left-footFantastic Phantom Slipperright-foot
Akihiko Shirai1)、Masaru Sato2)、Yuichiro Kume1)、Machiko Kusahara2)

1) Faculty of Engineering, Tokyo Institute of Polytechnics
2) Faculty of Arts, Tokyo Institute of Polytechnics

MOVIE (By Masaru Sato、WMV format、2MB, Sorry for Japanese Naration)

Most virtual reality systems use upper body parts, such as eyes, ears, arms and hands, for the interactions, and much information is concentrated to them. This situation is caused by some restrictions of current interface devices. People should be able to move and act freely in virtual environments as they do in the real world. People usually move with their legs and feet in the real world. We believe that they should be able to move freely with their legs and feet in virtual worlds.

From this viewpoint, we have developed a multimodal interface using human feet. Feet movements of the users are measured by a real-time optical motion capture system. The feedback information is transmitted to the users through tactile sensation on the feet, namely to the soles. These functions are realized by specially developed slippers. The only device the user should wear is a pair of the slippers, and he/she can move and act freely. Since we are accustomed to wear shoes, wearing such slippers, do not cause psychological/physical discomforts. Utilizing key technologies we have developed, we constructed an interactive amusement system using foot interface, "Fantastic Phantom Slipper".


A player sees a hemispherical floor screen and a pair of slippers in front of him/her. As a player wears the slippers, an internet browser-like opening page appears on the floor screen. It represents our concept behind: walking around in cyber spaces with one's own feet, not by clicking a mouse. The player can select one of the icons by stepping on it. As soon as the player steps on one of them, a journey to a cyber space starts.

There are two cyber worlds, each of them linked to one of the icons on the top of the opening page. One is a game world named "Mouse Attacks". A troop of mice are running around the player's feet. When the mice are close to the feet, the player feels vibration on the soles and recognize the mice's movement. This sensation enhances the reality, and the player can perceive the mice's movement through tactile sensation of the sole. Points are earned by stamping on the mice, and there are bonus points for stamping them on with both feet. When the time is over, the player returns to the opening page.

The other world is "Space World". When the player steps on the Space World icon, a space voyage starts. When the player travels toward a planet, a dragon head flies around the player's feet. When the player kicks the dragon head quickly, it goes away from the display and then return to the display. After the limited playing time passes, the planet collides with the player, and the player returns to the opening page.


Real-time Optical Motion Capture System Using PSD

We employ a semiconductor position sensing device(PSD) and infrared light emitting diode(LEDs) makers for motion capturing. In the Fantastic Phantom Slipper, two LEDs are fixed on each slipper. The locations and directions of slippers on the floor are measured in real-time. Since feet is usually on floor, two dimensional measurement is sufficient for this application.

Phantom Sensation

When two mechanical stimuli of the same intensity are applied to different locations of skin surface with appropriate spacing, two stimuli are fused and one sensation is perceived. When the intensity of one stimulus increases, the location of fused sensation shifts to the location of stronger stimulus. This psychophysical phenomenon has been known as phantom sensation, which was found by Bekesy, a Novel Prize Winner in 1961.

When people work on foot, various kinds of information, such as pressure, ruggedness and inclination of floors, are perceived through the skin sensations of their soles. We employ phantom sensation to transmit such kinds of information. In order to elicit phantom sensation, we use tiny vibration motors. The vibratorsfig are set in the sole of the slippers. Two vibrators are set in each sole. Fused sensation can be moved two-dimensionally around the feet, by controlling the intensities of the four vibrators appropriately.


The system configuration is schematically illustrated in right figure. A player wears the slippers, and the locations and motions of the feet are measured by the PSD camera. Two dimensional positions of LEDs on the slippers are obtained through analog calculation electronics, and the PC obtains the positions through A/D converter. The PC under Windows 95 and Direct 3D running generates graphics. The PC drives four vibrators through D/A converters. The entire system stands alone, and is controlled by only the PC.

(Click here to see the appearance of the system)

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