Inertial sensor residual gas noise testing method based on torsion balance system

Abstract

The invention provides an inertial sensor residual gas noise testing method based on a torsion balance system. The inertial sensor residual gas noise testing method comprises the steps that S1, the environment pressure intensity of the torsion balance system is set; s2, a damping coefficient-pressure relation curve is obtained by measuring data of the torsion balance system under set time free oscillation; s3, adjusting the environment pressure intensity of the torsion balance system, and repeating the step S2; and S4, performing data processing on the test data, evaluating the residual gas test noise level, calculating the relationship between amplitude attenuation and the periodicity, and calculating the residual gas noise damping. Compared with the prior art, the method has the advantages that by exploring and researching residual gas interference factors in a complex dynamic system influencing on-orbit operation of the inertial sensor, a brand new test and evaluation method is provided under the ground 1g gravity environment and complex interference conditions, and reliable experimental support is provided for optimization design of the space inertial sensor.

Description

Technical Field

[0001] This application belongs to the field of space science, and specifically relates to a method for testing the residual gas noise of an inertial sensor based on a torsion balance system. Background Art

[0002] For space gravitational wave detection missions, the detection ability of the detector is jointly determined by two top-level indicators: the residual acceleration noise level of the test mass of the inertial sensor and the laser ranging accuracy. The residual acceleration noise of the test mass of the inertial sensor is the acceleration noise of the test mass deviating from the free-fall motion in the gravitational field in the laser ranging (sensitive axis) direction, and is a key factor restricting the sensitivity level of gravitational wave detection in the mid-low frequency band. The test mass is the end point of the inter-satellite distance measurement. The main role of the inertial sensor system is to shield the interference and stray coupling from the space environment and the satellite internal environment as much as possible, and ensure that the test mass moves along the geodesic in the gravitational field as much as possible. Therefore, the accuracy level of the inertial sensor has a direct impact on the sensitivity of the space gravitational wave detection mission in the mid-low frequency band.

[0003] In the extremely high vacuum environment of deep space orbits, due to the outgassing effect of materials and the presence of surface-adsorbed gas molecules, there are a large number of residual gas molecules inside the sensitive structure of the inertial sensor. These molecules randomly impact the inertial test mass, and the resulting acceleration perturbation is one of the main noise sources in the mid-low frequency band.

[0004] The existing technologies mainly evaluate the noise through theoretical modeling and limited experimental data, but lack experimental verification means with strong pertinence and high precision. At the same time, due to the limitations of the test environment, it is difficult for the existing methods to truly simulate the high vacuum degree of the space environment under ground conditions, resulting in a gap in the fitting accuracy between the theory and experimental data. Therefore, a method capable of measuring the residual gas noise of the inertial sensor with high precision under ground conditions is needed. Summary of the Invention

[0005] The purpose of this application is to overcome the defect that it is difficult for the existing methods to truly simulate the high vacuum degree of the space environment under ground conditions.

[0006] To achieve the above purpose, this application proposes a method for testing the residual gas noise of an inertial sensor based on a torsion balance system, including:

[0007] Step S1: Set the environmental pressure of the torsion balance system;

[0008] Step S2: Obtain the damping coefficient-pressure relationship curve by measuring the data of the free oscillation of the torsion balance system for a set time;

[0009] Step S3: Adjust the environmental pressure of the torsion balance system and repeat Step S2;

[0010] Step S4: Process the test data, evaluate the residual gas test noise level, calculate the relationship between amplitude attenuation and the number of cycles, and calculate the residual gas noise damping.

[0011] As an improvement of the above method, the calculation method of the damping coefficient β is as follows:

[0012]

[0013] Where f represents the natural frequency of the torsion balance; and represent the amplitudes of the i-th and (i + j)-th vibration cycles; I r represents the moment of inertia of the torsion balance.

[0014] As an improvement of the above method, the noise level is obtained by fitting the damping coefficient-pressure relationship curve.

