Abstract:
An improved method and device for reflectively measuring a subject such as a throat area in a vane ring for a gas turbine engine uses improved lighting arrangements to improve the quality of reflection to thereby reduce problems associated with poor quality reflection which may adversely affect the image processing and thus reduce the accuracy of measurement.

Description:
FIELD OF THE INVENTION 
   The invention relates to a method of measuring the throat area of a vane ring for a gas turbine engine by irradiating or illuminating the vanes and shrouds bounding a selected throat, then measuring the resulting shadow area. 
   BACKGROUND OF THE INVENTION 
   To calibrate the stator ring relative to the gas turbine engine, the flow area of the stator must be determined. Conventionally, the flow area of a stator ring can be determined by use of a flow rig in which the pressure drop as air passes through the stator ring is used to determine its effective flow area. Another conventional method of determining the flow area of the stator ring involves mechanically measuring the dimensions of the throat area. This approach is time consuming and improvements are available. 
   SUMMARY OF THE INVENTION 
   It is one object of the present invention to provide an improved vane flow measurement system. 
   In accordance with one aspect of the present invention, there is a provided A device for measuring a throat area in a vane ring for gas turbine engines, the vane ring having an annular array of vanes defining a plurality of individual throats between adjacent leading and following vanes of the array, the device comprising at least one primary lighting source adapted to radiate light onto a vane ring in a manner to provide an area of reflectance surrounding an area of primary shadow, the area of primary shadow substantially corresponding to an area of a selected throat to be measured, the at least one primary lighting source being positioned sufficiently close to the vane ring such that the at least one lighting source provides the area of reflectance substantially without secondary shadow, said secondary shadow being caused by interruption of light from the at least one primary source caused by a portion of the vane ring; a detector positioned for capturing data regarding said area of reflectance and said shadow; and a processor for analyzing the data to determine dimensional data regarding the area of the selected throat. 
   In accordance with another aspect of the present invention, there is a provided a device for measuring a throat area in a vane ring for gas turbine engines, the vane ring having an annular array of vanes defining a plurality of individual throats between adjacent leading and following vanes of the array, the device comprising a plurality of primary lighting sources adapted to radiate light onto a vane ring in a manner to provide an area of reflectance surrounding an area of primary shadow, the area of primary shadow substantially corresponding to an area of a selected throat to be measured, the plurality of primary lighting sources providing respective adjacent radiating zones of light without substantial overlap or gap between said adjacent zones; a detector positioned for capturing data regarding said areas of reflectance and shadow; and a processor for analyzing the data regarding said areas to determine dimensional data regarding the area of the selected throat. 
   In accordance with another aspect of the present invention, there is a provided a device for measuring a throat area in a vane ring for gas turbine engines, the vane ring having an annular array of vanes defining a plurality of individual throats between adjacent leading and following vanes of the array, the device comprising: a at least one primary lighting source adapted to radiate light onto a vane ring in a manner to provide an area of reflectance surrounding an area of primary shadow, the area of primary shadow substantially corresponding to an area of a selected throat to be measured, the at least one primary source being positioned and focused light beams to provide an effective virtual lighting source located between the primary lighting source and the selected throat; a detector positioned for capturing data regarding said areas of reflectance and shadow; and a processor for analyzing data to determine dimensional data regarding the area of the selected throat. 
   In accordance with another aspect of the present invention, there is a provided a device for measuring a throat area in a vane ring for gas turbine engines, the vane ring having an annular array of vanes defining a plurality of individual throats between adjacent leading and following vanes of the array, the device comprising at least one primary lighting source adapted to radiate light onto a vane ring in a manner to provide an area of reflectance surrounding an area of primary shadow, the area of primary shadow substantially corresponding to an area of a selected throat to be measured; a detector positioned for capturing data regarding of said areas of reflectance and shadow; a polarizing filter co-operating with the detector to filter said data; and a processor for analyzing the data to determine dimensional data regarding the area of the selected throat. 
   In accordance with another aspect of the present invention, there is a provided a method of measuring a throat area in a vane ring for gas turbine engines, the vane ring having an annular array of vanes defining a plurality of individual throats between adjacent leading and following vanes of the array, the method comprising directing light towards a selected throat of the vane ring to provide at least one area of reflectance and at least one area of primary shadow, said array, be proportional to an area of the selected throat; selectively varying the intensity of reflected light across the area of reflectance to permit more uniform reflectance data to be received from the area of reflectance; acquiring reflectance data from the area of reflectance; and analyzing the data to determine dimensional data regarding the throat area of the selected throat. 
