Machine Design and CAD Lab Manual

8/20/2019 Machine Design and CAD Lab Manual

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Universiti Tenaga Nasional, 2015Mechanical Design and CAD La bor ator y

0

Bachelor of Mechanical Engineering (Hons.)Department of Mechanical Engineering

College of Engineering

Universiti Tenaga Nasional

MAY 2013


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TABLE OF CONTENTSITEMS PAGES============================================================================Course Overview 2Guidelines for Laboratory Report 3

Basic Laboratory Safety Rules 7

Lab Experiment Manual 8Experiment # 1: Slider Crank Chain Experiment (Informal report 9 Experiment # 2: Slotted Link Mechanism Experiment (Short report) 16 Experiment # 3: Cam and Tappet Experiment ( Informal Report and open ended) 22 Experiment # 4: Whitworth’s QRM Experiment (Short report) 29 Experiment # 5: Crank and Slotted Lever QRM (Informal report) 35 Experiment # 6: Hooke’s Coupling Experiment (Formal report) 43

CREO/SOLID WORK Manual

2D - CREO Simulation Tutorial

3D - CREO Simulation Tutorial3D - SOLIDWORKS Simulation Tutorial

References


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COURSE OVERVIEW

Course Description

This course provides the practical and laboratory basis for of the design of machines

based on kinematics and dynamic requirement. Introduction to basic concepts, mobility,

synthesis and machine elements such as linkages and cams is covered. Detailed analysis on

finding the position, velocity and acceleration of linkages is carried out. Introduction to

dynamic analysis of linkages is covered. Students will do a group work involving design

and analysis.

Course Objectives :

1) To introduce laboratory experiments on machine elements.

2) To expose to CAD /CAE software: CREO and SOLIDWORKS in the design of

machine components to students.

Transferrable Skills :

Ability to perform a practical laboratory and analyze the mechanism related

experiments. Students are also able to use commercially available simulation software to

analyze a structural behavior of a given part.


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GUIDELINE FOR LABAROTARY REPORT

a. Short Report Format

General Instructions: prepared individually or in group and must manually written and submit towards end of the lab

session.

No Items Description

1. Cover page

(10%)

1. Author’s name SID no.

2. Title of experiment

3. Day and date of experiment

4. Course and course code

5. Semester and Academic Year (e.g. Sem 1 2013/14)

6. Section and group number

2. Data , Observations and

calculation of results

(40%)

The data and observations obtained in the experiments should be presented in an orderly form –

in a data table if possible. Sample of calculation should be shown to confirm the calculation usedand understanding towards the theory and experiment.

3. Analysis and Discussions

(40%)

The data obtained will be analyzed with a view towards fulfilling the purpose stated at the

beginning of the report. If there is an accepted or expected value for a quantity that is to be

obtained by the experiment, the percentage difference between the expected and experimental

value should be calculated. In many cases, complete with graph, which is often a very helpful

way of showing the relationship between two quantities. The graph must have a title, each exist

will show scale, units, and a label. All data points must have a marking to show that it is an

observed data point and all data points must be connected showing the trend of the data.

Discussion should tie the results of the experiments to the purpose. Sources or error, deviations

and uncertainty should be discussed and how they might affect the results. Any points that are

specifically asked for in experiment instructions should be discussed in this section

4. Overall report (10%) Neat, clear labels and titles. With references is given.


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b. Informal Report Format

General Instructions: prepared individually or in group and must be printed properly.


1. Cover page

(10%)

7. Author’s name SID no. 8. Title of experiment

9. Day and date of experiment




2. Statement of Purpose /

Abstract / Objective (10%)

This should be a brief description of what the experiment is demonstrating. Be specific. It

should be consistent with the statement of the experiment instructions.

3. Data ,Observations and

calculation of results (30%)

The data and observations obtained in the experiments should be presented in an orderly form

– in a data table if possible. Sample of calculation should be shown to confirm the calculation

used and understanding towards the theory and experiment.

