Design of vehicle-mounted turntable dynamic monitoring system based on DSP and AD1674 AID conversion chip
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Turntables are optomechanical and electrical integrated equipment widely used in the fields of aviation, aerospace, weapons, navigation, etc. The vehicle-mounted turntable system has been widely used due to its excellent maneuverability. However, unlike land-based turntables, even for ground-based measurements, the differences in the ground surface and changes in the surrounding environment will cause significant changes in the horizontality of the vehicle-mounted turntable. Changes in the horizontal reference will affect the accuracy of the entire turntable, so the horizontal mechanism of the turntable must be adjusted.
The traditional method of leveling a turntable is to place a digital electronic level on point A of the turntable in a direction parallel to the line connecting points B and C, as shown in Figure 1, measure the level value at point A, then rotate the turntable 180°, and measure the level value at point A again. The difference between the two measured values is the level difference between points B and C. By adjusting the leveling mechanism at point B or C, the level values of the three points are made the same. In this way, a turntable determined by three points is considered to be horizontal.
Although this traditional leveling method is very convenient to use on a land-based turntable, it will bring a lot of inconvenience to the work if it is still used on a vehicle-mounted turntable. Figure 2 shows the working model of the electronic level applied to the vehicle-mounted turntable system. The shortcomings in the working process are specifically reflected in the following three aspects:
(1) The measuring base of the original electronic level is very sensitive to temperature changes, resulting in large differences in measurement results at different temperatures. Therefore, harsh climatic conditions and environmental interference will have a great impact on the measurement results of the level.
(2) During the working process, because the level is installed on the turntable, it will change with the continuous change of the turntable's working position. Therefore, the leveling personnel cannot see the reading of the level at any time and cannot grasp the appropriate leveling time;
(3) When leveling, the leveler must take into account the dual tasks of reading the readings on the vehicle and leveling under the vehicle at the same time. This will inevitably affect the accuracy and speed of leveling.
Therefore, in order to overcome the various drawbacks of the traditional leveling method when applied to the vehicle-mounted turntable, a method for dynamically monitoring the horizontality of the vehicle-mounted turntable is proposed. This method is applied to the current vehicle-mounted turntable equipment, ensuring the horizontal accuracy of the vehicle-mounted turntable, playing an important role in improving the maneuverability of the vehicle-mounted equipment, and also has far-reaching significance for the future research on the vehicle-mounted self-stabilization system.
1 Working principle of the new dynamic monitoring system
The main idea of dynamic monitoring of the levelness of the vehicle-mounted turntable is to synchronously transmit the levelness of the vehicle-mounted equipment to the digital tubes of the central machine and the side wall of the vehicle through the digital electronic level, so that the levelness of the turntable can be monitored in real time on the central machine, and the level value measured by the level can be seen on the side wall of the vehicle when the leveling personnel are leveling. The implementation of this method is mainly based on the principle that the digital electronic level will output an analog voltage proportional to the measurement result, and the voltage can be converted to a corresponding analog-to-digital value. The specific implementation method is as follows:
Adding an electronic level and sealing both electronic levels above or below the turntable can avoid the influence of the external environment on the measurement results. In addition, the measurement values of the level are output to two directions for synchronous display, one part of which guides the display value to the interface of the main control software, and the other part is synchronized to the side wall of the vehicle. The specific synchronization method is shown in Figure 3.
In this way, on the one hand, the leveling personnel can monitor the levelness of the vehicle-mounted turntable according to the real-time display of the levelness on the center machine interface to determine whether leveling is needed; on the other hand, during the leveling process, the leveling personnel can perform leveling under the vehicle according to the displayed value of the vehicle side wall, which improves the accuracy and speed of leveling.
2 Hardware Implementation of the System
2.1 Hardware Structure
The hardware structure block diagram of the system is shown in Figure 4, which consists of a level meter, AID conversion chip AD1674, DSP, BCD-7 segment latch/decoder/driver MCl4513, external voltage reference MAX6133, MAX488 interface chip and central computer.
2.2 Analysis of hardware working process
In this system, A/D conversion and digital display are relatively important parts. Their specific working processes are introduced below.
2.2.1 A/D Conversion
When the level meter displays a value of 1, it will output a voltage value of 1mV. Therefore, in this design, AD1674 uses an external voltage reference. The 12V voltage outputs a reference voltage of 4.096V after passing through MAX6133. Therefore, during the conversion process of the 12-bit MD converter, 1mV corresponds to one byte. This not only simplifies the data calculation process in the middle, but also reduces the error caused by the calculation. After AD1674 converts the analog voltage signal from the level meter into a 12-bit digital signal, it is transmitted to the DSP through the DSP data bus. After the DSP performs corresponding processing, it outputs the corresponding control signal to drive the digital tube on the side wall of the vehicle, so that it can display the same measurement value synchronously with the level meter.
2.2.2 Digital display
DSP converts the data read from the A/D converter into decimal data in its own register, and then outputs the BCD code of the display number from the IOPC port to the BCD-7 segment latch, decodes, and drives MCl4513. The remaining idle I/O port generates a BCD code input latch signal. When the BCD code is latched, it will be decoded by 7 segments, and the corresponding digital tube will generate the corresponding display value. At the same time, DSP sends the data from its own serial port, converts it into PS422 signal through the MAX488 chip, and transmits it to the central computer, and displays it in real time on the interface of the central computer. Figure 5 is the circuit schematic diagram of the synchronous display part of the level.
3 Software Design
The system software mainly includes two parts: digital tube display and central computer real-time monitoring.
3.1 Digital tube display program design
The digital tube display program is mainly controlled by DSP, which includes the following parts: main program, interrupt initialization program, decimal subroutine, serial port number transmission subroutine and display subroutine. Among them, the main program starts A/D conversion and waits for interruption; the interrupt initialization program is mainly responsible for setting the response mode of external interruption, the opening of external interruption and the opening of general interruption; the decimal subroutine converts 12-bit binary data into corresponding decimal data; the serial port number transmission subroutine sends the data read back from the A/D converter to the central computer through the serial port at a fixed baud rate; the display subroutine sends the BCD code of the number to be displayed to MCl4513 and sets the corresponding latch bit. The system program flow chart is shown in Figure 6.
3.2 Real-time monitoring program design
The task of the real-time monitoring program is to add two windows for real-time display of the level. The window converts the RS422 signal transmitted from the DSP into the measured value of the level and displays it. It is implemented using Visual C++ and specifically includes the following aspects: creation of the display window, serial port communication, and synchronous display of the level in the window. The real-time monitoring window is shown in Figure 7.
4 Experimental results and analysis
The values output by one of the electronic level gauges on the display interface and digital tube were compared with the display results of the level gauge itself, and the detection was carried out using the fixed-point equal time interval continuous measurement method, while the values of the display interface, digital tube display and level gauge display were recorded at the same time. Table 1 records the experimental data within two hours.
The curve drawn according to the display data is shown in Figure 8. The comparison results of Table 1 and Figure 8 show that the design method can make the error of the synchronous display results of the level meter, digital tube and display interface only within one code value (2 arc seconds), and the accuracy fully meets the horizontal control requirements of the vehicle-mounted turntable (within 10 arc seconds), realizing the real-time monitoring of the horizontality of the vehicle-carrying system on the central machine, and the leveling personnel can adjust the vehicle body more intuitively and quickly according to the digital display value of the vehicle side wall to make it level.
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提升卡
变色卡
千斤顶
京公网安备 11010802033920号