   The present invention in one aspect advantageously improves the accuracy and robustness of measurement by providing a more steady and homogenous lighting reflection to be measured, which improves contrast and reduces light saturation of the light sensors. In another aspect, the accuracy of the throat area measurement is improved by minimizing secondary shadow cast in the area of reflection surrounding the area of shadow corresponding to the throat area of the selected throat being measured. These advantages and other features of the present invention will be better understood with reference to the preferred embodiments described hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference will now be made to the accompanying drawings showing by way of illustration preferred embodiments, in which: 
       FIG. 1  is a perspective view of a single vane ring showing the trailing edges of an array of stator vanes confined between an inner and outer shroud; 
       FIG. 2  is a schematic view illustrating a vane throat measurement device according to a prior art measurement technique; 
       FIG. 3  is a schematic elevational sectional view of a device according to one embodiment of the present invention; 
       FIG. 4  is a schematic view of the device in an direction indicated by arrow C in  FIG. 3 ; 
       FIG. 4A  is an isometric view of a single light source according to an aspect the invention; 
       FIG. 5  is an enlarged partial view of  FIG. 4 , showing the adjustment of lighting zones; 
       FIG. 6  is a schematic view of the device in the longitudinal direction of the vane ring, as indicated by arrow L in  FIG. 3 ; 
       FIG. 7A  is a schematic view, similar to  FIG. 4 , of an alternate embodiment of the present invention; 
       FIG. 7B  is a schematic view, similar to  FIG. 4 , of an alternate embodiment of the present invention; and 
       FIG. 8  is a schematic view of a further embodiment of the present invention, similar to that of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A method and a device for measuring the throat area of a vane ring for gas turbine engines is described in the applicant&#39;s co-pending U.S. patent application Ser. No. 10/270,506, which is incorporated herein by reference. 
   Referring to  FIGS. 1 and 2 , a vane ring  8  has an annular array of stator vanes  9   a  and  9   b  which define a plurality of individual throats  10  therebetween. Each throat  10  is an opening bounded by a inner vane shroud  11 , an outer vane shroud  12 , the trailing edge  13  of the leading vane  9   a , and a line  14  (See  FIG. 3 ) projected onto the convex surface of the adjacent or following vane  9   b . The shrouds  11  and  12  extend above the trailing edge  13  and the throat  10  so as to obscure a view of the latter from some perspective angles. A plurality of light or other radiation sources  30  light the vane ring  8  in a suitable manner, and a camera  26  or other sensor is provided to capture an image of reflected radiation. The method of operation of this device is described in more detail in the incorporated reference, applicant&#39;s co-pending application Ser. No. 10/270,506, and thus need not be discussed further here. 
   Referring still to  FIGS. 1 and 2 , the vanes  9   a  and  9   b  defining the throat area can be positioned relatively deeply relative to the shrouds  11 ,  12 , and thus secondary shadows  34  tend to be cast by the radially outwardly extending peripheral portion of the shrouds  11 ,  12 , as illustrated in  FIG. 2 . These secondary shadows  34  tend to dilute the contrast between the areas of reflection and the areas of shadow, thereby creating errors during an image analyzing process conducted by a processor  37 . 
   The problem of secondary shadows can be addressed in part by having a low angle of incidence between the light and the vane ring as shown in  FIG. 2 , so that the secondary shadows are not cast by the shrouds. However, low incidence angles detrimentally decrease the amount of light that is reflected back towards the camera  26 , it being understood, with reference to  FIG. 2 , that the camera  26  is placed roughly perpendicularly relative to the trailing edge and therefore light having a high angle of incidence (i.e. striking the trailing edge more perpendicularly) would permit more light to be reflected in the direction of the camera  26 . This means that some hard-to-light areas of the vane ring, such as the shroud areas, do not reflect as well as other easier-to-light areas, such as the vane trailing edges. 
   The problem of low incidence angle lighting could be compensated for by increasing the light intensity, however, increasing light intensity will also tend to increase reflectance from the easier-to-light (and therefore typically brighter) areas of the vane ring, such as the trailing edges. Therefore, when an electronic light sensor is used, such as a digital camera, increasing the light intensity also tends causes a larger than desired reflectance from the easier-to-light areas of the vane ring, which can overload the light sensing device in the sensor (e.g. in a digital camera, the charge-coupled devices or CCDs). This results in an effect called “blooming” in which the overloaded sensor mishandles the light data the resultant image has light “bleeding” into adjacent areas of dark, thereby causing a distortion of the resultant image. Over-lighting thus tends to distort the light/dark boundary delineating the throat  10  of the vane ring  8 , and therefore leads to inaccuracies in measurement, and particularly so if the vane ring has a highly reflective or polished finish. 
