14th International Symposium on Measurement and Control in Robotics- Robotics for the Changing World Houston, Texas, USA September 16-18,2004

TELEXISTENCE:FUSING VIRTUAL REALITY, ROBOTICS AND NETWORKS TOGETHER
Susumu TACHI
Department of Information Physics & Computing, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 Japan
http://www.star.t.u-tokyo.ac.jp/

Abstract
Telexistence is fundamentally a concept named for thetechnology that enables a human being to have a real-time
sensation of being at a place other than where he or she
actually exists, and to interact with the remote environment,
which may be real, virtual, or a combination of both. It also
refers to an advanced type of teleoperation system thatenables an operator at the control to perform remote tasks
dexterously with the feeling of existing in a surrogate robot.
Although conventional telexistence systems provide anoperator the real-time sensation of being in a remoteenvironment, persons in the remote environment have only
the sensation that a surrogate robot is present, not theoperator. Mutual telexistence aims to solve this problem sothat the existence of the operator is apparent to persons in
the remote environment by providing mutual sensations ofpresence. This paper reviews how the original telexistence
technology has been developed, and describes a newly
developed method of mutual telexistence using projection
technology onto retro-reflective objects dubbed RPT (Retroreflective Projection Technology).

1 Introduction
Telexistence (tele-existence) is a technology that enables us
to control remote objects and communicate with others in aremote environment with a real-time sensation of presenceby using surrogate robots, remote/local computers, andcybernetic human interfaces.
This concept has been
expanded to include the projection of ourselves into
computer-generated virtual environments, and also the use ofa virtual environment for the augmentation of the realenvironment.
Before the concept of telexistence was proposed, there wereseveral systems that aimed for a similar goal. In the U.S.,
Sutherland [1] proposed the first head-mounted display
system, which led to the birth of virtual reality in the late1980s. In Italy, C. Mancini et al. [2] developed a mobile
teleoperated robot system, Mascot, as early as the 1960s. In
France, J. Vertut et al. [3] developed a teleoperation systemthat controlled a submarine for deep submergence

technology in 1977. Although these remote robots were
not a humanoid type and no sensation of presence wasprovided in a strict sense, the systems were closely related tothe concept of telexistence, and can be regarded as its
forerunner.
In order to intuitively control a remote humanoid robot, it isimportant to locally provide the operator a natural sensationof presence as if the operator felt directly in the remote site,by means of visual, auditory, tactile, and force sensations.
The concept of providing an operator with a natural
sensation of presence to facilitate dexterous remote robotic
manipulation tasks was called "telepresence" by Minsky [4]in USA and "telexistence" by Tachi et al. [5] in Japan.
The concept of telexistence was proposed and patented inJapan in 1980 [6], and became the fundamental guiding
principle of the eight year Japanese National Large Scale
Project of "Advanced Robot Technology in Hazardous
Environments," which was initiated in 1983 together withthe concept of Third Generation Robotics. Through thisproject, we made theoretical considerations, establishedsystematic design procedures, developed experimental
hardware telexistence systems, and demonstrated thefeasibility of the concept.
Through the efforts of twenty years of research anddevelopment in the U.S., Europe and Japan [7-24], it has
nearly become possible for humans to use a humanoid robot
in a remote environment as if it was an other self, i.e. they
are able to have the sensation of being just inside the robot in
the remote environment.
Although existing telexistence systems succeeded inproviding an operator a real-time sensation of being in aremote environment, human observers in the remoteenvironment did not have the sensation that the humanoperator is presented, but only a surrogate robot. Mutual
telexistence addresses this problem so that the existence ofthe operator is apparent by persons in the remoteenvironment by providing mutual sensations of presence [25,26].

S.TachiThis paper reviews the original telexistence technology, andintroduces a method of mutual telexistence based on the
projection of real-time images of the operator on thesurrogate robot, based on newly developed technology
dubbed RPT (Retro-reflective Projection Technology).

2 Short History of Telexistence
Figure 1 shows the concept of telexistence in realenvironments, virtual environments, and the realenvironment through a virtual environment (augmented
telexistence). The following describes the research anddevelopment conducted in order to realize the concept.
Our first report [5, 8] proposed the principle of thetelexistence sensory display, and explicitly defined its design
procedure. The feasibility of a visual display with asensation of presence was demonstrated throughpsychophysical measurements using experimental visualtelexistence apparatus.
A method was also proposed to develop a mobile
telexistence system that can be driven remotely with both anauditory and visual sensation of presence. A prototype
mobile televehicle system was constructed and the feasibilityof the method was evaluated [12].

