Published on April 9, 2013
MECHANISMS ANDMECHANICAL DEVICES SOURCEBOOK Fifth Edition NEIL SCLATER McGraw-Hill New York • Chicago • San Francisco • Lisbon • London • Madrid Mexico City • Milan • New Delhi • San Juan • Seoul Singapore • Sydney • Toronto
CONTENTSPREFACE xiCHAPTER 1 BASICS OF MECHANISMS 1 Introduction 2 Physical Principles 2 Efficiency of Machines 2 Mechanical Advantage 2 Velocity Ratio 3 Inclined Plane 3 Pulley Systems 3 Screw-Type Jack 4 Levers and Mechanisms 4 Levers 4 Winches, Windlasses, and Capstans 5 Linkages 5 Simple Planar Linkages 5 Specialized Linkages 6 Straight-Line Generators 7 Rotary/Linear Linkages 8 Specialized Mechanisms 9 Gears and Gearing 10 Simple Gear Trains 11 Compound Gear Trains 11 Gear Classification 11 Practical Gear Configurations 12 Gear Tooth Geometry 13 Gear Terminology 13 Gear Dynamics Terminology 13 Pulleys and Belts 14 Sprockets and Chains 14 Cam Mechanisms 14 Classification of Cam Mechanisms 15 Cam Terminology 17 Clutch Mechanisms 17 Externally Controlled Friction Clutches 17 Externally Controlled Positive Clutches 17 Internally Controlled Clutches 18 Glossary of Common Mechanical Terms 18CHAPTER 2 MOTION CONTROL SYSTEMS 21 Motion Control Systems Overview 22 Glossary of Motion Control Terms 28 Mechanical Components Form Specialized Motion-Control Systems 29 Servomotors, Stepper Motors, and Actuators for Motion Control 30 Servosystem Feedback Sensors 38 Solenoids and Their Applications 45 iii
CHAPTER 3 STATIONARY AND MOBILE ROBOTS 49 Introduction to Robots 50 The Robot Defined 50 Stationary Autonomous Industrial Robots 50 Some Robot History 51 The Worldwide Robot Market 51 Industrial Robots 51 Industrial Robot Advantages 52 Industrial Robot Characteristics 53 Industrial Robot Geometry 53 Four Different ABB Industrial Robots 56 IRB 2400 57 IRB 6400RF 57 IRB 6640 57 IRB 7600 57 Autonomous and Semiautonomous Mobile Robots 58 Options for Communication and Control 58 Land-based Mobile Robots Can Scout and Retrieve 58 Submersible Mobile Robots Can Search and Explore 58 Robotic Aircraft (Drones) Can Search and Destroy 58 Planetary Exploration Robots Can Examine and Report 59 Laboratory/Scientific Robots Can Mimic Human Behavior 59 Commercial Robots Can Deliver and Retrieve Goods 59 Consumer Robots Clean Floors and Mow Lawns 59 Some Robots Entertain or Educate 59 Seven Mobile Autonomous and Semiautonomous Robots 60 Two Robots Have Explored Mars for Six Years 60 This Robot Will Carry on the Work of Spirit and Opportunity 61 This Robot Responds to Civil Emergencies 62 Robot Delivers Hospital Supplies 62 A Military Remotely-Piloted Aircraft Can Observe and Attack the Enemy 63 Submarine Robot Searches for Underwater Mines and Obstructions 64 This System Offers Less Intrusive Surgery and Faster Recovery 65 Glossary of Robotic Terms 66 Modified Four-Limbed Robot Is a Better Climber 68 Six-Legged Robot Crawls on Mesh in Lunar Gravity 69 Two Robots Anchor Another Traversing Steep Slopes 70 Six-Legged Robot Can Be Steered While Hopping 71 CHAPTER 4 MECHANISMS FOR RENEWABLE POWER GENERATION 73 Overview of Renewable Energy Sources 74 Nuclear: The Unlikely Prime Renewable 74 Alternative Renewable Energy Sources 75 Baseload and Baseload Demand Power Plants 75 Windmills: Early Renewable Power Sources 75 Wind Turbines: Descendents of Windmills 76 Where Are Wind Turbines Located? 77 Concentrating Solar Thermal (CST) Systems 78 Parabolic Trough Mirror Solar Thermal (CST) Plants 78 Power-Tower Solar Thermal (CST) Plants 79 Linear Fresnel Reflector Thermal (CST) Plants 80 Parabolic Dish Stirling Solar Thermal (CST) Plants 81 How a Stirling Engine Works 82 The Outlook for CST Renewable Energy 83iv
Harnessing Moving-Water Power 84 Tidal Electric Power Generation 84 Ocean-Wave Power Generation 84 Another Possible Mechanical Hydropower Solution 84 The Relative Costs of Renewable Energy 85 Glossary of Wind Turbine Terms 86 Renewable Energy Resources 87CHAPTER 5 LINKAGES: DRIVES AND MECHANISMS 89 Four-Bar Linkages and Typical Industrial Applications 90 Seven Linkages for Transport Mechanisms 92 Five Linkages for Straight-Line Motion 95 Six Expanding and Contracting Linkages 97 Four Linkages for Different Motions 98 Nine Linkages for Accelerating and Decelerating Linear Motions 99 Twelve Linkages for Multiplying Short Motions 101 Four Parallel-Link Mechanisms 103 Seven Stroke Multiplier Linkages 103 Nine Force and Stroke Multiplier Linkages 105 Eighteen Variations of Differential Linkage 107 Four-Bar Space Mechanisms 109 Seven Three-Dimensional Linkage Drives 111 Thirteen Different Toggle Linkage Applications 116 Hinged Links and Torsion Bushings Soft-Start Drives 118 Eight Linkages for Band Clutches and Brakes 119 Design of Crank-and-Rocker Links for Optimum Force Transmission 121 Design of Four-Bar Linkages for Angular Motion 124 Multibar Linkages for Curvilinear Motions 125 Roberts’ Law Helps to Design Alternate Four-Bar Linkages 128 Design of Slider-Crank Mechanisms 129CHAPTER 6 