A modal test platform and a modal test method

Abstract

The present application relates to an experimental device. In view of the problem that the connection structure between the exciter and the system under test in the existing modal experimental platform is limited in application and experimental conditions, or the non-axial coupling effect cannot be completely eliminated, a modal experimental platform and a modal experimental method are provided, including an exciter, a flexible wire rope and an elastic force rod. The elastic force rod includes a force rod body, a force rod top cover and a force rod bottom cover. The force rod top cover is connected to one end of the force rod body through an elastic member with nonlinear stiffness characteristics. The force rod bottom cover is fixedly connected to the other end of the force rod body. One end of the flexible wire rope is connected to the force rod top cover, and the other end is connected to the preload adjustment device in the force rod bottom cover. The force rod bottom cover is connected to the exciter. By tensioning the flexible wire rope, the elastic member tends to a quasi-zero stiffness characteristic, thereby realizing the decoupling of the non-axial degrees of freedom of the excitation system and the system under test, and at the same time ensuring that the exciter axis and the force sensor are automatically aligned in the absence of external force.

Description

Technical Field

[0001] The present application relates to an experimental device, and specifically to a modal experimental platform and a modal experimental method. Background Art

[0002] Modal experiments are the core means to reveal the dynamic characteristics of structures. By accurately obtaining parameters such as natural frequency, damping ratio and vibration mode, they provide an irreplaceable physical benchmark for avoiding resonance in aerospace equipment, designing bridges to resist wind and earthquakes, and controlling the dynamic stability of precision instruments.

[0003] The shaker is the most common excitation device in modal testing. Piano wire, serving as a connection between the shaker and the system under test, eliminates non-axial interactions and reduces interference with the system's dynamic characteristics. However, this piano wire connection method is only suitable for specially constructed shakers and requires an additional mounting bracket. Furthermore, the system under test and the shaker must be fixed during testing to ensure the piano wire remains taut, limiting experimental conditions and making alignment between the shaker and the system under test difficult.

[0004] Alternatively, the force sensor can be mounted directly on the system under test and a force bar can be used between the exciter and the force sensor to transmit the force to the system under test. However, the use of a force bar cannot completely eliminate the non-axial coupling effect like piano wire, especially when the stiffness of the system under test is low. Summary of the Invention

[0005] This application provides a modal experimental platform and a modal experimental method to address the technical problems in existing modal experimental platforms, such as the connection structure between the exciter and the system under test is limited in application and experimental conditions, or the non-axial coupling effect cannot be completely eliminated.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions:

[0007] In a first aspect, the present application proposes a modal experimental platform, comprising an exciter and a flexible wire rope meeting a preset tensile strength, and also comprising an elastic force rod;

[0008] The elastic force rod comprises a force rod body, a force rod top cover and a force rod bottom cover; the force rod top cover is connected to one end of the force rod body via an elastic member having nonlinear stiffness characteristics, and the force rod bottom cover is fixedly connected to the other end of the force rod body; the force rod body is coaxially sleeved on the outside of the flexible wire rope; a preload adjustment device is provided in the force rod bottom cover; one end of the flexible wire rope is connected to the force rod top cover, and the other end is connected to the preload adjustment device, so as to adjust the flexible wire rope through the preload adjustment device;

[0009] A force sensor is installed on the top cover of the force rod and is used to be fixed to the system under test;

[0010] The force rod bottom cover is connected to the vibration exciter.

[0011] Furthermore, the elastic member is a butterfly spring.

[0012] Furthermore, when the elastic member is under pressure load, the relationship between the axial load and the displacement satisfies:

[0013]

[0014] in, is the axial load, is the elastic modulus, is the displacement, is Poisson's ratio, is the outer diameter of the washer, is a constant, is the free height minus the thickness, is the gasket thickness.

[0015] Furthermore, the constant The calculation method includes:

[0016]

[0017] in, is the inner diameter of the gasket.

[0018] Furthermore, the load when the elastic member is flattened is:

[0019]

[0020] in, The load when the elastic member is flattened.

