IEEWASME TRANSACTIONS ON MECHATRONICS, VOL. 1, NO, 1, MARCH 1996
10
tronics-An
Industrial Pers
Nobuhiro Kyura and Hirosuke Oho
Abstract- The term “Mechatronics” is defined to provide a
framework for technical and practical considerations.Within this
framework, the importance of “intimate and organic” integration
in mechatronics product designs is raised. Several issues pertaining to attaining this ideal integration of mechanical, electronic
controls, and system engineering in mechatronics product designs
are cited. To further advance the current mechatronics products,
areas of improvement are also presented.
I. INTRODUCTION
HE term “Mechatronics” was first introduced by a
Yaskawa Electric engineer in 1969. Trademark rights
were granted in 1972 [1], and the term soon became popular.
As its use became widespread, Yaskawa in 1982 released all
rights pertaining to the trademark.
In these 20-odd years the rapid development in computerrelated electronics, such as microprocessors, and in power
electronics such as high-capacity, high-speed switching characteristics has led to widespread adoption of electronics in
machinery. Products referred to as “mechatronics” now offer
significantly enhanced function and performance. With improving function and performance, a variety of “mechatronics”
products began to appear on the market. Many began to use the
term “mechatronics” liberally, fueling debate over its definition
and technical philosophies [2].
A technical committee on mechatronics, The International
Federation for the Theory of Machines and Mechanism
(IFTMM), provides a good definition of mechatronics:
“Mechatronics is the synergistic combination of precision
mechanical engineering, electronic control, and systems
thinking in design of products and manufacturing processes”
[3]. This definition helps to steer the philosophies of
mechatronics technology, including development, design, and
manufacturing.
With increasingly liberal use of the term, mechatronics,
there is a need to encompass mechatronics products excluded
from the above IFTMM definition. Some critical characteristics of IFTMM definition, such as the “synergistic combination of mechanical and electronic engineering” seem lacking
in numerous mechatronics products that range from digital
watches to electric robots. A classification based on product
configuration concept may help extend the IFTMM definition.
The Japan Society for the Promotion of Machine Industry
(JSPMI) in late 1970’s grouped mechatronics products into the
four following classifications of product configuration concept
~41.
Manuscript received November 6, 1995; revised December 18, 1995.
The authors are with the Yaskawa Electric Corporation, Yahatanishiku
Kitakyushu, 806 Japan.
Publisher Item Identifier S 1083-4435(96)02288-0.
The Class 1 mechatronics products are traditionally wholly
mechanical products in which the primary functions were enhanced by the introduction of electronic technology. Examples
of the Class 1 mechatronics products are numerical control
(NC) machine tools and robots, whose precision control functions were enhanced by electronic controllers.
The Class 2 mechatronics products are traditionally wholly
mechanical products which have retained their external configurations and primary functions, but have changed their internal
configuration with the introduction of electronic technology.
Examples of the Class 2 mechatronics products are sewing
machines, which experienced considerable internal overhaul.
The Class 3 mechatronics products are traditionally wholly
mechanical products which retained their primary functions
only. Example of this class of mechatronics products are digital
watches and push-button telephones, which have evolved
dramatically by combining electronic technology.
The Class 4 mechatronics products are any other products
that incorporate mechanical and electronic technology. Examples of this class includes a wide variety of products, such as
rice cookers, facsimile machines, and copiers. These products
have been improved dramatically by the advances in precision
mechanics and microprocessor technology.
Together, the IFTMM definition and the JSPMI classification provide a framework to pursue either theoretical or
practical work or both. The IFTMM definition sufficiently
describes the concept of mechatronics and its constituent
technologies. The JSPMI classification helps to define proper
categorization of products, or the implementation of theoretical
work. Concrete product configuration concepts are necessary
for the engineering process.
The mechatronics discipline covers a wide selection of
application areas. In consideration of the time and space
provided, the remainder of this paper focuses on the JSPMI’s
Class 1 of product configuration concept with emphasis on the
NC machine tools and industrial robots (NC/IR).
11.
FUNDAMENTALS OF
MECHATRONICS
EQUIPMENT
The following definition was introduced with the documents drawn up for the trademark application for the term
mechatronics.
“The word, Mechatronics, is composed of “mecha” from
mechanism and the “tronics” from electronics. In other words,
technologies and developed products will be incorporating
electronics more and more into mechanisms, intimately and
organically, and making it impossible to tell where one ends
and the other begins.” 151.
The phrase, “intimately and organically,” holds importance
in the consideration of the Class 1 mechatronics products.
