Laser centering of robotic arm

In a system and method of working tubes coupled to a tubesheet having a number of holes, wherein each hole in fluid communication with one of the tubes, an end-effector is positioned by a robot in coarse or rough alignment with a first hole in the tubesheet. Via lasers positioned on the end-effector, laser spots are formed on a surface of the tubesheet adjacent the first hole. The laser spots are detected by a camera and the alignment of the end-effector relative to the first hole in the tubesheet is refined via the robot based on the detected pattern of laser spots. The tool is then moved into the tube that is in fluid communication with the first hole in the tubesheet to work on (inspect, plug, sleeve or weld) the tube.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to working of tubes coupled to a tubesheet and, more particularly, to the use of robotics and light sources for such working.

Description of Related Art

In nuclear steam generator and balance of plant eddy current inspections, robots are often used to position a tool in alignment with one or more given tubes, one-at-a-time, in a tubesheet. The robot has an end-effector that supports the tool in position to be fed into holes in the tubesheet. The tool must be positioned directly in alignment with the tube to be inspected in order for the tool to run smoothly through the hole in a tubesheet and into the tube in fluid communication with the hole in the tubesheet.

Typically, a camera mounted on the end-effector is utilized to monitor the alignment of the tool to a particular hole in the tubesheet. Because the viewing axis of the camera is mounted transverse to the axis of the tubesheet and, hence, the hole desired to be aligned with the tool, an image of the end of the tool and the hole being aligned therewith suffers from a condition known as parallax which is the apparent displacement of an observed object due to a change in the position of the observer.

Because of this parallax, it is not uncommon to misalign the tool and a hole in a tubesheet, whereupon the tool cannot be successfully inserted into the desired hole in the tubesheet because of this misalignment. Because the insertion of the tool into each tube is often controlled by a motorized drive, there is a chance when the tool is misaligned with a hole in the tubesheet that the motorized drive will push the tool into the face of the tubesheet, instead of the hole thereby potentially damaging the tool.

SUMMARY OF THE INVENTION

Disclosed herein is method of working tubes coupled to a tubesheet having a plurality of holes, each hole in fluid communication with one of the tubes. The method includes: (a) providing a robot positioned in operable relation to the tubesheet, a guide-tube supported by the robot, a tool supported by the guide-tube and movable relative to the guide-tube, a camera coupled to the robot, and a plurality of lasers positioned around an exterior of the guide-tube and operable to output a plurality of laser beams toward the tubesheet; (b) via the robot, positioning the guide-tube in coarse alignment with a first hole in the tubesheet; (c) via the camera, detecting a pattern of laser spots formed by the laser beams on a surface of the tubesheet adjacent the first hole in the tubesheet; (d) via the robot, refining the alignment of the guide-tube in alignment with the first hole in the tubesheet based on the detected pattern of laser spots formed on the surface of the tubesheet; and (e) moving the tool into the tube that is in fluid communication with the first hole in the tubesheet.

The method can further include: (f) withdrawing the tool from the tube that is in fluid communication with the first hole in the tubesheet.

The method can further include repeating steps (b)-(f) for at least one other hole of the tubesheet.

The positioning in step (b) can be with or without reference to the laser spots formed by the laser beams on the surface of the tubesheet.

Following step (d), the guide-tube, the tool, the first hole, and the tube that is in fluid communication with the first hole can be positioned coaxially or substantially coaxially.

The robot can have two axes of rotation and/or a linear axis of motion.

The camera has a viewing axis that is non-parallel with an axis of the first hole.

The pattern of laser spots can be an arc or a ring of laser spots adjacent the first hole. Step (d) can include refining the alignment of the guide-tube in alignment with the first hole in the tubesheet based on a symmetry of the arc or a ring of laser spots around the first hole.

Also disclosed is a method of working tubes coupled to a tubesheet having a plurality of holes, each hole in fluid communication with one of the tubes. The method includes: (a) positioning a tool in alignment with a first hole in the tubesheet; (b) projecting a light pattern onto a surface of the tubesheet adjacent an outer boundary of the first hole; and (c) moving the tool into the tube that is in fluid communication with the first hole in the tubesheet based on the projected light path.

