DONG Wei-xin，YAO Yao
（Qinchuan Machinery Development Co.，Ltd.，Baoji 721009，China）
Abstract：In order to solve the problem of the poor positioning accuracy of rotary axis affected by the installation error of circulargrating-the key measuring element of fully-closed-loop NC rotary axis，based on the operating principle of angle measurement withcircular grating，the influence law of moire fringe affected by the run-out of positioning end face of grating during the installation wasanalyzed thoroughly，a cooresponding mathematic relationship was deduced and a mathematical model between rotary axis positioningerror and run-out error of positioning end face of grating was established as well. Numerical simulation shows that once theinstallationerror of positioning end face of circular grating occurs，the output light intensity varation of moire fringe goes through a cycle，whichapproximats a sine curve. Adjusting the former run-out error value of end face of circular grating from 70 μm to 16 μm，the positioningerror of rotary axis was measured with high precision single frequency laser interferometer，the error curves of measuring results were bothsine curves and the positioning accuracy was incresed 3 times over before. So correctness of the theoretical analysis was verified. At thesame time，the experimental results indicate that reducing the axial run-out error of positioning end face of circular grating can improvethe positioning accuracy of rotary axis effectively.
Key words：positioning accuracy；circle grating；end face run-out；error analysis