Systems and methods for arc welding a workpiece

Abstract

Methods and systems for positioning a welding head with respect to a groove in a rotating circular workpiece during an arc welding process, wherein a chain or other flexible measuring device is coupled about the workpiece. First and second scanners are respectively used to scan the groove and a link of the chain at a first rotational position of the workpiece. A third scanner is used to scan the chain link at a second rotational position of the workpiece that corresponds to the welding location. The scanners are collectively used to determine a profile of the groove and a change in position of the chain link between the first and second rotational positions of the workpiece. Data acquired through the scanning processes are used to generate instructions deliverable to a positioning system of the welding head to position the welding head so that arc welding properly occurs inside the groove.

Description

[0001] SYSTEMS AND METHODS FOR ARC WELDING A WORKPIECE

[0002] FIELD

[0003] This invention relates to systems and methods of arc welding workpieces, and in particular, the welding together of large diameter cylindrical structures.

[0004] BACKGROUND

[0005] The welding of large diameter workpieces generally entails supporting a first cylindrical section 10 on a first set of rollers 40 and supporting a second cylindrical section 20 on a second set of rollers 50 as shown in FIG. 1. The supporting structure and the first and second cylindrical sections are arranged to place an end 11 of the first cylindrical section 10 in close proximity to an end 21 of the second cylindrical section 20 such that a gap / groove 60 exists between them. One or more of rollers 40 and 50 is motor driven and acts to impart rotational movement to the workpiece 30 (collectively the first and second cylindrical sections 10 and 20) during the arc welding operation. According to some welding operations the arc welding head 70 is positioned above a top of the workpiece 30 as shown in FIG. 1 and is supported by a gantry or robotic arm 80 that is capable of moving the welding head in relation to the gap / groove 60.

[0006] As shown in FIG. 1, the workpiece 30 includes a central axis 31 and has a length that extends between the end face 14 of the first cylindrical section 10 and the end face 24 of the second cylindrical section 20.

[0007] Arc welding involves the formation of an arc between one or more a continuously fed electrodes 71 that protrudes from the welding head 70 and into the gap / groove 60 of the workpiece 30. With the welding head powered on, the one or more electrodes produce intense heat to produce an electric arc between the electrodes and the base metal of the workpiece 30. The heat melts the base metal and the electrode cores to form the weld that joins the first and second cylindrical sections to one another. Submerged arc welding is a common arc welding process used in welding together large diameter cylindrical sections. The process requires a continuously fed consumable solid or tubular (metal cored) electrode like that discussed above. The molten weld and the arc zone are protected from atmospheric contamination by being "submerged" under, for example, a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds. When molten, the flux becomes conductive and provides a current path between the electrode and the base metal. This thick layer of flux completely covers the molten metal thus preventing or minimizing spatter and sparks as well as suppressing the intense ultraviolet radiation and fumes that are a part of the shielded metal arc welding process.

[0008] The arc welding processes described above present a number of challenges that are brought about by unwanted movement of the workpiece during the welding process, and an inability to track the location of the groove / gap 60 at the welding location due to the groove / gap being submerged under the blanket of flux. With reference to FIG. 1, unwanted axial movement of the workpiece in a direction “x” can occur as the workpiece is rotated. The elevation of the weld area in a direction “z” may also change as the workpiece is rotated. Moreover, rotational slippage of the workpiece can occur between the outer circumferential surface of the workpiece and the rollers 40 and / or 50 while the workpiece is being rotated.

[0009] A current solution to monitor axial movement of the workpiece is through the use of an edge detector 90 that detects the axial movement of the end face 14 of the workpiece 30 as shown in FIG. 1. A speed wheel 95 associated with one of rollers 40 and 50 is also typically used to monitor the rotation speed of the workpiece. A problem with the use of the edge detector is that the sensing occurs far from the welding location and may not accurately determine a true axial movement at the weld location. A problem with the use of the speed wheel is that it is incapable of detecting rotational slippage of the workpiece and as a result may not accurately detect the true rotational speed of the workpiece. In addition, a floor-mounted speed wheel may not accurately compensate for ovality and concentricity of the workpiece. Each of these issues can adversely affect the welding process as a result of an improper placement of the weld head 70 with respect to the gap / groove 60. What is needed are solutions to overcome the aforementioned problems. SUMMARY

[0010] Disclosed herein are systems and methods aimed at solving one or more of the problems discussed above. Systems and methods are provided for positioning a welding head with respect to a groove / gap in a rotating circular workpiece during an arc welding process to ensure that the arc welding occurs inside the groove / gap in spite of axial and / or elevation movement of the workpiece during the welding process, and in spite of slippage occurring between the workpiece and a drive roller that imparts rotational movement to the workpiece during the welding process. According to some implementations the workpiece comprises first and second cylindrical structures that are joined together by the arc welding process.

