Flaw Detection Of Motor Ferrite Rotor Based On The Magnetic Resistance Dissimilarity

Ferrite is the most widely used ferromagnetic material, presently. It often exists in the motor rotor as a part of magnetic material. As a result of its crisp and fragile character, Ferrite is easy to be cracked by the external force when it’s producing, badly affect the motor’s performance. The surface flaw defect, which is perceptually invisible, is one of the most typical defect; such kinds of surface flaw defect will be badly affecting the Ferrite workpiece magnetic capacity. In order to satisfy the detect requirement of high efficiency and high precision, a flaw defect detect method based on the magnetic circuit theory has been proposed in this paper, which realized the detection of ferrite workpiece. Concrete workings are shown as followed.Ferrite is a kind of magnetic but insulates material; its defect cannot be detected by means of eddy current theory. This paper puts out the detect method adaptive to Ferrite, which is based on the difference of magnetic capacity between defect and non-defect position: At first, through deduce the relationship of flux’s change Φ and magnetic resistance Rm based on the magnetic circuit theory, the detect model can be got, then,through outside AC current excitation produce magnetic flux, build up the magnet loop between defect and non-defect position, using the magnetic ability getting worse when defect exists(magnetic resistance become higher), detect the different magnetic resistance correspond to different flux produced different induced voltage, which means the change of magnetic resistance can be reflected through detect induced voltage, realize the aim of NDT.Under the thinking mentioned above, by using of the Finite Element Method, the reasonability of detect model proposed above has been proved. Meantime, the 3-D quasi static magnetic field simulate model for Ferrite has been built up, this paper analysis the probe size, lift-off height, stimulation’s frequency and so many parameters’ effect on H-field distribution in the detect system, The electrical and structure parameters have also been given. To the question of minor flaw defection easy to be submerged by the noise, amplify the signal difference between defect and non-defect position, which means judge the defect degree through signal differential; Based on those thinking, this paper gives the probe optimize method, design the diff-probe to detect the Ferrite flaw defection, improve the detect performance.In the dispose of detect signal, to extract the minor flaw detect signal from strongly noisy background, this paper use the Lock-in Amplifier process the induce voltage signal, better depress noise from outside, further improve the detect performance.In the experiment verification stage, this paper builds up a NDT experiment platform. By using of stepping motor and ball screw, realize the Ferrite workpiece rectilinear motion and rotational motion, under cooperation of the differential probe and detect circuit; the magnetic resistance distribution of ferrite surface can be fully scanned. This paper design the constant current source stimulate circuit and Lock-in Amplify detect circuit, each is used as stimulate the motor Ferrite rotor and extract-process the detect signal, compare and analysis the detect result. The result proved that this method can distinguish whether the Ferrite has flaws or not, and the flaws location distribution, qualitatively.