4. Analysis and Discussions

(30%)

The data obtained will be analyzed with a view towards fulfilling the purpose stated at the beginning of the report. If there is an accepted or expected value for a quantity that is to be

obtained by the experiment, the percentage difference between the expected and experimental

value should be calculated. In many cases, complete with graph, which is often a very helpful

way of showing the relationship between two quantities. The graph must have a title, each

exist will show scale, units, and a label. All data points must have a marking to show that it is

an observed data point and all data points must be connected showing the trend of the data.

Discussion should tie the results of the experiments to the purpose. Sources or error, deviations and

uncertainty should be discussed and how they might affect the results. Any points that are specifically

asked for in experiment instructions should be discussed in this section

5. Conclusions (10%) This section summarizes the lab report. Any conclusions drawn from the results should be

given in this section. Express the implication of the results. Examine the outcome in the light

of the stated objectives.

6. References (2%)

(Note: Books and Journals

are highly recommended)

A list of all references used in writing the report should be included in this section. Use thefollowing format:

1. Book :a. Author (s). Year. Title. Edition. Place: Publisher. Page number. (example: L.H. vanVlack. 1989. Elements of Materials Science and Engineering. 6th Ed. Reading :Addison-Wesely Publ. pp100-105.)

b. Title. Year. Book Title. Edition. Place: Publisher. Page number. (Example: MaterialsScience Handbook. 1986. 20th Ed. Ohio: C.R.C. Press. pp. 1986)

2. Journals : Author (s), Year, Article Title; Journal Title, Volume, Page number. (Example:Brandt, A. 1977. Multtilevel adaptive solution to boundary value problems. Math of

Computation. 31: 333-390)

3. Internet : Title. Year. URL. (Example: Selected encyclopedias and major reference works

in polymer science and technology at Stanford University. 1998. http://www-

sul.stanford.edu/depts/swain/polymer/encys.html

7 Appendices (2%)

8 Overall report (6%) Neat, clear labels and titles. With references is given.

http://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.htmlhttp://www-sul.stanford.edu/depts/swain/polymer/encys.html


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c. Formal Report Structure

General Instructions:

* Formal Lab Report has to be prepared individually or in group and must be printed properly.


1. Title page (5 %) This page must include:

1. Title of experiment



4. Day and date experiment was performed and due date

5. (a)* Individual reports: Author’s name and matrix no; and Names and matrix no(s) of group

member

(b)* Group Reports: Names and matrix no(s) of group member

*Either (a) or (b)


7. Name of the lab instructor

2. Table of content

(3%)

This should be placed following the title page (for reports more than 10 pages). It should list up each

section of the report and corresponding page number.

3. Summary / Abstract

/Objectives

(6%)

This should encapsulate the major portion of the report and provides a concise overview of the

work. The length should be no more than 200-300 words or 2-3 paragraphs. It should highlight the

objectives, results and conclusions of the experiment.

4. Theory (10%) Any theory related to the experiment should be included. The theory must be clearly explained and

complete with diagrams where necessary. The relevant equations should be introduced. Each figure

should be labelled and numbered.

5. Equipment /

Description of

Experimental

Apparatus and

procedures (5%)

A list of equipment and specimen used should be included. This may be the same as the list on the

experiment instructions. Sketch of the equipment should also be included where necessary.

Procedures are a step-by-step explanation of what was done in the lab and why each step was

performed. The procedure listed in the experiment instructions may be used as a guide. The

description does not have to be very lengthy, but should enough detail so that a reader

knowledgeable in the field would understand what was done. Sufficient information should be

provided to allow the reader to repeat the experiment in an identical manner.

6. Data ,Observations

and calculation of

results (30%)

The data and observations obtained in the experiments should be presented in an orderly form – in a

data table if possible. A spreadsheet would be ideal, especially if there are many repetitive

calculations in the analysis of the data. Each table, figure and graph should be labelled andnumbered. Sample of calculation should be shown to confirm the calculation used and

understanding towards the theory and experiment.

