Introduction
CirculaFloor is a locomotion interface using a group of movable tiles. The movable tiles employ holonomic mechanism that achieves omni-directional motion. Circulation of the tiles enables the user to walk in virtual environment while his/her position is maintained. The user can walk in arbitrary direction in virtual environment. This project is a joint research with ATR Media Information Science Labs.
Basic Design of the CirculaFloor
Locomotion interfaces often require bulky hardware, because they have to carry whole body of the user. Also, the hardware is not easy to reconfigure to improve its performance or add new functions. Considering these issues, the goals of the CirculaFloor project are:
(1) To develop compact hardware for creation of infinite surface for walking.
The major disadvantage of existing locomotion interface is difficulty in its installation. We have to solve this problem for demonstration in SIGGRAPH2004.
(2) To develop scalable hardware architecture for future improvement of the system.
Another disadvantage of existing locomotion interface is difficulty in improvement of the system. We have to design a new hardware architecture in which we can easily upgrade the actuation mechanism or add new mechanism for creation of uneven surface
In order to achieve these goals, we designed a new configuration of locomotion interface by the use of a group of omni-directional movable tiles. Each tile is equipped with a holonomic mechanism that achieves omni-directional motion. Infinite surface is simulated by circulation of the movable tiles. The motion of the feet is measured by position sensors. The tile moves opposite to the measured direction of the walker, so that motion of the step is canceled. The position of the walker is fixed in the real world by this computer-controlled motion of the tiles. The circulation of the tiles has an ability to cancel the displacement of the walker in arbitrary direction. Thus, the walker can freely change direction while walking.
Fig.1 Overview of CirculaFloor
Fig.2 System configuration
Implementation of a prototype system
The hardware configuration and overview of the CirculaFloor system are shown in Figure 1 and 2. For the movable tiles, we use four holonomic omni-directional vehicles known as the Vmax Carrier made by RITECHS. The size of the movable tile is 568mm (W)x568mm (D)x92mm (H). Each tile weighs 16.2kg, and has ability to carry 80kg payload in 1200mm/s. To avoid getting tangled up the communication lines between the movable tiles and PC for controlling the tiles, the movable tiles and the PC are equipped with wireless RS232c modules. Also for position sensing of the tiles, we use a wireless ultrasonic position sensor known as the IS-600 mark2 made by InterSense. Two position sensors put on each movable tile, so that its position and orientation are measured. The positions of the walker is measured with a Laser range finder, the LMS200, made by SICK so that the user can walk with no sensor attachment. The operating system of the PC is Windows XP, and we developed all of the software using C language with VC++.
Creation omni-directional infinite surface
The method of circulation of the movable tiles can be divided into 2 phases; (1) detection of walking, (2) circulation of movable tiles.
Figure 3. Method of detection of walking motion
Detection of walking
The user’s position in virtual space is updated corresponding to the results of motion tracking of the feet.
Figure 3 illustrates basic idea of the detection of walking. A circular dead zone is placed in the center of the walking area. In this study, the dead zone is 200 mm diameter circle. The positions of the walker’s knees are measured by position sensors. The midpoint between these sensors can be assumed to be a central point below the body. Point G in Figure 3 represents the projection of the central position of the walker. The movable tiles don’t move while the point G is inside the dead zone. If the point G leaves the dead zone, the tiles move so that the point G returns to this area. The direction and distance between the point G and the circle determines the pulling back direction and velocity of the tiles respectively.
Circulation of movable tiles
Current circulation method of the movable tiles is designed to satisfy following conditions; (1) two of the movable tiles are used for pulling back the user to center of the dead zone. (2) The rest of the movable tiles are used for creation of a new front surface. (3) These tiles move the shortest distances to the next destination, while they avoid colliding other tiles. (4) Control program allocates all destinations of the tiles, when the tiles reach their destinations. (5) The tiles don’t rotate corresponding to walking direction for simplification of the algorism. (6) The walker can change walking direction anytime.
Considering above conditions, the circulation method has to be varied corresponding to the walking direction. Three modes, “alternative circulation”, “unidirectional circulation”, and “cross circulation” are designed corresponding to the direction (Figure 4). Typical motion of each mode is illustrated in Figure 5-7. The velocity of pulling back is proportion to the distance between the dead zone and the point G.
Figure 4. Pulling back modes corresponding to the walking direction
Figure 5. Circulation of the movable tiles in alternative mode.
Figure 6. Circulation of the movable tiles in unidirectional mode.
Figure 7. Circulation of the movable tiles in cross mode
Alternative circulation (Figure 5): This mode is adopted to the directions between ±15 deg and ±75-105 deg. The tiles for creating new front surface (white colored tiles in Figure 5) are sneaking around to the front of the tiles for pulling back (in Figure 5, gray colored tiles) from right /left side alternatively.
Unidirectional circulation (Figure 6): This mode is adopted to the directions between ±15-30 deg and ±60-75 deg. The tiles for creating new front surface are sneaking around to the right/left front of the tiles for pulling back with a unidirectional circulation.
Cross circulation (Figure 7): This mode is adopted to the directions between +30 to +60, -30--60 deg. The tiles for creating new front surface are sneaking around to the right/left front or the right/left side of the tiles for pulling back.
When a user of the CirculaFloor switches over the walking direction, the control program calculates the nearest phase of each tile by using template-matching technique corresponding to the new direction. Then the tiles take the shortest way to their destinations.
At this time, the maximum walking velocities are 330 mm/s in alternative circulation mode and unidirectional circulation mode, and 210 mm/s in crossed circulation mode.
Applications of the CirculaFloor
It has often been suggested that the best locomotion mechanism for virtual worlds would be walking. It is well known that the sense of distance or orientation while walking is much better than that while riding in a vehicle. However, the proprioceptive feedback of walking is not provided in most applications of virtual environments. The CirculaFloor is a new locomotion device which provides such a sense of walking. It will make revolution in entertainment or training simulators.
One of the serious applications will be an "evacuation simulator." Analysis of evacuation of people in disasters is important in social safety. However, it is impossible to carry out experiments with human subjects during an actual disaster. Virtual environment is inevitable for such experiments. Since evacuation is done by walking or running, the CirculaFloor will be an indispensable interface device for the experiments.
Combination of the CirculaFloor and an immersive projection display may provide ultimate sense of presence. The integrated system can greatly contribute to teleoperation or virtual travel.
Articles of the CirculaFloor
SIGGRAPH2004 emerging technologies