| A new hybrid dynamic controller
synthesis methodology for the successful convergence of force-control-led
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. |
