Control of rolling contacts in multi-arm manipulation

When multiple arms are used to manipulate a large object, it is beneficial and sometimes necessary to maintain and control contacts between the object and the effector (the contacting surface of an arm) through force closure. Rolling and/or sliding can occur at these contacts, and the system is, in general, characterized by holonomic as well as nonholonomic (including unilateral) constraints. In this paper, the control of planar rolling contacts is investigated. Multi-arm manipulation systems are typically redundant. In the authors' approach, a minimal set of inputs is employed to control the trajectory of the system while the surplus inputs control the contact conditions. The trajectory includes the gross motion of the object as well as the rolling motion at each contact. A nonlinear feedback scheme for simultaneous control of motion as well as contact conditions is presented. A new algorithm which adapts a two-effector grasp with rolling contacts to external loads and the trajectory is developed. Simulations and experimental results are used to illustrate the salient features in control and planning.>