JP2024098314A - Welding system - Google Patents

Abstract

To provide a welding system capable of maintaining constant welding quality over the whole length of a welding part of steel pipe.SOLUTION: In a welding system which controls a welding robot 1, when a tip of a welding torch 13 moves between an initiation position Pc2 of a curve part 8a of a steel pipe 8 and a steel pipe middle position which is the middle position between the initiation position Pc2 and a completion position Pc3 of the curve part 8a of the steel pipe 8, a control part controls a target position changing part so that a welding torch 13 moves at a first torch separation speed in such a direction that the welding torch is separated from the steel pipe 8, and the first torch separation speed is characterized in becoming small as a tip of the welding torch 13 comes close to the steel pipe middle position.SELECTED DRAWING: Figure 8

Description

The present invention relates to a welding system.

Large buildings such as high-rise buildings use steel pipe columns formed by welding together rectangular steel pipes. Patent Document 1 discloses a technology for determining the position of a welding torch when welding steel pipes using a welding robot that travels along a guide rail attached to the steel pipes, calculating the welding torch angle at the determined welding torch position, and controlling the welding torch angle based on the calculated welding torch angle.

JP 2022-1371 A

In order to maintain a constant weld quality over the entire length of the weld, it is preferable to keep the welding conditions constant throughout the weld. When welding a rectangular steel pipe, it is preferable to keep the welding conditions at the curved section at the corner of the steel pipe the same as those at the straight section of the steel pipe.
In many cases, the center of curvature of the curved portion of the steel pipe is different from the center of curvature of the curved portion of the guide rail. In this case, the distance between the steel pipe and the guide rail at the curved portion is not constant in the circumferential direction. For this reason, it is preferable to make the welding conditions of the curved portion of the steel pipe the same as those of the straight portion of the steel pipe by appropriately controlling the position and angle of the welding torch using a welding robot.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide a welding system that can maintain a consistent welding quality over the entire length of the welded part of a steel pipe.

<1> The welding system according to aspect 1 of the present invention is a welding system that controls a welding robot that welds the straight and curved portions of a steel pipe while moving in a predetermined direction on a rail that is arranged along the steel pipe and has straight and curved portions, and includes a welding torch possessed by the welding robot, a target position changing unit that changes the target position of the welding torch, and a welding system that, when the rail curvature center, which is the curvature center of the curved portion of the rail, is located closer to the center of the steel pipe than the steel pipe curvature center, which is the curvature center of the curved portion of the steel pipe, controls the curvature center and curvature radius of the curved portion of the steel pipe and the rail curvature center. and a control unit that controls the target position change unit according to the center of curvature and radius of curvature of the curved portion and the welding speed and position of the welding robot, and the control unit controls the target position change unit so that the welding torch moves in a direction away from the steel pipe at a first torch separation speed when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and a steel pipe intermediate position that is an intermediate position between the start position and the end position of the curved portion of the steel pipe, and the first torch separation speed becomes smaller as the tip of the welding torch approaches the steel pipe intermediate position.

According to this invention, the control unit controls the target position changing unit so that when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the middle position of the steel pipe, the welding torch moves in a direction away from the steel pipe at a first torch separation speed. This makes it possible to prevent the tip of the welding torch from coming too close to the steel pipe when the center of the rail curvature is located closer to the center of the steel pipe than the center of the steel pipe curvature.

Here, when the center of curvature of the rail is located closer to the center of the steel pipe than the center of curvature of the steel pipe, the distance between the rail and the steel pipe is the farthest between the straight portion of the rail and the straight portion of the steel pipe, and is the closest between the rail midpoint, which is the midpoint of the curved portion of the rail, and the steel pipe midpoint. In contrast, the first torch separation speed decreases as the tip of the welding torch approaches the steel pipe midpoint. This makes it possible to smoothly adjust the distance between the tip of the welding torch and the steel pipe. This makes it easier to ensure the quality of welding the steel pipe with the welding torch. This makes it possible to maintain a constant welding quality over the entire length of the welded portion of the steel pipe.

<2> The welding system according to aspect 2 of the present invention is the welding system according to aspect 1, characterized in that the control unit controls the target position changing unit so that the welding torch moves in a direction away from the steel pipe at a second torch separation speed when the tip of the welding torch moves between the straight portion of the steel pipe and the start position, and the second torch separation speed increases as the tip of the welding torch approaches the start position.

According to this invention, the control unit controls the target position changing unit so that when the tip of the welding torch moves between the straight section of the steel pipe and the start position of the curved section of the steel pipe, the welding torch moves in a direction away from the steel pipe at a second torch separation speed. This makes it possible to prevent the tip of the welding torch from coming too close to the steel pipe.

Here, when the center of curvature of the rail is located closer to the center of the steel pipe than the center of curvature of the steel pipe, the welding robot may be located at the curved section of the rail with the tip of the welding torch on the straight section of the steel pipe. Then, as the welding robot moves around the curved section, the speed at which the tip of the welding torch approaches the steel pipe accelerates. In contrast, the second torch separation speed increases as the tip of the welding torch approaches the starting position. This allows the distance between the tip of the welding torch and the steel pipe to be smoothly adjusted as the tip of the welding torch moves between the straight section of the steel pipe and the starting position.

<3> The welding system according to aspect 3 of the present invention is the welding system according to aspect 1 or 2, characterized in that the control unit controls the aim position changing unit so that the welding torch moves in a direction away from the steel pipe at a first torch separation acceleration when the tip of the welding torch moves between the straight portion of the steel pipe and the start position, and the control unit controls the aim position changing unit so that the welding torch moves in a direction away from the steel pipe at a second torch separation acceleration when the welding torch moves near the start position, and the second torch separation acceleration is greater than the first torch separation acceleration.

According to this invention, the control unit controls the target position changing unit so that when the tip of the welding torch moves between the straight section of the steel pipe and the start position of the curved section of the steel pipe, the welding torch moves in a direction away from the steel pipe at a first torch separation acceleration. This makes it possible to increase the speed at which the welding torch separates from the steel pipe as the tip of the welding torch approaches the start position. This allows the distance between the tip of the welding torch and the steel pipe to be adjusted smoothly.

Here, when the center of the rail curvature is located closer to the center of the steel pipe than the center of the steel pipe curvature, the speed at which the tip of the welding torch approaches the steel pipe when it is located at the curved portion of the steel pipe is greater than the speed at which the tip of the welding torch approaches the steel pipe when it is located between the straight portion of the steel pipe and the start position of the curved portion of the steel pipe. In response to this, the control unit controls the target position changing unit so that when the welding torch moves near the start position, the welding torch moves in a direction away from the steel pipe at a second torch separation acceleration, and the second torch separation acceleration is greater than the first torch separation acceleration. This makes it possible to accommodate the speed at which the tip of the welding torch approaches the steel pipe when it is located at the curved portion.

<4> The welding system according to aspect 4 of the present invention is the welding system according to any one of aspects 1 to 3, further comprising a speed change unit that changes the moving speed of the welding robot, and the control unit controls the speed change unit according to the center of curvature and radius of curvature of the curved portion of the steel pipe, the center of curvature and radius of curvature of the curved portion of the rail, and the welding speed and position of the welding robot when the center of curvature of the rail, which is the center of curvature of the curved portion of the rail, is located closer to the center of the steel pipe than the center of curvature of the steel pipe, which is the center of curvature of the curved portion of the steel pipe, and the control unit controls the speed change unit so that the welding robot moves at a first robot speed when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe, and the first robot speed becomes smaller as the tip of the welding torch approaches the intermediate position of the steel pipe.

Here, the length of the curved portion of the rail is longer than the length of the curved portion of the steel pipe. Therefore, in order to make the speed at which the tip of the welding torch moves along the curved portion of the steel pipe the same as the speed at which it moves along the straight portion of the steel pipe, the speed at which the welding robot moves along the curved portion of the rail needs to be faster than the speed at which the welding robot moves along the straight portion of the rail. In response to this, the control unit controls the speed change unit so that the welding robot moves at a first robot speed when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the middle position of the steel pipe. This makes it possible to make the speed at which the welding torch moves along the curved portion of the steel pipe the same as the speed at which it moves along the straight portion of the steel pipe.

When welding a curved section of a steel pipe, the orientation of the welding torch may be changed so that the orientation of the welding torch coincides with the normal direction of the curved section of the steel pipe. In contrast, the first robot speed decreases as the tip of the welding torch approaches the middle position of the steel pipe. This makes it possible to keep the speed of the tip of the welding torch constant even when the orientation of the welding torch is changed when welding a curved section of the steel pipe when the center of curvature of the rail is located closer to the center of the steel pipe than the center of curvature of the steel pipe. This makes it easier to ensure the quality of welding of the steel pipe.

<5> The welding system according to aspect 5 of the present invention is the welding system according to aspect 4, characterized in that the control unit controls the speed change unit so that the welding robot moves at a first robot deceleration when the tip of the welding torch moves between the start position and the steel pipe intermediate position, the control unit controls the speed change unit so that the welding robot moves at a first robot acceleration when the tip of the welding torch approximately reaches the start position, and the absolute value of the first robot acceleration is greater than the absolute value of the first robot deceleration.

According to this invention, the control unit controls the speed change unit so that the welding robot moves at a first robot deceleration when the tip of the welding torch moves between the start position of the curved section of the steel pipe and the intermediate position of the steel pipe. This makes it possible to reduce the speed at which the welding robot advances along the rail as the tip of the welding torch approaches the intermediate position of the steel pipe when the tip of the welding torch moves between the start position of the curved section of the steel pipe and the intermediate position of the steel pipe. This makes it possible to keep the speed of the tip of the welding torch constant. This makes it easier to ensure the quality of welding of the steel pipe.

As described above, in order to make the speed at which the tip of the welding torch moves along the curved section of the steel pipe the same as the speed at which it moves along the straight section of the steel pipe, the speed at which the welding robot moves along the curved section of the rail must be faster than the speed at which the welding robot moves along the straight section of the rail. Furthermore, the welding robot must accelerate immediately after the tip of the welding torch reaches the start position of the curved section of the steel pipe. In response to this, the control unit controls the speed change unit so that the welding robot moves at a first robot acceleration when the tip of the welding torch approximately reaches the start position of the curved section of the steel pipe, and the absolute value of the first robot acceleration is greater than the absolute value of the first robot deceleration. This makes it possible to make the movement speed of the welding robot appropriate when the tip of the welding torch moves along the curved section.

<6> The welding system according to aspect 6 of the present invention is the welding system according to any one of aspects 1 to 5, further comprising a torch direction change unit that changes the direction of the welding torch, and the control unit controls the torch direction change unit when the rail curvature center, which is the center of curvature of the curved portion of the rail, is located closer to the center of the steel pipe than the steel pipe curvature center, which is the center of curvature of the curved portion of the steel pipe, and the control unit controls the torch direction change unit so that the inclination of the welding torch in the specified direction decreases as the tip of the welding torch moves between the start position and the steel pipe intermediate position, and the control unit controls the torch direction change unit so that the inclination of the welding torch in the direction opposite to the specified direction increases as the tip of the welding torch moves between the steel pipe intermediate position and the end position of the curved portion of the steel pipe.

According to this invention, the control unit controls the torch orientation change unit so that when the tip of the welding torch moves between the start position and the intermediate position of the steel pipe, the inclination of the welding torch in a predetermined direction decreases as the tip moves. The control unit also controls the torch orientation change unit so that when the tip of the welding torch moves between the intermediate position of the steel pipe and the end position of the curved portion of the steel pipe, the inclination of the welding torch in the direction opposite to the predetermined direction increases as the tip moves. This makes it possible to change the orientation of the welding torch when welding the curved portion of the steel pipe so that the orientation of the welding torch coincides with the normal direction of the curved portion of the steel pipe.

<7> The welding system according to aspect 7 of the present invention is a welding system for controlling a welding robot that welds the straight and curved portions of a steel pipe while moving in a predetermined direction on a rail arranged along the steel pipe and having straight and curved portions, and includes a welding torch possessed by the welding robot, a target position changing unit that changes the target position of the welding torch, and a welding system that, when the steel pipe curvature center, which is the curvature center of the curved portion of the steel pipe, is located closer to the center of the steel pipe than the rail curvature center, which is the curvature center of the curved portion of the rail, controls the curvature center and curvature radius of the curved portion of the steel pipe and the curved portion of the rail. and a control unit that controls the target position change unit according to the center of curvature and radius of curvature of the rail and the welding speed and position of the welding robot, and the control unit controls the target position change unit so that the welding torch moves in a direction approaching the steel pipe at a first torch approach speed when the welding robot moves between the start position of the curved portion of the rail and a rail mid-position that is an intermediate position between the start position of the curved portion of the rail and the end position of the curved portion of the rail, and the first torch approach speed increases as the welding robot approaches the rail mid-position.

According to this invention, when the welding robot moves between the start position of the curved portion of the rail and the middle position of the rail, the control unit controls the target position changing unit so that the welding torch moves in a direction approaching the steel pipe at a first torch approach speed. This makes it possible to prevent the tip of the welding torch from moving away from the steel pipe when the center of curvature of the steel pipe is located closer to the center of the steel pipe than the center of curvature of the rail.

Here, when the center of curvature of the steel pipe is located closer to the center of the steel pipe than the center of curvature of the rail, the distance between the rail and the steel pipe is closest between the straight portion of the rail and the straight portion of the steel pipe, and is farthest between the rail midpoint, which is the midpoint of the curved portion of the rail, and the steel pipe midpoint. In contrast, the first torch approach speed increases as the welding robot approaches the rail midpoint. This makes it possible to smoothly adjust the distance between the tip of the welding torch and the steel pipe. This makes it easier to ensure the quality of welding the steel pipe with the welding torch. This makes it possible to maintain a constant welding quality over the entire length of the welded portion of the steel pipe.

<8> A welding system according to an eighth aspect of the present invention is the welding system according to the seventh aspect, wherein the control unit controls the target position changing unit so that the welding torch moves in a direction approaching the steel pipe at a second torch approach speed when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and a steel pipe intermediate position that is an intermediate position between the start position of the curved portion of the steel pipe and an end position of the curved portion of the steel pipe and when the welding robot moves along a straight portion of the rail;
The second torch approach speed increases as the welding robot approaches a start position of the curved portion of the rail.

According to this invention, the control unit controls the target position changing unit so that when the tip of the welding torch moves between the start position of the curved section of the steel pipe and the middle position of the steel pipe and the welding robot moves along the straight section of the rail, the welding torch moves in a direction approaching the steel pipe at the second torch approach speed. This makes it possible to prevent the tip of the welding torch from moving away from the steel pipe.

Here, when the center of curvature of the steel pipe is located closer to the center of the steel pipe than the center of curvature of the rail, when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the middle position of the steel pipe and the welding robot moves along the straight portion of the rail, the speed at which the tip of the welding torch leaves the steel pipe accelerates as the welding robot moves along the straight portion. In contrast, the approach speed of the second torch increases as the welding robot approaches the start position of the curved portion of the rail. This makes it possible to smoothly adjust the distance between the tip of the welding torch and the steel pipe as the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the middle position of the steel pipe.

<9> The welding system according to aspect 9 of the present invention is the welding system according to any one of aspects 7 and 8, characterized in that the control unit controls the aim position change unit so that the welding torch moves at a first torch approach acceleration in a direction approaching the steel pipe when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and a steel pipe intermediate position that is an intermediate position between the start position of the curved portion of the steel pipe and the end position of the curved portion of the steel pipe and the welding robot moves along the straight portion of the rail, the control unit controls the aim position change unit so that the welding torch moves at a first torch approach deceleration in a direction approaching the steel pipe when the welding robot moves near the start position of the curved portion of the rail, and the absolute value of the first torch approach deceleration is greater than the absolute value of the first torch approach acceleration.

According to this invention, the control unit controls the target position changing unit so that when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe, which is the intermediate position between the start position of the curved portion of the steel pipe and the end position of the curved portion of the steel pipe, and the welding robot moves along the straight portion of the rail, the welding torch moves in a direction approaching the steel pipe at a first torch approach acceleration. This makes it possible to increase the speed at which the welding torch approaches the steel pipe as the welding robot approaches the start position of the curved portion of the rail. This makes it possible to smoothly adjust the distance between the tip of the welding torch and the steel pipe.

Here, when the center of curvature of the steel pipe is located closer to the center of the steel pipe than the center of curvature of the rail, the speed at which the tip of the welding torch leaves the steel pipe when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the curved portion of the rail is smaller than the speed at which the tip of the welding torch leaves the steel pipe when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the straight portion of the rail. In response to this, the control unit controls the target position changing unit so that the welding torch moves in a direction approaching the steel pipe at a first torch approach deceleration when the welding robot moves near the start position of the curved portion of the rail, and the absolute value of the first torch approach deceleration is greater than the absolute value of the first torch approach acceleration. This allows the tip of the welding torch to move between the start position of the curved section of the steel pipe and the middle position of the steel pipe, and can accommodate the speed at which the tip of the welding torch leaves the steel pipe when the welding robot moves along the curved section of the rail.