[0021] Furthermore, the preload force adjustment device is a worm gear structure;

[0022] A hanging ring is provided inside the top cover of the force rod, and one end of the flexible wire rope is hung on the hanging ring.

[0023] Furthermore, the other end of the flexible wire rope is connected to the turbine of the worm gear structure, and the worm of the worm gear structure is installed in the bottom cover of the force rod.

[0024] Furthermore, the flexible wire rope is piano wire.

[0025] In a second aspect, the present application proposes a modal test method using the above-mentioned modal test platform, comprising:

[0026] The flexible wire rope is adjusted through the preload adjustment device to put the elastic part in a flattened state, and the exciter is started to perform the modal experiment.

[0027] Furthermore, the elastic member is a butterfly spring;

[0028] When the elastic member is in a flattened state, the ratio of the free height minus the thickness h to the thickness t of the gasket is 1.414.

[0029] Compared with the prior art, this application has the following beneficial effects:

[0030] The present application proposes a modal experimental platform, including an exciter, a flexible wire rope and an elastic force rod, the elastic force rod including a force rod body, a force rod top cover and a force rod bottom cover, the force rod top cover is connected to one end of the force rod body through an elastic member with nonlinear stiffness characteristics, the force rod bottom cover is fixedly connected to the other end of the force rod body, a preload adjustment device is provided in the force rod bottom cover, one end of the flexible wire rope is connected to the force rod top cover, and the other end is connected to the preload adjustment device, which is used to adjust the flexible wire rope through the preload adjustment device to provide preload, a force sensor is installed on the force rod top cover, and the force rod bottom cover is connected to the exciter. The present application utilizes a combined structure of a flexible wire rope and an elastic member with nonlinear stiffness characteristics to achieve decoupling of non-axial degrees of freedom, which can ensure that the exciter axis and the force sensor on the measured system are automatically aligned in the absence of external force, and is suitable for various experimental conditions such as ground fixation and free suspension. In addition, the flexible wire rope in the present application does not require an additional mounting bracket, and does not require special modification to the exciter.

[0031] This application also proposes a modal experiment method that has all the advantages of the above-mentioned modal experiment platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 A schematic diagram of an elastic force rod in the modal experimental platform of this application;

[0034] Figure 2 for Figure 1 Detailed diagram of

[0035] Figure 3 A schematic diagram of a modal experiment platform in an embodiment of the present application;

[0036] Figure 4 Schematic diagram of parameters of the butterfly spring in the embodiment of the present application;

[0037] Figure 5Schematic diagram of the axial load and displacement of the butterfly spring in the embodiment of the present application;

[0038] Figure 6 This is a schematic diagram of the result of normalizing the axial load-displacement curve of the butterfly spring with respect to the load during flattening as the parameter h / t changes in the embodiment of the present application.

[0039] Among them: 1-elastic part, 2-force rod body, 3-force rod top cover, 4-flexible wire rope, 5-force rod bottom cover, 6-bolt, 7-nut, 8-hanging ring, 9-turbine, 10-worm, 11-worm gear mounting seat, 12-acceleration sensor, 13-tested system, 14-vibrator, 15-vibrator base, 16-force sensor. DETAILED DESCRIPTION

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0041] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0042] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0043] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or the orientation or position relationship in which the product of the invention is usually placed when in use. This is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it should not be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0044] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0045] In the description of the embodiments of this application, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in this application based on specific circumstances.

[0046] Modal testing is a core experimental method for analyzing the dynamic characteristics of structures through excitation-response testing. Essentially, it leverages vibration theory to measure the structure's vibration response under external excitation, extracting key modal parameters such as natural frequency, damping ratio, and mode shape, and thereby quantitatively evaluating the structure's vibration characteristics. The shaker is the most common excitation device used in modal testing. The shaker's dynamic coil is designed to move only axially, enabling axial excitation of the system under test. This excitation is then measured using an axial force sensor. The shaker's dynamic coil provides excellent control over the excitation frequency range and amplitude, enabling high-quality test structures over a wide bandwidth. However, due to the influence of the system's modal shape, the location and direction of the excitation loading, and the suspension configuration, especially when the suspension is soft, the mechanical coupling between the shaker and the system under test can result in unnecessary torques in non-axial degrees of freedom that cannot be detected by the axial force sensor. This can introduce measurement errors into the frequency response function of the system under test, ultimately affecting the modal test results and sometimes even yielding misleading results.