GEARS: DEVICES, DRIVES, AND MECHANISMS 131 Gears and Eccentric Disk Provide Quick Indexing 132 Odd-Shaped Planetary Gears Smooth Stop and Go 133 Cycloid Gear Mechanism Controls Pump Stroke 136 Gears Convert Rotary-to-Linear Motion 137 Twin-Motor Planetary Gears Offer Safety and Dual-Speed 137 Eleven Cycloid Gear Mechanisms 138 Five Cardan-Gear Mechanisms 141 Controlled Differential Gear Drives 143 Flexible Face-Gears Are Efficient High-Ratio Speed Reducers 144 Rotary Sequencer Gears Turn Coaxially 145 Planetary Gear Systems 146 Noncircular Gears Are Balanced for Speed 153 Sheet-Metal Gears, Sprockets, Worms, and Ratchets for Light Loads 157 Thirteen Ways Gears and Clutches Can Change Speed Ratios 159 Gear and Clutch Shifting Mechanisms 161 Twinworm Gear Drive Offers Bidirectional Output 163 Bevel and Hypoid Gear Design Prevents Undercutting 164 Machining Method to Improve Worm Gear Meshing 165 Geared Speed Reducers Offer One-Way Output 166 Design of Geared Five-Bar Mechanisms 167 Equations for Designing Geared Cycloid Mechanisms 171 Design Curves and Equations for Gear-Slider Mechanisms 174 v
CHAPTER 7 CAM, GENEVA, AND RATCHET DRIVES AND MECHANISMS 179 Cam-Controlled Planetary Gear System 180 Five Cam-Stroke-Amplifying Mechanisms 181 Cam-Curve-Generating Mechanisms 182 Fifteen Different Cam Mechanisms 188 Ten Special-Function Cams 190 Twenty Geneva Drives 192 Six Modified Geneva Drives 196 Kinematics of External Geneva Wheels 198 Kinematics of Internal Geneva Wheels 201 Star Wheels Challenge Geneva Drives for Indexing 205 Ratchet-Tooth Speed-Change Drive 208 Modified Ratchet Drive 208 Eight Toothless Ratchets 209 Analysis of Ratchet Wheels 210 CHAPTER 8 CLUTCHES AND BRAKES 211 Twelve Clutches with External or Internal Control 212 Spring-Wrapped Clutch Slips at Preset Torque 214 Controlled-Slip Expands Spring Clutch Applications 216 Spring Bands Improve Overrunning Clutch 217 Slip and Bidirectional Clutches Combine to Control Torque 218 Slip Clutches Serve Many Design Functions 219 Walking Pressure Plate Delivers Constant Torque 220 Seven Overrunning Clutches 221 One-Way Clutch Has Spring-Loaded Pins and Sprags 222 Roller Clutch Provides Two Output Speeds 222 Seven Overriding Clutches 223 Ten Applications for Overrunning Clutches 225 Eight Sprag Clutch Applications 227 Six Small Clutches Perform Precise Tasks 229 Twelve Different Station Clutches 231 Twelve Applications for Electromagnetic Clutches and Brakes 234 CHAPTER 9 LATCHING, FASTENING, AND CLAMPING DEVICES AND MECHANISMS 237 Sixteen Latch, Toggle, and Trigger Devices 238 Fourteen Snap-Action Devices 240 Remote Controlled Latch 244 Toggle Fastener Inserts, Locks, and Releases Easily 245 Grapple Frees Loads Automatically 245 Quick-Release Lock Pin Has a Ball Detent 246 Automatic Brake Locks Hoist When Driving Torque Ceases 246 Lift-Tong Mechanism Firmly Grips Objects 247 Perpendicular-Force Latch 247 Two Quick-Release Mechanisms 248 Shape-Memory Alloy Devices Release Latches 249 Ring Springs Clamp Platform Elevator into Position 250 Cammed Jaws in Hydraulic Cylinder Grip Sheet Metal 250 Quick-Acting Clamps for Machines and Fixtures 251 Nine Friction Clamping Devices 253 Detents for Stopping Mechanical Movements 255 Twelve Clamping Methods for Aligning Adjustable Parts 257 Spring-Loaded Chucks and Holding Fixtures 259vi
CHAPTER 10 CHAIN AND BELT DEVICES AND MECHANISMS 261 Twelve Variable-Speed Belt and Chain Drives 262 Belts and Chains Are Available in Many Different Forms 265 Change Center Distance without Altering Speed Ratio 269 Motor Mount Pivots to Control Belt Tension 269 Ten Roller Chains and Their Adaptations 270 Twelve Applications for Roller Chain 272 Six Mechanisms for Reducing Pulsations in Chain Drives 276CHAPTER 11 SPRING AND SCREW DEVICES AND MECHANISMS 279 Flat Springs in Mechanisms 280 Twelve Ways to Use Metal Springs 282 Seven Overriding Spring Mechanisms for Low-Torque Drives 284 Six Spring Motors and Associated Mechanisms 286 Twelve Air Spring Applications 288 Novel Applications for Different Springs 290 Applications for Belleville Springs 291 Vibration Control with Spring Linkage 292 Twenty Screw Devices 293 Ten Applications for Screw Mechanisms 296 Seven Special Screw Arrangements 297 Fourteen Spring and Screw Adjusting Devices 298 A Long-Stroke, High-Resolution Linear Actuator 299CHAPTER 12 SHAFT COUPLINGS AND CONNECTIONS 301 Four Couplings for Parallel Shafts 302 Links and Disks Couple Offset Shafts 303 Disk-and-Link Couplings Simplify Torque Transmission 304 Interlocking Space-Frames Flex as They Transmit Shaft Torque 305 Coupling with Off-Center Pins Connects Misaligned Shafts 307 Universal Joint Transmits Torque 45° at Constant Speed 308 Ten Universal Shaft Couplings 309 Nineteen Methods for Coupling Rotating Shafts 311 Five Different Pin-and-Link Couplings 315 Ten Different Splined Connections 316 Fourteen Ways to Fasten Hubs to Shafts 318 Polygon Shapes Provide Superior Connections 320CHAPTER 13 MOTION-SPECIFIC