Abstract:
A method system and apparatus for cutting turbine bucket covers on a turbine rotor includes marking a cut path on a surface of the turbine bucket cover. The cut path includes a plurality of finite lines defined by a pair of end points, then directing a laser at each end point of each line of the cut path, storing a set of position coordinates of each end point for every line of the cut path; generating the cut path based on the respective end points; and following the cut path on the turbine bucket cover with a grinding machine attached to a robotic device; and cutting the turbine bucket cover according to the cut path.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to a robotic cutting machine. More specifically the invention is directed to a robotic cutting machine for cutting bucket covers for repair of turbine machines. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the construction of turbines (e.g., steam turbines), cover plates are employed for a variety of reasons and are generally secured to the tips of turbine buckets by peening fasteners formed on the buckets. To secure the bucket tips and cover plates to one another, solid fasteners on the bucket tips are peened into the bucket cover openings. 
         [0003]    It is sometimes necessary to remove the cover plates in order to repair the buckets or to replace the cover plates. Currently, removal of the turbine bucket cover plates is a manual process that requires a repair technician to hold a pneumatic grinder with an abrasive disc and guide the grinder over the top of the cover. This process exposes the technician to dust from the abrasive wheel, noise at a close distance from the grinder, flying sparks and debris from the wheel, and fatigue from holding the tool. The depth of cut using the manual process may vary depending on the skill of the technician. If the cut is too deep the tip of the bucket vane can be damaged which could lead to an extensive repair or bucket replacement. 
         [0004]    A method for removing bucket covers that does not require the use of manual cutting tools is accomplished by placing the turbine rotor into a rotor turning device or lathe. A tool bit is used to cut the covers up to the tenons of the buckets as the rotor is rotating at a constant speed. One drawback of this method is that a rotor turning device, tool compound, and cutting tools are needed to remove the covers. With the robotic cutting system a turning device or lathe is not required. 
         [0005]    What is needed is a system that allows for the operator to remain at a distance from the cutting operation and reduces the possibility of inhalation of grinding dust, debris in the eyes, and operator fatigue, and to precisely control the cuts made on each bucket cover. Also needed is a programmable robotic method and apparatus for cutting bucket covers which may virtually eliminate the possibility of cutting into a vane tip, and so that a steel grinding wheel may be used repeatedly without changing. 
       SUMMARY OF THE INVENTION 
       [0006]    In one embodiment a robotic apparatus for repairing a turbine bucket cover of a steam turbine machine includes a grinding device operable to drive a grinding wheel. A robotic arm is coupled to the grinding device. A base member is coupled to the robotic arm. The base member is mounted independently of the turbine bucket cover. A vision system is provided for locating the fastener on the turbine bucket cover. A control system is coupled to the vision system, the grinding device and the robotic apparatus, the control system controls movement of the robotic apparatus and the grinding device based upon vision system data and spatial information related to the turbine bucket cover. 
         [0007]    In another embodiment a method is disclosed for cutting turbine bucket covers on a turbine rotor. The method includes marking a cut path on a surface of the turbine bucket cover, the cut path comprising a plurality of finite lines defined by a pair of end points; directing a laser at each end point of each line of the cut path; storing a set of position coordinates of each end point for every line of the cut path; generating the cut path based on the respective end points; and following the cut path on the turbine bucket cover with a grinding machine attached to a robotic device; and cutting the turbine bucket cover according to the cut path. 
         [0008]    In yet another embodiment a system is disclosed for cutting turbine bucket covers on a turbine rotor, the system includes a turbine rotor with a turbine bucket cover having fasteners thereon, and a robotic device for cutting the turbine bucket cover. The robotic device includes a grinding device operable to rotatingly drive a grinding wheel. A robotic arm is coupled to the grinding device. A base member is coupled to the robotic arm. The base member is in contact with the surface independently of the portion of the turbine rotor. A vision system is provided for locating the fastener on the turbine bucket cover. A control system is in communication with the vision system, the grinding device and the robotic apparatus. The control system controls movement of the robotic apparatus and the grinding device based upon vision system data and spatial information about the turbine bucket cover. 
         [0009]    An advantage of the robotic cutting system is that it allows for the operator to remain at a much greater distance from the cutting operation which reduces the possibility of inhalation of grinding dust, debris in the eyes, and drastically reduces operator fatigue because they do not have to hold any tool to perform the operation. The depth of cut is precisely controlled on each cover and if programmed correctly virtually eliminates the possibility of cutting into a vane tip. The steel grinding wheel can be used repeatedly without changing like has to be done when using abrasive wheels. 
