A laser welding focal point monitoring device with self-calibration function

Abstract

The application provides a laser welding focus monitoring device with a self-calibration function and relates to the field of laser processing monitoring, and comprises a light source, a collimating lens, a rotatable beam splitter, a dichroic mirror, a galvanometer group, a focusing mirror, a focusing lens, a liquid lens, a pinhole, a photodiode and a data acquisition unit arranged in sequence along a coaxial confocal light path; the data acquisition unit applies a periodic scanning driving voltage to the liquid lens, continuously collects the output signal of the photodiode multiple times, extracts a position measurement sequence, evaluates the position measurement sequence by using a statistical dispersion index, corrects a threshold value for evaluation according to temperature, extracts a response characteristic quantity when the statistical dispersion index exceeds the threshold value for evaluation after temperature correction, and obtains a compensated defocusing amount output based on a pre-stored mapping relationship between the response characteristic quantity and the defocusing amount. The application guarantees the continuous reliability of focus measurement in the whole use cycle and improves the accuracy of aging determination.

Description

Technical Field

[0001] This invention relates to the field of laser processing monitoring technology, and in particular to a laser welding focus monitoring device with self-calibration function. Background Technology

[0002] In laser welding, the distance between the laser head and the workpiece (i.e., the defocus amount) directly determines the energy density distribution of the laser beam on the workpiece surface. When the defocus amount deviates from the optimal focal length, the weld depth-to-width ratio will change, accompanied by defects such as insufficient penetration and increased spatter, seriously affecting the consistency and stability of weld quality. Therefore, real-time and accurate measurement of the defocus amount during laser welding is of significant engineering importance.

[0003] Currently, a common laser welding focus monitoring scheme is based on a coaxial confocal optical path, utilizing the adaptive focal length characteristics of a liquid lens to achieve high-speed axial scanning. This scheme transmits the probe light emitted from the light source coaxially with the welding laser. The reflected light from the workpiece surface passes through the liquid lens and a small aperture, and is received by a photodiode. The confocal effect generates a signal peak at focus, and by recording the driving voltage corresponding to the peak and comparing it with a pre-calibrated voltage-defocus mapping relationship, non-contact real-time measurement is achieved. However, the liquid lens, as the core measuring element in this scheme, experiences performance degradation over time due to the internal liquid filling. This can lead to drift in response characteristics, or even, in severe cases, beam scattering caused by microbubbles within the lens, resulting in random distortion of the signal waveform and ultimately causing continuous deviation in the measurement results, affecting the accuracy of focus control. Existing monitoring devices based on this principle generally lack an online evaluation mechanism for the working status of the liquid lens itself. Once the liquid lens ages, the device can only passively wait for manual intervention and cannot autonomously identify and compensate for measurement deviations.

[0004] Chinese invention patent application number 202210818410.1 discloses a laser welding device integrating adaptive OCT. This device coaxially integrates an OCT imaging module, an adaptive optics module, and a laser welding module. It utilizes an electrically controlled adaptive optics lens to dynamically adjust the sample arm beam aperture, and combines this with a digital dispersion compensation algorithm to improve the lateral and axial resolution of OCT imaging in welding scenarios with different focal lengths. Furthermore, it can perform real-time measurement of weld penetration and post-weld quality assessment during the welding process. However, it cannot solve the problem of online identification and autonomous compensation for performance degradation of the liquid lens in the focus monitoring device after long-term use, thus interfering with the measurement results. Summary of the Invention

[0005] In view of this, the present invention provides a laser welding focus monitoring device with self-calibration function to solve the technical problem in the prior art that the liquid lens of the laser welding focus monitoring device cannot be autonomously identified and compensated in a timely manner after aging, thereby improving the accuracy of aging judgment and reducing the probability of missed judgment and false judgment.

[0006] The technical solution of this invention is implemented as follows: On one hand, this invention provides a laser welding focus monitoring device with self-calibration function, comprising a light source, a collimating lens, a rotatable beam splitter, a dichroic mirror, a galvanometer group, a focusing lens, a focusing lens, a liquid lens, a pinhole, a photodiode, and a data acquisition unit arranged sequentially along a coaxial confocal optical path; wherein, The bracket of the rotatable beam splitter is mechanically connected to the drive mechanism, and the drive mechanism is electrically connected to the data acquisition unit. A temperature sensor is mounted on the support of the liquid lens, and the temperature sensor is connected to the data acquisition unit. The data acquisition unit applies a periodic scanning driving voltage to the liquid lens, continuously acquires the output signal of the photodiode multiple times, extracts the position measurement sequence, evaluates the position measurement sequence using a statistical dispersion index, and performs temperature correction on the evaluation threshold based on the current reading of the temperature sensor and the factory calibration parameters. When the statistical dispersion index exceeds the temperature-corrected evaluation threshold, the data acquisition unit performs waveform analysis on the acquired signal of the photodiode to extract response feature quantities, and obtains the compensated defocus output based on the pre-stored mapping relationship between the response feature quantities and the defocus amount.

