Abstract:
A method for the ultrasound check of a test object involves moving a test probe along a test probe surface and sending ultrasound impulses into the test object by the test probe. Respective echo signals corresponding with the emitted ultrasound impulses are received by the test probe. An image of a predetermined test region of the test object is prepared on the basis of an overlapping and averaging of amplitude values of the received echo signals by a data processing unit. The respective position of the test probe when sending the ultrasound signals and/or when receiving the corresponding echo signals is captured by a capturing unit. The respectively captured positions of the test probe are considered when creating the image of the test region of the test object.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and hereby claims priority to International Application No. PCT/EP2014/050478 filed on Jan. 13, 2014 and German Application No. 10 2013 200 974.7 filed on Jan. 22, 2013, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a method and a system for the ultrasonic testing of a test object. 
         [0003]    For the nondestructive testing of test objects, a very wide variety of ultrasonic test methods are known. For better localization and separation of the defects during nondestructive testing with ultrasound, the SAFT (Synthetic Aperture Focusing Technique) analysis technique is known. The inspection is in this case carried out like a conventional ultrasonic test, but the data are recorded without rectification. During the subsequent analysis of the measurement data, amplitude sums are determined from a multiplicity of measurement signals for respective small volume elements, which are also referred to as so-called voxels. Ultrasonic testing with the aid of SAFT analysis is conventionally used in the case of automated movement of a test head emitting the ultrasound pulses and receiving the corresponding echo signals. 
         [0004]    By the use of so-called phased-array test heads, test objects can be scanned not only mechanically but also electronically, i.e. a plurality of measurements are carried out in a defined grid by a kind of electronic displacement of the test head. In the case of a stationary test head, data that have been recorded with the same electronic scan can be evaluated by SAFT analysis. This works both for an unmoved test head and for a test head moved during the electronic scan, when the exact emission and reception positions and incidence angle and focusing at the reconstruction time are known. 
       SUMMARY 
       [0005]    It is one possible object to allow improved, in particular hand-guided ultrasonic testing of a test object with the aid of SAFT analysis. 
         [0006]    The inventors propose a method for the ultrasonic testing of a test object comprises the following: moving a test head along a test object surface and emitting ultrasound pulses into the test object by the test head; receiving respective echo signals corresponding to the emitted ultrasound pulses by the test head; compiling an image of a predetermined test region of the test object on the basis of superposition and averaging of amplitude values of the received echo signals by a data-processing device. In other words, the method for the ultrasonic testing of a test object includes the method required for a SAFT analysis, the proposed method being distinguished in that the respective positions of the test head during emission of the ultrasound signals and/or during reception of the corresponding echo signals are detected by a detecting device, and the respectively detected positions of the test head are taken into account during generation of the image of the test object. 
         [0007]    According to the proposals, therefore, the position of the test head on the surface of the test object is measured over the duration of the test. The measurement of the respective position is in this case carried out within relatively short time intervals and with a defined time relationship relative to the ultrasound pulses emitted for inspection of the test object. Preferably, the position measurement is respectively carried out when an ultrasound pulse is emitted. In addition, a position measurement may furthermore respectively be carried out when the echo signal corresponding to the emitted ultrasound pulse is received. 
         [0008]    As a function of the respective detected or measured positions of the test head, a respective instantaneous position of the test head is determined, preferably at the time of a respective emission of the ultrasound pulse and is used in the SAFT analysis for determination of the distance between a voxel to be reconstructed and the actual measurement position. 
         [0009]    The method makes it possible to use the ultrasonic testing of a test object with the aid of SAFT analysis even in the case of a hand-guided test head. Preferably, the test head may in this case be moved manually along the test object surface. In particular, the test head may be guided freely on the test object surface in the proposed method. The localization of defects in the test object is improved significantly by the method, individual defects being distinguishable better from one another and the signal-to-noise ratio being improved, in particular for manual, i.e. hand-guided testing. During the compilation of the image of the test region of the test object, this gives an improved resolution of group artefacts, i.e. individual artefacts lying close to one another, which could not be separated from one another without SAFT analysis and would therefore be evaluated as one larger artefact, and in particular improved detection of small defects. Small defects are in this case intended to mean defects having a dimension which is small in relation to the ultrasound pulse wavelength used. Furthermore, the test results which are achieved with the method can be interpreted particularly intuitively by referencing to a three-dimensional digital model of the test object. 
