RU2705926C1 - Complex for measurement of absolute value of gravitational acceleration on movable base - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: invention relates to the field of geodetic instrument-making, in particular to gravimeters, and is intended for determination of absolute value of gravity on a movable base. Technical effect is achieved due to the fact that in the gravity meter there are two feedback systems operating on two engines, but controlled by one position sensor – a tunnel microscope. One of them is a stabilization system with a relatively large time constant. It controls, through the absolute gravimeter, the first motor at GT change frequency. Other one – servo system with lower time constant – controls the second motor through its booster at rpm. Probe body of relative gravity meter is arranged on elastic membrane fixed on contour made of material with high internal damping.

EFFECT: high accuracy of measuring acceleration of gravity in sea conditions.

1 cl, 1 dwg

Description

The invention relates to the field of geodetic instrumentation, in particular to gravimeters, and is intended to improve the accuracy of determining the absolute acceleration of gravity (UST) on a moving base.

The known scheme [1], in which a relative gravimeter installed next to an absolute gravimeter is used as a device to reduce the influence of translational displacements on the readings of an absolute gravimeter. A feedback loop is organized in the circuit in which the absolute gravimeter corrects the relative in the low-frequency region, and the relative gravimeter corrects the absolute gravimeter in the high-frequency region.

A relative gravimeter [2] is known, in which the load is suspended on flat springs, and gravity is determined by optical means. The disadvantages of the gravimeter are the impossibility of its operation on a moving base due to the low overload capacity and the occurrence of long-damped natural oscillations when exposed to external forces.

To eliminate these shortcomings, a relative gravimeter [3] has been developed, in which, to ensure operability on a moving base, the load on an elastic suspension is placed in a viscous liquid. Deviation of the load is measured by optical means. The disadvantages of this scheme are the large time constant of the gravimeter and an open measurement circuit in which the position of the load changes relative to the housing, which leads to errors determined by the flows in the liquid.

In the gravimeter [4] there is a tracking system with an optical displacement sensor that holds the load in a constant position relative to the housing. The load in this gravimeter is also placed in a viscous fluid, which creates a large time constant of the gravimeter, causing distortion of the phase of the signal at the rolling frequencies.

The objective of the invention is to improve the accuracy of measuring TSI in marine conditions.

This is achieved by the fact that, in contrast to the well-known technical solution using two: absolute and relative gravimeters with one tracking system, the complex uses two feedback systems that operate on two engines but are controlled by a single position sensor - a tunneling microscope [5]. One is a well-known stabilization system with a relatively large time constant. It controls through the absolute gravimeter the first engine at the frequency of change of TSI. Another - tracking system with a lower time constant controls the second engine through its amplifier at the frequencies of the pitching. The load of the relative gravimeter is placed on an elastic membrane fixed along the contour made of a material with high internal damping [6].

The technical result consists in increasing the accuracy of determining TSI by reducing the errors of measurement of inertial accelerations.

The system device is shown in the diagram. It depicts the following elements:

1 - relative gravimeter,

2 - absolute gravimeter,

3 - membrane

4 - test body,

5 - probe tunneling microscope,

6 - the substrate of the tunneling microscope,

7, 8 - fixed plates of the first (capacitive) engine,

9 - movable lining of the first (capacitive) engine,

10 - piezoelectric actuator of the second engine,

11 - Converter - amplifier of the second engine,

12 - converter-amplifier of the first engine.

The proposed complex contains a relative gravimeter 1 and an absolute gravimeter 2. In a relative gravimeter, a load 4 is fixed on the membrane 3, the invariability of which relative to the housing is supported by the stabilization system. The displacement sensor of the system is a tunnel microscope with a probe 5 and a substrate 6. In the relative gravimeter, the first one is a capacitive motor with plates 7, 8, 9, and the second is a piezoelectric motor with actuator 10. The transducer-amplifier 11 is connected to the tunneling microscope at the input, and on exit with an absolute gravimeter and actuator. The output of the absolute gravimeter is connected to the Converter - amplifier 12, the output of which is connected to the first engine.

