Shared Walk Environment Using Locomotion Interfaces
Hiroaki Yano
University of Tsukuba
1-1-1 Tennoudai
Tsukuba, 305-8573 JAPAN+81 298 53 5062
yano@vrlab.esys.tsukuba.ac.jp
Hiroo Iwata
University of Tsukuba
1-1-1 Tennoudai
Tsukuba, 305-8573 JAPAN+81 298 53 5362
iwata@kz.tsukuba.ac.jp

Haruo Noma
ATR Media Integration and Communications
Research Laboratories
Hikaridai, Seika-cho,
Kyoto, 619-0288 JAPAN+81 774 95 1401
noma@mic.atr.co.jp
Tsutomu Miyasato
ATR Media Integration and Communications
Research Laboratories
Hikaridai, Seika-cho,
Kyoto, 619-0288 JAPAN+81 774 95 1401
miyasato@mic.atr.co.jp

ABSTRACTINTRODUCTION

By sharing data regarding the sensations experienced byindividuals, as well as by sharing their knowledge, we arereadily able to communicate with each other, and there arepossibilities to further evolve this communication method.
The different sensations experienced during voluntary
walking and enforced walking give us different feelings.
Also, the number of individuals involved can create a
different feeling when walking. Networked computerassisted walking can support and enhance these different
experiences. In this paper, we introduce another walking
style, the shared power-assisted voluntary walk, which isrealized by a prototype networked locomotion system. Thissystem can be used in tele-rehabilitation, which allows
remote patients to share the sensation of walking. Also, it
can be used to teach a group of patients rehabilitative
walking. We developed two locomotion interfaces andconnected them via a network. We developed enforced andsemi-voluntary walking training systems using the sharedwalk environment and evaluated them with a series ofexperiments.

Currently the importance of CSCW is increasing in theoffice environment. Many commercialized CSCW software
packages are used in business. However, there are manyother communicative and cooperative situations that can be
encountered, such as those found in spatial communication,in the field of engineering, in medical applications and inamusements. CSCW is applicable not only to office work
but also to these situations. By sharing the sensation dataexperienced by each user, such as visual, auditory andhaptic sensations as well as their movements and by sharing
their knowledge of the work allows the users tocommunicate easily with each other. By using multi sensory
feedback, there is some scope to further evolve thecommunication method.

Keywords

shared environment, virtual reality, locomotion interface,rehabilitation

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CSCW’00, December 2-6, 2000, Philadelphia, PA.
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Now, traveling on foot is an intuitive and natural practice inthe real world. However, the problem of moving around in
the virtual environment (VE) on foot is one of the major
obstacles to be tackled in virtual reality research. We
usually explore a VE using a hand-held controller, even if
walking is the most natural locomotion method for humanbeings. In order to realize natural navigation in the VE, wedeveloped a networked walking system. It allows remotely
located people to walk together. Also, a person at one sideof the network can control the walking style of a person at
the other end of the network.
In this paper, we introduce a method of classification ofwalking. We have developed two types of locomotion
interface devices for walking, and we have created a sharedvirtual environment using those locomotion interfaces. We
applied this networked walking system to tele-rehabilitation
to evaluate the system.

For the shared haptic environment, we developed the VECS
system [5], which connected two haptic interfaces via theInternet and gave a shared haptic sensation for thefingertips. Also Brave and others have developed theinTouch system [6]. They connected force-feedback rollers
on remote sites, and by this means shared same physicalobjects (the rollers) and the haptic sensation for thefingertips. However, there are no systems available that canshare haptic sensation for feet. Our research is the firstexample of connecting locomotion interfaces via a network
to build a shared walking environment.
As a rehabilitation system, Volpe-BT et. al used a robot toimprove motor recovery of the upper limb [7]. Powered
feeding devices have been developed at the University of
Delaware [8]. Those devices help to assist the patient withfeeding. However there aren’t many rehabilitation systems
that are specific to walking, though there is a specialized
wheel chair to assist transfers [9]. Our system can support
not only the patient but also the therapist. Using our system,a therapist can regulate the motion of the patient’s foot andteach him/her how to move their legs directly, and with lessfatigue.

