The Proactive Desk : A New Force Display System for a Digital Desk
Using a 2-DOF Linear Induction Motor
Haruo Noma, Yasuyuki Yanagida, Nobuji Tetsutani
ATR Media Information Science Laboratories, Kyoto, Japan{noma, yanagida, tetsutani}@atr.co.jp

Abstract
The Proactive Desk is a new digital desk with haptic
feedback. The Proactive Desk allows a user to handle both
virtual and real objects on a digital desk with a realistic
feeling. We proposed it for a co-experience web that would
enable people to share the feelings and experiences ofother users via the Internet. In the Proactive Desk, two linear induction motors are equipped to generate an omnidirectional translational force on a user's hand or a physicalobject on the desk without any mechanical link nor wire,
thereby preserving the advantages of a digital desk. In thispaper, we report applications of the Proactive Desk and theperformance of the first trial model.

1. Introduction
The conventional style of Internet communication deals
with only digitalized information as it is. Due to the recent
IT revolution, we can share and transmit information on a
global scale, and we are confronted with communication
gaps between generations, cultures and so on. Therefore,a new communication style is necessary to help people
to recognize mankind's rich cultural diversity on a global
scale, and to enable them to obtain, share and transmit theirexperiences, feelings and emotions, regardless of their age,
locality, occupation, culture or society. To achieve this newcommunication style, we are developing the technology toform a digital "co-experience web" that will enable people
to record and share their experiences [1]. In other words, itwill allow us to experience other people vicariously in thesame manner as conventional web communication.
The research goal for our group in this project is to explore and develop technological support for the observationand sharing of experiences and emotions through a coexperience web. To provide a basis for this, we study ways
to obtain and communicate sensory information and takean integrated approach to the development of technology
for recreating information for the ﬁve sensory modalities.
Here, we focus on a co-experience web application ona desk, speciﬁcally a digital desk that integrates a GUI
desktop environment into a real desk. Wellner proposed theconcept of a digital desk in 1991 for the ﬁrst time [2,3]. A
typical digital desk enables the user to seamlessly handle

Proceedings of the IEEE Virtual Reality 2003 (VR’03)
1087-8270/03 $17.00 © 2003 IEEEthe both digital and physical objects on the desk with acommon standard. To realize a co-experience web application on a desk, the system also needs to seamlessly react
from digital objects toward the user and real objects on
a desk. Therefore, we developed a suitable force display
for a digital desk system called "the Proactive Desk". The
Proactive Desk will be able to sense actions and events on
a desk, and will eventually allow us to vicariously experience them.
In this ﬁrst paper, we report the concept and performance of the ﬁrst trial Proactive Desk. In the later section,
we describe the advantages of a digital desk with force
feedback and related research. Then we present the structure and features of the Proactive Desk, and the performance of the trial model.

2. Background and related research
Wellner's "The DigitalDesk" broke though the boundaries between the digitalized GUI desktop and our physicalworld. Since Wellner's proposition, many systems havebeen proposed, and they generally have three functions.
First, the system projects an image of a PC desktop screen
onto a common physical desk as a visual display. Then,the desk simultaneously acts as input device. The user canpoint to icons with his/her own hands or by using physicaltools directly without using a typical indirect input device
like a mouse or a trackball. The third function is registration. A digital desk can import a physical object's properties: shape, size, weight, color, number and so on, onto thedesktop as digitalized information. By using these functions, a user can seamlessly handle both digital and physical objects on the desk with a common standard. However,the direction of this function is limited, going only from thephysical world to the digital desktop. In this research, we
add a fourth function, i.e, physical reaction from the digitaldesktop to the physical world for our co-experience web.
Here, a user can handle objects with the feeling of haptic
sensation as if handling real objects, and real objects on thedesk can react in response to events on the digital desktop.
We will begin by summarizing related works abouta digital desk that support the former three functions. In
the orig i nal digital desk, Wellner used a conventional

