scotch yoke mechanis1
TRANSCRIPT
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SCOTCH YOKE MECHANISM
The Scotch yoke (also known as slotted link mechanism is a reciprocating motion
mechanism, converting the linear motion of a slider into rotational motion, or vice
versa. The piston or other reciprocating part is directly coupled to a sliding yokewith a slot that engages a pin on the rotating part. The location of the piston versus
time is a sine wave of constant amplitude, and constant frequency given a constant
rotational speed.
THEORY:
Scotch yoke is a mechanism used to convert rotary motion into Sliding motion.
This mechanism is obtained from an inversion of the double Slider crank chain.
Double slider crank chain is a four-bar kinematic chain having sliding !airs and turning pairs such that two pairs of the same kind are ad"acent. The general version
of the double slider crank chain is shown in fig. #. two Die-blocks, ! $ %, slide
along slots in a frame, and the pins ! $ % on the Die-blocks are connected by a
link !%
Scotch &oke 'echanism
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.
sam id)*+ codes)*true*
This inversion is obtained by fiing one of the sliders. /efer fig. . let Slider block
0p1 be fied. 2ink !% may then rotate relative to die blocks about The pins ! $ %.
thus link !% can rotate with pin ! as centre, and will therefore 3ause the frame to
reciprocate along the ais passing through !, slider block 0%1 will also reciprocate
in its slot. The stroke of the frame will depend upon the length of link !% and will
be double the length !%.
Description of the model:
4 model of scotch yoke mechanism is to be used for study. 4 diagram of the 'odel
is shown in fig .+. The model consist of a slider plate guides 5# and 5 'ounted
on the base plate of the model. The slider plate carries a slot 46 in which a slider
block 0%1 as centre, and drives the slider block %. arm 7/. the 4rm 7/ is free to
rotate about point 071 as centre, and drives the slider block 0%1. The position of
point 0/1 can be changed by selecting one of the four holes provided on the arm7/ and shifting the screw to the particular hole. The
3rank 7/ is further rigidly linked to a handle which is used to provide manual
/otation to the link, and thereby impart motion to the mechanism. 4n etension To
the rotating arm 7/ is provided which carries a pencil to trace the movement 7f
the arm.
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Prec!tion:
#. 8andle the model with care and attention. The model should not be
mishandled
. 9t should not be dismantled, unless for a specific purpose and then also,only
with the permission of the lab 9:c.
;. The moving parts of the model must be lubricated as and when necessary.
+. Defect,if any, noticed in the model must be brought to the attention of the
2ab 9:c immediately.
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INTROD#CTION
'ulti-operation machine as a research area is motivated by questions that arise in
industrial manufacturing, production planning, and computer control. 3onsider a large
automotive garage with speciali>ed shops. 4 car may require the following work, replace ehaustsystem, align wheels, and tune up. These three tasks may be carried out in any order. 8owever,
since the ehaust system, alignment, and tune-up shops are in different buildings, it is impossible
to perform two tasks for a car simultaneously. ?hen there are many cars requiring services at the
three shops, it is desirable to construct a service schedule that takes the least amount of total
time.
$%$ Scotch Yo&e Mechnism
The Scotch yoke is a mechanism for converting the linear motion of a slider into
rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a
sliding yoke with a slot that engages a pin on the rotating part. The shape of the motion of the
piston is a pure sine wave over time given a constant rotational speed.
http://en.wikipedia.org/wiki/Pistonhttp://en.wikipedia.org/wiki/Yokehttp://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Yokehttp://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Rotational_speedhttp://en.wikipedia.org/wiki/Piston
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'i(!re $%$ Sectionl )ie* of Scotch +o&e mechnism
'i(!re $%, 'ront )ie* of Scotch Yo&e Mechnism
$%, Constr!ction
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The scotch yoke mechanism is constructed with iron bars. 8ere the crank is made in
some length and the yoke is also made using the same material. 9t is noted that the minimum
length of the yoke should be double the length of the crank. The crank and yoke is connected
with a pin. 9ron bars are welded to both sides of the yoke to get the reciprocating motion. The
yoke with the iron bars is fied on the display board with the help of c clamp. @ow the crank is
welded to the end of the shaft of the motor. @ow the pin on the crank is connected to the yoke.
