A method and system for tracking free-curve welds by a robotic arm

Abstract

The present application discloses a method and system for tracking a free-curve weld by a robotic arm. In the process of scanning the weld by a linear laser profiler driven by the robotic arm to obtain the positioning of the weld in the robotic arm coordinate system, the control method aims to use the positioning result of the weld to realize accurate tracking of the robotic arm. The method mainly includes static error correction, data alignment, dynamic error correction, starting point location, free-curve tracking, shutdown reset and other links, which cooperate with weld positioning to realize accurate tracking of welds with a width of sub-millimeter level or above, effectively improving welding efficiency and quality.

Description

Technical Field

[0001] The invention relates to the technical field of robot arm motion control, and in particular to a robot arm tracking method and system for a free curve weld. Background Art

[0002] Laser welding processing technology is widely used in consumer electronics and new energy vehicles. Automated welding systems based on welding robots have gradually replaced manual welding. For a long time, domestic factories have mainly introduced foreign automated welding systems. The high price, long delivery time, untimely after-sales service, and high prices of spare parts have brought resistance to enterprises in reducing costs and increasing efficiency, and have also spawned the development of domestic self-developed welding systems.

[0003] Domestically developed welding systems mainly use two methods: manual "teaching and reproduction" and offline programming. These methods have relatively low welding efficiency, and there are deviations between the actual welds and the teaching trajectory during the production process, which cannot meet the factory's requirements for automation and intelligence. With the rapid development of science and technology such as computers and artificial intelligence, the intelligent recognition technology of welds has also ushered in rapid development. However, the matching operation and control cannot meet the requirements of high-precision tracking. Summary of the invention

[0004] Based on this, in view of the inadequacy of the tracking capability of the existing welding system, the embodiment of the present application provides a method and system for a robot arm to track a free curve weld, so as to achieve accurate and stable tracking of the weld, correct the deviation of the teaching trajectory in real time, and improve the efficiency, quality and accuracy of welding. The present application is not only applicable to the tracking of free curve welds by the robot arm, but can also be generalized to general robot arm control tasks that require free curve motion, where free curve is a general term for straight lines, arcs, curves and their free combinations.

[0005] On the first aspect, a method for tracking free curve welds by a robotic arm is provided, in which the robotic arm drives a linear laser profiler to scan the weld and obtain the position of the weld in the robotic arm coordinate system. During the positioning process, static error correction, data alignment, dynamic error correction, starting point positioning, free curve tracking and shutdown reset processes are performed in sequence.

[0006] Optionally, the static error correction specifically includes: correcting the accumulated errors of the hand-eye calibration of the line laser profiler and the TCP / TCF calibration of the tool.

[0007] Optionally, the data alignment specifically includes: performing timestamp matching on the point cloud data of the line laser profiler and the flange pose data of the robotic arm, and opening alignment correction parameters.

[0008] Optionally, the dynamic error correction specifically includes: selecting a fixed reference object, using the statically and dynamically calculated position deviation of the fixed reference object, and gradually adjusting the alignment correction parameters to minimize the deviation; wherein the fixed reference object is the starting point of the weld.

[0009] Optionally, the starting point positioning specifically includes: detecting the starting point according to the positioning result of the weld, and calculating the trajectory correction parameters according to the error between the actual starting point and the taught starting point to ensure that the robot arm tool accurately reaches the starting point of the weld.

[0010] Optionally, the free curve tracking specifically includes: obtaining the target point coordinates of each motion control cycle for the weld in the free curve shape, performing Kalman filtering based on the historical position of the robot arm tool to predict the motion position of the next control cycle, calculating the trajectory correction amount, and controlling the robot arm tool to move precisely on the free curve.

[0011] Optionally, the shutdown and reset specifically includes: detecting the end point according to the positioning result of the weld, and when the tool reaches the end point, shutting down the welding gun laser, ending the current welding cycle, and returning to the initial position.

[0012] In a second aspect, a system for tracking free curve welds by a robotic arm is provided, comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the method for tracking free curve welds by a robotic arm as described in any one of the first aspects above is implemented.

[0013] In a third aspect, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the method for tracking a free curve weld by a robotic arm as described in any one of the first aspects above is implemented.

[0014] In a fourth aspect, a computer program product is provided, comprising a computer program / instruction, which, when executed by a processor, implements the method for tracking a free curve weld by a robotic arm as described in any one of the first aspects above.

