Defects Inspection Of Steel Ball Based On Optical Fiber Sensing Technique

Surface quality of bearing ball is one of important factors to improve service performance,which plays a decisive role in the accuracy, campaign performance and the service life of the bearings. Defects of steel balls after processing can be classified as craze, spot, pitting, scratch, scoring and dent, which are a general taxonomy. It is difficult to detect bearing ball surface defects with high precision and low cost by conventional methods. In domestic factories for bearing or steel ball, the manual visual method is mostly adopted to inspect surface quality of steel ball, false inspecting rate of which is usually high because of many labile factors such as worker's technical ability, emotion, tiredness, etc. That is to say, one important reason of backward development of bearing industry lies in the lagging inspection technique. The automatic and low cost inspection instrument is urgently required.In this paper one new classification method based on optical fiber sensing technology was put forward from the longitudinal section angle to inspection of steel ball surface defects. The work is supported by Shandong Scientific Research Foundation for Excellent Young Scientists (BS2010ZZ001), Shandong Department of Education Foundation (J10LD22), Doctor Foundation of University of Jinan (XBS0854) and a project of enterprise entrustment.In order to quantify and identify defects automatically, we divide the defects into three categories in accordance with surface imperfection parameters such as surface imperfection depth, surface imperfection height, and surface imperfection reflectivity,so that: the problem for detecting defects is changed into detecting the displacement information and the change of reflected or scattered light, which reflects the change of reflectivityof defects.Inspection mechanism of fiber sensors with single transmitter and single receiver as well as single transmitter and multiple receivers were analyzed based on uniform distribution model and semi-Gaussian distribution model, the mathematical models of the two fiber sensors were established and numerical simulations were realized with Matlab software. Influence of optical fiber parameters on light intensity modulation characteristic regulation was studied,through which the optical fiber sensor parameters(core / cladding diameter, numerical aperture, etc.) for steel ball surface defect detection were established. Beckmann scattering theory and the assumption of Suganuma Shimamoto double-beam compensation were analysised to extract defect parameters .Light intensity modulation characteristic experiments were done with specimens of different reflectivity and processing methods. The results show optical fiber sensing technique is an effective method to separate different surface of steel ball with extracting of two parameters displacement and surface reflectivity.Trajectory path mechanism of steel ball in deployment system was established, the simulations of which were realized with Simulink.the principle and form of unfolded-wheel were analyzed,with which the steel ball was unfold completely,and also a simple deployment system was designed for experiment.Based on modulation and lock-based amplification technology, the signal processing systems was analyzed and designed, including laser excitation driver circuit, narrow-band filter circuit, phase sensitive detection circuit, division operation circuit,A/D conversion and the signal acquisition and processing, through the lock phase amplification technique, the signal to noise ratio was greatly improved, and also signal acquisition and data analysis and display was realized.The system for steel ball defects inspection based on optical fiber sensing technique were constructed, the experimental results shows that: when the steel ball was inspected using imperfection reflectivity, light intensity is not sensitive to the vibration of deployment system, the case that the good steel ball was identified as steel ball with defects did not happen. However, the miss-detect situation appeared. when the steel ball was inspected using surface imperfection depth and surface imperfection height, light intensity is sensitive to the vibration of deployment system, some surface defects signal are too weak to be distinguished from the background noise. If the deployment system is precise enough, the steel ball can be identified very well.Through analysis and design, the surface defect detection system based on optical fiber sensing technology was set up ,which lay the theoretical basis for automatic checking and sorting machine of steel ball.