Takaji Umeno

Tire-road friction is the most important piece of information used by active safety systems. However, most conventional friction estimation/detection methods are accurate only within the non-linear region. In addition, such methods require numerous sensors, such as yaw rate sensors, acceleration sensors, and steering angle sensors. In this paper, a friction estimation method using a tire vibration model is proposed. The method is based on the frequency characteristics of wheel speed vibration, which are related to tire-road friction. The recursive least squares and instrumental variable methods are applied for on-line estimation. The experimental results show that, when applied to a free-rolling tire, the proposed method detects friction change from dry asphalt to iced road while the vehicle travels at constant speed without braking, accelerating, or cornering.

A new full-dry processing method has been developed that includes a new sacrificial layer dry etching technique, which enables the microscopic structures used for microsensors and micro-electro-mechanical systems (MEMS) to be released from silicon substrates with high repeatability, and a new water-repellent dry coating technique, which prevents the released structures from sticking to the substrates during operation. The usefulness of this full-dry processing method from etching to coating, with respect to the length of releasable cantilevers, was evaluated by comparison with the conventional wet method. It was confirmed that the full-dry processing method permits sustainable cantilevers to be about three times longer than those released using the conventional wet method.

Hiroaki Makino, Mitsuru Asai,
Shin Tajima, Nobuo Kamiya

A conventional force sensor consists of a beam or a diaphragm to which a thin-metal film strain gauge or a semiconductor strain gauge is attached. The force is detected by the resistivity change in the strain gauge in accordance with the applied force. The phenomenon whereby resistivity varies with the applied force is called piezoresistivity. The necessity of attaching the gauges to the beam or the diaphragm limits the reduction in size and cost of the conventional force sensor. A material having both structural strength and the function to detect force, such as piezoresistivity, would render the beam or diaphragm unnecessary, and hence the sensor could be miniaturized and the cost would be reduced.

Therefore, the authors have developed a novel ceramic composite which has both the force detection function and structural strength by distributing an oxide material having piezoresistivity in a high-strength ceramic. As this composite enables the structural member itself to become a sensor, the size of the sensor can be markedly reduced. The authors expect that this sensor material will enable new potential applications in force detection.