Using Compliance in Lieu of Sensory Feedback for Automatic Assembly

摘要

A technique was developed for performing mechanical assembly without active sensory feedback when using a programmable assembly machine or assembly robot that has positional errors more than an order of magnitude larger than the clearances of the pieces to be assembled. This technique is based on designing a passive compliance structure or mechanism that will essentially mimic an active force feedback system. This thesis shows both theoretically and experimentally that forces that occur during the assembly process are a function of: (1) the values of the compliance matrix (a 6 x 6 symmetric matrix of the compliance seen at the assembly interface); (2) the initial positional errors; (3) the relative clearance of the pieces; and (4) the coefficient of friction between the pieces. Also, this thesis shows that the important parameters for the insertion of a shaft or a peg into a hole are the spatial center of compliance, the lateral stiffness, and the rotational stiffness. The compliance system was used both in experiments that measured assembly forces and moments and as part of a programmable assembly demonstration project. Seventeen parts of an automobile alternator were assembled in approximately two minutes thirty seconds using the compliance system mounted on an electrically actuated four-degree-of-freedom programmable assembly machine. The nominal clearances between the parts were as small as 0.01 mm (0.0004 in.).