Robust hybrid force/position control with experiments on an industrial robot

The aim of this paper is to report the results of an experimental investigation of hybrid force/position control algorithms for a robot manipulator, whose end effector is in contact with a nearly rigid spherical surface. The model of the constrained robot is derived using the classical Lagrangian multiplier approach. An inverse dynamics strategy is adopted to design the hybrid force/position controllers, comprising a proportional-derivative (PD) action on position, and either a proportional (P) action or a proportional-integral (PI) action on force. Then, in order to robustify the system in practical implementation, a parallel force/position control strategy is adopted along the constrained direction. Two typical contact tasks are executed and the various control algorithms are tested on an industrial robot with open control architecture and wrist force sensor.