2011 IEEE/RSJ International Conference onIntelligent Robots and Systems
September 25-30, 2011. San Francisco, CA, USA

Mutual Telexistence Surrogate System: TELESAR4- telexistence in real environments using autostereoscopic immersive display Susumu Tachi, Kouichi Watanabe, Keisuke Takeshita, Kouta Minamizawa,
Takumi Yoshida, and Katsunari Sato, Keio University


the Polycom Telepresence System, or telepresence surrogate
robot systems, such as TiLR, Vgo, and QB. Nonetheless,there have been several attempts to satisfy the above
conditions [1] - [10].
A method for mutual telexistence based on projection ofreal-time images of the operator onto a surrogate robot withretroreflective projection technology (RPT) was first
proposed in 1999 [7]. The feasibility of this concept wasdemonstrated by the construction of experimental mutual
telexistence systems using RPT in 2004 [8] and in 2011 [9].
However, the demonstrated systems had only a six degree of
freedom (6-DOF) head mechanism and no manipulation
mechanism.
In 2005, a mutual telexistence master-slave system called
TELESAR2 was constructed for the Aichi World Exposition.
In addition to conventional verbal communication, actions ofnonverbal communication such as gestures and handshakes
could be performed, because a master-slave manipulation
robot was used as the surrogate for a person [10]. Moreover, aperson who remotely visited a place where the surrogate robot
was located could be seen naturally and simultaneously by
several people standing around the surrogate robot. Although
the system had an autostereoscopic 3D display, the field ofview was less than 60° in the horizontal plane and no sense of
immersion was realized.
In order to move freely about an open space with several
other participants, an immersive autostereoscopic 3D display
is necessary, one with a visual range of at least 200° in thehorizontal plane and 360° when the head rotation is ideal.
In this study, we developed the mobile mutual telexistencesystem TELESAR4, which is equipped with a master-slave
manipulation capability and an immersive omnidirectional
autostereoscopic 3D display with a 360° field of view. Thus,
TELESAR4 satisfies the abovementioned three preliminary
conditions that previous TELESARs could not.

Abstract— Our aim is to afford a remote person
the opportunity to participate virtually in some event by using
a surrogate robot to communicate with local participants whilemoving about freely at the venue. Accordingly, we propose
a mutual telexistence surrogate robot system, called
TELESAR4, which was designed and constructed bydevelopment of the following: an immersive audiovisual system;
an omnidirectionally mobile robot with a robot arm and hand;an omnidirectional stereo camera system (VORTEX); a headwith a retroreflective screen for embodiment of the remoteparticipant; and a retroreflective projection system for local
participants. This paper describes the development of
the TELESAR4 system, whose efficacy has been verified
through demonstration experiments.

A

I. INTRODUCTION

T parties, meetings, or gatherings where each participant
communicates with many other participants while
walking freely about the venue, it would be convenient andconvivial for a person not physically present at the venue still
to have the ability to participate fully in the event.
In order to attain this goal through the use of a human-robot
system, it is essential for the system to have the following
capabilities in addition to the fundamental remote speaking
and hearing capabilities:(1) The system must provide the remote participant with theability to see the venue and local participants as naturally
as though actually present at the event; i.e., a wide-range,
life size stereo view (ideally 360°) of the event venue inreal time.
(2) Face-to-face communication must be provided. Thismeans that the local participants in the event see the faceand expressions of the remote participant in real time.
A local participant in front of the robot must see the fullface of the remote participant, while another local
participant seeing the robot from its side must see thefacial profile of the remote participant.
(3) The system must allow the remote participant not only tomove freely about the venue by means of the surrogate
robot but also to perform some manipulatory tasks suchas handshakes or gestures.
The above conditions are not satisfied by the present
commercially available teleconference systems, such as

II. GENERAL DESIGN OF TELESAR4 SYSTEM
The first condition can be satisfied by using ahead-mounted display (HMD) [11], a cave automatic virtualenvironment (CAVE) [12], or the telexistence wide-angle
immersive stereoscope (TWISTER) [13], [14], because eachof these displays can provide an immersive environment witha 360° field of view. However, the second condition requires
face-to-face communication and thus necessitates a real-time
capture of the facial expression of the remote participant,especially around the eyes. Thus, the visual display must be

Manuscript received March 14, 2011.
S. Tachi, K. Watanabe, K. Takeshita, K. Minamizawa, T. Yoshida, and
K. Sato are with the Keio University, 4-1-1 Hiyoshi, Kohoku-ku, Yokohama,JAPAN (telephone: +81-45-564-2499; e-mail: {tachi, kouichi, takeshita,kouta, takumi, sato}@tachilab.org).

