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Precision machine design
PRECIS Book Review Precision Machine Design Alexander H. Slocum Prentice Hall, 1992, 750 pp., $62.00 Alexander Slocum's Precision Machine Design provides an insight into the engineering design process for a precision machine. Slocum, a faculty member in the Department of Mechanical Engineering of the Massachusetts Institute of Technology and the author of numerous articles on precision fixtures and mechanisms, has written this book to serve as both an advanced engineering design textbook and a reference for the practicing engineer. The text begins by outlining the steps of the generic design process (e.g., economic analysis, project management, brainstorming, conceptual design), then goes on to discuss issues germane to the design of a precision machine, such as error budgets, metrology frames, and error mapping. Throughout his book, Slocum underscores the fact that a precision machine demands "painstaking attention to detail" in every aspect of the design process. Slocum's 700 + page work is not for the faint of heart. Not too far into the preface, the reader will undoubtedly sense the author's enthusiasm for the subject and will realize the impending challenge of keeping pace with the author. However, although this book covers a wide range of topics, most of the subjects are thoroughly discussed and, for those topics that are less detailed, numerous references are cited for further study. In addition, several case studies have been incorporated into the text to illustrate how precision engineering issues can be successfully addressed. In Chapter 1, Slocum introduces the elements of the design process. This introduction begins with brief discussions of economic analysis (e.g., the time value of money, cashflow analysis, rate of return calculation) and project management concepts and techniques (e.g., the CPM method, cost and time estimation). Next, Slocum lists the attributes of a PRECISION ENGINEERING
good design engineer, emphasizing the importance of thinking creatively, keeping informed, and observing the world around us. Next, methods are suggested for developing several conceptual designs and then systematically selecting the best design. The many considerations (e.g., kinematics, dynamics, ergonomics, maintenance) in the design of machine tools are presented in an outline that should prove useful to any engineer. The chapter concludes with very enlightening case studies of the design processes for a high-speed machining center and a coordinate-measuring machine. Chapter 2 discusses the performance issues of accuracy, repeatability, and resolution. The error budget is introduced as an excellent tool for the preconstruction estimation of machine and environmental errors. The homogeneous transformation matrix is presented as a method for modeling the effects of various machine errors. Typical error sources are identified (e.g., temperature variations, gravity, variable process loads), and various techniques are suggested for minimizing errors. Chapter 2 ends with a case study of leadscrew-induced carriage straightness-of-motion errors. Slocum devotes three chapters to the discussion of sensor issues. Chapter 3 defines various terms used in the discussion of sensors (e.g., accuracy, frequency response, hysteresis). Chapter 3 also discusses the operation, typical performance characteristics, and applications of nonoptical sensors such as capacitance probes, hall effect sensors, inductive sensors, LVDTs, and so forth. Chapter 4 is a discussion of operating principles, performance characteristics, and applications for various optical sensors, including autocollimators, optical encoders, and interferometric sensors. Chapter 5 presents sensorrelated issues, such as sensor location, alignment, mounting, and environment. The concept of the metrology frame is introduced as a means of achieving a reference that is unaf-
fected by the machine process. Sensor calibration issues (e.g., repeatability, systematic uncertainty, sampling rate) are discussed. Finally, a case study of the design of a laser telemetric system is presented. Chapter 6 is a detailed case study of machine error compensation. This case study discusses the construction of a homogeneous transformation matrix for a turning center, the mapping of the machine's geometric and thermal errors, and the development and implementation of a real-time error compensation scheme. Various design considerations are discussed in Chapter 7. These issues range from manufacturability and material selection to structural design and support system requirements. The chapter begins with a discussion of the available fabrication, heat treating, and plating techniques. Next is an examination of material selection issues (e.g., strength, thermal expansion, thermal conductivity). The sections on structural and joint design focus on issues such as minimizing vibration transmission and distortion and maximizing damping and thermal stability. Bolted joints, pinned joints, adhesive joints, etc., are examined in terms of stiffness, stability, permanence, and so forth. The section on support systems emphasizes the importance of systems and components such as safety systems, coolant system equipment, sealing systems, and tooling and fixturing hardware. Chapters 8 and 9 discuss contacting and noncontacting bearings, respectively. Slocum provides explanations of the various bearing designs, methods for analyzing existing bearing designs, and designing custom bearings. The information on the commercially available bearings includes system performance data (e.g., range of motion, accuracy, repeatability, load capability) and typical applications. In the final chapter, the issues related to power generation and transmission are discussed. The discussion begins with a procedure for 51
PRECIS the dynamic matching of these components to the specific machine requirements such as stiffness, force, or torque capacity. The chapter also includes an examination of various types of motors and actuators (e.g., voice coils, piezoelectrics, hydraulics), noninfluencing coupling mechanisms, and transmission components (e.g., belts, gears, traction drives, leadscrews). The book ends with a case study involving the use of real-time control to increase the axial stiffness of an instrument-positioning stage. Although a single text cannot fully address every issue encoun-
52
tered in the expansive realm of precision engineering, Precision Machine Design does consolidate a wealth of material into one volume. This book summarizes fundamental design principles, outlines analysis techniques, presents representative data for a range of machine components, and discusses how these component characteristics influence the performance of a precision machine. The author's casual writing style may appeal to some readers, but others may be distracted by the numerous tangential references and editorials. For the most part, the graphics are adequate (in several illustrations the
components are not well labeled), but a few more illustrations would have been helpful. This book could serve as a course text, although no homework problems are provided. This book should also prove to be a valuable reference despite the rather abbreviated index, which could make locating a specific subject difficult. However, because of the breadth of coverage, I would recommend the book to anyone interested in precision engineering design.
