Phase-shifted micromirror-based three-dimensional detection system for oil abrasive particles

Abstract

This invention provides a three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror, comprising: a light source system, a beam splitter, an abrasive particle imaging system, a phase modulation system, and a detection system; the light source system emits a parallel beam that is incident on the beam splitter; the beam splitter divides the parallel beam into two identical transmitted beams and reflected beams; the reflected beam passes through the abrasive particle imaging system and is incident on the oil abrasive particle detection area, generating a scattered beam that returns to the beam splitter along the original path; the transmitted beam is modulated by the phase modulation system to form a reference beam that returns to the beam splitter along the original path; the reference beam and the scattered beam interfere at the exit position of the beam splitter, forming an interference beam that is then incident on the detection system to obtain interference spectrum information; the amplitude and phase information of the cross-correlation term in the interference intensity expression are extracted from the interference spectrum information to construct a complex function of the interference beam signal, and then a Fourier transform is performed on the complex function to finally obtain a clear three-dimensional reconstructed image of lubricating oil abrasive particles.

Description

Technical Field

[0001] This invention relates to the field of imaging instrument technology, and in particular to a three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror. Background Technology

[0002] Aero engines are critical components of aircraft, with complex internal structures. Under high temperature and high load conditions, they are prone to component wear, seriously threatening operational safety. Of major aircraft accidents caused by mechanical reasons, approximately 40% are due to engine failure, with wear-related failures accounting for over 80%. Therefore, detecting the wear condition of aero engines is of great significance for accelerating their development, ensuring service safety, and preventing catastrophic accidents. Lubricating oil in aero engines is used to lubricate, cool, and clean bearings, gears, and other moving parts. When engine wear occurs, abrasive particles generated on the surfaces of components enter the lubricating oil system, resulting in oil containing abrasive particles of different shapes caused by various types of wear. A sudden increase in the abrasive particle generation rate indicates abnormal engine wear; the morphology and composition of the abrasive particles can identify the location of the wear; and the number, shape, and size of the abrasive particles can determine the type and degree of wear. Therefore, detecting the characteristic parameters such as the number, size, and shape of abrasive particles in the lubricating oil can effectively assess the wear condition of aero engine equipment.

[0003] Current abrasive particle detection methods employ optical, electromagnetic, and chemical methods to obtain various indicators of lubricating oil abrasive particles, thereby determining the wear condition of aero engines. Based on the detection method, these can be divided into offline and online detection. Offline detection typically involves collecting oil samples and then analyzing them using methods such as ferrography, scanning electron microscopy, or atomic emission spectroscopy. While this method offers high accuracy, it is resource-intensive and cannot provide timely information on engine wear conditions. Existing online detection methods primarily use detectors based on electromagnetic induction, which are mostly limited to detecting the size and quantity of lubricating oil particles, failing to acquire shape information. Currently, abrasive particle detection technology is improving in sensitivity and counting reliability, while abrasive particle information is evolving from simple raw signal feature extraction to image analysis and refined feature extraction and classification. Summary of the Invention

[0004] In view of the above problems, the purpose of this invention is to propose a three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror. This system extracts the three-dimensional information of the abrasive particles based on the principle of light interference, solving the problem that traditional detection methods struggle to achieve three-dimensional imaging of abrasive particles. Utilizing a Michelson interference structure, the system acquires the interference spectra of the sample beam and the reference beam, and performs Fourier transform and other processing to achieve three-dimensional imaging of the abrasive particles. Simultaneously, the use of a phase-shifting micromirror structure enables multi-channel static phase modulation, resolving the image and parasitic image problems of single-channel interference imaging. This system offers advantages such as fast imaging speed, high clarity, good stability, and a compact structure.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0006] This invention provides a three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror, comprising: a light source system, a beam splitter, an abrasive particle imaging system, a phase modulation system, and a detection system;

[0007] The light source system is used to emit a parallel beam of light that is incident on the beam splitter;

[0008] The beam splitter divides the parallel beam into two identical transmitted and reflected beams, which are then incident on the phase modulation system and the abrasive imaging system, respectively.

[0009] The abrasive imaging system is used to image lubricating oil samples at different locations on the abrasive detection area, which is used to hold lubricating oil samples extracted from aero engines.

[0010] Abrasive imaging systems include: a scanning mirror and an objective lens;

[0011] After being reflected by the scanning mirror and converged by the objective lens, the reflected beam is incident on the oil abrasive detection area, illuminating the oil abrasive detection area, and interacting with the abrasive particles in the lubricating oil sample to generate a scattered beam containing information about the lubricating oil sample, which returns to the beam splitter along the original path.