     FIG. 3  illustrates a device  20  according to the present invention which addresses this and other problems. Device  20  includes a fixture  22  preferably with a rotary indexing table  24  so that the vane ring  8  can be progressively rotated about its axis to permit a light detector  26 , for example a camera, to capture images of each throat and then permit a processor  37  to analyze the data to acquire dimensional data on the total throat area for the entire ring  8 . 
   The vane ring  8  is placed in the fixture  22  in an imaging position such that the periphery of a selected individual throat  10  is within an optical measuring field of view  28  of camera  26 . The device  20  further includes a plurality of primary lighting sources  30  (see also  FIG. 4 ), which are positioned in a throat-defining position in order to cast light (represented by area  31 ) such that an area of shadow is cast on the vane ring  8  in a desired manner to highlight the selected throat  10 . The area of shadow is preferably closely surrounded by and contrasted with an area of reflection where the light is reflected by the vane ring  8 , thereby delineating the throat area. An auxiliary lighting source  32  is preferably positioned to cast light (indicated by area  33 ) illuminate the trailing edge of the leading vane  9   a.    
   Referring still to  FIG. 3 , the viewing direction of the camera  26  (indicated as arrow C) is preferably substantially perpendicular to the field of view  28  of the selected throat  10  to maximize accuracy and ease of measure. The preferred viewing direction C is thus from slightly above perpendicular, in order to more precisely define the lower boundary of the shadow which is defined on the convex surface of the following vane  9   b . With the vane ring  8  positioned in the fixture  22  in the imaging position, shown with the periphery of the individual throat  10  within the measuring field of view  28 , the camera  26  can proceed to capture an image of a portion of the vane ring  8  within the field of view  28 , with the camera  26  or other radiation detector to suit the lighting sources  30  and  32 . 
   In use, the image captured by the camera  26  is processed by processor  37  which analyzes the image to calculate and acquire the dimensional data of the selected throat  10 . The processor  37  preferably also sums the measured data to acquire the dimensional data of a total throat area  10  of the vane ring  8 . In order to progressively capture the image of each throat  10  of the vane ring  8 , the vane ring  8  held in the fixture  22  is rotated with the rotary indexing table  24  from one position to another. 
   The primary lighting sources  30  and auxiliary lighting source(s)  32  are typically collimated to provide sharp definition to the light/shadow boundaries. However, in order to address the described problems associated with low incidence angle lighting and blooming, in one embodiment of the present invention best illustrated in  FIG. 4 , the invention includes a plurality of primary lighting sources  30  (four in this embodiment) which are positioned adjacent one another and angled with respect to each other, as will be described further below. Each of the primary lighting sources  30  radiates a beam which is substantially focused in one plane and substantially collimated in another plane, as shown in  FIG. 4A . (For convenience of illustration, light is represented as a solid in  FIG. 3   b .) Thus, each beam is preferably prismatic Further, the light beams are preferably all focused to coincide along an single axis, which thereby creates, in effect, a virtual light source  36  which is a line source. The combined effect is that light thus apparently radiates from the virtual light line source  36  and has a plurality of zones  38  which may be cast upon a selected region of the vane ring  8 , as desired, as shown in  FIG. 4 . Each lighting zone  38  of course corresponds to, and may therefore be independently controlled through, one of the primary lighting sources  30 . That is, the intensity of the primary lighting sources  30  is preferably adjustable, for example by the operator, or more preferably by a computer based on feedback received from the camera or other sensor(s) or in any other suitable manner, to permit the intensity of zones  38  to vary according to preference. 
