Module 4 : Drives and Mechanisms

Lecture 3 : Cams

Cams are mechanical devices which are used to generate curvilinear or irregular motion of mechanical elements. They are used to convert rotary motion into oscillatory motion or oscillatory motion into rotary motion. There are two links namely the cam itself which acts as an input member. The other link that acts as an output member is called the follower. The cam transmits the motion to the follower by direct contact. In a cam-follower pair, the cam usually rotates while the follower translates or oscillates. Complicated output motions which are otherwise difficult to achieve can easily be produced with the help of cams. Cams are widely used in internal combustion engines, machine tools, printing control mechanisms, textile weaving industries, automated machines etc.

Necessary elements of a cam mechanism are:

Figure 4.3.1 Cam mechanism

1.  Classification of cams

1.1 Wedge and Flat Cams

A wedge cam has a wedge of specified contour and has translational motion. The follower can either translate or oscillate. A spring is used to maintain the contact between the cam and t he follower. Figure 4.3.2 shows the typical arrangement of Wedge cam.

Figure 4.3.2 Wedge cam

1.2  Plate cam

In this type of cams, the follower moves in a radial direction from the centre of rotation of the cam (Figure 4.3.3). They are also known as radial or disc cam. The follower reciprocates or oscillates in a plane normal to the cam axis. Plate cams are very popular due to their simplicity and compactness.

Figure 4.3.3 Plate cam

1.3  Cylindrical cam  

Here a cylinder has a circumferential contour cut in the surface and the cam rotates about its axis (Figure 4.3.4). The follower motion is either oscillating or reciprocating type. These cams are also called drum or barrel cams.

Figure 4.3.4 Cylindrical cam