A vibration isolation device low-frequency transfer characteristic test system and test method

Abstract

The present application relates to a kind of vibration isolation device low-frequency transfer characteristic test system and test method, belong to spacecraft vibration reduction field.A kind of vibration isolation device low-frequency transfer characteristic test system, comprising: disturbance source simulator, vibration-isolated component, spacecraft simulation cabin, cabin unloading device, vibration-isolated component unloading device, suspension device, mass center alignment component and micro-vibration measuring device;Wherein, the disturbance source simulator is installed on the side plate of spacecraft simulation cabin, and the spacecraft simulation cabin is hung on the suspension device by the cabin unloading device;The vibration-isolated component is used to be set on the vibration isolation device to be tested, and is hung on the suspension device by the vibration-isolated component unloading device;The mass center alignment component is installed on the bottom plate of the spacecraft simulation cabin;The micro-vibration measuring device is used to test the micro-vibration parameter of different positions and the frequency characteristic of test system.

Description

Technical Field

[0001] This invention relates to a testing system and method for testing the low-frequency transmission characteristics of vibration isolation devices, belonging to the field of spacecraft vibration reduction and isolation. Background Technology

[0002] To achieve millisecond-level tolerance to micro-vibration environments for onboard sensitive components, these components require low-stiffness, high-damping vibration isolation devices. The frequency of these isolation devices will be below 2Hz, significantly lower than the frequency of typical vibration isolation devices (not lower than 20Hz). Traditional simulation testing systems cannot simulate excitation below 20Hz or test the low-frequency transmission characteristics of the isolation devices in vibration isolation efficiency testing. Consequently, they cannot evaluate the low-frequency isolation efficiency of the devices, directly impacting the evaluation of vibration isolation performance and product delivery.

[0003] Conventional vibration isolation device performance evaluation typically employs a simulation testing platform. This platform uses an excitation system to simulate the interference force output of a source, thereby assessing the vibration isolation performance of the device. However, due to the stiffness characteristics of existing vibration isolation devices and the limitations of current vibration isolation efficiency testing platforms, it is impossible to test the low-frequency vibration isolation efficiency of these devices; testing and evaluation can only be performed above 20Hz. For this type of testing, measurements and evaluations are generally conducted in real-world usage environments. However, this method is time-consuming, costly, and significantly delays product design improvements.

[0004] In response to the needs of low-frequency vibration isolation efficiency testing and vibration isolation performance evaluation of vibration isolation devices, a test system and implementation method for testing the low-frequency transmission characteristics of vibration isolation devices were designed and constructed. This system is used for transmission characteristic testing during the product design, development and verification stages to evaluate the product's vibration isolation performance, vibration isolation efficiency and compliance with its technical specifications. Summary of the Invention

[0005] In view of this, the present invention provides a low-frequency transmission characteristic testing system and method for vibration isolation devices. By simulating the characteristics of real vibration sources and the transmission characteristics of real structures, the vibration isolation efficiency of the vibration isolation device in the low-frequency range (20Hz and below) is tested, which is used to evaluate the vibration isolation efficiency of the vibration isolation device and determine the compliance of the vibration isolation index of the vibration isolation device.

[0006] The technical solution for implementing the present invention is as follows:

[0007] A low-frequency transmission characteristic testing system for vibration isolation devices includes: a vibration source simulator, a vibration isolation component, a spacecraft simulation cabin, a cabin unloading device, a vibration isolation component unloading device, a suspension device, a center of mass balancing component, and a micro-vibration measurement device.

[0008] The vibration source simulator is mounted on the side plate of the spacecraft simulation cabin, and the spacecraft simulation cabin is suspended on the suspension device via the cabin unloading device; the vibration isolation component is used to be mounted on the vibration isolation device to be tested, and is suspended on the suspension device via the vibration isolation component unloading device; the center of mass balancing component is mounted on the bottom plate of the spacecraft simulation cabin; the micro-vibration measuring device is used to test the micro-vibration parameters at different locations and the frequency characteristics of the test system.