         [0010]    According to an advantageous configuration, an orientation of the test head during emission of the ultrasound signals and/or during reception of the corresponding echo signals is detected by the detecting device and is taken into account during generation of the image of the test region of the test object. Particularly in the case of manual ultrasonic testing, i.e. guiding of the test object by hand, it is relatively straightforward to move the test head along a test object surface configured in a nonplanar fashion, so that even such a test object can be examined by ultrasonic testing in respect of defects. In such cases, the problem arises that, depending on the position of the test head on the test object surface, the ultrasound pulses may be introduced into the test object with different orientations to one another, i.e. different angles. The detection of the respective orientation of the test head may in this case, for example, be carried out relative to a fixed reference coordinate system, an initial orientation of the test head at the start of the ultrasonic testing, or the like, so that there is a unique reference for determination of the respective orientation of the test head. By taking the orientation into account, it is possible to take into account both different angles with which ultrasound pulses are introduced into the test object and respective surface inclinations of the test object, so that better imaging of the test object by the ultrasonic testing is made possible overall. 
         [0011]    According to another advantageous configuration, the central position of the active aperture of the test head during emission of the ultrasound signals is determined with the aid of the detected position and orientation of the test head and is taken into account during generation of the image of the test region of the test object. An active aperture is in this case intended to mean that region of the test head which is used as an active emission or reception surface for the ultrasound pulses or the echo signals, respectively. If a phased-array test head is used, for example, the central position of the active aperture is that region which has specifically been correspondingly driven for the emission of the ultrasound pulses or the reception of the corresponding echo signals. Advantageously, the central position is in this case determined during respective emission of the ultrasound pulses and/or during respective reception of the corresponding echo signals. By determining the central position of the currently active aperture of the test head, particularly accurate ultrasonic testing and generation of an image of the test region of the test object can be achieved. 
         [0012]    According to another advantageous configuration, the image of the test region of the test object is compiled during the movement of the test head along the test object surface. In other words, a corresponding analysis result of the ultrasonic testing may optionally be displayed already during the ongoing measurement. In this way, corresponding localized defects in the test object can be deduced particularly rapidly, i.e. even while the ultrasonic testing is being carried out. 
         [0013]    According to another advantageous configuration, data about the detected positions and/or orientations and times respectively assigned thereto are stored. These data may be provided for subsequent evaluation, for example as an indication that no relevant test positions have been omitted during the ultrasonic testing, or for subsequent visualization of a three-dimensional model of the test object. 
         [0014]    According to another advantageous configuration, the ultrasonic testing is carried out with a plurality of test heads. The detection of the respective positions and/or orientations is in this case carried out for all the test heads and is taken into account during the compilation of the image of the test object. By using a plurality of test heads, it is possible to subject even large test objects to ultrasonic testing in a relatively short time. 
         [0015]    The inventors also propose a system for the ultrasonic testing of a test object comprises a test head, which can be moved along an object surface and by which ultrasound pulses can be emitted into the test object and respective echo signals corresponding to the emitted ultrasound pulses can be received. The system furthermore comprises a data-processing device, by which an image of a predeterminable test region of the test object can be compiled on the basis of superposition and averaging of amplitude values of the received echo signals. The system is in this case distinguished in that the system comprises a detecting device, by which respective positions of the test head during emission of the ultrasound signals and/or during reception of the corresponding ultrasound signals can be detected, the image of the test region of the test object being compilable by the data-processing device while taking the respectively detected positions of the test head into account. Advantageous configurations of the proposed method may in this case be regarded as advantageous configurations of the proposed system, the system in particular carries out the method. 
