Abstract:
A visual feedback system and method for airfoil polishing is disclosed. In one aspect there is a system for providing visual feedback during a polishing operation of a workpiece. In this system there is a model having a representation of a desired shape of the workpiece. A scanning system generates a representation of a current shape of the workpiece while in-process during the polishing operation. A comparator compares the current shape of the workpiece to the desired shape of the workpiece. An illumination system highlights the workpiece with visible light during the polishing operation. The highlighting of the workpiece with visible light is a function of the comparison between the current shape and the desired shape. The illumination system highlights a portion of the workpiece that needs additional polishing to conform to the desired shape.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to manufacturing turbine buckets and more particularly to providing continuous visual feedback while performing a polishing operation on an airfoil used for a turbine bucket or a turbine nozzle. 
     Typically, a polish operator skilled in polishing turbine airfoils will manually polish each airfoil by hand to remove machining marks from the surface of the airfoil to attain its final desired shape. Often the operator will remove too much material from the airfoil during the polish operation. In order to account for the removal of too much material during the polish operation, a machinist that machines the airfoil will add more material to the base shape of the airfoil to account for the excess amount of material typically removed during the polishing. This is helpful in obtaining an airfoil that will be closer to its final desired shape. Despite this effort to bring the airfoil to its final desired shape, this process often results in an airfoil having a blade profile with tolerances that are greater than may be desired. An airfoil with greater tolerances often leads to variation in performance and mechanical properties. In addition, the greater tolerances that result from this polishing process make it difficult to manufacture airfoils having more advanced shapes with higher performance entitlements. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect of the present invention, a system for providing visual feedback during a polishing operation of a workpiece is provided. The system comprises a model having a representation of a desired shape of the workpiece. A scanning system generates a representation of a current shape of the workpiece while in-process during the polishing operation. A comparator compares the current shape of the workpiece to the desired shape of the workpiece. An illumination system highlights the workpiece with visible light during the polishing operation. The highlighting of the workpiece with visible light is a function of the comparison between the current shape and the desired shape. The illumination system highlights a portion of the workpiece that needs additional polishing to conform to the desired shape. 
     In another aspect of the present invention, a system for providing visual feedback during a polishing operation of a turbine bucket is provided. The system comprises a model having a representation of a desired shape of the turbine bucket. A scanning system generates a representation of a current shape of the turbine bucket while in-process during the polishing operation. A comparator compares the current shape of the turbine bucket to the desired shape of the turbine bucket. An illumination system highlights the turbine bucket with visible light in real-time during the polishing operation. The illumination system highlighting the turbine bucket as a function of the comparison between the current shape and the desired shape. The illumination system highlights a portion of the turbine bucket that needs additional polishing to conform to the desired shape with the visible light. 
     In a third aspect of the present invention, there exists a method for providing visual feedback during a polishing operation of a workpiece. The method comprises: generating a representation of a current shape of the workpiece while in-process during the polishing operation; obtaining a representation of a desired shape of the workpiece; comparing the current shape of the workpiece to the desired shape of the workpiece; determining a portion of the workpiece that needs additional polishing in response to comparing the current shape of the workpiece to the desired shape of the workpiece; and highlighting the portion of the workpiece that needs additional polishing with visible light during the polishing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a system that provides visual feedback during a polishing operation of a turbine bucket according to one embodiment of the present invention; 
         FIG. 2  is a schematic illustration showing some of the functionality components associated with the computing unit depicted in  FIG. 1  according to one embodiment of the present invention; and 
         FIG. 3  is a flow chart describing the process operations associated with using the system depicted in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At least one embodiment of the present invention is described below in reference to its application in connection with providing visual feedback to an operator performing a polishing operation of a turbine airfoil that may be used in a bucket or nozzle. However, it should be apparent to those skilled in the art and guided by the teachings herein that the present invention is likewise applicable to any workpiece that undergoes a process operation and where it is desirable to receive visual feedback in real-time during the operation in order to ascertain how well the workpiece is conforming to its desired shape. 
     Referring to the drawings,  FIG. 1  is a schematic illustration of a system  100  that provides visual feedback during a polishing operation of a turbine bucket. In  FIG. 1 , there is a polish operator  105  using a polishing unit  110  to polish a turbine bucket  115  placed horizontally on polishing unit  110 . Polishing unit  110  generally comprises a sandpaper strip  120  that polish operator  105  moves over the surface of bucket  115  to remove ridges from the surface that arose in the machining of bucket  115 . During the polishing of bucket  115 , a scanning system  125  generates a digital representation of the current shape of bucket  115  while in-process during the polishing operation. In particular, scanning system  125  uses well-known part-shape analysis methodologies to measure the current shape of bucket  115  and generate a three-dimensional surface map of bucket  115  in real-time, while it is in-process of being polished by polish operator  105 . 
     A computing unit  130  receives a representation of the current shape of bucket  115  generated from scanning system  125  in real-time during the polish operation. Computing unit  130  also obtains a model  135  having a digital representation of the desired shape of bucket  115 . In one embodiment, model  135  is a three-dimensional model of bucket  115  generated from a conventional computer-aided design (CAD) application that is utilized by computing unit  130 . Computing unit  130  is programmed to compare the current shape of bucket  115  generated from scanning system  125  in real-time during the polish operation to the desired shape of bucket  115  as set forth in model  135 . From this comparison, computing unit  130  assesses the thickness of bucket  115 . In particular, computing unit  130  determines where bucket  115  is too thick in comparison to its desired shape. Regions that are too thick are an indication that these regions need more polishing to remove excess material. 
