Curing monitoring-oriented phase contrast optical coherence tomography adaptive step length adjusting method

Abstract

The invention discloses a curing monitoring-oriented phase contrast optical coherence tomography adaptive step length adjusting method, which is used for adaptively adjusting a step length in a curing process, so that the problems of large error accumulation in a slow rate change interval, too large step length selection and low speed change rate caused by too small step length selection in incremental calculation are avoided. And the measurement accuracy of the phase-sensitive optical coherence tomography technology in practical application can be effectively improved, and high-precision monitoring of the curing process is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of non-contact curing monitoring, and in particular to a phase contrast optical coherence tomography adaptive step length adjustment method for curing monitoring. Background Art

[0002] Phase-sensitive optical coherence tomography (PCT) is currently the only method available for deep-resolved, full-field measurement of the curing process. This technique uses OCT to acquire phase-frequency information from interference spectra and reconstructs the out-of-plane displacement and strain fields by calculating the differential phase before and after deformation. This technique offers the advantages of being non-destructive, high-resolution, and highly sensitive, and is widely used in fields such as materials science, aerospace, and biomedicine. However, its range of measurement limits its ability to analyze the curing process. When the material undergoes excessive curing deformation in the depth direction, the post-deformation phase decorrelates, causing a sharp drop in the signal-to-noise ratio of the differential phase calculation. This results in inaccurate reconstruction of the displacement and strain fields, thus limiting its monitoring range during the curing process.

[0003] In order to overcome this limitation and realize the monitoring of the whole process of material curing, the traditional method is mainly through incremental calculation. By converting the spatially unmeasurable strain into the temporally measurable strain, the strain difference between any frame and its previous frame is calculated and accumulated, thereby realizing high-sensitivity tomographic strain measurement with depth resolution of the curing process. In order to avoid the phase decorrelation caused by setting the frame spacing (step size) too large, the traditional incremental calculation method generally sets the step size to a small constant. However, when the step size is too small, it may lead to large error accumulation. Therefore, considering that the curing rate has extremely strong nonlinear characteristics during the curing process, the peak and median values ​​of the curing rate differ by 2-3 orders of magnitude during the entire curing cycle. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring. By adaptively adjusting the step size during the curing process, it is avoided that the incremental calculation step size is too small, resulting in large error accumulation in the interval of slow rate change, and the step size is too large, resulting in the inability to meet the dynamic measurement range in the interval of drastic rate change. The method can effectively improve the measurement accuracy of phase-sensitive optical coherence tomography technology in practical applications and realize high-precision monitoring of the curing process.

[0005] To achieve the above objectives, the technical solutions provided by the present invention are:

[0006] An adaptive step-size adjustment method for phase contrast optical coherence tomography for curing monitoring includes:

[0007] S1, preset initial step size Δt0, strain rate threshold T, material refractive index n, and measurable upper limit of phase gradient in the depth z direction

[0008] S2, during the polymer curing process, the OCT system is used to detect the polymer at any time t after the initial time t1 = t0 + Δt0. n Collect interference spectrum S n , accumulate the step length Δt at the current moment n After that, in t n+1 =t n +Δt n Collect interference spectrum S at all times n+1 ;

[0009] S3. Calculate t n Time and t n+1 Phase difference distribution at each moment

[0010] S4, based on t n Time and t n+1 Phase difference distribution at each moment Reconstruct the contraction strain field ε during the solidification process n+1 (x,z);

[0011] S5. Based on the contraction strain field ε n+1 (x,z), reconstructing the shrinkage strain rate field during the solidification process

[0012] S6. Determine the maximum measurable strain rate at the current moment

[0013] S7. Determine the maximum theoretical strain rate at the current moment

[0014] S8, combined with the maximum measurable strain rate at the current moment The maximum theoretical strain rate at the current moment And the strain rate threshold T estimates the next step length Δt n+1 .

