Patent Document

RELATED APPLICATION 
       [0001]    The application claims priority under 35 U.S.C. §119(e) of European Patent Application No. 09 009 615.7, filed on Jul. 24, 2009, which is hereby incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a method and system for the automated testing and/or measuring of a plurality of substantially identical components using X-ray radiation. 
         [0003]    Such systems are used for example for automatic serial testing of castings, the system being connected into the manufacturer&#39;s production line (inline testing). With known systems of this type the X-ray source and detector are arranged on a multiaxial manipulator, wherein by means of simple radiography, X-ray images of the test object are recorded and evaluated. However, the projection of the volume of the tested component onto the X-ray image allows only limited conclusions to be drawn as to the internal structure of the component. 
         [0004]    To obtain precise information about the three-dimensional internal structure of components, it is known to laboratory test individual components by means of high resolution microtomography systems. X-ray tube and detector are mounted on a fixed support so as to be adjustable about a plurality of translational axes and the component is rotated about a vertical axis by means of a rotary table. Such systems are not suitable for automatic serial inline testing of components, in particular because the long period of time required for handling and high resolution investigation of a component is incompatible with the cycle times in a production line. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    It is the object of the invention to provide a method and system suitable for inline testing of components, with which information about the internal structure of the components may be obtained. 
         [0006]    Embodiments of the subject invention achieve this object with the means to be found in the independent claims. Computer tomographic evaluation of the X-ray signals makes it possible, in a manner known per se, to obtain information about the three-dimensional internal structure of the components, for example the precise location and shape of air inclusions in castings. Arrangement of the X-ray device on a continuously rotatable rotor makes it possible to convey the components through the rotor serially during testing; an additional manipulator such as, for example, a rotary table is unnecessary. In this way automatic serial investigation of components may be performed in a short period, which is compatible with the cycle times on a production line. 
         [0007]    Embodiments of the subject invention are different from methods and systems for testing items of luggage, for which evaluation has to be set extremely broadly to cover any desired luggage contents. Instead, the system according to embodiments of the subject invention for investigating a plurality of substantially identical components may be appropriately tailored to the component type to be tested, or to a mix of a limited number of component types. These systems are therefore completely differently configured in particular in terms of X-ray parameters and evaluation algorithms. The testing/measuring system according to embodiments of the subject invention is expediently set up for automatic identification of material defects, such as gas inclusions, porosity or material inclusions of higher density in a substantially homogeneous material. The system according to embodiments of the subject invention may, however, additionally or alternatively be used for materials testing for measuring internal and external component structures (metrology). It is then optionally possible to dispense with a separate coordinate measuring machine. 
         [0008]    Preferably, the method and system is set up to achieve a volume resolution in the X-ray image of less than or equal to 1 mm. In this way too, embodiments of the subject invention may be distinguished from systems for testing items of luggage, which generally operate with a resolution of several mm. 
         [0009]    To achieve sub-mm-resolution, the conveying device preferably comprises, in the region of the annular unit, a conveying means with a substantially constant rate of advance. Substantially constant preferably means that fluctuations in rate of advance amount to at most 10%, preferably at most 5%. 
         [0010]    With regard to the rough conditions prevailing in manufacturing environments, for example foundries, the protection cabin is preferably sealed in substantially airtight manner against the surrounding environment, in order to prevent penetration of dust and moisture into the protection cabin and the testing/measuring device arranged therein. To prevent penetration of dust and dirt through the openings for conveying the components in and out, the system preferably comprises a pipe connecting the two openings, extending through the rotor and defining a closed conveying duct, which additionally is preferably connected in airtight manner to the protection cabin. Furthermore, a cooling unit is preferably provided for cooling the interior of the protection cabin. Finally, the system preferably comprises a means for pressurising the protection cabin relative to the surrounding environment. Preferably the protection cabin is set up to shield the surrounding environment against X-ray radiation, in particular by means of an X-ray-absorbing layer, for example containing lead. 
         [0011]    Preferably the conveying device comprises a conveyor belt guided without interruption through the testing/measuring device and largely transparent to radiation, thereby preventing problems related to a measurement gap in the conveying device in a simple manner. 
         [0012]    Preferably the conveying device is height-adjustable in the region of the testing/measuring device for adaptation to components with different dimensions, so that the components may be passed through the testing/measuring device substantially centralized in height. 