[0015] As an improvement of the above method, extend the damping coefficient-pressure relationship curve to obtain the damping coefficient under lower vacuum.

[0016] As an improvement of the above method, the set time in step S2 is not less than 4×10 4 s.

[0017] As an improvement of the above method, the change range of the ambient pressure of the torsion balance system is from 10 -4 Pa to 10 -2 Pa.

[0018] As an improvement of the above method, it further includes:

[0019] Before the test, make the torsion balance system reach a stable state, including:

[0020] The test noise power spectrum of the optical readout laser interferometer circuit reaches 10 -12 ms -2 Hz -1 / 2 ;

[0021] The average temperature fluctuation in the vacuum chamber is less than 1°C.

[0022] As an improvement of the above method, it further includes:

[0023] Before the test, calibrate the torsion balance system to obtain the parameters of the torsion balance system, including: stiffness, eigenfrequency, and damping.

[0024] Compared with the prior art, the advantages of this application are:

[0025] 1. This application is oriented to the space gravitational wave detection mission, and innovatively constructs a ground test method for the residual gas noise of ultra-high-precision inertial sensors;

[0026] 2. By exploring and studying the residual gas interference factors in the complex dynamic system affecting the in-orbit operation of inertial sensors, a new test and evaluation method is provided under the ground 1g gravity environment and complex interference conditions;

[0027] 3. This application proposes a test method with adjustable pressure, providing reliable experimental support for the optimized design of space inertial sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure shows a schematic diagram of the working principle of the torsion balance;

[0029] Figure 2 The figure shows a sectional view of the residual gas test device;

[0030] Figure 3 The figure shows the residual gas measuring equipment;

[0031] Figure 4 The figure shows a flowchart of the method for testing the residual gas noise of an inertial sensor based on a torsion balance system;

[0032] Figure 5 The figure shows that at a pressure of 10 -4 Pa, the torsion balance system gradually decays under the action of damping and gradually reaches the equilibrium state of dissipation and fluctuation;

[0033] Figure 6 The figure shows that at a pressure of 10 -2 Pa, the torsion balance system gradually decays under the action of damping and gradually reaches the equilibrium state of dissipation and fluctuation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The technical solutions of this application will be described in detail below with reference to the accompanying drawings.

[0035] The present invention aims to break through the limitations of existing methods and propose a method for testing the residual gas noise of an inertial sensor based on a torsion balance system, which can accurately measure the gas damping coefficient and the corresponding acceleration noise characteristics inside the sensitive structure of the sensor under ground conditions, provide a reliable basis for improving the sensor design and optimizing the performance, and evaluate the complex interference factors affecting the in-orbit operation of inertial sensors from a more refined and comprehensive perspective.

[0036] A method for testing the residual gas noise based on a single test mass torsion balance system proposed by the present invention specifically includes:

[0037] 1. Test equipment

[0038] The core of the torsion balance system is the torsion balance unit and the angle measurement unit. The torsion balance unit consists of a test mass suspended by a suspension wire and is used to respond to weak force signals; the angle measurement unit mainly uses optical measurement equipment, such as an autocollimator, to measure the deflection angle and motion period of the torsion balance. The test mass rotates freely around the suspension wire. The torsion balance can measure the torque in a plane perpendicular to the gravitational field and is weakly coupled to ground micro-vibration noise. A schematic diagram of the principle of the torsion balance is shown in Figure 1 as follows.

[0039] When a torque N is applied to the torsion balance, the test mass suspended on the suspension wire will correspondingly generate a torsional angle φ. The time series data of the torsional angle φ(t) of the torsion balance can be obtained through the angle measurement unit. The torsion balance system follows the following dynamic equation along the degree of freedom φ:

[0040]

[0041] where is the torsional angular velocity, is the torsional angular acceleration, I is the moment of inertia of the pendulum, γ is the dissipation term (damping force), Γ is the torsional stiffness constant of the suspension wire, and N(t) is the torsional torque.

