Patent ID: 6064029
Filing Date: 2000-05-16
Classification: B23K

Abstract:
A resistance spot welding apparatus having a primary circuit, a secondary circuit and a transformer for controlling the quality of a resistance spot weld, wherein an electric voltage is applied to the primary circuit to thereby generate a welding current, the welding apparatus comprising:means for sensing the weld current from the primary circuit;means for calculating power factors based on the welding current;means for obtaining a dynamic resistance curve based on the calculated power factors; andmeans for generating a gate signal for controlling the weld current wherein the gate signal is obtained by using the dynamic resistance curve,wherein the generating means includes means for estimating a nugget size and a nugget penetration based on the dynamic resistance curve and means for generating the gate signal based on the nugget size and the nugget penetration, and wherein the estimating means includes:means for converting the dynamic resistance curve to a discrete observation symbol sequence;a HMM block having n.omega. number of groups .mu.i's for calculating the discrete observation symbol sequence at each of the groups .mu.i's to calculate a corresponding probability P(O.mu.i), wherein i.epsilon.{1, 2, n.omega.} and n.omega. is a predetermined positive integer;means for estimating the nugget size and the nugget penetration by selecting a group having a maximum probability value among the groups .mu.i's; andmeans for outputting the nugget size and the nugget penetration.