A method for testing the inherent modes of an accelerometer pendulum assembly

Abstract

This invention pertains to accelerometer testing technology, specifically a method for testing the inherent modes of an accelerometer pendulum assembly. The method utilizes the pendulum assembly's own electromagnetic torque generator to excite the assembly and produce the vibrations required for measurement. A non-contact laser vibration measurement method is employed to test the vibrations. By adjusting the type and frequency range of the applied excitation signal, as well as the position of the laser point projected onto the pendulum assembly, precise testing of multiple modes of the pendulum assembly is achieved. This allows for quantitative analysis and evaluation of the machining quality of each component of the pendulum assembly and the precision assembly results, ensuring controllable assembly quality and providing a basis for adjusting accelerometer system parameters, ultimately enabling the overall accelerometer system to meet performance requirements.

Description

Technical Field

[0001] This invention pertains to accelerometer testing technology and relates to a method for testing the inherent modes of an accelerometer pendulum assembly. Background Technology

[0002] The accelerometer pendulum assembly is located at the forefront of the entire accelerometer system. Any error in the pendulum assembly will be amplified throughout the closed-loop system, directly affecting the accelerometer's output accuracy. The pendulum assembly itself is actually a mechanical system with multiple frequency responses. Its first-order frequency directly represents the stiffness of the pendulum assembly, and its consistency affects the consistency of the overall accelerometer system. The response speed and sensitivity at the first-order frequency directly reflect the speed and sensitivity of the accelerometer system. The second-order frequency of the pendulum assembly affects the dynamic characteristics of the accelerometer system, including its stability and vibration errors. Other higher-order frequency motions of the pendulum assembly, such as torsional and translational motions, need to be tested and analyzed in as much detail as possible. This allows for comparison of the actual frequency response with the simulation analysis results of the design theory, eliminating potential error sources, and, if necessary, modifying the design to meet the performance requirements of the accelerometer system. Therefore, the test index of the pendulum assembly's natural modes is crucial for the design and assembly of the accelerometer. From a design perspective, the inherent modal parameters of the pendulum assembly can evaluate and optimize the design of the accelerometer pendulum assembly, reducing and eliminating harmful high-order modes such as torsional and translational motions, thereby improving the anti-interference capability of the entire accelerometer and enhancing its performance and accuracy. From an assembly perspective, the natural frequency of the first-order oscillation in the pendulum assembly's inherent modes can be used to calculate the stiffness of the pendulum assembly, which can be used to quantitatively evaluate the precision assembly quality of the pendulum assembly, ensuring quality control at the assembly stage and providing a basis for adjusting accelerometer system parameters. However, previously, the evaluation of this inherent modal parameter of the pendulum assembly could only be obtained through simulation to obtain theoretical models, which differed greatly from actual results, making accurate testing and analysis impossible. Summary of the Invention

[0003] The purpose of this invention is to provide a method for accurately testing the intrinsic modes of an accelerometer pendulum assembly. The technical solution of this invention is...

[0004] (1) Install the pendulum component to be tested on the suspension bracket, and then install the suspension bracket on the angle adjustment platform. Adjust the angle adjustment platform to make the pendulum component deflect at an angle, observe the activity state of the pendulum component, and ensure that it is in a suspended free swing state.

[0005] (2) Connect the output of the signal generator to the electromagnetic torque coil on the pendulum assembly, and connect a resistor in series between the electromagnetic torque coil and the signal generator.

[0006] (3) Project the vibration measuring laser beam of the laser vibration meter onto the surface of the pendulum assembly, and connect the output signal of the laser vibration meter to the spectrum analyzer;

[0007] (4) Input a continuous sinusoidal sweep frequency signal to the electromagnetic torquer coil through a signal generator. The sweep frequency range includes the range of modes of the pendulum component under test. The amplitude of the sweep frequency signal is determined according to the actual vibration amplitude of the pendulum component.

[0008] (5) Observe the frequency response curve in the spectrum analyzer, find a set of resonant frequency points, and record the frequency values;

[0009] (6) Project the vibration measuring laser beam of the laser vibration meter onto the suspension bracket on which the pendulum assembly is installed, repeat the test steps (4) to (5) to obtain another set of resonance frequency points, compare the two sets of resonance frequency points, remove the common resonance frequency points of the two, and obtain the resonance frequency points of the pendulum assembly itself.

[0010] (7) Project the vibration measuring laser beam of the laser vibrometer onto the surface of the pendulum assembly. The projection position is determined according to the vibration mode of the pendulum assembly. Based on the resonant frequency point of the pendulum assembly itself, a continuous sinusoidal sweep frequency signal with the resonant frequency value as the center frequency is input to the electromagnetic torque coil through the signal generator in sequence. The frequency range is 100Hz to 200Hz. At the same time, the precise frequency value of the resonant frequency point is tested in the spectrum analyzer. Change the position of the vibration measuring laser beam of the laser vibrometer projected onto the surface of the pendulum assembly and repeat the test of the resonant frequency points of other pendulum assemblies.