   As is illustrated in  FIG. 4 , the respective radiating zones  38  are adjacent to each other but preferably have little or no overlap or gap between adjacent zones  38 , to minimize unwanted increase or decrease in intensity around the perimeter of the throat  10 . The virtual lighting source  36  is preferably located in a close relationship relative to the selected throat  10  so that light can be radiated on the region of the vane ring  8  without substantial secondary shadow being cast by either one of shrouds  11 ,  12 , such that all surfaces surrounding the throat opening of the vane ring  8  are illuminated adequately. Preferably, the distance between the virtual primary lighting source  36  and the selected throat  10  of the vane ring  8  may be adjusted depending on the size of the vane ring  8  and the selected throat  10 . A larger vane ring  8 ′ having a selected throat  10 ′ (shown in broken lines in  FIG. 4 ) may require a greater distance between the virtual primary lighting source  36  and the selected throat  10 ′ of the vane ring  8 ′ for adequate lighting, for example. Adjustment of the position of the virtual source location relative to the subject vane ring may be achieved by moving the vane ring relative to the virtual source (preferred), repositioning the direction of lighting sources  30 , and/or through the use of a moveable lens system as described below with reference to  FIG. 8 . 
   The individual primary lighting sources  30  are preferably controlled independently, such that the intensity of each lighting zone  38  can be individually adjusted (automatically or manually, as desired) and the beam focusing angles “A” of the respective primary sources  30 , may adjusted. The angles A may be equal, as shown in  FIG. 4 , or may be different, as shown in  FIG. 5 , depending on the benefits which may be presented when lighting a particular subject. 
     FIG. 5  illustrates an example of an adjustment of the intensity of individual lighting zones for better delineating the throat area  10 . The surfaces surrounding the throat opening are typically disposed at different distances away from the virtual primary lighting source  36  because of the geometry of the vane ring  8  to be lighted. The surfaces around the throat opening may also be different with respect to light reflectance, perhaps because of different materials and surface conditions of such parts, light reflection angles, etc. The virtual primary lighting source  36  provides lighting zones  38  which can be advantageously adjusted in light intensity. Therefore, it may be preferable to arrange a virtual primary lighting source  36  having wider inner lighting zones (having angles A 2  and A 3 ) which substantially light the vanes  9   a  and  9   b , and narrower outer lighting zones (having angles A 1  and A 4 ) which substantially light the inner and outer shrouds  11  and  12 . The intensity and size of these inner and outer lighting zones  38  can preferably be adjusted according to the light reflecting features of the respective shrouds  11 ,  12  and vanes  9   a  and  9   b . Thus, the region for the selected throat  10  can be lighted in a manner to substantially avoid casting secondary shadow while causing no significant blooming problem. It is to be understood that the “zones” discussed are conceptual in nature and, in practice, they may be any size and number, and may also be provided by a common light or other radiation source having variable intensity “subzones”. 
   Referring to  FIGS. 3 and 6 , as mentioned an auxiliary lighting source  32  may be used to light the vane trailing edge  13  while avoiding illumination of the inside of the vane throat opening. The beam from the auxiliary lighting source  32  is projected at a low incidence angle (as shown in  FIG. 3 ), preferably just above the outer shroud  12  and about 10° to 15° above the horizontal line, in order to avoid the secondary shadow problem caused by the outer shroud  12 . Similar to the primary lighting source  30 , the auxiliary lighting source  32  is preferably radiates a beam collimated in one plane (see  FIG. 3 ) and focused in another plane (see  FIG. 6 ). The beam from the auxiliary lighting source  32  is thus also prismatic and focused on a straight line to thereby provide a virtual auxiliary lighting source  40 , which is in a close relationship to the trailing edge  13  of the vane  9   a . The resultant auxiliary lighting zone  42  is thus preferably sized and shaped for just lighting the trailing edge  13  of the vane  9   a . Use of the auxiliary lighting source  32  is optional, and may not add any improvement at all depending on how the primary lighting sources  30  are used in accordance with the present invention. 
   In an alternate arrangement shown in  FIG. 7A , one combined primary lighting source  36  and camera/sensor  26  is positioned in a close relationship relative to the selected throat  10 , such as the location of the virtual primary lighting source  36 , in order to radiate light on a region of the vane ring  8  covering the area of shadow and the area of reflection, thereby avoiding secondary shadow cast in the area of reflection resulting from inadequately radiating the area of reflection. In other words, the virtual lighting source  36  can be replaced by at least one physical lighting source positioned in the same location. To avoid interference, the light source and camera/sensor may be in effect combined (e.g. through the use of fibre optics), so that the presence of one does not interfere with the operation of the other). Similarly, the “single” source  30  may be, in fact, a source  30  comprising a single bundle of a plurality of fibre-optically delivered light sources, to thus provide a sort of hybrid between this and previously-described embodiments. The single source may be further improved by the optional addition of a filter  50  (shown as a broken line) on the light that allows the effective intensity of the light to be varied as a function of the location of the portion of the surface being illuminated (e.g. dimmer in the centre and brighter towards the outer shroud areas). This permits a net effect similar to the multiple source solution presented above. In another configuration, shown in  FIG. 7B , a plurality of primary lighting sources providing respective radiating zones have relatively small sizes and thus can be positioned closely to the throat so that they are illuminating to adequately without substantial secondary shadow to thereby radiate light generally evenly on a region of the vane ring  8 . The intensity of the respective radiating zones are preferably independently adjustable. The camera/sensor  26  (not shown in  FIG. 7B ) could be separate or made integral with (e.g. by fibre optics) the lighting arrangement. 
