JP7523988B2 - Welding method - Google Patents

Description

The present invention relates to a welding method.

Patent Document 1 describes a welding method using an automatic welding robot. In this welding method, multi-layer welding is performed on the area to be welded by performing multiple layers including an initial layer, an intermediate layer, and a finishing layer. The automatic welding robot repeatedly performs welding passes on each of the initial layer, intermediate layer, and finishing layer to weld the entire area to be welded.

JP 2019-155409 A

In an automatic welding robot such as that described in Patent Document 1, a sensor may be provided to acquire information about the welding area so that the welding robot can perform welding while checking the condition of the welding area. In this case, it is conceivable to plan a welding pass from the groove information acquired by the sensor and perform the welding pass according to the plan. However, in multi-layer welding, multiple welding passes are performed, so a deviation between the planned position and the welding pass position is likely to occur. Therefore, there is a demand for improving the positional accuracy of the welding relative to the area to be welded.

The present invention aims to provide a welding method that can improve the positional accuracy of welding relative to the area to be welded in multi-layer welding.

The welding method according to the present invention is a method for performing multi-layer welding on a welding target area set on a welding target using a welding robot having a welding end effector and a sensor, and includes a first sensing step of obtaining groove information of the welding target area by the sensor by sensing the welding target area before welding is performed, a path planning step of planning multiple welding passes for the welding target area based on the results obtained in the first sensing step, and a first welding step of welding the welding target area by repeatedly performing welding passes on the welding target area with the end effector after the path planning step, the first welding step including a second sensing step of obtaining groove information by the sensor while performing welding passes with the end effector, and a path position adjustment step of adjusting the position of the end effector so as to obtain the welding pass planned in the path planning step based on the information obtained in the second sensing step.

In the welding method according to the present invention, multiple welding passes are planned based on groove information of the area to be welded before welding is performed, and then welding passes are repeatedly performed in the first welding process. Here, in the first welding process, groove information is acquired by a sensor while performing a welding pass, and the position of the end effector is adjusted based on the groove information so that the welding pass planned in the pass planning process is performed. In this way, welding passes are performed while correcting errors with respect to the welding pass planned in the pass planning process. Therefore, the positional accuracy of the weld relative to the area to be welded can be improved in multi-layer welding.

In addition, in the welding method according to the present invention, in the pass position adjustment step, the position of the boundary between the region to be welded and the region not to be welded in the workpiece may be acquired as groove information, and the position of the end effector may be adjusted by setting the relative position of the welding pass with respect to the position of the boundary as the welding pass target position of the end effector. In this case, the relative position of the welding pass with respect to the position of the boundary that is very close to the region not to be welded is set as the welding pass target position of the end effector, so that even when part of the groove has been welded in multi-layer welding, the deviation of the position of the welding pass with respect to the region to be welded is reduced. Therefore, the positional accuracy of the welding with respect to the region to be welded can be particularly improved.

The welding method according to the present invention further includes a calculation step of calculating the position of a virtual point indicating a point where the groove and the surface of the weld bead formed in the groove contact each other on the cross section of the groove based on the groove information after at least one welding pass has been performed, and in the calculation step, an approximation line of a portion of the contour of the surface of the weld bead on the cross section of the groove that is not in contact with the groove may be calculated, and the position of the intersection between the groove and the approximation line may be calculated as the position of the virtual point. For example, when calculating the position of the virtual point where the groove and the surface of the weld bead contact each other, it is possible to use an approximation line calculated from the contour of the entire surface of the weld bead on the cross section of the groove. However, there are cases where a portion where a welding pass has not yet been performed (such as the joint surface of the welded object) is erroneously recognized as the surface of the weld bead, and in such cases, an appropriate approximation line cannot be obtained. In contrast, an approximation line of a portion of the contour of the surface of the weld bead that is not in contact with the groove is used, so that an approximation line for calculating the virtual point where the groove and the surface of the weld bead contact each other can be more appropriately obtained.

The welding method according to the present invention further includes a third sensing step of acquiring information on the groove after multiple welding passes have been performed, a pass replanning step of replanning multiple welding passes for the welding target area based on the information acquired in the third sensing step, and a second welding step of welding the welding target area by repeatedly performing the multiple welding passes replanned in the pass replanning step. In the pass replanning step, the multiple welding passes for the welding target area may be replanned using the results calculated in the calculation step. For example, the initially planned welding pass may not be suitable for the welding target area remaining after multiple welding passes have been performed. In response to this, the groove information is acquired again and the welding pass is replanned, so that in the second welding step, a welding pass according to the progress of welding can be performed. In addition, in the pass replanning step, the results obtained in the calculation step are used, so that a welding pass more suitable for the progress of welding is planned. Therefore, the positional accuracy of welding for the welding target area in multi-layer welding can be further improved.