         [0013]    Embodiments of the subject invention are illustrated below by means of advantageous embodiments with reference to the attached Figures. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0014]      FIG. 1  shows a system for testing components in a production line. 
           [0015]      FIG. 2  shows another embodiment of a device for testing components. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to  FIG. 1 , the system  10  comprises a testing/measuring device  11 , a conveying device  13  for conveying a plurality of substantially identical components  12  to be tested serially to and away from the testing/measuring device  11 , a control/evaluation unit  14  and a protection cabin  15  surrounding the testing/measuring device  11 . Testing/measuring device should here be understood to mean testing and/or measuring device. The testing/measuring system  10  is suitable for connecting into a production line for example in a foundry for metallic castings  12 . 
         [0017]    The testing/measuring device  11  comprises a support  17  fixed during testing and an annular rotor  18 . The support  17  comprises a pedestal  19  anchored to a base plate  23  and an annular supporting element  22  resting on said pedestal, here in the form of an octagonal plate. The annular supporting element  22  forms an annular rotational bearing  20  for the rotor  18 . Rotational bearing  20 , rotor  18  and optionally supporting element  22  form an annular unit  16 , which comprises a central annular opening  26  for conveying components  12  through the annular unit  16 . In order to allow horizontal orientation, the annular unit  16 , as shown in  FIGS. 1 and 2 , may be inclined by means of a horizontal swivel bearing  21  for example in a range of +−30° relative to the pedestal  19 , see embodiments according to  FIGS. 1 and 2 . The components  12  are preferably conveyed in an axially parallel manner, i.e. parallel to the rotor axis, through the rotor  18 . 
         [0018]    An X-ray tube  24  and an X-ray detector  25  are fastened opposite one another on the rotor  18 . The X-ray tube  24 , which preferably takes the form of a rotary anode tube, is preferably of the fan beam or cone beam type. The X-ray tube  24  is conveniently set up to illuminate the entire detector  25  and for this purpose preferably has in one direction a beam angle of at least 40°, preferably at least 60°. To achieve sub-mm image resolution the focus size of the X-ray beam is preferably below 1 mm, more preferably below 0.7 mm. The tube  24  is preferably operated with at least 80 kV of energy, more preferably at least 100 kV, more preferably at least 120 kV, for example approximately 140 kV. If a high penetration capacity is preferred, higher X-ray energies of up to 450 kV are feasible. To reduce the duration of testing and/or measuring, the X-ray tube  24  is preferably operated with a continuous output of at least 1 kW. To avoid problems due to excessive heat generation, the continuous output preferably amounts to less than 10 kW. 
         [0019]    In an embodiment which is not shown, only the tube  24  may be fastened to the rotor  18 , while the stationary detector  25  forms a 360° ring. 
         [0020]    The X-ray detector  25  is preferably digital, with direct conversion of the impinging X-ray radiation into electrical counts; preferably it is a line scanning detector with a plurality of preferably at least 16 parallel lines. The detector  25  preferably comprises a length which is sufficient to detect the largest possible angular range of X-ray radiation emitted by the tube  24 . It is preferably bent into a banana shape, such that the sensitive area is at a substantially constant distance from the source point of the X-ray tube  24  as far as possible everywhere. To achieve sub-mm image resolution the pixel size of the detector  25  amounts to at most 1 mm, preferably at most 0.7 mm. 
         [0021]    The correction conveniently performed in the control/evaluation unit  14  to compensate the beam hardening effect is adjusted to the investigation of typical materials, for example metals, alloys, composite materials, aluminium, iron, et cetera. 
         [0022]    During X-ray testing of a component  12  the rotor  18  is rotated continuously by means of rotary drives (not shown) fastened to the supporting element  22  about the central longitudinal axis of the annular unit  16 , wherein a large number of full 360° revolutions of the rotor  18  are carried out per component  12 . Electricity is supplied to the X-ray tube  24  and X-ray detector  25  rotating with the rotor  18  by means of a slip ring arrangement  27  arranged between the rotor  18  and the supporting element  22 . The axis of rotation of the rotor  18  or the longitudinal axis of the annular unit  16  is oriented substantially parallel to the direction in which the components are conveyed through the testing/measuring device  11 , preferably substantially horizontal. 
