A Shoulder Mechanism for Assisting Upper Arm Function with Distally Located Actuators.

Abstract

This paper presents a new design for a shoulder assistive device based on a modified double parallelogram linkage (DPL). The DPL allows for active support of the arm motion in the sagittal plane, while enabling the use of a distally located motor that can be mounted around the user's waist to improve the weight distribution. The development of the DPL provides an unobtrusive mechanism for assisting the movement of the shoulder joint with a wide range of motion. This design contains three degrees-of-freedom (DOFs) and a rigid structure for supporting the arm. The modified DPL uses a cable-driven system to transfer the torque of the motor mounted on the user's back through the links to the arm. The proposed design assists with the flexion/extension of the arm, while allowing the adduction/abduction and internal/external rotations to be unconstrained. A kinematic analysis of the cable system and linkage interaction is presented, and a prototype is fabricated to verify the proposed concept.