TORSO- Completion of Egocentric Telegnosis System Kouichi WATANABE∗
The University of Tokyo

Ichiro KAWABUCHI†KAWABUCHI Mechanical Engineering Laboratory, Inc.
Taro MAEDA§
Susumu TACHI¶
Osaka University
The University of Tokyo

Naoki KAWAKAMI‡The University of Tokyo

Abstract
We have proposed a system that can acquire natural and comfortable visual information and can accurately track the head motionof the person. The conventional imaging device for head-mounted
display was only able to express the 3-axis rotation of the neck but
our device has expressed the head motion as well as the translation
motion of the neck.
Keywords: Telexistence, Master-Slave, Torso, Head motion

1Overview

From a long time it has been the desire of human beings to project
themselves into a remote environment, i.e., to create the sensationof existence in a different place while actually maintaining theirposition. The phenomenon of projecting ourselves by using robots,computers, and a cybernetic human interface is called telexistence.
The operator of the robot can experience the sensation of existence
at a different location and behave as though he exists in the sameenvironment. Moreover, the operator can ideally meet and interact
with the person of the remote environment without any uncomfortable sensation. To achieve these goals, it is necessary to accurately
reconstruct the information of the operator’s position and posture
in a remote environment. Meanwhile, it is necessary to accurately
display the information of the remote environment to the operator.
In particular, the visual information constitutes a major part of it.
Therefore, it is indispensable to accurately acquire and display thisinformation in order to achieve the telexistence system.
At present, most of the imaging devices that are mounted on theremote robot for the purpose of the binocular head-mounted display
have two stereocameras with three rotational degrees of freedom;
they are positioned at the same level of a man’s neck. However,this cannot completely express the head motion that includes thetranslational motion of the neck.
We propose a system that achieves the acquisition of the naturaland comfortable visual information and the accurate tracking of thehead motion of a person. We have developed the neck and torsoof the all-in-one robot that not only has three rotational degrees ofFigure 1: Torso Robot.

freedom of the neck but also two rotational degrees of freedom andone translational degree of freedom of the waist. This device isshown in Figure 1. The head motion that could not be attained by aconventional robot head became achievable because it was possible
to express the translational motion of the neck by adding the threedegrees of freedom of the waist. For example, the motion of looking
around for an object and the motion of stretching became possible.
Moreover, the head portion of this robot can follow the operator’shead motion in real time because it is light.
In future, this robot will form an important part of robot-humancoexistence in the society.

∗ e-mail: Kouichi Watanabe@ipc.i.u-tokyo.ac.jp† e-mail:info@kawabuchi-lab.com‡ e-mail:kawakami@star.t.u-tokyo.ac.jp§ e-mail:t maeda@ist.osaka-u.ac.jp

2 Vision¶ e-mail:tachi@star.t.u-tokyo.ac.jp

The future goal of this project is the completion of an entire telexistence system.
In future, we should be able to treat the robot just like ourselves
so that it will lead to robot-human coexistence in the society. We
have focused on achieving accurate head motion, and our proposed
device concentrated on the acquisition and display of natural visual
information. In the near future, we would be able to create a surro-gate anthropomorphic robot that has a very high degree of realistic
sensation and presence by attaching an arm that is light and can beeasily maneuvered. This system not only forms a part of the future
robots but is also one of the complete robot forms.
Even though many telexistence systems have been developed, theproblems of realization of ”realistic sensation” and ”presence” have
not yet been achieved. Our proposed system can achieve the realistic sensation and the presence of movement. By capturing the visual
information of a remote robot that accurately reflects the head motion of the operator, the visual information obtained by the operator
will have a higher realistic sensation. Moreover, in a remote environment, since the head motion of the operator is accurately presented to a remote robot, the remote robot would be able to achieve
the presence of movement.
This device provides a large amount of information to the telecommunication system. For example, although a remote meeting system now primarily contains the video telephone, we will be able
to obtain a sensation as if we are actually participating in a meeting in a remote meeting room by using this system. Thereby themeeting will become invigorated debates. Moreover, in the present
shopping networks, we can obtain the information of commercialproducts only from a picture or statement. If our device is used, wewill be able to obtain this information of commercial products byactually viewing it. In addition, we can propose a new type of system and not only the extension of the telecommunication system.
For example, we can see ourselves from a second or third person
view. As a result, we will be able to propose a new sensation.

3

Technical innovation

The feature of this system is that it can express the six degrees of
freedom of the upper body as well as the translation motion of theneck; it can also obtain natural visual information that is equivalent
to human motion. Further details of this system are described asfollows.

3.1

System configration

This system has a master/slave configuration as shown in Figure
2. In the master side, the operator’s head position and posture ismeasured by a sensor, e.g., potentiometer. Further, the operator
employs the HMD or HMP that can project a remote environment
image. The data acquired by the sensor is transmitted to the slave
side. In the slave side, the motion angle of each joint is calculatedusing the data transmitted by the master, then the calculated values
are sent to each joint. Simultaneously, a remote environment image
that is captured by two cameras is transmitted to the master side.

