Device and method for detecting inherent frequency of broadband light interference type cantilever beam with high precision and strong anti-interference performance

Abstract

The invention provides a broadband light interference type cantilever beam inherent frequency detection device and method with high precision and strong anti-interference performance. The broadband light interference type cantilever beam inherent frequency detection device comprises near-infrared broadband light, a single-mode optical fiber coupler, a gradient refractive index lens, a single-point spectrometer and an upper computer, the light source radiates near-infrared broadband light with bandwidth, and the near-infrared broadband light enters the single-mode optical fiber coupler through the light inlet. The near-infrared broadband light is transmitted to the probe light outlet through the single-mode optical fiber coupler, and is divided into reference light and probe light after passing through the gradient refractive index lens; the probe light is focused to the surface of the cantilever beam through the graded index lens and is backscattered by the cantilever beam to be coupled with the reference light reflected by the end face of the graded index lens in the single-mode optical fiber coupler to form interference; and the interference signal is transmitted by the single-mode optical fiber coupler and is input into the single-point spectrometer through the light return port. According to the technical scheme, high precision can be kept while large-amplitude vibration measurement is achieved, and the accuracy and reliability of inherent frequency measurement of the cantilever beam are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of non-contact cantilever beam natural frequency measurement technology, and in particular to a broadband optical interferometric cantilever beam natural frequency detection device and method with high precision and strong anti-interference performance. Background Technology

[0002] Methods for detecting the natural frequency of cantilever beams can be broadly classified into two categories: contact and non-contact methods. Traditional contact methods require attaching sensors to the surface of the cantilever beam being measured. The added mass introduced alters the dynamic characteristics of the structure, thus affecting the accuracy of the natural frequency measurement. Therefore, non-contact measurement methods have emerged, which eliminate the need for sensor installation and avoid the added mass effect.

[0003] However, existing non-contact methods still have certain limitations: machine vision-based methods are limited by camera imaging quality, and vibration measurement accuracy is usually difficult to exceed the micrometer level; while laser vibrometers using the Michelson interferometer structure can achieve nanometer-level accuracy, but are limited by the 2π fuzzy effect, require a complex demodulation system to achieve large-range measurements, and are easily affected by environmental noise. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a high-precision broadband optical interferometric cantilever beam natural frequency detection device and method with strong anti-interference performance, which can maintain high precision while realizing large amplitude vibration measurement, and significantly improve the accuracy and reliability of cantilever beam natural frequency measurement.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a high-precision broadband optical interferometric cantilever beam natural frequency detection device with strong anti-interference performance, including near-infrared broadband light (1). Single-mode fiber coupler (2), graded refractive index lens (3), single-point spectrometer and host computer (5);

[0006] The The single-mode fiber coupler (2) consists of three ends: an input port, a return port, and a probe light output port. The light source radiates near-infrared broadband light (1) with a wide bandwidth, which enters the optical path through the input port. In the single-mode fiber coupler (2); the near-infrared broadband light (1) passes through The single-mode fiber coupler (2) transmits the probe light to the probe light output port, and after passing through the graded refractive index lens (3), it is split into a reference light and a probe light; the probe light is focused onto the surface of the cantilever beam (4) by the graded refractive index lens (3) and backscattered back by it, and then reflects back onto the reference light reflected back from the end face of the graded refractive index lens (3). A single-mode fiber coupler (2) couples and forms an interference signal; the interference signal is then coupled through... The single-mode fiber coupler (2) transmits the light from the return port to the single-point spectrometer.

[0007] In a preferred embodiment: the end of the gradient refractive index lens is coated with a semi-reflective film, which reflects half of the light as reference light and transmits the light as probe light.

[0008] In a preferred embodiment: the single-point spectrometer includes a collimator (9) for collimating incident light into parallel light, a linear CCD camera (6) for acquiring spectral data, a near-infrared transmission grating (8) for splitting incident light according to wavelength, and a convex lens (7) for focusing light onto the CCD camera; the linear CCD camera (6), the convex lens (7), the near-infrared transmission grating (8) and the collimator (9) are arranged in sequence.

