session 23 notes

7/27/2019 Session 23 Notes

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KINEMATICS OF CAM

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CAM Definition- Cam is a mechanical member used for transmitting desired motion to a

follower by direct contact.

Cam may be rotating, reciprocating or oscillating where as the follower may be

reciprocating or oscillating.

Complicated output motions which are otherwise difficult to achieve can be easily

produced with the help of cam

The cam and follower have line or point contact

and coming under higher pair

Application: IC engine, automatic machines,

machine tools, paper cutting machine& textile machine

Necessary elements of cam mechanism are:

1. Cam: The driving member is known as cam

2. Follower: The driven member is known as follower

3. Frame: It supports the cam and guides the follower 2


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Examples for cam

In IC engines to operate the inlet and exhaust valves


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Classification of Cams

Cams are classified according to :

(a) Shape

(b) Follower movement (c) manner of constraint of the follower

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(a)According to Shape

1. Wedge and Flat Cams 2. Radial or Disc Cams 3. Spiral Cams

4. Cylindrical Cams 5. Conjugate Cams 6. Globoidal Cams

7. Spherical Cams

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(b)According to Follower movement1. Rise-return-rise (RRR) 2. Dwell Rise-return Dwell (DRRD)

3. Dwell-rise-dwell-return-Dwell (DRDRD) 4. Dwell-rise-dwell (DRD)

(c)According manner of constraint of the follower1. Pre-loaded Spring Cam 2. Gravity Drive Cam

3. Positive Drive Cam


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1.Wedge and Flat Cams

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2. Radial or disc cams


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6. Globoidal Cams

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7.Spherical cams


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(b)According to Follower movement1. Rise-return-rise (RRR) 2. Dwell Rise-return Dwell (DRRD)

3. Dwell-rise-dwell-return-Dwell (DRDRD) 4. Dwell-rise-dwell (DRD)


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(c)According manner of constraint of the follower1. Pre-loaded Spring Cam 2.Gravity Drive Cam


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3. Positive-drive cam


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Types of Follower

Cams are classified according to :

(a) Shape

(b) movement

(c) location of line of movement

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1.Knife edge follower

2. roller follower

3. mushroom follower

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(b)According to movement1. Reciprocating follower

2. oscillating follower

(c)According to location of line of movement1. Radial follower

2. offset follower


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(a)according to shape:1. Knife-edge Follower 2. Roller Follower

3. Flat or Mushroom Follower


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(b) according to movement

1. Reciprocating follower 2. oscillating follower


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Follower

Trace

point

Pressure angle()

(maximum)

Radial cam nomenclature


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Follower

Trace

point

Pressure angle()

(maximum)

Radial cam nomenclature


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Terminology of a radial cam with reciprocating follower is shown.

1. Cam profile

Surface of cam which comes into contact with follower is known as cam profile

2. Base circle

Smallest circle that can be drawn to the cam profile. Radius of base circle known

as least radius of cam

3. Trace pointIt is reference point of follower to trace the cam profile. In knife edge follower

knife edge itself is tracing point. In roller follower, centre of roller is the tracing

point.

4. Pitch curveLocus of path of tracing point. For the purpose of drawing cam profile, it is

assumed that cam is fixed and the follower rotates around it.

5. Prime circle

The smallest circle drawn tangent to the pitch curve.19


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6. Pressure angle ()

It is angle between the direction of follower motion and a normal to the pitch

curve. This angle is very important. It represent steepness of cam profile.

7. Pitch point

It is the point on the pitch curve at which the pressure angle is maximum

8. Pitch circle

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

9. Cam angle

It is the angle of rotation of cam for a defined displacement of follower

10.Lift or stroke

It is the maximum displacement of the follower from the base circle of the cam.

Also called as throw of the cam

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Di l t Di


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Displacement Diagram

Movement of the trace point against the rotation of cam through an angle is called

displacement diagram.

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It represents angular displacement of cam and represents the corresponding angular

or linear displacement of follower from its initial position

X-axis displacement of cam

Y-axis displacement of follower

Angle of cam rotation () ((one full rotation3600 ))

Followerd

isplacement(h)


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1. Angle of ascent (or) out stroke angle (or) rise (0)

Angle of rotation of cam from the position when follower begins to rise till it

reaches its highest position.

2. Angle of dwell(d)

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

the highest or lowest position.

3. Angle of descent (or) return stroke angle (or) fall (R)

It is angle through which the cam rotates during the time the follower return to

initial position

4. Angle of action

It is the total angle moved by the cam during its rotation, between the beginning

of rise of follower and end of return of follower.


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Displacement Diagram for follower motion

Motion of the fol lower

During its travel follower may have one of the following motion

1. Uniform velocity motion

2. Simple harmonic motion (SHM)

3. Uniform acceleration and retardation (or) parabolic motion

4. Cycloidal motion

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1. Uniform velocity motion

The follower moves with uniform

velocity during its rise and fall, the

slope of the displacement curve

must be constant.

Velocity , v= constant

Acceleration,

a=0 (constant velocity),

a=dv/dt =0

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S (S )


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2. Simple harmonic motion (SHM)

When a body rotates on a circular

path with uniform angular

velocity, its projection on the

diameter will have simple

harmonic motion.

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h

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3. Uniform acceleration and retardation (or) parabolic motion

There is a acceleration in the first

half of follower motion where it is

deceleration during second half.

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4 C l id l ti


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4. Cycloidal motion

There is a acceleration in the first half of

follower motion where it is deceleration during

second half.

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h

4 C l id l ti


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4. Cycloidal motion

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h

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