video projector and CCD camera [2,3]. Leibe proposed
the Perspective Workbench [4], which could capture theshape of a physical object on the desk. Adding to the typical digital desk conﬁguration, the Perspective Workbench
was additionally equipped with IR illumination lamps andIR ﬁltered CCD cameras to import the object's shadowsand digitally construct its shape. The Enhanced Desk andAugmented Desk [5,6] by Koike was also equipped withan IR camera to capture the user's hand action as command
input. The user could handle digital objects naturally by using both hands. Smart Skin [7] by Rekimoto was equippedwith unique sensor array to detect the user's hands on its
table without CCD cameras. The sensor used an electric
capacitance meter that was affected by the user's body, andmany sensors were embedded under the desk. In his Pickand-Drop [8], the system emulated the cut & paste function
for digital data from a computer to the digital desk in thesame manner as physical cutting and pasting. Ishii's groupproposed a series of digital desk studies, i.e., meta desk [9],I/O Bulb & Urp [10], Sensetable [11] and Illusion clay [12].
These systems enable the user to handle digital data by using some specialized physical input devices, and were applied to enhance the functions of an urban planning CAD
system or optical instrument.
Focusing on the fourth function, "a reaction to the physical world on the digital desk," the desk has to be equippedwith a kind of force feedback device. There have only
been a few studies in that area because of the difﬁculty ofintegrating a force feedback mechanism into a digital desk
without spoiling its advantages. As a system that reacts to auser's hand, the desk should have enough power to control
both the hand position and reaction force. Therefore, a mechanical link approach is often used. Brederson proposed
the Virtual Haptic Workbench [13], which could generatea reaction force by making use of a commercially available mechanical link system, called PHANToM, beside its
screen. Ignoreing the advantage of a direct input functionof a digital desk, that is to say a system for a conventional
GUI desktop, a mouse-like device with a force feedback
mechanism could be used. Ramstein's Pantograph [14]employed a 2-DOF parallel link mechanism. Kelley also
proposed the MagicMouse [15] using a 2-DOF linear DC
motor. These devices could generate enough reaction force
for realistic reaction, but these motion range were restrictedmechanically within a small area. As another method, theData Tiles [16] by Rekimoto used a kind of passive force
feedback method. In this system, the user combined special
functional tiles on the digital desk to achieve some goal,
like a data browser. In the motion input tile, there was asmall trench as a guide, and the user drove a pen along thetrench to input commands certainly and easily.
As reaction for physical objects on a digital desk, a desk
simpley controls the position of the objects. The PsyBench

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[17] by Brave was equipped with an XY stage mechanism
under the desk. It had an electromagnet mounted to its end.
Putting another small magnet on the bottom of an object,the motion of the XY stage was reﬂected on the object's
movement on the desk. For the user, it would seem likethe object moved automatically with the user's action. The
Actuated Workbench [18] by Pangaro succeeded the PsyBench. In the Actuated Workbench, the XY stage mechanism
was replaced with set of a electromagnetic coils, and they
worked as a 2-DOF linear pulse motor. Controlling thedegree of magnetic ﬁeld for each coil, it could manipulate
two or more physical objects together on the desk. As another pulse motor approach, Fries proposed the Sawyer
motor driven system [19]. Using the motor, it could attainmicron-level object motion resolution, however, a moving
unit on the desk had to have sets of electromagnets andwires.
For the mechanical link approach, scalability is a critical problem. A sufﬁcently large link system was required
to support the entire working area with the size of a desk.
Such a huge mechanism on the desk, however, prevented
visual projection and spoiled the seamless usability of thedigital desk. Moreover, the singular point problem that is
peculiar to a complicate mechanical link is unavoidable.
On the other hand, the XY stage and linear pulse motor approach could move objects on the desk well, but they could
not generate enough reaction force on the user's hand on
the desk.
Against this background, we propose the Proactive
Desk, which was equipped with built-in linear induction
motors to provide an active force feedback to both theuser's hand and objects. The main advantage is that theProactive Desk does not prevent visual projection because
the whole mechanism of the motors is built into the desk.
Moreover, it is not necessary to attach any wires to theuser's hand or to the physical objects.

