球铰刚度计算模型及靠冗余支链实现并联机床刚度的改善

STIFFNESS COMPUTATION MODEL OF SPHERICAL JOINTS AND PKM'S STIFFNESS IMPROVEMENT BY REDUNDANT LEG

以Stewart机构为例提出一种基于解析法和有限元法的刚度分析新方法。应用有限元软件模拟球铰内的非线性接触变形,将计算结果抽象成一个特征参数带入机构的刚度解析模型中,然后得到机构的刚度矩阵,以解决在解析模型中无法处理铰链刚性的问题,并采用有限元软件证实该方法的可靠性。如果在解析模型中忽略球铰变形,则整个机构的刚度解析结果将产生较大误差。在此基础上,应用该方法定量研究采用主动冗余支链对提高并联机床刚性的效果。结果表明,在一定工作空间范围内,主动冗余支链可以显著提高并联机床的刚性。

With the Stewart platform as an example, a new method is proposed to analyze stiffness of parallel kinematic machines（PKM） based on analytical and finite element analysis（FEA） means. In this method, FEA software is used to simulate the nonlinear contact deformation inside spherical joints at first. A feature parameter is extracted from the FEA model and considered in the stiffness matrix of the mechanism. This method solves the problem of inability to treat joint stiffness in the analytical model and its reliability is verified using FEA software. If joint deformation is ignored in the analytical process to compute the mechanism stiffness, the overall stiffness results will produce rather large error. Based on the above analysis, quantitative study on improving stiffness by active redundant leg is carried out with the proposed method. The results show that in certain range of the workspace, active redundant leg can increase stiffness of PKM significantly.