An elbow passive exoskeleton with controllable assistance: Design and experimental

A passive exoskeleton is a wearable robotic device that is worn on the exterior of the user's body to provide physical support and facilitate movement. Existing elbow passive exoskeletons have limitations in their assistance capabilities and range of applications. In this paper, we propose a controllable elbow passive exoskeleton (CEPE) to address these limitations. The CEPE features a ratchet-based self-energy storage mechanism (RSSM) and a Candan gravity compensation mechanism (CGCM). The CGCM counteracts gravitational forces, while the RSSM stores and releases motion energy. This paper establishes a mathematical model for the RSSM, outlines design specifications for both the RSSM and CEPE, and analyzes the influence of design parameters on the power assistance performance. Three experiments were conducted to validate the feasibility of CEPE, including static strength testing, power assistance without load, and power assistance with load. Results show that, without loading, the CEPE provides compensation effects on elbow joint torque of 68.8%, 93.8%, and 70.7% at shoulder joint angles of 0°, 30°, and 60°, respectively. With a 5 kg loading, adjusting the shoulder joint angle from 30° to 60° results in an increase in the decrease of the average absolute torque directly acting on the elbow joint, from 86% to 91.2%. The adjustable RSSM enables the CEPE to operate in four different modes, expanding its potential applications.