A method for optimizing line laser sensors for welding

Abstract

The present invention discloses a line laser sensor for welding and an optimization method thereof, comprising: a power module, a laser generator, an imaging camera and a camera lens, a filter is detachably arranged at the end of the camera lens, and the filter is clamped and fixed by a clamping device; the filter is arranged in parallel with the camera lens; and the line laser sensor adopts a Sham structure line laser sensor. The present invention uses a Sham structure line laser sensor, takes the observation angle, imaging angle, object distance and imaging distance of the line laser sensor as optimization parameters, and optimizes the optimization parameters using a genetic algorithm, which can increase the depth of field of shooting and solve the problem that the camera receives projected laser stripes limited by the depth of field; at the same time, the length and width of the sensor are limited to reduce the volume of the sensor.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a line laser sensor for welding and an optimization method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Robot welding has been widely used in many fields of modern manufacturing, such as shipbuilding, pressure vessel processing, aircraft manufacturing, and high-speed rail vehicle manufacturing. Ordinary welding has high work intensity, harsh working environment, and strict precision requirements. Therefore, the full-position automatic welding technology of welding robots with the advantages of fast speed, good stability, and low cost came into being. The key technology of automatic welding by welding robots is the feature recognition of welds. Existing weld recognition methods include arc sensing, ultrasonic sensing, photoelectric sensing, and visual sensing, among which arc sensing and laser visual sensing are the main research directions.

[0004] Among them, passive vision sensors identify welds based on ambient light sources. During the welding process, interferences such as molten pool, arc light, spatter, and workpiece reflections will seriously affect their recognition accuracy. Active vision sensors based on structured light usually use a laser light source of a specific shape to project onto the surface of the workpiece. Due to the high brightness, high directionality, high monochromaticity, and high coherence of the laser light source, it still has high stability in the welding environment. The deformation caused by the laser at the weld groove can not only reflect the position of the weld, but also the three-dimensional shape of the weld.

[0005] At present, laser vision sensing is based on the principle of laser triangulation and can obtain three-dimensional information of welds. Its image processing process is simple and feature recognition is accurate. It has been widely used in weld recognition. However, when laser sensors are used in welding, they still face the following technical problems:

[0006] (1) Environmental interference: Environmental factors such as light intensity, dust, smoke, etc. may affect the performance of laser sensors, resulting in inaccurate measurement results. Since there is arc splashing during welding, line laser sensors dedicated to welding must have a good anti-interference solution.

[0007] (2) Measurement range limitation: The measurement range of ordinary line laser sensors is usually limited. Targets beyond their range may not be effectively measured, that is, the depth of field of line lasers is limited.

[0008] (3) Sensor volume problem: Most of the line laser sensors of welding robots are installed on the robotic arm. If the sensor is too large or too heavy, it will affect the movement trajectory of the welding robot and occupy the load of the robotic arm.

[0009] (4) The laser sensor filter is difficult to clean and replace: Most sensors on the market use fixed filters, and there is no way to switch them in time for different workpieces during the welding process. Summary of the invention

[0010] In order to solve the above problems, the present invention proposes a line laser sensor for welding and an optimization method thereof, adds a detachable filter structure, and optimizes the Sham structure of the line laser sensor to solve the problem that the camera is limited by the depth of field when receiving the projected laser stripes, while reducing the size of the sensor.

[0011] In some embodiments, the following technical solutions are adopted:

[0012] A line laser sensor for welding comprises: a power module, a laser generator, an imaging camera and a camera lens. A filter is detachably arranged at the end of the camera lens, and the filter is clamped and fixed by a clamping device; the filter is arranged parallel to the camera lens; the line laser sensor adopts a Sham structure line laser sensor.

[0013] Wherein, the clamping device comprises two upper and lower clamping plates, the filter is arranged between the two clamping plates, and the two clamping plates are fixed by bolts.

[0014] The camera lens is fixed to the base plate by a clamp, and the clamp and the base plate are matched by multiple positioning cylinders and oblong holes. The positioning cylinder can move in the corresponding oblong hole to adjust the incident angle of the camera lens, and the position of the positioning cylinder in the oblong hole can be fixed by a hand-tightening bolt.

[0015] In other embodiments, the following technical solutions are adopted:

[0016] A method for optimizing a line laser sensor for welding, comprising:

[0017] The optimization model is constructed with the observation angle, imaging angle, object distance and imaging distance of the line laser sensor as optimization parameters to meet the requirements of the Sham structure and maximize the minimum sensitivity;

[0018] Taking Gaussian imaging, sensor size, minimum sensitivity and field of view as constraints, the parameters in the optimization model are optimized by genetic algorithm to obtain the optimized sensor parameters.