[0009] This invention also provides a high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection method, and a high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection device, comprising the following steps:

[0010] Step S1: The near-infrared broadband light (1) is transmitted through... The single-mode fiber coupler (2) transmits the light to the probe light output port, and after passing through the graded refractive index lens (3), it is split into a reference light and a probe light; the reference light is reflected back by the end face of the graded refractive index lens (3), and the probe light is focused onto the surface of the cantilever beam (4) by the graded refractive index lens (3), and is backscattered back by the surface of the cantilever beam (4); the two beams of light are... The single-mode fiber couplers (2) re-interact and form interference;

[0011] Step S2: After being collimated by the fiber collimator (9), the interference light is split according to wavelength by the near-infrared transmission grating (8), focused by the convex lens (7), and then collected by the linear CCD camera (6); the collected interference signal The formula is expressed as shown in equation (1):

[0012] (1)

[0013] in, is the spectral density function of the light source; t is time; The wavelength of the light source; The starting wavelength of the light source; The wavelength at which the light source terminates; and These represent the reflected light intensities of the probe arm and the reference arm, respectively. The distance between the end face of the graded-index lens and the detection point on the cantilever beam varies with the vibration of the cantilever beam; due to and Since the term is DC and does not contain the sample's position information, these two terms are ignored, resulting in the simplified form of equation (1):

[0014] (2)

[0015] Step S3: By combining Fourier transform and the Hanning window energy centroid method, the interference signal acquired in S2 can be calculated to obtain... ;

[0016] Step S4: Excite the cantilever beam by tapping its fixed end and record a series of interference signals during the cantilever beam's vibration using a linear CCD camera. Then, using the algorithm in S3, the vibration data of the cantilever beam relative to the end face of the graded-index lens can be calculated. ;

[0017] Step S5: For The natural vibration frequency of the cantilever beam can be obtained by performing a Fourier transform.

[0018] Compared with existing technologies, this invention has the following advantages: It utilizes a graded-index lens with a semi-permeable film coated on its end face and a 1×2 fiber coupler to achieve co-path transmission of the reference and probe beams, avoiding the influence of external factors such as fiber bending, ambient temperature, and vibration noise on the vibration measurement results, thus significantly improving the system's noise immunity. Simultaneously, it introduces the Hanning window energy centroid method, effectively suppressing spectral energy leakage caused by signal truncation, achieving a spatial resolution at the nanometer scale. This system can maintain high precision while achieving large-amplitude vibration measurements, significantly improving the accuracy and reliability of cantilever beam natural frequency measurements. Attached Figure Description

[0019] Figure 1 This is a diagram of a cantilever beam vibration measurement system according to an embodiment of the present invention, where 1 represents infrared broadband light and 2 represents… 3 is a single-mode fiber coupler, 4 is a graded refractive index lens, 5 is a cantilever beam, 6 is a host computer, 7 is a linear CCD camera, 8 is a convex lens, 9 is a near-infrared transmission grating, and 10 is a collimator.

[0020] Figure 2 This is a diagram illustrating the signal processing procedure according to an embodiment of the present invention.

[0021] Figure 3 The graph shows the measurement results of the natural frequency of the cantilever beam according to an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0025] refer to Figure 1-3 A high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection device provides a sample, including near-infrared broadband light 1, 2. Single-mode fiber coupler, 3. Gradient refractive index lens, 5. Single-point spectrometer and host computer;

[0026] The The single-mode fiber coupler 2 consists of three ends: an input port, a return port, and a probe light output port. The light source radiates near-infrared broadband light 1 with a certain bandwidth, which enters the optical path through the input port. In single-mode fiber coupler 2; the near-infrared broadband light 1 passes through The single-mode fiber coupler 2 transmits the light to the probe light output port, and after passing through the graded-index lens 3, it is split into a reference light and a probe light. The probe light is focused by the graded-index lens 3 onto the surface of the cantilever beam 4 and backscattered by it, and then reflects back onto the reference light reflected from the end face of the graded-index lens 3. Single-mode fiber coupler 2 couples and forms interference; the interference signal is then... The single-mode fiber coupler 2 transmits the light from the return port to the single-point spectrometer.

[0027] Furthermore, the end of the gradient refractive index lens 3 is coated with a semi-reflective film, which can reflect half of the light as reference light and transmit the light as probe light.

[0028] Furthermore, the spectrometer includes a collimator 9 for collimating incident light into parallel light, a linear CCD camera 6 for acquiring spectral data, a near-infrared transmission grating 8 for splitting incident light according to wavelength, and a convex lens 7 for focusing light onto the CCD camera.

[0029] The high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection method includes the following steps:

[0030] Step S1: The broadband optical... The single-mode fiber coupler 2 transmits the probe light to the output port, and after passing through the graded-index lens 3, it is split into a reference light and a probe light. The reference light is reflected back by the end face of the graded-index lens 3, and the probe light is focused onto the surface of the cantilever beam 4 by the graded-index lens 3 (the measured point of the cantilever beam 4 should be close to its fixed end to reduce the amplitude and avoid interference ambiguity), and is backscattered back by the surface of the cantilever beam 4; the two beams of light... The two single-mode fiber couplers meet again and form interference.

