Active Control of Contact Force for a Quasi-Translational Flexible-Link Parallel Mechanism

For practical applications of interactive manipulation, active contact control is one of the fundamental functions that flexible-link parallel mechanisms (FLPMs) should be equipped with. In this paper, a force control approach is proposed for FLPMs to make active adjustment toward their payload, which cannot be directly achieved by their intrinsic passive compliance. To begin with, at a starting configuration the Jacobian matrix is accurately calculated with the finite difference method, while at non-starting configurations it is deduced with an increment-based approach. The compliance model is derived through mapping from the joint stiffness within each elastic rod. On this basis, the differential relation among pose, payload, and actuation variables is constructed to form the control logic, whose correctness and feasibility are then verified with simulations. Finally, interaction experiments under fixed environment and cooperative motion are carried out, and the results demonstrate that force control for a quasi-translational FLPM can be accomplished with enough pose accuracy.