Generalising series elastic actuation to flexible-link flexible-joint robot control using end-point position sensing

This paper proposes a task-space generalisation of series elastic actuation concepts for lightweight flexible-link flexible-joint robots with multiple degrees of freedom (dof). Using end-point sensing, the whole body of the flexible manipulator can effectively be considered a task-space series elastic actuator (SEA). This allows force control of the robot, with notable applications in physical human-robot interaction through admittance and impedance control schemes. Moreover, the proposed method allows whole-body interaction: physical interactions are not limited to the end-effector and can take place at any point on the robot structure. A known necessary condition on the maximum passively renderable stiffness for single-dof SEAs is generalised to multi-dof flexible structures. Finally, the task-space control schemes derived from the SEA literature are implemented and validated on a 3-dof flexible-link flexible-joint manipulator prototype. The results demonstrate low-frequency stiffness rendering on a lightweight manipulator with low apparent inertia at the interaction port.