (A) to (d) in FIG. 4 have the same contents as (a) to (d) in FIG.

  In FIG. 4, a state between timing (1) and timing (2) shows a state in the middle of a group pulse waveform (a state in the middle of charging) continuously applied between the electrodes. When a discharge occurs at timing (2), a pulse is output from the differentiation circuit unit 22 of the inter-electrode state detection circuit 16, and a signal is sent to the control unit 4 based on this. The control unit 4 detects the occurrence of discharge and performs control so as to extend the pulse pause time in the group pulse (pulse OFF time immediately after the pulse ON that generated the discharge).

  That is, as shown in FIG. 6A, the pulse pause time T2 after discharge detection (discharging occurs) with respect to the pulse pause time T1 at the time of non-discharge (open time) from timing (1) to timing (2). The pulse OFF time immediately after the ON pulse) is in a relationship of T2> T1. The pulse pause time T2 is set to the original pulse pause time T1 (not shown) if the next discharge is not detected even after an arbitrary time has elapsed. The elapsed time for returning from the pulse pause time T2 state to the pulse pause time T1 state may be the time when charging is completed (a state where the power supply voltage and the inter-electrode voltage are substantially the same voltage) or more. May be. At timing (3), after the pulse pause time T2, charging between the electrodes is resumed by turning on the pulse again. Charging is performed until timing (4).

  At timing (4), a state in which discharge has occurred again is shown. Since the charging voltage is insufficient compared to the discharge generated at the timing (2), the discharge current is low and the output pulse of the differentiation circuit unit 22 is also small. That is, it may be considered that the distance between the electrodes is small and the discharge is very easy. This state is a state in which discharge is likely to continue at the same location of the wire electrode, and disconnection is likely to occur. Therefore, the control unit 4 determines the discharge frequency based on the signal of the discharge intensity output from the inter-pole state detection circuit 16, and sets the pause time after the timing (4) to the pulse pause time T3 longer than the pulse pause time T2. Set to. That is, the pulse pause time has a relationship of T3> T2> T1. This pulse pause time T3 also operates so as to restore the pause time sequentially after confirming that the pulse pause time T2 and pulse pause time T1 and discharge are not continuous after an arbitrary time has elapsed. Of course, it may be set so as to return directly from the pulse pause time T3 to the pulse pause time T1.

  Here, the peak value of the waveform obtained by differentiating the charging voltage between the electrodes is used as an indicator of the continuity of discharge. However, as an indicator of discharge continuity, the time interval between discharges may be directly measured or used, or the differential waveform peak value together with the time interval may be used for control. Good. If only the interval between discharges is to be measured, the A / D converter 24 of the inter-pole state detection circuit 16 may be omitted, and the occurrence of discharge may be binarized and used, thus simplifying the circuit configuration. Is possible.

  Of course, even when the discharge intensity is used, a certain reference value is provided, and if it is equal to or higher than the reference value, the pulse pause time is T1 as the discharge after a sufficient charging time has elapsed, If there is, it may be switched to pulse pause time T2 or pulse pause time T3 as discharge within the charging time. By controlling in this way, the A / D converter 24 of the inter-pole state detection circuit 16 can be omitted, and the circuit configuration can be simplified.

  When water is used as the working fluid, the inter-electrode voltage waveform (c) is accompanied by a ripple in synchronization with the ON / OFF state of the pulse due to the resistance component of water, and the discharge generally starts to increase when the pulse is ON. It is easy to occur when. However, if oil is used as the working fluid, the floating resistance 15 between the electrodes is large, and the voltage between the electrodes does not decrease even during the pulse OFF (pulse pause time). In the present embodiment using the differentiation circuit unit 22, when water is used as the machining fluid, this ripple component becomes a factor that causes erroneous determination as noise. On the other hand, when oil is used for the machining fluid, the accuracy of the discharge determination is increased. That is, the structure shown in this embodiment can be said to be suitable for processing using oil.

<Example 2>
FIG. 5 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the second embodiment. (A) to (d) in FIG. 5 are the same as (a) to (d) in the first embodiment.

  In the first embodiment, when one discharge is generated in the group pulse, the pulse OFF time (pulse pause time) immediately after the pulse ON that generated the discharge is controlled to be changed. On the other hand, in the second embodiment, a case will be described in which the group pulse pause time between group pulses having a predetermined number of pulses is adjusted.