[0019] The optimization model is specifically as follows:

[0020]

[0021]

[0022] Among them, α is the observation angle, that is, the angle between the optical axis of the imaging camera CMOS and the vertical direction of the laser, β is the imaging angle, that is, the angle between the extended line of the imaging camera CMOS plane and the line connecting the CMOS imaging center and the object, is the object distance, that is, the distance between the object and the imaging camera lens, is the imaging distance, that is, the distance between the imaging camera and the lens; S is the distance the object moves within the working range, which here refers to the distance close to or away from the sensor.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The detachable filter structure of the present invention can filter most of the arc light generated by welding, and the filter can be replaced according to different welding conditions.

[0025] (2) The present invention makes the lens angle of the imaging camera adjustable by cooperating with a plurality of positioning cylinders and oblong holes. The adjustable angle can change the optical path angle of the camera lens, which is conducive to artificial compensation of processing errors. It is particularly suitable for scenes that require precise control of the lens angle to ensure accurate imaging. At the same time, the adjustable angle is also conducive to experiments at different angles.

[0026] (3) The present invention uses a Sham structure line laser sensor, takes the observation angle, imaging angle, object distance and imaging distance of the line laser sensor as optimization parameters, and uses a genetic algorithm to optimize the optimization parameters, which can increase the shooting depth of field and solve the problem that the camera is limited by the depth of field when receiving the projected laser stripes; at the same time, it limits the length and width of the sensor and reduces the size of the sensor.

[0027] Other features and advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the overall structure of a line laser sensor used for welding in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the connection structure between the lower base plate, the camera lens and the laser generator in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the back of the lower base plate in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of imaging of a linear laser sensor in an embodiment of the present invention;

[0032] Figure 5 The experimental results of the linear laser sensor photographing the V-shaped weld in the embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of various parameters of the linear laser sensor in an embodiment of the present invention;

[0034] Among them, 1. PCB power board, 2. power cord inlet, 3. laser generator, 4. line laser fixture, 5. imaging camera, 6. camera imaging center, 7. camera lens, 8. light path fixture, 9. filter, 10. clamping shell, 11. set screw, 12. bottom plate, 13. oblong hole, 14. positioning cylinder, 15. hand-tightened bolt. DETAILED DESCRIPTION

[0035] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] Terminology Note:

[0038] The zero position is usually located between the foreground depth of field and the background depth of field, which means that the object will be imaged clearly at this position; in photography, this position can also be called the focal plane.

[0039] Embodiment 1

[0040] In one or more embodiments, a line laser sensor for welding is disclosed, in combination with Figure 1 , specifically including: a power module, a laser generator 3, an imaging camera and a camera lens, a filter is detachably arranged at the end of the camera lens, and the filter is clamped and fixed by a clamping device; the filter is arranged parallel to the camera lens; wherein the line laser sensor adopts a Sham structure line laser sensor.

[0041] Specifically, combined Figure 1The power module adopts a PCB power board 1, which can convert a 24V power supply into a 12V power supply to provide power for the laser generator and the imaging camera respectively. A 24V power supply is provided to the PCB power board through a power line inlet 2. The laser generator adopts a 10mw laser generator, which can generate a 10mw 660nm near-infrared band line laser. The laser generator is clamped and fixed by a line laser fixture 4, and the line laser fixture is set on the bottom plate. The imaging camera 5 adopts the Hikvision MV-CB060-10GMGC-M camera, and the camera lens 7 adopts the M12 camera lens. The central axis of the M12 camera lens passes through the camera imaging center 6. The M12 camera lens is clamped and fixed by an optical path fixture 8. At the front end of the M12 camera lens, a filter 9 is set, which can filter most of the arc bands generated by welding to prevent the laser emitted by the laser generator from being submerged by the strong arc generated during the welding process. The optical filter is fixed by a clamping shell 10, and the clamping shell clamps the optical filter by four fixing screws 11. The optical filter can be replaced externally by loosening the four fixing screws.

[0042] Taking MIG welding as an example, the arc light generated by the welding metal is concentrated between 300nm-600nm wavelength, while the arc light generated by the welding shielding gas Ar is distributed between 700nm-100nm. Therefore, the filter can filter most of the arc light generated by welding, and the filter can be replaced according to different welding conditions.

