Project Report Motorized Scotch Yoke Mechanism

1. PROJECT REPORT
HITEC UNIVERSITY TAXILA
DEPARTMENT OF MECHANICAL ENGINEERING
SUBMITTED BY:
Nauman Naeem
PROJECT NAME:
Motorized Scotch Yoke Mechanism
SUBMITTED TO:
Mr. Bilal Haider

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Contents
ABSTRACT:-...............................................................................................................2
INTRODUCTION:-......................................................................................................3
CONSTRUCTION: -…………………………………………………………………4
MOBILITY / DOF: -…………………………………………………………………5
WORKING: -................................................................................................................6
ADVANTAGES / DISADVANTAGES:-...................................................................7
APPLICATIONS: -......................................................................................................8
WORKING PICTORIAL VIEWS:- ............................................................................9
REFERENCES: -…………………………………………………………………10

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ABSTRACT:
Understudying the working principle of the scotch yoke mechanism as regards
to how it converts circular motion into linear motion. Experimental apparatus was
set up which involves calibrating of the motor speed, calibrating the timing of the
circuit from theoretical knowledge which led to the scotch yoke mechanism model
construction. Mono–stable multi–vibrator and DC motor speed controller circuits
were introduced into the design. Linear velocity produced independently by
Tachometer and Timer circuit experiment was determined. There is close
relationship between the angular speed and linear velocity produced from the
Tachometer experiment and the timer circuit experiment, which helps to have a
model for demonstrating the motion conversion characteristics of the scotch yoke
mechanism. These findings demonstrated the motion characteristics of the scotch
yoke mechanism; also, the model will be useful in teaching and research purposes.

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INTRODUCTION:
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 yoke with a slot that engages a pin on the rotating part. The location of the
piston versus time is simple harmonic motion, i.e., a sine wave having constant
amplitude and constant frequency, given a constant rotational speed.
Scotch yoke mechanism is a type of a reciprocating motion. It makes use of a
slotted slider-based system to convert circular motion into linear motion and vice
versa. This mechanism is used to drive the piston. The widest usage of
this mechanism is in pumping systems for oil, gas and other liquids. So here we study
this mechanism by fabrication of a small piston driven by this mechanism. We use a
motor to drive the circular disc. The disc has a small yoke in order to connect with the
reciprocating arm. The arm has a slotted area just wide enough to adjust the yoke. The
other end of the arm is fitted in a piston cylinder. The whole setup is fabricated to get
the desired motion at least friction. This can also be used as a small part of other larger
projects where linear motion is needed.
Parts of Scotch Yoke Mechanism:
 Disc
 Yoke
 Couplings
 Slotted Part
 Cylinder
 Supporting Frame
 Joints & Screws

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CONSTRUCTION:
The main parts of Scotch Yoke Mechanism are Crank, Sliding Pin, Sliding Yoke
with Slot, Fixed Link, Connecting Rod or Piston which receives the output
reciprocating motion of Scotch Yoke Mechanism.
The piston or the reciprocating part is coupled to a sliding yoke.
This sliding Yoke has a slot that engages a sliding pin which slides inside the sliding
yoke and is a non-fixed slider of double slider crankshaft.
This sliding pin also attached to a crank which on the other side has a fixed link of
double slider crankshaft. This crank rotates around the fixed link as its center point
and the sliding pin as its endpoint.
When the crank rotates around the fixed link, the sliding pin slides in the slot of
the yoke and the yoke slide forward and backward.

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MOBILITY/ DOF:
The number of degrees of freedom of a mechanism is also called the mobility of
the device. The mobility is the number of input parameters (usually pair variables)
that must be independently controlled to bring the device into a particular position.
In most mechanical systems or models, you can determine the degrees of freedom
using the following formula:
𝑴𝒐𝒃𝒊𝒍𝒊𝒕𝒚 = 𝟑(𝑳 − 𝟏) − 𝟐𝑱𝟏 − 𝑱𝟐
𝑴𝒐𝒃𝒊𝒍𝒊𝒕𝒚 = 𝟑(𝟒 − 𝟏) − 𝟐(𝟒) − 𝟎
𝑴𝒐𝒃𝒊𝒍𝒊𝒕𝒚 = 𝟏
Links(L):
Any rigid body that possesses at least one node.
Joints(J):
It is a connection between two or more links on their common meeting point(node).
There are two kinds of joints
1. Half joint (𝑱𝟏)
2. Full Join (𝑱𝟐)
Full Joints(J1):
Joint that allows one degree of freedom.
Half Joints(J2):
Joint that allows two degrees of freedom.

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WORKING:
Scotch Yoke mechanism is a simple type of mechanism which
converts circular motion into reciprocating motion as discussed in
construction part above. The power is supplied to the DC motor,
shaft and crank attached to the shaft start rotating. As the crank
rotates the pin slides inside the yoke and also moves the yoke
forward. When the crank rotates through in clockwise direction
the yoke will get a displacement in the forward direction. The
maximum displacement will be equal to the length of the crank.
When the crank completes the next of rotation the yoke comes
back to its initial position. For the next of rotation, yoke moves in
the backward direction. When the crank completes a full rotation
the yoke moves back to the initial position. For 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.

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ADVANTAGES:
 Direct conversion of rotary motion into reciprocating motion.
 Easy construction & operation
 Can perform various operations such as cutting, slotting etc.
 Process can be automated
 Smooth Motion
 Dual Motion Conversion
 High torque output with a small cylinder size.
 Fewer moving parts.
 Smoother operation.
 Higher percentage of the time spent at top dead center (dwell)
improving engine efficiency.
 In an engine application, elimination of joint 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.
DISADVANTAGES:
 High wearing rate due to mechanical contact.
 Less application in real life
 Guide ways are necessary for proper reciprocating motion of arms.
 Rapid wear of the slot in the yoke caused by sliding friction and high
contact pressures.
 Lesser percentage of the time spent at the bottom dead centre
reducing the blow-down time for two-stroke engines.
 Guideways are necessary for proper reciprocating of arms.

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APPLICATIONS:
The Scotch yoke mechanism is most commonly used in control valve actuators in
high-pressure oil and gas pipelines, as well as in various internal combustion
engines, such as the Bourke engine, SyTech engine and many hot air engines and
steam engines. This mechanism does not create lateral forces on the piston. These
are the following applications;
 This setup is most commonly used in control valve actuators in high-pressure
oil and gas pipelines.
 It is used in making double hack saw. It is used in reciprocating pumps to
convert rotational motion into reciprocating motion required for piston
movement.
 It is used in beam engine pumps to convert rotational motion into
reciprocating motion.
 In making toys which have too & fro motion.

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WORKING PICTORIAL VIEWS:

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REFERENCES:
 http://www.mechanicalwalkins.com
 https://www.mekanizmalar.com
 https://nevonprojects.com/motorized-scotch-yoke