DEVICES, MECHANISMS, AND MACHINES 323 Timing Belts, Four-Bar Linkage Team Up for Smooth Indexing 324 Ten Indexing and Intermittent Mechanisms 326 Twenty-Seven Rotary-to-Reciprocating Motion and Dwell Mechanisms 328 Five Friction Mechanisms for Intermittent Rotary Motion 334 Nine Different Ball Slides for Linear Motion 336 Ball-Bearing Screws Convert Rotary to Linear Motion 338 Nineteen Arrangements for Changing Linear Motion 339 Eight Adjustable-Output Mechanisms 343 Four Different Reversing Mechanisms 345 Ten Mechanical Computing Mechanisms 346 Nine Different Mechanical Power Amplifiers 350 Forty-Three Variable-Speed Drives and Transmissions 353 Ten Variable-Speed Friction Drives 365 Four Drives Convert Oscillating Motion to One-Way Rotation 367 Eighteen Different Liquid and Vacuum Pumps 369 vii
Ten Different Pump Designs Explained 373 Glossary of Pump Terms 376 Bearingless Motor-Generators Have Higher Speed and Longer Life 377 Energy Exchange in Seawater Desalination Boosts Efficiency 378 Two-Cycle Engine Improves Efficiency and Performance 380 CHAPTER 14 PACKAGING, CONVEYING, HANDLING, AND SAFETY MECHANISMS AND MACHINES 381 Fifteen Devices That Sort, Feed, or Weigh 382 Seven Cutting Mechanisms 386 Two Flipping Mechanisms 388 One Vibrating Mechanism 388 Seven Basic Parts Selectors 389 Eleven Parts-Handling Mechanisms 390 Seven Automatic-Feed Mechanisms 392 Fifteen Conveyor Systems for Production Machines 395 Seven Traversing Mechanisms for Winding Machines 399 Vacuum Pickup for Positioning Pills 401 Machine Applies Labels from Stacks or Rollers 401 Twenty High-Speed Machines for Applying Adhesives 402 Twenty-Four Automatic Mechanisms for Stopping Unsafe Machines 408 Six Automatic Electrical Circuits for Stopping Textile Machines 414 Six Automatic Mechanisms for Assuring Safe Machine Operation 416 CHAPTER 15 TORQUE, SPEED, TENSION, AND LIMIT CONTROL SYSTEMS 419 Applications of the Differential Winch to Control Systems 420 Six Ways to Prevent Reverse Rotation 422 Caliper Brakes Keep Paper Tension in Web Presses 423 Control System for Paper Cutting 423 Warning System Prevents Overloading of Boom 424 Lever System Monitors Cable Tension 424 Eight Torque-Limiters Protect Light-Duty Drives 425 Thirteen Limiters Prevent Overloading 426 Seven Ways to Limit Shaft Rotation 429 Mechanical Systems for Controlling Tension and Speed 431 Nine Drives for Controlling Tension 435 Limit Switches in Machinery 438 Nine Automatic Speed Governors 442 Eight Speed Control Devices for Mechanisms 444 Cable-Braking System Limits Descent Rate 445 CHAPTER 16 INSTRUMENTS AND CONTROLS: PNEUMATIC, HYDRAULIC, ELECTRIC, AND ELECTRONIC 447 Twenty-Four Mechanisms Actuated by Pneumatic or Hydraulic Cylinders 448 Foot-Controlled Braking System 450 Fifteen Tasks for Pneumatic Power 450 Ten Applications for Metal Diaphragms and Capsules 452 Nine Differential Transformer Sensors 454 High-Speed Electronic Counters 456 Applications for Permanent Magnets 457 Nine Electrically Driven Hammers 460 Sixteen Thermostatic Instruments and Controls 462 Eight Temperature-Regulating Controls 466 Seven Photoelectric Controls 468viii
Liquid Level Indicators and Controllers 470 Applications for Explosive-Cartridge Devices 472 Centrifugal, Pneumatic, Hydraulic, and Electric Governors 474CHAPTER 17 3D DIGITAL PROTOTYPES AND SIMULATION 477 Introduction to 3D Digital Prototypes and Simulation 478 A Short History of Engineering Drawing 478 Transition from Board to Screen 479 CAD Product Features 480 3D Digital Prototypes vs. Rapid Prototyping 480 The Ongoing Role of 2D Drawings 480 Functions of Tools in 3D Digital Prototype Software 481 File Types for 3D Digital Prototypes 481 Computer-Aided Engineering (CAE) 482 Simulation Software 482 Simulated Stress Analysis 483 Glossary of Computer-Aided Design Terms 484CHAPTER 18 RAPID PROTOTYPING 487 Rapid Prototyping Focuses on Building Functional Parts 488 Rapid Prototyping Steps 489 Commercial Rapid Prototyping Choices 490 Commercial Additive RP Processes 491 Subtractive and R&D Laboratory Processes 498CHAPTER 19 NEW DIRECTIONS IN MECHANICAL ENGINEERING 501 The Role of Microtechnology in Mechanical Engineering 502 Micromachines Open a New Frontier for Machine Design 504 Multilevel Fabrication Permits More Complex and Functional MEMS 508 Electron Microscopes: Key Tools in Micro- and Nanotechnology 509 Gallery of MEMS Electron-Microscope Images 512 MEMS Actuators—Thermal and Electrostatic 516 MEMS Chips Become Integrated Microcontrol Systems 517 Alternative Materials for Building MEMS 519 LIGA: An Alternative Method for Making Microminiature Parts 520 The Role of Nanotechnology in Science and Engineering 521 Carbon: An Engineering Material with a Future 523 Nanoactuators Based on Electrostatic Forces on Dielectrics 528 The Lunar Electric Rover: A New Concept for Moon Travel 530INDEX 533 ix
