Abstract:
A method and apparatus for measuring an opening defined within object using an optical sensor system is provided. The method includes positioning an illumination source adjacent the opening, illuminating a perimeter circumscribing the opening, receiving an image of the illuminated boundary, and calculating an area within the received boundary. The system includes a light source oriented to project a first sheet of light intersected by a first portion of the opening perimeter, the light source projecting a second sheet of light intersected by a second portion of the opening perimeter, a light detector receiving a portion of the sheet of light intersected by the object opening perimeter and reflected toward the light detector, and an image processor communicatively coupled to the light detector, the image processor programmed to sample an image from the detector and programmed determine the dimensions of the object opening from the sampled image.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to optical systems and more particularly, to methods and apparatus for measuring an opening area defined within a flow nozzle.  
           [0002]    At least some known gas turbine engines include a compressor, a combustor, and at least one turbine coupled in a serial axial-flow relationship. The compressor compresses air which is then channeled to the combustor. The compressed air is mixed with fuel and ignited within the combustor to generate combustion gases which are channeled to the turbine. The turbine extracts energy from the combustion gases to power the compressor, as well as to produce useful work to propel an aircraft in flight or to power a load, such as an electrical generator.  
           [0003]    A nozzle throat area of the engine is a critical parameter affecting engine efficiency. Accordingly, the nozzle throat area is measured during periodic inspections to verify clearances in the engine fluid path. New nozzle throats are carefully designed to provide a specific area value. Accurately measuring an opening area of the nozzle may also be relevant in determining a manufacturing time of the nozzle, as well as subsequent maintenance and repair costs and activities.  
           [0004]    Conventional nozzle throat inspection methods include using a mechanical gauge. At least one known mechanical gauge includes a complex mechanical analog computer that multiplies a width of the throat by a height measured at several specified locations. Another known area gauge uses electronic linear voltage differential transformer (LVDT) sensors to measure the throat width and height values, and then a computer calculates the area. However, obtaining accurate measurements at the various orientations of the nozzle throat may be a difficult task. Furthermore, because of the contours and dimensions of the nozzle throat, using such gauges may be a costly and time-consuming process.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0005]    In one aspect, a method for measuring an opening defined within an object using an optical sensor system is provided. The method includes positioning an illumination source adjacent the opening, illuminating a perimeter circumscribing the opening, receiving an image of the illuminated perimeter, and calculating an area within the received boundary.  
           [0006]    In another aspect, an opening measurement system for measuring an area of an object opening is provided. The system includes a light source oriented toward a first side of the object, the light source projecting a first sheet of light intersected by a first portion of the opening perimeter, and the light source projecting a second sheet of light intersected by a second portion of the opening perimeter, a light detector receiving a portion of the sheet of light intersected by the object opening perimeter and reflected toward the light detector, and an image processor communicatively coupled to the light detector, the image processor programmed to sample an image from the detector and programmed determine the dimensions of the object opening from the sampled image. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic illustration of an exemplary gas turbine engine;  
         [0008]    [0008]FIG. 2 is a side view of an exemplary measurement device used to measure a nozzle throat opening area of a turbine nozzle;  
         [0009]    [0009]FIG. 3 is an enlarged view  300  of trailing edge  208 ; and  
         [0010]    [0010]FIG. 4 is a flow chart illustrating an exemplary method for measuring an opening of an object using an optical sensor system that includes a measurement device.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    [0011]FIG. 1 is a schematic illustration of a gas turbine engine  10  including a low-pressure compressor  12 , a high-pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high-pressure turbine  18 , a low-pressure turbine  20 , an exhaust frame  22  and a casing  24 . A first shaft  26  couples low-pressure compressor  12  and low-pressure turbine  20 , and a second shaft  28  couples high-pressure compressor  14  and high-pressure turbine  18 . Engine  10  has an axis of symmetry  32  extending from an upstream side  34  of engine  10  aft to a downstream side  36  of engine  10 . A turbine nozzle area  38  includes a plurality of nozzle throats (not shown in FIG. 1) circumferentially arranged about engine  10  between combustor  16  and high pressure turbine  18 . In one embodiment, gas turbine engine  10  is a GE90 engine commercially available from General Electric Company, Cincinnati, Ohio.  
         [0012]    In operation, air flows through low-pressure compressor  12  and compressed air is supplied to high-pressure compressor  14 . Highly compressed air is delivered to combustor  16 . Combustion gases from combustor  16  propel turbines  18  and  20 . High pressure turbine  18  rotates second shaft  28  and high pressure compressor  14 , while low pressure turbine  20  rotates first shaft  26  and low pressure compressor  12  about axis  32 .  
         [0013]    [0013]FIG. 2 is a side view of an exemplary measurement device  200  used to measure a nozzle throat opening area  202  of turbine nozzle  38 . Opening  202  defines a portion of a flow passage through turbine engine  10 . Opening  202  is formed from an arcuate first wall  204 , an arcuate second wall  206  and two substantially parallel sidewalls (not shown) that extend between walls  204  and  206 , to define a substantially rectangular opening  202 . Specifically, opening  202  is bounded by a trailing edge  208  of wall  204  and a portion of wall  206  identified by a transverse line  210  projected on an interior face  212  of wall  206  from trailing edge  208 , such that a distance of separation  214  is minimized within throat opening  202 . An area  213  bounds trailing edge  208 .  
