Analysis on the Impact of the Error Mapping for Structural Parameters of Parallel Machine Tool

Abstract

In order to improve the 6-DOF parallel machine tool motion accuracy and reduce error, the impact of the error mapping for Structural Parameters of Parallel Machine Tool is analyzed. The fixing platform and the moving platform of 6-DOF PMT are linked by six variable-length rod with the kinematic pair (hooke hinge or hooke hinge). By changing the length of the drive rod, causing moving platform position and attitude change, a variety of motion can be simulated and emulated. If the cut tool is installed on the moving platform, the various surface parts can be machined, shown in Figure 1. The above figure shown, in order to obtain the moving platform trajectory, we need measure hooke hinge space position of the fixing platform and the moving platform[1]. There are 6 hooke hinges on the fixing platform and there are 3 parameters (x, y, z) on every hooke hinge. There are 6 hooke hinges on the moving platform and there are 3 parameters (x, y, z) on every hooke hinge. So a total of 12 hooke hinges positions (36 parameters) need be measured. Due to the actual processing, assembly and measurement error, the actual measured values and theoretical values for 36 parameters can not be a complete match and lead to the moving platform errors. This paper will study the 36 parameters on the impact of mapping errors. Firstly, the error mapping formula between drive rod and the moving platform for PMT is established, secondly the performance evaluation index of the error mapping is deducted, and then the relationship between 36 parameters and the error mapping index is established. At last, to the different types of PMT structures and structural parameters, the ideal structural parameters with the aid of the performance evaluation index are optimized.