         [0023]    The conveying device  13  preferably takes the form, as in the exemplary embodiment according to  FIG. 1 , of a conveyor line, i.e. of a translational conveyor. For connection into a production line for the components  12 , the conveyor line comprises a loading section  28  and an unloading section  29 . Loading of the conveyor line  13  proceeds in the exemplary embodiment according to  FIG. 1  by means of a robot  30 , while unloading is effected manually. It goes without saying that loading and unloading may also proceed otherwise. 
         [0024]    In the exemplary embodiment according to  FIG. 1  the conveying device  13  comprises conveying carriages  31  for accommodating one component  12 , respectively, and at least one rail  32  along which the conveying carriages  31  are guided displaceably. The conveying device  13  may however also be differently constructed, in particular using conveyor belts. 
         [0025]    The conveying device  13  is preferably set up to convey the components  12  through the testing/measuring device  11  at a substantially constant rate of advance, i.e. with fluctuations in the rate of advance of less than 10%, preferably less than 5%. To this end the conveying device  13  preferably comprises a separate drive  34  in the region of the testing/measuring device  11 , preferably with servomotors, to achieve the required constant rate of advance. Accordingly, the drive  34  for conveying through the testing/measuring device  11  appropriately displays a more constant rate than other drives (not shown) for conveying to and away from the testing/measuring device  11 . 
         [0026]    In the preferred embodiment according to  FIG. 2  a separate conveying means  33  with a continuous, uninterrupted conveying means  34 , in particular a conveyor belt, is provided for conveying the components  12  through the testing/measuring device  11 . The conveying means  34  is expediently substantially transparent to X-ray radiation. The continuous, uninterrupted, largely radiation-transparent conveying means  34  has the advantage that the conveying means  33  does not have to comprise any gap for allowing the X-ray radiation through. 
         [0027]    On the other hand, in the embodiment according to  FIG. 1  the conveying device  13  passes into the testing/measuring device  11  from both sides, such that the smallest possible gap  35  remains for unhindered passage of X-ray radiation. In this case an embodiment of the conveying device  13  with rail  32  and conveying carriages  31  in the region of the testing/measuring device  11  is advantageous, because the conveying carriages  31  allow bridging of the gap in a manner which is precise with regard to position and rate of advance. 
         [0028]    In accordance with the above, the conveying device  13  is of translational construction over the entire conveying distance between the loading section  28  and the unloading section  29 . It is therefore possible to dispense with elaborate carousel-like pivoting conveyors for conveying the components  12  from the conveyor line  13  to the testing/measuring device  11  and back. Other manipulation of the components  12 , for example rotation of the components  12  about a vertical axis during X-ray investigation, may be dispensed with. 
         [0029]    The translational conveyance, occurring during testing, of the component  12  to be tested through the testing/measuring device  11  parallel to the axis of rotation of the rotor  18  and the simultaneous continuous rotation of the X-ray system  24 ,  25  about the component  12  to be tested results in an overall helical movement of the X-ray system  24 ,  25  about the component  12  to be tested. The control/evaluation unit  14  comprises a rapid CT reconstruction algorithm for converting the recorded X-ray data from the helical geometry into a volume or voxel representation. The control/evaluation unit  14  further comprises an algorithm for analysing the volume image depending on the intended application. This may in particular comprise automatic identification of internal defects or anomalies of the component  12 , for example air inclusions, using predetermined test parameters which are known in principle and do not therefore have to be explained in greater detail. Every component may optionally be classified as “compliant” or “non-compliant” and optionally marked optically accordingly or automatically rejected. Finally, the control/evaluation unit  14  may comprise a communication unit for data transmission with an external unit, for example the central control unit of the manufacturing plant. 
         [0030]    In addition or as an alternative to the helical scanning mode, the control/evaluation unit  14  may also perform axial scans and/or scans of just one part of a component  12 , for example individual slices or at specific positions. 
         [0031]    Alternatively or in addition, for the identification of internal defects or anomalies of the component  12  the control/evaluation unit  14  may also be set up to determine the three-dimensional geometric dimensions of the components  12 , i.e. internal and external component structures, from the X-ray data. It is then optionally possible to dispense with a separate coordinate measuring device. 
