Design of an ultra-compact elbow-joint for an eating assistive device: Meeting the growing demands of people with Duchenne Muscular Dystrophin

Ultra-compact is a valuable property in designs of assistive devices for people with Duchenne Muscle Dystrophy. Reducing the size of these medical devices will increase the cosmetic appearance. Current devices are large and stigmatizing in the eyes of the users. In other words, the users want a device to be small enough to be worn underneath the clothes, so it becomes unnoticeable. Additionally, they want the device to adjust the amount of assistance to the progression of their disease. The goals of this study are (1) to design an elbow joint for an unnoticeable eating assistive device meeting the growing demands of the users and (2) to evaluate this design based on performance indicators. In order to reach these goals, two evolving fields of study are brought together that have great potential to reduce the size of exoskeletons: smart materials and compliant rotational joints. This study presents the design of an ultra-compact actuated rotational joint that can be used in an eating assistive device. An antagonistic actuator is made from shape memory alloy muscle wires. It is able to carry an external load and to actuate to move to different positions. A compliant rotational joint is optimised to balance the weight of the arm. In addition, it is used to auto-align with the elbow joint. The device supports the user passively at an early stage of the disease. The passive support is increased as the disease progresses by increasing the amount of stacked leaf springs. When the muscles have deteriorated too much for full passive support, the antagonistic SMA actuator is added for active support. The device generates a stall torque of 7.22 10^3 Nm/m^3 and produces a work density of $7.70 10^3 J/m^3 based on isolating volumes and the efficiency of the whole system is 3.9 %.BMDBioMechanical EngineeringMechanical, Maritime and Materials Engineerin