Capacitive sensing passenger induction equipment on vehicles

The sensor is made of a printed circuit board. The bottom layer is a shielding layer and the top layer is two sensing electrodes. The equivalent model sensing electrode principle of the capacitive occupant sensing system is shown in the figure. The occupant sensing system consists of parts. The planar electrode capacitance sensor is placed on the top of the car, above the occupant's head. The capacitance sensor has a capacitance between the sensing electrodes, a capacitance between the sensing electrodes and the shielding layer, and a capacitance between the sensing electrodes and the shielding layer.

Which is to reflect whether the occupant is in the seat of the sensitive capacitance. According to the simulation and test results, based on the planar electrode capacitance sensor for occupant sensing, a tiny capacitance measuring circuit that can resist stray capacitance effects must be designed. In the micro-capacitance measurement circuit type, the amplitudes of the measurement signal and the reference information, and the month, respectively, are the coefficients of the measurement signal and the phase of the reference signal relative to the excitation signal. When the reference signal and the measurement signal are in phase, the output of the multiplier is .

A Butterworth filter with a cutoff frequency can filter out the AC signal. Its DC signal represents the capacitance value to be measured. From the table we can see that the sensitivity of the circuit is or, respectively, corresponding to the AC amplification and. A sinusoidal signal with a frequency of one is used as a voltage excitation source and the other is used as a reference signal. In order to keep the two signals synchronized, both frequency signals are provided by the same oscillator circuit. When the unknown capacitor is excited, the high-frequency amplifier converts the current into a voltage signal, which can be expressed as a graph. The two stray capacitances are denoted as, and respectively. Since the excitation voltage is directly applied to the unknown capacitor, the measurement result will not be affected and the inverse input terminal of the amplifier is the virtual ground terminal. Therefore, the voltage difference between both ends is almost zero, and the measurement result will not be caused. influences. Therefore, the effect of stray capacitance is cleared.

When the occupant's head is located directly below the sensor, the capacitive sensor output reaches its maximum. The output sequence of the sensor when the occupant enters and exits the sensor sensing range. The output-to-output AC voltage signal is amplified by a variable gain amplifier and the output voltage reaches several volts. The output AC signal is demodulated by an analog multiplier and the reference signal is provided. The phase of the reference signal can be fine-tuned with fine-tuning accuracy ", by fine-tuning the phase of the reference signal, keeping the measurement signal and the reference signal in phase, eliminating the delay of the measurement signal caused by the amplifier.

The results of the first rolling alignment are shown in the table. The results of the first rolling alignment are the number of the main journals. The rolling amount of the main axis is the amount of straightening and rolling. The amount of deformation after the bearing is the vector azimuth. The result of the first rolling alignment shows that the main journal runs off. Out-of-tolerance, expert system work, the results show that the maximum working pressure of the second rolling and straightening action on the connecting rod journal is: The second rolling and straightening result table shows the results of the third rolling and straightening. The deformation of the neck is qualified, and the rolling alignment is completed at this point.The test report shows that the working pressure corresponding to the rolling alignment under the guidance of the expert system is changed according to a certain law, and the law is that the same crankshaft journal crankshaft. Rolling head, the last time working pressure is increased compared with the previous one.If the above-mentioned test report reflects the process of the workpiece rolling and straightening, the situation that the straightening and rolling of the workpiece occurs in the same journal is repeated several times, the expert system It will automatically correct the operating parameters set at the start of operation of the equipment, such as increasing the working pressure at the time of strengthening the rolling of a shaft journal, etc., to improve the efficiency of the crankshaft rolling.

From this, it can be seen that the occupant is on the seat according to the output value of the capacitive sensor. When placing clothes and books in the position of the occupant's head, there is no major change in the output value of the capacitive sensor. In order to verify the adaptability of the sensor to the interior environment of the car, the author put the occupant sensing system in the Cherokee. When the engine is started and the car is moving, the sensing system still works. The planar capacitance sensor proposed by the author, the tiny measuring circuit against stray capacitance and the occupant sensing system formed thereby are the occupant sensing systems designed for the first time using the capacitive sensing principle. The system can clearly distinguish whether the occupant is in the seat, and at the same time the system can distinguish the human body from the non-human body, so that the system overcomes the deficiencies of the ultrasonic and mass induction principle system.

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