Study Of Type Of Slits And Sub-Pixel Subdivision Algorithm Of Multi-slit Photoelectric Autocollimator

Autocollimator is a kind of instrument for high-precision angle measurement, which was based on the principle of optical auto-collimation imaging to measure tiny angle change within a certain range. It has been widely used in measurement of small angles, ultra-precision angular adjustment and calibration, measurement of straightness and parallelism of machine ways, testing of flatness of high-precision plane surfaces, testing of the position uncertainty of rotary tables and so on, and it is an indispensable instrument for detection of production of mechanical/precise instruments in metrological laboratory, and assembly adjustment/testing of optical instrument. Autocollimator includes optical autocollimator and photoelectric autocollimator. The latter is the combination of optical autocollimator and photo-electricity technique. Up to now, high-precision, large-measurement-range, high- accuracy photoelectric autocollimators are only commercialized in Germany, Japan, and UK, etc. New technological breakthrough of similar domestic product was not made for a long time, so relative research is necessary.The main idea of this article was how to improve the resolution and the accuracy of the photoelectric autocollimator system. It was based on overall study of the working principle and the structure type of relative product and patent at home and abroad. Finally multi-slit photoelectric autocollimator was chosen as our research object. Furthermore, study of type of slit and study of algorithm was chosen as our starting point, and then relative theoretical research and experimental verification was done. So far, some progress was made as follows:1. Mathematical description of the whole multi-slit photoelectric autocollimator system was made, and frequency domain analysis was explored to draw a conclusion that the spectrum aliasing noise component of the system was restrained to someextent when 2~N ( N≥1 ) parallel slits with certain spacing interval were used. Aforesaid conclusion was proved by a software model based on MATLAB of a multi-slit photoelectric autocollimator, and then a design scheme of multi-slit was given to improve the accuracy of the system from hardware perspective.2. Using multiple multi-slit digital images relative to multiple angle position Obtained by principle experiments, various CCD sub-pixel subdivision algorithm were explored. And relative improved algorithms were put forward, and then implemented by MATLAB, and their suitability for the multi-slit photoelectric autocollimator system was compared by quantitative results. Especially, such algorithms as micro-displacement algorithm based on gradient operator, a universal algorithm for sub-pixel edge detection, and local Newton interpolation functions and so on were used in the system, and then the conclusion was drew: Among them, micro-displacement algorithm based on gradient operator, gray centroid algorithm and an universal algorithm for sub-pixel edge detection are superior in repeatability and accuracy; data fitting method is superior in dispersion and accuracy; interpolation algorithm is inferior to other algorithms.Aforesaid conclusions was analyzed theoretically and proved by simulation, but the further verification in experiment and real system is necessary.