A method for automatic calibration of laser welding trajectory for gapless welds

Abstract

The present invention proposes a method for automatically calibrating the laser welding trajectory of gapless welds, characterized in that a trajectory calibration system is used; the steps of the automatic calibration method are: step one: importing or generating a preset trajectory; step two: automatic focusing, controlling the welding head to move back and forth along the laser processing light path to perform CCD image acquisition, identifying the position with the highest clarity of the full-width CCD image, and setting this position as the reference point; step three: posture adjustment, extracting and identifying the light spot morphology in the CCD image; when an abnormal light spot morphology is found, adjusting the welding head posture; step four: optimizing the welding trajectory; step five: completing the welding trajectory inspection. The present invention uses coaxial image monitoring, avoiding the position error caused by the method of pre-structured light or laser rangefinder, as well as the problem of difficulty in identifying gapless welds, full-position fillet welds, or small-diameter pipe-to-pipe joints, or the reduction in accuracy caused by image splicing, and the cost is significantly lower than that of structured light sensors.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, in particular to a method for automatically calibrating a laser welding track of a gapless weld. Background Art

[0002] In the field of laser welding, in addition to special processes, the relative position of the focus and the workpiece needs to remain stable during the welding process to obtain a stable and uniform weld. Existing autofocus methods are generally divided into four types:

[0003] One method uses laser line structured light as a front scanning device to obtain weld surface morphology information. After obtaining the welding trajectory, it controls the rear laser welding head for calibration. However, this method is limited by the installation distance between the structured light and the welding head. Moreover, this method is mostly suitable for long straight welds and has a slightly poor recognition effect on joints without gaps or grooves.

[0004] The second method is to install a laser rangefinder on the laser welding head to directly measure the distance between a specific position and the workpiece. However, this method is more suitable for workpieces with a single structure and straight welds.

[0005] The third method is to use an external CCD camera to locate the welding position by taking pictures and identifying images, or to obtain three-dimensional information of the welding position through multi-angle cameras before welding. However, this method has difficulty in identifying welds at multiple angles or all positions, and requires more camera combinations or multi-angle three-dimensional recognition.

[0006] Fourth, a coaxial CCD camera or other sensor is used in conjunction with a nearby CCD camera or other device to jointly complete focusing and trajectory recognition. There is little research on using a coaxial sensor alone for autofocus and trajectory calibration.

[0007] The above four methods all have the problems of low recognition resolution, incomplete functions of a single method, and difficulty in finding the weld position in butt joints without gaps and grooves. In corner joints, they can only identify the joint position under certain conditions and have difficulty in identifying small-sized and spatial curve welds. Therefore, the above four methods cannot be applied in engineering under some working conditions. Summary of the Invention

[0008] In response to the problems existing in the prior art, the present invention proposes a method for automatic calibration of the laser welding trajectory of gapless welds. By improving the hardware design and cooperating with the image recognition system, the automatic focusing and trajectory calibration of gapless welds are completed, reducing the participation of manual teaching, improving welding efficiency and welding accuracy, and is particularly suitable for the automatic welding of small-diameter pipe-to-pipe butt welds and tube-to-plate fillet welds.

[0009] In view of this, the present invention provides an automatic calibration method for the laser welding trajectory of a gapless weld, which is implemented based on a welding robot with a trajectory calibration system; the welding robot is provided with a laser welding head with a coaxial monitoring optical path, the laser welding head including a laser processing optical path and a CCD imaging optical path coaxial with the laser processing optical path; the laser processing optical path includes a collimator lens, a spectrometer lens, a focusing lens and a high-transmittance glass protection lens arranged in sequence along the laser processing optical path, the CCD imaging optical path includes a CCD camera, a lens module, a reflective lens and a bandpass filter arranged in sequence, the CCD camera and the lens module are respectively electrically connected to the control system inside the welding robot; the CCD imaging optical path is arranged on one side of the spectrometer lens; the method comprises the following steps:

[0010] Step 1: Import or generate preset welding trajectory

[0011] Generate a welding trajectory according to the part model, import the welding trajectory into the trajectory calibration system, and move the laser welding head to the starting point of the welding trajectory;

[0012] Step 2: Autofocus

[0013] Adjust the aperture of the automatically adjustable iris in the lens module to 22mm-28mm, increase the CCD image brightness, and reduce the depth of field to less than 0.2mm. Control the laser welding head to move back and forth along the laser processing optical path through the control system to collect CCD images, identify the position of the CCD image with the highest clarity, and set the coordinates of the position of the laser welding head at this position as the reference point.