[0042] In the frequency domain, the dynamic equation of this degree of freedom can be written as:

[0043] -Iω 2 φ(ω)+Γ(1 + iδ)φ(ω) = N(ω)

[0044] where ω is the frequency, i is the imaginary unit, δ = 1 / Q, Q is the quality factor, and the angular displacement φ(ω) of the torsion balance system can be mutually converted through the transfer function H(ω) and the torque N(ω):

[0045] φ(ω) = H(ω)N(ω)

[0046] The transfer function H(ω) of the torsion balance is defined as:

[0047]

[0048] where ω0 is the natural resonance angular frequency.

[0049] Ideally, the main motion of the torsion balance is a torsional motion with a single degree of freedom. The torsional motion on the horizontal plane is perpendicular to the direction of gravity, so it is decoupled from gravity, which makes the torsion balance one of the main tools for ground-based weak force measurement. However, when considering the motion of the torsion balance in three-dimensional space, in addition to the torsional motion, the motion of the torsion balance will also include swinging in the vertical plane, elastic jitter along the direction of the suspension wire, and rolling of the inertial element on the horizontal plane, jointly constituting a six-degree-of-freedom motion model of the torsion balance. However, in the existing literature, the rolling of the inertial element on the horizontal plane has not been observed, so the actual motion of the torsion balance is mainly: 1). Torsional motion φ around the suspension wire; 2). Swinging in the vertical plane (two degrees of freedom η, θ); 3). Elastic jitter δ along the direction of the suspension wire.

[0050] To meet the requirements of various noise measurements, it is necessary to place the torsion balance measurement system in a vacuum chamber to avoid the influence of the external environment as much as possible.

[0051] As Figure 2 and Figure 3 shown, the partial equipment and components of the single test mass weak force measurement torsion balance are as follows:

[0052] Autocollimator: used to detect the rotation angle of the torsion balance.

[0053] Suspended test mass: a hollow aluminum test mass with a gold-plated outer surface.

[0054] Suspension member: used to support and control the motion of the test mass, and effectively isolate external interference.

[0055] Electrode cage: located outside the test mass, used to apply electrostatic drive excitation during the experiment.

[0056] Small vacuum chamber (not shown in the figure, all components are located inside the small vacuum chamber): used to control the pressure of the test environment, and the ultimate pressure of the torsion balance environment needs to be less than 3×10 -6 Pa.

[0057] Four-axis adjustment table: used to enable the suspension wire system to accurately position the test mass in multiple directions and perform fine adjustment.

[0058] Suspension wire: a quartz wire with a diameter of 50 μm, a Q value of about 1.2×106, a natural frequency of about 0.25 MHz, a vibration period of about 4000 s, and the suspension position is at the center of the upper surface of the test mass box. The high-Q quartz wire is less affected by other materials or mechanical damping, and a more accurate gas damping coefficient can be measured.

[0059] 2. Test scheme

[0060] For inertial sensors According to the index requirements, measure the damping force on the test mass inside the electrode cage, and extend the physical laws in combination with the actual internal dimensions and pressure of the inertial sensor to obtain the damping coefficient and corresponding acceleration noise under working conditions.

[0061] The inertial sensor is located in a deep space orbit with a high vacuum. Due to the adhesion of gas molecules to the material itself and the outgassing effect on the material surface, there will be a large number of residual gas molecules filling the sensitive structure inside, that is, the space between the electrode cage and the test mass. The stray acceleration caused by the random collision of the residual gas molecules with the test mass is the dominant noise source in the medium and low frequencies.

[0062] Adjust the pumping speed of the vacuum pump to change the internal pressure of the torsion balance vacuum chamber from 10 -4 Pa to 10 -2 Pa. The corresponding mean free path of the molecules is from 10 km to 10 m, that is, the internal gas molecules are completely in the molecular flow state. Measure the β-P curve by measuring the damping at different pressures.

