A laser three-dimensional vibration measuring instrument and a three-dimensional alignment and scanning method thereof

Abstract

The application relates to a laser three-dimensional vibration measuring instrument, which comprises three groups of laser vibration measuring probes, a front-end real-time processing system and a host computer. The probes are independent of each other, at least one of which is a main probe, and the rest are auxiliary probes; the auxiliary probes comprise two parts of an optical path and an electric control system, and the main probe comprises four parts of an optical path, an electric control system, a camera and a video transmission interface; the front-end real-time processing system is electrically connected with the host computer and comprises a data acquisition and demodulation module and a low-speed setting and interaction module; the optical paths in the probes are consistent, each optical path comprises a laser distance measuring module, a laser vibration measuring module, a front-end optical fiber collimator, an optical switch, a rear-end optical fiber collimator and a two-dimensional angle displacement table and a lens arranged on the two-dimensional angle displacement table; the switching of the optical switch is realized through electric signals generated by the low-speed setting and interaction module; through the switching of the optical switch, the laser vibration measuring probe is in an alignment mode or a vibration measuring mode.

Description

Technical Field

[0001] This invention relates to a laser three-dimensional vibration measurement system. Background Technology

[0002] In monitoring the state of objects and conducting scientific research, timely and accurate acquisition of vibration information is crucial. Vibration measurement technology is currently widely used in acoustics, aerospace, and quality inspection. Based on whether the sensor is attached to the surface of the object being measured, vibration measurement methods can be divided into contact measurement and non-contact measurement. Contact measurement is currently widely used; however, in actual measurement processes, it may affect the accuracy or vibration state of the object being measured. Laser vibration measurement technology, as a typical non-contact measurement method, features high measurement accuracy, fast signal acquisition speed, strong anti-interference capability, long measurement distance, high spatial resolution, short measurement time, and no added mass, making it widely used in the detection of weak vibration signals. This measurement method currently primarily uses single-point measurement, obtaining the vibration displacement and velocity of the object being measured along the optical path by detecting the frequency or direction deviation of the reflected light. Laser three-dimensional vibration measurement systems, based on single-point measurement, use three different probes to acquire the vibration displacement and velocity information of the object being measured in three-dimensional space, and have important applications in aerospace, biomedicine, vehicle safety, and military product inspection.

[0003] In the prior art, Chinese patents with application numbers 201810228438.3 and 201820378532.2 disclose a laser Doppler three-dimensional vibration testing method and system, which can measure the translational velocity along the laser incident direction and the first and second rotational velocities in mutually perpendicular directions. However, it cannot obtain the vibration information of an object in any direction in three-dimensional space under the world coordinate system, and its practical application is limited to a certain extent. Summary of the Invention

[0004] The purpose of this invention is to provide a laser three-dimensional vibration measurement system capable of acquiring vibration information of an object in any direction within three-dimensional space in the world coordinate system, and to provide its three-dimensional alignment and scanning methods. The technical solution is as follows:

[0005] A laser three-dimensional vibration meter includes three sets of laser vibration probes, a front-end real-time processing system, and a main control computer. The characteristic feature is that each set of probes is independent, with at least one being a main probe and the rest being secondary probes. Each secondary probe comprises an optical path and an electronic control system, while the main probe comprises an optical path, an electronic control system, a camera, and a video transmission interface.

[0006] The front-end real-time processing system is electrically connected to the main control computer and includes a data acquisition and demodulation module and a low-speed setting and interaction module;

[0007] The optical paths within each probe group are identical. Each optical path includes a laser ranging module, a laser vibration measurement module, a front-end fiber collimator, an optical switch, a rear-end fiber collimator, a two-dimensional angular displacement stage, and a lens placed on the two-dimensional angular displacement stage. The switching of the optical switch is achieved through electrical signal control generated by the low-speed setting and interaction module. By switching the optical switch, the laser vibration measurement probe is either in alignment mode or vibration measurement mode. The beam emitted by the laser ranging module is focused onto the fiber end face by the front-end fiber collimator for transmission. After passing through the optical switch, it is expanded into a beam by the rear-end fiber collimator. The low-speed setting and interaction module in the front-end real-time processing system controls the rotation of the two-dimensional angular displacement stage, and the lens placed on the two-dimensional angular displacement stage rotates accordingly, realizing the movement and alignment of the light spot on the sample surface.

