Absolute method modal force hammer calibration device and method based on machine vision

Abstract

The invention discloses an absolute method modal force hammer calibration device and method based on machine vision, the device comprises a vision alignment module, a pneumatic propulsion module, a laser absolute method measurement module, a data acquisition module and a master control module, and the master control module communicates with the vision alignment module, the data acquisition module and the pneumatic propulsion module. The data acquisition module communicates with the pneumatic propulsion module and the laser absolute method measurement module; the visual alignment module is used for acquiring an image to adjust a laser irradiation point to be aligned with the center of the suspended mass block; the pneumatic propulsion module is used for acquiring output signals of the standard force sensor to adjust the opening size of the electromagnetic valve; the laser absolute method measurement module is used for obtaining laser Doppler frequency shift; and the master control module is used for receiving signals acquired by the image and data acquisition module and calculating, controlling the visual alignment module and the pneumatic propulsion module according to a calculation result and obtaining the sensitivity of the modal force hammer. According to the invention, the size and direction of the force value of the force hammer can be controlled, and the calibration repeatability and precision are high.

Description

Technical Field

[0001] The present invention relates to the technical field of hammer sensitivity measurement, and in particular to an absolute method modal hammer calibration device and a calibration method based on machine vision. Background Art

[0002] The modal hammer is a commonly used device in structural mechanics tests. It is often used in scientific research work in the fields of national defense, scientific research, and universities. It is an important excitation device for obtaining the modal parameters of the structure through the "hammer method". Its working principle is to use the hammer head to excite the tested structure, and the force sensor measures the magnitude and waveform of the impact force. The acceleration response magnitude and waveform of the structural parts are also collected and analyzed by the acquisition device at the same time. The modal parameters of the structure are obtained by the fast Fourier transform (FFT) based on the pulse test principle and modal theory. Different hammer cap materials can be used to obtain different excitation pulse widths, and correspondingly, the response of the structure in different frequency bandwidths can be excited and measured. Therefore, the modal hammer can be regarded as a handheld impact excitation device. According to its working principle, the technical parameters of the modal hammer are mainly the force value and pulse width.

[0003] Existing hammer calibration systems can be referenced Figure 1 , 2 ,in, Figure 1 The system is calibrated using the pulse dynamic force comparison method. The hammer strikes the sensitive surface of the standard force sensor vertically, and the force between the two is measured by the standard force sensor to achieve the reproduction of the dynamic force value. The reproduced force value is compared with the output of the hammer to obtain the calibration result. The disadvantages of this system are: using a hand-held hammer to strike the standard force sensor downward for hammer calibration, there is no guarantee that the striking position is located at the center of the standard force sensor, which results in measurement errors. In addition, the reproducibility of the test cannot be guaranteed. The striking force depends on people's subjective feelings. The calibration point of the linearity of the hammer cannot be grasped. The only choice is to increase or decrease the force based on the results, and all of this is based on subjective judgment. Therefore, the repeatability of the measurement is poor and the calibration efficiency is relatively low. In addition, the sensitivity of a general force sensor only uses the sensitivity value at a typical working point, which will cause amplitude nonlinear errors. Figure 2The system includes a circular table top 1 and two cylindrical support rods 2 as a base, wherein the cylindrical support rods 2 are fixed on the circular table top 1 by threaded connection; a cylindrical mass block 3 is arranged between the two cylindrical support rods 2, and the cylindrical mass block 3 is fixed and suspended on the clamp 4 of the cylindrical support rod 2 by a thin rope 5. A unidirectional acceleration sensor is installed on the cylindrical mass block 3, and a hammer is used to strike the center point of the right end face along the center of the cylindrical mass block 3, and the output signals of the acceleration sensor and the hammer are collected. The striking force is obtained by using F=ma, and the sensitivity of the hammer is obtained by comparing it with the output voltage signal of the hammer. The disadvantages of this system are: (a) It adopts the method of striking the suspended mass block, and the center of the mass block is stimulated by a handheld hammer. The direction of force application can only rely on subjective judgment. When the direction of force application is inconsistent with the ideal direction, that is, perpendicular to the excited surface of the mass block, such as Figure 3 As shown in the figure, the force direction Fe and the ideal striking direction Fs have an angle a, so the actual striking force in the sensitive direction of the acceleration sensor is Fe·cos(a), which brings a large error; (ii) the error caused by the nonlinear amplitude of the acceleration sensor, the poor measurement repeatability and the low calibration efficiency.

[0004] There is no special calibration specification for modal force hammers at present. Generally, the force hammer is calibrated by referring to "JJG 632-1989 Dynamic Force Sensor Calibration Procedure". The commonly used method is to use a handheld force hammer to strike the suspended mass block, collect the output waveform of the force hammer and the response waveform of the accelerometer installed on the mass block, and use F=ma to calibrate the hammer indication. This calibration method has problems such as the magnitude and direction of the handheld force hammer's striking force value cannot be controlled, the force value is difficult to approach the upper limit of the hammer's working range, the striking position is inaccurate, and the striking direction is not perpendicular to the force surface of the mass block. Summary of the invention

[0005] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides an absolute method modal hammer calibration device and calibration method. The method measures the acceleration of the modal hammer excitation point based on the absolute method. Compared with the comparison method, it can obtain high-precision excitation force value. The calibration device can make the hammer generate an impact force with controllable force value, and the striking position is accurate and the striking direction is controllable. It overcomes the problems of uncontrollable force value and direction, poor repeatability, low calibration efficiency, etc. existing in the traditional hand-held hammer, and improves the calibration efficiency and calibration accuracy.

