手機相機裡自動對焦用線性致動器之創意設計與分析

Abstract

近年來，攝影者對相機高畫素的要求愈來愈高，且應用在手機相機裝置的體積愈來愈小，所以相機系統朝向高畫素、微小型與輕薄化的發展趨勢愈來愈明確，使得自動對焦之音圈致動器設計與精密定位控制，成為值得探討與研究的主題，而音圈致動器之主要結構則由永久磁鐵、導磁軛鐵和致動區域的空氣間隙所組成之磁路，因此為了得到更高效能的音圈致動器，選擇最佳的磁路設計更加重要。 本研究利用窮舉演算法，基於音圈馬達的特性，以圖論的方式定義，並列出所有的磁路設計，且利用拓墣矩陣與流值方法，進行刪除同構，然後比較磁能大小。在磁場分析方面，以有限元素方法分析音圈馬達之磁場分佈，以達到最佳的致動能力。最後，再對磁路中的各個元件，考慮其不同形狀所造成的磁漏影響，進而從中選擇最好的磁路設計。本研究建立了一個完整的磁路設計程序，並且適用於各種應用之音圈馬達。 在設計與分析方面，首先利用上述程序設計兩種新型的線性電磁致動器磁路，第一個新型的線性電磁致動器與一般音圈馬達採用勞侖茲力不同。當此電磁致動器的線圈通電，鐵心周圍的感應磁場會產生N極和S極，利用鐵心與永磁之間的同極相斥，異極相吸的特性，使致動器達到自動對焦的目的。第二個是新型的音圈馬達，無導磁元件體積小與傳統的做比較，結果顯示對焦所需之最大電流只需40 mA。最後使用三維耦合的有限元素方法來計算電磁與機械特性，包括驅動電流的變化，動件的位移，速度和致動器的推力。結果顯示，兩種致動器具有尺寸小、快速響應和低功耗等優點。

Recently, photographers demand higher pixel resolution of image sensors and smaller size in digital or mobile phone cameras, whose auto–focusing (AF) and precision positioning control become topics worthy to research. These techniques can effectively prevent taking camera images from blurring through compensating camera shakes when photographers are taking pictures. Voice coil motors (VCMs) consist of permanent magnets, yokes, and gaps, which are components of the magnetic circuit. For high efficiency, optimal magnetic design is very important. In this study, based on characteristics of VCMs, the graph theory is adopted to enumerate all magnetic circuit designs. Furthermore, rules representing design criteria and a flow value method are used to compare enumerated designs for achieving magnetic circuits. In the magnetic field analysis, this study uses the finite element method to analyze voice coil motors in achieving better optimal actuator force. This study considers the effect of different shapes in magnetic components and chooses the best design. This study presents a complete design process for applications of VCM. The above process is used to design two novel linear electromagnetic actuators (LEAs). In the first LEA, when coils are powered, induced magnetic field generates N and S poles around iron cores. Thus, unlike voice coil motors that employ Lorentz force, the motion of the moving part in this study is arisen from a magnetic field property － same poles repel each other while opposite poles attract each other. The second proposed VCM actuator does not contain springs that are usually used in conventional VCM actuators. Moreover, the maximum current required to displace the moving part of the novel VCM is 40 mA. This represents a current reduced by 50% compared to the conventional actuator, and leads to a significant improvement in the power efficiency of the device. Using a coupled three-dimensional finite element method, we calculate electromagnetic and mechanical characteristics of two actuators current variation of coils, displacement of the moving part, velocity, and motive force of actuators. The results show that the proposed two actuators have merits of rapid response and low power consumption.