<10> The welding system according to aspect 10 of the present invention is the welding system according to any one of aspects 8 and 9, further comprising a speed change unit that changes the moving speed of the welding robot, and the control unit controls the speed change unit according to the center of curvature and radius of curvature of the curved portion of the steel pipe, the center of curvature and radius of curvature of the curved portion of the rail, and the welding speed and position of the welding robot when the center of curvature of the curved portion of the steel pipe, which is the center of curvature of the curved portion of the steel pipe, is located closer to the center of the steel pipe than the center of curvature of the rail, which is the center of curvature of the curved portion of the rail, and the control unit controls the speed change unit so that the welding robot moves at a first robot speed when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe, and the first robot speed increases as the tip of the welding torch approaches the intermediate position of the steel pipe.

Here, the length of the curved portion of the rail is longer than the length of the curved portion of the steel pipe. Therefore, in order to make the speed at which the welding torch moves along the curved portion of the steel pipe the same as the speed at which it moves along the straight portion of the steel pipe, the speed at which the welding robot moves along the curved portion of the rail needs to be faster than the speed at which the welding robot moves along the straight portion of the rail. In response to this, the control unit controls the speed change unit so that the welding robot moves at a first robot speed when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the middle position of the steel pipe. This makes it possible to control the speed at which the welding torch moves along the curved portion of the steel pipe to be the same as the speed at which it moves along the straight portion of the steel pipe.

When welding a curved section of a steel pipe, the orientation of the welding torch may be changed so that the orientation of the welding torch coincides with the normal direction of the curved section of the steel pipe. In contrast, the first robot speed increases as the tip of the welding torch approaches the middle position of the steel pipe. This makes it possible to keep the speed of the tip of the welding torch constant even when the orientation of the welding torch is changed when welding a curved section of a steel pipe when the center of curvature of the steel pipe is located closer to the center of the steel pipe than the center of curvature of the rail. This makes it easier to ensure the quality of welding of the steel pipe.

<11> The welding system according to aspect 11 of the present invention is the welding system according to aspect 10, characterized in that the control unit controls the speed change unit so that the welding robot moves at a first robot acceleration when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the curved portion of the rail, the control unit controls the speed change unit so that the welding robot moves at a first robot deceleration when the welding robot approximately reaches the start position of the curved portion of the rail, and the absolute value of the first robot deceleration is greater than the absolute value of the first robot acceleration.

According to this invention, the control unit controls the speed change unit so that when the tip of the welding torch moves between the start position of the curved section of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the curved section of the rail, the speed at which the welding robot advances along the rail can be increased as the tip of the welding torch approaches the intermediate position of the steel pipe when the tip of the welding torch moves between the start position of the curved section of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the curved section of the rail. This makes it possible to keep the speed of the tip of the welding torch constant. This makes it easier to ensure the quality of welding of the steel pipe.

Here, the moving speed of the welding robot when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the curved portion of the rail is slower than the moving speed of the welding robot when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the straight portion of the rail. For this reason, it is necessary to decelerate the welding robot immediately after the welding robot reaches the start position of the curved portion of the rail. In response to this, the control unit controls the speed change unit so that the welding robot moves at a first robot deceleration when the welding robot approximately reaches the start position of the curved portion of the rail, and the absolute value of the first robot deceleration is greater than the absolute value of the first robot acceleration. This makes it possible to appropriately move the welding robot when the tip of the welding torch moves between the start position of the curved portion of the steel pipe and the intermediate position of the steel pipe and the welding robot moves along the curved portion of the rail.

<12> The welding system according to aspect 12 of the present invention is the welding system according to any one of aspects 8 to 11, further comprising a torch direction change unit that changes the direction of the welding torch, and the control unit controls the torch direction change unit when the steel pipe curvature center, which is the center of curvature of the curved portion of the steel pipe, is located closer to the center of the steel pipe than the rail curvature center, which is the center of curvature of the curved portion of the rail, and the control unit controls the torch direction change unit so that the inclination of the welding torch in the direction opposite to the specified direction becomes smaller as the tip of the welding torch moves between the start position and the steel pipe intermediate position, and the control unit controls the torch direction change unit so that the inclination of the welding torch in the specified direction becomes larger as the tip of the welding torch moves between the steel pipe intermediate position and the end position of the curved portion of the steel pipe.

According to this invention, the control unit controls the torch orientation change unit so that the inclination of the welding torch in the direction opposite to the predetermined direction decreases as the tip of the welding torch moves between the start position and the intermediate position of the steel pipe. The control unit also controls the torch orientation change unit so that the inclination of the welding torch in the predetermined direction increases as the tip of the welding torch moves between the intermediate position of the steel pipe and the end position of the curved portion of the steel pipe. This makes it possible to change the orientation of the welding torch when welding the curved portion of the steel pipe so that the orientation of the welding torch coincides with the normal direction of the curved portion of the steel pipe.

The present invention provides a welding system that can maintain consistent welding quality over the entire length of the welded portion of a steel pipe.

1 is an overall view showing a welding system according to a first embodiment; 1 is a block diagram illustrating an overview of a welding system according to a first embodiment. 1A and 1B are diagrams showing a welding robot according to a first embodiment, in which FIG. 1A is a side view, and FIG. FIG. 2 is a rear view of the welding robot according to the first embodiment. 1A is a side view showing a first rotation part of a welding robot according to a first embodiment, and FIG. 1B is a plan view showing a second rotation part of the welding robot. FIG. 2 is a side view of the welding robot according to the first embodiment. 1A and 1B are diagrams showing a steel pipe and a guide rail in the first embodiment, where FIG. 1A is a plan view and FIG. 5A to 5C are diagrams for explaining welding of curved portions in the first embodiment. FIG. 2 is a system block diagram of a system control device according to the first embodiment. FIG. 2 is a system block diagram of a control unit of the system control device according to the first embodiment. 5 is a flowchart showing an example of a flow of a welding process for a curved portion executed by the system control device in the first embodiment. 11 is a graph showing changes in the speed at which a welding robot moves in the left-right direction in areas 1 to 4 according to the first embodiment. 11 is a graph showing changes in the speed at which a welding robot moves in the forward and backward directions in areas 1 to 4 according to the first embodiment. 1 is a graph showing changes in the amount of movement of a welding torch around a first axis and a second axis in areas 1 to 4 according to a first embodiment. 13 is a diagram for explaining welding of a curved portion in a second embodiment. FIG. 10 is a flowchart showing an example of a flow of welding processing of a curved portion executed by a system control device in a second embodiment. 13 is a graph showing changes in the speed at which a welding robot moves in the left-right direction in areas 5 to 8 according to the second embodiment. 13 is a graph showing changes in the speed at which a welding robot moves in the forward and backward directions in areas 5 to 8 according to the second embodiment. 13 is a graph showing changes in the amount of movement of the welding torch around the first axis and the second axis in areas 5 to 8 according to the second embodiment.

First Embodiment
Hereinafter, a welding system 100 according to a first embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a welding system 100 is used to weld together the ends of steel pipes 8 arranged side by side in the vertical direction.
The steel pipe 8 is a square steel pipe having four arc-shaped curved portions 8a arranged at the corners and four straight portions 8b connecting the curved portions 8a (continuing the curved portions 8a without being broken). The axis of the steel pipe 8 extends in the vertical direction. In the initial state, the steel pipe 8 is temporarily fixed by an erection jig 9. The erection jig 9 is attached to the straight portions 8b of the steel pipe 8.

[Welding system overview]
1 and 2, an overview of a welding system 100 will be described. The welding system 100 controls a welding robot 1. The welding system 100 includes the welding robot 1, a guide rail 2, an imaging device 3, a welding power source 4, a wire feeder 5, and a system controller 6.

The welding robot 1 welds the straight section 8b and the curved section 8a of the steel pipe 8 while moving in a predetermined direction on the guide rail 2. The welding robot 1 includes a plurality of motors 32, a welding torch 13, an aim position changing unit that changes the aim position of the welding torch 13, a torch direction changing unit that changes the direction of the welding torch 13, and a speed changing unit that changes the moving speed of the welding robot. The welding robot 1 is also connected to a system control device 6 so as to be able to communicate with the system control device 6. The welding robot 1 includes a relay panel (not shown) that receives control from the system control device 6.
The motor 32 is a motor that drives the welding robot 1 under the control of the system control device 6. The motor 32 includes a servo motor (a speed change unit, a robot position change unit) that moves the welding robot 1 along the guide rail 2.

The welding torch 13 is used to weld the ends of the steel pipe 8 together. Welding with the welding torch 13 is performed, for example, by arc welding. A welding wire is placed inside the welding torch 13.

The guide rail 2 is disposed along the steel pipe 8. The guide rail 2 is disposed in an annular shape in the circumferential direction of the steel pipe 8 so as to surround the steel pipe 8. The guide rail 2 has four arc-shaped curved portions 2a disposed at the corners, and four straight portions 2b each connecting the curved portions 2a to each other.
The welding robot 1 is movable along a guide rail 2 .

The photographing device 3 is attached to the welding robot 1. The photographing device 3 photographs the welded portion of the steel pipe 8 in the sensing process before welding. The photographing device 3 also photographs the state of welding by the welding robot 1 in the welding process. The photographing device 3 is, for example, a camera. The photographing device 3 is connected to the system control device 6 so as to be able to communicate with it, and the images or videos (hereinafter referred to as the photographed results) acquired by the photographing device 3 are transmitted to the system control device 6.

The welding power source 4 supplies power to the wire feeder 5. The wire feeder 5 supplies welding wire to the welding torch 13. The welding torch 13 is connected to the wire feeder 5 via a welding torch cable. The wire feeder 5 supplies power to the welding torch 13.

The system controller 6 controls the operation of the welding system 100. Specifically, the system controller 6 controls the operation of the welding robot 1, the welding power source 4, and the wire feeder 5.
The welding robot 1 is connected to the system controller 6 via a control cable. The control cable transmits to the welding robot 1 a control signal that is sent from the system controller 6 and controls the welding robot 1.

[Welding robot configuration]
Next, the configuration of the welding robot 1 will be described with reference to FIGS.
Fig. 3(a) is a side view of the welding robot 1. Fig. 3(b) is a link diagram of Fig. 3(a). Fig. 4 is a rear view of the welding robot 1. Fig. 5(a) is a side view showing a first rotation unit 35 (described later) of the welding robot 1. Fig. 5(b) is a plan view showing a second rotation unit 36 (described later) of the welding robot 1.
In the following description, the direction along the vertical direction is referred to as the up-down direction x of the welding robot 1. The direction in which the welding robot 1 moves along the guide rail 2 is referred to as the left-right direction y of the welding robot 1. The direction perpendicular to the up-down direction x and the left-right direction y of the welding robot 1 is referred to as the front-rear direction z of the welding robot 1.

The welding robot 1 includes a main body 11 , a welding torch 13 , and a support 14 .
The main body 11 is a base of the welding robot 1. The main body 11 includes a motor 32. The main body 11 includes a wheel unit 12 attached to the guide rail 2. The welding robot 1 moves along the guide rail 2 by the wheel unit 12 sliding on the guide rail 2.

The support part 14 is provided between the main body part 11 and the welding torch 13, and supports the welding torch 13. The support part 14 has a case 21, a first link member 22, a second link member 23, and a third link member 24.

The case 21 is provided to cover the outside of the main body 11. The case 21 is movable in the forward/backward direction z of the welding robot 1 relative to the main body 11. The main body 11 and the case 21 form a forward/backward moving part 33 (target position changing part). In the link diagram shown in FIG. 3(b), the forward/backward moving part 33 is shown as a linear joint.

The first link member 22 includes a vertical arm 22a extending vertically downward, a horizontal arm 22b extending horizontally from a lower end of the vertical arm 22a, and a connection panel 22c connected to the horizontal arm 22b and extending vertically downward. The vertical arm 22a, the horizontal arm 22b, and the connection panel 22c are connected to each other so as not to be movable relative to each other.
An upper end of the vertical arm 22a is connected to the case 21 inside the case 21. The vertical arm 22a (first link member 22) is movable in the up-down direction x of the welding robot 1 relative to the case 21. The case 21 and the first link member 22 form a vertical movement unit 34 (target position changing unit). In the link diagram shown in Fig. 3(b), the vertical movement unit 34 is shown as a linear joint.

The second link member 23 is in the form of a panel. An upper end portion of the second link member 23 is connected to a lower end portion of the connection panel 22c via a first link pin 351.
As shown in Fig. 5(a), the second link member 23 is rotatable around the central axis of the first link pin 351 (hereinafter also referred to as the first axis) with respect to the connection panel 22c. The central axis of the first link pin 351 is parallel to the left-right direction y of the welding robot 1. The connection panel 22c and the second link member 23 form a first rotation part 35 (torch direction changing part). In the link diagram shown in Fig. 3(b), the first rotation part 35 is shown as a rotary joint. The first rotation part 35 rotates a second rotation part 36 (described later) together with the welding torch 13.

The third link member 24 is connected to a lower end of the second link member 23 via a second link pin 361. The third link member 24 is a holder for supporting the welding torch 13.
As shown in Fig. 5(b), the third link member 24 is rotatable about the central axis of the second link pin 361 (hereinafter also referred to as the second axis) relative to the second link member 23. When the second link member 23 is not rotated relative to the connection panel 22c, the central axis of the second link pin 361 is parallel to the up-down direction x of the welding robot 1. The second link member 23 and the third link member 24 form a second rotation unit 36 (torch direction changing unit). In the link diagram shown in Fig. 3(b), the second rotation unit 36 is shown as a rotary joint.

The forward/backward movement unit 33, the up/down movement unit 34, the first rotation unit 35, and the second rotation unit 36 are all driven by the motor 32.

[Control method]
A control method for welding system 100 having the above configuration will be described.
The control method according to the present embodiment is mainly characterized by welding of the periphery of the curved portion 8a (hereinafter, simply referred to as welding of the curved portion 8a) of the steel pipe 8. The curved portion 8a of the steel pipe 8 and the curved portion 2a of the guide rail 2 have different circumferential lengths. In addition, in many cases, the steel pipe curvature center C1, which is the curvature center of the curved portion 8a of the steel pipe 8, is different from the rail curvature center C2, which is the curvature center of the curved portion 2a of the guide rail 2. Therefore, the distance between the steel pipe 8 and the guide rail 2 at the curved portions 8a and 2a is not constant in the circumferential direction. In this embodiment, even in such a case, the movement amount of the welding robot 1 is adjusted according to the welding conditions, thereby realizing high-quality welding regardless of the position of the steel pipe 8.

First, the basic concept of the control method will be described below with reference to FIG.
Fig. 7(a) is a plan view showing the steel pipe 8 and the guide rail 2. Fig. 7(b) is a link diagram of Fig. 7(a).

The distance between the steel pipe 8 and the guide rail 2 varies depending on the positions of the curved sections 8a, 2a. Therefore, in this control method, the welding of the curved section 8a is divided into a plurality of areas, and the method of calculating the movement amount of the welding robot 1 is adjusted for each area.
When dividing the welding of the curved portion 8a into a plurality of areas, a steel pipe coordinate system is defined based on the steel pipe 8. This steel pipe coordinate system is defined for each of the curved portions 8a of the steel pipe 8.
Hereinafter, the vertical direction is referred to as the X direction in the steel pipe coordinate system. The direction perpendicular to the X direction and along one of the two straight line portions 8b connected to one curved portion 8a is referred to as the Y direction in the steel pipe coordinate system. The direction perpendicular to the X direction and the Y direction is referred to as the Z direction. The Z direction is the direction along the other of the two straight line portions 8b. For example, the origin position of the steel pipe coordinate system is set to a position that coincides with the X direction and the position (target position) of the tip of the welding torch 13 that satisfies the welding conditions described later, and coincides with the steel pipe curvature center C1 of the curved portion 8a of the steel pipe 8 in a top view (YZ plane).
In addition, among the X directions, the vertical upward direction is referred to as the +X direction, and the vertical downward direction is referred to as the -X direction. Among the Y directions, the direction toward the outside of the steel pipe 8 based on the origin position of the steel pipe coordinate system (steel pipe curvature center C1) is referred to as the +Y direction, and the direction toward the inside of the steel pipe 8 is referred to as the -Y direction.
Of the Z directions, the direction toward the outside of the steel pipe 8 based on the origin position of the steel pipe coordinate system (steel pipe curvature center C1) is defined as the +Z direction, and the direction toward the inside of the steel pipe 8 is defined as the -Z direction.

[Curved section of steel pipe and curved section of guide rail]
The curved portion 8a of the steel pipe 8 and the curved portion 2a of the guide rail 2 will be described.
The curved portion 8a is an arc having a radius of Rc and a quarter circle centered on the steel pipe curvature center C1 when viewed from above (YZ plane). The curved portion 2a is an arc having a radius of Rg and a quarter circle centered on the rail curvature center C2 when viewed from above.