7. Analysis and

discussion (24%)

The data obtained will be analysed with a view towards fulfilling the purpose stated at the beginning

of the report. When possible, part of the analysis may be combined with the data table in a

spreadsheet. If there is an accepted or expected value for a quantity that is to be obtained by the

experiment, the percentage difference between the expected and experimental value should be

calculated. In many cases, another part of the analysis will be the construction of the graph, which is


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often a very helpful way of showing the relationship between two quantities.

The graph must have a title, each exist will show scale, units, and a label. All data points must have

a marking to show that it is an observed data point and all data points must be connected showing

the trend of the data. If the student is using a computer software package to generate graphs, then

this package must convey the same information as would a hand generated graph.

Discussion section should tie the results of the experiments to the purpose. Sources or error,

deviations and uncertainty should be discussed and how they might affect the results. Any points

that are specifically asked for in experiment instructions should be discussed in this section.

8. Conclusions (10%) This section summarizes the lab report. Any conclusions drawn from the results should be given in

this section. Express the implication of the results. Examine the outcome in the light of the stated

objectives.

9. References (1%) A list of all references used in writing the report should be included in this section. Use the

following format:

Book :

1. Author (s). Year. Title. Edition. Place: Publisher. Page number. (example: L.H. van Vlack.1989. Elements of Materials Science and Engineering. 6th Ed. Reading :Addison-WeselyPubl. pp100-105.)

2. Title. Year. Book Title. Edition. Place: Publisher. Page number. (Example: MaterialsScience Handbook. 1986. 20th Ed. Ohio: C.R.C. Press. pp. 1986)

Journals : Author (s), Year, Article Title; Journal Title, Volume, Page number. (Example: Brandt, A.

1977. Multtilevel adaptive solution to boundary value problems. Math of Computation. 31: 333-390)

Internet : Title. Year. URL. (Example: Selected encyclopedias and major reference works in

polymer science and technology at Stanford University. 1998. http://www-

sul.stanford.edu/depts/swain/polymer/encys.html

Note: Books and Journals are highly recommended

10. Appendices (1%)

11. Overall report (5%) Neat, clear labels and titles. With references is given.


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BASIC LABAROTARY SAFETY RULES

Each and every students taking MEMB331 (Machine Design and CAD Lab) are expected to follow

these requirements in order to ensure the safety throughout the semester:

GENERAL GUIDELINES

1. Do not enter laboratory until you are instructed to do so.

2. Conduct yourself and your experiment in a responsible manner at all times in the laboratory.

3. When first entering laboratory do not touch any equipment, chemicals, or other materials in

the laboratory area until you are instructed to do so.

4. All personal belonging, which you do not need during the experiments, must be placed in the

cupboard.

5. Perform only those experiments authorized by your instructor. Unauthorized experiments are

not allowed.

6. Follow all written and verbal instructions carefully.

7. Never work alone in the laboratory. No student may work in the laboratory without the

presence of the instructor or technician.

8. Do not eat sweets, drink beverages, or chew gum in the laboratory.

9. Be prepared for your work in the laboratory. Read all procedures thoroughly before entering

the laboratory – remember you have to answer pre lab questions before performing the

experiments!

10. Never fool around in the laboratory.

11. Clean up all areas of the laboratory where you (and your group) worked.

12. Experiments must be monitored at all times. Do not wander around the room, distract other

students, startle other students or interfere with the laboratory experiments of others.

13. Dress properly and decently during a laboratory activity. Shoes must completely cover the

foot. No sandals and open toed shoes are allowed on lab days.

ACCIDENTS AND INJURIES

14. Report any accident (spill, breakage, etc.) or injury (cut, burn, etc.) to the instructor or

technician immediately.


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UNIVERSITI TENAGA NASIONAL Department of Mechanical Engineering

MEMB331

MACHINE DESIGN AND CAD LAB

LAB EXPERIMENT MANUAL

Prepared by

Eng Kian Hin, Ahmad Kamal Kadir

Edited by Nolia Harudin


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EXPERIMENT 1: SLIDER CRANK CHAIN EXPER IMENT

OBJECTIVES

The objectives of this experiment are to obtain a graph of piston velocity against crank

angle using the method of instantaneous centers, assuming that the crank rotates at a

constant angular velocity, to obtain the crank angles which correspond to the maximum

piston velocity, and to show that for a slider crank chain the piston motion tends to

approach simple harmonic motion with increasing values of connecting rod/crank ratio.