The pin used to connect yoke and crank is a bolt.
$%- .or&in( principle
?hen the power is supplied to the #v Dc motor, shaft and crank attached to the shaft start
rotating. 4s the crank rotates the pin slides inside the yoke and also moves the yoke forward. ?hen the
crank rotates through in clockwise direction the yoke will get a displacement in the forward direction. The
maimum displacement will be equal to the length of the crank. ?hen the crank completes the net of
rotation the yoke comes back to its initial position. Aor the net of rotation, yoke moves in the backward
direction. ?hen the crank completes a full rotation the yoke moves back to the initial position. Aor a
complete rotation of crank the yoke moves through a length equal to double the length of the
crank. The displacement of the yoke can be controlled by varying the length of the crank.
S37T38 &7BC 'C384@9S'
Scotch yoke is a mechanism for converting the linear motion of a slider into rotational
motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke
with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure
sine wave over time given a constant rotational speed. The double slider crank mechanism is a
mechanism having two sliding pairs and two turning pairs. Scotch yoke mechanism is formed
when one of the two sliding pairs in a double slider crank mechanism is fied. 9t has got two
turning pairs, one sliding pair and a fied link.
37@ST/3T97@
The scotch yoke mechanism is constructed with iron bars. 8ere the crank is made in
some length (say
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motion. The yoke with the iron bars is fied on the display board with the help of c clamp. @ow
the crank is welded to the end of the shaft of the motor. @ow the pin on the crank is connected to
the yoke. The pin used to connect yoke and crank is a bolt. The whole setup displayed in a
plywood board.
?7/B9@5
?hen the power is supplied to the #v dc motor, shaft and crank attached to the shaft
start rotating. 4s the crank rotates the pin slides inside the yoke and also moves the yoke
forward. ?hen the crank rotates through in clockwise direction the yoke will get a displacement
in the forward direction. The maimum displacement will be equal to the length of the crank.
?hen the crank completes the net of rotation the yoke comes back to its initial position. Aor
the net of rotation, yoke moves in the backward direction. ?hen the crank completes a full
rotation the yoke moves back to the initial position. Aor a complete rotation of crank the yoke
moves through a length equal to double the length of the crank. The displacement of the yoke
can be controlled by varying the length of the crank.
4DF4@T45CS
The advantages compared to a standard crankshaft and connecting rod setup are=
G Aewer moving parts.
G Smoother operation.
G 8igher percentage of the time spent at top dead center (dwellE improving theoretical
engine efficiency of constant volume combustion cycles, though actual gains have not been
demonstrated.
G 9n an engine application,use of connecting rod is eliminated when compared to slider
crank mechanism and thus reducing the vibrations produced on the connecting rod
D9S4DF4@T45CS
The disadvantages are=
G /apid wear of the slot in the yoke caused by sliding friction and high contact pressures.
G 9ncreased heat loss during combustion due to etended dwell at top dead center offsetsany constant volume combustion improvements in real engines.
G 2esser percentage of the time spent at bottom dead center reducing blow down time for
two stroke engines, when compared with a conventional piston and crankshaft mechanism.
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4!!2934T97@S
This setup is most commonly used in control valve actuators in high pressure oil and gas
pipelines.
9t has been used in various internal combustion engines, such as the 6ourke engine,SyTech engine, and many hot air engines and steam engines.