  The number of pulses of one group pulse is calculated based on the charging time between the electrodes, and is the number of pulses from the ground potential to the completion of charging (for example, about 95% of the power supply voltage) by one group pulse. Although not limited to this, especially in electric discharge machining using oil as the working fluid, the floating resistance value between the electrodes is extremely large as described above, so the voltage between the electrodes does not decrease even if the group pulse pause time is long, It remains held as shown in FIG. Furthermore, since the discharge current is maximized when the inter-electrode voltage is at the maximum value, the maximum discharge current can be limited to a predetermined value for a group of group pulses. Alternatively, even if a plurality of discharges are generated during the application of the group pulse, the discharge current at each time is a very small current, and thus there is a possibility that disconnection is difficult to occur.

  However, a state in which a plurality of discharges are generated in one group pulse, or a state in which the discharge is simply performed during the charging period can be regarded as a situation where the distance between the electrodes is short and the discharge tends to concentrate. That is, better processing can be obtained by extending the downtime in order to recover the distance between the electrodes or to recover the insulation state.

  Therefore, in the second embodiment, the group pulse pause time S2 after the timing (2) when the discharge during the charging time is detected is longer than the group pulse pause time S1 after the timing (1) when the original discharge is detected. It is set as follows. In FIG. 5, the same group pulse pause time S2 is present after the timing (3) at which the original discharge is detected, but the return from the group pulse pause time S2 to the group pulse pause time S1 is simply after several cycles (after several μs). ) May be set, or if discharge is not detected during the next charging period, control may be performed such that it is restored.

  In the second embodiment, the discharge frequency is detected once or several times per group pulse and reflected in the control of the group pulse pause time. The group pulse pause time may be controlled within a range of several hundreds μs to several ms. That is, a filter is applied to the measurement of the number of discharge pulses per unit time, for example, the number of discharges in the group pulse 100 group is measured, and the rest time of the next 100 group is determined according to the number of discharges. By making the control operation insensitive, statistical processing can be performed in consideration of variations in the discharge phenomenon, and stable machining can be obtained.

  That is, when the number of discharges per unit time indicated by the inter-pole state detected by the inter-pole state detection circuit 16 is greater than the set value, the control unit 4 sets the group pulse pause time for stopping the application of the group pulse to the set value. It has a function to make it longer than when there are fewer.

  In addition, by simply measuring the number of discharge pulses, the number of discharges per unit time is not controlled, but the numerical values after A / D conversion of the inter-electrode state detection circuit 16 are integrated to calculate the discharge energy per unit time. It may be controlled. If the cause of disconnection is excessive energy input per unit time, more accurate control can be performed by using discharge energy as an index.

  Specifically, when the inter-electrode state detected by the inter-electrode state detection circuit 16 indicates the start of discharge, the control unit 4 calculates the inter-electrode voltage value at the start of the discharge and the inter-electrode voltage value after the unit time has elapsed. A difference is detected as discharge energy input per unit time, integrated, and a function of controlling each pulse pause time of the group pulse to be applied is provided so that the integrated value approaches a set value.

<Example 3>
FIG. 6 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the third embodiment. (A) to (d) in FIG. 6 has the same contents as (a) to (d) in the first and second embodiments. However, FIG. 6 (d) does not show the state when discharging, but merely shows the state when not discharging (when open). In FIG. 6 (c), The state of the charging waveform after the short circuit is avoided is shown.

  In the first embodiment, in the open state, each group pulse OFF time (pulse pause time) is always the same time. On the other hand, in the third embodiment, a case where each pulse pause time of the group pulse in the open state is changed will be described.

  When the pulse immediately before the start of charging is close to the ground potential, charging is performed with a curve having a certain time constant if the same pulse ON time and pulse OFF time (pulse pause time). At this time, due to the nature of charging, a voltage is applied to the pulse immediately after the start of charging with a steep slope, and the slope gradually decreases as charging proceeds. However, from the viewpoint of discharge, application of a voltage waveform having a steep slope is not preferable if the distance between the electrodes is short immediately after the end of the previous discharge and the discharge is easily discharged. Rather, it is preferable that the waveform has a gentle slope immediately after the start of application, and the rising edge gradually increases with time. By setting it as such a waveform, even if it exists in the condition where discharge tends to continue, the flowing discharge current can be made low. Or after confirming that it does not discharge with a low voltage, it can be made to discharge with a high voltage charge waveform.

  FIG. 6 shows a charging waveform at the time of opening adjusted based on the above concept. Here, the pulse pause time is long at the initial stage of the group pulse application and the pulse pause time is gradually shortened so that the slope of charging is approximately constant. The occurrence of discharge is determined based on the output of the gap state detection circuit 16 as in the first and second embodiments. By adopting such a form of the pulse ON application method, it is possible to obtain stable machining with less discharge unevenness and discharge concentration.

  That is, when the inter-electrode state detected by the inter-electrode state detection circuit 16 is a non-discharge state, the control unit 4 increases the difference between the applied voltage and the inter-electrode voltage detected by the inter-electrode state detection means. A function for controlling each pause time of the applied group pulses to be long is provided.