In this embodiment, the position of the steel pipe curvature center C1 is different from the position of the rail curvature center C2.
The rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1.
If the distance between the straight portion 8b of the steel pipe 8 and the straight portion 2b of the guide rail 2 is l _cg , the distance e in the Y direction (or Z direction) between the center of curvature C1 of the steel pipe and the center of curvature C2 of the rail is expressed by the following formula.
e=Rc+l _cg -Rg
In other words, the rail curvature center C2 is a position shifted by −e in the Y direction and the Z direction from the steel pipe curvature center C1.

As shown in FIG. 8, the welding of the steel pipe 8 is divided into area 1, area 2, area 3, and area 4 according to the welding form.
In the following, the start position of curved portion 2a is designated as Pg1, and the end position as Pg2. The start position of curved portion 8a is designated as Pc2, and the end position as Pc3. The intersection of a straight line connecting rail curvature center C2 and position Pg1 with straight portion 8b of steel pipe 8 is designated as position Pc1. The intersection of a straight line connecting rail curvature center C2 and position Pg2 with straight portion 8b of steel pipe 8 is designated as position Pc4.

Area 1 is an area where the steel pipe 8 is welded from position Pc1 to position Pc2. That is, area 1 is an area where the tip of the welding torch 13 moves from position Pc1 to position Pc2. In area 1, the welding robot 1 welds the straight portion 8b of the steel pipe 8 while moving along the curved portion 2a of the guide rail 2. That is, in area 1, the welding robot 1 is positioned on the curved portion 2a of the guide rail 2, and the portion that the welding robot 1 welds is the straight portion 8b of the steel pipe 8.
Area 2 is an area where the steel pipe 8 is welded from position Pc2 to position Pc3. That is, area 2 is an area where the tip of the welding torch 13 moves from position Pc2 to position Pc3. In area 2, the welding robot 1 welds the curved portion 8a of the steel pipe 8 while moving along the curved portion 2a of the guide rail 2. That is, in area 2, the welding robot 1 is positioned on the curved portion 2a of the guide rail 2, and the portion that the welding robot 1 welds is the curved portion 8a of the steel pipe 8.
Area 3 is an area where the steel pipe 8 is welded from position Pc3 to position Pc4. That is, area 3 is an area where the tip of the welding torch 13 moves from position Pc3 to position Pc4. In area 3, the welding robot 1 welds the straight portion 8b of the steel pipe 8 while moving along the curved portion 2a of the guide rail 2. That is, in area 3, the welding robot 1 is positioned on the curved portion 2a of the guide rail 2, and the portion that the welding robot 1 welds is the straight portion 8b of the steel pipe 8.
Area 4 is an area other than areas 1 to 3 of the steel pipe 8. In area 4, the welding robot 1 welds the straight portion 8b of the steel pipe 8 while moving along the straight portion 2b of the guide rail 2. That is, in area 4, the welding robot 1 is positioned on the straight portion 2b of the guide rail 2, and the portion that the welding robot 1 welds is the straight portion 8b of the steel pipe 8.
In this embodiment, welding of the curved portion 8a means welding of areas 1 to 3.

[Welding conditions]
In order to obtain good welding quality, it is preferable to satisfy the following welding conditions <1> to <4> regardless of the area.
<1> The speed at which the tip of the welding torch 13 moves along the welded portion of the steel pipe 8 (hereinafter also referred to as the welding movement speed Vw) is constant.
<2> The direction of the welding torch 13 when viewed from above (hereinafter also referred to as the welding torch direction) coincides with the normal direction of the curved portion 8 a of the steel pipe 8 or is perpendicular to the straight portion 8 b of the steel pipe 8 .
<3> The target angle θn of the welding torch 13 is constant. Note that the target angle θn of the welding torch 13 is the direction of the welding torch 13 when the tip of the welding torch 13 is located at the groove of the steel pipe 8, as seen along the left-right direction y of the welding robot 1, as shown in Fig. 6. The target angle θn is appropriately adjusted depending on the state of the welding portion of the steel pipe 8 (e.g., groove information).
<4> The distance between the tip of the welding torch 13 and the welded portion of the steel pipe 8 (hereinafter also referred to as the target position of the welding torch 13) is constant.
The position in the X direction of the tip of welding torch 13 that satisfies the above welding conditions is constant and coincides with the origin position of the steel pipe coordinate system in the X direction. As shown in Fig. 6, the distance in the X direction (the vertical direction x of welding robot 1) between the X direction position of the tip of welding torch 13 that satisfies the above welding conditions and the lower end 2c of guide rail 2 is defined as H.

Here, in area 4, the distance between the steel pipe 8 (straight section 8b) and the guide rail 2 (straight section 2b) is constant. Therefore, the movement amount of the welding robot 1 that satisfies the above welding conditions is uniformly determined. In other words, by moving the welding robot 1 at the welding movement speed Vw with the welding torch direction, target angle, and target position of the welding torch 13 set to satisfy the above welding conditions <2> to <4>, welding that satisfies the above welding conditions can be performed.

On the other hand, in areas 1 to 3, the distance between the steel pipe 8 and the guide rail 2 varies depending on the circumferential position, so the movement amount of the welding robot 1 that satisfies the above welding conditions is not uniformly determined. In this embodiment, inverse kinematics is used for welding in areas 1 to 3 (welding of the curved section 8a) to <A> calculate the target position and target posture of the welding torch 13 that satisfy the above welding conditions (hereinafter also referred to as the target position and posture of the welding torch 13), and <B> determine the movement amount of the welding robot 1 to achieve this.

Specifically, a matrix U (corresponding to the above <A>) is generated that represents the target position and target posture of welding torch 13 that satisfies the above welding conditions. This matrix U is a matrix that represents the target position and target posture of welding torch 13 at the welding position at time t. The welding position at time t is determined based on Vw·t using the welding movement speed Vw of welding condition <1>. For example, if the welding position at time 0 is Pc1, it can be determined which of areas 1 to 3 the welding position at time t is located in, depending on the magnitude of Vw·t.
Also, a matrix T (corresponding to the above <B>) is generated which represents the position and posture of the welding torch 13 when the welding robot 1 moves a predetermined amount.
Welding that satisfies the above welding conditions can be performed by determining the amount of movement of the welding robot 1 that makes the matrix U equal to the matrix T and controlling the driving of the motor 32 according to the amount of movement. In other words, by making the matrices U and T equal, the amount of movement for realizing the target position and posture of the welding torch 13 at a given time t (welding position) can be determined.
By controlling the welding robot 1 so as to realize this amount of movement, welding of good quality can be achieved.

[Regarding matrix U]
The generation of the matrix U will be described in detail with reference to FIG.
The matrix U is a matrix for expressing the target position and target posture of the welding torch 13 that satisfy the above welding conditions, with the origin position (steel pipe curvature center C1) of the steel pipe coordinate system as a reference. The matrix U is the target position and posture of the welding torch 13 at a specific welding position. The matrix U is determined for each welding position of the steel pipe 8. The matrix U is determined regardless of the position of the welding robot 1.
In this embodiment, welding of straight line portion 8b is performed in areas 1 and 3, and welding of curved portion 8a is performed in area 2. Therefore, the target position and target posture of welding torch 13 that satisfy the above welding conditions are different for areas 1 to 3. For this reason, a matrix U is generated for each of areas 1 to 3. As described above, the position in the X direction of the tip of welding torch 13 that satisfies the above welding conditions is constant and is a position that coincides with the origin position of the steel pipe coordinate system in the X direction.

In area 1, the tip of the welding torch 13 moves from position Pc1 to position Pc2 at a welding movement speed Vw. The movement of the tip of the welding torch 13 in area 1 is a movement at a welding movement speed Vw in the Y direction (+Y direction). Therefore, the position of the tip of the welding torch 13 in the Y direction varies depending on the time. The position of the tip of the welding torch 13 in the Y direction at time t, where the time when the tip of the welding torch 13 reaches position Pc1 is set to 0, is a position moved in the Y direction by +Vw·t from position Pc1. The position of position Pc1 in the Y direction is a position moved in the Y direction by -e from the origin position (steel pipe curvature center C1) of the steel pipe coordinate system. In addition, in area 1, the position of the tip of the welding torch 13 in the Z direction is always a position moved in the Z direction by +Rc from the origin position (steel pipe curvature center C1) of the steel pipe coordinate system.
Furthermore, at the welding position at time t, the welding torch orientation of welding torch 13 that satisfies the above welding conditions is a direction perpendicular to straight portion 8b. At the welding position at time t, the target angle of welding torch 13 is always constant (θn). At the welding position at time t, the distance between the tip of welding torch 13 and straight portion 8b is always constant.
The matrix U in area 1 is generated as a homogeneous transformation matrix representing the position and posture of the welding torch 13 as described above.

In area 2, the tip of the welding torch 13 moves from position Pc2 to position Pc3 at a welding movement speed Vw. In area 2, the tip of the welding torch 13 moves along the curved portion 8a. That is, the movement of the tip of the welding torch 13 that satisfies the above welding conditions in area 2 is a rotational movement at a welding movement speed Vw around the steel pipe curvature center C1 on the YZ plane. In the YZ plane, the position of the tip of the welding torch 13 at time t, where the time when the tip of the welding torch 13 reaches position Pc2 is set to 0, is a position rotated from position Pc2 around the steel pipe curvature center C1 by a rotation amount θc (radian). However, the rotation amount θc is expressed by the following formula using the radius Rc of the curved portion 8a and the welding movement speed Vw.
θc=(Vw・t÷2πRc)×2π
Furthermore, at the welding position at time t, the welding torch orientation of welding torch 13 that satisfies the above welding conditions is a direction that coincides with the normal direction of curved portion 8a. At the welding position at time t, the target angle of welding torch 13 is always constant (θn). At the welding position at time t, the distance between the tip of welding torch 13 and curved portion 8a is always constant.
The matrix U in area 2 is generated as a homogeneous transformation matrix representing the position and posture of the welding torch 13 as described above.

In area 3, the tip of the welding torch 13 moves from position Pc3 to position Pc4 at a welding movement speed Vw. The movement of the tip of the welding torch 13 in area 3 is a movement at a welding movement speed Vw in the Z direction (-Z direction). Therefore, the position of the tip of the welding torch 13 in the Z direction varies depending on the time. The position of the tip of the welding torch 13 in the Z direction at time t, where the time when the tip of the welding torch 13 reaches position Pc3 is set to 0, is a position moved in the Z direction from position Pc3 by -Vw·t. The position of position Pc3 in the Z direction is the same as the origin position (steel pipe curvature center C1) of the steel pipe coordinate system in the Z direction. In addition, in area 3, the position of the tip of the welding torch 13 in the Y direction is always a position moved in the Y direction by +Rc from the origin position (steel pipe curvature center C1) of the steel pipe coordinate system.
Furthermore, at the welding position at time t, the welding torch orientation of welding torch 13 that satisfies the above welding conditions is a direction perpendicular to straight portion 8b. At the welding position at time t, the target angle of welding torch 13 is always constant (θn). At the welding position at time t, the distance between the tip of welding torch 13 and straight portion 8b is always constant.
The matrix U in area 3 is generated as a homogeneous transformation matrix representing the position and posture of the welding torch 13 as described above.

[About the movement distance of welding robots]
3 to 6, the movement amount of welding robot 1 will be described. In this embodiment, welding system 100 controls the movement amount Mx of welding torch 13 in the up-down direction x of welding robot 1, the movement amount My of welding robot 1 in the left-right direction y of welding robot 1, the movement amount Mz of welding torch 13 in the front-rear direction z of welding robot 1, the movement amount M _B of welding torch 13 about the first axis, and the movement amount M _T of welding torch 13 about the second axis. In other words, the movement amount of welding robot 1 includes the movement amount Mx, the movement amount My, the movement amount Mz, the movement amount M _B , and the movement amount M _T.
The movement amounts Mx, Mz, _MB , and _MT indicate the movement amounts from a reference position of the welding torch 13. The reference position of the welding torch 13 is the position and posture of the welding torch 13 in a state in which the welding torch 13 is not moving, rotating, or the like.
The movement amount My indicates the movement amount of the welding robot 1 based on a predetermined position of the guide rail 2. The predetermined position is set to, for example, a start position Pg1 of the curved portion 2a of the guide rail 2.

As shown in FIG. 3(a), the amount of movement Mx is controlled by the vertical movement unit 34. That is, the vertical movement unit 34 changes the position of the welding torch 13 in the vertical direction x of the welding robot 1 by moving the first link member 22 in the vertical direction x of the welding robot 1 relative to the case 21. The operation of the vertical movement unit 34 is controlled by driving the motor 32 (servo motor).

As shown in FIG. 4, the movement amount My is controlled by the motor 32 (servo motor) changing the movement speed of the welding robot 1.

As shown in FIG. 3(a), the amount of movement Mz is controlled by the forward/backward movement unit 33. That is, the forward/backward movement unit 33 changes the position of the welding torch 13 in the forward/backward direction z of the welding robot 1 by moving the case 21 relative to the main body 11 in the forward/backward direction z of the welding robot 1. The operation of the forward/backward movement unit 33 is controlled by driving the motor 32 (servo motor).

5(a), the amount of movement M _B is controlled by the first rotation unit 35. That is, the first rotation unit 35 rotates the second link member 23 about the first axis relative to the connection panel 22c, thereby rotating the welding torch 13 about the first axis. The first rotation unit 35 changes the orientation of the welding torch 13 about the first axis. The operation of the first rotation unit 35 is controlled by driving the motor 32 (servo motor).

5(b), the amount of movement M _-T is controlled by the second rotation unit 36. That is, the second rotation unit 36 rotates the third link member 24 about the second axis relative to the second link member 23, thereby rotating the welding torch 13 about the second axis. The second rotation unit 36 changes the orientation of the welding torch 13 about the second axis. The operation of the second rotation unit 36 is controlled by driving the motor 32 (servo motor).

[Regarding matrix T]
Matrix T is a matrix for expressing the position and posture of welding torch 13 with respect to the origin position of the steel pipe coordinate system (center of curvature C1 of the steel pipe) when the movement amount of welding torch 13 in the up-down direction x of welding robot 1 is _Mx , the movement amount of welding torch 13 in the front-rear direction z of welding robot 1 is Mz, the movement amount of welding torch 13 about the first axis is M _B , the movement amount of welding torch 13 about the second axis is M T, and the movement amount of welding robot 1 with respect to position Pg1 is My. In this embodiment, matrix T is a common matrix for areas 1 to 3.
In areas 1 to 3, the welding robot 1 moves on the curved portion 2a. That is, the movement of the welding robot 1 in areas 1 to 3 is a rotational movement around the rail curvature center C2 on the YZ plane. If the amount of rotation of the welding robot 1 around the rail curvature center C2 from position Pg1 on the YZ plane is θg (radian), the movement amount My can be expressed as the rotation amount θg as shown in the following formula. Rg is the radius of the curved portion 2a.
θg=(My÷2πRg)×2π

Matrix T is obtained by multiplying a matrix T1 for translating the origin position of the steel pipe coordinate system (steel pipe curvature center C1) to the position of the rail curvature center C2, a matrix T2 for expressing the position obtained by rotating the welding robot 1 from position Pg1 around the rail curvature center C2 by a rotation amount θg (i.e., the position obtained by moving the welding robot 1 by a movement amount My from position Pg1), and a matrix T3 for expressing the position and posture of the tip of the welding torch 13 when the welding robot 1 moves by the movement amounts Mx, Mz, _MB , and _MT at the position of the welding robot 1 after rotation by matrix T2.

Matrix T1 is generated by moving the origin position of the steel pipe coordinate system (steel pipe curvature center C1) by -e in the Y and Z directions.

Matrix T2 is generated by rotating position Pg1 by a rotation amount θg around rail curvature center C2. Position Pg1 is a position moved by +Rg in the Z direction from rail curvature center C2.

The matrix T3 will be described with reference to FIG.
3B shows the link structure of the welding robot 1 and the distance between each link when the welding torch 13 is in the reference position. In FIG. 3B, a indicates the distance in the front-rear direction z of the welding robot 1 between the first link pin 351 and the second link pin 361 when the welding torch 13 is in the reference position (also see FIG. 5A). b indicates the distance in the up-down direction x of the welding robot 1 between the first link pin 351 and the second link pin 361 when the welding torch 13 is in the reference position (also see FIG. 5A). c indicates the distance in the up-down direction x of the welding robot 1 between the lower end 2c of the guide rail 2 and the first link pin 351 when the welding torch 13 is in the reference position. d indicates the distance in the front-rear direction z of the welding robot 1 between the guide rail 2 and the first link pin 351 when the welding torch 13 is in the reference position. L indicates the distance from second link pin 361 to the tip of welding torch 13 (see also FIG. 5B). By using these parameters a to d and L, the position and posture of welding torch 13 at the reference position are expressed.
Matrix T3 is a homogeneous transformation matrix generated by moving and rotating the position and attitude of welding torch 13 at the reference position expressed using parameters a to d and L as described above by movement amounts Mx, Mz, M _B , and M _T.