3. Applications
We will now discuss applications of the digital deskwith haptic reaction before giving a technical descriptionof the Proactive Desk.
The Proactive Desk allows a user to handle objects on
the desk with a feeling of haptic sensation as if he/she werehandling real objects. It can also move physical objects
in response to events on the digital desktop. Applying theadvantages to our major target, the “co-experience web”
project, the digital desk can record the user s operation on
the desk digitally, and can allow other persond to relive theexperience of the operation. As shown in Figure 1-a, when
the trainer draws calligraphy on the desk, the drawing operation can be input. The student can then go over the writing as if his/her hand were being taken by the trainer.
We also propose to apply the force feedback into a di-System configuration
with visual & physicalreaction

Motion input

Haptized 3D button and window forassistance and failsafe operation

Motiontracker

CameraMotion and position
tracking
Projector

Quit the application?
OK

video image

GUI
controller

Instructor’s desk

Student’s desk

Projecting
visualimage of GUI(b) Haptized dialog box(a) Experiencing other people’s operation vicariously

Network

Forcedisplay
controller

Reaction force
SystemFile dragging motion

Attracting the finger
to the optimum path

Object motion control

Inertial force of the file(d)Assistance for menu selection
with haptic attractor(c)File icon dragging with haptic reaction
Pen shaped
interface

Eraser shaped
interface

Desktop force display
video
image

T scaleshapedinterface

Visual & physicalreaction(f)Virtual ink brush with realistic touch

Test bed inremote environment

Slave
robotsReal sample

Motioninput

Use a pen and an eraser
with the feeling of real tools.

Use a pen and a scale to draw correct lines with haptic reaction.

(e)Haptized virtual ruler for CAD

Font

File

(g) Teleoperation with haptic feedback

Fig. 1. Applications of the Proactive Desk
rect assistance function for the user as expansion of a conventional GUI. When the user has to respond to some alertdialog, the force feedback can raise the physical barriers on
critical options for fail-safe operation as shown in Figure
1-b. Here, the user needs to make a conscious action to
select the critical one. The system can also present physical information by expanding the visual GUI. For example,
the system can represent the size of some ﬁles as an inertial
force to the user. In other words, the user can feel the sizeof a dragged ﬁle as its weight (Figure 1-c ). Next, it is difﬁcult to select a sub menu in some GUI system, because
most GUIs require us to move the mouse exactly along anarrow path. Putting a virtual spring between the path andthe user's ﬁngertip by using force feedback as shown in
Figure 1-d, the user can select sub menus difﬁcult manipu-

lation.
Applying force feedback to CAD or drawing software
as shown in Figure 1-e and f, the user can use haptizedvirtual or real equipment, such as a virtual T square, a virtual pen, a virtual brush and other items with the feeling of
haptic sensation.
Of course the system can also be applied to an interface
device for teleoperation (Figure 1-g). Here, the motion of
the user's hand and some real instruments on the desk aretransmitted to slave robots in a remote place. Simultaneously, a reaction is received by both the user and the instruments as force and position feedback.
In these applications, we should note that the Proactive
Desk can offer direct haptic feedback without spoiling theadvantages of the digital desk.

4. Linear motor for a digital desk

Travelling magnetic field B
Eddy current i

Force F

ForcerInverter

Stator ( three pairs of coils )1:Coils generate travelling magnetic field B.
2:Avoiding the field, eddy current i is induced on the forcer.
3:The current i and magnetic field B generate force F on
the forcer using Fleming’s left hand rule.

Fig. 2 Principle of operation of the LIM

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We built linear induction motors into the digital desk forforce feedback in the Proactive Desk. Generally, a linear
motor consists of a stator and a forcer, which correspond to
the stator and the rotator in a rotary motor. Each one moves
straight along the other one and there is essentially no mechanical limitation in its range of movement.
Linear motors can be categorized into four types: theLinear Induction Motor (LIM), the Linear Synchronous
Motor (LSM), the Linear Pulse Motor (LPM) and the Linear Direct-current Motor (LDM) corresponding to existingrotary motors. The Actuated Workbench and the Sawyer
motor are a kind of LPM. The MagicMouse is a kind of

of the Proactive Desk, referring Ohira s LIM, and conducted experiments in order to measure the performance of the
LIM as a digital desk.

