Research Of High-accuracy Diameter Measurement System Based On Projection Method

In modern industrial manufacture and scientific research, small parts with high precision are widely used to meet with the needs in mechanical design. At the same time, automatic manufacturing systems of high intelligence are used more frequently as the production industry is developing fast. High accuracy measurement is greatly improved by the appearance of visual inspection technology. A synthetic system based on this has brought non-contact automatic measurement into use and makes much progress improving accuracy and efficiency. It is of great value in the practical field. The high accuracy diameter measurement system discussed in this paper belongs to the field of visual measurement.This paper discussed a high-accuracy measurement system based on double telecentric projection light path. After analyzing the theory of projection optical system, using super-resolution reconstruction thought and aiming at diameter measurements with relatively simple imaging surroundings and sufficient priori knowledge, a high accuracy of diameter measurement is reached. The research focuses mainly on the following parts:1.Analyze the optical imaging edge model based on Gaussian function which is commonly used in most projection measuring methods. Use the mathematical model with hyperbolic tangent function who has numerical solutions as a replacement, thus solves the shortcoming of non-integrable property. Test the validity of this model.2. A numerical search method named as Nelder-Mead simplex method is selected to realize fast and precise fitting of the hyperbolic tangent function model.3.Design and build up the double telecentric diameter measurement system which shows a fine result.The experimental system contains a common industrial 5 megapixel CMOS. Using the edge model and algorithm discussed in this paper, the system can reach a resolution of about 1.3um(0.05 pixel), accuracy of about 4um(0.2pixel) in the measurement range of 44mm. It also allows off-focusing of the object plane within ±9mm range and keeps the measuring accuracy. The measurement system discussed in this paper is more useful in real-time circumstance where object planes may be off-focused and vibrated.