Mechanisms with rotation of booms driven by telescopic cylinders have many applications in construction machinery. Kinematical relations between cylinder telescoping and rotation of booms in such a mechanism were studied herein, without any idealization of manufacturing，assembling and controlling conditions. The obtained results give an explanation of why some of harmful motions occurred, and their applications in engineering practice were illustrated by a real examples. 

针对通过油缸伸缩来控制臂架转动变幅在工程机械中的广泛应用，研究在不对安装、制造和油缸控制做任何理想化假设的前提下，给出双液压油缸伸缩运动与臂架转动之间的映射关系，以解释臂架有害摆动产生的原因。通过数值算例阐述了所得结果在安装、制造和系统控制方案上的实用价值。

变幅机构, 油缸伸缩, 臂架转动, 制造安装误差