Automatic stepper for resistance welding
First Claim
1. For use in a resistance welding process in which an alternating electrical current is delivered to a metal workpiece through a circuit including electrodes to produce a weld caused by localized melting of the workpiece, wherein the application of an excessive amount of said current results in expulsion of molten metal from said weld thereby diminishing the quality of said weld, a method of controlling the magnitude of current delivered to said workpiece through said electrodes, comprising the steps of:
- (A) determining the time interval t1 between the application of voltage to said electrodes and the following zero crossover of said voltage;
(B) determining the time interval t2 between said zero crossover point of said voltage and the following zero point of the current resulting from said application of voltage;
(C) determining the value of the power factor of said circuit using the time intervals t1, t2 determined in steps (A) and (B), the expulsion of molten metal from said weld being a function of the value of the power factor determined in step (B); and
(D) changing the magnitude of said current based at least in part on the value of the power factor determined in step (C).
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Accused Products
Abstract
A method is disclosed for controlling the magnitude of current delivered through welding electrodes to a workpiece to be welded using resistance welding techniques, in order to prevent weld expulsion and concomitant diminishment of weld quality. Weld expulsion is detected by determining changes in resistance during formation of the weld, by periodically determining the power factor, and the primary circuit of the welding transformer. The power factor is determined by determining the relative timing between the commencement of the applied voltage, the zero crossover point of the applied voltage, and the ensuing zero point of the applied current.
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Citations
17 Claims
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1. For use in a resistance welding process in which an alternating electrical current is delivered to a metal workpiece through a circuit including electrodes to produce a weld caused by localized melting of the workpiece, wherein the application of an excessive amount of said current results in expulsion of molten metal from said weld thereby diminishing the quality of said weld, a method of controlling the magnitude of current delivered to said workpiece through said electrodes, comprising the steps of:
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(A) determining the time interval t1 between the application of voltage to said electrodes and the following zero crossover of said voltage; (B) determining the time interval t2 between said zero crossover point of said voltage and the following zero point of the current resulting from said application of voltage; (C) determining the value of the power factor of said circuit using the time intervals t1, t2 determined in steps (A) and (B), the expulsion of molten metal from said weld being a function of the value of the power factor determined in step (B); and (D) changing the magnitude of said current based at least in part on the value of the power factor determined in step (C). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. For use with resistance welding apparatus of the type having a transformer including a primary circuit, said primary circuit including a source of alternating electrical current and switching means for selectively switching said alternating electrical current to the primary of said transformer, said transformer having a secondary circuit including a pair of electrodes for applying electrical current to a workpiece to be welded, wherein the application of an excessive level of current to said workpiece results in expulsion of molten material from said weld thereby diminishing the quality of said weld, a method of controlling the level of current applied to said weld, comprising the steps of:
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(A) determining the point in time when said switching means is switched to apply voltage from said current source to said transformer primary, said current commencing to flow in said primary and secondary circuits upon said application of voltage to said transformer primary; (B) determining the time intervals t1, t2 between the point in time determined in step (A) and the subsequent respective zero points of the alternating voltage and current applied to said transformer primary; (C) determining the change in impedance in said primary circuit based on the time intervals t1, t2 determined in step (B), said change in impedance being related to changes in the resistance in said primary circuit caused by the formation of said weld; and (D) changing the magnitude of said current based at least in part on the change in impedance determined in step (C). - View Dependent Claims (12, 13, 14, 15, 16, 17)
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Specification