CN115741698A - Rapid calibration system and method for field operation of mobile welding robot - Google Patents

Abstract

The invention discloses a rapid calibration system and method for on-site operation of a mobile welding robot, relates to the technical field of robot welding manufacturing, and solves the problems of long time-consuming, low precision, and high skill requirements for operators in the on-site calibration of a mobile welding robot Technical problem, the main point of the technical solution is that the operator manipulates the multi-axis robot arm to move the welding torch with special shape to the workpiece to be welded; The point cloud processing program identifies the robot tool coordinate system in the 3D model and calculates the position of the groove in the robot tool coordinate system, thereby completing the calibration of the groove position. It is not necessary for the operator to be proficient in the robot calibration method and key points. The operator is only required to hold a 3D scanner to obtain the 3D point cloud model of the welding site, and with the assistance of the program algorithm, the calibration task can be automatically, quickly and accurately completed.

Description

Rapid calibration system and method for on-site operation of mobile welding robot

technical field

The present application relates to the technical field of robot welding manufacturing, in particular to a rapid calibration system and method for on-site operation of a mobile welding robot.

Background technique

In welding applications such as energy, ships, rail transit, and engineering construction, there are a large number of on-site welding tasks for small batches of workpieces with complex shapes. The mobile welding robot combines the welding system, the mechanical arm and the mobile chassis. It has the advantages of a large range of motion and a high degree of flexibility, and meets the on-site welding needs of complex scenes. In the actual application process, because the mobile welding robot faces the problem of unstructured environment on the job site, it is difficult to meet the high-efficiency and intelligent welding requirements through teaching programming. It is an effective way to automatically generate the motion trajectory and execution file of the welding robot through the software program by using the off-line programming method.

In order to realize the off-line programming of the mobile welding robot on-site, it is necessary to determine the position of the welding groove in the robot tool coordinate system, that is, to find the transformation matrix from the workpiece coordinate system to the robot tool coordinate system. At this stage, there are two commonly used calibration strategies, one is the "eye in hand" method, that is, the camera and the robotic arm are rigidly fixed, and the conversion matrix of the camera coordinate system and the robot tool coordinate system is pre-calibrated, and then the camera is acquired. The groove position information is transformed into the robot tool coordinate system. In practical application of this method, personnel are required to control the position and direction of the robotic arm so that the target bevel is within the field of view of the camera. This process is complex, time-consuming and labor-intensive.

Another calibration strategy is the "eyes outside the hand" method, that is, the sensor is fixed next to the welding table, the relative position of the camera coordinate system and the table and the robot is determined in advance, and then the groove position is converted to the robot tool coordinate system. Due to the uncertainty of the site location of the mobile robot, this method takes a long time for site preparation, has low calibration accuracy, and requires high skill levels of operators.

The Chinese invention patent with application number 201811653845.5 discloses a laser camera hand-eye calibration method applied to arc additive materials, using a laser camera to determine the hand-eye relationship. Due to the "eye in hand" method, it is still necessary to manually control the robot to perform complex movements, and if the operation is not careful, it will collide with the workpiece and cause damage. In addition, the calibration process requires the use of a calibration plate, and the accuracy of the calibration plate directly affects the calibration accuracy.

The Chinese invention patent with application number 202111051769.2 discloses a welding robot positioning method based on the fusion of binocular vision and line laser sensor data. This method adopts the "eye outside the hand" method, and the binocular vision sensor is fixed next to the tooling table. During on-site application, because the shape of the workpiece will block the field of view of the visual sensor, for example, only the welding seam and the corner position bevel on one side can be calibrated, the flexibility in field use is poor, and it cannot be applied to complex welding seam scenarios.

The Chinese invention patent with the application number 202210417510.3 discloses a laser vision-guided robot automatic welding hand-eye calibration method. This method uses a three-dimensional calibration board with three calibration points to assist in the hand-eye calibration process, that is, to determine the camera coordinate system and the robot tool. Coordinate system relationship.

