1. Litvin, F.L.: Development of Gear Technology and Theory of Gearing. NASA Reference Publication, Cleveland, Ohio (1997)
2. Sarri, O.E.: Speed-reduction gearing, united states patent office, Patent No. 2696125 (1954)
3. Saari, O.E.: Skew axis gearing, United States Patent Office, Patent No. 2954704 (1960)
4. Zhao, Y., Kong, X., Peng, X.: Meshing principle of conical surface enveloping spiroid drive. Mech. Mach. Theo. 123, 1–26 (2018)
5. Zhao, Y.: Engineering Differential Geometry of Curves and Surfaces. Science Press, Beijing (2023)