Development of the mechanical framework for a minimal anthropomorphic prosthetic hand

Abstract

Upper limb amputation may severely affect the quality of life of amputees, as it hinders their ability to perform daily activities, especially bimanual activities. For this reason, numerous prosthetic solutions have been developed throughout the years. Unfortunately, amputees sometimes reject such devices, with the most common reason being dissatisfaction with various aspects of their design, such as appearance, function, and ease of control. However, designing an anthropomorphic prosthetic hand that replicates the human hand in its control, form and mechanical behaviour is exceedingly difficult, due to weight and size constraints. Hence, prosthetic hands either lack dexterous capabilities or make use of complex structures and subcomponents, resulting in bulky and heavy designs that are less usable. This incongruence regarding simplicity, dexterity and usability is one of the key issues in the development of commercial prosthetic hands. Thus, the aim of this work is to carry out a systematic exercise to seek a practical solution that optimizes the trade-off involving these three attributes. Previous research found in the literature has shown that despite the complexity of the human hand, the variance in the patterns of human hand configuration and movements can be described by a few parameters, giving rise to postural synergies (that is, common patterns of hand configurations). It implies that effective coupling of joints can simplify the control of the prosthetic hand as well as its design, while maintaining high dexterity. This work exploits this concept through an innovative approach to develop a non-dominant, minimal anthropomorphic prosthetic hand (that is, three active digits: the thumb, the index, and the middle finger), for additional support during bimanual activities. The postural synergies of the minimal anthropomorphic hand when carrying out bimanual activities were determined through a principal component analysis of new experimental data. These synergies were then exploited by means of extensive analytical and simulation work to develop a simple kinematic hand structure that exhibits an acceptable and optimum dexterity while maintaining high usability of the device. The effectiveness of the approach was then evaluated by developing and constructing a prototype of a prosthetic hand based on the resulting kinematic architecture. The final prototype, despite its simplicity, was able to execute various daily activities using only four fundamental motions that are highly usable and intuitive to the amputee.