Noma, Sugihara, Miyasayo, "Development of Ground Surface Simulator for
Tel-E-Merge System", Proc. of IEEE-Virtual Reality 2000, pp. 217-224, 2000

Development of Ground Surface Simulator for Tel-E-Merge System
Hauro NOMA

Toshiaki SUGIHARA

Tsutomu MIYASATO

ATR Media Integration & Communications Research Laboratories{noma, sugihara, miyasato}@mic.atr.co.jp
Abstract
In the paper, we describe a series of stages in the development of a new virtual locomotion device designed to enhance remote, interpersonal communications. The latest system, called GSS (Ground Surface Simulator) , inherits thefeatures of two previous locomotion interfaces, i.e. ATLAS(ATR Locomotion Interface for Active Self Motion) and ALF(ALive Floor). GSS also incorporates two different features
not found in ordinary treadmills: a movable belt and an
active belt speed controller.
We built an initial prototype of GSS and developed amethod that presents bumpy surfaces free from the mechanical limitations inherent in prior designs. Experimental results showed that the subject could distinguish a 1% difference in the virtual slope on the GSS.

1. Introduction
The Virtual Space Teleconferencing System (VSTS) [1],which provides a means of communications involving both
virtual reality and teleconferencing, was proposed by ATR
Communication Systems Laboratories and developed between April 1986 and March 1996. By using the system,
people in different locations can participate in meetings orcollaborative work while having the feeling of being together
just as though they were sharing the same space via a communications system. In the case of the VSTS, the users enter a virtual space from their real spaces and conduct conversations in the virtual space.
Following the VSTS, we at ATR Media Integration &Communications Research Laboratories have been concerned with communication media, especially media fordaily communications. Our primary consideration is when
we want to have a chat. For example, when a person travels
alone in a foreign country or when a person views an impressive picture alone, s/he may want to share this feelingwith family members. We have therefore introduced “TelE-merge” as a new communication method for such a situation, i.e., "I wish you were here" [2].

We coined the term Tel-E-Merge with a double meaning, i.e., Tel-E-Merge and Tel-Emerge. More specifically,
we want to make it possible to merge a remotely locatedperson, a tel-visitor, into a tel-inviter’s space through VR
systems.
One form of Tel-E-Merge that we can imagine is asshown in Fig. 1. In the figure, a friend (Tele-visitor) who isin a foreign country is invited into the communication boothof one's own home for a chat. In this case, the friend is invited into a scenic spot where the tele-inviter is, and thetele-visitor’s image is superimposed on some mobile robot.
On the tele-visitor's side, too, the image may become animage of that person visiting the scenic spot with some VR
devices.
In this research, we intend to shape Tel-E-Merge into a
type of medium that allows conversations to take place between remotely separated persons while they walk together.
In particular, our focus is on the sense of locomotion, thesense one feels while walking on the real ground.
Some VRML viewers called “walkthrough simulators,”
allow a user to move around a virtual world on a screen,visually. The user merely controls the direction and speedof the viewing point by using a mouse. A typical MUD (multiple-user dungeon) system is a shared walkthrough simulator, and users can meet and hike in the world. However, it
is difficult to feel where one’s partner is in the world withNetwork

Generate the existence ofa Tele-Inviter and theatmosphere of the remoteplace for a Tele-Visitor:
Tele-Existence System.

VR devices
for Tele-Visitor

Tele-Inviter
Site-A
Generate the existence of aTele-Visitor for a Tele-Inviter

Tele-Visitor
Site-B

Exchange existence in different ways for communications
based on the real space of a Tele-Inviter and a Tele-Visitor.

Figure 1. Concept of Tel-E-Merge

Figure 2. AIR: ATR Imaging Robotout some special sensors like a radar set.
When people walk together, their walking motion issometimes felt to be synchronous. Moreover, they can findout a lot of information, like the sound, scale, hardness, humidity, and so on of the space by walking on foot. People
usually do such a complicated task unconsciously and can
pay a great deal of attention to their partner. Such an unconscious interaction while walking on foot can be thought ofas a key point for the enhancement of reality or the existence of one’s partner.
We have been investigating a series of development programs for communication devices using locomotion for the
Tel-E-Merge system. Our trial system consists of a tele-robot and a locomotion interface. Fig. 2 shows a trial telerobot, AIR (ATR Imaging Robot), that was designed to represent the existence of a tele-visitor to his/her tele-inviter[3]. AIR can follow the tele-visitor’s motion and act as amobile TV phone to guide the tele-visitor to where s/he isinvited.
In this paper, we propose our latest locomotion interface
called GSS (Ground Surface Simulator), which allows a tele-