[0015] Furthermore, step S1 includes:

[0016] If the material type and curing light source characteristic parameters are known, the initial step size Δt0, strain rate threshold T, material refractive index n and the upper limit of the phase gradient measurable in the depth z direction are preset based on the material type and curing light source characteristic parameters.

[0017] If the material type and curing light source characteristic parameters are unknown, the minimum sampling step of the OCT system is used as the initial step Δt0, and the strain rate threshold T is set to 0.5, the refractive index n of the material is set to 1.45, and the upper limit of the phase gradient in the depth z direction is set to 0. The initial value of is set to 0.4π.

[0018] Furthermore, step S3 includes:

[0019] The phase-frequency information is demodulated from the interference spectrum signal according to Fourier transform, and t is calculated based on the phase-frequency information. n Time and t n+1 Phase difference distribution at each moment

[0020]

[0021] in, Indicates the pixel point (x, z) at t n The phase value at the moment, Indicates the pixel point (x, z) at t n+1 Phase value at the moment.

[0022] Furthermore, step S4 includes:

[0023] In order to obtain the phase difference distribution In the case of , by calculating the spatial gradient of the phase difference along the z direction, t n+1 Time relative to t n The contraction strain field ε at the moment n+1 (x,z):

[0024]

[0025] Among them, λ c represents the central wavelength of the interference light, δz is the depth resolution, and the value of the shrinkage strain represents the degree of curing at the pixel point (x, z).

[0026] Furthermore, step S5 includes:

[0027] In the obtained contraction strain field ε n+1 (x,z), combined with the current step length Δt n , calculate t n+1 Time relative to t n Strain rate field at time

[0028]

[0029] Furthermore, step S6 includes:

[0030] In the shrinkage strain rate field After that, traverse its matrix and determine when the step size is Δt n When t n+1 Time relative to t n The maximum measurable strain rate at time t n The moment is the current moment.

[0031] Furthermore, step S7 includes:

[0032] The upper limit of the phase gradient measurable in the z direction at the acquisition depth Then, combined with the optical calibration coefficient, calculate t n+1 Time relative to t n The theoretical maximum measurable strain rate at time

[0033]

[0034] ε n-max Indicates t n+1 Time relative to t n The theoretical maximum measurable strain at time λ c represents the central wavelength of the interference light, δz is the depth resolution; t n The moment is the current moment;

[0035] The upper limit of the measurable phase gradient in the depth z direction That is, the maximum phase change between adjacent pixels that the system can distinguish:

[0036]

[0037] Represents the phase difference of the pixel in the z+δz direction, Indicates the phase difference of the pixel in the z direction.

[0038] Furthermore, combined with the maximum measurable strain rate at the current moment The maximum theoretical strain rate at the current moment And the strain rate threshold T estimates the next step length Δt n+1 The formula is as follows:

[0039]

[0040] Compared with the existing technology, the principles and advantages of this technical solution are as follows:

[0041] This technical solution adaptively adjusts the step size during the curing process to avoid the problems of selecting a too small incremental calculation step size, which leads to large error accumulation in the interval of slow rate change, and selecting a too large step size, which leads to the inability to meet the dynamic measurement range in the interval of drastic rate change. This can effectively improve the measurement accuracy of phase-sensitive optical coherence tomography technology in practical applications and achieve high-precision monitoring of the curing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the services required for use in the embodiments or the prior art descriptions 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 these drawings without paying any creative work.

[0043] Figure 1 This is a principle flow chart of the phase contrast optical coherence tomography adaptive step length adjustment method for curing monitoring according to the present invention;

[0044] Figure 2 Schematic diagram of collecting interference spectra by an OCT system in the phase-contrast optical coherence tomography adaptive step-size adjustment method for curing monitoring of the present invention (L1-L3 are convex lenses; R is a reference surface; M is a reflective mirror; and G is a reflective diffraction grating). DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with specific embodiments:

[0046] like Figure 1 As shown, the phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring described in this embodiment includes:

[0047] S1, preset initial step size Δt0, strain rate threshold T, material refractive index n, and measurable upper limit of phase gradient in the depth z direction

[0048] The specific process of this step includes:

[0049] If the material type and curing light source characteristic parameters are known, the initial step size Δt0, strain rate threshold T, material refractive index n and the upper limit of the phase gradient measurable in the depth z direction are preset based on the material type and curing light source characteristic parameters.