THEOR Y

The Slider Crank Chain is one of the two basic mechanisms which form the basic for

many more complicated motions. (The other one is the Four Bar Chain or Chebyshev

linkage of which over 800 forms are known.)

To fi nd the velociti es the method of I nstantaneous Ce n t e r s

Consider a rigid body moving relative to axes OX and OY, as in the figure below.

Suppose that the velocities va and v b of points A and B relative to OXY are known. As far

as A is concerned the body appears to be rotating about a point anywhere on the line

through A perpendicular to va. Similarly the velocity v b can only result from rotation

about a point somewhere on a line through B perpendicular to v b. If these two lines meet


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at a point I, it is the point about which the body is rotating at the instant considered. I is

called the Instantaneous Centre.

If the two lines are co-linear the instantaneous centre may be anywhere on them. The two

velocities will be parallel but not necessarily equal. If the lines are parallel and not co-

linear, I is at infinity and the two velocities are parallel and equal. The body is therefore

moving translationally and every point has the same velocity.

An instantaneous centre is not the same thing as a fixed pivot; unless the body is

constrained so that its motion is always a rotation about the same point. Then the point of

rotation and the instantaneous centre are co-incident. Thus an instantaneous centre is atdifferent points at different instants. So whilst accelerations can be expressed relative to

the instantaneous centre, to do so is not usually helpful as the centre itself can have

acceleration.

Consider the mechanism, in the position shown below:-

The instantaneous centre of the connecting rod AB is at IAB. The linear velocity of A is:-

va = OA . ω


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Assuming that the angular velocity is unity

va = OA

Since the connecting rod is instantaneously rotating about point IAB

va = I AB A

v b I ABB

So the piston velocity is given by:-

vav b = I AB A

I ABB

Triangles IAB and OAX are similar, thus:-

I ABB

I AB A =

OX

OA

OX So v b = OA

OA = OX


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APPAR ATUS

12

Slider Crank Chain with a variable connecting rod length.


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PROCEDURES

1) Set the crank to zero on the circular scale.

2) Slacken both knurled nuts and adjust the position of the piston pivot so that the

connecting rod is 115mm long. Make sure that the spacer washer is between the

piston and the connecting rod. In normal use, the knurled nuts will be just slack.

However, the motion of the slider crank can be locked at any position by

tightening both knurled nuts.

3) For every 10º of crank rotation, record the piston displacement and the cross-scale

readings in the given tables. (Note: With the crank angle set to zero, note the

initial reading of the cross-scale. This will need subtracting from all subsequent

readings in order to obtain true reading.)

4) Repeat steps 1 to 3 for connecting rod lengths of 130, 140, 155 and 175mm.

RESULTS

1) Plot a graph of piston velocity versus crank angle for the five different connecting

rod length.

2) Plot a graph of the piston displacement against crank angle for the five different

connecting rod lengths.

3) Plot a graph of piston acceleration versus crank angle for the five different

connecting rod length.

DISCUSSION

1) Comment on the form of the graph.

2) Define Simple Harmonic Motion.

3) At what angles the maximum piston velocities occur? Are these 90º and 270º ? If

not, why not?

4) What is the effect of increasing ratio on the form of the graph?

5) From the graph of piston velocity versus crank angle or from the experimental

velocity data, at what crank angles does the maximum acceleration occur for the

five different connecting rod lengths?


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6) What is the value of maximum acceleration for the five different connecting rod

lengths?

7) Do the maximum acceleration and velocity occur at the same angle? Is there a

relationship between the crank angles at which they occur, assuming that they do

not occur at the same angle? If yes, what is the relationship?


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RESULT SHEET

Slinder Crank Exper iment

Connecting rod length: mm

Crank Radius: mm Ratio: .