[Formula for calculating the movement distance of a welding robot]
For the matrices U and T generated as above, a formula is derived for calculating the movement amounts Mx, My, Mz, M _B , and M _T of the welding robot 1 that satisfy the above welding conditions by setting matrix U = matrix T. This formula is derived for each of the movement amounts Mx, My, Mz, M _B , and M _T. This formula is derived for each of areas 1 to 3.

[Welding system control system]
Next, a control system of welding system 100 will be described with reference to FIGS.
As described above, the control system determines the amount of movement of the welding robot 1 such that the matrix U is equal to the matrix T, and controls the drive of the motor 32 in accordance with the amount of movement, thereby making it possible to perform welding that satisfies the above welding conditions.
9 is a diagram showing an example of a hardware configuration of the system control device 6 in the embodiment. The system control device 6 includes a processor 91 such as a CPU (Central Processing Unit) and a memory 92 connected by a bus, and executes a program. The system control device 6 functions as a device including a control unit 61, a communication unit 62, an input unit 63, a storage unit 64, and an output unit 65 by executing the program.

More specifically, in the system control device 6, the processor 91 reads out a program stored in the storage unit 64 and stores the read out program in the memory 92. When the processor 91 executes the program stored in the memory 92, the system control device 6 functions as a device including a control unit 61, a communication unit 62, an input unit 63, a storage unit 64, and an output unit 65.

The control unit 61 controls the operation of various functional units equipped in the system control device 6. The control unit 61 controls the operation of the welding robot 1, for example. The control unit 61 causes the welding robot 1 to perform welding, for example. The control unit 61 causes the welding robot 1 to perform welding of the curved section 8a, for example. When controlling the operation of the welding robot 1, the control unit 61 may also control the operation of the welding robot 1 by controlling the operation of the welding power source 4 and the operation of the wire feeder 5, for example.

The control unit 61 controls the target position changing unit and the speed changing unit according to the radius of curvature and center of curvature (steel pipe curvature center C1) of the curved portion 8a of the steel pipe 8, the radius of curvature and center of curvature (rail curvature center C2) of the curved portion 2a of the guide rail 2, and the welding speed and position of the welding robot 1. The control unit 61 also controls the torch direction changing unit. Other functions of the control unit 61 will be described later.

The communication unit 62 includes a communication interface for connecting the system control device 6 to an external device. The communication unit 62 communicates with the external device via a wired or wireless connection. The external device is, for example, the welding robot 1. The communication unit 62 communicates with the welding robot 1 via, for example, a control cable. The communication unit 62 transmits, for example, a control signal to the welding robot 1. The external device is, for example, the imaging device 3. The communication unit 62 acquires imaging results by communicating with the imaging device 3. The external device is, for example, the welding power source 4. The external device is, for example, the wire feeder 5.
The communication unit 62 acquires information about the position of the welding robot 1 (hereinafter referred to as welding robot position information) via, for example, a control cable. The welding robot position information is, for example, a target value (hereinafter also simply referred to as a target value) for controlling a servo motor (motor 32) related to the movement of the welding robot 1.

The input unit 63 includes input devices such as a mouse, a keyboard, and a touch panel.
The input unit 63 may be configured as an interface that connects these input devices to the system control device 6. The input unit 63 accepts input of various information to the system control device 6. To the input unit 63, for example, an instruction to start welding is input.

The storage unit 64 is configured using a computer-readable storage medium device such as a magnetic hard disk device or a semiconductor storage device. The storage unit 64 stores various information related to the welding system 100 including the system control device 6 itself. The storage unit 64 stores information inputted via the communication unit 62 or the input unit 63, for example. The storage unit 64 stores various information generated by the execution of processing by the control unit 61, for example. The storage unit 64 stores the imaging results acquired by the imaging device 3, for example.

The storage unit 64 stores in advance information on the shape of the steel pipe 8 (hereinafter also referred to as steel pipe shape information) for each type of steel pipe 8. The steel pipe shape information includes the radius Rc of the curved portion 8a, the curvature of the curved portion 8a, the position of the steel pipe curvature center C1 of the curved portion 8a, the length of the straight portion 8b, etc. The storage unit 64 stores in advance information on the shape of the guide rail 2 (hereinafter also referred to as guide rail shape information) for each type of guide rail 2. The guide rail shape information includes the radius Rg of the curved portion 2a, the curvature of the curved portion 2a, the position of the rail curvature center C2 of the curved portion 2a, the length of the straight portion 2b, etc.
The storage unit 64 stores in advance calculation formulas derived for each of the areas 1 to 3 for determining the movement amounts Mx, My, Mz, M _B , and M _T of the welding robot 1 when the matrix U and the matrix T become equal.
The memory unit 64 stores the target value (welding robot position information). The memory unit 64 stores a reference position of the welding torch 13. The memory unit 64 stores a predetermined position of the guide rail 2 that is the reference for the movement amount My.

The output unit 65 outputs various information. The output unit 65 includes a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display. The output unit 65 may be configured as an interface that connects these display devices to the system control device 6. The output unit 65 outputs information input to the input unit 63, for example. The output unit 65 may display the results of processing executed by the control unit 61, for example.

Figure 10 is a diagram showing an example of the functional configuration of the control unit 61 in this embodiment. The control unit 61 includes a data acquisition unit 610, a welding robot control unit 620, a memory control unit 630, an input control unit 640, and an output control unit 650.

The data acquisition unit 610 acquires welding robot position information stored in the storage unit 64. The data acquisition unit 610 acquires calculation formulas for determining the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1, which are stored in advance in the storage unit 64. The data acquisition unit 610 acquires the photographing results of the photographing device 3, which are stored in the storage unit 64.
The data acquisition unit 610 acquires, from the storage unit 64, steel pipe shape information corresponding to the type of steel pipe 8 to be used. The data acquisition unit 610 acquires, from the storage unit 64, guide rail shape information corresponding to the type of guide rail 2 to be used. Note that the type of steel pipe 8 and the type of guide rail 2 to be used are input to the input unit 63 by, for example, the user.

The welding robot control unit 620 controls the operation of the welding robot 1. The welding robot control unit 620 includes a position information acquisition unit 621, a shape information acquisition unit 622 (acquisition unit), a curvature center determination unit 623 (determination unit), a parameter setting unit 624, a welding time count unit 625, an area determination unit 626, a target torch position calculation unit 627, a movement amount setting unit 628, and a curved section welding execution control unit 629. The parameter setting unit 624, the target torch position calculation unit 627, and the movement amount setting unit 628 constitute the setting unit in this embodiment.

The position information acquisition unit 621 acquires welding robot position information via the memory unit 64 and the data acquisition unit 610.

The shape information acquisition unit 622 acquires steel pipe shape information and guide rail shape information via the memory unit 64 and the data acquisition unit 610.

The curvature center determination unit 623 determines whether the position of the steel pipe curvature center C1 and the position of the rail curvature center C2 coincide with each other based on the steel pipe shape information and the guide rail shape information acquired by the shape information acquisition unit 622. In addition, if the position of the steel pipe curvature center C1 and the position of the rail curvature center C2 do not coincide with each other, the curvature center determination unit 623 determines whether the steel pipe curvature center C1 or the rail curvature center C2 is located closer to the center of the steel pipe 8.

The parameter setting unit 624 acquires the imaging results of the imaging device 3 via the storage unit 64 and the data acquisition unit 610. The parameter setting unit 624 determines the shape and state of the welded portion (e.g., groove information) based on the imaging results of the imaging device 3 and the steel pipe shape information and guide rail shape information acquired by the shape information acquisition unit 622.
Based on the determined shape and state of the welded portion, the parameter setting unit 624 sets specific values of the welding movement speed Vw, welding torch direction, target angle θn, and target position of the welding torch 13 as welding conditions.

The welding time counting unit 625 counts the elapsed time t from the start of welding the curved section 8a (i.e., when the welding robot 1 reaches position Pg1 in area 1).

The area determination unit 626 acquires the welding movement speed Vw set by the parameter setting unit 624. The area determination unit 626 acquires the elapsed time t from the welding time counting unit 625. The area determination unit 626 calculates a target position of the tip of the welding torch 13 at the acquired elapsed time t. Specifically, since the tip of the welding torch 13 moves along the steel pipe 8 at the welding movement speed Vw, the position of the tip of the welding torch 13 at the time t is a position moved by Vw·t along the steel pipe 8 from the position Pc1.
Area determination unit 626 determines in which of areas 1 to 3 the calculated target position of the tip of welding torch 13 is located.

The target torch position calculation unit 627 acquires a calculation formula for calculating the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 via the memory unit 64 and the data acquisition unit 610. The target torch position calculation unit 627 acquires specific values of the welding movement speed Vw, welding torch orientation, target angle θn, and target position of the welding torch 13 set by the parameter setting unit 624. The target torch position calculation unit 627 reflects the specific values of the welding movement speed Vw, welding torch orientation, target angle θn, and target position of the welding torch 13 set by the parameter setting unit 624 in the above calculation formula.

The movement amount setting unit 628 determines the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 at a predetermined time t based on the calculation formula acquired by the target torch position calculation unit 627, and sets these as the movement amounts of the welding robot 1.
That is, based on the matrices U and T, the movement amount setting unit 628 sets the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 that satisfy the welding movement speed Vw, welding torch direction, target angle θn, and target position of the welding torch 13 under the above welding conditions.

The curved section welding execution control unit 629 changes the position of the welding robot 1 and the position and posture of the welding torch 13 in accordance with the movement amounts Mx, My, Mz, _MB , and _MT set by the movement amount setting unit 628, and causes the welding robot 1 to weld the curved section 8 a.
Specifically, the curved portion welding execution control unit 629 drives the motor 32 to operate the vertical movement unit 34, and changes the position of the welding torch 13 in the vertical direction x of the welding robot 1 according to the movement amount Mx set by the movement amount setting unit 628. The curved portion welding execution control unit 629 drives the motor 32 to operate the front-rear movement unit 33, and changes the position of the welding torch 13 in the front-rear direction z of the welding robot 1 according to the movement amount Mz set by the movement amount setting unit 628. The curved portion welding execution control unit 629 drives the motor 32 to operate the first rotation unit 35, and changes the orientation of the welding torch 13 around the first axis according to the movement amount M _B set by the movement amount setting unit 628. The curved portion welding execution control unit 629 drives the motor 32 to operate the second rotation unit 36, and changes the orientation of the welding torch 13 around the second axis according to the movement amount M _T set by the movement amount setting unit 628. The curved portion welding execution control unit 629 drives the motor 32 (servo motor) to change the position of the welding robot 1 in accordance with the movement amount My set by the movement amount setting unit 628 .

The memory control unit 630 records various information in the memory unit 64. The memory control unit 630 records various information generated by, for example, the operation of the control unit 61 in the memory unit 64. The information generated by the operation of the control unit 61 is, for example, information indicating the content of the control of the welding robot 1 by the welding robot control unit 620.

The input control unit 640 controls the operation of the input unit 63. The output control unit 650 controls the operation of the output unit 65.

[Example of control performed by the welding system]
An example of control executed by welding system 100 will be described with reference to FIG.
FIG. 11 is a flowchart showing an example of the flow of the welding process for the curved portion 8a executed by the system control device 6 in this embodiment.

Before welding the curved portion 8a, the curvature center determination unit 623 determines whether the position of the steel pipe curvature center C1 coincides with the position of the rail curvature center C2. If the position of the steel pipe curvature center C1 does not coincide with the position of the rail curvature center C2, the curvature center determination unit 623 determines which of the steel pipe curvature center C1 and the rail curvature center C2 is located closer to the center of the steel pipe 8.
Hereinafter, in this embodiment, the flow of the welding process of the curved section 8a will be described when the curvature center determination unit 623 determines that the rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1.

The welding process of the curved section 8a is started when the welding robot 1 reaches position Pg1. At this time, the tip of the welding torch 13 is located at position Pc1 in area 1. For example, the start of the welding process of the curved section 8a is determined by estimating the position of the welding robot 1 based on the welding robot position information acquired by the position information acquisition unit 621, and determining whether the estimated position of the welding robot 1 has reached position Pg1.

When the welding process of the curved portion 8a is started, the welding time counting unit 625 starts counting the elapsed time t from the start of the welding process of the curved portion 8a (step S101).
The area determination unit 626 calculates the target position of the tip of the welding torch 13 at the elapsed time t (step S102). The area determination unit 626 determines in which of areas 1 to 3 the calculated target position of the tip of the welding torch 13 is located (step S103).

When it is determined that the tip of welding torch 13 is located in area 1 (step S103: A1), movement amount setting unit 628 acquires a formula for calculating movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 corresponding to area 1. Based on the above formula, movement amount setting unit 628 calculates a rotation amount θg from position Pg1 of welding robot 1 on curved portion 2a of guide rail 2 at elapsed time t (step S111). Based on the above formula, movement amount setting unit 628 also calculates movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 at elapsed time t and sets them as movement amounts of welding robot 1 (step S112). After that, the process proceeds to step S105.

When it is determined that the tip of the welding torch 13 is located in area 2 (step S103: A2), the movement amount setting unit 628 acquires a formula for calculating the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 corresponding to area 2. Here, since the movement of the tip of the welding torch 13 in area 2 is a rotational movement around the steel pipe curvature center C1, the target torch position calculation unit 627 calculates the target position of the tip of the welding torch 13 calculated in step S102 as the rotation amount θc of the tip of the welding torch 13 at the curved portion 8a of the steel pipe 8 (step S121). The movement amount setting unit 628 calculates the rotation amount θg from the position Pg1 of the welding robot 1 at the curved portion 2a of the guide rail 2 at the elapsed time t based on the above formula (step S122). Further, the movement amount setting unit 628 calculates the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 at the elapsed time t based on the above calculation formula, and sets them as the movement amounts of the welding robot 1 (step S123). After that, the process proceeds to step S105.

When it is determined that the tip of welding torch 13 is located in area 3 (step S103: A3), movement amount setting unit 628 acquires a formula for calculating movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 corresponding to area 3. Based on the above formula, movement amount setting unit 628 calculates a rotation amount θg from position Pg1 of welding robot 1 on curved portion 2a of guide rail 2 at elapsed time t (step S131). Based on the above formula, movement amount setting unit 628 also calculates movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 at elapsed time t and sets them as movement amounts of welding robot 1 (step S132). Thereafter, the process proceeds to step S105.

The curved section welding execution control unit 629 drives each motor 32 to change the position of the welding robot 1 and the position and posture of the welding torch 13 according to the movement amounts Mx, My, Mz, _MB , and _MT set by the movement amount setting unit 628, and causes the welding robot 1 to weld the curved section 8a (step S105).

Thereafter, area determination unit 626 determines whether the position of the tip of welding torch 13 has reached end position Pc4 of area 3 (step S106).
When it is determined that the position of the tip of welding torch 13 has reached position Pc4 (step S106: YES), curved section welding execution control unit 629 ends the welding process of curved section 8a (step S206).
On the other hand, if the position of the tip of welding torch 13 has not reached position Pc4 (step S106: NO), the process returns to step S102. In this case, the welding process of curved portion 8a is continued.

The specific control content of the welding robot 1 in each area when the above control is performed is described below. Note that the control content of the welding robot 1 shown below is an example, and the present invention is not limited to this.

First, the control contents in area 4 (i.e., the area other than the welding of the curved portion 8a) will be described. In area 4, as shown in FIG. 12, the welding robot 1 moves at a constant speed (welding movement speed Vw). Hereinafter, the movement speed of the welding robot 1 in area 4 is also referred to as the reference speed. In addition, the movement amount Mx of the welding torch 13 in the up-down direction x is constant (hereinafter, also referred to as the up-down movement reference value). The movement amount Mz of the welding torch 13 in the front-back direction z is constant (hereinafter, also referred to as the front-back movement reference value). As shown in FIG. 13, in area 4, the speed of the robot in the front-back direction z is 0 (zero). As shown in FIG. 14, the movement amount M _B of the welding torch 13 around the first axis is constant (hereinafter, also referred to as the first axis rotation reference value), and the welding torch 13 is rotated vertically downward around the first axis. As shown in FIG. 14, the movement amount M _T of the welding torch 13 around the second axis is constant and is 0 (zero). That is, when viewed along the up-down direction x, the welding torch 13 is always perpendicular to the left-right direction y (i.e., the straight portion 8b of the steel pipe 8), which is the moving direction of the welding robot 1.
In the following description, the movement amount Mx increases when the welding torch 13 moves downward and decreases when it moves upward. The movement amount Mz increases when the welding torch 13 moves rearward (i.e., away from the steel pipe 8) and decreases when it moves forward (i.e., toward the steel pipe 8). The movement amount M _B increases when the vertical downward inclination of the welding torch 13 increases. The movement amount M _T is set to 0 when the welding torch 13 is perpendicular to the traveling direction of the welding robot 1 as viewed along the up-down direction x, increases when the welding torch 13 inclines toward the traveling direction of the welding robot 1, and decreases when the welding torch 13 inclines toward the opposite side to the traveling direction of the welding robot 1.