In addition, in the welding method according to the present invention, before the sensor acquires information about the groove after at least one welding pass has been performed, the sensor may be positioned away from the groove depending on the number of welding passes that have been performed. In this case, the sensor can acquire information about the groove at a position suitable for sensing depending on the number of welding passes that have been performed.

In addition, in the welding method according to the present invention, the depth of the groove obtained from the groove information acquired by the sensor may be corrected according to the inclination of the sensor. In this case, the depth of the groove can be acquired with high accuracy.

The present invention provides a welding method that can improve the positional accuracy of welding relative to the area to be welded in multi-layer welding.

FIG. 1 is a perspective view that typically illustrates a welding method according to an embodiment of the present invention. FIG. 2 is a side view showing the robot of FIG. FIG. 3 is a block diagram showing the functional configuration of the control unit. 4A and 4B are diagrams for explaining the sensing control unit. FIG. 5 is a diagram for explaining the tilt correction unit. FIG. 6 is a diagram for explaining the path planning unit. 7A and 7B are diagrams for explaining the pass position adjustment process performed by the welding control unit. 8( a ) and 8 ( b ) are diagrams for explaining the groove calculation unit. FIG. 9 is a flowchart showing the procedure of a welding method according to one embodiment. FIG. 10 is a flow chart showing the procedure for one welding pass in a welding process. FIG. 11 is a flowchart showing the procedure of the sensing process.

One embodiment will be described below with reference to the drawings. In the description of the drawings, identical or corresponding elements are given the same reference numerals, and duplicate descriptions may be omitted.

Figure 1 is a perspective view showing a schematic diagram of a welding method according to one embodiment of the present invention. Figure 1 shows a welding device 1 used in the welding method according to this embodiment, and objects to be welded (e.g., two column parts 3). The outer shape of the objects to be welded is, for example, angular. The objects to be welded include four side portions Ws and four corner portions Wc. Each of the four side portions Ws is formed flat, and two adjacent side portions Ws of the four side portions Ws intersect (are perpendicular to) each other at the corner portion Wc. The welding device 1 is an on-site welding device for welding, for example, column parts 3 as the objects to be welded together at a building construction site.

The column parts 3 are, for example, rectangular steel pipes, and a number of column parts 3 are stacked vertically and welded together to construct a rectangular steel pipe column. The column parts 3 to be welded are arranged so that their horizontal ends are close to each other and face each other over the entire circumference. The area where these ends face each other is the weld target area W to be welded by the welding device 1, and the groove of the weld target area W extends in the horizontal plane over the entire circumference of the column part 3 (i.e., over all side portions Ws). In the following, the column parts 3 that are welded together and that are located at the bottom are referred to as column part 3A, and the column parts 3 that are located at the top are referred to as column part 3B.

An erection is provided on each of the column parts 3A and 3B so as to straddle the welding target area W. The erection has an erection piece 5 welded to the center of each side of each of the column parts 3A and 3B near the welding target area W, and an erection jig 7. The erection piece 5 provided on the column part 3A and the erection piece 5 provided on the column part 3B are aligned vertically and connected to each other by the erection jig 7. The column part 3A and the column part 3B are temporarily connected by such an erection.

The welding device 1 includes a robot 9 (welding robot), rails 11 for moving the robot 9 around the column part 3, and a control unit 13 for controlling the operation and movement of the robot 9.

Figure 2 is a side view showing the robot of Figure 1. As shown in Figures 1 and 2, the robot 9 is a multi-joint robot, for example, a general-purpose 6-axis vertical multi-joint robot. The robot 9 is equipped with a welding tool 15 (for example, a welding torch for arc welding, or a laser head for laser welding, etc.) as an end effector. That is, the robot 9 is equipped with an end effector for welding. The robot 9 operates under the control of the control unit 13, and moves the welding tool 15 along the welding target area W to weld the welding target area W. The robot 9 also includes a groove sensor 17 (sensor) for acquiring information on the groove of the welding target area W. The groove sensor 17 is, for example, a laser sensor that senses the cross-sectional shape of the groove. The groove sensor 17 is fixed to the welding tool 15 via, for example, a mounting jig 16. The robot 9 operates under the control of the control unit 13, and moves the groove sensor 17 along the welding target area W to acquire the groove shape (for example, three-dimensional coordinate data of the groove). The acquired groove shape is temporarily stored in the control unit 13.

The rail 11 extends in an annular shape so as to surround the periphery of the column part 3 at a position slightly lower than the welding target area W, and is fixed and supported on the outer peripheral surface of the column part 3A. In a plan view, the rail 11 forms a ring centered on the material axis of the column part 3. A carriage 19 capable of sliding on the rail 11 is installed on the rail 11. By attaching the carriage 19, the robot 9 can travel around the column part 3 along the rail 11.