[0011] According to some implementations a system is provided that enables the welding head to be accurately positioned with respect to a groove / gap located between the first and second cylindrical structures while the workpiece is rotated. According to some implementations, the system includes a chain and first, second and third scanners that are strategically situated and function together to ultimately generate data that is transmissible to a welding head positioning system (e.g. robotic arm, gantry, etc.) where it is used to guide the welding head with respect to the groove while the workpiece is being rotated.

[0012] The chain is formed by links and is positioned on an outer circumferential surface of one of the first and second cylindrical structures. For the sake of discussion, the chain at least partially circumscribes and is tightened about the second cylindrical structure so that no relative movement occurs between the chain and the second cylindrical structure during the arc welding process. Preferably, the chain is longitudinally spaced apart from the groove / gap a sufficient distance to prevent slag and other welding debris (such as flux) from imposing on the chain during the welding process.

[0013] The first, second and third scanners each includes a laser light source and an image capture device (e.g. camera). The first scanner is configured to emit a first laser beam towards the groove and is further configured to capture reflected light in the image capture device to obtain a first groove profile. The first groove profile at least includes information regarding width dimensions of the first groove profile, and preferably also includes information regarding the depth dimensions of the groove. According to some implementations the image capture device itself generates the first groove profile. However, according to other implementations, the first groove profile is generated through the use of additional image processing equipment that receives data from the image capture device associated with the captured reflected light. The location of the first scanner and the longitudinal width of the first laser beam is set to ensure a full width of the groove is captured during an entirety of the welding process.

[0014] The second scanner is configured to emit a second laser beam towards a first link of the chain and to capture reflected light from the second laser beam to obtain a position of the first link with respect to the groove. The scanning location of the first link is always forward of the welding location with respect to a welding direction. The first and second scanners are located and oriented such that their emitted laser beams are coplanar. According to some implementations the first and second laser beams partially overlap, the overlapping occurring along a top line of the workpiece (e.g. along an outer surface of the workpiece).

[0015] The first and second scanners themselves, or in conjunction with other data generating and / or processing equipment, generate first electronic data associated with the obtained first groove profile and second electronic data associated with the position of the first link with respect to the groove. Once generated, the first and second electronic data is stored in an electronic storage device for later use.

[0016] The third scanner is positioned a fixed distance reward of the second scanner with respect to the welding direction, and is configured to emit a third laser beam towards the chain as the workpiece is rotated. The emitted third laser beam is longitudinally aligned with the actual welding location. During the welding operation the first link moves with the workpiece until it is intersected by the third laser beam. Because of the fixed spatial relationship between the second and third scanners, the number of links disposed between the scanners is known. As such, either of the second and third scanners can be configured to count the number of links intersected by their respective laser beams as the workpiece is rotated to determine when the first link is being intersected by the third laser beam. Because the chain is coupled to the workpiece in a manner that prevents it from slipping while the welding operation is underway, the second scanner and / or the third scanner can accurately determine the angular position of the groove and the rotational speed of the workpiece. Thus, the occurrence of weld defects associated with workpiece slippage are obviated.

[0017] As discussed above, the second scanner is used to determine the position of the first link at the scan location of the second scanner. Likewise, the third scanner uses reflected light from the third laser beam to obtain a position of the first link at the scan location of the third scanner. The third scanner itself, or in conjunction with other data generating and / or processing equipment, generates third electronic data associated with the position of the first link at the scan location of the third scanner. Once generated, the third electronic data is stored in the electronic storage device along with the second electronic data.

[0018] As previously discussed, because the workpiece can experience longitudinal / axial movement and / or a change in elevation while the workpiece is rotated, the position of the first link correspondingly changes as it is rotated from the scan location of the second scanner to the scan location of the third scanner. When this occurs, the second and third electronic data are processed to calculate a difference in position of the first link and third electronic data is generated that is related to the difference in position. The first electronic data and the third electronic data are thereafter processed to generate fourth electronic data representative of a second groove profile that is a modified version of the first groove profile. In particular, the second groove profile is shifted in position with respect to the first groove profile commensurate with the calculated difference in position of the first link. The fourth electronic data is thereafter used to generate electronic instructions deliverable to the positioning system of the welding head to properly position the welding head in alignment with the groove in the workpiece. One or more processors may be employed to process the electronic data and to the generate the electronic instructions.

[0019] The foregoing process is carried out with respect to each link in the chain as the workpiece is rotated during the welding process. As such, the position of the welding head can be intermittently or continuously altered to maintain an alignment with the groove. According to some implementations each of the welding head, first scanner, second scanner and third scanner have a fixed spatial relationship with respect to one another and may be supported in or on a common carrier.