[0008] The image of the object being measured, captured by the camera of the main probe, is sent to the main control computer for the correspondence between the image coordinate system and the world coordinate system during 3D scanning. During alignment, based on the image of the object being measured captured by the main control computer, the position to be focused at a certain moment is selected. The low-speed setting and interaction module controls the turntable to rotate at a certain angle through the electronic control system of each probe, and the light spot emitted by the probe is also deflected accordingly, so that the laser emitted by the three vibration probes is focused on a certain point on the object being measured. Based on the coordinates of the focal point in different probe coordinate systems, the transformation matrix between the probe coordinate system and the world coordinate system is calculated by the main control computer. Based on the vibration information measured by the three probes, the vibration displacement or velocity of the object being measured in the three-dimensional space in the world coordinate system is obtained through coordinate transformation.

[0009] Furthermore, the lens includes a fast-control mirror FSM and a 45° fixed plane mirror M1 for reflecting and translating the reflected light from the FSM. In the initial state, the FSM is at zero position, and a three-dimensional Oxyz coordinate system is established. The x-axis is the pitch scanning axis of the FSM, l is the azimuth scanning axis of the FSM, and n is the normal of the FSM. The light reaches the FSM along the positive y-axis, and after being reflected by the FSM and M1, it continues to propagate along the y-axis.

[0010] During the movement of the light spot, the FSM performs a pitch scan around the x-axis with a scanning angle of A, and a azimuth scan around the l-axis with a scanning angle of B.

[0011] In a certain probe coordinate system, the incident ray vector of the FSM is Obj = [0 1 0]. T The image vectors after being reflected sequentially by the FSM and M1 plane mirrors are represented as follows:

[0012]

[0013] In the formula, R M1 Let R be the reflection matrix of the plane mirror M1. FSM Here is the reflection matrix of the FSM;

[0014] The light spot is represented in this probe coordinate system as follows:

[0015] p c =L×Obj'

[0016] Where L is the distance between the light spot and the probe, obtained through laser ranging.

[0017] This invention also provides two alignment and scanning methods for the laser three-dimensional vibrometer described above.

[0018] One method involves a main probe (one main probe and two auxiliary probes, designated as a first and second auxiliary probes), using a monocular camera for measurement. The method is characterized by the three-dimensional alignment process of alignment point i, which includes:

[0019] For the main probe, control the main probe to move the light spot to the alignment point i, record the two scanning angles of the FSM and the distance between the main probe light spot and the main probe during this process, and calculate the coordinates of the main probe light spot in the main probe coordinate system; for each sub-probe, control the sub-probe to move the light spot to the alignment point i, record the two scanning angles of the FSM and the distance between the sub-probe light spot and the sub-probe coordinate system during this process, and calculate the coordinates of the sub-probe light spot in the sub-probe coordinate system.

[0020] Let the coordinates of the main probe spot in the main probe coordinate system be... The coordinates of the light spot from the first probe in the first probe coordinate system The coordinates of the second probe spot in the second probe coordinate system

[0021] Repeat the above operation n times, define n alignment points, obtain n sets of data, and calculate the rotation transformation matrices R1, R2 and R3 and the translation transformation vectors t1, t2 and t3 between the coordinate systems of the three probes and the world coordinate system of the object being measured.

[0022] Furthermore, the scanning method includes the following steps:

[0023] (1) Calibrate the camera on the main probe to obtain the camera's intrinsic parameter matrix K;

[0024] (2) Determine the scan point sequence;

[0025] (3) For the i-th scan point, read the image coordinates p of the i-th scan point in the main probe image coordinate system. (i) It satisfies the following relationship:

[0026]

[0027]

[0028]

[0029] The image vector coordinates Obj′1, Obj′2, and Obj′3 of the i-th scanning point in the main probe coordinate system, the first auxiliary probe coordinate system, and the second auxiliary probe coordinate system are calculated respectively; R1, R2, and R3 are the rotation transformation matrices between the coordinate systems of the three probes and the world coordinate system of the object being measured.

[0030] (4) Calculate the deflection angles A1 and B1 of the main probe FSM, the deflection angles A2 and B2 of the first auxiliary probe FSM, and the deflection angles A3 and B3 of the second auxiliary probe FSM from the coordinates of the image vector of the scanning point i in the probe coordinate system, so as to realize the automatic alignment of the light spot during the scanning process.

