Laser vibration meter calibration method adopting electro-optical modulation technology

Abstract

The invention discloses a laser vibration meter calibration method adopting an electro-optical modulation technology, which comprises the following steps that: electro-optical modulators or cascade combination of the electro-optical modulators are adopted to generate equivalent vibration signals of which the frequency range and the measuring range meet calibration requirements, and the calibration frequency depends on the type selection of the electro-optical modulators and can at least reach 24MHz; the measuring range of the equivalent vibration signal can be expanded by improving the driving voltage of the electro-optical modulator or the serial configuration of the electro-optical modulator; according to the technical scheme of a software and hardware collaborative real-time signal demodulation system, the reference standard laser vibration meter of which the amplitude and the phase delay can be effectively evaluated is established. According to the invention, the amplitude and phase delay calibration of the whole laser vibration meter is realized, and the limitation of the technical scheme of generating a reference signal through software demodulation in phase delay calibration is solved.

Description

Technical Field

[0001] The invention relates to the technical field of laser vibrometers, and in particular to a laser vibrometer calibration method using an electro-optical modulation technology. Background Art

[0002] Laser Doppler vibrometer (hereinafter referred to as laser vibrometer) is an instrument that uses laser Doppler effect and laser interferometry measurement technology to perform non-contact measurement of the vibration velocity, acceleration and displacement of an object. It consists of a laser heterodyne interferometer and a Doppler signal demodulation system. It has the advantages of high spatial resolution, short measurement time, wide response bandwidth, and high velocity resolution. Therefore, it is widely used in many fields such as surface wave detection, acoustic and vibration measurement, modal analysis, structural flaw detection, health care, etc.

[0003] Polytec of Germany is a major manufacturer of laser vibrometers. Its product performance is at the international leading level. The bandwidth of conventional models can cover up to 1MHz. In special applications, the bandwidth of the UHF-120 laser vibrometer can reach 1.2GHz. In recent years, the products of Optomet of Germany, Julight of Italy, Sunny Optical, Beijing Great Wall Metrology and Testing Technology Institute of Aviation Industry Corporation of China, and Institute of Space Information of Chinese Academy of Sciences have gradually matured. As a widely used test equipment, the accuracy and reliability of the measurement results of laser vibrometers need to be guaranteed by metrology. In response to the calibration requirements of laser vibrometers for vibration and shock, the calibration frequency range is 0.4Hz to 50kHz, and the comparison method is used to calibrate with standard acceleration sensors or standard laser interferometers. This method is limited by the high-frequency excitation capability of the vibration table, and the dynamic range of the excitation signal amplitude cannot cover the measurement capability of the laser vibrometer. In the frequency band from 50kHz to MHz, the synthetic Doppler signal method (electrical calibration method) and the Doppler signal spectrum analysis method based on Bessel function fitting are used. These two methods can only calibrate the Doppler signal processing system of the laser vibrometer, assuming that the optical path does not introduce any error. However, in fact, the frequency response of the photodetector in high-frequency applications affects the Doppler signal modulation, which is an error source that cannot be ignored. In the GHz frequency band, Polytec uses theoretical analysis and numerical simulation methods to evaluate the maximum measurement uncertainty of the laser vibrometer. Therefore, it is necessary to study new excitation methods to expand the calibration frequency range of the laser vibrometer.

[0004] In view of the above problems, the present invention provides a laser vibrometer calibration method using electro-optical modulation technology to achieve amplitude and phase delay calibration of the entire laser vibrometer. Summary of the invention

[0005] The invention provides a laser vibrometer calibration method using an electro-optical modulation technology for realizing amplitude and phase delay calibration of a laser vibrometer.