Free walktechnique(a) ATLAS

visitor to get a true feel, even when walking on a remote
uneven ground. In designing the GSS, we focused on two
functions, a method for canceling user’s free walking motion and a method of simulating natural terrain surfaces.
Until now, we have achieved these functions on ATLAS(ATR Locomotion Interface for Active Self Motion; Fig. 3a) [4] and ALF (ALive Floor; Fig. 3-c) [5], separately. Inheriting the results of ATLAS and ALF, we developed GSS
to integrate their solutions.
In the following sections, we mention related works on
locomotion interface, and then give an overview of ATLAS
and ALF. Finally, we present the GSS and experimental results to show the effectiveness of the method.

2. Related works and our design concept
When people want to go somewhere, they typically selectthe most suitable means of transportation: by foot, bicycle,car, or airplane. Many applications have been developed
and a lot of research has been done to simulate such a feeling of locomotion. Most of them have used a vehicle simulator as a training tool or as entertainment, and they havebeen nearly complete. In this paper, we limit our discussion
to a locomotion interface for walking or running motion.
As a start, we describe previous research related to locomotion interfaces. Then, we present the design concept of our
locomotion interface.

2.1. Locomotion interfaces in VR
Generally speaking, a locomotion interface should cancel a user’s self motion in a location to allow the user to go
to anywhere in a large virtual space on foot. Additionally,some of them can be designed to present textures of walking surface, i.e., slopes, roughness, hardness, and so on.
Several devices have been studied up to now and we clas-

Surfacesimulation
technique(b) GSS(c) ALF
Figure 3. A series of ATR locomotion interface: ATLAS, GSS, and ALF

sify them in the following.
2.1.1. Treadmill approach. In this approach a treadmill isused to cancel a user's motion by moving an infinite belt inthe opposite direction. The main advantage of using a treadmill is that the user does not have to wear obstacle devices.
One major problem, however, concerns how to control
the belt speed so as to keep the user from falling off. In thecase of a motor driven treadmill, the system has to adjust
the belt speed based on the user's motion [4,6]. With a passive treadmill, in contrast, the belt is driven by balancing
the user’s weight, so the user never falls off the belt. Thisapproach, however, can generate a flat surface only.
Another major problem is how to change the walking
direction. Brooks [7] and Hirose [8] employed a handle tochange the direction. Some unique mechanical 2D treadmills have been proposed. As a motor driven one, Iwata [9]developed a 2D infinite plate that can be driven in any direction and Darken [10] proposed an Omni directional treadmill that uses a mechanical belt. As a passive treadmill, Eyre[11] proposed a ‘Spherical Projection System’ employing ahuge semitransparent sphere. A user can walk inside of thesphere which also acts a visual screen for projectors.
2.1.2. Active footpad approach. This method also does
not to require the user to wear obstacle devices and can simulate various terrains. Latham [12] is developing OmniTrek,
which uses two footpads. These footpads track the feet ofthe user quickly and cancel the user’s motion so that s/hedoes not go out of the device. Roston [13] proposed a ‘Whole
Body Display’ that allows the user to walk on stairs, on sand,in mud and so on. Iwata [14] developed ‘Gait Master‘ which
consists of two three-DOF footpads and a turntable. Generally speaking, footpads have to support a user's whole weight
and track the feet motion quickly; therefore, require sufficient rigidity and a wide bandwidth.
2.1.3. Sliding Interface. Iwata [15] developed a series of
sliding interfaces. The user wears special shoes and a low
friction film is put in the middle of the soles. Since the user’s
body is supported by a harness or rounded handrail, the footmotion is canceled passively when the user walks. The system measures the foot motion and changes the user’s view
together with the walking motion.
2.1.4. Pedal Interface. Using a bicycle, the user's motion
is different from that when walking; however, the complicated walking motion is simplified and can be measured
easily by computer. Brogan [16] developed a pedal interface for people training for bicycle road races. Ensor [17]developed a VRML based bicycle simulator.

