Strapdown north seekers have become the mainstream development trend due to their fast speed, high reliability, no need for external geographical location information and simple structure with the development of inertial technology. North finders play an important role in missile launches, artillery aiming and other military applications. plays an important role. Signal acquisition is the core part of the strapdown north seeker, which directly affects its positioning and orientation accuracy. Therefore, it is of great practical significance to study the signal collection of strapdown north seeker.
1.Overall design of strapdown north seeking system
The strapdown north seeking system consists of data acquisition and processing system, turntable leveling system (inclinometer), indexing control system (servo unit), inertial measurement system (gyro and accelerometer), temperature control system (temperature control unit), etc. The data acquisition and processing system consists of a signal acquisition module, a signal processing module, a data display module and a data communication module. It is the central processing core of the north-seeking instrument and mainly implements the functions of data acquisition and processing and calculation of the north-seeking angle.
As shown in Figure (1), the signal acquisition module converts the current signal output by the gyroscope into a voltage signal, and then converts it into a digital signal through A / D; the signal processing module digitally filters the gyroscope data, and based on the multiple index positions The gyro data and encoder data are processed to calculate the north-seeking angle; the data display module displays the working status of the north-seeking instrument and the north-seeking angle data; the data communication module communicates with the servo control unit, temperature control unit, electronic inclinometer, and encoder through the serial port , the host computer communicates and sends and receives data.
The strapdown north seeking system installs the gyroscope vertically on the turntable, with its sensitive axis parallel to the table, sensing the earth's rotation angular velocity. The turntable is controlled to rotate counterclockwise from the starting position, pause, rotate, pause,..., and the turntable pauses at n corner positions at intervals within one week. The gyro signal is collected when it pauses at each corner position, and the gyro signal is collected at n corner positions θi in one week =(i-1)×2π/n, i = 1, 2...n, the mathematical model of the gyro output is:
yi=Ｒ+ωNcos(ψ－θi)+ωi，(1)
In the formula (1), yi is the gyro output; R is the gyro constant drift, ωN is the north component of the earth's rotation angular rate, Ψ is the initial azimuth angle, θi is the position of n rotation angles of the turntable, θi = ( i - 1 ) × 2π/n, i = 1, 2...n. ωi is the gyro measurement noise. According to the mathematical model, the principle curve of strapdown north seeking is a sinusoidal curve. When θi =ψ, the gyro output is maximum, which is the true north direction.
2.Signal acquisition system
The signal acquisition module converts the current signal output by the gyroscope into a voltage signal. The signal acquisition module of the north seeker is mainly composed of a sampling resistor, a non-phase adder, a low-pass filter, an A/D converter, etc. The circuit schematic is as shown in the figure (2) shown.
2.1Digital potentiometer:
A digital potentiometer is a digital-analog mixed-signal processing integrated circuit made using CMOS technology. It is also called a digitally controlled programmable resistor, or digitally controlled potentiometers (DCP) for short. Digital potentiometers have the characteristics of long life, reliable operation, stable performance, resistance to shock and vibration, small size, and flexible use. They are widely used in various instrumentation, computers and communication equipment, household appliances, industrial control and other fields. In recent years, they have The trend of replacing traditional mechanical potentiometers.
2.2Sampling resistor:
The sampling resistor R1 is used to convert the current signal output by the gyro into a voltage signal. The selection of its resistance value is firstly related to the current size of the gyro output, and secondly, it is related to the operating voltage range of the operational amplifier circuit and the A/D conversion circuit. In the actual use of the north seeker, the working latitude is from 65° south latitude to 65° north latitude. In the range of 0° to 65° earth latitude, the northward component ωN of the earth’s rotation angular velocity has a large variation range, and the gyro output signal has a large variation range. There will be a large difference in amplitude, which will have a certain impact on north finding.
Summary:
The above is the current information we have about the north seeker signal acquisition system. This shows that signal quality and processing play an important role in the overall performance of the strapdown north seeker. The choice of signal acquisition technology largely depends on the specific Application environmental conditions. At present, our north-seeking device have also done a lot of experiments in signal collection. In addition to the fiber optic gyro north finders ER-FNS-02 and ER-FNS-03, the MEMS north finders are also constantly optimized. For accuracy The control and improvement of products has always been Ericco's pursuit. In future research, we will also focus on developing more advanced signal processing algorithms and technologies to further improve the accuracy and robustness of the north finders in various complex environments.
More Technical Questions
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