978-1-61284-455-8/11/$26.00 ©2011 IEEE

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autostereoscopic, otherwise the remote participant appears
with an HMD or special eye glasses, like shutter glasses,
which are unsuitable for face-to-face communication.
Hence, an HMD or a CAVE is not a suitable display tosatisfy both of the first two conditions. TWISTER is suitable,
because this is an immersive omnidirectional full-color
autostereoscopic 3D booth that was designed according to aface-to-face telecommunication concept, a so-called mutual
telexistence, whereby people at distant locations cancommunicate as though present in the same
three-dimensional space. Each user occupies a cylindricalbooth, which displays live full-color 360° autostereoscopic
images without the need for any eyewear. At the same time,
the booth captures images of the user from every angle. With
multiple booths, people at remote locations can interact witheach other as though face-to-face. Moreover, the images ofparticipants can be captured at eye level using the rail camera
system of TWISTER without interrupting their fields of view.
The third condition can be satisfied by using a mobile
surrogate robot with manipulation capability in addition toaudiovisual capabilities. The surrogate robot must move
about freely and capture 360° full-color stereoscopic scenery,
which makes it necessary to design a 360° stereo camera
system that can be mounted on an omnidirectional vehicle.
Figure 1 shows a system that satisfies all three conditions
simultaneously by means of telexistence [15]. Remoteparticipant A in cockpit [A] can telexist through his surrogate
robot A′, while local participants B and C occupy the realenvironment [B]; e.g., an event venue. Cockpit [A] has thecapability to display 3D images of environment [B] in 360°
around participant A, who can enjoy the scenery of the realenvironment [B] without using any eyewear; i.e.,
autostereoscopically by using TWISTER. This 360° stereo
image is captured by a 360° stereo camera system (VORTEX)
mounted on surrogate robot A′. Using measurement andcontrol devices installed in the cockpit, remote participant A
can control his surrogate robot while having a sense ofpresence in the real environment [B]. The control system
consists of a motion capture system, data glove, and joystick.
Local participants B and C can project onto robot A′ theimages taken respectively by cameras B′ and C′, thereby
enabling them to see remote participant A seemingly exist
inside the robot through RPT (retroreflective projection
technology). The movable cameras on a rail installed outside
TWISTER are controlled so that local participants B and C
see remote participant A with respect to their directions fromsurrogate robot A′. The positions of participants B and C are
measured by a motion capture system on the ceiling ofenvironment [B], and the appropriate directional images ofparticipant A are transmitted to participants B and C. Thus,
mutual telexistence is realized.

Fig. 1. Concept of robotic mutual telexistence in a real environment.

The telexistence remote cockpit system consists of theimmersive 360° full-color autostereoscopic display
TWISTER, a rail camera system installed outside TWISTER,
an omnidirectional speaker system, an OptiTrack motion
capture system, a 5DT Data Glove 5 Ultra, a joystick, and a
microphone.
The telexistence surrogate robot system consists of anomnidirectional mobile system, the 360° stereo camera
system VORTEX, a retroreflective screen, an omnidirectional
microphone system, a robot arm with hand, and a speaker.
The RPT viewer system consists of a RPT handheld
projector, RPT head-mounted projector, and OptiTrackposition and posture measurement system.
The three fundamental functions described in section 1 are
installed in the TELESAR 4 system: i.e., (i) presentation of
the real environment—e.g., party venue—including local
participants’ figures and faces in the venue to a remoteparticipant in real time to satisfy condition (1); (ii) RPT
display of the remote participant’s face to the local
participants from any direction at the venue in real time tosatisfy condition (2); and (iii) mobility and manipulation
capability of the surrogate robot by the remote participant tosatisfy condition (3).

III. TELESAR4 SYSTEM CONFIGURATION
Figure 2 shows the overall configuration of the
TELESAR4 system: a telexistence remote cockpit system,
telexistence surrogate robot system, and RPT viewer system.

Fig. 2. System configuration of TELESAR4.

