| Steel balls are the key part of a bearing. The quality of the bearing lies greatly on the quality of the steel balls. Now the way of testing the surface flaw is the traditional 'light testing'. Its disadvantages are low efficiency, low reliability. So it cannot ensure the testing quality of the tested steel balls. How to increase the quality and efficiency of the testing technology is an important problem.The development of NDT calls for the greater development of testing technology. The testing instruments have been developed from the traditional instrument to the digitized instrument and the intelligentized instrument. After the virtual instrument (VI) has come forth. The flexible and stronger computer software replace some hardware in the traditional instruments, which have disappeared in some modern instruments.Their function are fulfilled by some computer software. So there are lesser hardware in VI, and more flexible testing system can be constructed easily by VI.The principles of all kinds of non-destructive testing (NDT) are analyzed and their advantages are compared in this paper. The eddy current testing for the surface flaw of the steel balls has many advantages such as high reliability of testing, high efficiency, no touching testing, and so on. And it is more important to realize automatic testing. To test the surface crack by the eddy current testing method is feasible.In this paper, the unfolding method of steel balls has been analyzed, and the figure of unfolding-wheel emluatored by MatLab has been protracted. Then unfolding-wheel machine is designed, Kinematic simulation analysis is carried out by Solidworks/COSMOSMotion.The technology of non-destructive testing, eddy current testing,virtual instrument and signal processing have been combined in this paper, and then the eddy current testing method for testing the surface crack of steel balls has been put forth.The aim of the system is described, and then the system is divided into many modules by its function in this paper. Functions are defined and designed for all of parts. Periphery circuit as an isolation circuit, excitation signal circuit is designed. At last, the eddy current testing system for testing the steel balls surface crack is constructed. It includes signal collection, signal processing and signal display based on virtual instrument.The relation between the signal input and the excitation frequency, lift-off, the length and width of flaw has been drawn from the experiment. So the surface flaw of the steel balls can be measured by amplitude and phase.The signal of testing steel ball is processed by wavelet, and its eigenvalues is acquired. A MatLab processing program is designed, and the LabVIEW called virtual instruments is built.The method is made by combineing the wavelet with neural network in the research. That is, get the eigenvalues of the acquired signals by wavelet, and then the necessary sample to train the neural network is get. After that, use the trained neural network to identify the whole sample, and inspect the neural network by test samples.A method is been proposed to test steel balls, in which the eigenvalues acquired by wavelet analysis are blended by neural network. |
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