[0012] Imaging of lubricating oil samples at different locations is achieved by rotating the scanning mirror and translating the oil abrasive detection area.

[0013] The transmitted beam, modulated by the phase modulation system, travels through different optical paths and returns to the beam splitter via the original path as a reference beam.

[0014] The reference beam and the scattered beam interfere at the exit position of the beam splitter, forming an interference beam that is then incident on the detection system to obtain the interference spectrum information of the interference beam;

[0015] The amplitude and phase information of the cross-correlation terms in the interference intensity expression are extracted from the interference spectrum information to construct a complex function of the interference beam signal. Then, a Fourier transform is performed on the complex function to finally obtain a clear three-dimensional reconstructed image of lubricating oil abrasive particles.

[0016] Preferably, the light source system includes: a light source and a collimating lens;

[0017] The light source is a near-infrared broadband light source. The low-coherence light emitted by the light source is incident on the collimating lens, and after being collimated by the collimating lens, it becomes a parallel beam that is incident on the beam splitter.

[0018] Preferably, the beam splitter is placed at a 45° angle to the optical axis, with a beam splitting ratio of 1:1.

[0019] Preferably, the phase modulation system includes a phase-shifting micromirror;

[0020] The phase-shifting micromirror is composed of steps, each step corresponding to a phase modulation channel. The light beam in each phase modulation channel travels through different optical paths under the modulation effect of the phase-shifting micromirror.

[0021] Phase-shifting micromirrors can be fabricated using the MOEMS process, with each step surface coated with a reflective film.

[0022] Preferably, the detection system includes: a dispersive grating, a cylindrical mirror, and an area array detector;

[0023] The interference beam is dispersed by the dispersion grating, and then refracted by the cylindrical mirror before converging to the area array detector to obtain the interference spectrum information of the interference beams in different phase modulation channels.

[0024] Preferably, the lubricating oil sample is scanned by the rotational motion of a scanning mirror. The scanning mirror is set to be rectangular and rotates around its axis of symmetry. The center of the rectangle coincides with the image-side focal point of the objective lens.

[0025] Preferably, the translational movement of the oil abrasive detection area is achieved by a high-precision stepper motor, and the scanning direction of the scanning mirror is perpendicular to the moving direction of the oil abrasive detection area.

[0026] Preferably, for a beam that has undergone static phase modulation in any phase modulation channel:

[0027] Let the reference beam signal be:

[0028] I R(k) =S R(k) e i2kr

[0029] Among them, S R(k) Let e ​​be the spectral power distribution function of the reference beam. i2kr is the phase, 2r is the optical path length of the reference beam, and k is the wave number;

[0030] Let the scattered beam signal be:

[0031]

[0032] Among them, S S(k，z) Let be the spectral power density function of reflected light from different depth layers of the lubricating oil sample, n be the refractive index of the lubricating oil sample, and r+nz be the optical path length of reflected light at depth z in the lubricating oil sample;

[0033] The interference spectrum signal I(k) generated after the reference beam and the scattered beam interfere is:

[0034]

[0035] The actual area array detector detects the real part I′(k) of the interference spectrum signal I(k), and the expression for the actual interference spectrum signal I′(k) is:

[0036]

[0037] By performing a Fourier transform on the intermediate terms of the actual interference spectral signal I′(k), the depth information of the lubricating oil sample in that channel can be obtained using FFT{I (k)},Right now:

[0038]

[0039] The acquisition of depth information of lubricating oil samples by a single channel is subject to interference from DC terms and cross-correlation terms of reflections from each depth layer. In addition, since the area array detector can only acquire the real part of the interference spectrum signal and cannot acquire the imaginary part, it also leads to conjugate image interference.

[0040] The interference signal I(k) with wavelength λ simplifies to:

[0041]

[0042] in,

[0043] I0 represents the DC term and the self-coherent term;

[0044] A and φ are the amplitude and phase of the interference signal, respectively;

[0045] The real part I′ of the interference signal with wavelength λ is obtained on the area array detector:

[0046]

[0047] Preferably, when the number of steps in the phase-shifting micromirror is n: the spatial arrangement of the steps can generate a phase shift of π / 2 in each phase modulation channel, and the interference spectrum signals of n channels at the test point can be obtained through a single imaging: the amplitude A and phase of the interference signal can be solved. By constructing a complex function of the interference signal and performing a Fourier transform on the complex function of the interference signal, the depth information of the lubricating oil abrasive particles can be obtained.