[0043] Combination Figure 2 and Figure 3 The line laser fixture and the light path fixture are both arranged on the bottom plate 12, wherein the line laser fixture can be arranged as a structure integrated with the bottom plate, three positioning cylinders are arranged at the bottom of the light path fixture, and an oblong hole 13 matching with the positioning cylinders is arranged on the bottom plate, and the positioning cylinder 14 can move in the oblong hole to achieve fine adjustment of the angle of the line laser fixture, and then achieve fine adjustment of the angle of the camera lens; the light path fixture is fixed to the bottom plate by hand-tightening bolts 15. The bottom plate of this embodiment can be generated by 3D printing technology.

[0044] Figure 4 The following is a schematic diagram of the imaging of the line laser sensor of this embodiment, which adopts the laser triangulation measurement technology. Figure 5 An example of experimental results of using a line laser sensor to photograph a V-shaped weld is given.

[0045] In this embodiment, a Sham structured line laser sensor is used, and a genetic algorithm is used to optimize the sensor's observation angle, imaging angle, object distance, imaging distance and other related parameters. This can solve the problem of the camera receiving the projected laser stripes being limited by the depth of field, and can also reduce the size of the sensor.

[0046] Figure 6A schematic diagram of the meaning of each parameter in the line laser sensor is given, where the distance unit is millimeter (mm) and the angle unit is degree (°).

[0047] Figure 6 In the figure, the meaning of the parameters of each size of the sensor is:

[0048] B is the distance between the laser generator and the camera CMOS imaging center, W is the distance between the laser generator and the farthest edge of the CMOS imaging element; H represents the farthest distance between the imaging camera CMOS and the center of the lens, that is, the minimum longitudinal distance of the sensor; H should be greater than the distance from the lens to the camera CMOS protective glass to prevent the lens from hitting the glass and getting scratched; ; α is the observation angle, that is, the angle between the optical axis of the imaging camera CMOS and the vertical direction of the laser; β is the imaging angle, that is, the angle between the extended line of the imaging camera CMOS plane and the line connecting the CMOS imaging center and the object. is the object distance, that is, the distance between the object and the imaging camera lens, is the imaging distance, i.e., the distance between the imaging camera and the lens; S is the distance the object moves within the working range, which here refers to the distance closer to or farther from the sensor;

[0049] L is the imaging length (the length of the object imaged on the photosensitive element), D is the working distance (the distance from the front surface of the sensor to the imaging zero position), B is the distance between the laser generator and the camera CMOS imaging center, V is the distance between the laser generator and the zero position, and R is the minimum axial length of the sensor.

[0050] Point A is the imaging center of the imaging camera CMOS, and point B is the intersection of the farthest boundary line of the imaging camera CMOS and the horizontal line passing through point A; |AB| represents the distance between point A and point B.

[0051] In this embodiment, in combination with the diagram, the conditions for the sensor to form a Sham structure are:

[0052] (1)

[0053] The optimization goal is to prioritize the establishment of the Sham structure.

[0054] Optical sensitivity is a key indicator for evaluating the accuracy of laser triangulation ranging systems. For laser triangulation ranging systems, the sensitivity of its optical structure refers to the ratio of the output change (displacement of the laser spot on the imaging device) to the input change (displacement of the measured object) when the working state is stable.

[0055] If the Sham structure is used as a constraint, it is more difficult to adjust, so the constraint sensitivity is determined so that the goal is to maximize the minimum sensitivity, so the Sham condition is adjusted as a constraint to the goal.

[0056] The sensitivity formula is as follows:

[0057] (2)

[0058] When the distance moved by the object in the working range is S, the calculation formula of S is:

[0059]

[0060] Therefore, this embodiment discloses a line laser sensor optimization method for welding, comprising:

[0061] (1) Based on the observation angle α, imaging angle β, and object distance of the line laser sensor and imaging distance In order to optimize the parameters to meet the requirements of the Sham structure and maximize the minimum sensitivity, an optimization model is constructed; the optimization model is specifically a combination of formulas (1) and (2).

[0062] (2) Using Gaussian imaging, sensor size, minimum sensitivity and field of view as constraints, the parameters in the optimization model are optimized through genetic algorithm to obtain the optimized sensor parameters.

[0063] The specific constraints are as follows:

[0064] ① Gaussian imaging constraints are specifically:

[0065]

[0066] This equation ensures that the image is clear and is the most basic formula for the imaging principle of cameras and lenses. In the optimization process, the transformation is in the form of.

[0067] ②The minimum sensitivity constraint is: ; val is the sensitivity threshold to be set.

