RU2578247C1 - Self-contained gravity gradient meter - Google Patents

Abstract

FIELD: geophysics.

SUBSTANCE: invention relates to geophysical instruments, specifically to gravity gradient meters. Gradient meter consists of a quadruple and gyro unit arranged on platform stabilised in horizontal plane and rotating around azimuthal direction. Rotation of gradient meter platform is used for self-compensation of errors of gyroscope azimuth. Gradient meter comprises a computer with a signal processing unit and quadrupole vertical gyroscope circuit. Second circuit of computer enables to accurately determine horizontal components of Earth's rotation, and unit calculates azimuth bearing. Computer, in addition to signal processing unit of quadrupole, includes: cell for signal indicating transition through zero, unit for differentiation and display of sign of derivative, an AND cell with two inputs and a switch.

EFFECT: technical result of invention is to improve accuracy and performance of gravity gradiometer.

1 cl, 5 dwg, 2 tbl

Description

The invention relates to geophysical instrumentation, namely to gravity gradiometers, and is intended to increase their accuracy and operational characteristics.

Static gradiometers are known [1, 2], in which a dipole (rocker arm, dumbbell) is installed in a low-moment suspension. Gravitational forces seeking to rotate it are counteracted by the forces of twisting of the filament or the electric forces of the tracking systems, which maintain the position of the dipole unchanged relative to the body. The disadvantage of static gradiometers is the need for one measurement of the gradient to set the dipole in several positions that differ in azimuths. This leads to a significant measurement duration.

Dynamic gradiometers with a quadrupole [3] or accelerometers [4] mounted on a rotating platform are deprived of this drawback. Such gradiometers continuously scan the measurement plane, yielding four gradient values per revolution. Their disadvantage is the limited ability to determine the direction of the isolines of the gravitational field.

To stabilize objects in the horizon, the channels of the gyro-vertical of inertial systems are used [5]. But in inertial systems, the accuracy of determining azimuth directions is low. The gyrohorizontcompass [6] lacks this disadvantage, in which self-compensation rotation around the vertical axis is used to separate the useful signal and noise.

The objective of the invention is the creation of a gradiometer that determines the direction of the level line of the gravitational field on a moving object.

The problem is solved by using the rotation of the gradiometer platform to automatically compensate for gyro azimuth errors. For this purpose, a quadrupole and a gyro block are placed on a platform stabilized in the horizon and turning in azimuth. The gradient meter contains a calculator with a quadrupole signal processing unit and a gyro-vertical circuit. A second circuit is installed in the calculator, in which a new output and a new input are used to ensure accurate measurement of the horizontal components of the Earth's rotation speed, and an azimuth block is installed to ensure azimuth calculation. In addition to the quadrupole signal processing unit, the calculator also includes: a cell for signal transition through zero, a unit for derivation and indication of the sign of the derivative, an “I” cell with two inputs, and a switch. The output of the measurement circuit of the horizontal components of the Earth's rotation speed is connected to the input of the azimuth calculation unit, the output of which is connected to one of the contacts of the switch. The second contact of the switch is connected to the output of the calculator. The outputs of the quadrupole information processing unit are connected to the inputs of the cell indicating the transition of the signal through zero and the differentiation unit and the derivation of the sign of the derivative, and their outputs are connected to the inputs of the cell “AND” connected by a control line to the switch.

List of drawings

In FIG. 1, 2, a uniaxial diagram of an inertial system [5] or gyrohorizontcompass [6] with different ways of connecting a linear velocity sensor is shown.

In FIG. 3, 4 a diagram of the channel for measuring the horizontal components of the Earth's rotation speed with different ways of connecting the linear velocity sensor is shown.

In FIG. 5 shows a general diagram of a gradiometer.

