Ebook: The Design of High Performance Mechatronics – 3rd Revised Edition

Motivation to the First Edition

A world without mechatronics is almost as unthinkable as a world without electric light. After its origin around the second world war the name mechatronics has become known for all kind of mechanical systems where mechanics and electronics are combined to achieve a certain function. The complexity of mechatronic systems ranges from a simple set of electronic controlled relay-switches to highly integrated precision motion systems. This proliferation of mechatronics has been described in many books, which each have been written with a different scope in mind depending on the specific technological anchor point of the author(s) within this wide multidisciplinary field of engineering.

This book distinguishes itself from other books in several ways. First of all it is a combination of a reference book for engineers working in the high-tech industry and a university textbook, due to the mixed industrial and academic background of the authors. The industry oriented part is based on extensive experience in designing the most sophisticated motion systems presently available, the stages of wafer scanners, which are used in the semiconductor industry. The academic part is based on advanced research on precision motion systems, including ultra precision metrology equipment with fast Scanning-Probe Microscopy and optical measurement systems with sub-nanometre accuracy. The high-tech industrial background focuses on high-precision positioning at very high velocity and acceleration levels. With this focus, the book does not include examples from other important application areas like robotics, machining centres and vehicle mechatronics, though the theory is also applicable to those areas of mechatronics.

The presented material is aimed at obtaining maximum understanding of all dynamic aspects of a motion system, which is the reason for the term “High Performance” in the title.

Another, more teaching related reason for writing this book is based on the observation that most students at the university are rather well trained in applying mathematical rules for solving purely mathematical problems, while they often have more difficulties in the application of these mathematics in the modelling of real designs. The industrial need for well educated engineers with both theoretical and practical skills, combined with a healthy critical attitude to the outcome of computer simulations, became a guiding motive for writing this book. The capability to swiftly switch between model and reality is one of the most important skills of a real multidisciplinary designer. This capability helps to quickly predict the approximate system behaviour in the concept phase of a design, where intuition and small calculations on the backside of an envelope are often more valuable than computer based detailed calculations by means of sophisticated modelling software. It is certainly true that these software tools are indispensable for further detailing and optimisation in the later phase of a design project but more attention is needed for basic engineering expert-knowledge to cover the concept-design phase where the most important design decisions are taken. In view of these main motivations to write this book, it was also decided to focus uniquely on the hardware part of mechatronic systems. This means that the important field of embedded software is not presented even though software often serves as the actual implementation platform for modern control systems. The reason for this exclusion is the intended focus of this book on the prime functionality of a mechatronic system, without the interfaces to other systems and human operators. The logical sequence algorithm of the controller, together with the sampling delay, is more important for this prime functionality than the way how this algorithm is described in C-code.

When writing a book on mechatronics, the broad range of contributing disciplines forces a limitation in the depth to which the theory on each of these disciplines can be treated. Where necessary for the explanation of certain effects the presented material goes deeper, but other subjects are treated in such a way that an overall understanding is obtained without specialised in depth knowledge of all details.

Like the work of a mechatronic engineer as system designer in a team of specialists, this book is aimed to be a binding factor to the related specialised books, rather than one that makes these other sources of knowledge redundant.

It is our sincere wish that this book serves its purpose.

Robert Munnig Schmidt, Georg Schitter, Adrian Rankers and Jan van Eijk

Comments to the Third Edition

As of the second edition from 2014 several users of this book have made comments, which again rapidly filled the errata pages.

Also the many courses given by the authors at universities or with training sessions for industrial engineers triggered attention to subjects that could be explained better or more adapted to the present level of knowledge.

Most changes have been made in Chapter 4 on motion control, where the focus in feedback control is shifted from pursuing a target bandwidth to a targeted low sensitivity for disturbances in combination with high-accuracy feedforward control using a solid trajectory planning, which is more in line with industrial practice. For this reason the PID guidelines are replaced by design steps that also include optimisation with loopshaping.

The presentation of “poles and zeros” and the different kinds of impedances is moved to the physics chapter as it is applied in different chapters. The physics chapter is the “must study first” chapter prior to studying any of the other chapters, as most of the used terms are introduced there.

Another change is the addition of a dB scale next to the absolute magnitude scale in the Bode plots of the motion control chapter, because it has often been mentioned that the use of dB is as common in the control community as it is in the electronics community.

