scotch yoke mechanism ppt

8/9/2019 Scotch Yoke Mechanism Ppt

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Aim of the Project To design and manufacture a working model o

yoke mechanism.

To get a practical exposure of machine tools amanufacturing equipments.


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Problem Statement To convert rotary motion into Reciprocatory m

a simple harmonic manner.

To build a working model which can be faeasily using the available tools and machinery.


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Scotch yoke mechanism


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The Scotch yoke is a mechanism for converting the linear motion of a

rotational motion or vice-versa.

Introduction


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Simple Harmonic MotionScotch yoke mechanism converts rotary motion into translatory motion whiharmonic in nature.

MATHEMATICAL EXPLAINATION

Suppose crankshaft is rotating at an angular velocity ‘Ω’. u

If r is the radius of the crank then,

tangential velocity, v= ‘rΩ’ .

From the mechanism we have the following relation; α

Component of tangential velocity in Y-direction is given by;

U = Reciprocating velocity of U-Slot.


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If α is the angle made by the tangential velocity with X-Axis at any pComponent of tangential velocity in Y direction is u = rΩsinα .

U = v.sinα So, velocity of U-Slot= rΩsinα .

As a result , Velocity of U-Slot is a sine function of α .

Now as we know,

α is directly proportional to time. this implies velocity of U-Sfunction of time. Hence, the motion of U-Slot is a simple harmoni

Advantage of SHM

The sinusoidal motion, cosinusoidal velocity, and sinusoidal accele

constant angular velocity) results in smoother operation of the mec


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Resources UsedMaterials DimensionsMild steel plates 1. 50 mm x 5 mm

2. 50 mm x 2.5 mm

Mild Steel Rod 1. φ20 mm2. φ25 mm

Mild steel hollow pipe φ30 mm (internal)φ34 mm (external)

Mild steel square pipe 25 mm x 25 mm (external)Thickness-2 mm


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Equipment Used

1. Lathe Machine2. Drilling machine

3. Shaper machine

4. Grinding machine

5. Power tools

6. Power Hacksaw

7. Electric arc welding machine


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Manufacturing Procedure


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Crank and Handle Lathe Machine

Electric arc welding

•Obtained Cylindrical Rods Of Required Dimension•Operations: Plain Turning And Parting

• Welded Handle And Crank With Crank-shaft

Handle

Cranksha


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Crank and Handle


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U-Slot Power Hacksaw

Power tools

• Obtained square pipe of required length

• Used surface grinding machine to obtain smooth surface•

Used power cutter to remove one face of the square pipe


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U-Slot


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Yoke (Slider Block) Lathe Machine

Shaping machine

Drilling machine

• Obtained a cylindrical block of required length

• Converted the cylindrical block into acuboid of required dimensions

• Hole is drilled in the middle of block to accommodate the crank


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Yoke (Slider Block)


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Foundation Power hacksaw

Drilling

Electric arc welding

• Obtained metallic Strips Of Required Lengths

• Welded the metallic strips to get arigid foundation

• Drilled holes to mount the crankshaft


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Foundation


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Guides Power hacksaw

Power cutter

• Obtained metallic strips of required lengths

• Obtained slots in the metallic strips


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Guides


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Piston and piston rod

Lathe machine

Welding

Power Hacksaw

• Obtained cylindrical rods of required diameters and lengths uturning and parting

• Welded piston to piston rod• Welded the above assembly to U-slot

Hollow Cylinder

• Cut the pipe of required length


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Piston and piston rod

Hollow Cylinder


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Step-by-step procedure


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Foundation And Crank Shaf

The crank shaft is made to passthrough the holes drilled in thefoundation

Constrained the linear motion androtation in two axes by above step

Welded washers to constrain linearmotion along the crank shaft axis

Now, we can rotate the crank byrotating the handle


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Guides and Foundation Guides are welded to the

foundation

Welding is done carefully so thatthe guides are perfectly vertical

and are parallel.


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Hollow cylinder is welded to the foundationusing metallic strips

Now the hollow cylinder

is completelyconstrained

Foundation and hollow cyl


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U-slot and Guides

In scotch yoke mechanism,the linear reciprocatingmotion of U-slot isconstrained by the guides.

Bolts (with metallic washers)

passing through the slot of theguide are welded to the U-slot

Now the U-slot is constrainedto move along the guide.


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Yoke, crank and U-slot Pin Joint between crank and

yoke:o Crank is made to pass through

the hole drilled in the yokeo This forms a pin joint i.e.; crank

can freely rotate in the hole of the yoke

Slider joint between yoke andU-slot:o Yoke is placed inside the U-slot,

so that it can freely slides insideit, forming a slider joint.


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Piston and Cylinder The hollow cylinder is already constrained (we

with the foundation.

Piston is made to slide inside the hollow cylind

This completes the assembly providing eaccomponent only one degree of freedom (efoundation and guides)


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Assembled Model

Final Assembly


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Challenges and difficulties •

Incorrect Selection of Crank Length1. The length of the crank was taken too large.

2. As a result , the radius of revolution ofcrank was too large which eventuallyrequired a longer U-Slot to facilitate

reciprocatory motion.

3. Longer guides were subjected tounbalanced dynamic forces and moments which restricted the free translatorymotion..


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• Using Wood-based Foundation1. The size of foundation required to keep the system in e

had to be bigger, bulkier and complex(because of bigger c

problem was tackled using big logs of wood.

2. The wood blocks were cut and joined accordingly using led to formation of weaker joints.

3. While operation , the wooden guides were subjecte vibrations which made the reciprocatory motion unsatisfactory.

4. Relatively larger force was required to rotate the crank ma


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Rejected wooden model


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Applications• This setup is most commonly used i

valve actuators in high pressure oil and gas pipelin

• Shaper uses a Scotch yoke which has been adjusteda slow speed forward stroke and a faster return.

• It has been used in various internal combustion enas the Bourke engine, SyTech engine, and maengines and steam engines.


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Bibliography

• http://en.wikipedia.org/wiki/Scotch_yoke

•http://www.tecquipment.com/Theory_of_Machinring-Science/RE300/M6.aspx

• Theory of Machines by R. S. Khurmi.

http://en.wikipedia.org/wiki/Scotch_yokehttp://www.tecquipment.com/Theory_of_Machines/Engineering-Science/RE300/M6.aspxhttp://www.tecquipment.com/Theory_of_Machines/Engineering-Science/RE300/M6.aspxhttp://www.tecquipment.com/Theory_of_Machines/Engineering-Science/RE300/M6.aspxhttp://www.tecquipment.com/Theory_of_Machines/Engineering-Science/RE300/M6.aspxhttp://www.tecquipment.com/Theory_of_Machines/Engineering-Science/RE300/M6.aspxhttp://www.tecquipment.com/Theory_of_Machines/Engineering-Science/RE300/M6.aspxhttp://en.wikipedia.org/wiki/Scotch_yoke


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scotch yoke mechanism ppt

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