Remote Laboratory for a Brushless DC Motor

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Nov 2, 2013 (3 years and 7 months ago)


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Remote Laboratory for a Brushless DC

Tatsuya Kikuchi,
Member, IEEE
, Takashi Kenjo,
Member, IEEE
, and Shuichi
Senior Member, IEEE


The objective of this study is to inve
stigate remote
learning methods
in the context of mechatronics education, and in particular, for the study of
brushless DC motors, which are extensively employed in robots, information
devices, home appliances and other areas. While hypermedia
ware and computer
assisted instruction are widely used in conventional
type learning, very few examples exist of remote learning that involve
experiments. The authors therefore developed a prototype client
server system
for remotely conducting experim
ents on brushless DC motors, including Web
based courseware and other software. The server computer is connected to the
motor laboratory, and the visual image and sounds of the experiment are
transmitted to the client computer in real time. The remotely lo
cated user can
operate the motors and conduct experiments through the client computer.
Through demonstrations to a class, the authors conclude that the remote lab
combined with a simulation of the motor’ s dynamic behavior can be a quite
effective teaching
aid for the study of precision motors.

I. Introduction

Each year, the Polytechnic University of Japan's Sagamihara campus attracts a number of technical
training instructors from various countries for refresher courses and high
tech training lasting seve
. The program covers different subject areas including electrical, electronics, mechanical,
architectural, and computer technology. The authors have been engaged in instruc
ting these foreign
trainees on motion control, computer
based control, and power electronics, where we offer both
theoretical and workshop training.

The authors are also engaged in instructing (Japanese) university
students on the subject of small m
otors and their driving methods using
microprocessors or PCs (i.e., mechatronics), where they have found workbench
demonstrations to be highly effective aids. They have so far developed several
instructional materials and experiment benches on mechatronics
, which are
currently being used in Japanese universities and technical schools as well as
overseas countries receiving ODA (official development assistance). The first
model of the mechatronics workbench, called MECHATRO LAB, can be used to
demonstrate va
rious kinds of electric motors and their electronic operations

Of these small precision motors, the use of the brushless DC motor (or DC
brushless motor) is growing at a spectacular
pace in many areas including PC
peripherals, robots, medical equipment, home appliances (air conditioners,
refrigerators, washing machines), and industrial applications (pumps and
ventilators). Brushless DC motors are supplanting conventional motors like
nduction motors, brush DC motors and stepping motors to become the major
actuator in mechatronics because of its simple construction, reliability and
saving characteristics.

Furthermore, they are not subject to certain weaknesses of these conventio
motor types: the brush
type DC motor generates arcs and is subject to
mechanical wear, the small induction motor has a very poor energy conversion
performance, while the stepping motor requires a very small air gap between
the rotor and stator core.

he brushless DC motor can be constructed in various arrangements, such as
the normal inner
rotor type seen in CPU coolers, outer
rotor type, axial
gap type
(pancake type), or with a air/magnet bearing configuration (
Fig. 1
), and so will
likely see many more applications in such areas as automobiles. Because of its
versatile construction, the brushless DC motor can be incorporated into various

Brushless DC motors can basically be
classified into single
phase and three
phase types. The former is widely used for small fans, while the latter finds
many applications requiring high performance. In this study, we employ the
latter type.

It is known that the rotor's position must be dete
cted by some means in a
brushless DC motor to generate switching signals for the six transistors or
MOSFETs in the drive circuit, known as an inverter (
). Hall
effect sensors
are wid
ely used for this purpose, though the so
called sensor
less method also
sees such applications as the spindle drives of hard disks. In the sensor
scheme, the current or voltage waveform is used to determine the rotor's
angular position. The use of Hal
effect sensors is considered to be the basic
method. Fig. 1 shows a typical construction of a brushless DC motor, consisting
of the following basic components:

1) Permanent magnet as the rotor,

2) Stator coils: At least three coils in this sample, but
often 6, 9, 12 coils wound
on teeth in the steel core as illustrated in

3) Three Hall
element sensors, which are basically placed at 120
intervals (
), but also often at 60
degree intervals (

4) Three
phase inverter consisting of six transistors (or MOSFETs) and its
control cir
cuit .

