Design of Self-adjusting Orthoses for Rehabilitation

Safety and comfort are primary concerns in rehabilitation devices and exoskeletons. However, the result of using simplified kinematic arrangements can be discomfort, or even injury, as a result of overconstraining the joint. In this paper, we describe a selfadjusting mechanism able to overcome misalignment between the rotational axis of the mechanism that is attached to the user’s limbs and the rotational axis of the anatomical joint. Additional degrees of freedom are added to the mechanism to eliminate internal residual forces. Furthermore, a new technique for the estimation of the Instantaneous Center of Rotation of the assisted joint based on velocity and position sensors is demonstrated. We illustrate this technique with a mechanism which is able to self-adjust with or without resorting to motorized add-ons. Kinematic analyses are presented and are validated by computer simulation on 2D examples.