5.1. Design of the trial 2-DOF LIM

Fig. 3. The first trial Proactive Desk
LDM.
The reason why we employed the LIM is that its moving part, a forcer, is just a conductive material plate. In
other words, by putting a small metal plate onto a user's
ﬁnger or some object, the LIM can control a translational
force on them. For the other linear motors, heavy permanent magnets or wired coils need to be attached to the user,which spoils the advantages of the digital desk in a waythat is similar to the mechanical link approach.
Let us brieﬂy explain the principle of the LIM. The LIM
has the same mechanism as the widely used standard AC
three-phase rotary motor. In the stator, three pairs of coilsets are lined up along the moving direction as shown in
Figure 2. When a three-phase current is turned on to eachcoil set, the traveling magnetic ﬁeld B is generated along
the coils. Avoiding the ﬁeld, the eddy current i is inducedon the forcer, and the current i and the magnetic ﬁeld B
generate the translational force F on the forcer by Fleming's left hand rule. The LIM is characterized in that it cancontrol the translational force by means of the frequency
and current applied to the stator, and the maximum force
is generated when the forcer is stopped. Of course there isno active mechanism on the forcer. The force is simply aconductive material. On the other hand, the LIM is inefﬁcient in converting between power and force, and it needs acooling mechanism.
Ohira proposed a bidirectional LIM [20,21] in 1982.
Two sets of coils were placed in orthogonal orientation
among the stator core, and each set of coils was driven
individually by two AC inverters. Therefore the motor can
generate any power of the traveling magnetic ﬁeld in any
direction on the table. He has applied the motor to a branchmechanism of a conveyance system in a factory. We aimed
at the advantages of force controllability and a simple wireless forcer, then implemented this to our Proactive Desk.

5. The trial 2-DOF LIM for the Proactive Desk
We made a trial 2-DOF LIM as the most important part

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We designed the trial 2-DOF LIM by consulting Ohira's
bidirectional LIM for the Proactive Desk. Figure 3 shows
the trial system. As for the primary iron core that acts as
the base part of the stator, non-directional silicon steel
plates that were punched out in a comb-shape were stacked
in the vertical and cross directions. The core was formedof a typical CPU heat sink, and it had nine x nine slots inwhich coils were placed. The dimensions of the desk were
285 mm x 285 mm. This was the area in which the desk
could generate force. The slots were placed 15 mm apartand the width of each slot was 15 mm. The height of theslot was 60 mm for lower the coils and 30 mm for the upper coils. The forcer should be placed just above the core
to obtain maximum effectiveness. However, we placed anacrylic resin board between the core and the forcer for alater mentioned reason. In this conﬁguration, the gap between the core and the forcer was 7 mm.
The primary coil sets consisted of three pairs of a seriesof two coils, and six coils in all were used in each direction. One coil was turned two hundred times. Two sets ofthe primary coils were placed inside both the upper andlower slots in orthogonal orientation. In this trial system,
the coil pitch was three slots, or 45 mm.
In order to close the magnetic circuit to obtain higher
effectiveness, we need to use a nonmagnetic conductive
plate stacked onto a magnetic conductive one, such as apair of aluminum and steel. However, the steel part wasalso attracted to the stator, and this reluctance force cause
a bigger frictional force than translational force. Therefore,
the forcer needed to be only a nonmagnetic conductive material plate.
The three pairs of coils are connected to an inverter
unit for a standard AC motor using a star connection. We
used one inverter unit for each axis. The capacity of each
inverter was 2.4 kW. Here, the voltage and current in thecoils were managed by the inverter itself, and we could
only control the frequency of the AC signal in the coils to
obtain the desired translational force on the forcer.
As shown in later experimental results, a few amperesof current are applied to the coils to obtain enough force.
Therefore, the user should be kept apart from the coils
as much as possible. Moreover, the gap between the core
and the forcer should be kept constant to obtain uniform
performance everywhere on the desk. Furthermore, as avisual display, a screen is necessary. For these reasons, thestator is covered with an acrylic resin box. A few fans wereattached to the side panel for the forced air cooling of the(a) Upper coils(b) Lower coils

t=1.0 100x200mm aluminium platet=1.0 100x200mm aluminium plate

5

1.5

5

1.5

Current of coils (A)Current of coils (A)Generated force (N)

0.6

0.3

1

0.3

0

0

0.6

1

20

40

60

80

100

Current (A)

2

2

120

0

20

40

60

80

100

Force (N)

0.9

0.9

0

1.2

Generated force (N)

3

3

0

4

1.2

Force (N)Current (A)

4

0

120

Drive frequency (Hz)Drive frequency (Hz)Fig. 4. Performance of current in the coil and translational force
100x200mm aluminium plate