[0014] Step 3: Laser welding head posture adjustment

[0015] Extracting and identifying the light spot morphology in the CCD image; when the light spot morphology is found to be abnormal, adjusting the laser welding head posture according to a predetermined adjustment strategy;

[0016] Step 4: Optimize welding trajectory

[0017] After completing the adjustment of the laser welding head posture, repeat steps 2 and 3 until the spot shape and the focus position of the reference point are normal, then optimize the welding trajectory, generate a new welding trajectory based on the optimized welding trajectory, and re-import the new welding trajectory into the trajectory calibration system;

[0018] Step 5: Complete welding track inspection

[0019] The laser welding head is controlled by the control system to continue to move along the welding track. When the clarity of the CCD image decreases and / or the halo morphology becomes abnormal, the welding track is recalibrated at this position according to the process of steps 2 to 4; after the calibration is completed, the welding track is re-inspected until the new welding track is normal, and the welding track calibration is completed.

[0020] Preferably, the automatic calibration method for the laser welding trajectory of the gapless weld further includes welding and process monitoring;

[0021] According to the monitoring needs of the welding process, the aperture of the automatic adjustable aperture is set to -5mm-+5mm, the laser power is 300W-2000W, the welding speed is 0.5m / min-2m / min, the shielding gas is Ar gas, and the flow rate is 10L / min-30L / min to complete the pre-welding preparation; during the welding process, a CCD camera is used to capture the coaxial image of the molten pool according to the CCD imaging optical path.

[0022] Preferably, the automatic calibration method for the laser welding trajectory of the gapless weld further comprises a post-weld inspection;

[0023] The appearance and internal quality of the weld after welding are inspected. The appearance morphology inspection is carried out through manual visual inspection or by setting the aperture of the automatic adjustable aperture to 5mm-15mm, and the laser welding head is moved to collect the surface image of the weld after welding. The surface defects of the weld after welding are inspected by fluorescence, and the internal quality of the weld after welding is inspected by X-ray.

[0024] Preferably, in step three, the predetermined adjustment strategy is to obtain the laser head deflection by identifying the light spot morphology characteristics, and adjust the laser welding head posture according to the laser welding head deflection to restore the light spot morphology to normal.

[0025] Preferably, in step three, after adjusting the aperture of the automatic adjustable diaphragm in the lens module to 10 mm-16 mm, the light spot morphology in the CCD image is extracted and identified.

[0026] Preferably, the method for optimizing the welding trajectory in step 4 is:

[0027] There are n characteristic trajectory points on the welding trajectory. During the movement of the laser welding head along the welding trajectory, when the distance between the calibrated coordinates of the laser welding head and the nearest characteristic trajectory point is not greater than a set value, the nearest characteristic trajectory point in the trajectory calibration system is deleted, and the coordinate point of the nearest characteristic trajectory point is replaced by a new characteristic trajectory point. When the distance between the calibrated coordinates of the laser welding head and the nearest trajectory point is greater than a set value, the calibrated coordinate point is inserted into the welding trajectory to become a new characteristic trajectory point. A new welding trajectory is generated according to the optimized new characteristic trajectory point, and the new welding trajectory is re-imported into the trajectory calibration system.

[0028] The beneficial effects of the present invention are:

[0029] 1. In the present invention, coaxial image monitoring is adopted to avoid the position error caused by the method of front structured light or laser rangefinder, as well as the problem of difficulty in identifying gapless welds, full-position fillet welds or small-diameter pipe-to-pipe joints, or the reduction in accuracy caused by image stitching, and the cost is significantly lower than that of structured light sensors.

[0030] 2. Compared with trajectory recognition using multiple cameras, the present invention reduces equipment costs. For multi-angle spatial curve welds, there is no need to arrange multiple cameras for recognition, which reduces the computational difficulty and improves recognition efficiency and accuracy. In particular, the recognition accuracy is higher for welds without gaps or small sizes.