[0020] According to some implementations a method for positioning a welding head with respect to a groove in a rotating circular workpiece involves coupling a chain formed by links to an outer surface of the workpiece so that the chain at least partially circumscribes the workpiece and so that no relative movement occurs between the workpiece and the chain during the arc welding process. The chain is longitudinally spaced apart from the groove a sufficient distance to prevent slag and other welding debris (such as flux) from imposing on the chain during the welding process. The method further includes emitting from a first scanner a first laser beam towards the groove and capturing reflected light from the first laser beam to obtain a first groove profile. Simultaneously with emitting the first laser beam, emitting from a second scanner a second laser beam towards a first link of the chain and capturing reflected light from the second laser beam to obtain a position of the first link with respect to the groove at a first location of the workpiece. The first location being located forward of the welding head with respect to a welding direction. The second laser beam being coplanar with the first laser beam and optionally overlapping the second laser beam along a portion of a topline of the outer surface of the workpiece.

[0021] Thereafter, first electronic data associated with the obtained first groove profile and second electronic data associated with the position of the first link with respect to the groove at the first location of the workpiece is stored in a memory device for later use.

[0022] During the welding process the workpiece continues to rotate until the first link is intersected by a third laser beam emitted by a third scanner located rearward of the second scanner. The third laser beam is preferably longitudinally aligned with the actual welding location and is emitted towards a second location of the workpiece rearward of the second scanner. Captured reflected light from the third laser beam is then used to obtain a position of the first link with respect to the second location of the workpiece. As discussed above, because the workpiece can experience longitudinal / axial movement and / or a change in elevation while the workpiece is rotated, the position of the first link correspondingly changes as it is rotated from the scan location of the second scanner to the scan location of the third scanner. When this occurs, the second and third electronic data are processed to calculate a difference in position of the first link and third electronic data is generated that is related to the difference in position. The first electronic data and the third electronic data are thereafter processed to generate fourth electronic data representative of a second groove profile that is a modified version of the first groove profile. In particular, the second groove profile is shifted in position with respect to the first groove profile commensurate with the calculated difference in position of the first link. The fourth electronic data is thereafter used to generate electronic instructions deliverable to the positioning system of the welding head to properly position the welding head in alignment with the groove in the workpiece.

[0023] These and other advantages and features will become apparent in view of the figures and the detailed disclosure.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows a prior art system for monitoring the position of rotating first and second cylindrical structures while being welded together.

[0026] FIG. 2 shows a groove tracking system according to one implementation.

[0027] FIG. 3 illustrates a section of a workpiece showing a number of chain links being positioned between the second and third laser beams of the respective second and third scanners.

[0028] FIG. 4 shows a cross-sectional view of a workpiece at the location of a groove positioned between first and second cylindrical structures. Also shown are the first and second laser beams respectively impinging on the groove and on a link of the chain. FIG. 5 illustrates a first groove profile produced by data generated by the first and second scanners, the first groove profile being expressed with respect to the location of the chain link LI that is intersected by the second laser beam.

[0029] FIG. 6A shows a section of the chain that partially or fully circumscribes the cylindrical outer surface of the workpiece.

[0030] FIG. 6B shows a top view of the chain depicted in FIG. 6A.

[0031] FIG. 7 is a top view of the workpiece shown in first and second axial positions that represents a shift in axial position of the workpiece during the arc welding operation.

[0032] FIG. 8 shows an axial shift in the location of the welding head that occurs as a result of the detected change in axial position of the chain link LI.

[0033] FIG. 9 shows the welding head and first, second and third scanners supported by a common carrier.

[0034] FIG. 10 shows a graphical representation of a change in axial position of link LI after being rotated from the location of the first laser beam to the location of the second laser beam.

[0035] FIG. 11 shows a graphical representation of a change in axial position and elevation of link LI after being rotated from the location of the first laser beam to the location of the second laser beam.

[0036] FIG. 12 is a schematic of a control system for positioning the welding head with respect to the groove in the workpiece.

[0037] FIGS. 13A-B respectively show front side and back sides of a flexible metering device according to one implementation.

[0038] FIGS. 14A depicts a sinusoidal / curved weld that may be formed by the methods and apparatus disclosed herein. FIGS. 14B depicts a zigzag weld that may be formed by the methods and apparatus disclosed herein.

[0039] DETAILED DESCRIPTION

[0040] Systems and methods are provided for positioning a welding head 70 with respect to a groove / gap 60 in a rotating circular workpiece 30 during an arc welding process to ensure that the arc welding occurs inside the groove / gap in spite of axial and / or elevation movement of the workpiece during the welding process, and in spite of slippage occurring between the workpiece and a drive roller (at least one of rollers 40 and 50) that imparts rotational movement to the workpiece during the welding process. According to some implementations the workpiece 30 comprises first and second cylindrical structures 10 and 20 that are joined together by the arc welding process.