[0047] There are usually two ways to connect the exciter and the system under test; (1) connect through piano wire. Piano wire can eliminate non-axial interactions and reduce interference with the dynamic characteristics of the system under test. In order to transmit the excitation force, the axial stiffness of the piano wire is provided by preload, and the preload is generally three to four times the amplitude of the excitation force. However, the piano wire connection method is only applicable to exciters with special structures and requires additional mounting brackets. In addition, during testing, it is usually necessary to fix the system under test and the exciter to ensure that the piano wire is always in a tensioned state, which not only limits the experimental conditions but also makes it difficult to align the exciter and the system under test. (2) In order to reduce the above-mentioned interactions and measure the force applied to the system under test, another method is to directly install the force sensor on the system under test and use a slender element, namely a force rod, between the exciter and the force sensor to transmit the force to the system under test. The force rod usually has high axial stiffness and low lateral and bending stiffness to ensure that the axial excitation is efficiently transmitted to the system under test while reducing non-axial interactions. However, the use of a force rod cannot completely eliminate the non-axial coupling effect like piano wire, especially when the stiffness of the measured system is low. In the prior art, the Chinese invention patent application with publication number CN111766030A and the Chinese invention patent with publication number CN103389195A respectively use a ball joint and a universal joint mechanism to connect the force rod and the measured system to perform all-directional decoupling, so that the torque that may be borne on the force rod cannot be transmitted to the measured system. However, similar to the piano wire connection method, the connection methods proposed in these two prior arts cannot ensure that the axial direction of the exciter is aligned with the axial force sensor on the measured system.

[0048] Based on the above situation, the present application proposes a modal experimental platform and a modal experimental method. In order to avoid the non-axial additional stiffness caused by the mechanical connection between the exciter 14 and the system under test 13 in the modal experiment, which causes unknown non-axial torque and then affects the test accuracy, the modal experimental platform of the present application innovatively proposes an elastic force rod structure with an embedded flexible wire rope 4, which is used to connect the exciter 14 and the system under test 13. There is no need to modify or specially design the exciter 14, and no additional flexible wire rope 4 mounting bracket is required.

[0049] The present application is described in detail below with reference to the embodiments and drawings.

[0050] As an embodiment of the modal experiment platform of the present application, it may include a vibration exciter 14, a flexible wire rope 4 meeting a preset tensile strength, and an elastic force rod.

[0051] The elastic force rod includes a force rod body 2, a force rod top cover 3 and a force rod bottom cover 5. The force rod top cover 3 is connected to one end of the force rod body 2 through an elastic member 1 with nonlinear stiffness characteristics, and the force rod bottom cover 5 is fixedly connected to the other end of the force rod body 2. The force rod body 2 is coaxially sleeved on the outside of the flexible wire rope 4. A preload adjustment device is provided in the force rod bottom cover 5. One end of the flexible wire rope 4 is connected to the force rod top cover 3, and the other end is connected to the preload adjustment device, which is used to adjust the flexible wire rope 4 through the preload adjustment device. A force sensor 16 is installed on the force rod top cover 3, and is used to be fixed to the measured system 13. The force rod bottom cover 5 is connected to the exciter 14.