The method can further include, between steps (b) and (c), the step of: (b2) refining the alignment of the tool in alignment with the first hole in the tubesheet based on a symmetry of the light pattern projected onto the surface of the tubesheet about the first hole.

The method can further include: (d) withdrawing the tool from the tube that is in fluid communication with the first hole in the tubesheet based on the projected light pattern.

Refining the alignment of the tool with the first hole in the tubesheet can further include turning the light pattern on and off.

The method can further include repeating any combination of steps (a), (b), (b2), (c) or (d) for a plurality of other holes of the tubesheet.

The light pattern can define an arc or a ring of light. The method can further include refining the alignment of the tool in alignment with a first hole in the tubesheet based on the light pattern projected onto the surface of the tubesheet. Refining the alignment can include refining the symmetry of the arc or ring of light about the first hole.

The light pattern can be one of the following: a plurality of spots of light, a cross hair, or a circle.

The plurality of spots of light can include light spots of different colors.

The method can further include determining whether the tool is out of the tube or in the tube based on being able to observe the entire light pattern or not, respectively.

Lastly, disclosed herein is a system for working tubes coupled to a tubesheet having a plurality of holes, each hole in fluid communication with one of the tubes. The system comprises: a multi-axis robot positioned in operable relation to the tubesheet; an end-effector supported by the robot; a tool supported by the end-effector and movable relative to the end-effector; a camera supported by the robot with an axis of the camera transverse to an axis of a hole in the tubesheet; and one or more lasers supported by the end-effector and operable to output laser beams in a direction of the tubesheet.

The one or more laser beams can be output parallel with the axis of the hole.

The tool can be positioned inside a guide-tube.

The system can include the one or more lasers are positioned about an exterior of the guide-tube.

The system can include a controller operative for controlling: movement of the robot to position the tool in alignment with each of a plurality of holes, one-at-a-time, based on camera images of a pattern of laser light formed by the projection of the one or more laser beams on the tubesheet adjacent the hole; and movement of the tool into and out of the tube in fluid communication with the hole.

The controller can be operative under the control of a control software program to enable the movement of the robot, the movement of the tool, or both to be controlled under manual, user control, automatic control, or a combination of manual control and automatic control.

The tool can be an eddy current probe.

The controller can be operative for turning the one or more lasers on and off and for positioning the tool based on first and second camera images acquired with the one or more lasers on and off, respectively.

The method of claim10, wherein refining the alignment of the tool with the first hole in the tubesheet further includes turning the light pattern on and off.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with reference to the accompanying figures where like reference numbers correspond to like elements.

With reference toFIGS. 1A-C, an industrial liquid-to-liquid heat exchanger2found in many industrial applications, such as, without limitation, a nuclear steam generation power plant, includes an elongated cylindrical housing4with end caps6and8coupled to opposite ends of housing4. Disposed within housing4is an internal assembly A that includes a plurality of heat exchange tubes10that are held in spaced relation by tubesheets12and14at opposite ends of tubes10and optionally one or more support plates16positioned between tubesheets12and14.

Each tubesheet12and14includes a plurality of holes18that extend therethrough. Each hole18is in fluid communication with one of the tubes10. Tubesheets12and14include flanges20and22that are configured to mate with flanges24and26of end caps6and8, respectively, in the assembled heat exchanger2. Suitable fasteners (not numbered) are utilized to secure flanges20and24together and to secure flanges22and26together.

In the assembled heat exchanger shown inFIG. 1A, the interiors of end caps6and8are in fluid communication via tubes10of internal assembly A disposed within the interior of housing4. Suitable fluid-tight seals can be disposed between assembled flanges20and24and assembled flanges20and22to maintain the fluid-tight integrity of end caps4and10to housing4, and avoid fluid inside of end cap6or end cap8from seeping into the interior of housing4, or vice versa.