[0031] Furthermore, the three-dimensional shape measurement of the object under test includes the following steps:

[0032] (1) Based on the surface shape of the object, set the scanning points on the object surface so that they cover the entire object surface;

[0033] (2) Read the image coordinates p of the i-th scanning point in the main probe image coordinate system. (i) According to image coordinates p (i) Calculate Obj′1 to obtain the deflection angles A1 and B1 of the main probe FSM at the i scanning points, and control the spot to move to the scanning point;

[0034] (3) Measure the distance L1 between the current scanning point and the main probe, and calculate the coordinates of the scanning point in the main probe coordinate system. The world coordinates of the scan point were calculated.

[0035] (4) Obtain the three-dimensional shape of the object under test based on the world coordinates of all scanning points.

[0036] Another method is:

[0037] There are two main probes, referred to as the first main probe and the second main probe, and a binocular camera measurement method is used. The characteristic feature is that the three-dimensional alignment process of alignment point i includes:

[0038] Control the first master probe and move its light spot to alignment point i. Record the scanning angles A1 and B1 of the FSM and the distance L1 between the light spot and the probe during this process. Calculate the coordinates p of the light spot of the first master probe in the first master probe coordinate system. 1CControl the second master probe and move its spot to alignment point i. Record the scanning angles A2 and B2 of the FSM and the distance L2 between the spot of the second master probe and the probe during this process. Calculate the coordinates p of the spot of the second master probe in the second master probe coordinate system. 2C Control the secondary probe to move its light spot to alignment point i. Record the scanning angles A3 and B3 of the FSM and the distance L3 between the secondary probe's light spot and the primary probe during this process. Calculate the coordinates p of the secondary probe's light spot in the secondary probe's coordinate system. 3C The coordinates p of point i in the world coordinate system w The method obtained by using a binocular camera is as follows: calibrate the cameras on the two main probes to obtain the intrinsic and extrinsic parameter matrices of the two cameras; use the images of the object being measured taken by the two cameras to determine the pixel coordinates of the alignment point on the two cameras, and use the least squares method to find the coordinates of the alignment point in the world coordinate system.

[0039] Repeat the above operation m times, define the alignment point, and use m sets of data {p 1C p 2C p 3C p w} Calculate the rotation transformation matrices R1, R2, R3 and the translation transformation vectors t1, t2, t3 between the coordinate systems of each probe and the world coordinate system of the object being measured.

[0040] Furthermore, the scanning method includes:

[0041] (1) Determine the scan point sequence;

[0042] (2) For the i-th scan point, read the image coordinates p of the i-th scan point in the first main probe image coordinate system. (i) It satisfies the following relationship:

[0043]

[0044]

[0045]

[0046] The image vector coordinates Obj′1 in the first main probe coordinate system, Obj′2 in the second main probe coordinate system, and Obj′3 in the secondary probe coordinate system of the i-th scanning point are calculated respectively.

[0047] (3) Calculate the deflection angles A1 and B1 of the first main probe FSM, the deflection angles A2 and B2 of the second main probe FSM, and the deflection angles A3 and B3 of the auxiliary probe FSM from the coordinates of the image vector of the scanning point i in the probe coordinate system, so as to realize the automatic alignment of the light spot during the scanning process.

[0048] The beneficial effects of this invention are as follows:

[0049] 1. Based on non-contact laser measurement, this invention provides a new three-dimensional vibration displacement and velocity measurement device, and provides its alignment and scanning methods. This allows the acquisition of velocity or displacement information of the measurement point in any direction in three-dimensional space under the world coordinate system. Compared with other vibration measurement methods, this invention decomposes the vibration vector of any point on the object surface into the world coordinate system in which the object itself is located, which can be aligned with the inherent structural features of the object. This increases the ability of the measurement results to characterize the object's features, making the information obtained from the measurement richer and more meaningful.

[0050] 2. This invention isolates the two modes of the instrument through an optical switch. Under the control of an electrical signal, it can switch between the distance measurement and vibration measurement modules, reducing the size and weight of the probe, lowering the system cost, and improving the system stability.

[0051] 3. The scanning process of the present invention achieves automatic alignment during the scanning process, which can be applied to the measurement of vibration information at multiple locations, greatly reducing the workload of measurement and increasing the speed of large-scale vibration measurement;

[0052] 4. This invention proposes two alignment and scanning methods for laser three-dimensional vibration measurement, which have a wide range of applications and can be used in laser vibration measurement technologies such as heterodyne Doppler vibration velocity measurement, laser interferometric displacement velocity measurement, and laser reflection modulation displacement velocity measurement.

