Grating Short Period Error Reduction Technique Based On Multiple Reading-heads

The grating measurement system is used as the length or angle reference of the CNC gear measuring center,and its measuring accuracy determines the measurement accuracy of the CNC gear measuring center.The CNC gear measuring center generally uses an open grating.The installation accuracy of the open grating reading-head has a great influence on the grating measurement accuracy.This paper studies the influence law and improvement measures of the grating reading-head mounting accuracy on the grating measurement accuracy(mainly the subdivision accuracy).Firstly,the principle of interferometric scanning and imaging scanning are analyzed quantitatively by single factor method,and the influence of installation deviation in four directions of grating reading-head on the measuring accuracy of grating is analyzed,including A-axis,B-axis,C-axis and Z-axis.Experiments show that the long grating measurement system does have short-cycle error,and the reading-head mounting error has a direct impact on the accuracy of the grating subdivision,and the influence of these four directions is significantly different.Among them,the grating B-axis direction of the interference scanning principle is the most sensitive,and it is most sensitive to the grating C-axis direction of the imaging scanning principle.Then the possibility of short-cycle error of multiple reading-head reduction grating measurement system is analyzed.The subtraction method of double reading-head phase modulation method is proposed.The experiment shows that the method can effectively reduce the short period error of long grating measurement system.Secondly,in order to verify whether the double reading-head phase modulation method can be applied to solve the problem that the circular grating short-cycle error and the installation eccentricity affect its cycle,an experimental test is carried out.Experiments show that the eccentricity of the circular grating installation does not affect the periodicity of the short-cycle error of the grating.Since the two reading-heads phase adjustment method makes the phase difference of the two reading-heads 180° fine-tuned within one pitch,it basically does not affect the eccentricity of the multiple reading-heads.Therefore,the double reading-head phase modulation method can also be applied to solve the short cycle error of the circular grating.Finally,the two different principle grating reading-heads used in this study are designed with readout heads which are individually adjustable in error sensitivity.In addition,a double reading-heads holder that can realize the double reading-heads phase modulation method to reduce the short-cycle error of the grating measuring system is designed.