  Differences between the third embodiment and the first embodiment will be described. In Example 1, the pulse pause time for each discharge is adjusted in accordance with the frequency and intensity of the discharge current so that the discharge amount per unit time does not increase. On the other hand, in the third embodiment, the focus is simply on the slope of the charging waveform after discharging. Before and after the occurrence of the discharge, both are controls in which the pulse pause time is changed from short to long, but the first embodiment is a control for the discharge that has occurred, whereas the third embodiment is a control. May be considered as control over what is likely to discharge.

<Example 4>
FIG. 7 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the fourth embodiment. (A) to (d) in FIG. 7 has the same contents as (a) to (d) in the first to third embodiments.

  In the third embodiment, the rising waveform of the charging voltage is controlled by controlling the pulse pause time at the time of opening. From the viewpoint of optimizing the charging waveform, not only the pulse pause time but also the pulse ON time may be controlled. In this case, with the pulse pause time kept constant, the pulse ON time is shortened at the start of charging, and the pulse ON time is set longer as the charging is completed. FIG. 7 shows a signal waveform at this time. The slope of charge between the electrodes is approximately the same as that in FIG. 6, and as in FIG. 6, uneven discharge and concentration of discharge can be suppressed, and stable processing characteristics can be obtained.

  That is, when the inter-electrode state detected by the inter-electrode state detection circuit 16 is a non-discharge state, the control unit 4 increases the difference between the applied voltage and the inter-electrode voltage detected by the inter-electrode state detection means. It has a function of controlling so that each pulse ON time of the group pulse to be applied is shortened.

<Example 5>
FIG. 8 is a diagram illustrating an example of a switching signal waveform and an inter-electrode voltage waveform for explaining the discharge control operation according to the fifth embodiment. In FIG. 8, (a) to (d) are the same as those in the first to fourth embodiments.

  As described above, when oil is used as the working fluid, the interelectrode voltage does not decrease during the pulse pause time or the group pulse pause time. That is, once charging is completed, it is not necessary to apply a pulse as long as no discharge occurs. Therefore, in the fifth embodiment, as shown in FIG. 8, the completion of charging is detected and the application of pulses is stopped.

  In FIG. 8, generation of pulses is stopped from the start of charging until the completion of charging is confirmed at timing (1) until the occurrence of discharge is confirmed at timing (2). The charging completion timing (1) may be, for example, a state in which the output of the gap state detection circuit 16 is low at the pulse ON timing. From timing (2) to timing (3), there is a continuous discharge, and charging and discharging are always repeated. Alternatively, the output level (d) of the differentiation circuit unit 22 is sufficiently high at the pulse ON timing, and the group pulse continuously repeats the ON and OFF operations in order to determine that the charging is not completed. At timing (3), when it is detected that the output level (d) of the differentiation circuit unit 22 is low at the timing of pulse ON, it is considered that the charging is completed and the application of the pulse is stopped again.

  That is, when the inter-electrode state detected by the inter-electrode state detection circuit 16 is a non-discharge state, the control unit 4 sets the difference between the applied voltage and the inter-electrode voltage detected by the inter-electrode state detection means to a predetermined value. In this case, a function of stopping the application of the group pulse is provided.

  The current flowing at the time of discharge is dominated by the inflow of charges stored in the interelectrode stray capacitance 14 between the electrodes, but there are not a few that flow from the power supply side. This also depends on the resistance value of the current limiting resistor 13. That is, when discharge occurs during the pulse ON, the surface roughness may deteriorate due to the current flowing between the electrodes from the power supply side. On the other hand, as shown in the fifth embodiment, if the generation of pulses is stopped upon completion of charging, it is not necessary to flow the power supply current unnecessarily, so that improvement in surface accuracy can be expected. Furthermore, the efficiency as a power source is improved by reducing unnecessary switching operations.

  Here, in the first to fifth embodiments, in order to detect discharge or detect completion of charging, the interpolar state detection circuit 16 is provided with a differentiating circuit unit 22 to detect a change in interelectrode voltage. However, the present invention is not limited to this as long as it can detect fluctuations in the voltage between the electrodes, and a configuration in which a plurality of comparators are provided in place of the differentiation circuit unit may be used. In this case, a detection circuit that is resistant to noise can be configured although the circuit scale is large.

  Moreover, in Examples 1-5, the example of unipolar operation | movement was described focusing on what uses oil for a process liquid. That is, the configuration of the finishing power supply unit is a full bridge circuit, but is driven by only one arm. If it is only oil processing, it does not need to be a full bridge, and may be a half bridge circuit. Alternatively, in the first to fifth embodiments, instead of performing a unipolar operation, a bipolar operation (operation of periodically switching group pulses for each diagonal arm and inverting the output polarity) may be performed. . In this case, the polarity of the signal waveform shown in the figure is inverted.

