The Real-time Length Measurement Of Fiber Coil Winding

Fiber coil is a component of interferometric fiber optic gyroscope (FOG), which is madeof multi-turn fiber coil to strength the SAGNAC phase difference by propagating two wavesin opposite direction. The winding length and the average diameter of fiber coil are theimportant factors to influence the performances of FOG. In the process of fiber coil winding,measuring length of fiber coil winding is not only a necessary step of producing FOG, butalso essential requirement of ensuring FOG accuracy. Therefore, the research on the real-timelength measurement technology of fiber coil winding is of important theoretical and practicalsignificance.The non-contact measurement method based on machine vision is applied to measure thelength of fiber in real time according to the physical characteristics of fiber. The measurementsystem is established to measure accurately the length according to the features of backbonefiber coil winding.The related algorithms are applied to measure the length of fiber coil winding in realtime based on the accuracy and speed in the process of measurement, the feasibility andpracticability of the measuring system is verified by experiments.The main research contents and results are shown as follows:1）The visual system was established according to the principle of lens imaging. Thesystem elements was chose by combining the characteristics of the fiber coil winding with therequirement of precisely locating the fiber position of images; then analyzing the systemcomposition and the software and the fixed way of camera.2）The calibration problem was researched and realized in the process of visualmeasurement. Based on the multiple freedom plane calibration method, the Zhang zhengyoucalibration method is improved according to the fiber shape in images; The improvedcalibration method is using a circular array target of more close to the measured fiber shape tocalibrate extrinsic parameters of camera, which is suitable for the optical fiber length measurement. In the process of the calibration, the circular array targets will be placed incoaxial with the fiber coil plane, which can improve the measurement accuracy of the system.3）The corresponding algorithm was proposed to extract feature points aiming at circulararray target template and solve the location problem of the calibration feature points. Thecanny edge detection operator was used to extract the outline of plane target in the circulararray. The least square ellipse fitting method was used to calculate long and short axis of theellipse. The cumulative array method of Hough transform was used to extract the outline ofplane target in the circular array.4）The image clarity evaluation methods were applied on solving image quality problemnot distinguished by the naked eyes in the process of adjusting the focus. The method can beused to determine the focusing position of clear imaging, which can instruct the subsequentimage acquisition. In acquainting fiber imaging, choose the suitable imaging plane to solvethe contraction between increase of the fiber winding lay and the limited the depth of field ofcamera which will cause out-of–focus image of fiber coil winding.5) The traditional moving target detection method was improved according to thecharacteristics of optical fiber winding. The improved method is more suitable to detect theprocess of fiber coil winding. The new fiber position is accurately detected in each imagewhich is suit to calculate the length of fiber subsequently.6) The geometrical optics imaging method was applied to accurately measure the lengthof fiber winding aiming at the characteristics of fiber and inaccurate length measurementproblem for winding defects. The measurement method is verified by measuring the knowndiameter of the fiber coil bearing spindle.The real measurement accuracy of the system achieves±0.076mm.