[0011] (8) Project the vibration measuring laser beam of the laser vibrometer onto the surface of the pendulum assembly. The projection position is determined according to the vibration mode of the pendulum assembly. Input a continuous fixed-frequency sinusoidal signal to the electromagnetic torque coil through the signal generator. The signal amplitude is determined according to the actual vibration amplitude of the pendulum assembly. The signal frequency is sequentially set to the frequency of the precise resonance frequency point measured in step (7). At the same time, measure the response amplitude of the pendulum assembly at the test position at the frequency in the spectrum analyzer. Change the position of the vibration measuring laser beam of the laser vibrometer projected onto the surface of the pendulum assembly according to the vibration mode of the pendulum assembly. Repeat the test at other positions of the resonance frequency point to obtain the natural mode of the pendulum assembly. Repeat the test at other resonance frequency points of the pendulum assembly to obtain the multi-order natural modes of the pendulum assembly.

[0012] The advantages and beneficial effects of this invention are as follows: (1) The signal generator and the electromagnetic torque of the accelerometer itself are used as electromagnetic vibration excitation to directly generate excitation on the pendulum assembly itself. The excitation effect is obvious, and the excitation direction is completely consistent with the swing direction of the pendulum assembly when the accelerometer is working normally. There is no frequency range limitation of the excitation. The excitation frequency and amplitude can be precisely controlled. The test process does not damage the pendulum assembly at all, which fully meets the technical requirements of excitation for the natural mode test of the accelerometer pendulum assembly; (2) The laser vibration meter and spectrum analyzer are used to measure the natural mode of the accelerometer pendulum assembly. The natural modes of the accelerometer pendulum assembly can be measured at any number of orders. The measurement results are accurate and have high precision; (3) This invention has a wide range of applications. Any pendulum accelerometer that uses an electromagnetic torque can use this invention to measure the natural mode of the pendulum assembly. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the testing system of the present invention. Detailed Implementation

[0014] This invention discloses a method for testing the inherent modes of an accelerometer pendulum assembly. It utilizes the pendulum assembly's own electromagnetic torque device to excite the assembly and generate the vibrations required for measurement. A non-contact laser vibration measurement method is employed to test the vibrations of the pendulum assembly. By adjusting the type and frequency range of the applied excitation signal, as well as the position of the vibration measurement laser beam projected onto the pendulum assembly, precise testing of the multi-mode characteristics of the pendulum assembly is achieved. This allows for quantitative analysis and evaluation of the machining quality of each component of the pendulum assembly and the precision assembly results, ensuring controllable assembly quality and providing a basis for adjusting accelerometer system parameters, thereby enabling the overall accelerometer system to meet performance requirements.

[0015] The specific measurement steps of this invention are as follows:

[0016] (1) Install the pendulum component M2 to be tested on the suspension bracket M1, and then install the suspension bracket M1 on the angle adjustment table M4. Adjust the angle adjustment table M4 to make the pendulum component M2 deflect at an angle, observe the activity state of the pendulum component M2, and ensure that it is in a suspended free swing state.

[0017] (2) Connect the output of signal generator D3 to the electromagnetic torque coil M3 on the pendulum assembly M2 as the vibration excitation source of the pendulum assembly M2. Connect resistor D4 in series between electromagnetic torque coil M3 and signal generator D3 to limit the amplitude of current in electromagnetic torque coil M3 and play a protective role.

[0018] (3) Project the vibration measurement laser beam of the laser vibration meter D1 onto the surface of the pendulum assembly M2 so that the laser vibration meter D1 can be sensitive to the vibration of the pendulum assembly M2. Connect the output signal of the laser vibration meter D1 to the spectrum analyzer D2 and observe the frequency domain response of the vibration of the pendulum assembly M2 through the spectrum analyzer D2.

[0019] (4) Input a continuous sinusoidal sweep frequency signal to the electromagnetic torquer coil M3 through the signal generator D3. The sweep frequency range is set with reference to the simulation results of the pendulum component M2 under test. It should include the modal frequencies of each order of the pendulum component M2 under test, and the range should be widened by 1KHz to 2KHz. The amplitude of the sweep frequency signal is determined according to the actual vibration amplitude of the pendulum component M2, so as to neither damage the pendulum component M2 nor allow the pendulum component M2 to swing freely.

[0020] (5) Observe the frequency response curve in the spectrum analyzer D2, find a set of resonant frequency points, and record the frequency values. If the resonant peaks on the frequency response curve are not obvious, the amplitude of the input signal of the signal generator D3 can be increased or the position of the vibration measurement laser beam of the laser vibrometer D1 projected on the surface of the pendulum component M2 can be adjusted by referring to the simulation results of the pendulum component M2 under test, and the measurement can be repeated.

