Trajectory tracking control for a tendon driven series elastically actuated robotic arm is considered. This bioinspired actuation concept enables an ultra lightweight and highly safe robot design that is very well suited for physical human-robot interaction. However, the high elasticity in the joint actuation imposes challenges on robot control, especially for the usual case that no joint torque measurements are available. In this paper, a trajectory tracking controller for this highly compliant robot is presented which does not need explicit joint torque measurements as required by related approaches for robots with elastic joints. A control concept is proposed which aims to be robust against inaccuracies in various model parameters (like robot dynamics, position initialization, drive train stiffness, transmission ratio and friction). It compensates for changes in robot dynamics by equilibrium controlled stiffness. The proposed controller is successfully applied and evaluated in simulated and physical experiments with the robot.
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