Fingertip stiffness control using polyarticular tendon drive system

This paper proposes a polyarticular tendon drive system to simulate a variable stiffness of a human fingertip. The stiffness determines displacement of the fingertip when an external force is affected to it. The stiffness should be adjusted not only according to measurement precision of object's dimensions in order to allow grasping position errors, but also according to tolerance of the assembly in order to allow position errors of assembly components. The variable stiffness therefore contributes to stable grasping and dexterous manipulation. A stiffness of a human fingertip in all directions increases as a grasping force of the human finger increases. The stiffness even in orthogonal direction to a grasping force increases in the same way. Through numerical simulations, feasible parameter settings of our proposed polyarticular tendon drive system are searched and then it is confirmed that the variable stiffness of a robotic finger driven by the proposed polyarticular tendon system is similar to the one of human finger through some experiments.