[0009] The cabin unloading device includes multiple suspension devices, each consisting of ropes, springs, and a height adjustment device, used to put the spacecraft simulated cabin in an unloading state;

[0010] The unloading device for the vibration-isolated component mainly consists of a suspension rope, a height adjustment device, a spring, and a force measuring device; it is used to unload the vibration-isolated component and simulate the on-orbit flight state of the vibration-isolated component.

[0011] Furthermore, each suspension device of the present invention contains multiple springs connected in series.

[0012] Furthermore, the stiffness k0 of the single spring described in this invention satisfies the following relationship:

[0013]

[0014] Where m1 is the load-bearing mass of a single suspension device, and L is the maximum allowable deformation of the spring.

[0015] Furthermore, the length l of the suspension rope described in this invention satisfies the following relationship:

[0016] pL0+l+Δl <h

[0017] Where Δl is the adjustable height of the height adjustment device, h is the suspension height, and pL0 is the total length of p springs.

[0018] Furthermore, the vibration measurement device described in this invention comprises various types of measurement sensors and corresponding measurement data acquisition systems, which are respectively arranged on the vibration transmission path for measuring the vibration characteristics on the vibration transmission path.

[0019] A method for testing the low-frequency transmission characteristics of a vibration isolation device includes the following specific steps:

[0020] (1) Determine whether the test system meets the test conditions:

[0021] a) Determining the unloading frequency of the vibration-isolated component: Measure whether the frequency of the vibration-isolated component after unloading meets the test requirements. If it does not meet the requirements, adjust the spring stiffness to ensure that the unloading frequency meets the test requirements.

[0022] b) Determination of unloading force of the vibration-isolated component: The force measuring device on the vibration-isolated component determines whether the vibration-isolated component is completely unloaded. If it is not completely unloaded, the suspension height is adjusted to unload the vibration-isolated component.

[0023] c) Test system unloading frequency: After the simulated cabin test system is unloaded, determine whether the system frequency meets the test requirements; if it does not meet the requirements, adjust the spring stiffness to ensure that the unloading frequency meets the test requirements;

[0024] (2) Simulated cabin modal testing

[0025] Conduct modal tests on the local structure of the simulated vibration source installation and the local structure of the vibration isolation device and the vibration-isolated component installation. If the set requirements are not met, make improvements to the local structure.

[0026] (3) Background noise test of the test system

[0027] Vibration and noise tests were conducted on the entire test system. If the noise did not meet the requirements, the background noise was adjusted.

[0028] (4) When the tests in steps (1)-(3) above meet the requirements, conduct low-frequency transmission characteristic tests on the vibration isolation device.

[0029] Furthermore, when performing modal tests on the local structure of the vibration isolation device and the vibration-isolated component, the present invention determines whether the stiffness characteristics of the local structure deviate from the stiffness of the actual structure within 10Hz. If so, it is determined that the requirements are met.

[0030] Furthermore, the condition for whether the background noise of the system described in this invention meets the measurement requirements is that the peak-to-peak value of the system noise in the low-frequency band is not higher than 0.5 mg.

[0031] Furthermore, the vibration and noise test of the entire test system described in this invention is as follows:

[0032] First, the collected noise signal is converted into a digital signal using an AD converter;

[0033] Secondly, the measured noise data is low-pass filtered to remove noise signals above 45Hz;

[0034] Finally, the data is interpreted. If the noise does not meet the requirements, the main characteristics and sources of the noise signal are analyzed.

[0035] Beneficial effects:

[0036] (1) The present invention designs a small cabin unloading device and a vibration isolation component unloading device. The small cabin unloading device is used to unload the simulated small cabin, the vibration isolation component unloading device is used to unload the vibration isolation component, and the centroid balancing component is used to balance the centroid of the test system, thereby ensuring that the system can test the vibration isolation efficiency of the vibration isolation device in the low frequency band (20Hz and below).

[0037] (2) In the design of this invention, the spring stiffness and rope length in the unloading device of the small compartment are constrained, thereby further ensuring that the designed system can meet the requirements for testing the vibration isolation efficiency in the low frequency band (20Hz and below).

[0038] (3) Before testing, the present invention determines the unloading frequency of the vibration isolation component, the unloading force of the vibration isolation component, the unloading frequency of the test system, the simulated cabin mode and the background noise of the test system, thereby ensuring the accuracy of the low-frequency transmission characteristics test of the vibration isolation device.

