# Rapid and Precise Zoom Lens Design Based on Voice Coil Motors with Tunnel Magnetoresistance Sensors
## 1 Introduction  
Continuous zoom optical lenses [1; 2; 3; 4], which support seamless adjustments in focal length, are crucial in maintaining the original image resolution throughout the zoom process. This feature makes them extremely valuable for applications in optical security, police enforcement, and unmanned aerial surveillance [5; 6]. However, lenses with a large magnification range often require considerable time to switch focus, presenting a significant zoom delay issue. Such delays can result in target loss during the zooming process, adversely affecting the efficiency of information gathering and timely data processing. High zoom speeds and accuracy significantly impact applications such as unmanned aerial surveillance and optical security. In unmanned aerial surveillance, faster zooming brings more time to respond to fast-moving targets, enabling operators to capture and identify targets more quickly and reducing the probability of losing sight of the target. In the field of optical security, high-precision zooming provides clearer images and more accurate target localization, which enhances the effectiveness and reliability of surveillance. Additionally, the ability to zoom quickly and accurately in complex and dynamic environments ensures more stable monitoring, especially in scenarios that require frequent zoom adjustments. The issue of zoom delay is primarily caused by two factors: Firstly, zoom lenses with a large magnification ratio often require a long travel distance for the moving lens group, which extends the overall zooming time. Secondly, the traditional drive methods for zoom lenses convert the motor's rotational motion into the linear motion of the lens group, whichlimits the speed of the lens group's movement. Efforts to reduce the travel distance of the moving lens group have succeeded in increasing the zoom speed but sometimes lead to increased optical tolerance sensitivity and degraded image quality. Therefore, to effectively address the delay issues in high-magnification zoom lenses, improvements in their drive mechanisms are needed. A voice coil motor (VCM), a linear drive motor operating on the principle of the Lorentz force, which is the force exerted on a charged particle moving through a magnetic field, has the advantages of a simple structure, lack of transmission mechanisms, and fast response time. Traditional zoom drive methods, such as cams and stepper motors, convert the rotational motion of the motor into the linear movement of the lens group. This conversion process inherently slows down the driving speed. Unlike conventional systems that convert rotational motor motion into the linear movement of the lens group, VCMs can directly drive lens groups to perform linear movement. This simplification reduces the mechanical complexity and significantly enhances the zoom speed and positioning accuracy. The rapid response time of VCMs brings much faster zoom operations. They have been widely used in short-travel focusing applications [7; 8; 9; 10; 11; 12; 13] such as smartphones and DSLR cameras. However, research on VCMs for long-travel zoom applications is relatively scarce, primarily due to numerous engineering challenges, such as the control of the zoom precision and energy consumption management. In recent years, rapid drive technology based on VCMs has attracted much interest in the field. [PERSON] et al. [12] introduced a miniature closed-loop VCM for autofocus in mobile phone cameras. Compared to traditional open-loop miniature VCMs, this drive motor, with a smaller size, higher positioning repeatability (less than 5 \(\upmu\)m), faster response time (less than 10 ms), and higher power efficiency (maintaining a current below 20 mA), is an ideal solution for mobile camera autofocus. [PERSON] et al. [7] proposed a compact VCM for optical zoom modules in smartphone cameras, featuring longer displacement (\(\pm\)5.25 mm), more stable performance (deviation of less than 5.57%), and a shorter response time (up to 50 ms). [PERSON] et al.