- Email: [email protected]
Mechatronics: From The 20th to 21st Century
Copyright ® IFAC Mechatronic Systems, Darmstadt, Gennany, 2000
MECHATRONICS: FROM THE 20TH TO 21 ST CENTURY
Masayoshi Tomizuka
Department of Mechanical Engineering University of California Berkeley, California 94720, U. S. A.
Abstract: This paper presents a Year-2000 (Y2K) status report of mechatronics. The Y2K definition of mechatronics is: "the synergetic integration of physical systems with information technology and complexdecision making in the design, manufacture and operation of industrial products and processes." Mechatronics may be interpreted as the best practice for synthesis of engineering systems, and it covers a broad area and scope. Mechatronics research should be driven by target physical systems and not by methodologies. Vehicle lateral control for automated highway systems, hard disk drives and media handling mechanisms for printing engines are reviewed as examples of mechatronics research. Engineering students should be exposed to mechatronics and to the culture of working in teams. Copyright @2000 IFAC Keywords: Mechatronics, mode ling, control, information technology
I.
INTRODUCTION
The term mechatronics, introduced in the late 1960s by Japan's Yaskawa Electric Company, was derived from the observation of the synergy achieved through the integration of mechanical and electronic technologies (Harashima, et aI., 1996; Kyura, 1996). Yaskawa subsequently released trademark rights to the name and it has been used since in education and industry to describe systems derived from this heritage. Today, that heritage includes a broad variety of physical systems operating under computer and electronic control. The defmition of mechatronics has evolved over the past three decades (Auslander, 1996). A Y2K defmition of mechatronics may be "The synergetic integration of physical systems with information technology and complex-decision making in the design, manufacture and operation of industrial products and processes." This defmition indicates that information technology
(IT) will play an increasingly significant role in mechatronics. IT in the mechatronics context includes computers and digital signal processors (DSPs), which store and process information, communications and the Internet, which transmit information, as well as various CAD (computer aided design) software packages. On the other hand, complex decision making includes methodologies such as feedback design theory, control theory, intelligent control, hybrid system theory and fault detection. Both the technologicaLbasis for IT and the knowledge basis for decision making have significantly broadened over the last three decades, which has also enlarged the application domain of mechatronics. This is an evolutionary aspect of mechatronics, and is illustrated in Fig. I. In particular, advances in communications such as the Internet and wireless communication have enlarged the range of mechatronic components from unit devices to large scale distributed systems. Notice
Discrete Event Theory Hybrid Systems Theory
~\\ Dee::;o M,wog
Fault Detection SOft-C~utin~ Design Methodology Control
TheOry
~
::;> -
Physical (Mechanical) Systems
19IO' .
) Electronics
t
:.::::::::S.
'
<
.1980
~
"-.-~ J
i
t
' 199.0
'ntC)'On ",i-L.
Micro-processors Computers
CAD systems Local Networks
Fig. 1 Evolution of Mechatronics
that we have used "physical systems" in the definition in place of "mechanical systems" to reflect this point
~
,Embedded DSP Wireless Comm. Information The Internet
Technology
many aspects of mechatronics. We will comment on mechatronics from the viewpoint of education in Section 4. Conclusions will be given in Section 5.
Mechatronics may sound like an interdisciplinary area, but that classification is not right. We are surrounded by mechatronic products: e.g. camcorders, computer hard disk drives (HDDs), paper copiers, cruise control systems, etc. Mechatronics, however, does not refer only to products ; it is much broader than this context. This point has been made clear in the Y2K definition, which may be interpreted as a "best practice" for synthesis by mechanical engineers and those in other engineering disciplines. In fact, a major driver of mechatronics comes from the needs of the industry. At a recent workshop on control education and research sponsored by the National Science Foundation, one industrial leader summarized general trends in the industry with the following points (Masten, 1998): I) Knowledge is king, 2) Innovation is essential, 3) Cost: What is "new" today becomes a "commodity" tomorrow, 4) Products are becoming more complex and system-based with higher performance, 5) Short design cycles are more common, 6) Markets are increasingly global and more competitive, and 7) Design teams are a preferred approach . Mechatronics offers the best practice to meet these challenges.
2.
(MECHANICAL) ENGINEERlNG IN THE 21 ST CENTRURY
The American Society of Mechanical Engineers (AS ME) recently published a report entitled "Mechanical Engineering in the 21 SI Century: Trends Impacting the Profession" prepared by the Hudson Institute, Inc. (1999). Its contents are highly relevant to the evolution of mechatronics from the 20 th to 21 sI century. It describes the trends of change in engineering in the following four categories: technological change, demographic change, economic change and social change. In terms of technological change, the following eight areas are identified to impact (mechanical) engineering in major ways: 1. 2. 3. 4. 5. 6. 7. 8.
The remainder of the paper is organized as follows . In Section 2, we will examine some key trends in the 21 sI century that will affect engineering. These trends are not necessarily new. In Section 3 we will review on-going research projects which exhibit
Information Technology Miniaturization Materials Science Bioengineering and Medicine Energy Transportation Environmental Engineering Manufacturing
Among these, the last five areas suggest where significant activities have been and will take place in the midstream in Fig. 1, i.e. physical systems, as the 20 th century ends and the 21 sI century begins.
2
There have been visible mechatronics research activities in these areas, and some of them will be reviewed in the next section. On the other hand, the first three areas may be understood as enabling technologies from the viewpoint of mechatronics.
diagram found in control textbooks with the two additional blocks: human-machine interfaces and link to other systems. Note that we have placed the computation block in the middle to emphasize that the computer plays the central role in modem mechatronic systems. This block may represent a variety of hardware devices such as programmable logic controllers, DSPs, embedded micro-controllers and their combinations as well as software that realizes decision making algorithms. Mechatronics research should start with a clear idea on the target In other words, mechatronics physical system. research should not be methodology driven. A technical paper on a new control methodology with an illustrative example may be a fine contribution to technical journals on controls, but most likely will not be appropriate for mechatronics journals. Having said this, many research topics addressed by researchers in the area of dynamic systems and control are relevant and of critical importance to mechatronics. For example, the following research topics address important aspects in the development of engineering systems and are relevant to mechatronics.
MEMS (MicroElectro Mechanical Systems) has been a popular research area in recent years. This is consistent with the second area identified in the ASME report, miniaturization. It is also a rapidly growing industry, the size of which has exceeded 10 billion dollars already, and millions of MEMS have been in products such as automotive air bags and ink jet printers The New York Times, 2000). MEMS technology has been applied to develop tiny optical switches for handling high volumes of data and voice traffic in communications. MEMS itself is a wonderful example of mechatronics. As another measure that indicates the importance of miniaturization, the US Government is investing $270 M in the year 2000 in the National Nanotechnology Initiative (NSTC, 2000). Regarding the demographic change, the ASME report states, "Demography is the second powerful force that is transforming the world's economies and societies. In the next 40 years, the world's human population is expected to grow by about 50% .. .. The baby boomers will enter advanced maturity and then old age." The report then touches several specific aspects including the trend in Europe and Japan that the population is rapidly aging. While not discussed in the ASME report, this trend will motivate mechatronics for taking care of elderly people (e.g. nursing robots). Tanie calls it human friendly mechatronics (1999).
3.
• • •
• • •
Modeling and identification dynamic systems Simple yet reliable tuning of robust controllers Comparison of various control methods in terms of performance and implementation costs including complexity Robust control without high gain nature for prolonged actuator life and minimized vibration Control with low frequency output measurements Simultaneous design of control algorithms and fault detection algorithms
Isermann (1997) presents a forceful argument that the development of mechatronic systems is a real challenge for control engineering.
MECHATRONICS-RESEARCH OPPORTUNITIES
It was mentioned that a major driver of mechatronics
is the needs of industry, and that mechatronics offers the best practice. This does not mean that mechatronics refers only to how things should be done in the development of products at industry. In fact, mechatronics provides a number of interesting research issues to university researchers. Mechatronics research in academia should be at the forefront of any existing fields (e.g. transportation, biomedical, and so on) or even define a new field . It should yet remain relevant to industries. Such industries may be existing, or yet to be formed in response to the need of society. In this section, we describe research opportunities for researchers primarily in dynamic systems and control.
Link to Other Systems The Internet, wireless communication
.. r
1
Human-Mach. Interface human factors
1
Corn puterslDSP decision making
I
,Ir
Instrumentation energy conversion signal conditioning
Actuation power modulation
~~
Physical Systems mechanical, electrical, etc. and their combinations
3.1 Modern Mechatronic System and Research Opportunities
Fig. 2 Modem Mechatronic System
Figure 2 shows a block diagram of modem mechatronic systems. It looks like a typical block
3
~
Automated Steering Automated Highways
If we consider mechatronics from the view point of concurrent engineering (Van Brussel, 1996), the "mechatronics nature" of research becomes more apparent when the consideration on control algorithms is coupled with the selection and placement of sensors and/or even the design of target physical (mechanical) systems. MEMS is relevant to this because it is a technology for co-location of sensors and actuators, which often makes the controller design easy.