In FIG. 1-4 introduced the following notation:

1, 2, 3 - information sources: accelerometer (ACS), angular velocity sensor (DOS), linear velocity sensor - lag or satellite navigation system (SNA), respectively;

4 - contour of the inertial system;

5, 6 - first and second integrators with transfer function $$\frac{\mathrm{one}}{p};$$

7 - non-integral filter with transfer function

и $$\frac{1}{R}$$

, соответственно, где $$g=9.8\frac{м}{{с}^2}$$

, $$R=\mathrm{6,4}*{10}^6м;$$

8, 9 - scaling devices $$\frac{\mathrm{one}}{g}$$

and $$\frac{\mathrm{one}}{R}$$

, respectively, where $$g=9.8\frac{m}{{\mathrm{from}}^2}$$

, $$R=6.4*{10}^{6}m;$$

10 - scaling device

10.1 - SNA signal filter with transfer function

10.2 - SNA signal filter with transfer function

11 - contour of measuring the horizontal components of the Earth's rotation speed (contour of the Earth's rotation speed);

B × 1, B × 2 - inputs for acceleration and angular velocity, respectively;

В × 3, В × 4, В × 5 - inputs at linear speed;

Exit 1 - exit by pitching angle;

Exit 2 - the output of the linear velocity or angular velocity of rotation of the Earth;

Exit 3 - the output of the angular velocity of rotation of the Earth.

In FIG. 5, the following notation is made:

12 - quadrupole;

13 - stabilized in the horizon and rotating in azimuth platform;

14 - gyro block;

15 - stabilization drive at the pitching angles;

16 - drive rotation in azimuth;

17 - a computer;

18 is a quadrupole signal processing unit;

19 - block calculation of the azimuth;

20 - block calculating the magnitude of the gravitational gradient;

21 - cell indicating the transition of the signal through zero;

22 - block differentiation and indication of the sign of the derivative;

23 - cell "And";

24 - switch.

The inertial system (ANN) [5] or the gyrohorizontcompass (GHC) [6] have the same circuit shown in FIG. 1, 2, and differ only in the type of output information used. In the ANN, the pitching angles and linear velocity are used as useful information, and the pitching angles and horizontal components of the angular velocity of the Earth's rotation are generated in the GGC. Linear velocity or angular velocity components are removed from one output — Output 2, and then separated on devices not shown in FIG. 12.

ANN, GGK and the channel for measuring the horizontal components of the Earth’s rotation speed (SVZ channel) work with three sources of information: about acceleration - from accelerometers 1, about angular velocity - from angular velocity sensors 2 and about linear velocity - from a lag or satellite navigation system 3 The basis of the ANN is a closed circuit 4 containing series-connected links: the first integrator 5, non-integral filter 7 and the second integrator 6. The circuit has three inputs: B × 1 - at the input of the first integrator 5, B × 2 - at the input of the second integrator 6 and B × 3 - at the input of the non-integral filter 7. When implementing the ANN, the SNS signal is split and for one part it is used B × 4 - at the output of the non-integral filter 7. The circuit has two outputs: Output 1 - at the output of the second integrator 6 at the pitch angles and Output 2 - at the output of the first integrator 5 in linear velocity or angular velocity of rotation of the Earth. AKS 1 through a scaling device 8 is connected to the B × 1 circuit 4. SAS 2 is connected to a B × 2 circuit 4. SNA 3 through a scaling device 9 and a filter 10.1 is connected to a B × 3 circuit 4. In the case of splitting the signal SNA, one part of it remains at B × 3, entering through a scale 10, and the second is fed to B × 4.

In FIG. 3, 4, the circuit for measuring the horizontal components of the Earth’s rotation speed 11 differs from circuit 4 with a new output - Output 3, located at the output of the non-integral filter. In connection with the introduction of the new transfer function of the filter 10.2 in FIG. 3, when splitting the SNS signal, a new B × 5 appears, as shown in FIG. four.

