Arc-welding system

Claim 2

In an arc-welding apparatus of the type having an electrode, a workpiece, a welding current generating means, and means for providing an input signal to the generating means which establishes an arc welding current between the electrode and workpiece proportional to the amplitude of the input signal, the improvement comprising: a. a plurality of control signal source means each providing a control signal having a different amplitude characteristic, b. gating means for selecting one of the control signals from said source means, and generating an output corresponding thereto, c. means for operating said gating means for alternately selecting control signals from a first of said source means which provides a control signal of relatively high magnitude and a second of said source means which provides a control signal of lower magnitude, d. means for detecting the amplitude of the arc welding current and generating a signal proportional thereto, and e. means responsive to the difference between the output of the gating means and the output of the means for detecting, for providing the input signal.

Claim 3

The invention as set forth in claim 1 further comprising switching logic for operating said gating means, said switching logic including a pulse generator means for repetitively providing pulses including successive portions of high level and low level, and means for applying the pulses to said gating means for alternately selecting said first and second sources when the pulses have one of said levels.

Claim 4

The invention as set forth in claim 2 wherein said switching logic also includes a flip-flop having a pair of stable states, a first comparator means responsive to the difference between the signal proportional to the arc current and a first reference signal for providing an output which enables the toggling of said flip-flop to a first state when the arc current is below a predetermined amplitude, means operated by said flip-flop when conditioned in one of its states and in the opposite of its states for respectively rendering said welding current generating means operative and inoperative to generate welding current, and means for toggling said flip-flop to start and stop the welding cycle.

Claim 5

The invention as set forth in claim 3 including means responsive to the enabling output of said first comparator for inhibiting said flip-flop operated means.

Claim 6

The invention as set forth in claim 4 including means operated by the output of said first comparator for inhibiting said pulse generating means.

Claim 7

The invention as set forth in claim 5 wherein said plurality of control signal source means includes a third source means which provides a control signal which slopes from a high level to a low level sufficient to reduce the welding current towards cutoff when applied to said means for proViding the input signal, means connecting the output of said flip-flop to said gating means for selecting the third source control signal when said flip-flop is in its opposite state so as to reduce the welding current and permit said flip-flop operated means to render said generating means inoperative after the welding current is reduced to the predetermined amplitude.

Claim 8

The invention as set forth in claim 6 including a fourth source means for providing a control signal which decreases at a greater rate than the third source control signal when applied to the means for providing the input signal and manual means for selecting the control signal of said fourth source means when said flip-flop is conditioned to its said opposite state.

Claim 9

The invention as set forth in claim 1 wherein each of said plurality of source means is a current source means, and including means for manually varying the amplitude of the current supplied from said first and second source means to provide the control signals from the first and second source means.

Claim 10

The invention as set forth in claim 2 wherein said welding current generating means includes a saturable reactor having a control winding, a welding current control circuit means responsive to said means for providing the input signal for supplying current to said control winding which is proportional in amplitude to the amplitude of the input signal and a power supply means including said reactor for converting AC into DC welding current having an amplitude dependent upon the amplitude of the current supplied to said control winding.

Claim 11

The invention as set forth in claim 9 wherein said welding current control circuit means comprises a. a first capacitor, b. current control means responsive to said means for providing the input signal for charging said first capacitor at a rate proportional to the amplitude of the input signal, c. a uni-junction transistor, d. means coupling said uni-junction transistor to said first capacitor for triggering said uni-junction transistor to pass a current pulse therethrough when said capacitor becomes charged to a certain voltage, e. a second capacitor, f. means for applying a constant voltage across said second capacitor, g. a transformer having a primary winding and at least one secondary winding, h. means for discharging said second capacitor through said primary winding when said uni-junction transistor passes the pulse, i. a rectifier connected in series with a source of alternating current having a frequency much higher than the frequency of the pulses provided by said pulse generator, and an SCR having a trigger electrode and two other electrodes connected in series with said rectifier and said source of alternating current, said rectifier also connected to supply current to said control winding, and j. means for connecting said secondary winding between the trigger electrode and one of the other electrodes of said SCR.

Claim 12

The invention as set forth in claim 3 including a second comparator means responsive to the difference between the output of said means for detecting and a second reference amplitude higher than the first reference amplitude for providing an output, said flip-flop operated means also being operated by the last named output for rendering said welding current generating means inoperative, whereby the welding current is cut off when it exceeds a safe magnitude.