Cam Mechanism

CAM and Follower CAM and Follower MECHANISMMECHANISM

DefinitionDefinitionA cam may be defined as a machine element

having a curved outline or a curved groove, which, by its oscillation, rotation or reciprocating motion, gives a predetermined specified motion to another element called the follower .

It is usually consists of a cam (the driver), the follower (the driven element), and the frame (the support for the cam and the follower).

PARTS OF CAM MECHANISM

Classification of Classification of CamsCamsAccording to ShapeAccording to Shape

Radial/Disc/Plate CamThe follower moves in a plane perpendicular to the axis of rotation of the cam. Mostly use type of cam.

Made up of a flat plate or disc with an edge profile to transmit motion.

Translation/Wedge CamThe cam moves over and back, reciprocating motion, which drives the follower vertically.

Cylindrical/Barrel CamThe roller follower operates in a groove cut on the periphery of a cylinder. The follower may translate or oscillate.

Face camIn its flat surface, this rotary cam has a groove cut within which a constrained follower moves. The groove ensures no need for a return spring.

End camIn this case the end of the cylindrical cam has the profile machined on the end.

Classification of Classification of FollowerFollowerReciprocating followerFollower arrangement

RECIPROCATING FOLLOWERS

Knife edged followerThis is the simplest type and not often used due to the rapid rate of wear.

It is usually use for reciprocating motion, running in slides and there is considerable side thrust.

Roller followerRoller followerUses a roller and eliminates rapid wear of follower.

This has the advantage that the This has the advantage that the only side thrust present is that only side thrust present is that due to the friction between the due to the friction between the follower and the cam.follower and the cam.

The spherical face of the follower The spherical face of the follower has a large radius that has a large radius that compensates for detrimental compensates for detrimental deflection or misalignment that deflection or misalignment that may occur with the flat mushroom may occur with the flat mushroom follower.follower.

According to motion of the follower

Follower Follower arrangementarrangement

In-line follower the center line of the follower passes

through the center line of the camshaft.

Offset follower the center line of the follower does not

pass through the center line of the cam shaft. The amount of offset is the distance between these two center lines. The offset causes a reduction of the side thrust present in the roller follower.

Radial follower rotates or oscillates as the cam is in rotational motion.

CAM NomenclatureCAM NomenclatureCam profile: The outer surface of

the disc cam.Base circle : The circle with the

shortest radius from the cam center to any part of the cam profile.

Trace point: It is a point on the follower, and its motion

describes the movement of the follower. It is used to generate the pitch curve.

Pitch curve : The path generated by the trace point as the follower is rotated about a stationery cam.

Prime circle: The smallest circle from the cam center through the pitch curve

Pressure angle: The angle between the direction of the follower movement and the normal to the pitch curve.

Pitch point: Pitch point corresponds to the point of maximum pressure angle.

Pitch circle: A circle drawn from the cam center and passes through the pitch point is called Pitch circleStroke: The greatest distance or angle through which the follower moves or rotates

Types of follower motionTypes of follower motion

1. Uniform motion ( constant velocity)

2. Simple harmonic motion3. Uniform acceleration and

retardation motion

A period is a part of the cam cycle and it includes the following:

Rise (Outstroke) the upward motion of the follower

caused by cam motion.Fall (Return stroke) the downward motion of the

follower caused by cam motion.Dwellthe stationary position of the

follower caused by cam motion.

Modes of Input / Output MotionRotating cam-translating follower Rotating follower

The follower arm swings or oscillates in a circular arc with respect to the follower pivot.

Translating cam-translating follower Stationary cam-rotating follower

The follower system revolves with respect to the center line of the vertical shaft.

1 .The most well known use of cams is in car engines. The Cam operated valve system can be found in modern car engines and incorporates a number of cams; the valves are opened by cams, four- and six-lobed cams govern the spark distribution and many car petrol oil pumps are cam driven.

2 . These are used in wall clock 3 . These are used in feed mechanism In automatic lathe machine

4. These are used in paper cutting machine.

5 . It is use in textile machine

6. Cams convert rotary oscillating or linear motion into a linear or reciprocating action to carry out useful work.

VI. Constraints on the VI. Constraints on the FollowerFollowerIn all cam systems it is important that

the follower is always in contact and following the motion of the cam.

Gravity constraintThe weight of the follower system is sufficient to maintain contact.

Spring constraintThe spring must be properly designed to maintain contact.

Positive mechanical constraintA groove maintains positive action. Example is the Constant-diameter cam shown in the left.

SIMPLE HARMONIC MOTION