Abstract:
An apparatus internally inspects a workpiece having a hollow cylindrical hole. The apparatus contains an ultrasound transducer configuration having a plurality of ultrasound transducer elements, which are arranged in at least one row, one next to the other, in an elastically deformable carrier which has the form of a segment of a hollow cylinder and has a plurality of sliding pimples which extend in the longitudinal direction of the carrier and project with a protrusion in the radial direction beyond the transmitting and/or receiving surfaces of the ultrasound transducer elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation, under 35 U.S.C. §120, of copending international application No. PCT/ EP2011/065212, filed Sep. 2, 2011, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2010 040 274.5, filed Sep. 6, 2010; the prior applications are herewith incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to an apparatus for internal inspection of a workpiece having a hollow cylindrical hole. 
         [0004]    Workpieces with an introduced hollow cylindrical hole, for example hollow screws or shafts, are frequently inspected with the aid of ultrasound starting from the hole side. Such an inspection technique is also designated as a boresonic inspection. As a rule, for this purpose an ultrasound transducer is inserted into the hole and guided there along a helical path. The ultrasound transducers used are in this case either conventional individual transducers or ultrasound transducer arrays that are constructed from a multiplicity of individual transducer elements and are operated using the emitter array inspection technique. In particular, because of the multiplicity of measuring channels, the emitter array inspection technique with an ultrasound transducer array that is guided in a helical movement on the inner circumference of the hollow cylindrical hole requires a complicated slip ring transmission of the signals to and from the individual transducer elements of the ultrasound transducer array. 
       SUMMARY OF THE INVENTION 
       [0005]    It is accordingly an object of the invention to provide an apparatus for the internal inspection of a workpiece having a hollow cylindrical hole which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which enables the workpiece to be inspected reliably starting from an internal surface of the hole with little technical outlay. 
         [0006]    With the foregoing and other objects in view there is provided, in accordance with the invention an apparatus for internally inspecting a workpiece having a hollow cylindrical hole. The apparatus contains an elastically deformable carrier having a form of a segment of a hollow cylinder and a front side, and an ultrasound transducer configuration having a plurality of ultrasound transducer elements disposed in at least one row next to one another in the elastically deformable carrier. The ultrasound transducer elements have transmitting and receiving surfaces. A plurality of sliding knobs extend in a longitudinal direction of the elastically deformable carrier and project with a protrusion in a radial direction along the transmitting and receiving surfaces of the ultrasound transducer elements. The elastically deformable carrier has a number of cutouts corresponding to a number of the ultrasound transducer elements. A matching film is disposed on the front side and functions as a matching layer for covering the cutouts. The ultrasound transducer elements are inserted in the cutouts and bonded to the matching film via the transmitting and receiving surfaces. 
         [0007]    In accordance with these features, the apparatus includes an ultrasound transducer arrangement with a plurality of ultrasound transducer elements that are arranged in at least one row next to one another in an elastically deformable carrier that has the form of a segment of a hollow cylinder and has a plurality of sliding knobs that extend in its longitudinal direction and project with a protrusion in a radial direction along the transmitting and receiving surfaces of the ultrasound transducer elements. 
         [0008]    The invention takes account here, on the one hand, of the fact that, particularly in small holes, it is impossible to couple the ultrasound transducer elements using the immersion or pilot technique with a long pilot path, since there is not sufficient space for this purpose, and the run time of the ultrasound in the pilot path must be longer than its run time inside the inspection item, since otherwise the multiple echoes produced within the pilot path would be superimposed on the actual useful signal from the inspection item. However, on the other hand, problems occur in relation to coupling in direct contact with the surface of the workpiece to be examined in the case of extended ultrasound transducer arrangements, because large changes in the measurement signals received by the transducer elements can then occur owing to small coupling gaps, which unavoidably vary from transducer element to transducer element. The use of sliding knobs that project with a defined protrusion beyond the transmitting or receiving surfaces of the ultrasound transducer array gives rise to a defined narrow coupling gap in the case of which—in conjunction with an optimized matching film for matching the oscillator impedance to the impedance of the coupling medium—on the one hand, the so-called ringing of the received measurement signals that is caused by the coupling gap can largely be avoided, and in which, on the other hand, a uniform coupling is also ensured for the individual transducer elements of an ultrasound transducer array. 