[0041] According to some implementations a system 100 is provided that enables the welding head 70 to be accurately positioned with respect to a groove / gap 60 located between the first and second cylindrical structures 10 and 20 while the workpiece is rotated. According to some implementations, the system includes a chain 110 and first, second and third scanners 120, 130 and 140 that are strategically situated and function together to ultimately generate data that is transmissible to a welding head positioning system 70 (e.g. robotic arm, gantry, etc.) where it is used to guide the welding head with respect to the groove / gap 60 while the workpiece is being rotated.

[0042] As shown in FIGS. 2, 3 and 6A-B, the chain 110 is formed by a plurality of links 111 and is positioned on an outer circumferential surface 33 of one of the first and second cylindrical structures 10 and 20. In the example of FIG. 2, chain 110 at least partially circumscribes and is tightened about the second cylindrical structure 20 so that no relative movement occurs between the chain and the second cylindrical structure during the arc welding process. Preferably, the chain is longitudinally spaced apart from the groove / gap 60 a sufficient distance to prevent slag and other welding debris (such as flux) from imposing on the chain during the welding process. According to some implementations a longitudinal distance between the chain 111 and groove 60 is at least 100 millimeters, and preferable between 120 to 180 millimeters. The first, second and third scanners each includes a laser light source 121, 131, 141 and an image capture device 122, 132, 142. Each of the first, second and third scanners use laser triangulation to obtain target profiles where a band of light is emitted onto the target and the reflected light is received using, for example, a 2D CMOS to determine the height / depth at numerous points across the width of the laser beams. According to some implementations the laser emitter and image capturing device of each of the respective first, second and third scanners are radially separated by 20 degrees to 30 degrees.

[0043] The first scanner 120 is configured to emit a first laser beam 126 towards the groove 60 and is further configured to capture reflected light 127 in the image capture device 122 to obtain a first groove profile 160 like that shown in FIG. 5. The first groove profile at least includes information regarding width dimensions “w” of the groove 60, and preferably also includes information regarding depth dimensions “d” of the groove 60. According to some implementations the image capture device 122 itself generates the first groove profile 160. However, according to other implementations, the first groove profile 160 is generated through the use of additional image processing equipment that receives data from the image capture device 122. The location of the first scanner 120 and the longitudinal width “w2” of the first laser beam 126 is set to ensure a full width of the groove 60 is captured during an entirety of the welding process.

[0044] The second scanner 130 is configured to emit a second laser beam 136 towards a first link “LI” of the chain 110 and to capture reflected light 137 from the second laser beam to obtain a position of the first link with respect to the groove 60. The scanning location of the first link “LI” is always forward of the welding location with respect to the welding direction 101. (Note that the welding direction 101 is opposite the rotational direction 103 of the workpiece 30.) As shown in FIG. 2, the first and second scanners 120 and 130 are located and oriented such that their emitted laser beams 126 and 136 are coplanar. According to some implementations the first and second laser beams partially overlap as shown in FIGS. 2-4, the overlapping occurring along a top line 25 of the workpiece (e.g. along an outer surface of the workpiece). The first and second scanners themselves, or in conjunction with other data generating and / or processing equipment, generate first electronic data associated with the obtained first groove profile and second electronic data associated with the position of the first link with respect to the groove. Once generated, the first and second electronic data is stored in an electronic storage device / memory 420 for later use.

[0045] According to some implementations the first and second scanners repeatedly emit the respective first and second laser beams at least 100 times per second. According to some implementations the first and second scanners repeatedly emit the respective first and second laser beams 100 to 120 times per second.

[0046] According to some implementations the third scanner repeatedly emits the third laser beam at least 100 times per second. According to some implementations the third scanner repeatedly emits the third laser beam between 100 to 160 times per second.

[0047] The third scanner 140 is positioned with respect to the second scanner 130 so that the third laser beam 146 is spaced a fix distance rearward of the second laser beam 136 with respect to the welding direction, and is configured to emit the third laser beam 146 towards the chain 110 as the workpiece is rotated. According to some implementations the distance d2 between the second laser beam 136 and third laser beam 146 is at least 100 millimeters, and preferably from 120 to 150 millimeters. The emitted third laser beam 146 is at least substantially longitudinally aligned with the actual welding location. As explained above, the welding location is at a location where the end portions of one or more electrodes 71 reside, which in the present case is a location inside the groove 60. The one or more electrodes 71 are typically oriented perpendicular to the workpiece. According to some implementations where the welding is carried out by more than one electrode, the weld location can be determined to be a location in the middle or middle region of the multiple electrodes. During the welding operation the first link “LI” moves / rotates with the workpiece 30 until it is intersected by the third laser beam 146. Because of the fixed spatial relationship between the second and third laser beams, the number of links disposed between them is known. As such, either of the second and third scanners can be configured to count the number of links intersected by their respective laser beams as the workpiece is rotated to determine when the first link “LI” is being intersected by the third laser beam.

