Abstract: A welding assembly is provided for welding a fastener to an object such as a vehicle body panel. The assembly includes a weld gun having first and second electrodes movable relative to one another between an open position and a closed position. The first electrode includes a housing assembly. A pin is received in the housing assembly and is movable when in said closed position between a desired nut position, and upside down nut position, and a no nut position. An optical sensor has a terminal end space from the pin for direction light thereon. The terminal end of the sensor received reflected light from the pin. A sensor control system processes the reflected light into a signal corresponding to one of the desired nut, upside down nut, and no nut positions.

Abstract: A method of monitoring a resistance welding system is provided. The method utilizes a sensor for isolating and determining movement of a pin that typically supports an object to be welded such as a fastener. The movement of the pin is used to determine various present welding operation parameters to reduce cycle time, and increase efficiency and quality of the weld. The present welding operation parameters are compared to learned or stored welding operation parameters, for example, to determine whether a fault should be generated or whether an acceptable weld was achieved.