Vol.2 No.2 2009

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Research paper : A secure and reliable next generation mobility (Y. Satoh et al.)−112−Synthesiology - English edition Vol.2 No.2 (2009) the traveling direction. The observation and detection of obstacles are done in all directions at all times regardless of these decision areas, and the risk decision can be done without delay, even if the decision area is switched suddenly by sudden joystick maneuver. Moreover, since the area lower than the floor is detected, level differences and descending stairs can be detected, and the wheelchair can automatically decelerate or stop if it is judged that the situation is beyond the performance of the wheelchair. Since a bump may have rounded corners to allow passage of automobiles or carts, passage may be possible even if there is a level difference. However, if it is judged that there is a level difference of more than 5 cm, the chair is stopped unconditionally. This is because the error of distance measurement by stereo image processing may occur in the order of 2~3 cm depending on the environment condition and a decision with sufficient margin of safety is not currently possible. To solve this problem and to realize more advanced and finer risk detection, we are working separately on the development of a stereo imaging processing system using near-infrared pattern projection, and have succeeded in observing level differences of a few mm order [12]. The application of this technology to the stereo omni-directional camera will be considered in the future.3.6 Gesture detectionWe implemented the function of capturing the changes in posture and gesture of the wheelchair rider in 3D, and controlling the electric wheelchair. Specifically, (1) the function to detect abnormality of the rider’s posture, and (2) the function to detect arm gesture were implemented. The space near the rider is divided into small cube regions (voxels), and recognition is conducted based on the pattern of the presence of objects within each voxels[11]. Seating position and gesturing are registered for each rider. The gesture and posture detection is done based on the comparison of the registered pattern and the observed pattern. Specific performance of the function will be described in detail in section 5.1. Although this function was not implemented at the beginning of the R&D, it was considered for implementation by request from the users after completion of the prototype.3.7 Information display user interfaceIn an experiment using the prototype, when the electric wheelchair entered the deceleration or stop mode, the rider felt very uncomfortable when he/she could not understand the reason for the movement. Therefore, we devised a user interface to notify the state of risk detection to the rider. First, we installed a small mobile information terminal in the rider’s hand region, and then considered how to display the information. In the initial stage, we thought it was better to communicate as much information as possible, and created a graphical display showing the direction and height of danger. However, it was difficult to see and understand the information that was displayed all at once when the wheelchair was moving. Therefore we devised a display that could be understood intuitively. Figure 9 left shows the display that was finally employed. The risks such as collision or fall are expressed by easy-to-understand pictograms displayed in the direction of the risk. By displaying “STOP” or “Slowdown” in large letters and in high contrast, the rider can intuitively understand “where the risk is and what kind of control is taking place.”This terminal also has a function of displaying the omni-directional image obtained by the stereo omni-directional camera. For example, it can be used to check the back view when backing up or to check the surrounding area in a bird’s eye view (Fig. 9 right). The screen is a touch panel, and the desired view can be displayed by touching the screen with a finger.Fig. 8 Control of decision area.The decision area is switched according to the direction the joystick is pushed. The figures take the vantage point directly above the electric wheelchair and the joystick. Top is the forward direction, and bottom is backward. Due to the limitation in space, only the forward straight (F0) ~ right turn on spot (R) are shown, but other directions are defined in a similar manner.Deceleration areaDirection the joystick is pushed80°F0F+1RF+240°20°0°: Stop area:Fig. 9 Information display user interface.The left photo shows the control status of the electric wheelchair. The type and direction of the existing risks are shown as pictograms. The right photo is the omni-directional spherical image from the vantage point of looking directly down at the rider. The sphere can be rotated freely on the touch panel.

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