Force regulation and contact transition control

This dissertation addresses an important problem in the area of robotics, the problem of design of a force regulating, contact transition stabilizing control; also called impact control. Impact control is required in most assembly tasks involving the interaction of the hand of the manipulator and the workpiece. For workpieces with low tolerance, force feedback is necessary to reduce the effect of the uncertain location and unknown stiffness of the environment.;Impact control is a challenging problem and includes all the difficulties and problems encountered in force control. In a general contact operation, a certain approach velocity is needed for high productivity; resulting in a collision with the contact surface. Collision is considered as a dangerous phenomenon compromising the safety of the equipment, it can give rise to a large peak impact force and possible bouncing.;In this dissertation, a novel robust impact control design is proposed using positive acceleration feedback based on the singular perturbation method, and a switching control strategy is developed for the robot impact control and force regulation. The robot dynamic model is feedback linearized and decoupled for the free motion mode, the phase transition mode, and the constrained motion mode. The transient force response during impact can be controlled such that large peak impact force and bouncing can be avoided. The switching control strategy deals with the inadvertent loss of contact of the end-effector. The stability of the overall system can be guaranteed and bouncing can be eliminated after a finite number of switches. Finally the output force can be regulated simultaneously after contact is established. A complete and rigorous stability analysis based on Liapunov-like methods is given for the proposed system. This scheme is implemented and tested on a 6 DOF PUMA 560 robot arm. A theoretical as well as experimental comparison with other schemes is also made. The results demonstrate the advantages of the proposed control methods. In addition, the orientation singularity problem which was encountered in the experiment is also discussed and solved in the dissertation.