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TERM PAPER

KINEMATICS OF MACHINE

MEC 202

TOPIC: Study the cam profiles used in manufacturing machines

Submitted to: Submitted by:

Mr. Sanjay Singh Samant Name: Hazrat Belal(Deptt. Of Mechanical) Reg. No: 10901869

Section: B4912

Roll No: A05

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ACKNOWLEDGEMENT

To many individuals I am indebted good counsel and assistance in

various ways in this respect one of my sincerest thanks to Mr. SANJAY

sir, Sir of Lovely Professional University, Phagwara, for their kind

cooperation and able guidance.

I owe a deep sense of ineptness of my pureness that has been source of

inspiration in every work of my life.

I deeply express our ineptness and thanks to all my faculty member and

friends for there in valuable, guidance which enable me to bring out this

project in a presentable manner.

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ABSTRACT

The term paper presents the analysis of various cam profiles used in manufacturing machines. It focuses mainly on the types of cam and its followers and how are they classified according to their shape, manner of movement and motion. It also focuses on the graphical representation of the cam profile, i.e., how are they constructed and what are the procedure to construct a cam profile and how they can be used in a machine.

INTRODUCTION

A cam is a mechanical member

used to impart desired motion to a

follower by direct contact. A cam

is a rotating or sliding piece in a

mechanical linkage used

especially in transforming rotary

motion into linear motion or vice-

versa. The cam may be rotating or

reciprocating whereas the

followers may be rotating,

reciprocating or oscillating. It is

often a part of a rotating wheel

(e.g. an eccentric wheel) or shaft

(e.g. a cylinder with an irregular

shape) that strikes a lever at one or

more points on its circular path.

The cam can be a simple tooth, as

is used to deliver pulses of power

to a steam hammer, for example,

or an eccentric disc or other shape

that produces a smooth

reciprocating (back and forth)

motion in the follower, which is a

lever making contact with the

cam.

The cam can be seen as a device

that translates from circular to

reciprocating (or sometimes

oscillating) motion. A common

example is the camshaft of an

automobile, which takes the rotary

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motion of the engine and

translates it into the reciprocating

motion necessary to operate the

intake and exhaust valves of the

cylinders. The opposite operation,

translation of reciprocating motion

to circular motion, is done by a

crank. An example is the

crankshaft of a car, which takes

the reciprocating motion of the

pistons and translates it into the

rotary motion necessary to operate

the wheels. Cams can also be

viewed as information-storing and

-transmitting devices.

A cam & the follower

combination belong to the

category of higher pairs.

Necessary elements of a cam

mechanism are

● A driver member known as the

cam

● A driven member called the

follower

● A frame which supports the cam

& guides the follower

An early cam was built into

Hellenistic water-driven automata

from the 3rd century BC. The use

of cams was later employed by Al-

Jazari who employed them in his

own automata. The cam and

camshaft appeared in European

mechanisms from the 14th

century.

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The binary cam is a design for the

pulley system of a compound bow.

Craig Yehle, director of research

and development at Bowtech

Archery, received a patent for the

design on December 11, 2007.

Bowtech started equipping its

bows with the new cam design in

the 2005 model year.

The binary cam is described as a

modified twin cam setup where

each cam is slaved to the other via

a loop of string connecting the two

cams. This is contrasted with a

typical twin cam setup where the

ends of the bowstring are

physically anchored onto each of

the bow limbs.

As a twin cam system relies on

each cam rotating independently,

based solely on the force of the

string and the resistance of the

bow limbs being absolutely

symmetrical, there is room for a

twin cam system to "lose tune"

through wear and tear, string

stretch, or just general age. The

effect of a detuned twin cam bow

is that the two cams rotate out of

sync with each other, causing the

bowstring to accelerate in two

alternating directions upon release.

This causes a number of adverse

consequences, the most obvious

being unsteady arrow flight.

The binary cam overcomes this by

'slaving' each cam to the other; as

one cam is unable to rotate

without the direct equivalent

action of the other, the two rotate

in near perfect synchronization,

with any possible differences in

rotation automatically correcting

themselves as the shot cycle is

completed.

TYPES OF CAMS

Cams are classified according to

1) Shape,

2) Follower movement, &

3) Manner of constraint of the

follower.