Systems for
Vehicles
on
The California Partners for Advanced Transit and Highway (PATH) Programs was established in 1986 to promote the application of advanced technology to help meet California's growing need for increased highway capacity to relieve congestion. The idea of Automated Highway Systems (AHS) was identified to be an attractive option for solving the congestion problem while improving the operation of highways in many regards including safety, fuel economy and pollution, AHS research has been a major part of the PATH program. AHS is one form of intelligent transportation systems (ITS). As identified in the ASME report, transportation is of critical importance in the 21 sI century. Each vehicle on AHS must be equipped with the longitudinal controller and the lateral controller. The longitudinal controller maintains the distance (or time headway) between the vehicle and another in front of it at a desired value.
Figure 3 summarizes the activities of Mechanical Systems Control Laboratory in the Mechanical Engineering department of the University of California at Berkeley. The Laboratory has worked on a variety of mechanical systems to study the role and utilization of control methodologies. It should be noted in the figure that balloons for application areas and the control theory balloon are connected by lines with arrows on both ends. Motivations for developing new ideas in the control theory balloon have their origins in problems encountered in specific application. Repetitive control (Tomizuka, Tsao and Chew, 1989) is such an example. The development of the discrete time repetitive control theory was motivated by noncircular machining (Tsao and Tomizuka, 1994) as well as disk file control to compensate for the eccentricity of data tracks on the disk relative to the center of disk rotation (Messner, et aI., 1993). The zero phase error tracking control (ZPETC) (Tomizuka, 1987) was conceived as a simple mean to realize feedforward control for x-y tables and other motion control devices. Almost all research projects in the laboratory have analytical and experimental components. This sty le of research naturally evolves into control oriented mechatronics research.
From the viewpoint of mechatronics, AHS is an excellent case of system integration incorporating items in Fig. 1 and other items. Vehicle longitudinal and lateral controls are sub-problems in AHS, but they include a number of mechatronics issues such as system integration, advanced controls, communications and selection of sensors for better controllability and fault management. The lateral controller ensures that the vehicle is kept on a specified lane. In vehicle lateral control for AHS, it is critically important how the vehicle's position and orientation relative to the road are obtained. Various road reference/sensing systems have been proposed in the past. PATH adopted the magnetic marker (nail) system with on-board magnetometers. In this method, magnets are buried at equally spaced interval along the automated lane. PATH researchers developed robust signal processing schemes for obtaining the lateral error, as well as, encoding schemes to embed other information such as preview road curvature information in binary form by alternating the polarity of the magnets. Furthermore, it compares favorably with other schemes in terms of evaluation criteria such as accuracy, reliability, maintainability, and cost. The road reference-sensing system based on magnetic markers is a look down system. If the magneto meter is placed under the front bumper, the system allows only a small amount of "look ahead" relative to the center of gravity of the vehicle. On the other hand, the vision camera defines a look-ahead system with am ample amount of look ahead. The nature of the open loop dynamics from the steering input to the sensor output makes feedback control design easier when the sensor is placed ahead of the vehicle, say by 5 m, to allow an ample look-ahead It is not practical to place a "real" distance.
Fig. 3 Control of Mechanical Systems
3.2 Mechatronic Projects-Examples In this section, we will review three research projects, each of which has some distinctive mechatronics nature.
4
The current research on the automated steering system at PATH is concentrated on heavy vehicle steering control. The experimental vehicle is a Freightliner FLD120 class 8 tractor and a Great Dane trailer (Hingwe, et al., 1999). Figure 6 shows the instrumentation on the experimental vehicle. The figure suggests the mechatronics nature involved in this problem. In particular, it is noted that three sets of magneto meters are placed on the vehicle: at the front and rear ends of the tractor and the rear end of the trailer. Also the independent trailer brake actuators act as a secondary input for lateral control. At curved sections of highways, the tractor's front wheel and the trailer's rear wheel follow different paths, which is known as off-tracking. The amount of off-tracking depends on the vehicle speed, and it must be taken into consideration in lateral control. Thus, the lateral control problem is not merely to keep the sensor output at zero.
magnetometer say 5 m ahead of the vehicle. Thus, PATH researchers devised an interesting mechatronics solution for realizing a larger lookahead distance based on multiple magnetometers. They installed magnetometers under both the front and rear bumpers: i.e. the lateral error at the front bumper, y., and at the rear bumper, y" were measured (see Fig. 4).
/ ,
/~
--------, / I
,
I
Jf)
/~, I //
virtual ':; ---·· .. i'"._ ~ensor wl '.
~'
;>,j
Fig. 4 Error Sensing by Front and Rear Sensors. Under the assumption that the road is straight, front and rear magneto meter measurements are converted to the lateral error at the tractor's CG and the relative yaw error by
Y
,
&,
=
Linear robust control algorithms and nonlinear adaptive control algorithms have been developed for the Freightliner test vehicle, and their effectiveness has been experimentally demonstrated. In vehicle control, the interaction between the road and tires, which generates the lateral force for vehicle to turn, is very complex, and the advantages of adaptive control have been pointed out by analysis and simulations.
I , IY .<[ +I ; IY"
= tan
/ [ 1+ 1' 1 _I
Y s[
-
y"
1[ 1 + / "
Y >/ - y"
'" ---"---
1[ 1+ / "
where I}, 12 , Y sfi Y sr and Er are defined as in Fig. 4. These two quantities can be combined to synthesize the lateral error at the virtual sensor located at any distance ahead of the vehicle. This makes it possible to allow the look down system based on magnetic markers behave like a look-ahead system : i.e.
Yv
= Yr
Another emphasis in the current research at PATH is on failure detection and fault tolerant control. The failure detection and fault management has been studied at PATH for some time, since safety is an important issue in any automated system. This has also been a motivation for our recent study on fault tolerant lateral control systems for AHS (Surayanarayanan, Tomizuka and Suzuki, 2000).
+dJir
PATH has developed a variety of algorithms based on the magnetic reference systems (Peng and Tomizuka, 1993 ; Patwardhan, et al. , 1997) leading to the successful demonstration at the 1997 NAHSC (National Automated Highway Systems Consortium) Demonstration in San Diego in 1997. The sensing scheme described above was a critical element in the success of the demonstration, which reminds us that the design of control systems is not merely a selection of control algorithms but is a synergistic integration of a variety of elements such as sensors, actuators and control algorithms.
(9) (12)~:cJ
(lO~ §=~=-_I
11 \
,C--on-I
(5)
• 1
(4)0
IC--
(\~)§§
(3)0
'tr--.I
lJftt(2) ): ~/,-I ' 1(1) .~L--I ,r1::I
!)
-
(9)
I
(8) I (6)1
I
~~
(1\)
Fig.6 Sensors and Actuators for Lateral Control (1) front magnetometer array (2) steering actuator (3) computer (4) gyroscope and accelerometer (5) rear magneto meter array (6) articulation angle sensor (7) gyroscope and accelerometer (8) trailer magnetometer array (9) tractor front braking actuators (10) tractor rear braking actuator (ll) independent trailer braking actuators (12) steering wheel angle sensor
Fig. 5 PATH Platoon Demonstration (NAHSC Demonstration in San Diego, 1997)
5
Computer Hard Disk Drives
(Ishikawa and Tomizuka, 1998). The design of a high bandwidth disk drive servo system using a suspension instrumented with strain gauge sensors is described in (Huang, et aI., 1999). As TPI increases every year, it is expected that the current single actuator technology will reach its fundamental limit. To prepare for this situation, the dual stage actuator is receiving an increased level of attention in the disk drive industry (Ohtsuki, et aI., 1992; Schroceck and Messner, 1999; Ding, Numasato and Tomizuka, 2000). The majority of dual stage actuators utilize the conventional voice coil motor primary stage and a piezoelectric secondary stage. MEMS offers an alternative option for second stage actuation (Horsley, Horowitz and Pisano, 1998).
Magnetic hard disk drives (HDDs) are representative mechatronics devices (Messner and Horowitz, 1998). Figure 7 shows a 3.5" hard disk drive . The HDD industry is striving for higher aereal storage density, higher data transfer rate and lower cost. The aereal data storage density of commercial drives has been increasing at a rate 60% per year. Since the first disk drive was introduced in 1957, the data storage density has increased by a factor of 5,000,000. There are a number of amazing technologies involved in disk drives. The slider, on which the recording head is mounted, flies over a rotating disk at a height of about 20 nm. This is analogous to a Boeing 747 flying at an altitude of less than 1 millimeter. The small flying height is required to maximize the storage density. The number of data tracks per radial length is currently about 15 to 20 K tracks per inch (TPI). TPI is expected to triple by end of next year. HDD can now store date at unbelievable densities exceeding 10 gigabits per square inch. Researchers are now looking into a variety of new technologies (Taigo, 2000). There are several different ways to increase the data transfer rate . Both the disk rotational speed and the track seeking time are important. Access time, which depends on these two factors, has been improved by a factor of three during the past ten years. The importance of the servo control is easy to recognize.
