Nonlinear Design, Analysis and Tests of a Compact Compliant Linear Guide with Internal Connection

Abstract The standard symmetric double parallel compliant mechanism (SDPCM) is commonly used in high-precision applications, as it provides large-range linear motion in the primary degree of freedom (DoF) with linear stiffness. However, the mechanism's topology causes a significant reduction in lateral bearing stiffness as the DoF displacement increases. This research proposes modified SDPCM designs with vertical footprints and augmented internal link connections that enhance stiffness in the bearing directions, or degree of constraint (DoC), while maintaining linear stiffness in the DoF and preserving the compact form of the structure. The nonlinear spatial beam constraint model (SBCM) is employed for design analysis, allowing accurate prediction of stiffness and parasitic motions, in comparison with nonlinear finite element analysis with linear material models. Experimental results for the new design confirm the improved stiffness, while also revealing the mechanism's sensitivity to assembly errors, which leads to lower stiffness in the DoC directions and larger parasitic motions than the theoretical predictions. In addition, the experimental results confirm the benefit of the vertical footprint design. The mean value of the in-plane and out-of-plane torsional stiffness over the target motion range is increased by 23% and 60%, respectively, compared with the SDPCM. The benefit of the internal link connection is also clearly demonstrated, as it resists the reduction of lateral bearing stiffness over the target motion range. This improvement is clearly observed at the maximum displacement, where an increase of 360% in lateral bearing stiffness is observed compared with the SDPCM.