[0048] Because the chain 110 is coupled to the workpiece 30 in a manner that prevents it from slipping while the welding operation is underway, the second scanner 130 and / or the third scanner 140 can accurately determine the angular position of the groove 60 and the rotational speed of the workpiece by counting the chain links 111 as discussed above. As such, the occurrence of weld defects associated with workpiece slippage are prevented.

[0049] As discussed above, the second scanner 130 is used to determine the position of the first link “LI” at the scan location of the second scanner. Likewise, the third scanner 140 uses reflected light 147 from the third laser beam 146 to obtain a position of the first link at the scan location of the third scanner. The third scanner itself, or in conjunction with other data generating and / or processing equipment, generates third electronic data associated with the position of the first link at the scan location of the third scanner. Once generated, the third electronic data is stored in the electronic storage / memory device 420.

[0050] As previously discussed, because the workpiece can experience longitudinal / axial movement and / or a change in elevation while the workpiece is rotated, the position of the first link “LI” correspondingly changes as it is rotated from the scan location of the second scanner to the scan location of the third scanner. As an example, FIG. 7 represents only a change in longitudinal position Ax of first link “LI” as the workpiece 30 is rotated from a first position Pl (where it is intersected by the second laser beam 136) to a second position P2 (where it is intersected by the third laser beam 146). FIG. 10 shows a graphical representation of the change in longitudinal position of the first link with “LI” representing the first link when the workpiece 30 is in position Pl and “LT” representing the first link when the workpiece 30 is in position P2. FIG. 11 is a graphical representation of a change in both longitudinal position (Ax) and elevation (Ay) of the first link, wherein “LI” represents the first link when the workpiece 30 is in position Pl and “LT” represents the first link when the workpiece 30 is in position P2. When a change of position of the first link occurs, the second and third electronic data stored in memory 420 are processed by a microprocessor 410 to calculate a difference in position of the first link and to generate third electronic data corresponding to the difference in position. The first electronic data and the third electronic data are thereafter processed by the microprocessor 410 (which implements one or more program codes 415 to generate fourth electronic data representative of a second groove profile that is a modified version of the first groove profile 160. In particular, the second groove profile is shifted in position with respect to the first groove profile commensurate with the calculated difference in position of the first link “LI”. The fourth electronic data is thereafter used to generate electronic instructions deliverable to a controller of the welding head positioning system 80 to properly position the welding head in alignment with the groove 60 in the workpiece 30. It is important to note that one or more processors in conjunction with one or more memory devices may be employed to process the electronic data and to generate the electronic instructions.

[0051] In the example above the first chain link “LI” experiences only a longitudinal change in position when it is rotated with the workpiece 30 between the first and second rotational positions Pl and P2. FIG. 8 depicts a corresponding change in position of the welding head 70 brought about by the instructions received in the controller of the welding head positioning system 80.

[0052] As shown in FIG. 9, according to some implementations each of the welding head 70, first scanner 120, second scanner 130 and third scanner 140 have a fixed spatial relationship with respect to one another and may be supported in or on a common carrier 102 that is supported and guided by positioning system 80.

[0053] FIG. 12 illustrates a system 500 for electronically storing and processing the above-described positional information for the purpose of accurately determining the location of the groove 60 when the workpiece is in the second rotational position. By virtue of knowing the actual position of the groove 60 as the workpiece 30 is rotated, instructions generated by processor 410 can be sent to the controller 510 of the welding head positioning system to properly and continuously align the welding head 70 and / or welding electrodes 71 with the groove 60 during the welding process. As illustrated in FIG. 12, the system 500 may comprise one or more processors 410, a memory 420 coupled to at least one of the processors 410, and a set of program instructions 415 stored in the memory and executable by at least one of the processors 410 to generate and to send positioning instructions to the welding head positioning system controller 510 where the positioning instructions are carried out to properly align the welding head 70 and / or welding electrodes 71 with the groove 60.

[0054] FIGS. 6A-B depict the construction of a portion of the chain 110 according to one implementation. The links 111 are formed by pairs of inner plates 112 and outer plates 113, and rollers 114 disposed between the inner plates. The chain is held together by pins 115 (also called rivets) that extend through openings in the inner plates 112, outer plates 113 and rollers 114. As best shown in FIG. 6B, the rollers 114 are separated by through openings 116. As explained above, the second and / or third scanners 130 and 140 can be configured to count the number of links 111 intersected by their respective laser beams as the workpiece is rotated to determine when the first link “LI” is being intersected by the third laser beam 146. According to some implementations the counting is achieved through the detection of the through openings 116 in the chain 110. In the example of FIGS. 6A-B, each detection of a through opening 114 by the second and / or third scanner represents a detection of a link.