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PREFACEThis is the fifth edition of a one-of-a-kind engineering reference book covering the past,present, and future of mechanisms and mechanical devices. It includes clear illustrationsand straightforward descriptions of specific subjects rather than the theory and mathe-matics found in most engineering textbooks. You will find that this book containshundreds of detailed line drawings that will hold your interest regardless of your back-ground in mechanical engineering. The text accompanying the illustrations is intendedto help you to understand the basic concepts of subjects that may or may not be familiarto you. You will find drawings and illustrations that are simply interesting and informativeand perhaps others that could spur your creativity and prompt you to recycle them intoyour new designs or redesigns. They may offer solutions you had not previously consid-ered because they were not visible inside contemporary products unless the product isdisassembled. Solid state electronics and computer circuitry have displaced many earliermechanical solutions, no doubt improving product reliability and efficiency while reduc-ing their price. Nevertheless, many of those displaced mechanical components have lives of their ownand may very well turn up in other products in different form performing different func-tions after undergoing dimensional and material transformations. Classical, proven mechanisms and mechanical devices may seem to disappear only toreappear in other forms and applications. Anyone who believes that all mechanisms willbe replaced by electronics need only examine the sophistication of the latest self-windingmechanical watches, digital cameras, gyro-stabilized vehicles, and navigational systems. This book illustrates the ongoing importance of classical mechanical devices as well asthe latest mechatronic devices formed by the merger between mechanics and electronics.It is a must addition to your personal technical library, and it offers you a satisfying wayto “get up to speed” on new subjects or those you may have studied in the past but havenow faded from your memory. Moreover, it is hoped that this book will encourage you torefresh your knowledge of these and other topics that interest you by accessing the manyrelated Web sites on the Internet.What’s New in This Book?This fifth edition contains three new chapters: Chapter 3, Stationary and Mobile Robots,Chapter 4, Mechanisms for Renewable Power Generation, and Chapter 17, 3D DigitalPrototypes and Simulation. Chapter 18, Rapid Prototyping, has been updated and com-pletely revised, and new articles have been added to Chapters 5 through 16 that make upthe archival core of the book. Five new articles have been added to Chapter 13, Motion-Specific Devices, Mechanisms, and Machines, which is part of the archival core. Also, fivenew articles have been added to Chapter 19, New Directions in Mechanical Engineering.A Quick Overview of Some ChaptersChapter 1 on basic mechanisms explains the physics of mechanisms including inclinedplanes, jacks, levers, linkage, gears, pulleys, genevas, cams, and clutches—all compo-nents in modern machines. A glossary of common mechanical terms is included. Chapter 2 on motion control explains open- and closed-loop systems with diagramsand text. Described and illustrated are the key mechanical, electromechanical, and elec-tronic components that comprise modern automated robotic and mechatronic systems,including actuators, encoders, servomotors, stepper motors, resolvers, solenoids, andtachometers. It includes a glossary of motion control terms. Chapter 3, a new discussion of robots, includes an overview of stationary industrialrobots and a wide range of mobile robots. Drawings and text explain the geometry ofindustrial robots and leading specifications are given for four of the newest robots. Sevenmobile robots are described accompanied by their illustrations and leading specifications.They operate on Mars, on Earth, in the air, and under the sea. Other articles describeinnovative NASA robots that climb, crawl, hop, and rappel down cliffs. In addition, aglossary defines common robot terms. Chapter 4, a new addition, describes the leading contenders for generating carbon-freerenewable power, which happen to be mechanical in nature. They are driven by the freeenergy of the wind, sun, and natural water motion. Examples described and illustratedinclude wind turbines and their farms, four different solar thermal farm concepts, andproposed methods for tapping ocean tidal and wave energy. Both the upsides and down-sides of these plants are stated. Attention is given to location, efficiency, public acceptance, xi