Augmented telexistence can be effectively used in numerous
situations. For instance, to control a slave robot in a poor
visibility environment, an experimental augmented
telexistence system was developed that uses a virtualenvironment model constructed from design data of the realenvironment. To use augmented reality in the control of aslave robot, a calibration system using image measurements
was proposed for matching the real environment and theenvironment model [16, 17].
The slave robot has an impedance control mechanism forcontact tasks and to compensate for errors that remain evenafter calibration. An experimental operation in a poor
visibility environment was successfully conducted by using
a humanoid robot called TELESAR (TELExistence
Surrogate Anthropomorphic Robot) (Fig.2) and its virtual
dual. Figure 3 shows the virtual TELESAR used in theexperiment and Figure 4 shows the master system for thecontrol of both real TELESAR and virtual TELESAR.
Experimental studies of tracking tasks demonstrated
quantitatively that a human being can telexist in a remote
and/or a computer-generated environment by using thededicated telexistence master slave system [15].
A networked telexistence paradigm called R-cubed (Realtime Remote Robotics) was proposed in 1985, and several
pertinent ongoing research efforts are being conducted,
including a real-time remote robot manipulation language
dubbed RCML [18, 19].

Fig.1 Concept of Telexistence.

In 1989, a preliminary evaluation experiment of telexistence
was conducted with the first prototype telexistence masterslave system for remote manipulation. An experimental
telexistence system for real and/or virtual environments was
designed and developed, and the efficacy and superiority ofthe telexistence master-slave system over conventional
master-slave systems was demonstrated experimentally [13,14, 15].

Fig. 3 Virtual TELESAR at Work (1993).

Fig. 4 Telexistence Master (1989).

Fig. 2 Telexistence Surrogate Anthropomorphic Robot (TELESAR) at
Work (1988).

Telexistence technology was adapted in the national fiveyear Humanoid Robotics Project (HRP) sponsored by the
Ministry of Economy, Trade and Industry (METI) to develop
a new type of cockpit system to control a humanoid bipedal
robot, as shown in Figure 5. The telexistence cockpit was14th International Symposium on Measurement and Control in Robotics- Robotics for the Changing World Houston, Texas, USA September 16-18,2004

completed for this project in March 2000 (Fig 6). It consistsof three main subsystems: an audio/visual display subsystem,a teleoperation master subsystem, and a communication
subsystem between the cockpit and the humanoid robot [20,21, 22, 24].

Fig.5 HRP Humanoid Robot at Work (2000).

Various teleoperation experiments using the developedtelexistence master system confirmed that kinesthetic
presentation through the master system with visual imagery
greatly improves both the operator's sensation of walking,and dexterity at manipulating objects.
If the operator issued a command to move the robot, therobot actually walked to the goal. As the robot walked
around, real images captured by a wide field of view multicamera system were displayed on four screens of thesurrounded visual display. This made the operator feel as if
he or she was inside the robot, walking around the robot site.

sensed the remote environment directly. Persons canvirtually exist in the remote environment without actually
being there.
For observers in the remote environment, however, thesituation is quite different: they see only the robot moving
and speaking. Although they can hear the voice and witness
the behaviour of the human operator through the robot, it
does not actually look like him or her. This means that thetelexistence is not yet mutual. In order to realize mutual
telexistence, we have been pursuing the use of projection
technology with retro-reflective material as a surface, which
we call RPT (Retro-reflective Projection Technology) [25,26].

3 Retro-reflective Projection Technology(RPT)
Two classic virtual reality visual display types are the Head
Mounted Display (HMD) and IPT (Immersive Projection
Technology), which although quite useful, are not without
their shortcomings, as shown in Figure 7 (C) and (D),respectively. The former has a tradeoff of high resolution
and wide field of view, and the latter has problems
concerning the user's body casting shadows on a virtualenvironment, and the interaction between the user's real
body and the virtual interface. In addition, both displays
have problems concerning occlusion when in use under theaugmented reality condition, i.e. virtual objects and real
objects are mixed.
Figure 7 (A) shows a virtual vase and a virtual ashtray on a
virtual desk. When a real hand is placed between two virtual
objects, an ideal occlusion should be depicted as in Figure 7(B), i.e., the real hand occludes the virtual vase and is
occluded by the virtual ashtray. However, a real hand cannot
occlude the virtual vase nor be occluded by the virtual
ashtray when an optical see-through HMD is used to display
virtual objects, and the hand and the ashtray look as if they
are transparent. This is simply due to the fact that thephysical display position of an HMD is always just in frontof the eyes of the user.

