阅读说明：本技术 基于激光传感器的变姿态实时焊缝跟踪方法 (Attitude-changing real-time welding seam tracking method based on laser sensor ) 是由 陈新禹 于 2019-11-15 设计创作，主要内容包括：本发明公开了一种基于激光传感器的变姿态实时焊缝跟踪方法,提出基于绝对焊缝路径的焊缝跟踪方法,可以适应变换姿态和变化速度的焊接跟踪过程；在焊缝跟踪过程中,提出使用样条插值算法实现当前焊枪在焊缝轨迹中的准确对应点计算方法；算法中引入非均匀有理B样条插值方式,使得本发明的跟踪方法同样适应于激光传感器采集数据间距不等的情况,具有跟踪精度高,焊接质量好等优点。(The invention discloses a variable-attitude real-time weld joint tracking method based on a laser sensor, and provides a weld joint tracking method based on an absolute weld joint path, which can adapt to a welding tracking process of changing attitude and changing speed; in the process of tracking the welding seam, a calculation method for realizing the accurate corresponding point of the current welding gun in the welding seam track by using a spline interpolation algorithm is provided; a non-uniform rational B-spline interpolation mode is introduced into the algorithm, so that the tracking method disclosed by the invention is also suitable for the condition that the distances among data acquired by a laser sensor are unequal, and the method has the advantages of high tracking precision, good welding quality and the like.)

1. A posture-changing real-time weld joint tracking method based on a laser sensor is characterized by comprising the following steps:

1) creating an FIFO stack, and distributing the size of the FIFO stack according to the front distance of the laser sensor relative to the welding gun and the sampling frame rate of the laser sensor, wherein the FIFO stack is used for caching the absolute welding seam track;

2) acquiring coordinates of a welding seam sampling point of a laser sensor;

3) converting the coordinates of the welding seam sampling point in the step 2) to the coordinates of the welding robot according to the transformation relation between the coordinate system of the laser sensor and the coordinate system of the welding robot to obtain the coordinates of a new welding seam sampling point, and pressing the coordinates of the new welding seam sampling point into an FIFO (first in first out) stack;

4) acquiring actual position coordinate P of welding gun in welding robot_TSearching the FIFO stack for the position coordinate closest to the actual position coordinate of the welding gun, and then searching the FIFO stack for the position coordinate closest to the actual position coordinate of the welding gun by using the closest position coordinate and 3 adjacent to the closest position coordinateTaking the position coordinate as a control point, and carrying out non-uniform rational B-spline interpolation to obtain the actual position coordinate P of a welding gun in the welding robot_TCorresponding position coordinate P 'on the weld track'_T

5) Calculating and obtaining the position deviation Err of a welding gun in the current welding robot by using the following formula, converting the position deviation Err of the welding gun into a welding gun coordinate system in the welding robot, and correcting the deviation of the welding robot;

Err＝P′_T-P_T；

6) and (5) circularly executing the steps 2) to 5) until the weld joint is completely tracked.

2. The method for the variable-attitude real-time weld tracking based on the laser sensor as claimed in claim 1, wherein the weld sampling point of the laser sensor in the step 2) is an intersection position point of a laser line and a weld in the laser sensor.

3. The method for tracking the varied-attitude real-time weld joint based on the laser sensor as claimed in claim 1, wherein the transformation relationship between the laser sensor coordinate system and the welding robot coordinate system in step 3) is specifically as follows:

wherein, P_RIs the homogeneous coordinate value of the new welding seam sampling point,Is a transformation matrix from a welding gun coordinate system to a welding robot coordinate system in the welding robot,

4. The laser sensor based posture-changing real-time weld joint tracking method according to claim 3, characterized in that a transformation matrix from a welding gun coordinate system to a welding robot coordinate system in the welding robot is adopted

5. The attitude-variable real-time weld joint tracking method based on the laser sensor as claimed in claim 1, characterized in that, before the new weld joint sampling point coordinates are pressed into the FIFO stack in step 3), the new weld joint sampling point coordinates are filtered based on Kalman filtering algorithm, if the difference between the new weld joint sampling point coordinates and the estimated point coordinates is greater than a threshold value, the new weld joint sampling point coordinates are regarded as noise point coordinates to be filtered, and the step 2) is returned;

otherwise, proceed to step 4).

Technical Field

The invention relates to the technical field of automatic welding, in particular to a variable-attitude real-time welding seam tracking method based on a laser sensor.

Background

Welding is one of the most important material forming and processing technologies in modern manufacturing industry, and the development of the welding manufacturing technology has great significance for China to become a manufacturing strong country. However, welding is a work with poor labor condition, much smoke, large heat radiation, high risk and strong repeatability, and meanwhile, as the welding manufacturing industry presents increasingly prominent problems of multiple batches, small batches and lack of personnel, how to realize automation of the welding process becomes a key technology for promoting the development of the manufacturing industry.