2.1.5. Other Methods. Some research has related the gesture of walking to locomotion. Choi [18] developed
CyberBoots. Four pressure sensors are put on the sole ofeach foot and a gesture detecting system using fuzzy logic
outputs motion patterns. Kadobayashi [19] developed a gesture interface, called VISTA Walk, that detects the user’s
motion visually. Kobayashi [20] reported a similar device
that measures the position of the center of balance by a sensor tile. They translate gestures into commands for moving
in a virtual space, so the user has to learn how to walk in a
virtual space in advance.

2.2. Design Concept of our Locomotion Interface
Our goal is to develop an intuitive locomotion interface
that allows a user to get a feeling of walking around a natural terrain surface without any bothersome equipment. To
achieve this goal, we divide the method into two parts: amethod for canceling a user’s free walking motion and amethod for simulating natural terrain surfaces.
As the first subject, we employ a motor-powered active
treadmill and turntable approach. Using the trial ATLAS, auser can get a feeling of walking in any direction on a flat
floor or slope. As the second subject, we use a movablefloor, ALF, that can move pieces of small panels on the floor
to simulate a natural terrain surface.
ATLAS and ALF have solved specific problems separately, so we have integrated them into our latest system,
i.e., GSS. Combining an active treadmill and movable floor,
GSS can simulate endless virtual terrain surfaces beyond
the restrictions of some mechanical limitations. In the following section, we summarize the solutions of ATLAS and
ALF briefly. Then, we describe GSS and its method of simulating terrain surfaces.

3. Locomotion Interface ATLAS
Using ATLAS, a user can get a feeling of walking on aflat ground or slope. The main advantage of the treadmill
approach is that it gives the user a very natural feeling ofwalking without any bothersome equipment. However, as
mentioned in section 2.1.1, we are confronted by two difficulties in this approach: how to keep the walker from falling off, and how to allow the walker to change directions.
On a solution for the first point, we have reported aneffective method that integrates a motor-powered active
treadmill with a visual motion detecting method. We arranged a CCD camera with an infrared light filter and an
infrared lamp in front of the treadmill (Fig. 4-a). Putting
small IR reflection markers on each toe of the walker, these
positions could be measured with a video tracking unit. Comparing them and the belt speed, the walking phase, stance,and swing phases, could be detected automatically. By observing ordinary walking motion on a flat floor, we could
see that the duration of stance phase is almost in inverse
proportion to the walking speed [3,21,22].
Using this relation, the system can estimate the walking
speed on the belt. As shown in Fig. 4-c, the belt speed controller adjusts the belt speed to keep the walker on the belt
using a combination of a feedforward controller for the walking speed and a PI-feedback controller as the user’s position .
Next, we discuss the second point of allowing a user toturn to any direction while walking. If a walker makes aturn on an ordinary treadmill, s/he will lose her/his footing
and fall off of the belt. To keep the user's foot on the belt atthat time, we have considered a method that would cancel
the turning motion by rotating the treadmill [3]. Fig. 4-bshows the top view of a treadmill with this method when awalker starts to turn to the right. The next step is supposed
to be taken with the right foot, and the foot will be placed
down at Pr. At that time, if the belt is rotated in the clockwise direction by the turntable, by synchronizing with thefoot motion as shown by the dotted line, Pr will look tomove only forward in the coordinate B fixed on the treadmill.
Walking direction
Y