[0052] The top cover 3 of the force rod is connected to one end of the force rod body 2 through an elastic member 1 with nonlinear stiffness characteristics. This nonlinear connection method can show different stiffness changes under different stress conditions, providing a more complex and adaptive mechanical response for the modal experiment platform. The bottom cover 5 of the force rod is fixedly connected to the other end of the force rod body 2 to form a stable rod-shaped structure. The force rod body 2 is coaxially sleeved on the outside of the flexible wire rope 4. The three cooperate with each other to build a basic framework for force transmission and regulation. The preload adjustment device set in the bottom cover 5 of the force rod can adjust the flexible wire rope 4 and then control the preload. The flexible wire rope 4 that meets the preset tensile strength plays the important role of connection and force transmission. The preset tensile strength ensures that the flexible wire rope 4 will not break under the force required for the experiment, ensuring the safety and reliability of the experiment. More importantly, the flexible wire rope 4 can reduce the coupling effect of the lateral vibration of the exciter 14 on the force sensor 16. In conjunction with the preload adjustment device, it can achieve soft and hard stiffness switching to meet the needs of different modal experiments. The force sensor 16 installed on the force rod top cover 3 is used to monitor and measure the magnitude of the force between the elastic force rod and the system under test 13 in real time. The data obtained by the force sensor 16 can accurately understand the force transmitted to the system under test 13 by the exciter 14, so as to accurately control and analyze the experimental process, and provide a key basis for data collection and result analysis of the modal experiment. The force rod top cover 3 is used to be fixed to the system under test 13, realizing the connection between the modal experimental platform and the system under test 13. The force rod bottom cover 5 is connected to the exciter 14, and the excitation force generated by the exciter 14 is transmitted to the elastic force rod and the entire modal experimental platform, ensuring the effective transmission of force in the modal experimental platform. It also works in conjunction with the elastic member 1, the preload adjustment device, etc. to maintain the mechanical balance and stability of the system.

[0053] By leveraging the nonlinear characteristics of the elastic element 1 and adjusting the preload of the flexible cable 4, dynamic structural behavior ranging from linear to strongly nonlinear can be simulated. The exciter 14 inputs vibrations through the force rod bottom cover 5, while the force sensor 16 outputs the excitation force through the force rod top cover 3, creating a decoupled "excitation-measurement" path. Compared to traditional single-ended fixed exciters, this design reduces reaction force interference, avoiding additional constraints imposed by the exciter 14's reaction force on the system under test 13. It also reduces signal phase lag, shortens the force transmission link, and improves phase matching accuracy in the high-frequency band.

[0054] like Figure 1 As shown in FIG, it is a schematic diagram of the elastic force rod in the modal experimental platform of this application. Figure 2 As shown, Figure 1 Detailed diagram of the Figure 3 The figure shows a schematic diagram of the modal test platform of this embodiment. In this embodiment, the elastic member 1 is a butterfly spring, the flexible wire rope 4 is a piano wire, and the preload adjustment device is a worm gear structure. This embodiment is used to further explain the present application in detail.

[0055] Multiple butterfly springs can be provided, symmetrically installed between the force rod top cover 3 and the force rod body 2. The force rod top cover 3 is provided with a boss at one end close to the force rod body 2, and the force rod body 2 is provided with a recess at one end close to the force rod top cover 3. Multiple butterfly springs are symmetrically installed between the boss and the recess. With the pre-tightening effect of the piano wire, the butterfly springs bear the pressure load. The end of the force rod top cover 3 away from the force rod body 2 is connected to the force sensor 16, and the force sensor 16 is fixed to the system under test 13, and then the axial load transmitted to the system under test 13 by the exciter 14 is tested. The force rod body 2 is a hollow rod, and the piano wire passes through the hollow inside the force rod body 2. A hanging ring 8 is provided inside the force rod top cover 3, and one end of the piano wire is hung at the hanging ring 8 inside the force rod top cover 3. The hanging ring 8 can also be replaced with a hook, ear shaft hanging plate or other structures. The worm gear structure is installed inside the force rod bottom cover 5 through the worm gear mounting seat 11. A columnar mounting platform is provided on the turbine 9. A through hole is provided on the side wall of the columnar mounting platform. The other end of the piano wire is passed through the through hole. After the driving worm 10 rotates, the turbine 9 rotates accordingly, and the piano wire is retracted and released. The friction self-locking mechanism of the worm gear structure itself is used to wind and tighten the piano wire. The preload force of the piano wire is adjusted by driving the worm 10. The force rod bottom cover 5 is detachably connected to the force rod body 2 by bolts 6, and can also be replaced by other quick connection mechanisms, such as buckles, magnetic joints, quick release pins, etc. At the same time, the force rod bottom cover 5 is connected to the exciter 14 by a nut 7. The exciter 14 is fixed by the exciter base 15. An acceleration sensor 12 is also installed on the measured system 13.

