UNIT – III

CAM

• A cam is a mechanical member used to produce desired motion to a follower

by direct contact. The cam may be rotating or reciprocating whereas the

follower may be rotating, reciprocating or oscillating

FOLLOWER

• It is the driven member.

CLASSIFICATIONS OF CAM

Cams are classified according to their

• Basic shapes

• Types of follower movement

• Manner of constraints of the follower

Based On Their Shapes

• Wedge or flat cams

• Plate cam

• Cylindrical cam

• Spiral cams

• Globoidal cam

Based on movement of the follower

• The motion of the followers is distinguished from each other by the dwells,

rises and returns they have.

• Rise of a cam: The motion of the cam which tend to lift the follower

is known as the rise motion.

• Dwell of a cam: The rotation of the cam for which the follower is

stationary at its position is known as dwell of the cam.

• Return of a cam: The motion (rotation) of the cam for which the

follower tends to move its original position is known as the return

motion of the cam.

Based On Movement Of The Follower

1. Rise-Return-Rise (R-R-R)

• In this, there is alternate rise and return of the follower

with no periods of dwells. It’s use is very limited in the

industry. The follower has a linear or an angular displacement.

2. Dwell-Rise-Return-Dwell (D-R-R-D)

• In such a type of cam, there is rise and return of the follower

after a dwell (as shown in figure). This type is used more

frequently than the R-R-R type of cam.

3. Dwell-Rise-Dwell-Return-Dwell (D-R-D-R-D)

• It is the most widely used type of cam. The dwelling of the cam is

followed by rise and dwell and subsequently by return and

dwell.

4. Dwell-Rise-Dwell (D-R-D)

• The dwelling of the cam is followed by dwell, rise and then dwell

of the follower.

Based On Manner Of Constraint Of The Follower

1. Pre-Loaded Spring Cam:

• A pre-loaded compression spring is used for the purpose of keeping

the contact between the cam and the follower.

2. Positive-drive Cam:

• In this type, constant touch between the cam and the follower is

maintained by a roller follower operating in the groove of a cam.

The follower cannot go out of this groove under the normal working

operations. A constrained or positive drive is also obtained by the use

of a conjugate cam.

3. Gravity Cam:

• If the rise of the cam is achieved by the rising surface of the cam

and the return by the force of gravity or due to the weight of the

cam, the cam is known as a gravity cam. However, these cams arc not

preferred due to their uncertain behavior

CLASSIFICATION OF FOLLOWER

• According to the follower shape

• According to the motion of the follower

• According to the path of motion

According to the follower shape

• Knife edge follower

• Roller follower

• Mushroom or flat faced follower

• Spherical faced follower

According to the motion of the follower

• Reciprocating or translating follower

• Oscillating or rotating follower

According to the path of motion

• Radial follower

• Offset follower

According to the follower shape

According to the motion of thefollower

• Reciprocating follower

• Oscillating follower

According to the path of motion

• Radial follower

• Offset follower

RADICAL CAM NOMENCLATURE

Cam profile

The surface of the cam which comes in contact with the follower

Base Circle

It is the smallest circle, keeping the center at the cam center, drawn

tangential to cam profile.

Trace Point

I t is a point on the follower, and it is used to generate the pitch curve. Its

motion describing the movement of the follower.

Pitch Curve

It is the curve drawn by the trace point assuming that the cam is fixed,

and the trace point of the follower rotates around the cam, i.e. if we hold the cam

fixed and rotate the follower in a direction opposite to that of the cam, then the

curve generated by the locus of the trace point is called pitch curve.

Pressure Angle

It is the measure of steepness of the cam profile. The angle between the

direction of the follower movement and the normal to the pitch curve at any point

is called pressure angle.

Pitch Point

The point corresponds to the point of maximum pressure angle is called

pitch point.

Prime Circle

The prime circle is the smallest circle that can be drawn so as to be

tangential to the pitch curve, with its center at the cam Centre

Pitch circle

It is the circle passing through the pitch point and concentric with the

base circle.

Cam angle

It is the angle of rotation of the cam for a definite displacement of the

follower.

Lift or stroke

It is the maximum displacement of the follower from the basic circle of the

cam.

ANGLE OF ASCENT, DWELL, DESCENT & ACTION

Angle Of Ascent

The angle of rotation of cam from the position of the follower begins to rise till it

reaches its highest position.

Angle Of Dwell

It is the angle through which cam rotates while the follower remains stationary

at the highest or lowest position.

Angle Of Descent

It is the angle through which cam rotates while the follower returns to the initial

position.

Angle Of Action

It is the total angle moved by the cam during tis rotation

CAM PROBLEMS

1. Draw the profile of a cam operating a roller

reciprocating follower and the following data.

Minimum radius of cam = 25 mm

Lift = 30 mm

Roller follower = 15 mm

The cam lifts the follower for 1200

with SHM, followed by a dwell

period of 300.

Then the follower lowers down during 1500

of cam rotation

with uniform acceleration and retardation followed by a dwell period. If the

cam rotates at a uniform speed of 150rpm. Calculate the maximum velocity and

acceleration of the follower during the descent period.