According to Shape:-

1. Wedge & Flat Cams: A

wedge generally has a

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translational motion. The

follower can either translate or

oscillate. Spring is used to

maintain the contact between

the cam & the follower. The

cam is stationary & the

follower causes the relative

motion of the cam.

2. Radial & Disc Cams: A cam

in which the follower moves

radially from the centre of

rotation of the cam is known

as a radial or a disc cam.

3. Spiral Cams: A spiral cam is

a face cam in which a groove

is cut in the form of a spiral.

The spiral groove consists of

teeth which mesh with a pin

gear follower.

4. Cylindrical Cams: A cylinder

which has a circumferential

contour cut in the surface,

rotates about its axis.

5. Conjugate Cams: Conjugate

cams are a double-disc cam,

the two discs being keyed

together & are in constant

touch with the two rollers of a

follower.

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6. Globoidal Cams: A globoidal

cam can have two types of

surfaces, convex or concave.

7. Spherical Cams: In a

spherical, the follower

oscillates about an axis

perpendicular to the axis of

rotation of the cam.

According to follower

movement

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

R): In this, there is

alternate rise & return of

the follower with no

periods of dwells. 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 & return of the

follower after a dwell.

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 &

dwell & subsequently by

return & dwell.

According to Manner of

Constraint of the Follower

1. Pre-loaded spring cam: Is

used for the purpose of

keeping the contact

between the cam & the

follower.

2. Positive-drive cam:

Constant touch between

the cam & the follower is

maintained by a roller

follower operating the

groove of cam.

3. Gravity cam: If the rise of

the cam is achieved by the

rising surface of the cam &

the return by the force of

gravity or due to the

weight of the cam, the cam

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is known as the gravity

cam.

TYPES OF FOLLOWERSCam followers are classified

according to the

1. Shape

2. Movement &

3. Location of line of

movement.

According to shape

1. Knife-edge Follower:

Simple in construction.

However, its use is limited

as it produces a great wear

of the surface at the point

of contact.

2. Roller Follower: Widely

used cam follower & has a

cylindrical roller free to

rotate about a pin joint. At

low speed, the follower has

a pure rolling action, but at

high speeds, some sliding

also occurs.

According to Movement

1. Reciprocating Follower:

As the cam rotates, the

follower reciprocates or

translates in the guides.

2. Oscillating Follower: The

follower is pivoted at a

suitable point on the frame

& oscillates as the cam

makes the rotary motion.

According to Location of Line of

Movement

1. Radial Follower: The

follower is known as a

radial follower if the line

of movement of the

follower passes through

the center of rotation of the

cam.

2. Offset Follower: If the

line of movement of the

roller follower is offset

from the center of rotation

of the cam, the follower is

known as offset follower.

CAM PROFILES

DESIGN PRINCIPLE

The method termed kinematic

inversions is commonly used in

cam profile design. For example,

in a disk cam with translating

follower mechanism, the follower

translates when the cam turns.

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This means that the relative

motion between them is a

combination of a relative turning

motion and a relative translating

motion. Without changing this

feature of their relative motion,

imagine that the cam remains

fixed. Now the follower performs

both the relative turning and

translating motions. We have

inverted the mechanism

Cam Nomenclature

• Base circle: It is the

smallest circle tangent to

the cam profile (contour)

drawn from the center of

rotation of a radial cam.

• Trace point: It is the

reference point on the

follower to trace the cam

profile such as the knife-

edge follower and the

center of the roller of a

roller 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.

• Pressure angle: It

represents the steepness of

the cam profile, it is the

angle between the normal

to the pitch curve at a point

and the direction of

follower motion. It varies

in magnitude at all instants

of follower motion.

• Pitch point: It is the point

on the pitch curve at which

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pressure angle is

maximum.

• Pitch circle: It is the circle

passing through the pitch

point and concentric with

the base circle.

• Prime circle: The smallest

circle drawn tangent to

pitch curve is known as the

prime circle.

• Angle of Ascent

(outstroke): It is the angle

turned by cam during the

time of rise of follower.

• Angle of Dwell: It is the

angle turned by cam while

the follower remains

stationary at the highest or

lowest position.

• Angle of descent (Return

stroke): It is the angle

turned by cam when

follower returns to its

initial position.

• Angle of action: It is the

angle turned by cam during

beginning of rise and the

end of return of the

follower.

