Controller for wire electric discharge machine

• US 20060091113A1
• Filed: 10/27/2005
• Published: 05/04/2006
• Est. Priority Date: 10/28/2004
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Kita, Yuki, Hiraga, Kaoru
• Granted Patent: US 7,262,381 B2
• Time in Patent Office: Days
• US Class Current: 219/69.12
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor

Abstract

A controller for a wire cut electric discharge machine which can provide stable finish machining and corner-region machining with high corner-form accuracy. An electric discharge gap detection device detects a voltage between a wire electrode and a workpiece. A machining rate detection device obtains an average machining voltage and a drop voltage value Ex which is a difference between the obtained average machining voltage and a no-load voltage. A comparison device obtains the ratio Es/Ex between a reference drop voltage value Es stored in a reference machining rate relative value storage device and the obtained drop voltage value Ex. In machining of a corner portion, when the drop voltage value Ex exceeds a entrance-into-corner determination reference machining rate, a set feed speed switch device supplies a corner set feed speed, and when the machining of the corner portion finishes, so that the drop voltage value Ex decreases to a leaving-from-corner determination reference machining rate or lower, the set feed speed switch device supplies a normal set feed speed. A feed pulse calculation device obtains a feed speed which makes the rate of machining constant, on the basis of the ratio Es/Ex and the supplied feed speed, to thereby drive motors. Since the rate of machining is kept constant, the surface accuracy of finish machining is high and stable machining can be performed.

Claims

1. A controller for a wire electric discharge machine for performing machining of removing part of a workpiece by electric discharge generated between a wire electrode and the workpiece while moving the wire electrode relative to the workpiece, said controller comprising:

machining rate determining means for determining a machining rate which is an amount of removed part of the workpiece in a predetermined time period;

motion control means for controlling motion of the wire electrode relative to the workpiece in accordance with the determined machining rate such that a motion rate, which is an amount of motion of the wire electrode relative to the workpiece in the predetermined time period, decreases when the machining rate increases;

switching means for switching a set value of the motion rate for a reference value of the machining rate from a first value to a second value smaller than the second value when the machining rate increases to be greater than a first threshold, and changing the set value of the motion rate back to the first value when the machining rate decreases to be lower than a second threshold.

2. A controller for a wire electric discharge machine according to claim 1, wherein said machining rate determining means obtains the number of repetitions of electric discharge in each predetermined time period, and said motion control means controls the motion of the wire electrode relative to the workpiece based on comparison of the obtained number of repetitions of electric discharge with a reference number of repetitions of electric discharge in the predetermined time period.

3. A controller for a wire electric discharge machine according to claim 2, wherein said machining rate determining means obtains an average drop voltage based on a set no-load voltage and an average machining voltage, and said motion control means controls the motion of the wire electrode relative to the workpiece based on comparison of the obtained average drop voltage with a reference drop voltage.

4. A controller for a wire electric discharge machine for performing machining of removing part of a workpiece by electric discharge generated between a wire electrode and the workpiece while moving the wire electrode relative to the workpiece, said controller comprising:

machining rate determining means for determining a machining rate which is an amount of removed part of the workpiece in a predetermined time period;

motion control means for controlling motion of the wire electrode relative to the workpiece along a machining path in accordance with the determined machining rate such that a motion rate, which is an amount of motion of the wire electrode relative to the workpiece in the predetermined time period, decreases when the machining rate increases;

switching means for switching a set value of the moving rate for a reference value of the machining rate from a first value to a second value lower than the first value when the machining rate increases to be greater than a first threshold in machining a corner portion of the machining path, and changing the set value of the moving rate back to the first value when the machining of the corner portion is completed.

5. A controller for a wire electric discharge machine according to claim 4, wherein said machining rate determining means obtains the number of repetitions of electric discharge in each predetermined time period, and said motion control means controls the motion of the wire electrode relative to the workpiece based on comparison of the obtained number of repetitions of electric discharge with a reference number of repetitions of electric discharge in the predetermined time period.

6. A controller for a wire electric discharge machine according to claim 4, wherein said machining rate determining means obtains an average drop voltage based on a set no-load voltage and an average machining voltage, and said motion control means controls the motion of the wire electrode relative to the workpiece based on comparison of the obtained average drop voltage with a reference drop voltage.