[0015] The technical solution provided in the embodiment of the present application uses a robotic arm to drive a linear laser profiler to scan the weld, obtain the location of the weld in the robotic arm coordinate system, and perform static error correction, data alignment, dynamic error correction, starting point location, free curve tracking, and shutdown reset processes in sequence during the positioning process. By performing comprehensive error correction on the entire control system, accurate tracking of welds of various shapes can be achieved, and automated welding can be performed quickly and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0017] Figure 1 A flowchart of a method for tracking a free-curve weld by a robotic arm provided in an embodiment of the present application;

[0018] Figure 2 A schematic diagram of static error correction provided in an embodiment of the present application;

[0019] Figure 3 A schematic diagram of data alignment provided in an embodiment of the present application;

[0020] Figure 4 A schematic diagram of dynamic error correction provided in an embodiment of the present application;

[0021] Figure 5 A schematic diagram of starting point location provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] In the description of the present invention, the terms "comprises", "has" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may also include other steps or units that are not explicitly listed but are inherent to these processes, methods, products or apparatuses, or steps or units added based on further optimization schemes conceived by the present invention.

[0024] This method is aimed at the automatic tracking of free curve welds in welding systems, where free curves are a general term for straight lines, arcs, curves and their free combinations. In a typical welding system, a taught robotic arm drives a linear laser profiler to scan and identify welds, obtain the precise positioning of the welds in the robotic arm base coordinate system, and drive the robotic arm tool to the specified position in real time based on these precise positioning to achieve automatic and precise tracking of welds. Weld identification is not within the scope of this method. This method aims to use the positioning results of the welds to achieve a control method for precise tracking of the robotic arm. This method mainly includes static error correction, data alignment, dynamic error correction, starting point positioning, free curve tracking, shutdown reset and other links, which cooperate with weld positioning to achieve precise tracking of welds with a width of sub-millimeter level or above, effectively improving welding efficiency and quality.

[0025] The purpose of the present invention is to solve the deficiencies of the prior art and provide a method for a robot arm to track a free curve weld, which includes static error correction, data alignment, dynamic error correction, starting point positioning, free curve tracking, shutdown reset and other links. Among them, static error correction, data alignment and dynamic error correction data offline processing flow, starting point positioning, free curve tracking, shutdown reset belong to the online processing flow.

[0026] This method uses a robotic arm to drive a linear laser profiler to scan the weld and obtain the location of the weld in the robotic arm coordinate system. Please refer to Figure 1 , which shows a flow chart of a method for tracking a free curve weld by a robotic arm provided in an embodiment of the present application, wherein static error correction, data alignment, dynamic error correction, starting point positioning, free curve tracking and shutdown reset processes are performed in sequence during the positioning process.

[0027] In the offline processing flow, the static error correction characteristics are: Figure 2 As shown in the figure, place two plates flat on the workbench to simulate the weld, and draw a marking line perpendicular to the weld at any position of the weld, such as Figure 2 -a, adjust the robot tool posture to: rx0=180, ry0=0, rz0=0, drive the robot arm to make the scanning line of the line laser profiler coincide with the marking line, then perform a 3D visual weld spot recognition, and obtain the coordinates of the weld spot at the marking line in the line laser profiler coordinate system, recorded as , and at the same time obtain the position and posture of the flange at the end of the robot arm at the current moment, recorded as ,in, is the position of the flange end in the robot base coordinate system, are the angles of rotation around the XYZ axis of the base coordinate system. At this time, the position of the flange is represented by Euler angles, which need to be converted into the form of a rotation matrix. The three-dimensional rotation formula can be obtained:

[0028] (1)

[0029] in, is the rotation matrix from the flange coordinate system to the base coordinate system, are the rotation matrices around the XYZ axis of the base coordinate system respectively. The homogeneous expression of the rotation and translation matrix from the flange coordinate system to the base coordinate system is: , where the translation matrix In addition, the transformation matrix from the line laser coordinate system to the flange coordinate system is obtained by the hand-eye calibration of the line laser profiler and the robot arm. , the coordinates of the above welding points in the robot base coordinate system It can be calculated by the following formula:

[0030] (2)