10834435/96$05.00 0 1996 IEEE
KYURA AND O H 0 MECHATRONICS-AN
INDUSTRIAL PERSPECTIVE
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Sensitivity
Layer
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Structural
Layer
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i
Operator
Layer
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--.I
Human-Interface BUS
Language
InterpreterIProcessing
f
Sub-system Bus
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Various
Penpheral
Equipment
ii
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System Total
Management
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1I
,
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Actuator
Control
(1st Axis)
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:
Actuator
Control
(Nth Axis)
(i!:)
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-
Machine, Controller
DiagnosisSensor
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l
Various External
Sensors
T
Machine
Fig. 1, Controller configuration.
The “synergistic combination” of IFTMM definition embodies
the essence of the phrase, “intimately and organically,” as it
was originally expressed in Japanese. Mechatronics products
are combinations of mechanical and electronic engineering
disciplines. “Intimate and organic” integration takes advantage
of both engineering disciplines to complement the deficiencies
of each other. Cooperative interaction among mechanical and
electronic agents would create an enhanced combined effect
that is larger than the sum of the individual effects. It seems
that current NC/IR have yet to achieve such “intimate and
organic” integration of their mechanical and electronics parts.
The use of microprocessor-based controllers and highperformance servomechanisms in NCAR have steadily
improved. In particular, user operability and trajectory
control precision have progressed significantly in functional
breadth and performance. The mechanical and electronic
parts (servomotor systems and controllers) of the NC/IR are
integrated as a method to implement the motion system. It is
difficult to say, however, if the systems available today achieve
the synergistic integration “intimately and organically.”
Controllers in Class 1 mechatronics products perform a
major portion of system functions, such as machining functions, motion performance, and operation functions. Following
observations are made on the functions of these controllers.
A typical controller has a hierarchical structure as shown
in Fig. 1 [6]. The uppermost Sensitivity Layer contains the
man-machine interface for machine operations. The Structural
Layer, below the Sensitivity Layer, implements the functions
which give the equipment its attributes. The Regulatory Layer
implements the primary machine functions and the functions
for coordinated control of required peripheral devices. The
lowermost layer, the Operator Layer, is composed of operational devices, such as actuators, that are directly connected
to corresponding components in the Regulatory Layer. Class
1 mechatronics equipment has a servosystem connected to
the motion monitoring and generation components in the
Regulatory Layer. Servosystems typically consist of actuators,
mechanisms, detectors, power amplifiers, and controllers as
shown in Fig. 2. In general, actuators in servosystems, are
directly connected to the mechanisms. Hence, the servosystem functions as che interface between the mechanical and
electronic portions.
A typical configuration of servosystems in NC machine
tools and industrial robots is shown in Fig. 2.
The servosystem is a semi closed-loop system, where the
position and velocity detectors mounted on the nonload side
of the servomotor provide data which are fed back to the
system. Fig. 3 illustrates the servosystem block diagram, when
the actuator and tlhe load are viewed as a 2-inertia system.
For multiaxis configurations, where motion is defined by the
relations between iutes, actuators for each axis are controlled
independently [7]. Consequently, the control system processes
only the information from the actuators. Effects of mechanisms
on the same axis, or mechanisms on adjoining axes, are
processed as torque disturbances on the actuators. The actuator
servosystem is designed to assume these disturbances noise.
For example, the velocity control system, a commonly used
actuator control for NC/IR, is designed to consider only
step-wise torque disturbance effects. This technique, while
sufficient for gross machine motion, is unsuitable for precision
IEEEIASME TRANSACTIONS ON MECHATRONICS, VOL. 1, NO 1, MARCH 1996
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Position
Reference
Input
Feedforward
Controller
Fig. 2.
Conceptual configuration
Current Feedback
of 1-axis servosystem
I-....-....-.-.-___-.~--------.-----...........--------.---,
Micro-Processor Based Controller
(Software-Servosystem)
GF(S) : Feedforward Loop Controlier
Gi(S) : Position Loop Controller
Gz(S) : Velocity Loop Controller
G3(S) : Current Loop Contrplier
Kt : Torque Constant of Motor
JM: Moment of inertia of Motor-Rotor
Rg: Ratio of Reduction Gear
KL : Compliance of Mechanism (Load)
JL : Moment of inertia of Mechanism (Load)
DL: Damping Coefficient of Mechanism (Load)
Fig. 3. Block diagram of 1-axis servosystem.
motion control. Appropriate engineering attention to individual
portion is necessary for servosystems to achieve the “intimate
and organic” integration.
111. CONSIDERATIONS IN APPLICATION
In general, servosystems consist of actuators, mechanisms,
and mechanism controllers (see Fig. 2). Designing servosystems requires careful consideration, not only of their parts, but
also of the combinatorial effects. In particular, there are many
challenges in designing the mechanism and its controls.
Today, computerized design tools (software packages) or
computer-aided design (CAD) systems are commonly used
in designing mechanical system controller. Analysis of mechanical elements are also possible with a variety of computerized analysis packages or computer-aided engineering
(CAE). These tools allow engineers to investigate virtual
models on computers and help understand the detailed effects
of the designed machinery in operation. Also, development
cost can be reduced by fabricating only the minimum number
of prototypes [8], [SI.