In FIG. 5, the quadrupole 12 is located on a platform 13 stabilized in the horizon and rotating in azimuth, on which a gyro block 14 with ACSs and DUSs is installed. Stabilization in the horizon is carried out by drive 15 connected to Output 1 of circuit 4. Rotation in azimuth is carried out by drive 16. Signals from the gyro block and quadrupole are fed to calculator 17 to signal processing unit quadrupole 18 and to circuits 4 and 11. Output 3 of circuit 11 is connected to the calculator azimuth 19, the output of which, in turn, is connected to the switch 24. the second contact of the switch 24 is connected to the outputs 2 of the calculator. The output of the processing unit 18 through the gradient calculation unit 20 is connected to the outputs 1 of the calculator 17. The inputs of the cell indicating the transition of the signal through zero 21 and the differentiation and indication unit of the derivative 22 are connected to the output of the processing unit 18, and their outputs to the inputs of the cell “And”, the output which controls the state of the switch 24.

Consider the operation of a uniaxial ANN or GGK circuit in FIG. 1, 2. Assume that information sources measure the following signals:

where p is the differentiation operator, V is the linear velocity, Ω is the angular velocity, α is the pitching angle, ω _3g are the horizontal components of the Earth's rotation speed, and _pu are the portable pitching accelerations.

и преобразования на фильтре 10.1 на входы основного контура 4 поступают сигналы:After scaling

and transformations on the filter 10.1 to the inputs of the main circuit 4 receives signals:

The output signals of the circuit are:

датчиков угловых скоростей - Δ_дус, спутниковой навигационной системы -

и с учетом

получимWe introduce the instrumental errors of information sources: accelerometers -

angular velocity sensors - Δ _dus , satellite navigation system -

and given

we get

или в случае ГГК угловую скорость

.The signal W _{1 is} used for stabilization in the horizon of the platform. In the case of W ₂ , in the case of ANN, the linear velocity

or in the case of GGC angular velocity

.

In the second option, you can get rid of the interference in the form of a linear velocity by subtracting it from the signal, taking into account the error of the SNA

(Таблица 1). T₀, Т₁, T_k - постоянные времени. В таблице показаны передаточные функции для крайних диапазонов частот ω→∞ и ω→0.In order to evaluate the disadvantages of this method of signal extraction ω _3g , we present a table of transfer functions with the simplest expression

(Table 1). T ₀ , T ₁ , T _k - time constants. The table shows the transfer functions for the extreme frequency ranges ω → ∞ and ω → 0.

We conventionally assign pitching α and vibrations of the dynamic vertical α _PU to the high-frequency range ω → ∞, and the remaining signals to the low-frequency range ω → 0. In this approximation, the difference between the signals of the second output and the linear velocity takes the form

и большая помеха от переносных ускорений качки

Колебания динамической вертикали слабо сглаживаются в зоне ЛАХ с наклоном 20 ^дБ/_дек. The drawback of isolating ω _3g from this expression is the dependence on the square of the time constant

and big interference from portable pitching accelerations

The vibrations of the dynamic vertical are slightly smoothed in the LAH zone with an inclination of 20 ^dB / _dec.

. Сигнал на Вых 3 запишется в видеIn FIG. 3 shows a diagram for calculating the horizontal components of the speed of rotation of the Earth, in which, in comparison with the diagram in FIG. 1 is excluded Output 2, Output 3 is installed and the transfer function of the filter is accepted 10.2

. The signal at Output 3 is written as

Turning to the table, we write the first approximation:

выбором малого коэффициента

можно уменьшить влияние помехи от переносного ускорения.This expression in the variable ω _{3r is} invariant to

the choice of a small coefficient

the effect of interference from portable acceleration can be reduced.

то в соответствии с таблицей 2 приближение приобретет видIf you take a high-order non-integral filter

then, in accordance with table 2, the approximation takes the form

The slope of the LAH at the pitching frequencies can be made arbitrarily large, and the influence of portable accelerations arbitrarily small. Therefore, introducing Exit 3, one obtains independence of the calculated value of ω _3g from the parameters of the circuit and from oscillations of the dynamic vertical, which significantly increases the accuracy of measurements.

