The Measurement System Of Spherical Circular Hole Series Basing On Machine Vision

In the recent years, the technology of optical-electronic three dimensional profile measurement has been developed very quickly and it has been applied widely in industry, agriculture, biomedicine and many other fields. As a branch of it, the photoelectric measuring technology has its special advantages of non-touch, high precision, high speed, being easy to realize , ect. So it has been put on wider and wider emphasis and has become the best choice in the field of three dimensional measurement.Presently, the domestic three-dimensional measurement mostly make use of the three-dimensional coordinate measuring machine .Because the three-dimensional coordinate measuring machine is a touching measurement system, it's possible to scrape the surface of workpiece, it's price is high and can't measure those holes that those diameter less than detect head. Base on those reasons ,this paper brings forward optical-electronic three dimensional profile measurement.This paper introduces the construction, working principles and process of the measurement system, together with some photoelectric technology used by this system such as CCD, raster sensor and photoelectric rotary encoder. The mostly characteristics are as follows:Firstly, on the basis of spherical characteristic, this measurement system transforms three-dimensional measurement on the coordinate of spherical circular hole series to planar measurement by the optical imaging technology, then translating to three-dimensional measurement after computer processes.Secondly, Using the linear array CCD which is cheap and the CCD camerawhich is low-resolution representation, in addition, working with raster sensor together, making use of the specialty that the step motor drives, and achieving the effect that it is big CCD camera, so, the measurement system obtains high quality and low price.Thirdly, the embedded controller based on the ISA Bus is designed, and has sloved the problem that Windows OS can't control the step montor real time.Fourthly, according to the idea of Object-Oriented Promgraming, the author uses VC++ 6.0 to develop the application software for the human-machine communication interface and background database, to control the step motor and gain the three dimensional data of spherical circular hole.Fifthly, during the course of experiment, using three image capturing methods :"Full Area Capture", "Partial Area Capture", "Double Segment Area Capture", and comparing each other and analyzing. This paper presents some common digital image processing technology, including median filter, auto-binary threshold and extracting of circular hole edge.Sixthly, expatiates two kinds of method for the center of circular hole, i.e. "Circle Chord Center" and "Least Square Circularity Based On Circle Fitting", suiting to the measurement system.The experiment result proves that the method which is used by this measurement system is feasible and validity, which satisfies the requirements of designing.