[0039] (4) When conducting vibration and noise tests on the entire test system, the collected noise data is interpreted and the main characteristics and sources of the noise signal are analyzed, so as to facilitate the adjustment of the background noise and make the test environment noise meet the requirements of low-frequency testing.

[0040] (5) When performing modal tests on the local structure of the vibration isolation device and the vibration isolation component, the present invention requires that the stiffness characteristics of the local structure deviate from the stiffness of the real structure within 10Hz. Therefore, it can realistically simulate the characteristics of the vibration disturbance source and the transmission characteristics of the vibration disturbance source on the structure, obtain the micro-vibration environment transmitted from the vibration disturbance source to the vicinity of the vibration isolation component installation location, and realize the indirect simulation of the micro-vibration test at the spacecraft system level. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 Diagram of the low-frequency transmission characteristics testing system for vibration isolation devices;

[0043] Figure 2 This is a diagram showing the components of a vibration isolation parameter measuring device.

[0044] Figure 3 To simulate the configuration of the small cabin and its external interfaces;

[0045] Figure 4 Diagram showing the configuration of the small compartment unloading device;

[0046] Figure 5 This is a diagram showing the structure of the unloading device for the vibration-isolated components. Detailed Implementation

[0047] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0048] This invention provides a low-frequency transmission characteristic testing system for vibration isolation devices, such as... Figure 1 As shown, it includes: a vibration source simulator 1, a vibration isolation component 3, a spacecraft simulation cabin 4, a cabin unloading device 5, a vibration isolation component unloading device 6, a suspension device 7, a center of mass balancing component 8, and a micro-vibration measurement device 9.

[0049] The vibration source simulator 1 is mounted on the side plate of the spacecraft simulation cabin 4; the spacecraft simulation cabin 4 is suspended on the suspension device 7 via the cabin unloading device 5; the vibration isolation component 3 is used to be mounted on the vibration isolation device 2 to be tested, and is suspended on the suspension device 7 via the vibration isolation component unloading device 6; the center of mass balancing component 8 is mounted on the bottom plate of the spacecraft simulation cabin 4; and the micro-vibration measuring device 9 is used to test the micro-vibration parameters at different locations and the frequency characteristics of the test system.

[0050] The cabin unloading device 5 includes multiple suspension devices, each of which consists of a rope 5-1, a spring 5-2, and a height adjustment device 5-3; used to put the spacecraft simulated cabin in an unloading state.

[0051] The unloading device 6 for the vibration-isolated component mainly consists of a suspension rope 6-1, a height adjustment device 6-2, a spring 6-3, and a force measuring device 6-4; it is used to unload the vibration-isolated component and simulate the on-orbit flight state of the vibration-isolated component.

[0052] This embodiment designs the cabin unloading device 5 and the vibration isolation component unloading device 6. The cabin unloading device 5 is used to unload the simulated cabin 4, the vibration isolation component unloading device 6 is used to unload the vibration isolation component 3, and the center of mass balancing component 8 is used to balance the center of mass of the test system, thereby ensuring that the system can test the vibration isolation efficiency of the vibration isolation device in the low-frequency band (20Hz and below).

[0053] The following is a detailed description of each component of the system:

[0054] Common electromagnetic excitation sources can only simulate excitation frequencies above 20Hz. The vibration source simulator 1 used in this solution can employ real vibration source products, electrical performance products, or simulated components (interference sources identical to real components are used to simulate low-frequency interference characteristics, enabling it to simulate test environments below 20Hz). Figure 2In section 1-1, the simulation of disturbance characteristics (including disturbance frequency characteristics and amplitude characteristics) is realized. The disturbance source simulator 1 can be directly mounted on the side plate of the simulation cabin, or it can be mounted on a bracket such as... Figure 2 As shown in Figure 1-2, it is installed on the side plate of the simulation cabin 3.

[0055] Vibration isolation device 2 is the actual product to be tested, and the vibration-isolated component 3 is a mass simulation component that simulates the mass and inertia of the vibration-isolated component, such as... Figure 2 As shown, the vibration isolation device 2 is installed on the bottom plate of the simulated cabin 4, and the vibration isolation component 3 is installed on the vibration isolation device 2.