[0006] The first object of the present invention is to provide an absolute modal hammer calibration device based on machine vision.

[0007] The second object of the present invention is to provide an absolute modal hammer calibration method based on machine vision.

[0008] The first object of the present invention can be achieved by adopting the following technical solutions:

[0009] A machine vision-based absolute modal hammer calibration device, the device comprises a visual alignment module, a pneumatic propulsion module, a laser absolute measurement module, a data acquisition module and a master control module, the master control module communicates with the visual alignment module, the data acquisition module and the pneumatic propulsion module respectively, the data acquisition module communicates with the pneumatic propulsion module and the laser absolute measurement module respectively, wherein:

[0010] The visual alignment module is used to acquire an image to adjust the laser irradiation point to align with the center of the suspended mass block to ensure that the knocking position is at the center of the suspended mass block;

[0011] The pneumatic propulsion module is used to obtain the output signal of the standard force sensor to adjust the opening size of the solenoid valve and calibrate the modal hammer by striking with the cylinder clamping hammer;

[0012] The laser absolute method measurement module is used to obtain the laser Doppler frequency shift near the center of the suspended mass block;

[0013] The data acquisition module is used to collect the output signal of the standard force sensor, as well as the output signal of the laser Doppler frequency shift and the calibrated modal hammer, and convert the collected analog signal into a digital signal;

[0014] The master control module is used to receive images, perform calculations based on the images, and adjust the position of the laser irradiation point based on the calculation results; and to receive digital signals, perform calculations on the digital signals, adjust the size of the solenoid valve opening based on the calculation results, and obtain the modal hammer sensitivity.

[0015] Furthermore, the visual alignment module includes a camera, a dual-motor slide mechanism, a fixture and a laser line projector; the dual-motor slide mechanism includes a base, a first motor slide mechanism is installed on the base, and a second motor slide mechanism is installed on the slider of the first motor slide mechanism in a direction perpendicular to the first motor slide mechanism; the fixture is installed on the second motor slide mechanism, and the laser line projector is installed on the fixture; the laser line projector is used to place the emitted laser irradiation point on the surface of the suspended mass block, wherein the surface of the suspended mass block is engraved with a mark; the camera is used to capture an image of the surface of the suspended mass block with the laser irradiation point, and send the image to the main control module; the first motor slide mechanism is used to control the movement of the slider according to the signal sent by the main control module to drive the fixture to move; the second motor slide mechanism is used to control the fixture to move in a direction perpendicular to the movement direction of the slider according to the signal sent by the main control module; the position of the laser line projector is adjusted by the movement of the fixture so that the laser irradiation point is located at the center of the mark of the suspended mass block.

[0016] Furthermore, the first motor slide rail mechanism comprises a guide rail, a motor, a ball screw and a slider, one end of the guide rail and one end of the ball screw are both mounted on a base, and the other end of the guide rail is mounted with a motor; the output shaft of the motor is connected to the ball screw shaft through a coupling, and the slider is slidably connected to the ball screw; the rotation of the output shaft of the motor drives the rotation of the ball screw shaft to drive the slider to move along the track direction in the guide rail, and the movement of the slider drives the movement of the second motor slide rail mechanism, that is, drives the fixture to move;

[0017] The second motor slide rail mechanism includes a guide rail, a motor and a ball screw. The guide rail and the ball screw are installed on a slider, and a motor is installed at one end of the guide rail. The output shaft of the motor is connected to the ball screw shaft through a coupling, and the fixture is installed on the ball screw. The rotation of the output shaft of the motor drives the ball screw shaft to rotate, thereby driving the fixture to move along the track direction in the guide rail.

[0018] Further, performing calculation according to the image and adjusting the position of the laser irradiation point according to the calculation result includes:

[0019] The image is subjected to image binarization, spatial filtering, feature extraction and coordinate calculation in sequence to obtain the distance between the laser irradiation point and the center of the suspended mass block;

[0020] If the distance is greater than a first set threshold, the first motor slide rail mechanism and the second motor slide rail mechanism are controlled to adjust the position of the laser line projector so that the laser irradiation point is located at the center of the suspended mass block mark.

[0021] Furthermore, the pneumatic propulsion module includes an air pressure controller, a solenoid valve, a gas tank, a cylinder and a standard force sensor, the cylinder is installed on a fixture, the end fixture of the cylinder clamps the modal hammer to be calibrated, and the height of the suspended mass block is adjusted according to the distance between the end clamping center and the tip of the hammer head; the air outlet of the gas tank is connected to the air inlet of the solenoid valve, and the air outlet of the solenoid valve is connected to the air inlet of the cylinder; the standard force sensor is installed on the surface of the suspended mass block and communicates with the data acquisition module; the air pressure controller communicates with the main control module, and is used to adjust the opening size of the solenoid valve according to the signal sent by the main control module.