[0031] 3. Compared with the existing coaxial calibration method, the present invention improves the trajectory calibration system, utilizes the correspondence between aperture and depth of field, adopts a large aperture to control the focusing range, improves the focusing accuracy, and adjusts the position of the laser welding head at the same time, so that the laser head always maintains a certain distance and angle with the weld surface during welding, ensuring the consistency of weld formation.

[0032] 4. The present invention is suitable for gapless thin plate laser welding, which can realize rapid positioning and trajectory calibration before welding, reduce manual teaching participation, greatly improve the production efficiency of parts welding, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of the automatic calibration method for the laser welding trajectory of a gapless weld according to the present invention;

[0034] Figure 2 This is a schematic structural diagram of a laser welding head with a coaxial monitoring optical path according to the present invention;

[0035] Figure 3 This is the typical spot shape of the butt joint of the present invention;

[0036] In the figure: 1. Collimating lens; 2. Beam splitter; 3. Focusing lens; 4. High-transmittance glass protection lens; 5. CCD camera; 6. Lens module; 7. Reflecting lens; 8. Bandpass filter. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] See also Figure 1-3 As shown, the present invention is a method for automatically calibrating the laser welding trajectory of a gapless weld, using a welding robot, which is provided with a laser welding head with a coaxial monitoring optical path, see Figure 2 As shown, the laser welding head includes a CCD imaging optical path along and coaxial with the laser processing optical path. The laser processing optical path includes a collimator 1, a beam splitter 2, a focusing lens 3, and a high-transmittance glass protective lens 4, arranged in sequence. The CCD imaging optical path includes a CCD camera 5, a lens module 6, a reflective lens 7, and a bandpass filter 8. The CCD camera 5 and lens module 6 are each electrically connected to the welding robot's internal control system. The CCD imaging optical path is located on either side of the beam splitter 2. The CCD camera 5 uses a universal interface and has a resolution of at least 480×480 pixels. The lens module 6 consists of an automatically adjustable iris and optical lenses. The aperture range of the automatically adjustable iris is 0mm-30mm. The bandpass filter has a passband of 400nm-750nm, with a cutoff depth of OD2-4 in other bands. The welding robot also includes a trajectory calibration system.

[0040] Based on this, the present invention provides a method for automatically calibrating a laser welding trajectory for a gapless weld, comprising the following steps:

[0041] Step 1: Import or generate preset welding trajectory

[0042] Generate welding trajectory according to the part model, import welding trajectory points into trajectory calibration system, the welding trajectory includes starting point and end point, and move the welding robot to the starting point of the welding trajectory point;

[0043] Step 2: Autofocus

[0044] Adjust the aperture of the automatically adjustable iris in the lens module 6 to 22mm-28mm, increase the brightness of the CCD image, and reduce the depth of field to less than 0.2mm. Use the control system in the welding robot to control the laser welding head on it to move back and forth along the laser processing optical path to collect CCD images, identify the position with the highest CCD image clarity, and set the coordinates of the position of the laser welding head at this position as the reference point;

[0045] Step 3: Posture Adjustment

[0046] Extract and identify the light spot shape in the CCD image; when the light spot shape is found to be abnormal, adjust the laser welding head posture according to the established adjustment strategy;

[0047] Step 4: Optimize welding trajectory

[0048] After completing the adjustment of the laser welding head posture, repeat steps 2 and 3 until there are no abnormalities in the spot shape and the focus position of the reference point. Then optimize the welding trajectory, generate a new welding trajectory based on the optimized welding trajectory, and re-import the new welding trajectory into the trajectory calibration system;

[0049] Step 5: Complete welding track inspection

[0050] The laser welding head is controlled by the control system to continue to move along the welding track. When the clarity of the CCD image decreases and / or the halo shape becomes abnormal, the welding track is recalibrated at this position according to steps 2 to 4. After the calibration is completed, the welding track is re-inspected until the new welding track is normal and the welding track calibration is completed.