[0007] Based on the above technical solutions, preferably, the driving mechanism is a servo motor, the output shaft of the servo motor is mechanically connected to the bracket of the rotatable beam splitter, and a mechanical limit switch is provided between the rotatable beam splitter and the data acquisition unit.

[0008] Based on the above technical solutions, preferably, the data acquisition unit controls the rotatable beam splitter to switch between measurement mode and calibration mode through a drive mechanism: In measurement mode, the rotatable beam splitter is rotated to the first angle position, and the probe light enters the main measurement optical path after being transmitted through the rotatable beam splitter to perform focus monitoring on the workpiece surface. In calibration mode, the rotatable beam splitter is rotated to the second angle position. The probe light is reflected by the rotatable beam splitter and guided to the internal self-test optical path. The optical path is decoupled from the workpiece, and the data acquisition unit independently evaluates the current state of the liquid lens without being affected by the state of the workpiece. The data acquisition unit automatically triggers mode switching after each measurement cycle ends.

[0009] Based on the above technical solutions, preferably, the periodic scanning drive voltage applied by the data acquisition unit to the liquid lens is a sawtooth wave voltage.

[0010] More preferably, the data acquisition unit is equipped with a non-volatile memory, which stores a mapping lookup table between response feature quantities and defocus quantity, the factory initial dispersion reference value, and the temperature sensitivity coefficient.

[0011] On the other hand, the present invention also provides a laser welding focus monitoring method with self-calibration function, applied to a laser welding focus monitoring device with self-calibration function as described above, comprising: After powering on, the laser welding focus monitoring device enters calibration mode, which specifically includes: A periodic scanning driving voltage is used to drive the liquid lens, and the output signal of the photodiode is continuously acquired multiple times to obtain a position measurement sequence; the variance statistics method is used to analyze the dispersion of the position measurement sequence to obtain the real-time measurement variance. Based on the current temperature reading of the temperature sensor, the initial variance of the factory calibration, and the temperature sensitivity coefficient, the judgment threshold is corrected using a temperature compensation factor to obtain the temperature-corrected judgment threshold. Compare the real-time measurement variance with the temperature-corrected decision threshold: When the real-time measurement variance does not exceed the temperature-corrected judgment threshold, the current defocusing amount is obtained by interpolation calculation based directly on the peak voltage of the photodiode and the pre-stored mapping lookup table. When the real-time measurement variance exceeds the temperature-corrected threshold, the measurement mode is activated. In the measurement mode, the acquired signal of the photodiode is reconstructed by using a low-pass filtering method and a curve fitting method in sequence, the peak response voltage is extracted, and interpolation is performed based on the peak response voltage and a pre-stored mapping lookup table to obtain the compensated defocus amount.

[0012] Based on the above technical solutions, preferably, the temperature compensation factor is determined by the difference between the current operating temperature of the liquid lens and the factory-calibrated reference temperature, and the calculation formula is as follows: in, For temperature compensation factor, This is the current reading from the temperature sensor. This is the standard reference temperature used for factory calibration. This is the temperature sensitivity coefficient.

[0013] Based on the above technical solutions, the preferred method for calculating the temperature sensitivity coefficient is as follows: Repeated measurements were performed on the unaged liquid lens under multiple constant temperature environments to obtain the measurement variance at each temperature point; Using the deviation of each temperature point from the standard reference temperature as the independent variable and the natural logarithm of the ratio of the measurement variance to the initial variance as the dependent variable, a linear fit is performed using the least squares method, and the resulting fitting slope is the temperature sensitivity coefficient.

[0014] Based on the above technical solutions, preferably, the formula for calculating the temperature-corrected judgment threshold is: in, This is the temperature-corrected threshold. This represents the initial variance at the time of manufacture. For temperature compensation factor, The proportionality coefficient was determined by the accelerated aging comparative experiment.