The mounting seat 21 of the carriage 19 is inclined with respect to the vertical plane. The mounting seat 21 is parallel to the sliding direction of the carriage 19. The first axis 23 (rotation axis) of the robot 9 attached to this mounting seat 21 is perpendicular to the mounting seat 21 and inclined with respect to both the vertical direction and the horizontal plane. In other words, the first axis 23 is neither a vertical axis nor a horizontal axis. With this configuration, it becomes easy to adjust the movement range of the welding tool 15 and groove sensor 17 that move along the horizontally extending welding target area W to a suitable movement range within the movement range of the robot 9. In other words, it becomes easy to avoid a state in which the robot 9 operates near the movement limit of the arm, for example.

Figure 3 is a block diagram showing the functional configuration of the control unit. As shown in Figure 3, the control unit 13 has a memory unit 31, a travel control unit 32, a sensing control unit 33, a tilt correction unit 34, a path planning unit 35, a welding control unit 36, and a groove calculation unit 37 as functional configurations (hereinafter referred to as "functional modules"). These functional modules are merely a division of the functions of the control unit 13 into multiple modules for convenience, and do not necessarily mean that the hardware constituting the control unit 13 is divided into such modules. Each functional module may be realized by executing a program, or may be realized by a dedicated electric circuit (e.g., a logic circuit) or an integrated circuit (ASIC: Application Specific Integrated Circuit) that integrates the same.

The travel control unit 32 controls the robot 9 to travel along the rails 11. This allows the robot 9 to move around the column part 3 in the vicinity of the welding target area W. The travel control unit 32 may cause the robot 9 to travel at a constant speed, or may cause the robot 9 to travel while changing the speed. For example, the travel control unit 32 causes the robot 9 to travel at a preset speed obtained from the memory unit 31.

The sensing control unit 33 acquires information on the groove of the welding target area W by the groove sensor 17. Figures 4(a) and 4(b) are diagrams for explaining the sensing control unit. Figures 4(a) and 4(b) show the welding target area W and its surroundings as viewed from a direction intersecting the extension direction of the groove. As shown in Figures 4(a) and 4(b), the welding target area W is an area defined by the column parts 3A and 3B and the backing metal 3C provided on the inner surface of the column parts 3A and 3B.

The sensing control unit 33 executes a first sensing process (see FIG. 4(a)) for acquiring information on the groove of the welding target area W before welding is performed, a second sensing process for acquiring information on the groove of the welding target area W in a state where a welding pass is being performed by the welding tool 15, and a third sensing process (see FIG. 4(b)) for acquiring information on the groove of the welding target area W after at least one welding pass (as an example, multiple welding passes) has been performed. The groove information is the depth and height of each point on a cross section (hereinafter referred to as a "groove cross section") that intersects with the extension direction of the groove. The sensing control unit 33 transmits the groove information acquired in the first sensing process and the third sensing process to the inclination correction unit 34. The sensing control unit 33 transmits the groove information acquired in the second sensing process to the welding control unit 36.

The sensing control unit 33 also performs a process of adjusting the distance of the groove sensor 17 to the groove depending on the number of welding passes that have been performed. As shown in FIG. 4(a), when performing the first sensing process (i.e., when the number of welding passes that have been performed is zero), the sensing control unit 33 moves the groove sensor 17 to an initial measurement position. The initial measurement position is, for example, a position that is a predetermined focal length L1 away from the deepest part of the groove (here, the backing metal 3C) in the depth direction of the groove. When the groove sensor 17 is placed at this initial measurement position, the camera provided in the groove sensor 17 can be well focused on each required part (for example, the surface of the backing metal 3C).

Also, as shown in FIG. 4(b), when performing the third sensing process, the sensing control unit 33 moves the groove sensor 17 backward to the re-measurement position. The re-measurement position is a position moved a predetermined distance L2 in the direction away from the groove (i.e., backward) along the depth direction of the groove from the initial measurement position. The predetermined distance L2 is set according to the number of welding passes that have been performed. As an example, the predetermined distance L2 is a value obtained by adding up the design thickness of each layer of the welding pass that has been performed. In other words, the sensing control unit 33 moves the position of the groove sensor 17 away from the groove according to the number of welding passes that have been performed. As a result, the distance L3 in the depth direction of the groove between the deepest part of the groove (here, the surface of the weld bead WB formed by the welding pass that has been performed) and the groove sensor 17 when the third sensing process is performed is approximately the same as the above-mentioned predetermined focal distance L1. Therefore, the camera equipped with the groove sensor 17 can be well focused on each required area (e.g., the surface of the weld bead WB) even during the third sensing process.

The inclination correction unit 34 corrects the depth of the groove obtained from the groove information acquired by the sensing control unit 33 according to the inclination of the groove sensor 17. FIG. 5 is a diagram for explaining the inclination correction unit. The inclination correction unit 34 calculates the inclination angle θ of the groove sensor 17 with respect to the depth direction of the groove, and derives the corrected groove depth D12 by multiplying the apparent depth D11 of the groove acquired by the sensing control unit 33 by the cosine value (i.e., cos θ) of the inclination angle θ. For example, the inclination correction unit 34 acquires posture information of the robot 9, and calculates the inclination angle of the welding tool 15 with respect to the horizontal direction in the posture information as the inclination angle θ of the groove sensor 17. The inclination correction unit 34 stores the correction value of the groove information obtained by calculation in the memory unit 31.

