Galvanometer laser welding full-width OCT penetration depth measurement system and method

Abstract

The application discloses a galvanometer laser welding full-width OCT (Optical Coherence Tomography) penetration measurement system and method, and relates to the technical field of laser welding quality monitoring.The method is based on the cooperative control of a welding galvanometer and a measurement galvanometer, and comprises a pre-calibration stage and an online measurement stage.The pre-calibration stage establishes a mapping relationship between the welding galvanometer coordinates and the measurement galvanometer offset compensation value;in the online measurement stage, the controller acquires the welding galvanometer coordinates in real time, calls the mapping relationship to drive the measurement galvanometer to perform offset compensation, makes the measurement light and the welding light coincide on the workpiece surface, and then synchronously triggers the welding and the OCT measurement.The system comprises a welding laser, an OCT measurement module, a welding galvanometer, a measurement galvanometer, a scanning objective and a controller.The application solves the problem that the OCT measurement light and the welding light cannot coincide in the full-width of the galvanometer due to the wavelength difference through programmed automatic compensation, and realizes accurate measurement of the welding penetration in the full-width.

Description

Technical Field

[0001] This invention relates to the field of laser welding quality monitoring technology, specifically to a galvanometer laser welding full-width OCT penetration measurement system and method. Background Technology

[0002] In high-end manufacturing industries, such as welding flat copper wires for motor stators and laser welding for power batteries, the quality of the welded joints directly determines the mechanical, electrical, and lifespan of the product. However, there is a lack of effective real-time monitoring methods for potential defects during the welding process.

[0003] Optical coherence tomography (OCT) technology has been applied in recent years to online monitoring of laser welding penetration depth due to its high resolution, non-contact, and real-time imaging capabilities. OCT systems emit low-coherence light (such as 840nm and 1310nm), splitting it into a reference beam and a probe beam. The interference signal reflected from the two beams is then used to analyze the depth information of the object being measured.

[0004] However, in practical applications, the wavelengths of the OCT measurement light and the welding laser are different. When these two beams of light with different wavelengths pass through the same scanning objective of the laser welding head, they experience different angles of refraction due to the dispersion effect of the lens material, i.e., the refractive index varies with wavelength. This results in the two beams only overlapping within a very small area near the lens's optical axis. When the welding galvanometer is deflected to the edge for welding, the OCT measurement light cannot be focused on the same point on the workpiece surface as the welding laser, thus failing to detect the true bottom of the welding keyhole, leading to inaccurate penetration depth measurement data. This limitation severely restricts the widespread application of OCT technology in galvanometer laser welding systems that require full-area scanning.

[0005] Therefore, there is a persistent technical challenge in the existing technology: how to design a systematic compensation method and corresponding control system that can accurately and in real time correct the lateral optical path offset caused by wavelength differences, and ensure that the OCT measurement light and the welding laser can be strictly overlapped in the entire working area of ​​the galvanometer, thereby providing a technical basis for realizing reliable online measurement of full-area welding penetration. Summary of the Invention

[0006] The purpose of this invention is to provide a full-width OCT weld depth measurement system and method for galvanometer laser welding. The core technical problem to be solved is that because the wavelengths of the welding laser and the OCT measurement laser are different, a lateral chromatic aberration occurs when they pass through the same scanning objective lens, causing the two beams to fail to overlap in the non-central area of ​​the galvanometer working area, thus making it impossible for the OCT system to accurately measure the weld depth across the entire width.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for measuring the full-width OCT penetration depth of galvanometer laser welding, characterized by comprising the following steps:

[0008] Pre-calibration step: For the welding galvanometer at multiple coordinate positions within the full-width area, determine and store the corresponding measurement galvanometer offset compensation values, and establish a mapping relationship between the welding galvanometer coordinates and the measurement galvanometer offset compensation values;

[0009] Online measurement steps:

[0010] Obtain the current welding coordinates of the welding galvanometer;

[0011] Based on the current welding coordinates and the mapping relationship, the measuring galvanometer is driven to perform corresponding deflection compensation;

[0012] Subsequently, the welding laser is synchronously triggered to perform welding, and the OCT measurement module is triggered to perform optical coherence tomography to obtain welding penetration data.

[0013] Furthermore, the mapping relationship is pre-stored in the controller's memory in the form of a data lookup table or a compensation formula.

[0014] Preferably, in the pre-calibration step, the mapping relationship is established in the following manner:

[0015] Multiple test points are selected within the full width of the welding galvanometer;

[0016] At each test point, the deflection of the measuring galvanometer is adjusted until the measuring laser and the welding laser coincide on the workpiece surface, and the corresponding offset compensation value is recorded.

