A measurement and separation method for perpendicular errors of rotary axes

Measurement and compensation of error components are critically important to improve the precision of a measuring system, however, high precision error measurement and separation of rotary axes in the system are difficult for the moving parts. Interferometry is a widely used method to measure errors of axes but can only measure errors at some special location of rotary axes which is not enough to compensate the errors. As a result, this paper proposed a 3-point method based on confocal sensor and optic flat to measure and separate perpendicularity errors with submicron precision, in which the errors at any position of an axis can be measured. Simulation studies based on multi-body kinematics and homogeneous transformation indicate that the six degree-of-freedom errors only have influence on the display of sensors but have no impact on the separation results of perpendicularity errors. Experimental studies were also undertaken. An optic flat with a peak-to-peak value (PV) of 27nm was used as the reference plane of the rotating axis and three confocal sensors with an accuracy of 85nm is used as the measuring sensors. Experimental results show that the proposed method can achieve an accuracy of 5μrad in measuring perpendicularity errors of rotary axes.