Fig. 7 Hard Disk Drive Unite (I) voice coil motor, (2) actuator pivot (3) actuator arm, (4) read/write (recording) head (5) data track (6) spindle motor axis
The current disk drives use the so called sector servo method. In this method, the disk is divided into angular sections (sectors) and servo information is written at every sector. The recording head reads the position error signal (PES) once in each sector. A challenge in the design of these systems is to minimize the number of sectors (equivalently the sampling rate), while continuing to meet tracking performance requirements. There has been a number of interesting control ideas introduced to disk file controls. Repetitive control is such an idea (Tomizuka, Tsao and Chew, 1989). In standard digital control, the control input is updated at every instant of output (error) measurement. This standard scheme is called the single rate scheme. The updating rate of control input, however, can be more frequent than the measurement sampling rate. Such control methods belong to multirate control, and several kinds of mutilate control have been proposed for hard disk drives (Chiang, 1990; Kobayashi, et aI. , 1998; Hara and Tomizuka, 1999). A multirate approach has also been suggested to decrease the implementation cost of repetitive control (Smith, Takeuchi and Tomizuka, 1999). PES is the major information source in the disk drive servo system. There have been several attempts to improve performance by utilizing information from additional sensors. Accelerometers have shown to improve the track following performance by canceling the effect of external vibration on PES (White and Tomizuka, 1997) and eliminating the effect of pivot friction
Media Handling Mechanisms /or Printing Engines A significant amount of the dissatisfaction with current printers and copiers is associated with malfunctions in their media handling system. In typical copiers, papers must travel along the paper path from the feeder to the finisher making many turns and going through nip rollers. There is essentially no feedback control of paper motions except at the final printing stage. The lack of control often results in the so-called soft jam. If a sheet does not arrive at a checking station as expected, the machine is automatically shut down. In an NSF sponsored project entitled "Mechatronic Design and Control of Media Handling Mechanisms for Printing Engines" the University of California at Berkeley and Xerox are jointly studying the integration of sensing, control and decision making methodologies in the mechanical design and the real time control of copying machines. Figure 8 shows a bench fixture built for studying feedback control of paper motions along the paper path. The unique feature of this setup is that an independent motor is placed at each section of the paper path. This added flexibility enables independent position control of sheets in different sections by running the sections at different velocities. Additional optical sensors and encoders are used to improve the sheet position estimates. The increased level of flexibility naturally leads to a more
6
complicated machine. From a control theoretic point of view, the overall system becomes a hybrid system: it is a dynamical system in the usual sense but changes its configuration as well as operation principles at discrete points in time. It is an excellent mechatronics project. Details of the experimental setup along with some simulation and experimental results are given in Kruchinski, et al. (2000).
diagram of a typical telesurgical workstation resembles the diagram in Fig. 2. A recent article in Business Week, Port (2000) states "Mechanical body parts could someday make disabilities irrelevant in the workplace." Artificial organs (and projected dates of availability) compiled in the article include artificial-vision brain implants (2001), permanent mechanical heart implants (2010), lungs and kidneys (2015). synthetic muscles (2019), and artificial eye implants (2024). These biomedical applications show that the human body may be an important component of mechatronic systems or that the human and mechatronic devices interact in synergistic ways. The interface between human and machine rely on the human's five senses, among which visual and haptic are most popular. In particular, research on haptics has expanded and branched out in new directions such as real-time transmission and display of haptic information. The IEEE/ ASME Transactions on Mechatronics is planning a focused section on haptic devices and applications for publication in the latter half of this year. Another interesting integration of human and machine is studied at the Human Engineering Laboratory at VC Berkeley. The members of this laboratory carry out research efforts on design and control of a class of robot manipulators worn by humans to augment human mechanical strength, while the wearer's intellect remains the central control system for manipulating the robot. The key point in their systems is the exchange of both information signals and physical power. A recent accomplishment of this group was the development of a machine that successfully maneuvered heavy loads in isolated areas for extended periods of time (Neuhaus and Kazerooni, 2000). Human is involved in the operation of this machine.
Fig. 8 Experimental Set-up for Paper Motion Control Other Research Areas There are a number of other research areas where mechatronics thinking is extremely important. They include but are not limited to: robotics and automation, manufacturing, biomedical engineering, energy and the environment, and large scale structures such as bridges and buildings. There is no question that robots represent a challenging area from the mechatronics point of view, and most compelling examples ofmechatronics are often found in the robotics area. In fact, many challenging problems such as design and construction of light weight robots (e.g. DLR Lightweight Robot, www.robotic.dlr.de). intelligent robotics and robotic surgery require mechatronic approaches.
As we look into the next decade, we may predict several natural trends based on the ASME report. We may safely state that mechatronics in the 21 51 century will heavily depend on information technology and miniaturization. Such technology will make it possible to provide remote monitoring of home appliances, automobiles and elderly or handicapped people.
Mechatronics has been and will be playing an important role in the area of medicine and surgery (Hewit, 1995; Cavusoglu, et aI., 1999). For example, minimally invasive surgery (MIS) is a revolutionary In MIS, the surgery is approach in surgery. performed with instruments and viewing equipment inserted into the body through small incisions, minimizing the surgical trauma and damage to the healthy tissue. It is a telesurgery similar to the remote operation for handling hazardous materials. While MIS results in shorter patient recovery time, there are a number of research issues associated with reduced dexterity, workspace, and sensory input to the surgeon that is only available through a monoscopic video image (Cavsoglu, 1999). MIS defines a human-machine system, and the block
4.
MECHA TRONICS-EDUCA TIONAL CHALLENGES
Engineering education is facing challenges in the midst of rapid progress of information technology. In terms of starting salaries offered by industries to new graduates, computer science has been the leader at all levels (BS, MS and PhD) for some years. High school students often do not have a clear idea of what they want to do. Often their decisions are based on conversation with parents, older relatives or friends, which combined with headline news on IT, motivates many of them to send applications specifying
7
"computer science." At the University of California at Berkeley, our current experience is that nearly 50 % of undergraduate applications to the Engineering College are concentrated in computer science. In Berkeley's Electrical Engineering and Computer Science (EECS) Department, the ratio of undergraduate enrollment was two EE students for every CS student five years ago. This ratio has reversed and it is now two CS students for every EE student. The popularity of computer science is not a new phenomenon. In the 1980's, Computer Science (CS) once attracted many applications. At that time, many universities struggled to keep us with the demand for computer science courses to provide students with knowledge about programming languages, operating systems and computer architecture. This boom did not last for a long time. CS graduates with programming skills were not necessarily appreciated by industry executives either. No fundamental curricula revision, however, was considered at that time to respond to the need of industries.
bright, curious, intellectual, and unafraid of leaning new things." This statement is highly relevant when we talk about mechatronics education. Craig (1998) states, "In mechatronics, balance is paramount. The essential characteristic of a mechatronics engineer and the key to success in mechatronics is a balance between two skills: •
•
mode ling (physical and mathematical), analysis (closed form and numerical simulation), and control design (analog and digital) of dynamic physical systems experimental validation of models and analysis (for computer simulation without experimental verification is at best questionable, and at worst useless) and understanding the key issues in hardware implementation of designs ."
Carryer (1998) emphasizes integration. While these comments are not necessarily fresh, they are all essential. In fact, the points made by Craig and Carryer are important in engineering education. Every undergraduate students in mechanical and electrical engineering as well as in other engineering disciplines should be trained so that they can effectively utilize IT tools along with their analytical skills to solve engineering system problems. Effective communication with others is a necessary requirement. Furthermore, students should be trained to be forward looking and curious. Issues surrounding integration as well as working in team cannot be taught in lecture courses. Students must experience them, and in this regard laboratory courses are essential in mechatronics education.
The strong application demand from students and the strong supply demand from all segments of industries that universities are currently facing in IT are more than a temporary boom. Educators have recognized that engineering curricula must be revised in fundamental ways so that universities may supply leaders to advance IT and professionals to apply IT in various industries (Wilson, 1998). Lee and Messerschmidt (1998) state: "We believe that the center of gravity of most undergraduate curricula today is too far on the side of attempting to train the small cadre of technical experts, a hopeless task within a four-or-five-year program. Because of the hopelessness of the task, we cram too much content into the program, thinking it makes it better (and somehow less hopeless). This shuts out other fundamental knowledge that we believe will be extremely valuable to them in their design careers. Students have been seriously shortchanged by not understanding the big picture.
At the University of California at Berkeley (UCB), Professor Kazerooni converted a senior level course on mechanical engineering design to a new course on mechatronics design. During a 15 week period, he covers microcontrollers, real-time software, electric motors, pneumatics and hydraulics, transmission systems, brakes and clutches, power electronics, bearings, and sensors. The course ends with the inventors' open house, where students present their projects. For projects, students normally work in a group of three to four. Feedback control is not a prerequisite for the course, but projects are often quite sophisticated involving feedback control. Project titles from recent offering of the course include automatic bicycle gear shifter, automated rice cooker, and walking robots.
We advocate an alternative vIsIon in which the undergraduate program focuses on a limited and carefully chosen set of core ideas, supplemented by real-world examples and importantly by student self-exploration and learning. Such an undergraduate program also emphasizes breadth, an exposure to a range of technical issues, as well as mathematics, science, humanities, and social sciences.
Figures 9 and 10 are several examples of laboratory sessions from a UCBs' graduate course on switching control and computer interfacing by Professor David Auslander.
In a field as dynamic as ours, no set of vocational skills has any significant longevity. It is far more important that our graduates be
8
the best industrial practice in the present day global and competitive market. At the same time, mechatronics thinking is the basics of the modem engineering education. Engineers must be innovative and utilize the best tools available. This is a common sense. The mechatronics approach is particularly relevant in mechanical engineering and electrical engineering. In particular, in mechanical engineering departments, faculty members specializing in control and design must act as leaders to bring into mechatronics in the engineering curriculum.