more than 3 persons

Locomotion interfaces can be classified into the treadmill
type, pedaling devices, the gesture recognition type and thelarge manipulator type. The treadmill type is a simple
device, ordinarily used for physical fitness. A virtual
building simulator was developed at UNC [1]. Their
treadmill has a steering bar similar to that of a bicycle. An
omni-directional treadmill has been developed at VirtualSpace Devices, Inc. This device employs two perpendiculartreadmills, one inside of the other. Each belt is made ofapproximately 3400 separate rollers, woven together into amechanical fabric. The motion of the lower belt istransmitted by the rollers to a walker [2]. A unicycle-likepedaling device is used for the battlefield simulator of the
NPSNET project [3]. A player on the system changes
direction by twisting his/her waist. Slater et al [4] developed
a gesture recognition system. They proposed locomotion in
the virtual environment by “walks in place”. The walking
motion is recognized by a position sensor and a neuralnetwork. A large manipulator type locomotion interface
named BiPort has been developed at the University of Utah.
This device is driven by hydraulic actuators and is attachedto the feet of a walker. Therefore, it is clear that manydifferent types of locomotion interfaces have now beendeveloped.

(4)Grouptherapy/training(6)Group walk(5)Threelegged race

2 persons

RELATED WORK

(1)CPM

1 person

The effectiveness of the shared walk environment is shown
through the experiments.

(2)Operation inrehabilitation(3)Ordinary walk

SpringVoluntary

Enforcedspontaneity

Figure 1. Classification of walking in the real world.
CONCEPT OF THE SHARED WALK ENVIRONMENTClassification of Walking

There are many different types of walking situation, such as
the ‘ordinary’ walk, the group walk and the training walk.
Diagrammatically, walking can be categorized byspontaneity and the number of participants involved, as
shown in Figure 1. The ordinary stroll is placed in a highvoluntary position (Figure 1(3)). The group walk, such as asight seeing tour, is placed above it (Figure 1(6)). This typeof walk is less spontaneous than the ordinary walk, even if
several different people lead the group. The grouptherapy/training walk is placed in the upper left area (Figure1(4)). The patients/trainees follow the motion of thetherapist/trainer. This is almost an enforced situation. If
there are a large number of patients/trainees, it becomesvery difficult for the therapist to train them. The threelegged race is placed in the middle of group training andgroup walks (Figure 1(5)). Synchronization of theparticipant’s steps is necessary in order for them to walk
together. CPM (Continuous Passive Motion) is placed near
the origin (Figure 1(1)). In this situation the patient is forced
to move their body using simple mechanical equipment suchas a spring.
Shared walk environment

In this paper, we propose the concept of a shared walk
environment, which supports and enhances all of thesevirtual walking situations. In this networked environment,
users can share space by exchanging live video images,
computer generated images, and data from sensors. Our
locomotion interfaces can simulate uneven terrain surfaces.

more than 3 persons
2 persons
1 person

SYSTEM CONFIGURATION(4)Grouptherapy/training(1)CPMandoperation inrehabilitation(5)Group walk(2)Semivoluntarywalk(3)Virtual walkVoluntary

