machines and mechanisms.pdf

MACHINES AND MECHANISMS

APPLIED KINEMATIC ANALYSIS

Fourth Edition

David H. Myszka

University of Dayton

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Library of Congress Cataloging-in-Publication Data

Myszka, David H.

Machines and mechanisms : applied kinematic analysis / David H. Myszka.—4th ed.

p. cm.

Includes bibliographical references and index.

ISBN-13: 978-0-13-215780-3

ISBN-10: 0-13-215780-2

1. Machinery, Kinematics of.

2. Mechanical movements.

I. Title.

TJ175.M97 2012

621.8'11—dc22

2010032839

10987654321

ISBN 10: 0-13-215780-2

ISBN 13: 978-0-13-215780-3

PREFACE

The objective of this book is to provide the techniques

necessary to study the motion of machines. A focus is placed on

the application of kinematic theories to real-world machinery.

It is intended to bridge the gap between a theoretical study of

kinematics and the application to practical mechanisms.

Students completing a course of study using this book should

be able to determine the motion characteristics of a machine.

The topics presented in this book are critical in machine design

process as such analyses should be performed on design con-

cepts to optimize the motion of a machine arrangement.

This fourth edition incorporates much of the feedback

received from instructors and students who used the first three

editions. Some enhancements include a section introducing

special-purpose mechanisms; expanding the descriptions of

kinematic properties to more precisely define the property;

clearly identifying vector quantities through standard boldface

notation; including timing charts; presenting analytical

synthesis methods; clarifying the tables describing cam fol-

lower motion; and adding a standard table used for selection of

chain pitch. The end-of-chapter problems have been reviewed.

In addition, many new problems have been included.

It is expected that students using this book will have a

good background in technical drawing, college algebra, and

trigonometry. Concepts from elementary calculus are

mentioned, but a background in calculus is not required.

Also, knowledge of vectors, mechanics, and computer

application software, such as spreadsheets, will be useful.

However, these concepts are also introduced in the book.

The approach of applying theoretical developments to

practical problems is consistent with the philosophy of

engineering technology programs. This book is primarily

oriented toward mechanical- and manufacturing-related

engineering technology programs. It can be used in either

associate or baccalaureate degree programs.

Following are some distinctive features of this book:

Every chapter concludes with at least one case study.

Each case illustrates a mechanism that is used on

industrial equipment and challenges the student to

discuss the rationale behind the design and suggest

improvements.

Both static and dynamic mechanism force analysis

methods are introduced.

Every major concept is followed by an example

problem to illustrate the application of the

concept.

Every Example Problem begins with an introduction

of a real machine that relies on the mechanism being

analyzed.

10.

Numerous end-of-chapter problems are consistent

with the application approach of the text. Every

concept introduced in the chapter has at least one

associated problem. Most of these problems include

the machine that relies on the mechanism being

analyzed.

11.

Where applicable, end-of-chapter problems are

provided that utilize the analytical methods and are

best suited for programmable devices (calculators,

spreadsheets, math software, etc.).

Initially, I developed this textbook after teaching mech-

anisms for several semesters and noticing that students did

not always see the practical applications of the material. To

this end, I have grown quite fond of the case study problems

and begin each class with one. The students refer to this as

the “mechanism of the day.” I find this to be an excellent

opportunity to focus attention on operating machinery.

Additionally, it promotes dialogue and creates a learning

community in the classroom.

Finally, the purpose of any textbook is to guide the

students through a learning experience in an effective

manner. I sincerely hope that this book will fulfill this inten-

tion. I welcome all suggestions and comments and can be

reached at dmyszka@udayton.edu.

Pictures and sketches of machinery that contain

mechanisms are incorporated throughout the text.

The focus is on the application of kinematic theories to

common and practical mechanisms.

Both graphical techniques and analytical methods are

used in the analysis of mechanisms.

ACKNOWLEDGMENTS

I thank the reviewers of this text for their comments and

suggestions: Dave Brock, Kalamazoo Valley Community

College; Laura Calswell, University of Cincinnati; Charles

Drake, Ferris State University; Lubambala Kabengela,

University of North Carolina at Charlotte; Sung Kim,

Piedmont Technical College; Michael J. Rider, Ohio

Northern University; and Gerald Weisman, University of

Vermont.

An examination copy of Working Model ® , a commer-

cially available dynamic software package (see Section 2.3

on page 32 for ordering information), is extensively used

in this book. Tutorials and problems that utilize this

software are integrated into the book.

Suggestions for implementing the graphical techniques

on computer-aided design (CAD) systems are included

and illustrated throughout the book.

Dave Myszka

iii

CONTENTS

Introduction to Mechanisms and

Kinematics

Building Computer Models of

Mechanisms Using Working Model ®

Software

Objectives

1.1

Introduction

Objectives

1.2

Machines and Mechanisms

2.1

Introduction

1.3

Kinematics

2.2

Computer Simulation of Mechanisms

1.4

Mechanism Terminology

2.3

Obtaining Working Model Software

1.5

Kinematic Diagrams

2.4

Using Working Model to Model a Four-Bar

Mechanism

1.6

Kinematic Inversion

2.5

Using Working Model to Model a Slider-

Crank Mechanism

1.7

Mobility 8

1.7.1 Gruebler’s Equation

Problems 41

Case Studies

1.7.2 Actuators and Drivers

1.8

Commonly Used Links and Joints

1.8.1 Eccentric Crank 14

1.8.2 Pin-in-a-Slot Joint

3Vectors43

Objectives

1.8.3 Screw Joint

1.9

Special Cases of the Mobility Equation

3.1

Introduction

1.9.1 Coincident Joints 16

1.9.2 Exceptions to the Gruebler’s

Equation 18

1.9.3 Idle Degrees of Freedom

3.2

Scalars and Vectors

3.3

Graphical Vector Analysis

3.4

Drafting Techniques Required in Graphical

Vector Analysis

1.10

The Four-Bar Mechanism

3.5

CAD Knowledge Required in Graphical Vector

Analysis

1.10.1 Grashof ’s Criterion

1.10.2 Double Crank 20

1.10.3 Crank-Rocker 20

1.10.4 Double Rocker 20

1.10.5 Change Point Mechanism

3.6

Trigonometry Required in Analytical Vector

Analysis 44

3.6.1 Right Triangle 44

3.6.2 Oblique Triangle

1.10.6 Triple Rocker

3.7

Vector Manipulation

1.11

Slider-Crank Mechanism

3.8

Graphical Vector Addition

(

)

1.12

Special Purpose Mechanisms 22

1.12.1 Straight-Line Mechanisms

3.9

Analytical Vector Addition

(

)

: Triangle

Method

1.12.2 Parallelogram Mechanisms

3.10

Components of a Vector

1.12.3 Quick-Return Mechanisms

3.11

Analytical Vector Addition

(

)

: Component

1.12.4 Scotch Yoke Mechanism

Method

1.13

Techniques of Mechanism Analysis 23

1.13.1 Traditional Drafting Techniques

3.12

Vector Subtraction

(

-7

)

3.13

Graphical Vector Subtraction

(

-7

)

1.13.2 CAD Systems 24

1.13.3 Analytical Techniques

3.14

Analytical Vector Subtraction

(

-7

)

: Triangle

Method

1.13.4 Computer Methods

3.15

Analytical Vector Subtraction

(

-7

)

Problems 25

Case Studies

Component Method

3.16

Vector Equations

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