Design of vehicle width and height detection system based on laser ranging technology

In order to realize the automation and intelligence of the management of over-width and over-height vehicles on highways, an intelligent vehicle width and height detection system based on laser pulse ranging technology is designed. The system uses LMS two-dimensional laser ranging sensor , under the control of a new high-performance microprocessor , to perform high-speed dynamic scanning of the vehicle profile, analyze and process the received real-time data, and realize the width and height detection of the moving vehicle and the over-limit sound and light alarm. The experimental results show that the system measurement accuracy is ±0.15m, the measurement accuracy rate reaches 95%, and the system performance meets the requirements of highway management departments for vehicle width and height over-limit detection.

With the rapid development of China's economy, the construction of expressways and the scale of road transportation have achieved unprecedented development, and the resulting phenomenon of overloaded vehicles has become increasingly serious. On the one hand, overloaded transportation will shorten the service life of roads and bridges, and on the other hand, it will cause changes in the shape of the vehicle body and a decline in vehicle performance, forming a serious hidden danger to traffic safety. At present, as an important part of overload control work, the management of vehicle overwidth and overheight is mostly still in the manual stage, mainly measured by staff with tape measures or bamboo poles, which not only increases the workload of staff, but also reduces work efficiency. In order to realize the automation and intelligence of overload and overheight management work, laser ranging technology is used, and the LM3S8962 processor based on the ARM Cortex-M3 core is selected to design and develop an intelligent vehicle width and height detection system. This system can perform high-precision dynamic scanning of moving vehicles to achieve width and height detection.

1. Selection of laser ranging sensor

Lasers are widely used in various measurement fields due to their high brightness, high directivity, and high monochromaticity. Compared with infrared ranging and ultrasonic ranging, laser ranging has the characteristics of fast speed, strong real-time performance, and high data accuracy. Laser ranging technology has been widely used in the fields of automobile collision avoidance, building or open space safety monitoring, rail transportation, etc. In order to meet the requirements of fast measurement speed and high measurement accuracy of the highway vehicle width and height detection system, and considering that the system can work in an environment with poor visibility or even at night, the system uses the LMS dual-pulse laser ranging sensor produced by the German SICK company.

The LMS laser sensor is an outdoor non-contact high-precision, high-resolution external sensor. Its working principle is based on the measurement of the laser beam flight time. It emits laser pulses at defined time intervals, and calculates the time interval between the emitted pulse and the received pulse through a timer to obtain the distance to the measured object. The pulsed laser beam is reflected by a rotating reflector inside the ranging sensor to form a fan-shaped scan of the surrounding environment. The working principle of laser scanning ranging is shown in Figure 1.

The contour of the target object is determined by a series of pulse sequences received. The scanning frequency of the LMS laser sensor is 25 Hz/50 Hz, the angle frequency is 0.25°/0.5°, the scanning angle range is 0°~270°, the maximum scanning distance is 20 m, the standard measurement accuracy is ±30 mm, the safety protection level is IP67, and it is safe for human eyes. Harsh environmental factors have no effect on the measurement range, and it can be used in an outdoor temperature environment of -30~+50℃.

2 System composition and working principle

The intelligent vehicle width and height detection system collects the vehicle's profile information by continuously and dynamically scanning the vehicle, and transmits the sampled data to the control unit in real time. The control unit processes, analyzes, and calculates the sampled data to obtain the actual width and height of the vehicle, and displays the measured values ​​on the LCD screen for on-site staff to view. At the same time, it determines whether the tested vehicle can pass according to the national width and height limits. This system can manually set the width and height limits, can perform real-time detection of moving vehicles, and has sound and light alarm and voice prompt functions. In actual application, the system requires the speed of moving vehicles to be controlled below 20km/h. Real-time and fast measurement can also avoid traffic congestion.

The intelligent vehicle width and height detection system uses LM3S8962 as the main controller. LM3S8962 is a low-power, high-speed processor based on the ARMCortex-M3 core. The LMS laser sensor transmits the measurement data to the main controller through a 500kb/s high-speed serial interface without causing data loss. The controller processes the received scan data. Due to its large internal data storage space, there is no need to expand the data storage externally. The system structure block diagram is shown in Figure 2.

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3 Hardware Circuit Design

The electrical control part of the intelligent vehicle width and height detection system uses the LM3S8962 processor based on the ARMCortex-M3 core as the control core. It can be divided into the following modules according to function: 电源模块\'); companyAdEvent.show(this,\'companyAdDiv\',[5,18])"> power module , main controller module, clock module, data communication module, keyboard input module, LCD display module, relay control module, etc. The following is a detailed introduction to the three parts.