Fig. 9 Working on the Milling Machine (Picture: Courtesy of Professor D. Auslander)
REFERENCES Auslander, D. M.(1996): What is Mechatronics?, IEEEIASME Transactions on Mechatronics, Vol. 1, pp. 5-9. Carryer, 1. E. (1998): Controllers or Components: Deciding What (and What not) to Teach in Mechatronics Courses, DSC-Vo!. 64, Proceedings of the ASME Dynamic Systems and Control Division, pp. 377-382. Cavusoglu, M. c., F. Tendick, M. Cohn, and S. S. Sastry (1999): A Laparoscopic Telesurgical Workstation," IEEE Trans. Robotics and Automation, Vol. 15, No. 4, pp. 728-739. Chiang, W.-W. (1990): Multi-rate state-space digital controller for sector servo systems, Proceedings of the 29th IEEE Conference on Decision and Control, pp. 1902-1907. Craig, K. (1998): Mechatronics in University and Professional Education, DSC-Vo!. 64, Proceedings of the ASME Dynamic Systems and Control Division, pp. 369-375 . Hara, T. and M. Tomizuka (1999): Performance Enhancement of Multi-rate Controller for Hard Disk Drives, IEEE Magnetics, pp. 898-903. Harashima, F., Tomizuka, M. and Fukuda, T. (1996): Mechatronics-"What Is It, Why, and How?" An IEEEIASME Transactions on Editorial, Mechatronics, Vol. 1, pp. 1-4 (1996). Hingwe, P. and M. Tomizuka (1997), "Robust and Gain Scheduled Hoo Controllers for Lateral Guidance of Passenger Vehicles in AHS," Proceedings of the ASME Dynamic Systems and Control Division, DSC-Vol. 61, pp. 707-713. Hingwe, P., M. Tai, 1.-Y. Wang, 1.-Y. and M. Tomizuka (1999): Lateral Control of TractorSemitrailer Combination for Automated Highway Systems-An Experimental Study, Proceedings of the ASME, Dynamic Systems and Control Division -1999, DSC-Vol. 67, pp. 195-202. Hewit, 1. (1995): Mechatronics Design - The Key to Performance Enhancement, Proceedings of the International Conference on Recent Advances in Mechatronics, Istanbul, Turkey, pp. 18-24. Horsley, D. A., R. Horowitz, and A. P. Pisano (1998): Microfabricated Electrostatic Actuators for Hard Disk Drives, IEEEIASME Transactions on Mechatronics, Vol. 3, No. 3, pp. 175-183.
Fig. 10 Automatic Train Loading (Picture: Courtesy of Professor D. Auslander) At the graduate level, in particular doctorate students should be exposed to a broad spectrum of fundamental theories such as control theory. "Fundamentals are fundamental" (Masten, 1998) is important for future academic and industrial leaders. As stated already, many high school students have a simple equation Information Technology = Computer Science Department and do not realize how other engineering disciplines are changing with IT. In this regard, the role of educators must go beyond how mechatronics should be taught. It is important that we direct the attention of high school students and college freshmen and sophomores to the exciting At the University of field of mechatronics. California at Berkeley, the College of Engineering admits a good number of freshmen under category of undeclared major. They decide their majors when they are advanced to the junior level. Freshman seminar courses are intended to expose newly admitted students to a variety of engineering disciplines. Incorporating mechatronics flavors to such presentations make any engineering discipline more attractive to undergraduate students.
5. CONCLUSIONS This paper described the evolution of mechatronics and opportunities and challenges in mechatronics research and education. Mechatronics is essential as
9
Control: System Analysis," Proceedings of American Control Conference, pp. 1598-1602. Peng, H. and M. Tomizuka: Preview Control for Vehicle Lateral Guidance in Highway Automation, ASME Journal of Dynamic Systems, Measurement and Control, Vol. 115, No. 4, pp. 679- 686. Port, O. (2000): Artificial eyes, turbine hearts, Business Week, March 20, pp. 72-73 . Schroceck, S. J. and W. C. Messner (1999): On Controller Design for Linear Time-Invariant DualInput Single-Output Systems, Proceedings of the American Control Conference, San Diego, pp. 4122-4126. Smith, c., K. Takeuchi and M. Tomizuka (1999): Cost Effective Repetitive Controllers for Data Storage Systems, Proceedings of the I4,h IFAC World Congress, Beijin, China, Vol. B, pp. 407412 Suryanarayanan, S., M. Tomizuka and T. Suzuki (2000): Fault Tolerant Lateral Control of Automated Vehicles Based on Simultaneous Stabilization, Proceedings of the IS' IFAC Conference on Mechatronic Systems, Darmstadt. Taigo, J. W. (2000): Avoiding a Data Crunch, Scientific American, May, pp. 58-74. Tanie, K. (1999): Mechatronics - Past, Present and Future, Proceedings of the 1999 IEEEIASME International Conference on Advanced Intelligent Mechatronics, September, Atlanta, page 2. The New York Times (2000): A Big Step Forward In Tiny Technology, Monday, May 8, 2000. Tomizuka, M. (1987): Zero Phase Error Tracking Algorithm for Digital Control, ASME Journal of Dynamic Syst., Meas. and Control, Vol. 109, No. I, pp. 65-68. Tomizuka, M., T-C. Tsao and K-K. Chew (1989): Discrete-Time Domain Analysis and Synthesis of Repetitive Controllers, ASME Journal of Dynamic Systems, Meas. and Control, Vol. Ill, No. 3, pp. 353-358 Tsao, T-C. and M. Tomizuka (1994): Robust Adaptive and Repetitive Digital Tracking Control and Application to a Hydraulic Servo for Noncircular Machining, ASME Journal of Dynamic Systems, Meas. and Control, Vol. 116, No. I, pp. 24-32. Von Brussel, H. M. 1. (1996): Mechatronics - A Powerful Concurrent Engineering Framework, IEEElASME Transactions on Mechatronics, Vol. I, No. 2, pp. 127-136. White, M. T. and M. Tomizuka (1997): Increased Disturbance Rejection in Magnetic Disk Drive by Acceleration Feedforward Control, IFAC Journal of Control Engineering Practice, Vol. 5, No. 6. Wilson, J. M. (1998): Gearing Up for Information Technology, Syllabus, Vol. 11, No. 10, pp. 26-28.
Huang, Y., M. Banther, P. Mathur, and W. C. Messner (1999): Design and Analysis of a High Bandwidth Disk Drive Servo System Using an IEEElASME Instrumented Suspension, Transactions on Mechatronics, Vol. 4, No. 2. Hudson Institute, Inc. (1999): Mechanical Engineering in the 21 SI Century - Trends Impacting the Profession, ASME. Ishikawa, J. and M . Tomizuka (1998): Pivot Friction Compensation Using and Accelerometer and a Disturbance Observer for Hard Disk Drives, IEEEIA SME Transactions on Mechatronics, Vol. 3, No. 3, pp. 194-20 I. Isermann, R. (1997): Mechatronic Systems - A challenge for control engineering, Proceedings of the 1997 American Control Conference, June, Albuquerque, New Mexico Kobayashi, M, T. Yamaguchi, I. Oshimi, Y. Soyama, Y. Hata, Y. and H. Hirai (1998): Multi-rate zero phase error feedforward control for magnetic disk drives, Proceedings of lIP '98, JSME Publication No. 98-26, pp. 21-22 (in Japanese). Kruchinski, M., C. Cloet, R. Horowitz and M. Tomizuka (2000): A Mechatronics Approach to Copier Paperpath Control, Proceedings of the IFAC Conference on Mechatronic Systems, Darmstadt. Kyura, N . and Oho (1996), H.: Mechatronics-An Industrial Perspective, IEEEIASME Transactions on Mechatronics, Vol. I, pp. 10-15. E. A. and D. G. Messerschmit Lee, (1998):Engineering an Education for the Future, Computer, pp. 77-85 . Masten, M. (1998): Industrial Perspective of Control Engineering Education, presented at NSF Workshop on New Directions in Control Engineering Education, Urbana, IL .. Messner, W. , C. Kempf, M. Tomizuka and R. Horowitz (1993): A Comparison of Four Discrete Time Repetitive Control, IEEE Control Systems, Vol. 13, No. 6, pp. 48-54. Messner, W. C. and R. Horowitz.(I998): Guest Editorial, Focused Section on Mechatronics for Magnetic Disk File Storage Systems, IEEEIASME Transactions on Mechatronics, Vol. 3, No. 3, pp. 153-155 . Neuhaus, P. and H. Kazerooni (2000): Design and Control of Human Assisted Walking Robot, Proceedings of the 2000 IEEE International Conference on Robotics and Automation, San Francisco, April, pp. 563-569. Ohtsuki, H., K. Mori, T. Munemoto and K. Akagi (1992): Track Following Control of2-Stage Access Servo System for Magnetic Disk Drives, Trans. of Electro-Information-Communication Society (Japan), Vol. J756-C, pp. 653-662 . NSTC (National Science and Technology Council) (2000), "National Nanotechnology Initiative: Leading to the Next Industrial Revolution," Washington, D. C. Patwardhan, S., H-S. Tan, and J. Guldner (1997). "A General Framework for Automatic Steering
10
MECHATRONICS: FROM THE 20TH TO 21 ST CENTURY
Masayoshi Tomizuka
Department of Mechanical Engineering University of California Berkeley, California 94720, U. S. A.