[0048] Compared with existing technologies, this invention extracts the three-dimensional information of lubricating oil abrasive particles based on the principle of light interference, solving the problem that traditional detection methods are difficult to achieve three-dimensional imaging of abrasive particles. It utilizes a Michelson interference structure to obtain the interference spectrum of the scattered beam and the reference beam, and performs Fourier transform and other processing to achieve three-dimensional imaging of the abrasive particles. Simultaneously, a phase-shifting micromirror structure is employed to achieve static phase modulation of the same test point across multiple channels in a single operation, significantly improving the system's imaging efficiency. It solves the problems of mirror images and parasitic images in single-channel imaging, and has the advantages of fast imaging speed, high clarity, good stability, and compact structure. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of a three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror, provided according to an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of the optical path when a grating generates dispersion according to an embodiment of the present invention.

[0051] Figure 3 This is a schematic diagram of the spectral information distribution of each channel of the area array detector provided in an embodiment of the present invention.

[0052] Figure 4 This is a schematic diagram of the optical path for oscillating scanning imaging provided according to an embodiment of the present invention.

[0053] The reference numerals in the accompanying drawings include: light source 1, collimating lens 2, beam splitter 3, scanning mirror 4, objective lens 5, oil abrasive detection area 6, phase-shifting micromirror 7, dispersive grating 8, cylindrical mirror 9, and area array detector 10. Detailed Implementation

[0054] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0056] Figure 1 A schematic diagram of the structure of a three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror provided according to an embodiment of the present invention is shown.

[0057] like Figure 1As shown, the three-dimensional detection system for lubricating oil abrasive particles based on phase-shifting micromirrors provided in this embodiment of the invention adopts a Michelson interferometer structure and includes: a light source system, a beam splitter 3, an abrasive particle imaging system, a phase modulation system, and a detection system.

[0058] The light source system includes: light source 1 and collimating lens 2; light source 1 is a broadband light source, which can be a near-infrared point light source with strong penetration capability of lubricating oil. The low coherence light emitted is incident on collimating lens 2, and after being collimated by collimating lens 2, it becomes a parallel beam and is incident on beam splitter 3.

[0059] The beam splitter is placed at a 45° angle to the optical axis, with a splitting ratio of 1:1. Beam splitter 3 splits the parallel beam into two identical transmitted and reflected beams, which are then incident on the phase modulation system and the abrasive imaging system, respectively.

[0060] The abrasive imaging system is used to image lubricating oil samples on the abrasive detection area 6, which holds lubricating oil samples extracted from aero-engines. The abrasive imaging system includes: a scanning mirror 4 and an objective lens 5;

[0061] The phase modulation system includes a phase-shifting micromirror 7. The phase-shifting micromirror 7 consists of multiple steps, each corresponding to a phase modulation channel. The beam in each phase modulation channel travels through different optical paths under the modulation effect of the phase-shifting micromirror. The phase-shifting micromirror 7 can be fabricated using MOEMS technology. Each step surface is coated with a reflective film, and each step corresponds to a phase modulation channel. Static phase modulation is achieved through the different spatial positions of each step, eliminating the need for additional movable structures.

[0062] In one embodiment of the present invention, the phase-shifting micromirror 7 has 5 steps.

[0063] in,

[0064] The reflected beam is reflected by the scanning mirror 4 and converged by the objective lens 5 before being incident on the oil abrasive detection area 6, illuminating the oil abrasive detection area 6. After interacting with the abrasive particles in the lubricating oil, it generates a scattered echo (sample light). The scattered beam carrying the lubricating oil sample information returns to the beam splitter 3 along the original path.

[0065] The transmitted beam is reflected after passing through the stepped surfaces at different spatial positions of the phase-shifting micromirror 7. Under the modulation effect of each step of the phase-shifting micromirror 7, it travels through different optical paths and returns to the beam splitter 3 as a reference beam.

[0066] The reference beam and the scattered beam interfere at the exit position of beam splitter 3, forming an interference beam that is then incident on the detection system.

[0067] The detection system includes: a dispersive grating 8, a cylindrical mirror 9, and an area array detector 10.

[0068] Figure 2 A schematic diagram of the optical path when a grating generates dispersion according to an embodiment of the present invention is shown.

[0069] like Figure 2 As shown, the interference beam is dispersed by the dispersion grating 8, and then converged to the area array detector 10 after being refracted by the cylindrical mirror 9 to obtain the interference spectrum information of the interference beams of different phase modulation channels.

[0070] Figure 3 A schematic diagram of the spectral information distribution of each channel of the area array detector provided according to an embodiment of the present invention is shown.

