ForceTile:Tabletop Tangible Interface with Vision-based Force Distribution Sensing
Yasuaki Kakehi∗
Kensei Jo†
Katsunori Sato†Kouta Minamizawa††††
Hideaki Nii
Naoki Kawakami
Takeshi Naemura
Susumu Tachi†∗ Presto, Japan Science and Technology Agency† The University of Tokyo

Figure 1: Photo Viewer with ForceTiles

1Figure 2: Pinching/stretching interaction

Introduction

Today, placing physical objects on a tabletop display is common for
intuitive tangible input [Ullmer and Ishii 1997]. The overall goal ofour project is to increase the interactivity of tabletop tangible interfaces. To achieve this goal, we propose a novel tabletop tangibleinterface named ‘ForceTile.’ This interface can detect the force distribution on its surface as well as its position, rotation and ID by using a vision-based approach. In our previous optical force sensors“GelForce” [Kamiyama et al. 2004], an elastic body and cameras
are fixed together. Contrarily, on this system, users can place andmove multiple tile-shaped interfaces on the tabletop display freely.
Furthermore, users can interact with projected images on the tabletop screen by moving, pushing or pinching the ForceTiles.

2

Technical Innovations of ForceTile

In our ForceTile, we offer core technical innovations as following.
One is the design of the interface and the table-based camera system
to detect the force distributions of each tiles on the tabletop. The tileinterface consists of a transparent acrylic case filled with an elastic
body, two layers of markers attached within the body for the force
distribution sensing and a marker attached underneath the case forthe position sensing. Inside the table, cameras and IR light emitters
are installed underneath. When users put ForceTiles on the tabletop,
the system detects their locations and ID by the shape of position
marker. Furthermore, to calculate the force vectors on the surface,
we adopt the method of GelForce. When forces are applied on thesurface of the ForceTile, this system derives the force vectors bydetecting the internal strain of the body through the movement of
the force markers. Note that no electric devices are attached on thetabletop interfaces and users need not wear any special equipment
for interaction.
Secondly, this system can show images on the tabletop screen andForceTile surfaces. By making a force marker with a transparent
heat insulating material that passes the visible incoming light andblocks the infrared incoming light, this system can adopt a back∗ e-mail: tabletop@hc.ic.i.u-tokyo.ac.jp

Copyright is held by the author / owner(s).
SIGGRAPH 2008, Los Angeles, California, August 11–15, 2008.
ISBN 978-1-60558-466-9/08/0008

Figure 3: Interaction with force vectors

projection so that the interface bodies and user’s hands don’t disturb
the projection light.
Third innovation is a software architecture design for recognizing
users’ actions and generating projection images. According to various input information such as position, rotation, ID of tiles, intensity and direction of forces applied on them, users can control
projected images in real-time.

3Applications

While ForceTile offers brand new interactions on tabletop, it can integrate several functions of previous interfaces simultaneously suchas touch panel, pointing device (i.e. mouse), tangible physical interface and small-sized screen. We have already implemented someinteractive applications.
One is photo viewer application (see Figure 1). Initially photo images are displayed on the tabletop. By pushing the ForceTiles, youcan change the displayed photo or the image size. In the second application, you can control the tabletop image with multiple fingers.
When you pinch or stretch the tile’s surface, the scale of the tabletop image changes according to the intensity and the direction of
the force (see Figure 2). The third application is for entertainment.
On the tabletop screen, an image of a lady beetle is walking around.
When you cover the ForceTile on the lady beetle and apply a force
on it, it flys away according to the magnitude and direction of theapplied force as Figure 3. In the future, we plan to develop much
more applications by using the ForceTiles in various situations.

References
K AMIYAMA , K., K AJIMOTO , H., K AWAKAMI , N., M IZOTA , T.,
TACHI , S., AND V LACK , K. 2004. GelForce. In SIGGRAPH
Emerging Technologies, ACM.
U LLMER , B., AND I SHII , H. 1997. The metadesk: Modelsand Prototypes for Tangible User Interfaces. In Proceedings ofUIST’97, ACM, 223–232.