Simple Upper Limb Prosthesis with External Power Support for Cineplastic Control

Abstract

The work presented in the thesis was motivated by the history of cineplasty and aims to create a supportive system for the body powered upper limb prostheses. A mechanical signal (pulling) from a cineplastic site or a harness system (e.g. shoulder harness) is used to control a prosthetic device. These signals are often too weak to comfortably control the prosthesis leading to fatigue and discomfort. The goal of the thesis was to develop a prosthesis supplying supportive force allowing amputees to use smaller input forces to operate the device. A prototype was realized as a cable-controlled voluntary closing device with an external power support for the force amplification. Easily manufacturable designs and cheap commercial products were preferred while designing the prototype. The mass, pinch force, input cable force, input cable excursion and locking mechanism efficiency were measured using different configurations, and then compared to each other and to commercial products.The support system was able to reduce the necessary input force needed to pinch 15N by 60%, and increase the achieved pinch using a 50N input force by 340%. The system performance was highly dependent on the control gains and the input cable speed. Increased controller gains and decreased input velocity had a similar effect resulting in a higher output force while degrading controllability. After a short training session (30 min) using a prosthesis simulator I was able to use a pair of tweezers to pick and place pieces of wire. The system showed very promising results allowing to decrease the needed force for operating the device; however, the force amplification system has an effect on the feedback quality which should be investigated before making any definitive conclusions. The device can serve as a basis to investigate the effects of control methods on assistive body-powered prostheses