Towards compliant and compact arm supports: Design of a single degree of freedom arm support based on thin McKibben muscles and a compliant shell mechanism

Patients with degenerative neuromuscular diseases experience decreasing muscle function, starting from a very young age. While a wheelchair can partially replace the lost use of the legs, many activities needed in daily life require the use of the arms. For these activities patients rely on the help of caregivers. Several devices designed to support the arms of patients with decreased muscle function exist: some use static balancing techniques to reduce the force required to lift the arm, some use actuators to supplement or replace muscle force and some use a combination of both. Most of these devices are bulky and conspicuous, and can be seen as stigmatizing by the patients for whom they are designed.In this project, the combination of pneumatic artificial muscles and compliant shell mechanisms was explored with the goal of designing compact, close-to-body arm supports that can support the arms of patients with little to no muscle function. The design of a single degree of freedom arm support is presented, which supports the weight of the lower arm using a combination of just two soft pneumatic artificial muscles and a compliant shell mechanism, designed using a shape optimization procedure based on isogeometric analysis. In the motion under consideration, the designed device reduces the torque required of the user’s biceps by 96%.