To sum up, the existing methods need a calibration board as an intermediary to obtain the hand-eye matrix, that is, the transformation matrix from the camera coordinate system to the robot tool coordinate system. And it is often accompanied by manual teaching. The operation is complex, time-consuming and labor-intensive, and requires high skills and knowledge of the operator, which adds time and labor costs to the on-site operation of the mobile welding robot.

Contents of the invention

This application provides a rapid calibration system and method for on-site operation of mobile welding robots. Its technical purpose is to shorten the time-consuming calibration of mobile robots on-site, improve calibration accuracy, and reduce the skill requirements for operators.

The above-mentioned technical purpose of the application is achieved through the following technical solutions:

A rapid calibration system for on-site operation of a mobile welding robot, including a mobile welding robot subsystem and a calibration subsystem, the mobile welding robot subsystem includes a mobile chassis, a multi-axis mechanical arm, a special shape welding gun, a working A platform and a workpiece to be welded; the calibration subsystem includes a hand-held three-dimensional scanner, a computer, a display, a three-dimensional point cloud model of a welding site, and a welding robot tool coordinate system;

One end of the multi-axis mechanical arm is set on the mobile chassis, and the other end is connected to the special shape welding torch; the workpiece to be welded is placed on the working platform;

Both the handheld three-dimensional scanner and the display are connected to the computer, and the computer controls the three-dimensional point cloud model of the welding site and the coordinate system of the welding robot tool to be displayed on the display.

A rapid calibration method for on-site operation of a mobile welding robot, comprising:

S1: The operator manipulates the mobile welding robot subsystem to adjust the distance between the welding torch with special shape and the starting point of the bevel of the workpiece to be welded;

S2: The operator obtains the 3D point cloud model including the special shape welding torch and the workpiece to be welded through the handheld 3D scanner;

S3: Process the 3D point cloud model, identify the tool coordinate system, and construct the target coordinate system corresponding to the groove position;

S4: Obtain the conversion matrix through the tool coordinate system and the target coordinate system, and obtain the relative position of the bevel in the tool coordinate system through the conversion matrix, and the relative position is the calibration position.

The beneficial effect of the present application is that: the rapid calibration system and method for the mobile welding robot on-site operation described in the present application, the operator does not need to have proficient robot kinematics knowledge and robot control skill proficiency, when using the handheld three-dimensional scanning In the case of the instrument, the pose relationship between the tool coordinate system of the mobile welding robot and the welding groove is obtained, and the operation is simple. At the same time, there is no need to prepare a high-precision calibration plate or target surface, and there is no need to calibrate the relationship between the camera coordinate system and the robot tool coordinate system, with fewer steps. In addition, the application uses an algorithm to identify the external markers of the welding torch, which is simple, fast and accurate.

Description of drawings

Fig. 1 is a schematic diagram of the system described in the present application;

Fig. 2 is the flowchart of the calibration process of the present application;

Fig. 3 is a structural schematic diagram of a welding torch with a special shape;

Fig. 4 is a flow chart of the groove position calibration algorithm;

Figure 5 is a schematic diagram of the application effect;

In the figure: 1-mobile chassis; 2-multi-axis robotic arm; 3-special shape welding torch; 4-working platform; 5-workpiece to be welded; 6-handheld 3D scanner; 7-operator; 8-computer; 9-display; 10-3D point cloud model of welding site; 11-tool coordinate system of welding robot.

Detailed ways

The technical solution of the present application will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the rapid calibration system for mobile welding robot on-site operations described in this application includes a mobile welding robot subsystem and a calibration subsystem, and the mobile welding robot subsystem includes a mobile chassis 1, multiple Axis manipulator 2, special shape welding torch 3, working platform 4 and workpiece 5 to be welded; one end of the multi-axis manipulator 2 is set on the mobile chassis 1, and the other end is connected to the special shape welding torch 3; The workpiece 5 to be welded is placed on the working platform 4 .