A cam operating a knife edge follower has the following data:

a) Follower moves outward through 30mm during 1200

of cam rotation

with uniform and retardation motion.

b) Follower dwells for the next 300

c) Follower returns to its original position during next 900 rotation with

SHM.

d) Follower rest for the rest of the rotation

The least radius of the cam is 50mm and rotates counter- clockwise at a

uniform speed of 800 rpm. Draw the profile of the cam when, the axis of the

follower passes through the cam axis. And also draw the displacement, velocity

and acceleration diagrams for the motion.

OFF SET ROLLER (For Example)

UNIT III

KINEMATICS OF CAM

PART-A (2 MARKS)

1. What is a cam?

2. Give some examples for cams

3. State the expressions f o r m a x i m u m acceleration of a follower

moving with cycloidal mot ion . [NOV/DEC 2012]

4. Define tangent cam?

5. Write the procedure to draw the CAM profile. [NOV/DEC 2013]

6. Where are the roller follower extensively used?

7. Define pressure angle with respect to cams. [NOV/DEC 2011/NOV/DEC

2013]

8. Define undercutting in cam. How it occurs?

9. Define Lift (or) Stroke in cam.

10. What do you know about Nomogram?

11. Which type of cam follower motion is used in high speed engines?

Why? [MAY/JUNE 2012.]

12. How can you prevent undercutting in cam ?

13. What do you know about gravity cam?

14. Why large pressure angle is not preferred in cam curves?

[MAY/JUNE 2012.]

15. List the classifications of cam followers based on shape. [AU NOV/DEC

2006]

16. What are the essential design features of high speed cams? [AU NOV/DEC

2006]

17. State the expressions for maximum velocity and acceleration of a follower

moves with Cycloidal motion. [AU APRIL / MAY 2007]

18. What is prime circle of a cam? What is the radial distance between the prime

circle and base circle for a cam with knife edge follower? [AU APRIL /

MAY 2007]

19. What is a circular arc cam? [AU NOV/DEC 2007]

20. State the expressions for maximum velocity and acceleration of a follower

moves with cycloidal motion. [AU NOV/DEC 2007]

21. Define pitch curve of the cam. [AU APRIL / MAY 2008]

PART-B (16 Marks)

1. A cam is to give the following motion to a knife edged follower:

(a) Outstroke during 60° of cam rotation

(b) Dwell for the next 45° of cam rotation

(c) Return stroke during next 90° of cam rotation and

(d) Dwell for the remaining of cam rotation

The stroke of the follower is 40 mm and the minimum radius of the cam is 50

mm. The follower moves with uniform velocity during both the outstroke and

return strokes. Draw the profile of the cam when (a) the axis of the follower

passes through the axis of the cam shaft, and (b) the axis of the follower is

offset by 20 mm from the axis of the cam shaft.

2. Draw the profile of a cam operating a Knife-edged follower from the

following data: (a) Follower to move outward through 40 mm during 60° of a

cam rotation; (b) Follower to dwell for the next 45° (c) Follower to return its

original position during next 90° (d)Follower to dwell for the rest of cam

rotation. The displacement of the follower is to take place with simple harmonic

motion during both the outward and return strokes. The least radius of the

cam is 50mm. If the cam rotates at 300 r.p.m., determine the maximum

velocity and acceleration of the follower during the outward stroke and return

stroke. [MAY/JUNE 2011] – MODEL; [MAY/JUNE 2014] – MODEL;

[MAY/JUNE 2009]

3. A cam, with a minimum radius of 50 mm, rotating clockwise at a uniform

speed, is required to giver a knife-edged follower the motion as described below:

(a) To move outwards through 40 mm during 100° rotation of the cam; (b) to

dwell for next 80° (c) To return to its starting position during next 90 ° and (d)

To dwell for the rest period of revolution. Draw the profile of the cam (i) When

the line of stroke of the follower passes through the centre of the cam shaft and

(ii) When the line of stroke of the follower is to take place with Uniform

acceleration and uniform retardation. Determine the maximum velocity and

acceleration of the follower when the cam shaft rotates at 900 r.p.m. [NOV/DEC

2011] – MODEL; [MAY/JUNE 2011] – MODEL.

4. Draw the profile of a cam operating a roller reciprocating follower and with the

following data: Minimum radius of cam =25 mm; lift=30mm; Roller diameter=

15mm. The cam lifts the follower for

120° with SHM, followed by a dwell period of 30°. Then the follower lowers

down during 150° of cam rotation with uniform acceleration and retardation

followed by a dwell period. If the cam rotates at a uniform speed of 150 RPM.

Calculate the maximum velocity and acceleration of follower during the descent

period. [NOV/DEC2013]; [NOV/DEC 2012] – MODEL

5. It is required to set out the profile of a cam to give the following motion to the

reciprocating follower with a flat mushroom contact surface: (i) Follower to have

a stroke of 20 mm during 120° of cam rotation, (ii) Follower to dwell for 30° of

cam rotation, (iii) Follower to return to its initial position during 120° of cam

rotation, (iv) Follower to dwell for remaining 90° of cam rotation. The

minimum radius of the cam is 25 mm. The out stroke of the follower is

performed with SHM and return stroke with equal uniform acceleration and

retardation. [NOV/DEC2013] – MODEL

6. A tangent cam to drive a roller follower through a total lift of 12.5 mm for a

cam rotation of 75°. The cam speed is 600 rpm . The distance between cam

centre and follower centre at full lift is 45 mm and the roller is 20 mm in

diameter. Find the cam proportions and plot displacement, velocity and

acceleration for one full cycle. [NOV/DEC 2009]