Crank Angle Piston Displacement (mm) Piston Velocity (mm/s) 0

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30

40

50

60

70

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90

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120

130

140 150

160

170

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190

200 210

220

230 240

250

260

270

280 290

300

310 320

330

340

350

360


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EXPERIMENT 2: SLOTTED LINK MECHANISM EXPER IMENT

OBJECTIVE

The objective of this experiment is to investigate the motion of a slotted link and to see ifthe piston rod moves with Simple Harmonics Motion

THEOR Y

Simple Harmonic Motion is defined as when a mass or point moves in such a way that its

accelerations is proportional to its displacement from a fixed point in its path and is

directed to that point, the motion is said to be simple harmonic.

The Simple Harmonic Circle enables us to establish a relationship between displacement

and accelerations. Consider the diagram below:

Q is a point which rotates at constant at constant velocity ω in a circle of a radius r. AB is

a diameter and O the center of the circle of rotation. Point P is the projection of Q upon

the diameter AB at any instant. The displacement of P from O is x. Clearly point P

oscillates between A and B as q moves around the circle. So P can only have velocities

along AB at any instant in time, similarly for accelerations. Now if we resolve the

centripetal accelerations into two components parallel and perpendicular to AB, then the

parallel components will represents the accelerations of P.


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Acceleration parallel to AB given by this equation:

AB =ω 2 r . cos ω.t

Now displacement x is

x = r .cos ω.t

So the accelerations of P is

P = a

P =ω 2 x

Thus the accelerations of P is proportional to its displacement, x, from O and is clearly

towards O. Therefore the motion is Simple Harmonic Motions.

Alternatively we may consider the following method:

But:

The minus sign indicates that the accelerations is to the left and thus the center of

rotations O.


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What do you note about the displacement, velocity and accelerations? They v a r y

sinusoidally

Periodic Time

This is the time taken for a complete oscillation from B to A and back again. The time

taken is also that for a complete revolution of particle Q which is an angular distance is

2π radians, so:

τ =2π

ω

However from previous analysis we know that:

Slotted Link Mechanism or Scotch Yoke

The apparatus is diagrammatically below:

It is clear that the driving pin which is fixed to the crank is similar to the point Q

on the SHM circle. The piston rod with a slotted link is constrained to move is a straight

line. The limits of the motions are either end of a diameter of the circle of the drive pin

rotations. So the motions of the slotted link and piston rod are identical to point P in the

foregone analysis. Thus the link and anything attached there to will move with SHM.


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APPARATUS

Slotted link Mechanism


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P R O C E D U R E S

1 . Set the crank at zero degrees. Record the piston displacement.

2. Move the crank by 10° and record the displacement.

3. Repeat steps 1 and 2 for one complete revolution of the crank.

4. Tabulate your results in the table given.

5. Calculate the theoretical piston rod displacement in the table.

RESULTS

1. Plot a graph of the experimental piston rod displacement versus crack angle.

2. Plot on the same graph the theoretical piston rod displacement against crank angle

3. From the experimental piston rod displacement data plot a graph of experimentalvelocity and accelerations versus crank angle.

4. From the theoretical Simple Harmonic Motion equations, plot a graphs of

theoretical velocity and accelerations versus crank angle.

DISCUSSIO N

1. Prove the theoretical displacement x = r (1− cosθ )

2. Compare the experimental and theoretical piston rod displacement, velocity and

accelerations. How well do your experimental results agree with theory?

3. What is the motion produced by the Slotted Link mechanism? Explain your

answer.

4. Where do maximum displacement, velocity and acceleration on the slide occur?

Explain your answer


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RESULT SHEET

Slotted Link Mechanism Experiment

Crank Radius = 35 mm

Crank Angles,

θ

Experimental Piston Rod displacement, x, (mm)

Theoretical,

x = r (1− cosθ ) (mm) 0

10 20

30

40

50

60

70 80

90

100 110

120

130

140 150

160

170

180

190

200

210 220

230

240

250

260 270

280

290

300

310

320

330 340 350

360


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EXPERIMENT 4: WHITWORTH’S QUICK RETURN MOTION

EXPERIMENT

OBJECTIVES

The objectives of this experiment are to investigate the performance of a Whitworth’s

Quick Return Motion and to verify that the motion does have a quick stroke and a slow

cutting or forward stroke.