         [0016]    According to an advantageous configuration of the system, the detecting device comprises an optical movement sensor, which is fitted on the test head and by which the respective position relative to a reference point can be detected. The reference point may, for example, be the position at which the test head was arranged at the start of the ultrasonic testing. Advantageously, the detecting device in this case comprises a further optical movement sensor, which is fitted on the test head at a predetermined distance away from the other optical movement sensor and by which the respective position relative to a reference point can be detected. By the use of two movement sensors, which may for example operate according to the so-called optical flow measurement principle, and which are known from computer input devices, for example computer mice, locally varying optical properties of the test object surface can be used for the movement detection, in order to be able to determine the respective position of the test head at different times of the measurement. By addition of the second optical movement sensor, the movement detection can be expanded from two translational degrees of freedom to a third degree of freedom, namely a rotational degree of freedom. 
         [0017]    According to another advantageous configuration of the system, the detecting device comprises a multiplicity of ultrasound emitters fitted on the test head and at least one ultrasound receiver, which is arranged at a distance from the test head and by which the position and orientation of the test head can be determined with the aid of the ultrasound pulses emitted by the ultrasound emitters. In this way three-dimensional position information and respective orientations of the test head about the three spatial axes can be determined particularly reliably. A plurality of ultrasound receivers may also be provided. Furthermore, the positions of the ultrasound emitters and of the ultrasound receiver or ultrasound receivers may be interchanged. In other words, the ultrasound emitters or emitters may be provided on the test head, the ultrasound sensor being arranged stationary and at a corresponding distance from the test head. 
         [0018]    According to another advantageous embodiment, the detecting device comprises a swivelable holding device, on which the test head is fitted so that it can be moved in rotation, the holding device comprising a distance and rotation transducer, by which the position and/or orientation of the test head can be determined. In this way, respective positioning of the test head in all three spatial directions, as well as the orientation of the test head about all three spatial axes, can likewise be detected reliably. 
         [0019]    According to another advantageous configuration of the system, the detecting device and comprises an image acquisition device, by which a multiplicity of optical markings applied on the test head can be detected, and on the basis thereof the position and orientation of the test head can be determined. The optical markings may for example be active markings, i.e. light-emitting markings, or passive markings which reflect the ambient light or auxiliary illumination. By corresponding detection of the optical markings, three-dimensional positioning and orientation of the test head can be determined continuously, for example relative to a predetermined coordinate system. 
         [0020]    According to another advantageous embodiment of the system, the detecting device comprises an image acquisition device fitted on the test head, by which a multiplicity of optical markings applied on the test head can be detected, and on the basis thereof the position and orientation of the test head can be determined. Preferably, the detecting device comprises a projection device, by which the optical markings can be projected onto the test object surface with a predetermined pattern. The predetermined pattern may for example be a dot, strip or checkerboard pattern, or the like. Configuration of the pattern, which is locally varied in a predetermined way, for example by encoding by the dot shape, the arrangement of the dots, the wavelength or the like, is in this case advantageous. In this way, particularly simple and reliable determination of the positioning and orientation of the test head is made possible. 
         [0021]    Lastly, according to another advantageous configuration of the system, the test head is configured as a perpendicular test head, angled test head or phased-array test head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
           [0023]      FIG. 1  shows a schematic perspective view of a system for the ultrasonic testing of a test object, two optical movement sensors for detecting the position and orientation of the test head being arranged on the latter; 
           [0024]      FIG. 2  shows a schematic perspective view of an alternative embodiment of the system for the ultrasonic testing of a test object, an ultrasound receiver being arranged on one arm above a T-shaped test head on which three ultrasound emitters are in turn fitted; 
           [0025]      FIG. 3  shows a perspective view of another alternative embodiment for the ultrasonic testing of a test object, a hand-guided test head being arranged on a swivelable holding device; 
           [0026]      FIG. 4  shows a schematic perspective view of another embodiment of the system for the ultrasonic testing of a test object, a multiplicity of optical markings being applied on a test object and an image acquisition device arranged above the test head being provided; and 
           [0027]      FIG. 5  shows a schematic perspective view of another embodiment of the system for the ultrasonic testing of a test object, an image acquisition device, by which a multiplicity of optical markings applied on the test object surface can be detected, being fitted on the test head. 
