Reflection spectrum filtering with threshold value of laser confocal range sensor and its error suppressing effect on machined surface profile measurement

Abstract

This paper describes the experimental results on the error inducing factors in the high-precise surface profile measurement by a laser confocal range sensor. One of their factors is tilt angle of a surface at a measuring point. According to the experimental results, the more the tilt angle increases, the more the measurement error increases, regardless of the nominal measuring distance. The possible cause of this factor is the existence of multiple peaks in the reflection spectrum of laser beam. Although the prime peak reflection indicates the just confocal position, it may cross over with the second peak reflection or include some noise reflection in a case. For suppressing the error inducing factor described above, the filtering for the reflection spectrum is presented in this paper. The experimental result clarified the relationship between measurement error and the threshold value of filter and confirmed that the standard deviation of measurement error by the filtering decreases over 30%. Finally the conclusion including the design remarks on the spectrum filtering and further study are mentioned briefly.