In operation, a relative gravimeter is mounted on the same platform as an absolute gravimeter. An absolute gravimeter measures the sum of gravitational and inertial accelerations at a frequency exceeding f _ag = 5 kHz. To obtain the true value of the acceleration of gravity (TSI), it is necessary to subtract from the measured sum the inertial component, which on the moving base can reach a = 100 Gal, and then, using statistical methods, reduce the measurement errors to those comparable to those obtained on a fixed base. The more accurately inertial accelerations are measured, the smaller the array of measurements is necessary for averaging with a given accuracy, and with a constant array the measurement accuracy increases. In existing marine relative gravimeters, in order to increase the overload capacity and smooth out oscillations at the pitching frequency, the load is placed in a damping fluid, providing a mechanical system time constant of about T = 1000 s [7] and a cutoff frequency f cutoff of ₁ = 10 ^-3 Hz. In this case, the signals, regardless of their origin with pump frequencies f _k = 0.1 Hz, are suppressed. There is a contradiction to the requirement, on the basis of which, in order to ensure correction of the absolute gravimeter, the signal of the relative gravimeter at the pumping frequency, of the order of f _k = 0.1 Hz, should be generated with minimal amplitude and phase distortions. To achieve this, it is necessary to build a system with a cutoff frequency of the order of f _cres2 = 10 ³ Hz. Such a frequency can be obtained in a dry gravimeter [2]. However, it is difficult to provide a measurement range of δg _abs = 10 ⁹ (accuracy at the level Δ a = 1 μGal in the range g = 1000 Gal). The task is facilitated by the fact that most of this range is constant. From the relative gravimeter in the proposed complex, it is required to measure the acceleration increments caused by the rocking of the ship, the value of not more than a _rock = 100 Gal. Given further averaging, the accuracy requirements can be reduced by two orders of magnitude, which will reduce the range to δg _rel = 10 ⁶ . In circuits [2, 3] with an open measurement circuit, it is difficult to obtain such a range of measurement of inertial accelerations. Therefore, a complex with a dry gravimeter and two closed tracking systems is proposed.

In the absence of damping fluid in the mechanical system of the gravimeter, elastic vibrations can occur with an amplitude exceeding the range of operation of the tunneling microscope and a frequency exceeding the range of operation of the tracking system. Therefore, the membrane of the relative gravimeter should be made of materials with high internal damping [6].

Известны формулы для прогиба упругой пластины, нагруженной в центре и закрепленной по окружности [8]Let us evaluate the deflection L of a steel membrane with a radius of R = 10 ^-2 [m] loaded with a test body with a mass of m = 0.01 kg, with acceleration of gravity -

Known formulas for the deflection of an elastic plate, loaded in the center and fixed around the circumference [8]

where P = mg = 0.1 [N] is the load in the center of the plate

h [m] - plate thickness

E = 2 * 10 ¹¹ [Pa], is the modulus of elasticity

μ = 0.28 - Poisson's ratio

учтем, что

[м²], перепишем выражение для прогиба в более удобном виде и рассчитаем величину максимального прогиба при ускорении g.Will accept

take into account that

[m ² ], we rewrite the expression for the deflection in a more convenient form and calculate the value of the maximum deflection during acceleration g.

In the first stabilization system, a capacitive motor is used to eliminate deflection. We assume that the capacitor plates are round flat disks [9]. It was assumed above that a load is used, with a mass of 10 g developing a force of F = 0.1H. Let’s determine the diameter of the capacitor’s disk developing this force,

In the formula [9], the dimensions are taken - for the gap d [mm], for the area - S [cm ² ] We write the formula with the same linear dimension [cm]

F = 3.5 * 10 ^-5 (ND) ²

- напряженность поля, К - коэффициент запаса,Where

- field strength, K - safety factor,

- допустимая напряженность поля в вакууме.

- permissible field strength in vacuum.

With a safety factor K = 1000 we get the diameter of the capacitor plates

Under marine conditions, the inertial accelerations of pitching and orbital motion reach 0.1 g, under the action of which the membrane will bend at L _1max = 10 ^-6 m. Such a deflection is compensated by a piezoceramic actuator [10].