4.0

0.5mm
1.0mm
1.5mm
2.0mm

3.0

100x100mm aluminium plate

1.2

0.5mm
1.0mm
1.5mm
2.0mm

1.0

Force (N)Force (N)

0.8
2.0

0.6
0.4

1.0

0.2
0.0

0
0

20

40

60

80

100

120

0

20

40

60

80

100

120

Drive frequency (Hz)Drive frequency f (Hz)Fig. 5. Translational force on forcers
with different thicknesses

Fig. 6. Translational force
on half-size forcers

coils. Many small exhaust holes were drilled in top of thedesk, and the emitted air was used as an air cushion for theforcer to reduce friction between the forcer and the table.

measure the force, we used a spring balance scale, and we
also used a clamp meter to measure the current in one of
the coils. Figure 4 shows the results. The x-axis indicatesthe frequency of the AC signal. The left and right y-axis
indicates the current in the coil and the translation force on
the forcer. As we supposed, the results conﬁrmed that theupper set of coils could generate twice the force of the lower one. In the lower set, the maximum force was 0.72 N at
12.5 Hz, and the maximum current was 3.13 A at 10.5 Hz.
In the upper set of coils, the maximum force was 1.30 N at
17 Hz, and the maximum current was 4.40 A at 13.0 Hz.
In both coils' results, there is a slight increase in both current and force during lower frequencies and they rise to thepeak. Then the curves fall gently. The coils show slightly
different electrical characteristics even though we used thesame inverter unit in the same conﬁguration for each setof coils. This is due to the individual speciﬁcity of each setof coils and the difference of the electromagnetic circuit
between the coils. From the results, we conﬁrmed that thetranslational force could be controlled by the frequency of
the AC signal in the coils.

5.2. Performance of the trial 2-DOF LIM
5.2.1. Upper coils and lower coils. As mentioned above,
the two sets of coils are overlapped, so we supposed thatthe power of the traveling magnetic ﬁeld generated by thelower set on the desk would be weaker than that by the upper sets considering the distance between the sets of coils
and the forcer. This reduction corresponds to a reduction ofgenerated force on the forcer. Therefore, we measured thetranslational force generated by the upper and lower setsof coils individually. We used an aluminum forcer withdimensions of 100 x 200 x 0.5 mm at ﬁrst. The controlled
condition is the frequency of the AC signal sent to thecoils. Before the experiment, we obtained the frequency atwhich the LIM can generate maximum force. We recorded
the translational force at every 0.5 Hz around the maximum force frequency, and at every 5 Hz in other ranges. To

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5.2.2. Thickness of the forcer. Next, we focused on
the conditions for the forcer. At the low frequency used
here, the traveling magnetic ﬁeld could permeate a few
centimeters of the forcer due to the surface effect, and an
eddy current was induced within the forcer. In the LIM,
the force is obtained from the product of the eddy current
in the forcer and the magnetic ﬁeld strength. From this,we supposed that a thicker forcer would generate a larger
force under the same conditions. We measured the force
using four aluminum plates with 0.5, 1.0, 1.5 and 2.0 mmof thickness. The dimensions of the plates were 100 x 200
mm and we used the upper set of coils. Figure 5 shows
the results. The x-axis and y-axis indicate frequency andtranslational force, respectively the maximum force was 3.5
N degrees of force using the plate that was 2.0-mm-thickat 13.5 Hz. As for the other plates, the 1.5-mm-thick plate
generated 1.72 N degrees of force at 15.0 Hz, the 1.0-mmthick plate generated 1.28 N at 14.5 Hz and the thinnest
plate, the 0.5-mm-thick one generated only 0.56 N degreeof force at 17 Hz. In every forcer, the curves show thesame trend as the previous results.
5.2.3. Dimensions of the forcer. In addition to its thickness, the eddy current quantity is also inﬂuenced by thearea of the forcer. We measured the force by using a halfsized aluminum forcer under the same conditions as theprevious experiment. The dimensions of the forcer were
100 x 100 mm, and the thickness was 0.5, 1.0, 1.5 and 2.0
mm. Figure 6 shows that the thickest forcer can generate amaximum 1.04 N degrees of force at 16 Hz. As for the other plates, the 1.5-mm-thick plate generated 0.88 N degrees
of force at 14.0 Hz, the 1.0-mm-thick plate generated 0.59
N at 19.0 Hz and the thinnest plate, the 0.5-mm-thick one
generated only 0.3 N degree of force at 19 Hz. This showsthat the half-sized forcer could generate only a third of thetwice-as-large forcer with the same thickness.