     Computing unit  130  identifies all regions of bucket  115  that are too thick (i.e., needs additional polishing) and directs an illumination system  140  to highlight these regions of bucket  115  with visible light during the polishing operation. Polish operator  105  uses the visible light as a guide indicating that these regions of bucket  115  need additional polishing. Like the generation of the current shape of bucket  115  from scanning system  125  and comparison with the current shape by computing unit  130 , the illumination of bucket  115  with visible light occurs in real-time during the polish operation. The generation of the current shape of bucket  115 , comparison with desired shape  135  and illumination of regions still requiring polishing continues until computing unit  130  determines that bucket  115  conforms to the desired shape. Those skilled in the art will recognize that conforming to the desired shape can also include being within a predetermined tolerance level. 
     In one embodiment, scanning system  125  comprises an optical scanning system such as an optical coordinate measuring machine (optical CMM). Optical CMMs are well-known and commercially available. One example, of an optical CMM that can be used to implement the present invention is an NVision MAXOS scanner. Those skilled in the art will recognize that other scanning systems can be used in place of the optical CMM to analyze and assess the shape of bucket  115  during the polishing operation. For example, a CMM that uses a contact probe can be used to generate a representation of bucket  115 . 
     Illumination system  140  can be any type of illumination system that can be controlled to direct visible light onto a workpiece such as bucket  115  to guide operation thereon. For ease of illustration,  FIG. 1  portrays illumination system  140  as a liquid crystal display (LCD) projector, however, those skilled in the art will recognize that a multitude of possibilities exist. For example, in one embodiment, illumination system  140  can include a laser illumination system. Other possibilities may include a Digital Light Projecting (DLP) projector or a cathode ray tube (CRT). 
       FIG. 2  is a schematic illustration showing some of the functionality components associated with computing unit  130  depicted in  FIG. 1  according to one embodiment of the present invention.  FIG. 2  only shows the components of computing unit  130  that facilitate a general understanding of the approach used to receive a current representation of bucket  115  while in-process of undergoing a polishing operation, obtain a desired shape of bucket  115 , compare the current shape to the desired shape, identify regions that need further polishing, and control illumination system  140  to provide visual feedback to polish operator  105 . Those skilled in the art will recognize that computing unit  130  can have additional components not shown in  FIG. 1 . For example, the controller  104  may have a user interface component that enables an operator to input commands, data and/or to monitor the polish operation. 
     As shown in  FIG. 2 , computing unit  130  comprises a comparator  205  that receives a representation of the current shape of bucket  115  generated from scanning system  125  in real-time during the polish operation and a representation of the desired shape of bucket  115  from CAD model  135 . Comparator  205  compares the current shape to the desired. A thickness assessor  215  assesses the thickness of bucket  115 . Thickness assessor  215  assesses the thickness by noting regions of the blade that are not in tolerance. Region identifier  220  identifies all regions of bucket  115  that are too thick (i.e., needs additional polishing). Illumination control  225  directs illumination system  140  to highlight these regions of bucket  115  with visible light. In an embodiment where the illumination system  140  is a laser illumination system, illumination control  225  highlights regions with visible light by controlling mirrors to reflect laser light onto the appropriate regions of the airfoil. The comparison of the current shape with desired shape, thickness assessment, region identification and illumination of regions with visible light continues until computing unit  130  determines that bucket  115  conforms to the desired shape. Those skilled in the art will recognize that in one embodiment the functions associated with thickness assessor  215  and region identifier  220  can be performed directly by comparator  205  thus obviating the need for thickness assessor  215  and region identifier  220 . In this embodiment, output from comparator  205  is fed directly to illumination control  225 . 
     In various embodiments of the present invention, computing unit  130  can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the processing functions performed by the computing unit  130  are implemented in software, which includes but is not limited to firmware, resident software, microcode, etc. 
     Furthermore, the processing functions performed by computing unit  130  can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the computer, instruction execution system, apparatus, or device. The computer readable medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include a compact disk-read only memory (CD-ROM), a compact disk-read/write (CD-R/W) and a digital video disc (DVD). 
       FIG. 3  is a flow chart  300  describing the process operations associated with using the online system depicted in  FIG. 1 . As shown in  FIG. 3 , the polishing operation of bucket  115  begins at  305  to remove ridges at the surface that arose in the machining of the bucket. Scanning system  125  generates a representation of the current shape of bucket  115  in real-time while in-process during the polishing operation at  310 . Computing unit  130  obtains a representation of the desired shape of bucket  115  at  315 . Computing unit  130  compares the current shape of bucket  115  generated from scanning system  125  to the desired shape of bucket  115  at  320 . If it is determined at  325  that bucket  115  needs additional polishing, then computing unit  130  identifies all regions of bucket  115  that are too thick (i.e., needs additional polishing) at  330 . Computing unit  130  directs illumination system  140  to highlight these regions of bucket  115  with visible light during the polishing operation at  335 . Polish operator  105  uses the visible light as a guide to follow while polishing bucket  115 . In the mean time, process operations  310 - 335  continue until it is determined at process block  325  that bucket  115  does not need additional polishing. When that determination is made, then the polishing of bucket  115  is over as shown at process block  340 . 
     The foregoing flow chart shows some of the processing functions associated with providing visual feedback in real-time to an operator performing polishing of a bucket. In this regard, each block represents a process act associated with performing these functions. It should also be noted that in some alternative implementations, the acts noted in the blocks may occur out of the order noted in the figure or, for example, may in fact be executed substantially concurrently or in the reverse order, depending upon the act involved. Also, one of ordinary skill in the art will recognize that additional blocks that describe the processing functions may be added. 
     While the disclosure has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be appreciated that variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.