Design And Research Of A New Ball Screw Shaft Measurement System

Ball screw shaft is a ideal product to turn angle displacement to line displacement, or line displacement to angle. It can implement both driving and locating at the same time. Besides driving and locating, it can be a measuring piece. Because of the use of ball as the media, it reduces the function of friction significantly, and improves the efficiency. Ball screw shaft has the virtue of high efficiency and precision, micro-diving,long life-span etc, therefore it becomes the most popular driving piece in tool-machine and precision-machine.In modern NC machine tool, ball screw shaft plays a very important role. As the driving and locating piece of the mobile system in NC machine tool, the pricison of ball screw shaft always affects the precision of machine tool. Because of the limit of manufacturing process and method, it is very difficult to improve the precision of the ball screw shaft. The measurement of ball screw shaft with high precision is the important approach to optimize the parameter of manufacture and improve the precision of NC machine tool. In China, static measurement has been widely used for a long time,which is low efficient and can bring man-made error. Recently, the dynamic measurement system used in China usually adopts the double frequency interferometers as length benchmark and round raster as angle benchmark. The defect of the system is that, it can measure only one generatrix of the ball screw shaft. It can't synthetically analyse the multiple generatrixes of ball screw shaft. In this paper we will use a new method to measure the pitch error of ball screw shaft.1. The raster displacement sensor serves as measuring tool of the displacement in axial direction. The inductance sensor serves as measuring tool of the displacement in radial direction. Locate the position of the point on dental pattern curve.2. Erect a virtual two-dimensional coordinate system, define the location of the point which is measured on the dental pattern curve in the coordinate system, and fitting the equation of the curve.3. Through the control of the stepping motor, implement fixed distance driving,and measure the points in fixed interval.4. Through the processing of the equation of the screw dental pattern curve, get the length of single pitch or accumulative pitches of ball screw shaft.This paper gives the mechanical construction of the measuring system, the acquisition of the measuring data, and the design of the software and the arithmetic method of the measurement. It implement the pitch measurement on multiple generatrixes of ball screw shaft.