Another form of design tools is the various theoretical
work by researchers in mechanical, electronic controls, and
systems engineering. There has been a substantial amount of
research in system identification as a part of control theory
[ 101 to provide details on servosystems and the characteristics
of the controlled mechanism. Considerable work on control
methodology, such as linear constant parameter system control, linear time varying control, nonlinear control, stochastic
system control [11]-[13], and continuous (analog) or discrete
(digital, software algorithm) [14], H-infinite control [15], [16],
and robust control theory [171-[191.
Control methods of operation control in mechatronics equipment show that advances in mechanical and electronic engineering are not utilized effectively. The mechanical and
electronic parts have yet to be integrated “intimately and
KYURA AND OHO: MECHATRONICS-AN
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INDUSTRIAL PERSPECTIVE
organically.” To this end, the following sections provide a list
of problems and suggestion, in achieving the ideal integration
of mechanics and electronics.
the “intimate ancl organic” integration of mechanism and
electronics.
C. Issues in Designing Advanced Machine Control
A. Issues in Designing Mechanisms
Current CAD and CAE systems emphasize the design
and analysis of the mechanism. This raises the following
systematic problems.
Software systems for mechanism designs do not take
control methods into account. It is difficult to adequately
specify the choice of the control system into design.
Computer and related software technologies have advanced to a point where a common database can be
shared between design and analysis systems. However,
difficulties remain in specifying or analyzing dependent
characteristics, such as control performance indices of
mechanical operation. For the most part, dependency
evaluations rely on the experience and intuition of the
engineer.
Computer analysis results are quantitative, but do not provide information on the qualitative relationships between
quantitative factors in the data.
The gross or systemic characteristics of the mechanism
can be understood, but it is difficult to obtain analysis
which can also accurately describe detail characteristics.
Many of the operational characteristics of the mechanism are dynamic, but these changes are not accurately
reflected in the analysis results.
Analyses of the mechanism operation performance remains difficult to evaluate.
B. Issues in Designing Mechanism Controls
In designing mechanism controls, the following problems
become evident.
The relationship between the degree to which theoretical
preconditions are met, and the resulting level of control
performance, remains difficult to analyze.
The relationship between the precision desired to identify
the object of control, and the control performance attainable through control methods based on this precision,
remains unclear.
The relationship between the operational precisions of the
mechanism control system and the overall control system
in combination is not well-defined.
The theoretical relationships needed to determine sensor data, response characteristics, and resolution, and
to configure a control system with the requisite control
performance, based on control performance indices, are
difficult to characterize.
The stability of a class of systems is well-defined, but
some aspects, such as the speed of convergence, become
unclear as the system order increases.
As these problems are resolved, it should be possible to
implement controls which take operational state into consideration. Optimal mechanisms designs for requisite functions and
selection of appropriate control methods become attainable.
Mechatronics equipment created in this way would achieve
Improvement off the semi closed-loop servosystem (shown
in Fig. 2) to a full closed-loop feedback control system requires
not only the use of the observer, commonly used in control
methods, but also controls based on the detected signals of
operational states of individual components with feedback to
the controller. This type of feedback control system would
allow precise operation, not available from the mechanism or
controller performance alone, but would rather offer motion,
taking advantage of the mechanism characteristics, which also
considers the mechanism states.
Research and development into advanced mechatronics
equipment require solutions to the above mechanical and
control issues. Also critical is the development of sensor
technology, such as detecting and processing state signals
of mechanical components. Comprehensive data for the
operational states of mechanical components are essential
for obtaining high speed, precision, and performance. Intimate
and organic integration of mechanisms and control will require
the utilization of a variety of sensors.
Physical parameters directly related to the configuration of
the servosystem are position, velocity, acceleration, and rate
of acceleration change. For optimum state control and highprecision operation of the mechanism, sensor data, such as
temperature, vibration, stress, and deformation, are required.
Many currently available position and velocity sensors are
inadequate for full closed-loop feedback control systems.
Issues in resolving the inadequacies of sensors include the
following:
1) compactness;
2) high reliability;
3) high durability to environmental factors, such as temperature, humidity, or vibration;
4) response characteristic suitable for real-time control;
5 ) component accessibility;
6) data and signal processing;
7) communication between sensors via network;
8) price.
There are sensors that already meet some of these requirements. Continuing advancements in materials, nanotechnology, and other fabrication technologies, would further improve
these sensors.