End caps6and8include ports28and30, respectively. In use, fluid entering one of port28and30passes exclusively through holes18in tubesheets12and14and tubes10disposed in housing4and exits the other of port28and30.

Housing4includes ports32and34at opposite ends thereof. In use, fluid introduced into one of ports32and34passes through the interior of housing4contacting the exterior of tubes10disposed in housing4and exits the other of port32and34.

Typically, process fluid, such as a heated liquid, gas, steam, and the like (or cooling fluid) flows through tubes10disposed in the interior of housing4between end caps6and8, while cooling fluid (or process fluid) flows through the interior of heat exchanger2, in contact with the exterior of tubes10, between ports32and34. Because of the construction of housing4, process fluid and cooling fluid do not come into contact with each other as they pass through heat exchanger2.

Because of the lengths of tubes10, it is impractical to perform physical inspection of or otherwise work on said tubes. Moreover, because of the high pressures typically involved it is necessary to identify in advance of a failure whether a tube10is exhibiting a symptom indicative of an impending failure. To this end, it is well known in the art to perform non-destructive testing of such tubes via eddy current probes. Eddy current probes and the use thereof for detecting and pinpointing flaws in tubing, such as tubes10, is well known in the art and will not be described further herein for the purpose of simplicity. Hereinafter, the present invention will be described in connection with the use of an eddy current probe for performing eddy current inspection of one or more tubes10in communication with one or more holes18in tubesheet12or14. However, this is not to be construed as limiting the invention since it is envisioned that the present invention can also be utilized in connection with, without limitation, a tool which inserts a plug into the end of a tube10, a tool for cleaning the interior of a tube10, a tool for adding a sleeve to a tube10, a tool for repairing (e.g., welding) a tube10, a tool for inspecting a tube10, a tool for sleeving a tube, a tool for stabilizing a tube, and/or any other tool that can work on a tube10. Herein, “work” or “working” on a tube10means any act or action that can be performed on a tube10including, without limitation, inspection, testing, plugging, cleaning, sleeving, repairing, stabilizing, and the like.

The present invention will now be described with reference toFIGS. 2 and 3and with continuing reference toFIGS. 1A-1C.

In certain applications, it is not only desirable but necessary to perform robotic eddy current inspection of the tubes10of the internal assembly A of heat exchanger2, for example, where the fluid passing through tubes10is radioactive, such as the water used to cool nuclear reactors. In an example of a system and method for eddy current testing of tubes10of heat exchanger2, a robot36is mounted to or positioned in operative relation to tubesheet12(or tubesheet14). For the purpose of this example, it will be assumed that robot36is mounted to tubesheet12. However, this is not to be construed as limiting the invention since it is envisioned that robot36can also or alternatively be mounted to tubesheet14.

In an example, robot36is a multi-axis robot having two or more axes of motion. In the illustrated example, robot36has axes of rotation38and40and a motor driven base unit42which is rotatable about axis38, as shown by arcuate arrow45. Robot36can be position in operable relation to tubesheet12in any suitable and/or desirable manner. In an example, base unit42is coupled to tubesheet12via a base plate44and suitable hangers or fasteners. The manner in which robot is positioned on or in operable relation to tube12is not to be construed as limiting the invention.

The example robot36shown inFIG. 2also includes a motorized intermediate drive unit46that can rotate an arm48of robot36about axis40, as shown by arcuate arrow49.

As shown inFIG. 2, axis40is separated from axis38by a distance D whereupon intermediate drive unit46can be rotated by base drive unit42about axis38while, simultaneously or separately, intermediate drive unit46can rotate arm48about axis40. Finally, arm48can include a linear drive50that facilitates the movement of arm48linearly toward and away from intermediate drive unit46in the directions shown by arrow52. By way of robot36, eddy current probe testing of one or many tubes10via tubesheet12(or tubesheet14) can be accomplished in the manner described herein.