[0022] Furthermore, the digital signal is calculated, and the opening size of the solenoid valve is adjusted according to the calculation result, and the modal hammer sensitivity is obtained, including:

[0023] If the digital signal is the output signal of the standard force sensor, the output signal of the standard force sensor is compared with the force value of the modal force hammer calibration point, and if the comparison result is greater than the second set threshold, the pneumatic controller is controlled to adjust the opening size of the solenoid valve;

[0024] If the digital signal is the output signal of the laser Doppler frequency shift and the calibrated modal hammer, the standard vibration acceleration is calculated according to the laser Doppler frequency shift; the standard force value is obtained by using Newton's second law according to the standard vibration acceleration; and the modal hammer sensitivity is obtained according to the standard force value and the output signal of the calibrated modal hammer.

[0025] Furthermore, the laser absolute method measurement module includes a laser vibrometer, the laser vibrometer includes a laser controller and an optical head, and the laser controller communicates with the optical head and the data acquisition module respectively;

[0026] The laser controller is used to control the optical head to emit laser to the vicinity of the center of the suspended mass block, and send the laser Doppler frequency shift collected near the center of the suspended mass block to the data acquisition module.

[0027] The second object of the present invention can be achieved by adopting the following technical solutions:

[0028] An absolute method modal hammer calibration method based on machine vision, the method comprising:

[0029] Aim the laser irradiation point emitted by the laser projection instrument at the center of the suspended mass block to ensure that the knocking position is the center of the suspended mass block;

[0030] Replace the laser line projector with a cylinder, clamp the modal hammer to be calibrated with a clamp at the end of the cylinder, raise the suspended mass block so that the increased distance is equal to the distance between the center of the clamp and the tip of the hammer head; install the standard force sensor on the surface of the suspended mass block, and align the center of the force-bearing surface of the standard force sensor with the center of the suspended mass block, and adjust the opening size of the solenoid valve according to the output signal of the standard force sensor and the force value of the calibration point to calibrate the modal hammer;

[0031] Remove the standard force sensor, control the emission of laser to the surface near the center of the suspended mass block, obtain the laser Doppler frequency shift near the center of the suspended mass block and the output signal of the calibrated modal hammer;

[0032] The standard force value is calculated according to the laser Doppler frequency shift; the sensitivity of the quasi-modal hammer is obtained according to the standard force value and the output signal of the calibrated modal hammer.

[0033] Furthermore, the step of aligning the laser irradiation point emitted by the laser projection device with the center of the suspended mass block comprises:

[0034] The laser irradiation point emitted by the laser line projector is made to fall on the surface of the suspended mass block, and an image of the surface of the suspended mass block with the laser irradiation point is obtained by a camera; wherein the surface of the suspended mass block is engraved with a mark;

[0035] The distance between the laser irradiation point and the center of the surface of the suspended mass block is calculated based on the image. If the distance is greater than the set threshold, the position of the laser line projector installed on the fixture is adjusted to align the laser irradiation point with the center of the surface of the suspended mass block.

[0036] Further, the calculating of the standard force value according to the laser Doppler frequency shift includes:

[0037] Calculate the vibration acceleration based on the laser Doppler frequency shift;

[0038] According to the vibration acceleration, the standard force value is obtained using Newton's second law;

[0039] The step of calculating the vibration acceleration according to the laser Doppler frequency shift includes:

[0040] According to the laser Doppler frequency shift, the vibration velocity near the center of the suspended mass block is obtained:

[0041] V=f D λ / 2

[0042] In the formula, f D is the laser frequency shift, λ is the laser wavelength, and V is the vibration speed;

[0043] From the relationship between acceleration and velocity in the complex frequency domain:

[0044] A(jω)=jω·V(jω)

[0045] The vibration velocity signal is differentiated to obtain the acceleration spectrum A(jω), and then the acceleration amplitude a is obtained.

[0046] The present invention has the following beneficial effects compared with the prior art:

[0047] 1. The present invention adjusts the laser irradiation point by cooperating with the visual alignment module and the master control module, thereby ensuring that the position of striking the suspended mass block is the center of the suspended mass block, avoiding torsional vibration of the suspended mass block caused by eccentric striking position, and improving calibration accuracy;

[0048] 2. The present invention cooperates with the pneumatic propulsion module, the data acquisition module and the master control module, and adjusts the opening size of the electromagnetic valve to control the value of the knocking force by using the cylinder clamping hammer to knock, thereby achieving the repeatability of calibration and improving the calibration efficiency;

[0049] 3. The present invention uses a pneumatic propulsion module, a laser absolute method measurement module, a data acquisition module and a master control module to cooperate with each other, and adopts a laser absolute method to measure the vibration acceleration of the suspended mass block, thereby avoiding the problem of low calibration accuracy caused by the linear error of the traditional accelerometer itself and improving the calibration accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0051] Figure 1 A dynamic calibration system for a hammer according to the background technology of the present invention;

[0052] Figure 2 The hammer calibration system of the background technology of the present invention;

[0053] Figure 3 A schematic diagram of the force direction and the ideal direction of the background technology of the present invention;