Enforcedspontaneity

Figure 2. Classification of shared walk environment.
We can generate a haptic (force feedback) sensation to theuser’s foot. Since the locomotion interfaces are networked,
it is not necessary for the users to be together in the sameroom. Furthermore, the image of each of the walkers can be
virtually superimposed in the shared walk environment.
Using our system with HMD and real time computer
graphics images, we can superimpose the movements of one
user’s body onto the body of another user. This means thatthe users can feel each other’s step-patterns directly with theaid of visual, audio and haptic sensations, and the users canthen move their own feet accordingly. We can construct theenvironment for a group walk, a three-legged race, grouptherapy/training, CPM and rehabilitation, as shown in
Figure 2. In this group walking environment, we can travel
anywhere with other remote users. We can go sightseeing oreven make a study tour.
In this paper, we apply the shared walk environment torehabilitation,
manipulation
andsemi-voluntary(spontaneous) walking. Due to perhaps a traffic accident or
aging, people can need to undergo rehabilitation. In the
rehabilitation of walking, the motion of the body all isimportant. Most rehabilitation sessions are conductedverbally or by handling the patient’s body to teach them
how to move correctly. However, the therapist often finds it
difficult to explain the required motion to the patient using
only these methods. Applying our system to these situations,the therapist can operate the patient’s body easily and avoid
fatigue. The patient can learn the motion required by having
their foot moved directly, as well as by words. Furthermore,
the patients and therapists can communicate while they areseparated by hundreds of kilometers.

To build the shared walking environment, we prepared an
audio-visual data channel and locomotion interfaces for thehaptic sensation required for the feet. The prototype telerehabilitation system consists of two locomotion interfaces,
GaitMaster and ATLAS. There are many types of theselocomotion interfaces, as described in the chapter referring
to related work. The users do not always have the same
locomotion interfaces. In any shared walking environment
we should be able to support many configurations oflocomotion interfaces. We choose two typical locomotion
interfaces, a large manipulator type (GaitMaster) and atreadmill type (ATLAS). The GaitMaster [8] was developed
at the University of Tsukuba, and ATLAS [9] wasdeveloped at ATR. They are 600km apart, and areconnected by a 64Kbps network (ISDN). The details of theconfiguration of our system are shown below.
GaitMasterA new locomotion interface that simulates an omnidirectional uneven surface has been designed. The device isnamed “GaitMaster.” The core elements of the device are
two 6 DOF motion-bases mounted on a turntable. Figure 3
illustrates the basic configuration of the GaitMaster.
A walker stands on top of the plate on the motion-base.
Each motion-base is controlled so that it can trace different
positions of the foot, and the turntable traces the orientationof the walker.

Figure 3. Basic concept of the GaitMaster.

Figure 4. Overview of the GaitMaster.
The motion of the turntable removes any interference
between the two motion-bases.
The X and Y motion of the motion-base traces thehorizontal position of the feet and cancels out the effects of
their motion by moving in the opposite direction. The
rotation around the yaw axis traces the horizontal
orientation of the foot. The Z motion traces the vertical
position of the foot and similarly cancels its motion. The
rotation around the roll and pitch axis simulates inclinationof a virtual surface.
The control algorithm of the GaitMaster keeps the positionof the walker at the neutral position of the GaitMaster. In
order to keep the walker at this fixed position, the motionplatforms have to cancel the motion of his/her feet. The
algorithm of the cancellation mechanism is:(1) Suppose a snapshot of a walking action, and the rightfoot is ahead of the left foot.
(2) When the walker moves the left foot forward, theweight of the walker is on the right foot.
(3) The motion-platform for the right foot goes backwardin accordance with the displacement of the left foot, sothat the center of gravity of the walker is maintained.
(4) The motion-platform for the left foot follows the
position of the left foot.

Figure 5. Overview of the ATLAS.
When the walker finishes stepping forward, the motionplatform supports the left foot. When the walker climbs up
or goes down stairs, a similar procedure is applied. The
vertical motion of the foot is canceled in the same way. The
vertical displacement of the forward foot is canceled inaccordance with the motion of the backward foot, so that thecentral position of the walker is maintained at the neutral
height.
We have developed a prototype GaitMaster system [8]. In
order to simplify the mechanism of the motion-platform, we
defined the surface of a virtual space as consisting ofseveral sets of plain surfaces. Since most buildings andurban spaces can be simulated without inclination of thefloor, we can neglect the roll and pitch axis of the motionplatforms. Each platform of the prototype GaitMaster iscomposed of three linear actuators on top of which a yaw
joint is mounted. We made two XYZ stages. Three linear
guides are applied to support the orientation of the top plateof the motion-platform. The payload of each motionplatform is approximately 150Kg. A rotational joint aroundthe yaw axis is mounted on each motion platform. The joint
is equipped with a spring that moves the feet towards theneutral direction.
Figure 4 shows an overall view of the prototype GaitMaster.
We implemented the control algorithm mentioned above
and succeeded in the successful presentation of various
virtual staircases.

