Subject: Kinematics of Machinery

Topic: CAM Mechanism

Difficulty: High

The follower may be classified as discussed below:

1. According to the surface in Contact: The followers, according to surface in contact, are as follows:

(a) Knife edge follower. When the contacting end of the follower has a sharp edge, it is called a knife edge follower, as shown in fig. (a). The sliding motion takes place between the contacting surface (i.e. The knife edge and the cam surface). It is seldom used in practice because of the small area of contacting surface results in excessive wear. In knife edge followers, a considerable side thrust exists between the follower and the guide.

(b) Roller follower. When the contacting end of the follower is a roller, it is a called roller follower. As shown in fig. (b). Since the rolling motion takes place between the contacting surfaces (i.e.the roller and the cam), therefore the rate of wear is greatly reduced. In rollers followers also the side thrust exists between the follower and the guide. The roller followers are extensively used where more space is available such as stationary gas and oil engines and aircraft engine.

(c) Flat faced or mushroom follower. When the contacting end of the follower is a perfectly flat face, it is called a flat-faced follower, as shown in fig. (c).It may be noted that the side thrust between the follower and the guide is much reduced in case of flat faced followers. The only side thrust is due to friction between the contact surfaces of the follower and the cam. The relative motion between these surfaces is largely of sliding nature but wear may be reduced by offsetting the axis of the follower, as shown in fig. (f) so that when the cam rotates, the follower also rotates about its own axis. The flat faced follower is generally used where space is limited such as in cams which operate the valve of an automobile engine.

(d) Spherical faced follower. When the contacting end of the follower is of spherical shape, it is called a spherical faced follower, as shown in fig. (d). It may be noted that when a flat-faced follower is used in automobile engines, high surface stresses are produced. In order to minimize these stresses, the flat end of the follower is machined to a spherical shape.

2. According to the motion of the follower.

(a) Reciprocating or translating follower. When the follower reciprocates in guides as the cam rotates uniformly, it is known as the reciprocating or translating follower. The followers as shown in fig. (a) to (d) are all reciprocating or translating followers.

(b) Oscillating or rotating follower. When the uniform rotary motion of the cam is converted into predetermined oscillatory motion of the follower, it is called oscillating or rotating follower. The follower, as shown in fig. (e) is an oscillating or rotating follower.

3. According to the path of motion of the follower. The followers, according to its path of motion, are of the following two types.

(a) Radial follower. When the motion of the follower is along an axis passing through the center of the cam, it is known as radial follower. The followers, as shown in fig. (a) to (e) are all radial followers.

(b) Off-set follower. When the motion of the follower is along an axis passing through the Centre, it is called off-set follower. The follower, as shown in fig. (f), is an off-set follower.