[0071] like Figure 3 As shown, the array detector receives interference information from five channels of the lubricating oil sample in the direction of parallel grating fringes. The grayscale output of each row of pixels in each channel of the array detector is the same. The average grayscale value of the above pixels can be used as the initial data for three-dimensional reconstruction to reduce the influence of random errors. In the direction of perpendicular grating fringes, the array detector receives spectral information from five channels.

[0072] The amplitude and phase information of the cross-correlation terms in the interference intensity expression are extracted from the interference spectrum to construct a complex function of the interference beam signal. Then, Fourier transform is performed on the reconstructed complex function to eliminate parasitic terms and mirror images, resulting in a clear three-dimensional reconstructed image of lubricating oil abrasive particles.

[0073] The above calculation process includes:

[0074] For a beam that has undergone static phase modulation in a phase modulation channel of the three-dimensional detection system provided by this invention, its interference spectrum is obtained after the interference of the reference beam and the scattered beam. Let the reference beam signal be:

[0075] I R(k) =S R(k) e i2kr

[0076] Among them, S R(k) Let e ​​be the spectral power distribution function of the reference beam. i2kr is the phase, 2r is the optical path length of the reference light, and k is the wave number.

[0077] Let the signal of the scattered beam reflected back from the lubricating oil sample be:

[0078]

[0079] Among them, S S(k，z) Let be the spectral power density function of reflected light from different depth layers of the lubricating oil sample, n be the refractive index of the sample, and r+nz be the optical path length of reflected light at depth x in the sample.

[0080] The interference spectrum signal I(k) generated after the reference beam and the scattered beam interfere is:

[0081]

[0082] The actual area array detector detects the real part I′(k) of the interference spectrum signal I(k), and the expression for the actual interference spectrum signal I′(k) is:

[0083]

[0084] The above formula consists of three terms: the first term is the DC component, the second term is the sum of multiple cosine functions, which contains the depth structure information of the lubricating oil sample, and the third term is the mutual interference between different reflective layers of the lubricating oil sample.

[0085] By performing a Fourier transform on the second term of the actual interference spectral signal I′(k), the depth information of the lubricating oil sample in that channel can be obtained using FFT{I (k)},Right now:

[0086]

[0087] The acquisition of depth information of lubricating oil samples by a single channel is subject to interference from DC terms and cross-correlation terms of reflections from each depth layer. In addition, since the area array detector can only acquire the real part of the interference spectrum signal and cannot acquire the imaginary part, it also leads to conjugate image interference.

[0088] Then the interference signal I(k) with wavelength λ can be simplified as:

[0089]

[0090] in,

[0091] I0 represents the DC term and the self-coherent term, while A and φ represent the amplitude and phase of the interference signal, respectively. Only by calculating these two terms can the complex function of the interference signal be reconstructed, thereby eliminating interference such as mirror images and parasitic images.

[0092] The real part I′ of the interference signal with wavelength λ is obtained on the area array detector:

[0093]

[0094] Through the modulation effect of the phase-shifting micromirror of the present invention, when the number of steps in the phase-shifting micromirror is n (n>1), the spatial arrangement of the steps can make each modulation channel generate a phase shift of π / 2, and the interference spectrum signal of n channels of the test point can be obtained in one imaging.

[0095] Taking a five-step scale as an example, the spatial arrangement of the steps can cause each modulation channel to generate a phase shift of π / 2. In this case, the interference spectral signals of all five channels at the point under test can be obtained in a single imaging operation.

[0096]

[0097] The amplitude A and phase of the cross-correlation term in the expression for interference light intensity can be directly obtained from the above equation.

[0098]

[0099]

[0100] Figure 4 A schematic diagram of the oscillating scanning imaging optical path provided according to an embodiment of the present invention is shown.

[0101] To acquire a three-dimensional image of the entire oil abrasive detection area 6, the three-dimensional detection system provided by this invention requires a scanning mirror 4 to scan the lubricating oil sample, and a high-precision stepper motor to move the oil abrasive detection area 6. The scanning direction of the scanning mirror 4 is perpendicular to the moving direction of the oil abrasive detection area 6. Figure 4 As shown, the scanning mirror 4 is set as a rectangle and rotates around its axis of symmetry. The center of the rectangle coincides with the image-side focal point of the objective lens 5, realizing scanning imaging at different positions in the oil abrasive detection area 6. Finally, the depth information at different positions is used for three-dimensional reconstruction to obtain the three-dimensional structural information of all abrasive particles in the oil abrasive detection area 6.

