OCT (optical coherence tomography)-based fusion depth monitoring system and method capable of automatically following laser welding focal plane

Abstract

The invention relates to the technical field of laser welding, and provides a fusion depth monitoring system and method based on an OCT automatic following laser welding focal plane, and the system comprises a light source, an optical fiber coupler, a sample arm, a reference arm, a spectrometer and a data processing module; the light source is used for generating broadband low-coherence light; the optical fiber coupler is used for splitting the broadband low-coherence light into sample arm light and reference arm light, and synthesizing the returned sample arm light and reference arm light into an interference light signal; the sample arm is used for guiding and focusing the sample arm light to a target area in the laser welding process to form returned sample arm light; the reference arm is used for reflecting the reference arm light through a reflection assembly to form returned reference arm light; the spectrograph is used for carrying out spectrum analysis on the interference light signal; the data processing module is used for calculating the welding penetration depth in real time according to the spectrum analysis result. According to the invention, through integration of the high-response linear motor and the closed-loop control algorithm, rapid matching of the optical path of the reference arm is realized.

Description

Technical Field

[0001] This invention belongs to the field of laser welding technology, and in particular relates to a system and method for monitoring the penetration depth of laser welding based on OCT automatic tracking of the focal plane of laser welding. Background Technology

[0002] Laser welding, as a high-precision and high-efficiency welding technology, is widely used in new energy, automotive manufacturing, and aerospace fields. Real-time monitoring of weld penetration is crucial during laser welding, directly affecting weld quality and product reliability. Optical coherence tomography (OCT) technology, due to its high resolution and non-contact characteristics, is used for online detection of laser welding penetration.

[0003] However, traditional OCT systems have limitations in dynamic welding processes. For example, during welding, the workpiece position may shift, and the welding focus may change accordingly, causing a mismatch between the OCT probe optical path and the reference arm optical path, thus leading to measurement errors.

[0004] In existing technologies, OCT reference arms are mostly fixed or manually adjusted, which cannot track changes in workpiece position in real time and make it difficult to guarantee measurement accuracy and signal-to-noise ratio. Summary of the Invention

[0005] In view of the above-mentioned deficiencies of the prior art, the present invention first proposes a penetration depth monitoring system based on OCT automatic tracking of the focal plane of laser welding, comprising: Light source, fiber optic coupler, sample arm, reference arm, spectrometer, and data processing module; The light source is used to generate broadband, low-coherence light; The fiber coupler is used to split the broadband low-coherence light into sample arm light and reference arm light, and to combine the returned sample arm light and reference arm light into an interference light signal. The sample arm is used to guide and focus the sample arm light onto the target area of ​​the laser welding process, forming a returned sample arm light; The reference arm is used to reflect the reference arm light through the reflection component to form the returned reference arm light; The spectrometer is used for spectral analysis of the interference light signal; The data processing module is used to calculate the welding penetration depth in real time based on the spectral analysis results.

[0006] Preferably, the reflective component is driven by a linear motor with a displacement accuracy of ±1μm and a response time of less than 10ms from receiving the control command to completing the displacement.

[0007] Preferably, the scanning rate of the spectrometer for spectral analysis is not less than 120 kHz.

[0008] Preferably, the system further includes a control unit, comprising: The control unit is used to receive external sensing signals and drive the reflective component to automatically adjust the optical path of the reference arm according to the external sensing signals.

[0009] Preferably, the control unit is configured to perform closed-loop feedback control, including: The target displacement of the reflective component is calculated based on the external sensing signal. Output control commands to drive the reflective component to move to the target position; The system receives a feedback signal indicating the actual position of the reflective component and compares it with the target position for correction.

[0010] Preferably, the control cycle for the closed-loop feedback control performed by the control unit is no more than 5ms.

[0011] Preferably, the external sensing signal is provided by a laser displacement sensor and / or a vision sensor for real-time monitoring of the workpiece surface height or welding focus position.

[0012] This invention further provides a method for monitoring weld penetration based on OCT automatic following of the focal plane of laser welding, applied to the aforementioned system for monitoring weld penetration based on OCT automatic following of the focal plane of laser welding, comprising: S1: Generates broadband low-coherence light; S2: Split the broadband low-coherence light into sample arm light and reference arm light, and combine the returned sample arm light and reference arm light into an interference light signal; S3: Guide and focus the sample arm light onto the target area of ​​the laser welding process to form a returning sample arm light; S4: The reference arm light is reflected by the reflective component to form the returned reference arm light; S5: Perform spectral analysis on the interference light signal; S6: Calculate the welding penetration depth in real time based on the spectral analysis results.

