Inverse Dynamics in the Joint Space of a Redundantly Actuated Parallel Mechanism Constrained by Two Point-Contact Higher Kinematic Pairs

This paper presents the rigid-body inverse dynamics of a spatial redundantly actuated parallel mechanism (RAPM) constrained by two point-contact higher kinematic pairs (HKPs). Firstly, its constrained motions are analysed comprehensively, Then the dynamic model is built by the decoupled natural orthogonal complement (DeNOC) in the joint space, which is very suitable for the model-based motion control. The influences by HKPs in the model structure, the computational time, and the torque cost are discovered clearly. The NOC matrix is decoupled into three matrices, which is very different from those in PMs without actuation redundancy. The comparisons between the RAPM and its counterpart free of HKPs clearly validate that the constraints at HKPs considerably increase the computational cost, and the torques required by the parasitic motions of the end effector are significantly smaller than those by the corresponding DOFs.