KINEMATIC STABILITY ISSUES IN FORCE CONTROL OF MANIPULATORS.

In active force or compliance implementations for multilink manipulators, there is typicially a kinematic coordinate transformation in the feedback path. A coordinate transformation will affect the dynamics of the closed-loop system and possibly make it unstable. It is shown that the hybrid force/position control method of M. H. Raibert and J. J. Craig (1981) exhibits such kinematically induced instabilities for revolute manipulators, whereas other force control methods, such as the stiffness control and the operational space methods, do not. Both theoretical analyses and experimental results on the MIT Serial Link Direct Drive Arm are given.