[0013] Beneficial effects: 1. This application, through the rapid response of the linear motor and control unit, can actively and in real time adjust the optical path of the reference arm, effectively overcoming the changes in the focal position caused by workpiece vibration, thermal deformation or clamping error, and ensuring that the OCT interference signal is always in the best state. 2. This application adopts closed-loop feedback control based on the optical path matching principle, combined with a linear motor with ±1μm accuracy. The system can not only accurately measure the depth of the molten pool, but also calculate the height of the reference surface of the workpiece in real time through the synchronous information of the reference arm position, thereby directly outputting a high-precision (such as ±5μm) absolute molten depth value. The measurement results are more stable and more direct. 3. This application integrates high-scanning-rate spectral domain OCT with a millisecond-level response automatic adjustment mechanism, resulting in a short control cycle. This allows it to perfectly match high-speed continuous processing such as welding of new energy battery modules, enabling true online, real-time, and non-contact penetration monitoring, and providing a powerful process monitoring tool for welding quality control. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the system structure of a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of a linear motor drive reference arm structure according to a preferred embodiment of the present invention; Figure 3 This is a schematic diagram of the system control logic flow of a preferred embodiment of the present invention. Detailed Implementation

[0015] The embodiments of the present invention will be described in detail below. The embodiments described below are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the embodiments described below.

[0016] This invention designs a penetration depth monitoring system based on OCT (Optical Characteristic Telemetry) to automatically follow the focal plane of laser welding, such as... Figure 1-3 As shown, the technical solution specifically includes: Light source, fiber optic coupler, sample arm, reference arm, spectrometer, and data processing module; The light source is used to generate broadband, low-coherence light; Fiber optic couplers are used to split broadband low-coherence light into sample arm light and reference arm light, and combine the returned sample arm light and reference arm light into an interference light signal; The sample arm is used to guide and focus the sample arm light onto the target area of ​​the laser welding process, forming a returned sample arm light. The reference arm is used to reflect the reference arm light through the reflective component to form the returned reference arm light; A spectrometer is used to perform spectral analysis on interference light signals; The data processing module is used to calculate the weld penetration depth in real time based on the spectral analysis results.

[0017] Specifically, the fiber coupler is a 2×2 fiber coupler, which is used to split the incident light into sample arm light and reference arm light, and to combine and interfere the two optical signals returning from the sample arm and reference arm, and finally guide the resulting interference signal to the spectrometer.

[0018] In addition, the sample arm includes a collimating mirror, a scanning galvanometer, and a focusing lens, which are used to focus the sample arm light onto the molten pool and keyhole area generated during the laser welding process, and collect the backscattered light from this area as the returned sample arm light.

[0019] In addition, the data processing module processes the spectral data output by the spectrometer in real time, extracts the weld penetration information, and synchronizes the penetration information with the real-time position data of the reference arm to generate a real-time penetration curve and reference surface height information.

[0020] Preferably, the reflective component is driven by a linear motor with a displacement accuracy of ±1μm and a response time of less than 10ms from receiving the control command to completing the displacement.

[0021] Specifically, the reference arm includes a reflector assembly, which is a reflector. The reflector is rigidly connected to the output shaft of a linear motor via a coupling and can move linearly along a guide rail to provide a reference optical path. Its optical path length can be precisely adjusted by the linear motor.

[0022] In addition, a linear motor with an accuracy of ±1μm and a stroke of 120mm is selected. Its driver is electrically connected to the control unit and is used to directly drive the reflector of the reference arm to make fast and accurate linear movements along the guide rail in order to achieve real-time compensation of optical path.

[0023] Preferably, the scanning rate of the spectrometer for spectral analysis is not less than 120 kHz.

[0024] Specifically, the spectrometer receives interference signals from the fiber optic coupler, performs spectral analysis to obtain depth domain information, and outputs the data to the data processing module.

[0025] Preferably, the system further includes a control unit, comprising: The control unit is used to receive external sensing signals and drive the reflective component to automatically adjust the optical path of the reference arm according to the external sensing signals.

[0026] Preferably, the control unit is configured to perform closed-loop feedback control, including: Calculate the target displacement of the reflective component based on external sensor signals; Output control commands to drive the reflective component to the target position; It receives feedback signals of the actual position of the reflective component and compares them with the target position for correction.

[0027] Preferably, the control cycle for the control unit to perform closed-loop feedback control is no more than 5ms.

[0028] Preferably, the external sensing signal is provided by a laser displacement sensor and / or a vision sensor for real-time monitoring of the workpiece surface height or welding focus position.

[0029] Specifically, the control unit receives signals from the laser displacement sensor or vision sensor that characterize the position of the welding focus or the change in the height of the workpiece surface, calculates the amount of displacement that the reference arm needs to compensate according to the preset control algorithm, and outputs the corresponding control commands to the linear motor driver.

