I. Project overview
Laser ranging has the advantages of high angular resolution and strong anti-jamming ability, which can avoid the multi-path effect of microwave near the ground and the problem of geophysical interference. It also has the advantages of light weight, compact structure and convenient installation and adjustment. It is one of the most ideal instruments for high-precision ranging at present. After the completion of construction, the surrounding rock of railway tunnel has a slow changing trend, and the convergence can be measured by using distance measuring instrument.
1.2 Project Background/Motivation
According to our research market, the price of ordinary hand-held laser rangefinder is about 1000 yuan, with serial port and other communication interfaces more than 2000 yuan, and the function is single and the interface is simple. Therefore, we use AVR 128 processor to construct a new laser ranging detection system, which has the advantages of multi-function, high precision, automation and price, and is applied to the convergence monitoring of surrounding rock of railway tunnel.
II. Demand Analysis
2.1 Functional Requirements
The range finder designed in this paper can measure the convergence of railway tunnels all-weather and save the data to SD card and transmit it to the monitoring center.
2.2 Performance Requirements
The designed range finder has an angle of more than 0.1mm, and the module is stable and reliable.
III. Scheme Design
3.1 System Function Realization Principle
By utilizing the characteristics of short duration and high instantaneous power of laser pulse, the distance measurement can be carried out by receiving the diffuse reflection signal of the measured target even if there is no cooperative target. The principle of pulse laser ranging is similar to that of radar ranging. Pulse laser is used to transmit a single laser pulse or laser pulse train to the target. The counter measures the time when the laser pulse reaches the target and returns to the receiver. The distance between the target and the receiver is calculated.
3.2 Selection of Hardware Platform and Resource Allocation
Selection of hardware platform: AVR XMEGA-A1 Xplained Evaluation Kit is based on 8-bit ATMEGA128 chip.
Use resources on board: SPI interface, temperature sensor, light sensor, language speaker, serial module.
3.3 System Software Architecture
The system first collects three important information: distance location, temperature and humidity, and external light intensity. According to the corresponding data, the influence of temperature and external light intensity on spot location is eliminated. When the distance position exceeds the set threshold, the speaker on the board is used to send out the alarm sound. The collected data are stored by SD card, LCD display and serial port to the monitoring center.
3.4 The expected results of the system
It is applied to the convergence monitoring of tunnel surrounding rock.