Abstract:
The three-dimensional real structure of a component can be captured by means of best fit by simply recording two-dimensional images and comparing a known three-dimensional model. A component is placed on a measurement stage having reference marks and is photographed several times in two-dimensions. The photo recordings are compared with a three-dimensional model of the component. A three-dimensional model is produced using best fit of the two-dimensional recordings and the stored model.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a 35 U.S.C. §111 Continuation in Part of International Application PCT/EP2012/068046, filed Sep. 14, 2012, which claims priority of European Patent Application No. 11187504.3, filed Nov. 2, 2011, the contents of which are incorporated by reference herein. The PCT International Application was published in the German language. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a three-dimensional surface inspection system using two-dimensional recordings. 
       TECHNICAL BACKGROUND 
       [0003]    For many components, 100% optical examination of the entire three-dimensional component surfaces is necessary. This comprises, for example in turbine blades, the orientation of the cooling-air holes and the entire coating. 
         [0004]    Optical examination and three-dimensional capture of a component involves known processes and apparatus. But, three-dimensional capture by two-dimensional photography is not rapidly and easily accomplished by known three-dimensional capture processes and apparatus. Furthermore, when an objective of the three-dimensional capture is to enable a component to be marked with markings relevant to further handling or treatment of the component, known systems and methods are time consuming and costly. 
         [0005]    Known three-dimensional capturing systems are very time-consuming to use and costly. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore the object of the present invention to solve the foregoing problems. A further object is to simplify the procedure of three-dimensional capture. 
         [0007]    The objects are achieved by a three-dimensional surface inspection system and a method according to the invention. 
         [0008]    A three-dimensional surface inspection system has a measurement stage on which a component may be placed for three-dimensional capture. At least one and particularly a plurality of cameras takes typically more than one two-dimensional recording of the component on the stage. The captured two-dimensional recordings are compared in a computer to a stored three-dimensional model. Then a three-dimensional model of the component is produced using a best fit of the two-dimensional photographed recordings and the stored three-dimensional model. 
         [0009]    A plurality of reference marks are provided, which are typically used during the photographic stage as reference mark for the component being photographed. The reference marks are particularly on the measurement stage. 
         [0010]    At least one of the reference marks preferably includes a plurality of markings arranged in a particular pattern. The reference marks may be arranged on a front end of the measurement stage or at least on corners of the stage. 
         [0011]    There is illumination for surface inspection and the illumination unit may make selective illumination of the component. Extraneous light is suppressed. 
         [0012]    The invention also concerns a method for three-dimensional capturing of a component. The method preferably uses an embodiment of the system described above. The component is placed in at least two different positions on the measurement stage to be two-dimensionally captured by the cameras. Then the three-dimensionality of the component is determined using a best fit with a known three-dimensional model of the component. The reference marks are used for ascertaining the orientation of the component on the stage, including after the orientation of the component has been changed. The component is captured by the individual two-dimensional images and the orientation of the component is captured with the assistance of the reference marks. The component is then finally adjusted to the known three-dimensional model using a best-fit analysis. Then individual images are mapped onto the three-dimensional model. This would enable for example the individual two-dimensional recordings to be combined with the known three-dimensional stored model to produce a three-dimensional contour of the component that was photographed. 
         [0013]    The advantages of the invention are simple handling of the system and more accurate measurements. 
     
    
     
         [0014]    In the figures: 
           [0015]      FIGS. 1-6  show exemplary embodiments of the invention. 
           [0016]      FIG. 7  shows a turbine blade. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]    The description and the figures illustrate merely exemplary embodiments of the invention. 
         [0018]      FIG. 1  illustrates a three-dimensional surface inspection system  1  according to the invention. The three-dimensional surface inspection system  1  has a measurement stage  10 , on which the component  4 ,  120 ,  130  to be inspected is located. 
         [0019]    Around the component  4 ,  120 ,  130 , at least one camera  7 ′ is present, the position of which is changed. Alternatively, a plurality of cameras  7 ′, . . . ,  7   V , . . . , which are preferably fixedly mounted, are used. 
         [0020]    The cameras  7 ′,  7 ″ are arranged such that they capture the entire surface of the component  4 ,  120 ,  130  which faces away from the measurement stage  10 . 
         [0021]    The mounting of the cameras  7 ′,  7 ″, . . . can be varied, depending on the types of components. For turbine blades  120 ,  130  of varying size and type (moving blade  120  or guide vane  130 ), the same fixed mounting of cameras  7 ′,  7 ″, . . . can be used. 
         [0022]    At least one reference mark  13 ′,  13 ″, . . . (as illustrated in  FIGS. 2 to 6 ) is present on the measurement stage  10  according to  FIG. 1 . In this case, there are preferably eight reference marks. 
