Ebook: The Design of High Performance Mechatronics
Since they entered our world around the middle of the 20th century, the application of mechatronics has enhanced our lives with functionality based on the integration of electronics, control systems and electric drives. This book deals with the special class of mechatronics that has enabled the exceptional levels of accuracy and speed of high-tech equipment applied in the semiconductor industry, realising the continuous shrink in detailing of micro-electronics and MEMS. As well as the more frequently presented standard subjects of dynamics, motion control, electronics and electromechanics, this book includes an overview of systems engineering, optics and precision measurement systems, in an attempt to establish a connection between these fields under one umbrella.
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 mechatronics ranges from a simple set of electronic controlled relay-switches to highly integrated precision motion systems. This proliferation of mechatronics has been accompanied by many books that 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.
The book that you are reading now distinguishes itself from other books in several ways. First of all it is written as a balancing act between both the industrial and the academic background of the authors. The industrial part is based on extensive experience in designing the most sophisticated motion systems presently available, the stages of wafer scanners that are used in the semiconductor industry. The academic part is based on advanced research on ultra precision metrology equipment with fast Scanning-Probe Microscopy and optical measurements with sub-nanometre accuracy. Closely related to the industrial background is the focus on high precision positioning at very high velocity and acceleration levels. With this focus, the book does not include other important applications like robotics and vehicle mechatronics. All presented material is focused on obtaining a maximum of control of all dynamic aspects of a motion system. This is the reason for the term “High Performance” in the title.
A second reason for writing this book next to all others is the observation, when teaching engineering at the university, that most students are rather well trained in applying mathematical rules but too often fail to understand the full potential of these mathematics in real mechanical designs. The need for the education of real engineers with both theoretical and practical skills, combined with a healthy critical attitude to the outcome of computer simulations, became a guiding motive to finish the tedious job of writing. 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 on the theoretical 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 somewhat deeper, but most subjects are treated in such a way that an overall understanding is obtained that is based on first principles rather than on 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 rather a binding factor to the related specialised books than one that makes these redundant.
It is our sincere hope this book serves its purpose.
Also on behalf of the co-authors Georg Schitter and Jan van Eijk
Robert Munnig Schmidt
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. Unfortunately it is impossible to mention all without forgetting some names so as example only the three most important students are mentioned.
The first is Ton de Boer, who accepted the impossible task as MSc-student to write the rough material that started this book as lecture notes by following the lectures on Mechatronic System Design. Initially, in spite of professional advice, this writing was done in a well-known WYSIWYG program and only later it was transferred into LATEXwhich proved indeed the only realistic way to create a professional technical textbook.
Leon Jabben and Jonathan Ellis have been working as PhD-students at our laboratory in Delft and parts of their theses are used in the measurement chapter.
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.
From ASML especially Hans Butler, Patrick Tinnemans and Jan Mulkens (thanks to the volcano on Iceland!) have helped in reviewing some chapters.
We further thank all other companies and individuals that kindly gave permission to use their illustrations. These all are separately mentioned at the related figures.
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. For reason of readability we decided not to include references in the text but instead we included a list of the most relevant books that we found to be applicable.
Finally also a word of respect and gratitude should be given to the many contributors of Wikipedia. Even though this huge source of information is not always as consistent and flawless as might be required by the scientific community, Wikipedia has proven to be very useful to quickly find the right 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.
Short summary and introduction of the contents
This book is written in such a way that it is useful both for a high-level student who wants to learn about advanced mechatronics and for engineers in the high-tech industry who want to learn more about adjacent specialisations. To accommodate this dual approach, the first and last chapter determine the environment that makes use of the material of the theoretical chapters in between. It is not a surprise that this first and last chapter are connected by the wafer scanners of ASML as these might well be the most advanced mechatronic systems that are ever designed.
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 foothold of high-precision mechatronic system design in the Netherlands and are exemplary for the specific photon-physics oriented approach in this country, so 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 is the first of a series of chapters on the basic theory that is applied in controlled motion systems. It consists of a short overview of the principles of electricity, frequencies, waves and signal responses. The chapter starts with basic electricity, the linking element in a mechatronic system. Followed by signal theory this chapter explains the reason why the properties of mechatronics are so often described in the frequency domain next to the more mechanical oriented time-related step and impulse responses. The chapter also introduces different graphical representations of these responses as this material is used throughout most chapters in this book.
The hard-core of a mechatronic system is still the mechanics that represent the real, dynamic, hardware world that has to be mastered when positioning objects in a controlled way. In most cases, the dynamic properties of the mechanical construction determine the 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 uncontrolled properties of standard mechanical elements consisting of a multitude of springs, masses and dampers. As a first step towards active motion control this theory enables to determine dynamic causes for observed instability issues in controlled motion systems.
Immediately related to the mechanical dynamics is the important field of active motion control in Chapter 4. This chapter concentrates on a thorough understanding of the working principle and tuning of the still widely used PID controllers. Also a short introduction is given in more modern model-based control approaches that are expected to play an increasing role in mechatronic systems. A strong emphasis is put on the insight that control both adds virtual elements from the mechanical domain like springs and dampers and new elements like integration.
Electromechanic actuators and analogue electronics are two closely related hardware components of a mechatronic system. Their interaction is increasingly underestimated by system designers, because of two reasons. Firstly the field is controlled by experts in physics and electronics. These specialists have a fundamentally different more abstract frame of view than the mostly concrete-mechanical visually oriented system designers. The second reason for underestimating these related fields is caused by the overwhelming amount of electronics and electro-motors that are around us, giving rise to the idea that their principle is simple and mastered by many. This idea is a dangerous delusion as the difficulty in electronics is related to its dynamic analogue behaviour and unfortunately the number of people that master that part is rather decreasing than increasing. It is the analogue side of electronics that deals with measurement and actuation that needs most of the attention of the mechatronic designer.
With this purpose in mind Chapter 5 first presents linear electromechanic actuators. This chapter mainly focuses on electromagnetic actuators but also piezoelectric actuators are presented as these 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, that are presented in the following chapter, is made clear.
Chapter 6 deals with analogue electronics for measurement and power and starts at a very basic level with passive components because most mechanical engineering students 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 that act as the interface between the controller and the actuators.
Optics has become a main driver of mechatronic advancement in the past decades and for that reason Chapter 7 gives an introduction to optics from the perspective of a mechatronic designer. Optics are important in two ways. 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 in a plurality of sensors, that enables us 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 presents the basic principles of sensors for force and dynamic position measurements 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 presents the mechatronic design for precision positioning in waferscanners 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.