·Table of Contents ·Methods and Instrumentation | The Research for the On-Line Metal Detector which Based on Genetic AlgorithmZhao Jiyin, Huang Ting, Gai Shuang, Zhao Jingrong,School of Information Science & Engineering, Jilin University of Technology,Changchun, China 130025 Contact |
Fig 1: the main structure of metal detector |
The samples pass the Fluxgate Magnetometers one by one, which can be regarded as the source of the magnetic field. This will effect circumstance-magnetic field all around. When some small metal objects mix in the samples, the take-over loop will produce remarkable change, we can estimate the result. The Fluxgate Magnetometers phenomenon is a kind of electromagnetism phenomenon [ 1 ] , and the principle obeys Faraday electromagnetism faradic law.
We consider this physical model as the research object. We wire emission loop and take over loop on a magnet core which is made by soft-magnetism material. The area of the cross section is S, the conductance of magnetism is m, the magnetic field intensity constituted by the emission loop is H, and the circle-count of the take-over-loop is W_{2}.
Supposing the parameter S, m , H and are not functions of t (time), we can get the faradic volt in the faradic coil based on the Faraday electromagnetism faradic law.
When parameter S and W_{2} are invariable and the magnet core far from the status of saturation, the parameter mis approximately constant, the faradic volt will only relational with magnetizing field H. If the magnetic field intensity is:
Where H_{m} is the amplitude of the magnetizing field and f_{1} is the frequency of the magnetizing power. The formula (1) will be:
This is the model of ideal transformer.
Because the magnetization-curve of the magnet core is non-linear, the variety of the magnetizing field will bring about the change of the conductance of magnetism (m). In such instance, we can get the real mathematics-model of the transformer as below:
The magnetizing field has two polarity and varies periodically, but the conductance of magnetism(m)only has one polarity and varies one-way. So m(t) is a even function. We can open out m(t) as Fourier-progression:
Where the m_{om} is the constant of m(t), them_{2m}, m_{4m}, m_{6m}is the amplitude of even syntonic wave.
We take the formula (5) into the formula(4), then we can get the formula(6):
This is mathematical model of transformer effect which magnet core conductance (m) changes following the magnetic field. Compare the formula (6) with formula (3), we can know that there will be odd times waves following the change of magnet core conductance(m)
Any transformer will always locate an environmental magnetic-field, so the addition magnetic field of magnet core includes magnetizing field and environmental magnetic field at least. When we think of the parameter H^{//} that the environmental field put on the magnet core axis in fact, the formula (4) will be:
When H^{//} is far smaller than the amplitude of magnet core saturation magnetic field intensity H_{s}and the amplitude of magnetizing coil magnetic field intensity H_{m}, its influence to the magnetic conductance can be ignored. Now the first two parts of formula (7) are equal to that of the formula (4), and the last part or formula (7) is the increment e(H_{0}^{//}) of faradic voltage e that come from H_{0}^{//}. So we can get e(H_{0}^{//}) by take the formula (5) to the formula(7).
Procedure genetic algorithm
Begin
During the t times circulation, every resolution X_{1}^{t }in the resolution group of the retentive resolutions in genetic algorithm X_{1}^{t }, X_{1}^{t},...X_{1}^{t }(the number of the group N is fixed) is "evaluated" through calculating adaptive degree, and on the base of adaptive degree, the individual is selected to recombine and form the new group. In the gene recombination of our system, two operations - "hybridization" and "variation" are important. "Evaluation" shows the performance of the property, and because choosing the individual is based on the principle of superiors win and inferiors lost, the "better" individual will propagate and the "worse" individual will be eliminated. Then, through some evaluations the properties of the whole group will incline to improving, which can make the group incline to the best. In our system, the treat object is the joint weight of ANN whose value can be coded by binary character string figure 2 is the ANN testing and controlling frame of genetic algorithm.
Fig 2: the ANN testing and controlling frame of genetic algorithm |
Our system, which uses genetic algorithm to optimize the initial joint weight of ANN and adjusts it by studying during running, detects and controls the detected metal and disturbances in real-time. The running on-the-spot shows that our system achieves high stable and high sensitive detecting and controlling.
Fig 3: The main structure of the metal detector |
When the sample mixed some metal objects through the metal detector, we can display the equal-value of the metal object through the LED, then inform the worker to dispose.
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