[0050] If the material type and curing light source characteristic parameters are unknown, the minimum sampling step of the OCT system is used as the initial step Δt0, and the strain rate threshold T is set to 0.5, the refractive index n of the material is set to 1.45, and the upper limit of the phase gradient in the depth z direction is set to 0. The initial value of is set to 0.4π.

[0051] S2, during the polymer curing process, the OCT system is used to detect the polymer at any time t after the initial time t1 = t0 + Δt0. n Collect interference spectrum S n , accumulate the step length Δt at the current moment n After that, in t n+1 =t n +Δt n Collect interference spectrum S at all times n+1 ;

[0052] like Figure 2 As shown in Figure 1, the OCT system consists of a low-coherence broadband light source, a fiber coupler, a reference plane (R), a reflective diffraction grating (G), convex lenses (L1-L3), a mirror (M), and a linear scan camera (CCD). Light from the low-coherence light source is split into a reference arm and a sample arm via a fiber coupler. The reflected light from the reference and sample arms is recombined at the fiber coupler to produce interference signals. These interference signals are captured by the linear scan camera and processed using a fast Fourier transform.

[0053] S3, demodulate the phase-frequency information from the interference spectrum signal according to Fourier transform, and calculate t based on the phase-frequency information n Time and t n+1 Phase difference distribution at each moment

[0054]

[0055] in, Indicates the pixel point (x, z) at t n The phase value at the moment, Indicates the pixel point (x, z) at t n+1 Phase value at the moment.

[0056] S4, based on t n Time and t n+1 Phase difference distribution at each moment Reconstruct the contraction strain field ε during the solidification process n+1 (x,z);

[0057] This step is specifically as follows:

[0058] In order to obtain the phase difference distribution In the case of , by calculating the spatial gradient of the phase difference along the z direction, t n+1 Time relative to t n The contraction strain field ε at the moment n+1 (x,z):

[0059]

[0060] Among them, λ c represents the central wavelength of the interference light, δz is the depth resolution, and the value of the shrinkage strain represents the degree of curing at the pixel point (x, z).

[0061] S5. Based on the contraction strain field ε n+1 (x,z), reconstructing the shrinkage strain rate field during the solidification process

[0062] This step is specifically as follows:

[0063] In the obtained contraction strain field ε n+1 (x,z), combined with the current step length Δt n , calculate t n+1 Time relative to t n Strain rate field at time

[0064]

[0065] S6, after obtaining the shrinkage strain rate field After that, traverse its matrix and determine when the step size is Δt n When t n+1 Time relative to t n The maximum measurable strain rate at time t n The moment is the current moment.

[0066] S7. Determine the maximum theoretical strain rate at the current moment

[0067] This step is specifically as follows:

[0068] The upper limit of the phase gradient measurable in the z direction at the acquisition depth Then, combined with the optical calibration coefficient, calculate t n+1 Time relative to t n The theoretical maximum measurable strain rate at time

[0069]

[0070] ε n-max Indicates t n+1 Time relative to t n The theoretical maximum measurable strain at time λ c represents the central wavelength of the interference light, δz is the depth resolution; t n The moment is the current moment;

[0071] The upper limit of the measurable phase gradient in the depth z direction That is, the maximum phase change between adjacent pixels that the system can distinguish:

[0072]

[0073] Represents the phase difference of the pixel in the z+δz direction, Indicates the phase difference of the pixel in the z direction.

