study the cam profiles used in manufacturing machines
TRANSCRIPT
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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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10..www.howstuffworks.com ...
cams Types of Cams
www.compcams.com