为了弥补传统的沿光轴切向移入移出变倍镜组方式与沿光轴同向移动变倍镜组方式的变倍机构存在占用空间大、机构复杂、变倍时间长、控制精度低以及断电不能自锁等缺点，设计了一种超声电机驱动的光轴旋转方式移入移出的变倍机构。新变倍机构具有占用空间小、机构简单、变倍完成时间短、转角控制精确、可重复性强以及断电自锁等优点。实验结果表明，该变倍机构在100次可重复性关断特性试验中，平均转速为150 r/min，试验得到最长的关断时间为0.756 ms，最短的关断时间为0.748 ms，关断时间最大误差为0.008 ms，旋转变倍机构的最大转角误差为0.432′。最大转角误差在成像面上的偏移量＜0.015 mm，其误差在系统所要求的范围内。

A rotary varifocal mechanism driven by ultrasonic motor was designed to remedy the shortcomings of a traditional varifocal mechanism in moving along the axial or radial directions,such as large occupation space, complicated configuration, long time consumption, low control precision, and the lack of self-locking function.This new varifocal mechanism has the advantages of the small space, simple configuration, short time for zoom completed, high control precision of rotating angle, strong repeatability, and self-locking function. The results of 100 shutoff characteristics of repeatability experiments show that the longest and the shortest shutoffs are 0.756 ms and 0.748 ms,respectively, when the average rotation speed is 150 r/min. Therefore, the maximum error of the shutoff time is 0.008 ms, the largest rotating angle error of the rotary varifocal mechanism is 0.432′,and the largest angle error displacement in the imager is less than 0.015 mm.These data can meet the system requirement.