The redefinition of the SI base units in May 2019 required slight changes in some numbers and it further appeared useful to mention the units with the equations to avoid confusion.

Due to the addition of several subjects also some pruning of “ancient” technology has been done. Especially the large part on linear power amplifiers is reduced to the bare minimum, because at present almost all power amplifiers apply switched-mode technology.

Finally the “Main Design Rules for Precision” section, which was omitted from the second edition returns at the end of Chapter 9 after a complaint of an enthusiastic reader who worked with both the first and second edition and said he really used them.

Contributions and Acknowledgements

Besides much material from our own experience, this book also includes material created by many other people.

Several university staff members and students have contributed to and reviewed the material. Some are cited in the text but even then it is impossible to mention all without forgetting some names. For this reason only the most important contributors who are not cited separately are mentioned here. The first is Ton de Boer, the MSc student who had the near impossible task to write the rough material that started this book as lecture notes by following the lectures on Mechatronic System Design. Johan Vogel and Oscar vd Ven, also from the Mechatronic System Design group at Delft University of Technology reviewed the first versions and helped with the physics and electromechanics chapters, while Markus Thier from the Automation and Control Institute at Vienna University of Technology helped with the new section in the second edition on digital motion control.

For the third edition the comments from several colleagues from the research groups “Control Systems Technology” and “Electromechanics and Power Electronics” of Eindhoven University of Technology were very helpful.

Our partners from industry deserve gratitude for their support, financially, in equipment or advice, by permission to use company illustrations or by reviewing the material. The three most important to mention are the Dutch high-tech company ASML and the metrology companies Heidenhain from Germany and Agilent Technologies from the United States.

We further thank all other companies and individuals who kindly gave permission to use their illustrations. Where appropriate these are separately mentioned at the related figures or cited in the bibliography.

It is true to say that this textbook is based on the knowledge of many others as laid down in books, patents and journal articles. Several are cited in the text but most are not, because their knowledge entered the public domain very long ago. Still it are these giants on whose shoulders we all stand (Cited with a slight variation to the words of Bernard de Chartres ≈1115.) and who deserve our gratitude. In that respect it is worthwhile to mention the increasing value of Wikipedia. Besides the possibility to quickly find certain physical and mathematical terms or derivations, it also provided information about small trivia like the date of birth or the full name of a famous scientist from the past.

Errata

For the third edition a new dedicated website domain is created.

While the rmsmechatronics errata site (errata.rmsmechatronics.nl) will remain for some time with the errata in the first and second edition, all errata will be published on the new website:

high-performance-mechatronics.nl

Summary

This book is intended for Bsc level students as an introduction to mechatronics, for Msc-level students who want to extend their knowledge on all aspects of advanced mechatronics and for engineers in the high-tech industry who want to learn more about adjacent specialisations. To accommodate this broad approach and define the application environment, the first and last chapter describe the waferscanners of ASML as these complex systems are symbolic for the high level of advancement that modern mechatronic systems have achieved.

The nine chapters are summarised as follows:

The introduction in Chapter 1 gives the context of Mechatronics in the Dutch High-Tech Industry with the historical background, some general observations on the international differences in approach towards mechatronics and the close link with “Systems Engineering”. Subjects include the development of the optical Video Long Play (VLP) disk and the wafer stepper at Philips Research Laboratories. These developments have strongly determined the dominant position of high-precision mechatronic system design in the Netherlands and are exemplary for the specific photon-physics oriented approach in this country, quite different from the machining oriented approach in most other countries. The overview on systems engineering and design introduces some functional design and development methodologies that have proved to be crucial for the success of the high-tech industry. These methods are based on industrial practice where complex multidisciplinary designs have to be realised. Systems Engineering is a field closely related to mechatronics and the corresponding principles are used in structuring the design of a mechatronic system.

Chapter 2 on the Applied Physics in Mechatronic Systems is the first of a series of chapters on the theory behind controlled motion systems. After an introduction to some relevant items from the mechanical domain, like coordinate systems and the physical laws on force and motion, the chapter introduces the core physics of electricity and magnetism as applied in mechatronic positioning systems. This is followed by a section on signal theory and wave propagation. This chapter explains why the properties of mechatronics are so often described in frequency responses next to the real-world time-domain related responses. The chapter also introduces the mathematical background of different graphical representations of frequency responses, which are used in several chapters of this book. For reasons of historic consciousness with most physical units the scientists who borrowed their name to the units are mentioned with the period they lived in.

