A dynamic rotating body vibration mode measuring method

Abstract

The application relates to a dynamic rotating body vibration mode measuring method, which establishes a point coordinate system (x', y') on a workpiece and a coordinate system (x, y) on a camera image, and establishes a mapping relation (x, y)=g'(x', y', t) containing rotating time, and also establishes a mapping relation between two-axis galvanometer rotating angles and the camera image coordinate system (x, y). When the workpiece rotates, a camera is used to capture a triggering point on the workpiece surface, a laser is triggered to emit triggering laser to the triggering point on the workpiece surface when the triggering point appears at a fixed position, and the two-axis galvanometer rotating angles are adjusted according to the vibration of the point (x', y') to be measured so that a detection laser is fixed at a set position on the camera image, and the vibration of (x', y') at any time tau is obtained through calculation. Even in the case of high-speed rotation of the workpiece, the vibration can be measured.

Description

Technical Field

[0001] This invention uses pulsed laser to excite high-frequency broadband ultrasonic signals within a workpiece, and uses a laser vibrometer to measure the vibration modes of a high-speed rotating dynamic workpiece. It belongs to the field of vibration measurement, and specifically relates to non-contact vibration mode measurement of high-speed rotating objects. Background Technology

[0002] Vibration measurement has a wide range of applications in scientific research and engineering. For example, measuring the vibration of MEMS devices can optimize device design and improve fabrication processes; vibration measurement of piezoelectric materials and devices can be used to study material properties and device quality; vibration measurement of automobiles, airplanes, and rail trains can be used to improve the vibration characteristics of mechanical equipment and achieve superior NVH; and the study of vibration characteristics of tissues and organisms can deepen human understanding of biological behavior.

[0003] Vibration measurement methods can be broadly categorized into two types: contact measurement and non-contact measurement. Contact measurement can be mechanical or electrical sensor-based. Electrical sensor methods require attaching a sensor to the vibrating workpiece, converting variables such as acceleration, velocity, and displacement into electrical signals for analysis. Because contact vibration measurement requires attaching a finite-mass sensor to the vibrating workpiece, it alters the workpiece's vibration characteristics, leading to a decrease in measurement accuracy. Non-contact vibration measurement technology avoids the influence of attached mass; a common instrument is the laser vibrometer. It uses a probe laser beam to illuminate the workpiece surface, allowing the vibrator to accurately measure the workpiece's vibration signal. Laser vibrometers have been applied in numerous fields, including materials research and testing, electronics, solar energy, semiconductor industries, industrial online monitoring, aerospace testing, automotive, biology and medicine, acoustics and ultrasound, and micro / nanotechnology.

[0004] While measuring the vibration of conventional static workpieces is relatively easy, testing the vibration of rotating workpieces presents considerable challenges, such as car tires, rotating flywheels, and cutting blades. Measuring these workpieces in a rotating state can accurately reflect their operating conditions and obtain crucial parameters that are impossible to obtain statically, thus possessing significant practical implications.

[0005] To address this issue, the German company Polytec developed a beam rotation system to keep the probe beam of the laser vibrometer rotating at the same speed as the workpiece. However, the beam rotation system requires that the rotation speed not be too high, making this measurement method difficult to implement for workpieces rotating at high speeds (5000 rpm).

[0006] The existing patent "CN108254063A" (a vibration measurement device for tracking rotating blades) guides the detection laser to track the vibration test position in real time by adjusting the XY guide lens. However, in its solution, if the rotating blade to be tested rotates too fast, the speed of adjustment of the XY guide lens is limited and real-time tracking cannot be achieved. In addition, its high-speed camera adopts a low-resolution mode, which limits the clarity of the captured image and thus affects the tracking of the test position. Summary of the Invention

[0007] The purpose of this invention is to provide a method for measuring the vibration modes of a dynamic rotating body, which solves the problem of how to measure the vibration of a high-speed rotating workpiece.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for measuring the vibration modes of a dynamic rotating body. It utilizes a laser vibrometer, a biaxial galvanometer, a camera, and a nanosecond-level laser for measurement. The camera is directly facing the workpiece and its field of view covers the area to be measured. The probe laser emitted by the laser vibrometer is directed onto the workpiece via the biaxial galvanometer, and the excitation laser emitted by the laser emits an excitation laser onto the workpiece, forming a non-contact excitation. The method is characterized by comprising:

[0010] Establish a rectangular coordinate system (x, y) with a point on the camera image as the origin coordinate;

[0011] Establish the mapping relationship (x,y) = f(φ, θ) between the rotation angle (φ, θ) of the two-axis galvanometer and the camera image coordinate system (x,y);

[0012] Mark point P on the workpiece, and establish a point coordinate system (x', y') on the workpiece with point P as the origin. Establish the mapping relationship between (x, y) and (x', y') when the workpiece rotates by any angle Φ. Since the rotation angle Φ is related to the rotational angular velocity ω and time t of the workpiece, it is expressed as Φ = ωt. Then, the mapping relationship between the workpiece coordinates (x', y') and the camera coordinates (x, y) is obtained as (x, y) = g'(x', y', t).