         [0010]    Another advantage in using the robotic cutting system is the robotic cutting system provides extremely accurate cuts in following the programmed cut path. The system will follow the programmed cut path exactly the same on each bucket. The depth of cut is precisely controlled by use of the touch probe thus eliminates the mistakes often seen by cutting covers using manual processes. 
         [0011]    Also, by using the robotic cutting system the number of operators may be reduced while at the same time the rate of cover removal is not compromised. This enables the same volume of repairs to be completed at a lower cost. 
         [0012]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1-3  show fragmentary views of portions of a turbine for a turbine bucket cover repair process. 
           [0014]      FIG. 4  shows a side schematic view of an apparatus for cutting turbine bucket covers according to an exemplary embodiment. 
           [0015]      FIG. 5  shows an environment of a robotic apparatus for machining a tenon according to an exemplary embodiment. 
           [0016]      FIG. 6  shows an environment of a robotic apparatus for cutting bucket covers of a turbine rotor according to an exemplary embodiment. 
           [0017]      FIG. 7  shows an exemplary layout for a cut path on a turbine bucket cover. 
           [0018]      FIG. 8  shows an exemplary Human-Machine Interface (HMI) screen. 
           [0019]      FIG. 9  shows a flow diagram of an exemplary method for cutting bucket covers of a turbine rotor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    An automated robotic turbine bucket cover removal system is disclosed that replace the manual cutting process currently used by turbine repair technicians. The system, which will be discussed in detail below, includes a robotic arm that supports and guides an electric grinder with a diamond coated cutting wheel along a turbine bucket cover. Cover material is removed from the turbine rotor by the grinding wheel as it passes over the cover, which makes it possible to remove the cover from the bucket tip. The cut path, cut depth, and cut speed are substantially identical with respect to each corresponding turbine bucket in a row of adjacent turbine buckets because the motion of the robot arm is controlled by a robotic controller. Turbine bucket covers must be removed when the condition of the turbine bucket cover warrants repair, but the turbine buckets themselves are in operational condition. 
         [0021]    The turbine bucket cover removal system incorporates a robotic arm mounted to a structural base, robotic control system, laser distance finder, touch probe, vision system, and grinder end effector. The arm supports all of the weight of the grinder and enables the movement of the grinder. The robotic control system is used to program and control the movement of the arm. The touch probe, laser distance finder, and vision system are used to program the robotic motion. The grinder is the primary tool used to grind or cut the covers off of the turbine buckets. The grinder incorporates a steel cutting wheel with diamond coated serrated teeth, a custom made adapter bracket to mount to the robotic arm, and a tool changer that provides power to the tool. The operator programs the cut path that the grinder will follow on the bucket cover using the laser, touch probe, and vision system. 
         [0022]    After the cut path is programmed, the robotic controller guides the arm and end effector along the cut path on the first bucket. Upon finishing cutting the cover on the first bucket, the robot indexes itself to the next bucket and repeats the cut path. The robot will continue to index to the next bucket until it the robot arm is fully extended. The robot motion is programmed each time a new row of bucket covers is to be removed. 
         [0023]      FIGS. 1-3  illustrate portions of the bucket cover plate removal process of a section of a turbine machine.  FIG. 1  shows a plurality of buckets  11  forming part of a rotating component of a turbine, e.g., a steam turbine,  12 . A cover plate  14  is shown secured to the outer tips of buckets  11 , where cover plate  14  extends in a circumferential direction about buckets  11 .  FIGS. 2-3  show the tips of buckets  11  having one or more tenons  16  projecting radially outward therefrom. Each cover plate  14  may include an arcuate circumferentially extending segment for spanning a plurality of buckets  11  (e.g., four or five buckets). Each cover plate  14  may include a plurality of openings  18  for receiving tenons  16 . Tenons  16  may be received in openings  18  and peened to form a substantially flush cover design, as shown in  FIG. 3 . 
         [0024]    Referring to  FIG. 4 , an exemplary robotic apparatus or robot  10  for cutting a cover plate  14  of a turbine bucket  11  is shown. Robot  10  may include a grinder  24  grinding wheel  26 . Grinder  24  may include any conventional milling head  26  capable of machining a tenon at an end of a vane or bucket. In one embodiment, grinder  24  may be, e.g., a right angle electric grinder manufactured by Metabo angle grinder, Model No. W23-230 or W25-230, manufactured by Metabo Corporation of West Chester, Pa. Grinding wheel  26  may be formed of a metal, e.g., steel with a diamond grinding disk, which is capable of cutting steel or similar material used for turbine bucket cover plates  14 . 
