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Acknowledgements
“It is not possible to prepare a project report without the
assistance & encouragement of other people. This one is
certainly no exception.”
On the very outset of this project, we would like to extend our
sincere and heartfelt obligation towards all the personages who
have helped us in this endeavor. Without their active guidance,
help, cooperation and encouragement, we would not have made
head way in the project. First and foremost, we would like toexpress our sincere gratitude to our project guide, Prof. r. !ajid
kamran. We were privileged to experience a sustained
enthusiastic and involved interest from his side. "his fuelled our
enthusiasm even further and encouraged us to boldly step into
what was a totally dark and unexplored expanse before us. #e
always fuelled our thoughts to think broad and out of the box. We
would also like to thank our parents, friends and class mates for
their encouragement and all their help at times of need. We would
also like to thank our teachers and other sta$ for their
cooperation in our research.
"hanking you,
#amid %a&a, 'sama (ja& and group
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Abstract
"he major objective of our project is to design a reciprocating arm
and to move the metal piece in to and fro motion and to stop it for
a speci)ed time period at the end of stroke length. "his project isbased on our study of machinery and *uid mechanics. (t is not an
easy task as there are many methods and experiments to do the
same job. +s an engineer our task is to design the thing with
maximum eciency and least cost. "he reciprocating motion
means a motion in which the body moves about a mean position
in to and fro motion. "here are many methods to do the job like
scotch yoke mechanism, rack and pinion mechanism, speci)ed
gear trains, worm and worm wheel mechanism, -uick returnmechanism, slider crank mechanism. "hen there are many other
mechanisms based on motion of *uid like pneumatic arms and
hydraulic arms. "he mechanism we chose was scotch yoke
mechanism to simplify our design.
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ontents/. (ntroduction..........................................................................................................0
/1 Purpose.............................................................................................................0
21 3ack ground......................................................................................................0
41 5ethod of investigation....................................................................................0
61 !cope................................................................................................................7
2. 5ethodology........................................................................................................8
(ntroduction to design................................................................................................ 9
5echanism and 5achine.........................................................................................9
egrees of Freedom and :rubler;s riterion of Plane 5echanism...........................<
!uitable Project esign 5echanisms.......................................................................<ack and pinion............................................................................................../=
!cotch "oke....................................................................................................../=
!cotch "oke with dwell at one end..............................................................//
!cotch yoke with dwell at both ends...........................................................//
#neumatic arm................................................................................................/2
$uick return mechanism.............................................................................../2
%orm and worm wheel................................................................................../4
!elected design...................................................................................................../6
Adantages...................................................................................................... /6
'raw backs...................................................................................................... /6
"ime plan for project................................................................................................ /6
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( Introduction
(.(#urpose "his is an initial report of *uid mechanics project of designing and
manufacturing a reciprocating arm. "his report will cover all the
research and methods of production used to ful)ll the objective.
(.)*ack ground%eciprocating motion >a motion in which a body moves to and fro
about its mean position1 is a very important mechanism and it
had been a permanent source of an engineer;s interest from the
very start. (t is serving engineers well with its di$erent
applications including reciprocating internal combustion engines,
knuckle joints in production molds, and lead screws in lathe
machines, worm and worm wheels to change speed of motion and
many others.
"he basic task looks simple that we just have to move a body in
to and fro motion using any mechanism of our choice. 3ut from
engineering point of view it is not as simple as it seems. First youhave to analy&e your system and it need then you have to collect
data about all the designs currently available. +fter this you need
to make the very important decision of which design you are
going to choose and then come the testing stage if your design
fail at this stage you have to re analy&e all that you have done so
far in the project and that is what we will be doing during the task
assigned to us.
"here are many designs and mechanisms devised to perform
reciprocating motion as discussed earlier as well. !ome of the
designs we considered are Four !top %eciprocating 5otion, One
%otation "wo !troke, and %ack +nd Pinion %eciprocate, %ack +nd
Pinion, !cotch ?oke, !cotch ?oke well at 3oth @nds, am
5echanism with Pause, %otary to Ainear, %eciprocate, "raversing
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#ead !haper, !cotch ?oke with dwell at one end. 3ut to make our
design simple and economical we chose scotch yoke mechanism.
(.+,ethod of inestigation
(n order to make the best product we can. We will study articles,scienti)c journals, watch videos and animations on this topic. "he
complete project will be analy&ed using data available on internet
and in scienti)c papers. !ome other books will also be used to
make references.
(.-!cope(n order to understand the project one must know about its
establishment, working and method of working. We made our
best e$orts in this regard and studied the project from its base.
"he things that interested us were majorly di$erent mechanisms
used to perform reciprocating motion and its wide ranged
applications. "he project will be analy&ed comprehensively and
everything from surface roughness to time of stroke and
mechanism of automating it will be discussed.
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) ,ethodology(n order to understand the problem comprehensively background
study has been done and some of many mechanisms have been
short listed. "hese designs will now be further analy&ed and the
best one will be selected to do the job.
!o far the best design is scotch yoke mechanism but in case of
any problems or design failure other options like -uick return
mechanism, gear trains worm and worm wheel mechanism, slider
crank mechanism will also be analy&ed.
alculations will be done and experiments will be performed in
coming weeks to select and manufacture the best possible
product.
'p till now we have read some research papers and analy&ed
some results of previous experiments performed by other
engineers in the past.
