Power supply system for an electric discharge machine

• US 5,770,831 A
• Filed: 12/19/1995
• Issued: 06/23/1998
• Est. Priority Date: 04/26/1994
• Status: Expired due to Term

• Current Assignee: Sodick Company Limited (Plustech, Inc.), ROHM Co., Ltd.
• Original Assignee: Sodick Company Limited (Plustech, Inc.)
• Inventors: Ueda, Tadao, Kaneko, Yuji
• Primary Examiner(s): Evans, Geoffrey S.
• Application Number:
  US08/564,324
• Time in Patent Office: 917 Days
• Field of Search: 219/69.12, 219/69.13, 219/69.18
• US Class Current: 219/69.18
• CPC Class Codes: B23H 1/022 for shaping the discharge pulse train B23H1/024 takes precedence
• CPC Class Codes: B23H 2300/20 Relaxation circuit power supplies for supplying the machining current, e.g. capacitor or inductance energy storage circuits
• CPC Class Codes: B23H 2300/22 Circuits using or taking into account line impedance to shape the discharge pulse

Abstract

First power supply circuit 8, second power supply circuit 6, and third power supply circuit 9 are connected to form a power supply unit 5. The first power supply circuit 8 includes a direct current power supply 8A and switching element 8B. The power supply circuit 8 does not include any substantial resistance, and has comparatively low inductance and impedance characteristics. The power supply circuit 6 includes a direct current power supply 6A, switching element 6B, and current limiting resistor 6C. The power supply circuits 6, 8, and 9 are connected to the gap using a cable 11 as a common interconnect. A high frequency alternating current circuit is formed by the power supply circuit 8, conductor 11, coupling transformer 13, and the gap. In this event, switches 6F, 6G, 9F, and 9G, associated with power supply circuits 6 and 9, are opened, and the power supply circuits 6 and 9 are completely disconnected from the above high frequency alternating current circuit. It is preferable that the switches 6G, 6F, 9F, and 9 G be butt-type switch devices which will completely disconnect and connect the power supply circuits 6 and 8. Also, when using the high frequency alternating current, it is desirable to use an appropriate detection device 30 having a photocoupler 35 as the means for detecting the gap voltage.

Claims

1. A power supply system for supplying machining pulses to a machining gap formed between a tool electrode and a workpiece comprising:

a first power supply circuit for generating a dc pulse including a dc power supply and at least one switching element;

a conversion means disposed between the first power supply circuit and the machining gap for converting the dc pulse into an ac pulse, said conversion means comprising a ring core, a primary winding wound around the ring core and connected to the first power supply circuit, and a secondary winding wound around the ring core and connected to the machining gap;

a bypass path for connecting the first power supply circuit to the gap;

a first switching means disposed between the first power supply circuit and the machining gap for selectively switching between the conversion means and the bypass path;

a second power supply circuit including at least one switching element and a serial circuit including a current limiting resistor and a switching element;

a pulse generating means, connected to the switching elements of the first and second power supply circuits, for delivering a stream of pulses thereto; and

a second switching means disposed between the first power supply circuit and the machining gap, for connecting the second power supply circuit to the machining gap via the bypass path when the bypass path is connected to the machining gap, and for disconnecting the second power supply circuit from the machining gap when the conversion means is connected to the first power supply circuit.

2. The power supply system according to claim 1 wherein the power supply system supplies machining pulses having an ON time in the range of about 50˜

1,000 ns and an OFF time in the range of about 500˜

10,000 ns.

3. The power supply system according to claim 1, further comprising a third power supply circuit including a dc power supply and a switching element, said third power supply circuit being connected in parallel to the first and second power supply circuits.

4. The power supply system according to claim 1, wherein the first switching means comprises a butt contact switch.

5. The power supply system according to claim 1, wherein the second switching means comprises a butt contact switch.

6. The power supply system according to claim 1, wherein the second switching means comprises at least two switches and further comprising a relay circuit for switching said at least two switches simultaneously.

7. The power supply system according to claim 1, wherein said pulse generating means is responsive to a command signal and said relay is driven by a signal based on said command signal.

8. The power supply system according to claim 1, wherein said first and second power supply circuits include a pair of common terminals and further comprising a cable including a first conductor, one terminal of which is connected to one of said common terminals, and a second conductor, one terminal of which is connected to the other of said common terminals, said first and second conductors having low inductance to generally maintain the pulse waveform of the generally pulse which flows through the switching elements of said first and second power supply circuit during transmission to the vicinity of the machining gap.

9. The power supply system according to claim 8, wherein the cable comprises a coaxial cable.

10. The power supply system according to claim 8, wherein the cable comprises a shielded cable.

11. The power supply system according to claim 1, wherein the conversion means and the first switching means are disposed in a housing positioned proximate to the machining gap.

12. The power supply system according to claim 1 further comprising a detection circuit for detecting machining gap voltage, said detection circuit being connected in parallel with the machining gap and including an output means for converting an electrical signal into an output optical signal.

13. The power supply system according to claim 1, further comprising a first detection circuit connected in parallel to the machining gap for detecting a dc voltage at the machining gap and a second detection circuit connected in parallel to the machining gap for detecting an ac voltage at the machining gap.

14. The power supply system according to claim 13 further comprising a third switching means for connecting the first detection circuit to the machining gap and for disconnecting the second detection circuit from the machining gap when the bypass path is connected to the machining gap, and for disconnecting the first detection circuit from the machining gap and connecting the second detection circuit to the machining gap when the conversion means is connected to the first power supply circuit.

15. The power supply system according to claim 14, wherein said switching means includes a butt contact switch.

16. A power supply system for an electric discharge machine having a machining gap formed between a tool electrode and a workpiece electrode, comprising:

a first power circuit including a dc power source and a switching element, said first power circuit comprising a low resistance circuit;

a dc to ac conversion device including a ring core, a primary winding and a secondary winding wound on said ring core, said primary winding being selectively connectable to said first power circuit, and said secondary winding being selectively connectable to said machining gap;

a bypass path for bypassing said conversion device and connecting said first power circuit directly to said machining gap;

a first switching device for selectively connecting said first power circuit to the machining gap either via the conversion device or the bypass path;

a second power supply circuit including a series connected dc power source, a switching element and a current limiting resistance; and

a second switching device for connecting said second power supply circuit into said power supply system when said first power supply circuit is connected to said machining gap via said conversion device.

17. The power supply system according to claim 16, further comprising a pulse generator connected to deliver gate pulses to the switching elements of said first and second power circuits whereby said power supply system delivers a machining pulse to said machining gap having an ON time in the range of about 50˜

1,000 ns and an OFF time in the range of about 500˜

10,000 ns.

18. The power supply system according to claim 16, wherein the first and second switching devices each include butt contact type switches.

19. The power supply system according to claim 16, further comprising a first spark detection circuit connected across the machining gap for detecting a dc voltage across the machining gap, and a second spark detection circuit connected across the machining gap for detecting an ac voltage across the machining gap.

20. The power supply system according to claim 19, further comprising a third switching device for connecting the first spark detection circuit across the machining gap and disconnecting the second spark detection circuit from the machining gap when the first power circuit is connected to the machining gap via the bypass path, and for disconnecting the first spark detection circuit from across the machining gap and connecting the second spark detection circuit across the machining gap when the first power circuit is connected to the machining gap via the conversion device.