Abstract: The theory on Lateral Motions of the Belt on pulleys introduced in this paper deals with a serles of problems of the Belting. It has generalized these problems into a complete system and purified some vaguenesses and mistakes in many literatures, and has been proved by several experimeuts. The laferal motions of the belt on pulleys should be divided into the lateral move and the lateral slip. There are many essential differences between them, such as their causes, effects, analysis methods and measures ete. The lateral move is caused by the oblique wrap supported by friction and is unstable certainly. The "Law of Belting" is pointed to prevent the oblique wrap andvshould be obeyed by all beltings, not only the Quarter-turn Belting but also the Open Belting. To analyse the problems of lateral move should start with the tension and deformation analysis of the belt, find cut the actual direction of the belt on the approaching side of the pulleys and finally decide the tendency of the lateral move of the belt. The Crown pulley is an effective measure to stabilize the lateral move and prevent the belt wrap down. The lateral slip may be stable or not. It is caused the lateral forces acting on the contact section of the belt. The lateral slip decreases the load capacity and the transmissing efficiency of the belting. The back border may be used to prevent the belt slip down.

Key words: Assistant driving control degree, Lane tracking, Man-machine coordination, Assistant driving