[0056] Spacecraft simulation pod 4, such as Figure 3 As shown, it is a semi-enclosed structure that provides installation support for the vibration source simulator, vibration isolation device, and vibration-isolated components. It adopts a structural plate with the same mechanical properties as the real structure. The local stiffness of the structural plate is consistent with the stiffness characteristics of the local installation structure of the vibration source and vibration-isolated components on the spacecraft. Without loss of generality, the size and dimensions of the cabin can be adaptively modified according to the local structural characteristics of the installation location of the vibration source, vibration isolation device, and vibration-isolated components on the spacecraft. The simulation cabin provides three types of interfaces, including vibration source simulator 1 interface 3-1, vibration isolation device installation interface 3-2, and center of gravity balancing component installation interface 3-3.

[0057] The small compartment unloading device 5 consists of several spring assemblies, each spring assembly being configured as follows: Figure 4 As shown, a single spring assembly consists of several suspension ropes (5-1), a height adjustment device (5-2), and several springs (5-3). The springs can be composed of several connected in series. The key points of the unloading device are spring selection and stiffness estimation.

[0058] Spring stiffness selection method:

[0059] Assuming the test system (combination of cabin and sensitive components) has a mass of M, the required frequency is below f, the test system is unloaded from n suspension points, the stiffness of a single suspension device is k1, then the stiffness of the parallel spring system is nk1, the load-bearing mass of a single suspension device is m1, and the natural frequency of the system is:

[0060]

[0061] but:

[0062]

[0063] Assuming a single suspension device consists of p springs connected in series with stiffness k0, then:

[0064]

[0065] Then we have:

[0066] k0≤4π 2 f 2 m1p (1)

[0067] Meanwhile, to ensure that the spring has sufficient load-bearing capacity, assuming the maximum allowable deformation L of a single spring, the stiffness of a single spring should meet the following condition:

[0068]

[0069] In the formula, g is the acceleration due to gravity, which is generally taken as 9.8 m / s². 2 .

[0070] When selecting a spring, it is necessary to comprehensively design the spring selection based on Equations 1 and 2.

[0071] The spring is connected to the suspension rope, which is in turn connected to the suspension device and the height adjustment device. After preliminary calculations, the initial length of the suspension rope is determined, and the system is assembled and adjusted. After the initial assembly is completed, the test system is unloaded by adjusting the height adjustment device.

[0072] Assuming the length of a single spring during unloading is L0 (including spring deformation), then the total length of the springs in the entire suspension device is pL0, the suspension height is h, the length of the suspension rope is l, and the adjustable height of the height adjustment device is Δl, then we have:

[0073] pL0+l+Δl <h

[0074] Given the suspension height h and the adjustable height Δl of the height adjustment device, by initially estimating pL0, the length l of the suspension rope is calculated such that:

[0075] pL0+l <h-Δl

[0076] Based on this, the unloading device is initially assembled and adjusted, and the height adjustment device is used to ensure that the test system is in the unloading state.

[0077] The cabin unloading device 5 is connected to the simulated cabin 4 to unload the simulated cabin, ensuring that it is in a free-to-free state after unloading, simulating the spacecraft's on-orbit flight state. This ensures the test frequency is below 5Hz, preventing inaccurate simulation of the test system's boundary conditions, which could prevent testing in the 5-30Hz low-frequency range and affect the test results. The spring parameters can be designed according to the simulated cabin's mass and the test system's frequency requirements; generally, the test system requires that the frequency across the three axes not exceed 5Hz.

[0078] The vibration isolation component unloading device 6, such as Figure 5As shown, the device consists of a suspension rope 6-1, a height adjustment device 6-2, a spring 6-3, and a force measuring device 6-4. It is used to unload the vibration-isolated component, simulating the on-orbit flight state of the sensitive component, ensuring that the frequency state of the sensitive component is consistent with the flight state, and avoiding differences between the test state and the flight state of the sensitive component. This device can be selected according to the characteristics of the vibration isolation device and the vibration-isolated component. It is not a mandatory device. It can be selected when the vibration-isolated component needs to be unloaded. The spring parameters are determined by the test frequency requirements of the vibration-isolated component. The force measuring device is used to evaluate whether the vibration-isolated component has met the unloading requirements. For low-frequency transmission characteristic tests, the frequency of the vibration-isolated component after unloading should not be higher than the actual on-orbit frequency. For example, the frequency requirement of a certain vibration-isolated component after unloading should not be higher than 3Hz.

