Cam & follower Types with description.

Cam and follower.

a cam is a rotating machine element which gives reciprocating or oscillating motion to another element known as follower. The cam and follower have a line contact and are higher order pair. 

◼️Classification of followers.

On the basis of point of contact.

a) Knife edge follower.

                                When contacting end of the follower has a sharp knife edge, it is called knife edge follower. The sliding motion takes place between knife edge and the cam surface. Because of small area of contacting surface results in excessive wear. In knife edge followers a considerable side thrust exist between the followers and the guide.

b) Roller follower.

                            When the contacting end of the follower is a roller , it is called a roller follower. Since the rolling motion takes place between the roller and cam therefor 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. It may be noted that the side thrust between the follower and the guide is much reduced in case of flat faced followers. The relative motion between these surfaces is largely of sliding nature but wear may be reduced by offsetting the axis of the followers. The flat faced followers are generally used where space is limited such as in cams which operate the vales of automobile engine.

When the flat faced follower is circular, it is then called a mushroom follower.

d) Spherical faced follower.

When the contacting end of the follower is of spherical shape, it is called 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 reduce these stresses, the flat end of the follower is machined to a spherical shape.  

2, on the basis of motion of followers. 

a) Reciprocating or translating follower.

when the follower reciprocates in guides are as the came rotate 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.

3, on the basis of path of motion of the followers. Or exis of followers and cam.

a) Radial follower.

Whe the motion of the follower is along an exis passing through the centre of the cam, it known as radial follower, show in fig 20.1,(a),to(e)

b) Off set follower.

Whe the motion of the follower is along an exis away from the exis of the cam centre, it is known as off set follower.

  ◼️Classification of cams

a) Radial or disc cam.

In radial cams, the follower reciprocates or oscillates in the direction perpendicular to the cam exis as show in fig 2.1  all are radial cams.

b) Cylindrical cams.

In cylindrical cams, the follower reciprocate or oscillate in a direction parallel to the cam exis as show in bellow fig.

◼️Term used in radial cam or nomenclature of cam

For cam profile we assume cam is stationery and follower is moving.

Shaft 

Shaft is a rotating machine element used to transmit power or motion from one part to another part.

 

the followeing terms are important in order to draw the cam profile.

1)Base circle

It is the smallest cirlce that can be drawn to the cam profile.

Trace point.It is a reference point on the follower and is used to generate the pitch cureve. In case of knife edge follower , the knife edge represent the trace point and the pitch curve correspond to the cam profile. In a roller follower, the centre of the roller represents the trace point.

2) Pressure angle.

It is the angle between the direction of the follower motion and a normal to the pitch curve.the maximum pressure angle = 30 in case of greater than 30 then a reciprocating follower will jam in its bearing.

3) Pitch point.

It is a point on the pitch curve having maximum pressure angle.

4)Pitch circle.

It is a circle drawn from the centre of the cam through the pitch points.

5)Pitch curve.

It is the curve generated by the trace point as the follower moves relative to the cam. For a  knife edfe follower, the pitch curve and the cam profile are same wherease for a roller follower, they are seperted by the radious of the roller.

6) Prime circle.

It is the smallest circle that can be drawn from the centre of the cam and tangent to the pitch curve. For a knife edge and flat face follower, the prime circle and the base circle are identical. For a roller follower, the prime circle is larger than the base circle by the radiou of the roller.

Leift or strok

It is the maximum travel of the follower from its lowert position to the top most position.

Outstroke and dwe stroke periods.

Out stroke period allow the motion of the follower.

Dwe stroke period resist the motion of the follower.

as cam rotation is 3600.

Published by Science Tube, September 08, 2020