A Target-Approachable Force-Guided Control with Adaptive Accommodation for Complex Assembly

In this paper, a target approachable force-guided control with adaptive accommodation for the complex assembly is presented. The complex assembly (CA) is defined as a task which deals with complex shaped parts including concavity or whose environment is so complex that unexpected contacts occur frequently during insertion. CA tasks are encountered frequently in the field of the manufacturing automation and various robot applications. To make CA successful, both the bounded wrench condition and the target approachability condition should be satisfied simultaneously during insertion. The bounded wrench condition can be satisfied by properly designing accommodation parameters, which depends on the tolerable stiffness for an assembly task, not to exceed the prescribed contact wrench. On the other hand, the target approachability condition can be satisfied by determining an admissible twist minimizing the deviation between the current and the target twist. By applying the convex optimization technique, an optimum target approaching twist can be determined at each instantaneous contact state as a global minimum solution. Incorporated with an admissible perturbation method, a new CA algorithm using only the sensed resultant wrench and the target twist is developed without motion planning nor contact analysis which requires the geometry of the part and the environment. To verify the feasibility of the new assembly algorithm, a wench sensor model based on a minimum distance algorithm has been developed and used to estimate contact wrenches in graphic assembly simulation. Finally, a VME-bus based real-time control system is built to experiment various CA tasks. T-insertion task as a planar CA and double-peg assembly task as a spatial assembly were successfully executed by implementing the new forceguided control with adaptive accommodation.