For these components to work properly as a motor, which in the brushless DC
motor can take various configurations, they must be arranged and operated
according to certain rules or principles. The aim of the present remote lab lies in
imparting to s
tudents an understanding of this rule. Although brushless DC
motor technology is an important subject, it is not taught in most technical
schools or universities. The authors therefore see the need for post
education, where effective experimenta
l tools can be of great value. Yet,
Mechatro Lab is the only lab apparatus that the authors are aware of that can
demonstrate the basic operations of the brushless DC motor. This general
unavailability of lab material can be remedied to some extent by the
use of
remote learning, which can also contribute to increasing the pool of qualified
technical instructors.

The use and study of remote educational systems via the Internet or through
satellite broadcasting is becoming a global trend. The authors too see

potential applications for such remote systems for education/training conducted
across national boundaries, particularly in the training of technical instructors.
The authors made an initial study on a related subject aimed at Japanese
students with

particular reference to a claw
pole stepping motor
. Remote
international study/training can supplement and improve training programs,
such as the one described above. For instance, th
e overseas training period
can be shortened, or more material covered over the same period, if trainees
can prepare for the course beforehand by Web
based courseware, review the
material covered afterwards in their home country over the Internet, or follow

with advanced topics and remotely conducted labs. When such remote learning
tools are made widely available and the necessary communication networks
have been installed, this should greatly expand the sphere for international

In particula
r, we feel that such remote learning systems can be highly useful in
training technical instructors in developing countries on the subject of motion
control (or mechatronics) and other technical subjects for which practical
workshop experience is invaluabl

The following section briefly surveys related works on electrical motors and
distance learning, sections III and IV present the system configuration and
outline of the remote lab, section V discusses reactions by overseas instructors
and issues for fur
ther improvement. Finally, our conclusions are given in section

Fig. 1. Brushless DC motor assembled in a dental piece, with a typical
construction using only three simple coils. The rotor has three perma
magnets: the largest is for generating torque and the two thin ones are
magnetic bearings. The white ceramic pipe, together with the rotor’ s ceramic
sleeve, constitutes an air
film bearing.

Fig. 2. Bru
shless DC motor drive system with a three
phase bridge inverter and
Hall sensors.

Fig. 3. Typical stator of three
phase brushless DC motor (cross section): (a)
pole, six
coil configuration, (b) eight
ole, nine
coil configuration, and (c)
pole, 12
coil configuration. Each tooth carries one coil.

Fig. 4. Printed circuit board with four Hall
element sensors. The three units
placed at 60
degree interv
als are used as the position sensors. The peripheral
rack is for rotating the board, combined with a stepping motor (see Fig. 8).

II. Related Works on Electrical Motors and Distance Learning

With the wide availability of high
performance personal comput
ers along with popular Internet use in
recent years, many computer
based educational materials have been developed using computer
multimedia courseware and Web
based courseware (WBC). WBC are study aids that are assisted by a
Web browser. For instanc
e, there are 19 items under 'motor' in the National Engineering Education
Delivery System (NEEDS)
, an electronic database for engineering educational courseware, including
15 Web
software, 2 Macintosh HyperCard software and 2 Microsoft Word documents.

Yet, all of these WBC are "closed" systems in the sense that they are self
contained within the user’ s personal computer. This has led R. Jain to
propose "wiring the laboratory"

. Among such studies involving remote
laboratories, B. Aktan et al. stress the importance of combining theory and
practice in the study of control engineering. They developed a paradigm for

remote laboratory use and demonstrated its feasibility through its
implementation in robot control
. They give three points that must be
considered when developing remote labs: 1) acti
ve learning, 2) data collection
facilities, and 3) safety.

Meanwhile, H. Shen et al. developed a remotely operated lab apparatus for
semiconductor experiments
. Such a system "gives st
udents the opportunity
to work with sophisticated equipment, of the kind they are only likely to find in
an industrial setting, and which may be too expensive for most schools to
purchase." They state that remote laboratories offer advantages that "cannot
replaced by simulation software packages."

The authors too have developed an effective study aid based on networking
technology that would enable the student to connect via his/her terminal to the
laboratory (in particular, MECHATRO LAB), that is, we a
imed to provide a
remote laboratory environment tied into a WBC.

III. Outline of Remote Laboratory Setup

Here we describe the remote laboratory system’s components and study subjects covered by the system.

A. System description

As shown in
Fig. 5

Fig. 6
, the remote laboratory system consists of a client
server computer architecture and software.

he client is the remote computer at the user end. The client
specification consists of a Windows multimedia type computer with a LAN card.
Also, we use Microsoft Internet Explorer 5.0 (IE5) and NetMeeting 2.1 (NM2).
The former is for WBC browsing, while we

use NM2’ s streaming video
function for transmitting the experiment’ s images. The loudspeaker conveys
the atmosphere of the experimental via sounds.

