Yuji Muragishi, Eiichi Okuda

To improve the performance of a vehicle's braking control, it is important to be able to estimate the friction force characteristics between the vehicle's tires and the road. Over the last few years, we have proposed a method that allows us to estimate the slope of the friction force against the slip velocity at the operation point, based on the fluctuation of the wheel velocity as a parameter that corresponds to the margin of the friction force between the tires and the road. Moreover, we have proposed a braking control strategy that is based on estimating the parameter for achieving the maximum braking force. Although this produced good braking control, valve switching noise became a problem. In addition, a pressure sensor is needed to control the pressure. This is not needed in conventional braking systems.

This study addresses the application of hybrid control to braking to ensure that braking performance is maintained while reducing the valve switching frequency. Moreover, a control system design that does not need the above-mentioned pressure sensor is proposed. This design incorporates a mathematical model that estimates the brake pressure and then uses the estimated values. Tests with an actual vehicle verified that the valve switching frequency is reduced, and that good control is realized despite the absence of a pressure sensor.

In this paper we propose a new lane detection method for expressway lane departure warning. The use of the extended Hough transform and a bird's-eye view image effectively improve the robustness and resolution of lane detection. Hardware cost is reduced by using a rear-view camera from an existing system and by implementing the system on an embedded CPU.

Mineki Soga, Keiichi Yamada,
Mitsuhiko Ohta, Yoshiki Ninomiya

An outdoor scene, where a driver looks through a blind spot monitor, for instance a rear view monitor, occasionally has a very wide brightness range. However, the dynamic range of a liquid crystal display, which is commonly used as an in-vehicle display, is considerably narrow in comparison with the dynamic range of the outdoor scene and the camera to capture the image. Therefore, the darker regions in the image would be under the noise level of the display, otherwise the brighter regions in the image would saturate. To solve the problem, we propose a method to compress the overall brightness range of the image keeping the contrast of objects using image processing. This method suppresses the lower spatial frequency component of the captured image according to the brightness of each pixel. As a result, the image of the outdoor scene can be displayed on an in-vehicle display with high visibility and no side effects, even if the scene has very wide dynamic range.

Hiroyuki Matsubara, Toshihiko Tsukada,
Hiroshi Ito, Takashi Sato,
Yuji Kawaguchi

We have developed a 3D measuring system that uses two pan-tilt cameras to accurately measure the position of a robot's hand. With this system, a target is set up at the tip of the robot's hand. The pan-tilt cameras are controlled so that the mid-point of the target view is centered within the camera frames. Then, its 3D position is calculated using a triangulation method from the azimuth and elevation angles of the two cameras and the distance between them. Because measurement precision is essential to such a system, we proposed a new method of the target with the concentric circle patterns, for which the center was measured precisely from the gravity centers of those circles. As a result, we achieved a high degree of precision (within 0.03 mm) with a single camera, for a camera-target distance of between 200 and 1000 mm, and where the tilt angle of the target relative to the camera was less than 70^｡. It was verified, by experiment, that the 3D measurement precision of the trial system is 0.15 mm for a 500-mm cube.

Hideo Nakane

The effects of negative air ions on psychological stresses (i.e., the Stroop task and computer operation) were examined with biochemical indices of stress response (i.e., salivary chromogranin A (CgA) and cortisol). Both CgA and cortisol levels were increased by the Stroop task, and exposure to negative air ions somewhat attenuated the increase. On the other hand, only CgA level increased after computer operation and cortisol level did not. The increase in CgA level by computer operation was attenuated by exposure to negative air ions during the task. Exposure to the ions during the recovery period (a rest period after the task) was effective for a rapid decrease of CgA level, which had increased after the task. These effects of negative air ions on the computer operation were also observed by the subjective evaluation of stress with the State form of the State-Trait Anxiety Inventory questionnaire. Task performance of computer operation was slightly but significantly improved by the presence of negative air ions. These results suggest that negative air ions are effective for the reduction of and the prompt recovery from psychological stress.

Masahiko Ishii

Influence of several operating conditions on luminance decay in a green organic light-emitting diode with tris (8-hydrooxyquinoline) aluminum (Alq3) has been investigated by the analysis of its luminance decay curves. The conditions varied were operating current mode (DC or pulse) and environmental temperature (25-120 ^｡C). The decay curves measured were analyzed by fitting the curves to stretched exponential ones. The analysis results showed that the curves measured under both operation modes well fit to the stretched exponential ones, and that the curves measured under the pulse mode were closer to simple exponential curves than those measured under the DC mode. A rapid decline in the initial stages of operation appeared in the DC mode, though it was not clearly observed in the pulse mode. Thus, the luminance decay was divided into two major components: a simple exponential during operation and a rapid decline in the initial stages of operation. The simple exponential decline was due to a chemical degradation of Alq3, while the rapid decline is probably due to the generation of an internal electric field. The results also showed that the environmental temperature has little effect on the shape of the decay curves, suggesting that the relative contributions of the two decay components are independent of temperature.