Types Of Cam And Followers-Basic Of Theory Of machine
A cam is a rotating machine element which gives reciprocating or oscillating motion to another element known as follower. The cam and the follower have a line contact and constitute a higher pair. The cams are usually rotated at uniform speed by a shaft, but the follower motion is pre- determined and will be according to the shape of the cam. The cam and follower is one of the simplest as well as one of the most important mechanisms found in modern machinery today.
The cams are widely used for operating the inlet and exhaust valves of internal combustion engines, automatic attachment of machinery, paper cutting machines, spinning and weaving textile machinery, feed mechanism of automatic lathes etc.
1. According to the surface in contact.
The followers, according to the surface in contact, are as follows:
(a) Knife edge follower.
When the contacting end of the follower has a sharp knife edge, it is called a knife edge follower, as shown in Fig.. The sliding motion takes place between the contacting surfaces (i.e. the
knife edge and the cam surface). It is seldom used in practice because 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.
|Types Of Followers according to surface of contacts|
(b) Roller follower.
When the contacting end of the follower is a roller, it is called a roller follower, as shown in Fig. 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 roller 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 in stationary gas and oil engines and aircraft engines.
(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. 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 off-setting the axis of the follower, as shown in Fig so that when the cam rotates, the follower also rotates about its own axis. The flat faced followers are generally used where space is limited such as in cams which operate the valves of automobile engines.
(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. 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.
The followers, according to its motion, are of the following two types:
|a. oscillating Follower b. Reciprocating followers|
(a) Reciprocating or translating follower.
When the follower reciprocates in guides as the cam rotates uniformly, it is known as reciprocating or translating follower.
(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 ., 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. Raidal b. Off-set follower|
(a) Radial follower.
When the motion of the follower is along an axis passing through the centre of the cam, it is known as radial follower.
(b) Off-set follower.
When the motion of the follower is along an axis away from the axis of the cam centre, it is called off-set follower,
Cams can be classified into the following three types based on their shapes.
|Types Of Cams|
1.) Plate or disk cams:
Plate or disk cams are the simplest and most common type of cam. A plate cam is illustrated in figure. This type of cam is formed on a disk or plate. The radial distance from the center of the disk is varied throughout the circumference of the cam. Allowing a follower to ride on this outer edge gives the follower a radial motion.
2) Cylindrical or drum cam:
A cylindrical or drum cam is illustrated in figure . This type of cam is formed on a cylinder. A groove is cut into the cylinder, with a varying location along the axis of rotation. Attaching a follower that rides in the groove gives the follower motion along the axis of rotation.
3) Linear cam:
A linear cam is illustrated in figure. This type of cam is formed on a translated block. A groove is cut into the block with a distance that varies from the plane of translation. Attaching a follower that rides in the groove gives the follower motion perpendicular to the plane of translation.
Applications of cams
Cams are widely used in automation of machinery, gear cutting machines, screw machines, printing press, textile industries, automobile engine valves, tool changers of machine centers, conveyors, pallet changers, sliding fork in wearhouses etc.
Cams are also used in I.C engines to operate the inlet valves and exhaust valves.The cam shaft rotates by using prime moveres. It causes the rotation of cam. This rotation produces translatory motion of tappet against the spring. This translatory motion is used to open or close the valve.