This paper presents an approach that enables the stiffness of parallel kinematic machines considering the rigidity of the machine frame to be estimated using semi-analytical approach. This approach can be implemented by three steps: (1) Decomposition of the system into two substructures associated with the moving components and the machine frame; (2) Formulation of the moving components using the analytical approach and the machine frame using static condensation; and (3) Assembly of all substructures by linear superposition. The stiffness distribution of a 5-DOF hybrid robot is studied as an example to illustrate this approach. The results are compared with those obtained by finite element analysis.
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