backup power sources, and connections to the power grid. Included is a glossary of wind turbine terms. Chapter 17, also new, explains the features of the latest computer software making it possible to design new or revise old products in 3D right on the computer screen, taking advantage of features including the ability to manipulate, “slice and dice,” and re- dimension the virtual model in a range of colors to finalize the design complete with manufacturing data. Compatible simulation software permits a model to be subjected to virtual mechanical and multiphysics stresses to verify its design and choice of materials without the need to build a physical model for testing. Included in the chapter is a glossary of CAD/CAE terms. Chapter 18, an update of an earlier chapter on rapid prototyping, explains and illus- trates innovations and new additions to the many commercial additive and subtractive processes for building 3D solid prototypes. They are being made from soft or hard mate- rials for “hands-on” evaluation. Some prototypes are just for display while others are built to withstand laboratory stress testing. However, the newer applications include the fabrication of replacement parts for older machines, specialized metal tools, and molds for casting. Chapter 19 is an update of a collection of articles discussing cutting-edge topics in mechanical engineering. These include the latest developments in microelectromechani- cal devices (MEMS) and progress in developing practical applications for the carbon allotropes, nanotubes, and graphene in products ranging from transparent sheets, strong fiber, cable, capacitors, batteries, springs, and transistors. Other topics include electron microscopes for R&D and a proposed long-range Moon rover. The central core of the book, Chapters 5 through 16, contains an encyclopedic col- lection of archival drawings and descriptions of proven mechanisms and mechanical devices. This revised collection is a valuable resource for engineers, designers, teachers, and students as well as enthusiasts for all things mechanical. New entries describe a pre- cision linear actuator, polygon connections, slip clutches, shape memory alloy latches, and an energy exchanger for making desalination more efficient. A complete Index makes it easy for readers to find all of the references to specific mechanisms, mechanical devices, components, and systems mentioned in the book. Engineering Choices to Examine Renewable Energy versus Fossil Fuel for Power Generation The chapter on renewable power generation discusses three of the most promising mechanical methods for generating carbon-free, grid-compatible electric power. Wind turbine farms and concentrating solar thermal (CST) plants are the most likely candidates for government subsidies. These technologies are described and illustrated, and their upsides and downsides are explained. Electricity can also be generated by ocean waves and tides, but these technologies lag far behind wind and solar thermal plants. The U.S. government is offering financial incentives for building electrical generating plants fueled by renewable energy, primarily for reducing atmospheric carbon dioxide (CO2) emissions, considered by some to be the principal source of manmade global warming. The administration has set the goal of increasing the number of carbon-free, non-hydro power plants from about 3 percent today to 20 percent by 2020. Wind and solar thermal power plants have the best chance of meeting this goal, but many worry that the building of these plants and eliminating many fossil-fueled plants could endanger the utility industries’ efforts to meet the nation’s growing demand for low-cost, readily avail- able electric power. Renewable energy power sources are handicapped by the inability of the overbur- dened power grid to transport electricity from remote parts of the country where most of these installations will be located to metropolitan areas where electricity demand is highest. When the wind dies or after sunset, these plants must be able to provide backup genera- tion or energy storage to meet their power commitments to the grid. This backup could include banks of batteries, heat stored in molten salt vats, and natural gas-powered steam generators, but the optimum choices have not been resolved because of variables such as plant power output and climate. Digital 3D versus Rapid Prototyping Recently introduced computer software makes it possible to design a product in a 3D for- mat from concept sketch to shop documentation on a computer. This process, 3D digital prototyping or modeling, can begin as an original design or be imported from another source. The software permits a 3D image to be disassembled and its dimensions, materi- als, and form changed before being reassembled as a new or modified product design on the same screen. The designer can work cooperatively with other specialists to merge valuable contributions for the achievement of the most cost-effective design. Changes can easily be made before the design is released for manufacture.xii