[0006] The object of the present invention is to provide a laser vibrometer calibration method using electro-optic modulation technology, comprising a data acquisition system, a signal generator, an electro-optic modulator driver, an electro-optic modulator, a reflector, a polarizer, a laser vibrometer to be measured and a standard laser vibrometer, and the specific steps of the method are as follows:

[0007] Step 1: The signal generator generates a sinusoidal signal, which is driven by the voltage amplifier to drive the electro-optic modulator to work;

[0008] Step 2: The measuring beams of the laser vibrometer to be calibrated and the standard laser vibrometer are combined by a beam splitter, and then incident on an electro-optic modulator through a polarizer, where their phases are modulated, and then incident on the electro-optic modulator again after passing through a reflector;

[0009] Step 3: The modulation phase is doubled, and the measurement beam carrying the modulation phase information returns to the laser vibrometer to be calibrated and the standard laser vibrometer. The equivalent velocity, displacement and acceleration signals output by the demodulation are synchronously collected by the data acquisition system. The demodulation result of the standard laser vibrometer is used as a reference signal to calibrate the amplitude response and phase delay of the laser vibrometer to be calibrated.

[0010] Furthermore, the standard laser vibrometer also includes an AWView host computer, an AD acquisition control module, an automatic gain control module, a FIR low-pass filter module for demodulation, a FIR low-pass filter module for output, and a CIC extraction module. The demodulation step includes the following:

[0011] Step 31, the AWView host computer controls the AD acquisition control module, the automatic gain control module, the FIR low-pass filter module, the FIR low-pass filter module and the CIC extraction module through the PCIe interface, so that FIR filters with different parameters and data extraction multiples can be selected according to the specific application scenario.

[0012] The present invention has the following advantages: the present invention realizes the calibration of the amplitude and phase delay of the laser vibrometer as a whole by adding a standard laser vibrometer composed of a laser heterodyne interferometer and a software and hardware coordinated real-time signal demodulation system as a reference, specifically comprising: using an electro-optic modulator or a cascade combination of electro-optic modulators to generate an equivalent vibration signal whose frequency range and measuring range meet the calibration requirements, the calibration frequency depends on the selection of the electro-optic modulator, and can reach at least 24MHz, and the measuring range of the equivalent vibration signal can be expanded by increasing the driving voltage of the electro-optic modulator or the series configuration of the electro-optic modulator; a technical solution of a software and hardware coordinated real-time signal demodulation system is proposed, a reference standard laser vibrometer that can effectively evaluate both the amplitude and phase delay is established, the amplitude and phase delay calibration of the laser vibrometer as a whole is realized, and the limitation of the technical solution of generating reference signals by software demodulation in phase delay calibration is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A schematic diagram of the calibration of the laser vibrometer based on the electro-optical modulation technology of the present invention;

[0014] Figure 2 This is a diagram of the software and hardware collaborative real-time signal demodulation system of the present invention. DETAILED DESCRIPTION

[0015] The present invention provides a laser vibrometer calibration method using electro-optic modulation technology, comprising a data acquisition system, a signal generator, an electro-optic modulator driver, an electro-optic modulator, a reflector, a polarizer, a laser vibrometer to be measured and a standard laser vibrometer, and the method specifically comprises the following steps:

[0016] Step 1: The signal generator generates a sinusoidal signal, which is driven by the voltage amplifier to drive the electro-optic modulator to work;

[0017] Step 2: The measuring beams of the laser vibrometer to be calibrated and the standard laser vibrometer are combined by a beam splitter, and then incident on an electro-optic modulator through a polarizer, where their phases are modulated, and then incident on the electro-optic modulator again after passing through a reflector;

[0018] Step 3: The modulation phase is doubled, and the measurement beam carrying the modulation phase information returns to the laser vibrometer to be calibrated and the standard laser vibrometer. The equivalent velocity, displacement and acceleration signals output by the demodulation are synchronously collected by the data acquisition system. The demodulation result of the standard laser vibrometer is used as a reference signal to calibrate the amplitude response and phase delay of the laser vibrometer to be calibrated.

[0019] Furthermore, the standard laser vibrometer also includes an AWView host computer, an AD acquisition control module, an automatic gain control module, an FIR low-pass filter module, an FIR low-pass filter module and a CIC extraction module, and the demodulation step includes the following:

[0020] Step 31, the AWView host computer controls the AD acquisition control module, the automatic gain control module, the FIR low-pass filter module for demodulation, the FIR low-pass filter module for output, and the CIC extraction module through the PCIe interface, so that FIR filters with different parameters and data extraction multiples can be selected according to specific application scenarios.

