Abstract
Cam mechanisms with a negative radius roller-follower allow the design of simple machines capable of exerting remarkably high forces. Furthermore, the concave-convex nature of the contact surface between the cam and the follower results in a low contact stress and the ready formation of a lubricating layer. This paper presents a simple method for the design and analysis of a cam mechanism with a negative radius roller-follower. In the proposed approach, conjugate surface theory is employed to derive a kinematic model of the cam mechanism. Analytical expressions for the pressure angle and principal curvatures of the cam profile are then derived. The validity of the proposed design methodology is demonstrated by machining a cam mechanism having a negative radius rollerfollower with a radius of 100 mm.
Highlights
The results showed that the cam mechanism with a concavefaced follower produced a lower maximum contact stress than that with a common flat-faced follower
In order to analyze the contact stress in a cam mechanism, it is first necessary to determine the profile of the cam
The follower rises to a total lift height h over a specified rise angle, remains in a high dwell position over the high dwell angle, falls through a distance h over the return angle, and remains in a low dwell position over the low dwell angle
Summary
In order to analyze the contact stress in a cam mechanism, it is first necessary to determine the profile of the cam. To express the surface of the roller in terms of frame (xyz)0, it is first necessary to establish the frame of the roller-follower, namely (xyz)r. The surface equation, rS, and unit outward normal, rn, of the roller can be expressed with respect to frame (xyz)r as follows:. Once the input-output relation of the cam mechanism has been defined, the conjugate points and cam profiles can be determined via the formulation. Dt where 0n and 0S are the unit outward normal and surface equation of the cam profile with respect to frame (xyz)0,
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