Wire electric discharge machine capable of detecting machining state

• US 8,975,554 B2
• Filed: 06/02/2011
• Issued: 03/10/2015
• Est. Priority Date: 08/26/2010
• Status: Active Grant

• Current Assignee: Fanuc Corporation
• Original Assignee: Fanuc Corporation
• Inventors: Kawahara, Akiyoshi, Murai, Masao, Furuta, Tomoyuki
• Primary Examiner(s): Evans, Geoffrey S
• Application Number:
  US13/151,769
• Publication Number:
  US 20120048833A1
• Time in Patent Office: 1,377 Days
• Field of Search: 219/69.13, 219/69.18, 219/69.12, 219/69.16
• US Class Current: 219/69.12
• CPC Class Codes: B23H 1/022 for shaping the discharge pulse train B23H1/024 takes precedence
• CPC Class Codes: 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
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor

Abstract

A voltage is applied to a machining gap between a wire electrode and a workpiece for a period of one microsecond or less with a quiescent time longer than the duration of voltage application between each two adjacent cycles of voltage application provided, and the number of duty cycles and a machining-gap voltage are detected. An open-circuit state in which electric discharge does not occur after the voltage is applied is identified by the detected machining-gap voltage, and the number of open-circuits is counted. An average machining-gap voltage is obtained based on the numbers of duty cycles and open-circuits and the supply voltage or an average voltage for each duty cycle.

Claims

1. A wire electric discharge machine configured to apply a high-frequency voltage to a machining gap between a wire electrode and a workpiece located at a predetermined distance from the wire electrode, thereby generating electric discharge to machine the workpiece, the wire electric discharge machine comprising:

a voltage application unit configured to apply a bipolar voltage to the machining gap between the wire electrode and the workpiece for a period of one microsecond or less with a quiescent time longer than the duration of voltage application between each two adjacent cycles of voltage application provided;

a machining-gap voltage detection unit configured to detect a machining-gap voltage produced in the machining gap;

a duty cycle number counting unit configured to count the number of duty cycles of the voltage applied by the voltage application unit for each unit time;

an open-circuit state identification unit configured to identify an open-circuit state where no electric discharge occurs after the voltage is applied, based on the machining-gap voltage detected by the machining-gap voltage detection unit; and

an open-circuit number counting unit configured to count the number of open-circuits identified by the open-circuit state identification unit for each unit time,

wherein an average machining-gap voltage is obtained based on (i) the number of duty cycles per unit time counted by the duty cycle number counting unit, (ii) the number of open-circuits per unit time counted by the open-circuit number counting unit, and (iii) a supply voltage or an average voltage for each duty cycle.

2. The wire electric discharge machine according to claim 1, wherein the open-circuit state identification unit configured to

compare a full-wave-rectified machining-gap voltage waveform with a predetermined reference voltage within the quiescent time,

identify the open-circuit state if the reference voltage is exceeded by the full-wave-rectified machining-gap voltage waveform, and

identify a closed-circuit state if the reference voltage is not reached by the full-wave-rectified machining-gap voltage waveform.

3. A wire electric discharge machine configured to apply a high-frequency voltage to a machining gap between a wire electrode and a workpiece located at a predetermined distance from the wire electrode, thereby generating electric discharge to machine the workpiece, the wire electric discharge machine comprising:

a voltage application unit configured to apply a bipolar voltage to the machining gap between the wire electrode and the workplace for a period of one microsecond or less with a quiescent time longer than the duration of voltage application between each two adjacent cycles of voltage application provided;

a machining-gap voltage detection unit configured to detect a machining-gap voltage produced in the machining gap;

a duty cycle number counting unit configured to count the number of duty cycles of the voltage applied by the voltage application unit for each unit time;

an open-circuit state identification unit configured to identify an open-circuit state where no electric discharge occurs after the voltage is applied, based on the machining-gap voltage detected by the machining-gap voltage detection unit; and

an open-circuit number counting unit configured to count the number of open-circuits identified by the open-circuit state identification unit for each unit time,

wherein

an electric-discharge ratio is obtained from (i) an open-circuit ratio, which is calculated based on the number of duty cycles per unit time counted by the duty cycle number counting unit and the number of open-circuits per unit time counted by the open-circuit number counting unit, (ii) a short-circuit ratio, and (iii) a relation of the electric discharge ratio and the short-circuit ratio to the open-circuit ratio within unit time, and

a frequency of electric discharge per unit time or per unit distance is obtained based on (a) the counted number of duty cycles per unit time and (b) the obtained electric-discharge ratio.

4. The wire electric discharge machine according to claim 3, wherein

the number of short-circuits per unit time is obtained based on the number of duty cycles per unit time and the short-circuit ratio, and

a machining amount per unit time or per unit distance is obtained based on the frequency of electric discharge per unit time and the number of short-circuits per unit time.

5. The wire electric discharge machine according to claim 3, wherein the open-circuit state identification unit is configured to

compare a full-wave-rectified machining-gap voltage waveform with a predetermined reference voltage within the quiescent time,

identifies the open-circuit state if the reference voltage is exceeded by the full-wave-rectified machining-gap voltage waveform, and

identify a closed-circuit state if the reference voltage is not reached by the full-wave-rectified machining-gap voltage waveform.