[0051] Example 2

[0052] The present embodiment provides a method for automatically calibrating a laser welding trajectory for a gapless weld, comprising the following steps:

[0053] Step 1: Import or generate preset tracks

[0054] Generate a welding trajectory based on the part model, import the welding trajectory into the trajectory calibration system, the welding trajectory includes a starting point and an end point, and move the welding robot to the starting point of the welding trajectory; the welding trajectory includes but is not limited to a curved welding trajectory or a straight welding trajectory;

[0055] Step 2: Autofocus

[0056] Adjust the aperture of the automatically adjustable iris in the lens module 6 to 22mm-28mm, increase the brightness of the CCD image, and reduce the depth of field to less than 0.2mm. Use the control system inside the welding robot to control the laser welding head on it to move back and forth along the laser processing optical path to collect CCD images, identify the position with the highest CCD image clarity, and set the coordinates of the position of the laser welding head at this position as the reference point;

[0057] Step 3: Posture Adjustment

[0058] Adjust the aperture of the automatic adjustable iris in the lens module 6 to 10mm-16mm, and extract and identify the light spot shape in the CCD image; see Figure 3 As shown, Figure 3 (a) is the normal spot shape, Figure 3(b), (c), (d) and (e) are abnormal spot shapes. By identifying the spot state, it is possible to determine whether the laser head posture is correct and then correct it. When the spot shape is found to be abnormal, the deflection of the laser welding head is obtained by identifying the spot shape characteristics. The laser welding head posture is adjusted according to the deflection of the laser welding head to restore the spot shape to normal. Adjusting the laser welding head posture includes offsetting and rotating the laser welding head.

[0059] Step 4: Trajectory Optimization

[0060] After completing the adjustment of the laser welding head posture, repeat steps 2 and 3 until there are no abnormalities in the spot shape and the focus position of the reference point, and then optimize the welding trajectory. Set n characteristic trajectory points on the welding trajectory. When the welding robot moves along the welding trajectory, when the distance between the calibrated coordinates of the laser welding head and the nearest characteristic trajectory point is not greater than the set value, delete the nearest characteristic trajectory point in the trajectory calibration system, and replace the coordinate point of the nearest characteristic trajectory point with a new characteristic trajectory point. When the distance between the calibrated coordinates of the laser welding head and the nearest trajectory point is greater than the set value, insert the calibrated coordinates into the welding trajectory to become a new characteristic trajectory point. Generate a new welding trajectory based on the optimized characteristic trajectory points, and re-import the new welding trajectory into the trajectory calibration system; wherein, the set value is set manually according to the part model or automatically calibrated and set by the trajectory calibration system based on the part model;

[0061] Step 5: Complete trajectory verification

[0062] The laser welding head is controlled by the control system to continue to move along the welding track. When the CCD image clarity decreases and / or the halo morphology becomes abnormal, the welding track is recalibrated at that position according to steps 2 to 4. When the laser welding head moves to the end point of the welding track and all calibrations are completed, it returns to the starting point of the welding track and repeats the welding track recheck until the new welding track is normal, completing the welding track calibration.

[0063] Step 6: Welding and process monitoring

[0064] According to the monitoring requirements of the welding process, the aperture of the automatically adjustable diaphragm of the lens module 6 is set to -5mm-+5mm, the laser power is 300W-2000W, the welding speed is 0.5m / min-2m / min, and the shielding gas is Ar gas with a flow rate of 10L / min-30L / min to complete the pre-welding preparation; during the welding process, the CCD camera 5 is used to capture the coaxial image of the molten pool according to the CCD imaging optical path;

[0065] Step 7: Post-weld inspection

[0066] The appearance and internal quality of the weld after welding are inspected. The appearance morphology inspection is carried out by manual visual inspection or by setting the aperture of the automatic adjustable aperture to 5-15mm. The laser welding head is moved to collect the surface image of the weld after welding. The surface defects of the weld after welding are usually inspected by fluorescence, and the internal quality of the weld after welding is usually inspected by X-ray.

[0067] Example 3

[0068] The only difference between this embodiment and embodiment 1 is that the following steps are added in step 1: pre-welding assembly and positioning

[0069] The parts to be welded are processed to the corresponding precision as required, and the surfaces on both sides of the parts are polished or cleaned after processing; they are assembled on the fixture to complete the positioning welding.

