Estimation of Human Interaction Forces on a Parallel Kinematic Manipulator for Upper-Limb Physiotherapy Exercises

In this paper, an estimation algorithm for human interaction forces is presented, which can potentially be applied when a Parallel Kinematic Manipulator (PKM) is used on supervised physiotherapy exercises. The estimation algorithm is based on the dynamic model of the PKM, which is calculated with a 3-RRRS configuration (three arms with three rotational joints and a spherical joint); the underline denotes the active joints. The proposed algorithm estimates human interaction forces only in terms of the calculation of the robot dynamic state and control signals of the active joints of the PKM, without the need of force or torque sensors; therefore, the proposed method reduces the complexity, inertia and passive mass associated with the addition of 6-DOF force/torque sensors. A full description of the design of the robotic platform is also presented, followed by a validation test of estimated data against measured forces and relevant experimental results for static and dynamic tests.