[0015] Based on the above technical solutions, preferably, the cutoff frequency of the low-pass filter is 300 Hz.

[0016] The present invention has the following advantages over the prior art: (1) By evaluating and adaptively compensating for liquid lens in a coaxial confocal focus monitoring device, the device can automatically identify and switch to compensation measurement mode when signs of aging appear in the liquid lens, thus ensuring the continuous reliability of focus measurement throughout the entire service life. (2) By integrating a temperature sensor on the liquid lens holder, the temperature data is transmitted back in real time, which effectively prevents false alarms caused by ambient temperature fluctuations and improves the accuracy of aging determination. (3) The judgment threshold is constructed by combining the initial variance calibrated at the factory with the temperature compensation factor, instead of using a uniform fixed threshold. This makes the aging judgment standard adaptable to individual differences and reduces the probability of missed judgment and misjudgment. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a laser welding focus monitoring device with self-calibration function according to the present invention. Figure 1 ; Figure 2 This is a schematic diagram of a laser welding focus monitoring device with self-calibration function according to the present invention. Figure 2 ; Figure 3This is a flowchart of a laser welding focus monitoring method with self-calibration function according to the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Workpiece; 2. Focusing lens; 3. First galvanometer; 4. Second galvanometer; 5. Dichroic mirror; 6. Rotatable beam splitter; 7. Focusing lens; 8. Liquid lens; 9. Pinhole; 10. Photodiode; 11. Data acquisition unit; 12. Collimating lens; 13. Light source; 14. Welding laser; 15. Servo motor; 16. Temperature sensor. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this invention provides a laser welding focus monitoring device with self-calibration function, comprising a light source, a collimating lens, a rotatable beam splitter, a dichroic mirror, a galvanometer group, a focusing lens, a focusing lens, a liquid lens, a pinhole, a photodiode, and a data acquisition unit arranged sequentially along a coaxial confocal optical path; wherein, The bracket of the rotatable beam splitter is mechanically connected to the drive mechanism, and the drive mechanism is electrically connected to the data acquisition unit. A temperature sensor is mounted on the support of the liquid lens, and the temperature sensor is connected to the data acquisition unit. The data acquisition unit applies a periodic scanning driving voltage to the liquid lens, continuously acquires the output signal of the photodiode multiple times, extracts the position measurement sequence, evaluates the position measurement sequence using a statistical dispersion index, and performs temperature correction on the evaluation threshold based on the current reading of the temperature sensor and the factory calibration parameters. When the statistical dispersion index exceeds the temperature-corrected evaluation threshold, the data acquisition unit performs waveform analysis on the acquired signal of the photodiode to extract response feature quantities, and obtains the compensated defocus output based on the pre-stored mapping relationship between the response feature quantities and the defocus amount.

[0022] As shown in the figure, the probe light (usually in the infrared band) emitted by the light source 13 is collimated into parallel light by the collimating lens 12, transmitted through the rotatable beam splitter 6, reflected by the dichroic mirror 5, and enters the scanning system composed of the galvanometer group. Finally, it is focused onto the surface of the workpiece 1 by the focusing lens 2 (such as an F-Theta mirror). The backscattered light from the surface of the workpiece 1 returns along the original path, passes through the dichroic mirror 5, enters the detection branch, and passes sequentially through the focusing lens 7, the liquid lens 8, and is filtered through the confocal space of the aperture 9 (50μm to 100μm in diameter). It is then received by the photodiode 10 and converted into an electrical signal. The welding laser 14 and the probe light are transmitted coaxially. The spectral characteristics of the dichroic mirror 5 allow them to be independently separated without interference. The galvanometer group includes a first galvanometer 3 and a second galvanometer 4, both of the same specifications.

[0023] In one embodiment of the present invention, the rotatable beam splitter is a beam splitter with a 50:50 beam splitting ratio.

[0024] In one embodiment of the present invention, the driving mechanism is a servo motor, the output shaft of the servo motor is mechanically connected to the bracket of the rotatable beam splitter, and a mechanical limit switch is provided between the rotatable beam splitter and the data acquisition unit.

