An actuation configuration of inter-module coordination and the evaluation for the mechanical implementation to a prosthetic hand

It is known that the muscles actuate human hand joints with a coordinated manner and the hand postures can be reconstructed by a few (usually two) inputs through postural synergies, which has been applied in robotic hand design for reproducing the human versatile grasp function. As for the mechanical implementation, in terms of the joints implemented postural synergies, due to the excessive number of the output and the high contribution ratio of two inputs to one output, the mechanical implementation size is usually too bulky. In this paper, to make the implemented mechanism size smaller and possible to be integrated in the palm, we divided the joints of four fingers into five modules according to the statistical analysis results of each hand joint angle recorded from the human grasp experiment. In order to meet the three needs of prosthetic hand design: versatile grasp function, anthropomorphic physical property and easy-control, three different actuation configurations of postural synergies were evaluated. The actuation configuration of inter-module coordination shows an acceptable reconstruction error, a smaller implementation size and a keeping of the clear corresponding relation between principle components (PCs) and joints.