[0079] The suspension device 7, provided by the test site, supports and connects the unloading device of the small cabin and the unloading device of the vibration isolation component. The suspension height must meet the requirements of the test system. The suspension height requirement of the test system is determined by the spring displacement in the unloading device of the small cabin, the spring displacement of the unloading device of the vibration isolation component, and the height of their respective suspension ropes. The highest of the two is taken, and it is generally not less than 3 meters.

[0080] The center of gravity balancing component 8 is installed on the bottom or side plate of the simulation chamber to balance the center of gravity of the test system, so as to avoid the simulation chamber from becoming eccentric or tilted due to uneven center of gravity, in order to adapt to the testing of various vibration sources and vibration isolation devices. The simulation chamber has a reserved interface for the center of gravity balancing component.

[0081] Micro-vibration measuring device 9, such as Figure 2 As shown, it consists of several types of measuring sensors ( Figure 2 As shown in Figures 9-1a and 9-2a) and the corresponding measurement data acquisition system ( Figure 2 Composed of components (as shown in Figures 9-1b and 9-2b), it can be arranged at various positions along the transmission path, such as the vibration source simulator 1, the mounting plate of the vibration isolation device 2, the vibration-isolated component 3, the side plate of the simulation cabin 4, and the base plate, to achieve parameter measurement along the transmission characteristic path. The data acquisition system of the measuring device ( Figure 2 The 9-1b and 9-2b (among others) are placed next to the test system to amplify, sample, process, and analyze the sensor measurement signals, providing parameter basis for evaluating the test system, the vibration isolation efficiency of the vibration isolation device, and the mechanical transmission characteristics of the simulated cabin structure.

[0082] After the above components are assembled into a system, the low-frequency transmission characteristics of the vibration isolation device will be tested according to the following steps and methods:

[0083] 1) Determine whether the test system meets the test conditions.

[0084] a) Unloading frequency of the vibration-isolated component: Measure whether the frequency of the vibration-isolated component after unloading meets the test requirements by means of laser vibration measurement and other methods. If necessary, adjust the stiffness of the unloading spring to ensure that the unloading frequency meets the test requirements.

[0085] b) Unloading force of the vibration-isolated component: The force measuring device on the vibration-isolated component determines whether the vibration-isolated component is completely unloaded. If necessary, the suspension height is adjusted to unload the vibration-isolated component.

[0086] c) Unloading frequency of the test system: After the simulated cabin test system is unloaded, the frequency of the test system is measured by the free oscillation method and the random excitation method to ensure that the unloading frequency meets the test requirements. If the test requirements are not met, the spring stiffness is adjusted (e.g., the spring is replaced, or a spring group that meets the stiffness requirements is formed by connecting the springs in series) to ensure that the unloading frequency meets the test requirements.

[0087] 2) Simulated cabin modal testing

[0088] a) Modal testing of the local structure where the simulated vibration source is installed: Using the random excitation method and a measuring device, the stiffness characteristics of the local structure where the simulated vibration source is installed are measured to determine whether the structural characteristics are coupled with the stiffness characteristics of the vibration source, and the local structure is improved if necessary.

[0089] b) Modal testing of the local structure of the vibration isolation device and the vibration-isolated component: The random excitation method is used to test the stiffness characteristics of the local structure of the above components, and to determine whether the stiffness characteristics of the local structure are consistent with the actual structure. The stiffness deviation is controlled within 10Hz, and the local structure is improved if necessary.

[0090] 3) Background noise test of the test system

[0091] After completing step 1) of the unloading frequency test and step 2) of the simulated cabin modal test for the low-frequency transmission characteristics test system and meeting the test requirements, vibration and noise tests were conducted on the entire test system. First, the collected noise signals were converted into digital signals using an AD converter. Then, the measured noise data was low-pass filtered to remove noise signals above 45Hz. Next, the data was interpreted. If the noise did not meet the requirements, the main noise signal characteristics and possible sources were analyzed, such as air conditioning noise, crane system noise, signal interference, etc. These sources that may cause excessive noise were investigated and eliminated to ensure that the noise met the test requirements. In the low-frequency transmission characteristics test, the peak-to-peak value of the system noise in the low-frequency band (below 45Hz) should not exceed 0.5mg.

