Research On Contact Measurement For Micro-hole Based On Fiber Probe

With the rapid development of contemporary industrial and scientific technology,the manufacturing industry has been developing towards the extremes of ultra-large and miniaturization.Because the micro-hole devices are more and more widely used in the development of miniaturization and the precision of micro-hole processing directly determines the performance of the device,the micro-hole precision detection is widely concerned.The contact micro-hole measurement based on fiber probe is studied in this thesis,which combines the optical non-contact measurement and the mechanical contact measurement,which can realize the measurement of micro-holes with large depth-todiameter ratio.The main contents are as follows:(1)The basic principle of micro-hole measurement based on contact fiber optic probe is studied.The positional relationship between fiber optic probe,micro-hole to be measured and CCD camera is mainly discussed.It is not necessary to adjust the focal length of the camera when measuring micro-holes of different depths due to the fiber optic probe and the CCD camera are relatively stationary,which reduces the difficulty of measurement.Furthermore,a contact micro-hole measurement platform based on fiber optic probe is built.The theory and data processing method of micro-hole measurement based on contact fiber probe are verified by experiments.The relevant parameters and performance of the measurement platform are analyzed.(2)Two-sided telecentric camera is applied to micro-hole measurement.The ideal imaging mathematical model of two-sided telecentric camera based on principal point coordinates is proposed.The type and cause of camera distortion are analyzed.Combined with the improved Tsai two-step calibration method,the internal and external parameters of the telecentric camera are obtained.The experimental results show that calibration error and camera distortion based on the camera imaging model deduced in this thesis are smaller than the generally accepted projection model,which proves the superiority of telecentric camera projection model based on principal point coordinates.(3)The properties of optical fiber probe were improved by the technology of polishing and evaporation.The principle of the point Hough transform circle detection algorithm is derived,The point Hough transform circle detection algorithm is improved and applied to the fiber probe measurement.The Mitutoyo calibration ring gauge with a diameter of 0.997 mm and an accuracy of ±1.5?m was measured.The average diameter of the micro-hole was 0.99819 mm.On this basis,the standard micro-hole and tapered blind holes was detected.According to the test data,the shape of the measured micro-hole is fitted,and finally the factors affecting the accuracy of the micro-hole measurement are analyzed.