The path planning unit 35 executes a process of planning multiple welding passes for the welding target area W based on the groove information acquired from the memory unit 31. FIG. 6 is a diagram for explaining the path planning unit. The path planning unit 35 executes a path planning process of planning multiple welding passes for the welding target area W before welding is performed based on a correction value of the groove information acquired in the first sensing process, and a path replanning process of replanning multiple welding passes for the welding target area W after multiple welding passes are performed based on a correction value of the groove information acquired in the third sensing process.

As the path planning process and the path replanning process, the path planning unit 35 executes a process of setting multiple path sections P to be assigned to the groove section. In the path replanning process of this embodiment, the groove section set by the groove calculation unit 37 described later is used as the groove section. The process of setting multiple path sections P includes a first process of calculating the number of layers of the path section P (the number of layers in the depth direction of the groove), a second process of calculating the number of stages of the path section P (the number of layers in the height direction of the groove), and a third process of assigning multiple path sections to the groove section so as to satisfy the calculation results of the first process and the calculation results of the second process.

In the first process, the number of layers of the pass cross section P is calculated according to the depth of the groove cross section (e.g., the depth D2 of the lower end of each layer) so that the thickness of each layer (e.g., the thickness D1 of the lower end of each layer) is within a predetermined range (e.g., less than 9 mm). The range of the thickness D1 may be set to, for example, 4.5 mm or more and less than 9 mm. The number of stages of the pass cross section P is calculated for each layer. In the second process, the number of stages of each layer of the pass cross section P (in the example of FIG. 4(b), the second layer from the back of the groove) is calculated according to the height of each layer of the groove cross section (e.g., the height D4 of the deepest part of each layer) so that the width of each stage (e.g., the vertical width D3 of the deepest part of each stage) is within a predetermined range (e.g., less than 9 mm). The range of the width D3 may be set to, for example, 4.5 mm or more and less than 9 mm. In the third process, the groove cross section is divided (e.g., equally divided) according to the calculated number of layers and number of stages to perform pass division.
The path planning unit 35 sets each division point obtained by the division as a target position K of the welding tool 15.

The welding control unit 36 executes a welding pass by the welding tool 15 according to the pass plan planned by the pass plan unit 35. Specifically, the welding control unit 36 executes a process of switching the welding state of the welding tool 15 ON/OFF. The welding control unit 36 may further execute a process of adjusting the welding state of the welding tool 15. In the process of adjusting the welding state, the welding control unit 36 adjusts, for example, the welding current value and the filler metal supply speed for each welding pass. The welding control unit 36 may adjust the welding state by referring to a table in which the position of each pass cross section P (for example, which layer is from the back of the groove and which layer is from the bottom in the target layer, etc.) is previously associated with the welding conditions (for example, the welding current value and the filler metal supply speed, etc.).

The welding control unit 36 also executes a pass position adjustment process to adjust the position of the welding tool 15 so as to obtain the welding pass planned by the pass planning unit 35 based on the groove information acquired from the sensing control unit 33. Figures 7(a) and 7(b) are diagrams for explaining the pass position adjustment process by the welding control unit. Specifically, while performing a welding pass, the welding control unit 36 acquires the positions of the boundaries B1 and B2 between the welding target area W and the non-welding target area (here, the side surface portion Ws) in the welding target object (column parts 3A and 3B) from the sensing control unit 33 as groove information by the second sensing process.

Next, as shown in FIG. 7(a), the welding control unit 36 calculates the vertical distances L11, L12 and the horizontal distance L13 from each of the boundaries B1, B2 to the target position K planned by the path planning unit 35. Then, as shown in FIG. 7(b), the welding control unit 36 adjusts the position of the welding tool 15 so that the relative position of the target position K to the positions of the boundaries B1, B2 is the welding pass target position of the welding tool 15.

The groove calculation unit 37 executes a process for setting the groove cross section after multiple welding passes have been performed. Figures 8(a) and 8(b) are diagrams for explaining the groove calculation unit. Specifically, the groove calculation unit 37 executes a process for calculating the positions of virtual points V1 and V2 indicating the points where the groove and the surface of the weld bead WB formed in the groove contact on the groove cross section based on the groove information after multiple welding passes have been performed acquired from the memory unit 31. For example, the groove calculation unit 37 acquires from the memory unit 31 a correction value of the groove information acquired in the third sensing process as the groove information after multiple welding passes have been performed.

