Design of a 3-DOF PKM module for large structural component machining

This paper presents a novel 3-DOF PKM module named the A3 head that can be employed to form a 5-axis manufacturing cell for large structural component machining. The architecture behind the A3 head is a 3-RPS parallel mechanism. A semi-analytic stiffness model of the A3 head is formulated by taking into account the component compliances associated with actuations and constraints. With the dimensionless treatment of the stiffness model, a global performance index is proposed for minimization subject to a set of appropriate constraints generated as a result of in-depth discussion, leading to only one of four geometric parameters to be determined for achieving a compact, lightweight yet rigid design. Stiffness evaluation of the optimized A3 head is carried out throughout the workspace and comparisons are made with those evaluated by finite element analysis at the reference configuration.