Virtual simulation software permits the 3D digital prototype to be given one or morevirtual stress tests with the results appearing graphically in color on the computer screen.These simulations can include both mechanical and physical stress, and their results cor-relate so closely with actual laboratory tests results that, in many cases, these tests can beomitted. This saves time and the expense of ordering physical prototypes and can accel-erate the whole design process and reduce time-to-market There are, however, many reasons why physical models are desired. These include theadvantages of having a solid model for “hands on” inspection, giving all persons withresponsibilities for its design and marketing an opportunity to evaluate it. However, someproducts require mandatory laboratory testing of a physical model to determine its com-pliance with industry and consumer safety standards. Rapid prototyping has gained moreacceptance as the cost of building prototypes has declined. Solid prototypes can be made from wax, photopolymers, and even powdered metals,but those built for laboratory testing or as replacement parts can now be made from pow-dered metal fused by lasers. After furnace firing they gain the strength to match that ofmachined or cast parts. Rapid prototyping depends on dimensional data derived from aCAD drawing for the preparation of software that directs all additive and subtractive rapidprototyping machines.The Origins of This BookMany of the figures and illustrations in the archival Chapters 4 through 16 originallyappeared in foreign and domestic engineering magazines, some 50 or more years ago.They were originally collected and republished in three McGraw-Hill reference booksdating back to the 1950s and 1960s. The author/editor of those books, Douglas C.Greenwood, was then an editor for McGraw-Hill’s Product Engineering magazine. Thelate Nicholas Chironis, the author/editor of the first edition of this book, selected illus-trations and text from these books that he believed were worthy of preservation. He sawthem as a collection of successful design concepts that could be recycled for use in newand modified products and would be a resource for engineers, designers, and students. New illustrations and text were added in the subsequent four editions of this book.The older content has been reorganized, redrawn as necessary, and in some cases deleted.All original captions have been edited for improved readability and uniformity of style.All illustrations are dimensionless because they are scalable to suit the intended applica-tion. References to manufacturers and publications that no longer exist were deleted but,where available, the names of inventors were retained for readers wishing to research thestatus of the inventors’ patents. All government and academic laboratories and manufac-turers mentioned in this edition have Internet Web sites that can be explored for furtherinformation on specific subjects.About the IllustrationsWith the exception of illustrations obtained from earlier publications and those contributedby laboratories or manufacturers, the figures in this book were drawn by the author on adesktop computer. The sources for these figures include books, magazines, and InternetWeb sites. The author believes that clear 3D line or wireframe drawings with callouts com-municate engineering information more rapidly and efficiently than photographs, whichoften contain extraneous or unclear details.AcknowledgmentsI wish to thank the following companies and organizations for granting me permission touse selected copyrighted illustrations and providing other valuable technical informationby various means, all useful in the preparation of this edition:• ABB Robotics, Auburn Hills, Michigan• Sandia National Laboratories, Sandia Corporation, Albuquerque, New Mexico• SpaceClaim Corporation, Concord, Massachusetts —Neil Sclater xiii
ABOUT THE EDITORNeil Sclater began his career as a microwave engineer in the defense industry and as aproject engineer at a Boston consulting engineering firm before changing his career pathto writing and editing. He was an editor for Electronic Design magazine and laterMcGraw-Hill’s Product Engineering magazine before starting his own technical com-munications firm. He served clients by writing and editing marketing studies, technical articles, andnew product releases. His clients included manufacturers of light-emitting diodes,motors, switching-regulated power supplies, and lithium batteries. During this 30-yearperiod he contributed many bylined technical articles to various engineering publica-tions on subjects ranging from semiconductor devices and servomechanisms to indus-trial instrumentation. Mr. Sclater holds degrees from Brown and Northeastern Universities. He is theauthor or coauthor of 12 books including 11 engineering reference books published byMcGraw-Hill’s Professional Book Group. The subjects of these books includemicrowave semiconductor devices, electronics technology, an electronics dictionary,electrical power and lighting, and mechanical subjects. After the death of Nicholas P.Chironis, the first author/editor of Mechanisms and Mechanical Devices Sourcebook,Mr. Sclater became the author/editor of the four subsequent editions.
