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.