         [0025]    An exemplary embodiment of a robotic apparatus  28  may include a robotic arm  30  coupled to grinder  24 . Robotic apparatus  28  and grinder  24  may be coupled in any conventional manner, e.g., via joints, welds, clamps, etc. Robotic arm  30  may include a plurality of segments  32  and joints  34  allowing robotic arm  30  to assist in machining tenons at different locations on a machine. Robotic apparatus  28  is also shown including a base member  36  coupled to robotic arm  30 . It is understood that robotic apparatus  28  including robotic arm  30  and base member  36  may include electrical and electro-mechanical components capable of actuating movement of robotic arm  30  and/or grinder  24 . These electrical and electro-mechanical components are known in the art of robotics, and are not described herein for clarity. 
         [0026]    A vision system  38  is disclosed for locating a cover  16  or other reference point on a machine element, e.g., a tenon ( FIG. 1 ). Vision system  38  may include a conventional two-dimensional or three-dimensional optical recognition system which may detect a location of a fastener on the machine element. Vision system  38  may be capable of high speed image acquisition and processing, and may locate a shape of a cover  16  by optically recognizing the original fastener design (e.g., the original shape of a tenon as indicated by spatial information  140 , described with reference to  FIG. 2 ). 
         [0027]    Robot  22  may also include a computer system  120  coupled to vision system  38 , grinder  24 , and robotic apparatus  28 . Computer system  120  may be configured to control movement of robotic apparatus  28  and grinder  24  via a robotic control system  40  ( FIG. 2 ), based upon data received from vision system  38  and spatial information about the fastener and the machine element. Also shown in  FIG. 4  is a shock absorbing member  42  coupled to base member  36 . Shock absorbing member  42  may include one or more types of material capable of absorbing forces caused by vibrations within robotic apparatus  28 . For example, shock absorbing member  42  may include a plurality of (e.g., three) distinct rubber vibration dampening pads, which may isolate the vibration of robotic apparatus  28  from a surface (not shown). In any case, shock absorbing member  42  may be configured to reduce vibration in robotic apparatus  28  and grinder  24 , and improve the performance of robot  22 . 
         [0028]    Referring next to  FIG. 5 , an illustrative environment  100  for robotic machining tenons is disclosed. To this extent, environment  100  includes computer system  120 , which can perform processes described herein in order to machine tenons using apparatus  22 . In particular, computer system  120  is shown including a robotic control system  40 , which makes computer system  120  operable to provide instructions to apparatus  22  for machining tenons by performing a process described herein. 
         [0029]    Computer system  120  is shown in communication with apparatus  22 , which may include grinder  24  and vision system  38 . Further, computer system  120  is shown in communication with a user  136 . A user  136  may be, for example, a programmer or operator. Interactions between these components and computer system  120  will be discussed in subsequent portions of this application. Computer system  120  is shown including a processing component  122  (e.g., one or more processors), a storage component  124  (e.g., a storage hierarchy), an input/output (I/O) component  126  (e.g., one or more I/O interfaces and/or devices), and a communications pathway  128 . In one embodiment, processing component  122  executes program code, such as robotic control system  40 , which is at least partially embodied in storage component  124 . While executing program code, processing component  122  can process data, which can result in reading and/or writing the data to/from storage component  124  and/or I/O component  126  for further processing. Pathway  128  provides a communications link between each of the components in computer system  120 . I/O component  126  can comprise one or more human I/O devices or storage devices, which enable user  136  to interact with computer system  120  and/or one or more communications devices to enable user  136  to communicate with computer system  120  using any type of communications link. To this extent, robotic control system  40  can manage a set of interfaces (e.g., graphical user interface(s), application program interface, and/or the like) that enable human and/or system interaction with robotic control system  40 . 
         [0030]    Computer system  120  can include one or more general purpose computing articles of manufacture, e.g., computing devices, capable of executing program code installed thereon. As used herein, it is understood that “program code” means any collection of instructions, in any language, code or notation, that cause a computing device having an information processing capability to perform a particular function either directly or after any combination of the following: (a) conversion to another language, code or notation; (b) reproduction in a different material form; and/or (c) decompression. To this extent, robotic control system  40  can be embodied as any combination of system software and/or application software. In any event, the technical effect of computer system  120  is to provide processing instructions to apparatus  22  in order to machine tenons. 