[0031] Step S2: After being collimated by the fiber collimator 9, the interference light is split according to wavelength by the near-infrared transmission grating 8, focused by the convex lens 7, and then collected by the linear CCD camera 6; the formula for the collected interference signal is shown in equation (1):

[0032] (1)

[0033] in, is the spectral density function of the light source; t is time; The wavelength of the light source; The starting wavelength of the light source; The wavelength at which the light source terminates; and These represent the reflected light intensities of the probe arm and reference arm 4, respectively. The distance between the end face of the graded refractive index lens 3 and the detection point of the cantilever beam 4 varies with the vibration of the cantilever beam 4; due to and Since the term is DC and does not contain the sample's position information, these two terms are ignored, resulting in the simplified form of equation (1):

[0034] (2)

[0035] Step S3: By combining Fourier transform and the Hanning window energy centroid method, the interference signal acquired in S2 can be calculated to obtain... ;

[0036] Step S4: Excite the cantilever beam 4 by tapping its fixed end and record a series of interference signals during the vibration of the cantilever beam 4 using a linear CCD camera. Then, the vibration data of the cantilever beam 4 relative to the end face of the graded refractive index lens can be calculated using the algorithm in S3. .

[0037] Step S5: For The natural vibration frequency of the cantilever beam 4 can be obtained by performing a Fourier transform.

Claims

1. A high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection device, characterized in that: Including near-infrared broadband light (1), Single-mode fiber coupler (2), graded refractive index lens (3), single-point spectrometer and host computer (5); The The single-mode fiber coupler (2) consists of three ends: an input port, a return port, and a probe light output port. The light source radiates near-infrared broadband light (1) with a wide bandwidth, which enters the optical path through the input port. In the single-mode fiber coupler (2); The near-infrared broadband light (1) is transmitted through The single-mode fiber coupler (2) transmits the probe light to the probe light output port, and after passing through the graded refractive index lens (3), it is split into a reference light and a probe light; the probe light is focused onto the surface of the cantilever beam (4) by the graded refractive index lens (3) and backscattered back by it, and then reflects back onto the reference light reflected back from the end face of the graded refractive index lens (3). A single-mode fiber coupler (2) couples and forms an interference signal; the interference signal is then coupled through... The single-mode fiber coupler (2) transmits the light from the return port to the single-point spectrometer.

2. The high-precision, high-interference-resistance broadband optical interferometric cantilever beam natural frequency detection device according to claim 1, characterized in that: The end of the gradient refractive index lens is coated with a semi-reflective film, which reflects half of the light as reference light and transmits the light as probe light.

3. The high-precision, high-interference-resistance broadband optical interferometric cantilever beam natural frequency detection device according to claim 1, characterized in that: The single-point spectrometer includes a collimator (9) for collimating incident light into parallel light, a linear CCD camera (6) for acquiring spectral data, a near-infrared transmission grating (8) for splitting incident light according to wavelength, and a convex lens (7) for focusing light onto the CCD camera; the linear CCD camera (6), the convex lens (7), the near-infrared transmission grating (8) and the collimator (9) are arranged in sequence.

4. A high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection method, characterized in that, The high-precision, high-interference-resistant broadband optical interferometric cantilever beam natural frequency detection device according to any one of claims 1 to 3 includes the following steps: Step S1: The near-infrared broadband light (1) is transmitted through... The single-mode fiber coupler (2) transmits the light to the probe light output port, and after passing through the graded refractive index lens (3), it is split into a reference light and a probe light; the reference light is reflected back by the end face of the graded refractive index lens (3), and the probe light is focused onto the surface of the cantilever beam (4) by the graded refractive index lens (3), and is backscattered back by the surface of the cantilever beam (4); the two beams of light are... The single-mode fiber couplers (2) re-interact and form interference; Step S2: After being collimated by the fiber collimator (9), the interference light is split according to wavelength by the near-infrared transmission grating (8), focused by the convex lens (7), and then collected by the linear CCD camera (6); the collected interference signal The formula is expressed as shown in equation (1): （1） in, is the spectral density function of the light source; t is time; The wavelength of the light source; The starting wavelength of the light source; The wavelength at which the light source terminates; and These represent the reflected light intensities of the probe arm and the reference arm, respectively. The distance between the end face of the graded-index lens and the detection point on the cantilever beam varies with the vibration of the cantilever beam; due to and Since the term is DC and does not contain the sample's position information, these two terms are ignored, resulting in the simplified form of equation (1): （2） Step S3: By combining Fourier transform and the Hanning window energy centroid method, the interference signal acquired in S2 can be calculated to obtain... ; Step S4: Excite the cantilever beam by tapping its fixed end and record a series of interference signals during the cantilever beam's vibration using a linear CCD camera. Then, using the algorithm in S3, the vibration data of the cantilever beam relative to the end face of the graded-index lens can be calculated. ; Step S5: For The natural vibration frequency of the cantilever beam can be obtained by performing a Fourier transform.

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