Fig.6 Telexistence Cockpit for Humanoid Control (2000).

A CG model of the robot in the virtual environment wasrepresented and updated according to the current locationand orientation received from sensors on the real robot. The
model was displayed on the bottom-right screen of thesurround visual display, and by augmenting real images
captured by the camera system, it supported the operator'snavigation of the robot. Since the series of real images
presented on the visual display are integrated with the
movement of the motion base, the operator feels the realtime sensation of stepping up and down.
Persons can control the robot by just moving their bodies
naturally, without using verbal commands. The robot
conforms to the person's motion, and through sensors on
board the robot the human can see, hear and feel as if theyFig. 7 (A) A virtual vase and a virtual ashtray on a virtual desk; (B) An
ideal occlusion when a real hand is placed between two virtual objects;(C) Unfavorable results when optical see-through HMD is used; (D)Unfavorable results when IPT (Immersive Projection Technology) like
CAVE is used.

S.TachiConversely, the virtual ashtray cannot occlude a real handwhen IPT like the CAVE (CAVE Automatic Virtual
Environment) is used, as shown in Figure 7 (D). This is dueto the fact that the display position of virtual objects isalways on the screen surface, which is one to two meters
away from the human user when IPT displays are used.
In our laboratory at the University of Tokyo, a new type ofvisual display is being developed called X'tal (pronounced
crystal) vision [27,28,29,30], which uses retro-reflective
material as its projection surface. We call this type of
display technology RPT (Retro-reflective Projection
Technology).
Under the RPT configuration, a projector is arranged at theaxial symmetric position of a user's eye with reference to ahalf-mirror, with a pinhole placed in front of the projector toensure adequate depth of focus, as shown in Figure 8.
Images are projected onto a screen that is constructed,
painted, or covered with retro-reflective material [27].

Fig.8 The principle of RPT system.

A retro-reflective surface reflects back the projected light
only in the direction of projection, while conventional
screens normally used for IPT scatter projected lights in all
directions ideally as a Lambertian surface (Fig.9). Figure 10
shows how a retro-reflective surface behaves. It is covered
with microscopic beads of about 50 micrometers in diameter,
which reflect the incident light back to the incident direction.
It can also be realized with a microstructure of prism-shaped
retro-reflectors densely placed on a surface.

Fig. 9 Three typical reflections.

Fig. 10 Retro-reflective surface densely covered with microscopic beads
with about 50 micrometer diameter. Ideally, the refractive index shouldbe 2.

The retro-reflector screen, together with the pinhole, ensuresthat the user always sees images with accurate occlusion
relations. In the construction of an RPT system, screen
shapes are arbitrary, i.e., any shape is possible. This is due tothe characteristics of the retro-reflector, and the pinhole inthe conjugate optical system.
By using the same characteristics of an RPT system,
binocular stereovision becomes possible using only one
screen with an arbitrary shape. Figure 11 shows how
stereovision can be realized using RTP. In the figure, theDisplay Unit is an arbitrarily shaped object covered or
painted with retro-reflective material. The light projected by
the right projector is retro-reflected on the surface of thedisplay unit and is observed by the right eye, while the light
projected by the left projector is retro-reflected also by thesame display surface and can be observed by the left eye.
By using the same display surface, the right eye observes theimage projected by the right projector and the left eyeobserves the image projected by the left projector. Thus bygenerating CG images with appropriate disparity, the humanobserver perceives the stereo view of an object at theposition of the display unit. By using measurements of theposition sensor on the display unit, it is possible to display athree-dimensional object image, which changes its
appearance according to the position and orientation
indicated by the motion of the display. This enables the user
to have the sensation that he or she is handling a real object.
The projector can be mounted on the head of a user, which
we call an HMP (Head Mounted Projector) system. Figure
12 shows a general view of a prototype HMP.

14th International Symposium on Measurement and Control in Robotics- Robotics for the Changing World Houston, Texas, USA September 16-18,2004

Fig.11 Principle of stereo display using RPT.

Fig. 12 General view of a Head Mounted Projector (HMP).

Figure 13 shows an example of an image projected on asphere painted with retro-reflective material. As apparent in
the figure, the projected image looks like a real object, and ispartly hindered naturally by human fingers.

Fig. 14 Another example of application of RPT to optical camouflage.