The calibration subsystem includes a handheld three-dimensional scanner 6, a computer 8, a display 9, a welding site three-dimensional point cloud model 10 and a welding robot tool coordinate system 11; the handheld three-dimensional scanner 6 and the display 9 are all compatible with the The computer 8 is connected, and the computer 8 controls the three-dimensional point cloud model 10 of the welding site and the tool coordinate system 11 of the welding robot to be displayed on the display 9 .

Specifically, the distance between the special shape welding torch 3 and the bevel starting point of the workpiece 5 to be welded is 50mm-300mm.

Specifically, as shown in FIG. 3 , the welding torch 3 with special shape is a cylinder with a triangular pyramid-shaped marker at its front end, and the tip of the triangular pyramid-shaped marker points to the X _t axis of the tool coordinate system.

As shown in Figure 2, the rapid calibration method for on-site operations of mobile welding robots described in this application includes:

S1: The operator manipulates the mobile welding robot subsystem to adjust the distance between the welding gun with special shape and the starting point of the bevel of the workpiece to be welded.

Specifically, step S1 includes:

S11: The operator manipulates the mobile chassis 1 to move the mobile chassis 1 to the vicinity of the working platform 4 .

S12: The operator manipulates the multi-axis robotic arm 2 to move the special-shaped welding torch 3 to the starting point of the bevel of the workpiece 5 to be welded.

S13: Adjust the distance between the special shape welding torch 3 and the starting point of the bevel. Specifically, by roughly adjusting the position of the multi-axis mechanical arm 2, the distance between the welding torch 3 with special shape and the starting point of the bevel of the workpiece 5 to be welded is usually controlled within a range of 50mm-300mm.

S2: The operator obtains the three-dimensional point cloud model including the welding torch 3 with special shape and the workpiece 5 to be welded through the handheld three-dimensional scanner 6 .

Specifically, the operator is required to perform scanning operations with a handheld 3D scanner within the working range of the 3D scanner. Taking the Artec Eva 3D scanner as an example, the working distance is 0.4m to 1.0m. The operator uses the hand-held 3D scanner 6 to scan around the welding torch 3 with special shape and the workpiece 5 to be welded to obtain a 3D point cloud model including the welding torch 3 with special shape and the workpiece 5 to be welded.

S3: Process the 3D point cloud model, identify the tool coordinate system, and construct the target coordinate system corresponding to the groove position.

Specifically, as shown in Figure 4, step S3 includes:

S31: The software program of the computer 8 reads the position coordinate data of each point in the three-dimensional point cloud model, and then establishes a world coordinate system.

S32: The algorithm of the computer 8 recognizes the outer contour circle at the front end of the special shape welding torch 3, and obtains the circle center O _t (x _o , y _o , z _o ) through a circle fitting algorithm.

S33: Identify the triangular pyramid-shaped marker at the front end of the special-shaped welding torch 3, and fit the outer boundary of the triangular pyramid-shaped marker on the same end face as the special-shaped welding torch 3, and obtain the boundary line intersection point C _t (x _c , y _c , z _c ).

S34: Connect O _t and C _t , determine O _t C _t as the X _t axis of the tool coordinate system, then the direction vector of the X _t axis is expressed as:

其中，

其中，点D(x_d,y_d,z_d)和点E(x_e,y_e,z_e)均位于特殊形貌焊枪3前端端部的外廓圆上；Calculate the cylindrical central axis Z _t of the main body of the welding torch 3 with special shape, and obtain the direction vector of the Z _t axis as:

in,

Wherein, point D(x _d , y _d , z _d ) and point E(x _e , y _e , z _e ) are both located on the outer contour circle of the front end of the welding torch 3 with special shape;

则得到工具坐标系{T}＝{X_t,Y_t,Z_t}。The Y _t- axis is determined according to the right-hand rule, i.e.

