A straightness error measurement method matched new generation GPS

The axis of the non-diffracting beam produced by an axicon is very stable and can be adopted as the datum line to measure the spatial straightness error in continuous working distance, which may be short, medium or long. Though combining the non-diffracting beam datum-line with LVDT displace detector, a new straightness error measurement method is developed. Because the Non-diffracting beam datum-line amends the straightness error gauged by LVDT, the straightness error is reliable and this method is matchs new generation GPS. 1. Introdution Measurement of the straightness error is one of the traditional, basic, and important dimensional measurement items [1]. The enlarged laser beam of the He-Ne laser is one of the most successful datum-lines for contemporary straightness error measurement’s methods [2-4]. The measuring resolution of this measurement datum-line is usually about 1 ̋ and the maximum of the error is nearly 4.9μm·m. In order to reduce the error of the datum-line, the non-diffracting beam is adopted as a datum-line for measurement of the straightness error. The study of the theory and the realization of the non-diffracting beam began in 1983. Durnin [5] gave the solution with the type of zero-order Bessel function in 1987. Since then, many ways have been developed to produce non-diffracting beams, such as axicons [6], holograms, spatial light modulators, phase gratings, and spherical aberration lenses. Among all these methods, an axicon is the most efficient for producing nearly non-diffracting beams [7]. The axis of the non-diffracting beam produced by an axicon is very stable [8-10] and it can be adopted as the datum line to measure the spatial straightness error in continuous working distance, which may be short, medium or long. Though combining the non-diffracting beam datum-line with LVDT displace detector, a new straightness error measurement method is developed. 2. Principle of the straightness error measuring system The principle of the straightness error measuring system is shown in figure 1. The coordinates are shown in figure 1, the datum-line of the straightness error measurement is along Z-direction and the displacement detector is fixed along the vertical direction, Y-direction. The imaging detector is CCD which is fixed on the same rod as the displacement detector is. The principle of the straightness error measuring system is as follows: Firstly, a Z-direction linear worktable drives the displacement detector and the CCD to the positions along Z-direction and this makes sure that the measuring error gauged by the displacement detector is in its measuring range and the Bessel fringe rings’ image of the Non-diffracting beam can always illuminate CCD. Secondly, set the initial value of the surface of workpiece Yi=0. Z-direction the linear worktable drives the displacement detector and the CCD to the position z= z0. The displacement detector gauges the first value (Y0) of the surface of the workpiece. At the same time, the CCD captures the Bessel fringe rings’ image of Institute of Physics Publishing Journal of Physics: Conference Series 13 (2005) 402–405 doi:10.1088/1742-6596/13/1/092 7th International Symposium on Measurement Technology and Intelligent Instruments 402 © 2005 IOP Publishing Ltd surface of workpiece Displace detector Non-diffrating beam CCD