Walking Speed: Vw

B

J1

X1
X

X

CCD Camera

Pr
Ang

e

Pr

X0

Pl

We applied this method to the trial ATLAS. When thevisual motion detecting system found that a swinging footmoved in the lateral direction more than a certain threshold,it reported that the turning motion could be detected. Simultaneously, the turntable rotated the treadmill to keep theswinging foot on the center of the belt.
Fig. 5 gives an overview of the trial ATLAS. It employsa video tracking system, QuickMug™ manufactured by
OKK. It can track bright markers at 60 Hz. Furthermore, it
uses Fastrack™ to measure the walker’s head direction, tosupport head-tracked visual display as an optional extension.
Our altered treadmill is a commercially-available product. The walking area of the belt is 145 cm (D) x 55 cm(W). The belt speed can be controlled by a PC, from 0 to 4
m/s continuously, the time delay is 0.09 sec, and the time
constant is 0.10 sec within the walking speed. The treadmill
is mounted on a custom made three-axis motion platform.
It can tilt and rotate the walking surface in any direction.
The maximum rotational speed is 1.0 rad/s.
Two computers, a PC and a SGI ONYX™ control thesedevices. The PC acts as an interface I/O for the video tracker,
the magnetic tracker, the treadmill, and the motion platform.
All data is exchanged via ethernet. The motion analyzing
subsystem and belt speed controller are built in the
ONYX™. These subsystems operate at 60 Hz. The virtualworld simulator subsystem is also implemented in the
ONYX™. A visual image feedback subsystem generates images of the world on a projector screen in front of the walker.

Speed ofthe belt: Vb
Magnetic
sensorPr0
Belt driving direction
Reel(a) Mode for forwarding motion(b) Model for turning motion
J3
IR CCDcamera&IR lamp

Optical position trackingof toe positions Pr & Pl

Analysis of walking
motion on the belt

Estimation of walker's
position on the belt

Detection of turning
motion on the belt

Estimation of walking
speed: Vw'

Computation of
positional error

Computation of positional
error in the lateral direction

Treadmill&
3 axis motion platform

J2
J1

Visual image feedback
Belt & motion
platform
driver+Positional PI
Feedback Controller

Positional PI
Feedback Controller

Belt speed controller

Turn table controller

Target belt speed: Vb

ONYX

Foot motion

Head motion

Feed forward controller +for walking speed

Projector
screenMagnetic
position
sensorVideo
tracker
Body motion

Locomotion
display drivercontroller

Sensorcontroller
PC

System controller&
Virtual world simulator
Motion analyzer&
Locomotion feedback

Target rotational angle: J1
Ethernet(c) Diagram of controllers of ATLAS

Figure 4. Control method of ATLAS

Figure 5. Overview of trial ATLAS

4. Terrain Surface Simulator ALF

pull down motion is done by its dead load. It uses electricalactuator units and a PC based controller. The system also
has a projection system that can project texture graphics
onto the tiling panels to form a more realistic terrain surface.
As shown in Fig. 7, the controller unit is based on a PC
system, and uses a factory automation programmable logic
controller (PLC) unit for its stepping motor. The control
logic for the controller unit is implemented by software run
on a built-in PC system. Here, the system's host CPU gives
surface data to the controller unit, and the control softwareinterprets the data and issues PLC control commands. The
PLC unit drives each stepping motor in the actuator cylinder. In this first prototype system, an actuator unit can drivea 100 mm stroke vertically.

The ALF system is a mechanical device for simulating
natural terrain surfaces from flat and smooth to rough andbumpy, similar to a natural field on which a user can walk.
The basic idea of the ALF system is very simple. As
shown in Fig. 6, the trial ALF system consists of many combinations of vertically moving small tiling panels and actuator units. These tiling panels can elevate to a designatedheight when driven by the actuator units, under the controlof the actuators controller. The system's host PC/WS canaccommodate real surface data captured from natural terrains or virtual surface data generated by 3-D computer
graphics, and issue control commands to the actuators’ controller. Then, the system can represent the 3-D shape of eachof these terrain surfaces.
In the development of ALF, we intended to make a practical device. To achieve this, we focused on the following
points: (1) small tiling panels, to enable a high-resolution
device, (2) large maximum and small unit strokes of theelevation height, to enhance the capability of shape representation, and (3) real-time operation. These were important points for making realistic simulated terrain surfaces,
and were reflected in our implementation.
To cope with these points, we proposed a surface patching methodology. In this proposed methodology, each tiling panel is an equilateral triangle plate, and six of theseplates are gathered into a hexagon as a drive unit. This hexagonal unit is arranged in a matrix to fill the movable floor
surface (Fig. 6). Each hexagonal unit is driven by an actuator unit. The actuator unit can push up or pull down thecenter of the hexagonal unit. This mechanical configuration can represent a smooth contour. The trial system has
168 tiling panels and 28 actuator units in a 1m x 2m area.
Each triangle plate is made of machined aluminum, and the

