多極磁性元件之設計與製作在高精密定位系統之應用

Abstract

時序進入微米及次微米的時代，並已投入對奈米尺寸的技術開發，各種量測儀器的精密度不斷地被要求提升以符合所需。由於編碼器是精密量測系統中不可或缺的關鍵元件，因此開發一個小尺寸具有高解析度的編碼器，來增進量測系統的功能為一重要的基本研究。一般而言，編碼器可分為兩類，一為光學式，利用光反射或是透射的特性，造成光線明暗的效果，來作為偵測的訊號；另一為磁性式，藉由磁性南極與北極的差異，來作為檢測的訊號。 磁性編碼器是由一個磁性感測器，以及一個多極磁性元件具有微小磁極距所組成，解析度的高低由磁極距的大小所決定。使用傳統的方法，要製作出磁極距小於1mm是非常困難的，精密的機械加工技術以及昂貴且複雜的充磁系統是必備的條件。為了克服製作微小磁極距小於1mm，來提升磁性編碼器的解析能力，本論文所提出的創新方法，是利用印刷電路板的製程技術，來製作出一特殊的線路圖形於基板上，具有均勻的磁極結構，依據安培定律，在供給線路電流之後，便會感應產生出交錯且規則的磁場分佈，從而獲得一多極磁性元件具有微小磁極距。 為了量測此微小磁極距的磁場分佈，我們設計製作出一個精密的磁場量測系統，使用高解析度的霍爾探棒，其感測面積只有165□165□m2，因此可以量測出微小磁極距小於1mm。不同多極磁性元件具有微小磁極距300□m、350□m和400□m，已成功製作出來，同時也量測出其表面上方200□m與300□m處的磁場分佈變化，清楚的磁性邊界顯示出此微小磁極距的大小，分別為300□m、350□m和400□m。因此，磁性編碼器的解析能力可以大幅地提升3.33倍 (1mm/300□m)。此外，利用有限函數疊加計算微小磁極距內之磁場公式也已經推導出來，理論計算的數值與實驗量測的結果有很好的一致性。 另外，藉由使用雙層的線路結構，可以將其微弱的磁場強度有效地提升1.37倍。再者，在磁場最佳化的研究中，使用不同的線路寬度190□m與235□m，其所對應出來的最佳磁極距大小為465□m與495□m，相較於其他尺寸的磁極距，具有較大的磁場強度與變化，上述這些特性是非常有助於後續訊號的檢測與處理。印刷電路板的製程技術已經驗證可以有效地縮減磁極距小於1mm，不需要精密的機械加工技術，以及昂貴複雜的充磁系統，而且大量生產很容易，不同磁極數目與磁極距尺寸也可以輕易的完成於基板上。

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.