[0017] The mapping relationship is generated based on the coordinates and offset compensation values ​​of all test points.

[0018] Furthermore, the plurality of test points include at least the center point, edge center point, and corner point of the full-width surface; and the method for generating the mapping relationship is as follows: performing surface fitting on the coordinates and offset compensation values ​​of all test points to obtain the compensation formula.

[0019] Preferably, in the pre-calibration step, the mapping relationship is established in the following manner:

[0020] When the welding galvanometer is measured at multiple key positions by a camera, the deviation of the spot position of the welding laser and the measuring laser on the workpiece surface is measured.

[0021] The positional deviation is converted into the offset compensation value required for the measuring galvanometer;

[0022] Based on the coordinates and offset compensation values ​​of the multiple key locations, a data lookup table covering the entire area is generated using a bilinear interpolation algorithm.

[0023] Preferably, in the pre-calibration step, the mapping relationship is established in the following manner:

[0024] Calculations are performed based on the wavelengths of the welding laser and the measurement laser, the optical parameters of the scanning objective, and combined with Snell's law and a geometric optics model.

[0025] Based on the coordinates or deflection angle of the welding galvanometer, the offset compensation value required by the measuring galvanometer to correct the optical path is calculated, and the compensation formula is formed.

[0026] Secondly, the present invention provides a galvanometer laser welding full-width OCT penetration depth measurement system for implementing the above method, comprising:

[0027] Welding laser, used to generate welding laser light;

[0028] The OCT measurement module is used to generate a measurement laser and acquire weld penetration information based on optical coherence tomography (OCT) technology.

[0029] A welding galvanometer is disposed in the optical path of the welding laser and is used to deflect and guide the welding laser to a predetermined position on the surface of the workpiece.

[0030] A measuring galvanometer is positioned in the optical path of the measuring laser to deflect the measuring laser.

[0031] A scanning objective lens is positioned downstream of both the welding galvanometer and the measuring galvanometer to focus two laser beams onto the surface of the workpiece.

[0032] The controller is connected to the welding laser, the OCT measurement module, the welding galvanometer, and the measurement galvanometer, respectively.

[0033] The controller is configured as follows:

[0034] Based on the pre-stored mapping relationship and the real-time coordinates of the welding galvanometer, the measuring galvanometer is driven to perform offset compensation.

[0035] After compensation is completed, the welding laser and the OCT measurement module are triggered synchronously or sequentially to achieve synchronous acquisition of welding and penetration data.

[0036] Preferably, both the welding galvanometer and the measuring galvanometer are two-dimensional galvanometers.

[0037] Preferably, the controller controls the welding laser to emit light and the OCT measurement module to collect data using the same trigger signal or two trigger signals with a fixed delay relationship.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] By measuring the real-time dynamic compensation of the galvanometer, the measurement blind zone caused by lateral chromatic aberration is fundamentally overcome, and the effective range of OCT melt depth monitoring technology is extended from a small area near the optical axis to the entire working area of ​​the galvanometer.

[0040] This ensures that the OCT measurement beam can be accurately aligned with the bottom of the keyhole at any welding position, and that the obtained penetration depth data truly reflects the welding quality, providing a reliable basis for process optimization and quality assessment.

[0041] The integrated experimental design method, camera calibration method, and theoretical calculation method can be flexibly selected or cross-validated according to different application stages and accuracy requirements, which enhances the practicality and adaptability of the system. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method of the present invention;

[0043] Figure 2 This is a detailed flowchart of the pre-calibration stage and the online measurement stage of the present invention;

[0044] Figure 3 This is a schematic diagram of the system structure of the present invention;

[0045] Figure 4 This is a schematic diagram of the Design of Experiments (DOE) method of this invention;

[0046] Figure 5 This is a schematic diagram of the camera calibration method of the present invention;

[0047] Figure 6 This is a diagram of the geometric optical model of the theoretical calculation method of this invention; Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0050] Please refer to Figure 1 , Figure 3 This invention provides a full-width OCT weld depth measurement system for galvanometer laser welding, the hardware of which includes: a welding laser, an OCT measurement module, a welding galvanometer, a measuring galvanometer, a scanning objective lens, a controller, and a workpiece. These components are connected and controlled by specific optical paths to form an organic whole.

[0051] The welding laser emitted from the welding laser is collimated and then incident on the welding galvanometer. The measurement laser emitted from the OCT measurement module is collimated and then incident on the measurement galvanometer. The two beams of light, reflected by the welding galvanometer and the measurement galvanometer, are combined by a beam combiner and then incident on the scanning objective lens, ultimately being focused onto the surface of the workpiece. The controller is electrically connected to the welding laser, the OCT measurement module, the welding galvanometer, and the measurement galvanometer via data cables, and is used to send control commands and receive status information.