THEORY

Defi ni tion of a Mechanism

A mechanism is a simplified model, usually in the form of a line diagram which is used to

reproduce exactly the motion occurring in a machine. The purpose of this reproduction is to

enable the nature of the motion to be investigated without the encumbrance of the various

solid bodies which form the machine elements.

The various parts of the mechanism are called links or elements. Where two links are in

contact and relative motion is possible, then they are known as pair. An arbitrary set of links

which form a closed chain that is capable of relative motion, and that can be made into rigidstructure by the addition of a single link, is known as a kinematics chain. To form a

mechanism from a kinematics chain one of the links must be fixed. However as any of the

links can be fixed, it follows that there are as many mechanisms as there are links in the

chain. The technique of obtaining different mechanisms by fixing the various links in turn is

known as inversion.


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Kinematics Pairs

The relative motion between two links of a pair can take different forms. Three types of

pairs are known as lower pairs and these are the frequently occurring ones:-

Sliding : such as occurs between a piston and cylinder

Turning : such as occurs with the wheel on axle

Screw motion : such as occurs between a nut and a bolt.

All other cases are considered to be combination of sliding and rolling and are called higher

pairs. Strictly screw motion is a higher pair as it combines turning and sliding.

Sli der- Crank Mechanism

The slider-crank mechanism is well known as the basis of a reciprocating engine. As shown

in the diagram below it contains of three turning pairs and one sliding pair.

In the previous diagram the link1 is fixed. If we now fix link 2, that is consider an inversion

of the slider-crank mechanism we obtain the mechanism below. This is known as

Whitworth’s Quick return.


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EXPERIMENT 5: CRANK AND SLOTTED LEVER QUICK

RETURN MOTION EXPER IMENT

OBJECTIVES

The objective of this experiment is to investigate the kinematics motion of a Crank and

Slotted Lever Quick Return mechanism. The investigation is to show that it is indeed a

quick return mechanism and to evaluate the increase in efficiency that this would offer if

applied to a machine tool.

THEOR Y

Defin ition of a Mec han i sm

A mechanism is a simplified model, usually in the form of a line diagram, which is used

to reproduce the motion occurring in a machine. The purpose of this reproduction is to

enable the nature of the machine. The purpose of this reproduction is to enable the nature

of the motion to be investigated without the encumbrance of the various solid bodies

which form the machine elements

The various parts of the mechanism are called links or elements. Where two links are in

contact and a relative motion is possible, then they are known as a pair. An arbitrary set

of a links which form a closed chain that is capable of relative motion, and that can be

made into a rigid structure by the addition of a single link, is known as a kinematics

chain. To form a mechanism from a kinematics chain one of the links must be fixed.

However as any of the links can be fixed, it follows that there are as many mechanism as

there are links in the chain. The technique obtaining different mechanism by fixing the

various links in turn is known as inversion.


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Kinematics Pa i r s

The relative motion between two links of a pair can take different form. Three types of a

pairs are known as lower pairs and these are the frequently occurring ones:

Sliding : such as occurs between a piston and a cylinder

Turning : such as occurs with a wheel on an axle

Screw motion: such as occurs between a nut and a bolt

All other cases are considered to be combinations of sliding and rolling are called higher

pairs. Strictly screw motion is a higher pair as it combines turning and sliding.

Slider – Crank Mec han i sm

The slider- crank mechanism is well known as the basis of a reciprocating engine. As

shown in the diagram below it consists of three turning pairs and one sliding pair

In the above diagram, the link 1 is fixed. If we now fix link 2, that is consider an

inversion of the mechanism, we obtain the mechanism shown below. This is known as

Whitworth’s Quick Return Mechanism.


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Expansion of a Revolute P a i r s

Consider the four bar linkage shown below:-

The revolute pair R 3 can be expanded so that it becomes a block, 3. When the crank 2

form a complete revolution the block, 3, only transverses a small are from E1 to E2.