[0053] 5. Embodiment 2 of the present invention obtains the world coordinates of the alignment point by measurement, which reduces the number of unknowns in the equation solving process, reduces the number of alignment points required in the alignment process, and makes the solving speed and alignment speed faster. Attached Figure Description

[0054] Figure 1 This is the overall measurement scheme for the laser three-dimensional vibration meter in Example 1;

[0055] Figure 2 The optical path diagrams inside the laser vibration probes in Examples 1 and 2 are shown.

[0056] Figure 3 This is a schematic diagram of a reflective FSM application;

[0057] Figure 4 This is the overall measurement scheme for the laser three-dimensional vibration meter in Example 2. Detailed Implementation

[0058] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0059] Example 1

[0060] 1. Overall Structure

[0061] The overall measurement scheme of the laser three-dimensional vibration meter is as follows: Figure 1 As shown, three independent laser vibration probes are used: a main probe, secondary probe 1, and secondary probe 2. Each secondary probe includes an optical path and an electronic control system, while the main probe includes an optical path, an electronic control system, a camera, and a video transmission interface. The camera is used to map the image coordinate system to the world coordinate system during 3D scanning. During alignment, the mouse selects the desired focus point on the screen. The low-speed setting and interaction module in the front-end real-time processing system controls the turntable to rotate at a certain angle via the probe's internal electronic control system. The laser beam emitted by the probes also deflects accordingly, ultimately focusing the lasers emitted by the three vibration probes onto a specific point on the object being measured. Based on the coordinates of the focal point in different probe coordinate systems, the main control computer can calculate the transformation matrix between the probe coordinate system and the world coordinate system. Therefore, based on the vibration information measured by the three probes, the vibration displacement or velocity of the object in 3D space can be obtained through coordinate transformation.

[0062] The optical paths inside the three probes are identical, such as... Figure 2 As shown, the optical path includes a laser ranging module, a laser vibration measurement module, fiber collimator 1, an optical switch, fiber collimator 2, a two-dimensional angular displacement stage, and a lens. The switching of the optical switch is controlled by an electrical signal generated by the low-speed setting and interaction module. When the optical switch contacts the upper node, the laser ranging module operates, performing the alignment function; when the optical switch contacts the lower node, the laser vibration measurement module operates, performing the vibration measurement function. The beam emitted by the laser ranging module is focused onto the fiber end face by the first fiber collimator for transmission, then spread into a beam by the second fiber collimator after passing through the optical switch. The low-speed setting and interaction module in the front-end real-time processing system controls the rotation of the two-dimensional angular displacement stage, and the lens fixed on the stage also rotates accordingly, thereby realizing the movement and alignment of the light spot on the sample surface.

[0063] 2. Alignment process

[0064] This invention uses a Fast Steering Mirror (FSM) to align the emitted light spots of the three probes. As the FSM rotates, the laser beam deflects, and the light spot moves. Initially, the FSM is in its zero position, at which point the FSM's mirror surface is parallel to the plane mirror's surface. Figure 2 Establish a three-dimensional Oxyz coordinate system, with the x-axis perpendicular to the paper and pointing outwards. M1 is a 45° fixed plane mirror, the x-axis is the pitch scan axis of the FSM, l is the azimuth scan axis of the FSM, and n is the normal of the FSM. Light rays arrive at the FSM along the positive y-axis, and after being reflected by the FSM and M1, continue to propagate along the y-axis.

[0065] During the beam movement, the FSM first performs a pitch scan around the x-axis at an angle of A, and then performs an azimuth scan around the l-axis at an angle of B. These two angles can be directly determined from the motor's rotation angle. The matrix representing the action of the FSM's unit normal vector scanning angle A around the x-axis is:

[0066]

[0067] After elevation scan, the azimuth scan axis is no longer l, but rather the vector l after l has been rotated A around the x-axis. 01 The action matrix for rotating the unit normal vector of the FSM around the l01 axis is:

[0068]

[0069] The unit normal vector of the FSM, after elevation and azimuth scans, is represented as:

[0070]

[0071] By R FSM =I-2n 02 (n 02 ) T The reflection matrix R of the FSM can be obtained. FSM for:

[0072]

