Constant Torque Mechanism for Gravity Balancing in Wrist Support Application

Abstract

Individuals suffering from neuromuscular conditions, such as Duchenne muscular dystrophy (DMD), experience a progressive weakening of muscles. During the progression, the affected patients require supporting devices like orthoses or exoskeletons to perform their daily activities. Although immense efforts are put into the development of exoskeletons, due to the challenge involved in balancing the weight on the hand, where the torque at the wrist changes with the position of the hand, there are limited wrist support devices available. Existing solutions either rely on rigid body mechanisms or active power sources, which come with drawbacks like bulkiness and discomfort. This research introduces an innovative approach to passively counterbalance hand weight using a simplified torque profile for a single degree of freedom in hand movement, namely flexion and extension. By employing parametric optimization, a compliant mechanism has been developed that can compensate for the weight of the hand against gravity. The resultant compliant mechanism design is compact, lightweight, and safe, rendering it an optimal choice for supporting the wrist’s degrees of freedom and for the application of the device. Through the experimental validation of the model, the results are interpreted as the mechanism’s usefulness in wrist flexion and extension support. In short, this study underscores the utility of employing compliant mechanisms in wrist support orthoses, particularly for individuals with neuromuscular conditions like DMD.