[0025] Understandably, the rotatable beam splitter bracket is rigidly connected to the output shaft of the servo motor 15, and the servo motor 15 is electrically connected to the data acquisition unit 11. In measurement mode, the servo motor 15 drives the beam splitter to rotate to a positive 45-degree angle (see...). Figure 1 The probe light, after being transmitted through the rotatable beam splitter 6, normally enters the main measurement optical path to monitor the focal point on the surface of workpiece 1; in calibration mode, the servo motor 15 drives the beam splitter to rotate to a negative 45-degree angle (see...). Figure 2The probe light, after being reflected by the rotatable beam splitter 6, is guided to the internal self-test optical path. Specifically, the light from the light source 13 sequentially passes through the collimating lens 12, the rotatable beam splitter 6, the focusing lens 7, the liquid lens 8, and the pinhole 9, and is finally received by the photodiode 10. At this point, the optical path is completely decoupled from the workpiece, allowing the data acquisition unit 11 to independently evaluate the current state of the liquid lens 8 without being affected by the workpiece's condition. A mechanical limit switch is provided between the rotatable beam splitter 6 and the data acquisition unit 11 to ensure the repeatability and accuracy of the optical path after the beam splitter is rotated into position. In actual laser welding scenarios, the workpiece surface materials are diverse. Different metals such as copper, iron, and aluminum alloys show significant differences in reflectivity to the same wavelength of probe light. Changes in the surface state of the same material before and after welding can also cause significant fluctuations in the reflected light intensity. The light source 13 used in the calibration mode outputs constant parallel light after being shaped by the collimating lens 12. Its light intensity and beam quality remain stable throughout the entire service life of the device, ensuring that the boundary conditions faced in each calibration are completely consistent with those at the factory calibration, thereby making the initial variance reference value and temperature sensitivity coefficient obtained from the factory calibration effective throughout the entire service life.

[0026] In one embodiment of the present invention, the temperature sensor is attached to or integrated on the mechanical support of the liquid lens, so that the temperature sensed by the sensor is highly consistent with the temperature of the liquid inside the lens. The output end of the temperature sensor 16 is connected to the data acquisition unit 11 to realize the real-time transmission of temperature data, effectively preventing false alarms caused by ambient temperature fluctuations and improving the accuracy of aging determination.

[0027] In one embodiment of the present invention, the periodic scanning drive voltage applied by the data acquisition unit to the liquid lens is a sawtooth wave voltage.

[0028] In one embodiment of the present invention, the data acquisition unit controls the rotatable beam splitter to switch between measurement mode and calibration mode via a drive mechanism: In measurement mode, the beam splitter can be rotated to the first angular position (positive 45 degrees, such as...). Figure 1 The probe light is transmitted through a rotatable beam splitter and enters the main measurement optical path to monitor the focus on the workpiece surface. In calibration mode, the rotatable beam splitter can be moved to the second angle position (negative 45 degrees, e.g.) Figure 2 The probe light is reflected by a rotatable beam splitter and guided to the internal self-test optical path. The optical path is decoupled from the workpiece, and the data acquisition unit independently evaluates the current state of the liquid lens without being affected by the state of the workpiece. The data acquisition unit automatically triggers mode switching after each measurement cycle ends.

[0029] In one embodiment of the present invention, the data acquisition unit is provided with a non-volatile memory, which stores a mapping lookup table of response characteristic quantity (peak voltage) and defocus amount, factory initial dispersion reference value and temperature sensitivity coefficient.

[0030] Understandably, factory calibration is performed in two stages: The first stage is the establishment of the zero-point reference: a standard high-reflectivity plane (calibration plate) is placed on the theoretical focal plane of the optical system. The data acquisition unit applies a sawtooth wave scanning drive voltage to the liquid lens. The photodiode captures the signal peak within one complete scan cycle and records the corresponding drive voltage. This point is the zero defocus reference point; The second stage involves constructing the lookup table: A high-precision displacement stage (such as a piezoelectric ceramic displacement stage or a CNC lead screw) is used to move the calibration plate axially in fixed steps (e.g., every 0.05 mm). During positive defocusing, the calibration plate moves away from the focusing lens; during negative defocusing, the calibration plate moves closer to the focusing lens. The driving voltage corresponding to the signal peak value is recorded at each position point, forming a series of ordered (…) , ) data pairs.

[0031] Because the relationship between the focal length change of a liquid lens and voltage is usually not strictly linear (affected by hysteresis), the data acquisition unit will process the data pairs ( , The data is stored in ascending order of voltage as a mapping lookup table. During real-time measurement, the defocusing amount corresponding to any voltage value is calculated by linear interpolation. When the peak voltage captured in real time exceeds the maximum or minimum voltage range in the table, the device outputs an alarm.

