The design and test of an anthropomorphic hand prosthesis with multigrasp capability
University of New Brunswick
Commercially available myoelectric hand prosthesis designs remained largely unchanged from their inception in the 1960’s until 2007. They possessed a single motor actuating two non-articulating digits opposing the thumb. Surveys into myoelectric hand use in 2007 highlighted the need for aesthetic, light weight, life-like, functional hands. New multifunction hands have become available with articulating digits and, most recently, with the addition of powered thumb rotation. These new advances come at a cost, with prices as high as $40,000 for the latest hand. The problem of how to improve the functionality, reliability, and appearance of the hand, while at the same time reducing the weight and cost, is the dilemma of modern prosthetic hand designers and was the focus of this research. A prototype hand was designed, built and evaluated for functionality using the Southampton Hand Assessment Procedure (SHAP) functional assessment tool and a Clothespin Relocation task, with the author wearing a prosthetic socket simulator. The hand prototype was capable of achieving seven fundamental grip patterns and carrying out activity of daily living tasks. The design incorporates independently actuated thumb rotation and angle of separation, and a main actuator and whiffletree force balancing mechanism to flex articulating fingers. A set of actuated digit locking pins allow the main drive to act on selected fingers only, to achieve different grip patterns. Using this configuration of mechanisms, it was possible to build a prosthetic hand that provides high functionality. Initial SHAP testing showed encouraging results with the Prototype hand out preforming the other multifunction hands in the coins task. It was comparable in the jar lid, full jar, and empty tin tasks; however, it was slower on the majority of other tests. With optimisation, the concept has the potential to be lighter than current multifunctional hands and could be manufactured relatively cheaply. Issues surrounding cosmetic covering and motor selection need to be resolved to reach the full potential of the design concept.