[0092] 4) Low-frequency transmission characteristics test of vibration isolation device

[0093] After completing steps 1-3) and meeting the system characteristic tests, conduct low-frequency transmission characteristic tests on the vibration isolation device. During the tests, the vibration isolation efficiency of the device under different working conditions is tested by controlling the output of the vibration disturbance source simulator. The main test conditions (but not limited to these conditions) are as follows:

[0094] a) 0.5~100Hz frequency sweep test, the upper limit of the frequency sweep can be determined according to the upper limit of the actual working frequency of the vibration source;

[0095] b) Fixed frequency test from 5 to 30 Hz, with a test frequency interval of 5 Hz and a test time of not less than 30 seconds;

[0096] c) Fixed frequency test from 0.5Hz to 5Hz, with a test frequency interval of 0.5Hz and a test time of not less than 30s;

[0097] d) If necessary, the frequency sweep test can be increased or decreased by 0.5 to 30 Hz;

[0098] During various operating condition tests, the micro-vibration measurement parameters of various sensors are measured using a micro-vibration measurement device.

[0099] 5) Data Analysis and Interpretation

[0100] After completing the tests under various working conditions, the measurement data are analyzed and processed in accordance with relevant data processing requirements and standards, and the vibration isolation efficiency of the vibration isolation device is evaluated and calculated to determine whether the vibration isolation efficiency of the vibration isolation device meets the development requirements. Specific Implementation

[0102] To meet the high-precision acceleration measurement requirements, a satellite is equipped with a high-precision accelerometer. In response to the micro-vibration suppression requirements of the accelerometer, the satellite is equipped with a vibration isolation device to ensure that the micro-vibration environment after vibration isolation meets the accelerometer's suppression requirements.

[0103] To test the low-frequency transmission characteristics (30Hz and below) of vibration isolation devices, a low-frequency transmission characteristic testing system for vibration isolation devices was developed according to this invention, and tests were conducted according to the test method. The test results of the test system are as follows:

[0104] The triaxial rigid body modes of the test system are all less than 0.6 Hz, which meets the requirement of not exceeding 5 Hz;

[0105] After being unloaded from the vibration isolation components, the rigid body mode is 2.6Hz, which meets the requirement of not exceeding 3Hz;

[0106] The local mode of the vibration source installation structure is 45Hz, and the local mode of the vibration isolation component installation location is 70Hz, which is consistent with the actual structural characteristics of the spacecraft.

[0107] The maximum background noise of the test system is 0.424 mg, which meets the requirement of not exceeding 0.5 mg.

[0108] Under the condition that the test system meets the test requirements, the vibration isolation device is tested at each test frequency point in the low frequency band according to the specified test conditions. The test results are shown in Table 1. The vibration isolation efficiency of the vibration isolation device at each frequency point in the low frequency band is above 95%, which meets the requirement that the vibration isolation efficiency is not less than 90%. Moreover, the acceleration response of the product after vibration isolation is less than 0.1mg, which meets the vibration isolation requirement of the isolated component not exceeding 0.5mg.

[0109] Table 1. Acceleration response parameters under various operating conditions after vibration isolation.

[0110]