An end-effector54is coupled to the end of arm48opposite intermediate drive unit46. A guide-tube56is supported by robot36and, more specifically, by end-effector54. Guide-tube56is hollow and is configured to receive an eddy current probe58therein. In use, eddy current probe58is introduced into end60of guide-tube56and is advanced through the lumen of guide-tube56by a motorized drive62until eddy current probe58exits end64of guide-tube56for entry into a tube10in alignment with the hole18that is aligned with guide-tube56and eddy current probe58. In one example, the axes of eddy current probe58, guide-tube56, hole18, and tube10in communication with hole18are coaxial, or substantially coaxial (subject to minor variances in the tolerances thereof). However, this is not to be construed as limiting the invention.

To facilitate the alignment of guide-tube56and hole18in a way that enables eddy current probe58to be inserted into the tube10in fluid communication with hole18, a camera66is coupled to robot36, e.g., to end-effector54. Camera66is aimed at end64of guide-tube56. Because of the arrangement of eddy current probe58, guide-tube56, hole18, and the tube10in communication with hole18, the viewing axis68of camera66is offset at an angle70from the axis of guide-tube56. Because of angle70, an image acquired by camera66and displayed on a display72suffers from a condition known as parallax, namely, the apparent displacement of an observed object due to the change in position of the observer, in this case, camera66.

Because of this parallax, an image acquired by a controller74and either used thereby and/or displayed on display72for observation by a human operator cannot be accurately relied upon for ensuring that the guide-tube56is aligned with hole18and the tube10in fluid communication with hole18. In this regard, a human machine interface (HMI)75can be provided and coupled to controller74whereupon a user viewing an image acquired by camera66and displayed on display72can utilize HMI75to control robot36to move guide-tube56into alignment with hole18in a manner known in the art. Also or alternatively, controller74can be programmed to automatically align guide-tube76with hole18. Also or alternatively, it is envisioned that some combination of the programming of controller74and a user via display72and HMI75can be utilized to automatically and manually position guide-tube56in alignment with hole18. For example, it is envisioned that controller74operating under the control of a control program can cause robot36to move guide-tube76into coarse or rough alignment with one of the holes18of tubesheet12. Thereafter, via display72and HMI75, an operator can refine the alignment of guide-tube in alignment with the hole18, i.e., perform fine alignment of guide-tube56into alignment with hole18of tubesheet12.

To facilitate the accurate automated, manual, or combination of automated and manual alignment of eddy current probe58and guide-tube56to one or more holes18of tubesheet12, a laser collar76or other comparable light source can be disposed on end-effector54and, more particularly, guide-tube56, desirably adjacent end64of guide-tube56.

With reference toFIG. 4and with continuing reference to all previous figures, laser collar76includes a collar element78that includes a plurality of holes80around the outer circumference of collar76, with each hole80adapted to receive and support a laser diode82in a manner such that, when laser collar76is mounted on guide tube56, a laser beam output by each laser diode82is projected toward tubesheet12. In an example, when laser collar76is disposed on guide-tube56the laser beam output by each laser diode82is parallel or substantially parallel to a central axis84of laser collar76. Laser collar also includes a sleeve86configured to mate with collar78thereby covering the electrical connection ends88of laser diodes82.

In an example, sleeve86can include an O-ring groove90for receiving an O ring92that facilitates frictionally holding laser collar76to guide-tube56. Sleeve86can further include a cable hole94for connecting the electrical connection ends88of laser diodes82to controller74which can control the supplying or withholding of electrical power to or from laser diodes82.

In an example, laser collar76includes eight laser diodes which, when energized by electrical power provided by controller74, project eight laser beams toward the surface of tubesheet12where said laser beams interact with said surface forming light or laser spots96on said surface.

In an example, laser collar76supports laser diodes82in a manner such that when energized by electrical power from controller74, laser diodes82form a ring of laser spots96. Also or alternatively, in another example laser diodes82can be configured to form an arc of laser spots96. In an example, the symmetry of the ring or arc of laser spots96about a hole18can be utilized to fine position the axis of guide-tube56with the axis of hole18and, hence, the tube10in communication with hole18. In this regard, if the ring or arc of laser spots96(an arc of laser spots96being a subset of a ring of laser spots96) are not symmetrical about hole18, the position of guide-tube56can be moved by robot36automatically under the control of controller74and/or via an operator observing an image acquired by camera66and displayed on display72and HMI75. The process of fine positioning guide-tube56can continue until it is determined via an image acquired by camera66that the arc or ring of laser spots96is positioned symmetrically about hole18.

