Dynamic hybrid position/force control of robot manipulators: On-line estimation of unknown constraint

Abstract

For the application of robot manipulators to complex tasks, it is often necessary to control not only the position of a manipulator but also the force exerted by the end effector on an object. For this purpose, Raibert and Craig proposed the hybrid position/force control method. Extending their method, we proposed the dynamic hybrid control method which takes into consideration the manipulator dynamics and the constraints on the end effector specified by the given task. One difficulty in implementing our method is that we usually do not have precise information on the size and position of the object with which the end effector contacts. To cope with this difficulty a problem of dynamic hybrid control with unknown constraint is studied in this paper.

After introducing the dynamic hybrid control approach, we first develop an on-line estimation algorithm which estimates the local shape of the constraint surface from measured data. Then we show by experiments using a SCARA type robot that the combination of this algorithm with the dynamic hybrid control method works fairly well. This approach decreases the burden on the operator of giving precise data on the constraint and makes the dynamic hybrid control approach more practical.