In the present paper, we take the complaint double parallel guiding mechanism as a particular case study to investigate a modified pseudo-rigid-body (MPRB) modeling approach for beam flexure based mechanisms by considering the nonlinear effects of the center-shift and the load-stiffening. In particular, through incorporating the elastic stretch of the beam flexure into the linear Bernoulli-Euler equation, a more accurate model of the beam flexure is derived. Accordingly an MPRB model for a beam flexure is established, which consists of two rigid links joined at a revolute joint and a torsional spring along the beam. Different from traditional PRB model, the location of the torsion spring is not only determined by the characteristic radius factor, but also a purely elastic stretch under the action of the axial force. Meanwhile, both the characteristic radius factor and the equivalent stiffness of the beam flexure are no longer constan-t values, but affected by the applied general tip load, especially the axial force. Based on the analysis results of a beam flexure, we obtain a more accurate model of the double parallel guiding mechanisms, which is further verified by the finite element analysis (FEA) results. The proposed MPRB model provides a more parametric method to predict the performance characteristics such as deformation capability, stiffness variation, as well as error motions of the beam flexure based complaint mechanisms, and offers a new look into the design and optimization of beam-based compliant mechanisms.
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