CONTROLLER FOR A WIRE ELECTRICAL DISCHARGE MACHINE

• US 20050269296A1
• Filed: 06/01/2005
• Published: 12/08/2005
• Est. Priority Date: 06/02/2004
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Ogata, Toshiyuki, Hiraga, Kaoru, Arakawa, Yasuo
• Granted Patent: US 6,998,562 B2
• Time in Patent Office: Days
• US Class Current: 219/69.120
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor
• CPC Class Codes: B23H 7/065 Electric circuits specially adapted therefor
• CPC Class Codes: B23H 7/20 for programme-control, e.g. adaptive programme-control systems in general G05B19/00

Abstract

Set feed speed is lowered when a short circuit is detected in a range within which machining is unstable, the range starting from the point at which discharge is detected after machining starts from a machining start point, thus control is carried our according to a machining rate, thereby preventing successive occurrence of short circuits. When machining proceeds beyond the unstable range, the lowered feed speed is returned to the normal feed speed.

Claims

1. A controller for a wire electrical discharge machine that supplies discharge pulse current between a wire electrode and a workpiece to perform electrical discharge machining while causing relative motion between the wire electrode and the workpiece, the controller comprising:

discharge pulse counting means for counting the number of supplied discharge pulses every preset time;

moving means for causing relative motion between the wire electrode and the workpiece along a machining path according to motion commands;

reference discharge pulse count storage means for storing a reference number of discharge pulses per unit time;

discharge pulse count comparing means for comparing a value obtained from the discharge pulse counting means with a value obtained from the reference discharge pulse count storage means and obtaining a ratio therebetween;

feed pulse calculating means for obtaining a distance by multiplying a relative movement of the wire electrode with respect to the workpiece, which is determined from a set feed speed and said preset time, by the ratio and for sending the obtained distance to the moving means as a movement command every said preset time;

discharge start point detecting means for detecting a discharge start point by detecting occurrence of a discharge;

machining travel distance calculating means for calculating a machining travel distance from the discharge start point;

comparing means for comparing the machining travel distance with a predetermined distance;

short circuit detecting means for detecting a short circuit between the wire electrode and the workpiece; and

feed speed setting switching means for switching a set feed speed;

wherein, according to a comparison result obtained from the comparing means and to detection output from the short circuit detecting means, the feed speed setting switching means switches to a low feed speed when a short circuit is detected while the machining travel distance is within the predetermined distance, and switches to a normal feed speed when the machining travel distance exceeds the predetermined distance.

2. The controller according to claim 1, wherein the discharge start point detecting means detects the discharge start point according to the number of discharge pulses.

3. A controller for a wire electrical discharge machine that supplies discharge pulse current between a wire electrode and a workpiece to perform electrical discharge machining while causing relative motion between the wire electrode and the workpiece, the controller comprising:

discharge pulse current integrating means for integrating supplied discharge pulse current every preset time;

moving means for causing relative motion between the wire electrode and the workpiece along a machining path according to commands;

reference integrated discharge pulse current value storage means for storing time-integrated value of a reference discharge pulse current;

integrated discharge pulse current value comparing means for comparing a value obtained from the discharge pulse current integrating means with a value obtained from the reference integrated discharge pulse current value storage means and for obtaining a ratio therebetween;

feed pulse calculating means for obtaining a distance by multiplying a relative movement of the wire electrode with respect to the workpiece, which is determined from a set feed speed and said preset time, by the ratio and for sending the obtained distance to the moving means as a movement command every said preset time;

discharge start point detecting means for detecting a discharge start point by detecting occurrence of a discharge;

machining travel distance calculating means for calculating a machining travel distance from the discharge start point;

comparing means for comparing the machining travel distance with a predetermined distance;

short circuit detecting means for detecting a short circuit between the wire electrode and the workpiece; and

feed speed setting switching means for switching the feed speed setting;

wherein, according to a comparison result obtained from the comparing means and to detection output from the short circuit detecting means, the feed speed setting switching means switches to a low feed speed when a short circuit is detected while the machining travel distance is within the predetermined distance, and switches to a normal feed speed when the machining travel distance exceeds the predetermined distance.

4. The controller according to claim 3, wherein the discharge start point detecting means detects the discharge start point according to an integrated value of the discharge pulse current.

5. The controller according to claim 1, further comprising discharge quiescent time control means for controlling a discharge quiescent time according to the comparison result from the discharge pulse count comparing means so that the value that the discharge pulse counting means obtains every preset time matches the value stored in the reference discharge pulse count storage means.

6. The controller according to claim 1, further comprising discharge quiescent time control means for controlling a discharge quiescent time according to the comparison result from the discharge pulse count comparing means so as to restrain the supply of extra energy.

7. The controller according to claim 3, further comprising discharge quiescent time control means for controlling the discharge quiescent time according to the comparison result from the discharge pulse current integrated value comparing means so as to restrain the supply of extra energy.

8. The controller according to claim 1, wherein coolant flow is controlled according to the ratio obtained by the discharge pulse count comparing means.

9. The controller according to claim 3, wherein the coolant flow is controlled according to the ratio obtained by the discharge pulse current integrated value comparing means