5. Ground surface simulation for locomotion
interface
5.1. Object and basic Idea of GSS
The trial ATLAS can display in an infinite tilted way
using its three axis motion platform below the treadmill,
but a user always walks on a flat slope such as a paved concrete road or a board. On the other hand, the trial ALF system can simulate terrain surfaces ranging from flat andsmooth to rough and bumpy, but each surface is limited
within the movable floor. By solving these limitations, we
designed GSS to have the mutual advantages of both ATLAS and ALF.
The basic design of the GSS is quite simple. We employ
a movable supporting stage under the belt of an active treadmill. When the supporting stage changes into some shape,
Projection unit

Movable floor
Actuator
Controller
FA-PLC

free vertex

Built-inPC system

Hinge
Actuator head(up/down)

RGB

NTSC
Triangle plate

Host
CPU

Serial connection

VCR,
etc.

Close up of the actuator unit.

Figure 6. Movable floor surface of trial ALF

Figure 7. Overview of trial ALF

* A part of the upper
belt is omitted in the
figure for yourunderstanding

A pair of upperholding rollers

One set of five lower
supporting rollers

One unit of
the moving stage
Tensional axisof the belt

Figure 8. Photo of the deformed belt

Figure 9. Sketch of belt stage structure

the belt is moved in accordance with this change. Using thetechniques of ATLAS, GSS can simulate where a walker iswalking. Therefore, if there is a small bump in a virtualworld, GSS bulges a part of the belt. Furthermore, GSS cansimulate a higher bulge or a lower hollow than the deformations possible with mechanical limited “offset compensation” method. The details of the simulation method aredescribed in a later section.

the configuration, the maximum belt speed is 2.3 m/s.
Fig. 10 shows a block diagram of the trial GSS. In thesystem, we employ magnetic position sensors to measureuser’s foot position and estimate his/her motion. The belt
speed controller of GSS uses the same results as ATLAS.
GSS also manages a terrain map that contains height dataon the simulated world. Using these results, GSS finds theshape of the ground surface where the user is walking, andchanges the height of each sub stage to simulate the surface.

5.2. Overview of the trial GSS
We have built a first-trial GSS (Fig. 3-b). As this systemappears to be an ordinary treadmill, its supporting stage
consists of six sub stages that can be moved up and down
individually. Fig. 8 shows a close-up of the belt in the shapeof a sine wave. The belt size is 1.5 m (D) x 0.6 m (W), andeach sub stage is 0.25 m(D) x 0.6 m(W).
The detailed structure of the stages is represented in Fig.
9. Each of the sub stage has nine rollers: five of them arelower supporting rollers and the rest are upper holding rollers. The lower rollers support the weight of the user, so they
are made of machined metal. Three of them have a radiusof 3 cm and the rest have a radius of 1.5 cm. They are arranged alternately to minimize the gaps between them. The
upper rollers are made of engineered plastic and have a radius of 3 cm. The belt is held between the upper and lower
rollers. Therefore, the belt rotates along the sub stages when
they are up and down. One AC servo motor drives one stage,
so the trial GSS has six servo motors. The stroke of thestage is 6 cm and the maximum speed is 6 cm/s.
Additionally, GSS has a belt tension regulator. When thesix sub stages are up and down, the treadmill needs a longer
belt length than when they are level. In other words, thebelt is driven by a frictionally coupled-motor powered axis,
therefore the belt tension should be kept constant. In thetrial GSS, an air piston and an air pressure regulator movethe other end of the belt axis to maintain the belt tension. In

5.3. Design of ground surface simulation
In this section, we describe how the system simulates aterrain shape. The maximum stroke of a sub stage is 6 cm inthe trial GSS. If the defences in height between the top andthe bottom in the simulation world is within this mechanical limitation, the system merely reflects the surface shape

