1、Fundamentals of Engineering High-Performance Actuator Systems 6654_Book.indb 1 10/25/16 2:56 PMOther SAE books of interest: Advances in Aircraft Landing Gear Robert Kyle Schmidt (Product Code: PT-169) Advances in Aircraft Brakes and Tires Robert Kyle Schmidt (Product Code: PT-171) Advanced Engine De
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6、 books.sae.org 6654_Book.indb 4 10/25/16 2:56 PMv Contents Chapter 1: Introduction .1 1.1 Fundamentals 2 1.2 Performance 2 1.3 Loads 3 1.4 Constraints . 3 1.5 Design Margin 4 1.6 Environment . 4 1.7 Component Strength 5 1.8 Component Stiffness. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7、 . . . . . . . . . . . . . . . . 5 1.9 Reliability 5 1.10 Maintainability . 6 1.11 Cost . 6 1.12 Summary 6 1.13 References . 8 Chapter 2: Project Management .9 2.1 Scope 9 2.2 Requirements . 9 2.3 Schedule 10 2.4 Cost 13 2.4.1 Design Cost . 14 2.4.2 Prototype Cost . 15 2.4.3 Production Cost 17 2.4.4
8、 Operating Cost . 19 2.4.5 Decommissioning Cost 19 2.4.6 Cost Estimating Techniques 20 2.5 Risk 21 2.5.1 Schedule 22 2.5.2 Cost 22 2.5.3 Technology 22 2.5.4 Customer Acceptance . 22 2.5.5 Risk Management 23 2.6 Project Close Out . 24 2.7 References 25 6654_Book.indb 5 10/25/16 2:56 PMvi Contents Cha
9、pter 3: Requirements Analysis 27 3.1 Performance . 28 3.1.1 Work . 30 3.1.2 Impulse . 31 3.1.3 Momentum 31 3.1.4 Energy 31 3.1.5 Power 32 3.1.6 Equations of Motion 33 3.1.6.1 Summary 42 3.1.6.1.1 Velocity 42 3.1.6.1.2 Acceleration 43 3.1.6.1.3 Position. . . . . . . . . . . . . . . . . . . . . . . .
10、. . . . . . 44 3.2 Loads . 46 3.3 Component Stiffness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.3.1 Linear Stiffness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.3.2 Rotary Stiffness 50 3.3.3 Materials 52 3.4
11、Component Strength . 53 3.4.1 Yield Strength and Elastic Analysis . 54 3.4.2 Ultimate Strength and Plastic Analysis 59 3.4.3 Fatigue Strength . 61 3.5 Constraints 65 3.5.1 Mounting Configuration 65 3.5.1.1 Pinned Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.5.1.2
12、Simply Supported Joints . 66 3.5.1.3 Fixed Support Joints 66 3.5.1.4 Joint Combinations . 66 3.5.2 Environment 67 3.5.2.1 Operation . 67 3.5.2.2 Storage 67 3.5.2.3 Shipping and Transportation . 68 3.5.3 Pollution 68 3.5.4 Safety . 68 3.5.4.1 Personnel Safety 69 3.5.4.2 Machine Safety . 69 3.5.4.3 En
13、vironmental Safety . 69 3.5.4.4 Safety Summary 69 3.5.5 Reliability . 70 3.5.6 Maintenance . 71 3.5.6.1 Preventative Maintenance . 71 3.5.6.2 Repair 72 3.6 Verification and Validation 73 3.7 Summary . 73 3.8 References 73 6654_Book.indb 6 10/25/16 2:56 PMvii Contents Chapter 4: Design to Requirement
14、s 75 4.1 Performance Allocations 75 4.2 References 80 Chapter 5: Power Sources .81 5.1 Hydraulic . 81 5.1.1 Hydraulic Symbols . 81 5.1.2 Power Source 82 5.1.3 Hydraulic Power Unit 83 5.1.4 HPU Component Selection 84 5.1.5 Fluids . 84 5.1.6 Tank or Reservoir 86 5.1.7 Pumps 87 5.1.8 Prime Mover 88 5.1
15、.9 Filters . 88 5.1.10 Accumulators 89 5.1.11 Heat Exchangers . 91 5.1.12 General Hydraulic Power Unit Valves . 92 5.1.13 High-Performance Actuator Control Valves 93 5.1.14 References . 94 5.2 Pneumatic Systems . 95 5.2.1 References . 98 5.3 Electric . 98 5.3.1 References 101 5.4 Actuator Detailed D
16、esign 101 5.4.1 Motor Selection . 101 5.4.1.1 Motor Shaft Loads . 101 5.4.1.2 Motor Torque Requirements 102 5.4.1.3 Motor Speed Requirements . 104 5.4.1.4 Electric Motor Selection 104 5.4.1.4.1 AC induction (synchronous) motors 106 5.4.1.4.2 DC stepper motors . 106 5.4.1.4.3 DC brushless motors . 10
17、7 5.4.1.4.4 DC brushed permanent magnet motors . 109 5.4.1.5 Hydraulic Motor Selection 109 5.4.1.5.1 Gear motors 112 5.4.1.5.2 Vane motors 112 5.4.1.5.3 Gerotor/Geroler motors . 113 5.4.1.5.4 Axial and bent axis piston motors . 113 5.4.1.5.5 Radial piston motors 114 5.4.1.6 Pneumatic Motors 115 5.4.