9n internal combustion engines, scotch yoke mechanism is connected to the piston instead
of using the slider crank mechanism. 9t results in elimination of connecting rod which reduces
the vibrations caused in the connecting rod. 9t has got etended dwell times. Cperiments have
shown that etended dwell time will not work well with constant volume combustion (7tto,
6ourke or similarE cycles. 5ains might be more apparent using a stratified direct in"ection (diesel
or similarE cycle to reduce heat loss
37@32S97@
The scotch yoke mechanism is made and its advantages and disadvantages are discussed.
9ts motion characteristics are studied. 9t is concluded that this mechanism is a good choice to
convert rotating motion into reciprocating motion because of fewer moving parts and smoother
operation. 9t can be used in direct in"ection engines like diesel engines.
The Scotch +o&e is mechnism for converting the linear motion of a slider into rotationalmotion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke
with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure
sine wave over time given a constant rotational speed.
Scotch/+o&e mechnism, pictured in Aig. functions in a manner similar to that of the simplecrank mechanism ecept that its linear output motion is sinusoidal. 4s wheel 4, the driver,
rotates, the pin or roller bearing at its periphery eerts torque within the closed yoke 6H this
causes the attached sliding bar to reciprocate, tracing a sinusoidal waveform. !art a shows thesliding bar when the roller is at IJK, and part b shows the sliding bar when the roller is at JK.
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Applictions
This mechanism is most commonly used in control )l)e ct!tors in hi(h press!re oil nd
(s pipelines. 4lthough not a common metalworking machine nowadays, crude shapers can usea Scotch +o&e. 4lmost all those use a .hit*orth lin&(e, which gives a slow speed forward
cutting stroke and a faster return. 9t has been used in various internal combustion engines, suchas the 6ourke engine, SyTech engine, and many hot air engines and steam engines.
The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational
motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke
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with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure
sine wave over time given a constant rotational speed.
This mechanism is an inversion of the do!0le slider crn& mechnism% The inversion is
obtained by fiing either the link # or link ;. 9n Aig, link # is fied. 9n this mechanism, when
the link (which corresponds to crankE rotates about 6 as centre, the link + (which correspondsto a frameE reciprocates. The fied link # guides the frame.
7ther inversions of the double slider crank mechanism include 7ldham coupling and elliptical
trammel.
Histor+
• This linkage is being called by a Scotsman in #LMN a Ocrank and slot-headed sliding rodP
6ut now it is known as a Scotch yoke because, in 4merica at least, a OScotchO was a
slotted bar that was slipped under a collar on a string of well-drilling tools to support
them while a section was being added
• 9n #N+J /ussell 6ourke applied this mechanism to the internal combustion engine called
6ourke ;J engine
SIMP1E HARMONIC MOTION! )
Suppose crankshaft is rotating
at an angular velocity ‘Ω’.
9f r is the radius of the crank then,
Tangential velocity, v= ‘rΩ’ .
Arom the mechanism we have the following relationH
3omponent of tangential velocity in &-direction is given byH
u ) /eciprocating velocity of -Slot.
9f α is the angle made by the tangential velocity with Q-4is at any point of time,
α
x-axis
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3omponent of tangential velocity in & direction is u = rΩsinα.
u = v.sinα
So, velocity of -Slot) rΩsinα.
4s a result, Felocity of -Slot is a sine function of α.
@ow as we know,α is directly proportional to time. Thisimplies velocity of -Slot is a sine
function of time. 8ence, the motion of -Slot is a simple harmonic motion.
Ad)nt(e of SHM
The sinusoidal motion, cosinusoidal velocity, and sinusoidal acceleration (assuming constant
angular velocityE results in smoother operation of the mechanism.
AD2ANTA3ES AND DISAD2ANTA3ES
The advantages compared to a standard crankshaft and connecting rod setup are:
• 8igh torque output with a small cylinder si>e.
• Aewer moving parts.
• Smoother operation.
• 8igher percentage of the time spent at top dead centre (dwellE improving engine
efficiency.
• 9n an engine application, elimination of "oint typically served by a wrist pin, and near
elimination of piston skirt and cylinder scuffing, as side loading of piston due to sine of
connecting rod angle is eliminated.