Locomotion interface
controller

Locomotion interface
controller

Walking motion
detecting unit

Walking motion
detecting unit

ISDN 64kbps

B's leftfoot motion

A's right
foot motion

Motioncanceling unit
controller

User AA's leftfoot motion

B's right footmotionRemoteuser

Motioncanceling unit
controller

User B
Local
user

MotionsensorMotionsensor
Virtualrestriction

Locomotion Interface ATLAS
Locomotion Interface GaitMasterFigure 6. Overview of the shared walk environment.
ATLAS

ATLAS is a treadmill-like locomotion interface. The user
can get the sensation of walking on flat ground or on aslope. The main advantage of the treadmill approach is thatit gives the user a very natural feeling of walking without
any bothersome equipment. We mounted a CCD camera
with an infrared light filter and an infrared lamp in front of
the treadmill. The relative positions of the small IR
reflection markers fitted to each ankle of the walker can bemeasured by a video-tracking unit. The walking phase,stance and swing phases can be determined by the positionsof these markers and the belt speed. By observing an
ordinary walking motion on a flat floor, we could see thatthe duration of the stance phase is almost in inverse
proportion to the walking speed. Using this relation, thesystem can estimate the walking speed while on the belt.
Figure 5 gives an overview of the ATLAS. It also employs avideo tracking system, known as QuickMugTM manufactured
by OKK. It can track bright markers at 60 Hz. It also uses
magnetic position sensors to measure the walker’s headdirection to support a head-tracked visual display as an
optional extension.
Our 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 continuously controlled by a PC from 0 to
4 m/s, with a time delay of 0.09s, and the time constant of
0.10s, within the walking speed. The treadmill is mounted
on a custom made three-axis motion platform. It can tilt androtate the walking surface in any direction. The maximum
rotational speed is 1.0 rad/s.
Two computers, a PC and an SGI ONYX control thesedevices. The PC acts as an interface I/O for the video
tracker, the magnetic sensors, the treadmill, and the motion

platform. All the data is exchanged via Ethernet. The
motion analysis sub-system and belt speed controller resideon the ONYX. These sub-systems operate at 60 Hz. The
virtual world simulator sub-system is also implemented on
the ONYX. A visual image feedback sub-system generates
images of the world on a projector screen in front of thewalker.
Configuration of the Shared Walk Environment

The prototype system consists of the two locomotion
interfaces that are directly connected via a digital network(ISDN). This system has two digital network lines. One isused to exchange information on the user’s foot position oneach locomotion interface via UDP/IP. If we use anothernetwork line, such as an ATM or analog phone line using amodem, we can switch the data line easily. Another digitalline is used to exchange NTSC live video and audio data for
a TV phone. The users can share their walking experience
with other people by watching the same live image, talking
with each other and sharing the sense of locomotion.
Both digital network lines have 64kbytes bandwidth. The
data is updated at 30Hz. The frame rate of the video images
is 15Hz with a time delay of a few frames. The voicechannel has no time delay.
TELE- REHABILITATION: LEG OPERATIONAs a first example of the shared walk environment, we
implement a leg operation system. Usually, a therapist
explains the motion of walking to the patient with words orby physically handling the patient’s body. However, using
the shared walk environment, the therapist and the patient
can be superimposed virtually, as shown in Figure 7. In thissystem, the ATLAS is used by a therapist/trainer and thePatient

Tapping

Superimposed
patient andtherapist

Patient

Virtual corridor

Therapist
Real environment Shared walk environment

Therapist Remote
Therapist
patient
Real environment Shared walk environment

Figure 7. Basic concept of the leg operating system.

