Book excerpt: In the surfaces theory, it is well-known that a surface is called to be a ruled surface if it is generated by a continuously moving of a straight line in the space. Since a ruled surface is obtained by a line movement, its geometry has many nice properties and such surfaces have been studied by many authors, see: [4, 5, 6] and references therein. Ruled surfaces are also important subject in many applications. In particular, such surfaces have been used in computer aided engineering design (CAD) [7].