Abstract: This paper presents a Year-2000 (Y2K) status report of mechatronics. The Y2K definition of mechatronics is: "the synergetic integration of physical systems with information technology and complexdecision making in the design, manufacture and operation of industrial products and processes." Mechatronics may be interpreted as the best practice for synthesis of engineering systems, and it covers a broad area and scope. Mechatronics research should be driven by target physical systems and not by methodologies. Vehicle lateral control for automated highway systems, hard disk drives and media handling mechanisms for printing engines are reviewed as examples of mechatronics research. Engineering students should be exposed to mechatronics and to the culture of working in teams. Copyright @2000 IFAC Keywords: Mechatronics, mode ling, control, information technology
I.
INTRODUCTION
The term mechatronics, introduced in the late 1960s by Japan's Yaskawa Electric Company, was derived from the observation of the synergy achieved through the integration of mechanical and electronic technologies (Harashima, et aI., 1996; Kyura, 1996). Yaskawa subsequently released trademark rights to the name and it has been used since in education and industry to describe systems derived from this heritage. Today, that heritage includes a broad variety of physical systems operating under computer and electronic control. The defmition of mechatronics has evolved over the past three decades (Auslander, 1996). A Y2K defmition of mechatronics may be "The synergetic integration of physical systems with information technology and complex-decision making in the design, manufacture and operation of industrial products and processes." This defmition indicates that information technology
(IT) will play an increasingly significant role in mechatronics. IT in the mechatronics context includes computers and digital signal processors (DSPs), which store and process information, communications and the Internet, which transmit information, as well as various CAD (computer aided design) software packages. On the other hand, complex decision making includes methodologies such as feedback design theory, control theory, intelligent control, hybrid system theory and fault detection. Both the technologicaLbasis for IT and the knowledge basis for decision making have significantly broadened over the last three decades, which has also enlarged the application domain of mechatronics. This is an evolutionary aspect of mechatronics, and is illustrated in Fig. I. In particular, advances in communications such as the Internet and wireless communication have enlarged the range of mechatronic components from unit devices to large scale distributed systems. Notice
Discrete Event Theory Hybrid Systems Theory
~\\ Dee::;o M,wog
Fault Detection SOft-C~utin~ Design Methodology Control
TheOry
~
::;> -
Physical (Mechanical) Systems
19IO' .
) Electronics
t
:.::::::::S.
'
<
.1980
~
"-.-~ J
i
t
' 199.0
'ntC)'On ",i-L.
Micro-processors Computers
CAD systems Local Networks
Fig. 1 Evolution of Mechatronics
that we have used "physical systems" in the definition in place of "mechanical systems" to reflect this point
~
,Embedded DSP Wireless Comm. Information The Internet
Technology
many aspects of mechatronics. We will comment on mechatronics from the viewpoint of education in Section 4. Conclusions will be given in Section 5.
Mechatronics may sound like an interdisciplinary area, but that classification is not right. We are surrounded by mechatronic products: e.g. camcorders, computer hard disk drives (HDDs), paper copiers, cruise control systems, etc. Mechatronics, however, does not refer only to products ; it is much broader than this context. This point has been made clear in the Y2K definition, which may be interpreted as a "best practice" for synthesis by mechanical engineers and those in other engineering disciplines. In fact, a major driver of mechatronics comes from the needs of the industry. At a recent workshop on control education and research sponsored by the National Science Foundation, one industrial leader summarized general trends in the industry with the following points (Masten, 1998): I) Knowledge is king, 2) Innovation is essential, 3) Cost: What is "new" today becomes a "commodity" tomorrow, 4) Products are becoming more complex and system-based with higher performance, 5) Short design cycles are more common, 6) Markets are increasingly global and more competitive, and 7) Design teams are a preferred approach . Mechatronics offers the best practice to meet these challenges.
2.
(MECHANICAL) ENGINEERlNG IN THE 21 ST CENTRURY
The American Society of Mechanical Engineers (AS ME) recently published a report entitled "Mechanical Engineering in the 21 SI Century: Trends Impacting the Profession" prepared by the Hudson Institute, Inc. (1999). Its contents are highly relevant to the evolution of mechatronics from the 20 th to 21 sI century. It describes the trends of change in engineering in the following four categories: technological change, demographic change, economic change and social change. In terms of technological change, the following eight areas are identified to impact (mechanical) engineering in major ways: 1. 2. 3. 4. 5. 6. 7. 8.
The remainder of the paper is organized as follows . In Section 2, we will examine some key trends in the 21 sI century that will affect engineering. These trends are not necessarily new. In Section 3 we will review on-going research projects which exhibit
Information Technology Miniaturization Materials Science Bioengineering and Medicine Energy Transportation Environmental Engineering Manufacturing
Among these, the last five areas suggest where significant activities have been and will take place in the midstream in Fig. 1, i.e. physical systems, as the 20 th century ends and the 21 sI century begins.
2
There have been visible mechatronics research activities in these areas, and some of them will be reviewed in the next section. On the other hand, the first three areas may be understood as enabling technologies from the viewpoint of mechatronics.
diagram found in control textbooks with the two additional blocks: human-machine interfaces and link to other systems. Note that we have placed the computation block in the middle to emphasize that the computer plays the central role in modem mechatronic systems. This block may represent a variety of hardware devices such as programmable logic controllers, DSPs, embedded micro-controllers and their combinations as well as software that realizes decision making algorithms. Mechatronics research should start with a clear idea on the target In other words, mechatronics physical system. research should not be methodology driven. A technical paper on a new control methodology with an illustrative example may be a fine contribution to technical journals on controls, but most likely will not be appropriate for mechatronics journals. Having said this, many research topics addressed by researchers in the area of dynamic systems and control are relevant and of critical importance to mechatronics. For example, the following research topics address important aspects in the development of engineering systems and are relevant to mechatronics.
MEMS (MicroElectro Mechanical Systems) has been a popular research area in recent years. This is consistent with the second area identified in the ASME report, miniaturization. It is also a rapidly growing industry, the size of which has exceeded 10 billion dollars already, and millions of MEMS have been in products such as automotive air bags and ink jet printers The New York Times, 2000). MEMS technology has been applied to develop tiny optical switches for handling high volumes of data and voice traffic in communications. MEMS itself is a wonderful example of mechatronics. As another measure that indicates the importance of miniaturization, the US Government is investing $270 M in the year 2000 in the National Nanotechnology Initiative (NSTC, 2000). Regarding the demographic change, the ASME report states, "Demography is the second powerful force that is transforming the world's economies and societies. In the next 40 years, the world's human population is expected to grow by about 50% .. .. The baby boomers will enter advanced maturity and then old age." The report then touches several specific aspects including the trend in Europe and Japan that the population is rapidly aging. While not discussed in the ASME report, this trend will motivate mechatronics for taking care of elderly people (e.g. nursing robots). Tanie calls it human friendly mechatronics (1999).
3.
• • •
• • •
Modeling and identification dynamic systems Simple yet reliable tuning of robust controllers Comparison of various control methods in terms of performance and implementation costs including complexity Robust control without high gain nature for prolonged actuator life and minimized vibration Control with low frequency output measurements Simultaneous design of control algorithms and fault detection algorithms
Isermann (1997) presents a forceful argument that the development of mechatronic systems is a real challenge for control engineering.
MECHATRONICS-RESEARCH OPPORTUNITIES
It was mentioned that a major driver of mechatronics
is the needs of industry, and that mechatronics offers the best practice. This does not mean that mechatronics refers only to how things should be done in the development of products at industry. In fact, mechatronics provides a number of interesting research issues to university researchers. Mechatronics research in academia should be at the forefront of any existing fields (e.g. transportation, biomedical, and so on) or even define a new field . It should yet remain relevant to industries. Such industries may be existing, or yet to be formed in response to the need of society. In this section, we describe research opportunities for researchers primarily in dynamic systems and control.
Link to Other Systems The Internet, wireless communication
.. r
1
Human-Mach. Interface human factors
1
Corn puterslDSP decision making
I
,Ir
Instrumentation energy conversion signal conditioning
Actuation power modulation
~~
Physical Systems mechanical, electrical, etc. and their combinations
3.1 Modern Mechatronic System and Research Opportunities
Fig. 2 Modem Mechatronic System
Figure 2 shows a block diagram of modem mechatronic systems. It looks like a typical block
3
~
Automated Steering Automated Highways
If we consider mechatronics from the view point of concurrent engineering (Van Brussel, 1996), the "mechatronics nature" of research becomes more apparent when the consideration on control algorithms is coupled with the selection and placement of sensors and/or even the design of target physical (mechanical) systems. MEMS is relevant to this because it is a technology for co-location of sensors and actuators, which often makes the controller design easy.