Most of the current welding robots work in a teaching mode, for example, in the fields of automobile manufacturing, heavy machinery production, shipbuilding and the like, the space track, the operation condition, the operation sequence and the like of a robot operation mechanism need to be taught in advance, and the requirements on the installation and positioning accuracy of a tool and a clamp of a welded workpiece are very strict. In addition, most of plates are affected by thermal deformation factors in the welding process, so that the initial teaching welding path inevitably has different-degree deviations compared with the real welding line, and the precision requirements cannot be met for high-precision welding processes (laser welding, argon arc welding and the like). If form complete welding automation system through a set of frock of high accuracy, not only manufacturing cost is too high, can reduce production efficiency, and the equipment transformation upgrading degree of difficulty is big moreover. Therefore, the welding robot is endowed with the ability of keenly sensing the environment and intelligently analyzing and processing, and the realization of automation, flexibility and intellectualization of the welding manufacturing process is an urgent need of a plurality of industries at present.

With the continuous development of vision measurement technology and industrial robots, if the advantages of non-contact, high speed and high precision of a vision measurement sensor are combined with the advantages of high degree of freedom of the industrial robot, the online guiding welding process is solved by researching and developing corresponding algorithms of weld joint identification, online tracking, real-time feedback, intelligent control and the like. Therefore, the production efficiency can be improved, the welding quality can be ensured, the production cost caused by high-precision tooling can be reduced, and real automation, flexibility and intellectualization are realized.

However, in the actual production process, it is found that: the following problems mainly exist in the real-time tracking process of the welding seam, particularly in the real-time tracking of the welding seam which needs to change the welding attitude or speed in the welding process:

1) a certain preposed distance exists between the welding gun and the laser line of the sensor, so that welding seam data detected by the sensor cannot be immediately used for correcting welding gun deviation;

2) aiming at the application of variable-attitude welding, in the welding process, the advancing direction and the welding attitude of a welding gun need to be properly adjusted so as to meet the condition that a welding seam is always in the visual field range of a sensor and the welding gun can also carry out welding operation in a proper attitude. This welding requirement to change the attitude increases the difficulty of real-time weld tracking;

3) the welding speed change may occur in the welding process, which causes the problems of non-uniform distance between the acquisition points of the sensor, low tracking precision, poor welding quality and the like.

Therefore, how to develop a novel weld tracking method to solve at least one or more of the above problems is a problem to be solved.

Disclosure of Invention

In view of the above, the invention discloses a posture-changing real-time weld joint tracking method based on a laser sensor, so as to at least solve the problems that the existing tracking method cannot be applied to the working condition that the welding posture or speed needs to be changed, the tracking precision is low, the welding quality is poor, and the like.

The technical scheme provided by the invention is specifically that a variable-attitude real-time welding seam tracking method based on a laser sensor comprises the following steps:

1) creating an FIFO stack, and distributing the size of the FIFO stack according to the front distance of the laser sensor relative to the welding gun and the sampling frame rate of the laser sensor, wherein the FIFO stack is used for caching the absolute welding seam track;

2) acquiring coordinates of a welding seam sampling point of a laser sensor;

3) converting the coordinates of the welding seam sampling point in the step 2) to the coordinates of the welding robot according to the transformation relation between the coordinate system of the laser sensor and the coordinate system of the welding robot to obtain the coordinates of a new welding seam sampling point, and pressing the coordinates of the new welding seam sampling point into an FIFO (first in first out) stack;

4) acquiring actual position coordinate P of welding gun in welding robot_TSearching a position coordinate closest to the actual position coordinate of the welding gun in the FIFO stack, and performing non-uniform rational B-spline interpolation by taking the closest position coordinate and 3 position coordinates close to the closest position coordinate in front of and behind as control points to obtain the actual position coordinate P of the welding gun in the welding robot_TCorresponding position coordinate P 'on the weld track'_T

5) Calculating and obtaining the position deviation Err of a welding gun in the current welding robot by using the following formula, converting the position deviation Err of the welding gun into a welding gun coordinate system in the welding robot, and correcting the deviation of the welding robot;

Err＝P′_T-P_T；

6) and (5) circularly executing the steps 2) to 5) until the weld joint is completely tracked.

Preferably, the welding seam sampling point of the laser sensor in the step 2) is an intersection position point of a laser line and a welding seam in the laser sensor.

