# US 2014/0190941 A1 · Power supply device for electric discharge machining > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0190941 A1 - Document ID: US20140190941A1 - Status: Published application - Kind: A1 - Application number: 14/139,264 - Filed: 2013-12-23 - Published: 2014-07-10 - Earliest claimed: 2013-01-08 - Assignees: Fanuc Corporation - Applicants: Fanuc Corporation - Inventors: Masao MURAI; Tomoyuki FURUTA - Web page: https://patentgrep.com/patent/US20140190941A1 ## CPC - B23H 1/02: Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges - B23H 1/024: {Detection of, and response to, abnormal gap conditions, e.g. short circuits (preventing short circuits or other abnormal discharges by altering machining parameters using adaptive control B23H7/16)} - B23H 7/16: for preventing short circuits or other abnormal discharges {by altering machining parameters using adaptive control} - B23H 7/04: Apparatus for supplying current to working gap; Electric circuits specially adapted therefor - B23H: WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL (processes for the electrolytic or electrophoretic production of coatings, electroforming, or apparatus therefor C25D; processes for the electrolytic removal of material from objects C25F; manufacturing printed circuits using precipitation techniques to apply the conductive material to form the desired conductive pattern H05K3/18) ## Abstract In a power supply device for electric discharge machining, the polarity of the voltage to be applied is determined on the basis of a result of determination whether the machining gap is in open state or not, an average value of voltages applied across the machining gap voltage during machining, and the number of successive open states with the same polarity. This eliminates the need to significantly vary the voltages to be applied from positive to negative and from negative to positive, thereby reducing the output energy required by the machining power supply. ## Claims ### Claim 1 A power supply device for electric discharge machining, the device comprising: a voltage applying means for alternately applying positive and negative voltages across a machining gap between an electrode and a workpiece at intervals of not longer than one microsecond with a quiescent period equal to or longer than each voltage application period provided between individual voltage applications, a machining-gap open-state determining means for determining whether the machining gap between the electrode and the workpiece is in open state or not before individual voltage applications, an average voltage detecting means for detecting an average machining gap voltage during machining, the average machining gap voltage being an average value of the voltages applied across the machining gap over a period from a preset reference time to a present time, an open-state counting means for counting a number of successive machining gap open states having the same polarity, and an applied polarity determining means for determining polarities of the voltages to be applied across the machining gap on the basis of the result of determination by the machining-gap open-state determining means, the average machining gap voltage detected by the average voltage detecting means, and the number of successive machining gap open states counted by the open-state counting means, wherein the voltages of the polarities determined by the applied polarity determining means are applied across the machining gap. ### Claim 2 (depends on 1) The power supply device for electric discharge machining according to claim 1, wherein the applied polarity determining means is configured such that, when the machining gap is in open state before voltage application, the applied polarity determining means compares a preset maximum number of successive open states with the value counted by the open-state counting means and, if the value counted by the open-state counting means does not reach the maximum number of successive open states, the applied polarity determining means applies the same polarity as a last one across the machining gap, whereas if the value counted by the open-state counting means reaches the maximum number of successive open states, the applied polarity determining means applies a voltage of a polarity opposite to the last one, and when the machining gap is not in open state before voltage application, if the average voltage detecting means detects a positive polarity, the applied polarity determining means determines application of a negative polarity as the polarity to be applied next and, if the average voltage detecting means detects a negative polarity, the applied polarity determining means determines application of a positive polarity as the polarity to be applied next. ### Claim 3 (depends on 1) The power supply device for electric discharge machining according to claim 1, wherein, when an absolute value of a voltage applied across the machining gap between the electrode and the workpiece exceeds a preset maximum voltage, voltage application is inhibited. ### Claim 4 (depends on 1) The power supply device for electric discharge machining according to claim 1, wherein, when an average value of the currents output from the voltage applying means during machining over a period from the preset reference time to the present time exceeds a preset maximum current, voltage application is suspended and is resumed after a predetermined quiescent period.