[0074] S8, combined with the maximum measurable strain rate at the current moment The maximum theoretical strain rate at the current moment And the strain rate threshold T estimates the next step length Δt n+1 , the formula is as follows:

[0075]

[0076] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any changes made based on the shape and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring, characterized in that: include: S1, preset initial step size Δt0, strain rate threshold T, material refractive index n, and measurable upper limit of phase gradient in the depth z direction S2, during the polymer curing process, the OCT system is used to detect the polymer at any time t after the initial time t1 = t0 + Δt0. n Collect interference spectrum S n , accumulate the step length Δt at the current moment n After that, in t n+1 =t n +Δt n Collect interference spectrum S at all times n+1 ; S3. Calculate t n Time and t n+1 Phase difference distribution at each moment S4, based on t n Time and t n+1 Phase difference distribution at each moment Reconstruct the contraction strain field ε during the solidification process n+1 (x,z); S5. Based on the contraction strain field ε n+1 (x,z), reconstructing the shrinkage strain rate field during the solidification process S6. Determine the maximum measurable strain rate at the current moment S7. Determine the maximum theoretical strain rate at the current moment S8, combined with the maximum measurable strain rate at the current moment The maximum theoretical strain rate at the current moment And the strain rate threshold T estimates the next step length Δt n+1 .

2. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Step S1 includes: If the material type and curing light source characteristic parameters are known, the initial step size Δt0, strain rate threshold T, material refractive index n and the upper limit of the phase gradient measurable in the depth z direction are preset based on the material type and curing light source characteristic parameters. If the material type and curing light source characteristic parameters are unknown, the minimum sampling step of the OCT system is used as the initial step Δt0, and the strain rate threshold T is set to 0.5, the refractive index n of the material is set to 1.45, and the upper limit of the phase gradient in the depth z direction is set to 0. The initial value of is set to 0.4π.

3. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Step S3 includes: The phase-frequency information is demodulated from the interference spectrum signal according to Fourier transform, and t is calculated based on the phase-frequency information. n Time and t n+1 Phase difference distribution at each moment in, Indicates the pixel point (x, z) at t n The phase value at the moment, Indicates the pixel point (x, z) at t n+1 Phase value at the moment.

4. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Step S4 includes: In order to obtain the phase difference distribution In the case of , by calculating the spatial gradient of the phase difference along the z direction, t n+1 Time relative to t n The contraction strain field ε at the moment n+1 (x,z): Among them, λ c represents the central wavelength of the interference light, δz is the depth resolution, and the value of the shrinkage strain represents the degree of curing at the pixel point (x, z).

5. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Step S5 includes: In the obtained contraction strain field ε n+1 (x,z), combined with the current step length Δt n , calculate t n+1 Time relative to t n Strain rate field at time 6. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Step S6 includes: In the shrinkage strain rate field After that, traverse its matrix and determine when the step size is Δt n When t n+1 Time relative to t n The maximum measurable strain rate at time t n The moment is the current moment.

7. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Step S7 includes: The upper limit of the phase gradient measurable in the z direction at the acquisition depth Then, combined with the optical calibration coefficient, calculate t n+1 Time relative to t n The theoretical maximum measurable strain rate at time ε n -max means t n+1 Time relative to t n The theoretical maximum measurable strain at time λ c represents the central wavelength of the interference light, δz is the depth resolution; t n The moment is the current moment; The upper limit of the measurable phase gradient in the depth z direction That is, the maximum phase change between adjacent pixels that the system can distinguish: Represents the phase difference of the pixel in the z+δz direction, Indicates the phase difference of the pixel in the z direction.

8. The phase contrast optical coherence tomography adaptive step size adjustment method for curing monitoring according to claim 1, characterized in that: Combined with the maximum measurable strain rate at the current moment The maximum theoretical strain rate at the current moment And the strain rate threshold T estimates the next step length Δt n+1 The formula is as follows:

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