CHAPTER 1 BASICS OFMECHANISMS
INTRODUCTIONComplex machines from internal combustion engines to heli-copters and machine tools contain many mechanisms. However,it might not be as obvious that mechanisms can be found in con-sumer goods from toys and cameras to computer drives andprinters. In fact, many common hand tools such as scissors,screwdrivers, wrenches, jacks, and hammers are actually truemechanisms. Moreover, the hands and feet, arms, legs, and jawsof humans qualify as functioning mechanisms as do the paws andlegs, flippers, wings, and tails of animals. There is a difference between a machine and a mechanism:All machines transform energy to do work, but only some mech-anisms are capable of performing work. The term machinerymeans an assembly that includes both machines and mecha-nisms. Figure 1a illustrates a cross section of a machine—aninternal combustion engine. The assembly of the piston, con-necting rod, and crankshaft is a mechanism, termed a slider-crankmechanism. The basic schematic drawing of that mechanism,Fig. 1b, called a skeleton outline, shows only its fundamen- Fig. 1 Cross section of a cylinder of an internal combustiontal structure without the technical details explaining how it is engine showing piston reciprocation (a), and the skeleton outline ofconstructed. the linkage mechanism that moves the piston (b).PHYSICAL PRINCIPLESEfficiency of Machines orSimple machines are evaluated on the basis of efficiency and output power Percent efficiency ϭ ϫ 100mechanical advantage. While it is possible to obtain a larger input powerforce from a machine than the force exerted upon it, this refersonly to force and not energy; according to the law of conserva- A machine has high efficiency if most of the power suppliedtion of energy, more work cannot be obtained from a machine to it is passed on to its load and only a fraction of the power isthan the energy supplied to it. Because work ϭ force ϫ distance, wasted. The efficiency can be as high as 98 percent for a largefor a machine to exert a larger force than its initiating force or electrical generator, but it is likely to be less than 50 percent foroperator, that larger force must be exerted through a correspond- a screw jack. For example, if the input power supplied to a 20-hpingly shorter distance. As a result of friction in all moving motor with an efficiency of 70 percent is to be calculated, themachinery, the energy produced by a machine is less than that foregoing equation is transposed.applied to it. Consequently, by interpreting the law of conservationof energy, it follows that: output power Input power ϭ ϫ 100 Input energy ϭ output energy ϩ wasted energy percent efficiency 20 hp This statement is true over any period of time, so it applies to ϭ ϫ 100 ϭ 28.6 hp 70any unit of time; because power is work or energy per unit oftime, the following statement is also true: Mechanical Advantage Input power ϭ output power ϩ wasted power The mechanical advantage of a mechanism or system is the ratio The efficiency of a machine is the ratio of its output to its of the load or weight W, typically in pounds or kilograms, dividedinput, if both input and output are expressed in the same units of by the effort or force F exerted by the initiating entity or opera-energy or power. This ratio is always less than unity, and it is usu- tor, also in pounds or kilograms. If friction has been consideredally expressed in percent by multiplying the ratio by 100. or is known from actual testing, the mechanical advantage, MA, of a machine is: output energy load W Percent efficiency ϭ ϫ 100 MA ϭ ϭ input energy effort F2
However, if it is assumed that the machine operates without distance. This property is known as the velocity ratio. It isfriction, the ratio of W divided by F is called the theoretical defined as the ratio of the distance moved by the effort per sec-mechanical advantage, TA. ond divided by the distance moved by the load per second for a machine or mechanism. It is widely used in determining the load W TA ϭ ϭ mechanical advantage of gears or pulleys. effort FVelocity Ratio distance moved by effort/secondMachines and mechanisms are used to translate a small amount VR ϭof movement or distance into a larger amount of movement or distance moved by load/secondINCLINED PLANEThe inclined plane, shown in Fig. 2, has an incline length l (AB) ϭ raised vertically through a height BC of 3 ft without using an8 ft and a height h (BC) ϭ 3 ft. The inclined plane permits a inclined plane, a force F of 1000 lb must be exerted over thatsmaller force to raise a given weight than if it were lifted directly height. However, with an inclined plane, the weight is movedfrom the ground. For example, if a weight W of 1000 lb is to be over the longer distance of 8 ft, but a force F of only 3/8 of 1000 or 375 lb would be required because the weight is moved through a longer distance. To determine the mechanical advantage of the inclined plane, the following formula is used: height h F ϭ W sin u sin u ϭ length l where height h ϭ 3 ft, length l ϭ 8 ft, sin ϭ 0.375, and weight W ϭ 1000 lb. F ϭ 1000 ϫ 0.375 F ϭ 375 lb load W 1000Fig. 2 Diagram for calculating mechanical advantage of an Mechanical advantage MA ϭ ϭ ϭ ϭ 2.7inclined plane. effort F 375PULLEY SYSTEMSA single pulley simply changes the direction of a force so itsmechanical advantage is unity. However, considerable mechani-cal advantage can be gained by using a combination of pulleys.In the typical pulley system, shown in Fig. 3a, each block con-tains two pulleys or sheaves within a frame or shell. The upperblock is fixed and the lower block is attached to the load andmoves with it. A cable fastened at the end of the upper blockpasses around four pulleys before being returned to the operatoror other power source. Figure 3b shows the pulleys separated for clarity. To raise theload through a height h, each of the sections of the cable A, B,C, and D must be moved to a distance equal to h. The operatoror other power source must exert a force F through a distances ϭ 4h so that the velocity ratio of s to h is 4. Therefore, the the-oretical mechanical advantage of the system shown is 4, corre-sponding to the four cables supporting the load W. The theoret-ical mechanical advantage TA for any pulley system similar tothat shown equals the number of parallel cables that support the Fig. 3 Four cables supporting the load of this pulleyload. combination give it a mechanical advantage of 4. 3