Further preferably, the transformation relationship between the laser sensor coordinate system and the welding robot coordinate system in step 3) is specifically:

wherein, P_RIs the homogeneous coordinate value of the new welding seam sampling point,

Is a transformation matrix from a welding gun coordinate system to a welding robot coordinate system in the welding robot,

For transformation matrix, P, from laser sensor coordinate system to welding gun coordinate system in welding robot_SThe homogeneous coordinate value of the welding seam sampling point of the laser sensor.

Further preferably, the welding robot is a transformation matrix from a welding gun coordinate system to a welding robot coordinate system

According to the actual position coordinate P of the welding gun in the welding robot_TAnd calculating the attitude of the welding gun.

Further preferably, before the new welding point sampling point coordinates are pressed into the FIFO stack in the step 3), filtering the new welding point sampling point coordinates based on a Kalman filtering algorithm, and if the difference between the new welding point sampling point coordinates and the estimated point coordinates is greater than a threshold value, filtering the new welding point sampling point coordinates as noise point coordinates, and returning to the step 2);

otherwise, proceed to step 4).

The variable-attitude real-time weld joint tracking method based on the laser sensor has the following beneficial effects:

1) the welding seam tracking method based on the absolute welding seam path is provided, and can adapt to the welding tracking process of changing the posture and the changing speed;

2) in the process of tracking the welding seam, a calculation method for realizing the accurate corresponding point of the current welding gun in the welding seam track by using a spline interpolation algorithm is provided;

3) a non-uniform rational B-spline interpolation mode is introduced into the algorithm, so that the tracking method is also suitable for the situation that the distances among the data acquired by the laser sensor are unequal.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.

FIG. 1 is a schematic diagram of a process for real-time weld seam tracking;

FIG. 2 is a schematic diagram of a weld tracking system in a variable-attitude real-time weld tracking method based on a laser sensor according to an embodiment of the disclosure;

FIG. 3 is a pictorial view of a workpiece being tracked for a circular weld using the tracking method of the disclosed embodiment of the invention;

FIG. 4 is an absolute path curve for circular weld tracking using the tracking method in the disclosed embodiment of the invention;

FIG. 5 is a tracking error curve for circular weld tracking using the tracking method in the disclosed embodiment of the invention;

FIG. 6 is a diagram of a workpiece in which a tracking method according to an embodiment of the present disclosure is used to track a weld of a different shape;

FIG. 7 is an absolute path curve for a profile weld trace using the trace method in the disclosed embodiment of the invention;

FIG. 8 is a tracking error curve for tracking a weld of a dissimilar shape using the tracking method in the disclosed embodiment of the present invention;

FIG. 9 is a pictorial view of a workpiece undergoing S-seam tracking using the tracking method of the disclosed embodiment of the invention;

FIG. 10 is an absolute path curve for S-seam tracking using the tracking method in the disclosed embodiment of the invention;

FIG. 11 is a tracking error curve for S-seam tracking using the tracking method in the disclosed embodiment of the invention.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of methods consistent with certain aspects of the invention, as detailed in the appended claims.

In order to solve the problems that the existing tracking method cannot be suitable for the working condition that the welding attitude or speed needs to be changed, the tracking precision is low, the welding quality is poor and the like, see figure 1, O_RBX_RBY_RBZ_RBRepresenting a welding robot coordinate system; o is_RTX_RTY_RTZ_RTRepresenting a welding gun coordinate system in the welding robot;

representing the coordinates of the ith welding seam sampling point, which correspond to the solid circles in the graph; the open circle represents the actual position coordinate P of the current welding gun_TThe position and weld of the welding gun can be seenThere is a certain deviation between the paths. In view of this, the present embodiment provides a laser sensor based attitude-changing real-time weld seam tracking method, which is an absolute position-based weld seam tracking method, and a tracking platform used in the tracking method, see fig. 2, where the tracking platform includes: a welding robot controller 1, a sensor controller 2, a welding robot 3, a laser sensor 4, a mounting frame 5, a welding gun 6, and a welding machine 7, wherein a represents a plate material. As can be seen from the figure 1, the laser sensor 4 collects the welding seam position data in real time, sends the position information to the sensor controller 2 through the TCP to calculate the real-time tracking control quantity, and then transmits the position information to the welding robot controller 1 through the TCP to realize the real-time correction of the welding robot 3 relative to the welding seam position, so as to form a closed-loop control system.