[0052] See the core workflow of the system's online measurement for details. Figure 1 The process is as follows: The controller first drives the welding galvanometer to the welding coordinates set in the program. Then, the controller queries or calculates a pre-stored mapping relationship based on these coordinates to obtain the corresponding measurement galvanometer compensation value, and drives the measurement galvanometer to complete real-time optical path compensation. After confirming optical path alignment, the controller sends a synchronization trigger signal, and the welding laser and OCT measurement module start simultaneously (or after a fixed delay), respectively performing welding and penetration depth scanning. The interference signal acquired by the OCT module is processed in real time, ultimately obtaining and displaying the penetration depth value at that location.

[0053] Example 1: Calibration and Measurement Based on Design of Experiments (DOE)

[0054] This embodiment details the process of establishing the mapping relationship using experimental design and completing online measurement.

[0055] The core task of the pre-calibration stage is to establish the mapping relationship between the welding galvanometer coordinates and the measurement galvanometer offset compensation values. This is achieved through Design of Experiments (DOE), and the process can be found in the following documentation. Figure 2 and Figure 4 Schematic diagram.

[0056] Step S11: Within the full-width area of ​​the welding galvanometer (e.g., a 100mm × 100mm square region), select multiple test points using the Design of Experiments (DOE) method. The test points must include at least the center point of the full-width area, the center points of the four edges, and the four corner points to ensure the representativeness and comprehensiveness of the calibration.

[0057] Step S12: Place a white ceramic plate or treated aluminum plate as the observation target at the workpiece location. The controller controls the welding galvanometer to move to the first test point, for example, the (-20, -60) position.

[0058] Step S13: The controller triggers the welding laser to emit light at low power, forming an ablation mark on the target. Subsequently, the welding laser is turned off, and the measuring galvanometer is controlled to point the OCT measuring light approximately to the same area.

[0059] Step S14: The operator observes the light spot on the target material through an infrared observation camera. Using the controller's software interface, the operator manually fine-tunes the deflection angle of the measuring galvanometer, i.e., the deflection command values ​​in the X and Y directions, so that the center of the OCT measuring light spot completely coincides with the center of the ablation mark left by the welding laser.

[0060] Step S15: Record the coordinates of the welding galvanometer at this time, as well as the deflection control value of the measuring galvanometer input to make the light spots coincide. This deflection control value is the offset compensation value for this test point.

[0061] Step S16: Repeat steps S12 to S15, iterating through all test points (e.g., 25 points) to obtain multiple sets of data pairs, namely the welding galvanometer coordinates and the corresponding measurement galvanometer offset compensation values. For example, the DOE data obtained in the experiment are shown in the table below:

[0062] X-coordinate of welding galvanometer Y-coordinate of welding galvanometer Keyhole offset coordinate X Keyhole offset coordinate Y -20 -60 -0.05 0.3 -40 -80 0.05 0.35 -40 20 0.09 -0.02 -20 -40 -0.02 0.22 -60 60 0.15 -0.18 -60 -80 0.22 0.35 -80 0 0.22 0.08 0 -40 -0.08 0.26

[0063] Table 1

[0064] Step S17: In the controller, use mathematical software to perform surface fitting on the coordinates and offset compensation values ​​of all test points to obtain the compensation formula. For example, through regression analysis, a compensation formula of the following form may be obtained (the specific coefficients vary depending on the system):

[0065] Offset compensation value X = -0.07062 - 0.004220 × welding galvanometer X coordinate - 0.000189 × welding galvanometer Y coordinate + 0.000001 × welding galvanometer X coordinate × welding galvanometer Y coordinate

[0066] Offset compensation value Y = 0.08765 + 0.000290 × welding galvanometer X coordinate - 0.003470 × welding galvanometer Y coordinate + 0.000001 × welding galvanometer X coordinate × welding galvanometer Y coordinate

[0067] These two formulas, along with all the fitting coefficients, are stored in the controller's non-volatile memory, forming a positional mapping relationship in the form of the compensation formula.

[0068] The online measurement phase is the actual workflow of the system, and the process can be referenced. Figure 1 The "online measurement phase".

[0069] Step S21: The system starts up and is ready to weld at the (30,50) coordinate position of the workpiece.

[0070] Step S22: The controller drives the welding galvanometer to move to the target coordinates (30, 50).

[0071] Step S23: The real-time control program of the controller substitutes the coordinates (30,50) into the pre-stored compensation formulas for the X and Y directions to calculate the required measurement galvanometer offset compensation value. The result is assumed to be (ΔX=0.25V, ΔY=0.40V).

