For disk cam mechanisms, the motion relationship between cam and follower is not completely determined. It needs some auxiliary forces, e.g., the gravity force or spring force, to avoid the separation between cam and follower during operation. Therefore, the positive motion cam mechanism is the one whose cam can determinately drive the follower, i.e., cam and follower keeps contact during the overall operation, without using auxiliary forces. For the shown models, this cam mechanism has a disk cam whose profile is formed by three equal-radius arcs. Based on this special geometry, its cam and follower can keep contact over the cycle of motion.