Kinematic stability of hybrid position/force control for robots

The stability of the hybrid position/force control for manipulators is examined using Lyapunov´s direct method for decentralized controllers which are in the form of linear feedback of projected joint errors. This paper aims in clarifying the kinematic instabilities that have been reported to exist for the original hybrid control scheme using the Jacobian inverse for mapping cartesian errors to joint errors, and which have been later remedied in a control scheme using the Jacobian pseudoinverse. Stability conditions demonstrate the importance of the joint error projection matrix and the contact state. Experimental results for a 2-degrees-of-freedom planar manipulator using a PUMA 560 are given both in free space and in contact with a stiff wall