Assembly of parts with irregular surfaces using active force sensing

A new approach to force guided assembly is developed for the assembly of unsurfaced parts having sharp burrs and irregular surfaces. Due to friction at burrs and irregular surfaces, force signals are very noisy and erratic, preventing reliable sensing and monitoring of the assembly process. In this paper, instead of simply measuring contact forces, we take positive actions by actively shaking the end effector and observing the reaction forces to the perturbation in order to obtain rich, reliable information. By taking the correlation between the input perturbation and the resultant reaction forces, we can determine the direction of the part surface and guide the hand-held part correctly despite burrs and poor surface finish. The principle of active force sensing using a correlation technique is described. An algorithm for guiding an assembly part by using the correlation information is developed based on the theory of direct adaptive control. The method is then applied to a practical task: the assembly of sheet metal parts with sharp edges and burrs. Experiments demonstrate the effectiveness and feasibility of the active force sensing method