Tillage is one of important operations to improve and maintain surface soil in farm land. Theoptimal tillage condition is dependent remarkably on the soil types as sandy soil or cohesivesoil, and soil conditions such as hardness, moisture content, and so on. Various tillagemethods and tools have been developed up to present. However mechanical interactionbetween soil and tillage tool, and soil deformation and soil cutting phenomena during tillageoperation are very complex system in general. Ther ...