[0073] The reflection matrix of plane mirror M1 is: In the probe coordinate system, the incident ray vector of the FSM is Obj = [0 1 0]. T The image vectors after being reflected by the FSM and M1 plane mirrors in sequence are represented as follows:

[0074]

[0075] The light spot can then be represented in each probe coordinate system as follows:

[0076] p c =L×Obj′#(6)

[0077] Where L is the distance between the light spot and the probe. The coordinates of the i-th alignment point in each coordinate system... Satisfy the following mathematical relationship:

[0078]

[0079]

[0080]

[0081] The specific process of 3D alignment is as follows:

[0082] First, control the main probe 1 to move the light spot 1 to a certain point, and record the scanning angles A1 and B1 of the FSM and the distance L1 between the light spot and the probe during this process. Then, use formula (6) to calculate the coordinates p of the light spot 1 in the coordinate system of the main probe. 1C Control the secondary probe 1 to move the light spot 2 to the same point, and record the scanning angles A2 and B2 of the FSM and the distance L2 between the light spot and the probe during this process. Use formula (6) to calculate the coordinates p of the light spot 2 in the coordinate system of the secondary probe 1. 2C Control the secondary probe 2 to move the light spot 3 to the same point, and record the scanning angles A3 and B3 of the FSM and the distance L3 between the light spot and the probe during this process. Use formula (6) to calculate the coordinates p of the light spot 3 in the coordinate system of the secondary probe 2. 3C .

[0083] During the alignment process, the light spot at each alignment point is imaged by the camera. The positional error between the image points of the three light spots and the positional error between the image points and the set point are compared to ensure the overlap between the three light spots and the accuracy of the overlap position.

[0084] Repeat the above operation ten times, define 10 alignment points, and obtain ten sets of data {p 1C p 2C p 3C Using formulas (7) to (9), calculate the transformation matrices [R1|t1], [R2|t2], and [R3|t3] between the coordinate systems of the three probes and the world coordinate system of the object being measured, as well as the world coordinates of each point.

[0085] 3. Scanning process

[0086] After aligning the three probes, the transformation matrix between the probe coordinate system and the world coordinate system at the current position can be obtained. Before measurement, the camera on the main probe needs to be calibrated to obtain the camera's intrinsic parameter matrix K. After determining a series of scanning points, the image coordinates p of the i-th scanning point in the main probe image coordinate system are read. (i) .

[0087]

[0088]

[0089]

[0090] Using equations (10), (11), and (12), the deflection angles A1 and B1 of the main probe FSM, the deflection angles A2 and B2 of the sub-probe 1 FSM, and the deflection angles A3 and B3 of the sub-probe 2 FSM can be calculated, thus achieving automatic alignment of the light spot during the scanning process. During the scanning measurement, the velocity or displacement measured by each probe at each scanning point can be represented as components on the x, y, and z axes of the probe coordinate system. Using the obtained transformation matrix, the components in the probe coordinate system can be converted into components in the world coordinate system, thereby obtaining the vibration information of the measured object in any direction in three-dimensional space.

[0091] 4. Measurement of three-dimensional morphology

[0092] Based on the surface shape of the object, scanning points can be set at certain intervals to cover the entire surface. After determining a series of scanning points, the image coordinates p of the i-th scanning point in the main probe image coordinate system are read. (i) According to image coordinates p ( i ) Using formula (10), Obj′1 can be calculated to obtain the deflection angles A1 and B1 of the main probe FSM at the i-th scanning point, thereby controlling the spot to move to that scanning point. The distance L1 between the current scanning point and the probe is measured, and the coordinates of the scanning point in the main probe coordinate system are calculated according to formula (6). Will Substituting into equation (13), the world coordinates of the scan point can be calculated. The three-dimensional shape of the object being measured can be obtained from the world coordinates of all scan points.

[0093]

[0094] Example 2

[0095] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0096] 1. Overall Structure

[0097] The overall measurement scheme of the laser three-dimensional vibration meter is as follows: Figure 4As shown, three independent laser vibration probes are used: main probe 1, main probe 2, and auxiliary probe. The auxiliary probe includes an optical path and an electronic control system, while the main probe includes an optical path, an electronic control system, a camera, and a video transmission interface. The two cameras on the two main probes form a binocular camera measurement system used to measure the position coordinates of the measured point in the world coordinate system. The binocular cameras need to be calibrated before alignment and scanning. During alignment, the mouse selects the focus point on the screen. The low-speed setting and interaction module in the front-end real-time processing system controls the turntable to rotate at a certain angle through the probe's internal electronic control system. The light spot emitted by the probe also deflects accordingly, ultimately focusing the laser emitted by the three vibration probes onto a specific point on the measured object. The binocular camera calculates the coordinates of the focal point in the world coordinate system, and the main control computer can calculate the transformation matrix between the probe coordinate system and the world coordinate system. Based on this, the vibration displacement or velocity of the measured object in three-dimensional space can be obtained through coordinate transformation based on the vibration information measured by the three probes.

