When two or more open chain manipulators cooperate to manipulate the same object— such as in mechanical grippers, walking machines, and cooperating manipulator systems—closed kinematic chain, redundantly actuated mechanisms are formed. Control approaches for this type of system focus on the more computationally intensive inverse plant control laws or on hybrid force-position techniques. Although local control schemes, using only position and rate errors to generate control forces, are widely used for control of open-chain serial-link robotic mechanisms, these simple and effective control laws have not been considered for control in cooperating manipulator applications because of concerns over instability due to the unspecified distribution of control forces among the redundant control actuators. Recent work has shown that the local approach to cooperating system control results in a known force distribution among the control actuators and can be proven globally stable with a reasonable choice of control parameters. In this work, the known distribution of forces in the cooperating systems is used to develop an analytic description of the internally transmitted forces seen by the cooperating systems using the local control scheme. This description of the internal forces is used to modify the trajectory command in such a way as to control the internal forces of the system. The resulting control law is shown in simulation to produce good trajectory tracking as well as desired internal forces.
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