[0055] In determining a spatial relationship between the chain 110 and a part of the groove 60, the reference point of the chain may a centerline 117 of the chain 110 or an edge of the chain (e.g. the edge 13a of outer links 13) and the reference point of the groove 60 may be a center or edge thereof. When the reference point of the chain is its centerline 117, according to some implementations the second and / or third scanner 130 and 140 are configured to detect the edges of either the inner and outer plates 112 and 113 and the processor 410 is configured to calculate the location of the centerline based on said edge detection.

[0056] Throughout this disclosure, a chain is used in conjunction with three scanners to track an actual location of a groove in a workpiece during a welding process. It is appreciated, however, that an apparatus other than a chain may be used. For example, any flexible metering device having scannable features that can be used to accurately track the rotation of the workpiece may be used. Like the chain 110, the flexible metering device must be couplable to the workpiece so that no relative movement occurs between them during the arc welding process. According to one such implementation as shown in FIGS. 13A-B, the flexible metering device 210 includes a front side 211 that includes scannable features 212 that are arranged facing the second and third scanners during the welding process. The scannable features may be two dimensional objects (e.g. lines, numbers, or other printed or inscribed indicia) or three dimensional objects (e.g. through openings, protrusions, etc.). According to some implementations, the backside 214 of the flexible metering device 210 includes a slip resistant surface 215 that is configured to press against the outer surface of the workpiece 30. The backside 214 may alternatively include barbs or other types of slip resistant features to achieve the same purpose.

[0057] According to some implementations a method for positioning a welding head with respect to a groove in a rotating circular workpiece 30 involves coupling a chain 110 formed by links 111 to an outer surface 33 of the workpiece so that the chain at least partially circumscribes the workpiece and so that no relative movement occurs between the workpiece and the chain during the arc welding process. The chain 110 is longitudinally spaced apart from the groove 60 a sufficient distance to prevent slag and other welding debris (such as flux) from imposing on the chain during the welding process. The method further includes emitting from a first scanner 120 a first laser beam 126 towards the groove 60 and capturing reflected light 128 from the first laser beam to obtain a first groove profile 160. Simultaneously with emitting the first laser beam 126, emitting from a second scanner 130 a second laser beam 136 towards a first link “LI” of the chain 110 and capturing reflected light 138 from the second laser beam to obtain a position of the first link with respect to the groove 60 at a first rotational position (shown as Pl in FIG. 7) of the workpiece 30. The first rotational position is located forward of the welding head 70 with respect to the welding direction 101. The second laser beam 136 being coplanar with the first laser beam 126 and optionally overlapping the second laser beam along a portion of a topline 25 of the outer surface 33 of the workpiece 30.

[0058] Thereafter, first electronic data associated with the obtained first groove profile 160 and second electronic data associated with the position of the first link “LI” with respect to the groove 60 at the first rotational position of the workpiece is stored in memory 420 for later use. During the welding process the workpiece continues to rotate until the first link “LI” is intersected by a third laser beam 146 emitted by a third scanner 140 located rearward of the second scanner 130. The third laser beam is preferably longitudinally aligned with the actual welding location and is emitted towards a second rotational position of the workpiece (shown as P2 in FIG. 7) rearward of the second scanner 130. Captured reflected light 148 from the third laser beam 146 is then used to obtain the position of the first link “LI” with respect to the second rotational position of the workpiece.

[0059] As discussed above, because the workpiece can experience longitudinal / axial movement (Ax) and / or a change in elevation (Az) while the workpiece is rotated, the position of the first link correspondingly changes as it is rotated from the scan location of the second scanner 130 to the scan location of the third scanner 140. When this occurs, the second and third electronic data are processed to calculate a difference in position of the first link and third electronic data is generated that is related to the difference in position. The first electronic data and the third electronic data are thereafter processed to generate fourth electronic data representative of a second groove profile that is a modified version of the first groove profile. In particular, the second groove profile is shifted in position with respect to the first groove profile commensurate with the calculated difference in position of the first link. The fourth electronic data is thereafter used to generate electronic instructions deliverable to a controller 510 of the positioning system 80 of the welding head 70 to properly position the welding head in alignment with the groove 60 in the workpiece 30.