туннельный микроскоп [5] с разрешениемWith specific deflection

tunnel microscope [5] with resolution

for moving L _bit = 10 ^-12 [m] gives the resolution for acceleration

гравитационная аномалия длиной Q=100 м, преодолевается за t=10 с. Амплитуда гравитационной аномалии на море не превышает Δg<10^-3g. Следовательно, скорость изменения УСТ при измерениях на движущимся корабле не превышает

Ускорения, вызванные качкой, корабля имеет период порядка Т_кач≈10 с и амплитуду а _кач=10^-1g. Скорость изменения ускорения качки порядка

Отношение скоростей изменения гравитационных и инерционных ускоренийWhen the ship moves at speed

the gravitational anomaly with a length of Q = 100 m is overcome in t = 10 s. The amplitude of the gravitational anomaly at sea does not exceed Δg <10 ^-3 g. Consequently, the rate of change of TSI during measurements on a moving ship does not exceed

Acceleration caused by the pitching of the ship has a period of the order of T _Qual ≈10 sec and amplitude and _Qual = 10 ^-1 g. The rate of change of the acceleration of the pitching order

The ratio of the rates of change of gravitational and inertial accelerations

должно быть в первой следящей системе по отношению ко второй.Approximate same time constant ratio

must be in the first tracking system with respect to the second.

The technical effect is to increase the accuracy of absolute measurements of the TSI on a moving base.

A complex for measuring the absolute acceleration of gravity on a moving base, consisting of an absolute gravimeter and a relative gravimeter with a tracking system, characterized in that a tunnel microscope is used as a displacement sensor in the relative gravimeter, the test body of the relative gravimeter is mounted on a membrane made of an alloy with a high internal damping, a second tracking system was introduced into the complex to keep the gap between the probe and the microscope substrate constant, for both systems Use This Criterion one displacement sensor and various engines: a system with a larger time constant is closed through the absolute gravimeter for the first motor, and the system with a lower time constant is shorted to the second motor.

Information sources

1. The method of measuring on a moving basis the absolute value of the acceleration of gravity and gravimeters for its implementation. RF patent No. 2523108 of 02.28.2013. Author and patent holder A. Popov

2. The gravimeter. RF patent No. 2253882 dated 11.28.2003. Authors: Bykov A.P., Kulesh V.P., Moskalik L.M., Enina O.E. Patent holder: Open Joint-Stock Company "Oil Instrumentation" ("Neftekip").

3. Quartz gravimeter. RF patent No. 2171481 dated 03.02.2000. Authors and patent holders: Bronstein I.G., Livshits I.L., Elinson L.S.

4. Static gravimeter RF Patent 2427008 of 08/26/2009. Authors of the invention: Neronov N.N., Denesyuk E.A. Patentee: Open Joint-Stock Company State Scientific Research Navigation and Hydrographic Institute of the Russian Ministry of Defense.

5. Mironov V.L. The basics of scanning probe microscopy. RAS. Institute of Physics of Microstructures. Nizhny Novgorod. 2004 year

6. Bershtam Ya.M., Evstifeev M.I., Eliseev D.P. Study of alloys with high internal damping in the design of micromechanical gyroscopes. 7th Russian multi-conference on management issues. St. Petersburg, 2014.

7. L.K. Zheleznyak, E.I. Popov. New resilient marine gravimeter system. Gravial inertial equipment in geophysical research. M: IFZ AN SSSR, 1988, p. 92.

8. Sargsyan Structural mechanics П17-1 DOK. StudFiles.net> preview / 3189876 / page 2.

9. Atsyukovsky VA, Capacitive differential displacement sensors. Automation Library, vol. 12, Gos. energo. Publishing House, 1960, sheet 15, f. fifteen.

10. Bobtsov A.A., Boykov V.I., Bystrov S.V., Grigoryev V.V. Actuators and systems for micromotion. Saint-Petersburg State University of Information Technologies, Mechanics and Optics. St. Petersburg, 2011.

Claims (1)

A complex for measuring the absolute acceleration of gravity on a moving base, consisting of an absolute gravimeter and a relative gravimeter with a tracking system, characterized in that a tunnel microscope is used as a displacement sensor in the relative gravimeter, the test body of the relative gravimeter is mounted on a membrane made of high alloy internal damping, a second tracking system was introduced into the complex to keep the gap between the probe and the microscope substrate constant, for both systems one displacement sensor and different motors were used: the system with the greater time constant is closed through the absolute gravimeter to the first engine, and the system with the lower time constant is closed to the second engine.

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