[0030] Furthermore, the specific steps of the closed-loop feedback control strategy are as follows: Real-time acquisition of the focal offset Δz detected by the displacement sensor; calculation of the required compensation displacement ΔL = 2 × Δz for the reference arm based on the optical path matching principle; the control unit sending pulse commands to the linear motor driver to drive the motor to move a distance ΔL; the motor's built-in encoder providing real-time feedback of the actual position, which the control unit uses for closed-loop correction to ensure positioning accuracy. The control cycle of the control unit is no greater than 5ms.

[0031] In addition, during the welding process, the control unit monitors the changes in workpiece surface height and welding focal point position in real time using a laser displacement sensor or a vision sensor. When the sensor detects a change in focal point position exceeding a set threshold (e.g., 0.01 mm), it triggers the control unit to initiate the automatic adjustment process of the reference arm.

[0032] In addition, the system's OCT scanning rate is set to ≥120kHz, and the depth scanning range is set to 0-12mm and is adjustable to meet the melting depth measurement requirements under different working conditions.

[0033] This invention further provides a method for monitoring weld penetration based on OCT automatic following of the focal plane of laser welding, applied to the aforementioned system for monitoring weld penetration based on OCT automatic following of the focal plane of laser welding, comprising: S1: Generates broadband low-coherence light; S2: Split the broadband low-coherence light into sample arm light and reference arm light, and combine the returned sample arm light and reference arm light into an interference light signal; S3: Guide and focus the sample arm beam onto the target area of ​​the laser welding process to form the returning sample arm beam; S4: The reference arm light is reflected by the reflective component to form the returned reference arm light; S5: Perform spectral analysis on the interference light signal; S6: Calculate the welding penetration depth in real time based on the spectral analysis results.

[0034] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A penetration depth monitoring system based on OCT automatic tracking of the focal plane of laser welding, characterized in that, include: Light source, fiber optic coupler, sample arm, reference arm, spectrometer, and data processing module; The light source is used to generate broadband, low-coherence light; The fiber coupler is used to split the broadband low-coherence light into sample arm light and reference arm light, and to combine the returned sample arm light and reference arm light into an interference light signal. The sample arm is used to guide and focus the sample arm light onto the target area of ​​the laser welding process, forming a returned sample arm light; The reference arm is used to reflect the reference arm light through the reflection component to form the returned reference arm light; The spectrometer is used for spectral analysis of the interference light signal; The data processing module is used to calculate the welding penetration depth in real time based on the spectral analysis results.

2. The penetration depth monitoring system based on OCT automatic following laser welding focal plane according to claim 1, characterized in that, The reflective component is driven by a linear motor with a displacement accuracy of ±1μm and a response time of less than 10ms from receiving the control command to completing the displacement.

3. The penetration depth monitoring system based on OCT automatic following laser welding focal plane according to claim 1, characterized in that, The scanning rate of the spectrometer for spectral analysis is not less than 120 kHz.

4. The penetration depth monitoring system based on OCT automatic tracking of the focal plane of laser welding according to claim 1, characterized in that, The system also includes a control unit, comprising: The control unit is used to receive external sensing signals and drive the reflective component to automatically adjust the optical path of the reference arm according to the external sensing signals.

5. The penetration depth monitoring system based on OCT automatic tracking of the focal plane of laser welding according to claim 4, characterized in that, The control unit is configured to perform closed-loop feedback control, including: The target displacement of the reflective component is calculated based on the external sensing signal. Output control commands to drive the reflective component to move to the target position; The system receives a feedback signal indicating the actual position of the reflective component and compares it with the target position for correction.

6. The penetration depth monitoring system based on OCT automatic tracking of the focal plane of laser welding according to claim 5, characterized in that, The control cycle for the closed-loop feedback control executed by the control unit is no more than 5ms.

7. The penetration depth monitoring system based on OCT automatic tracking of the focal plane of laser welding according to claim 4, characterized in that, The external sensing signals are provided by a laser displacement sensor and / or a vision sensor, and are used to monitor the workpiece surface height or welding focus position in real time.

8. A method for monitoring weld penetration based on OCT automatic tracking of the focal plane of laser welding, applied to the weld penetration monitoring system based on OCT automatic tracking of the focal plane of laser welding as described in claim 1, characterized in that, include: S1: Generates broadband low-coherence light; S2: Split the broadband low-coherence light into sample arm light and reference arm light, and combine the returned sample arm light and reference arm light into an interference light signal; S3: Guide and focus the sample arm light onto the target area of ​​the laser welding process to form a returning sample arm light; S4: The reference arm light is reflected by the reflective component to form the returned reference arm light; S5: Perform spectral analysis on the interference light signal; S6: Calculate the welding penetration depth in real time based on the spectral analysis results.

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