On Stiffness Control of Tendon-Driven Robotic Mechanismwith Redundant Tendons.

摘要

Tendon-driven mechanisms have been used mainly in articulated-finger hands because of the small size and the light weight. Recently, for the necessity of forcecontrolled robot arms, several researchers developed tendon driven robot arms. In the case, since robot arms are much heavier and longer than robot hand fingers, tendons increase in the length significantly and also must run through very complicated paths. Therefore usual N+1 type or 2N type tendon-driven mechanisms are not enough to move robot arms and a number of redundant tendons are used to divide the total load into each of tendons and reduce the individual burden. For example, due to the gravity force, if the load in the clockwise direction is different significantly from the one in the counter-clockwise direction, we can use different number of tendons for each direction, respectively. There are additional advantages in a redundant tendon mechanism. For example, we can move the robot arm with the other tendons when some tendons have been broken and we can also adjust the mechanical joint impedance using non-linear elasticity of tendons.In this paper, several basic issues on the joint compliance adjustability for a robot arm controlled with redundant tendons are discussed. Namely, local maximum sets of stiffness elements which are adjustable simultaneously, and conditions under which the joint impedance can be adjusted using non-linear compliance tendons are discussed.