Figure 9. Basic concepts of semi voluntary walk system.

GaitMaster is used by a patient/trainee. When thetherapist/trainer moves his/her left foot, the top plate of the
GaitMaster traces the motion. As a result, thepatient/trainee’s foot is forced to move along with thetherapist/trainer’s motion. This is particularly effective foruse in rehabilitation (Figure 1-(2)). Using the system thetherapist/trainer can teach the motion easily to his/herpatients without fatigue, and can also adjust the applied
force to the patient/trainee.

Z position(

Three-dimensional positional data of the therapist/trainer’s
left ankle is sent to the GaitMaster. The GaitMaster traces itin real time. Therefore the trainer on the ATLAS can
operate the left foot of the trainee on the GaitMaster.
Furthermore the therapist/trainer can tell what has occurredat the remote site with the aid of the live video image andsound. By using this technique the therapist can adjust
his/her patient’s motion. On the other hand, thepatient/trainee can learn how to move his/her body not only
from video and sound, but also from force feedback to theirfoot. Of course, they can also talk to each other with the TV
phone. However, because of the differences in the working
volumes of each of the locomotion interfaces, the position
data from the ATLAS (therapist/trainer’s site) are scaled
down by 50 %.

-200

-100

120
100
80
60
40
20
0
-20 0
-40
-60
-80
-100
X position(m m )Trajectory of trainer
Trajectory of trainee
Working volume

100

200

Figure 8. Trajectory of each motion of locomotion
interfaces

Experiment with Leg Operating System

We conducted an experiment to examine a leg operating
system. We measured the trajectories of a user’s left foot on
the ATLAS and on the top plate of the GaitMaster for a user
who is 60kg in weight. As shown in Figure 8, theGaitMaster can follow the user’s left foot on the ATLAS.
According to the subject, who is a specialist in
rehabilitation, the GaitMaster has sufficient working volume
and renders sufficient ‘feel’ of walking to be used as a
primary rehabilitation stage. The other advantage of thissystem is that a trainer who isn’t strong enough tomanipulate the body of patient can operate them via theequipment.
TELE- REHABILITATION: SEMI VOLUNTARY WALKAs a second example of the shared walk environment, we
implemented a semi-voluntary walking environment for use
in rehabilitation. Usually the therapist explains the timing ofeach step during the walk to the patient by using words andtapping out a rhythm. Using the shared walk environment,
the therapist and the patient can share their leg motion
naturally, as shown in Figure 9. This environment is like thethree-legged race, and is the next stage of the CPM. The
patient can learn the timing of the step. To generate force
feedback there is a simultaneous exchange of motion data
between the users. As shown in Figure 6, the left footmotion data of the user of the GaitMaster and the right footmotion data of the user of the ATLAS were exchanged
between the two sub-systems. Therefore, the locomotion
interfaces restricted the foot motion of each user as if they
were actually tied. Accordingly, the users had tosynchronize their walking steps. The patient also learns thetiming from visual and audio feedback.
Experiment with Semi Voluntary Walk System

