1. Juhong Cao, in: Wall-climbing CAM Contact Stress Induced Main curvature, edited by Mechanical Design (2001. 11) in Chinese.
2. Daren Wu, in Differential Geometry Handouts, edited by People Education Press (Beijing, 1960).
3. K. L. Johnson, in: Contact Mechanics, edited by Higher Education Press (1992).
4. A. K. Dhingra, S. S. Rao in: ASME J. Mech. Des. 113, 306 (1991).
5. Chengguang Ren, Zukang Shi, Chaopeng Zhang, in: The Ball Bcrew Transmission Design Basis, edited by Machinery Industry Press (Beijing, 1987).