Study the cam profiles used in manufacturing machines

8/8/2019 Study the cam profiles used in manufacturing machines

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TERM PAPER

KINEMATICS OF MACHINE

MEC 202

TOPIC: Study the cam profiles used in manufacturing machines

Date of allotment: 14/10/2010

Date of Submission: 15/11/2010

Submitted to: Submitted by:

Mr. Kamlesh Mishra Name: Sachin Rana

(Deptt. Of Mechanical) Reg. No: 10904976

Section: K4901

Roll No: RK 4901 B35


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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. Kamlesh,

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.

Sachin


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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.


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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 motion of the engineand 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


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automata. The cam and camshaft appeared

in European mechanisms from the 14th

century.

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:-


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1. Wedge & Flat Cams: A wedge

generally has a 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.

6. Globoidal Cams: A globoidal cam can

have two types of surfaces, convex or

concave.


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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 contactbetween 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 ofthe cam & the return by the force of

gravity or due to the weight of the

cam, the cam is known as the gravity

cam.

TYPES OF FOLLOWERS

Cam 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


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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 makesthe 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. 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


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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 drawnbythe 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 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


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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.

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

().Construct the plate cam profile

Step1: construct the prime circle with radius

r0.


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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

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


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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

1. http://www.google.co.in/images?

hl=en&q=cam+profiles&um=1&ie=

UTF-

8&source=univ&ei=2yXcTMeNOM

WecPfB5MQG&sa=X&oi=image_result_group&ct=title&resnum=3&ved

=0CDQQsAQwAg&biw=1024&bih

=606

2. http://www.technologystudent.com/c

ams/cam2.htm

3. http://hdabob.com/Cam

%20Profiles.htm

4. http://www.marposs.com/product.ph

p/eng/camshaft_profile_automatic_in

spection

5. http://www.technologystudent.com/c

ams/cam2.htm

6. http://www.maplesoft.com/applicatio

ns/view.aspx?SID=32587

7. http://www.cs.cmu.edu/~rapidproto/

mechanisms/chpt6.html

8. http://www.wisegeek.com/what-is-a-

camshaft.htm

9. http://mechprojects.blogspot.com/20

08/01/technical-terms-used-in-cam-

diagram.html


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Study the cam profiles used in manufacturing machines