         [0023]    The three-dimensional surface inspection takes place as follows:
   1. Providing an arrangement of the measurement stage  10 , camera system (one or more cameras  7 ′,  7 ″, . . . ), and illumination device  8 ′,  8 ″;   2. Providing reference marks  13  on the measurement stage  10 , or the measurement stage  10  already has them;   3. Positioning the component  4 ,  120 ,  130  on the measurement stage  10 . It is preferred to position the component in a flat manner if the component is of elongate construction;   4. Recording individual images using all fixedly mounted cameras  7 ′,  7 ″, . . . or one camera  7 ′ in various positions;   5. Capturing the orientation of the component  4 ,  120 ,  130  from the individual images;   6. Finely adjusting the component to the known three-dimensional model using best fit analysis;   7. Mapping the individual images onto the associated three-dimensional model;   8. Optimizing the overlapping image regions by averaging, contrast setting or edge sharpness;   9. Turning components  4 ,  120 ,  130  and repeating from step 3;   10. Combining individual recordings two-dimensional with known stored three-dimensional model to produce “three-dimensional contour of the component.”   
 
         [0034]    After the images have been recorded by the camera  7 , as stated in Step 4 above, the succeeding steps in this inspection are performed preferably by a computer  20  which is a normal workplace computer, a micro controller, a special image processing unit or the like. One skilled in the art would understand how to program and operate the computer to achieve the operational functions 5-8 and 10 described above. 
         [0035]    The surfaces of the components  4 ,  120 ,  130  are captured optionally using a projected light structure, in particular stripes, such that edges of the component  4 ,  120 ,  130  are captured better. 
         [0036]    Optionally, the component  4 ,  120 ,  130  is selectively illuminated, in particular using projection devices, such that strongly reflective regions are not illuminated or illuminated less. This is for turbine blades  120 ,  130 , for example the blade root  183 ,  400  ( FIG. 7 ). 
         [0037]    Extraneous light is preferably suppressed by monochromatic illumination and image evaluation. 
         [0038]    A ring light on the camera objective is preferably used and/or lateral dark-field illumination is used to highlight small defects such as scratches, unevennesses, pressure points. 
         [0039]    The reference mark  13 ,  13 ′ is preferably of annular design and/or arranged in the shape of a ring and has markings  14 ′- 14   IV . The markings  14 ′, . . .  14   IV  can be line-shaped or point-shaped ( FIGS. 3 ,  4 ,  5 ,  6 ). 
         [0040]      FIGS. 2-6  illustrate different reference marks which can be arranged or introduced on the measurement stage  10 . 
         [0041]      FIG. 2  shows a reference mark  13  having two line-shaped markings  14 ′,  14 ″, which extend radially from a circle line  16 , and two V-shaped markings  14 ″,  14 ″′, the tips of which likewise extend radially. The sequence of the different markings  14 ′, . . . ,  14   IV  of a reference mark  13  is unimportant (likewise in  FIG. 5 ). 
         [0042]      FIG. 3  shows a circular structure of a reference element  13 , which is formed by at least two, in this case four curved line-shaped markings  14 ′, . . .  14   IV , which in this case preferably form a circular structure. 
         [0043]    The outer closed, circular line  16  can be present, or simply is an imaginary line representing the profile of the arrangements of the markings  14 ′,  14 ″, . . . ( FIGS. 2-5 ). 
         [0044]    One alternative to the line-shaped markings  14 ′,  14 ″ according to  FIG. 3  is a plurality of point-shaped markings  14 ′,  14 ″, . . . , according to  FIG. 4  a reference element  13 ,  13 ′,  13 ″, which likewise form a circle or oval shape. 
         [0045]    Likewise conceivable is a combination of line-shaped and circle-shaped (points) markings  14 ′,  14 ″, . . . , which preferably enclose a circle-shaped or oval-shaped structure, as is shown in  FIG. 5 . 
         [0046]    The markings  14 ′,  14 ″, . . . can also be arranged in a square or rectangular shape. 
         [0047]      FIG. 6  shows a measurement stage  10 , on which preferably two reference marks  13 ′,  13 ″ are arranged. 
         [0048]    The reference marks  13 ,  13 ′ are in this case line-shaped elements, which are preferably arranged on the front ends of the measurement stage  10 . 
         [0049]    At least two or preferably four reference marks  13 ,  13 ′,  13 ″,  13 ′″ according to  FIG. 2 ,  3 ,  4 ,  5  or  6  can likewise be arranged in the corners of a measurement stage  10  (not illustrated). 
         [0050]    Optionally, an identification (binary code) of the reference marks can take place, which is detectable using the camera  7 ′,  7 ″. 
         [0051]    It is also possible optionally for the reference marks to be projected onto a desired stage using a projection device and to be measured subsequently (measuring tape). This option should preferably be used in a mobile system without coded examination stage. 
         [0052]    The reference marks  13  serve to ascertain the orientation of the component  4 ,  120 ,  130 , if the orientation thereof has been changed, in particular rotated (step 9). The recording of the component  4 ,  120 ,  130  from both sides can thus be stitched together. No reference marks on the component  4 ,  120 ,  130  are necessary. 
