CN106017834A - Non-contact modality testing method, device, and system - Google Patents

Abstract

The invention relates to a non-contact mode testing method, device and system. The method includes the steps of: arranging each measuring point of the test piece according to the image of the test piece acquired by the laser head; selecting several measuring points from each measuring point, and measuring several measuring points when the piezoelectric wafer vibrates at various positions The vibration response signal, wherein the piezoelectric wafer vibrates when receiving the excitation signal output by the signal generator; determine the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points; when the piezoelectric wafer is in the fixed position , to obtain the excitation signal output by the signal generator and the vibration response signal of each measuring point; according to the obtained excitation signal and the vibration response signal of each measuring point, obtain the frequency response function of each measuring point relative to the excitation signal; according to the frequency response The function obtains the modal parameters of the test piece. The invention improves the excitation energy utilization rate and the signal-to-noise ratio of the vibration response signal, and at the same time, the noise on the test site is very small.

Description

Non-contact modal testing method, device and system

technical field

The invention relates to the technical field of modal testing, in particular to a non-contact modal testing method, a non-contact modal testing device and a non-contact modal testing system.

Background technique

Modal analysis is the basis for studying the vibration response characteristics of linear structural systems under various dynamic loads and the dynamic optimization design of structures. Modal test is the process of obtaining the modal parameters of linear structural systems through experiments, and it is the main tool for verifying or correcting the results of theoretical modal analysis.

Traditional modal tests usually use a hammer or a vibrator to apply excitation, and a sensor is pasted on the structure. By measuring the excitation signal of the hammer or vibrator and the vibration response of the structure, the structural frequency response function is obtained to further identify the structural mode. parameter. Traditional methods are suitable for large structures, such as those with large size, mass, and stiffness. However, for light and small structures, such as circuit boards, electronic components, key components, etc., the traditional method will cause large errors due to the impact of additional mass and additional stiffness brought by the excitation source and the pasted sensor.

At present, non-contact acoustic excitation and laser vibrometer system are usually used to measure the vibration response of light and small structure modal tests to obtain modal parameters. This method eliminates the influence of additional mass and additional stiffness, and is especially suitable for thin plate structures. However, the non-contact acoustic excitation has the disadvantages of large excitation energy loss, low excitation energy utilization rate, high noise at the test site, and low signal-to-noise ratio of vibration response to non-thin plate structures such as irregular electronic components and key components.

Contents of the invention

Based on this, it is necessary to address the above problems and provide a non-contact modal testing method, device and system that can economically, efficiently and accurately obtain the modal parameters of various light and small structures (including thin plates). Piezoelectric chip contact excitation solves the problems of low excitation energy utilization rate, poor signal-to-noise ratio of vibration response, and large noise at the test site existing in sound excitation.

In order to achieve the above object, the technical scheme that the present invention takes is as follows:

A non-contact modal testing method comprising the steps of:

Arrange each measuring point of the test piece according to the image of the test piece acquired by the laser head;

Select several measuring points from each measuring point, and measure the vibration response signals of several measuring points when the piezoelectric wafer vibrates at different positions, wherein the piezoelectric wafer vibrates when receiving the excitation signal output by the signal generator;

Determine the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points;

When the piezoelectric wafer is located at the fixed position, the excitation signal output by the signal generator and the vibration response signal of each measuring point are obtained;

According to the obtained excitation signal and the vibration response signal of each measurement point, the frequency response function of each measurement point relative to the excitation signal is obtained;

The modal parameters of the test piece are obtained according to the frequency response function.

A non-contact modal test setup comprising:

The measuring point layout module is used to arrange each measuring point of the test piece according to the image of the test piece obtained by the laser head;

The vibration response signal measurement module is used to select several measuring points from each measuring point, and measure the vibration response signals of several measuring points when the piezoelectric wafer vibrates at different positions, wherein the piezoelectric wafer receives the signal generator output Vibration occurs when the excitation signal;

The fixed position determination module is used to determine the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points;

The excitation signal and vibration response signal acquisition module is used to obtain the excitation signal output by the signal generator and the vibration response signals of each measuring point when the piezoelectric wafer is located at the fixed position;

The frequency response function acquisition module is used to obtain the frequency response function of each measurement point relative to the excitation signal according to the obtained excitation signal and the vibration response signal of each measurement point;

The modal parameter obtaining module is used to obtain the modal parameters of the test piece according to the frequency response function.