[0021] (6) The vibration measuring laser beam of the laser vibration meter D1 is projected onto the suspension bracket M1 on which the pendulum component M2 is installed. Repeat the test steps (4) to (5) to obtain another set of resonance frequency points. Compare the two sets of resonance frequency points, remove the common resonance frequency points, and obtain the resonance frequency points of the pendulum component M2 itself.

[0022] (7) Project the vibration measurement laser beam of the laser vibrometer D1 onto the surface of the pendulum assembly M2. The projection position is determined according to the specific vibration mode simulation results of the pendulum assembly M2. Based on the resonance frequency point of the pendulum assembly M2 itself, the signal generator D3 sequentially inputs a continuous sinusoidal sweep frequency signal with the resonance frequency value as the center frequency to the electromagnetic torque coil M3. The frequency range is 100Hz~200Hz. At the same time, the precise frequency value of the resonance frequency point is tested in the spectrum analyzer D2. Change the position of the vibration measurement laser beam of the laser vibrometer D1 projected onto the surface of the pendulum assembly M2. The resonance frequency points of the other pendulum assemblies M2 are tested using this method.

[0023] (8) Project the vibration measuring laser beam of the laser vibrometer D1 onto the surface of the pendulum assembly M2. The projection position is determined according to the simulation results of the specific vibration mode of the pendulum assembly M2. Input a continuous fixed-frequency sinusoidal signal to the electromagnetic torque coil M3 through the signal generator D3. The signal amplitude is determined according to the actual vibration amplitude of the pendulum assembly M2. The signal frequency is set sequentially to the frequency of the precise resonance frequency point measured in step (7). At the same time, measure the response amplitude of the pendulum assembly M2 at the test position at the frequency in the spectrum analyzer D2. Change the position of the vibration measuring laser beam of the laser vibrometer D1 hitting the surface of the pendulum assembly M2 according to the simulation results of the specific vibration mode of the pendulum assembly M2. Repeat the test at other positions of the resonance frequency point to obtain the natural mode of the pendulum assembly M2. Repeat the test at other resonance frequency points of the pendulum assembly M2 using the method in this step to obtain the multi-order natural modes of the pendulum assembly M2.

[0024] Example

[0025] The natural modes of a certain type of accelerometer pendulum assembly were tested using the method of this invention. The measurement steps are as follows:

[0026] (1) Install the pendulum component to be tested on the suspension bracket, and then install the suspension bracket on the angle adjustment platform. Adjust the angle adjustment platform to make the pendulum component deflect at a small angle. Observe manually to make the pendulum component in a free swinging state under suspension.

[0027] (2) Connect the output of the signal generator to the electromagnetic torque coil that is fixed to the pendulum assembly itself as the vibration excitation source of the pendulum assembly. To limit the current, connect a certain value resistor in series between the electromagnetic torque coil and the signal generator. The resistance value is 5KΩ.

[0028] (3) Project the vibration measurement laser beam of the laser vibration meter onto the surface of the pendulum assembly so that the laser vibration meter can be sensitive to the vibration of the pendulum assembly. Connect the output signal of the laser vibration meter to a spectrum analyzer and observe the frequency domain response of the pendulum assembly vibration through the spectrum analyzer.

[0029] (4) Input a continuous sinusoidal sweep signal to the electromagnetic torquer coil through a signal generator. The signal amplitude is 50mV and the frequency range of the signal is 0Hz to 10KHz. This frequency range includes the third-order frequency point of the pendulum component obtained from simulation.

[0030] (5) Observe the frequency response curve of the pendulum assembly in the spectrum analyzer and find four resonant frequency points with frequency values ​​of 50Hz, 100Hz, 628Hz and 2590Hz respectively.

[0031] (6) Project the vibration measurement laser beam of the laser vibration meter onto the suspension bracket on which the pendulum assembly is installed, repeat the test steps (4) to (5) to obtain the corresponding frequency response curve, find the resonance frequency point of 100Hz, compare it with the previous frequency response curve, remove the common resonance frequency point of 100Hz, and obtain the frequency values ​​of the resonance frequency point of the pendulum assembly itself: 50Hz, 628Hz, and 2590Hz.

[0032] (7) Project the vibration measuring laser beam of the laser vibrometer onto the surface of the pendulum assembly, and input a continuous sinusoidal sweep frequency signal to the electromagnetic torque coil through the signal generator. The signal amplitude is 50mV, and the signal frequency range is 0Hz~100Hz, 500Hz~700Hz, and 2500Hz~2700Hz respectively. At the same time, observe the frequency response curve of the pendulum assembly in the spectrum analyzer and accurately measure the frequency values ​​of the three resonance frequency points, which are 50.25Hz, 628.68Hz, and 2589.74Hz respectively.