The attitude-changing real-time welding seam tracking method based on the laser sensor specifically comprises the following steps:

1) creating an FIFO stack, and distributing the size of the FIFO stack according to the front distance of the laser sensor relative to the welding gun and the sampling frame rate of the laser sensor, wherein the FIFO stack is used for caching the absolute welding seam track so as to solve the problem of the front distance between the laser sensor and the welding gun;

2) acquiring coordinates of a welding seam sampling point of a laser sensor;

3) converting the coordinates of the welding seam sampling point in the step 2) to the coordinates of the welding robot according to the transformation relation between the coordinate system of the laser sensor and the coordinate system of the welding robot to obtain the coordinates of a new welding seam sampling point, and pressing the coordinates of the new welding seam sampling point into the FIFO stack, such as square points in fig. 1;

4) acquiring actual position coordinate P of welding gun in welding robot_TSearching the FIFO stack for the actual position coordinates P of the welding gun_TNearest position coordinatesThen, the nearest position coordinate is used

And 3 position coordinates adjacent to the nearest position coordinate before and after are used as control points,namely to

For the control point, non-uniform rational B-spline interpolation is carried out to obtain the actual position coordinate P of the welding gun in the welding robot_TCorresponding position coordinate P 'on the weld track'_T；

5) Calculating and obtaining the position deviation Err of the welding gun in the current welding robot by using the following formula, converting the position deviation Err of the welding gun into a welding gun coordinate system in the welding robot, and correcting the deviation of the welding robot;

Err＝P′_T-P_T；

6) and (5) circularly executing the steps 2) to 5) until the weld joint is completely tracked.

Wherein, the transformation relation between the laser sensor coordinate system and the welding robot coordinate system in the step 3) is as follows:

wherein, P_RIs the homogeneous coordinate value of the new welding seam sampling point,

Is a transformation matrix from a welding gun coordinate system to a welding robot coordinate system in the welding robot,

For transformation matrix, P, from laser sensor coordinate system to welding gun coordinate system in welding robot_SThe homogeneous coordinate value of the welding seam sampling point of the laser sensor.

The transformation matrix from the welding gun coordinate system to the welding robot coordinate system in the welding robot

According to the actual position coordinate P of the welding gun in the welding robot_TAnd calculating the posture of the welding gun.

In order to remove noise points, filtering the new welding point sampling point coordinates based on a Kalman filtering algorithm before the new welding point sampling point coordinates are pressed into the FIFO stack in the step 3), and if the difference between the new welding point sampling point coordinates and the estimated point coordinates is greater than a threshold value, filtering the new welding point sampling point coordinates as noise point coordinates, and returning to the step 2); otherwise, proceed to step 4). Wherein, the threshold value of difference size can be adjusted according to different welding conditions, for example different welding speed, the shape of welding seam etc. and the threshold value is 0.6 ~ 1.5mm usually.

In order to verify the feasibility and the precision of the method, a set of welding seam tracking test platform is set up. The experimental platform mainly comprises an Anthrachian DX200 control cabinet, a MOTOMAN-MA1440 universal robot (functional modules such as opened network communication and Motoplus), a linear laser welding seam tracking sensor, various welding test pieces, welding seam tracking control software and the like.

In the welding process, the advancing speed of the welding robot is set to be 10mm/s, and the speed can meet the welding speed requirements of most argon arc welding and gas shield welding. To verify the feasibility and accuracy of the method provided in the above embodiment, tracking experiments were performed on circular arc, special-shaped, and S-shaped welds, respectively. And displaying and analyzing the calculated absolute welding seam track and the deviation amount of the welding gun position in the tracking process, wherein the experimental results are respectively shown in fig. 3-11.

FIGS. 3-5 illustrate a standard part circle workpiece 400mm in diameter; FIGS. 6-8 illustrate a shaped workpiece having straight edges, beveled edges, an R-angle, and requiring a complete trace of one revolution; fig. 8 to 11 are a tracking object including a wave curve. As can be seen from the tracking error curves of the figures, the tracking process has larger error only in the initial stage, which is mainly due to the larger initial position deviation between the welding gun and the workpiece to be tracked, but the welding gun position error is rapidly reduced along with the intervention of the tracking algorithm. And in the case of neglecting the initial position deviation, the error of the normal tracking process can be controlled within 0.5 mm. Of course, the accuracy of the seam tracking is also affected by the detection accuracy of the laser sensor, the welding advancing speed, the calibration accuracy of the welding gun tool coordinate system and other factors, so that various factors should be comprehensively considered in the actual welding application to achieve the optimal result.

The experimental result shows that the method provided by the embodiment can well solve the problem of variable-attitude welding seam tracking, realizes continuous and uninterrupted tracking on arc, special-shaped and S-shaped welding seams respectively, and has tracking precision superior to 0.5mm, which indicates that the proposed tracking technology can meet the requirements of common welding application.

Attention is paid to: the real-time tracking algorithm of the present invention is not only suitable for the case where the welding robot described herein is used as an actuator, but also suitable for the case where the actuator has multiple degrees of freedom, such as a welding machine, and therefore, the tracking technique of the present invention has the extensibility of the application object, and it should be considered to be within the scope of the present invention when the actuator is changed by using the tracking technique of the present invention.

It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.