5.2.4. Material of the forcer. Moreover, we measured thetranslational force using different materials for the forcer. As
described above, the LIM can employ any kind of conductive, but nonmagnetic material as a forcer. In the experiment,
we compared forcers that are made of aluminum, copper andbrass. The nonmagnetic permeability of these materials is 1.0.
However, the electric resistivity of copper is twice as high asthat of aluminum, and the electric resistivity of brass is halfthat of aluminum. The dimensions of the forcers were 100
x 200 x 0.5 mm and we used the upper set of coils. Figure
7 shows the results using the same manner as previously
described. The curves tell us that the copper forcer can generate 1.00 N degree of force at 17 Hz, the aluminum forcer
can generate 0.56 N at 17 Hz and the brass forcer marks thesmallest force, 0.21 N at 14.5 Hz. From this, we can see thatthe translational force increases relative to electric resistivity.

5.2.5. Direction control. Next, we did an experiment toverify that the 2-DOF LIM could generate the translational
force in optional directions by driving two inverters individually connected to the upper and lower sets of coils. In
the experiment, the driving frequency of the upper set ofcoils was ﬁxed at 50 Hz, and we adjusted the frequency ofthe lower set of coils to achieve force in the target direction
as an experimental condition. We used a string and protractor to measure the direction of the force: one end of thestring was ﬁxed to the desk and the other end was ﬁxed tothe center of the forcer. Here, the forcer pulled the string in
the direction in which the integrated force was generated,
and we obtained the degree of the angle by the protractor.
The forcer used in the experiment was an aluminum platewith 100 x 100 x 1.5 mm dimensions. The target degree ofthe angle was from 0 to 50 degrees in 5-degree intervals.
Figure 8 shows the results. The curve tells us that the 2-DOF
LIM can control the direction of translational force by using
5.0
Drive frequency of the lower coils (Hz)

1.2
Aluminum
CopperBrass

Force (N)

0.9

0.6

0.3

The drive frequency of theupper set of coils is 50 Hz,
The size of the 1.5 mm
thick forcer is 100 x 100
mm, and the material isaluminum.

4.0

3.0

2.0

Lower set of coil output
is adjusted
PinUpper set of coiloutput is fixed at 50Hz

1.0

Generated
force
Controlledforce
direction

0
0

20

40

60

80

100

Drive frequency (Hz)Fig. 7. Translational force on forcers
with different materials

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120

0.0

0

10

20

30

40

Direction of generated force (degrees)Fig. 8. Controllability of the direction50

Temperature in the upper set of coil (C)

160
140
120
100

f=10Hz
f=11Hzf=12Hzf=13Hz
f=14Hz
f=15Hz
f=16Hz
f=17Hz
f=18Hz

80
60
40
20
0

60

120

180

240

300

360

Operating time (sec)Fig. 9. Thermal condition in steady operation

the frequency control method.
5.2.6. Thermal condition. The weakest point of the LIM isheat. A typical rotary AC motor has a built-in fan to cool
itself down. In the trial LIM, the coils are placed inside thecore, therefore, they have to be equipped with a forced-air
cooling apparatus. To measure the thermal transient of thetrial LIM, a small thermocouple thermometer was installedinside of the lower set of coils. To measure the worst case,two sets of coils were driven continuously at the same frequency. The target frequency was selected from 1 Hz to 20
Hz at 1 Hz intervals, and 25, 30, 35 and 40 Hz. Since themaximum rating temperature of the insulated membrane of
the coils is 150 degrees centigrade, each measurement was
stopped when it reached 130 degrees centigrade. Figure 9shows only some critical results. When the coils generated
maximum force, the maximum current was sent and thetemperature reached the operating limitation within threemin. Under other frequency conditions, it reached a thermal balance under 100 degrees centigrade.
5.2.7. Conclusion of experiments. From these experimental results, we can conclude that the trial 2-DOF LIM
can generate a few Newton degrees of force in any direction using a copper plate with dimensions of 100 x 100 x 1.0mm as a forcer. Of course we can use only a metal plate as
the forcer on the desk, and it will never disturb the visual
image by the front projection and seamless direct manipulation of the Proactive Desk.

