Measurement of parallelism and perpendicularity of large-size workpieces by laser alignment method

A system designed for measuring large-size parallelism and perpendicularity of large-size workpieces by laser alignment was developed. This paper mainly focuses on three questions. First, the building of long distance alignment optical beam based on laser diode, single mode optical fiber and phase plate diffraction technique. Second, the building of datum planes that parallel or perpendicular to each other by using pentagonal prism. Third, a new image processing algorithm called orthogonal projection method. The algorithm converts two-dimension image into two one-dimension images, which can speed up the data processing and restrain noise. The performance of this system was tested and verified in National CIMS Engineering Technology Research Center in China. The experimental results show that the relative measurement accuracy of the alignment system attains micron (μm) (0.3×10^-6L) in 10 meters measurement range.