The groove calculation unit 37 executes a process of calculating an approximation line N of the weld bead WB based on the correction value of the groove information acquired in the third sensing process (see FIG. 8(a)), a process of calculating the intersections of the approximation line N and the groove as virtual points V1 and V2 (see FIG. 8(b)), and a process of setting a rectangular portion including the virtual points V1 and V2 as vertices as the groove cross section (see FIG. 8(b)).

As shown in FIG. 8(a), in the process of calculating the approximation line N, the groove calculation unit 37 calculates the approximation line N of the portion of the contour of the surface of the weld bead WB on the cross section of the groove that is not in contact with the groove. The range of the portion of the contour of the surface of the weld bead WB that is not in contact with the groove is set according to the number of welding passes that have been performed. As an example, the groove calculation unit 37 sets a range that is slightly narrower than the designed surface of the outermost layer of the performed welding pass (i.e., from a position a predetermined amount above the designed lower end of the outermost layer to a position a predetermined amount below the designed upper end of the outermost layer) as the range of the portion that is not in contact with the groove. Then, from the contour of the surface of the weld bead WB within the set range, the approximation line N of the contour is calculated, for example, by the least squares method.

As shown in FIG. 8(b), after the imaginary points V1 and V2 are derived as the intersections between the approximation line N and the groove, in the process of setting the groove cross section, the groove calculation unit 37 sets a quadrangular portion having the imaginary points V1 and V2 and the boundaries B1 and B2 as vertices as the groove cross section. This groove cross section is used as the target groove cross section for resetting multiple path cross sections P in the path replanning process.

The hardware of the control unit 13 is composed of, for example, one or more control computers. When the control unit 13 is composed of multiple computers, each of the above-mentioned functional modules may be realized by a single computer, or may be realized by a combination of two or more computers.

Next, an overview of the on-site welding process by the control unit 13 will be described as an example of a welding method. In the on-site welding process according to this embodiment, the target welding section is the area W to be welded, from a position covered by the erection jig 7 of one erection to a position covered by the erection jig 7 of the adjacent erection. In other words, one welding section is set in the groove of one-quarter of the area W to be welded. Figure 9 is a flowchart showing the procedure of the on-site welding process by the control unit 13.

9, the control unit 13 first executes step S01. In step S01, the sensing control unit 33 executes a process to control the robot 9 so that the groove sensor 17 acquires information on the groove in the welding target area W before welding is performed (first sensing process). First, as shown in FIG. 4(a), the sensing control unit 33 moves the groove sensor 17 to an initial measurement position and executes the first sensing process. Through this first sensing process, the sensing control unit 33 acquires the depth and height of each point on the groove cross section as groove information. In this first sensing process, while the robot 9 moves the groove sensor 17 along the welding target area W, sensing is performed by the groove sensor 17 over the entire length of the welding target area W, and information on each groove is acquired for each groove cross section at a predetermined pitch (for example, 50 mm pitch).

Then, the inclination correction unit 34 corrects the groove depth obtained from the groove information acquired by the sensing control unit 33 according to the inclination of the groove sensor 17. Specifically, as shown in FIG. 5, the inclination correction unit 34 calculates the inclination angle θ of the groove sensor 17 with respect to the groove depth direction, and derives the corrected groove depth D12 by multiplying the apparent groove depth D11 acquired by the sensing control unit 33 by the cosine value of the inclination angle θ. The inclination correction unit 34 stores the calculated correction value of the groove information in the memory unit 31.

Next, the control unit 13 executes step S02. In step S02, the path planning unit 35 executes a process of planning multiple welding passes for the welding target region W based on the results acquired in step S01 (path planning process). Specifically, as shown in FIG. 6, the path planning unit 35 executes a process of setting multiple path sections P to be allocated to the groove cross section. In addition, the path planning unit 35 sets each division point obtained by dividing the groove cross section when allocating the path sections P as the target position K of the welding tool 15.

Next, the control unit 13 executes step S03. In step S03, the welding control unit 36 executes a welding process in which the robot 9 is controlled so as to weld at least a portion of the welding target area W by repeatedly performing welding passes on the welding target area W with the welding tool 15 (first welding process). Performing a welding pass means that the robot 9 moves the welding tool 15 along the welding target area W, while the welding tool 15 forms a weld bead in the groove of the welding target area W. The specific processing content of step S03 will be described later.

Next, the control unit 13 executes step S04. In step S04, the sensing control unit 33 executes a sensing process to control the robot 9 so that the groove sensor 17 acquires information about the groove after multiple welding passes have been performed. The specific process content of step S04 will be described later.

Next, the control unit 13 executes step S05. In step S05, the path planning unit 35 executes a process of re-planning multiple welding passes for the welding target region W based on the information acquired in step S04 (path re-planning process). At this time, the path planning unit 35 executes a process of setting multiple path cross sections P to be assigned to the groove cross sections set in step S04.

