Abstract: Manipulators with large numbers of degrees of freedom, from the human hand to the trunk of an elephant, are common in the biological world. These freedoms allow highly flexible and robust performance of complex tasks. However, progress in developing and controlling artificial high-degree-of freedom manipulators has been slow. The main problem is that traditional robotics has focussed on the solution of systems of kinematic equations where there is a unique solution. Such approaches tend not to generalize well to situations with a high-dimensional solution space, and controlling redundant systems has acquired a reputation as a hard problem. However, this need not be the case. In this paper, we describe a behavioral method for using extra degrees of freedom to simplify rather than complicate manipulation problems, while at the same time obtaining more flexibility than would be available with a simpler system. The method is developed in the context of a high DOF robot hand, but it has the potential to generalize to other sorts of manipulators.
The basic idea is based on the observation that, for a particular task, using a custom-designed fitting can greatly simplify the control problem. Using a wrench sized for a particular nut is an extreme example. We use the extra degrees of freedom to dynamically configure or ``tailor'' the manipulator to match the particular object and task at hand. This creates a virtual tool. The tailoring is accomplished by imposing low-level, task-specific constraints on the degrees of freedom. These constraints are selected dynamically from a large set of potential constraints in response to the demands of the current task. The process of smoothly transitioning from one virtual tool to another in the course of task execution is referred to as morphing. We apply the technique to the control of a 16-DOF Utah/MIT hand, and perform fine manipulations on a range of objects using virtual tools that are dynamically instantiated on the basis of sensory information.