Then the tool coordinate system {T}={X _t , Y _t , Z _t } is obtained.

X_g轴为坡口起始点指向坡口终点的方向；

S35: Construct the target coordinate system {G} with the starting point of the groove as the origin N _g , {G}={X _g , Y _g , Z _g }; wherein, the Z _g axis is the direction vertical to the working platform 4, and its direction vector for

The X _g axis is the direction from the groove start point to the groove end point;

S4: Obtain the conversion matrix through the tool coordinate system and the target coordinate system, and obtain the relative position of the bevel in the tool coordinate system through the conversion matrix, and the relative position is the calibration position.

Specifically, step S4 includes:

为(x_n-x_o,y_n-y_o,z_n-z_o)。S41: The origin of the tool coordinate system {T} is expressed as point O _t (x _o , y _o , z _o ), and the origin of the target coordinate system {G} is expressed as N _g (x _n , y _n , z _n ), then The translation vector from the tool coordinate system {T} to the target coordinate system {G}

is (x _n -x _o , y _n -y _o , z _n -z _o ).

表示目标坐标系{G}主轴方向的单位矢量，将工具坐标系{T}作为参考坐标系，计算得到三个单位矢量

及

S42: pass

Indicates the unit vector in the direction of the main axis of the target coordinate system {G}, using the tool coordinate system {T} as the reference coordinate system, and calculates three unit vectors

and

的顺序排列成3*3的矩阵，则对旋转变换矩阵

进行计算，表示为：S43: According to

The order of is arranged into a 3*3 matrix, then the rotation transformation matrix

Calculated, expressed as:

Among them, the scalar r _ij represents the component of each vector projected in the axis direction of its reference coordinate system;

和旋转变换矩阵

得到坡口起始点对应工具坐标系{T}的位姿关系，则得到转换矩阵表示为：S44: According to the translation vector

and the rotation transformation matrix

Get the pose relationship of the groove starting point corresponding to the tool coordinate system {T}, then the transformation matrix can be expressed as:

S45: Calibrate the relative position of the groove through the transformation matrix.

Fig. 5 is a schematic diagram of the effect after rapid calibration by the method described in this application. To sum up, the rapid calibration method and system described in this application do not need to prepare a high-precision calibration plate or target surface, and do not need to calibrate the relationship between the camera coordinate system and the robot tool coordinate system. There are few steps, and it is simple, fast and accurate to identify the external marks of the welding torch things.

The above are exemplary embodiments of the present application, and the protection scope of the present application is defined by the claims and their equivalents.

Claims (7)