With the help of auto-compensation, the sum (ω _3g + Δ _dus ) is separated, since the components of the Earth's rotation speed in the instrument coordinate system ω _zig - and ω _zg depend on the azimuth, and Δ _dus does not depend on it. In block 19, instrumental projections of the angular velocity of the Earth's rotation are distinguished:

and calculate the azimuth

The quadrupole signal is a sine wave at a double rotational speed of the platform. Since the quadrupole is symmetric with respect to the center and its signal does not have a definite sign, it is necessary, first of all, to introduce asymmetry, taking one of the ends of the dipoles as the base one. When the base ends of the dumbbells are located on one side of the isoline, they tend to approach each other, and when on opposite sides, they move away. The values of the quadrupole signals at the convergence of the ends will be considered positive, with the sign “+”, the values of the signals at the divergence of the ends will be considered negative, with the sign “-”. The intersection of the contour corresponds to the transition from the minus sign to the plus sign, that is, the positive sign “+” of the derivative.

The moment of transition of the signal through zero is fixed by cell 21, and the derivative is calculated and its sign is displayed in block 22. When the transition through zero occurs with the positive sign of the derivative, the “23” cell is activated and switches on 24, which supplies the isoline azimuth value to the output 1 of the calculator .

On a ship, for example, if the gradiometer is installed on a platform stabilized in the horizon and rotating in azimuth, you can determine the direction of the contour in the horizontal instrument coordinate system, then design it in the inclined instrument system. Then consistently transfer to the ship inclined and horizontal ship. The last action, adding a course, we calculate the azimuth in a geographical coordinate system. The invention proposes to replace four coordinate transformations with one direct measurement, which will increase the accuracy of the gradiometer.

Literature

1. Grushinsky N.V. "Fundamentals of gravimetry", M., Science, 1983.

2. RF patent No. 2 172 976 200108 27. “Gravity variometer”.

3. US patent No. 2012 222 481 2012 09 16. "Quadrupole transponder for gravity gradiometers OQR".

4. US patent No. 2002 0440 621 2009 02 19. “Accelerometer and software package for evaluating sensitivity for gravity gradiometer”.

5. Rivkin S.S., Berman Z.I., Okon I.M. “Determining the orientation parameters of an object by a strapdown inertial system”, St. Petersburg, Central Research Institute “Elektropribor”, 1996.

6. Ignatiev S.V. “Girohorizontkompas on fiber-optic gyroscopes with rotation of the block of sensitive elements.” - “Gyroscopy and navigation”, 2000, No. 3.

Claims (1)

Gravity gradiometer containing a quadrupole and gyroblock mounted on a horizontal platform and rotating in azimuth, as well as a calculator that houses a quadrupole signal processing unit, a gradient value calculation unit and consisting of a series of connected first integrator, non-integral filter and second integrator, circuit gyro verticals with an output along the pitch angle and four inputs, two of which are connected to the gyro unit, and two connected to the input and output of the non-integral filter, with a traveler’s navigation system, characterized in that the calculator has a contour for measuring the horizontal components of the Earth’s rotation speed, the output of which is the output of a non-integral filter, and one of the linear velocity inputs is the input of the second integrator, the calculator also has an azimuth calculation unit, a differentiation and indication block derivative sign, a cell indicating the transition of the signal through zero, an “I” cell with two inputs and a switch, and the output of the measurement circuit of the horizontal components of the The rotational axis of the Earth is connected to the input of the azimuth calculator, the output of which is connected to one of the contacts of the switch, the second contact of the switch is connected to the output of the calculator, the inputs of the cell indicating the transition of the signal through zero and the block of differentiation and indication of the sign of the derivative are connected to the output of the quadrupole information processing unit, and their the outputs are connected to the inputs of the cell "And", the output of which is connected to the switch.

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