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Stereo images captured by the 360° stereo camera system
VORTEX are fed to a computer (PC1) mounted on the mobile
robot. Real-time compensation and combination of theimages are performed to transform these into 360° images for
TWISTER. The processed images are sent to TWISTER and
unprocessed sound from the omnidirectional microphonesystem is sent directly to the corresponding speaker system in
TWISTER.
Cameras are controlled to move on the circular rail and toimitate the relative positions of the surrogate robot and the
local participants at the venue. The images taken of theremote participant by these cameras outside TWISTER are
fed to a computer (PC3) and sent to another computer (PC2)mounted on the mobile surrogate robot. These images are sent
to the handheld and head-mounted projectors after being
adjusted using the posture information acquired by the
position and posture measurement system (OptiTrack), which
consists of seven infrared cameras installed on the ceiling of
the venue. These processed images are in turn projected onto
the retroreflective screen atop the mobile robot. The voice ofthe remote participant is also sent directly to the speaker ofthe mobile surrogate robot.
The joystick is located inside TWISTER and is controlled
by the left hand of the remote participant. The data of thejoystick are fed to PC3 and sent to PC1 via the network.
Based on the information received, PC1 generates andexecutes a motion instruction to have the mobile surrogate
robot move in any direction or turn freely on the spot; i.e.,
omnidirectional locomotion is possible. Using the motion
capture system (OptiTrack) installed on the ceiling of
TWISTER, the position and posture of the right arm of theremote participant are obtained. The position and posture data
are also fed to PC3 and sent to PC2 via the network. Based on
the received data, PC2 controls the robot arm to imitate thearm motion of the remote participant. In addition, handmotion data acquired by the 5DT Data Glove 5 Ultra are sent
to the hand of the surrogate robot to imitate the hand motionof the remote participant. Figure 3 shows a general view of
the constructed TELESAR4 system.

Fig. 3. General view of TELESAR4 system.

basis. TWISTER V displays binocular stereo images using 36
display units, each consisting of two LED arrays (one per eye)and a parallax barrier that rotates at high speed (1.7 rps). Thissystem captures 3D images of the observer by simultaneously
employing stereo cameras installed outside the rotating
cylinder. Thus, the observers inside two TWISTERs can view
3D images of each other in real time [14]. The horizontal
resolution is 3168 pixels for a 360° horizontal field of view,and the vertical resolution is 600 pixels for a 61.9° verticalfield of view. Figure 4(a) shows the principle of the rotating
parallax barrier method and rail camera attachment, while Fig.
4(b) shows a general view of TWISTER.
Since TWISTER is the only immersive full-color
autostereoscopic display with a 360° omnidirectional view,its use as the visual display is quite reasonable. In order to use
TWISTER as the control cockpit of a mobile surrogate robot,
it was necessary to develop a compatible 360° stereo camera
system.
As the capture device of the omnidirectional image for
TWISTER, we developed the 360° stereo camera system
VORTEX. The principle of the 360° stereo camera system isshown in Fig. 5(a). As shown in the left half of Fig. 5(a), theeyes of a participant move around the rotational axis as thehead is turned. The eyes lie on the circumference of a circle,
maintaining the same distance from each other. If we arrange
an infinite number of stereo camera pairs along thecircumference of the circle, as implied by the right half ofFig. 5(a), then we attain the ideal omnidirectional stereo
camera system. The VORTEX system arranges eight stereo
camera pairs (16 individual cameras) on the circumference ofa circle with a 120 mm radius to match the head and eye
arrangement of the average person. The distance between

IV. FUNCTIONAL EXPERIMENTS ON TELESAR4
A. Capture and display of 360 degree stereo images
TWISTER(telexistence
wide-angle
immersive
stereoscope) is an immersive omnidirectional full-color
autostereoscopic 3D booth that was designed for theface-to-face telecommunication concept of mutual
telexistence, whereby people in distant locations cancommunicate as though present in the same
three-dimensional virtual space. Each user occupies acylindrical booth, which displays live full-color 360°
autostereoscopic images without the need for any eyewear. At
the same time, the booth captures images of the user fromevery angle. With multiple booths, people at remote locations
can interact with each other as though face-to-face.
This concept was proposed in 1996 [13], and five prototype
models, TWISTERs I through V, were constructed on thatabFig. 4. (a) Principle of rotating parallax barrier method and movable stereo
camera attachment. (b) General view of TWISTER.