[0098] The optical paths inside the three probes are identical, such as... Figure 2 As shown, the optical path includes a laser ranging module, a laser vibration measurement module, fiber collimator 1, an optical switch, fiber collimator 2, a two-dimensional angular displacement stage, and a lens. The low-speed setting and interaction module in the front-end real-time processing system controls the rotation of the two-dimensional angular displacement stage, and the lens fixed on the displacement stage also rotates accordingly, thereby realizing the movement and alignment of the light spot on the sample surface.

[0099] 2. Calibration and coordinate calculation of the binocular camera

[0100] Before measuring world coordinates using binocular cameras, each camera needs to be calibrated. Camera calibration methods can be divided into two types. The first is the traditional calibration method, which requires a reference object. Traditional calibration methods typically use a checkerboard pattern as a reference object, where the size, dimensions, and number of each checkerboard grid are known. The second type is the object feature point calibration method, which does not require a reference object. In this method, a 3D model of the object to be measured is first obtained, and then the object is photographed multiple times using the cameras. Through calibration, the transformation matrix between the two camera coordinate systems and the world coordinate system can be calculated. Then, using the images of the object captured by the two cameras, the pixel coordinates of each measured point on both cameras are determined, and the coordinates of each measured point in the world coordinate system are calculated using the least squares method.

[0101] 3. Alignment process

[0102] In implementation method 2, the fast-control mirror is still used to control the alignment of the light spots emitted by the three probes. The image vector after reflection by the FSM and M1 plane mirror is as follows:

[0103]

[0104] The light spot can be represented in various probe coordinate systems as follows:

[0105] p c =L×Obj'

[0106] Where L is the distance between the light spot and the probe. The coordinates of the i-th alignment point in each coordinate system... It satisfies the mathematical relations of formulas (7)-(9) above.

[0107] The specific process of 3D alignment is as follows:

[0108] First, control the main probe 1 to move the light spot 1 to a certain point, and record the scanning angles A1 and B1 of the FSM and the distance L1 between the light spot and the probe during this process. Then, use formula (6) to calculate the coordinates p of the light spot 1 in the coordinate system 1 of the main probe 1. 1C Control the main probe 2 to move the light spot 2 to the same point, and record the scanning angles A2 and B2 of the FSM and the distance L2 between the light spot and the probe during this process. Use formula (6) to calculate the coordinates p of the light spot 2 in the coordinate system of the main probe 2. 2C Control the secondary probe to move spot 3 to the same point, and record the scanning angles A3 and B3 of the FSM and the distance L3 between the spot and the probe during this process. Calculate the coordinates p of spot 3 in the secondary probe coordinate system using formula (6). 3C The coordinates p of this point in the world coordinate system w Obtained using a binocular camera.

[0109] During the alignment process, the light spot at each alignment point is imaged by the camera. The positional error between the image points of the three light spots and the positional error between the image points and the set point are compared to ensure the overlap between the three light spots and the accuracy of the overlap position.

[0110] Repeat the above steps five times, defining five alignment points, and finally using five sets of data {p 1C p 2C p 3C p w}, calculate the transformation matrix [R1|t1], [R2|t2], [R3|t3] between the probe coordinate system and the world coordinate system of the object under test using formulas (7) to (9).

[0111] 4. Scanning process

[0112] After aligning the three probes, the transformation matrix between the probe coordinate system and the world coordinate system at the current position can be obtained. After determining a series of scanning points, the image coordinates p of the i-th scanning point in the image coordinate system of the main probe 1 are then read. (i) .

[0113] Using equations (10), (11), and (12), the deflection angles A1 and B1 of the main probe 1 corresponding to the FSM, the deflection angles A2 and B2 of the main probe 2 corresponding to the FSM, and the deflection angles A3 and B3 of the auxiliary probe corresponding to the FSM can be calculated, thus achieving automatic alignment of the light spot during the scanning process. During the scanning measurement process, the velocity or displacement measured by each probe at each scanning point can be expressed as components on the x, y, and z axes of the probe coordinate system. Using the obtained transformation matrix, the components in the probe coordinate system can be converted into components in the world coordinate system, thereby obtaining the vibration information of the measured object in any direction in three-dimensional space.

