Gravity compensation mechanisms are widely used in manipulators and exoskeletons as passive components which generate counter-gravity force and save energy. While there have been making great progresses in the design of the planar gravity compensator and its spatial counterpart, a strict condition that the axes of the gravity compensators are aligned with the axes of the links being balanced (LBBs) exactly is usually assumed implicitly. In this paper, the design method of the wearable spatial gravity compensator compatible to the misalignment and drift of the rotation center of the LBB is carefully studied. First, the design of the planar gravity compensation unit (PGCU) is presented, and then it is adapted into the spatial gravity compensation unit (SGCU) by the motion features of the fixed-point rotation. Then, the type synthesis of the SGCU is conducted followed by the analyses of the acting patterns of synthesized SGCUs on the LBBs and gravity compensation performances when the misalignments and drifts of rotation centers of the LBBs occur. Finally, the SGCUs can be combined with timing belt mechanisms (TBMs) to construct gravity compensation mechanisms for spatial serial linkages. Simulations of the exoskeleton constructed by SGCUs are conducted to verify the performance of gravity balance and the effectiveness of the proposed design method.

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