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each two cameras was set to 65 mm, which is the average
distance between two human eyes. Figure 5(b) shows thedesign concept of VORTEX, Fig. 5(c) shows the dimensionsof the VORTEX design, and Fig. 5(d) shows the constructed
VORTEX.
For each camera, the Firefly MV (Point Grey Research)with a lens of focal length 2.9 mm was used. Its horizontal
and vertical fields of view are 53.2° and 67.8°, respectively.
The resolution is 480 × 640 pixels (horizontal × vertical),which fits the resolution of TWISTER, i.e., 3168 × 600 pixels,
through the use of eight camera images combined byblending.
Each camera is taken offline to conduct the calibration of
the intrinsic parameters; i.e., the lens distortion and therelative orientation between the lens and CCD. The
transformations from camera coordinates to cylindrical
TWISTER coordinates were executed in real time as were therealizations of high dynamic range images that considered thelighting environment. Once processed, the images from thecameras were displayed on TWISTER.
A preliminary directional discrimination experiment using
cardioid unidirectional microphones (Radius 45 HD, Monitor
Audio Ltd.) and speakers revealed a significant difference
between systems composed of four and six of the microphoneand speaker combinations, while there was no difference
between systems composed of six and eight.
Thus, six microphones for the omnidirectional soundsystem were sufficient for our purposes. The six-microphonesystem was designed and placed on top of VORTEX, as
shown in Fig. 5(e). The six speakers were placed on thestationary part of TWISTER at positions corresponding tothose of the microphones.

a

As a demonstration experiment, we selected a room (90m2) as the remote environment and introduced the mobile
surrogate robot. The robot moved about the room to capture
360° images and sound. More than ten men and women, aged
between 23 and 64 years, interacted with this system. All
reported an ability to experience the realistic 360° stereo color
scenery and to feel a strong presence as though the person andscenery in the remote place were in the immediate vicinity.
Figure 6 shows the scenery taken by VORTEX.
B. Projection of remote participant on surrogate robot
In order to realize mutual telexistence, a technology
utilizing a retroreflective material as the projection surface
has been pursued. The original concept was proposed in 1999
[7]. In order to display the face of the remote participant with
the TELESAR4 system, this method for projecting the imageof the human on the robot is used. Local participants at thevenue use the RPT handheld projector [9] or the RPT
head-mounted projector with a half-mirror to view a real-time
image of the remote participant. The principle of RPT isshown in Fig. 7(a), while the structures of the RPT handheld
and head-mounted projectors are shown in Figs. 7(b) and 7(c),respectively.
The head of the mobile surrogate robot is covered withretroreflective material, which is used as a screen. To capture
the image of the remote participant, stereo cameras are
installed on a rail outside TWISTER. These stereo cameras
are controlled to imitate the relative positions of the mobile
surrogate robot and the local participants. Each stereo camera
corresponds to one local participant at the venue. The camera
can look through to the remote participant as TWISTER
rotates, as shown in Fig. 3. Thus, the camera serves to capture
the image of the remote participant from any perspective
outside the display. An active projection corresponding to the
movement of the local participant is enabled by controllingthe camera unit according to position data on the participant
and the mobile surrogate robot.
The robot captures omnidirectional images and soundwhile the rail camera unit outside TWISTER captures images

b

d

c

e

Fig. 5. 360° stereo camera system VORTEX: (a) human eye trajectory as
head rotates; (b) design concept of VORTEX; (c) dimensions of
VORTEX design; (d) constructed VORTEX; and (e) microphonearrangement.

Fig. 6. Scenery taken by VORTEX.

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c
a
a

b

c

d

Fig. 7. (a) Principle of RPT. (b) RPT handheld projector. (c) RPT
head-mounted projector.

bFig. 8. Experimental results for projection of remote participant on RPT
head: (a) remote and local arrangements; (b) local participants at venue; (c)remote participant image from head-mounted projector; and (d) remoteparticipant image from handheld projector.

of the remote participant to project on the head of
the surrogate robot. At the same time, the voice of the remoteparticipant from the microphone is sent to the speaker on thesurrogate robot. Figure 8 shows the experimental results for
RPT viewing. In particular, Fig. 8(c) shows a front view andFig. 8(d) shows a side view. The black dots in Figs. 8(c) and8(d) correspond to holes in the retroreflective screen head at
the lens positions of the 360° stereo camera system.
Figures 8(c) and 8(d) show that two of these 16 holes coincidewith the eye positions of the remote participant on the screen;i.e., the local participants are seen from the eye positions of
the surrogate robot. Thus, face-to-face communication was
simulated. When each of the local participants looked into theeyes of the remote participant on the robot head, virtual eye
contact was thereby established.