Claims

1. A laser three-dimensional vibration meter, comprising three sets of laser vibration probes, a front-end real-time processing system, and a main control computer, characterized in that, Each group of probes operates independently, with at least one being a main probe and the rest being secondary probes. Each secondary probe comprises an optical path and an electronic control system, while the main probe comprises an optical path, an electronic control system, a camera, and a video transmission interface. The front-end real-time processing system is electrically connected to the main control computer and includes a data acquisition and demodulation module and a low-speed setting and interaction module; The optical paths within each probe group are identical. Each optical path includes a laser ranging module, a laser vibration measurement module, a front-end fiber collimator, an optical switch, a rear-end fiber collimator, a two-dimensional angular displacement stage, and a lens placed on the two-dimensional angular displacement stage. The switching of the optical switch is achieved through electrical signal control generated by the low-speed setting and interaction module. By switching the optical switch, the laser vibration measurement probe is either in alignment mode or vibration measurement mode. The beam emitted by the laser ranging module is focused onto the fiber end face by the front-end fiber collimator for transmission. After passing through the optical switch, it is expanded into a beam by the rear-end fiber collimator. The low-speed setting and interaction module in the front-end real-time processing system controls the rotation of the two-dimensional angular displacement stage, and the lens placed on the two-dimensional angular displacement stage rotates accordingly, realizing the movement and alignment of the light spot on the sample surface. The image of the object being measured, captured by the camera of the main probe, is sent to the main control computer for the correspondence between the image coordinate system and the world coordinate system during 3D scanning. During alignment, based on the image of the object being measured captured by the main control computer, the position to be focused at a certain moment is selected. The low-speed setting and interaction module controls the turntable to rotate at a certain angle through the electronic control system of each probe, and the light spot emitted by the probe is also deflected accordingly, so that the laser emitted by the three vibration probes is focused on a certain point on the object being measured. Based on the coordinates of the focal point in different probe coordinate systems, the transformation matrix between the probe coordinate system and the world coordinate system is calculated by the main control computer. Based on the vibration information measured by the three probes, the vibration displacement or velocity of the object being measured in three-dimensional space in the world coordinate system is obtained through coordinate transformation. The lens includes a fast-control mirror (FSM) and a fixed-plane mirror (M1) for reflecting and translating the light reflected by the FSM. In the initial state, the FSM is in zero position, establishing a three-dimensional... Oxyz coordinate system x The axis is the pitch scan axis of the FSM. l It is the azimuth scan axis of the FSM. n It is the normal of the FSM, and the light rays follow it. y The axis reaches FSM in the positive direction, and after reflection from FSM and M1, it continues along... y Axial propagation; During the movement of the light spot, the FSM circumferentially... x The axis performs a pitch scan, with a scanning angle of . A , around l Axis azimuth scanning, scanning angle is B ; In a certain probe coordinate system, the incident ray vector of the FSM is... The image vectors after being reflected by the FSM and M1 plane mirrors in sequence are represented as follows: In the formula, Let M1 be the reflection matrix of the plane mirror. Here is the reflection matrix of the FSM; The light spot is represented in this probe coordinate system as follows: in, L The distance between the light spot and the probe is obtained through laser ranging.

2. A method for aligning and scanning a laser three-dimensional vibrometer as described in claim 1, wherein the main probe is one, and the other two probes are respectively a first auxiliary probe and a second auxiliary probe, and a monocular camera measurement method is used, characterized in that... The process of 3D alignment of alignment point i includes: For the main probe, control the main probe to move the light spot to the alignment point i, record the two scanning angles of the FSM and the distance between the main probe light spot and the main probe during this process, and calculate the coordinates of the main probe light spot in the main probe coordinate system; for each sub-probe, control the sub-probe to move the light spot to the alignment point i, record the two scanning angles of the FSM and the distance between the sub-probe light spot and the sub-probe coordinate system during this process, and calculate the coordinates of the sub-probe light spot in the sub-probe coordinate system. Let the coordinates of the main probe spot in the main probe coordinate system be... The coordinates of the light spot from the first probe in the first probe coordinate system The coordinates of the second probe spot in the second probe coordinate system ; Repeat the above operation n times, define n alignment points, obtain n sets of data, and calculate the rotation transformation matrices R1, R2, and R3 and the translation transformation vectors between the coordinate systems of the three probes and the world coordinate system of the object being measured. , , .

