Method for detecting current transfer in a plasma arc

Patent metadata

Field	Value
Publication number	US-9878395-B2
Application number	US-40321709-A
Country	US
Kind code	B2
Filing date	Mar 12, 2009
Priority date	Mar 14, 2008
Publication date	Jan 30, 2018
Grant date	Jan 30, 2018

Abstract

Methods and systems for transferring a plasma arc from between an electrode and a tip to between an electrode and a workpiece and back as dictated by the conditions at the cutting arc are provided. The present disclosure allows for arc transfer detection without use of a current sensor at the workpiece or knowledge of a precise pilot circuit limit value through a novel plasma arc control circuit. In one embodiment, the plasma arc control circuit provides a programmable current source and a current sink configured to limit current in a pilot arc control circuit. The pilot arc circuit may be configured to signal its limiting status to a controller, which may switch the pilot arc control circuit in or out of the current path. Certain embodiments may include a pulse width modulation control in the pilot arc control circuit for controlling current flow through the pilot arc circuit.

First claim

The invention claimed is:

1. A plasma cutting system, comprising:
a current source that in operation provides a programmable current output;
a current regulator comprising a switch and being configured to receive the programmable current output from the current source;
a pilot arc circuit current path that in operation is established between the current source, the current regulator, an electrode, and a tip to establish a pilot arc between the electrode and the tip when the pilot arc circuit current path is active;
a cutting arc circuit current path that in operation is established between the current source, a workpiece, and the electrode to establish a cutting arc between the workpiece and the electrode when the cutting arc circuit current path is active;
a pilot control that in operation limits a current amplitude level through the pilot arc circuit current path from the current source to the tip by cycling the switch between an enable state and a disable state to maintain the pilot arc between the electrode and the tip; and
a power control that in operation, once the pilot arc is established between the electrode and the workpiece, increases a set point of the programmable current output and, as the set point is increased, determines, without detecting current to the workpiece via a current sensor, when a transfer of the pilot arc to the workpiece to establish the cutting arc has occurred by detecting when the switch in the current regulator ceases cycling and remains in the enable state.

2. The plasma cutting system of claim 1 , comprising a buck converter located along the pilot arc circuit current path and configured to limit the current amplitude level at the tip.

3. The plasma cutting system of claim 1 , comprising a sensor and an inductor aligned in series between the switch and the tip, wherein the sensor is configured to provide a current feedback to the pilot control.

4. The plasma cutting system of claim 3 , wherein the pilot control comprises a hysteretic control circuit.

5. The plasma cutting system of claim 1 , wherein the current source comprises an inverter.

6. The plasma cutting system of claim 1 , comprising a sensor and an inductor aligned in series between the electrode and the current source, wherein the sensor is configured to provide a current feedback to the power control.

7. A method of transferring a plasma arc of a plasma cutter, comprising:
establishing a pilot arc between an electrode and a tip through a pilot arc circuit current path between a current source, a current regulator comprising a switch, the electrode, and the tip;
limiting a current amplitude level through the pilot arc circuit current path by toggling the switch between an enable state and a disable state to maintain the pilot arc between the electrode and the tip;
increasing a set point of the current source; and
detecting, as the set point of the current source is increased, when a transfer of the pilot arc to a workpiece to establish a cutting arc has occurred by detecting when the switch ceases cycling and remains in the enable state.

8. The method of claim 7 , comprising setting the set point of the current source to a cutting current level when the transfer of the pilot arc to the cutting arc is detected.

9. The method of claim 7 , comprising stabilizing current flow between the electrode and the current source with an inductor.

10. The method of claim 7 , comprising limiting the current amplitude level using a hysteretic control circuit configured to toggle the switch based on a current feedback received from a sensor positioned between the switch and the tip.

11. The method of claim 7 , comprising stopping current flow through the pilot arc circuit current path when a predetermined level of current flow between a work lead and the electrode is obtained.

12. The method of claim 11 , comprising reinitiating current flow through the pilot arc circuit current path when an indication of cutting arc failure is identified.

13. The method of claim 7 , wherein the current source is pulse width modulated.

14. A plasma cutting control system, comprising:
a pilot arc control circuit that in operation controls a current regulating switch to cycle between an enable state and a disable state to establish a pilot arc between an electrode and a tip and to limit current flow through a pilot arc circuit comprising a current source, the current regulating switch, the electrode, and the tip; and
a cutting arc control circuit that in operation, once the pilot arc is established, increases a set point of the current source and, as the set point of the current source is increased, determines, by detecting when the current regulating switch ceases cycling, when a transfer occurs from the pilot arc to a cutting arc between a workpiece and the electrode.

15. The plasma cutting system of claim 14 , wherein the pilot arc control circuit comprises a hysteretic control circuit.

16. The plasma cutting system of claim 14 , wherein, in operation, the cutting arc control circuit disables current flow through the pilot arc circuit when the transfer occurs from the pilot arc to the cutting arc.

17. The plasma cutting system of claim 14 , wherein, in operation, the cutting arc control circuit sets the set point of the current source to a cutting arc level when the transfer of the pilot arc to the cutting arc is detected.

18. The plasma cutting system of claim 14 , wherein the current source comprises an inverter.

19. The plasma cutting system of claim 14 , wherein the pilot arc circuit comprises a buck converter.

20. The plasma cutting system of claim 16 , wherein, in operation, the cutting arc control circuit reinitiates current flow through the pilot arc circuit when an indication of cutting arc failure is identified.

Assignees

• Salsich Anthony V
• Manthe Alan A
• Illinois Tool Works

Inventors

• Salsich Anthony V
• Manthe Alan A

Classifications

• B23K9/067

  Starting the arc · CPC title

• B23K10/00 Primary

  Welding or cutting by means of a plasma · CPC title