safe. A pneumatic robot arm was used for the TELESAR4
system. This robot arm works by using the compressibility of
air and has mechanical compliance [16], which is effective
when the robot interacts with a person through handshaking at
an event. Even if the control program malfunctions, there islittle possibility of the robot harming someone. The arm has 7
DOF and a mass of 2.6 kg. Its upper-arm and forearm lengths
are 300 mm and 220 mm, respectively.
A robot hand with five fingers, electrically driven by DC
motors, was attached to the end of the pneumatic arm. Its
thumb has 3 DOF, while the four remaining fingers have
1 DOF each, and the hand itself has 1 DOF for abduction,yielding a total of 8 DOF. The hand is similar in size to that ofa typical human, with length 185 mm, width 100 mm, andthickness 35 mm. The mass of the hand is 0.5 kg. All
mechanisms such as motors, gears, and encoders are packed
inside the hand, which is connected by a single cable to its
control system; i.e., a servo amplifier and computers.
To achieve locomotion of the surrogate robot and operationof the robot arm simultaneously, the left hand of the remoteparticipant controls the movement of the surrogate robot
through the joystick, while the right hand controls the robot
arm and hand through the OptiTrack system and the data
glove. Specifically, the pneumatic robot arm is controlled by

C. Mobility of surrogate robot with an arm
Omnidirectional mobility is necessary for a surrogate robot
to move about freely on a floor crowded with people, such as
an event venue. Therefore, a truck-type mobile robot that canmove omnidirectionally was designed and developed. This
robot has two drive wheels and one passive wheel. The drive
wheels are controlled by motors to adjust the speed andsteering angle. Figure 9 shows the arrangement of thesewheels. We constructed a locomotion model of the robot andcontrolled the drive wheels through software that applies thismodel to achieve the omnidirectional motion.
A joystick was selected as the input device because its
operation is intuitive. The control of the drive wheels for rigid
movements of translation and rotation is applied using the
locomotion model through rotations of the instantaneous
center. In addition, the model considers the range of steering
motion and applies an inverse wheel rotation when thedesired motion exceeds the steering range.
In order to achieve the embodiment of the remote person in
the surrogate robot, an arm is necessary to get active motion
in addition to mobility. Since contact between a person andthe surrogate robot occurs frequently, the robot arm must be

Fig. 9. Omnidirectional mobility mechanism.

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the motion capture system (OptiTrack) installed within
TWISTER, while the hand is controlled by the data glove.
Figure 10 shows examples of handshaking and gesturing withthe pneumatic robot arm and electrically driven robot hand.
Figure 11 shows a demonstration experiment. A remoteparticipant inside TWISTER joined a gathering by means of
his surrogate robot and moved freely in a room with two local
participants, who were able not only to see his face in realtime through RPT handheld and head-mounted projectors but
also to communicate with him naturally. The local participant
in front of the robot saw the full face of the remote participant,while the local participant on the right side of the robot saw
his right profile at the same time. The remote participant wasable not only to see and hear the environment as though hewere there but also to communicate face-to-face with each
local participant. Moreover, he was able to shake hands andexpress his feelings with gestures.

A local participant in front of the robot saw the full face of theremote participant, while another local participant seeing therobot from its side saw the facial profile of the remoteparticipant.
It was further confirmed that the system allowed the remoteparticipant not only to move freely about the venue by meansof the surrogate robot but also to perform some manipulatory
tasks such as a handshake and several gestures.
ACKNOWLEDGMENT
This work was partly supported by the Strategic
Information and Communications R&D Promotion Program(SCOPE).
REFERENCES[1]

V. CONCLUSIONSWe propose the mutual telexistence surrogate mobile robot
system TELESAR4 to afford a remote person the opportunity
to virtually participate in some event, such as a party, ameeting or a gathering, by using a surrogate robot tocommunicate with local participants of the event whilemoving about freely in the venue. TELESAR4 is constructedfrom an immersive audiovisual system, an omnidirectional
mobile robot with a robot arm and hand, and RPT projectionof the remote participant’s image to the robot.
The TELESAR4 system was implemented as a prototype,and feasibility experiments confirmed that the systemprovided the remote participant with the ability to see theevent venue and local participants as naturally as though at
the event; i.e., a life size 360° wide-range stereo view of theevent venue was observed in real time.
It was also confirmed that face-to-face communication wasprovided, as the local participants at the event were able to see
the face and expressions of the remote participant in real time.

abFig. 10. (a) Handshake. (b) Gestures.

abFig. 11. (a) Remote participant virtually attending an event. (b) Local
participants and surrogate robot in the venue.

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