Geometric accuracy design and error compensation of a one-translational and three-rotational parallel mechanism with articulated traveling plate

Abstract

The demands for advanced and flexible docking equipment are increasing in the fields of aerospace, shipbuilding and construction machinery. Position and orientation accuracy is one of the most important criteria, which would directly affect the docking quality. Taking a novel one-translational and three-rotational docking equipment, referred to as PaQuad parallel mechanism as example, this article proposed an accuracy improvement strategy by geometric accuracy design and error compensation. Drawing mainly on screw theory, geometric error modeling of PaQuad parallel mechanism was first carried out via four independent routes. Joint perturbations and geometric errors were included in each route error twist. Wrenches due to articulated traveling plate were applied to eliminate joint perturbations. Then, geometric accuracy design was implemented at component and substructure levels. The basic principle was to transfer geometric errors into dimensional or geometric tolerance. High-precision machining/assembling techniques were applied to satisfy the tolerance. Finally, error compensation resorting to kinematic calibration was implemented at mechanism level. It can be summarized as identification modeling, measurement planning, and parameter identification and modification. Maximum deviations of PaQuad parallel mechanism before calibration experiment were 0.01 mm, À0:197 8 , À0:522 8 , and 2:908 8. And they become 0.01 mm, 0:027 8 , 0:046 8 , and 0:521 8 after kinematic calibration. Orientation accuracy of PaQuad parallel mechanism has improved one order of magnitude. It proves the effectiveness of accuracy improvement in terms of geometric accuracy design and error compensation.

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