Evolution History of Non-circular Gears

Recently variable-ratio gears are increasingly being used to drive the modern machines. For this purpose cams and non-circular gears are often used. In the past, the production of non-circular gears was a very complicated process, which explains their relatively limited use in practice. In the 20th century, Professor F. Litvin played a great role in the development of theory and manufacture of noncircular gears. Modern technologies of the 21st century make the manufacturing relatively cheap and easy, using high-precision machine-tools, 3D prototyping and spraying. The paper considers the history of non-circular gears evolution and application.