[0054] Figure 4 It is a structural schematic diagram of an absolute method modal hammer calibration device based on machine vision according to Example 1 of the present invention;

[0055] Figure 5 Schematic diagram of a dual-motor slide rail mechanism according to Embodiment 1 of the present invention;

[0056] Figure 6 is a schematic diagram of the surface of the suspended mass block engraved with marks according to Example 1 of the present invention;

[0057] Figure 7 is a structural block diagram of the pneumatic propulsion module of embodiment 1 of the present invention;

[0058] Figure 8 This is a structural block diagram of a laser absolute method measurement module according to Embodiment 1 of the present invention;

[0059] Fig. 9 Schematic diagram of the distance between the laser irradiation point (intersection point in the figure) and the center of the suspended mass block in Example 1 of the present invention;

[0060] in, Figure 5 The middle number indicates:

[0061] 6-guide rail 1, 7-ball screw, 8-motor 1, 9-guide rail 2, 10-motor 2, 11-fixture. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It should be understood that the specific embodiments described are only used to explain the present application and are not used to limit the present application.

[0063] Embodiment 1:

[0064] like Figure 4 As shown, the absolute method modal hammer calibration device based on machine vision provided in this embodiment is composed of a visual alignment module, a general control module, a data acquisition module, a pneumatic propulsion module and a laser absolute method measurement module. The general control module communicates with the visual alignment module, the data acquisition module and the pneumatic propulsion module respectively, and the data acquisition module communicates with the pneumatic propulsion module and the laser absolute method measurement module respectively.

[0065] The calibration principle of the calibration device is:

[0066] The laser line projector is used to align the center of the suspended mass block, and the camera is installed on the double-slide rail fixture. The camera collects images and transmits them to the master control module. The master control module calculates the relative distance between the center of the camera and the center of the cross laser on the surface of the suspended mass block in the horizontal and vertical directions, and controls the rotation of the motor. The movement of the fixed fixture is realized through the movement of the lead screw. When the center of the camera is aligned with the center of the cross laser on the surface of the suspended mass block, the cylinder is installed on the fixed fixture. The end fixture of the cylinder supports the modal force hammer to be calibrated. The hammer head of the modal force hammer passes through the centering fixture, and the center of the hammer head is aligned with the center of the cross laser on the surface of the suspended mass block. The master control module sets the opening and closing size of the solenoid valve according to the force value of the calibration point. The laser vibrometer collects the laser Doppler frequency shift near the excitation point (center) of the suspended mass block. The vibration velocity near the excitation point of the suspended mass block is obtained by the Doppler frequency shift through the following formula:

[0067] V=f D λ / 2

[0068] In the formula, f D is the laser frequency shift, λ is the laser wavelength, and V is the measured vibration velocity.

[0069] From the relationship between acceleration and velocity in the complex frequency domain, we can get:

[0070] A(jω)=jω·V(jω)

[0071] Differentiate the vibration velocity signal to obtain the acceleration spectrum A(jω), and then obtain the acceleration amplitude a. The standard force value is Fs=ma. Compare the modal hammer output voltage amplitude Vx with the standard force value Fs to obtain the modal hammer sensitivity. Through absolute calibration, the acceleration value is directly traced back to the laser wavelength value, which is more accurate and avoids the error caused by the linearity of the acceleration sensor amplitude.

[0072] The following is an introduction to each module in the absolute method modal hammer calibration device based on machine vision:

[0073] (1) Visual alignment module.

[0074] The visual alignment module is used to assist in aligning the knocking position with the center of the suspended mass block to reduce the error caused by the eccentricity of the knocking position.

[0075] The visual alignment module consists of a camera, a motor slide mechanism, and a laser line projector. Figure 5 As shown, the motor guide mechanism includes a base, a guide rail 1 and a ball screw 1 installed on the base, and a slider is arranged on the ball screw 1; one end of the guide rail 1 is vertically installed on the base, and the other end is installed with a motor 1, and the output shaft of the motor 1 is connected to the ball screw shaft through a coupling; the rotation of the output shaft of the motor 1 drives the rotation of the ball screw 1 shaft to drive the slider to move in the vertical direction. The guide rail 2 and the ball screw 2 are horizontally fixed on the slider by bolt connection, and a fixture is arranged on the ball screw 2; one end of the guide rail 2 is installed with a motor 2, and the output shaft of the motor 2 is connected to the ball screw shaft through a coupling, and the rotation of the output shaft of the motor 2 drives the rotation of the ball screw shaft to drive the fixture to move in the horizontal direction. The rotation of the output shaft of the motor 1 drives the fixture to move in the vertical direction, and the rotation of the output shaft of the motor 2 drives the fixture to move in the horizontal direction. The laser line projector is installed on the fixture and moves with the fixture. The position of the laser irradiation point on the surface of the suspended mass block can be adjusted by adjusting the position of the fixture. The surface of the suspended mass block is engraved with marks, such as Figure 6 As shown; the light emitted by the laser projector is perpendicular to the surface of the suspended mass block.

