Abstract
The work presents an analytical approach for designing disk cam mechanisms with a translating follower having an extraneously added dual-concave-faced intermediate link. When the cam and its follower are pressed into contact, high contact stresses may occur due to very small actual contact area. The arrangement of the follower can affect the contact stress between the cam and the follower. According to the Hertz theory, the contact stress between two cylinders is affected by the normal force and the cylinder radius curvatures. This work proposes a modified arrangement of the common translating follower to reduce the contact stress. That is, an extraneous intermediate link having dual-concave faces is added between the cam and the common follower. Introducing this novel arrangement is intended to result in two convex-to-concave contact points so as to significantly increase the actual contact area. As a first step, the profile of the cam with a translating single-concave-faced follower having a compensatively adjusted motion curve is calculated by applying the concept of velocity instant center. The obtained cam profile is then employed as a substitute cam to drive the presented novel follower. Because the motion curve of the original common follower has been compensatively adjusted, the presented novel follower driven by this substitute cam profile can achieve the expected dwells and the expected total rise during the motion cycle. The contact points between the substitute cam and the dual-concave faces of the intermediate link are determined according to the profile geometries of the substitute cam. The rise motion curve and the fall motion curve of the presented novel follower driven by this substitute cam profile is analyzed. After a force analysis of the cam mechanism has been undertaken, the Hertz contact stress theory is applied to determine the caused contact stresses; the results are compared with those of disk cam mechanisms with single-concave-faced follower. Then, the effect of each design parameter as well as the asymmetric factors of the follower motion curve on the induced contact stress is analyzed. Finally, it is found that through the application of this novel follower, the contact stress can be reduced by 13% to 22%.