Abstract: In consideration of the disadvantages of traditional measuring methods, a new measuring method for motion accuracy of 3-axis numerical control equipments based on composite trajectory including circle and non-circle (straight line, polygonal line) by using cross grid encoder is proposed. The principles and techniques of the new measuring method are discussed in detail. 8 feasible measuring strategies based on different measuring sequences are summarized. The optimized strategy is carried out in the 3-axis CNC vertical machining center Cincinnati 750 arrow by using cross grid encoder. The whole measuring time of 21 error components of the new method is cut down to 1-2 h because of easy installation, adjustment, operation and the characteristics of non-contact measurement. Result shows that the new method is suitable for on machine measurement and has good prospects of wide application.

Key words: Composite trajectory, Geometric motion error, Numerical control machine tool, Precision measurement