[0060] According to some implementations the entire length of the chain 111 or flexible metering device 210 are spaced apart from the groove 60 by a fixed distance around the entire circumference of the workpiece 30. However, other spatial relationships between the chain 11 / flexible metering device 210 and groove 60 are also contemplated. For example, when it is desirable for the weld 180 to have a curved shape as shown in FIG. 14A or zigzag shape as shown in FIG. 14B, the chain 111 or flexible metering device 210 may take a path about the circumference of the workpiece 30 that corresponds to the desired path of the weld. That is, the chain or flexible metering device may have a curved shape, zigzag shape, or any other shape that corresponds to a desired weld pattern. While the present disclosure makes reference to certain implementations, numerous modifications, alterations and changes to the described implementations are possible without departing from the sphere and scope of the present disclosure, as defined. Accordingly, it is intended that the present disclosure not be limited to the described implementations.

Claims

CLAIMS1. A method for positioning a welding head with respect to a groove in a rotating circular workpiece during an arc welding process, the workpiece having a length and a longitudinal central axis, the method comprising: coupling a chain formed by links to an outer surface of the workpiece so that the chain at least partially circumscribes the workpiece and so that no relative movement occurs between the workpiece and the chain during the arc welding process, the chain being longitudinally spaced apart from the groove; at a first rotational position of the workpiece simultaneously scanning the groove and a first link of the chain respectively using first and second scanners that respectively emit first and second coplanar laser beams onto the groove and onto the first link, the scanning of the groove generating first electronic data representative of a first groove profile, the scanning of the first link generating second electronic data representative of a position of the first link while the workpiece is in the first rotational position; rotating the workpiece to a second rotational position that corresponds to an arc welding location and scanning the first link using a third scanner that emits a third laser beam onto the first link to obtain a position of the first link while the workpiece is in the second rotational position, the scanning of the first link generating third electronic data representative of the position of the first link while the workpiece is in the second rotational position; comparing the third electronic data with the second electronic data to calculate a difference in position of the first link between the first and second rotational positions of the workpiece and generating fourth electronic data representative of the difference in position; using the first electronic data and fourth electronic data to generate fifth electronic data representative of a second groove profile that is offset from the first groove profile by an amount equivalent to the calculated difference in position of the first link; and processing the fifth electronic data to generate electronic instructions deliverable to a controller of a positioning system of the welding head to position the welding head so that the arc welding location occurs inside the groove.

2. The method according to claim 1, wherein the first and second laser beams overlap along a portion of a topline of the outer surface of the workpiece.

3. The method according to any of the preceding claims, wherein the first and second electronic data collectively represent width and depth dimensions of the groove and a longitudinal distance between a part of the scanned first link and a part of the scanned groove.

4. The method according to any of the preceding claims, wherein the fourth electronic data representative of the difference in position of the first link at least partially represents a change in longitudinal position (Ax) of the first link.

5. The method according to any of the preceding claims, wherein the fourth electronic data representative of the difference in position of the first link at least partially represents a change in elevation (Az) of the first link.

6. The method according to claim 3, wherein the part of the first link is a centerline or edge of the link.

7. The method according to claim 6, wherein the part of the groove is a centerline or edge of the groove.

8. The method according to any of the preceding claims, wherein each of the first, second and third laser beams has a fixed spatial relationship with the welding head.

9. The method according to any of the preceding claims, wherein the third laser beam is substantially longitudinally aligned with the arc welding location.

10. The method according to any of the preceding claims, wherein a centerline of the chain is spaced part from a centerline of the groove by a longitudinal distance of 100 to 200 millimeters.

11. The method according to any of the preceding claims, wherein the second and third laser beams are circumferentially spaced apart from one another by a distance of 100 to 150 millimeters.

12. The method according to any of the preceding claims, further comprising measuring a time for the first link to travel between the second laser beam to the third laser beam, and using the measured time to determine a rotational speed of the chain.

13. The method according to any of the preceding claims, wherein each of the first, second and third scanners comprises a laser emitter and an image capturing device, the laser emitter of each of the first, second and third scanners respectively emits the first, second and third laser beams and the image capturing device of each of the first, second and third scanners respectively captures light reflected from the first, second and third laser beams.

14. The method according to claim 13, wherein the laser emitter and image capturing device of each of the respective first, second and third scanners are radially separated by 20 degrees to 30 degrees.

15. The method according to any of the preceding claims, wherein the first and second scanners repeatedly emit the respective first and second laser beams at least 100 times per second.

16. The method according to any of the preceding claims, wherein the third scanner repeatedly emits the third laser beam at least 100 times per second.