[0076] The camera collects images with laser irradiation points on the surface of the suspended mass block and sends them to the master control module; the master control module calculates the relative position and distance between the laser point and the center of the mark in the horizontal and vertical directions based on the received images, and controls the output shaft of the dual motor to rotate to move the fixture based on the calculation results, thereby driving the laser line projector to move.

[0077] Specifically, after the camera captures an image with a laser irradiation point on the surface of the suspended mass block, the captured image is sent to the main control module, which performs calculations based on the image data and controls the output shafts of motors 1 and 2 to rotate to move the fixture based on the calculation results, thereby adjusting the position of the laser line projector installed on the fixture so that the laser irradiation point is located at the center of the mark on the suspended mass block.

[0078] In this embodiment, the camera is installed on the fixture; all components in the visual alignment module are existing structures.

[0079] (2) Pneumatic propulsion module.

[0080] The pneumatic propulsion module is used to clamp the calibrated modal hammer, and the pneumatic transmission in the cylinder pushes the piston to generate impact motion, which drives the modal hammer to generate impact motion and strike the suspended mass block.

[0081] like Figure 7 As shown, the pneumatic propulsion module includes an air pressure controller, a solenoid valve, an air tank, a cylinder and a standard force sensor. The cylinder is installed on the fixture, and the end fixture of the cylinder clamps the modal force hammer to be calibrated. The height of the suspended mass block is adjusted according to the distance between the end clamping center and the tip of the hammer head; the standard force sensor is installed on the surface of the suspended mass block, and the center of the force-bearing surface of the standard force sensor is adjusted to align with the center of the suspended mass block; the air outlet of the air tank is connected to the air inlet of the solenoid valve, and the air outlet of the solenoid valve is connected to the air inlet of the cylinder; the standard force sensor communicates with the data acquisition module to send the output signal of the standard force sensor to the data acquisition module; the air pressure controller communicates with the master control module, and the air pressure controller is controlled by the master control module to adjust the opening size of the solenoid valve.

[0082] The standard force sensor is used to calibrate the entire pneumatic propulsion module before the calibration work begins. The air pressure control is performed in combination with the air pressure control algorithm in the master control module, so that the pneumatic propulsion module can generate a dynamic force close to the calibration force value at the calibration point. The air pressure controller controls the opening size of the solenoid valve according to the force value set in the master control module, so that the impact force of the hammer is controllable and repeatable.

[0083] Specifically, after the laser irradiation point is located at the center of the mark, remove the laser line projector, install the cylinder on the fixture, and use the end clamp of the cylinder to clamp the modal hammer to be calibrated. The distance between the center of the clamping fixture and the tip of the hammer head is measured, and the height of the suspended mass block is adjusted so that the increased distance of the suspended mass block is equal to the distance measured previously; the center of the force surface of the standard force sensor installed on the suspended mass block is adjusted to be aligned with the center of the suspended mass block, and the standard force sensor in the pneumatic propulsion module sends the measured value to the main control module through the data acquisition module. The main control module controls the air pressure controller to adjust the opening size of the solenoid valve according to the obtained value to achieve a force value close to the calibration point, thereby realizing the calibration of the modal hammer.

[0084] In this embodiment, all components in the pneumatic propulsion module are existing structures.

[0085] (3) Laser absolute measurement module.

[0086] The laser absolute measurement module is used to measure the laser frequency deviation near the impact position of the suspended mass block. Figure 8 As shown, the laser absolute method measurement module includes a laser vibrometer, and the optical vibrometer includes a laser controller and an optical head. The laser controller is connected to the optical head and the data acquisition module respectively.

[0087] Specifically, remove the standard force sensor, connect the output interface of the calibrated modal force hammer to the input channel of the data acquisition module, and connect the output of the laser vibrometer to the data acquisition module. The laser controller controls the optical head to emit laser near the knocking position of the suspended mass block, and the laser controller collects the laser Doppler frequency shift near the excitation point of the suspended mass block and sends it to the data acquisition module; the master control module calculates the vibration velocity based on the laser Doppler frequency shift collected by the data acquisition module, and obtains the acceleration of the surface vibration of the suspended mass block through differential operation; based on the acceleration, the standard knocking force value is obtained using Newton's second law.

[0088] In this embodiment, all components in the laser absolute method measurement module are existing structures.

[0089] (4)Data acquisition module.

[0090] The data acquisition module is used to collect analog input signals, convert the analog signals into digital signals, and transmit them to the master control module through the communication protocol. The collected signals include the output signal of the standard force sensor of the pneumatic propulsion module, the output signal of the modal hammer after the modal hammer is calibrated, and the laser Doppler frequency shift.

[0091] In this embodiment, the data acquisition module is an existing structure.

[0092] (5) Master control module.

[0093] The main control module is mainly used for: receiving the image sent by the visual alignment module, calculating the image, and controlling the operation of motor 1 and motor 2 according to the calculation results, so that the laser irradiation point emitted by the laser projection device is located at the center of the mark of the suspended mass block; receiving the digital signal sent by the data acquisition module, the digital signal includes the output signal of the standard force sensor of the pneumatic propulsion module, and the output signal and laser Doppler frequency shift of the calibrated modal hammer; according to the output signal of the standard force sensor, controlling the air pressure controller to adjust the opening size of the solenoid valve; according to the laser Doppler frequency shift, calculating the standard vibration acceleration; according to the standard vibration acceleration, using Newton's second law to obtain the standard force value; according to the standard force value and the output signal of the calibrated modal hammer, obtaining the modal hammer sensitivity.