6. Issues and future work
We were able to clarify some issues of the trial Proactive Desk through the experiments. First, since we employed ready-made inverters for rotary AC motors to drive
the LIM, we were able to control only the frequency of thesignal. Driving it in a low frequency range, we sometimes
observed vibration in the forcer. Even though we could

Proceedings of the IEEE Virtual Reality 2003 (VR’03)
1087-8270/03 $17.00 © 2003 IEEEnot discuss this issue mathematically, it seems that this isdue to the discrete driving method of the digital inverter.
The inverter generated an AC signal by pulse width modulation, so it is designed to drive a higher frequency than
the range we used. As a solution, we will employ currentcontrol based ampliﬁers to drive the LIM by using custom
made inverter units.
As for the thermal condition, the trial system could not
be driven for a long time with maximum performance, as
shown in the results. We need to provide a more powerfulcooling apparatus for the stator. Moreover, we also have toconsider the thermal condition of the forcer. Some of theeddy current that does not contribute to the translational
force is transferred to heat, and this accumulated inside theforcer. This is the same principle as that of an induction
heating stove in a kitchen. We have to develop a coolingapparatus for the forcer without a troublesome mechanism
while preserving the advantages of the LIM.
Moreover, the sets of coils generate the traveling magnet ic ﬁ eld uniformly in the entire desk surface in thisconﬁguration, and the movable forcer is just a small part.
Therefore, the majority of the electric power is discharged
as heat and magnetism of no use. Furthermore, the worst
weakness is that, when some forcers are put on the desk,
the system generates translational force on every forcer
according to its material and size in the same direction.
Additionally, since the coil pitch of the trial LIM is 45 mm,a small forcer of less than 45 mm cannot ride on the traveling magnetic ﬁeld and is ﬁxed to a point on the desk.
To solve these issues, we are designing the next-generation Proactive Desk as shown in Figure 10. We will replace
the sets of big coils with a number of small coils woundaround each column of the stator core, and each coil will
be connected to the same number of ampliﬁers individually. When the motor is operated, a PC will control a partof the sets of ampliﬁers and coils to generate the travelingmagnetic ﬁeld around the forcer. This means that this system will drive the minimum parts of the coil around theforcer, therefore, lowering the power consumption and improving the thermal condition. Furthermore, two or more
Controller

Operationcommand

Drive
area B
Drive
area A

Driving current

Set of amplifiers( as same number as coils)

Set of coils in the stator

Fig. 10 . The next-generation Proactive Desk

forcers can be driven individually and simultaneously. In
this conﬁguration, additionally, all coils will be placedin equal conditions: the same gap and the same magnetic
and electric circuit, so that the system will not exhibit any
differences such as the difference between the upper andlower sets of coils in the ﬁrst trial system. Moreover, toachieve a stronger magnetic ﬁeld, it will be equipped withlong columns to increase the number of turns of each coil.
Consequently, we can design a smaller coil pitch, so a thesmaller forcer, such as an eraser or a pen-shaped force, canbe driven on the desk.

7. Conclusion
In this paper, we proposed the Proactive Desk, a new
digital desk with haptic feedback for a co-experience webthat enables people to share the feelings and experiences ofother users via the Internet. We employed a linear induction motor based actuator so as to preserve the advantagesof the digital desk. Here, the stator of the motor is built
into the desk and the user handles only a small metal plate,the forcer, to feel haptic sensation in the digital desk environment. Therefore our digital desk enables the user toseamlessly handle both digital and physical objects on thedesk with a common standard.
We have developed the ﬁ rst trial Proactive Desk.
Through an experiment using the trial system, we concluded that it could generate a maximum 3 N degrees of force
to the forcer in any direction. We also clariﬁed some issues
about the trial system, i.e., stability, thermal condition andmultiple forcers control. We also proposed a next-generation system to solve these issues.

Acknowledgment
This research was conducted as part of "Research oninteraction media for the high-speed & intelligent networking." with funding from the Telecommunications Advancement Organization of Japan.

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