17. A method for positioning a welding head with respect to a groove in a rotating circular workpiece during an arc welding process, the workpiece having a length and a longitudinal central axis, the method comprising: coupling a chain formed by links to an outer surface of the workpiece so that the chain at least partially circumscribes the workpiece and so that no relative movement occurs between the workpiece and the chain during the arc welding process, the chain being longitudinally spaced apart from the groove; emitting from a first scanner a first laser beam towards the groove and capturing reflected light from the first laser beam to obtain a first groove profile;simultaneously with emitting the first laser beam, emitting from a second scanner a second laser beam towards a first link of the chain and capturing reflected light from the second laser beam to obtain a position of the first link with respect to the groove at a first rotational position of the workpiece, the first rotational position being rotationally forward of the arc welding location, the second laser beam being coplanar with the first laser beam and overlapping the second laser beam along a portion of a topline of the outer surface of the workpiece; electronically storing first electronic data representative of the obtained first groove profile and second electronic data representative of the position of the first link with respect to the groove at the first rotational position of the workpiece; rotating the workpiece to a second rotational position that corresponds to the welding location, and at the second rotational position emitting from a third scanner a third laser beam towards the first link of the chain and capturing reflected light from the third laser beam to obtain a position of the first link at the second rotational position of the workpiece; calculating a difference in position of the first link between the first and second rotational positions of the workpiece and generating third electronic data representative of the difference in position; using the first electronic data and third electronic data to generate fourth electronic data representative of a second groove profile that is offset from the first groove profile by an amount equivalent to the calculated difference in position of the first link; and processing the fourth electronic data to generate electronic instructions deliverable to a positioning system of the welding head to position the welding head so that the arc welding location occurs inside the groove.

18. The method according to claim 17, wherein each of the first, second and third laser beams has a fixed spatial relationship with the welding head.

19. The method according to any of the preceding claims, wherein the chain is longitudinally spaced part from the groove by a distance of 100 to 200 millimeters.

20. The method according to any of the preceding claims, wherein the second and third laser beams are circumferentially spaced apart from one another by a distance of 100 to 150 millimeters.

21. The method according to any of the preceding claims, further comprising measuring a time for the first link to travel between the second laser beam to the third laser beam, and using the measured time to determine a rotational speed of the chain.

22. The method according to any of the preceding claims, wherein each of the first, second and third scanners comprises a laser emitter and an image capturing device that respectively captures light reflected from the first, second and third laser beams.

23. The method according to claim 22, wherein the laser emitter and image capturing device of each of the respective first, second and third scanners are radially separated by 20 degrees to 30 degrees.

24. The method according to any of the preceding claims, wherein the first and second scanners repeatedly emit the respective first and second laser beams at least 100 times per second.

25. The method according to any of the preceding claims, wherein the third scanner repeatedly emits the third laser beam at least 100 times per second.

26. The method according to any of the preceding claims, wherein the longitudinal distance between the link and the groove is measured between a centerline of the first link and a centerline of the groove.

27. The method according to any of claims 16-25, wherein the longitudinal distance between the link and the groove is measured between an edge of the firsts link and an edge of the groove.

28. A system for positioning a welding head with respect to a groove in a rotating circular workpiece during an arc welding process, the system comprising: a chain coupled about the workpiece;a first scanner configured to scan the groove at a first rotational location of the workpiece through the use of a first laser emitter and a first image capturing device, the first laser emitter being configured to produce a planar first laser beam; a second scanner configured to scan a link of the chain through the use of a second laser emitter and a second image capturing device, the second laser emitter being configured to produce a planar second laser beam that is coplanar with the planar first laser beam; and a third scanner configured to scan the chain link at a second rotational position of the workpiece through the use of a third laser emitter and a third image capturing device, the third laser emitter being configured to emit a third planar laser beam that is aligned with a designated welding location, the second rotational position of the workpiece being rearward of the first rotational position with respect a welding direction.

29. The system according to claim 28, wherein the first and second scanners are configured to simultaneously scan the respective groove and chain link.

30. The system according to any of claims 28-29, wherein the first and second scanners are configured to respectively emit the planar first laser beam and planar second laser beam so that a portion of the planar second laser beam overlaps with a portion of the planar first laser beam.

31. The system according to claim 28, wherein the first scanner is configured to generate first electronic data representative of a profile of the groove at the first rotational position and the second scanner is configured to generate second electronic data representative of a position of the first link while the workpiece is in the first rotational position.

32. The system according to claim 31, wherein the third scanner is configured to generate third electronic data representative of the position of the chain link while the workpiece is in the second rotational position.

33. The system according to claim 32, further comprising a processing system that is configured to compare the third electronic data with the second electronic data to calculate a difference inposition of the chain link between the first and second rotational positions of the workpiece and generating fourth electronic data representative of the difference in position.

34. The system according to claim 33, wherein the processing system is configured to process the first electronic data and fourth electronic data to generate fifth electronic data representative of a second groove profile that is offset from the first groove profile by an amount equivalent to the calculated difference in position of the chain link.

35. The system according to claim 34, wherein the processing system is configured to process the fifth electronic data to generate electronic instructions deliverable to a controller of a positioning system of the welding head.

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