[0070] Example 4

[0071] The present embodiment provides a method for automatically calibrating a laser welding trajectory for a gapless weld, comprising the following steps:

[0072] Step 1: Import or generate preset tracks

[0073] Generate a welding trajectory based on the part model, import the welding trajectory into the trajectory calibration system, the welding trajectory includes a starting point and an end point, and move the welding robot to the starting point of the welding trajectory; the welding trajectory includes but is not limited to a curved welding trajectory or a straight welding trajectory;

[0074] Step 2: Autofocus

[0075] Adjust the aperture of the automatic adjustable diaphragm in the lens module 6 to 24 mm, increase the brightness of the CCD image, and reduce the depth of field to 0.1 mm. Use the control system inside the welding robot to control the laser welding head on it to move back and forth along the laser processing optical path to collect CCD images, identify the position with the highest CCD image clarity, and set the point where the laser welding head is located in the laser processing optical path at this position as the reference point;

[0076] Step 3: Posture Adjustment

[0077] Adjust the aperture of the automatic adjustable iris in the lens module 6 to 14 mm, and extract and identify the light spot shape in the CCD image; see Figure 3 As shown, Figure 3 (a) is the normal spot shape, Figure 3(b), (c), (d) and (e) are abnormal spot shapes. By identifying the spot state, it is possible to determine whether the laser head posture is correct and then correct it. When the spot shape is found to be abnormal, the deflection of the laser welding head is obtained by identifying the spot shape characteristics. The laser welding head posture is adjusted according to the deflection of the laser welding head to restore the spot shape to normal. Adjusting the laser welding head posture includes offsetting and rotating the laser welding head.

[0078] Step 4: Trajectory Optimization

[0079] There are n characteristic trajectory points on the welding trajectory. When the welding robot moves along the welding trajectory, when the distance between the coordinates of the laser welding head after calibration and the nearest characteristic trajectory point is not greater than a set value, the nearest characteristic trajectory point in the trajectory calibration system is deleted, and the coordinate point of the nearest characteristic trajectory point is replaced with a new characteristic trajectory point. When the distance between the coordinates of the laser welding head after calibration and the nearest trajectory point is greater than a set value, the calibrated coordinates are inserted into the welding trajectory to become new characteristic trajectory points. A new welding trajectory is generated according to the optimized characteristic trajectory points, and the new welding trajectory is re-imported into the trajectory calibration system. Wherein, the surface of the part to be welded is circular, and the radius of the circle is 17 mm. The specific setting value is set manually according to the part model or automatically calibrated by the trajectory calibration system according to the part model and set between 0 mm and 17 mm.

[0080] Step 5: Complete trajectory verification

[0081] The laser welding head is controlled by the control system to continue to move along the welding track. When the clarity of the CCD image decreases or the halo morphology becomes abnormal, the welding track is recalibrated at that position according to steps 2 to 4. All calibrations are completed until the laser welding head moves to the end point of the welding track. Then, it returns to the starting point of the welding track and repeats the welding track recheck until the new welding track is normal and the welding track calibration is completed.

[0082] Step 6: Welding and process monitoring

[0083] According to the monitoring requirements of the welding process, the aperture of the automatically adjustable diaphragm of the lens module 6 is set to 4 mm, the laser power is 600 W, the welding speed is 1 m / min, and the shielding gas is Ar gas with a flow rate of 20 L / min. The pre-welding preparation is completed. During the welding process, the CCD camera 5 is used to capture the coaxial image of the molten pool according to the CCD imaging optical path.

[0084] Step 7: Post-weld inspection

[0085] The appearance and internal quality of the weld after welding are inspected. The appearance morphology inspection is carried out by manual visual inspection or by setting the aperture of the automatic adjustable aperture of the light to 10mm, and collecting the surface image of the weld after welding by moving the laser welding head. The surface defects of the weld after welding are usually inspected by fluorescence, and the internal quality of the weld after welding is usually inspected by X-ray.

