A new 3-PUU parallel CMM is proposed in this paper, and according to kinematic model space coordinate of measuring head is solved with the readings of three grating reading heads. Measuring accuracies affected by errors of parallel structure parameters are mainly analyzed and measuring error model is established. The error analysis interface of measuring head coordinate and data processing results are finished by using Matlab, and based on the results of key errors analysis 3-PUU parallel CMM is further optimized by improving accuracy of manufacturing and assembling workpiece, calibration and error compensation of structure parameters.
The spherical joint clearance is a key error factor, which influenced and restricted the application of parallel mechanism in high precision field. This paper discusses the regularity of the spherical joint clearance in the parallel mechanism and its influence on the accuracy of the parallel mechanism in both theoretical and experimental aspects. A spherical joint clearance measuring instrument is introduced and used to measure the joint clearance. And the relationship between the clearance and its work pose is revealed. Based on the theoretical and experimental analysis, it is concluded that the clearance of the spherical joint is near-linear proportional to the applied load as well as the clearances in different poses obey the Rayleigh distribution approximately under the same load.