         [0014]    In the exemplary embodiment, measurement device  200  uses an illumination source, such as a laser  216 , and a combination of lenses and mirrors  218  to generate planar sheets of light. A beam, emitted from laser  216  may be directed toward the combination of lenses and mirrors to refocus the beam into one or more planes of light, or light sheets. The combination of lenses and mirrors are oriented to project a first light sheet  220  in a plane substantially orthogonally toward trailing edge  208  and a second light sheet  222  in a plane substantially parallel to light sheet  220 . Measurement device  200  is positioned in alignment with opening  202  such that light sheet  220  intersects trailing edge  208  forming an illuminated line across trailing edge  208 . The orientation of light sheet  222  is fixed in relation to light sheet  220  such that a second illuminated line formed at the intersection of light sheet  222  and wall  206  substantially coincides with transverse line  210 . More specifically, an orientation of light sheet  222  is adjusted, prior to use, to substantially illuminate transverse line  210 . Light sheet  222  also illuminates a line on each sidewall that extends between walls  204  and  206 . The illuminated lines at trailing edge  208 , transverse line  210  and across the sidewalls define a boundary that is representative of a height and width of opening  202 . Although opening  202  is substantially rectangularly-shaped, each illuminated line may have deformities due to deformities in trailing edge  208 , transverse line  210  and the sidewalls.  
         [0015]    One or more optical sensors  224  are positioned to view the width and height of opening  202 . In the exemplary embodiment, at least one optical sensor  224  is a video camera. In an alternate embodiment, at least one optical sensor  224  is a digital camera. A sensor alignment fixture  225  is coupled to measurement device  200  to position optical sensors  224  in alignment with respect to opening datums to facilitate measuring opening area  202  accurately. Specifically, optical sensors  224  are positioned at known angles relative to light sheets  220  and  222  to sense the illuminated lines and measure their location relative to an image plane of optical sensors  224 . Each sensor  224  is communicatively coupled to an image processor  226  through conduit  228 . A digital representation of the illuminated lines circumscribing the boundary of opening  202  is transmitted to image processor  226 . In the exemplary embodiment, a filter coupled to the light receiving end of each optical sensor  224  filters each light stripe to substantially prevent all non-illuminated line illumination. In an alternative embodiment, the receiving end of optical sensor  224  is unfiltered. Calibration functions are executed in processor  226  to extract dimensional coordinates of the location of the illuminated lines defining a perimeter of opening  202 . In one embodiment, the perimeter includes four substantially straight illuminated lines. In an alternative embodiment, the perimeter is defined by curved or wavy lines due to design complexity and/or part distortion during use. In the exemplary embodiment, processor  226  includes a digitizer that receives an image from optical sensor  224  and converts the received image into a pixelized image, and an extractor that determines an area in within the boundaries of the pixelized image. Processor  226  displays an image from the field of view of optical sensors  224  and may output the image to a printer. Additionally, processor  224  may interface directly to a network to transmit images and part data to other systems.  
         [0016]    Sensor alignment fixture  225  is coupled to a body  230  of measurement device  200 . Body  230  includes a handle  232  for manually positioning measurement device  200  with respective to opening  202 . Body  230  includes an emitting end  234  for projecting light toward opening  202 , and an alignment finger  236  that extends from body emitting end  234 . Alignment finger  236  includes an attachment portion  240  for coupling alignment finger  236  to body  230 , an extension portion  242  for adjusting a length of alignment finger  236 , and an engagement portion  244  for engaging a portion of the perimeter defining opening  202 , such as, for example, trailing edge  208 . A second end  246  of body emitting end  234  includes a shoulder  248  that extends outwardly from body  230  towards engagement portion  244  and is substantially perpendicular with respect to alignment finger  236 . Shoulder  248  includes an attachment end  250  for coupling shoulder  248  to body  230 , and a contact end  252  that includes a biased support assembly  254 . In the exemplary embodiment, support assembly  254  is a ball bearing support assembly that includes an end  256  that extends outwardly at least partially beyond an outer surface  257  of shoulder  248 .  
         [0017]    Optical sensors  224  receive a large number of discrete points from the illuminated lines defining the perimeter of opening  202 . Sensors  224  use this data to compute the area circumscribed by the illuminated lines. In one embodiment, an area of nozzle throat opening  202 , is computed by using measurement device  200  together with a known fixture (not shown) to measure the area of two half throat openings adjacent to a principal throat of the nozzle. Combining the results yields the area of a complex shape or a total area of a plurality of noncontiguous openings.  
