Electrical discharge machine and method for manufacturing machined object using the same

Patent metadata

Field	Value
Publication number	US-9802263-B2
Application number	US-201514635400-A
Country	US
Kind code	B2
Filing date	Mar 2, 2015
Priority date	Feb 28, 2014
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

In an electrical discharge machine that applies a voltage between an electrode and a workpiece to generate electrical discharge, an electrode holder holds the electrode. An ultrasonic motor has a fingertip that comes into contact with electrode holder, and moves electrode holder in a driving direction by moving the fingertip in an annular manner at an ultrasonic-range frequency. A roller bearing guides the movement of the electrode holder in the driving direction. A control circuit controls a position of the electrode in the driving direction by driving the ultrasonic motor, and moves the electrode holder based on an abnormality occurring in resistance against the movement of the electrode holder in the driving direction such that the electrode holder is moved by a movement distance equivalent to when the largest roller element among a plurality of roller elements of the roller bearing rolls and rotates once without sliding or longer.

First claim

What is claimed is:

1. An electrical discharge machine for applying a voltage between an electrode and a workpiece to generate electrical discharge such that the workpiece is melted by the electrical discharge and machined, the electrical discharge machine comprising:
an electrode holder that holds the electrode;
an ultrasonic motor that has a fingertip that comes into contact with the electrode holder, and moves the electrode holder in a predetermined driving direction by moving the fingertip in an annular manner at an ultrasonic-range frequency;
a roller bearing that guides the movement of the electrode holder in the driving direction, the roller bearing comprising:
movement blocks that are fixed to the electrode holder;
a rail that supports the movement blocks and guides movement of the movement blocks; and
a plurality of roller elements that are interposed between the movement blocks and the rail; and

a control circuit that controls a position of the electrode in the driving direction by driving the ultrasonic motor, the control circuit being configured to move the electrode holder based on an abnormality occurring in resistance against the movement of the electrode holder in the driving direction, the electrode holder being moved by a movement distance equivalent to when a largest roller element among the plurality of roller elements rolls and rotates once or longer without sliding.

2. The electrical discharge machine according to claim 1 , wherein the control circuit is configured to determine whether or not an abnormality occurs in resistance against the movement of the electrode holder, by comparing a movement speed in the movement of the electrode holder in the driving direction with a predetermined reference speed.

3. The electrical discharge machine according to claim 2 , wherein the movement speed compared with the reference speed is:
a movement speed of the electrode holder when the electrode holder moves from a predetermined original position in a predetermined direction towards the workpiece so that a single hole machining is started; or
a movement speed of the electrode holder when the electrode holder is returned to the original position in the predetermined direction after the single hole machining is completed.

4. The electrical discharge machine according to claim 1 , wherein the control circuit is configured to determine that an abnormality occurs in resistance against the movement of the electrode holder when at least one of a first condition and a second condition is satisfied,
the first condition being a condition that a first movement speed in a first direction in the driving direction of the electrode holder is lower than a first reference speed, and
the second condition being a condition that a second movement speed in a second direction opposite to the first direction in the driving direction of the electrode holder is lower than a second reference speed.

5. The electrical discharge machine according to claim 4 , wherein the control circuit is configured to determine whether or not an abnormality occurs in resistance against the movement of the electrode holder by comparing the first movement speed with the second movement speed.

6. The electrical discharge machine according to claim 5 , further comprising:
a discharge state detection circuit that detects a discharge state between the electrode and the workpiece to produce a discharge state signal, and outputs the discharge state signal,
the control circuit being configured to:
move the electrode holder in the driving direction based on the discharge state signal output by the discharge state detection circuit, such that when the electrode and the workpiece are short-circuited, the electrode moves in a direction away from the workpiece; and
further determine that an abnormality occurs in resistance against the movement of the electrode holder based on when a period of time during which the electrode and the workpiece are short-circuited exceeds a reference time.

7. The electrical discharge machine according to claim 6 , wherein the control circuit is configured to move the electrode holder based on an abnormality occurring in resistance against the movement of the electrode holder in both of the first direction and the second direction, such that the electrode holder is moved by the movement distance.

8. The electrical discharge machine according to claim 1 , wherein the control circuit is configured to determine whether or not an abnormality occurs in resistance against the movement of the electrode holder by comparing a first movement speed in a first direction along the driving direction of the electrode holder with a second movement speed in a second direction opposite to the first direction along the driving direction of the electrode holder.

9. The electrical discharge machine according to claim 1 , further comprising:
a discharge state detection circuit that detects a discharge state between the electrode and the workpiece to produce a discharge state signal, and outputs the discharge state signal,
the control circuit being configured to:
move the electrode holder in the driving direction based on the discharge state signal output by the discharge state detection circuit, such that when the electrode and the workpiece are short-circuited, the electrode moves in a direction away from the workpiece; and
further determine that an abnormality occurs in resistance against the movement of the electrode holder based on when a period of time during which the electrode and the workpiece are short-circuited exceeds a reference time.

10. The electrical discharge machine according to claim 1 , wherein the control circuit is configured to move the electrode holder based on an abnormality occurring in resistance against the movement of the electrode holder in both of a first direction and a second direction opposite to the first direction along the driving direction of the electrode holder, such that the electrode holder is moved by the movement distance.

11. A method for manufacturing a machined object, comprising:
(i) a step of providing a workpiece for the machined object with respect to an electrical discharge machine for applying a voltage between an electrode and the workpiece to generate electrical discharge such that the workpiece is melted by the electrical discharge and machined, the electrical discharge machine comprising:
an electrode holder that holds the electrode;
an ultrasonic motor that has a fingertip that comes into contact with the electrode holder, and moves the electrode holder in a predetermined driving direction by moving the fingertip in an annular manner at an ultrasonic-range frequency;
a roller bearing that guides the movement of the electrode holder in the driving direction, the roller bearing comprising:
movement blocks that are fixed to the electrode holder;
a rail that supports the movement blocks and guides movement of the movement blocks; and
a plurality of roller elements that are interposed between the movement blocks and the rail; and

a control circuit that controls a position of the electrode in the driving direction by driving the ultrasonic motor, the control circuit being configured to move the electrode holder based on an abnormality occurring in resistance against the movement of the electrode holder in the driving direction, the electrode holder being moved by a movement distance equivalent to when a largest roller element among the plurality of roller elements rolls and rotates once or longer without sliding; and

(ii) a step of machining the workpiece using the electrical discharge machine.

Assignees

• Denso Corp

Inventors

• Yasuda Kouichirou
• Inobe Yasuji
• Itoh Akira
• Nagai Nobuhiko
• Yamaguchi Tetsuji
• Ootani Hiroyuki

Classifications

• B23H9/14

  Making holes · CPC title

• B23H1/04 Primary

  Electrodes specially adapted therefor or their manufacture (B23H9/00 takes precedence) · CPC title

• B23H11/00

  Auxiliary apparatus or details, not otherwise provided for · CPC title

• B23H7/30 Primary

  Moving electrode in the feed direction (B23H7/32 takes precedence) · CPC title

• B23H1/00

  Electrical discharge machining, i.e. removing metal with a series of rapidly recurring electrical discharges between an electrode and a workpiece in the presence of a fluid dielectric · CPC title