variable frequence variable speed 基本例句 变频 The imported frequency control of motor speed adapts to different printing speeds.进口变频电机调速，适应不同印刷速度。 The doffer is driven by an inverter and a synchronous toothed belt which permits stepless variations of the speed.道夫采用变频电机，同步齿形带传动，实现无级调速。