Description of Projects

Theory of Nonlinear Robust Control

Robust control is an important concept of advanced control
which takes into account
mismatches between mathematical models and true behavior
of physical systems in analysis and design of control.
The mismatches are considered as ``uncertainty'' in systems.
The last two decades have seen the emergence of sophisticated
mathematical techniques for dealing with robustness with
respect to such uncertainty in linear control systems.
The corresponding quest for theoretical and computational tools
which tackle nonlinear systems has fallen short of expectations
although gradual but steady progress has been made in several
fundamental issues.
Recently, a new framework called ``statedependent scaling approach''
has been developed by this project conductor and it
provides us with a new successful route to
robustness issues in nonlinear systems control.
An objective of this project is to tackle unsolved problems of
nonlinear robust control by means of solutions to statedependent scaling
problems. A part of the project also includes the establishment of
a more generalized theory encompassing broad classes of truly nonlinear and
complex systems which have not been studied yet.
Compared with theories of linear control,
it is sometimes said that nonlinear
control tends toward domain specific theories.
It is reasonable in the sense that nonlinear control should
tackle various nonlinearities causing diverse
phenomena.
This is a reason why analytic computation by hand
or ad hoc symbolic computation by machines have dominated the
practice of nonlinear control theories.
We need a new theory which unifies the treatment of diverse
nonlinearities.
The new theory would provide us with a unified mathematical formulation
which can be solved numerically in an efficient manner.

Theory of SampledData Control

This project focuses on `nonsynchronism' or `asynchronism' in sampleddata
control systems.
A sampleddata control system exhibits the nonsynchronism
when timing of control action and that of measurement
acquisition are independent of each other.
In practice, nonsynchronous implementation of sampleddata controllers
often takes place unintentionally or intentionally.
The nonsynchronism may influence the control performance
if the sampling frequency is slow relative to the plant or if
the controller is decentralized.
Recently, the use of vision sensor in feedback control has gained
increased attention in mobile robot navigation, manipulation and
autonomous driving.
Hybrid sensorbased controllers
which combine vision sensors with conventional sensors, such as
potentiometer, rotary encoder and laser range sensor, are becoming a
necessary strategy.
The combination yields two levels possessing substantially
different time constants.
One includes intelligent processing of image information and
calculation of the control inputs based on a bundle of visual information.
The other includes the control based on conventional sensors.
If one or few microprocessors are shared by the two levels,
each level occupies the processors in turn.
This timesharing creates a phase shift among two control
levels with different hold intervals, which results in a
nonsynchronous system.
Another common situation of nonsynchronism also
arises from largescale interconnected systems such as communication
network systems where distributed multiple processors are operated.
We yet often encounter nonsynchronism in process control
where multirate control operates a huge plant consisting of systems
having widely different time constants.
Unfortunately the treatment of the nonsynchronism is believed to
be mathematically complex and delicate, and
theoretical investigation of the nonsynchronism
has not received much attention, despite the existence of
strong motivations in application.
The fundamental goal of this project is to address those new issues
and solve those problems mathematically.

Control of Magnetic Disk Drives

An important phenomenon which motivates this project is the enormous
increase in capacity of computer storage devices,
which has pushed its control performance into areas which until
recently have been impossible.
The control of magnetic disk drives is an important area of control
where sophisticated mathematical tools of robust control theory is
indispensable.
Areal density of magnetic disk storages has been increasing by
more than 60% every year. In other words, the track pitch has
reached 100 nm recently. For the purpose of super swift and
accurate head positioning, replacement of
conventional singleactuator mechanism with
dualstage actuators
has attracted much attention by engineers in advanced research and
development sections.
This project seeks an effective way of exploiting the
potential of dualstage actuators.
The strategy of this project, which is believed to be an key to
successful design, is cooperative multirate control.
The most challenging point is how to circumvent
the unique situation of magnetic disk drives
which demand faster and more accurate positioning by feedback
controllers with considerably less frequent acquisition of head
position information.

Control of Wastewater Treatment Plants

Every modern society places great emphasis on environment
conservation. There are increasing demands of technology which
saves our earth.
Control engineers are now trying to solve environmental problems
arising from wastewater treatment.
The progress is, however, still far from rapid development in
other fields of engineering.
This project is to develop a new technology of
controlling biological wastewater treatment systems to
make the effect of wastewater on the environment minimum
in a cost effective way.
In modern wastewater treatment plants,
activated sludge processes have been used for
the purpose of removing pollutants such as
organic carbons, nutrients and some chemical compounds.
In recent years, many governments are planing to
introduce more comprehensive regulations including
extensive removal of organic carbon, nitrogen and phosphorus.
In order to meet such tight legislation, this project
focuses on the configuration the AnaerobicAnoxicOxic(A2O) process
which places a numbers of biological reactors with and without
aeration in an effective manner.
The interconnected systems are highly nonlinear and complex in nature
so that application of nonlinear feedback control and model
reduction theories is inevitable in order
to enhance the quality of wastewater treatment.
The project is concerned with
process analysis, modeling, simulation,
diagnosis and control design.
 Theory of Complex LargeScale Systems

Given the current rate of technological innovation,
the role of control in many engineering disciplines would increase
dramatically in the near future.
Most of future control applications will require sophisticated design tools
which can accommodate large numbers of components in a system.
Autonomy and coordination are crucial factors in controlling and
designing complex largescale systems.
The project focuses on these issues theoretically.
One of applicationoriented themes is flow control of communication networks.
Power control of wireless communication is also an important topic.

Analysis and Design of biological systems

This project is motivated by an analogy between artificial
systems and biological systems, which has been attracted
few bioengineers until recently.
This analogy is less understood especially in view of
control mechanisms furnished automatically in every
biological system.
A main reason of this lack of progress seems to be that
only few scientists were able to pay attention to dynamics.
Importance of control theory for elucidating dynamics of biological processes
has not been noticed properly yet.
This project brings sophisticated theoretical and mathematical tools of
control of nonlinear dynamics into bioscience, and they are exploited to do
simulation, modeling and design of biological and metabolic systems.
The analysis of sensitivity and robustness would is imperative in
understanding functions of biological cell networks and
extracting principles of biological systems.
Theories of Nonlinear control and stability would play an important role
in the research.

Control of Artful Machines

The project focuses on designing and building laboratory experimental
machines which furnish unique or acrobatic movement, capability of
various actions and control functions.
An example is a double cart system which was developed in our laboratory
several years ago.
The double cart system has been an excellent test bed for
demonstrating effectiveness of recentlydeveloped
theoretical tools of control, such as multirate sampleddata control,
frequency separating cooperative control, robust nonlinear
control.
The project is challenging since experimental machines
sometimes suffer from severe uncertainties
and dynamic environments.
This project is a great means
for exposing students not only to usefulness of stateofart
control theories, but also to
system engineering approaches to designing, building,
managing, and maintaining complex systems.
There is no deadend in research!
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