[0013] Rotate the workpiece and mark an excitation point on it. Define a set of measurement points Ω' in the (x',y') coordinate system. The measurement time for each point is T. The measurement information at any time τ is mapped to the set of points in the camera coordinate system (x,y) as Ω. τ When the camera captures the excitation point on the workpiece appearing at a fixed position, it triggers the laser to emit an excitation laser to the excitation point to excite the ultrasonic wave. The deflection angle of the galvanometer is calculated according to (x,y)=g'(x',y',t) and (x,y)=f(φ, θ), and the deflection angle of the galvanometer is adjusted according to the calculation result, so as to measure the vibration of the point (x',y') on the workpiece at time τ.

[0014] Preferably, the excitation point during measurement is point P marked on the workpiece.

[0015] Preferably, multiple points (x', y') are selected, and the vibration at any time τ is measured to obtain the corresponding vibration modes.

[0016] Preferably, the angular velocity ω of the workpiece rotation is measured using a laser vibrometer.

[0017] Preferably, the workpiece is mounted on a rotary motor for rotation.

[0018] Preferably, the establishment of (x,y)=f(φ, θ) is achieved by point-to-point mapping through fitting interpolation. That is, multiple points are taken on the camera image, and the detection laser of the laser vibrometer is made to coincide with the points. The rotation angle (φ, θ) of each point is recorded. Based on the geometric relationship between the galvanometer scanning angle (φ, θ) and the camera coordinates (x,y), and on this basis, a correction term is introduced, and the corresponding mapping relationship is established through interpolation fitting.

[0019] Furthermore, the detection point of the galvanometer at any scanning angle (φ, θ) is checked to see if it falls on the corresponding point. If the deviation is large, the calibration points are added until the corresponding predicted value is reached, and finally the mapping relationship between the camera coordinates and the galvanometer rotation angle (x,y)=f(φ, θ) is accurately established.

[0020] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0021] The dynamic rotating body vibration mode measurement method of the present invention measures point by point and time by time, and finally synthesizes all data into the time waveform of each point. After spectrum transformation, the two-dimensional vibration mode of the corresponding frequency can be obtained. Therefore, the vibration can be measured even when the workpiece is rotating at high speed. Attached Figure Description

[0022] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0023] Figure 1 This is a schematic diagram illustrating the principle of the present invention;

[0024] The reference numerals in the attached figures are explained as follows:

[0025] 1. Laser vibration meter;

[0026] 2. Optical camera;

[0027] 3. Two-dimensional scanning galvanometer;

[0028] 4. Sample;

[0029] 5. Rotary electric motor;

[0030] 6. Pulsed laser. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The dynamic rotating body vibration modal measurement method of the present invention is illustrated in the following diagram: Figure 1 As shown, a nanosecond-level laser 6 generates an excitation laser to irradiate the workpiece 4, exciting high-frequency broadband ultrasonic waves to replace traditional vibratory hammers and exciters. The principle is based on the photoacoustic effect, specifically as follows: the excitation laser irradiates the workpiece, which absorbs the light energy and converts it into heat energy. This heat energy causes thermal expansion within a micro-region of the workpiece, generating thermal stress, which ultimately propagates in the form of elastic waves. Compared to traditional vibration excitation methods, the photoacoustic effect can generate ultrasonic waves with a bandwidth of hundreds of megabits, achieving non-contact excitation. The former enables the measurement of broadband vibration modes, while the latter is indispensable in this invention.

[0033] The laser probe emitted by the laser vibrometer 1 is projected onto the workpiece through a two-axis galvanometer 3. Changing the rotation angle (φ, θ) of the two galvanometers 3 allows the laser probe point to scan the workpiece. To track the position of the laser spot of the laser vibrometer, a camera 2 is mounted on the side of the galvanometer 3, facing the workpiece, with a field of view covering the area to be measured. A rectangular coordinate system is established using a point on the image from camera 2 as the origin coordinate, denoted here as (x, y).