The core of a mechatronic system is the mechanical structure that represents the real hardware. In most cases the dynamic properties of this structure determine the ultimately achievable control performance. Expert knowledge of this field is a prerequisite for a mechatronic designer. For that reason Chapter 3 deals with these Dynamics of Motion Systems and mainly concentrates on the vibrational properties of standard mechanical elements consisting of a multitude of springs, bodies and dampers. It includes a more in depth treatise of modal decomposition, a method to describe the dynamic response to external forces by means of individual vibration modes, which allow to optimise the structural dynamics for controlled motion.

The important field of Motion Control in Chapter 4 is directly related to the mechanical dynamics. This chapter introduces both feedforward control for following a known trajectory and feedback control to cope with unknown disturbances and unstable systems. The presented treatise of the working principle and tuning of the still widely used PID controllers gives the required background knowledge to achieve a good controller design. The practice of loop-shaping for optimising a PID feedback controller is introduced and the design steps to an optimal PID-controller are clearly presented. Also an introduction is given in state-space control with direct pole placement as this method plays an increasing role in the design of mechatronic systems where computer simulations and optimisation algorithms have largely replaced experimental design. A strong emphasis is given to the physical aspects of control. It is shown that feedback control adds virtual elements from the mechanical domain to the system, like springs and dampers together with new elements like an integrator and observer.

Chapter 5 on Electromechanic Actuators focuses on linear actuators rather than standard rotating motors for several reasons. First of all many books exist describing the application of these standard motors, while secondly in most cases they require transmissions. Finally they are aimed to be used in off-the-shelf design solutions with limited performance specifications which is not the scope of this book on high-performance mechatronics. This chapter presents both electromagnetic actuators and piezoelectric actuators as the latter are increasingly applied in precision mechatronic systems. This chapter will help in the selection process of actuation systems and creates a knowledge base for further study on the subject. Also the relation with power-amplifier constraints, which are presented in the following chapter, is made clear.

Chapter 6 on Analogue Electronics in Mechatronic Systems presents the applied electronics for measurement and power conversion and starts at a very basic level with passive components, because most mechanical engineers have hardly any knowledge about electronics. The introduction of the active components leads to their application in the basic design of the operational amplifier, the most universal and widely used analogue electronic building block. The last section in this large chapter gives an overview of the basic design of power amplifiers, which act as the energy supplying interface between the controller and the actuators.

Chapter 7 on Optics in Mechatronic Systems gives an introduction to the important field of optics from the perspective of a mechatronic designer. The application of optics has become a main driver of mechatronic advancement in the past decades. Firstly it is an application area where mechatronics are used to control and correct optical properties of imaging systems and other instrumentation. Secondly, optics are used to determine distances and dimensions in a plurality of sensors, which enables the designer to create measurement systems with extreme precision. Starting with basic physics on optics with sources and the duality of light, an overview of geometrical and physical optics is presented including limiting factors for the performance of imaging systems. The chapter concludes with an introduction on adaptive optics.

Chapter 8 on Measurement in Mechatronic Systems presents the basic principles of sensors for force and dynamic position measurement based on several physical principles including strain-, inductive-, capacitive- and optical sensors. The theory in this chapter will enable the first selection of suitable sensors when designing a mechatronic system. Laser interferometry and encoders will also be presented as these are most frequently applied in high precision mechatronic systems. Even though metrology in general will be shortly touched, the chapter concentrates on measurement for control. For this reason also the principle of dynamic error budgeting is included, a statistical method to determine the total error in a dynamic precision system from contributions of different error sources.

As closure of the book Chapter 9 on Precision Positioning in Wafer Scanners presents the mechatronic design in the exposure machines of ASML, where all theory is applied to its most extreme level. This chapter includes the basic design of positioning stages, the need for and active control of vibration isolation, and the motion control approach to achieve a position accuracy of less them a nanometre at speeds of more than 1 m/s and accelerations of more than 30 m/s². Even though the presented material reflects the situation of several years ago it is still relevant for present day engineers as the design principles as described in this book are still applied.