The control content in area 1 will be described below. The control of the control unit 61 in area 1 is as follows.
For example, when the tip of welding torch 13 moves between straight portion 8b of steel pipe 8 and start position Pc2, control unit 61 controls the target position changing unit so that welding torch 13 moves in a direction away from steel pipe 8 at a second torch separating speed. At this time, the second torch separating speed increases as the tip of welding torch 13 approaches start position Pc2.

The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the straight portion 8b of the steel pipe 8 and the starting position Pc2, the welding torch 13 moves in a direction away from the steel pipe 8 at a first torch separation acceleration.
For example, when the welding torch 13 moves in the vicinity of the start position Pc2, the control unit 61 controls the target position change unit so that the welding torch 13 moves in a direction away from the steel pipe 8 at the second torch separation acceleration. In this embodiment, the vicinity of the start position Pc2 refers to a region having a length of 20% of the radius of curvature of the curved portion 8a of the steel pipe 8 along the circumferential direction of the steel pipe 8, with the start position Pc2 at the center. That is, for example, when the radius of curvature of the curved portion 8a of the steel pipe 8 is 40 mm, the length of the region related to the vicinity of the start position Pc2 is 8 mm. Both ends of the region related to the vicinity of the start position Pc2 are located in portions that are moved 4 mm on both sides from the start position Pc2 along the circumferential direction of the steel pipe 8.
At this time, the second torch separation acceleration is greater than the first torch separation acceleration.

12, in area 1, the moving speed of welding robot 1 becomes slower than the reference speed. That is, welding robot 1 instantaneously decelerates to the moving speed in area 1. "Instantaneous" refers to the timing at which welding robot 1 reaches area 1 from area 4.
The amount of movement Mx is equal to the vertical movement reference value.
13, in area 1, the speed of welding robot 1 in the forward/backward direction z increases. That is, the movement amount Mz increases from the forward/backward movement reference value as the tip of welding torch 13 moves from position Pc1 to position Pc2. That is, welding torch 13 moves in a direction away from steel pipe 8 as the tip of welding torch 13 moves from position Pc1 to position Pc2.
14, the amount of movement _MB increases from the first axis rotation reference value as the tip of welding torch 13 moves from position Pc1 to position Pc2. In other words, as the tip of welding torch 13 moves from position Pc1 to position Pc2, the downward vertical inclination of welding torch 13 increases.
14, the amount of movement _MT increases from 0 as the tip of welding torch 13 moves from position Pc1 to position Pc2. That is, as viewed along the up-down direction x, welding torch 13 tilts toward the traveling direction of welding robot 1 as the tip of welding torch 13 moves from position Pc1 to position Pc2.

The control content in area 2 will be described. The control of the control unit 61 in area 2 is as follows.
The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between a start position Pc2 of the curved portion 8a of the steel pipe 8 and a steel pipe intermediate position that is an intermediate position between the start position Pc2 and an end position Pc3 of the curved portion 8a of the steel pipe 8, the welding torch 13 moves in a direction away from the steel pipe 8 at a first torch separating speed. At this time, the first torch separating speed becomes smaller as the tip of the welding torch 13 approaches the steel pipe intermediate position.

The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc3, the welding torch 13 moves in a direction approaching the steel pipe 8 at a first torch approach speed. At this time, the first torch approach speed increases as it approaches the end position Pc3.

The control unit 61 controls the speed change unit so that the welding robot 1 moves at a first robot speed, for example, when the tip of the welding torch 13 moves between the start position Pc2 and the middle position of the steel pipe. At this time, the first robot speed decreases as the tip of the welding torch 13 approaches the middle position of the steel pipe.

The control unit 61 controls the speed change unit so that the welding robot 1 moves at a first robot deceleration, for example, when the tip of the welding torch 13 moves between the start position Pc2 and the middle position of the steel pipe.
For example, the control unit 61 controls the speed change unit so that the welding robot 1 moves at a first robot acceleration when the tip of the welding torch 13 approximately reaches the start position Pc2. Here, in this embodiment, the tip of the welding torch 13 approximately reaches the start position Pc2 means that the tip of the welding torch 13 reaches the vicinity of the start position Pc2.
At this time, the absolute value of the first robot acceleration is greater than the absolute value of the first robot deceleration.

The control unit 61 controls the torch orientation changing unit so that, for example, when the tip of the welding torch 13 moves between the starting position Pc2 and the middle position of the steel pipe, the inclination of the welding torch 13 in a specified direction becomes smaller as the tip moves.
The control unit 61 controls the torch orientation changing unit so that, for example, when the tip of the welding torch 13 moves between the middle position of the steel pipe and the end position Pc3, the inclination of the welding torch 13 in the direction opposite to the specified direction increases as the tip moves.

The control unit 61 controls the speed change unit so that the welding robot 1 moves at the second robot speed when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc3, for example. At this time, the second robot speed increases as the tip of the welding torch 13 approaches the end position Pc3.

The control unit 61 controls the speed change unit so that the welding robot 1 moves at a second robot acceleration, for example, when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc3.
The control unit 61 controls the speed change unit so that, for example, when the tip of the welding torch 13 approximately reaches the end position Pc3, the welding robot 1 moves at the second robot deceleration. Here, in this embodiment, the tip of the welding torch 13 approximately reaches the end position Pc3, meaning that the tip of the welding torch 13 reaches the vicinity of the end position Pc3. The vicinity of the end position Pc3 refers to a region with a length of 20% of the radius of curvature of the curved portion 8a of the steel pipe 8 along the circumferential direction of the steel pipe 8, with the end position Pc3 as the center. That is, for example, when the radius of curvature of the curved portion 8a of the steel pipe 8 is 40 mm, the length of the region related to the vicinity of the end position Pc3 is 8 mm. Both ends of the region related to the vicinity of the end position Pc3 are located in portions that are moved 4 mm on both sides from the end position Pc3 along the circumferential direction of the steel pipe 8.
At this time, the absolute value of the second robot deceleration is greater than the absolute value of the second robot acceleration.
In area 2, as shown in FIG. 12, the movement speed of the welding robot 1 becomes higher than the reference speed. That is, the welding robot 1 instantaneously accelerates to the movement speed in area 2. The instantaneous acceleration is the timing when the welding robot 1 reaches area 2 from area 1. Also, when the tip of the welding torch 13 is in the range from position Pc2 to the intermediate position between positions Pc2 and Pc3, the welding robot 1 continues to decelerate at a predetermined negative acceleration from the start position Pc2 of area 2 to the intermediate position . Note that even in this case, the movement speed of the welding robot 1 is higher than the reference speed. After that, when the tip of the welding torch 13 is in the range from the intermediate position between positions Pc2 and Pc3 to position Pc3, the welding robot 1 continues to accelerate at a predetermined positive acceleration from the intermediate position to the end position Pc3 of area 2.
The amount of movement Mx is equal to the vertical movement reference value.
13, the movement speed of the welding robot 1 in the front-rear direction z is positive when the tip of the welding torch 13 moves from position Pc2 to the intermediate position between positions Pc2 and Pc3 in area 2. That is, the movement amount Mz increases as the tip of the welding torch 13 moves from position Pc2 to the intermediate position between positions Pc2 and Pc3. As shown in FIG. 13, the movement speed of the welding robot 1 in the front-rear direction z is negative when the tip of the welding torch 13 moves from the intermediate position between positions Pc2 and Pc3 to position Pc3 in area 2. That is, the movement amount Mz decreases as the tip of the welding torch 13 moves from the intermediate position between positions Pc2 and Pc3 to position Pc3.
In other words, when the tip of welding torch 13 is in the range from position Pc2 to the intermediate position between positions Pc2 and Pc3, it moves in a direction away from steel pipe 8, and when the tip of welding torch 13 is in the range from the intermediate position between positions Pc2 and Pc3 to position Pc3, it moves in a direction toward steel pipe 8.
14, the amount of movement _MB decreases as the tip of welding torch 13 moves from position Pc2 to an intermediate position between positions Pc2 and Pc3, and increases as the tip of welding torch 13 moves from the intermediate position between positions Pc2 and Pc3 to position Pc3. Even in this case, the amount of movement _MB does not become smaller than the first axis rotation reference value. That is, as the tip of welding torch 13 moves from position Pc2 to an intermediate position between positions Pc2 and Pc3, the downward vertical inclination of welding torch 13 decreases, and as the tip of welding torch 13 moves from the intermediate position between positions Pc2 and Pc3 to position Pc3, the downward vertical inclination of welding torch 13 increases.
As shown in FIG. 14, the movement amount M _T decreases as the tip of the welding torch 13 moves from the position Pc2 to the position Pc3. The movement amount M _T is 0 when the tip of the welding torch 13 is located at the intermediate position between the positions Pc2 and Pc3. The value of the movement amount M _T is negative when the tip of the welding torch 13 is between the intermediate position between the positions Pc2 and Pc3 and the position Pc3. That is, when viewed along the vertical direction x, the tip of the welding torch 13 is located at the position Pc3, which is the end position of the area 1, the welding torch 13 is inclined toward the traveling direction of the welding robot 1. As the tip of the welding torch 13 moves from the position Pc2 to the intermediate position between the positions Pc2 and Pc3, the inclination of the welding torch 13 toward the traveling direction of the welding robot 1 becomes smaller, and when the tip of the welding torch 13 reaches the intermediate position between the positions Pc2 and Pc3, the welding torch 13 is perpendicular to the traveling direction of the welding robot 1. Thereafter, as the tip of welding torch 13 moves from the intermediate position between positions Pc2 and Pc3 to position Pc3, welding torch 13 tilts in the direction opposite to the traveling direction of welding robot 1.

The control content in area 3 will be described below. The control of the control unit 61 in area 3 is as follows.
The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the end position Pc3 of the curved portion 8a of the steel pipe 8 and the straight portion 8b of the steel pipe 8, the welding torch 13 moves at the second torch approach speed in the direction approaching the steel pipe 8. At this time, the second torch approach speed becomes smaller as it approaches the straight portion 8b.

For example, when the tip of the welding torch 13 moves near the end position Pc3, the control unit 61 controls the target position changing unit so that the welding torch 13 moves in a direction approaching the steel pipe 8 at a first torch approach deceleration.
The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the end position Pc3 and the straight section 8b, the welding torch 13 moves in a direction approaching the steel pipe 8 at a second torch approach deceleration.
At this time, the first torch approach deceleration is greater than the second torch approach deceleration.

12, in area 3, the moving speed of the welding robot 1 becomes slower than the reference speed. That is, the welding robot 1 instantaneously decelerates to the moving speed in area 3. The instantaneous deceleration occurs at the time when the welding robot 1 reaches area 3 from area 2.
The amount of movement Mx is equal to the vertical movement reference value.
As shown in Fig. 13, the movement speed of the welding robot 1 in the forward/backward direction z increases from a negative value toward 0 (zero) until the tip of the welding torch 13 moves from position Pc3 to position Pc4 in area 3. That is, the movement amount Mz decreases as the tip of the welding torch 13 moves from position Pc3 to position Pc4. As shown in Fig. 13, when the tip of the welding torch 13 reaches position Pc4 in area 3, the movement speed of the welding robot 1 in the forward/backward direction z becomes 0 (zero). That is, when the tip of the welding torch 13 reaches position Pc4, the movement amount Mz becomes equal to the forward/backward movement reference value. That is, as the tip of the welding torch 13 moves from position Pc3 to position Pc4, the welding torch 13 moves in a direction approaching the steel pipe 8.
14, the amount of movement _MB decreases as the tip of welding torch 13 moves from position Pc3 to position Pc4, and becomes equal to the first axis rotation reference value when the tip of welding torch 13 reaches position Pc4. In other words, as the tip of welding torch 13 moves from position Pc3 to position Pc4, the downward vertical inclination of welding torch 13 becomes smaller.
14, the amount of movement _MT increases as the tip of welding torch 13 moves from position Pc3 to position Pc4, and becomes 0 when the tip of welding torch 13 reaches position Pc4. That is, when viewed along the up-down direction x, when the tip of welding torch 13 is located at position Pc3 which is the end position of area 2, welding torch 13 is inclined toward the opposite side to the traveling direction of welding robot 1. As the tip of welding torch 13 moves from position Pc3 to position Pc4, the inclination of welding torch 13 toward the opposite side to the traveling direction of welding robot 1 becomes smaller, and when the tip of welding torch 13 reaches position Pc4, welding torch 13 is perpendicular to the traveling direction of welding robot 1.

As described above, according to the welding system 100 of this embodiment, the control unit 61 controls the target position changing unit so that when the tip of the welding torch 13 moves between the start position Pc2 of the curved portion 8a of the steel pipe 8 and the middle position of the steel pipe, the welding torch 13 moves in a direction away from the steel pipe 8 at the first torch separation speed. This makes it possible to prevent the tip of the welding torch 13 from coming too close to the steel pipe 8 when the rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1.

Here, when the rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1, the distance between the guide rail 2 and the steel pipe 8 is the farthest between the straight portion 2b of the guide rail 2 and the straight portion 8b of the steel pipe 8, and is the closest between the guide rail intermediate position, which is the intermediate position of the curved portion 2a of the guide rail 2, and the steel pipe intermediate position. In contrast, the first torch separation speed becomes smaller as the tip of the welding torch 13 approaches the steel pipe intermediate position. This makes it possible to smoothly adjust the distance between the tip of the welding torch 13 and the steel pipe 8. Therefore, it is easier to ensure the quality of the welding of the steel pipe 8 by the welding torch 13. Therefore, a constant welding quality can be maintained over the entire length of the welded portion of the steel pipe 8.

The control unit 61 also controls the target position changing unit so that when the tip of the welding torch 13 moves between the straight portion 8b of the steel pipe 8 and the start position Pc2 of the curved portion 8a of the steel pipe 8, the welding torch 13 moves in a direction away from the steel pipe 8 at the second torch separation speed. This makes it possible to prevent the tip of the welding torch 13 from coming too close to the steel pipe 8.

Here, when the rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1, the welding robot 1 may be located at the curved portion 2a of the guide rail 2 with the tip of the welding torch 13 located at the straight portion 8b of the steel pipe 8. Then, as the welding robot 1 moves along the curved portion 2a, the speed at which the tip of the welding torch 13 approaches the steel pipe 8 increases at an accelerated rate. In contrast, the second torch separation speed increases as the tip of the welding torch 13 approaches the starting position Pc2. This allows the distance between the tip of the welding torch 13 and the steel pipe 8 to be smoothly adjusted as the tip of the welding torch 13 moves between the straight portion 8b of the steel pipe 8 and the starting position Pc2.

Furthermore, the control unit 61 controls the target position changing unit so that when the tip of the welding torch 13 moves between the straight portion 8b of the steel pipe 8 and the start position Pc2 of the curved portion 8a of the steel pipe 8, the welding torch 13 moves in a direction away from the steel pipe 8 at a first torch separation acceleration. This allows the speed at which the welding torch 13 separates from the steel pipe 8 to increase as the tip of the welding torch 13 approaches the start position Pc2. This allows the distance between the tip of the welding torch 13 and the steel pipe 8 to be smoothly adjusted.

Here, when the rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1, the speed at which the tip of the welding torch 13 approaches the steel pipe 8 when the tip of the welding torch 13 is located at the curved portion 8a of the steel pipe 8 is greater than the speed at which the tip of the welding torch 13 approaches the steel pipe 8 when the tip of the welding torch 13 is located between the straight portion 8b of the steel pipe 8 and the start position Pc2 of the curved portion 8a of the steel pipe 8. In response to this, when the welding torch 13 moves near the start position Pc2, the control unit 61 controls the target position change unit so that the welding torch 13 moves in a direction away from the steel pipe 8 at a second torch separation acceleration, and the second torch separation acceleration is greater than the first torch separation acceleration. This makes it possible to correspond to the speed at which the tip of the welding torch 13 approaches the steel pipe 8 when the tip of the welding torch 13 is located at the curved portion 8a.

Here, the length of the curved portion 2a of the guide rail 2 is longer than the length of the curved portion 8a of the steel pipe 8. Therefore, in order to make the speed at which the tip of the welding torch 13 advances on the curved portion 8a of the steel pipe 8 the same as the speed at which it advances on the straight portion 8b of the steel pipe 8, it is necessary to make the speed at which the welding robot 1 advances on the curved portion 2a of the guide rail 2 faster than the speed at which the welding robot 1 advances on the straight portion 2b of the guide rail 2. In response to this, the control unit 61 controls the speed change unit so that the welding robot 1 moves at the first robot speed when the tip of the welding torch 13 moves between the start position Pc2 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position. This makes it possible to make the speed at which the welding torch 13 advances on the curved portion 8a of the steel pipe 8 the same as the speed at which it advances on the straight portion 8b of the steel pipe 8.

