Wire electric discharge machine capable of detecting machining state and determining average voltage in machining gap

• US 8,735,762 B2
• Filed: 11/19/2012
• Issued: 05/27/2014
• Est. Priority Date: 02/01/2012
• Status: Active Grant

• Current Assignee: Fanuc Corporation
• Original Assignee: Fanuc Corporation
• Inventors: Murai, Masao, Furuta, Tomoyuki
• Primary Examiner(s): Ross, Dana
• Assistant Examiner(s): Bae, Gyounghyun
• Application Number:
  US13/680,392
• Publication Number:
  US 20130193112A1
• Time in Patent Office: 554 Days
• Field of Search: 219/69.12, 219/69.13, 700/162
• US Class Current: 219/69.12
• CPC Class Codes: B23H 1/02 Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges
• 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
• CPC Class Codes: B23H 7/14 Electric circuits specially adapted therefor, e.g. power supply B23H3/02 takes precedence
• CPC Class Codes: B23H 7/18 for maintaining or controlling the desired spacing between electrode and workpiece

Abstract

In order to detect a machining state of a wire electric discharge machine, the state of a machining gap is classified into three categories; an open-circuit state in which electric discharge does not occur after a first predetermined level is reached or surpassed by a machining-gap voltage, an electric discharge state in which electric discharge occurs after a second predetermined level is reached or surpassed by the machining-gap voltage, whereby the machining-gap voltage becomes lower than the second predetermined level, and a short-circuit state wherein a third predetermined level is not reached or surpassed by the machining-gap voltage. An average voltage in the machining gap is determined based on voltages in these states and the number of cycles of voltage application to the machining gap, number of open-circuits, number of discharges, and number of short-circuits per unit time.

Claims

1. A wire electric discharge machine capable of detecting a machining state and determining an average voltage in a machining gap between a wire electrode and a workpiece, comprising:

a voltage application unit configured to apply positive and negative voltages to the machining gap for a period of one microsecond or less with an off time equal to or longer than a voltage application time set during each cycle of voltage application;

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

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

an open-circuit determination unit configured to determine an open-circuit state in which electric discharge does not occur after a predetermined open-circuit determination voltage level is reached or surpassed by the machining-gap voltage detected by the machining-gap voltage detection unit;

an open-circuit number counting unit configured to count for each unit time the number of voltage application cycles determined to be in an open-circuit state by the open-circuit determination unit, as an open-circuit number;

an electric discharge determination unit configured to determine an electric discharge state in which electric discharge occurs after a predetermined electric discharge determination voltage level is reached or surpassed by the machining-gap voltage detected by the machining-gap voltage detection unit, then the machining-gap voltage becomes lower than the electric discharge determination voltage level; and

a discharge number counting unit configured to count for each unit time the number of voltage application cycles determined to be in an electric discharge state by the electric discharge determination unit, as a discharge number,

wherein the average voltage in the machining gap is determined based on a first predetermined voltage corresponding to the machining-gap voltage in the open-circuit state, a second predetermined voltage corresponding to the machining-gap voltage in the electric discharge state, the number of voltage application cycles per unit time counted by the application cycle number counting unit, the open-circuit number per unit time counted by the open-circuit number counting unit, and the discharge number per unit time counted by the discharge number counting unit.

2. The wire electric discharge machine according to claim 1, wherein the average voltage in the machining gap is calculated as follows:

Average machining-gap voltage={(open-circuit number×

first predetermined voltage) (discharge number×

second predetermined voltage)}/(application cycle number).

3. The wire electric discharge machine according to claim 1, wherein at least one of the determination voltage levels for the determination of the open-circuit state and the electric discharge state is variable depending on a power supply voltage of the voltage application unit, a workpiece thickness, a wire diameter, and/or a workpiece material.

4. The wire electric discharge machine according to claim 1, wherein at least one of the first and second predetermined voltages is variable depending on a power supply voltage of the voltage application unit, a workpiece thickness, a wire diameter, and/or a workpiece material.