Next, the control unit 13 executes step S06. In step S06, the welding control unit 36 executes a process of controlling the robot 9 so as to weld the welding target area W by repeatedly performing the multiple welding passes replanned in step S04 (second welding process). Note that step S06 may be performed in the same manner as step S03. Furthermore, the control unit 13 repeatedly executes the above-mentioned steps S04 to S06 until welding of the entire area of the welding target area W is completed (step S07). Note that it is not necessary to repeat the processes of steps S04 to S06 multiple times, and the processes of steps S04 to S06 may be executed only once. When welding of the entire area of the welding target area W in the target welding section is completed ("Yes" in step S07), the control unit 13 ends the on-site welding process for that welding section. Then, this on-site welding process is executed for each welding section, and welding of the entire circumference of the groove of the welding target area W is completed.

An example of the specific processing content of step S03 (first welding process) will be described. FIG. 10 is a flowchart showing the procedure for one welding pass in the welding process. As shown in FIG. 10, the control unit 13 first executes step S31. In step S31, the welding control unit 36 executes processing to control the robot 9 so as to start a welding pass on the welding target area W. Specifically, the welding control unit 36 controls the robot 9 so as to switch the welding state of the welding tool 15 to ON.

While performing the welding pass, the control unit 13 executes steps S32 and S33 in order. In step S32, the sensing control unit 33 executes a second sensing process to control the robot 9 so that the groove sensor 17 acquires information on the groove in the welding target area W (second sensing step). Through this second sensing process, the sensing control unit 33 acquires the depth and height of each point on the groove cross section as groove information at any time. This second sensing process is executed while the welding pass is being performed. In this welding pass, the robot 9 moves the welding tool 15 and the groove sensor 17 along the welding target area W with the welding tool 15 and the groove sensor 17 aligned in the movement direction. Then, in the second sensing process, the groove cross section at a position several centimeters ahead of the welding tool 15 in the movement direction is sensed by the groove sensor 17, and the groove information is acquired.

In step S33, based on the information acquired in step S32, the welding control unit 36 executes a process of adjusting the position of the welding tool 15 so as to obtain the welding pass planned in step S02 (pass position adjustment process). Specifically, as shown in FIG. 7(a), the welding control unit 36 acquires the positions of the boundaries B1 and B2 from the sensing control unit 33 as groove information at any time. The welding control unit 36 also calculates the vertical distances L11 and L12 and the horizontal distance L13 from each of the boundaries B1 and B2 to the target position K at any time. Then, as shown in FIG. 7(b), the welding control unit 36 adjusts the position of the welding tool 15 at any time, using the relative position of the target position K to the positions of the boundaries B1 and B2 as the welding pass target position by the welding tool 15.

By repeatedly executing steps S32 and S33 at short intervals (e.g., about 500 milliseconds) until the welding tool 15 reaches the end of the target welding section (step S34: "Yes"), the position of the welding tool 15 is feedback-controlled and the welding pass target position is correctly maintained. After that, when the welding tool 15 reaches the end of the target welding section (step S34: "Yes"), the control unit 13 executes step S35. In step S35, the welding control unit 36 executes a process to control the robot 9 so as to end the welding pass for the welding target area W. Specifically, the welding control unit 36 controls the robot 9 so as to switch the welding mode by the welding tool 15 to OFF. In this way, the control unit 13 ends one welding pass in the welding process. Then, the above welding passes are repeatedly executed, and the welding process in step S03 is completed.

Next, an example of the specific processing content of step S04 will be described. FIG. 11 is a flowchart showing the procedure of the sensing process. As shown in FIG. 11, the control unit 13 first executes step S41. In step S41, the sensing control unit 33 controls the robot 9 to move the position of the groove sensor 17 away from the groove, as shown in FIG. 4(b), depending on the number of welding passes already performed in step S03. Specifically, the sensing control unit 33 moves the groove sensor 17 backward to a remeasurement position (here, a position moved a predetermined distance L2 in a direction away from the groove along the depth direction of the groove from the initial measurement position). As described above, the predetermined distance L2 is, for example, a value obtained by adding the design thickness of each layer of the already performed welding pass. If the focus of the camera of the groove sensor 17 can be adjusted to a required location, the processing of step S41 may be omitted.

Next, the control unit 13 executes step S42. In step S42, the sensing control unit 33 controls the robot 9 so that the groove sensor 17 acquires information on the groove after the multiple welding passes are performed in step S03 (third sensing step). That is, the sensing control unit 33 executes the third sensing process. Through this third sensing process, the sensing control unit 33 acquires the depth and height of each point on the groove cross section as groove information. In this third sensing process, in the welding target area W (see, for example, FIG. 8) where the weld bead WB has been formed by the previous welding pass, the robot 9 moves the groove sensor 17 along the welding target area W, while the groove sensor 17 senses the entire length of the welding target area W, and information on each groove cross section at a predetermined pitch (for example, 50 mm pitch) is acquired.

