A comparison of the grip force distribution in natural hands and in prosthetic hands.
The aim of this study is to analyse the grip force distribution for different prosthetic hand designs and the human hand fulfilling a functional task. A cylindrical object is held with a power grasp and the contact forces are measured at 20 defined positions. The distributions of contact forces in standard electric prostheses, in a experimental prosthesis with an adaptive grasp, and in human hands as a reference are analysed and compared. Additionally, the joint torques are calculated and compared. Contact forces of up to 24.7 N are applied by the middle and distal phalanges of the index finger, middle finger, and thumb of standard prosthetic hands, whereas forces of up to 3.8 N are measured for human hands. The maximum contact forces measured in a prosthetic hand with an adaptive grasp are 4.7 N. The joint torques of human hands and the adaptive prosthesis are comparable. The analysis of grip force distribution is proposed as an additional parameter to rate the performance of different prosthetic hand designs.