This paper presents a simple yet comprehensive approach to quickly estimating the stiff-ness of a tripod-based parallel kinematic machine. This approach can be implemented in two steps. Inthe first step, the machine structure is decomposed into two substructures associated with the machineframe and parallel mechanism. The stiffness models of these two substructures are formulated bymeans of virtual work principle. This is followed by the second step that enables the stiffness model ofthe machine structure as a whole to be achieved by linear superposition. The 3D representations of themachine stiffness within the usable workspace are depicted and the contributions of different componentrigidities to the machine stiffness are discussed. The result is compared with that obtained through finiteelement analysis.
The kinematic design of a reconfigurable miniature parallel kinematic machine is dealt with. It shows that the reconfigurability may be realized by packaging a tripod-based parallel mechanism with fixed length struts into a compact and rigid frame with which the different configurations can be formed. Utilizing a dual parameter model, the influences of the geometrical parameters on the dexterous performance and the workspace/machine volume ratio are investigated. A novel global performance index for the dimensional synthesis is proposed and optimized, resulting in a set of dimensionless geometrical parameters.
By taking a 3-DOF translational milling machine as an example, this paper investigates the kinematic calibration of PKM systems with fewer than 6-DOF. The error mapping function is formulated in such a way that the geometric errors affecting the compensatable and uncompensatable pose errors can be separated. Based upon the previous investigation, a hierarchical approach to the geometric error identification is proposed. The compensation strategy is developed which is particularly suitable for the PKM systems with translational moving capability. The experiment has been carried out to verify the effectiveness of the proposed approach and the results show that the accuracy can be significantly improved.