The remote server consists of a multimedia server and a motor control server.
The reason for using two PCs

is that the closed loop operation of the brushless
DC motor requires a high execution speed, where sensor signals must be
received and switching signals generated at close to 50 microsecond intervals,
and also that continuous measurement of the motor curr
ent is needed.

The role of the computer which we call a multimedia server is to provide the
clients with multimedia tools, such as WBC, simulation, and video. The
experiments are captured by a CCD camera and digitized by a video capture
card and sound car
d. The motor control server (MCS) is used for operating the
motor and measuring the voltages, and incorporates a 12
bit A/D converter
(AD574) and digital I/O (8255) card. The signal lines are connected to the
control bench, which is discussed later.



For the lab apparatus, we used Mechatro Lab 2
. A
brushless DC motor can be constructed with a four
pole, six
coil stator, a
magnet disk, and a printed circuit board having

three Hall
element sensors, as
shown in
. Mechatro Lab2 has a MOSFET power circuit that serves
multiple purposes; here it is used as a three
phase inverter to drive the motor.
By gi
ving the proper switching signals to the inverter based on the Hall sensor
signals, the rotor will start up and keep running.

To use Mechatro Lab 2 in the remote lab, we built a control bench and a
microcontroller with an RS
232C transmission function. Wi
th this, the motor's
line voltage, neutral point voltage, and input current are transmitted via
an insulated transformer and filter circuit to the A/D converter in the MSC. A
relay is used to change the motor connection between star and delta. The
element board is driven using a stepping motor (

B. Client window

The client window is shown in
. I
t consists of three subwindows: WBC,
video window, and the I/O remote
control board. As Window 1 shows, the WBC
is an electronic textbook that can be read using a WWW browser, and has a
hypertext structure employing multimedia including textual explanation
s, photos,
sectional drawings, and animated schematic drawings.

Image size and
color of the live video, Window 2, are set at 320pixels x 240pixels (width x
height) and 16
bit color. Video quality of the client may be below server video
settings beca
use of increased network traffic.

The I/O remote
control board supports the remote laboratory, as illustrated in
Window 3. On this window, one can select either 120

or 180
degree operation,
in either CW or CCW. Moreover, one can rotate the remote Hall se
nsor board
by pressing down on the mouse at the CW or CCW button for 'Hall Sensor
Position' and observe this on the live video. By releasing the mouse button, the
sensor board will stop and hold its position. An oscilloscope window is provided
to observe t
he line
line voltage and neutral position voltage. >From this, the
user can learn how the driving mode, winding connection and sensor position
affect the motor's characteristics. This program and the simulation software
discussed below were written in M
icrosoft Visual Basic (VB). Here, we adopted
Microsoft Active X for making these programs usable as Internet applications.

Fig. 5. System diagram connecting server and client.

Fig. 6. Function diagram for client
server system.

Fig. 7. Brushless DC motor construction used for experiments.

Fig. 8. Brushless DC mot
or assembly; the position of the Hall sensor board is
adjusted by rotating with a stepping motor.

Fig. 9. Client windows for brushless DC motor lab. 1) Web
based courseware;
2) video window of motor lab; a
nd 3) I/O remote
control board.

IV. Course Content

Here we describe the courseware contents, which are listed in Table I. These subjects are considered to be
fundamental for understanding the motor's principle.

Chapters 1 and 2 describe the basic const
ruction of a modern brushless DC
motor. Chapter 1 focuses on the mechanical construction, and Chapter 2 deals
with the connection for the three sets of coils, for which there are two basic
schemes: star and delta. Chapter 3 discusses the two fundamental sw
modes in relation to the delta and star connections, which constitute a logic
circuit problem with regard to the position
sensor signals. In this study, a Z
microprocessor and software is used for this purpose instead of a hardware
logic circuit
. Chapter 4 gives explanations on the rotor's permanent magnet and
the back
emf waveform in relation to the two connection types and switching

As stated above, one can start the motor after selecting the following items:

or 180
degree operatio
n, delta or star connection, and CW or CCW. In the
degree mode with the correct sensor positions, the input current will be
minimized, the neutral potential will be triangularly
shaped, and the line
voltage trapezoidal
shaped, as in
(a). Neutral point here means the
common terminal of the three coils in the star connection. If the sensor is
positioned correctly, the terminal voltage's waveform and frequency and the

current do not change even when the rotating direction is reversed. If the
Hall sensor position is shifted to either direction, the line
line voltage will be
as shown in Fig.10(b), and there will be a noticeable speed difference when the
revolving dire
ction is reversed.

