A NEW COMPOSITE TRAJECTORY METHOD FOR MOTION ACCURACY MEASUREMENT OF 3-AXIS MACHINE TOOLS

Geometric motion error measurement has been considered as an important task for accuracy enhancement and quality assurance of NC machine tools and CMMs. In consideration of the disadvantages of traditional measuring methods, such as Laser interferometer and Double Ball Bar method, a new measuring method for motion accuracy of 3-axis NC equipments based on composite trajectory including circle and non-circle(straight line and/or polygonal line) is proposed. The principles and techniques of the new measuring method are discussed in detail. 8 feasible measuring strategies based on different measuring groupings are summarized and optimized. The experiment of the most preferable strategy is carried out on 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.