[0063] The experimental measurement expression of the damping strength is:

[0064]

[0065] As long as the natural frequency f of the torsion balance, the amplitudes and of the selected i-th and (i + j)-th vibration periods, and the moment of inertia I of the torsion balance r are obtained, the damping coefficient of the torsion balance can be calculated.

[0066] (1) Test method

[0067] The test method for residual gas noise is to use a single test mass torsion balance to measure the damping force on the test mass inside the electrode cage, and extend the physical laws in combination with the actual internal dimensions and pressure of the inertial sensor to obtain the damping coefficient and corresponding acceleration noise under working conditions. The noise level is obtained by fitting the relationship curve between the damping coefficient and the pressure, where the damping coefficient is calculated by measuring the frequency of the torsion balance, the amplitude of the vibration period, and the moment of inertia of the torsion balance.

[0068] The experimental procedure for residual gas noise testing is as Figure 4 shown. First, calibrate the test equipment and components (calibration of the weak force measurement system of the torsion balance, electronics system). After the test system is stable (temperature and pressure), adjust the pumping speed of the vacuum pump to change the internal pressure of the torsion balance vacuum chamber from 10 -4 Pa to 10 -2It varies between Pa. The test mass is driven to move initially at different pressures, and the β-P curve is obtained by measuring the data during long-time free oscillation. Since it is difficult to achieve the required vacuum degree in the inertial sensor in space during the ground verification experiment, it is necessary to extrapolate to obtain the damping coefficient value at lower vacuum. The test data is processed and analyzed, and finally the residual gas noise is evaluated.

[0069] (2) Preparation of data acquisition equipment

[0070] 1) Adjust the residual gas noise test system based on the single test mass torsion balance to make it reach a stable state;

[0071] 2) Confirm that the test noise power spectrum of the optical readout laser interference circuit reaches 10 -12 ms -2 Hz -1 / 2 of the design index;

[0072] 3) Confirm that the average temperature fluctuation in the vacuum tank is less than 1°C;

[0073] 4) The software and hardware system is in the test state.

[0074] (3) Test method process

[0075] Step 1: Before the experiment, calibrate the test equipment / components, calibrate the weak force measurement system of the torsion balance, and obtain the parameters of the torsion balance system, such as stiffness, eigenfrequency, damping, etc. Based on these parameters, complete the calibration of the electronics system.

[0076] Step 2: Complete the test preparation according to what is described in the preparation of data acquisition equipment.

[0077] Step 3: Set the system environmental pressure.

[0078] Step 4: Obtain the β-P curve by measuring the data during long-time free oscillation. Use the optical readout system to continuously record the rotation angle and amplitude data of the sensitive structure. The data recording time for each position is not less than 4×10 4 s (days order), and the experimental data is segmented and averaged.

[0079] Step 5: Adjust the system environmental pressure and repeat Step 4.

[0080] Step 6: Process and analyze the test data to evaluate the residual gas test noise level. The dynamic readout data of the torsion balance and the environmental monitoring data are collected, archived and processed, and the relationship between the amplitude attenuation and the number of cycles and the residual gas noise damping are calculated using the existing calculation methods.

[0081] (4) Requirements for the test environment of the scheme

[0082] Environmental temperature: 22±1°C

[0083] Relative humidity: 20 - 80% RH

[0084] Atmospheric pressure: Normal atmospheric pressure

[0085] Grounding: Anti - static grounding.

[0086] Example 1

[0087] (1) Parameter setting

[0088] Pressure: 10 -4 Pa

[0089] Initial deviation angle of the torsion balance from the equilibrium position: 50 μrad

[0090] Measurement duration: 4×10 4 s, about 12 hours, meeting the requirement of statistically counting the amplitude decay ratio for 10 cycles.