The motion of 3 is still described by means of an angle referred to B. The curved slider is

thus still a revolute form and 3 are described by an angle and not by linear distance.The curved slider remains a revolute pair as long as its radius of curvature is finite. If the

radius of a curvature of a revolute pair becomes infinite, i.e. its center of rotation is at


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infinity. Then the revolute pair becomes prismatic pair variable change from an angular

measurement to a linear distance measurement.

For Bar Chains:-

Thus a prismatic pair may be considered as a revolute pair whose center is at infinity in

the direction perpendicular to the generatrix.


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Here we can see that a four bar mechanism when taken to the limit can be shown to

become slider-crank mechanism. This is very useful in the synthesis of a planar

mechanism as the properties of a four bar mechanism become the properties of the slider-

crank mechanism.

Now consider the crank and slotted lever quick return motion.

It is evident that we have a four bar chain with a prismatic pair as a limiting case of a

revolute pair. Superimposed upon this is an inversion of the slider-crank chain.


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The crank radius, OB is 40 mm. The slotted lever length, AC, is 240 mm. It is a matter of

a trigonometry to develop an expression for x in terms of the crank angle, θ, and the

length of the links. On the apparatus x is 70 mm when θ is 0° and 180°.

APPARATUS

Crank and Slotted Lever Quick Return Mechanism


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PROCEDURES

1 . Set the crank so that the pointer is at zero on the scale. Note the crosshead

position, x.

2. Rotate the crank by 10° increments and for every increment, note the

corresponding crosshead position, x.

RESULTS

1. Find an expression for theoretical distance (x) in term of θ.

2. Plot a graph of experimental crosshead position, x, versus crank angle.

3. Plot on the same graph, a graph of theoretical crosshead position versus crank

angle.4. On both graphs, show the return and cutting stroke.

5. Plot a graph of crosshead velocity versus crank angle. On the graph, show the

return and cutting stroke.

DISCUSSION

1. How well does the experimental result agree with the predictions from the theory?

2. What rotation angle is required for the cutting and return strokes?

3. Discuss the motion of the slider and verify that it is indeed a quick return

mechanism.

4. What is the increase in efficiency (in term of the time required for each stroke in

one revolution of crank) obtainable in the mechanism?


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RESULT SHEET

Crank and Slotted Lever Quick Return Motion Experiment

Crank Angles, θ

(degrees)

Experimental Slider

position, x, (mm)

Theoretical Slider

position, x, (mm)0

10

20

30

40

50

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70

80 90

100

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140

150

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190

200 210

220 230

240

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270

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310 320

330

340

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360


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Universiti Tenaga Nasional , 2015Mechanical Design and CAD La bor ator y

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EXPERIMENT 6: HOOKE’S COUPLING EXPERIMENT

OBJECTIVES

The objective of this experiment is to investigate the variation in displacement for a

single joint at various angles and to show that when two joints are used together with the

same intermediate angle, the variation in displacement is cancelled out.

THEOR Y

A flexible coupling or universal joint is frequently used to link two shafts and transmit

circular motion from the other. Indeed continuous circular motion is perhaps the single

largest thing that mankind produces in the world with the available energy. A universal

joint is simply a combination of machine elements which transmit rotation from one axis

to another. A universal join can accommodate larger angles between the shafts. An

arbitrary and accepted lower limit is 3o. In general if the angularity between two shafts is

less than 3o

a flexible coupling is used. A universal joint is used where the angularity

between the shafts is intentional. Kinematically universal joints may be divided into two

types the Hook e’s Cardan coupling ant the constant velocity joint. These name although

frequently used do not clarify the difference between them. A Hooke’s coupling is a fixed

arm coupling and a constant velocity joint is a variable arm coupling. We are concernedhere with a fixed arm coupling only.

The following analysis will show that the angle as the angle between the shafts increases

there is a periodic speed and hence torque fluctuation. Such fluctuation cannot be

tolerated in machinery so it is usual to have two coupling with small intermediate shaft.