Systems for
Vehicles
on
The California Partners for Advanced Transit and Highway (PATH) Programs was established in 1986 to promote the application of advanced technology to help meet California's growing need for increased highway capacity to relieve congestion. The idea of Automated Highway Systems (AHS) was identified to be an attractive option for solving the congestion problem while improving the operation of highways in many regards including safety, fuel economy and pollution, AHS research has been a major part of the PATH program. AHS is one form of intelligent transportation systems (ITS). As identified in the ASME report, transportation is of critical importance in the 21 sI century. Each vehicle on AHS must be equipped with the longitudinal controller and the lateral controller. The longitudinal controller maintains the distance (or time headway) between the vehicle and another in front of it at a desired value.
Figure 3 summarizes the activities of Mechanical Systems Control Laboratory in the Mechanical Engineering department of the University of California at Berkeley. The Laboratory has worked on a variety of mechanical systems to study the role and utilization of control methodologies. It should be noted in the figure that balloons for application areas and the control theory balloon are connected by lines with arrows on both ends. Motivations for developing new ideas in the control theory balloon have their origins in problems encountered in specific application. Repetitive control (Tomizuka, Tsao and Chew, 1989) is such an example. The development of the discrete time repetitive control theory was motivated by noncircular machining (Tsao and Tomizuka, 1994) as well as disk file control to compensate for the eccentricity of data tracks on the disk relative to the center of disk rotation (Messner, et aI., 1993). The zero phase error tracking control (ZPETC) (Tomizuka, 1987) was conceived as a simple mean to realize feedforward control for x-y tables and other motion control devices. Almost all research projects in the laboratory have analytical and experimental components. This sty le of research naturally evolves into control oriented mechatronics research.
From the viewpoint of mechatronics, AHS is an excellent case of system integration incorporating items in Fig. 1 and other items. Vehicle longitudinal and lateral controls are sub-problems in AHS, but they include a number of mechatronics issues such as system integration, advanced controls, communications and selection of sensors for better controllability and fault management. The lateral controller ensures that the vehicle is kept on a specified lane. In vehicle lateral control for AHS, it is critically important how the vehicle's position and orientation relative to the road are obtained. Various road reference/sensing systems have been proposed in the past. PATH adopted the magnetic marker (nail) system with on-board magnetometers. In this method, magnets are buried at equally spaced interval along the automated lane. PATH researchers developed robust signal processing schemes for obtaining the lateral error, as well as, encoding schemes to embed other information such as preview road curvature information in binary form by alternating the polarity of the magnets. Furthermore, it compares favorably with other schemes in terms of evaluation criteria such as accuracy, reliability, maintainability, and cost. The road reference-sensing system based on magnetic markers is a look down system. If the magneto meter is placed under the front bumper, the system allows only a small amount of "look ahead" relative to the center of gravity of the vehicle. On the other hand, the vision camera defines a look-ahead system with am ample amount of look ahead. The nature of the open loop dynamics from the steering input to the sensor output makes feedback control design easier when the sensor is placed ahead of the vehicle, say by 5 m, to allow an ample look-ahead It is not practical to place a "real" distance.
Fig. 3 Control of Mechanical Systems
3.2 Mechatronic Projects-Examples In this section, we will review three research projects, each of which has some distinctive mechatronics nature.
4
The current research on the automated steering system at PATH is concentrated on heavy vehicle steering control. The experimental vehicle is a Freightliner FLD120 class 8 tractor and a Great Dane trailer (Hingwe, et al., 1999). Figure 6 shows the instrumentation on the experimental vehicle. The figure suggests the mechatronics nature involved in this problem. In particular, it is noted that three sets of magneto meters are placed on the vehicle: at the front and rear ends of the tractor and the rear end of the trailer. Also the independent trailer brake actuators act as a secondary input for lateral control. At curved sections of highways, the tractor's front wheel and the trailer's rear wheel follow different paths, which is known as off-tracking. The amount of off-tracking depends on the vehicle speed, and it must be taken into consideration in lateral control. Thus, the lateral control problem is not merely to keep the sensor output at zero.
magnetometer say 5 m ahead of the vehicle. Thus, PATH researchers devised an interesting mechatronics solution for realizing a larger lookahead distance based on multiple magnetometers. They installed magnetometers under both the front and rear bumpers: i.e. the lateral error at the front bumper, y., and at the rear bumper, y" were measured (see Fig. 4).
/ ,
/~
--------, / I
,
I
Jf)
/~, I //
virtual ':; ---·· .. i'"._ ~ensor wl '.
~'
;>,j
Fig. 4 Error Sensing by Front and Rear Sensors. Under the assumption that the road is straight, front and rear magneto meter measurements are converted to the lateral error at the tractor's CG and the relative yaw error by
Y
,
&,
=
Linear robust control algorithms and nonlinear adaptive control algorithms have been developed for the Freightliner test vehicle, and their effectiveness has been experimentally demonstrated. In vehicle control, the interaction between the road and tires, which generates the lateral force for vehicle to turn, is very complex, and the advantages of adaptive control have been pointed out by analysis and simulations.
I , IY .<[ +I ; IY"
= tan
/ [ 1+ 1' 1 _I
Y s[
-
y"
1[ 1 + / "
Y >/ - y"
'" ---"---
1[ 1+ / "
where I}, 12 , Y sfi Y sr and Er are defined as in Fig. 4. These two quantities can be combined to synthesize the lateral error at the virtual sensor located at any distance ahead of the vehicle. This makes it possible to allow the look down system based on magnetic markers behave like a look-ahead system : i.e.
Yv
= Yr
Another emphasis in the current research at PATH is on failure detection and fault tolerant control. The failure detection and fault management has been studied at PATH for some time, since safety is an important issue in any automated system. This has also been a motivation for our recent study on fault tolerant lateral control systems for AHS (Surayanarayanan, Tomizuka and Suzuki, 2000).
+dJir
PATH has developed a variety of algorithms based on the magnetic reference systems (Peng and Tomizuka, 1993 ; Patwardhan, et al. , 1997) leading to the successful demonstration at the 1997 NAHSC (National Automated Highway Systems Consortium) Demonstration in San Diego in 1997. The sensing scheme described above was a critical element in the success of the demonstration, which reminds us that the design of control systems is not merely a selection of control algorithms but is a synergistic integration of a variety of elements such as sensors, actuators and control algorithms.
(9) (12)~:cJ
(lO~ §=~=-_I
11 \
,C--on-I
(5)
• 1
(4)0
IC--
(\~)§§
(3)0
'tr--.I
lJftt(2) ): ~/,-I ' 1(1) .~L--I ,r1::I
!)
-
(9)
I
(8) I (6)1
I
~~
(1\)
Fig.6 Sensors and Actuators for Lateral Control (1) front magnetometer array (2) steering actuator (3) computer (4) gyroscope and accelerometer (5) rear magneto meter array (6) articulation angle sensor (7) gyroscope and accelerometer (8) trailer magnetometer array (9) tractor front braking actuators (10) tractor rear braking actuator (ll) independent trailer braking actuators (12) steering wheel angle sensor
Fig. 5 PATH Platoon Demonstration (NAHSC Demonstration in San Diego, 1997)
5
Computer Hard Disk Drives
(Ishikawa and Tomizuka, 1998). The design of a high bandwidth disk drive servo system using a suspension instrumented with strain gauge sensors is described in (Huang, et aI., 1999). As TPI increases every year, it is expected that the current single actuator technology will reach its fundamental limit. To prepare for this situation, the dual stage actuator is receiving an increased level of attention in the disk drive industry (Ohtsuki, et aI., 1992; Schroceck and Messner, 1999; Ding, Numasato and Tomizuka, 2000). The majority of dual stage actuators utilize the conventional voice coil motor primary stage and a piezoelectric secondary stage. MEMS offers an alternative option for second stage actuation (Horsley, Horowitz and Pisano, 1998).
Magnetic hard disk drives (HDDs) are representative mechatronics devices (Messner and Horowitz, 1998). Figure 7 shows a 3.5" hard disk drive . The HDD industry is striving for higher aereal storage density, higher data transfer rate and lower cost. The aereal data storage density of commercial drives has been increasing at a rate 60% per year. Since the first disk drive was introduced in 1957, the data storage density has increased by a factor of 5,000,000. There are a number of amazing technologies involved in disk drives. The slider, on which the recording head is mounted, flies over a rotating disk at a height of about 20 nm. This is analogous to a Boeing 747 flying at an altitude of less than 1 millimeter. The small flying height is required to maximize the storage density. The number of data tracks per radial length is currently about 15 to 20 K tracks per inch (TPI). TPI is expected to triple by end of next year. HDD can now store date at unbelievable densities exceeding 10 gigabits per square inch. Researchers are now looking into a variety of new technologies (Taigo, 2000). There are several different ways to increase the data transfer rate . Both the disk rotational speed and the track seeking time are important. Access time, which depends on these two factors, has been improved by a factor of three during the past ten years. The importance of the servo control is easy to recognize.