A method of working, e.g., without limitation, eddy current inspecting, tubes10coupled to tubesheet12having a plurality of holes18, with each hole18in fluid communication with one of the tubes10will now be described.

Initially, robot36is positioned in operable relation to tubesheet12with end-effector54and guide-tube56supported by robot36. Eddy current probe58is supported by and, more particularly, by guide-tube56and is movable relative to end-effector54and, more particularly, to guide-tube56, e.g., slidable in the interior of guide-tube56. Camera66is coupled to robot36and, more particularly, to end-effector54, and a plurality of lasers82(in an example, supported by laser collar76) is positioned on end-effector54and, more particularly, around an exterior of guide-tube56. The lasers are operable to output a plurality of laser beams toward tubesheet12.

Via robot36, end-effector54and guide-tube56are positioned in coarse alignment with a first hole18in tubesheet12. Thereafter, via camera66, a pattern of laser spots96formed by the projection of the laser beams on the surface of tubesheet12adjacent the first hole18in tubesheet12is detected. Next, via robot36, the alignment of end-effector54and, more particularly, guide-tube56in alignment with the first hole18in tubesheet12is refined based on the detected pattern of laser spots96formed on the surface of tubesheet12. More particularly, the alignment of the guide-tube56with the first hole18in tubesheet12is refined based upon the symmetry of the detected pattern of laser spots96formed on the surface of the tubesheet12. Thereafter, via motorized drive62, under the automatic or manual (via HMI75) control of controller74, eddy current probe58(shown in phantom inFIG. 3) is moved from the interior of guide-tube56into the tube10that is fluid communication with the first hole18in the tubesheet.

During working or eddy current testing of the tube10, motorized drive62is controlled to move eddy current probe58along the length of tube10during the acquisition of eddy current data by controller74. Upon completion of eddy current testing of tube10, eddy current probe58is withdrawn into guide-tube56from the tube10that is in fluid communication with the first hole18in tubesheet12.

Thereafter, as desired, the foregoing steps can be repeated for one or more other holes18of tubesheet12by way of robot36moving end-effector54and, more particularly, guide-tube56into alignment with said one or more other holes18of tubesheet12(or tubesheet14).

In an example, the step of positioning end-effector54and, more particularly, guide-tube56in coarse alignment with the each hole18can be based upon X, Y coordinates of said hole18programmed into controller74which automatically controls robot36to move end-effector54and, more particularly, guide-tube58into coarse alignment with said hole18. Thereafter, the fine alignment of end-effector54and, more particularly, guide-tube56in alignment with each hole in tubesheet12can be refined automatically by controller74using standard computer vision techniques based on an image acquired by camera66or by a human operator via HMI75and an image acquired by camera66and displayed on display72.

In a non-limiting example, prior to moving eddy current probe58into a tube10in fluid communication with a hole18in tubesheet12, the eddy current probe58, the guide-tube56, the hole18, and the tube10in fluid communication with the hole18are aligned, e.g., without limitation, coaxially or substantially coaxially, whereupon minor variances in the alignment of eddy current probe58, guide-tube56, hole18, and tube10in fluid communication with hole18do not affect the movement of eddy current probe58into the tube10that is in fluid communication with the hole18in tubesheet12.

In the illustrated embodiment, robot36has two axes of rotation and one axis of linear motion. However, this is not to be construed as limiting the invention since it is envisioned that a robot having any suitable and/or desirable number of axis or axes of rotation or axis or axes of linear motion that is capable of moving guide-tube56into alignment with any number of holes18of tubesheet12can be utilized.