[0021] In this embodiment, the AD acquisition control module adopts TI's ADS42LB69.

[0022] In this embodiment, the automatic gain control module uses TI's LMH6881, and uses the PL end of the Zynq MPSoC in the signal processing module to implement gain adjustment through the SPI interface, with a step of 0.25 dB.

[0023] In this embodiment, the CIC extraction module adopts AMD's XCZU7EV-2FFVB1156I.

[0024] In this embodiment, Figure 1 As shown, an electro-optic modulator is used to simulate mechanical vibration to phase modulate the laser vibrometer measurement beam as a calibration signal, which is assigned by a standard laser vibrometer as a reference signal to calibrate the amplitude and phase delay of the entire laser vibrometer. The standard laser vibrometer consists of a laser heterodyne interferometer with traceable process data and a real-time signal demodulation system coordinated by hardware and software.

[0025] In this embodiment, Figure 1 As shown, the role of the polarizer is to control the polarization state of the measuring beam so that the polarization direction of the measuring beam is consistent with the refractive index principal axis of the electro-optical crystal. In this configuration, the measuring beam only changes its phase but not its polarization state when passing through the electro-optical crystal, thus avoiding the influence of the birefringence effect and improving the stability of the equivalent Doppler signal generated by the electro-optical phase modulation method.

[0026] In this embodiment, Figure 1 As shown, the amplitude of the modulation phase introduced by the laser vibrometer when the light beam passes through the electro-optic modulator twice is related to the driving voltage of the electro-optic modulator. Therefore, the amplitude range of the modulation phase can be expanded by increasing the driving voltage of the electro-optic modulator or connecting multiple electro-optic modulators in series.

[0027] In this embodiment, Figure 1 As shown in the figure, the real-time demodulation of Doppler signals is realized by using a software-hardware collaborative real-time signal demodulation system. The phase delay introduced thereby is stable and can be quantitatively evaluated, thus avoiding the limitations of the software demodulation method in phase delay calibration.

[0028] Although the specific embodiments of the present invention are described in detail in conjunction with the accompanying drawings, it should not be understood as limiting the scope of protection of the present invention. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still belong to the scope of protection of the present invention.

Claims

1. A laser vibrometer calibration method using electro-optic modulation technology, comprising a data acquisition system, a signal generator, an electro-optic modulator driver, an electro-optic modulator, a reflector, a polarizer, a laser vibrometer to be measured and a standard laser vibrometer, characterized in that: The specific steps of the method are as follows: Step 1: The signal generator generates a sinusoidal signal, which is driven by the voltage amplifier to drive the electro-optic modulator to work; Step 2: The measuring beams of the laser vibrometer to be calibrated and the standard laser vibrometer are combined by a beam splitter, and then incident on an electro-optic modulator through a polarizer, where their phases are modulated, and then incident on the electro-optic modulator again after passing through a reflector; Step 3: The modulation phase is doubled, and the measurement beam carrying the modulation phase information returns to the laser vibrometer to be calibrated and the standard laser vibrometer. The equivalent velocity, displacement and acceleration signals output by the demodulation are synchronously collected by the data acquisition system. The demodulation result of the standard laser vibrometer is used as a reference signal to calibrate the amplitude response and phase delay of the laser vibrometer to be calibrated.

2. A laser vibrometer calibration method using electro-optical modulation technology as claimed in claim 1, characterized in that: The standard laser vibrometer also includes an AWView host computer, an AD acquisition control module, an automatic gain control module, an FIR low-pass filter module, an FIR low-pass filter module and a CIC extraction module. The demodulation step includes the following: Step 31, the AWView host computer controls the AD acquisition control module, the automatic gain control module, the FIR low-pass filter module for demodulation, the FIR low-pass filter module for output, and the CIC extraction module through the PCIe interface, so that FIR filters with different parameters and data extraction multiples can be selected according to specific application scenarios.

Images