In the 180
degree mode, however, the waveforms of the line
line voltage and
neutral point voltage are both rectangular regardless of the sensor position, and
so the correct position is found by first finding a range where current is
minimized and then honing into a position where the waveform frequency is
unaffected when the motor is reversed.

We stated above that the brushless DC motor is built into various devices.
While the required motor construction is simple, certain rules must

be observed
in order for these arrangements to work as a proper motor, which are deeply
related to electromagnetics, dynamics and electronic circuitry. If these
equations are properly described and computed by a computer, this can provide
a basis for simu
lation. We created such software using VB.
Figure 11

shows the
Window of this simulation program. As will be stated in Section V, the
usefulness of simulation software was pointed out by

a foreign trainee who had
studied simulation techniques for analyzing stepping motor behavior from the


Course contents




Fundamental construction: stator core, stator windings, rotor, and position sensor.


phase: delta and star connection, neutral point.


Switching: 6
step operation: 120
degree and 180


Magnet and back
emf, waveform.

Fig. 10. Remote oscilloscope window showing line
line vo
ltages in 120
degree switching. (a) Good condition between Hall sensor positions and drive
timing, (b) Irregular condition.

Fig. 11. Simulating the brushless DC motor's behavior. One can set parameters
select switching mode (120

or 180
degree) and vary Hall sensor positions.
Shown (from top to bottom) are the neutral point voltage, line
line voltage and
input current. The Hall sensor position can be changed even after the RUN
button has been clicke

V. Discussion

To obtain initial responses, we conducted the remote lab with a class of foreign trainees at our university,
consisting of instructors engaged in technical training in Indonesia, Malaysia, Mexico, Philippines, and
Thailand. The remote l
ab was conducted on a campus network (intranet). After the lab, we asked the
trainees to answer a questionnaire and state their impressions in an interview. Below we expand on the
trainees' responses and discuss some general issues regarding remote labs.

A. Positive response of foreign trainees

Positive responses from the trainees are now discussed. First, several saw that
the remote lab could improve the training program conducted in Japan. The
training program currently lasts for about six months, but a

remote lab could
shorten the period of stay in Japan since it would become possible to study
some lab subjects from their home countries. The oversea training period can
be shortened if remote learning can be employed for preparatory study or
up. T
his could reduce the costs of such a training program.

Or it could be used to follow up on their training program on a continuing basis
to study the subject in more depth (upgrading, updating of skills).

Monographs on specialized topics and lab equipment

are often expensive or not
readily available in many developing countries, and students and researchers
would benefit greatly if they could access WBC or remote labs with relative
ease at a relatively low cost. While the costs of purchasing computers and
installing networks can be high initially, once they are in place, as in many
technical training facilities abroad, the use of instructional aids through
networking can cut further costs if they can substitute for conventional books
and equipment. Some tra
inees mentioned the benefits of being able to receive
instruction directly from experts abroad.

The foreign trainees also displayed a keen interest in the remote laboratory's
subject itself, the brushless DC motor. Many hoped that the remote lab could be
made available so that they could study the subject back in their home
countries. A major reason for this interest could be the unavailability of this kind
of lab equipment on small motors in most developing countries. The high
interest was also due perhap
s to the widespread use of the brushless DC motor
in computers and other information devices. This suggests that the subject of
remote labs such as ours should be tailored to meet the needs of expected
users. For instance, there is likely to be a low need
for a remote lab using
materials and equipment that are readily available anywhere, or on very simple
subjects that can be demonstrated locally. It seems that remote labs can be of
more service when they require expensive or relatively unavailable equipmen
or deal with advanced or specialized topics.

B. Limitations of the remote lab

What the trainees viewed as the remote lab's disadvantages centered on its
operational aspects. Below are some of their comments.

1) Since there is only a single lab setup,

it is not possible for several people to
access the lab independently at the same time.

2) The lab topic is limited to only one: the brushless DC motor that we prepared.
The user cannot change the topic to another one (such as the stepping motor,
which w
as developed in a previous study

3) How would the client lab participant deal with any problems that occurred
during the experiment? "If the experimenter had mechanical or electrical

with the brushless DC motor lab, he cannot fix it on
line." This is a very real
shortcoming of the remote lab, the solution for which is to have an on
site lab
attendant, who can take care of any problems should they arise.

