Force Control Command Synthesis for Constrained Hybrid Dynamic Systems with Friction

A new hybrid dynamic controller synthesis methodology for the successful convergence of force-controlled assembly tasks with friction is presented. Hybrid dynamic modeling has been shown to be a very effective strategy to incorporate both the continuous-time and discrete-event natures of an assembly task. Previously, hybrid dynamic controllers have used velocity control. This paper develops a hybrid dynamic controller that uses force control, the accepted paradigm for constrained motion systems such as assembly tasks. Frictional forces present a significant problem for force control and cannot be neglected in the development of a controller. Constraints on the control command are developed for each type of single-contact transition, and then further constraints are developed to ensure that superposition can be used for multicontact situations. Experimental results are presented for the new controller synthesis method performing an assembly task with a 0.8 mm tolerance and requiring four degrees of freedom for completion. These experiments demonstrate the effectiveness of the combination of hybrid dynamic control and force control for assembly tasks, successfully completing the assembly with positioning errors of up to 50 mm and orientation errors of up to 10 degrees. KEY WORDS—hybrid dynamic system, force control, constrained motion The International Journal of Robotics Research Vol. 20, No. 9, September 2001, pp. 753-764, ©2001 Sage Publications