Jamming-free Impedance Control of UVMS Based on Contact Mechanisms for Peg-in-Hole Tasks

This work addresses the jamming issue for under-water peg-in-hole tasks. Owing to random currents, transient forces acting on the contact points during underwater peg-in-hole tasks may lead to jamming when inserting. To this end, a compliant jamming-free impedance controller is designed based on the contact mechanisms analysis. Firstly, general dynamic model of the underwater vehicle-manipulator system considering hydrodynamics is established, and the contact forces can be formulated intuitively by using the mass-spring-damper model. Secondly, the contact mechanisms of peg-in-hole tasks, when the peg has been inserted into the hole, are analyzed via the standard cylindrical model mainly including one-point and two-point contact states. To avoid jamming, the jamming diagrams of insertions are obtained by calculating the constraints of forces and positions in these two states. Then the adaptive parameters are derived from the jamming diagrams which indicate the deviation between current state and desired jamming-free state. Furthermore, the jamming-free impedance controller is designed considering the adaptive parameters. Finally, numerical simulations show that contact forces and moment are less than 0.5N and 0.4N·m respectively, and jamming can be rapidly mitigated, which demonstrates superiority of the proposed jamming-free impedance control strategy.