Embedded laser ranging system using μC/OS-II

Introduction

The most basic principle of a laser ranging system is to measure the time interval during which the laser pulse propagates in space to obtain the measured distance. Aiming at the basic principle and implementation method of phase-based laser ranging, this paper combines the advantages of embedded, difference-frequency measurement equal-correlation technology and real-time operating system μC/OS-II. The hardware structure is reasonable and the software implementation method is flexible. Requirements for networked real-time high-speed information extraction and transmission.

It avoids the problems of high labor intensity, slow data acquisition, long data processing time, low calculation accuracy and data cannot be directly output to other systems in the traditional ranging system. The system is relatively simple to implement, and has the advantages of high measurement accuracy, good stability, and high speed. It has a large application space in production mines, scientific research schools, metrology institutes, etc., and has high practical value.

1 Basic principles of the system

1.1 Phase laser ranging principle

For the continuous wave laser ranging, phase ranging is generally used, which mainly refers to illuminating the object to be measured with a continuously modulated laser beam, and converting the phase change relationship generated from the measurement beam to and from the target between the laser sensor and the object to be tested. Distance D.

Ranging

Equation (1) is a phase-based ranging formula, where C is the propagation velocity of the light wave in the air, φ is the phase difference produced by the modulated laser signal after reflection, and f is the modulation frequency of the signal. It can obtain the accuracy of the measurement over the pulse time-of-flight measurement method, but the measurement speed is slow, the structure is more complicated, and there is a Doppler effect on high-speed moving objects.

Figure 1 is a schematic diagram of phased laser ranging, where Δφ is the portion where the phase delay of the signal is less than 2π, where φ = 2Nπ + Δφ, where N is the number of wavelengths included in the laser round trip. Thus, given a modulation frequency, the measurement of the distance becomes a measure of the number of integer wavelengths involved in the laser reciprocating once and a phase less than one wavelength. With the development of modern radio phase measurement technology, phase measurement can achieve high precision, so phase laser ranging can also achieve high precision.

Principle of ranging

1.2 Principle of difference frequency measurement

The principle of the so-called difference frequency method is that the multiplication of the main vibration frequency and the local oscillator frequency is used to obtain the superposition of the signal components of the two new frequencies. After the low-pass filter, it becomes the medium-low frequency signal. The difference frequency signal still maintains the corresponding phase relationship of the original high frequency signal, and the phase of the low frequency signal measured is equivalent to measuring the phase delay of the main vibration signal after the round trip distance. This can reduce circuit complexity and improve range accuracy.

Ranging

Multiplying these two signals with the applied signal U3 = I3 cos(ω1 t + φ3) can be obtained by:

Ranging

Then the newly obtained two signals 1 W and 2 W are respectively passed through a low-pass filter, and the high-frequency components are filtered out to obtain a low-frequency signal containing the (ω - ω1 ) spectral component, and the corresponding phase information φ1 and φ2 are still It is retained in the filtered signal and does not cause loss of phase information. Then the two signals are AD sampled, and then the microprocessor obtains the phase difference Δφ through the digital signal processing algorithm, and then the emitted laser light can be calculated. The distance between the objects to be tested.

2 system hardware structure and working principle

The hardware composition of the system is shown in Figure 2, including ARM9 (S3C2440A) processor module, laser modulation drive circuit, local oscillator signal generator, laser emission circuit, laser receiving circuit, mixing filter circuit, liquid crystal display module, keyboard input. The module is composed of parts. The S3C2440A is an ARM 9 microcontroller from SAM SUNG. The core is a 32-bit ARM920T. Its system clock is the 400MHz CPU core operating frequency generated by the internal PLL. It also has 64 MB Flash and 64 MB SDRAM external memory. The integrated SDRAM and FLASH controllers are rich in functions and interfaces. It is a high-speed, low-power, high-performance new processor that can be widely used in the development of communications, automotive, industrial control, PDA, medical and other systems. In this paper, the ARM9 core board is used as the data acquisition control core, which generates various control signals and basic data processing of the A/D converter.

Ranging

The hardware working principle of the system is: The system is mainly composed of a local oscillator signal generator, a laser transmitting circuit and a receiving circuit, a mixing and filtering circuit, a processor and a display circuit. The local oscillator signal generator can generate two sinusoidal signals with a frequency difference of 1KHz, and the power of the emitted laser light is modulated by the laser transmitting circuit, and then the transmitting laser and the receiving laser are respectively converted into corresponding electric signals, and then the mixing and filtering amplifying circuit will be adopted. The phase difference information is transferred to the two low frequency signals. Finally, the two low frequency signals are acquired by the ARM 9 processor, and the phase difference is calculated and converted into a distance, which is finally displayed by the display module. System peripheral circuits include system clock, analog-to-digital conversion ADC, external interrupt, timing system, signal capture module (Capture), pulse width modulation output (PWM), and so on.

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