         [0031]    Further, robotic control system  40  can be implemented using a set of modules  132 . In this case, a module  132  can enable computer system  20  to perform a set of tasks used by robotic control system  40 , and can be separately developed and/or implemented apart from other portions of robotic control system  40 . Robotic control system  40  may include modules  132  which comprise a specific use machine/hardware and/or software. Regardless, it is understood that two or more modules, and/or systems may share some/all of their respective hardware and/or software. Further, it is understood that some of the functionality discussed herein may not be implemented or additional functionality may be included as part of computer system  120 . 
         [0032]    When computer system  120  comprises multiple computing devices, each computing device may have only a portion of robotic control system  40  embodied thereon, e.g., one or more modules  132 . However, it is understood that computer system  120  and robotic control system  40  are only representative of various possible equivalent computer systems that may perform a process described herein. To this extent, in other embodiments, the functionality provided by computer system  120  and robotic control system  40  can be at least partially implemented by one or more computing devices that include any combination of general and/or specific purpose hardware with or without program code. In each embodiment, the hardware and program code, if included, can be created using standard engineering and programming techniques, respectively. 
         [0033]    The computing devices can communicate over any type of communications link. Further, while performing a process described herein, computer system  120  can communicate with one or more other computer systems using any type of communications link. In either case, the communications link can comprise any combination of various types of wired and/or wireless links; comprise any combination of one or more types of networks; and/or utilize any combination of various types of transmission techniques and protocols. 
         [0034]    As discussed herein, robotic control system  40  enables computer system  120  to provide processing instructions to apparatus  22  for machining tenons. Robotic control system  40  may include logic, which may include the following functions: an obtainer  43 , a determinator  53 , an actuator  63  and a user interface module  73 . In one embodiment, robotic control system  40  may include logic to perform the above-stated functions. Structurally, the logic may take any of a variety of forms such as a field programmable gate array (FPGA), a microprocessor, a digital signal processor, an application specific integrated circuit (ASIC) or any other specific use machine structure capable of carrying out the functions described herein. Logic may take any of a variety of forms, such as software and/or hardware. However, for illustrative purposes, robotic control system  40  and logic included therein will be described herein as a specific use machine. As will be understood from the description, while logic is illustrated as including each of the above-stated functions, not all of the functions are necessary according to the teachings of the invention as recited in the appended claims. 
         [0035]    Referring next to  FIG. 6 , a tool changer assembly  46  may include electric, pneumatic and control connections  48 , a camera or vision system  38  and a touch probe  50 . The grinder or cutter  24  follows a cut path  52  ( FIG. 7 ) programmed into controller  40  based on operator input, i.e., training. The operator also establishes the camera programming during the setup to recognize a tenon  16 . The cutter then follows the cut path  52 , moves to next tenon, and camera  38  orients the cut path based on a programmed image. After tenon  16  is located robotic arm  30  follows the cut path  52  programmed into the recipe based on the 0, 0 point. 
         [0036]    Referring to  FIG. 8 , an HMI  54  may be used to select a cutting program from a menu of various functions. Grinding programs may be separated into (a) TEACH &amp; (b) CUT programs. Setup and alignment programs are operated from a control pendant or controller  40  of the robotic apparatus  28 . HMI  54  may include selection elements or buttons  56  for selecting a mode of operation of the robotic apparatus  28 , e.g., grinding TEACH or grinding CUT modes or programs. Other programmed operator selections may include, e.g., grinding recipe, number of cuts and cover thickness associated with the respective cover. 
         [0037]    A method for robotically performing cutting of turbine bucket covers is shown in  FIG. 9 . The method begins at step  102  by laying out a desired cut path on a cover  14 . Black lines  51  or similar markings that are recognizable by a camera or vision detection system  38  are drawn on cover  14  to layout a desired cut path  52 . After lines  51  are drawn on cover  14 , at step  104  robotic apparatus  28  is manually actuated so that the laser is directed at an end point  60  of each line  51  of cut path  52 . Laser  39  ( FIG. 4 ) is directed at the selected end point and an operator triggers laser  39  ( FIG. 4 ) to store the coordinates of the robotic arm  30  associated with the selected end point(s)  60 . The robotic arm coordinates for the respective end points  60  are then stored in the robot controller storage component or memory  124  at step  106 . At step  108 , the robotic apparatus  28  generates a line extending between the stored end points  60  for each of the lines  51  which grinder  24  will follow during the cutting operation. At step  110 , robotic arm  30  is actuated by controller  40  to cut cover  14  along the cut path  52  generated at step  108 . At step  112 , the robotic apparatus  28  is indexed to an adjacent bucket cover  14  and robotic apparatus repeats cutting covers  16  along the stored cut path until all bucket cover cuts are completed. 
         [0038]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.