Next, the control unit 13 executes step S43. In step S43, the inclination correction unit 34 corrects the groove depth obtained from the groove information acquired by the sensing control unit 33 in step S42 according to the inclination of the groove sensor 17. Specifically, as shown in FIG. 5, the inclination correction unit 34 first calculates the inclination angle θ of the groove sensor 17 with respect to the groove depth direction. In addition, the inclination correction unit 34 derives the corrected groove depth D12 by multiplying the apparent groove depth D11 acquired by the sensing control unit 33 by the cosine value of the inclination angle θ. Then, the inclination correction unit 34 stores the calculated correction value of the groove information in the memory unit 31.

Next, the control unit 13 executes a process of calculating the positions of virtual points V1 and V2 on the groove cross section, which indicate the points where the groove and the surface of the weld bead WB formed in the groove contact each other, based on the groove information obtained in steps S42 and S43 after the multiple welding passes have been performed (calculation process). Specifically, the control unit 13 executes steps S44, S45, and S46 in order.

In step S44, the groove calculation unit 37 first acquires from the memory unit 31 the correction value of the groove information acquired in steps S42 and S43. Then, the groove calculation unit 37 executes a process of calculating an approximation line N of the weld bead WB based on the correction value of the groove information. Specifically, as shown in FIG. 8(a), the groove calculation unit 37 calculates an approximation line N of the portion of the contour of the surface of the weld bead WB on the cross section of the groove that is not in contact with the groove. As an example, the groove calculation unit 37 sets a range that is slightly narrower than the design surface of the outermost layer of the executed welding pass as the range of the portion that is not in contact with the groove, and calculates an approximation line N of the contour from the surface contour of the weld bead WB within that range by the least squares method.

In step S45, as shown in FIG. 8(b), the groove calculation unit 37 executes a process of deriving virtual points V1 and V2 as the intersection points between the approximation line N calculated in step S44 and the groove. In step S46, the groove calculation unit 37 executes a process of setting a quadrangular portion including the virtual points V1 and V2 derived in step S45 as vertices as the groove section. Specifically, the groove calculation unit 37 sets a quadrangular portion having the virtual points V1 and V2 and the boundaries B1 and B2 as vertices as the groove section. With the above, the control unit 13 ends the sensing process in step S04. The groove section set in step S04 (step S46) is used as the groove section for which the multiple path sections P are reset in step S05.

The effect of the welding method described above will be described. In the welding method according to this embodiment, multiple welding passes are planned for the welding target area W in step S02 (pass planning process) based on groove information of the welding target area W before welding is performed, and then welding passes are repeatedly performed in step S03 (first welding process). Here, in step S03, while performing the welding pass, the position of the welding tool 15 is adjusted based on the groove information acquired by the groove sensor 17 so that the welding pass planned in step S02 is performed. As a result, the welding pass is performed while correcting the error with respect to the welding pass planned in step S02. Therefore, the positional accuracy of the welding for the welding target area W in multi-layer welding can be improved.

In addition, in this welding method, in step S33 (pass position adjustment process), the positions of the boundaries B1 and B2 between the welding target area W and the non-welding target area (here, the side surface Ws) in the welding target object (column parts 3A and 3B) are obtained as groove information, and the position of the welding tool 15 is adjusted by setting the relative position of the welding pass to the positions of the boundaries B1 and B2 as the welding pass target position by the welding tool 15. With this configuration, the relative position of the welding pass to the positions of the boundaries B1 and B2, which are very close to the non-welding target area (here, the side surface Ws), is set as the welding pass target position of the welding tool 15, so that even when part of the groove has been welded in multi-layer welding, the deviation of the position of the welding pass with respect to the welding target area W is reduced. Therefore, the positional accuracy of the welding with respect to the welding target area W can be particularly improved.

This welding method further includes steps S44, S45, and S46 (calculation steps) for calculating the positions of virtual points V1 and V2 indicating the points at which the groove and the surface of the weld bead WB formed in the groove meet on the cross section of the groove based on groove information acquired by the groove sensor 17 after at least one welding pass has been performed. In steps S44, S45, and S46, an approximation line N of the contour of the surface of the weld bead WB on the cross section of the groove that is not in contact with the groove is calculated, and the position of the intersection between the groove and the approximation line N is calculated as the position of virtual points V1 and V2.

As a comparative example, there is a method in which an approximation line calculated from the contour of the entire surface of the weld bead on the cross section of the groove is used to calculate the position of the virtual point where the groove and the surface of the weld bead meet. However, with this method, there are cases where a part where a welding pass has not yet been performed (such as the joint surface of the welded object) is erroneously recognized as the surface of the weld bead, and in such cases, an appropriate approximation line cannot be obtained.

In contrast, in the welding method according to this embodiment, an approximation straight line N of the portion of the contour of the surface of the weld bead WB that is not in contact with the groove is used, so that an approximation straight line N for calculating the imaginary points V1 and V2 where the groove and the surface of the weld bead WB are in contact can be obtained more appropriately.