[0102] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

[0103] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror, characterized in that, include: Light source system, beam splitter, abrasive particle imaging system, phase modulation system, and detection system; The light source system is used to emit a parallel beam of light that is incident on the beam splitter; The beam splitter divides the parallel beam into two identical transmitted beams and reflected beams, which are respectively incident on the phase modulation system and the abrasive imaging system. The abrasive imaging system is used to image lubricating oil samples at different locations on the abrasive detection area, which is used to hold lubricating oil samples extracted from aero engines. Abrasive imaging systems include: a scanning mirror and an objective lens; The reflected beam, after being reflected by the scanning mirror and converged by the objective lens, is incident on the oil abrasive detection area, illuminating the oil abrasive detection area. After interacting with the abrasive particles in the lubricating oil sample, it generates a scattered beam carrying the information of the lubricating oil sample, which returns to the beam splitter along the original path. Imaging of the lubricating oil sample at different locations is achieved through the rotational motion of the scanning mirror and the translational motion of the oil abrasive detection area. The transmitted beam, modulated by the phase modulation system, travels through different optical paths and returns to the beam splitter via the original path as a reference beam. The phase modulation system includes a phase-shifting micromirror. Each phase-shifting micromirror is composed of steps, each step corresponding to a phase modulation channel. The beam in each phase modulation channel travels through different optical paths under the modulation of the phase-shifting micromirror. When the number of steps in the phase-shifting micromirror is n: the spatial arrangement of the steps allows each phase modulation channel to generate... The phase shift is obtained by acquiring the interference spectral signals of n channels at the test point through a single imaging operation: The reference beam and the scattered beam interfere at the exit position of the beam splitter, forming an interference beam which is then incident on the detection system to obtain the interference spectrum information of the interference beam; The amplitude and phase information of the cross-correlation terms in the interference intensity expression are extracted from the interference spectrum information to construct a complex function of the interference beam signal. Then, a Fourier transform is performed on the complex function to finally obtain a clear three-dimensional reconstructed image of lubricating oil abrasive particles.

2. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 1, characterized in that, The light source system includes: a light source and a collimating lens; The light source is a near-infrared broadband light source. The low-coherence light emitted by the light source is incident on the collimating lens, and after being collimated by the collimating lens, it becomes a parallel beam that is incident on the beam splitter.

3. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 2, characterized in that, The beam splitter is placed at a 45° angle to the optical axis, with a beam splitting ratio of 1:

1.

4. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 3, characterized in that, The phase-shifting micromirror can be fabricated using the MOEMS process, with each step surface coated with a reflective film.

5. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 4, characterized in that, The detection system includes: a dispersive grating, a cylindrical mirror, and an area array detector; The interference beam is dispersed by the dispersion grating, and then refracted by the cylindrical mirror before converging into the area array detector to obtain the interference spectrum information of the interference beams in different phase modulation channels.

6. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 5, characterized in that, The lubricating oil sample is scanned by the rotation of a scanning mirror, which is rectangular and rotates around its axis of symmetry. The center of the rectangle coincides with the image-side focal point of the objective lens.

7. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 6, characterized in that, The translational movement of the oil abrasive detection area is achieved by a high-precision stepper motor, and the scanning direction of the scanning mirror is perpendicular to the moving direction of the oil abrasive detection area.

8. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 7, characterized in that, For any phase-modulated beam in any phase-modulated channel: Let the reference beam signal be: in, Let be the spectral power distribution function of the reference beam. For phase, The optical path length of the reference beam. Wave number; Let the signal of the scattered beam be: in, Let be the spectral power density function of the reflected light from different depth layers of the lubricating oil sample. The refractive index of the lubricating oil sample is... The depth of the lubricating oil sample is The optical path length of the reflected light; The interference spectrum signal generated after the reference beam and the scattered beam interfere. for: The area array detector actually detects an interferometric spectral signal. real part The actual interference spectral signal The expression is: For actual interferometric spectral signals By performing a Fourier transform on the intermediate term in the equation, the depth information of the lubricating oil sample in that channel can be obtained. ,Right now: The acquisition of depth information of lubricating oil samples by a single channel is subject to interference from DC terms and cross-correlation terms of reflections from each depth layer. In addition, since the area array detector can only acquire the real part of the interference spectrum signal and cannot acquire the imaginary part, it also leads to conjugate image interference. Then the wavelength is Interference signal Simplified to: in, These are DC terms and self-coherent terms; φ and φ represent the amplitude and phase of the interference signal, respectively; The wavelength obtained on the array detector is... The real part of the interference signal : 。 9. The three-dimensional detection system for lubricating oil abrasive particles based on a phase-shifting micromirror according to claim 8, characterized in that, Solve for the amplitude of the interference signal and phase By constructing a complex function of the interference signal and performing a Fourier transform on the complex function of the interference signal, the depth information of the lubricating oil abrasive particles can be obtained.

Images