Iv. PROSPECTS OF MECHATRONICS
PRODUCTS
Present Class 1 mechatronics products show symptoms of
designs, narrowly ffocused on Class 1 specification. Many such
products, including dc servomotors, ac servomotors, position
and velocity detectors for motors, and their various drives,
were developed for machine tools. The same observation can
be made of the controllers, i.e., the numerical controllers
used for machine tools. The situation, however, has changed
dramatically over the past twenty years, and can be surmised
from the situation of controllers.
IEEWASME TRANSACTIONS ON MECHATRONICS, VOL. 1, NO. 1, MARCH 1996
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Specialized controllers were developed to solve reliability
issues stemming from the environment where the equipment
is used. Personal computers (PC’s) and their peripheral equipment, have evolved to solve many problems of their environment. Benefiting from this, PC’s have penetrated the machine
tools industry extensively. General availability of operating
systems and various software packages have accelerated the
spread of PC’s. Creating mechatronics equipment controllers
on existing computer resources reduces development time and
allows ease of customizing through the involvement of many
engineers. The PC is likely to become an important part of
the controller in the future. “Open architecture” controllers
are already on the market, with a variety of motion controllers
on PC-based systems. It is expected that these systems will
continue to improve and provide functions and characteristics
needed for sophisticated mechatronics equipment controllers.
Presently, Class 1 mechatronics equipment, especially
NC/IR, is designed under the assumption that operators are
provided ample training. Given the current trend, such an
assumption is unlikely to continue.
Consequently, mechatronics equipment will need to attain
the desired performance regardless of users/operators, including novices. The human-machine interface aspect is most
important. In addltion to assuring safe operation, operators
should be able to use the machine to complete the necessary
work, even with little knowledge or experience. For the human
interface, primary elements include an ergonomic control
panel, interactive systems suited to the immediate tasks at
hand, a database, and knowledge of engineering technologies.
Another requirement for Class 1 equipment controllers is
simple networking capab es. Controllers should be able to
link to other controllers with the same ease as a computer
network, such as a Local Area Network in office environment.
Simple networking would clearly define the functions and
Performance of the constituent equipment, as well as the
communication protocol. Reduction of required resources in
production system installation would become possible. The
following items add to reduce the total cost:
1) system setup and running costs due to centralization of
human interface;
2) remote diagnosis of equipment;
3) centralized management of distributed equipment layout;
4) flexibility and scalability during system expansions,
changes, and upgrades.
V. CONCLUSIONS
A definition of mechatronics by the International Federation
for the Theory of Machines and Mechanism was combined
with the rnechatronics products classification defined by the
Japan Society for the Promotion of Machine Industry to
give an expansive framework for the pursuit of mechatronics
endeavors. In this framework, the synergistic combination
of mechanical and electronic disciplines has been shown to
be an important contributor in the designing of “intimately
and organically” integrated mechatronics products. Issues in
attaining this ideal integration have been shown in designing
mechanisms, mechanism controllers, and advanced machine
controls. Areas of improvement have been suggested to further
advance the current state of mechatronics products.
ACKNOWLEDGMENT
The authors thank Albert Choi of Yaskawa Electric America
Inc. for proofreading the draft of this paper and providing
useful comments. They also acknowledge the anonymous
reviewers for their constructive comments that have helped
to improve the quality of this paper.
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1996.
[3] R. Comerford, “Mech . . . what?’ IEEE Spectrum, pp. 4 6 4 9 , Aug. 1994.
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E51 T. Mori, “Mecha-tronics,” Yaskawa Internal Trademark Application
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Nobuhiro Kyura was born on February 12, 1942
He received B.S., M.S., and Ph.D. degrees in electrical engineenng from Kyushu University in 1964,
1966, and 1992, respectively.
He has been with Yaskawa Electric Corporation
in Japan since 1964. He is currently the General
Manager of the Research Laboratory His current
research interests include motion controller architecture, optimum motion control, and robot manipulator control
Dr. Kyura is a recipient of the Outstanding Award
for a paper submtted to the Japan Society of Precision Engineering in 1985
He also received the Outstanding Conference Paper Award “Robots 10” held
by the Robotics International of SME (Society of Manufacturing Engineers)
in 1986 He is a member of the Institute of Electrical Engineers of Japan,
the Society of Instrument and Control Engineers of Japan, the Japan Society
of Precision Engineering, the Robotics Society of Japan, and the Institute of
Systems, Control, and Information of Japan
KYURA AND OHO: MECHATRONICS-AN
INDUSTRIAL PERSPECTIVE
Hirosuke Oho was born on November 14, 1940.
He received the B.S. degree in electncal engineering
from Kyushu University In 1963.
He joined Yaskawa Electric Corporation as a
system engineer in 1963. He has more than 20 years
of experience in system engineering for industrial
drives and control systems. He is a director and
a general manager of the technical administration
department, and is responsible for corporate R&D
management.
Mr. Oho is a member of the Institute of Electncal
Engineering of Japan.
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