求翻译：依靠旋转的滚筒与输送带之间的摩擦力使输送带运动，从而达到运送物料的目的。为了使输送带有合适的张紧度，还设有张紧装置。是什么意思？

Relying on rotating friction between rollers and conveyor belt conveyor belt movement, so as to achieve the purpose of delivering materials. In order to make transportation with an appropriate degree of tension, also with tensioning device.