         [0009]    Owing to the coupling of the ultrasound signals into and/or out of the workpiece via a small coupling gap that is preferably between 0.4λ and 1.1λ, and to the thereby reduced overall height of the ultrasound transducer arrangement, and owing to the use of an elastically deformable carrier that has the form of a segment of a hollow cylinder, a multiplicity of ultrasound transducer elements can be arranged next to one another on the carrier in a circumferential direction such that a larger region of the inside circumference of the hole can be covered in an axial inspection run. Owing to their comparatively small dimension, which is preferably of the order of magnitude of λ/2 for the longitudinal direction, the individual ultrasound transducer elements themselves generate a sound beam with very large aperture angles. By superimposing the signal information of the individual ultrasound transducer elements and, in particular, by using the dynamic signal profiles resulting from axial movement of the probe (“synthetic aperture”), it is possible to reconstruct the detected indications, this being equivalent to the inspection statement of “conventional” emitter array inspection technique. It is thereby possible to carry out a complete internal inspection with the aid of a few axial inspection runs such that there is no longer any need for a movement of the carrier including the ultrasound transducer arrangement in a circumferential direction, or for correspondingly complicated slip-ring contacts for signal transmission. This additionally reduces the overall size of the ultrasound transducer arrangement. 
         [0010]    When the carrier has the form of a segment of a hollow circular cylinder that occupies at least a quarter of the circumference of the circular cylinder, it is possible to inspect the entire hole with at most four axial runs. 
         [0011]    In a further advantageous refinement of the invention, the ultrasound transducer elements are arranged in the carrier in a plurality of mutually parallel rows such that they form a two-dimensional matrix. The inspection statement is substantially improved thereby. 
         [0012]    The production of the apparatus is simplified when the carrier is provided with a number of cutouts corresponding to the number of the ultrasound transducer elements and, on its front side, with a matching film that serves as matching layer and covers the cutouts, and the ultrasound transducer elements are inserted into the cutouts and bonded to the matching film with their transmitting and/or receiving surfaces. 
         [0013]    In a further preferred embodiment, there is arranged in the carrier at least one channel for guiding a coupling fluid which communicates with openings arranged in the front side of the carrier. The coupling fluid flows out of the openings into the gap formed by the skids between the inner surface and the ultrasound transducer elements and, furthermore, improves the acoustic coupling of the ultrasound transducer array to the inner surface of the workpiece. Moreover, the coupling fluid, in particular an oil, reduces the wear of the skids which, in particular, consist of a ceramic material, and so the defined coupling gap set up is maintained over a long period of use. 
         [0014]    In a further particularly preferred refinement of the invention, there is provided a pressure exerting device that acts on the rear side of the carrier and can be supported on the inner wall of the hole averted from the carrier. This ensures a uniform coupling gap even in the case of varying geometric dimensions of the hole—deviation from an ideal circular cylindrical form. 
         [0015]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0016]    Although the invention is illustrated and described herein as embodied in an apparatus for internal inspection of a workpiece having a hollow cylindrical hole, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0017]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0018]      FIG. 1  is a diagrammatic, cross-sectional view of an apparatus in an operating position on an inner surface of a hole located in a workpiece according to the invention; 
           [0019]      FIG. 2  is a diagrammatic, perspective view of the apparatus; 
           [0020]      FIG. 3  is an illustration showing the apparatus in a fashion operationally connected to a pressure exerting device; and 
           [0021]      FIG. 4  is an illustration showing an alternative refinement of a pressure exerting device acting on the apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown an apparatus that contains a carrier  2  that is provided with a plurality of cuboid cutouts  4  which are covered on a convex front side of the carrier  2  by a matching film  8  with the aid of which the cutouts  4  are sealed on a front side  6  of the carrier  2 . Ultrasound transducer elements  10  are respectively introduced into the cutouts  4  and bonded to the matching film  8 . A thickness of the matching film  8  is approximately a quarter of a wavelength λ of the ultrasound used for inspection, and serves the purpose of matching the acoustic impedance of the transducer elements  10  to the acoustic impedance of a coupling fluid. The matching film  8  is, moreover, optimized with regard to its sound damping properties, which contributes additionally to minimizing the so-called ringing of the ultrasound signals. 
         [0023]    The ultrasound transducer elements  10  have a rectangular transmitting and/or receiving surface with a length I in a circumferential direction of typically 2λ to 3λ, and a width b ( FIG. 2 ) in the longitudinal direction of typically λ/2. Damping bodies  12  are integrally cast into the cutouts  4  in each case adjoining the rear side of the ultrasound transducer elements  10 . 