[0072] Step S24: The controller immediately sends the corresponding drive command (0.25V, 0.40V) to the driver of the measuring galvanometer via the analog voltage output card. The measuring galvanometer deflects according to this command to complete the optical path offset compensation.

[0073] Step S25: After confirming that the measuring galvanometer is stably in place, the controller generates a synchronization trigger signal. This signal is simultaneously sent to the welding laser and the OCT measurement module. The welding laser 1 emits light at its operating power for welding, while the OCT measurement module starts up to scan the welding keyhole below and acquire interference signal data.

[0074] Step S26: The collected OCT data is transmitted back to the host computer software of the controller, and processed in real time through algorithms such as Fourier transform to finally obtain and display the weld depth value of the weld point.

[0075] Through the above methods, the system achieves automatic compensation and accurate measurement at any position across the entire width of the screen.

[0076] Example 2: Implementation based on camera calibration method

[0077] This embodiment has the same system structure and online measurement process as Embodiment 1. The main difference is that the method for establishing the mapping relationship in the pre-calibration stage adopts the camera calibration method. The process can be referred to Figure 5 A schematic diagram.

[0078] Pre-calibration stage:

[0079] Step S21: Precisely fix a high-resolution CCD or CMOS camera as the calibration camera at the focal plane position of the scanning objective lens, and ensure that the camera's imaging plane is parallel to the focal plane. Perform intrinsic and extrinsic parameter calibration on the camera, and establish the conversion relationship between pixel coordinates and actual physical coordinates.

[0080] Step S22: The controller controls the welding galvanometer to move sequentially to multiple key positions. Preferably, the key positions are selected from the four corner points, the center points of the four sides, and the center point of the web, for a total of 9 points.

[0081] Step S23: The first key position is that the controller first triggers the welding laser with low power to form a spot on the camera target surface. The camera takes an image and records the center pixel coordinates of the welding laser spot.

[0082] Step S24: Subsequently, the welding laser is turned off, the controller triggers the OCT measurement module to emit light, and the measuring galvanometer is placed in an initial position. The camera captures an image again, recording the center pixel coordinates of the OCT measurement light spot.

[0083] Step S25: Calculate the center deviation between the two light spots. Based on the camera's calibration parameters, convert this pixel deviation into the actual physical position deviation on the workpiece surface.

[0084] Step S26: Based on the deflection sensitivity of the measuring galvanometer, convert the physical position deviation into the offset compensation value required for the measuring galvanometer.

[0085] Step S27: Repeat steps S22 to S26 to complete the calibration of all key positions and obtain multiple sets of welding galvanometer coordinate and offset compensation value data pairs.

[0086] Step S28: Based on these data points, the controller uses a bilinear interpolation algorithm to generate a high-precision data lookup table covering the entire working area. This lookup table is stored in the controller's memory, forming a mapping relationship in the form of a data lookup table. During online measurement, for any given welding galvanometer coordinates, the controller can quickly obtain the corresponding offset compensation value by looking up the table and combining it with interpolation of nearby points.

[0087] The process for the online measurement phase is exactly the same as in Example 1, except that the method of obtaining the compensation value changes from "formula calculation" to "table lookup and interpolation".

[0088] Example 3: Implementation Method Based on Theoretical Calculation

[0089] This embodiment is basically the same as the system structure and online measurement process in Embodiment 1. Its core lies in directly calculating the position mapping relationship through a theoretical optical model. The process can be referred to... Figure 6 The geometric optics model.

[0090] Pre-calibration stage:

[0091] Step S31: Obtain the key optical parameters of the system: welding laser wavelength λ w =1070nm, measuring laser wavelength λ m =1310nm, the focal length of the scanning objective is f=163mm, and the refractive index N of the lens material at wavelengths of 1070nm and 1310nm are... w and N m .

[0092] Step S32: Establish the geometric optical model. When the welding galvanometer is deflected by an angle θ, the ideal welding laser focusing point P is... w Located on the focal plane. Due to the chromatic aberration of the scanning objective lens, for the same incident angle, the actual focal point P is different. m It will deviate from P w .

[0093] Step S33: Based on Snell's law and the lens imaging formula, calculate the additional deflection angle Δθ required by the measuring galvanometer to focus the measuring light onto P. w Point. This Δθ is the theoretical offset compensation value. This calculation process will form a function Δθ=F regarding the welding galvanometer deflection angle θ.