Claims

1. A method for automatically calibrating the laser welding trajectory for gapless welds, implemented based on a welding robot with a trajectory calibration system; the welding robot is provided with a laser welding head with a coaxial monitoring optical path, the laser welding head comprising a laser processing optical path and a CCD imaging optical path coaxial with the laser processing optical path; the laser processing optical path comprises a collimator lens, a beam splitter lens, a focusing lens, and a high-transmittance glass protective lens sequentially arranged along the laser processing optical path; the CCD imaging optical path comprises a CCD camera, a lens module, a reflective lens, and a bandpass filter sequentially arranged; the CCD camera and lens module are respectively electrically connected to a control system within the welding robot; the CCD imaging optical path is arranged on one side of the beam splitter lens; and the method is characterized in that: The steps include: Step 1: Import or generate preset welding trajectory Generate a welding trajectory according to the part model, import the welding trajectory into the trajectory calibration system, and move the laser welding head to the starting point of the welding trajectory; Step 2: Autofocus Adjust the aperture of the automatically adjustable iris in the lens module to 22mm-28mm, increase the CCD image brightness, and reduce the depth of field to less than 0.2mm. Control the laser welding head to move back and forth along the laser processing optical path through the control system to collect CCD images, identify the position of the CCD image with the highest clarity, and set the coordinates of the position of the laser welding head at this position as the reference point. Step 3: Laser welding head posture adjustment Extracting and identifying the light spot morphology in the CCD image; when the light spot morphology is found to be abnormal, adjusting the laser welding head posture according to a predetermined adjustment strategy; Step 4: Optimize welding trajectory After completing the adjustment of the laser welding head posture, repeat steps 2 and 3 until the spot shape and the focus position of the reference point are normal, then optimize the welding trajectory, generate a new welding trajectory based on the optimized welding trajectory, and re-import the new welding trajectory into the trajectory calibration system; Step 5: Complete welding track inspection The laser welding head is controlled by the control system to continue to move along the welding track. When the clarity of the CCD image decreases and / or the halo morphology becomes abnormal, the welding track is recalibrated at this position according to the process of steps 2 to 4; after the calibration is completed, the welding track is re-inspected until the new welding track is normal, and the welding track calibration is completed.

2. The automatic calibration method for laser welding trajectory of gapless weld according to claim 1, characterized in that: It also includes welding and process monitoring; According to the monitoring needs of the welding process, the aperture of the automatic adjustable aperture is set to -5mm-+5mm, the laser power is 300W-2000W, the welding speed is 0.5m / min-2m / min, the shielding gas is Ar gas, and the flow rate is 10L / min-30L / min to complete the pre-welding preparation; during the welding process, a CCD camera is used to capture the coaxial image of the molten pool according to the CCD imaging optical path.

3. The automatic calibration method for laser welding trajectory of gapless weld according to claim 1, characterized in that: It also includes post-weld inspection; The appearance and internal quality of the weld after welding are inspected. The appearance morphology inspection is carried out through manual visual inspection or by setting the aperture of the automatic adjustable aperture to 5mm-15mm, and the laser welding head is moved to collect the surface image of the weld after welding. The surface defects of the weld after welding are inspected by fluorescence, and the internal quality of the weld after welding is inspected by X-ray.

4. The automatic calibration method for laser welding trajectory of gapless weld according to claim 1, characterized in that: In the step three, the established adjustment strategy is to obtain the laser head deflection by identifying the light spot morphology characteristics, and adjust the laser welding head posture according to the laser welding head deflection to restore the light spot morphology to normal.

5. The automatic calibration method for laser welding trajectory of gapless weld according to claim 1, characterized in that: In the step three, after adjusting the aperture of the automatic adjustable diaphragm in the lens module to 10mm-16mm, the light spot morphology in the CCD image is extracted and identified.

6. The automatic calibration method for laser welding trajectory of gapless weld according to claim 5, characterized in that: The method for optimizing the welding trajectory in step 4 is: There are n characteristic trajectory points on the welding trajectory. During the movement of the laser welding head along the welding trajectory, when the distance between the calibrated coordinates of the laser welding head and the nearest characteristic trajectory point is not greater than a set value, the nearest characteristic trajectory point in the trajectory calibration system is deleted, and the coordinate point of the nearest characteristic trajectory point is replaced by a new characteristic trajectory point. When the distance between the calibrated coordinates of the laser welding head and the nearest trajectory point is greater than a set value, the calibrated coordinate point is inserted into the welding trajectory to become a new characteristic trajectory point. A new welding trajectory is generated according to the optimized new characteristic trajectory point, and the new welding trajectory is re-imported into the trajectory calibration system.

Images