         [0024]    The carrier  2  and the damping body  12  are elastically deformable, in the absence of forming forces the carrier  2  having the form of a segment of a hollow cylinder and a basic shape matched to the radius of the hole  24  located in a workpiece  22 . The carrier  2  extends in a longitudinal direction perpendicular to the plane of projection. The ultrasound transducer elements  10  are arranged with their narrow sides next to one another in at least one row  100  extending in a circumferential direction of the carrier  2  and running parallel to the plane of projection, only one row  100  containing four ultrasound transducer elements  10  being represented, for reasons of clarity. In a practical exemplary embodiment, an ultrasound transducer arrangement formed by the ultrasound transducer elements  10  contains, for example, 6 rows  100  each having 8 ultrasound transducer elements  10 . 
         [0025]    Bonded onto the matching film  8  between the ultrasound transducer elements  10  are a plurality of flat sliding knobs  26  between which the ultrasound transducer elements  10  are respectively arranged, and with which a defined coupling gap  28  is produced between an inner surface  20  of the hole  24  and the matching film  8 , that is to say the transmitting and/or receiving surfaces of the ultrasound transducer elements  10 , when the carrier  2  is pressed against the inner surface  20  with the aid of a pressure exerting device  30  (only indicated in a partial illustration by dashes) such that the sliding knobs  26  bear against the inner surface  20  without a gap. The protrusion s of the sliding knobs  26  beyond the matching film  8 , that is to say beyond the transmitting and/or receiving surfaces of the ultrasound transducer array  10 , and the width, resulting in this way, of a coupling gap  28  are in this case preferably between 0.4λ and 1.1λ. 
         [0026]    Arranged parallel to the longitudinal direction, that is to say perpendicular to the plane of projection, in the carrier are longitudinal channels  32  through which a coupling fluid can be introduced via the exit openings  40  ( FIG. 2 ) into the coupling gap  28  formed between the matching film  8  and the inner surface  20  of the hole  24 . 
         [0027]    Electrical contact is made with the ultrasound transducer elements  10  on the transmitting and/or receiving surfaces via a thin conductive layer  34  with a thickness of only a few μm that is applied to the flat side, facing the ultrasound transducer elements  10 , of the matching film  8 , conductive foil strips making contact with the layer  34 , and via contact clips  36  that are arranged on the rear side of the carrier  2 , for example bonded, and which, via contact tongues—cast into the damping bodies  12 —produce a conductive connection to the soldered on contact wire  38  between the rear side of each individual ultrasound transducer element  10 . 
         [0028]    In accordance with  FIG. 2 , the ultrasound transducer elements  10  are arranged in a plurality of rows  100  in the carrier  2  which are arranged sequentially in the longitudinal direction of the carrier  2  and arranged parallel to one another. The ultrasound transducer elements  10  of adjacent rows  100  are arranged offset from one another in the circumferential direction with an offset  101  so as to produce a matrix-shaped ultrasound transducer arrangement whose gaps  102  are oriented obliquely to the longitudinal axis  200  of the carrier  2 , and obliquely to its circumferential direction. Such an offset  101  ensures that in the case of an axial inspection run in the hole the workpiece is completely recorded on its partial circumference covered by the carrier  2  and is displayed with a good circumferential resolution. 
         [0029]    In the perspective illustration of  FIG. 2 , there are to be seen, moreover, openings  40  that are arranged in the front side of the carrier  2  or the matching film  8  and which open into the coupling gap  28  ( FIG. 1 ) fixed by the sliding knobs  26  and communicate with the longitudinal channels  32 . 
         [0030]    Illustrated in  FIG. 3  in a schematic sketch is the carrier  2  with a pressure exerting device  30 , which is acting on it and is resiliently supported on the inner surface  20  of the hole  24  opposite the carrier  2 , and presses the carrier  2  resiliently against the inner surface  20 , for example via a spring arrangement  42 , symbolically illustrated by helical springs, such that the elastically deformable carrier  2  bears against the inner surface  20  with an identical coupling gap with its sliding knobs (not illustrated in  FIG. 3  for reasons of clarity), even if the inner surface deviates from the ideal circular basic shape. 
         [0031]    An alternative refinement of the pressure exerting device  30  is illustrated in  FIG. 4  in accordance with which an inflatable tube  44  is inserted into the hole  24  and likewise presses the carrier  2  against the inner surface  20  of the hole  24  and is supported at the rear on the inner surface  20  via an opposing shell  46 .