Abstract
This paper presents the absolute measurement of free form surface based on the use of interferometric technique to obtain the absolute height of surface, which utilizes the interference fringe obtained with an interferometric microscope to locate the points of surface and obtain the height information through a three-dimensional displacement stage. A theoretical model is established for this method based on the response of interference microscope to identify the main influence factors through analysis. A measurement system is developed based on a three-dimensional stage and a Linnik interference microscope. As the key operative part, the stage has two-grade positioning accomplished by a vertical scanning displacement function mechanism with a laser interference measuring system and driven by a servo-motor and a piezo-electronic transducer respectively. Performance tests show the stage meets the requirements for the measurement of large range surface according to the zero-order interference fringe tracing measurement method. Experimental results show that the measurement system has a vertical range of 8mm, vertical resolution of 0.002μm, and a repeatability error of less than 5%.
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