[0032] like Figure 3 As shown, the present invention also provides a laser welding focus monitoring method with self-calibration function, applied to a laser welding focus monitoring device with self-calibration function as described above, comprising: After powering on, the laser welding focus monitoring device enters calibration mode, which specifically includes: A periodic scanning driving voltage is used to drive the liquid lens, and the output signal of the photodiode is continuously acquired multiple times to obtain a position measurement sequence; the variance statistics method is used to analyze the dispersion of the position measurement sequence to obtain the real-time measurement variance. Based on the current temperature reading of the temperature sensor, the initial variance of the factory calibration, and the temperature sensitivity coefficient, the judgment threshold is corrected using a temperature compensation factor to obtain the temperature-corrected judgment threshold. Compare the real-time measurement variance with the temperature-corrected decision threshold: When the real-time measurement variance does not exceed the temperature-corrected judgment threshold, the current defocusing amount is obtained by interpolation calculation based directly on the peak voltage of the photodiode and the pre-stored mapping lookup table. When the real-time measurement variance exceeds the temperature-corrected threshold, the measurement mode is activated. In the measurement mode, the acquired signal of the photodiode is reconstructed by using a low-pass filtering method and a curve fitting method in sequence, the peak response voltage is extracted, and interpolation is performed based on the peak response voltage and a pre-stored mapping lookup table to obtain the compensated defocus amount.

[0033] After the device is powered on, the monitoring method first enters the calibration mode. At this time, the optical path is completely decoupled from the workpiece, and the signal collected by the receiver comes entirely from the internal fixed light source. It is not affected by the difference in reflectivity of different welding objects such as cast iron and copper alloy. Compared with the backscattered light of the workpiece in the ordinary measurement mode, the parallel light used in the calibration mode is a constant boundary condition, which is consistent with the boundary condition when it is calibrated at the factory. This ensures the stability of the liquid lens state assessment and the effectiveness of the judgment threshold.

[0034] This invention enables the device to autonomously identify and switch to the compensation measurement mode when signs of aging appear in the liquid lens by performing liquid lens evaluation and adaptive compensation in a coaxial confocal focus monitoring device, without interrupting welding operations or relying on manual inspection, thereby ensuring the continuous reliability of focus measurement throughout the entire service life.

[0035] Specifically, the data acquisition unit applies a periodic sawtooth wave scanning drive voltage to the liquid lens, driving the liquid lens to perform continuous axial scanning within a set focal length range. Each voltage value corresponds to a focal length value of the liquid lens. Within each complete scanning cycle, the output signal of the photodiode is synchronously acquired, and the corresponding focal position measurement value is extracted. For the position measurement sequence obtained from 30 consecutive scans (completed within 3 seconds), the variance statistical method is used to calculate the real-time measurement variance. , which serves as a statistical dispersion index reflecting the current working state of the liquid lens.

[0036] In one embodiment of the present invention, the measurement cycle is 30 scans, and the state switching is automatically performed after each measurement cycle. The switching between the two working states does not require manual intervention.

[0037] In one embodiment of the present invention, the temperature compensation factor is determined by the difference between the current operating temperature of the liquid lens and the factory-calibrated reference temperature, and the calculation formula is as follows: in, For temperature compensation factor, This is the current reading from the temperature sensor. This is the standard reference temperature used for factory calibration. This is the temperature sensitivity coefficient.

[0038] Understandably, the viscosity of the liquid inside a liquid lens decreases with increasing temperature, causing the measurement variance itself to systematically drift with temperature even under unaged conditions. If this effect is not corrected, misjudgments are likely to occur at high temperatures. Therefore, a temperature compensation factor is introduced. The judgment criteria were revised.

[0039] In one embodiment of the present invention, the factory-calibrated The temperature is 25℃.

[0040] In one embodiment of the present invention, the method for calculating the temperature sensitivity coefficient is as follows: Repeated measurements were performed on the unaged liquid lens under multiple constant temperature environments to obtain the measurement variance at each temperature point; Using the deviation of each temperature point from the standard reference temperature as the independent variable and the natural logarithm of the ratio of the measurement variance to the initial variance as the dependent variable, a linear fit is performed using the least squares method, and the resulting fitting slope is the temperature sensitivity coefficient.

[0041] In one embodiment of the present invention, the temperature sensitivity coefficient The value ranges from 0.02 to 0.05. The value is written into the non-volatile memory of the data acquisition unit at the factory.