       
    
    
       [0028]    In the figures, elements which are the same or functionally the same are provided with the same references. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0030]    A system denoted overall by  10  for the ultrasonic testing of a test object  12  is shown in a schematic perspective view in  FIG. 1 . The system  10  comprises a test head  16 , which can be moved along a test object surface and by which ultrasound pulses can be emitted into the test object  12  and respective echo signals corresponding to the emitted ultrasound pulses can be received. The system  10  furthermore comprises a data-processing device  18  (not represented here) by which an image  20  (likewise not represented here) of a test region of the test object  12  can be compiled on the basis of superposition and averaging of amplitude values of the received echo signals. In other words, the system  10  for the ultrasonic testing of the test object  12  is configured in order to carry out so-called SAFT (Synthetic Aperture Focusing Technique) analysis in the scope of the ultrasonic testing of the test object  12 . 
         [0031]    The system  10  furthermore comprises a detecting device (not referred to in detail here), by which respective positions of the test head  16  during emission of the ultrasound signals and during reception of the corresponding echo signals can be detected. By the data-processing device  18 , the image  20  of the test object  12  can be compiled as a function of the respectively detected positions and/or orientations of the test head  16 . 
         [0032]    In the case represented here in  FIG. 1 , the detecting device comprises two optical movement sensors  22 ,  24 , which are fitted at a distance from one another on respective sides of the test head  16 . The movement sensors  22 ,  24  in the present case are 2D movement sensors that operate for example according to the optical flow measurement principle, which is known for example from computer mice. In this case, locally varied optical properties of the test object surface  14  are used for movement detection. With the aid of the two optical movement sensors  22 ,  24 , the respective position relative to a reference point, for example an initial position of the test head  16  at the start of the ultrasonic testing, can be detected. By using the two optical movement sensors  22 ,  24 , besides two-dimensional position detection of the test head  16  during the ultrasonic testing, the orientation of the test head in the form of a respective rotational movement about the normal to the test object surface  14  can also be detected as an additional degree of freedom. 
         [0033]    A method for ultrasonic testing of the test object  12  will be explained below. The test head  16  is moved manually, i.e. by hand, along the test object surface  14 , ultrasound pulses being emitted into the test object  12 . Echo signals respectively corresponding to the emitted ultrasound pulses are in this case received by the test head  16 . During the movement of the test head  16  along a test object surface  14 , the respective position and orientation of the test head during emission of the respective ultrasound pulses and during reception of the corresponding echo signals are detected with the aid of the optical movement sensors  22 ,  24 . 
         [0034]    On the basis of superposition and averaging of amplitude values of the received echo signals, an image  20  of a region to be tested of the test object is compiled by the data-processing device  18 . In this case, depending on which part of the test object  12  has been examined by the ultrasonic testing, an image  20  is compiled only of a subregion or of the entire test object  12 . 
         [0035]    The respectively detected positions and orientations of the test head  16  are taken into account during the generation of the image  20  of the test object  12 . The instantaneous position and orientation and of the test head  16  at the time of each ultrasound are detected from the measured positions and orientations and the respective time relationship and are used in so-called SAFT analysis for determining the distance between a respective reconstructed voxel and a measurement position. In this case, the central position of the active aperture of the test head during emission of the ultrasound is determined with the aid of the detected position and orientation of the test head  16  and is taken into account during the generation of the image of the test region of the test object  12 . The active aperture is in this case intended to mean the part of the test head  16  which is used as an effective emission or reception surface. A spatial offset between the respective position measurement and the position of the test head  16  is compensated for with the aid of the detected information about the test head orientation. 
         [0036]    The image  20  of the test object  12  is in this case already compiled during the movement of the test head  16  along the test object surface  14 . Corresponding fault positions, defects and the like in the test object  12  are therefore already identified early on and visualized by the image  20  compiled, for example, on a monitor  26  (not represented here). 
         [0037]    The data acquired during the ultrasonic testing about respective positions and times respectively assigned thereto are stored so that this information, or these data, are available for subsequent evaluation, for example as an indication that no relevant test position on the test object  12  has been omitted during the ultrasonic testing, or for visualization by a subsequent 3D model of the test object  12 . 
         [0038]    Unlike the representation shown here, the ultrasonic testing may also be carried out with a plurality of further test heads, which is suitable in particular when the test object  12  or the region to be studied of the test object  12  is particularly large. The test head  16 , or the further test heads, may in this case be configured as a perpendicular test head, angled test head or as a phased-array test head. 