A non-contact modal testing system comprising a piezoelectric wafer and a laser vibration measurement system, the laser vibration measurement system including a laser head, a signal generator and the non-contact modal testing device; the piezoelectric wafer It is connected with the output end of the signal generator, and the non-contact mode test device is respectively connected with the laser head and the output end of the signal generator.

The non-contact modal testing method, device and system of the present invention have the following advantages when compared with the prior art:

(1) The present invention utilizes the piezoelectric chip to directly perform contact excitation, which improves the utilization rate of excitation energy and the signal-to-noise ratio of the vibration response signal, and the noise at the test site is very small;

(2) The piezoelectric chip adopted in the present invention has the characteristics of light weight and small excitation amplitude, can be arranged on the auxiliary structure of the test piece for excitation, and the impact on the additional mass and additional stiffness of the light and small structure can be ignored, and the measurement accuracy is high;

(3) The present invention is applicable to various light and small structures (including thin plates);

(4) The present invention directly uses the excitation signal output by the signal generator to calculate the frequency response function without additional measurement of the input signal, which is convenient and simple.

Description of drawings

Fig. 1 is the schematic flow chart of the embodiment of the non-contact modal testing method of the present invention;

Fig. 2 is the schematic diagram of each measuring point arranged on the test piece of the present invention;

Fig. 3 is a schematic structural view of an embodiment of the non-contact modal testing device of the present invention;

Fig. 4 is a schematic structural diagram of an embodiment of a fixed position determining module of the present invention;

Fig. 5 is a schematic structural view of an embodiment of the non-contact modal testing system of the present invention;

6 is a schematic diagram of a specific embodiment of the placement position of the piezoelectric wafer of the present invention;

Fig. 7 is the frequency response function of the hermetic packaging structure of the present invention;

Fig. 8(a) to Fig. 8(h) are the mode shapes of the hermetic packaging structure of the present invention.

detailed description

In order to further illustrate the technical means adopted by the present invention and the achieved effects, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and preferred embodiments.

As shown in Figure 1, a non-contact modal testing method includes steps:

S110, according to the image of the test piece acquired by the laser head, arrange each measuring point of the test piece;

S120, select several measuring points from each measuring point, and measure the vibration response signals of several measuring points when the piezoelectric wafer vibrates at various positions, wherein the piezoelectric wafer vibrates when receiving the excitation signal output by the signal generator ;

S130. Determine the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points;

S140. When the piezoelectric wafer is located at the fixed position, obtain the excitation signal output by the signal generator and the vibration response signal of each measuring point;

S150. According to the obtained excitation signal and the vibration response signal of each measurement point, obtain the frequency response function of each measurement point relative to the excitation signal;

S160. Obtain the modal parameters of the test piece according to the frequency response function.

In step S110, the test piece includes various light and small structures (including thin plates), such as the hermetic packaging structure of the power module and the like. The laser head is a laser scanning head, which is arranged along the excitation direction and used to measure the vibration response signal of the test piece. There is a tiny camera on the laser head, which can take images of the test piece.

After the image of the test piece is obtained by the camera, each measuring point is arranged on the image of the test piece. For example, as shown in Figure 2, it is a schematic diagram of various measuring points (black dots) arranged on the image of the hermetic packaging structure, where the hermetic packaging structure is a rectangular parallelepiped metal shell, and the measuring points are arranged on the surface of the metal shell.

In step S120, the present invention uses a piezoelectric chip with a smaller volume. The terminal of the piezoelectric wafer is connected with the output port of the signal generator, and the connected device can use a test cable. The signal generator directly inputs the excitation signal to the piezoelectric chip to make the piezoelectric chip vibrate, thereby causing the test piece to vibrate.