[0034] To establish the mapping relationship between the rotation angle (φ, θ) of galvanometer 3 and the camera image coordinates (x, y), a point-to-point mapping method is used, involving point selection and fitting interpolation. The specific process is as follows:

[0035] 1. Randomly select a point (x1, y1) at the upper edge of the image of camera 2, and adjust (φ, θ) until the probe laser point in the image of camera 2 coincides with the selected point (x1, y1). Record the angle (φ) corresponding to the galvanometer. 1, θ1);

[0036] 2. Continue by selecting other points on the camera image to establish point-to-point data (x i ,y i ) (φ) i, θ i), where i represents the i-th point;

[0037] 3. After obtaining the corresponding data for each point, based on the geometric relationship between the scanning angle (φ, θ) of galvanometer 3 and the coordinates (x, y) of camera 2, and on this basis, a correction term is introduced, and the corresponding mapping relationship is established through interpolation fitting;

[0038] 4. Randomly select a point (x, y) in the area to be measured on the image of camera 2. Predict the rotation angle (φ, θ) of galvanometer 3 based on the mapping relationship established in step 3. After rotating the galvanometer by the corresponding angle, observe whether the probe laser point falls on the corresponding point. If the deviation is large, continue to add calibration points until the corresponding predicted value is reached. Finally, establish the mapping relationship (x, y) = f(φ, θ) between the coordinates of camera 2 and the rotation angle of galvanometer 3.

[0039] Workpiece 4 rotates under the drive of rotary motor 5, and the measuring point of laser vibrometer 1 is fixed on the image coordinates of camera 2. Since workpiece 4 rotates periodically, laser vibrometer 1 can measure the rotational angular velocity ω of the workpiece.

[0040] When workpiece 4 is stationary, the laser excitation point P is marked on workpiece 4, and a point coordinate system (x', y') is established on the workpiece with point P as the origin. When workpiece 4 rotates, both point P and the workpiece 4 coordinate system (x', y') are in motion in the image coordinates of camera 2. To establish the time mapping relationship between coordinate systems (x, y) and (x', y'), the following is used:

[0041] 1. Rotate the workpiece by a certain angle Φ to obtain the coordinates (x1, y1) of point P in the coordinate system (x, y).

[0042] 2. Following step 1, take a finite number of rotation angles Φ i And record the coordinates (x, y) of point P in the camera 2 coordinate system. i ,y i ), to obtain the corresponding data for each point, where i represents the i-th point;

[0043] 3. Based on the point-to-point data and geometric relationships obtained in step 2, the mapping relationship between the coordinates of point P in the camera 2 coordinate system and the rotation angle (x,y)=g(Φ) can be obtained by fitting.

[0044] 4. Based on the mapping relationship in step 3, the mapping relationship between the workpiece 4 coordinate system (x', y') and the camera 2 coordinate system (x, y) at any rotation angle Φ can be obtained.

[0045] Since the rotation angle Φ is related to the rotational angular velocity ω of workpiece 4 and time t, it can be expressed as Φ=ωt. The mapping relationship (x,y) of workpiece 4 coordinates (x',y') on camera 2 coordinates (x,y) can be calculated at any time t: (x,y)=g'(x',y',t).

[0046] Based on the information above, perform the following operations:

[0047] S1. Mark a small dot on the workpiece 4. The excitation laser from the pulsed laser 6 hits the corresponding point to generate ultrasonic waves. Start the rotary motor 5 to drive the workpiece 4 to rotate.

[0048] S2. Measure the angular velocity ω of the rotation using a laser vibrometer, and establish the coordinate relationships (x,y) = f(φ, θ) and (x,y) = g'(x',y',t). Define the set of measurement points of interest Ω' on the (x',y') coordinate system, with the measurement time length of each point being T. Then, the measurement information at any time τ can be mapped to the set of points Ω on the camera 2 coordinate system (x,y). τ .

[0049] S3. When camera 2 captures the origin P on the workpiece appearing in a fixed position, it triggers pulsed laser 6 to emit a laser beam that hits point P and generates ultrasonic waves. To measure the vibration of point (x',y') on workpiece 4 at time τ, it is only necessary to determine the corresponding coordinates according to (x,y)=g'(x',y',t) and calculate the deflection angle of galvanometer 3 according to (x,y)=f(φ, θ).

[0050] S4. By repeating step S3, the vibration of any point (x', y') on workpiece 4 at any time τ can be measured. Although it takes a little longer, it can effectively solve the vibration problem of high-speed rotating workpiece 4, and the corresponding vibration modes can be obtained by measuring multiple points.

[0051] This example uses point P as the excitation point, which reduces the amount of computation, but points other than point P can also be selected as excitation points.