[0042] In one embodiment of the present invention, the multiple constant temperature environments are 15°C, 20°C, 25°C, 30°C, 35°C, and 40°C.

[0043] In one embodiment of the present invention, the formula for calculating the temperature-corrected judgment threshold is: in, This is the temperature-corrected threshold. This represents the initial variance at the time of manufacture. For temperature compensation factor, The proportionality coefficient was determined by the accelerated aging comparative experiment.

[0044] This invention constructs the judgment threshold by combining the initial variance calibrated at the factory with the temperature compensation factor, instead of using a uniform fixed threshold. This makes the aging judgment standard adaptable to individual differences and reduces the probability of missed judgments and false judgments.

[0045] Specifically, The method for determining it is as follows: Liquid lenses of the same model were divided into a normal group (brand new, unaged, sizes 1-10) and an aged group (operated for 500 hours at 70°C and continuous high-frequency drive until observable bubbles or turbidity appeared inside, sizes 11-20). Each group was reinstalled into the monitoring device, and 30 consecutive measurements were performed at multiple temperature points. The variance of each group was recorded, and the temperature compensation factor for the normal and aged groups was calculated through fitting. The ratio of the minimum temperature compensation factor of the aged group to the maximum temperature compensation factor of the normal group was taken as the... Value, in this embodiment =1.34. This proportionality coefficient places the judgment threshold between the upper bound of normal dispersion and the lower bound of aging dispersion, ensuring that the aging state is effectively identified while reducing the probability of misjudgment caused by temperature fluctuations.

[0046] The temperature correction mechanism quantitatively separates the aging effect of the liquid lens from the temperature drift effect, enabling the device to accurately distinguish between normal operation and performance degradation under different temperature environments, effectively improving the reliability of aging determination.

[0047] In one embodiment of the present invention, the acquisition signal of the photodiode is first preprocessed using a low-pass filter with a cutoff frequency of 300 Hz. The sampling frequency of the photodiode is typically 200 kHz, and the frequency of the driving sawtooth wave is 10 Hz. This filters out high-frequency random disturbances caused by scattering from bubbles inside the liquid lens and electrical noise, resulting in a smoothed signal waveform. Then, a Gaussian function is used to fit the smoothed waveform to a curve. The driving voltage corresponding to the extreme point of the fitted curve is the peak response voltage. The fitted model is: in, This is the driving voltage for the liquid lens. This represents the amplitude of the output signal of the photodiode under the corresponding driving voltage. To fit the magnitude of the Gaussian function, For the peak voltage to be determined, The standard deviation of the Gaussian function is used to fit the signal waveform and reflect its broadening. Finally A lookup table interpolation operation is performed with the mapping lookup table in the non-volatile memory to obtain the compensated defocus output.

[0048] Understandably, as liquid lenses age, the deterioration of the internal liquid or the presence of microbubbles leads to enhanced beam scattering, a decrease in the peak signal-to-noise ratio, waveform broadening, and even random distortion, resulting in significant errors when directly reading the peak voltage. The combined low-pass filtering and Gaussian fitting approach, by suppressing high-frequency noise and parametrically modeling the signal waveform, can effectively locate peak values ​​even under conditions of liquid lens performance degradation. This allows the device to maintain normal measurement capabilities without replacing components, reducing the frequency of unplanned downtime.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser welding focus monitoring device with self-calibration function, characterized in that, It includes a light source, a collimating lens, a rotatable beam splitter, a dichroic mirror, a galvanometer group, a focusing lens, a focusing lens, a liquid lens, a pinhole, a photodiode, and a data acquisition unit arranged sequentially along a coaxial confocal optical path; among which, The bracket of the rotatable beam splitter is mechanically connected to the drive mechanism, and the drive mechanism is electrically connected to the data acquisition unit. A temperature sensor is mounted on the support of the liquid lens, and the temperature sensor is connected to the data acquisition unit. The data acquisition unit applies a periodic scanning driving voltage to the liquid lens, continuously acquires the output signal of the photodiode multiple times, extracts the position measurement sequence, evaluates the position measurement sequence using a statistical dispersion index, and performs temperature correction on the evaluation threshold based on the current reading of the temperature sensor and the factory calibration parameters. When the statistical dispersion index exceeds the temperature-corrected evaluation threshold, the data acquisition unit performs waveform analysis on the acquired signal of the photodiode to extract response feature quantities, and obtains the compensated defocus output based on the pre-stored mapping relationship between the response feature quantities and the defocus amount.

