Passive Gravity Compensation for Parallel Mechanism with Both Spatial Translations and Angular Orientations

Passive compensation has been proven to be effective in reducing gravitational joint loads and improving the output capability of mechanisms. Existing methods for passive compensation are not satisfactory in terms of mechanism complexity and implementation convenience, while cases with variable angular orientations are more complicated. This letter presents a feasible design to achieve approximate compensation for multi-DOF parallel mechanisms with both translations and orientations. The counterweights employed to provide vertical forces are connected with the moving platform by 2T1R stands and pantographs as external components. Conventional approaches using springs or counterweights in the chains are also calculated for comparisons. By contrast, the proposed method is easy to be realized and possesses strong robustness to orientations. Finally, an experimental prototype is implemented to verify the performance. The results show that the maximum torques and energy consumption are reduced by 49.44% and 78.08% for the translation mechanism, respectively, and by 35.77% and 43.43% for the rotation mechanism.