1 Introduction
With the rapid development of high-speed railways, the speed of speed of the train is increasingly important on a high-speed rail line that is more than 350 km / h. The traditional rail circuit positioning method is not enough to position, and it is difficult to meet the positioning requirements of the high-speed train. There is also a motor mode to achieve a speedometer, which is only available for a low speed of the train. The speed and positioning can also directly acquire the position and speed information of the train by an additional input signal, but the measurement accuracy of this manner is constrained by some factors, and there is a limitations in the cost performance. The sensor has become the current mainstream product in the speed and positioning technology of the high-speed railway, widely used, and has multiple types: pulse speed sensors, inertial acceleration sensors, relative sensors, ground sensors, absolute sensors, and the like.
2 train speed
2.1 Wheel Shaft Pulse Turning Speed Sensor
There are many types of speed sensors, with magnetoelectric, photoelectric, centrifuge, Hall-based speed sensors. The wheel shaft pulse rotary speed sensor is widely used in the high-speed railway. The basic working principle of the wheel shaft pulse rotary speed sensor speed: Using the circumference of the wheel as a "ruler" measurement train walking distance, according to the speed of the train, the basic formula is:
V = πDN / 3.6
In the formula, π = 3.14, D is the wheel diameter, and N is the wheel speed.
As can be seen from the above, the measurement train speed is to detect the train wheel speed and the train path. The pulse speed sensor is mounted on the axle, and the axle is rotated once, and the sensor outputs a certain number of pulses, making the pulse frequency to be proportional to the wheel axis. The output pulse is separated and placed directly into the computer CPU to perform frequency measurement, and then converts the vehicle speed and walking distance. The schematic block diagram is shown in Figure 1.
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2.2 inertial acceleration sensor
The acceleration sensor is an electronic device capable of measuring acceleration. The accelerator is the force acting on the object during the acceleration process, which can be a constant or variable. Generally, the acceleration sensor operates according to the principle of piezoelectric effect, the acceleration sensor utilizes the crystal deformation generated by the acceleration due to the acceleration, as long as the generation of the generated voltage and the applied acceleration can be converted to a voltage output. There are still many other methods to make acceleration sensors, such as capacitive effects, hot bubble effects, and optical effects, but their most basic principles are due to the deformation of the acceleration, by measuring their deformation amount and converted to voltage output.
The wheel shaft pulse transistor also has a certain defect: that is, the wheel idling or slip will cause the measurement result of the train speed to solve such problems, add an acceleration sensor on the train axle, and use the pulse speed sensor. This method works: During the train slip, the internal acceleration of the locomotive is used as the source of measurement, which is not related to the state of the rotation of the wheel, and the operating time is still used in the remaining working time, which is referred to as the wheel shaft pulse sensor. Measurement of the inertial acceleration sensor. When the wheel is slippery, the acceleration sensor is measured by the acceleration sensor. The tilt component of the acceleration of the acceleration and the wheel slip is calculated, and the train runs acceleration when the wheel slip is calculated, and the value of the train is run in real time when the value is smashed. The specific principle is shown in Figure 2.
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3 train positioning
During the high-speed train operation, it is guaranteed to obtain train position information accurately and timely a safe and effective operation of the train.
3.1 relative sensor
The relative sensor is an apparatus installed in accordance with predetermined or previously measured distance, location and other information. This mode is currently realized by a axle sensor. Its working principle: Pulse signals proportional to the sensor output frequency and the wheel axis rotation, by performing a speed of the frequency, and then integrates the time to the time.
3.2 Ground Sensor
The relative sensor must first determine its absolute position and orientation relative to the earth. To this end, the ground sensor must be installed in the proper position, commonly known as the beacon. When the locomotive passes, the inductor on the vehicle receives the absolute position information provided by the ground sensor, so that the train is updated to the distance information, obtain a new initial position, thereby overcoming the error defect of the relative sensor.
3.3 absolute sensor
Due to the limitations of relative sensor work, the absolute sensor becomes mainstream technology for train positioning in the future high-speed railway operation. The absolute sensor can directly provide absolute position and orientation information, thereby realizing ranging positioning of the train.
4 Conclusion
Through the above discussion, the speed of speed and positioning method is simple, economical, and the measurement data error is widely used, and the use of the high-speed railway is widely used in the high-speed railway. The currently appearing GPS mobile communication and satellite positioning techniques are to achieve speed and positioning by directly acquiring the position and speed information of the train, but the measurement accuracy of this manner is constrained by some factors. It is not yet promoted. However, with its technical maturation, mobile communications, satellite positioning in high-speed rails will be broader.
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