Crash sensor

For fixed-guided cantilever beams, the spring constant for each beam would be 

If we have the support arms made from Poly2 in the PolyMUMPS process that are 1.5 pm thick, 10 pm wide, and 1 mm long, the spring constant would be 

If the center plate is formed from a 1 mm stack of Poly 1 (2 pm) and Poly2 (1.5 pm), the mass would be 

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Miniaturized and integrated sensor systems were developed early for pressure and accelerometer sensors. The technology of silicon micromachining leads to sensitive pressure sensors which were marketed early [4]. Also accelerometers were developed mainly driven by the huge market of air bag application and crash sensors [5]. 

Small voltage generators (sensors) car crash sensors to activate air-bags, noise cancellation, active suspension for cars, anti- knock sensor for i.c. engines, liquid level sensing, etc. 

Crash sensor detects rapid deceleration and sends signal to air bag module. 

Crash sensors to release airbags in passenger cars... 

An example of an automotive crash sensor that could be used to deploy an air-bag safety system is shown in Figure 2.18. Here a proof mass is suspended by four fixed-guided support arms of length L that are attached to a stiff frame. The frame is rigidly attached to the car. 

Figure 2.18 Crash sensor. (Reprinted with permission of Sandeep Akkaraju from IntelliSuite v8.6 (2010), IntelliSense Software Corporation.)...

Safety Systems. A safety system is provided with built in safety shutdowns and emergency stop buttons. Crash buttons are located in the laser room, the laser table enclosure and the dome. The laser system is tied into the Observatory emergency stop system. Included both in the laser room and on the laser table are surveillance cameras, heat exchangers, alcohol sensors and fire detectors. In addition to personnel safety features, extensive interlocks have been installed in the laser to prevent the operator from inadvertently damaging it. 

Applications for physical sensors are dominated by the automotive industry. Engines are monitored and controlled by various sensors, and most cars are equipped with systems to enhance safety for brakes, steering, chassis, and even crashes. Controlling airflow and temperature in the cabin enhances the comfort of drivers. 

Most modern cars come equipped with airbags that are designed to save lives in head-on collisions. The airbags are inflated using a chemical reaction. When a car is involved in a crash, a sensor inside the car detects a rapid decrease in speed. The sensor then flips a switch that completes an electrical circuit. This starts a chemical reaction that inflates the airbag. 

One requirement of crash-detection accelerometers is to provide a self-test feature. In one manifestation of this feature, a portion of the accelerometer is used to actuate the structure on demand. Fig. 7.1.12g shows an example of a lateral accelerometer from Motorola and the associated self-test actuation section of the design. In this case, the self-test actuates the structure to an equivalent 20 g (versus the 40 g range for the crash-detection application). Self-test is performed upon initial vehicle ignition turn-on to determine the health of the sensor before operation. 

In developing these new algorithms, the requirements for sensors added more of them outside of the central control module for two reasons. First, some types of crash were difficult to detect within the short time frame required for deployment (such as offset pole crashes) and the solution was to provide a high-g precrash sensor within the front of the vehicle. And second, the need for side-impact detection required deployment decisions even faster that the frontal crashes (within approximately 5 ms). Both of these requirements moved accelerometers to satellite positions closer to the perimeter of the vehicle where they are more likely to pick up impacts from small objects. 

Government safety regulations have been the compelling market driver for crash-detection accelerometers. Initially, mechanical sensors were used at several locations within the car to obtain the crash signal. The MEMS accelerometer enabled... 

The application of yaw-rate sensors in vehicles requires particular attention. The dynamic requirements for the sensors are high Coriolis accelerations in the range of milli-g must be detected correctly, and at the same time the accelerations occurring in the range of several g must not interfere with the sensor function (such as when driving over potholes). In the case of the roll-over sensor this even applies for accelerations > 30 g, such as in a crash. 

Fig. 7.7.11 shows the pre-crash roadmap. In the first stage (pre-set), radar sensors provide information such as relative speed to obstacle and expected moment of collision. The system includes this information in its triggering decision. Because the radar sensors cannot provide any information on mass or condition of the obstacle, the system decides on actual triggering of a restraint medium based on acceleration sensors. For example, this pre-set function allows the belt to be tightened earlier or the triggering point can be optimized for the second airbag... 

The lift doors closed, and they descended to the command centre. It had been designed to handle every conceivable civil emergency, from a plane crash in the heart of the city to outright civil war, a windowless room which took up half of the floor. Twenty-four separate coordination hubs were arranged in three rows, circles of consoles with fifteen operators apiece. Their access authority to the continent s net was absolute, providing them with unparalleled sensor coverage and communications linkages. 

Appropriate measures to achieve the same vehicle safety levels as conventional vehicles are, for example, the installation of all relevant hydrogen components in crash safe positions, instaUatitHi of hydrogen sensors as well as appropriate shut down mechanism. In addition, for example hydrogen tanks are subjected to intensive type approval tests. 

FIGURE 10.10 Hybrid m anthropometric dummy designed for use in motor-vdiicle frontal crash tests, showing elements of constmction and sensors. (AGARD-AR-330,1997.)... 

The evaluation of measures, which are active during the pre-crash phase, includes all possible system responses. As those systems are subject to a variety of uncertainties (e.g., due to limitations of the sensors, variability in the situation when making predictions, etc.) they will not work ideally [2]. That means they will produce unintended side effects together with the intended effects they can be visualized using a classification matrix [3] as given in Table2.1. 

The Netherlands Organization for Applied Scientific Research TNO has developed another simulative approach called PreScan . It includes the complete road situation, vehicle sensors, system controls, and vehicle dynamics [64]. Based on Matlab , Simulink , and Stateflow , PreScan claims not only to simulate the pre-crash phase, but also to calculate the crash consequences via a UnktoMADYMO [48]. 

All methods described above can be categorized as automated case-by-case simulations based on accidents. There are two more aspects which are of importance for a sound system evaluation during the pre-crash phase. Many processes involved are deterministic, e.g., the participants dynamics, the technical functions implemented, as well as many physical boundary conditions. However, some of the key processes do have a stochastic nature for example, the driver action and reaction as well as some characteristics, e.g., of the sensors modeled. Due to the sensitivity of the results to those processes, stochastic elements are an important feature of any representative evaluation (see also Sect. 3.4). 

A review of the current state of scientific and technical knowledge on evaluation of the pre-crash phase set the starting point for this thesis (Chap. 2). Safety evaluation can be conducted at different levels (e.g., component-, system-, vehicle-based or with focus on the overall benefits in traffic). The method of choice depends on the level of evaluation and the underlying research question. Functions of active safety rely on sensors which perceive information from their environment and are thus subjeet to uneertainty. Besides possible technical limitations, the prediction of future movements of all involved participants contributes to this inherent uncertainty. As a eonsequenee, systems subject to uncertainties will not work perfectly in the sense of reliability. False-positive activations, e.g., due to misinterpretation of information or technical limitations, will occur with consequences on acceptance and controllability of the system. With an increasing number of false-positive activations, acceptance by the driver will decrease. In case of severe interventions in traffic, such as high velocity reductions and sharp decelerations, false-positive activations become a matter of controllability for the driver and the surrounding traffic and can ultimately have a negative impact on safety. 

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