The disadvantages are:
• /apid wear of the slot in the yoke caused by sliding friction and high contact pressures.
• 2esser percentage of the time spent at bottom dead centre reducing blow down time for
two stroke engines.
The shape of the motion of the piston is a pure sine wave over time given a constant rotational
speed.
RESO#RCES #SED
Mterils Dimensions
'ild steel plates #.
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'ild steel hollow pipe R;J mm (internalE
R;+ mm (eternalE
'ild steel square pipe < mm < mm (eternalE
Thickness- mm
E4#IPMENT #SED
#. 2athe 'achine
. Drilling machine
;. Shaper machine
+. 5rinding machine
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Dimensions:4s shown in the following figure
,% #/slot
• 7btained square cross section pipe of required length by cutting the long pipe
with the power hacksaw
• sed surface grinding machine to obtain smooth eterior surface on the pipe
• sed power cutter to remove one face of the square pipe
Dimensions: as shown in the following figure-
-% Yo&e 5Slider 0loc&6
• 7btained a cylindrical block of required length by turning and parting on 2athe
machine.• 3onverted the cylindrical block into a cuboid of required dimensions on Shaping
'achine.
• 8ole is drilled in the middle of block to accommodate the crank using the drilling
machine.
Dimensions: s shown in the following figure-
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7% 'o!ndtion
•
7btained metallic strips of required lengths by cutting the long bar using the power hacksaw
• Drilled holes to mount the crankshaft on the proper metallic strips using drilling
machine
• ?elded the metallic strips to get a rigid foundation
Dimensions: s shown
8% 3!ides
• 7btained metallic strips of required lengths by cutting from long bar using the
power hacksaw
• 7btained slots in the metallic strips using the power cutter
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Dimensions:
9% Piston nd piston rod
• 7btained cylindrical rods of required diameters and lengths using plain turning
and parting on the 2athe machine.
•?elded piston to piston rod using electric arc welding
• ?elded the above piston assembly with the -slot
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Dimensions:
% Hollo* C+linder
• 3ut the pipe of required length using power hacksaw
Dimensions:
ASSEM;1Y PROCED#RE
$%
APP1ICATIONS
This setup is most commonly used in control valve actuators in high pressure oil and gas
pipelines.
4lthough not a common metalworking machine nowadays, a Shaper uses a Scotch yoke which
has been ad"usted to provide a slow speed forward stroke and a faster return.
9t has been used in various internal combustion engines, such as the 6ourke engine, SyTech
engine, and many hot air engines and steam engines.
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Internl Com0!stion En(ine #ses
nder ideal engineering conditions, force is applied directly in the line of travel of the assembly.
The sinusoidal motion, cosinusoidal velocity, and sinusoidal acceleration (assuming constant
angular velocityE results in smoother operation. The higher percentage of time spent at top dead
centre (dwellE improves theoretical engine efficiency of constant volume combustion cycles. 9t
allows the elimination of "oints typically served by a wrist pin, and near elimination of piston
skirts and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is
mitigated. The longer the distance between the piston and the yoke, the less wear that occurs, but
greater the inertia, making such increases in the piston rod length realistically only suitable for
lower /!' (but higher torqueE applications.
The Scotch &oke is not used in most internal combustion engines because of the rapid wear of
the slot in the yoke caused by sliding friction and high contact pressures. 4lso, increased heat
loss during combustion due to etended dwell at top dead centre offsets any constant volume
combustion improvements in real engines. 9n an engine application, less percentage of the time is
spent at bottom dead centre when compared to a conventional piston and crankshaft mechanism,
which reduces blow down time for two stroke engines. Cperiments have shown that etended
dwell time does not work well with constant volume combustion 7tto 3ycle Cngines. 5ains
might be more apparent in 7tto 3ycle Cngines using a stratified direct in"ection (diesel or
similarE cycle to reduce heat losses.