Before the test, it is necessary to determine the excitation signal output by the signal generator, the sampling parameters, and the bandwidth of the excitation frequency band. The excitation signal includes random white noise or transient sine frequency sweep signal, etc. Sampling parameters and excitation frequency bandwidth can be set according to the analysis frequency.

The signal generator outputs an excitation signal to vibrate the piezoelectric wafer, select several measuring points from each measuring point, adjust the position of the piezoelectric wafer, and measure the vibration response signal of the test piece synchronously.

In step S130, the fixed position of the piezoelectric wafer is determined according to the vibration response signals of several measuring points. In one embodiment, the step of determining the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points may include:

S1301, selecting a vibration response signal with a smooth curve and containing the most frequency information from the vibration response signals of several measuring points;

S1302. Determine the position of the piezoelectric chip corresponding to the acquired vibration response signal as a fixed position.

The fixed position of the piezoelectric chip includes that the piezoelectric chip is located on the test piece or on the accessory structure of the test piece, wherein the accessory structure of the test piece includes the connection between the test piece and the fixture, etc. Generally speaking, for the test piece with high rigidity, the piezoelectric chip can be directly pasted on the test piece, and for the ultra-thin plate test piece, the piezoelectric chip can be pasted on the auxiliary structure of the test piece.

Since the piezoelectric chip needs to be fixed on the test piece or the accessory structure of the test piece, the size of the piezoelectric chip is generally smaller than the structural size of the test piece. When fixing the piezoelectric chip, the piezoelectric chip can be pasted on the test piece or the accessory structure of the test piece through an adhesive material, and the adhesive material can be glue or the like.

In step S140, the piezoelectric wafer is fixed at a determined fixed position, and the vibration response signals of each measuring point when the signal generator outputs an excitation signal at this time are measured.

In step S150, the excitation signal output by the signal generator is used as a reference signal, and the frequency response function of each measuring point relative to the reference signal is calculated by using the existing method in the prior art.

In step S160, the frequency response function is identified using an existing modal identification method, and modal parameters such as frequency and mode shape of the test piece are obtained.

Based on the same inventive concept, the present invention also provides a non-contact modal testing device. The specific implementation of the device of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in Figure 3, a non-contact modal test device includes:

The measuring point arrangement module 110 is used for arranging each measuring point of the test piece according to the image of the test piece acquired by the laser head;

The vibration response signal measurement module 120 is used to select several measuring points from each measuring point, and measure the vibration response signals of several measuring points when the piezoelectric wafer vibrates at different positions, wherein the piezoelectric wafer receives the vibration response signal of the signal generator Vibration occurs when the excitation signal is output;

Fixed position determination module 130, for determining the fixed position of piezoelectric wafer according to the vibration response signals of several measuring points;

The excitation signal and vibration response signal acquisition module 140 is used to obtain the excitation signal output by the signal generator and the vibration response signals of each measuring point when the piezoelectric wafer is located at the fixed position;

The frequency response function obtaining module 150 is used to obtain the frequency response function of each measuring point relative to the excitation signal according to the obtained excitation signal and the vibration response signal of each measuring point;

The modal parameter obtaining module 160 is configured to obtain the modal parameters of the test piece according to the frequency response function.

In one embodiment, as shown in FIG. 4, the fixed position determination module 130 may include:

A vibration response signal selection unit 1301, configured to select a vibration response signal with a smooth curve and the most frequency information contained in the vibration response signals of several measuring points;

The fixed position determining unit 1302 is configured to determine the position of the piezoelectric chip corresponding to the acquired vibration response signal as a fixed position.

The fixed position of the piezoelectric chip includes that the piezoelectric chip is located on the test piece or on the accessory structure of the test piece, wherein the accessory structure of the test piece includes the connection between the test piece and the fixture, etc. Generally speaking, for the test piece with high rigidity, the piezoelectric chip can be directly pasted on the test piece, and for the ultra-thin plate test piece, the piezoelectric chip can be pasted on the auxiliary structure of the test piece.

Since the piezoelectric chip needs to be fixed on the test piece or the accessory structure of the test piece, the size of the piezoelectric chip is generally smaller than the structural size of the test piece. When fixing the piezoelectric chip, the piezoelectric chip can be pasted on the test piece or the accessory structure of the test piece through an adhesive material, for example, the adhesive material can be glue or the like.

