The Power of Pneumatics: Design of a Novel Elbow Prosthesis

Introduction: Almost 57 percent of above elbow amputees stop using their prosthesis. One of the main factors of non-wear is the high weight. Pneumatic actuation can be more lightweight than electronic actuation, and might therefore help with reducing the mass of a prosthesis and increase its comfort. To illustrate this potential, the goal of this thesis was: "To show the potential of pneumatic prostheses by designing a lightweight pneumatic elbow prosthesis, with a functionality equivalent to existing prostheses". Methods: The design process was divided into five phases: Analysis, Conceptualization, Embodiment, Manufacturing and Assembly, and Testing. The analysis brought to light the functions, requirements, wishes, and design values. The two design phases, conceptualization and embodiment, translated these into a potentially viable prosthesis. Afterwards, a prototype was manufactured, assembled, and tested to see if the functions, wishes, and requirements were met. Results: The prototype weighs almost 1300 [g]. A payload of 4.0 [kg] can be lifted to 87 [°]. In theory, 2.5 [kg] can be lifted throughout the entire range of motion, up to 140 [°]. The maximum pronation/supination torque is over 2.8 [Nm] throughout the entire range of motion of ± 90 [°]. The locking mechanism is theoretically capable of passively holding over 6 [kg] in any position. In theory, an average of 125 cycles can be achieved per 25 [g] CO2 cartridge. Discussion: The prototype does not have an integrated fuel source. The weight of the prototype exceeds the maximum by almost 280 [g]. Switching to electronic control significantly decreases the prosthesis mass. The frame of the prototype was under-constrained, leading to an increased friction for higher angles of flexion. Conclusion: The combination of the high functionality and low mass of the prototype shows potential for pneumatic actuation for prostheses.