On Impact Behavior of Force Controlled Robots in Environments with Varying Contact Stiffness
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In the field of industrial robotics many tasks require predefined contact forces between the environment and the robot's end-effector. In tasks like cutting, assembly, grinding or polishing it is also necessary to follow a given trajectory. To reach this goal a parallel force/position control of the robot, suggested in  and also implemented in  and , is used. With this method the desired trajectory is modified by the force controller, so that the position controlled robot applies the desired force in the force-controlled directions and follows the trajectory in the remaining directions. In an environment with varying contact stiffness, and especially when the robot's end?effector hits the surface, the stability depends on the controller parameters and the contact stiffness itself. In the case of uncertain system parameters one simple way is to calculate directly a feed-back torque from the force control law, to increase the stability of the force control. Otherwise a more robust behavior can be achieved by taking the dynamics of the robot into account.