Freebal: Design of a Dedicated Weight-Support System for Upper-Extremity Rehabilitation

Most rehabilitation devices for the upper extremities include a weight-support system. In recent publications, weight support is shown to be effective for stroke rehabilitation. But current devices are often complex, have significant movement inertia, and/or limit the movement range. The goal of this study is to improve on current designs by introducing a novel, dedicated weight-support device, the Freebal. This passive mechanical device uses balanced spring mechanisms for constant-but-scalable forces to support the arm. It has a large workspace of roughly 1 m3, low movement impedance, and independent support at the elbow and wrist of up to 5 kg. An explorative cross-sectional study with eight patients shows the Freebal to instantly extend the range of motion of the affected arm by 7%. In conclusion, most requirements are met for patients to benefit from therapy with the Freebal, potentially progressing earlier to more motivating, functional training.