Other technical features of the device of the present invention are the same as those of the method of the present invention, and will not be repeated here.

The present invention also provides a non-contact modal test system. The system of the present invention will be briefly introduced below in conjunction with the accompanying drawings.

As shown in Figure 5, a kind of non-contact mode testing system comprises piezoelectric wafer and laser vibrometer system, and described laser vibrometer system comprises laser head, signal generator and described non-contact mode test device ; The piezoelectric wafer is connected to the output end of the signal generator, and the non-contact modal test device is connected to the laser head and the output end of the signal generator respectively.

The non-contact modal testing device has the functions of signal acquisition and storage, frequency response function calculation, and modal recognition. The specific technical features are the same as those of the non-contact modal testing device of the present invention described above, and will not be repeated here. The signal generator can be connected with the piezoelectric wafer and the non-contact modal test device through the test cable, and the laser head can be connected with the non-contact modal test device through the test cable.

The implementation process of the present invention will be described below by taking the modal test of a hermetic packaging structure of a certain power module as an example.

A piezoelectric excitation modal test system with a hermetically sealed structure, including a piezoelectric wafer and a Polytec PSV-500-3D-M laser vibration measurement system. The laser vibration measurement system includes a laser head, a dual-channel data acquisition and analysis module (that is, a non-contact modal test device), and a single-channel signal generator. PSV data acquisition and analysis software and modal recognition software are installed in the data acquisition and analysis module. A piezoelectric wafer with a diameter of 35mm (mm) and a thickness of less than 1mm is selected. The piezoelectric chip is connected to the signal generator channel of the laser vibration measurement system through the test cable, and the signal generator channel of the laser vibration measurement system is connected to one of the channels of the dual-channel data acquisition and analysis module at the same time, and the other channel is connected to the laser through the test cable. header connection. The laser head is placed directly in front of the hermetic packaging structure.

A piezoelectric excitation modal test method for a hermetically sealed package structure, comprising the following steps:

(1) Start the PSV data acquisition and analysis software, and arrange measuring points in the image area through the image of the test piece taken by the micro-camera on the laser head, a total of 90 measuring points, as shown in Figure 6 (Figure 6 contains two air Hermetic packaging structure, each hermetic packaging structure has 45 measuring points).

(2) Determine the analysis frequency from 0 to 2000 Hz, and set the output of the signal generator as a transient sine frequency sweep signal, and the sweep frequency range is from 0 to 2000 Hz.

(3) The output signal of the signal generator causes the piezoelectric chip to vibrate, and the signal triggers the PSV data acquisition and analysis software to measure the vibration response signal of the test piece synchronously. Select several measuring points, adjust the position of the piezoelectric chip, obtain the vibration response signal curves of several measuring points, find out the vibration response signal with smooth curve and contain more frequency information among the measured vibration response signals, and correspond to the vibration response signal The excitation point of is used as the optimal excitation position of the piezoelectric wafer.

Because the hermetic packaging structure is very thin, the test found that the 0.7g sensor will cause the first-order frequency to decrease by 12%. Finally, it is determined to arrange the piezoelectric wafer at the junction of the hermetic package structure and the fixture, as shown in Figure 6.

(4) Paste the piezoelectric chip on the connection between the hermetic package structure and the fixture, and measure the vibration response signals of all measuring points when the signal generator outputs a transient sine frequency sweep signal.

(5) The PSV data acquisition and analysis software uses the channel signal of the signal generator as a reference signal to calculate the frequency response function of all measuring points relative to the reference signal, and the obtained frequency response parameters are shown in Figure 7.

(6) Import the frequency response function data into the modal recognition software, and use the PolyMAX modal recognition method to calculate the modal parameters. A total of 8 natural frequencies and mode shapes are obtained, as shown in Fig. 8(a) to Fig. 8(h).