[0091] (2) Calculation results

[0092] As Figure 5 shown, by calculating the amplitude decay ratio for the interval of 10 cycles, the obtained damping coefficient is 2.724×10 -8 N·s / m2.724×10 -8 N·s / m, and the relative error compared with the theoretical value of 2.561×10 -8 N·s / m is 6.3%.

[0093] Example 2

[0094] (1) Parameter setting

[0095] Pressure: 10 -2 Pa

[0096] Initial deviation angle of the torsion balance from the equilibrium position: 50 μrad

[0097] Measurement duration: 4×10 4 s, about 12 hours, meeting the requirement of statistically counting the amplitude decay ratio for 10 cycles.

[0098] (2) Calculation results

[0099] As Figure 6 shown, through calculation, it can be known that after about 10 cycles, the rotation amplitude will be less than 100 nrad, approaching the resolution of the measuring device, which makes the measurement uncertainty larger.

[0100] The technical solution of this application innovatively constructs a ground test scheme for the residual gas noise of ultra - high - precision inertial sensors, bringing the following advantages:

[0101] (1)Accurately simulate the noise impact in the space environment;

[0102] By measuring the damped oscillation data under different pressures, the β-P curve is obtained. Through extrapolation, the damping coefficient in a lower vacuum environment in space can be obtained, and finally the residual gas noise is evaluated.

[0103] (2)Promote the performance improvement of inertial sensors;

[0104] Through comprehensive noise assessment and interference factor identification, a reliable basis is provided for the design and optimization of inertial sensors, thus helping to improve the performance of the sensors.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present application does not depart from the spirit and scope of the technical solutions of the present application, and they should all be covered by the scope of the claims of the present application.

Claims

1. A method for testing the residual gas noise of an inertial sensor based on a torsion balance system, comprising: Step S1: Set the ambient pressure of the torsion balance system; Step S2: Obtain a damping coefficient-pressure relationship curve by measuring the data of the free oscillation of the torsion balance system for a set time; Step S3: Adjust the ambient pressure of the torsion balance system and repeat Step S2; Step S4: Process the test data, evaluate the residual gas test noise level, calculate the relationship between amplitude decay and the number of cycles, and calculate the residual gas noise damping.

2. The residual gas noise test method for an inertial sensor based on a torsion balance system according to claim 1, characterized in that The calculation method of the damping coefficient β is: where f represents the natural frequency of the torsion balance; and represent the amplitudes of the i-th and (i + j)-th vibration periods; I r represents the moment of inertia of the torsion balance.

3. The residual gas noise test method for an inertial sensor based on a torsion balance system according to claim 1, characterized in that, The noise level is obtained by fitting the damping coefficient-pressure relationship curve.

4. The method for testing residual gas noise of an inertial sensor based on a torsion balance system according to claim 3, wherein Extend the damping coefficient-pressure relationship curve to obtain the damping coefficient at a lower vacuum.

5. The method for testing residual gas noise of an inertial sensor based on a torsion balance system according to claim 1, wherein The set time in the step S2 is not less than 4×10 4 s.

6. The method for testing residual gas noise of an inertial sensor based on a torsion balance system according to claim 1, characterized in that, The variation range of the environmental pressure of the torsion balance system is from 10 -4 Pa to 10 -2 Pa.

7. The method for testing the residual gas noise of an inertial sensor based on a torsion balance system according to claim 1, wherein It further includes: Before the test, make the torsion balance system reach a stable state, including: The measured noise power spectrum of the optical readout laser interference circuit reaches 10 -12 ms -2 Hz -1 / 2 ; The average temperature fluctuation in the vacuum chamber is less than 1°C.

8. The method for testing residual gas noise of an inertial sensor based on a torsion balance system according to claim 7, wherein It further includes: Before the test, calibrate the torsion balance system to obtain the parameters of the torsion balance system, including: stiffness, eigenfrequency, and damping.

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