A sensor based assembly technique is described which uses a part position sensor to locate certain part features prior to a mating operation. The rigid parts assembly process is divided into three phases: part acquisition, alignment and mating. The part position sensor is used to increase the accuracy of the part alignment phase and decrease the system compliance requirements for the mating phase. The system is shown to be relatively insensitive to robot kinematic errors. A prototype system is described which assembles a number of closely fitting parts.