SCREW-TYPE JACKMechanisms are often required to move a large load with a smalleffort. For example, a car jack allows an ordinary human to lift acar which may weigh as much as 6000 lb, while the person onlyexerts a force equivalent to 20 or 30 lb. The screw jack, shown in Fig. 4, is a practical application ofthe inclined plane because a screw is considered to be an inclinedplane wrapped around cylinder. A force F must be exerted at theend of a length of horizontal bar l to turn the screw to raise theload (weight W) of 1000 lb. The 5-ft bar must be moved througha complete turn or a circle of length s ϭ 2 l to advance the loada distance h of 1.0 in. or 0.08 ft equal to the pitch p of the screw.The pitch of the screw is the distance advanced in a completeturn. Neglecting friction: W ϫ h F ϭ swhere s ϭ 2 l ϭ 2 ϫ 3.14 ϫ 5, h ϭ p ϭ 0.08, and W ϭ 1000 lb 1000 ϫ 0.08 80 F ϭ ϭ ϭ 2.5 lb Fig. 4 Diagram for calculating the mechanical advantage of a 2 ϫ 3.14 ϫ 5 31.4 screw jack. load 2p l 31.4 Mechanical advantage MA ϭ ϭ p ϭ ϭ 393 effort 0.08LEVERS AND MECHANISMSLeversLevers are the simplest of mechanisms; there is evidence thatStone Age humans used levers to extend their reach or power;they made them from logs or branches to move heavy loads suchas rocks. It has also been reported that primates and certain birdsuse twigs or sticks to extend their reach and act as tools to assistthem in obtaining food. A lever is a rigid beam that can rotate about a fixed pointalong its length called the fulcrum. Physical effort applied to oneend of the beam will move a load at the other end. The act ofmoving the fulcrum of a long beam nearer to the load permits alarge load to be lifted with minimal effort. This is another way toobtain mechanical advantage. The three classes of lever are illustrated in Fig. 5. Each iscapable of providing a different level of mechanical advantage.These levers are called Class 1, Class 2, and Class 3. The differ-ences in the classes are determined by:• Position along the length of the lever where the effort is applied• Position along the length of the lever where the load is applied• Position along the length of the lever where the fulcrum or pivot point is located Class 1 lever, the most common, has its fulcrum located at orabout the middle with effort exerted at one end and load posi-tioned at the opposite end, both on the same side of the lever.Examples of Class 1 levers are playground seesaw, crowbar, scis- Fig. 5 Three levers classified by the locations of their fulcrums,sors, claw hammer, and balancing scales. loads, and efforts.4
Class 2 lever has its fulcrum at one end; effort is exerted at the advantage. These machines are essentially Class 1 levers: effortopposite end, and the opposing load is positioned at or near the is applied to a lever or crank, the fulcrum is the center of themiddle. Examples of Class 2 levers are wheelbarrow, simple bot- drum, and the load is applied to the rope, chain, or cable.tle openers, nutcracker, and foot pump for inflating air mattresses Manually operated windlasses and capstans, mechanically theand inflatable boats. same, were originally used on sailing ships to raise and lower Class 3 lever also has its fulcrum on one end; load is exerted anchors. Operated by one or more levers by one or more sailors,at the opposite end, and the opposing effort is exerted on or about both had barrels or drums on which rope or chain was wound. Inthe middle. Examples of Class 3 levers are shovel and fishing rod the past, windlasses were distinguished from capstans; windlasseswhere the hand is the fulcrum, tweezers, and human and animal had horizontal drums and capstans had vertical drums. The mod-arms and legs. ern term winch is now the generic name for any manual or power- The application of a Class 1 lever is shown in Fig. 6. The lever operated drum for hauling a load with cable, chain, or rope. Theis a bar of length AB with its fulcrum at X, dividing the length of manually operated winch, shown in Fig. 7, is widely used todaythe bar into parts: l1 and l2. To raise a load W through a height on sailboats for raising and trimming sails, and sometimes forof h, a force F must be exerted downward through a distance s. weighing anchors.The triangles AXC and BXD are similar and proportional; there- Ignoring friction, the mechanical advantage of all of thesefore, ignoring friction: machines is approximately the length of the crank divided by the diameter of the drum. In the winch example shown, when the left end of the line is held under tension and the handle or crank is s l1 l1 turned clockwise, a force is applied to the line entering on the ϭ and mechanical advantage MA ϭ right; it is attached to the load to perform such useful work as h l2 l2 raising or tensioning sails.Fig. 6 Diagram for calculating the mechanical advantage of asimple lever for raising a weight.Winches, Windlasses, and CapstansWinches, windlasses, and capstans are machines that convert Fig. 7 Diagram for calculating the mechanical advantage of arotary motion into linear motion, usually with some mechanical manually operated winch for raising anchors or sails.LINKAGESA linkage is a mechanism formed by connecting two or more Simple Planar Linkageslevers together. Linkages can be designed to change the direc-tion of a force or make two or more objects move at the same Four different simple planar linkages shown in Fig. 8 are identi-time. Many different fasteners are used to connect linkages fied by function:together yet allow them to move freely such as pins, end-threaded • Reverse-motion linkage, Fig. 8a, can make objects or forcebolts with nuts, and loosely fitted rivets. There are two general move in opposite directions; this
Englisch-Deutsch-Übersetzung für mechanisms im Online-Wörterbuch dict.cc (Deutschwörterbuch).
Mechanisms definition, an assembly of moving parts performing a complete functional motion, often being part of a large machine; linkage. See more.
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