[0031] like Figure 2 -b, the coordinates of the above welding points in the robot base coordinate system are obtained Finally, drive the robot arm to make the tool end reach the position Due to the existence of calibration error, the tool point may not completely coincide with the welding point, and manual intervention is required for correction. Use the teach pendant to drive the robot arm tool so that the tool end and the welding point completely coincide. Figure 2 -c, the position of the robot flange at the current moment is obtained again, recorded as , then the static error correction is: , so far, the initial static error correction is completed. In the subsequent actual operation, the position and posture of the robot tool will change. The change of static error follows the law of three-dimensional rotation. Suppose the position and posture of the tool at any time is (rx1, ry1, rz1), and the rotation angle around the X axis is: , rotation angle around the Y axis: , rotation angle around the Z axis: , then the static error correction amount under the current posture is:

[0032] in, It can be calculated by formula (1).

[0033] In the offline processing flow, the data alignment features are: the operation of the tracking system requires the collection of point cloud data from the line laser profiler and the position data of the robot flange, and the time stamp matching of the point cloud data and the flange position data of the robot to obtain time-synchronized data for calculating the coordinate transformation of the weld. Since the point cloud data and flange position data come from different devices, the delays in data collection and transmission are different. Therefore, the data received at the receiving end at the same time are not the data collected at the same time. It is necessary to determine the delay parameters and then perform minimum error matching according to the new timestamp. The time delay parameter is the alignment correction parameter required by this method.

[0034] like Figure 3 As shown, the timestamp of the robot flange posture data packet is , m is the length of the data packet, the time interval is 4ms; the timestamp of the point cloud data packet of the laser profiler is , n is the packet length, the time interval is 1ms; let the alignment correction parameter be It should be noted that the time interval value is only used in this system, and other intervals are still applicable. Further calculation, The best match occurs when , is the location of the minimum value. In the offline processing flow, the dynamic error correction feature is: the above data alignment link establishes the data alignment method, and this link determines the alignment correction parameter as Specific value of Figure 4 -a, first select a fixed and known reference point. This system selects the starting point of the weld as the reference point. Place two plates flat on the workbench to simulate the weld, and use the teach pendant to drive the robot arm so that the end of the tool reaches the starting point of the weld. At this time, the position of the end of the tool is recorded as: , move the robot arm again so that the line laser is outside the starting point of the weld, such as Figure 4 -b, drive the robot arm to make it move along the direction of the weld, and start the weld detection at the same time. The first valid weld point is regarded as the starting point. Its coordinates in the online laser profiler coordinate system are , using formula (2) we can get the coordinates of the starting point of the system detection in the base coordinate system , and the true starting point coordinates The error is: Repeat the above process and adjust the alignment correction parameters ,make When the dynamic error is minimized, the correction is complete.

[0035] The online processing flow is characterized by: the system runs according to the teaching path, receives the line laser profiler point cloud data and the robot arm flange posture data in real time, aligns the data in real time according to the alignment method, calculates the weld point coordinate set in the base coordinate system using formula 2, obtains a series of weld point coordinates based on the calculation, and controls the robot arm tool in real time so that the end of the tool can accurately track the weld. The control process can be divided into three stages: starting point positioning, free curve tracking, and shutdown reset.

[0036] In the online processing flow, the starting point location feature is: according to the positioning result of the weld, the starting point is detected, and according to the error between the actual starting point and the teaching starting point, the trajectory correction parameters are calculated to ensure that the robot tool accurately reaches the starting point of the weld. Figure 5 As shown, the robot arm tool is actually located Since the line laser position is relatively forward relative to the tool (relative to the forward direction), when the robot tool moves to a position between the starting point and the actual starting point of the weld When the line laser has scanned the weld starting point, the weld detection module calculates the actual weld position. Since teaching is only rough positioning, the starting point of teaching The actual starting point of the weld There is a deviation, and the purpose of starting point positioning is to correct this deviation and drive the robotic arm to move to the actual starting point of the weld.

[0037] Furthermore, the middle position is first calculated and The distance between the two is the remaining distance, and the speed of the teaching motion is known to be v s , the robot motion control cycle is t s , then the number of control cycles required for the remaining distance is: , where n is rounded up, because it needs to be reached before the teaching is completed.