18、2 References . 116 6654_Book.indb 7 10/25/16 2:56 PMviii Contents 5.5 Control Element Design and Selection 116 5.6 Linear Actuator Design . 116 5.6.1 Cylinders 121 5.6.1.1 Hydraulic Cylinders . 123 5.6.1.2 Pneumatic Cylinders . 134 5.6.2 Motor and Rack . 135 5.6.3 Screws . 136 5.6.4 Spring Rate for
19、Power Screw Actuators . 144 5.6.4.1 Mounting Structure and Load Structure Stiffness 144 5.6.4.2 Screw Stiffness 145 5.6.4.3 Nut Stiffness 145 5.6.4.4 Total Screw/Nut Stiffness. . . . . . . . . . . . . . . . . . . . . . . 146 5.6.4.5 Bearings 147 5.6.5 Screw Critical Speed . 147 5.6.6 Electric Soleno
20、ids . 149 5.6.7 Electric Linear Motors . 152 5.6.8 References 155 5.7 Rotary Actuator Design 156 5.7.1 Direct Drive Motors . 156 5.7.2 Gear Boxes . 156 5.7.3 Mechanical Mechanisms . 160 5.7.4 Racks 161 5.7.5 References 163 5.8 Feedback Systems . 163 5.8.1 Sensor Type 163 5.8.1.1 Rotary Sensors 164 5
21、.8.1.2 Linear Sensors 165 5.8.1.3 Inertial Sensors 167 5.8.2 Sensor Location . 169 5.8.3 Actuator Components to Stop/Hold a Load 170 5.8.4 References 172 5.9 Verification and Validation . 172 Chapter 6: Prototyping .173 6.1 Fabrication . 173 6.2 Assembly 175 6.3 Prototype Verification and Validation
22、 176 Chapter 7: Verification and Validation.177 7.1 Engineering Judgment . 177 7.2 Comparison 178 7.3 Analysis . 178 7.4 Testing . 178 6654_Book.indb 8 10/25/16 2:56 PMix Contents Chapter 8: Production.181 Bibliography . 183 Appendix A: Hydraulic Symbols . 187 Training SupplementProblems by Chapter
23、. 193 Chapter 1 Problems . 193 Chapter 2 Problems . 193 Chapter 3 Problems . 194 Chapter 4 Problems . 197 Chapter 5 Problems . 197 5.1 Problems . 197 5.2 Problems . 198 5.4 Problems . 198 5.6 Problems . 198 5.7 Problems . 200 5.8 Problems . 201 Chapter 7 Problems . 201 About the Author 203 Index 205
24、 6654_Book.indb 9 10/25/16 2:56 PM6654_Book.indb 10 10/25/16 2:56 PM1 Chapter 1 Introduction Today, actuators play an increasingly important role in our society. They are the elements that make everything around us move, increasingly by remote control through software commands. Robotic devices can h
25、ave multiple actuators for independent motion in many degrees of freedom. Less sophisticated systems may only have a single actuator to perform the motion required. In all cases, the actuator needs to be engineered correctly to perform its function reliably and at the lowest achievable cost. Actuato
26、rs are the key to allowing machines to become more sophisticated and perform complex tasks that were previously done by humans. Now a multitude of tasks, large and small, are performed by machines. Some tasks are performed with complete auto- mation where the operator just designates the task to be
27、done and the machine completes it without any further input from the operator. Other tasks are done with various levels of input from the operator to guide the machine and make decisions along the way. In either case, actuators need to provide motion in a safe, controlled manner. The fundamental app
28、roach to actuator design is the same for large or small loads. It is really just a matter of scaling. Of course, the engineer needs to utilize technologies relevant for the size of the task, but as technologies mature, an approach that was not feasible a few years ago may now be the best choice. For
29、 example, a few years ago, the best actuator for moving large loads were hydraulic based, but now electric drive options are available and may be the best choice for many applications. Most readily available commercial actuators are for mid-size applications. Very large or very small applica- tions
30、require additional design effort to create custom components to satisfy the design requirements. As the designer gains experience with the design process, components available, and manufacturing/assembly constraints, the ability to transfer this knowl- edge to other large and small designs increases
31、. As defined in this book, actuator design is a subset of mechanical design. It involves engineering the mechanical components necessary to make a product move as desired. This includes defining loads, move profiles, associated mechanisms, and prime movers. 6654_Book.indb 1 10/25/16 2:56 PM2 Chapter
32、 1 In addition, operating and storage environments need to be defined and considered so that the end product has satisfactory behavior and reliability. All these should be defined in a stable set of requirements that can be used to guide the design and judge its maturity. The main difference between
33、 a designed product and an engineered product is the level of knowledge about how the product is going to perform before it is built. A designed product may look good and can perform as the user/customer expects, but it may be bigger or heavier or use more energy than necessary because its design is
34、 based on limited analysis. On the other hand, an engineered products design and features are based on engineering analysis, so performance, weight, and energy usage are optimized. From the engineers viewpoint, customers include internal company representatives from management, sales, and marketing.
