Cooperative manipulation with unilateral constraints

Cooperative manipulation provides multiple robots the capability to perform tasks that are difficult or even impossible to be executed by a single manipulator. Among these tasks are, for instance, carrying heavy or large payloads, conducting multi-part assembly, and handling of flexible objects. If a large object with no special features (e.g. handle) will be manipulated, the object may not be grasped rigidly and relative motion between the manipulators and the object mayoccur. When the robots are initially not in contact with the manipulated object and brought to contact to perform the desired manipulation task, there will be a change in the dynamics of the system due to contact. Furthermore, according to the relative motion between the robots and the object, the contact condition can change from rolling to sliding contact. Besides that when the 3-dimensional case with only rolling contacts is considered, the constraints are nonholonomic. The control objectives in such cooperative tasks is not only to control the position of the object, but also to accomodate the internal forces (or stresses) and external contact forces between the object and the environment.