[0033] (8) Project the vibration measurement laser beam of the laser vibrometer onto the surface of the pendulum assembly. The projection position is determined according to the mode shape of the first order at 50.25 Hz in the modal simulation results of the pendulum assembly. Input a continuous fixed-frequency sinusoidal signal to the electromagnetic torque coil through the signal generator. Set the signal amplitude to 50 mV and the signal frequency to 50.25 Hz. At the same time, observe the frequency response curve of the pendulum assembly in the spectrum analyzer and measure the response amplitude at that frequency at that position. Then, change the position of the vibration measurement laser beam projected onto the surface of the pendulum assembly according to the mode shape of the first order at 50.25 Hz in the modal simulation results of the pendulum assembly. Repeat the test at other positions of the same frequency. Find the maximum response amplitude of 0.2 μm at a certain position of the frequency to obtain the first natural mode of the pendulum assembly. Using this method, find the maximum response amplitude of 0.3 nm at the 628.68 Hz frequency point and the maximum response amplitude of 0.5 pm at the 2589.74 Hz frequency point to obtain the second and third natural modes of the pendulum assembly. This test result is completely consistent with the simulation results of the vibration mode of the pendulum assembly.

Claims

1. A method for testing the inherent modes of an accelerometer pendulum assembly, characterized in that, (1) Install the pendulum component (M2) to be tested on the suspension bracket (M1), and then install the suspension bracket (M1) on the angle adjustment table (M4). Adjust the angle adjustment table (M4) to make the pendulum component (M2) deflect at an angle, observe the activity state of the pendulum component (M2), and ensure that it is in a suspended free swing state. (2) Connect the output of the signal generator (D3) to the electromagnetic torque coil (M3) on the pendulum assembly (M2), and connect a resistor (D4) in series between the electromagnetic torque coil (M3) and the signal generator (D3); (3) Project the vibration measurement laser beam of the laser vibration meter (D1) onto the surface of the pendulum assembly (M2), and connect the output signal of the laser vibration meter (D1) to the spectrum analyzer (D2); (4) Input a continuous sinusoidal sweep frequency signal to the electromagnetic torque coil (M3) through the signal generator (D3). The sweep frequency range includes the range of modes of the pendulum assembly (M2) under test. The amplitude of the sweep frequency signal is determined according to the actual vibration amplitude of the pendulum assembly (M2). (5) Observe the frequency response curve in the spectrum analyzer (D2), find a set of resonant frequency points, and record the frequency values; (6) Project the vibration measurement laser beam of the laser vibration meter (D1) onto the suspension bracket (M1) on which the pendulum assembly (M2) is installed, repeat the test steps (4) to (5) to obtain another set of resonance frequency points, compare the two sets of resonance frequency points, remove the common resonance frequency points of the two, and obtain the resonance frequency points of the pendulum assembly (M2) itself. (7) Project the vibration measurement laser beam of the laser vibrometer (D1) onto the surface of the pendulum assembly (M2). The projection position is determined according to the vibration mode of the pendulum assembly (M2). Based on the resonant frequency point of the pendulum assembly (M2), the electromagnetic torque coil (M3) is sequentially input with a continuous sinusoidal sweep frequency signal centered on the resonant frequency point through the signal generator (D3). The frequency range is 100Hz to 200Hz. At the same time, the precise frequency value of the resonant frequency point is tested in the spectrum analyzer (D2). The position of the vibration measurement laser beam of the laser vibrometer (D1) projected onto the surface of the pendulum assembly (M2) is changed, and the test of other resonant frequency points of the pendulum assembly (M2) is repeated. (8) Project the vibration measurement laser beam of the laser vibrometer (D1) onto the surface of the pendulum assembly (M2). The projection position is determined according to the vibration mode of the pendulum assembly (M2). Input a continuous fixed-frequency sinusoidal signal into the electromagnetic torque coil (M3) through the signal generator (D3). The signal amplitude is determined according to the actual vibration amplitude of the pendulum assembly (M2). The signal frequency is sequentially set to the frequency of the precise resonance frequency point measured in step (7). At the same time, measure the response amplitude of the pendulum assembly (M2) at the test position at the frequency in the spectrum analyzer (D2). Change the position of the vibration measurement laser beam of the laser vibrometer (D1) onto the surface of the pendulum assembly (M2) according to the vibration mode of the pendulum assembly (M2). Repeat the test at other positions of the resonance frequency point to obtain the natural mode of the pendulum assembly (M2). Repeat the test at other resonance frequency points of the pendulum assembly (M2) to obtain the multiple natural modes of the pendulum assembly (M2).

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