Research On The Nocontact Measurement System Of Spherical Circular Hole Series

The fast development of spaceflight and aviation technology leads to rigorous precision requirement of the machining position of circular hole on the spherical work-piece. Accordingly, it requires much higher detecting precision on the position of spherical circular hole, and adopting noncontact measuring methods when detecting.The measurement system raised by this paper used some advanced photoelectric and digital image processing technology to measure the relative position of the spherical circular hole series in noncontact method. This measurement system transforms the three-dimensional measurement on the coordinates of spherical circular hole series to planar measurement by the optical imaging technology. By the digital image processing technology, this measurement system software identifies the center of circular hole in the image, which is captured by the measurement system by means of mechanical scanning using linear CCD and raster sensor cooperating with mobile mechanism. The planar measure and calculating results are converted into three-dimensional measure results automatically by the measurement system software.This paper firstly introduces the elements and working principle 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 designing principle and method of software and hardware for the single-chip control system of step motor are secondly introduced in the paper. Thirdly, this paper illustrates how the upper computer to control the single-chip control system and the imagecapturing system in the foreground to accomplish the image capturing process of the spherical circular hole in mechanical method, and aiming at the time and precision requirements of the project, it brings up four kinds of image capturing methods: "Full Area Capture", "Double Segment Capture", "Variant Speed Capture", and "Partial Area Capture". Fourthly, this paper presents some common digital image processing technology, including median filter, binary threshold and extracting of circular hole edge, and besides, expounds three kinds of recognising method for the center of circular hole, i.e. "Circle Chord Center", "Circle Fixed by Three Points", and "Least Square Circularity", according to this measurement system. Finally, based on the geometric model and arithmetic for the coordinates of spherical circular hole series, this paper demonstrates how to convert the planar measuring and calculating results to three-dimensional measuring results, and exhaustive experiment results validate the precision this measurement could achieve.