3.2

Institution of deviceThe accurate head motion of the human can be achieved by theneck and torso all-in-one robot that has not only the three rotational
degrees of freedom of a neck but also the two rotation degrees of
freedom and one translational degree of freedom of the waist. The
conventional imaging device for the head-mounted display could
achieve only three axes of rotation of the neck. Our device can not
only express the three rotational degrees of freedom of the neck but
also its translational motion. Therefore, it is possible to achieve
the head motion in a remote environment that is almost similar tohuman motion.

Figure 3: Schematic representation of the Torso.

The dimensions and available range of each joint of our device areshown in Figure 3.
The three rotational degrees of freedom of the head are arranged
so that each of the axes intersects at one point (Figure 4). The
two rotational degrees of freedom of the waist are also arrangedin the same manner. This allocation of the degrees of freedom isalmost equivalent to the allocation of the degrees of freedom of ahuman. The translation degree of freedom of the waist not only enables stretch motion but also resolves the difference of body height
among individuals. The range of motion of each joint is slightly
narrower than the range of human; however, it would be sufficientif the human executes natural movement. In Figure 5, we show thecomparison of the movable range of the joint of human with that ofour device. The driving performance of each joint is adequate because each joint moves at a speed higher than the maximum speedof the motion of a human head. In the head part, two CCD cameras(diameter of 7 mm) are installed and the distance between both thecameras is almost the same as that of the eyes of the human (65mm). The angle of view of the camera is about 45 along the horizontal. This angle of view is in good agreement with the field ofview of the head-mounted display or head-mounted projector.

3.3 Tracking performance
We have already evaluated the tracking performance of our device.
First, we measured the maximum frequency of the back-and-forthmotion of the head yaw rotation and the waist pitch rotation. Then,
we introduced a sinusoidal signal with known frequency into thehead yaw joint and the waist pitch joint of our device. We evaluatedthe time of delay from the input of signal to the start of motion. WeMasterSlave

remote image
image

position&posturehead sensor
Control
PC

Display

Network
position
postureimage

Control
PCCamerareference angle

Motor
Encoder
joint angle

Figure 2: The Schematic Representation of the System.

60deg

CCD Camera

60deg

40deg

180deg 180deg
40deg

50deg

30deg

50deg

30deg
30deg 30deg

Rotational
Axis

Intersection
Point30deg
45deg
50deg 60deg

584.7mm

4 Context
The head-mounted display [Sutherland 1968] or the head-mounted
projector [Inami et al. 1999] and other projection-based virtual reality systems such as CAVE [Cruz-Neira et al. 1993] have been

45deg

30deg
45deg

600.0±100mm

Figure 5: Movable Range of Joint.

Figure 4: Head of the Torso.

observed in the result that the time of delay of the head yaw rotation
joint was 2 3 ms and that of the waist pitch rotation joint was 1ms. The influence of the tracking delay on the display of image isvery small because the frequency of the camera was 60 Hz, i.e., it
captures image at 17 ms time periods.

30deg

developed.
The imaging device for the projection-based virtual reality systemsuch as CAVE was proposed. [Yanagida et al. 1999]
Their proposed method is to maintain the orientation of the cameras, regardless of the orientation of the operator’s head. Their proposed device ”constant-oriented link” can solve the problems involved in constructing the exact head-tracked stereoscopic display
using fixed-screen display systems. This is owing to the change inthe shape of the viewing volume and the rotation of direction of thecamera according to the operator’s head motion (Figure 6).
In contrast, the imaging device for HMD or HMP generally has thethree rotational degrees of freedom at the neck. For example, HRP

I NAMI , M., K AWAKAMI , N., S EKIGUCHI , D., M AEDA , T., AND
TACHI , S. 1999. Head-mounted projector. In Conference Abstracts and Applications of SIGGRAPH ’99, 179.
S UTHERLAND , I. E. 1968. A head-mounted three dimensional display. In Proceedings of Fal Joint Computer Conference, AFIPSConf. Proc., 757–764.
YANAGIDA , Y., M ITSUHASHI , A., M AEDA , T., AND TACHI , S.
1999. Implementation of fixed-screen-based telexistence visualsystem. In Proceedings of the ICAT ’99 (9th International Conference on Artificial Reality and Telexistence), 123–130.

Figure 6: Constant-orientation Link.
HMD
Torso Robot
Own Image

1~2 m

Figure 7: Plan of SIGGRAPH 2007.

and ASIMO employ such a device.
The goal of our project is to obtain the sensation of existence ina remote place. However, it is difficult to achieve this goal ina projection-based system wherein the operator can see his own
hands and legs. Also, the imaging device for HMD or HMP cannot express the translation motion of the human neck; therefore,
the operator experiences image mismatching. The HRP solved thisproblem by using an additional camera that captures the surrounding image. We tried to solve this problem by using the method thatis proposed in this paper.

5 User Experience
This device is positioned at a distance from the participant and facing towards the participant (Figure 7). The participant wears HMD
and experiences the image transmitted by the slave. Here, we have
employed only one device. The participant can experience his own
image from the view of second person. In addition, the participant
can throw a soft object (for example, soft ball, soft arrow, etc.) towards the device for interaction. The participant experiences anuncanny feeling by avoiding and receiving it.

References
C RUZ -N EIRA , C., S ANDIN , D. J., AND D E FANTI , T. A. 1993.
Surround-screen projection-based virtual reality: The design andimplementation of the cave. In Proceedings of SIGGRAPH ’93,135–142.