When the present invention compares with prior art, possess following advantage:

(1) The present invention utilizes the piezoelectric chip to directly perform contact excitation, which improves the utilization rate of excitation energy and the signal-to-noise ratio of the vibration response signal, and the noise at the test site is very small;

(2) The piezoelectric chip adopted in the present invention has the characteristics of light weight and small excitation amplitude, can be arranged on the auxiliary structure of the test piece for excitation, and the impact on the additional mass and additional stiffness of the light and small structure can be ignored, and the measurement accuracy is high;

(3) The present invention is applicable to various light and small structures (including thin plates);

(4) The present invention directly uses the excitation signal output by the signal generator to calculate the frequency response function without additional measurement of the input signal, which is convenient and simple.

The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. A non-contact mode testing method, characterized in that, comprising steps: Arrange each measuring point of the test piece according to the image of the test piece acquired by the laser head; Select several measuring points from each measuring point, and measure the vibration response signals of several measuring points when the piezoelectric wafer vibrates at different positions, wherein the piezoelectric wafer vibrates when receiving the excitation signal output by the signal generator; Determine the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points; When the piezoelectric wafer is located at the fixed position, the excitation signal output by the signal generator and the vibration response signal of each measuring point are obtained; According to the obtained excitation signal and the vibration response signal of each measurement point, the frequency response function of each measurement point relative to the excitation signal is obtained; The modal parameters of the test piece are obtained according to the frequency response function. 2. The non-contact modal testing method according to claim 1, wherein the step of determining the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points comprises: Select the vibration response signal with a smooth curve and the most frequency information from the vibration response signals of several measuring points; The position of the piezoelectric chip corresponding to the acquired vibration response signal is determined as a fixed position. 3. The non-contact modal testing method according to claim 1 or 2, characterized in that the fixed position of the piezoelectric wafer includes that the piezoelectric wafer is located on the test piece or on an auxiliary structure of the test piece. 4. The non-contact modal testing method according to claim 3, characterized in that, the accessory structure of the test piece includes the joint between the test piece and the fixture. 5. The non-contact modal testing method according to claim 1 or 2, characterized in that the size of the piezoelectric wafer is smaller than the structural size of the test piece. 6. A non-contact modal testing device, characterized in that it comprises: The measuring point layout module is used to arrange each measuring point of the test piece according to the image of the test piece obtained by the laser head; The vibration response signal measurement module is used to select several measuring points from each measuring point, and measure the vibration response signals of several measuring points when the piezoelectric wafer vibrates at different positions, wherein the piezoelectric wafer receives the signal generator output Vibration occurs when the excitation signal; The fixed position determination module is used to determine the fixed position of the piezoelectric wafer according to the vibration response signals of several measuring points; The excitation signal and vibration response signal acquisition module is used to obtain the excitation signal output by the signal generator and the vibration response signals of each measuring point when the piezoelectric wafer is located at the fixed position; The frequency response function acquisition module is used to obtain the frequency response function of each measurement point relative to the excitation signal according to the obtained excitation signal and the vibration response signal of each measurement point; The modal parameter obtaining module is used to obtain the modal parameters of the test piece according to the frequency response function. 7. The non-contact modal testing device according to claim 6, wherein the fixed position determining module comprises: The vibration response signal selection unit is used to select the vibration response signal with a smooth curve and the most frequency information contained in the vibration response signals of several measuring points; The fixed position determining unit is configured to determine the position of the piezoelectric chip corresponding to the acquired vibration response signal as a fixed position. 8. The non-contact modal testing device according to claim 6 or 7, wherein the fixed position of the piezoelectric wafer comprises that the piezoelectric wafer is located on the test piece or on the attached structure of the test piece; the attached structure of the test piece Including the connection between the test piece and the fixture. 9. The non-contact modal testing device according to claim 6 or 7, characterized in that the size of the piezoelectric wafer is smaller than the structural size of the test piece. 10. A non-contact modal testing system, characterized in that it comprises a piezoelectric wafer and a laser vibration measurement system, and the laser vibration measurement system comprises a laser head, a signal generator and as claimed in any one of claims 6 to 9 The non-contact modal test device; the piezoelectric chip is connected to the output end of the signal generator, and the non-contact modal test device is connected to the laser head and the output end of the signal generator respectively.