In an embodiment, the pattern of laser spots96formed on the surface of tubesheet12can be an arc or a ring of laser spots about, around, or adjacent a hole18. The refining of the alignment of guide-tube56in alignment with the hole18in tubesheet12can be based upon the symmetry of the arc or ring of laser spots about, around, or adjacent the hole18. In another, more general example of eddy current inspection of tubes10coupled to tubesheet12having a plurality of holes18, with each hole18in fluid communication one of the tubes10, eddy current probe58is positioned in alignment with a hole18in tubesheet12. A plurality of spots of light96is projected onto a surface of tubesheet adjacent the hole18. Eddy current probe58is then moved into the tube10that is in fluid communication with the hole18in tubesheet12.

The alignment of eddy current probe58in alignment with the hole18in tubesheet12can be refined based on a symmetry of the spots of light96projected onto the surface of the tubesheet12about the hole18.

Upon completion of eddy current testing of the tube10, eddy current probe58can be withdrawn from the tube10that is in fluid communication with the hole18in the tubesheet12.

Any one or combination of the steps of positioning the eddy current probe, projecting the plurality of light spots, refining the alignment of the eddy current probe, moving the eddy current probe into the tube, and/or withdrawing the eddy current probe from the tube can be repeated for one or more other holes18of tubesheet12.

In an example, the spots of lights can define an arc or ring of light spots. The refining of the alignment of the eddy current probe in alignment with a hole18in tubesheet12can include refining the symmetry of the arc or ring of light spots about the hole18.

As can be seen, guide-tube56must be positioned sufficiently in alignment with the tube10to be inspected and the hole18in the tubesheet in alignment with the tube10to be inspected in order for eddy current probe58to run smoothly out of guide-tube56and into the hole18in the tubesheet in alignment with the tube10to be inspected. The position of the end64of guide-tube56is remotely monitored using camera66. The parallax of the camera view makes it difficult to determine when guide-tube56is positioned in alignment with the hole of tubesheet12and the tube10in alignment therewith.

To overcome this, laser diodes82mounted on end-effector54and, more particularly, guide-tube56are aimed at tubesheet12. When the hole18of tubesheet12is positioned relative to the laser spots96formed on the surface of tube12, end-effector54and, more particularly, guide-tube56is in operative position with the hole18and the tube10in alignment with hole18.

In addition to a discrete number of laser diodes82, other configurations of laser collar76can include line lasers to create a crosshair and/or a complete circle. Laser collar76can be used for automated or manual centering. The position of the laser spots96on the camera view of tubesheet12can be determined by blinking laser diodes82on and off and comparing two images, one with the lasers on and one with the lasers off. The parts of these two images that are different are the laser spots96. Another possibility is to use a filter to find the unique color of the reflected laser spots96. Each hole18in tubesheet12can be recognized using standard computer vision techniques. By scanning the image in the vicinity of the laser spots96it can be determined if the laser spots96are symmetric about the hole18, and thus when guide-tube56is aligned with a hole18in tubesheet12.

In an example, laser collar76can also be used to determine if eddy current probe58is in or out of a tube10. This is important since robot36must not be moved while eddy current probe58is in a tube10as this would destroy the eddy current probe58. This can be done by automatically or manually counting the laser spots96on the surface of tubesheet12. If the eddy current probe58is in a tube10, at least one of the laser spots96will be blocked by the eddy current probe58or the cable coupled thereto.

The present invention has been described with reference to exemplary non-limiting embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. For example, eddy current probe58is but one example of a tool that can be used for working tubes10coupled to a tubesheet. In this regard, other tools that can be utilized with or in a replacement of eddy current probe58include, without limitation, tools for plugging, cleaning, sleeving, repairing, inspection and/or stabilizing of tubes10coupled to tubesheet12. Accordingly, the present invention is not to be construed as limited to the tool described in the above example, namely, an eddy current probe58. Finally, some tools may not require the use of guide tube56or the use of a guide tube56is optional to work a tube10. Accordingly, with such tools, a guide tube56is either not used or the use of a guide tube56is optional. It is envisioned that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.