         [0039]      FIG. 2  shows a perspective view of an alternative embodiment of the system  10 . In the present case, the detecting device (not referred to in detail here) comprises three ultrasound emitters  28 , which are arranged on the test head  16  configured with a T-shape in this case, or more precisely a T-shaped part on which the ultrasound emitters  28  are arranged being fitted on the test head  16 . An ultrasound receiver  30  arranged at a distance from the test head  16  is furthermore provided, by which the position and orientation of the test head  16  can be determined with the aid of the ultrasound pulses emitted by the ultrasound emitters  28 . In other words, the detection of the orientation is thus carried out by so-called acoustic tracking. With the aid of time-of-flight measurements, the distances between the ultrasound emitters  28  and the ultrasound receiver  30  can be determined and converted by triangulation into a three-dimensional position and orientation in space, so that the respective positionings and orientations of the test head  16  can be determined reliably during its movement along the test object surface  14 . 
         [0040]    Another alternative embodiment of the system  10  for ultrasonic testing of the test object  12  is shown in a perspective view in  FIG. 3 . In the case shown here, the detecting device comprises a swivelable holding device  32 , which is formed as a kind of swivel arm. On the holding device  32 , at its end, a test head  16  is fitted so that it can rotate, the holding device  32  comprising a multiplicity of position and rotation transducers (not referred to in detail here), by which the position and orientation of the test head  16  can be determined. The test head  16  can in this case be moved along the test object surface  14  in accordance with the available degrees of freedom of the holding device  32 , the positioning and orientation of the test head  16  respectively being detectable reliably by the position and rotation transducers. 
         [0041]      FIG. 4  shows a schematic perspective view of another embodiment of the system  10  for ultrasonic testing of the test object  12 . The detecting device in the present case comprises an image acquisition device  34 , by which a multiplicity of optical markings  36  applied on the test head  16  can be detected, and on the basis thereof the position and orientation n of the test head  16  can be determined. The position measurement is thus carried out by external optical tracking. The mobile test head  16  comprises optical markers, which can be detected in the form of optical markings  36 . The optical markings  36  may for example be configured as active markings, i.e. light-emitting markings, or passive markings which reflect the ambient light or auxiliary illumination. The image acquisition device  34  may for example be configured as a stereo camera system, by which the optical markings  36  are detected, and on the basis thereof their three-dimensional positioning and orientation in space relative to a reference coordinate system are determined continuously. 
         [0042]    Lastly,  FIG. 5  shows another alternative embodiment of the system  10  for ultrasonic testing of the test object  12 . The detecting device in the present case comprises an image acquisition device  38 , which is fitted on the test head  16  and by which a multiplicity of optical markings  40  applied on the test object surface  14  can be detected, and on the basis thereof the position and orientation of the test head  16  can be determined. The position measurement or orientation measurement of the test head  16  is carried out in the case shown here by internal optical tracking. 
         [0043]    The detecting device comprises a projection device  42  mounted statically, which projects suitable patterns in the form of the optical markings  40  onto the test object surface  14 . The mobile test head  16  comprises an optical tracking device in the form of the image acquisition device  18 , which may for example be configured as a stereo camera system, by which the position of the test head  16  relative to the projected pattern can be determined continuously. By the projection device  42 , the optical markings  40  can be projected onto the test object surface  14  with a predeterminable pattern. The pattern may for example be a dot, strip or checkerboard pattern. The pattern is in this case varied locally over the test object surface  14  by providing encoding by the dot shape, the arrangement of the dots or the wavelength. In this way, the positioning and orientation of the test head  16  can be determined particularly simply and reliably. 
         [0044]    By the various embodiments of the system  10  and the explained method for the ultrasonic testing of a test object, the SAFT method known per se can be used reliably even with manual guiding of a test head, by carrying out position and orientation detection of the test head  16  in the manner explained during the ultrasonic testing of the test object  12  and taking this into account during the compilation of an image of a region to be tested of the test object  12 . 
         [0045]    The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV , 69 USPQ2d 1865 (Fed. Cir. 2004).