scotch yoke mechanis1

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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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.

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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


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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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.

scotch yoke mechanis1

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