Combined Position & Force Control for a robotic manipulator

The ARM is a 6 DOF robotic manipulator used by disabled people with a severe handicap at the upper extremities The present ARM is position and velocity controlled. The desired position of the robot is given by the user. However, in constraint scenario's, manipulation becomes too difficult and an assistant-controller is wanted. This assistant is based on external forces on the gripper of the robot, measured using a force-torque sensor. A new control strategy is designed for measured forces and user input. The basic principle of this strategy is derived from the way that humans steer their hand. Sensed forces are followed until they are not present anymore, except when the user wants to do a manipulation in that direction. Therefore a combined position/force controller was designed. All 6 DOF of the robot can be steered by both the user and the force controller at the same time. Beside the design of the control strategy, it is also implemented on the ARM and tested in four test-cases.