3.1 Main controller module design

The microcontroller LM3S8962 with ARMCortex-M3 core is used as the system control core. The Cortex-M3 core adopts the ARMv7-M architecture, which compactly combines the Thumb-2 instruction set and adopts the Harvard processor architecture. Compared with ARM7TDMI, the efficiency per MHz of Thumb instructions is increased by 70% and that of ARM instructions by 35%. Since Thumb-2 instructions are an extension of Thumb instructions, 16-bit and 32-bit instructions coexist in the same mode, the complexity is greatly reduced, and the code density and performance are improved. The LM3S8962 has a clock frequency of up to 50 Hz, up to 36 interrupt sources with 8 priority levels, and provides system clock, 256 kB FALSH, 64 kB SRAM, sleep module, universal asynchronous receiver and transmitter, general timer, PC interface and other rich peripheral interfaces, which can conveniently and effectively control various field devices. Figure 3 shows the peripheral interface of LM3S8962 and its peripheral circuits (clock, reset, UART interface, etc.).

3.2 Data communication module design

The extreme value coordinate signal obtained by the laser sensor scanning is transmitted to the microcontroller through the universal asynchronous receiver and transmitter (UART), and MAX232 is selected for RS232 level conversion, as shown in Figure 4.

LM3S8962 has two serial interfaces UART0 and UART1. This system uses UART1 for RS232 communication. UART is a widely used short-distance serial transmission interface. As long as the two communicating parties use the same frame format and baud rate, the communication process can be completed with only two signal lines (Rx and Tx). There are independent transmit FIFO and receive FIFO. There is a programmable baud rate generator that allows a rate of up to 460.8 kb/s. The data transmitted through UART in the system is stored in the SRAM memory at high speed for real-time and fast calculation by the microcontroller.

3.3 Input and output module design

The system is equipped with 4 buttons for setting the width and height limits of vehicles, setting and modifying the system time, etc., realizing the function of modifying information at any time. In order to facilitate the staff to check the width and height of passing vehicles, LCD display is adopted. The LCD liquid crystal display module LCM192642 produced by Qingyun Innovation Company is selected. It is a Chinese character graphic dot matrix liquid crystal display module that can display Chinese characters and graphics. The working power supply of the module is 5 V; changing the value of the positioner W1 can adjust the display contrast of the LCD screen; the entire LCD screen is divided into three parts 16~18 are screen selection signal lines, and any part can be selected for display. Two 12V relays are set in the system. When the driving vehicle exceeds the standard width and height after inspection, the system will connect the power supply of the warning light and the outdoor loudspeaker through the relay to generate an audible and visual alarm, which prompts the on-site staff to handle it on the one hand, and informs the driver that the vehicle exceeds the limit and needs to stop for processing on the other hand. The schematic diagram of the input and output module is shown in Figure 5 below.

4 System Software Design

This system uses LAR5.11 as the development environment, C language programming, and modular program design. The software design is divided into several parts, including the main control module, initialization module, interrupt processing module, data sending and receiving module, data processing module, keyboard and display module. The main program workflow is shown in Figure 6. After the system is powered on, the system is initialized first, then a command is sent to the sensor, the sensor scan is started, the data sent from the serial port is received, the required data is extracted from the serial port buffer, and the data information is converted, judged, compared, and stored. After data analysis and processing, the corresponding execution subroutine is called to complete the corresponding function, such as calling the LCD subroutine to display the width and height information of the vehicle, and the program enters a continuous loop working state.

Data acquisition uses serial communication mode, sending data is completed by query mode, and receiving data is completed by interrupt mode. The receiving interrupt process is shown in Figure 7. The sensor and the main controller send and receive data through a pre-agreed communication protocol. The main controller only needs to set the corresponding serial port number, baud rate and corresponding port settings, send the measurement command, and wait for reception. The single data read command is: RNLMDscandatata; the continuous data read command is: EN LMDscandata1; the continuous stop data command is: EN LMDscandata0.

5 Simulation Experiment

After the overall design of the system was completed, a simulation experiment was conducted in the laboratory before entering the over-limit point for on-site debugging. The laser sensor was fixed on a 3 m high bracket, and a cart with a cube under test passed under the laser sensor at a speed of 10 km/h, as shown in Figure 8. The laser sensor was set to a scanning angle of 0°~180° and an angular resolution of 0.5°. When the cart completely passed, the maximum width and height of the cube under test were displayed on the LCD screen, and the outline of the object could be simulated by MATLAB , as shown in Figure 9. Under the same conditions, the cart was allowed to pass under the sensor several times and the results were statistically analyzed. The measured value was compared with the actual value, and the error within 0.15m reached 95%, which met the measurement accuracy requirements.

6 Conclusion

In order to solve the problem of overloaded vehicles on highways, a width and height detection system based on laser ranging technology was designed to realize real-time dynamic measurement of moving vehicles. During the experiment, the system worked reliably and stably, with low power consumption, fast calculation speed, high measurement accuracy, strong anti-interference ability, and the experimental error met the requirements of the highway management department for overloaded vehicles. Through repeated experiments, the design was proven to be effective and feasible, and fully prepared for the next stage of on-site commissioning.