   In another embodiment of the present invention, the camera  26  may include a polarizing filter  44  (see  FIG. 3 ) such that the intensity of polarized reflected light being received by the camera  26  is reduced, which is preferably done to reduce the occurrence of blooming. This technique may be employed with lighting techniques according to the present invention, or when conventional lighting sources are employed. 
   In accordance with another embodiment of the present invention (not shown), a coating material is selectively applied to the vane ring  8  to selectively reduce the intensity of reflectance the vane ring  8  around the perimeter of throat  10 . With such a coating material on the vane ring  8 , the intensity of the light from both the primary and auxiliary lighting sources  30  and  32 , can be selectively decreased at desired locations to minimize blooming problems, even when conventional lighting sources are employed. For example, areas of problematically high reflectance (e.g. the trailing edge) can be preferentially coated with such powder to reduce the reflectance of this area and thereby achieve a more uniform reflectance of the subject to be measured. (Conversely, a coating may be use to enhance the reflectance of the subjects that typically have a lower reflectance). The method of measuring the throat area in such a vane ring with the coating material thereon is otherwise similar to other embodiments as above described. 
   In general, both the primary and auxiliary lighting sources  30  and  32  for the above-described embodiments can be alternatively replaced by any suitable radiation sources radiating other than visible light, such as infrared or ultraviolet. 
   A laser may also be used, as shown in  FIG. 8 . A laser projection apparatus  60  and a moveable lens apparatus  62  is provided. The laser projection apparatus  60  comprises a suitable laser assembly  64  for projecting preferably a single laser beam B onto a rotatable mirror  66 , such as a galvanometer mirror or other moveable reflecting device, for reflection through a lens  68 . The mirror and lens permit the laser beam B to be ‘steered’ into a variety of directions which result in a variable trajectory for the beam B (two examples of which are depicted in  FIG. 8 ). A controller  70  permits control of the mirror angle. Moveable lens apparatus  62  comprises a second lens  68  for redirecting the leaser beam B towards the subject throat  10  of the vane ring  8 . As the mirror  66  angle is changed, lenses  68  co-operate to direct the laser beam always through a virtual source  72 , the location of which may be varied by movement of lens apparatus  62 . As with previous embodiments, movement of the virtual source  72  might be desired, for example, to permit proper setup of a particular vane arrangement (i.e. the desired distance between the vane ring  8  and the virtual source  72  may vary from one vane ring configuration to the next depending, for example, on the height of the shrouds relative to the width between the shrouds). In use, the controller  72  adjusts mirror  66  to direct laser beam B to trace an outline of the throat  10 , which outline may be captured by camera  26  (not shown) in a similar manner as described above for analysis and determination of throat area. in contrast to previous embodiments, in this approach the an image of the throat area is captured through a sequential capture of the boundary as traced by the laser, rather than the entire boundary being captured at once as before. By providing the virtual source  72 , secondary shadow is avoided. In a further embodiment, controller  72  may also control the intensity of the laser  64  so that beam B may have variable intensity as the throat perimeter is traced, as, desired. 
   Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. For example, multiple cameras  26  may be employed, in which each camera  26  may measure a defined portion of the throat area, the results of which are then summed to obtain a total. Alternately, each camera may be used to measure the entire throat and results then averaged to improve accuracy. Though the terms ‘light’ and ‘camera’ pervade this description and claims, it will be understood that this in intended to encompass any suitable radiation source(s) and detecting device(s) that may be used, and that a single type need not be relied upon, but combinations thereof may also be employed. Although CCD technology has been discussed, other sensors may employ light sensitive devices such as charge injection devices (CIDs) of complementary metal oxide semiconductor (CMOS) sensors, and the present invention is not intended to be limited to the use of a particular sensing technology. The skilled reader will understand that the laser “tracing” technique may also be employed with other types of light, as well. The foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.