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+ Introduction to design
+.(,echanism and ,achine
(n daily life, we encounter many machines which receive energy
and transform it into useful work. @very machine consists of no. of
parts which moves relative to one another these parts are called
kinematic links or simply links or elements. when these links are
connected together they form pairs. (f the motion of the pair is
completely or successfully constrained >only one type of motion is
allowed1 it is called kinematic pair. Bow if four of more kinematic
pairs are connected in such a way that last link is joined to )rst
link to transmit motion it is called kinematic chain.
+ mechanism is de)ned as a kinematic chain in which one of the
link is )xed. (t may be used to transmit power some kind of
motion or transform motion e.g. engine indicator, type writer etc.
5echanism can be spatial >three plane1 or plane mechanism
>single plane1 no. of planes in which links can move.
+ plane mechanism which consists of four links is called simple
mechanism if the no. of links is greater than four the mechanismis called compound mechanism.
+ mechanism becomes a machine if it is used to transmit power
and work. @xample of use of mechanism as is shown in )gure >/1
below. Figure >a1 is an inversion of slider crank mechanism that is
used in engine to transmit power as shown n )gure >b1
Fig. b) piston and crank Fig. a) inversion of slider
crank
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+.)'egrees of reedom and /rubler0s 1riterion of#lane ,echanism
(n design of mechanisms degrees of freedom is a very important
concept. (n mechanics; degrees of freedom are de)ned as Bo. of
independent motion re-uired to completely de)ned the state of
motion of a body. (n 2 there are three degrees of freedom >one
rotational and two translational1 and in 4 there are six degrees
of freedom, in total, >three rotational and three translational1 for
completely unconstrained motion of bodies.
(n mechanics of machines, OF or mobility or movability of
mechanism is de)ned as Bo. of independent input motion leading
to single useful follower motion. "he degrees of freedom of plane
mechanism is given by Cut&bach criterion.
N =3 (l−1)−2 j−h
e-u./
Where B D no. of OF, A D no. of links, j D no. of lower pairs
>having surface contact1, # D Bo. of higher pairs >having line
contact1.
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For simple plane mechanism with / degree of freedom and no
higher pairs above e-uation becomes
1=3 ( l−1 )−2 j−0
e-u. 2
3 l−2 j−4=0
e-u.4
@-u. 4 is known as :rubler;s criterion for plane mechanisms with
constrained motion. "he simplest possible mechanisms based on
this criterion are slider crank and four bar linkage mechanisms.
+.+!uitable #roject 'esign ,echanisms "o start a detailed discussion on our project we must make clear
to our readers what are we trying to do in this project. First let us
discuss what is reciprocating motion which we are trying to
achieve. +ccording to Wikipedia article available
“Reciprocating motion, also called reciprocation, is a repetitive
up-and-down or back-and-forth linear motion. It is found in a wide
range of mechanisms, including reciprocating engines and
pumps. The two opposite motions that comprise a single
reciprocation ccle are called strokes!.
+ccording to Oxford dictionary
“"#f a part of a machine move backwards and forwards in astraight line.! Aike a reciprocating blade.
"o achieve this motion there are many di$erent mechanism
invented by di$erent scientists with the passage of time the oneswhich are under our discussion are discussed below
+.+.( ack and pinion(t is an assembly pair of two gears one is circular and other is *at
bar with teeth.
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"he circular gear rotates over the *at bar and this causes the
reciprocating motion. "he rack and pinion arrangement is
commonly found in the steering mechanism of cars or other
wheeled, steered vehicles.
+.+.) !cotch "oke "he !cotch ?oke is a mechanism for converting the linear motion
of a slider into rotational motion or viceEversa. "he piston or other
reciprocating part is directly coupled to a sliding yoke with a slot
that engages a pin on the rotating part.
+.+.+ !cotch "oke with dwell at one end(t is a modi)ed form of scotch yoke mechanism. (n this
mechanism the reciprocating part is made to stop for a brief
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period of time at the end of the stroke due to a dwell in scotch as
shown in )gure below.
+.+.- !cotch yoke with dwell at both ends
(t is a further modi)ed form of simple scotch yoke. (n this
mechanism there is dwell at both ends of the scotch and due to
this the reciprocating part stays for a short while at both ends the
mechanism is shown in )gure below
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+.+.2 #neumatic arm(t is a hydraulic arm which does the reciprocating motion due to
the *uid present in it there is simple piston cylinder arrangement
to do the job.
+.+.3 $uick return mechanism "his is also a suitable mechanism to perform reciprocation motion
but has its own limitations
+.+.4 %orm and worm wheel(n this mechanism there is a cylindrical gear known as worm. (t
has tapered threads on it. (t rolls over a circular gear to produce
reciprocating motion. "he assembly is shown in )gure below
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:ears assembly following gear assembly can also be used to
perform the reciprocating motion
+.-!elected design+fter considering our need and analy&ing above given designs we
conclude that the mechanism most suitable for our design is
scotch yoke with dwells at both ends.
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Bow let us tell you some of the advantages and disadvantages of
the mechanism
+.-.( Adantages
#igh tor-ue output with a small cylinder si&e. Fewer moving parts. !moother operation. #igher percentage of the time spent at top dead center
>dwell1 improving engine eciency. (n an engine application, elimination of joint typically served
by a wrist pin, and near elimination of piston skirt and
cylinder scung, as side loading of piston due to sine of
connecting rod angle is eliminated.
Bow some of the draw backs are
+.-.) 'raw backs
%apid wear of the slot in the yoke caused by sliding friction
and high contact pressures. Aesser percentage of the time spent at bottom dead center
reducing blowdown time for two stroke engines.
- Time plan for project
"asks Wee
k /
Week
2
Week
4
Week
6
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Week
7Aiterature
reviewesign
analysisFabrication
+utomation "esting of
designPresentation