[0052] In this embodiment, the target workpiece 4 is a slicing tool. It is necessary to measure the two-dimensional vibration mode of the tool when it rotates at high speed. The blade speed is as high as 50,000 rpm, the entire blade diameter is 10 cm, the target sampling points are 20, and the single-point measurement time is 500 μs.

[0053] The pulsed laser 6 used is a laser with a pulse width of 10 ns, a wavelength of 532 nm, and a single pulse energy of up to 50 mJ. The spot size and the energy ultimately irradiated onto the workpiece 4 can be pre-controlled using optical components. The laser vibrometer 1 has a bandwidth of dc-0.1 MHz, and its analog signal is acquired by a data acquisition card at a depth of 14 bits and a speed of 10 MSa / s. A Hamamatsu industrial camera with a zoom lens is used. A Thorlabs standard galvanometer of the corresponding wavelength is used. The mapping relationship between the coordinates is fitted using least squares regression.

[0054] Following the steps described above, measurements are taken point-by-point and time-by-time. Finally, all data are synthesized to produce the time waveform for each point. After spectral transformation, the corresponding two-dimensional vibration modes at the appropriate frequencies can be obtained.

[0055] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for measuring the vibration modes of a dynamic rotating body, comprising a laser vibrometer, a biaxial galvanometer, a camera, and a nanosecond laser, wherein the camera is directly facing the workpiece and its field of view covers the area to be measured; the probe laser emitted by the laser vibrometer is directed onto the workpiece via the biaxial galvanometer; and the excitation laser emitted by the laser irradiates the workpiece to form a non-contact excitation, characterized in that it... include: Establish a rectangular coordinate system (x, y) with a point on the camera image as the origin coordinate; Establish the mapping relationship (x,y) = f(φ,θ) between the rotation angle (φ, θ) of the two-axis galvanometer and the camera image coordinate system (x,y); Mark point P on the workpiece, and establish a point coordinate system (x', y') on the workpiece with point P as the origin. Establish the mapping relationship between (x, y) and (x', y') when the workpiece rotates by any angle Φ. Since the rotation angle Φ is related to the rotational angular velocity ω and time t of the workpiece, it is expressed as Φ = ωt. Then, the mapping relationship between the workpiece coordinates (x', y') and the camera coordinates (x, y) is obtained as (x, y) = g'(x', y', t). Rotate the workpiece and mark an excitation point on it. Define a set of measurement points Ω' in the (x',y') coordinate system. The measurement time for each point is T. The measurement information at any time τ is mapped to the set of points in the camera coordinate system (x,y) as Ω. τ When the camera captures the excitation point on the workpiece appearing at a fixed position, it triggers the laser to emit an excitation laser to the excitation point to excite the ultrasonic wave. The deflection angle of the galvanometer is calculated according to (x,y)=g'(x',y',t) and (x,y)=f(φ, θ), and the deflection angle of the galvanometer is adjusted according to the calculation result, so as to measure the vibration of point (x',y') on the workpiece at time τ.

2. The method for measuring the vibration modes of a dynamic rotating body according to claim 1, characterized in that: The excitation point during measurement is point P marked on the workpiece.

3. The method for measuring the vibration modes of a dynamic rotating body according to claim 1, characterized in that: Multiple points (x', y') are selected, and the vibration at any time τ is measured to obtain the corresponding vibration modes.

4. The method for measuring the vibration modes of a dynamic rotating body according to claim 1, characterized in that: The angular velocity ω of the workpiece rotation is measured using a laser vibration meter.

5. The method for measuring the vibration modes of a dynamic rotating body according to claim 1, characterized in that: The workpiece is mounted on a rotary motor and rotates.

6. The method for measuring the vibration modes of a dynamic rotating body according to claim 1, characterized in that: Establishing (x,y)=f(φ, θ) is achieved by fitting interpolation points to realize point-to-point mapping. That is, multiple points are taken on the camera image, and the detection laser of the laser vibrometer is made to coincide with the points. The rotation angle (φ, θ) of each point is recorded. Based on the geometric relationship between the galvanometer scanning angle (φ, θ) and the camera coordinates (x,y), and on this basis, a correction term is introduced, and the corresponding mapping relationship is established through interpolation fitting.

7. The method for measuring the vibration modes of a dynamic rotating body according to claim 6, characterized in that: The detection point of the galvanometer at any scanning angle (φ, θ) is checked to see if it falls on the corresponding point. If the deviation is large, the calibration points are added until the corresponding predicted value is reached, and finally the mapping relationship between the camera coordinates and the galvanometer rotation angle (x,y)=f(φ, θ) is accurately established.

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