Performance evaluation of twisted strings driven robotic finger

Actuation and control of robotic hands is one of the problems in engineering that still needs to be satisfactorily solved. In this paper we present a robotic finger actuated by twisted strings mechanism that we call Twist Drive. A principle of the proposed actuation is described and its basic characteristics are presented. The structure of a developed robotic finger with the proposed actuation method is explained. Forward kinematics of a finger with non-linearly coupled joints was solved and the obtained Jacobian was used for two directional force control on the finger´s tip. Experimental results of the force control and measured frequency characteristics of the force control are presented in the paper. The results show that the developed robotic finger has capabilities similar to that of a human finger. Additionally, because there is no gear reducer used in the transmission, the finger is of lightweight, low-cost, and provides zero mechanical impedance when the strings are untwisted.