Multiple whole-limb manipulation: An analysis in the force domain

It is expected that future applications of robotic manipulators will require the skilled use of multiple mechanical systems interacting with the environment in more flexible and powerful manners than those allowed by a single device equipped with a standard end effector. In fact, these multiple systems (e.g. multi-fingered hands, legged robots, cooperating manipulators) can interact with the enviornment not only by a specific part of their bodies, i.e. the gripper, but more generally with any part of their external surfaces. In this paper, the problem of the analysis of the force systems acting in static conditions in such mechanical devices is considered. The goals of the analysis are the following: to understand which sets of farces, belonging to the joint torque space, the contact force space, and the external wrench space, are present or applicable to/by the system, to know in which manner forces in these sets can be obtained, and to extend to this class of manipulators well known definitions of manipulability measures. The solutions to these problems, crucial in problems of grasp optimization and control, are not trivial in case of limited mobility (of some) of the manipulators present in the system, a common situation when multi-arm cooperating systems are considered. A technique is proposed for the solution of these problems, and examples are presented and discussed.