Magnetic
position
sensorAirtensioner
Belt drive
motor

Servo motor
for each stage

Systemcontroller

Surface simulator&
Stage controller

GSS driver unit

Motion analyzer&
Belt speed controller

Surfaceshapedata
Map manager

PC

Figure 10. Overview of trial GSS

on the stage where the user is in the world. However, whena bulge is higher than the mechanical limitation, like a longslope, all of the sub stages are raised to their uppermost
position.
We applied new method called “offset compensation” toprevent such a saturation condition. The term offset indicates how high the level of GSS is in the simulated world.
When GSS needs to simulate a higher terrain shape than themechanical saturation, the system compensates the surface
shape with the offset. This offset is revised in the standing
phase.
For example, for the user who is going up a long unevenslope in Fig. 11., there are two control modes running simultaneously: “simulation mode” and “offset control mode”.
The sub stages in front of the standing foot (No. 1, 2, 3 inFig.) are controlled according to the former mode. They
simulate the terrain surface in front of the user identical to
the simple simulation. One point of difference is that theterrain shape data is compensated by the offset. On the other
hand, the remaining stages are controlled under the offset
control mode. These motions are synchronized and lower
the standing foot gradually in the case of an upper slope.
The amount of lowered motions is added up to give the offset.
As a result, a user always has to step relatively higher
location than the standing foot. Using the proposed method,
the trial GSS can display a 5% infinite slope while walking
speed is within 1 m/s.

We conducted a simple experiment to examine the surface simulating method.

6.1. Experimental setup
Our subjects were asked to walk two virtual slopes on
the trial GSS in succession, and to provide an answer whichslope was steeper by "former", "latter", or "the same". As
shown in Fig. 12, we employed four virtual slopes at inclines of 1%, 2%, 3%, and 4% using the previously mentioned method. In each trial, the subject tried the first slopewith ten steps at first. Then, GSS presented a flat surface
for five steps, and generated the second slope until the subject gave ab answer. We did not fix the number of steps forthe second slope. Each of the subjects got 80 trials (twelve
pairs of different slopes and four pairs of the same slope;
five trials in each pair). The stimulus pairs were randomly
selected. We had six subjects (22-39 years old, male), so we
obtained results on 480 trials in total. Before the trials, allof the subjects experienced a training phase for GSS.

6.2. Result and discussion
Table 1 indicates the rates of right answers added up for
all trials for each pair of slopes. The best rate was obtained
for the 1% versus 4% slope pair. The worst rate was obtained for the in 4% versus 4% slope pair. The table showsthat the rates of right answers increase difference between
stimuli forming a pair. On the other hand, the rates for pairs
with the same slope were worse than the rates for the oth-

Virtual slope 1%
2%
3%
4%

Standing footOffsetSwinging foot

6. Results of slope simulation

Simulation mode
positionof theOffset control mode
positionof the standstage ID
under the standing footOne trial

First slope
manager

Revising shapedata by offset

10 stepsMoving the sub stages
to the level height

Updating offset

Figure 11 Control method for a large slope

Second slope

First slope

5 stepslevel

10 steps

Time

level

Answer"Former","Latter""The same"

Figure. 12 Procedure of the experiment

Table 1. Experimental Results
1%
2%
3%
4%

1%
0.767
0.817
0.950
0.983

2%

3%

4%

0.500
0.667
0.850

0.467
0.550

0.400

ers. As a result, the trial GSS could present some stimulusthat the subjects could feel. Moreover, the results tell usthat the subjects could distinguish a difference of 1% on
GSS.
In the experiment, we just compared stimuli on GSS. We
have yet to compare real walking motions on slopes or
bumpy grounds and motions on GSS.

7. Conclusion
In this paper, we described a series of development programs for communication devices using locomotion. The
latest system called GSS inherits the advantages of locomotion interface ATLAS and terrain surface simulator ALF.
GSS differ in two ways from an ordinary treadmill, i.e., it
has a movable belt and an active belt speed controller.
We built the 1st trial GSS and developed a method that
presents bumpy surfaces free from mechanical limitations.
Experimental results showed that our subjects could distinguish a virtual slope difference of 1% on GSS.
At the beginning of the paper, we presented our new communication style “Tel-E-Merge” and then proposed a conversation tool between people separated but having the feelof walking together. As future work, we intend to built GSS
into the Tel-E-Merge system.
Furthermore, we expect GSS to be applied for rehabilitation purposes, especially for training machines that teaches
people walking skills. GSS can dynamically generate any
shape of a walkable surface on a belt as walking motion. A
patient can therefore select a suitable training course according to his/her skills and training level. For a doctor,
GSS can generate and test a variety of walking ways dynamically, enabling the therapist easily and objectively findout the level of treatment a patient will require.

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