When welding the curved portion 8a of the steel pipe 8, the orientation of the welding torch 13 may be changed so that the orientation of the welding torch 13 coincides with the normal direction of the curved portion 8a of the steel pipe 8. In contrast, the first robot speed decreases as the tip of the welding torch 13 approaches the middle position of the steel pipe. This makes it possible to keep the speed of the tip of the welding torch 13 constant even when the orientation of the welding torch 13 is changed when welding the curved portion 8a of the steel pipe 8 when the rail curvature center C2 is located closer to the center of the steel pipe 8 than the steel pipe curvature center C1. This makes it easier to ensure the quality of the welding of the steel pipe 8.

In addition, the control unit 61 controls the speed change unit so that the welding robot 1 moves at the first robot deceleration when the tip of the welding torch 13 moves between the start position Pc2 of the curved portion 8a of the steel pipe 8 and the intermediate position of the steel pipe. This allows the speed at which the welding robot 1 advances along the guide rail 2 to be reduced as the tip of the welding torch 13 approaches the intermediate position of the steel pipe when the tip of the welding torch 13 moves between the start position Pc2 of the curved portion 8a of the steel pipe 8 and the intermediate position of the steel pipe. This allows the speed of the tip of the welding torch 13 to be constant. This makes it easier to ensure the quality of the welding of the steel pipe 8.

Here, as described above, in order to make the speed at which the tip of the welding torch 13 advances on the curved portion 8a of the steel pipe 8 the same as the speed at which the tip of the welding torch 13 advances on the straight portion 8b of the steel pipe 8, the speed at which the welding robot 1 advances on the curved portion 2a of the guide rail 2 must be faster than the speed at which the welding robot 1 advances on the straight portion 2b of the guide rail 2. Furthermore, the welding robot 1 must be accelerated immediately after the tip of the welding torch 13 reaches the start position Pc2 of the curved portion 8a of the steel pipe 8. In response to this, the control unit 61 controls the speed change unit so that the welding robot 1 moves at a first robot acceleration when the tip of the welding torch 13 approximately reaches the start position Pc2 of the curved portion 8a of the steel pipe 8, and the absolute value of the first robot acceleration is greater than the absolute value of the first robot deceleration. This allows the movement speed of the welding robot 1 when the tip of the welding torch 13 moves on the curved portion 8a to be appropriate.

The control unit 61 also controls the torch orientation change unit so that when the tip of the welding torch 13 moves between the start position Pc2 and the steel pipe intermediate position, the inclination of the welding torch 13 in a predetermined direction decreases as the tip of the welding torch 13 moves. The control unit 61 also controls the torch orientation change unit so that when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc3 of the curved portion 8a of the steel pipe 8, the inclination of the welding torch 13 in the direction opposite to the predetermined direction increases as the tip of the welding torch 13 moves. This makes it possible to change the orientation of the welding torch 13 so that the orientation of the welding torch 13 coincides with the normal direction of the curved portion 8a of the steel pipe 8 when welding the curved portion 8a of the steel pipe 8.

Second Embodiment
A welding system 100 according to a second embodiment of the present invention will now be described with reference to FIGS.
In this embodiment, a control method in the welding system 100 will be described in the case where the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2. The basic configuration and operation of the welding system 100 used in this embodiment are similar to those of the welding system 100 of the first embodiment.

[Curved section of steel pipe and curved section of guide rail]
The curved portion 8a of the steel pipe 8 and the curved portion 2a of the guide rail 2 will be described with reference to FIG.
15 , in this embodiment, the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2. The rail curvature center C2 is located at a position shifted by e in the Y direction and the Z direction from the steel pipe curvature center C1.

In this embodiment, the welding of the steel pipe 8 is divided into areas 5, 6, 7, and 8 according to the welding form.
In the following, the start position of curved portion 8a is designated as Pc5 and the end position as Pc6. The start position of curved portion 2a is designated as Pg6 and the end position as Pg7. The intersection of a straight line connecting the steel pipe curvature center C1 and position Pc5 with straight portion 2b of guide rail 2 is designated as position Pg5. The intersection of a straight line connecting the steel pipe curvature center C1 and position Pc6 with straight portion 2b of guide rail 2 is designated as position Pg8.

Area 5 is an area in which the welding robot 1 moves from position Pg5 to position Pg6 on the guide rail 2. In area 5, the welding robot 1 welds the curved portion 8a of the steel pipe 8 while moving along the straight portion 2b of the guide rail 2. That is, in area 5, the welding robot 1 is located on the straight portion 2b of the guide rail 2, and the portion that the welding robot 1 welds is the curved portion 8a of the steel pipe 8.
Area 6 is an area where the welding robot 1 moves from position Pg6 to position Pg7 on the guide rail 2. In area 6, the welding robot 1 welds the curved portion 8a of the steel pipe 8 while moving along the curved portion 2a of the guide rail 2. That is, in area 6, the welding robot 1 is located at the curved portion 2a of the guide rail 2, and the portion that the welding robot 1 welds is the curved portion 8a of the steel pipe 8.
Area 7 is an area in which the welding robot 1 moves from position Pg7 to position Pg8 on the guide rail 2. In area 7, the welding robot 1 welds the curved portion 8a of the steel pipe 8 while moving along the straight portion 2b of the guide rail 2. That is, in area 7, the welding robot 1 is located on the straight portion 2b of the guide rail 2, and the portion that the welding robot 1 welds is the curved portion 8a of the steel pipe 8.
Area 8 is an area other than areas 5 to 7 of the steel pipe 8. In area 8, the welding robot 1 welds the straight portion 8b of the steel pipe 8 while moving along the straight portion 2b of the guide rail 2. That is, in area 8, the welding robot 1 is positioned on the straight portion 2b of the guide rail 2, and the portion that the welding robot 1 welds is the straight portion 8b of the steel pipe 8.
In this embodiment, welding of the curved portion 8a means welding of areas 5 to 7.

[Welding conditions]
As in the first embodiment, in order to obtain good welding quality, it is preferable to satisfy the welding conditions shown in <1> to <4> below regardless of the area.
<1> The speed at which the tip of the welding torch 13 moves along the welded portion of the steel pipe 8 (hereinafter also referred to as the welding movement speed Vw) is constant.
<2> The direction of the welding torch 13 when viewed from above (hereinafter also referred to as the welding torch direction) coincides with the normal direction of the curved portion 8 a of the steel pipe 8 or is perpendicular to the straight portion 8 b of the steel pipe 8 .
<3> The target angle θn of the welding torch 13 remains constant.
<4> The distance between the tip of the welding torch 13 and the welded portion of the steel pipe 8 (hereinafter also referred to as the target position of the welding torch 13) is constant.

In area 8, the distance between the steel pipe 8 (straight section 8b) and the guide rail 2 (straight section 2b) is constant. Therefore, the movement amount of the welding robot 1 that satisfies the above welding conditions is uniformly determined.

On the other hand, in areas 5 to 7, the distance between the steel pipe 8 and the guide rail 2 varies depending on the circumferential position, so the movement amount of the welding robot 1 that satisfies the above welding conditions is not uniformly determined. Therefore, in this embodiment, as in the first embodiment, for welding in areas 5 to 7 (welding of the curved portion 8a), inverse kinematics is used to <A> calculate the target position and target posture of the welding torch 13 that satisfy the above welding conditions, and <B> determine the movement amount of the welding robot 1 to achieve this.
Specifically, a matrix U (corresponding to the above <A>) is generated that represents the target position and target posture of welding torch 13 that satisfies the above welding conditions. Also, a matrix T (corresponding to the above <B>) is generated that represents the position and posture of welding torch 13 when welding robot 1 moves a predetermined amount. By determining the amount of movement of welding robot 1 that makes matrix U equal to matrix T and controlling the drive of motor 32 according to this amount of movement, welding that satisfies the above welding conditions can be performed.

[Regarding matrix U]
The matrix U is a matrix for expressing the target position and target attitude of the welding torch 13 that satisfy the above welding conditions, with the origin position of the steel pipe coordinate system (center of curvature C1 of the steel pipe) as a reference.
In this embodiment, welding is performed on the curved portion 8a in all of the areas 5 to 7.
Therefore, a matrix U common to areas 5 to 7 is generated.

In areas 5 to 7, the tip of the welding torch 13 moves along the curved portion 8a. That is, the movement of the tip of the welding torch 13 that satisfies the above welding conditions in areas 5 to 7 is a rotational movement at a welding movement speed Vw around the steel pipe curvature center C1 on the YZ plane. In the YZ plane, the position of the tip of the welding torch 13 at time t, where the time when the tip of the welding torch 13 reaches position Pc5 is set to 0, is a position rotated by a rotation amount θc (radians) around the steel pipe curvature center C1 from position Pc5. However, the rotation amount θc is expressed by the following formula using the radius Rc of the curved portion 8a and the welding movement speed Vw.
θc=(Vw・t÷2πRc)×2π
Furthermore, at the welding position at time t, the welding torch orientation of welding torch 13 that satisfies the above welding conditions is a direction that coincides with the normal direction of curved portion 8a. At the welding position at time t, the target angle of welding torch 13 is always constant (θn). At the welding position at time t, the distance between the tip of welding torch 13 and curved portion 8a is always constant.
The matrix U is generated as a homogeneous transformation matrix representing the position and orientation of the welding torch 13 as described above.

[Regarding matrix T]
Matrix T is a matrix for expressing the position and posture of welding torch 13 relative to the origin position of the steel pipe coordinate system (center of curvature C1 of the steel pipe) when the movement amount of welding torch 13 in the up-down direction x of welding robot 1 is _Mx , the movement amount of welding torch 13 in the forward-backward direction z of welding robot 1 is Mz, the movement amount of welding torch 13 about the first axis is M _B , the movement amount of welding torch 13 about the second axis is M T, and the movement amount of welding robot 1 relative to position Pg5 is My.
In this embodiment, the welding robot 1 moves along the straight line portion 2b in areas 5 and 7, and moves along the curved line portion 2a in area 6. Therefore, the matrix T is generated for each of areas 5 to 7.

The generation of matrix T in area 5 will be described. Matrix T in area 5 is obtained by multiplying matrix T4, which represents the position of welding robot 1 obtained by moving it from position Pg5 by movement amount My, and matrix T3, which represents the position and attitude of the tip of welding torch 13 when welding robot 1 moves by movement amounts Mx, Mz, _MB , and _MT at the position of welding robot 1 after the movement according to matrix T4.
In area 5, the welding robot 1 moves in the Y direction (+Y direction) on the straight section 2b.
Therefore, the matrix T4 is generated by moving the position Pg5 by +My in the Y direction. The position Pg5 is a position moved by +Rg in the Z direction from the steel pipe curvature center C1.
Note that since matrix T3 is similar to matrix T3 in the first embodiment, description thereof will be omitted here.

The generation of matrix T in area 6 will be described. Matrix T in area 6 is obtained by multiplying a matrix T1 for translating the origin position of the steel pipe coordinate system (steel pipe curvature center C1) to the position of the rail curvature center C2, a matrix T5 for expressing a position obtained by rotating the welding robot 1 from position Pg6 around the rail curvature center C2 by a rotation amount θg (i.e., a position obtained by moving the welding robot 1 by a movement amount My from position Pg6), and a matrix T3 for expressing the position and posture of the tip of the welding torch 13 when the welding robot 1 moves by the movement amounts Mx, Mz, _MB , and _MT at the position of the welding robot 1 after the rotation by matrix T5.
In area 6, the welding robot 1 moves on the curved portion 2a. That is, the movement of the welding robot 1 in area 6 is a rotational movement about the rail curvature center C2 on the YZ plane.
In the YZ plane, if the amount of rotation of the welding robot 1 from the position Pg6 around the rail curvature center C2 is θg (radian), the amount of movement My can be expressed as the amount of rotation θg as shown in the following equation, where Rg is the radius of the curved portion 2a.
θg=(My÷2πRg)×2π
The matrix T2 is generated by rotating the position Pg6 by a rotation amount θg around the rail curvature center C2. The position Pg6 is a position moved by +Rg in the Z direction from the rail curvature center C2.
Note that matrices T1 and T3 are similar to matrices T1 and T3 in the first embodiment, and therefore description thereof will be omitted here.

The generation of matrix T in area 7 will be described. Matrix T in area 7 is obtained by multiplying matrix T6 representing the position of welding robot 1 moved by movement amount My from position Pg7, and matrix T3 representing the position and attitude of the tip of welding torch 13 when welding robot 1 moves by movement amounts Mx, Mz, _MB , and _MT at the position of welding robot 1 after the movement according to matrix T6.
In area 7, the welding robot 1 moves in the Z direction (-Z direction) on the straight portion 2b.
Therefore, matrix T6 is generated by moving position Pg7 by −My in the Z direction. Note that position Pg7 is a position moved by +Rg in the Y direction and +e in the Z direction from the steel pipe curvature center C1.
Note that since matrix T3 is similar to matrix T3 in the first embodiment, description thereof will be omitted here.

[Formula for calculating the movement distance of a welding robot]
For the matrices U and T generated as described above, a formula is derived for calculating the movement amounts Mx, My, Mz, MB, and _MT of the welding robot 1 that satisfy the above welding conditions by setting matrix U = matrix T. This formula is derived for each of the movement amounts Mx, My, Mz, _{MB ,} and _MT . This formula is derived for each of areas 5 to 7.

[Welding system control system]
The basic structure and operation of the control system of the welding system 100 in this embodiment are similar to those of the control system in the first embodiment.
On the other hand, in this embodiment, the matrix U is generated as a matrix common to the areas 5 to 7. The matrix T is generated for each of the areas 5 to 7.
Memory unit 64 stores in advance calculation formulas derived for each of areas 5 to 7 for determining the movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 when matrix U is equal to matrix T. Target torch position calculation unit 627 acquires the above calculation formulas via memory unit 64 and data acquisition unit 610. Movement amount setting unit 628 determines the movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 at a predetermined time t based on the above calculation formulas, and sets these as the movement amounts of welding robot 1.
The configuration and operation of the control system other than those described above are similar to those of the control system of the first embodiment, and therefore description thereof will be omitted.

[Example of control performed by the welding system]
An example of control executed by welding system 100 will be described with reference to FIG.
FIG. 16 is a flowchart showing an example of the flow of the welding process for the curved portion 8a executed by the system control device 6 in this embodiment.

Before welding the curved portion 8a, the curvature center determination unit 623 determines whether the position of the steel pipe curvature center C1 coincides with the position of the rail curvature center C2. If the position of the steel pipe curvature center C1 does not coincide with the position of the rail curvature center C2, the curvature center determination unit 623 determines which of the steel pipe curvature center C1 and the rail curvature center C2 is located closer to the center of the steel pipe 8.
Hereinafter, in this embodiment, the flow of the welding process of the curved section 8a will be described when the curvature center determination unit 623 determines that the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2.

The welding process of the curved section 8a is started when the welding robot 1 reaches position Pg5. At this time, the tip of the welding torch 13 is located at position Pc5 in area 5. For example, the start of the welding process of the curved section 8a is determined by estimating the position of the welding robot 1 based on the welding robot position information acquired by the position information acquisition unit 621, and determining whether the estimated position of the welding robot 1 has reached position Pg5.

When the welding process of the curved portion 8a is started, the welding time counting unit 625 starts counting the elapsed time t from the start of the welding process of the curved portion 8a (step S201).
The area determination unit 626 calculates the target position of the tip of the welding torch 13 at the elapsed time t (step S202). In this embodiment, since the movement of the tip of the welding torch 13 is a rotational movement around the steel pipe curvature center C1 in all of areas 5 to 7, the target torch position calculation unit 627 calculates the target position of the tip of the welding torch 13 calculated in step S202 as the amount of rotation θc of the tip of the welding torch 13 at the curved portion 8a of the steel pipe 8 (step S203).

The area determination unit 626 determines in which of areas 5 to 7 the calculated target position of the tip of the welding torch 13 is located (step S204).

When it is determined that the tip of welding torch 13 is located in area 5 (step S204: A5), movement amount setting unit 628 acquires a calculation formula for determining movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 corresponding to area 5. Based on the above calculation formula, movement amount setting unit 628 calculates movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 at elapsed time t and sets them as the movement amounts of welding robot 1 (step S211). After that, the process proceeds to step S205.