         [0018]    In operation, body  230  is manually positioned proximate opening  202  such that engagement portion  244  engages trailing edge  208  and such that contact end  256  contacts an exterior surface  304  of wall  206 . In the engaged position, light sheet  220  illuminates trailing edge  206 , and light sheet  222  illuminates transverse line  210  and the sidewalls defining opening  202 . Optical sensor  224  is aligned with respect to opening  202  such that the lines illuminating trailing edge  208 , transverse line  210 , and the sidewalls are within a field of view of optical sensors  224 . Each optical sensor  224  receives the illuminated line image and transmits the image to processor  226  via cables  228 . Processor  226  determines the area bounded by the illuminated lines based on the predetermined angular alignment of light sheets  220  and  220 , engagement end  244 , and optical sensors  224 . Processor  226  displays the results of the calculations in a form commanded by a user.  
         [0019]    [0019]FIG. 3 is an enlarged view  300  of trailing edge  208 . Trailing edge  208  includes an interior surface  302  that defines opening  202  and is opposite side  206 . Engagement portion  244  engages interior surface  302 , and when manual pressure is exerted through handle  232 , portion  244  maintains body  230  in alignment with opening  202 . Light sheet  220  intersects trailing edge  208  on an exterior surface  304  of trailing edge  208 . A distance  306  represents a corrected distance that is accounted for in processor  226  when the area of opening  202  is calculated. In actuality, opening  202  is bounded in part by interior surface  302 , and measurement device  200  measures the area defined by the illuminated line boundaries, and as such distance  306  is accounted for during the calculations executed by processor  226 .  
         [0020]    [0020]FIG. 4 is a flow chart illustrating an exemplary method  400  for measuring an opening of an object using an optical sensor system that includes a measurement device, such as device  200  (shown in FIG. 2). The method includes positioning  402  an illumination source adjacent the opening. In the exemplary embodiment, the illumination source includes at least one laser diode. The laser light beam from the laser diode is split into two beams that are directed to a cylindrical lens that redirects the laser beams into two laser light sheets that exit the illumination source substantially parallel with respect to one another. An alignment finger coupled to the illumination source engages a surface defining the opening to be measured such that the illumination source is aligned with a predetermined opening boundary, such as, but not limited to, a trailing edge of a nozzle opening and a predetermined reference area to be measured. More specifically, the illumination source is aligned such that, when the alignment finger engages the surface, the light sheets illuminate predetermined portions of the opening to be measured without further adjustment of the illumination source. Furthermore, the alignment is adjustable to compensate for measuring different size objects and objects with different shapes. The illumination source illuminates  404  the boundary that circumscribes and defines the opening using the light sheets. In the exemplary embodiment, the boundary of the opening is defined by two laser light sheets. In an alternative embodiment, depending on the complexity of the opening, additional light sheets may be required to illuminate the opening boundary. Each light sheet intersects a surface of the object near the object opening such that the intersection creates an illuminated line on the object near the object opening. The illuminated line is aligned substantially parallel with the opening boundary, such that the object boundary may be correlated to the position of each illuminated line. Other boundaries of the opening may be similarly illuminated by one or more illuminated lines until the entire perimeter of the opening is defined by lines illuminated from the illumination source. In an alternative embodiment, portions of the boundary not illuminated by light lines are inferred by processing software in the image processor, such that the entire perimeter of the opening is defined by a combination of light lines and inferred boundaries.  
         [0021]    A light detector, or optical receiver is positioned in substantial alignment with the illuminated line boundaries in the receiver field of view such that the optical receiver samples  406  the illuminated boundary. In one embodiment, a receiving lens within the optical receiver includes a filter that substantially removes non-illuminated line illumination from the optical receiver view, such as, for example, ambient lighting and sunlight. Filtering the optical receiver input may facilitate increasing the contrast of the opening perimeter, thereby facilitating enhancing the effectiveness the optical receiver. In the exemplary embodiment, the optical receiver is a video camera. In an alternative embodiment, the optical receiver is a digital camera.  
         [0022]    The received image is transmitted to a digital image processor that includes a digitizer that digitizes the received video image. The area of the opening bounded by the illuminated lines in the digital image is calculated  408  by the image processor. In the exemplary embodiment, the image processor calculates  408  a minimum area within the received boundary. The image processor extracts two-dimensional coordinate information from the digitized image, and using alignment and calibration information accessible to the image processor, determines the coordinates that are within the received boundary. The area represented by the total coordinates is calculated  408  and output from the image processor in a predetermined format selected by the user.  
         [0023]    While the present invention is described with reference to an engine nozzle throat opening area, numerous other applications are contemplated. For example, it is contemplated that the present invention may be applied to any system wherein opening perimeters may be illuminated and the illuminated perimeters viewed from a determinable angle and distance, such as, but not limited to, heat exchangers, valves, and cooling passages.  
         [0024]    The above-described opening measurement system is cost-effective and highly reliable for determining the dimensions of an opening in an object. More specifically, the methods and systems described herein facilitate determining the boundaries of the opening, and the area bounded by the boundaries. In addition, the above-described methods and systems facilitate providing an accurate and repeatable measurement of the opening quickly with minimal set-up time or operator training. As a result, the methods and systems described herein facilitate reducing outage duration and maintenance costs in a cost-effective and reliable manner.  
         [0025]    Exemplary embodiments of opening measurement systems are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each system component can also be used in combination with other system components.  
         [0026]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.