[0094] Specifically, the image is calculated, including image binarization, spatial filtering, feature extraction and coordinate calculation in sequence. The image binarization adopts the adaptive threshold method, and the spatial filtering adopts the Gaussian filtering algorithm; the feature extraction adopts the HOG feature for image recognition; the coordinate calculation is to calculate the horizontal distance dx and the vertical distance dy between the two feature points of the laser irradiation point and the center of the surface of the suspended mass block, such as Fig. 9 shown.

[0095] In this embodiment, the functions of the master control module are implemented by a host computer.

[0096] The calibration steps of the calibration device are:

[0097] (1) Adjust the laser irradiation point to the center of the suspended mass block to ensure that the striking position is the center of the suspended mass block.

[0098] The laser irradiation point emitted by the laser line projector is made to fall on the surface of the suspended mass block, and an image of the surface of the suspended mass block with the laser irradiation point is obtained through the camera. The image is sent to the main control module through the data acquisition module. The main control module calculates the position and distance between the laser irradiation point and the center of the surface of the suspended mass block according to the image, and adjusts the position of the laser line projector installed on the fixture according to the calculation result so that the laser irradiation point is aligned with the center of the surface of the suspended mass block.

[0099] Specifically, the camera and the laser line projector are installed on the fixture of the visual alignment module, and the position of the fixture on the slide rail is manually adjusted so that the center of the camera lens is roughly aligned with the center of the mark of the suspended mass block, and then the motor is powered on, the slide rail is in the electric drive mode, and the fixture is stabilized on the slide rail;

[0100] The motor is connected to the master control module through the serial port, the camera output interface is connected to the image acquisition card, and the image acquisition card is connected to the master control module through the network port. The camera collects images of the center mark on the surface of the suspended mass block and the cross-line of the laser projection instrument. The image acquisition card converts the analog signal of the camera into a digital signal and transmits it to the master control module for digital image processing. The master control module calculates the horizontal and vertical distances between the center position of the suspended mass block and the intersection of the cross-line through image binarization, spatial filtering, feature extraction, and coordinate calculation, and controls the motor rotation to adjust the position of the fixture to determine whether the distance is less than 3mm. If it is less than 3mm, the motor stops moving.

[0101] (2) Adjust the solenoid valve opening size to calibrate the modal hammer.

[0102] After the laser irradiation point is aligned with the center of the suspended mass block, remove the laser line projector, install the cylinder on the fixture, and clamp the modal hammer to be calibrated with the end fixture of the cylinder. Measure the distance between the center of the clamping fixture and the tip of the hammer head, and adjust the height of the suspended mass block so that the increased distance of the suspended mass block is equal to the distance measured previously; adjust the center of the force surface of the standard force sensor installed on the suspended mass block to align with the center of the suspended mass block, and the standard force sensor in the pneumatic propulsion module sends the measured value to the main control module through the data acquisition module. The main control module adjusts the size of the solenoid valve opening according to the obtained value to achieve a force value close to the calibration point.

[0103] Specifically, remove the laser line projector, install the cylinder on the fixture and install the modal force hammer to be calibrated on the cylinder clamping fixture, measure the distance from the center of the clamping fixture to the tip of the hammer head, and adjust the height of the suspended mass block so that the height increase of the suspended mass block is equal to the distance from the center of the clamping fixture to the tip of the hammer head;

[0104] Install the standard force sensor on the surface of the suspended mass block, and align the center of the force-bearing surface of the standard force sensor with the center of the suspended mass block. Connect the output interface of the standard force sensor to the input channel of the data acquisition module, turn on the air tank and the air pressure controller air inlet switch, set the modal hammer calibration points, such as 200N, 400N, 600N, 800N, 1000N, 1200N, 1400N, 1600N, 1800N, 2000N, 2200N, 2400N, read the output of the standard force sensor in the data display module of the master control module, adjust the opening size of the solenoid valve through PID feedback control, and obtain the force values ​​close to the above force calibration points.

[0105] (3) Collect the output signal of the modal hammer and the laser Doppler frequency shift near the excitation point of the suspended mass block.

[0106] The standard force sensor is removed, and the laser controller in the laser absolute method measurement module is used to collect the laser Doppler frequency shift near the excitation point of the suspended mass block.

[0107] Specifically, the standard force sensor is removed, and the output interface of the calibrated modal hammer and the output interface of the laser controller are connected to the input channel of the data acquisition module. The output signal and laser Doppler frequency shift of the calibrated modal hammer are collected by the data acquisition module and sent to the master control module.

[0108] (4) Calculate the vibration acceleration based on the output signal of the modal hammer and the laser Doppler frequency shift.

[0109] The master control module calculates the sensitivity and amplitude linearity of the hammer according to the output signal and Doppler frequency shift of the calibrated modal hammer.