  Note that the switching signal waveforms shown in FIGS. 3 to 8 show an example, and it goes without saying that various signals generated based on various viewpoints may be used.

  In addition, the detection result of the inter-pole state detection circuit 16 may be applied to servo drive. Although it is common to use the average voltage between the electrodes as an indicator of the state between the electrodes, this does not capture the processing energy itself. In finishing, since the straight shape deteriorates when the balance between the running speed and the machining energy is lost, the optimum machining can be performed if the machining energy is monitored more directly and applied to the control. Since the processing energy is dominated by the flow of charges stored in the inter-electrode stray capacitance between the electrodes, the shape accuracy can be obtained by using the charge voltage between the electrodes during discharge (the output of the inter-electrode state detection circuit 16). Can be obtained.

  As described above, according to the present embodiment, even in the method of applying a group pulse that repeats ON and OFF operations intermittently, a gap state is detected and a group pulse is generated according to the discharge state at the time of discharge. Therefore, the concentration of electric discharge can be prevented, the processing can be stabilized and the processing speed can be improved.

  As described above, the electric discharge machining apparatus according to the present invention is useful as an electric discharge machining apparatus that prevents uneven discharge, stabilizes machining, and improves the machining speed even in a group pulse application method using a finishing machining power supply. It is.

DESCRIPTION OF SYMBOLS 1 Electrical discharge machining apparatus 3 Power supply part and electrical discharge machining part 4 Control part 5 Host controller 6 Memory | storage part which stores machining parameter 7 Operation | movement identification process part 10 DC power supply 11 Workpiece 12 Electrode for processing 13 Current limiting resistor 14 Floating capacitance component DESCRIPTION OF SYMBOLS 15 Floating resistance component 16 Inter-pole state detection circuit SW1-SW4 Switching element which comprises a full bridge circuit D1, D2 DC terminal D3, D4 AC terminal

Claims (10)

In an electric discharge machining apparatus that performs machining by applying a group pulse between a machining electrode and a workpiece,
In order to detect a state between the electrode between the machining electrode and the workpiece by application of the group pulse, a voltage between the electrode between the machining electrode and the workpiece is detected and detected. An inter-electrode state detection means for calculating a change in the inter-electrode voltage,
An electric discharge machining apparatus comprising: control means for controlling an application pattern of the group pulse based on a change in the voltage between the electrodes. The control means includes
2. When a discharge start between the electrodes is detected based on a change in the voltage between the electrodes, each pulse pause time of a group pulse to be applied is made longer than a pulse pause time before the discharge start. The electric discharge machining apparatus according to 1. The control means includes
When the start of discharge between the electrodes is detected based on the change in the voltage between the electrodes, the change in the voltage between the electrodes from the start of the discharge to the lapse of unit time is detected as discharge energy input per unit time, The electric discharge machining apparatus according to claim 1, wherein each pulse pause time of a group pulse to be applied is controlled so that the integrated value approaches a set value. The control means includes
When the number of discharges per unit time detected based on the change in the interelectrode voltage is greater than a set value, the group pulse pause time during which the application of the group pulse is paused is compared with the case where the number of discharges is less than the set value. The electrical discharge machining apparatus according to claim 1, wherein the electrical discharge machining apparatus is elongated. The control means includes
When it is determined that no discharge has occurred between the electrodes based on the change in the voltage between the electrodes, the pause time of the group pulse to be applied becomes longer as the difference between the applied voltage and the voltage between the electrodes increases. The electric discharge machining apparatus according to claim 1, wherein the electric discharge machining apparatus is controlled. The control means includes
When it is determined that no discharge has occurred between the electrodes based on the change in the interelectrode voltage, the larger the difference between the applied voltage and the interelectrode voltage, the shorter the pulse ON time of the applied group pulse. The electric discharge machining apparatus according to claim 1, wherein the electric discharge machining apparatus is controlled. The control means includes
When it is determined that no discharge has occurred between the electrodes based on the change in the voltage between the electrodes, the application of the group pulse is stopped when the difference between the applied voltage and the voltage between the electrodes reaches a predetermined value. The electric discharge machining apparatus according to claim 1. The inter-electrode state detection means is
The electrical discharge machining apparatus according to claim 1, further comprising a differentiating circuit for detecting a change in the voltage between the electrodes. The inter-electrode state detection means is
The electrical discharge machining apparatus according to claim 1, comprising a plurality of comparators for detecting the inter-electrode voltage.   The electrical discharge machining apparatus according to claim 1, wherein the machining fluid that fills a gap between the machining electrode and the workpiece is oil.

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