35、 External customers include the person or orga- nization buying the actuator as well as users who may not directly buy the machine or equipment but work for the purchaser and can influence the purchasers decisions. This book is written as a text to supplement actuator design courses and a reference
36、to engineers involved in the design of high-performance actuator systems. It highlights the design approach and features that should be considered when moving a payload at precision levels and/or speeds that are not as important in low-performance applica- tions. However, there are specialized areas
37、 such as military and aerospace applications that may have their own set of additional or unique features or processes not addressed in this book. Some sections of this book contain considerable equation background and derivation. The intent is to help the reader understand the basic principles so t
38、hat they can be applied correctly and how equations are related. There is also a desire to minimize the mystery on how an equation is derived from the previous one. 1.1 Fundamentals The fundamentals for actuator design include many of the basic machine design prac- tices used in other mechanical eng
39、ineering design tasks. One has to consider basics such as performance requirements, loading, constraints, component strength, stiffness, and safety margin along with the environment that the product is exposed to and must operate in. Each of these areas is briefly explored and reviewed in this secti
40、on. 1.2 Performance In the context of this book, an actuator or products performance involves how fast it can move a payload between defined positions with the desired level of control. High perfor- mance does not necessarily mean that the payload is large or the motion is exception- ally fast, but
41、rather that the load is consistently moved as desired with the appropriate combination of product size, mass, reliability, maintainability, efficiency, and cost. Most design efforts start with defining an approach and/or configuration that can meet the desired payload, move time or velocity, and ran
42、ge of motion. These parameters define configuration, forces and component size options. These options can then be compared 6654_Book.indb 2 10/25/16 2:56 PM3 Introduction to determine the best combination that satisfies all the other design requirements. An actuator rapidly moving a load from positi
43、on A and slamming it into a stop at position B would not be defined as a high-performance actuator. An actuator that consistently moves the payload from A to B within the specified boundary conditions, over the speci- fied range of environmental conditions (temperature, rain, snow, ice, etc.), exter
44、nally imposed disturbances (mobility loads, shock, vibration), and system drive variations (hydraulic pressure, voltage variation, friction, etc.) is a high-performance actuator. 1.3 Loads Loads that the actuator and its surrounding structure must accommodate include static loads, dynamic (transient
45、) loads, inertial loads, and environmental loads. These loads cause the structural components to be in tension or compression or have internal moments and can be applied as concentrated (point) or distributed loads. For most engineers, static loads are the easiest ones to define and in some cases pr
46、ovide enough information to perform initial component sizing. Static loads may come from the struc- tural mass, externally applied loads, and loads from any item being moved by the actuator. Dynamic loads can be generated by the actuator moving its load or can come from external influences such as m
47、ovement of nearby equipment or movement of the structure that mounts the actuator. Some of these loads may be vibration loads that can excite system frequencies and need to be evaluated for high-cycle fatigue or shock loads that cause less-frequent high loads that need to be evaluated for low-cycle
48、fatigue and strength. Inertial loads come from accelerating or decelerating the load, structure, and actuator components. One also needs to consider loads imposed upon the compo- nents when stopping due to an internally or externally declared emergency stop or stop brought about due to some system f
49、ailure. In all cases, it is desired to bring the load to a carefully controlled stop. Unless the motion is slow, inertial loads need to be included in both structural and drive load calculations. Finally, environmental loads can be static loads from wind, rain, snow, or ice directly loading the components or can be thermal loads that cause the equipment to expand or contract. Some environmental loads such as wind can be transient, and as such, their dynamic effect on actuator force and structural excitation needs to be considered. Design loads are explored in more depth in chapter 3. 1