When it is determined that the tip of the welding torch 13 is located in the area 6 (step S204: A6), the movement amount setting unit 628 acquires a formula for calculating the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 corresponding to the area 6. In the area 6, the movement of the welding robot 1 is a rotational movement around the rail curvature center C2, so the movement amount setting unit 628 first calculates the rotation amount θg from the position Pg6 of the welding robot 1 on the curved portion 2a of the guide rail 2 at the elapsed time t based on the above formula (step S221). The movement amount setting unit 628 also calculates the movement amounts Mx, My, Mz, _MB , and _MT of the welding robot 1 at the elapsed time t based on the above formula, and sets them as the movement amounts of the welding robot 1 (step S222). Then, the process proceeds to step S205.

When it is determined that the tip of welding torch 13 is located in area 7 (step S204: A7), movement amount setting unit 628 acquires a calculation formula for determining movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 corresponding to area 7. Movement amount setting unit 628 calculates movement amounts Mx, My, Mz, _MB , and _MT of welding robot 1 at elapsed time t based on the above calculation formula, and sets them as the movement amounts of welding robot 1 (step S231). After that, the process proceeds to step S205.

The curved section welding execution control unit 629 drives each motor 32 to change the position of the welding robot 1 and the position and posture of the welding torch 13 according to the movement amounts Mx, My, Mz, _MB , and _MT set by the movement amount setting unit 628, and causes the welding robot 1 to weld the curved section 8a (step S205).

Thereafter, area determination unit 626 determines whether the position of the tip of welding torch 13 has reached end position Pc6 of area 7 (step S206).
When it is determined that the position of the tip of welding torch 13 has reached position Pc6 (step S206: YES), curved section welding execution control unit 629 ends the welding process of curved section 8a.
On the other hand, if the position of the tip of welding torch 13 has not reached position Pc6 (step S206: NO), the process returns to step S202. In this case, the welding process of curved portion 8a is continued.

The specific control content of the welding robot 1 in each area when the above control is performed is described below. Note that the control content of the welding robot 1 shown below is an example, and the present invention is not limited to this.

First, the control contents in area 8 (i.e., the area other than the welding of the curved portion 8a) will be described. In area 8, as shown in FIG. 17, the welding robot 1 moves at a constant speed (welding movement speed Vw). Hereinafter, the movement speed of the welding robot 1 in area 8 is also referred to as the reference speed. In addition, the movement amount Mx of the welding torch 13 in the up-down direction x is constant (hereinafter, also referred to as the up-down movement reference value). The movement amount Mz of the welding torch 13 in the front-back direction z is constant (hereinafter, also referred to as the front-back movement reference value). As shown in FIG. 18, in area 8 , the speed of the robot in the front-back direction z is 0 (zero). As shown in FIG. 19, the movement amount M _B of the welding torch 13 around the first axis is constant (hereinafter, also referred to as the first axis rotation reference value), and the welding torch 13 is rotated vertically downward around the first axis. As shown in FIG. 19, the movement amount M _T of the welding torch 13 around the second axis is constant and is 0 (zero). That is, when viewed along the up-down direction x, the welding torch 13 is always perpendicular to the left-right direction y (i.e., the straight portion 8b of the steel pipe 8), which is the moving direction of the welding robot 1.

The control content in area 5 will be described below. The control of the control unit 61 in area 5 is as follows.
The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between a start position Pc5 of the curved portion 8a of the steel pipe 8 and a steel pipe intermediate position that is an intermediate position between the start position Pc5 and an end position Pc6 of the curved portion 8a of the steel pipe 8 and the welding robot 1 moves along the straight portion 2b of the guide rail 2, the welding torch 13 moves at a second torch approach speed in a direction approaching the steel pipe 8. At this time, the second torch approach speed increases as the welding robot 1 approaches the start position Pg6 of the curved portion 2a of the guide rail 2.

The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the start position Pc5 and the steel pipe intermediate position, which is the intermediate position between the start position Pc5 and the end position Pc6, and the welding robot 1 moves along the straight section 2b of the guide rail 2, the welding torch 13 moves in a direction approaching the steel pipe 8 at a first torch approach acceleration.
For example, when the welding robot 1 moves in the vicinity of the start position Pg6, the control unit 61 controls the target position changing unit so that the welding torch 13 moves in a direction approaching the steel pipe 8 at the first torch approach deceleration. In this embodiment, the vicinity of the start position Pg6 refers to a region having a length of 20% of the radius of curvature of the curved portion 8a of the steel pipe 8 along the circumferential direction of the steel pipe 8 with the start position Pg6 as the center. That is, for example, when the radius of curvature of the curved portion 8a of the steel pipe 8 is 40 mm, the length of the region related to the vicinity of the start position Pg6 is 8 mm. Both ends of the region related to the vicinity of the start position Pg6 are located in portions that are moved 4 mm on both sides from the start position Pg6 along the circumferential direction of the steel pipe 8.
At this time, the absolute value of the first torch approach deceleration is greater than the absolute value of the first torch approach acceleration.

17, in area 5, the movement speed of welding robot 1 becomes higher than the reference speed. That is, welding robot 1 instantaneously accelerates to the movement speed in area 5. "Instantaneous" refers to the timing at which welding robot 1 reaches area 5 from area 8. After that, welding robot 1 continues to decelerate at a predetermined negative acceleration from start position Pg5 to end position Pg6 of area 5. Note that even in this case, the movement speed of welding robot 1 is higher than the reference speed.
The amount of movement Mx is equal to the vertical movement reference value.
18, in area 5, the speed of the welding robot 1 in the forward/backward direction z decreases. That is, the movement amount Mz decreases from the forward/backward movement reference value as the welding robot 1 moves from position Pg5 to position Pg6. That is, the welding torch 13 moves in a direction approaching the steel pipe 8 as the welding robot 1 moves from position Pg5 to position Pg6.
19, the movement amount _MB increases from the first axis rotation reference value as the welding robot 1 moves from position Pg5 to position Pg6. In other words, as the welding robot 1 moves from position Pg5 to position Pg6, the downward tilt of the welding torch 13 in the vertical direction increases.
19, the amount of movement _MT decreases from 0 as the welding robot 1 moves from position Pg5 to position Pg6. That is, when viewed along the up-down direction x, the welding torch 13 tilts in the direction opposite to the moving direction of the welding robot 1 as the welding robot 1 moves from position Pg5 to position Pg6.

The control content in area 6 will be described below. The control of the control unit 61 in area 6 is as follows.
The control unit 61 controls the speed change unit so that the welding robot 1 moves at a first robot speed when the tip of the welding torch 13 moves between, for example, the start position Pc5 and the steel pipe intermediate position which is the intermediate position between the start position Pc5 and the end position Pc6. At this time, the first robot speed increases as the tip of the welding torch 13 approaches the steel pipe intermediate position.

The control unit 61 controls the speed change unit so that, for example, when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position which is the intermediate position between the start position Pc5 and the end position Pc6, and when the welding robot 1 moves along the curved portion 2a of the guide rail 2, the welding robot 1 moves at a first robot acceleration.
The control unit 61 controls the speed change unit so that the welding robot 1 moves at a first robot deceleration when the welding robot 1 approximately reaches the start position Pg6 of the curved portion 2a of the guide rail 2. Here, in this embodiment, the welding robot 1 approximately reaching the start position Pg6 means that the welding robot 1 reaches the vicinity of the start position Pg6.
At this time, the absolute value of the first robot deceleration is greater than the absolute value of the first robot acceleration.

The control unit 61 controls the target position changing unit so that when the welding robot 1 moves between, for example, the start position Pg6 and the guide rail intermediate position, which is the intermediate position between the start position Pg6 and the end position Pg7 of the curved portion 2a of the guide rail 2, the welding torch 13 moves in a direction approaching the steel pipe 8 at a first torch approach speed. At this time, the first torch approach speed increases as the welding robot 1 approaches the guide rail intermediate position.

The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc6 of the curved portion 8a of the steel pipe 8 and the welding robot 1 moves along the curved portion 2a of the guide rail 2, the welding torch 13 moves in a direction away from the steel pipe 8 at a first torch separation speed. At this time, the first torch separation speed increases as it approaches the end position Pc6.

The control unit 61 controls the speed change unit so that the welding robot 1 moves at the second robot speed, for example, when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc6 and the welding robot 1 moves along the curved portion 2a of the guide rail 2. At this time, the second robot speed decreases as the tip of the welding torch 13 approaches the end position Pc6.

The control unit 61 controls the speed change unit so that, for example, when the tip of the welding torch 13 moves between the intermediate position of the steel pipe and the end position Pc6 and the welding robot 1 moves along the curved portion 2a of the guide rail 2, the welding robot 1 moves at a second robot deceleration.
The control unit 61 controls the speed change unit so that the welding robot 1 moves at the second acceleration when the tip of the welding torch 13 approximately reaches the end position Pc6. Here, in this embodiment, the tip of the welding torch 13 approximately reaches the end position Pc6, which means that the tip of the welding torch 13 reaches the vicinity of the end position Pc6. The vicinity of the end position Pc6 refers to a region having a length of 20% of the radius of curvature of the curved portion 8a of the steel pipe 8 along the circumferential direction of the steel pipe 8, with the end position Pc6 as the center. That is, for example, when the radius of curvature of the curved portion 8a of the steel pipe 8 is 40 mm, the length of the region related to the vicinity of the end position Pc6 is 8 mm. Both ends of the region related to the vicinity of the end position Pc6 are located in portions that are moved 4 mm on both sides from the end position Pc6 along the circumferential direction of the steel pipe 8.
At this time, the absolute value of the second robot acceleration is greater than the absolute value of the second robot deceleration.

The control unit 61 controls the torch orientation changing unit so that, for example, when the tip of the welding torch 13 moves between the starting position Pc5 and the middle position of the steel pipe, the inclination of the welding torch 13 in the direction opposite to the specified direction becomes smaller as the tip of the welding torch 13 moves.
The control unit 61 controls the torch orientation changing unit so that, for example, when the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc6, the inclination of the welding torch 13 in a specified direction increases as the tip moves.

The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves near the end position Pc6 and the welding robot 1 moves along the curved portion 2a of the guide rail 2, the welding torch 13 moves in a direction away from the steel pipe 8 at the first torch separation acceleration.
The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the end position Pc6 and the straight section 8b of the steel pipe 8 and the welding robot 1 moves along the straight section 2b of the guide rail 2, the welding torch 13 moves in a direction away from the steel pipe 8 at the first torch separation deceleration.
At this time, the absolute value of the first torch separation deceleration is greater than the absolute value of the first torch separation acceleration.
In area 6, as shown in FIG. 17, the moving speed of the welding robot 1 is higher than the reference speed, but lower than the moving speed in area 5. That is, the welding robot 1 instantaneously decelerates to the moving speed in area 6. "Instantaneous" refers to the timing when the welding robot 1 reaches area 6 from area 5. Also, in the range from position Pg6 to the intermediate position between positions Pg6 and Pg7, the welding robot 1 continues to accelerate at a predetermined positive acceleration from the start position Pg6 of area 6 to the intermediate position. After that, in the range from the intermediate position between positions Pg6 and Pg7 to position Pg7, the welding robot 1 continues to decelerate at a predetermined negative acceleration from the intermediate position to the end position Pg7 of area 6. Note that even in this case, the moving speed of the welding robot 1 is higher than the reference speed and lower than the moving speed in area 5.
The amount of movement Mx is equal to the vertical movement reference value.
18, in area 6, the movement speed of the welding robot 1 in the front-rear direction z is negative from position Pg6 to the intermediate position between positions Pg6 and Pg7. That is, the movement amount Mz decreases as the welding robot 1 moves from position Pg6 to the intermediate position between positions Pg6 and Pg7. As shown in FIG 18, the movement speed of the welding robot 1 in the front-rear direction z is positive from the intermediate position between positions Pg6 and Pg7 to position Pg7. That is, the movement amount Mz increases as the welding robot 1 moves from the intermediate position between positions Pg6 and Pg7 to position Pg7.
In other words, the welding torch 13 moves in a direction approaching the steel pipe 8 when the welding robot 1 is in the range from position Pg6 to the intermediate position between positions Pg6 and Pg7, and moves in a direction away from the steel pipe 8 when the welding robot 1 is in the range from the intermediate position between positions Pg6 and Pg7 to position Pg7.
19, the amount of movement _MB decreases as the welding robot 1 moves from position Pg6 to the intermediate position between positions Pg6 and Pg7, and increases as the welding robot 1 moves from the intermediate position between positions Pg6 and Pg7 to position Pg7. Even in this case, the amount of movement _MB does not become smaller than the first axis rotation reference value. That is, as the welding robot 1 moves from position Pg6 to the intermediate position between positions Pg6 and Pg7, the downward vertical inclination of the welding torch 13 decreases, and as the welding robot 1 moves from the intermediate position between positions Pg6 and Pg7 to position Pg7, the downward vertical inclination of the welding torch 13 increases.
As shown in FIG. 19, the movement amount M 1 _T increases as the welding robot 1 moves from position Pg6 to position Pg7. The movement amount M _{1 T} is 0 when the welding robot 1 is located at the intermediate position between positions Pg6 and Pg7. The value of the movement amount M _{1 T} is positive when the welding robot 1 is located between the intermediate position between positions Pg6 and Pg7 and position Pg7. That is, when viewed along the vertical direction x, when the welding robot 1 is located at position Pg6, which is the end position of area 5, the welding torch 13 is inclined to the opposite side to the traveling direction of the welding robot 1. As the welding robot 1 moves from position Pg6 to the intermediate position between positions Pg6 and Pg7, the inclination of the welding torch 13 to the opposite side to the traveling direction of the welding robot 1 becomes smaller, and when the welding robot 1 reaches the intermediate position between positions Pg6 and Pg7, the welding torch 13 is perpendicular to the traveling direction of the welding robot 1. Thereafter, as welding robot 1 moves from the intermediate position between positions Pg6 and Pg7 to position Pg7, welding torch 13 tilts toward the moving direction of welding robot 1.

The control content in the area 7 will be described below. The control of the control unit 61 in the area 7 is as follows.
The control unit 61 controls the target position changing unit so that, for example, when the tip of the welding torch 13 moves between the end position Pc6 and a steel pipe intermediate position that is an intermediate position between the start position Pc5 and the end position Pc6 of the curved portion 8a of the steel pipe 8, and the welding robot 1 moves along the straight portion 2b of the guide rail 2, the welding torch 13 moves in a direction away from the steel pipe 8 at a first torch separating speed. At this time, the first torch separating speed becomes smaller as the tip of the welding torch 13 approaches the end position Pc6.
17, in area 7, the movement speed of welding robot 1 is greater than the reference speed and greater than the movement speed in area 6. That is, welding robot 1 instantaneously accelerates to the movement speed in area 7. "Instantaneous" refers to the timing at which welding robot 1 reaches area 7 from area 6. After that, welding robot 1 continues to accelerate at a predetermined positive acceleration from start position Pg7 to end position Pg8 of area 7. Note that even in this case, the movement speed of welding robot 1 is greater than the reference speed and the movement speed in area 6.
The amount of movement Mx is equal to the vertical movement reference value.
18, the movement speed of the welding robot 1 in the forward/backward direction z from position Pg7 to position Pg8 in area 7 decreases from a positive value toward 0 (zero). That is, the movement amount Mz decreases as the welding robot 1 moves from position Pg7 to position Pg8. As shown in FIG. 18, when the welding robot 1 reaches position Pg8 in area 7, the movement speed of the welding robot 1 in the forward/backward direction z becomes 0 (zero). That is, when the welding robot 1 reaches position Pg8, the movement amount Mz becomes equal to the forward/backward movement reference value. That is, the welding torch 13 moves in a direction away from the steel pipe 8 as the welding robot 1 moves from position Pg7 to position Pg8.
19, the movement amount _MB decreases as the welding robot 1 moves from position Pg7 to position Pg8, and becomes equal to the first axis rotation reference value when the welding robot 1 reaches position Pg8. In other words, as the welding robot 1 moves from position Pg7 to position Pg8, the downward vertical inclination of the welding torch 13 becomes smaller.
19, the amount of movement _MT decreases as the welding robot 1 moves from position Pg7 to position Pg8, and becomes 0 when the welding robot 1 reaches position Pg8. That is, when viewed along the up-down direction x, when the welding robot 1 is located at position Pg7, which is the end position of area 6, the welding torch 13 is inclined toward the traveling direction of the welding robot 1. As the welding robot 1 moves from position Pg7 to position Pg8, the inclination of the welding torch 13 toward the traveling direction of the welding robot 1 becomes smaller, and when the welding robot 1 reaches position Pg8, the welding torch 13 is perpendicular to the traveling direction of the welding robot 1.

As described above, according to the welding system 100 of the second embodiment, the control unit 61 controls the target position changing unit so that the welding torch 13 moves in a direction approaching the steel pipe 8 at the first torch approach speed when the welding robot 1 moves between the start position Pg6 of the curved portion 2a of the guide rail 2 and the middle position of the guide rail. This makes it possible to prevent the tip of the welding torch 13 from moving away from the steel pipe 8 when the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2.