[0056] The vibrations generated by the exciter 14 are transmitted to the force rod body 2 via the rigidly connected force rod bottom cover 5. After nonlinear filtering by the elastic element 1, they are output to the system under test 13 via the force rod top cover 3. When the elastic element 1 is in the linear deformation zone, its stiffness is low, making it suitable for low-frequency modal testing. When the elastic element 1 enters the nonlinear hardening zone, its stiffness increases, simulating hard contact or gap impact scenarios. The force sensor 16 monitors the axial load output by the force rod top cover 3 in real time. Combined with the input signal from the exciter 14, it extracts the modal parameters of the system under test 13 through frequency response function analysis.

[0057] The butterfly spring has nonlinear stiffness characteristics, that is, its stiffness changes with the external load. Figure 4 As shown in the figure, it is a parameter diagram of butterfly spring. Figure 5 The figure below shows the schematic diagram of the axial load and displacement of the butterfly spring. For the butterfly spring, under pressure load, the relationship between the axial load and displacement (F-δ) is:

[0058]

[0059] in, is the axial load, is the elastic modulus, is the displacement, is Poisson's ratio, is the outer diameter of the washer, is a constant, is the free height minus the thickness, is the gasket thickness.

[0060] The calculation formula of the constant M is:

[0061]

[0062] in, is the inner diameter of the gasket.

[0063] Press the butterfly spring flat. δ = h The load when the elastic member 1 is flattened is:

[0064]

[0065] in, It is the load when the elastic member 1 is flattened.

[0066] As the parameter h / t changes, the axial load-displacement curve of the butterfly spring is normalized with respect to the load at flattening (F / F0) as shown below: Figure 6 As shown in Figure 2, it can be seen that when h / t ≈ 1.414, the pressure of the butterfly spring is approximately constant within a certain range of the flattened state, that is, it exhibits a quasi-zero stiffness characteristic.

[0067] It should be noted that in other embodiments of the present application, the elastic member 1 can also adopt other nonlinear stiffness elements, such as disc spring groups, multi-section springs, shape memory alloy springs, etc., as long as it can meet the requirements of presenting quasi-zero stiffness characteristics under a specific preload, that is, the flat area of the axial load-displacement curve. The flexible wire rope 4 can also adopt other flexible materials with high tensile strength, such as carbon fiber rope, Kevlar fiber rope, titanium alloy wire, etc., which can ensure high axial stiffness and low bending stiffness and withstand preload. In actual applications, the preload adjustment device can also be adjusted to adapt to new materials. As a preload adjustment device, structures such as ratchet mechanisms, hydraulic tensioners, electric winches, etc. can also be used, which have a self-locking function, can prevent the preload from loosening, and can also support precise adjustment. It can be selected according to the requirements of installation space and operational convenience.

[0068] According to the nonlinear stiffness characteristics of the butterfly spring, the present application pre-tightens the piano wire so that the butterfly spring symmetrically arranged between the force rod top cover 3 and the force rod body 2 is in a flattened state. At this time, the butterfly spring has a quasi-zero stiffness characteristic, and the piano wire only provides axial (tensile direction) stiffness but not bending stiffness. Similarly, the butterfly spring in the quasi-zero stiffness (flattened) state does not provide bending stiffness, or the provided bending stiffness is much smaller than the stiffness of the elastic force rod and the system under test 13, thereby achieving decoupling of the axial degrees of freedom and non-axial degrees of freedom of the exciter 14 and the system under test 13, avoiding the non-axial additional stiffness caused by the mechanical connection between the two in the modal experiment, causing unknown non-axial torque, and then affecting the test accuracy.

