Automobile positioning system based on acoustic and optical detection

Figure 3 is the distance measurement system circuit. The circuit consists of a single-chip microcomputer and four groups of ultrasonic transceiver units. Only one group of ultrasonic transceiver units is drawn in the figure. The transmitting unit consists of a 40 kHz oscillator and a gate circuit. The gate circuit generates a low-frequency pulse signal with a very small duty cycle, a pulse duration of 160 ms, and a pulse interval of 30 to 50 ms (adjustable as needed). One path of this pulse signal is used as the setting pulse of the oscillator; the other path is sent to the single-chip microcomputer as the start pulse of the timer. During the setting period, the oscillator outputs a modulated pulse signal with a frequency of 40 kHz, which is emitted by the ultrasonic transmitter T40-16. The echo is received using the universal FPS409I infrared receiving component, but it is necessary to replace the infrared receiving tube PH302 with the ultrasonic receiving head R40-16, so that within the effective distance measurement range, it can be ensured that the output of the received signal reaches the TTL level. The received signal is shaped and amplified and sent to the single-chip microcomputer as the stop pulse of the timer. The single chip microcomputer calculates the time t between the start pulse and the stop pulse, and calculates the distance s according to formula (1).

Figure 3 Distance measurement system circuit

The ranging system adopts a "one-to-four" structure. To avoid mutual interference among multiple groups of ultrasonic units, they should work in turns under the control of the single-chip microcomputer. The pulse interval in this circuit is 30-50 ms, corresponding to a ranging range of about 5-15 m. If the ranging range is increased, the pulse interval needs to be increased. In addition, the ranging circuit has a ranging blind area of ​​about 30 cm. The distance between the ranging device and the measured object should be kept at a distance of more than 30 cm. At the same time, when the single-chip microcomputer times the start and stop pulses, it should also avoid the interference of false stop pulses in the blind area.

4 Control Software Design

The control software includes host software and single-chip microcomputer software. The main software flow is shown in Figure 4. Single-chip microcomputer 1 generates the switch signal and shift clock required by the infrared electronic shift line-by-line scanning circuit, and collects the receiving status data once in each shift clock cycle. After completing a scan, the data is uploaded to the host; the scanning speed and scanning intensity can also be changed through program control according to the host instruction. Single-chip microcomputer 2 controls the detection of 4 ultrasonic devices respectively, and the counted time is uploaded to the host after simple processing. Due to the existence of blind spots, it is necessary to avoid the interference of false stop pulses coming from this interval. The delayed interrupt is used, that is, after the start pulse starts the timer timing, wait for the blind spot to pass before the interrupt is opened, so that the single-chip microcomputer interrupt port receives the actual effective stop pulse to stop the timer timing. The host program reads the longitudinal detection data and the lateral detection data from the two single-chip microcomputers in turn in an active query mode, and then processes and analyzes the detection data according to a certain algorithm, first judging whether there is a car, and if there is a car, judging the type of car, calculating the parking position parameters and the geometric parameters of the car box.

The host software is written in Delphi and can display measurement parameters and set working parameters.

Figure 4 Main software process

5 Tests and Results

The test was conducted at an outdoor industrial site. The working area was 5 m × 21 ITI, the spacing of the infrared modules was 5 cm, and the number of modules of the infrared transceiver array was 425. 100 vehicles were positioned continuously, including various models, and all were successfully positioned. The positioning data of 5 vehicles were selected during the day and night for on-site comparison with the actual data. The results are shown in Table 1. The measurement error of the length and front distance of the vehicle box does not exceed 5 cm, and the measurement error of the width and side distance of the vehicle box does not exceed 6 cln. The single positioning time can be as fast as 1 s.

6 Conclusion

The results show that the acoustic and optical detection technology can achieve non-contact positioning of objects in a plane. The automobile positioning system based on acoustic and optical detection has significantly improved positioning speed, positioning accuracy and positioning reliability compared with other current positioning methods. At present, the system has been used in the automatic sampling control system of automobile materials and has been applied in many steel and power enterprises with good operation effect.