The welding method according to this embodiment further includes step S04 (third sensing step) of acquiring information about the groove after multiple welding passes have been performed, step S05 (pass replanning step) of replanning multiple welding passes for the welding target area W based on the information acquired in step S04, and step S06 (second welding step) of welding the welding target area W by repeatedly performing the multiple welding passes replanned in step S05. In step S05, the multiple welding passes for the welding target area W are replanned using the results calculated in steps S44, S45, and S46.

For example, the originally planned welding pass may not be suitable for the welding target area W remaining after multiple welding passes have been performed. In contrast, in the welding method according to this embodiment, groove information is acquired again and the welding pass is re-planned, so that in step S06, a welding pass can be performed according to the progress of welding. In addition, in step S05, the results obtained in steps S44, S45, and S46 are used, so that a welding pass more suitable for the progress of welding is planned. Therefore, the positional accuracy of welding with respect to the welding target area W in multi-layer welding can be further improved.

In addition, in the welding method according to this embodiment, before the groove sensor 17 acquires groove information after at least one welding pass has been performed, the position of the groove sensor 17 is moved away from the groove according to the number of welding passes that have been performed. With this configuration, the groove sensor 17 can acquire groove information at a position suitable for sensing according to the number of welding passes that have been performed.

In addition, in the welding method according to this embodiment, the apparent depth D11 of the groove obtained from the groove information acquired by the groove sensor 17 is corrected according to the inclination of the groove sensor 17. With this configuration, the groove depth D12 can be acquired with high accuracy.

The above embodiment describes one embodiment of the welding method according to the present invention. The welding method according to the present invention can be any modification of the above-mentioned welding method.

For example, the welding method according to the above embodiment includes steps S01 to S06, but steps S04 to S06 may be omitted. The welding method may be performed by only steps S01 to S03. In the welding method according to the above embodiment, the groove information (groove depth) obtained in each of the first sensing step in step S01 and the third sensing step in step S42 is corrected by the inclination correction unit 34, but the process of correcting the groove information by the inclination correction unit 34 may be omitted as appropriate. In addition, the groove information obtained in the second sensing step may be corrected by the inclination correction unit 34. Similarly, a calculation step (i.e., a process of calculating the position of a virtual point indicating a point where the groove and the surface of the weld bead formed in the groove contact each other on the cross section of the groove) may be performed based on the groove information obtained in the second sensing step. Before acquiring the groove information in the second sensing step, a process may be performed in which the sensing control unit 33 controls the robot 9 to move the position of the groove sensor 17 away from the groove according to the number of welding passes that have been performed.

3A, 3B...column parts (objects to be welded), 9...robot (welding robot), 15...welding tool (end effector), 17...groove sensor (sensor), B1, B2...boundary, D11, D12...depth, N...approximation line, V1, V2...virtual point, W...area to be welded, Ws...side surface (area not to be welded), WB...weld bead.

Claims (4)

A welding method for performing multi-layer welding on a welding target area set on a welding target using a welding robot having a welding end effector and a sensor,
A first sensing step of sensing the welding target area before welding is performed, and acquiring information about the groove of the welding target area by the sensor;
a path planning step of planning a plurality of welding passes for the welding target area based on the results acquired in the first sensing step;
a first welding step of welding the welding target area by repeatedly performing a welding pass on the welding target area by the end effector after the path planning step,
The first welding step includes:
A second sensing step of acquiring information about the groove by the sensor while performing the welding pass by the end effector;
a pass position adjustment process of adjusting a position of the end effector based on the information acquired in the second sensing process so as to achieve the welding pass planned in the pass planning process,
A calculation step of calculating a position of a virtual point indicating a point where the groove and a surface of a weld bead formed in the groove contact each other on a cross section of the groove based on information of the groove after at least one welding pass is performed, the calculation step further includes:
In the calculation step, an approximation line of a portion of the contour of the surface of the weld bead on the cross section of the groove that is not in contact with the groove is calculated, and the position of the intersection between the groove and the approximation line is calculated as the position of the virtual point.
Welding method. A third sensing step of acquiring information about the groove after a plurality of the welding passes are performed;
a pass re-planning step of re-planning the plurality of welding passes for the welding target region based on the information acquired in the third sensing step;
A second welding process of welding the welding target area by repeatedly performing the plurality of welding passes replanned in the pass replanning process,
In the pass re-planning step, a plurality of welding passes for the welding target region are re-planned using a result calculated in the calculation step.
The welding method according to claim 1 . Before acquiring information about the groove by the sensor after at least one welding pass has been performed, the position of the sensor is moved away from the groove according to the number of welding passes that have been performed.
The welding method according to claim 1 or 2 . The depth of the groove obtained from the groove information acquired by the sensor is corrected according to the inclination of the sensor.
The welding method according to any one of claims 1 to 3 .

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