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ME 302 DYNAMICS OF ME 302 DYNAMICS OF MACHINERYMACHINERY

Cam Dynamics

Dr. Sadettin KAPUCU

© 2007 Sadettin Kapucu

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Introduction to Cam MechanismsIntroduction to Cam Mechanisms

A CAM changes the input motion, which is usually rotary motion (a rotating motion), to a reciprocating motion of the follower.

They are found in many machines. A CAM has two parts, the FOLLOWER and the CAM PROFILE.

http://www.technologystudent.com/cams/cam1.htm

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Introduction to Cam MechanismsIntroduction to Cam Mechanisms

ONE CYCLE One rotation/revolution of the cam. DWELL When the cam rotates but the follower does not rise or fall.  THE RISE That part of the cam that causes the follower to rise.THE RETURN That part of the cam that causes the follower to fall.

http://www.technologystudent.com/cams/cam1.htm

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Classification of cam mechanismsClassification of cam mechanisms

1- Joint configurations

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Classification of cam mechanismsClassification of cam mechanisms2- Cam Shape

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Classification of cam mechanismsClassification of cam mechanisms3- Costraint on the Follower

Force closed Form Closed

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Classification of cam mechanismsClassification of cam mechanisms4- Modes of input/output and Follower arrangements

In-line followerOff-line follower

Rot

atin

g fo

llow

er

Tra

nsla

ting

follo

wer

Roller follower Spherical-faced follower Flat-faced follower

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Cam DesignCam Design

Cam design

1- Low Speed Cam: Kinematic requirement

2- High Speed Cam: Not only kinematic requirement but also kinetics should be taken into consideration.

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Cam MotionsCam Motions

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Cam MotionsCam Motions

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Motion ProfilesMotion Profiles1- Linear Motions

0

H

Hs )(

HV V

a

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Motion ProfilesMotion Profiles2- Simple Harmonic Motions

s

H

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Motion ProfilesMotion Profiles2- Simple Harmonic Motions

cos12

1Hs

sin2

1 Hv

cos2

12

Ha

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Motion ProfilesMotion Profiles3- Constant Acceleration Motion

s

H

1 2 3 4 5 6 7

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Motion ProfilesMotion Profiles3- Constant Acceleration Motion

2

2

Hs

24

Hv

2

4

Ha

2

121

Hs

14Hv2

4

Ha

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Motion ProfilesMotion Profiles4- Cycloidal Motion

Çapı H/

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Motion ProfilesMotion Profiles4- Cycloidal Motion

2

sin2

1Hs

2

cos1H

v

2

sin42

2Ha

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Motion ProfilesMotion Profiles5- Trapezoidal Acceleration Motion

Parabolik eğriye göre titreşimi ve gürültüsü daha az, aşınma ve şok etkisi daha uygun

Üçünü derece hareket veya sikloidal harekete göre daha küçük kam ebatları ve daha düşük ivme değerleri elde edilir.

Bağlama açısı, aynı taban dairesi için üçüncü derece hareket eğrisine nazaran daha iyidir.

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Motion ProfilesMotion Profiles6- Third Order Polynomial Motion

3

4

Hs2

12

Hv

2

24Ha

3

141

Hs

14Hv

1242

Ha

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Motion ProfilesMotion Profiles7- Third Order Polynomial Motion 2

232

Hs

16Hv

2162

Ha

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Motion ProfilesMotion Profiles8- 3-4-5 Polynomial Motion

23

61510

Hs

22

2130

Hv

22

23160

Ha

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Hareket EğrileriHareket Eğrileri

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Eccentric Cam MechanismsEccentric Cam MechanismsAn eccentric cam is a disc with its centre of rotation positioned ‘off centre’. This means as the cam rotates the flat follower rises and falls at a constant rate. This type of cam is the easiest to make and yet it is one of the most useful.

http://www.technologystudent.com/cams/cam10.htm

The diagrams (1 to 7) seen below show the cam rotating in an counterclockwise direction. As it rotates it pushes the flat follower upwards and then allows it to drop downwards. The movement is smooth and at a constant speed.

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Eccentric Cam MechanismsEccentric Cam Mechanisms

e

k

y

m

y

m

NA NB

Fc Fs=k(y+d)

mg

coseey

tey sin

tey cos2

ymF

)( ykFFFF csc

)(cos)( 2 ektkmeFc

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Mathematical ModelsMathematical ModelsCross section showing the overhead valve in an automotive engine and a

mathematical model

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Mathematical ModelsMathematical ModelsCross section showing the overhead valve in an automotive engine and a

mathematical model

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Mathematical ModelsMathematical ModelsCross section showing the overhead valve in an automotive engine and a

mathematical model

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Motion ProfilesMotion Profiles

Shedding Mechanism

em

eceky

x

Model of the shedding mechanism

What type of profile should be used for high speed shedding??

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Motion ProfilesMotion Profiles

em

eceky

x

Model of the shedding mechanism

Simple Harmonic

Motion

Cycloidal Profile

Proposed Profile

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

No

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ized

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1.Cycle 2.Cycle

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1.Cycle 2.Cycle

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over

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