Abstract: For multi-rope hoist,sliding rope is a very important safety issue.Therefore,real-time online monitoring of the sliding rope is also an essential safety tip for multi-rope hoist.But for tower hoist with non guild wheel,the encoder of measuring rope speed can not be installed since there is no sheave or guide wheels.So there exist technical difficulties.The abandoned roller upon cage is proposed to measure the slippage of steel wire rope,and this proposal is analyzed and demonstrated from the theory.

Key words: Tower hoist, Measured sheave, Scroll wheel