Preliminary Design and Development of a Selectable Stiffness Joint for Elbow Orthosis

The rehabilitation of a patient with a brachial plexus injury comprises of motor activities aimed at preventing muscular atrophy and fibrosis. Patients are frequently prescribed passive orthoses for shoulder and forearm support and muscle exercises using elastic bands as part of their functional treatment. Despite the clear need for assistive technology to help patients with upper extremity disability, research and development for upper extremity assistive technologies is not particularly prospering. In this scenario, developing an elbow orthosis that is compact, lightweight, and combines different functionalities customizable to the patient needs can maximizing the rehabilitation process. Here we show a new wearable passive elbow orthosis for the upper limb that has been designed to allow the output impedance of the joint to be modulated between three discrete modes depending on the user needs and motor task performed: free swing mode (1), allowing for the free flexion/extension of the elbow. Compliant mode (2), the elbow provides an elastic torque (customizable) opposed to the flexion/extension movements. Finally, the stiff mode (3) enables the patient to lock-hold the arm in a specific position. The alpha prototype has been developed, integrated and kinematic verified according to the technical specifications.