Electric discharge machine position finding apparatus

• US 4,820,895 A
• Filed: 08/07/1985
• Issued: 04/11/1989
• Est. Priority Date: 12/23/1983
• Status: Expired due to Fees

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Obara, Haruki
• Primary Examiner(s): Paschall, M. H.
• Assistant Examiner(s): Evans, Geoffrey S.
• Application Number:
  US06/767,267
• Time in Patent Office: 1,343 Days
• Field of Search: 219/69 C, 219/69 S, 219/69 G, 219/69 M, 219/69 P, 219/69 R, 328/34, 328/35, 328/36
• US Class Current: 219/69.13
• CPC Class Codes: B23H 2500/20 Methods or devices for detecting wire or workpiece position
• CPC Class Codes: B23H 7/26 Apparatus for moving or positioning electrode relatively to workpiece; Mounting of electrode

Abstract

A position finding apparatus of an electric discharge machine has a switching device including a relay 3 set into operation when tool electrode position finding starts, so that the switching device turns off machining power applied across a workpiece W and a tool electrode P. At such time, a differentiated waveform, which is obtained by differentiating in a differentiating circuit 15, a square wave produced by a pulse oscillator, is applied across the workpiece W and tool electrode P. Thereafter, position finding is performed with regard to the tool electrode P. A resistor in the differentiating circuit 15 can be made variable in value to alter the differentiated waveform applied across the workpiece W and tool electrode P.

Claims

1. An electric discharge machining position finding apparatus for repeatedly impressing a pulse-shaped voltage of positive and negative polarity across a tool electrode and a workpiece, and for determining the relative positions of the tool electrode and the workpiece by sensing contact between the tool electrode and the workpiece, comprising:

a machining power supply unit for applying power for electric discharge machining across the tool electrode and the workpiece;

a pulse oscillator for generating a square wave of a prescribed period at output terminals;

a differentiating circuit, coupled to said pulse oscillator, for receiving the square wave generated by said pulse oscillator and for producing a differentiated waveform, said differentiating circuit comprising a capacitor and a resistor coupled in series with the output terminals of said pulse oscillator, said differentiating circuit having output terminals at the terminals of said resistor; and

a switching device, coupled to said differentiating circuit, said machining power supply unit and the workpiece, for applying the power for electric discharge machining from said machining power supply unit across the tool electrode and the workpiece when machining is to be performed, and for applying the differentiated waveform produced by said differentiating circuit across the tool electrode and the workpiece when position finding is to be performed.

2. An electric discharge machining position finding apparatus according to claim 1, wherein said resistor of said differentiating circuit has a resistance value which is capable of being adjusted.

3. An electric discharge machine having a tool electrode and a workpiece, and having a position finding signal generator circuit connected to the tool electrode for determining the relative positions of the tool electrode and the workpiece, comprising:

a machining power supply unit for supplying power for electric discharge machining;

generating means for generating a square wave having a predetermined period; and

means for differentiating the square wave generated by said generating means to produce a differentiated waveform; and

switching means for applying the supplied power for electric discharge machining from said machining power supply unit across the tool electrode and the workpiece when machining is to be performed, and for applying the differentiated waveform across the tool electrode and the workpiece when position finding is to be performed, said differentiating means comprising a differentiating circuit including;

a capacitor coupled to said generating means and connected to the tool electrode at a first node; and

a resistor coupled to the first node and coupled to said switching means.

4. An electric discharge machine according to claim 3, wherein said generating means comprises a pulse oscillator.

5. An electric discharge machine according to claim 4, wherein said switching means comprises a relay coupled to the workpiece, said resistor and said machining power supply unit.