Donnie Moorefield
J A N U A R Y 1993 VOL 15 NO 1
good design engineer, emphasizing the importance of thinking creatively, keeping informed, and observing the world around us. Next, methods are suggested for developing several conceptual designs and then systematically selecting the best design. The many considerations (e.g., kinematics, dynamics, ergonomics, maintenance) in the design of machine tools are presented in an outline that should prove useful to any engineer. The chapter concludes with very enlightening case studies of the design processes for a high-speed machining center and a coordinate-measuring machine. Chapter 2 discusses the performance issues of accuracy, repeatability, and resolution. The error budget is introduced as an excellent tool for the preconstruction estimation of machine and environmental errors. The homogeneous transformation matrix is presented as a method for modeling the effects of various machine errors. Typical error sources are identified (e.g., temperature variations, gravity, variable process loads), and various techniques are suggested for minimizing errors. Chapter 2 ends with a case study of leadscrew-induced carriage straightness-of-motion errors. Slocum devotes three chapters to the discussion of sensor issues. Chapter 3 defines various terms used in the discussion of sensors (e.g., accuracy, frequency response, hysteresis). Chapter 3 also discusses the operation, typical performance characteristics, and applications of nonoptical sensors such as capacitance probes, hall effect sensors, inductive sensors, LVDTs, and so forth. Chapter 4 is a discussion of operating principles, performance characteristics, and applications for various optical sensors, including autocollimators, optical encoders, and interferometric sensors. Chapter 5 presents sensorrelated issues, such as sensor location, alignment, mounting, and environment. The concept of the metrology frame is introduced as a means of achieving a reference that is unaf-
fected by the machine process. Sensor calibration issues (e.g., repeatability, systematic uncertainty, sampling rate) are discussed. Finally, a case study of the design of a laser telemetric system is presented. Chapter 6 is a detailed case study of machine error compensation. This case study discusses the construction of a homogeneous transformation matrix for a turning center, the mapping of the machine's geometric and thermal errors, and the development and implementation of a real-time error compensation scheme. Various design considerations are discussed in Chapter 7. These issues range from manufacturability and material selection to structural design and support system requirements. The chapter begins with a discussion of the available fabrication, heat treating, and plating techniques. Next is an examination of material selection issues (e.g., strength, thermal expansion, thermal conductivity). The sections on structural and joint design focus on issues such as minimizing vibration transmission and distortion and maximizing damping and thermal stability. Bolted joints, pinned joints, adhesive joints, etc., are examined in terms of stiffness, stability, permanence, and so forth. The section on support systems emphasizes the importance of systems and components such as safety systems, coolant system equipment, sealing systems, and tooling and fixturing hardware. Chapters 8 and 9 discuss contacting and noncontacting bearings, respectively. Slocum provides explanations of the various bearing designs, methods for analyzing existing bearing designs, and designing custom bearings. The information on the commercially available bearings includes system performance data (e.g., range of motion, accuracy, repeatability, load capability) and typical applications. In the final chapter, the issues related to power generation and transmission are discussed. The discussion begins with a procedure for 51
PRECIS the dynamic matching of these components to the specific machine requirements such as stiffness, force, or torque capacity. The chapter also includes an examination of various types of motors and actuators (e.g., voice coils, piezoelectrics, hydraulics), noninfluencing coupling mechanisms, and transmission components (e.g., belts, gears, traction drives, leadscrews). The book ends with a case study involving the use of real-time control to increase the axial stiffness of an instrument-positioning stage. Although a single text cannot fully address every issue encoun-
52
tered in the expansive realm of precision engineering, Precision Machine Design does consolidate a wealth of material into one volume. This book summarizes fundamental design principles, outlines analysis techniques, presents representative data for a range of machine components, and discusses how these component characteristics influence the performance of a precision machine. The author's casual writing style may appeal to some readers, but others may be distracted by the numerous tangential references and editorials. For the most part, the graphics are adequate (in several illustrations the
components are not well labeled), but a few more illustrations would have been helpful. This book could serve as a course text, although no homework problems are provided. This book should also prove to be a valuable reference despite the rather abbreviated index, which could make locating a specific subject difficult. However, because of the breadth of coverage, I would recommend the book to anyone interested in precision engineering design.
Donnie Moorefield
J A N U A R Y 1993 VOL 15 NO 1