Fig. 7 Hard Disk Drive Unite (I) voice coil motor, (2) actuator pivot (3) actuator arm, (4) read/write (recording) head (5) data track (6) spindle motor axis
The current disk drives use the so called sector servo method. In this method, the disk is divided into angular sections (sectors) and servo information is written at every sector. The recording head reads the position error signal (PES) once in each sector. A challenge in the design of these systems is to minimize the number of sectors (equivalently the sampling rate), while continuing to meet tracking performance requirements. There has been a number of interesting control ideas introduced to disk file controls. Repetitive control is such an idea (Tomizuka, Tsao and Chew, 1989). In standard digital control, the control input is updated at every instant of output (error) measurement. This standard scheme is called the single rate scheme. The updating rate of control input, however, can be more frequent than the measurement sampling rate. Such control methods belong to multirate control, and several kinds of mutilate control have been proposed for hard disk drives (Chiang, 1990; Kobayashi, et aI. , 1998; Hara and Tomizuka, 1999). A multirate approach has also been suggested to decrease the implementation cost of repetitive control (Smith, Takeuchi and Tomizuka, 1999). PES is the major information source in the disk drive servo system. There have been several attempts to improve performance by utilizing information from additional sensors. Accelerometers have shown to improve the track following performance by canceling the effect of external vibration on PES (White and Tomizuka, 1997) and eliminating the effect of pivot friction
Media Handling Mechanisms /or Printing Engines A significant amount of the dissatisfaction with current printers and copiers is associated with malfunctions in their media handling system. In typical copiers, papers must travel along the paper path from the feeder to the finisher making many turns and going through nip rollers. There is essentially no feedback control of paper motions except at the final printing stage. The lack of control often results in the so-called soft jam. If a sheet does not arrive at a checking station as expected, the machine is automatically shut down. In an NSF sponsored project entitled "Mechatronic Design and Control of Media Handling Mechanisms for Printing Engines" the University of California at Berkeley and Xerox are jointly studying the integration of sensing, control and decision making methodologies in the mechanical design and the real time control of copying machines. Figure 8 shows a bench fixture built for studying feedback control of paper motions along the paper path. The unique feature of this setup is that an independent motor is placed at each section of the paper path. This added flexibility enables independent position control of sheets in different sections by running the sections at different velocities. Additional optical sensors and encoders are used to improve the sheet position estimates. The increased level of flexibility naturally leads to a more
6
complicated machine. From a control theoretic point of view, the overall system becomes a hybrid system: it is a dynamical system in the usual sense but changes its configuration as well as operation principles at discrete points in time. It is an excellent mechatronics project. Details of the experimental setup along with some simulation and experimental results are given in Kruchinski, et al. (2000).
diagram of a typical telesurgical workstation resembles the diagram in Fig. 2. A recent article in Business Week, Port (2000) states "Mechanical body parts could someday make disabilities irrelevant in the workplace." Artificial organs (and projected dates of availability) compiled in the article include artificial-vision brain implants (2001), permanent mechanical heart implants (2010), lungs and kidneys (2015). synthetic muscles (2019), and artificial eye implants (2024). These biomedical applications show that the human body may be an important component of mechatronic systems or that the human and mechatronic devices interact in synergistic ways. The interface between human and machine rely on the human's five senses, among which visual and haptic are most popular. In particular, research on haptics has expanded and branched out in new directions such as real-time transmission and display of haptic information. The IEEE/ ASME Transactions on Mechatronics is planning a focused section on haptic devices and applications for publication in the latter half of this year. Another interesting integration of human and machine is studied at the Human Engineering Laboratory at VC Berkeley. The members of this laboratory carry out research efforts on design and control of a class of robot manipulators worn by humans to augment human mechanical strength, while the wearer's intellect remains the central control system for manipulating the robot. The key point in their systems is the exchange of both information signals and physical power. A recent accomplishment of this group was the development of a machine that successfully maneuvered heavy loads in isolated areas for extended periods of time (Neuhaus and Kazerooni, 2000). Human is involved in the operation of this machine.
Fig. 8 Experimental Set-up for Paper Motion Control Other Research Areas There are a number of other research areas where mechatronics thinking is extremely important. They include but are not limited to: robotics and automation, manufacturing, biomedical engineering, energy and the environment, and large scale structures such as bridges and buildings. There is no question that robots represent a challenging area from the mechatronics point of view, and most compelling examples ofmechatronics are often found in the robotics area. In fact, many challenging problems such as design and construction of light weight robots (e.g. DLR Lightweight Robot, www.robotic.dlr.de). intelligent robotics and robotic surgery require mechatronic approaches.
As we look into the next decade, we may predict several natural trends based on the ASME report. We may safely state that mechatronics in the 21 51 century will heavily depend on information technology and miniaturization. Such technology will make it possible to provide remote monitoring of home appliances, automobiles and elderly or handicapped people.
Mechatronics has been and will be playing an important role in the area of medicine and surgery (Hewit, 1995; Cavusoglu, et aI., 1999). For example, minimally invasive surgery (MIS) is a revolutionary In MIS, the surgery is approach in surgery. performed with instruments and viewing equipment inserted into the body through small incisions, minimizing the surgical trauma and damage to the healthy tissue. It is a telesurgery similar to the remote operation for handling hazardous materials. While MIS results in shorter patient recovery time, there are a number of research issues associated with reduced dexterity, workspace, and sensory input to the surgeon that is only available through a monoscopic video image (Cavsoglu, 1999). MIS defines a human-machine system, and the block
4.
MECHA TRONICS-EDUCA TIONAL CHALLENGES
Engineering education is facing challenges in the midst of rapid progress of information technology. In terms of starting salaries offered by industries to new graduates, computer science has been the leader at all levels (BS, MS and PhD) for some years. High school students often do not have a clear idea of what they want to do. Often their decisions are based on conversation with parents, older relatives or friends, which combined with headline news on IT, motivates many of them to send applications specifying
7
"computer science." At the University of California at Berkeley, our current experience is that nearly 50 % of undergraduate applications to the Engineering College are concentrated in computer science. In Berkeley's Electrical Engineering and Computer Science (EECS) Department, the ratio of undergraduate enrollment was two EE students for every CS student five years ago. This ratio has reversed and it is now two CS students for every EE student. The popularity of computer science is not a new phenomenon. In the 1980's, Computer Science (CS) once attracted many applications. At that time, many universities struggled to keep us with the demand for computer science courses to provide students with knowledge about programming languages, operating systems and computer architecture. This boom did not last for a long time. CS graduates with programming skills were not necessarily appreciated by industry executives either. No fundamental curricula revision, however, was considered at that time to respond to the need of industries.
bright, curious, intellectual, and unafraid of leaning new things." This statement is highly relevant when we talk about mechatronics education. Craig (1998) states, "In mechatronics, balance is paramount. The essential characteristic of a mechatronics engineer and the key to success in mechatronics is a balance between two skills: •
•
mode ling (physical and mathematical), analysis (closed form and numerical simulation), and control design (analog and digital) of dynamic physical systems experimental validation of models and analysis (for computer simulation without experimental verification is at best questionable, and at worst useless) and understanding the key issues in hardware implementation of designs ."
Carryer (1998) emphasizes integration. While these comments are not necessarily fresh, they are all essential. In fact, the points made by Craig and Carryer are important in engineering education. Every undergraduate students in mechanical and electrical engineering as well as in other engineering disciplines should be trained so that they can effectively utilize IT tools along with their analytical skills to solve engineering system problems. Effective communication with others is a necessary requirement. Furthermore, students should be trained to be forward looking and curious. Issues surrounding integration as well as working in team cannot be taught in lecture courses. Students must experience them, and in this regard laboratory courses are essential in mechatronics education.
The strong application demand from students and the strong supply demand from all segments of industries that universities are currently facing in IT are more than a temporary boom. Educators have recognized that engineering curricula must be revised in fundamental ways so that universities may supply leaders to advance IT and professionals to apply IT in various industries (Wilson, 1998). Lee and Messerschmidt (1998) state: "We believe that the center of gravity of most undergraduate curricula today is too far on the side of attempting to train the small cadre of technical experts, a hopeless task within a four-or-five-year program. Because of the hopelessness of the task, we cram too much content into the program, thinking it makes it better (and somehow less hopeless). This shuts out other fundamental knowledge that we believe will be extremely valuable to them in their design careers. Students have been seriously shortchanged by not understanding the big picture.
At the University of California at Berkeley (UCB), Professor Kazerooni converted a senior level course on mechanical engineering design to a new course on mechatronics design. During a 15 week period, he covers microcontrollers, real-time software, electric motors, pneumatics and hydraulics, transmission systems, brakes and clutches, power electronics, bearings, and sensors. The course ends with the inventors' open house, where students present their projects. For projects, students normally work in a group of three to four. Feedback control is not a prerequisite for the course, but projects are often quite sophisticated involving feedback control. Project titles from recent offering of the course include automatic bicycle gear shifter, automated rice cooker, and walking robots.
We advocate an alternative vIsIon in which the undergraduate program focuses on a limited and carefully chosen set of core ideas, supplemented by real-world examples and importantly by student self-exploration and learning. Such an undergraduate program also emphasizes breadth, an exposure to a range of technical issues, as well as mathematics, science, humanities, and social sciences.
Figures 9 and 10 are several examples of laboratory sessions from a UCBs' graduate course on switching control and computer interfacing by Professor David Auslander.
In a field as dynamic as ours, no set of vocational skills has any significant longevity. It is far more important that our graduates be
8
the best industrial practice in the present day global and competitive market. At the same time, mechatronics thinking is the basics of the modem engineering education. Engineers must be innovative and utilize the best tools available. This is a common sense. The mechatronics approach is particularly relevant in mechanical engineering and electrical engineering. In particular, in mechanical engineering departments, faculty members specializing in control and design must act as leaders to bring into mechatronics in the engineering curriculum.