[0110] This embodiment also provides an absolute method modal hammer calibration method based on machine vision, including:

[0111] Aim the laser irradiation point emitted by the laser projection instrument at the center of the suspended mass block to ensure that the knocking position is the center of the suspended mass block;

[0112] Replace the laser line projector with a cylinder, clamp the modal hammer to be calibrated with a clamp at the end of the cylinder, raise the suspended mass block so that the increased distance is equal to the distance between the center of the clamp and the tip of the hammer head; install the standard force sensor on the surface of the suspended mass block, and align the center of the force-bearing surface of the standard force sensor with the center of the suspended mass block, and adjust the opening size of the solenoid valve according to the output signal of the standard force sensor and the force value of the calibration point to calibrate the modal hammer;

[0113] Remove the standard force sensor, control the emission of laser to the surface near the center of the suspended mass block, obtain the laser Doppler frequency shift near the center of the suspended mass block and the output signal of the calibrated modal hammer;

[0114] The vibration acceleration is calculated according to the laser Doppler frequency shift; the standard force value is obtained according to the vibration acceleration using Newton's second law; and the quasi-modal hammer sensitivity is obtained according to the standard force value and the output signal amplitude of the modal hammer.

[0115] The specific implementation of each step in the above calibration method can be referred to the above calibration device, which will not be described in detail here.

[0116] Those skilled in the art will appreciate that all or part of the steps in the method for implementing the above embodiments may be completed by instructing related hardware through a program, and the corresponding program may be stored in a computer-readable storage medium.

[0117] It should be noted that although the method operations of the above embodiments are described in a specific order, this does not require or imply that these operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. On the contrary, the steps depicted can be performed in a different order. Additionally or alternatively, some steps can be omitted, multiple steps can be combined into one step, and / or one step can be decomposed into multiple steps.

[0118] The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solution and inventive concept of the present invention within the scope disclosed by the present invention, which shall fall within the protection scope of the present invention.

Claims

1. An absolute modal hammer calibration device based on machine vision, characterized in that: The device comprises a visual alignment module, an aerodynamic propulsion module, a laser absolute method measurement module, a data acquisition module and a master control module, wherein the master control module communicates with the visual alignment module, the data acquisition module and the aerodynamic propulsion module respectively, and the data acquisition module communicates with the aerodynamic propulsion module and the laser absolute method measurement module respectively, wherein: The visual alignment module is used to acquire an image to adjust the laser irradiation point to align with the center of the suspended mass block to ensure that the knocking position is at the center of the suspended mass block; The pneumatic propulsion module is used to obtain the output signal of the standard force sensor to adjust the opening size of the solenoid valve and calibrate the modal hammer by striking with the cylinder clamping hammer; The laser absolute method measurement module is used to obtain the laser Doppler frequency shift near the center of the suspended mass block; The data acquisition module is used to collect the output signal of the standard force sensor, as well as the output signal of the laser Doppler frequency shift and the calibrated modal hammer, and convert the collected analog signal into a digital signal; The master control module is used to receive images, perform calculations based on the images, and adjust the position of the laser irradiation point based on the calculation results; and to receive digital signals, perform calculations on the digital signals, adjust the size of the solenoid valve opening based on the calculation results, and obtain the modal hammer sensitivity.

2. The absolute method modal hammer calibration device according to claim 1, characterized in that: The visual alignment module includes a camera, a dual-motor slide mechanism, a fixture and a laser line projector; the dual-motor slide mechanism includes a base, on which a first motor slide mechanism is installed, and a second motor slide mechanism is installed on a slider of the first motor slide mechanism in a direction perpendicular to the first motor slide mechanism; the fixture is installed on the second motor slide mechanism, and the laser line projector is installed on the fixture; the laser line projector is used to place the emitted laser irradiation point on the surface of the suspended mass block, wherein the surface of the suspended mass block is engraved with a mark; the camera is used to capture an image of the surface of the suspended mass block with the laser irradiation point, and send the image to the main control module; the first motor slide mechanism is used to control the movement of the slider according to the signal sent by the main control module to drive the fixture to move; the second motor slide mechanism is used to control the fixture to move in a direction perpendicular to the movement direction of the slider according to the signal sent by the main control module; the position of the laser line projector is adjusted by the movement of the fixture so that the laser irradiation point is located at the center of the mark of the suspended mass block.

3. The absolute method modal hammer calibration device according to claim 2, characterized in that: The first motor slide rail mechanism comprises a guide rail, a motor, a ball screw and a slider, one end of the guide rail and one end of the ball screw are both mounted on a base, and the other end of the guide rail is mounted with a motor; the output shaft of the motor is connected to the ball screw shaft through a coupling, and the slider is slidably connected to the ball screw; the rotation of the output shaft of the motor drives the ball screw shaft to rotate, so as to drive the slider to move along the track direction in the guide rail, and the movement of the slider drives the movement of the second motor slide rail mechanism, that is, drives the fixture to move; The second motor slide rail mechanism includes a guide rail, a motor and a ball screw. The guide rail and the ball screw are installed on a slider, and a motor is installed at one end of the guide rail. The output shaft of the motor is connected to the ball screw shaft through a coupling, and the fixture is installed on the ball screw. The rotation of the output shaft of the motor drives the ball screw shaft to rotate, thereby driving the fixture to move along the track direction in the guide rail.