[0069] Therefore, based on the aforementioned modal experiment platform, this application also proposes a modal experiment method, in which the flexible wire rope 4 is adjusted through a preload adjustment device to put the elastic part 1 in a flattened state, and the exciter 14 is started to perform a modal experiment.

[0070] The present application utilizes a combination structure of a flexible wire rope 4 and an elastic member 1 having nonlinear stiffness characteristics, and utilizes the nonlinear stiffness characteristics of the elastic member 1 to achieve decoupling of non-axial degrees of freedom by loading the pre-tightening force of the flexible wire rope 4. Unlike the ball joint and universal joint mechanism in the prior art, the combination structure of the flexible wire rope 4 and the elastic member 1 having nonlinear stiffness characteristics of the present application can ensure that the axial direction of the vibrator 14 and the force sensor 16 on the measured system 13 are automatically aligned in the absence of external force, and is suitable for various experimental conditions such as ground fixation and free suspension. Furthermore, the elastic force rod design with a built-in flexible wire rope 4 proposed in the present application does not require an additional flexible wire rope 4 mounting bracket, and does not require special modification to the vibrator 14.

[0071] The above are merely preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A modal experimental platform, comprising an exciter (14) and a flexible wire rope (4) having a preset tensile strength; characterized in that: Also included is an elastic force rod; The elastic force rod comprises a force rod body (2), a force rod top cover (3) and a force rod bottom cover (5); the force rod top cover (3) is connected to one end of the force rod body (2) via an elastic member (1) having nonlinear stiffness characteristics, and the force rod bottom cover (5) is fixedly connected to the other end of the force rod body (2); the force rod body (2) is coaxially sleeved on the outside of the flexible wire rope (4); a preload adjustment device is provided in the force rod bottom cover (5); one end of the flexible wire rope (4) is connected to the force rod top cover (3), and the other end is connected to the preload adjustment device, for adjusting the flexible wire rope (4) via the preload adjustment device; When the elastic member (1) is under pressure load, the relationship between the axial load and the displacement satisfies: in, is the axial load, is the elastic modulus, is the displacement, is Poisson's ratio, is the outer diameter of the washer, is a constant, is the free height minus the thickness, is the gasket thickness; A force sensor (16) is installed on the force rod top cover (3) and is used to be fixed to the measured system (13); The force rod bottom cover (5) is connected to the vibration exciter (14).

2. A modal experiment platform according to claim 1, characterized in that: The elastic member (1) is a butterfly spring.

3. A modal experiment platform according to claim 1, characterized in that: constant The calculation method includes: in, is the inner diameter of the gasket.

4. A modal experiment platform according to claim 2, characterized in that: The load when the elastic member (1) is flattened is: in, It is the load when the elastic member (1) is flattened.

5. A modal experiment platform according to claim 1, characterized in that: The preload force adjustment device is a worm gear structure; A hanging ring (8) is provided inside the force rod top cover (3), and one end of the flexible wire rope (4) is hung on the hanging ring (8).

6. A modal experiment platform according to claim 5, characterized in that: The other end of the flexible wire rope (4) is connected to a turbine (9) of a worm gear structure, and the worm (10) of the worm gear structure is installed in a bottom cover (5) of the force rod.

7. The modal experiment platform according to claim 1, characterized in that: The flexible wire rope (4) is a piano wire.

8. A modal test method using the modal test platform according to any one of claims 1 to 7, characterized in that: include: The flexible wire rope (4) is adjusted by a preload adjustment device to place the elastic member (1) in a flattened state, and the vibration exciter (14) is started to perform a modal experiment.

9. A modal test method according to claim 8, characterized in that: The elastic member (1) is a butterfly spring; When the elastic member (1) is in a flattened state, the ratio of the free height minus the thickness h to the gasket thickness t is 1.414.

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