Fig. 9 Working on the Milling Machine (Picture: Courtesy of Professor D. Auslander)
REFERENCES Auslander, D. M.(1996): What is Mechatronics?, IEEEIASME Transactions on Mechatronics, Vol. 1, pp. 5-9. Carryer, 1. E. (1998): Controllers or Components: Deciding What (and What not) to Teach in Mechatronics Courses, DSC-Vo!. 64, Proceedings of the ASME Dynamic Systems and Control Division, pp. 377-382. Cavusoglu, M. c., F. Tendick, M. Cohn, and S. S. Sastry (1999): A Laparoscopic Telesurgical Workstation," IEEE Trans. Robotics and Automation, Vol. 15, No. 4, pp. 728-739. Chiang, W.-W. (1990): Multi-rate state-space digital controller for sector servo systems, Proceedings of the 29th IEEE Conference on Decision and Control, pp. 1902-1907. Craig, K. (1998): Mechatronics in University and Professional Education, DSC-Vo!. 64, Proceedings of the ASME Dynamic Systems and Control Division, pp. 369-375 . Hara, T. and M. Tomizuka (1999): Performance Enhancement of Multi-rate Controller for Hard Disk Drives, IEEE Magnetics, pp. 898-903. Harashima, F., Tomizuka, M. and Fukuda, T. (1996): Mechatronics-"What Is It, Why, and How?" An IEEEIASME Transactions on Editorial, Mechatronics, Vol. 1, pp. 1-4 (1996). Hingwe, P. and M. Tomizuka (1997), "Robust and Gain Scheduled Hoo Controllers for Lateral Guidance of Passenger Vehicles in AHS," Proceedings of the ASME Dynamic Systems and Control Division, DSC-Vol. 61, pp. 707-713. Hingwe, P., M. Tai, 1.-Y. Wang, 1.-Y. and M. Tomizuka (1999): Lateral Control of TractorSemitrailer Combination for Automated Highway Systems-An Experimental Study, Proceedings of the ASME, Dynamic Systems and Control Division -1999, DSC-Vol. 67, pp. 195-202. Hewit, 1. (1995): Mechatronics Design - The Key to Performance Enhancement, Proceedings of the International Conference on Recent Advances in Mechatronics, Istanbul, Turkey, pp. 18-24. Horsley, D. A., R. Horowitz, and A. P. Pisano (1998): Microfabricated Electrostatic Actuators for Hard Disk Drives, IEEEIASME Transactions on Mechatronics, Vol. 3, No. 3, pp. 175-183.
Fig. 10 Automatic Train Loading (Picture: Courtesy of Professor D. Auslander) At the graduate level, in particular doctorate students should be exposed to a broad spectrum of fundamental theories such as control theory. "Fundamentals are fundamental" (Masten, 1998) is important for future academic and industrial leaders. As stated already, many high school students have a simple equation Information Technology = Computer Science Department and do not realize how other engineering disciplines are changing with IT. In this regard, the role of educators must go beyond how mechatronics should be taught. It is important that we direct the attention of high school students and college freshmen and sophomores to the exciting At the University of field of mechatronics. California at Berkeley, the College of Engineering admits a good number of freshmen under category of undeclared major. They decide their majors when they are advanced to the junior level. Freshman seminar courses are intended to expose newly admitted students to a variety of engineering disciplines. Incorporating mechatronics flavors to such presentations make any engineering discipline more attractive to undergraduate students.
5. CONCLUSIONS This paper described the evolution of mechatronics and opportunities and challenges in mechatronics research and education. Mechatronics is essential as
9
Control: System Analysis," Proceedings of American Control Conference, pp. 1598-1602. Peng, H. and M. Tomizuka: Preview Control for Vehicle Lateral Guidance in Highway Automation, ASME Journal of Dynamic Systems, Measurement and Control, Vol. 115, No. 4, pp. 679- 686. Port, O. (2000): Artificial eyes, turbine hearts, Business Week, March 20, pp. 72-73 . Schroceck, S. J. and W. C. Messner (1999): On Controller Design for Linear Time-Invariant DualInput Single-Output Systems, Proceedings of the American Control Conference, San Diego, pp. 4122-4126. Smith, c., K. Takeuchi and M. Tomizuka (1999): Cost Effective Repetitive Controllers for Data Storage Systems, Proceedings of the I4,h IFAC World Congress, Beijin, China, Vol. B, pp. 407412 Suryanarayanan, S., M. Tomizuka and T. Suzuki (2000): Fault Tolerant Lateral Control of Automated Vehicles Based on Simultaneous Stabilization, Proceedings of the IS' IFAC Conference on Mechatronic Systems, Darmstadt. Taigo, J. W. (2000): Avoiding a Data Crunch, Scientific American, May, pp. 58-74. Tanie, K. (1999): Mechatronics - Past, Present and Future, Proceedings of the 1999 IEEEIASME International Conference on Advanced Intelligent Mechatronics, September, Atlanta, page 2. The New York Times (2000): A Big Step Forward In Tiny Technology, Monday, May 8, 2000. Tomizuka, M. (1987): Zero Phase Error Tracking Algorithm for Digital Control, ASME Journal of Dynamic Syst., Meas. and Control, Vol. 109, No. I, pp. 65-68. Tomizuka, M., T-C. Tsao and K-K. Chew (1989): Discrete-Time Domain Analysis and Synthesis of Repetitive Controllers, ASME Journal of Dynamic Systems, Meas. and Control, Vol. Ill, No. 3, pp. 353-358 Tsao, T-C. and M. Tomizuka (1994): Robust Adaptive and Repetitive Digital Tracking Control and Application to a Hydraulic Servo for Noncircular Machining, ASME Journal of Dynamic Systems, Meas. and Control, Vol. 116, No. I, pp. 24-32. Von Brussel, H. M. 1. (1996): Mechatronics - A Powerful Concurrent Engineering Framework, IEEElASME Transactions on Mechatronics, Vol. I, No. 2, pp. 127-136. White, M. T. and M. Tomizuka (1997): Increased Disturbance Rejection in Magnetic Disk Drive by Acceleration Feedforward Control, IFAC Journal of Control Engineering Practice, Vol. 5, No. 6. Wilson, J. M. (1998): Gearing Up for Information Technology, Syllabus, Vol. 11, No. 10, pp. 26-28.
Huang, Y., M. Banther, P. Mathur, and W. C. Messner (1999): Design and Analysis of a High Bandwidth Disk Drive Servo System Using an IEEElASME Instrumented Suspension, Transactions on Mechatronics, Vol. 4, No. 2. Hudson Institute, Inc. (1999): Mechanical Engineering in the 21 SI Century - Trends Impacting the Profession, ASME. Ishikawa, J. and M . Tomizuka (1998): Pivot Friction Compensation Using and Accelerometer and a Disturbance Observer for Hard Disk Drives, IEEEIA SME Transactions on Mechatronics, Vol. 3, No. 3, pp. 194-20 I. Isermann, R. (1997): Mechatronic Systems - A challenge for control engineering, Proceedings of the 1997 American Control Conference, June, Albuquerque, New Mexico Kobayashi, M, T. Yamaguchi, I. Oshimi, Y. Soyama, Y. Hata, Y. and H. Hirai (1998): Multi-rate zero phase error feedforward control for magnetic disk drives, Proceedings of lIP '98, JSME Publication No. 98-26, pp. 21-22 (in Japanese). Kruchinski, M., C. Cloet, R. Horowitz and M. Tomizuka (2000): A Mechatronics Approach to Copier Paperpath Control, Proceedings of the IFAC Conference on Mechatronic Systems, Darmstadt. Kyura, N . and Oho (1996), H.: Mechatronics-An Industrial Perspective, IEEEIASME Transactions on Mechatronics, Vol. I, pp. 10-15. E. A. and D. G. Messerschmit Lee, (1998):Engineering an Education for the Future, Computer, pp. 77-85 . Masten, M. (1998): Industrial Perspective of Control Engineering Education, presented at NSF Workshop on New Directions in Control Engineering Education, Urbana, IL .. Messner, W. , C. Kempf, M. Tomizuka and R. Horowitz (1993): A Comparison of Four Discrete Time Repetitive Control, IEEE Control Systems, Vol. 13, No. 6, pp. 48-54. Messner, W. C. and R. Horowitz.(I998): Guest Editorial, Focused Section on Mechatronics for Magnetic Disk File Storage Systems, IEEEIASME Transactions on Mechatronics, Vol. 3, No. 3, pp. 153-155 . Neuhaus, P. and H. Kazerooni (2000): Design and Control of Human Assisted Walking Robot, Proceedings of the 2000 IEEE International Conference on Robotics and Automation, San Francisco, April, pp. 563-569. Ohtsuki, H., K. Mori, T. Munemoto and K. Akagi (1992): Track Following Control of2-Stage Access Servo System for Magnetic Disk Drives, Trans. of Electro-Information-Communication Society (Japan), Vol. J756-C, pp. 653-662 . NSTC (National Science and Technology Council) (2000), "National Nanotechnology Initiative: Leading to the Next Industrial Revolution," Washington, D. C. Patwardhan, S., H-S. Tan, and J. Guldner (1997). "A General Framework for Automatic Steering
10