Miniature camera module with a hollow linear ultrasonic motor-based focus feature

Abstract

The construction of a miniature camera module that can explore inside limited spaces is of great interest for the design of millimeter-scale devices, such as endoscopes. This article presents a miniature camera module with a focus feature using a hollow linear ultrasonic motor. The hollow stator, which is simplified by the expansion and thickness-shear piezoelectric effects, is suitable for the miniaturization of the camera module because it can contain a lens group. The linear slider, which is thin and cylindrical with a slit, is inserted into the stator’s hole and generates a preload that exploits optimal motor performance measures. The resultant camera module is 4.6 mm × 4.6 mm square, which is the smallest one of camera modules reported to date. The motion of the miniature camera module is demonstrated by the wire-driven mechanism and a visual feedback control system. The orientation of the camera module head is controlled by a wire-driven mechanism until the target object is set in the range of view. The lens group placed inside the slider is controlled by the hollow linear ultrasonic motor in a visual feedback-loop system.