2. The laser welding focus monitoring device with self-calibration function as described in claim 1, characterized in that: The driving mechanism is a servo motor, and the output shaft of the servo motor is mechanically connected to the bracket of the rotatable beam splitter. A mechanical limit switch is provided between the rotatable beam splitter and the data acquisition unit.

3. The laser welding focus monitoring device with self-calibration function as described in claim 1, characterized in that: The data acquisition unit controls the rotatable beam splitter to switch between measurement mode and calibration mode via a drive mechanism: In measurement mode, the rotatable beam splitter is rotated to the first angle position, and the probe light enters the main measurement optical path after being transmitted through the rotatable beam splitter to monitor the focus of the workpiece surface. In calibration mode, the rotatable beam splitter is rotated to the second angle position. The probe light is reflected by the rotatable beam splitter and guided to the internal self-test optical path. The optical path is decoupled from the workpiece, and the data acquisition unit independently evaluates the current state of the liquid lens without being affected by the state of the workpiece. The data acquisition unit automatically triggers mode switching after each measurement cycle ends.

4. The laser welding focus monitoring device with self-calibration function as described in claim 1, characterized in that: The periodic scanning drive voltage applied by the data acquisition unit to the liquid lens is a sawtooth wave voltage.

5. A laser welding focus monitoring device with self-calibration function as described in claim 1, characterized in that: The data acquisition unit is equipped with a non-volatile memory, which stores a mapping lookup table between response characteristic quantities and defocus quantity, the initial factory dispersion reference value, and the temperature sensitivity coefficient.

6. A method for monitoring the laser welding focus with self-calibration function, characterized in that: An application to a laser welding focus monitoring device with self-calibration function as described in any one of claims 1-5, comprising: After powering on, the laser welding focus monitoring device enters calibration mode, which specifically includes: A periodic scanning driving voltage is used to drive the liquid lens, and the output signal of the photodiode is continuously acquired multiple times to obtain a position measurement sequence; the variance statistics method is used to analyze the dispersion of the position measurement sequence to obtain the real-time measurement variance. Based on the current temperature reading of the temperature sensor, the initial variance of the factory calibration, and the temperature sensitivity coefficient, the judgment threshold is corrected using a temperature compensation factor to obtain the temperature-corrected judgment threshold. Compare the real-time measurement variance with the temperature-corrected decision threshold: When the real-time measurement variance does not exceed the temperature-corrected judgment threshold, the current defocusing amount is obtained by interpolation calculation based directly on the peak voltage of the photodiode and the pre-stored mapping lookup table. When the real-time measurement variance exceeds the temperature-corrected threshold, the measurement mode is activated. In the measurement mode, the acquired signal of the photodiode is reconstructed by using a low-pass filtering method and a curve fitting method in sequence, the peak response voltage is extracted, and interpolation is performed based on the peak response voltage and a pre-stored mapping lookup table to obtain the compensated defocus amount.

7. The laser welding focus monitoring method with self-calibration function as described in claim 6, characterized in that: The temperature compensation factor is determined by the difference between the current operating temperature of the liquid lens and the factory-calibrated reference temperature, and the calculation formula is as follows: ； in, For temperature compensation factor, This is the current reading from the temperature sensor. This is the standard reference temperature used for factory calibration. This is the temperature sensitivity coefficient.

8. The laser welding focus monitoring method with self-calibration function as described in claim 7, characterized in that: The method for calculating the temperature sensitivity coefficient is as follows: Repeated measurements were performed on the unaged liquid lens under multiple constant temperature environments to obtain the measurement variance at each temperature point; Using the deviation of each temperature point from the standard reference temperature as the independent variable and the natural logarithm of the ratio of the measurement variance to the initial variance as the dependent variable, a linear fit is performed using the least squares method, and the resulting fitting slope is the temperature sensitivity coefficient.

9. A laser welding focus monitoring method with self-calibration function as described in claim 6, characterized in that: The formula for calculating the temperature-corrected threshold is: ； in, This is the temperature-corrected threshold. This represents the initial variance at the time of manufacture. For temperature compensation factor, The proportionality coefficient was determined by the accelerated aging comparative experiment.

10. A laser welding focus monitoring method with self-calibration function as described in claim 6, characterized in that: The cutoff frequency of the low-pass filter is 300 Hz.

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