The second coupling introduces equal and opposite fluctuations, thus the overall effect is

of smooth and uniform transmission. However both the input and the output shaft must

make the same angle with the intermediate shaft for this to work.

A Hook e’s coupling consists of a cruciform spider which pivots in two fork ends formed

in the end of the shafts. For practical manufacturing reasons the fork ends are made as


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Universiti Tenaga Nasional , 2013Mechanical Design And CAD La bor ator y

38

P P’ is the plan view of the plane of rotation of CD and Q Q’ is the plan view of the plan

view of the plane rotation of EF. If we now draw RO at right- angles to C1D1 and project

R to R 1 in the plan view we can take radius O R 1 and draw an arc to cut Q Q’ at R 2. We

may now project this point to meet RS at T1. Then angle TOS equals, the angle moved

through by the arm EF in the plane of rotation where P P’ is the plan view

Consider;

so;

The above equation gives the displacement. The velocity equation may be obtained by

differentiating equation (2)

Velocity;

The graph below shows the relationship between input and output angles from 0 to 90o

for displacement where the joint angle is 10o

to 50o


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The graph below gives the velocity variation for a single coupling for shaft angle from

10o

to 50o.


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APPAR ATUS

Hooke’s Coupling Apparatus


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PROCEDURE

Part 1

1. Set the left hand Bracket over so that the angle α1 between the shaft is 45º

2. Set the other joint to be straight, α2 = 0º

3. Start the scale on the input shaft at zero. Rotate the shaft by 10º at each turn. Note

the reading on the input and output scales.

4. Repeat for 360º that is one complete rotation for the shaft input.

5. Tabulate results in the data sheet

6. Repeat procedures 1 through 5 for α1 = 15º and 30º

Part 2

1. Set both α1 and α2 equal at 30º, both bend at the same side.

2. For one revolution of the input shaft (at10º intervals), take readings of the scale of

the output shaft

3. Tabulate results on the data sheet.

4. Repeat the experiment with the input and output shaft parallel but still keep at the

same value of 30º.

5. Tabulate results in the table given.

GRAPH ANDRESULT

From the result in part 1:

1. Plot the output shaft angle versus the input shaft angle for α1 = 15º, 30º and 45o

(all in one plot).

2. Plot tan (input shaft angle) versus tan (output shaft angle)1.

3. Plot the output shaft velocity (experimental and theoretical) versus input shaft

angle for α1 = 15º, 30º and 45o.

From the result in part 2:

1. Plot the output shaft angle versus the input shaft angle for both readings, parallel

and same side readings in the same graph.

1 Only plot from 100o to 260o for both x and y-axis as Tan 90,270 = infinity.


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DISCUSSION

1. Comment on the output shaft angle versus input shaft angle plot that you have

obtained2.

2. What is the significance of the tan (input shaft angle) versus tan (output shaft

angle) plot?3 In other words, what information can you obtain from the plot? Does

the plot show the validity of the analysis that was shown in the laboratory?4

3. Comment on the output shaft velocity versus input shaft angle plot that you have

obtained. How well do the velocity variations you found compare with those

predicted in theory.

4. What is the purpose of the second part of the experiment? Does the result justify

the purpose?

5. What is the effect if α1 is not the same as α2

2 Minimum 3 comments, hint(1): what happen at 0o& 90o& 180o& 270o& 360o 3 Refer equation 2, recap order of the equation 4 Please recap the boundary of cos(θ).


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RESULT SHEET

Hooke’s Coupling Experiment Part 1

For alpha1, α1 = degrees

Input, θ Output, φ Tan θ Tan φ, Output Velocity0

10

20 30

40

50

60

70

80

90 100

110 120

130

140

150

160 170

180

190

200 210

220

230

240

250 260

270

280

290

300

310 320

330

340

350

360


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Input, θ Output, φ

0 10

20

30 40

50

60

70

80

90

100

110

120

130

140 150

160

170

180

190

200

210

220

230

240 250

260

270

280

290

300

310

320 330

340

350 360

Documents

Machine Design and CAD Lab Manual