3. The alignment and scanning method according to claim 2, characterized in that, The scanning method includes the following steps: (1) Calibrate the camera on the main probe to obtain the camera's intrinsic parameter matrix. ; (2) Determine the scan point sequence; (3) For the i-th scanning point, read the image coordinates of the i-th scanning point in the main probe image coordinate system. It satisfies the following relationship: The image vector coordinates of the i-th scanning point in the main probe coordinate system were calculated respectively. Image vector coordinates in the first probe coordinate system and the image vector coordinates in the second probe coordinate system R1, R2, and R3 are the rotation transformation matrices between the coordinate systems of the three probes and the world coordinate system of the object being measured, respectively. (4) Calculate the deflection angle of the corresponding main probe FSM from the coordinates of the image vector of scanning point i in the probe coordinate system. The first probe corresponds to the deflection angle of the FSM. And the deflection angle of the second probe corresponding to the FSM This enables automatic alignment of the light spot during the scanning process.

4. The alignment and scanning method according to claim 3, characterized in that, The three-dimensional topography measurement of the object being measured includes the following steps: (1) Based on the surface shape of the object, set the scanning points on the object surface so that they cover the entire object surface; (2) Read the image coordinates of the i-th scanning point in the main probe image coordinate system. According to image coordinates ,calculate The deflection angles A1 and B1 of the main probe FSM at i scanning points are obtained, and the light spot is controlled to move to the scanning point. (3) Measure the distance between the current scanning point and the main probe. L 1 Calculate the coordinates of the scanning point in the main probe coordinate system. The world coordinates of the scan point are calculated. ; (4) Obtain the three-dimensional shape of the object under test based on the world coordinates of all scanning points.

5. A method for aligning and scanning a laser three-dimensional vibrometer as described in claim 1, characterized in that, There are two main probes, referred to as the first main probe and the second main probe, and a binocular camera measurement method is used. The characteristic feature is that the three-dimensional alignment process of alignment point i includes: Control the first main probe and move its light spot to alignment point i, recording the scanning angle of the FSM during this process. A 1 , B 1 and the distance between the light spot and the probe L 1 Calculate the coordinates of the light spot of the first main probe in the first main probe coordinate system. Control the second main probe to move its light spot to alignment point i, and record the scanning angle of the FSM during this process. A 2 , B 2 and the distance between the light spot of the second main probe and its own probe. L 2 Calculate the coordinates of the light spot from the second main probe in the coordinate system of the second main probe. Control the secondary probe to move its light spot to alignment point i, and record the scanning angle of the FSM during this process. A 3 , B 3 and the distance between the light spot of the secondary probe and its primary probe. L 3 Calculate the coordinates of the light spot of the secondary probe in the secondary probe coordinate system. The coordinates of point i in the world coordinate system The method obtained by using a binocular camera is as follows: calibrate the cameras on the two main probes to obtain the intrinsic and extrinsic parameter matrices of the two cameras; use the images of the object being measured taken by the two cameras to determine the pixel coordinates of the alignment point on the two cameras, and use the least squares method to find the coordinates of the alignment point in the world coordinate system. Repeat the above operation m times, define the alignment point, and use m sets of data {p 1C , p 2C , p 3C , } Calculate the rotation transformation matrices R1, R2, R3 and the translation transformation vectors between each probe coordinate system and the world coordinate system of the object being measured. , , .

6. The alignment and scanning method according to claim 5, characterized in that, Scanning methods include: (1) Determine the scan point sequence; (2) For the i-th scanning point, read the image coordinates of the i-th scanning point in the first main probe image coordinate system. It satisfies the following relationship: The image vector coordinates of the i-th scanning point in the first main probe coordinate system were calculated respectively. Image vector coordinates in the second main probe coordinate system and the image vector coordinates in the secondary probe coordinate system ; (3) Calculate the deflection angle of the first main probe FSM from the coordinates of the image vector of scanning point i in the probe coordinate system. The deflection angle of the second main probe corresponding to the FSM And the deflection angle of the secondary probe corresponding to the FSM This enables automatic alignment of the light spot during the scanning process.

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