4. The absolute method modal hammer calibration device according to claim 2, characterized in that: The step of calculating according to the image and adjusting the position of the laser irradiation point according to the calculation result includes: The image is subjected to image binarization, spatial filtering, feature extraction and coordinate calculation in sequence to obtain the distance between the laser irradiation point and the center of the suspended mass block; If the distance is greater than a first set threshold, the first motor slide rail mechanism and the second motor slide rail mechanism are controlled to adjust the position of the laser line projector so that the laser irradiation point is located at the center of the suspended mass block mark.

5. The absolute method modal hammer calibration device according to claim 2, characterized in that: The pneumatic propulsion module includes an air pressure controller, a solenoid valve, a gas tank, a cylinder and a standard force sensor. The cylinder is installed on a fixture. The end fixture of the cylinder clamps the modal force hammer to be calibrated, and the height of the suspended mass block is adjusted according to the distance between the end clamping center and the tip of the hammer head; the air outlet of the gas tank is connected to the air inlet of the solenoid valve, and the air outlet of the solenoid valve is connected to the air inlet of the cylinder; the standard force sensor is installed on the surface of the suspended mass block and communicates with the data acquisition module; the air pressure controller communicates with the main control module, and is used to adjust the opening size of the solenoid valve according to the signal sent by the main control module.

6. The absolute method modal hammer calibration device according to claim 5, characterized in that: The step of calculating the digital signal, adjusting the opening size of the solenoid valve according to the calculation result, and obtaining the modal hammer sensitivity includes: If the digital signal is the output signal of the standard force sensor, the output signal of the standard force sensor is compared with the force value of the modal force hammer calibration point, and if the comparison result is greater than the second set threshold, the pneumatic controller is controlled to adjust the opening size of the solenoid valve; If the digital signal is the output signal of the laser Doppler frequency shift and the calibrated modal hammer, the standard vibration acceleration is calculated according to the laser Doppler frequency shift; the standard force value is obtained by using Newton's second law according to the standard vibration acceleration; and the modal hammer sensitivity is obtained according to the standard force value and the output signal of the calibrated modal hammer.

7. The absolute method modal hammer calibration device according to any one of claims 1 to 6, characterized in that: The laser absolute method measurement module includes a laser vibrometer, the laser vibrometer includes a laser controller and an optical head, and the laser controller communicates with the optical head and the data acquisition module respectively; The laser controller is used to control the optical head to emit laser to the vicinity of the center of the suspended mass block, and send the laser Doppler frequency shift collected near the center of the suspended mass block to the data acquisition module.

8. An absolute modal hammer calibration method based on machine vision, characterized in that: The method comprises: Aim the laser irradiation point emitted by the laser projection instrument at the center of the suspended mass block to ensure that the knocking position is the center of the suspended mass block; Replace the laser line projector with a cylinder, clamp the modal hammer to be calibrated with a clamp at the end of the cylinder, raise the suspended mass block so that the increased distance is equal to the distance between the center of the clamp and the tip of the hammer head; install the standard force sensor on the surface of the suspended mass block, and align the center of the force-bearing surface of the standard force sensor with the center of the suspended mass block, and adjust the opening size of the solenoid valve according to the output signal of the standard force sensor and the force value of the calibration point to calibrate the modal hammer; Remove the standard force sensor, control the emission of laser to the surface near the center of the suspended mass block, obtain the laser Doppler frequency shift near the center of the suspended mass block and the output signal of the calibrated modal hammer; The standard force value is calculated according to the laser Doppler frequency shift; the sensitivity of the quasi-modal hammer is obtained according to the standard force value and the output signal of the calibrated modal hammer.

9. The absolute modal hammer calibration method according to claim 8, characterized in that: The step of aligning the laser irradiation point emitted by the laser projection device at the center of the suspended mass block comprises: The laser irradiation point emitted by the laser line projector is made to fall on the surface of the suspended mass block, and an image of the surface of the suspended mass block with the laser irradiation point is obtained by a camera; wherein the surface of the suspended mass block is engraved with a mark; The distance between the laser irradiation point and the center of the surface of the suspended mass block is calculated based on the image. If the distance is greater than the set threshold, the position of the laser line projector installed on the fixture is adjusted to align the laser irradiation point with the center of the surface of the suspended mass block.

10. The absolute modal hammer calibration method according to any one of claims 8 and 9, characterized in that: The method of calculating the standard force value according to the laser Doppler frequency shift comprises: Calculate the vibration acceleration based on the laser Doppler frequency shift; According to the vibration acceleration, the standard force value is obtained using Newton's second law; The step of calculating the vibration acceleration according to the laser Doppler frequency shift includes: According to the laser Doppler frequency shift, the vibration velocity near the center of the suspended mass block is obtained: V=f D ·l / 2 In the formula, f D is the laser frequency shift, λ is the laser wavelength, and V is the vibration speed; From the relationship between acceleration and velocity in the complex frequency domain: A(jω)=jω·V(jω) The vibration velocity signal is differentiated to obtain the acceleration spectrum A(jω), and then the acceleration amplitude a is obtained.

Images