Classification of CAMS and Followers

A cam is a mechanical element used to drive another element, called the follower, through a specified motion by direct contact. Cam-and-follower mechanisms are simple and inexpensive, have few moving parts, and occupy a very small space. Furthermore, follower motions having almost any desired characteristics are not difficult to design. For these reasons, earn mechanisms are used extensively in modern machinery.

The versatility and flexibility in the design of earn systems are among their more attractive features, yet this also leads to a wide variety of shapes and forms and the need for terminology to distinguish them.

Cams are classified according to their basic shapes. Figure 5.1 illustrates four different types of cams:

(a) A plate cam, also called a disk cam or a radial cam

(b) A wedge earn

(d) An end cam orface cam

The least common of these in practical applications is the wedge earn because of its need for a reciprocating motion rather than a continuous input motion. By far the most common is the plate earn. For this reason, most of the remainder of this chapter specifically addresses plate cams, although the concepts presented pertain universally.

Cam systems can also be classified according to the basic shape of the follower. Figure 5.2 shows plate cams acting with four different types of followers:

(a) A knife-edge follower

(b) Afiat-face follower

(d) A spherical-face or curved-shoe follower

Notice that the follower face is usually chosen to have a simple geometric shape and the motion is achieved by careful design of the shape of the earn to mate with it. This is not always the case; and examples of inverse cams, where the output element is machined to a complex shape, can be found.

Another method of classifying cams is according to the characteristic output motion allowed between the follower and the frame. Thus, some cams have reciprocating (translating) followers, as in Figs. 5.la, 5.lb, and 5.ld and Figs. 5.2a and 5.2b, while others have oscillating (rotating) followers, as in Fig. 5.lc and Figs. 5.2c and 5.2d. Further classification of reciprocating followers distinguishes whether the centreline of the follower stem relative to the center of the earn is offset, as in Fig. 5.2a, or radial, as in Fig. 5.2b