There are many known types of welding systems used for many different welding processes. Welding system, or system for welding, as used herein, includes one or more of a power source, controller, wire feeder, and a source of gas, it may also include peripherals such as robots etc. Welding power supply, as used herein, includes any device capable of supplying welding, plasma cutting, and/or induction heating power including power circuitry, control circuitry and other ancillary circuitry associated therewith.
One type of welding system includes a CC welding power source. A CC welding power source, as used herein, is a current controlled power source, wherein the output current is monitored, and the output is adjusted to provide the desired current. The current may be constant during the welding process, or may have a desired waveform of varying current.
Another type of welding system includes a CV power source. A CV welding power source, as used herein, is a voltage controlled power source, wherein the output voltage is monitored, and the output is adjusted to provide the desired voltage. The voltage may be constant during the welding process, or may have a desired waveform of varying voltage. Some CV welding power sources use a current command, and adjust the current in response to the monitored voltage, thereby adjusting the arc voltage by the change in current across the load.
One known welding process is a pulsed MIG process. The pulsed MIG process typically has a cyclical output having at least a peak segment with a relatively high current and a background segment with a relatively low current. Generally, it is desirable to maintain a constant arc length during each segment, to help keep the process consistent. Unfortunately, during the process the torch angle and/or distance to the work piece may be inadvertently varied by the welder. This results in undesirable changes to the arc length.
Prior art control schemes attempted to control arc length by using a CV control because arc (load) voltage is generally related to arc length for a given welding current. Thus, keeping a constant voltage for a given current maintains a constant arc length. Most prior art CV controllers for pulsed MIG average the arc voltage over at least one cycle, and then adjust the output for the next cycle in response to the average. The average has been taken over a plurality of cycles, an entire cycle, over only the background segment, or over only the peak segment. Because the average is taken over at least one cycle, the output (and arc length) is not changed until at least the following pulse cycle.
Averaging over one or more cycles yields a control scheme with a relatively slow response. The slow response forced a choice between a tighter arc (which provides better control of the weld puddle), and explosive clearing of shorts and spatter (which adversely affects the quality of the weld).
Accordingly, a control scheme for pulsed MIG that provides fast response to control the arc, and does not result in undesirable short clearing, is needed. Preferably such a control scheme will be able to be used in other processes such as CMT (controlled metal transfer or short circuit) or AC MIG.
USPTO Backgrounds
USPTO Backgrounds