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Obtaining real-time and reliable traffic information has always been a bottleneck problem in the development of intelligent transportation systems. Establishing an intelligent traffic vehicle information collection system can provide good auxiliary testing and verification for the study of driving behavior characteristics, traffic data collection and field testing in intelligent transportation systems. The platform can also provide strong technical support for the construction and development of multi-functional experimental vehicles for intelligent transportation systems in China. This paper introduces the design and research of intelligent traffic vehicle information acquisition system based on virtual instrument technology.
The intelligent traffic vehicle information collection platform mainly uses satellite positioning technology, sensor technology and data acquisition technology to establish the environment necessary for the development, research and experiment of intelligent transportation system related technologies, research on driving behavior characteristics in intelligent transportation systems, traffic data collection and Field testing provides a good auxiliary testing and verification platform. Its main functions are: real-time synchronous acquisition of various on-board sensor data, and save these records according to a certain format; using a variety of multi-sensor information fusion algorithms to offline processing each sensor data, thereby verifying various multi-sensor information fusion algorithms and comparing them The advantages and disadvantages of each algorithm; the results processed by the multi-sensor information fusion algorithm can be used to improve the accuracy of the positioning system and improve the system reliability. By collecting and processing the information such as speed and acceleration, the driver's driving behavior can be performed. Analyze and study its driving behavior characteristics.
The hardware of the intelligent traffic vehicle information collection platform of this design mainly includes three parts: vehicle sensor, I/O interface device and vehicle computer. The software of the platform uses LabView, which is a 32-bit software development platform developed by NI using virtual instrument technology for virtual instruments in the field of computer measurement and control. It can run under multiple operating systems. The software design of the entire data acquisition platform adopts a modular and structured design idea, which includes many functional modules. The real-time control part module includes an I/O interface device initialization module, a data acquisition module, a data display module, a data storage module and a motion detection module, a data reading module, and a multi-sensor information fusion module.
System hardware design
The system hardware consists of GPS OEM board, MicroGyro100 dual-axis gyroscope, ADXL202EA dual-axis accelerometer, SCC signal conditioning module, data acquisition card DAQPad-6015 and computer.
GPS ITrax02 is directly connected to the serial port of the PC. After ADCC202EA and MicroGyro100 are conditioned by SCC signal, DAQpad-6015 is used for data acquisition. The system structure block diagram is shown as 1.
Figure 1 System block diagram
The GPS supply voltage range is 3.4 to 6V, the ADXL202EA supply voltage range is 3 to 5.25V, and the gyroscope supply voltage range is 2.2 to 5.5V. Therefore, the output 5V power supply is uniformly selected as the power supply. The data outputted by GPS ITrax02 is input to the computer through RS232 to complete the extraction of time and position information. The accelerometer and gyroscope signals are amplified and isolated by the signal conditioning circuit SCC, and then the DAQpad-6015 is used to complete the A/D conversion input computer to calculate the vehicle. Information such as acceleration, velocity, position and attitude angle.
The accelerometer is a key component of the inertial measurement unit. It is used to measure the motion of the moving vehicle relative to the inertial coordinate system. The components of the acceleration in the carrier coordinate system are transformed by the strap-down matrix to the components along the geographic coordinate system, and then the speed and position of the carrier can be obtained after one integration and two integrations. With the development of inertial technology, accelerometers are constantly evolving. ADI's ADXL202EA is a micromechanical accelerometer based on integrated circuit and micromachining processes. It is small in size, light in weight, low in power consumption, low in cost, easy to integrate, and highly overloadable.
Although the medium and low precision gyro can not meet the requirements of the inertial measurement system, it can be combined with the global satellite positioning system to form a low-cost miniature integrated navigation system, which is a development direction. In such an integrated navigation system, the gyroscope and the GPS complement each other. The long-term accuracy of the integrated navigation system is ensured by the GPS whose error does not accumulate over time. When the GPS signal is lost for a short time, the dynamic parameters and state of the motion are provided by the micro inertial component. Information, while the GPS is working normally, the micro-inertial component is corrected by GPS information to improve the accuracy. Therefore, the system uses a micro-mechanical gyroscope as the vehicle-mounted sensor.
National Instruments' SCC module is a highly modular, low-cost signal conditioning system for PC-based measurement and automation systems. SCC provides a compact, portable system for single/dual channel signal conditioning and connectivity.
The DAQPad-6015 data acquisition card used in this system is a 16-bit precision NI USB multifunction DAQ product with a single channel sampling rate of up to 200kS/s. The device also has a built-in threaded terminal connection, eliminating the need for additional cables and wiring blocks.
System software design
The software design of the system mainly includes the software design of the GPS information acquisition module and the software design of the data acquisition and processing module of the inertial sensor.
Generally, the GPS positioning information receiving system is mainly composed of a GPS receiving antenna, a frequency converter, a signal channel, a microprocessor, a memory, and a power supply. Since the GPS positioning information content is small, the positioning information (NEMA0183 statement) is transmitted from the GPS receiver to the computer for information extraction processing by using the RS-232 serial port. As long as the GPS receiver is in working state, it will continuously transmit and calculate the GPS navigation and positioning information received to the computer through the serial port, receive data from the serial port and place it in the cache. Before further processing, the cache is a long stream of bytes. This information cannot be utilized until it has been sorted and extracted. Therefore, the information of each field must be extracted from the cached byte stream by the program. It translates into meaningful location information data for high-level decision making. Similar to other communication protocols, LabView is used to extract the GPS positioning information read by the RS232 serial port according to the frame structure.
The program flow chart of serial port information reading is shown in Figure 2. Serial port initialization completes serial port parameter setting, including serial port number, data bit, stop bit, parity bit, data flow control and baud rate. According to the number of characters in the serial port buffer, it is judged whether the signal reaches the serial port, that is, whether the hardware circuit is normal. If it is normal, read the serial port data.
Figure 2 Flow chart of serial port information reading
The flow chart of the inertial measurement unit entering the computer through the data collected by the data acquisition card is shown in Figure 3. First, the data collected by the inertial measurement unit is read from the data acquisition card, the initial alignment is performed, and the initial value of the strapdown matrix is ​​solved, and then The strap-down matrix is ​​updated to obtain the rotation angle of the geographic coordinate system relative to the inertial coordinate system. Considering the angular velocity output of the gyro, the direction cosine matrix between the carrier coordinate system and the geographic coordinate system can be calculated. By decomposing the cosine matrix in this direction, the output of the accelerometer can be changed into the acceleration component of the carrier along the geographic coordinate system. Then, using the general expression of acceleration, the harmful acceleration is compensated, and the acceleration of the carrier along the ground is obtained; when it is integrated, the ground-speed components Va and Ve of the north-south direction and the east-west direction are obtained. With the ground speed component, after the corresponding transformation, the rate of change of latitude and longitude is obtained; and then integrated, the longitude and latitude of the instantaneous position of the carrier are finally obtained. Then use the elements of the pose matrix to extract the pose and direction information.
Figure 3 Inertial Measurement Unit Software Flow Chart
Conclusion
The realization of intelligent traffic vehicle information collection system has greatly accelerated the research and development of relevant technologies of intelligent transportation systems, improved traffic order, eased traffic congestion, and obtained real-time and reliable traffic information. Applying virtual instrument technology to intelligent traffic vehicle information collection system can not only meet the requirements of current multi-sensor information collection and fusion in intelligent transportation, but also the most important thing is to flexibly expand the function according to the needs of technological development. Therefore, for the rapid development of intelligent transportation technology, this information acquisition system based on virtual instrument technology has very practical significance.
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