[0038] Next, change the starting point of the teaching The actual starting point of the weld The deviation is evenly distributed in the above control cycle n, where the step of the control cycle is calculated separately on the three components of the base coordinate system XYZ. The actual starting point of the weld The deviation is: , then the stride on the X component is: , here Still rounding up, after rounding up, the control cycle required to complete the motion changes, and the new number of cycles is: , still rounded up, after rounding, the stride of the last cycle changes, recorded as: Similarly, the stride length and number of motion cycles on the Y component can be obtained as: , and ; The stride and number of motion cycles on the Z component are: , and The final number of control cycles required , the remaining two non-maximum components are filled with zero strides.

[0039] In the online processing flow, the free curve tracking features are: obtaining the target point coordinates of each motion control cycle for the free curve weld, performing Kalman filtering to predict the motion position of the next control cycle based on a certain historical position of the robot tool, calculating the trajectory correction, and controlling the robot tool to move accurately on the free curve. Assume that the distance between the tool end and the line laser is L, and the weld detection module returns the weld points within the span of L / 2 each time, and the number of weld points changes with the speed; the free curve weld point position is , get the historical points within the past L / 2 trip For Kalman filter prediction, the trajectory correction at the next control cycle is: .

[0040] In the online processing flow, the free curve tracking feature is: when the robot arm tool is tracking the free curve, it detects the end point based on the positioning result of the weld. When the tool reaches the end point, it turns off the welding gun laser, ends the current welding cycle, returns to the initial position, and waits for the next tracking movement.

[0041] A system for tracking free-curve welds by a robotic arm is provided in an embodiment of the present application, and is used to implement the above-mentioned method for tracking free-curve welds by the robotic arm. For the specific definition of the system for tracking free-curve welds by the robotic arm, please refer to the definition of the method for tracking free-curve welds by the robotic arm above, which will not be repeated here. Each module in the above-mentioned system for tracking free-curve welds by the robotic arm can be implemented in whole or in part by software, hardware, and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory in the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above-mentioned modules.

[0042] In one embodiment of the present application, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned method for tracking a free curve weld by a robotic arm are implemented.

[0043] In one embodiment of the present application, a computer program product is provided, including a computer program / instruction, which implements the steps of the above-mentioned method for tracking a free curve weld by a robotic arm when the computer program / instruction is executed by a processor.

[0044] The computer-readable storage medium and computer program product provided in this embodiment have similar implementation principles and technical effects to those of the above method embodiments, and are not described in detail here.

[0045] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in M ​​forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (SyMchliMk) DRAM (SLDRAM), memory bus (RaMbus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0046] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for tracking a free-curve weld by a robotic arm, wherein the robotic arm drives a linear laser profiler to scan the weld to obtain the location of the weld in the robotic arm coordinate system, characterized in that: During the positioning process, static error correction, data alignment, dynamic error correction, starting point location search, free curve tracking and shutdown reset processes are carried out in sequence; The static error correction specifically includes: correcting the accumulated errors of the hand-eye calibration of the line laser profiler and the TCP / TCF calibration of the tool; The data alignment specifically includes: performing timestamp matching on the point cloud data of the line laser profiler and the flange pose data of the robot arm, and opening alignment correction parameters; The dynamic error correction specifically includes: selecting a fixed reference object, using the statically and dynamically calculated position deviation of the fixed reference object, gradually adjusting the alignment correction parameters to minimize the deviation; wherein the fixed reference object is the starting point of the weld; The starting point location search specifically includes: detecting the starting point according to the positioning result of the weld, and calculating the trajectory correction parameter according to the error between the actual starting point and the teaching starting point to ensure that the robot arm tool accurately reaches the starting point of the weld; The free curve tracking specifically includes: obtaining the target point coordinates of each motion control cycle for the weld in the free curve shape, performing Kalman filtering to predict the motion position of the next control cycle according to the historical position of the robot tool, calculating the trajectory correction amount, and controlling the robot tool to move accurately on the free curve; The shutdown and reset specifically includes: detecting the end point according to the positioning result of the weld, and when the tool reaches the end point, shutting down the welding gun laser, ending the current welding cycle, and returning to the initial position.

2. A tracking system for a free-curve weld by a robotic arm, characterized in that: The invention comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the method for tracking a free curve weld by a robot arm as claimed in claim 1 is implemented.

3. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, the method for tracking a free curve weld by a robot arm as claimed in claim 1 is implemented.

4. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the method for tracking a free curve weld by a robot arm as described in claim 1 is implemented.

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