Design and Fabrication of Multi-Pole Magnetic Components for High Precision Position System Application
|關鍵字:||磁性編碼器;印刷電路板;磁極距;充磁;Magnetic encoder;PCB (Printed circuit board);Magnetic pole pitch;Magnetization|
Micro-, submicro- and nano-related industries have been growing rapidly in recent years. The technologies of precise measurements thus become increasingly more demanding. Since encoders are the key component in precise control systems, developing a high-resolution and small-sized encoder is essential to enable the systems more competitive in performance and price. Encoders can be classified into optical and magnetic types. The optical type uses the light reflection or transmission as the detection signals. The magnetic type utilizes magnetic south and north poles as the sensing sources. A magnetic encoder comprises a magnetic sensor and a multi-pole magnetic component with a fine magnetic pole pitch. A smaller magnetic pole pitch yields a higher resolution in applications. Using traditional methods, a multi-pole magnetic component magnetized with a fine magnetic pole pitch of less than 1mm is very difficult to achieve. Moreover, it requires a precise mechanical processing and a complicated magnetization system. In order to overcome the limitation of 1mm in fabricating the magnetic pole pitch, an innovative method by using the printed circuit board (PCB) technology was employed. A special wire circuit pattern was designed and fabricated on the PCB with a periodic structure. According to Ampere’s Law, an alternate and regular magnetic field distribution is induced after applying a current to the wire circuit. Thus, a multi-pole magnetic component with a fine magnetic pole pitch is obtained. Additionally, a precise magnetic field measuring system was designed and set up to measure the field distribution in the fine magnetic pole pitch. A high-sensitivity Hall-effect probe with a fine sensing area of 165□165□m2 was used and therefore it is capable of determining the field distribution with a fine magnetic pole pitch of less than 1mm. Various multi-pole magnetic components with different magnetic pole pitches of 300□m, 350□m and 400□m were accomplished. The field distributions were measured at the detection spacing of 200□m and 300□m above the surface of the wire circuit. The explicit boundaries between magnetic poles are found, indicating the fine magnetic pole pitches are 300□m, 350□m and 400□m, respectively. Correspondingly, the resolution of magnetic encoders can be markedly improved by a factor of 3.33 (1mm/300□m). Moreover, the field formulae for computing the field distribution in the fine magnetic pole pitch have been also derived. These field solutions are expressed in terms of finite sums of elementary functions and easily implemented in any programming environments. As a comparison, the calculated values of magnetic flux density in the z direction agree with the measurement data. A dual-layered wire circuit structure was used to improve the field strength. After measurements, a gain factor of 1.37 was obtained in the field enhancement. Furthermore, various wire widths of 190□m and 235□m were used to investigate the field optimization and the corresponding optimal magnetic pole pitches are 465□m and 495□m. Such an optimal design has larger strength and steeper variation in the field distribution. Both of them are useful to the signal detection and processing. PCB manufacturing technology has been demonstrated to effectively fabricate a multi-pole magnetic component with a fine magnetic pole pitch to be less than 1mm. This innovative method provides a simple process without using the complicated technologies such as machining technique, magnetizing head and magnetization machine. Additionally, it is also a cost-effective method to enable mass production easily. Different pole numbers and pitch sizes can be also easily fabricated on the PCB through this flexible approach.
|Appears in Collections:||Thesis|
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