Operational space modeling and control are important techniques for robot manipulation. A key element of operational space control is the operational space inertia matrix (OSIM). The OSIM matrix represents a mapping between end-effector spatial forces and spatial accelerations and is configuration-dependent. In the case of multiple end-effectors, the OSIM also encapsulates the dynamics cross coupling between the endeffectors. The rich structure of the OSIM for tree systems has been exploited by researchers for analysis and the development of low-order computational algorithms. Extending such techniques to the OSIM for closed-chain robotic systems is the focus of this short paper. We derive explicit analytical expressions for the closed-chain OSIM that reveals its close relationship to an extended tree-system OSIM.
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