HIGH-SPEED CAMS

A real follower always has some

mass & when multiplied by

acceleration, inertia force of the

follower is obtained. This force is

always felt at the contact point of

the follower with the cam surface

& at the bearings. An acceleration

curve with abrupt changes exerts

abrupt stresses on the cam

surfaces & at the bearings

accompanied by detrimental

effects such as surface wear &

noise. All this may lead to an

early failure of the cam system.

Thus, it is very important to give

due consideration to velocity &

acceleration curves while

choosing a displacement diagram.

In low-speed applications, cam

with discontinuous acceleration

characteristics may not show any

undesirable characteristic, but at

higher speeds such cams are

certainly bound to show the same.

The higher the speed, the higher is

the need for smooth curves. At

very high speeds, even the jerk is

made continuous as well.

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LAYOUT OF CAM PROFILES

A cam profile is constructed on

the principle of kinematic

inversion, i.e., considering the cam

to be stationary & the follower to

be rotating about it in the opposite

direction of the cam rotation.

↓INVERSION

Graphical Representation of

Cam Profile

For the case of

reciprocating knife-edge

follower

Step1: divide the displacement-

diagram Abscissa into a number of

segments.

Step2: divide the prime circle into

Corresponding segments.

Step3: transfer distances, by

means of dividers, from the

displacement diagram directly

onto the cam layout to locate the

corresponding positions of the

trace point.

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Step4: draw a smooth curve

through these points. The curve is

just the required cam profile.

For the case of reciprocating offset roller follower

As shown in above figure, the

displacement diagram of the

follower is given, s=s

(φ).Construct the plate cam profile

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Step1: construct the prime circle

with radius r0.

Step2: construct the offset circle

with radius equal to the amount of

offset e.

Step3: divide the displacement-

diagram abscissa into a number of

segments.

Step4: divide the offset circle into

corresponding segments and

assign station numbers to the

boundaries of these segments.

Step5: construct lines tangent to

the offset circle from these station,

dividing the prime circle into

corresponding segments.

Step6: transfer distances, by

means of dividers, from the

displacement diagram directly

onto the cam layout to locate the

corresponding positions of the

trace point, always measuring

outward from the prime circle.

Step7: draw a smooth curve

through these points. The curve is

just the required cam profile.

UNDERCUTTING

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Sometimes, it may happen that the

prime circle of a cam is

proportional to provide a

satisfactory pressure angle, still

the follower may not be

completing the desired motion.

This can happen if the curvature of

the pitch curve is too sharp.

It can easily be observed

that the cam curve loops over

itself in order to realize the profile

of the pitch curve. As it is

impossible to produce such a cam

profile, the result is that the cam

will be undercut & become a

pointed cam. Now when the roller

follower will be made to move

over this cam, it will not be

producing the desired motion.

It may be observed that the

cam will be pointed if the radius

of the roller is equal to the radius

of curvature of the pitch curve.

Thus to minimum radius of

curvature of the cam profile, the

radius of curvature of the prime

circle must always be greater than

that of the radius of the roller.

CAMPRO ENGINE

The Campro engine is the first

automotive engine ever developed

together with Lotus by the

Malaysian carmaker, Proton. The

name Campro is short for Cam

Profiling. This engine powers the

Proton Gen-2, the Proton Satria

Neo, the Proton Waja Campro, the

Proton Persona as well as Proton's

future models. The Campro engine

is aimed to show Proton's ability

to make their own engines that

produce good power output and

meet newer emission standards.

All Campro engines

incorporate drive-by-wire

technology (specifically electronic

throttle control) for better response

eliminating the need for friction-

generating mechanical linkages

and cables.

REFERENCE

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1. http://www.google.co.in/images?hl=en&q=cam+profiles&um=1&ie=UTF-8&source=univ&ei=2yXcTMeNOMWecPfB5MQG&sa=X&oi=image_result_group&ct=title&resnum=3&ved=0CDQQsAQwAg&biw=1024&bih=606

2. http://www.technologystudent.com/cams/cam2.htm

3. http://hdabob.com/Cam%20Profiles.htm

4. http://www.marposs.com/product.php/eng/camshaft_profile_automatic_inspection

5. http://www.technologystudent.com/cams/cam2.htm

6. http://www.maplesoft.com/applications/view.aspx?SID=32587

7. http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt6.html

8. http://

www.wisegeek.com/what-

is-a-camshaft.htm