5. A wire electric discharge machine capable of detecting a machining state and determining an average voltage in a machining gap between a wire electrode and a workpiece, comprising:

a voltage application unit configured to apply positive and negative voltages to the machining gap for a period of one microsecond or less with an off time equal to or longer than a voltage application time set during each cycle of voltage application;

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

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

an open-circuit determination unit configured to determine an open-circuit state in which electric discharge does not occur after a predetermined open-circuit determination voltage level is reached or surpassed by the machining-gap voltage detected by the machining-gap voltage detection unit;

an open-circuit number counting unit configured to count for each unit time the number of voltage application cycles determined to be in an open-circuit state by the open-circuit determination unit, as an open-circuit number;

an electric discharge determination unit configured to determine an electric discharge state in which electric discharge occurs after a predetermined electric discharge determination voltage level is reached or surpassed by the machining-gap voltage detected by the machining-gap voltage detection unit, then the machining-gap voltage becomes lower than the electric discharge determination voltage level;

a discharge number counting unit configured to count for each unit time the number of voltage application cycles determined to be in an electric discharge state by the electric discharge determination unit, as a discharge number;

a short-circuit determination unit configured to determine a short-circuit state in which a predetermined short-circuit determination voltage level is not reached or surpassed by the machining-gap voltage detected by the machining-gap voltage detection unit during 1 cycle of the voltage application; and

a short-circuit number counting unit configured to count for each unit time the number of voltage application cycles determined to be in a short-circuit state by the short-circuit determination unit, as a short-circuit number,

wherein the average voltage in the machining gap is determined based on a first predetermined voltage corresponding to the machining-gap voltage in the open-circuit state, a second predetermined voltage corresponding to the machining-gap voltage in the electric discharge state, a third predetermined voltage corresponding to the machining-gap voltage in the short-circuit state, the number of application cycles per unit time counted by the application cycle number counting unit, the open-circuit number per unit time counted by the open-circuit number counting unit, the discharge number per unit time counted by the discharge number counting unit, and the short-circuit number per unit time counted by the short-circuit number counting unit.

6. The wire electric discharge machine according to claim 5, wherein the average voltage in the machining gap is calculated as follows:

Average machining-gap voltage={(open-circuit number×

first predetermined voltage) (discharge number×

second predetermined voltage) (short-circuit number×

third predetermined voltage)}/(application cycle number).

7. The wire electric discharge machine according to claim 5, wherein at least one of the determination voltage levels for the determination of the open-circuit state, the electric discharge state, and the short-circuit state is variable depending on a power supply voltage of the voltage application unit, a workpiece thickness, a wire diameter, and/or a workpiece material.

8. The wire electric discharge machine according to claim 5, wherein at least one of the first to third predetermined voltages is variable depending on a power supply voltage of the voltage application unit, a workpiece thickness, a wire diameter, and/or a workpiece material.

9. A wire electric discharge machine capable of detecting a machining state and determining an average voltage in a machining gap between a wire electrode and a workpiece, comprising:

a voltage application unit configured to apply positive and negative voltages to the machining gap for a period of one microsecond or less with an off time equal to or longer than a voltage application time set during each cycle of voltage application;

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

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

a short-circuit determination unit configured to determine a short-circuit state in which a predetermined short-circuit determination voltage level is not reached or surpassed by the machining-gap voltage detected by the machining-gap voltage detection unit during 1 cycle of the voltage application; and

a short-circuit number counting unit configured to count for each unit time the number of voltage application cycles determined to be in a short-circuit state by the short-circuit determination unit, as a short-circuit number,

wherein the average voltage in the machining gap is determined based on a fourth predetermined voltage corresponding to the machining-gap voltage in the open-circuit state and the electric discharge state, the number of application cycles per unit time counted by the application cycle number counting unit, and the short-circuit number per unit time counted by the short-circuit number counting unit.

10. The wire electric discharge machine according to claim 9, wherein the average voltage in the machining gap is calculated as follows:

Average machining-gap voltage=(application cycle number−

short-circuit number)×

(fourth predetermined voltage)/(application cycle number).

11. The wire electric discharge machine according to claim 9, wherein the determination voltage level for the determination of the short-circuit state is variable depending on a power supply voltage of the voltage application unit, a workpiece thickness, a wire diameter, and/or a workpiece material.

12. The wire electric discharge machine according to claim 9, wherein the fourth predetermined voltage is variable depending on a power supply voltage of the voltage application unit, a workpiece thickness, a wire diameter, and/or a workpiece material.