We conducted an experiment to examine the degree ofsynchronization of the user’s walking motion with thissystem. Four pairs of subjects were asked to walk together
as fast as they could. To estimate the degree ofsynchronization, we measured two time lags in the motionof their bound feet for each step. t1 was the time lag instarting the swing phase, and t2 was the time lag in finishingthe swing phase. We asked the subjects to walk for 15
minutes and recorded the time lags of the entire step. They
were defined by basing them on the motion of the ATLAS
user; in short, when the subject on the GaitMaster started
his/her motion later than the subject on the ATLAS, thetime lag was given a positive value. All the subjects were
novice users. The subject on the ATLAS was allowed tocall out to his/her partner on GaitMaster to synchronize
their steps through the TV-phone.
Figure 10 shows the results of the user testing. We divided
each trial into three periods, i.e., the first, middle, and final
periods. One period lasted five minutes. One column in the
figure represents the average time lag for one period and theerror bar represents the standard errors.
In the first period, t1 and t2 vary widely, but they converge
as the trial goes on. The converged value t1, i.e., the time
lag in starting the swing phase, depends on the particularpair. On the other hand, t2, i.e., the time lag in finishing theswing phase, converges to about 0.4s for all pairs. Fromthese results, we focused on the standard errors of t1 and t2,
which represented the degree of convergence of the timelags. As a result of statistical analysis, there was asignificant difference in the standard errors for the measured
periods (P(F=9.50)=0.01) and between the time lags
(P(F=6.14)=0.048). There was no difference in the standard
errors between the subjects (P(F=0.98)=0.46).
The user testing showed that the subjects could synchronize
their motion step by step, but it seemed that the way inwhich the walking motions were harmonized depended oneach pair’s strategy. Furthermore, it was more difficult tosynchronize the motion finishing the swing phase than it
was the motion starting the swing phase. In fact, observing
the trials, the subjects failed to synchronize their motion at
this first period, even if they confirmed their steps by callingout to each other. In the final period, however, they could
synchronize their steps successfully even if some subjects
didn’t call out to each other. These results lead to theconclusion that the subjects could become aware of theirpartner’s motions through the locomotion interfaces andadjust their motion by referring to their partner’s motion.
DISCUSSION

We classified various ways of walking from the viewpointof spontaneity and number of people taking part.
The shared walk environment can support and enhance theprocess of learning to walk among remote users. In
particular, we expect to be able to use the shared walk
environment system for rehabilitation and group walktherapy.
This system can improve current training methods, such as
those that use only verbal commands and the operation of
simple training machines. This system can send motion in-

Figure 10. Time lag of starting and finishing swing
phase between bound feetformation from the therapist/trainer to the patient directly,
and their motion can also be digitized. The therapist cancheck the progress of the training quantitatively and plan thenext training schedule. Also this system can be applied to asituation where one person needs to communicate withmany others, such as group therapy. The precise motion
data of the therapist can be sent to the patientssimultaneously without fatigue. This is very efficient forunder-populated areas where the therapist cannot go easily.
The therapist can take care of many patients simultaneously.
Needless to say, care should be taken to ensure the user’s
own safety.
Additionally, the shared walk environment can support andenhance the presence of walking through systems forenvironmental simulators, architectural simulators andtravel simulators. We can share experiences, not only in avisual and auditory sense, but also with a heightened senseof actually walking within those applications. Our system
can also be applied to city planning. In any city planningsystem, we should consider the needs of aging persons [13].
The aging person’s sight and hearing ability can become
diminished and their muscular strength can become weak.
We can simulate those situations using our system.
For future work, we need to develop an algorithm that canconnect more than three locomotion interfaces. We should
consider how to transmit positional data and how to share
live video images among them. We should also consider thesymmetry of the locomotion interfaces. There are manydifferent types of locomotion interfaces and associatedcontrol algorithms. This system also consists of two
different types of locomotion interfaces. A mechanism tomerge the differences, such as a scaling factor needs to be
developed.

To generate a sense of presence in a remote location, we areplanning to combine a special visual display such as animmersive projection display like CAVE [14][15].
CONCLUSION

In this paper, we proposed the shared walk environment as
one of new ‘shared environments’ concerned with using
body motion. We classified different types of walking in thereal and virtual worlds. We developed a shared walk
environment using two networked locomotion interfaces.
Two trial applications for the rehabilitation of patients havebeen implemented using the system. The experimental
results showed that the subjects could operate andsynchronize their walking motion step by step, as expected.
As the next step of this study, we need to investigate theway in which subjects recognize and react to their partner’s
motion through a motion synchronizing process using oursystem. We also plan to develop a group walking
environment and a group therapy environment byconnecting the locomotion interfaces through the Internet.
ACKNOWLEDGMENTS

The authors would like to thank Hideyuki Saito, who is aphysical therapist, and Yuichiro Nara, a graduate school
student of the University of Tsukuba, for their many usefulsuggestions and their cooperation.

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