7. A controller for a wire electric discharge machine for performing machining of removing part of a workpiece by electric discharge generated between a wire electrode and the workpiece while moving the wire electrode relative to the workpiece, said controller comprising:

electric discharge repetition number determining means for determining the number of repetitions of electric discharge in each predetermined time period;

motion control means for control the motion of the wire electrode relative to the workpiece in accordance with a motion command;

reference electric discharge repetition number storage means storing a reference number of repetitions of electric discharge;

means for obtaining a ratio between the determined number of repetitions of electric discharge and the stored reference number of repetitions of electric discharge;

means for determining an amount of motion of the wire electrode relative to the workpiece in each predetermined time period by multiplying the determined ratio by a product of a set feed speed and the predetermined time period, and outputting the determined amount of motion to said motion control means as the motion command; and

switching means for switching the set feed speed from a first value to a second value smaller than the first value when the determined ratio decreases to be lower than a first threshold ratio or the determined number of repetitions of electric discharge increases to be greater than a first threshold number, and switching the set feed speed back to the first value when the determined ratio increases to be greater than a second reference ratio or the determined number of repetitions of electric discharge decreases to be lower than a second threshold number.

8. A controller for a wire electric discharge machine for performing machining of removing part of a workpiece by electric discharge generated between a wire electrode and the workpiece while moving the wire electrode relative to the workpiece, said controller comprising:

electric discharge repetition number counting means for determining the number of repetitions of electric discharge in each predetermined time period;

motion control means for control the motion of the wire electrode relative to the workpiece along a machining path in accordance with a motion command;

reference electric discharge repetition number storage means storing a reference number of repetitions of electric discharge;

means for obtaining a ratio between the determined number of repetitions of electric discharge and the stored reference number of repetitions of electric discharge;

means for determining an amount of motion of the wire electrode relative to the workpiece in every predetermined time period by multiplying the determined ratio by a product of a set feed speed and the predetermined time period, and outputting the determined amount of motion to said motion control means as the motion command; and

switching means for switching the set feed speed from a first value to a second value smaller than the first value when the determined ratio decreases to be lower than a first threshold ratio or the determined number of repetitions of electric discharge increases to be greater than a first threshold number in machining a corner portion of the machining path, and switching the set feed speed back to the first value when the machining of the corner portion is completed.

9. A controller for a wire electric discharge machine for performing machining of removing part of a workpiece by electric discharges generated between a wire electrode and the workpiece while moving the wire electrode relative to the workpiece, said controller comprising:

drop voltage calculation means for determining an average drop voltage which is a difference between a set no-load voltage and an average machining voltage between the wire electrode and the workpiece;

motion control means for controlling the motion of the wire electrode relative to the workpiece in accordance with a motion command;

reference value storage means storing a reference value of the average drop voltage;

means for obtaining a ratio between the determined average drop voltage and the reference value stored in said reference value storage means;

means for determining an amount of motion of the wire electrode relative to the workpiece in every predetermined time period by multiplying the determined ratio by a product of a set feed speed and the predetermined time period, and outputting the determined amount of motion to said motion control means as the motion command; and

switching means for switching the set feed speed from a first value to a second value smaller than the first value when the determined ratio decreases to be lower than a first threshold ratio or the determined number of repetitions of electric discharge increases to be greater than a first threshold number, and switching the set feed speed back to the first value when the determined ratio increases to be greater than a second reference ratio or the determined number of repetitions of electric discharge decreases to be lower than a second threshold number.

10. A controller for a wire electric discharge machine for performing machining of removing part of a workpiece by electric discharges generated between a wire electrode and the workpiece while moving the wire electrode relative to the workpiece, said controller comprising:

drop voltage calculation means for determining an average drop voltage which is a difference between a set no-load voltage and an average machining voltage between the wire electrode and the workpiece;

motion control means for controlling the motion of the wire electrode relative to the workpiece along a machining path in accordance with a motion command;

reference value storage means storing a reference value of the average drop voltage;

means for obtaining a ratio between the determined drop voltage value and the value stored in said reference value storage means;

means for determining an amount of motion of the wire electrode relative to the workpiece in every predetermined time period by multiplying the determined ratio by a product of a set feed speed and the predetermined time period, and outputting the determined amount of motion to said motion control means as the motion command; and

switching means for switching the set feed speed from a first value to a second value smaller than the first value when the determined ratio decreases to be lower than a first threshold ratio or the determined number of repetitions of electric discharge increases to be greater than a first threshold number in machining a corner portion of the machining path, and switching the set feed speed back to the first value when the machining of the corner portion is completed.