Kinematic and geometric analysis-of a pure-rolling epicyclic train

This paper reports an innovative design of epicyclic (planetary) cam trains based on pure-rolling contact, intended to overcome the drawbacks of gear trains, such as Coulomb friction and backlash. The kinematic relations of the mechanism with a given speed-reduction ratio are analyzed; accordingly, the profiles of the sun cam and ring cam, key elements of the mechanism, are obtained. Furthermore, the condition for undercutting avoidance of the ring cam is derived. For mechanical design, different layouts of the epicyclic cam trains are discussed for the structure and transmission optimization. Finally, an epicyclic cam-roller speed reducer is designed and prototyped.