Fig. 15 A schematic diagram of the RPT system used for the opticalcamouflage in Fig.14.

Fig.13 Projected image on a spherical retro-reflective screen.

Figure 14 shows how optical camouflage can be achieved
using real-time video information. Figure 15 shows how
RPT is applied to realize the situation of Figure 14. The coatis made of retro-reflective material so that the coming lightis reflected back to the same direction that it comes from.
Microscopic beads on the surface of the coat have thefunction of retro-reflection.
A half mirror makes it possible for a spectator to see
virtually from the position of the projector. An HMP projects
an image of the background scenery captured by the video
camera behind the camouflaged subject. A computer
calculates the appropriate perspective and transforms thecaptured image to the image to be projected on the subject
using image-based rendering techniques. Since the cloak thesubject is wearing is made of a special retro-reflective
material, which reflects back the incident light just the same
direction it comes from, an observer looking through a half
mirror sees a very bright image of the scenery so that he isvirtually transparent.

4 Mutual Telexistence using RPT
More than twenty years have passed since we initially
proposed the concept of telexistence, and it is now possible
to telexist in the remote and/or virtual environment with asensation of presence. We can work and act with the feelingthat we are present in several real places at once. However,in the location where the user telexists, people see only the
robot but cannot feel that the person is actually present.
Simply placing a TV display on board the robot to show theface of the user is not very satisfying, since it appears mostly
comical and far from reality.
By using RPT, the problem can be solved as shown in Figure
16 [25]: suppose a human user A uses his telexistence robot
A' at the remote site where another human user B is present.
The user B in turn uses another telexistence robot B', which
exists in the site where the user A works. 3-D images of theremote scenery are captured by cameras on board both
robots A' and B', and are sent to the HMP's of human users
A and B respectively, both with a sensation of presence.
Both telexistence robots A' and B' are seen as if they were
their respective human users by projecting the real image ofthe users onto their respective robots.

S.TachiMotion Control / Tactile Control
Visual & Auditory Information

HMP

3D image observed by
Telexistence Robot B’is projected and observedby Human User B witha sensation of presence.

3D image observed by
Telexistence Robot A’
is projected and observed by
Human User A with asensation of presence.

Human
User A

Telexistence
Robot A’

Telexistence Robot B’
Telexistence Robot B’ isobserved as if it is Human
User B by the projectionof real image of B on
the robot B’.

Telexistence Robot A’ is HMP
observed as if it is Human
User A by the projectionof real image of A on
the robot A’.

Human
User B

Mutual telexistence is one of the most important
technologies for the realization of networked telexistence,
because users "telexisting" in a robot must know whom they
are working with over the network. A method using RPT,
especially an HMP and a robot with retro-reflective covering
was proposed and proved to be a promising approach toward
the realization of mutual telexistence.
In this paper, a short history of telexistence is reviewed,
mutual telexistencethe principle of RPT is explained, and an
experimental mutual telexistence system using RPT was
designed and constructed to demonstrate its feasibility andefficacy.

Visual & Auditory Information
Motion Control / Tactile Control

Fig. 16 Concept of Robotic Mutual Telexistence (adopted from [25]).

6 Acknowledgments
The research presented here has been conducted in part under
the CREST Telexistence Communication Systems Project,supported by JST (Japan Science and Technology Corporation).

7 References[1] I.E.Sutherland: A Head-Mounted Three Dimensional
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Fig. 17 (A) Miniature of the HONDA Humanoid Robot,(B) Painted with Retro-reflective Material,(C) Example of Projecting a Human onto it,(D) Another Example (adopted from [25]).

Figure 17 presents an example of how mutual telexistence
can be achieved through the use of RPT. Figure 17(A)shows a miniature of the HONDA Humanoid Robot, while
Figure 17(B) shows the robot painted with retro-reflective
material. Figures 17(C) and (D) show how they appear to ahuman wearing an HMP. The telexisted robot looks just likethe human operator of the robot, and telexistence can benaturally performed [25, 31, 32]. However, this preliminary
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experiments are yet to be conducted by constructing andusing a mutual telexistence hardware systetem.
An experimental mutual telexistence system using RPT has
been designed and constructed [33].

5 Conclusions
Projection technology on Retro-reflective surfaces is called
RPT (Retro-reflective Projection technology), which is a
new approach to augmented reality (AR). The first
demonstration of RPT together with HMP (Head Mounted
Projector) was made at SIGGRAPH98, followed bydemonstrations at SIGGRAPH99 and SIGGRAPH2000.

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