         [0053]    The advantages are:
       no three-dimensional measurement of the component  4 ,  120 ,  130  is necessary;   complete capturing of the surface, since no obstruction by clamping apparatus;   free positioning of the cameras is possible (alignments using reference marks);   no time-consuming three-dimensional measurement is necessary;   no obstruction through reference marks on the object under examination. Exact orientation illustration of all noticeable points of the examination object surface in three-dimensional;   subsequent measurement on the three-dimensional model is possible;   small data amounts (&lt;10 MB) with respect to typical three-dimensional recordings (&gt;100 MB);   quick illustration of the two-dimensional individual images on three-dimensional model.       
 
         [0062]      FIG. 7  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0063]    The turbomachine may be a gas turbine of an aircraft or of a power plant for electricity generation, a steam turbine or a compressor. 
         [0064]    The blade  120 ,  130  comprises, successively along the longitudinal axis  121 , a fastening zone  400 , a blade platform  403  adjacent thereto as well as a main blade  406  and a blade tip  415 . 
         [0065]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its blade tip  415 . 
         [0066]    A blade root  183  which is used to fasten the rotor blades  120 ,  130  on a shaft or a disk (not shown) is formed in the fastening zone  400 . 
         [0067]    The blade root  183  is configured, for example, as a hammerhead. Other configurations as a fir tree or dovetail root are possible. 
         [0068]    The blade  120 ,  130  comprises a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade  406 . 
         [0069]    In conventional blades  120 ,  130 , for example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade  120 ,  130 . 
         [0070]    Such superalloys are known for example from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A, WO 99/67435 or WO 00/44949. 
         [0071]    The blade  120 ,  130  may in this case be manufactured by a casting method, also by means of directional solidification, by a forging method, by a machining method or combinations thereof. 
         [0072]    Workpieces with a single-crystal structure or single-crystal structures are used as components for machines which are exposed to heavy mechanical, thermal and/or chemical loads during operation. 
         [0073]    Such single-crystal workpieces are manufactured, for example, by directional solidification from the melt. These are casting methods in which the liquid metal alloy is solidified to form a single-crystal structure, i.e. to form the single-crystal workpiece, or is directionally solidified. 
         [0074]    Dendritic crystals are in this case aligned along the heat flux and form either a rod crystalline grain structure (columnar, i.e. grains which extend over the entire length of the workpiece and in this case, according to general terminology usage, are referred to as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of a single crystal. It is necessary to avoid the transition to globulitic (polycrystalline) solidification in these methods, since nondirectional growth will necessarily form transverse and longitudinal grain boundaries which negate the beneficial properties of the directionally solidified or single-crystal component. 
         [0075]    When directionally solidified structures are referred to in general, this is intended to mean both single crystals which have no grain boundaries or at most small-angle grain boundaries, and also rod crystal structures which, although they do have grain boundaries extending in the longitudinal direction, do not have any transverse grain boundaries. These latter crystalline structures are also referred to as directionally solidified structures. 
         [0076]    Such methods are known from U.S. Pat. Nos. 6,024,792 and EP 0 892 090 A1. 
         [0077]    The blades  120 ,  130  may also have coatings against corrosion or oxidation, for example MCrAlX (M is at least one element from the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0078]    The density is preferably 95% of the theoretical density. 
         [0079]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an interlayer or as the outermost layer). 
         [0080]    The layer composition preferably comprises Co—30Ni—28Cr—8Al—0.6Y—0.7Si or Co—28Ni—24Cr—10Al—0.6Y. Besides these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers such as Ni—10Cr—12Al—0.6Y—3Re or Ni—12Co—21Cr—11Al—0.4Y—2Re or Ni—25Co—17Cr—10Al—0.4Y—1.5Re. 
         [0081]    On the MCrAlX, there may furthermore be a thermal barrier layer, which is preferably the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is not stabilized or is partially or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0082]    The thermal barrier layer covers the entire MCrAlX layer. Rod-shaped grains are produced in the thermal barrier layer by suitable coating methods, for example electon beam physical vapor deposition (EB-PVD). 
         [0083]    Other coating methods may be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier layer may comprise porous, micro- or macro-cracked grains for better thermal shock resistance. The thermal barrier layer is thus preferably more porous than the MCrAlX layer. 
         [0084]    Refurbishment means that components  120 ,  130  may need to be stripped of protective layers (for example by sandblasting) after their use. The corrosion and/or oxidation layers or products are then removed. Optionally, cracks in the component  120 ,  130  are also repaired. The component  120 ,  130  is then recoated and the component  120 ,  130  is used again. 
         [0085]    The blade  120 ,  130  may be designed to be hollow or solid. If the blade  120 ,  130  is intended to be cooled, it will be hollow and optionally also comprise film cooling holes  418  (indicated by dashes).