[0094] Step S34: Implement the theoretical function F as an algorithm and embed it into the underlying driver software of the controller. Simultaneously, establish the conversion relationship between the welding galvanometer coordinates (X, Y) and the deflection angle θ. Thus, the entire theoretical compensation formula constitutes the mapping relationship of this invention.

[0095] During online measurement, the controller uses the real-time acquired welding galvanometer coordinates to perform internal coordinate and angle conversion, and then calls the theoretical compensation formula algorithm to calculate the offset compensation value (deflection angle or corresponding voltage command) required for the measuring galvanometer in real time. The subsequent process is the same as in Example 1.

[0096] Although embodiments of the present invention have been shown and described, it is obvious that 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, it will be understood by those skilled in the art that all other embodiments obtained by making various changes, modifications, substitutions and variations to these embodiments without departing from the principles and spirit of the present invention and without creative effort are within the scope of protection of the present invention.

Claims

1. A method for measuring the full-width OCT penetration depth of galvanometer laser welding, characterized in that, Includes the following steps: Pre-calibration step: For the welding galvanometer at multiple coordinate positions within the full-width area, determine and store the corresponding measurement galvanometer offset compensation values, and establish a mapping relationship between the welding galvanometer coordinates and the measurement galvanometer offset compensation values; Online measurement steps: Obtain the current welding coordinates of the welding galvanometer; Based on the current welding coordinates and the mapping relationship, the measuring galvanometer is driven to perform corresponding deflection compensation; Subsequently, the welding laser is synchronously triggered to perform welding, and the OCT measurement module is triggered to perform optical coherence tomography to obtain welding penetration data.

2. The method according to claim 1, characterized in that, The mapping relationship is pre-stored in the controller's memory in the form of a data lookup table or a compensation formula.

3. The method according to claim 1 or 2, characterized in that, In the pre-calibration step, the mapping relationship is established in the following way: Multiple test points are selected within the full width of the welding galvanometer; At each test point, the deflection of the measuring galvanometer is adjusted until the measuring laser and the welding laser coincide on the workpiece surface, and the corresponding offset compensation value is recorded. The mapping relationship is generated based on the coordinates and offset compensation values ​​of all test points.

4. The method according to claim 3, characterized in that, The plurality of test points include at least the center point, edge center point, and corner point of the full-width surface; and the method for generating the mapping relationship is as follows: performing surface fitting on the coordinates and offset compensation values ​​of all test points to obtain the compensation formula.

5. The method according to claim 1 or 2, characterized in that, In the pre-calibration step, the mapping relationship is established in the following way: When the welding galvanometer is measured at multiple key positions by a camera, the deviation of the spot position of the welding laser and the measuring laser on the workpiece surface is measured. The positional deviation is converted into the offset compensation value required for the measuring galvanometer; Based on the coordinates and offset compensation values ​​of the multiple key locations, a data lookup table covering the entire area is generated using a bilinear interpolation algorithm.

6. The method according to claim 1 or 2, characterized in that, In the pre-calibration step, the mapping relationship is established in the following way: Calculations are performed based on the wavelengths of the welding laser and the measurement laser, the optical parameters of the scanning objective, and combined with Snell's law and a geometric optics model. Based on the coordinates or deflection angle of the welding galvanometer, the offset compensation value required by the measuring galvanometer to correct the optical path is calculated, and the compensation formula is formed.

7. A galvanometer laser welding full-width OCT penetration measurement system, used to implement the method according to any one of claims 1 to 6, characterized in that, include: Welding laser, used to generate welding laser light; The OCT measurement module is used to generate a measurement laser and acquire weld penetration information based on optical coherence tomography (OCT) technology. A welding galvanometer is disposed in the optical path of the welding laser and is used to deflect and guide the welding laser to a predetermined position on the surface of the workpiece. A measuring galvanometer is positioned in the optical path of the measuring laser to deflect the measuring laser. A scanning objective lens is positioned downstream of both the welding galvanometer and the measuring galvanometer to focus two laser beams onto the surface of the workpiece. The controller is connected to the welding laser, the OCT measurement module, the welding galvanometer, and the measurement galvanometer, respectively. The controller is configured as follows: Based on the pre-stored mapping relationship and the real-time coordinates of the welding galvanometer, the measuring galvanometer is driven to perform offset compensation. After compensation is completed, the welding laser and the OCT measurement module are triggered synchronously or sequentially to achieve synchronous acquisition of welding and penetration data.

8. The system according to claim 7, characterized in that, Both the welding galvanometer and the measuring galvanometer are two-dimensional galvanometers.

9. The system according to claim 7 or 8, characterized in that, The controller controls the welding laser to emit light and the OCT measurement module to collect data using the same trigger signal or two trigger signals with a fixed delay relationship.

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