| The evolution of autocollimator experienced visual type stage, photoelectric null-indication type stage and digital display type stage. The technological advance of photoelectric null-indication type stage was the usage of analog photoelectric line-to-line type, which means the way reading is still visual and manual. There was no qualitative leap in the stage and it is only a transitional stage. The digital display type autocollimator is used as a universal measuring instrument. The direction of evolution is to improve the resolution and the indicating stability. High stability guarantees high resolution, which ensures high accuracy. The autocollimator technology trend is to expand the scope of application to meet the special needs of various industries, such as measuring from the static to dynamic measurement, and from common measuring instruments to the special equipment. Based on an autocollimator situation at home and abroad and development trend analysis, the subject of the thesis is meaning to study the resolution and indicating stability of autocollimator, analyze relevant issues, explore measures and experiment.A unique approach is adopted to improve the resolution: an optical zoom path is added on the optical path of autocollimator, which substantially increased the equivalent focal length. The optical zoom path is added on digital type autocollimator at home and abroad for the first time. The difficulty is: the shift of autocollimating image is enlarged, while the aberrations of the collimating lens and the rising space affected are also enlarged. So the collimating lenses with relatively small aperture are used. The "distortion" as a major aberration is reduced, and various measures are taken to reduce the rising space.The indicating stability of the digital display type autocollimator includes the transient indicating stability (the rising space) and the short-term indicating stability (the drift). The transient indicating stability can be divided into the native rising space (internal) and the rising space caused by airflow (external). External causes are common but difficult to handle. The mechanism of the rising space is that the refractive index of air changes with the change of temperature, pressure and humidity. So the refractive index is variable for the air flow. The rising space is produced by the changes of reflection angle which affects the autocollimator, according to law of refraction. Using isolating shield is simple, effective, common method, but the equipment in the shield requires automatic or remote controlling. Otherwise the effect of reducing the rising space for the air flow will be affected. So "differential mirror" method is proposed to cover the situation where the shield can not be used. If a fixed mirror and a movable mirror are installed in accordance with the same axis and the same reflecting area, the effect of the air flow is similar. Then the rising space for the air flow can be reduced by subtracting.Differential sine bar small angle laser measurement instrument as standard equipment is used to comprehensively calibrate the autocollimator. A piecewise linear compensation is used to compensate indicating error, which improves the accuracy of the autocollimator effectively.A high resolution digital display type autocollimator is developed based on the study of resolution and indicating stability. The minimum display value is 0.001", resolution <0.005", the indicating error in measuring range of±10" is±0.01". The autocollimator reaches the current world's most high-end level like HR-type autocollimator made by M?LLER Company in German; except the total measurement range is smaller.
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