[0068] ③ The sensor size constraints are as follows:

[0069] ;

[0070] ;

[0071]

[0072] a and b are the lower and upper limits of W, respectively; c and d are the lower and upper limits of H, respectively.

[0073] ④ The constraints of the shooting field of view are as follows:

[0074]

[0075] Among them, FOV represents the field of view, FOV≥ , is the visual field threshold, is the long side size of the CMOS sensor, and f is the lens .

[0076] As a specific example, the specific parameters of the sensor device are as follows:

[0077] f = 25 focal length, L = 5.32, S = 25, D = 300

[0078] The genetic algorithm constraints are:

[0079] Gauss's theorem:

[0080] Sensitivity constraints: , where val is set to 0.05.

[0081] Sensor size constraints: , W∈ Although the range of H is not written here, it can be constrained by the value of α.

[0082] Constraints on the field of view: , Take the long side size here =L=5.32; FOV≥ , is the visual field threshold.

[0083] Parameters that need to be optimized: observation angle α, imaging angle β, object distance and imaging distance ; Parameter optimization range: α∈ , β∈ , ∈ , ∈ .

[0084] Through genetic algorithm, the optimization parameters are 4, 100 parameters are selected in each generation, 1000 iterations are performed, and the parameter accuracy is 1e -7 .

[0085] Input the above calculation conditions into MATLAB. First, find the GA (Genetic Algorithm) in the Optimization toolbox in the App, input the above constraints, and then you can calculate the optimized parameters.

[0086] Or use python to write GA (genetic algorithm) implementation, or the algorithm library provided by geatpy officially.

[0087] Take the result once and optimize the parameters: finally get the following four parameters:

[0088] α = 2.99528167e-01; β = 1.40934836e+00;

[0089] = 3.03251321e+02; = 1.52523326e+01.

[0090] Designing a line laser sensor based on the above parameters can increase the shooting depth of field and solve the problem that the camera is limited by the depth of field when receiving the projected laser stripes; at the same time, it limits the length and width of the sensor and reduces the size of the sensor.

[0091] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for optimizing a line laser sensor for welding, characterized in that: include: The optimization model is constructed with the observation angle, imaging angle, object distance and imaging distance of the line laser sensor as optimization parameters to meet the requirements of the Sham structure and maximize the minimum sensitivity; Taking Gaussian imaging, sensor size, minimum sensitivity and field of view as constraints, the parameters in the optimization model are optimized by genetic algorithm to obtain the optimized sensor parameters. Constraining sensitivity, so that the goal is to maximize the minimum sensitivity while taking the Sham condition as the optimization goal; The optimization model is specifically: Among them, α is the observation angle, that is, the angle between the optical axis of the imaging camera CMOS and the vertical direction of the laser, β is the imaging angle, that is, the angle between the extended line of the imaging camera CMOS plane and the line connecting the CMOS imaging center and the object, is the object distance, that is, the distance between the object and the imaging camera lens, is the imaging distance, i.e., the distance between the imaging camera and the lens; S is the distance the object moves within the working range, which here refers to the distance closer to or farther from the sensor; is the minimum sensitivity.

2. A method for optimizing a line laser sensor for welding as claimed in claim 1, characterized in that: The Gaussian imaging constraints are specifically: in, For the lens , is the object distance, that is, the distance between the object and the imaging camera lens, is the imaging distance, that is, the distance between the imaging camera and the lens.

3. A method for optimizing a line laser sensor for welding as claimed in claim 1, characterized in that: The sensor size constraints are as follows: ； in, ； ； W is the distance between the laser generator and the farthest boundary of the CMOS imaging element; H represents the farthest distance between the imaging camera CMOS and the center of the lens, that is, the minimum longitudinal distance of the sensor; a and b are the lower and upper limits of W, respectively, and c and d are the lower and upper limits of H, respectively; L is the imaging length; B is the distance between the laser generator and the imaging center of the camera CMOS; |AB| represents the distance between point A and point B; point A is the imaging center of the imaging camera CMOS, and point B is the intersection of the farthest boundary line of the imaging camera CMOS and the horizontal line passing through point A.

4. A method for optimizing a line laser sensor for welding as claimed in claim 1, characterized in that: The minimum sensitivity constraint is specifically: ； Among them, val is the sensitivity threshold set.

5. A method for optimizing a line laser sensor for welding as claimed in claim 1, characterized in that: The shooting field of view constraints are as follows: ； Among them, FOV represents the field of view, FOV≥ , is the visual field threshold, is the long side size of the CMOS sensor, and f is the lens .

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