Design of a signal processing algorithm for error-minimized optical triangulation displacement sensors

Abstract

Optical triangulation displacement sensors are widely used for their non-contact measurement characteristic, sub-micrometre order resolution, simple structure and long operation range. However, errors originating from surface inclination, speckle effect, light source fluctuation and detector noise restrict the wider use. In order to minimize these errors, a structure for an optical triangulation displacement sensor, which is composed of an incoherent source and a linear CCD (charge coupled device), has been proposed. However, using a linear CCD causes several problems in signal processing. Because CCDs consist of spatially discrete pixels, it is impossible to detect the peak position movement within a pixel. This is an inherently severe problem of CCDs. Therefore, a new approach is needed. In this paper, we propose an adequate signal processing algorithm to overcome the limited resolution problem of a CCD for the proposed sensor structure. The signal processing algorithm is composed of a pre-processing algorithm and a modified cross correlation algorithm. With the help of the proposed algorithm, the limited resolution problem of the CCD can be solved.