With regard to 1) abov
e, there are many possible modes of remote learning, as
B. Collis points out
, they can be broadly divided into self
(asynchronous) and group study (synchronous) situations. If
several users are
sharing a single lab setup, they must either take turns or collaborate as a group.

Thus, remote learning can take place with or without an instructor. With an
instructor present, he or she will determine or coordinate the general flow of

how to proceed with the remote lab. For instance, the instructor may directly
explain the lab procedures to the users, or he/she may have them read an
electronic textbook or instruction manual on the lab subject. When users access
the remote lab for self
study, however, they must be able to read and follow a
lab manual on their monitors.

In the present study, the authors prepared a WBC that included the remote lab
exercises and a simulation program. Used before the lab, the simulation
provides the user wi
th analytical practice on some theoretical aspects, and after
the lab, it could be used to gain insights on the lab results obtained. Or the
WBC and simulation can be used apart from the lab, on a PC unit not part of the
network environment. In this study,

the combination of WBC, simulation, and
the remote lab was received favorably by the class of foreign trainees.

VI. Conclusion

Although the three
phase brushless DC motor has wide applications in many areas, there are very few
textbooks or lab material
s on the subject. To fill this gap, the authors have developed a remote lab system
for use in a client
server environment consisting of Web
based courseware, streaming video, VB
programmed remote control board and simulation software.

The lab exercises fo
cus on the relationship between the rotor magnet's sensor
positions and the switching signals supplied to the inverter to drive the motor.
The aim here is to show that there exists a proper position in relation to the
phase windings and the inverter'
s operating modes, so that proper motion
control and energy
saving design can be realized. The users can operate the
motor by remote operation and view the generated voltage waveforms on

The prototype system was demonstrated to a class of foreign
trainees. They
showed a keen interest in this remote lab, demonstrating that remote learning
systems can induce a more active learning process than when printed or screen
explanations are read alone. We also found that a suitable simulation of the
dynamic behavior complements the remote lab well. From this
experience, we believe that such remote lab systems can be a helpful
component of international technical cooperation.


The authors would like to thank R. Takeguchi, who kindly b
rushed up their English.


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ht into the
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Author Contact Information

Tatsuya Ki

Department of Electrical and Electronic Engineering

Tokyo Institute, Polytechnic University of Japan

1, Ogawanishi, Kodaira, Tokyo 187
0035 JAPAN

Phone: +81

Fax: +81


Takashi Kenjo

Department of Electrical Engineering and Power Electronics

Polytechnic University of Japan

1, Hashimotodai, Sagamihara, Kanagawa 229
1196 JAPAN

Phone: +81

Fax: +81


Shuichi Fukuda

Department of Production, Information and Systems Engineering

Tokyo Metropolitan Institute of Technology

6, Asahigaoka, Hino, Tokyo 191
0065 J



Fax: +81


Author Biographies

Tatsuya Kikuchi

(M'95) received the B.S. (1984) and M.S. degrees (1997) in electronic engineering
from the Polytec
hnic University, Kanagawa, Japan. From 1985 to 1992, he worked as a design engineer
of servomotor controls. From 1992 to 1998, he was an Instructor in the Department of Electrical
Engineering and Electronics at the Polytechnic Centers in Aichi, then Kanaga
wa prefectures.
Since 1998,
he has been working at the Tokyo Institute of the Polytechnic University of Japan. His interests include
mechatronics and multimedia computing.

Takashi Kenjo

(M'97) was born in Japan on February 2, 1940. He received the

Degree in 1964 and the Doctor
Engineering Degree in 1971 from
Tohoku University, Sendai, Japan. His area of interest is in small precision
motors and their controls, and he has written several monographs published by
Oxford University Press. He has bee
n with the Polytechnic University of Japan
since 1965 and is currently a Professor in the Department of Electrical
Engineering and Power Electronics.

Shuichi Fukuda

SM'99) received his B.S., M.S. and Ph.D. in Mechanical
Engineering from the Universi
ty of Tokyo in 1967, 1969 and 1972, respectively.
He is currently Professor of Production, Information and Systems Engineering
at Tokyo Metropolitan Institute of Technology. He worked as associate
professor at the Welding Research Institute, Osaka Universi
ty from 1976
and concurrently as associate professor at the Institute of Industrial
Science,University of Tokyo from 1989

He was chairman of the design and systems division, JSME from 1992
He was visiting professor at Stanford University

and Osaka University
concurrently in 1998. He was chair ASME Japan chapter 1996
1998 and is
chair of the IEEE Reliability Society 1999

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