Performance limitations of a force-controlled industrial manipulator

In this thesis, system performance is investigated in the case where forces are applied by a robotic manipulator to a constraint. The forces are controlled using the hybrid position/force control method. Force control is achieved by adjusting the end effector position normal to the contact surface based on the feedback received from a wrist-mounted force sensor. The relationship between force control accuracy and system stiffness is derived and then verified experimentally. A computer algorithm is proposed for tracking and measuring flat and curved surfaces with unknown dimensions based on the force control approach. The algorithm is coded into a robot control language and tested experimentally by characterizing the performance of a two degree of freedom Adept manipulator. Factors affecting the performance of the system are identified. It is shown that the robotic manipulator tracks the constraint faster when the force tolerance to reach the desired normal force to the constraint is greater than the force resolution of the system. Therefore, there is a tradeoff between tracking speed and tracking accuracy. It is also shown that the more deformation the constraint experiences, the less accurate the constraint measurements are.