Here, when the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2, the distance between the guide rail 2 and the steel pipe 8 is closest between the straight portion 2b of the guide rail 2 and the straight portion 8b of the steel pipe 8, and is farthest between the guide rail intermediate position, which is the intermediate position of the curved portion 2a of the guide rail 2, and the steel pipe intermediate position. In contrast, the first torch approach speed increases as the welding robot 1 approaches the guide rail intermediate position. This makes it possible to smoothly adjust the distance between the tip of the welding torch 13 and the steel pipe 8. Therefore, it is easier to ensure the quality of the welding of the steel pipe 8 by the welding torch 13. Therefore, a constant welding quality can be maintained over the entire length of the welded portion of the steel pipe 8.

The control unit 61 also controls the target position changing unit so that when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe middle position and the welding robot 1 moves along the straight portion 2b of the guide rail 2, the welding torch 13 moves in a direction approaching the steel pipe 8 at the second torch approach speed. This makes it possible to prevent the tip of the welding torch 13 from moving away from the steel pipe 8.

Here, when the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2, when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position and the welding robot 1 moves along the straight portion 2b of the guide rail 2, the speed at which the tip of the welding torch 13 leaves the steel pipe 8 increases at an accelerated rate as the welding robot 1 moves along the straight portion 2b. In contrast, the second torch approach speed increases as the welding robot 1 approaches the start position Pg6 of the curved portion 2a of the guide rail 2. This allows the distance between the tip of the welding torch 13 and the steel pipe 8 to be smoothly adjusted as the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position.

In addition, the control unit 61 controls the target position change unit so that when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position, which is the intermediate position between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the end position Pc6 of the curved portion 8a of the steel pipe 8, and the welding robot 1 moves along the straight portion 2b of the guide rail 2, the welding torch 13 moves at a first torch approach acceleration in a direction approaching the steel pipe 8. This makes it possible to increase the speed at which the welding torch 13 approaches the steel pipe 8 as the welding robot 1 approaches the start position Pg6 of the curved portion 2a of the guide rail 2. This makes it possible to smoothly adjust the distance between the tip of the welding torch 13 and the steel pipe 8.

Here, when the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2, the speed at which the tip of the welding torch 13 leaves the steel pipe 8 when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position and the welding robot 1 moves along the curved portion 2a of the guide rail 2 is smaller than the speed at which the tip of the welding torch 13 leaves the steel pipe 8 when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position and the welding robot 1 moves along the straight portion 2b of the guide rail 2. In response to this, the control unit 61 controls the target position change unit so that the welding torch 13 moves in the direction approaching the steel pipe 8 at the first torch approach deceleration when the welding robot 1 moves near the start position Pc5 of the curved portion 2a of the guide rail 2, and the absolute value of the first torch approach deceleration is greater than the absolute value of the first torch approach acceleration. This allows the tip of the welding torch 13 to move between the start position Pc5 of the curved section 8a of the steel pipe 8 and the middle position of the steel pipe, and allows the speed at which the tip of the welding torch 13 leaves the steel pipe 8 when the welding robot 1 moves along the curved section 2a of the guide rail 2.

Here, the length of the curved portion 2a of the guide rail 2 is longer than the length of the curved portion 8a of the steel pipe 8. Therefore, in order to make the speed at which the welding torch 13 advances on the curved portion 8a of the steel pipe 8 the same as the speed at which it advances on the straight portion 8b of the steel pipe 8, the speed at which the welding robot 1 advances on the curved portion 2a of the guide rail 2 must be faster than the speed at which the welding robot 1 advances on the straight portion 2b of the guide rail 2. In response to this, the control unit 61 controls the speed change unit so that the welding robot 1 moves at the first robot speed when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the steel pipe intermediate position. This makes it possible to control the speed at which the welding torch 13 advances on the curved portion 8a of the steel pipe 8 to be the same as the speed at which it advances on the straight portion 8b of the steel pipe 8.

When welding the curved portion 8a of the steel pipe 8, the orientation of the welding torch 13 may be changed so that the orientation of the welding torch 13 coincides with the normal direction of the curved portion 8a of the steel pipe 8. In contrast, the first robot speed increases as the tip of the welding torch 13 approaches the middle position of the steel pipe. This makes it possible to keep the speed of the tip of the welding torch 13 constant even when the orientation of the welding torch 13 is changed when welding the curved portion 8a of the steel pipe 8 when the steel pipe curvature center C1 is located closer to the center of the steel pipe 8 than the rail curvature center C2. This makes it easier to ensure the quality of the welding of the steel pipe 8.

In addition, the control unit 61 controls the speed change unit so that the welding robot 1 moves at the first robot acceleration when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the intermediate position of the steel pipe and the welding robot 1 moves along the curved portion 2a of the guide rail 2. As a result, when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the intermediate position of the steel pipe and the welding robot 1 moves along the curved portion 2a of the guide rail 2, the speed at which the welding robot 1 advances along the guide rail 2 can be increased as the tip of the welding torch 13 approaches the intermediate position of the steel pipe. This makes it possible to keep the speed of the tip of the welding torch 13 constant. This makes it easier to ensure the quality of the welding of the steel pipe 8.

Here, the moving speed of the welding robot 1 when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the intermediate position of the steel pipe and the welding robot 1 moves along the curved portion 2a of the guide rail 2 is slower than the moving speed of the welding robot 1 when the tip of the welding torch 13 moves between the start position Pc5 of the curved portion 8a of the steel pipe 8 and the intermediate position of the steel pipe and the welding robot 1 moves along the straight portion 2b of the guide rail 2. For this reason, it is necessary to decelerate the welding robot 1 immediately after the welding robot 1 reaches the start position Pg6 of the curved portion 2a of the guide rail 2. In response to this, the control unit 61 controls the speed change unit so that the welding robot 1 moves at the first robot deceleration when the welding robot 1 approximately reaches the start position Pg6 of the curved portion 2a of the guide rail 2, and the absolute value of the first robot deceleration is greater than the absolute value of the first robot acceleration. This allows the tip of the welding torch 13 to move between the start position Pc5 of the curved section 8a of the steel pipe 8 and the middle position of the steel pipe, and allows the welding robot 1 to move at an appropriate speed when moving along the curved section 2a of the guide rail 2.

The control unit 61 also controls the torch orientation change unit so that the inclination of the welding torch 13 in the direction opposite to the specified direction decreases as the tip of the welding torch 13 moves between the start position Pc5 and the steel pipe intermediate position. The control unit 61 also controls the torch orientation change unit so that the inclination of the welding torch 13 in the specified direction increases as the tip of the welding torch 13 moves between the steel pipe intermediate position and the end position Pc6 of the curved portion 8a of the steel pipe 8. This makes it possible to change the orientation of the welding torch 13 so that the orientation of the welding torch 13 coincides with the normal direction of the curved portion 8a of the steel pipe 8 when welding the curved portion 8a of the steel pipe 8.

[When the center of curvature C1 of the steel pipe and the center of curvature C2 of the rail coincide]
Hereinafter, a control method in the welding system 100 when the steel pipe curvature center C1 and the rail curvature center C2 coincide with each other will be described.
In this case, the circumferential distance between the steel pipe 8 (curved portion 8a) and the guide rail 2 (curved portion 2a) is constant. Therefore, by setting the welding torch direction, target angle, and target position of the welding torch 13 to satisfy the above welding conditions <2> to <4>, and then setting the movement speed of the welding robot 1 so that the tip of the welding torch 13 moves at the welding movement speed Vw, welding that satisfies the above welding conditions can be performed. Note that the movement speed of the welding robot 1 in this case is constant.

The present invention is not limited to the above-described embodiment described with reference to the drawings, and various modifications are possible within the technical scope.

For example, in the above embodiment, welding conditions <1> to <4> are described as the welding conditions. However, the movement amount of the welding robot 1 may be controlled so as to satisfy at least one of the welding conditions <1> to <4>.

In the above embodiment, the movement amount Mx of welding torch 13 in the up-down direction x of welding robot 1, the movement amount My of welding robot 1 in the left-right direction y of welding robot 1, the movement amount Mz of welding torch 13 in the front-rear direction z of welding robot 1, the movement amount M _B of welding torch 13 about the first axis, and the movement amount M _T of welding torch 13 about the second axis have been described as objects to be controlled by welding system 100. However, the object to be controlled by welding system 100 may be at least one of the above movement amounts.

In the above embodiment, the steel pipes 8 are arranged vertically, but the steel pipes 8 may also be arranged horizontally.

In addition, all or part of the functions of the welding system 100 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

In addition, the components in the above embodiment may be replaced with well-known components as appropriate without departing from the spirit of the present invention, and the above-mentioned modifications may be combined as appropriate.

100 Welding system 1 Welding robot 2 Guide rail (rail)
2a Curved section 6 System control device 8 Steel pipe 8a Curved section 13 Welding torch 33 Front-rear moving section (target position changing section)
34 Up/down movement unit (target position change unit)
35 First rotating part (torch direction changing part)
36 Second rotating portion (torch direction changing portion)
620 Welding robot control unit 621 Position information acquisition unit 622 Shape information acquisition unit (acquisition unit)
623 Center of curvature determination unit (determination unit)
624 Parameter setting unit (setting unit)
625 Welding time count unit 626 Area determination unit 627 Target torch position calculation unit (setting unit)
628 Movement amount setting unit (setting unit)

Claims (12)

A welding system for controlling a welding robot that moves in a predetermined direction on a rail arranged along a steel pipe, the rail having a straight portion and a curved portion, and welds the straight portion and the curved portion of the steel pipe,
A welding torch provided in the welding robot;
A target position changing unit that changes the target position of the welding torch;
a control unit that controls the target position changing unit in accordance with the center of curvature and radius of curvature of the curved portion of the steel pipe, the center of curvature and radius of curvature of the curved portion of the rail, and the welding speed and position of the welding robot, when the center of curvature of the rail, which is the center of curvature of the curved portion of the rail, is located closer to the center of the steel pipe than the center of curvature of the steel pipe, which is the center of curvature of the curved portion of the steel pipe;
Equipped with
The control unit controls the target position changing unit so that the welding torch moves in a direction away from the steel pipe at a first torch separation speed when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and a steel pipe intermediate position that is an intermediate position between the start position and an end position of the curved portion of the steel pipe,
The first torch separation speed becomes smaller as the tip of the welding torch approaches the intermediate position of the steel pipe.
A welding system comprising: The control unit controls the target position changing unit so that the welding torch moves in a direction away from the steel pipe at a second torch separation speed when the tip of the welding torch moves between the straight portion of the steel pipe and the start position,
the second torch separation speed increases as the tip of the welding torch approaches the start position;
The welding system of claim 1 . The control unit controls the target position changing unit so that the welding torch moves in a direction away from the steel pipe at a first torch separation acceleration when the tip of the welding torch moves between the straight portion of the steel pipe and the start position,
The control unit controls the target position changing unit so that, when the welding torch moves near the start position, the welding torch moves in a direction away from the steel pipe at a second torch separation acceleration,
The second torch separation acceleration is greater than the first torch separation acceleration.
The welding system of claim 2 . a speed change unit that changes the moving speed of the welding robot;
Further comprising:
the control unit controls the speed change unit in accordance with the center of curvature and radius of curvature of the curved portion of the steel pipe, the center of curvature and radius of curvature of the curved portion of the rail, and the welding speed and position of the welding robot when a rail center of curvature, which is the center of curvature of the curved portion of the rail, is located closer to the center of the steel pipe than a steel pipe center of curvature, which is the center of curvature of the curved portion of the steel pipe;
The control unit controls the speed change unit so that the welding robot moves at a first robot speed when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and an intermediate position of the steel pipe,
the first robot speed decreases as the tip of the welding torch approaches the intermediate position of the steel pipe;
The welding system of claim 3 . the control unit controls the speed change unit so that the welding robot moves at a first robot deceleration when the tip of the welding torch moves between the start position and the steel pipe intermediate position;
the control unit controls the speed change unit so that the welding robot moves at a first robot acceleration when the tip of the welding torch substantially reaches the start position;
The absolute value of the first robot acceleration is greater than the absolute value of the first robot deceleration.
The welding system of claim 4. The welding system further includes a torch direction changing unit that changes the direction of the welding torch,
The control unit controls the torch orientation change unit when a rail curvature center, which is the curvature center of the curved portion of the rail, is located closer to the center of the steel pipe than a steel pipe curvature center, which is the curvature center of the curved portion of the steel pipe,
the control unit controls the torch direction changing unit so that, when the tip of the welding torch moves between the start position and the steel pipe intermediate position, the inclination of the welding torch in the predetermined direction becomes smaller as the tip of the welding torch moves,
The control unit controls the torch direction changing unit so that, when the tip of the welding torch moves between the intermediate position of the steel pipe and the end position of the curved portion of the steel pipe, the inclination of the welding torch in the direction opposite to the predetermined direction increases as the tip of the welding torch moves.
The welding system of claim 5 . A welding system for controlling a welding robot that moves in a predetermined direction on a rail arranged along a steel pipe, the rail having a straight portion and a curved portion, and welds the straight portion and the curved portion of the steel pipe,
A welding torch provided in the welding robot;
A target position changing unit that changes the target position of the welding torch;
a control unit that controls the target position changing unit in accordance with the center of curvature and radius of curvature of the curved portion of the steel pipe, the center of curvature and radius of curvature of the curved portion of the rail, and the welding speed and position of the welding robot, when the center of curvature of the steel pipe, which is the center of curvature of the curved portion of the steel pipe, is located closer to the center of the steel pipe than the center of curvature of the rail, which is the center of curvature of the curved portion of the rail;
Equipped with
the control unit controls the target position changing unit so that the welding torch moves in a direction approaching the steel pipe at a first torch approach speed when the welding robot moves between a start position of the curved portion of the rail and a rail intermediate position that is an intermediate position between the start position of the curved portion of the rail and an end position of the curved portion of the rail;
the first torch approach speed increases as the welding robot approaches the rail middle position;
A welding system comprising: The control unit controls the target position changing unit so that the welding torch moves in a direction approaching the steel pipe at a second torch approach speed when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and a steel pipe intermediate position that is an intermediate position between the start position of the curved portion of the steel pipe and the end position of the curved portion of the steel pipe and when the welding robot moves along the straight portion of the rail,
the second torch approach speed increases as the welding robot approaches a start position of the curved portion of the rail;
The welding system of claim 7 . The control unit controls the target position changing unit so that the welding torch moves in a direction approaching the steel pipe at a first torch approach acceleration when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and a steel pipe intermediate position that is an intermediate position between the start position of the curved portion of the steel pipe and the end position of the curved portion of the steel pipe and when the welding robot moves along the straight portion of the rail,
the control unit controls the target position changing unit so that, when the welding robot moves near a start position of the curved portion of the rail, the welding torch moves in a direction approaching the steel pipe at a first torch approach deceleration;
The absolute value of the first torch approach deceleration is greater than the absolute value of the first torch approach acceleration.
The welding system of claim 8 . a speed change unit that changes the moving speed of the welding robot;
Further comprising:
the control unit controls the speed change unit in accordance with the center of curvature and radius of curvature of the curved portion of the steel pipe, the center of curvature and radius of curvature of the curved portion of the rail, and the welding speed and position of the welding robot, when a steel pipe center of curvature, which is the center of curvature of the curved portion of the steel pipe, is located closer to the center of the steel pipe than a rail center of curvature, which is the center of curvature of the curved portion of the rail;
The control unit controls the speed change unit so that the welding robot moves at a first robot speed when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and an intermediate position of the steel pipe,
the first robot speed increases as the tip of the welding torch approaches the intermediate position of the steel pipe;
Characterized in that
The welding system of claim 9. the control unit controls the speed change unit so that the welding robot moves at a first robot acceleration when the tip of the welding torch moves between a start position of the curved portion of the steel pipe and an intermediate position of the steel pipe and when the welding robot moves along the curved portion of the rail;
the control unit controls the speed change unit so that the welding robot moves at a first robot deceleration when the welding robot substantially reaches a start position of the curved portion of the rail;
The absolute value of the first robot deceleration is greater than the absolute value of the first robot acceleration.
The welding system of claim 10. The welding system further includes a torch direction changing unit that changes the direction of the welding torch,
The control unit controls the torch orientation changing unit when a steel pipe curvature center, which is the curvature center of the curved portion of the steel pipe, is located closer to the center of the steel pipe than a rail curvature center, which is the curvature center of the curved portion of the rail;
The control unit controls the torch direction changing unit so that, when the tip of the welding torch moves between the start position and the steel pipe intermediate position, the inclination of the welding torch in the direction opposite to the predetermined direction becomes smaller as the tip of the welding torch moves,
The control unit controls the torch direction changing unit so that, when the tip of the welding torch moves between the intermediate position of the steel pipe and the end position of the curved portion of the steel pipe, the inclination of the welding torch in the predetermined direction increases as the tip of the welding torch moves.
The welding system of claim 11 .

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