1. A fast calibration system for on-site operation of a mobile welding robot, characterized in that it comprises a mobile welding robot subsystem and a calibration subsystem, and the mobile welding robot subsystem includes a mobile chassis (1), a multi-axis Manipulator (2), welding gun with special shape (3), work platform (4) and workpiece to be welded (5); described calibration subsystem includes hand-held three-dimensional scanner (6), computer (8), monitor (9) ), welding site three-dimensional point cloud model (10) and welding robot tool coordinate system (11); One end of the multi-axis mechanical arm (2) is set on the mobile chassis (1), and the other end is connected to the special shape welding torch (3); the workpiece to be welded (5) is placed on the working platform (4) on; The handheld three-dimensional scanner (6) and the display (9) are all connected to the computer (8), and the computer (8) controls the welding site three-dimensional point cloud model (10) and the welding robot The tool coordinate system (11) is displayed on the display (9). 2. The rapid calibration system according to claim 1, wherein the special shape welding torch (3) is a cylinder, and its front end is provided with a triangular pyramid marker, and the tip of the triangular pyramid marker points to the tool The X _t axis of the coordinate system. 3. A quick calibration method for on-site operation of a mobile welding robot, characterized in that it comprises: S1: The operator manipulates the mobile welding robot subsystem to adjust the distance between the welding torch (3) with special shape and the starting point of the bevel of the workpiece (5) to be welded; S2: The operator obtains the three-dimensional point cloud model including the welding torch (3) with special shape and the workpiece to be welded (5) through the handheld three-dimensional scanner (6); S3: Process the 3D point cloud model, identify the tool coordinate system, and construct the target coordinate system corresponding to the groove position; S4: Obtain the conversion matrix through the tool coordinate system and the target coordinate system, and obtain the relative position of the bevel in the tool coordinate system through the conversion matrix, and the relative position is the calibration position. 4. The quick calibration method according to claim 3, wherein said step S1 comprises: S11: The operator manipulates the mobile chassis (1) to move the mobile chassis (1) to the vicinity of the working platform (4); S12: The operator manipulates the multi-axis mechanical arm (2) to move the special shape welding torch (3) to the starting point of the groove of the workpiece (5) to be welded; S13: Adjust the distance between the special shape welding torch (3) and the starting point of the bevel. 5. The quick calibration method according to claim 4, wherein said step S2 comprises: The operator is within the working range of the hand-held three-dimensional scanner, and the operator uses the hand-held three-dimensional scanner (6) to scan the welding torch (3) with special shape and the workpiece (5) to be welded around, and obtains the special shape welding torch ( 3) and the three-dimensional point cloud model of the workpiece to be welded (5). 6. The quick calibration method according to claim 5, wherein said step S3 comprises: S31: The computer (8) reads the position coordinate data of each point in the three-dimensional point cloud model, and then establishes a world coordinate system; S32: Identify the outer contour circle at the front end of the welding gun with special shape (3), and obtain the circle center O _t (x _o , y _o , z _o ) through a circle fitting algorithm; S33: Identify the triangular pyramid-shaped marker on the front end of the special-shaped welding torch (3), and fit the outer boundary of the triangular pyramid-shaped marker on the same end surface as the special-shaped welding torch (3), and obtain the boundary line intersection point C _t (x _c ,y _c ,z _c ); S34: Connect O _t and C _t , determine O _t C _t as the X _t axis of the tool coordinate system, then the direction vector of the X _t axis is expressed as:

Calculate the cylindrical central axis Z _t of the main body of the special shape welding torch (3), and obtain the direction vector of the Z _t axis as:

in,

Wherein, point D(x _d , y _d , z _d ) and point E(x _e , y _e , z _e ) are both located on the outer contour circle at the front end of the special shape welding torch (3); The Y _t- axis is determined according to the right-hand rule, i.e.

Then get the tool coordinate system {T}={X _t , Y _t , Z _t }; S35: Construct the target coordinate system {G} with the starting point of the groove as the origin N _g , {G}={X _g , Y _g , Z _g }; wherein, the Z _g axis is the direction vertical to the working platform (4), and The direction vector is

The X _g axis is the direction from the groove start point to the groove end point;

7. The quick calibration method according to claim 6, wherein said step S4 comprises: S41: The origin of the tool coordinate system {T} is expressed as point O _t (x _o , y _o , z _o ), and the origin of the target coordinate system {G} is expressed as N _g (x _n , y _n , z _n ), then The translation vector from the tool coordinate system {T} to the target coordinate system {G}

is (x _n -x _o ,y _n -y _o ,z _n -z _o ); S42: pass

Indicates the unit vector in the direction of the main axis of the target coordinate system {G}, using the tool coordinate system {T} as the reference coordinate system, and calculates three unit vectors

and

S43: According to

The order of is arranged into a 3*3 matrix, then the rotation transformation matrix

Calculated, expressed as:

Among them, the scalar r _ij represents the component of each vector projected in the axis direction of its reference coordinate system; S44: According to the translation vector

and the rotation transformation matrix

Get the pose relationship of the groove starting point corresponding to the tool coordinate system {T}, then the transformation matrix can be expressed as:

S45: Calibrate the relative position of the groove through the transformation matrix.

Images