When designing an auto-focusing actuator for use in cell phone cameras, it is essential to minimize the device size, maximize the positioning repeatability, and minimize the power consumption. In a previous study, we presented a miniature auto-focusing voice coil motor (VCM) actuator for cell phone camera applications in which the lens was precisely positioned by a closed-loop feedback signal generated by a Hall element. Our study characterizes the performance of this device by using an experimental approach. The results show that the proposed actuator is not only smaller than a conventional VCM actuator with an open-loop positioning system, but also has improved positioning repeatability, a more rapid response, and lower power consumption.

This paper presents a miniature autofocus (AF) voice coil motor (VCM) actuator with retaining force in a restricted space that can be applied in an optical AF apparatus. A position encoder consisting of a permanent magnet (PM) and a Hall-effect sensor is used to detect magnetic signals; the displacement of the AF VCM actuator can be obtained from the encoder, thus enabling closed-loop control. The proposed miniature AF VCM actuator consists of a high-permeability magnetoconductive plate and a PM on another side to generate a retaining force when the exciting current is switched off. Using a 3-D finite-element analysis simulation and the Maxwell stress tensor method, the electromagnetic Lorentz force within a movable displacement was determined to be ~16 mN. Blur caused by variable force and load disturbance was observed in images captured during AF operation. This adaptive fuzzy proportional-integral-derivative (PID) control approach compensates for the nonuniform friction, disturbance variation, and even load changes of the movable part of the AF VCM actuator that occur when a subject is photographed in various positions. The adaption mechanism reduced control effort, despite the variable force and load disturbance, and exhibited fast dynamic performance and minimal steady-state error.