[0111] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-frequency transmission characteristic testing system for vibration isolation devices, characterized in that: The system comprises: The disturbance source simulator, the vibration-isolated assembly, the spacecraft simulation cabin, the cabin unloading device, the vibration-isolated assembly unloading device, the suspension device, the center of mass balancing assembly, and the micro-vibration measuring device; The disturbance source simulator is installed on the side plate of the spacecraft simulation cabin, the spacecraft simulation cabin is hung on the suspension device through the cabin unloading device, the vibration-isolated assembly is arranged on the vibration-isolation device to be tested and is hung on the suspension device through the vibration-isolated assembly unloading device, the center of mass balancing assembly is installed on the bottom plate of the spacecraft simulation cabin, and the micro-vibration measuring device is used to test the micro-vibration parameters at different positions and the frequency characteristics of the test system. The cabin unloading device comprises a plurality of suspension devices, each suspension device is composed of a rope, a spring and a height adjusting device, and is used to place the spacecraft simulation cabin in an unloaded state. The vibration-isolated assembly unloading device is mainly composed of a suspension rope, a height adjusting device, a spring and a force measuring device, is used to unload the vibration-isolated assembly, and simulates the in-orbit flight state of the vibration-isolated assembly. The spring in each suspension device is a plurality of springs connected in series. single spring stiffness satisfies the following relation: wherein m 1 is the load mass of a single spring, L is the maximum deformation allowed by the spring; The spring stiffness selection method is as follows: Assume a test system, including a small cabin and a sensitive assembly combination, mass M, frequency requirement is lower than , the test system is unloaded by n suspension points, the stiffness of a single suspension device is k 1, the stiffness of the parallel spring system is Then: 1, the carrying capacity of a single suspension device is m 1, the natural frequency of the system is: Then: Assuming that a single suspension device is made of p a root stiffness of k 0 springs in series, then there is: The spring is selected according to formula 1 and formula 2. At the same time, in order to ensure the spring has the carrying capacity, the maximum deformation allowed by a single spring is assumed L, The stiffness of a single spring should meet the following conditions: where g is the acceleration due to gravity, taken as 9.8 m / s 2 ; The vibration measuring device comprises a plurality of types of measuring sensors and corresponding measuring data acquisition systems, is arranged on the vibration transmission path, and is used to measure the vibration characteristics on the vibration transmission path.

2. The low frequency transmissibility test system for an isolation device of claim 1, wherein: The length of the suspension rope satisfies the following relationship: wherein, The height adjustment device can adjust the height, The suspension height, To Root spring total length.

3. The low frequency transmissibility test system for an isolation device of claim 1, wherein: The method comprises the following specific processes:

4. A method for testing the low-frequency transfer characteristics of a vibration isolation device based on the system for testing the low-frequency transfer characteristics of a vibration isolation device according to any one of claims 1 to 3, characterized by, (1) judging whether the test system meets the test conditions: a) vibration-isolated assembly unloading frequency judgment: measuring whether the frequency of the unloaded vibration-isolated assembly meets the test requirements, when it does not meet the requirements, adjusting the spring stiffness of the vibration-isolated assembly unloading device to ensure that the unloading frequency meets the test requirements; b) vibration-isolated assembly unloading force judgment: judging whether the vibration-isolated assembly is completely unloaded through the force measuring device on the vibration-isolated assembly, when it is not completely unloaded, adjusting the suspension height to unload the vibration-isolated assembly; c) test system unloading frequency: judging whether the frequency of the unloaded test system meets the test requirements, when it does not meet the requirements, adjusting the spring stiffness of the cabin unloading device to ensure that the unloading frequency meets the test requirements; (2) simulation cabin modal test carrying out simulation disturbance source installation local structure modal test and vibration-isolation device and vibration-isolated assembly installation local structure modal test, and improving the local structure if the set requirements are not met; (3) test system background noise test carrying out vibration noise test on the entire test system, and adjusting the background noise when the noise does not meet the requirements; (4) when the tests in steps (1)-(3) meet the requirements, carrying out vibration-isolation device low-frequency transmission characteristic test. When the vibration-isolation device and vibration-isolated assembly installation local structure modal test is carried out, judging whether the local structure stiffness characteristic deviates from the real structure stiffness by 10 Hz or not, and determining that the requirements are met if yes.

5. The method of claim 4, wherein: The condition that the system background noise meets the measurement requirements is that the peak-to-peak value of the system noise in the low-frequency band is not higher than 0.5 mg.

6. The method of claim 4, wherein: The vibration noise test on the entire test system is as follows:

7. The method of claim 4, wherein: ​ Firstly, the collected noise signal is converted into digital signal by AD converter; Secondly, the measured noise data is low-pass filtered to remove noise signal above 45 Hz; Finally, the data is interpreted, and if the noise does not meet the requirements, the main characteristics and sources of the noise signal are analyzed.

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