         [0032]    To shield the surrounding environment against the X-ray radiation generated by the X-ray tube  24 , the system  10  comprises a radiation protection cabin  15  surrounding the testing/measuring device  11 . The radiation protection cabin  15  comprises a frame  36 , which may consist for example of metal tubes or rods, and plate-shaped wall elements  37   a ,  37   b ,  37   c ,  37   d  etc., which are merely indicated in  FIG. 2  for the top wall  37   a , the side wall  37   b  remote from the observer, the front wall  37   c  facing the observer through which the components  12  are conveyed into the protection cabin  15 , and the rear wall  37   d  remote from the observer through which the components  12  are conveyed out of the protection cabin  15 . The wall elements  37  contain an X-ray-absorbing, in particular lead-containing, layer of sufficient thickness. 
         [0033]    An inlet opening  39  and a corresponding outlet opening  40  are provided in the wall elements  37   c ,  37   d  for conveying the components  12  through the protection cabin  15 . Each passage opening  39 ,  40  in each case has a passage lock  41 ,  42  associated with it, which comprises a slide  41   a ,  42   a , respectively, for closing an inlet opening of the passage lock  41 ,  42  and a slide  41   b ,  42   b , respectively, for closing an outlet opening of the passage lock  41 ,  42 . The passage locks  41 ,  42  and the slides  41   a ,  41   b ,  42   a ,  42   b  are likewise set up for substantially complete absorption of X-ray radiation. In operation one slide  41   a ,  41   b  or  42   a ,  42   b , respectively, of a passage lock  41 ,  42  is closed at all times, such that radiation protection is ensured at all times. 
         [0034]    To prevent penetration of dust and moisture into the protection cabin  15 , the latter is closed in airtight manner, for example with the aid of sealing elements  38  between the wall elements  37 , the frame  36  and the base plate  23 . To achieve a substantially completely sealed interior for the testing/measuring device  11 , i.e. apart from any air-conditioning openings, a conveniently substantially radiation-transparent pipe  43  is provided, which extends through the protection cabin  15  from one passage opening  39  to the other passage opening  40  and passes through the annular opening  26  in the annular unit  16 . The conveying device  13  passes through the pipe  43  in the region of the testing/measuring device  11 , said pipe defining a conveying duct  46  or conveying tunnel. The pipe  43  is preferably free of openings in the pipe wall, such that dirt particles transported with the conveying device  13  or the components  12  arranged thereon cannot enter the testing/measuring device  11 . At its ends the pipe is preferably connected in airtight manner with the wall elements  37   c ,  37   d  at the edge defining the passage openings  39 ,  40 , in particular with the aid of corresponding sealing elements  44 ,  45 . The diameter of the pipe  43  is conveniently adapted to the internal diameter of the annular unit  16 , in order to allow testing of the largest possible components  12 . In accordance with the above, the testing/measuring device  11  is substantially completely enclosed in the protection cabin  15 . 
         [0035]    In order to dissipate the heat generated when the testing/measuring device  11  is in operation and keep the interior of the protection cabin  15  at a sufficiently low operating temperature even in very warm environments, for example a foundry, at least one temperature-controlled, in particular electrically operated cooling unit  46 , for example an air-conditioning system, is fitted to the protection cabin  15 . 
         [0036]    So that no dust/moisture can enter the protection cabin  15  in the case of any leaks, and through any functional openings such as for example an exhaust air opening for the air-conditioning system  46 , a means is preferably provided for pressurising the cabin  15 . This may for example be a compressed air connection  47 , which may be connected to an external compressed air source via a compressed air line  48 . Pressurisation may alternatively also proceed by way of the cooling unit  46 . 
         [0037]    As a result of the protection cabin  15  and the pipe  43 , which also protects the annular unit  16  from damage by malpositioned components  12 , no separate housing is needed for the annular unit  16 . Dispensing with such a housing for the annular unit  16  in turn simplifies heat removal from the annular unit  16 . 
         [0038]    The conveying device  13  may be height-adjustable in the region of the testing/measuring device  11  for adaptation to components  12  with different dimensions, so that the components  12  may be passed through the annular unit  16  substantially centrally. 
         [0039]    The system  10  may optionally comprise a device  50  connected upstream of the testing/measuring device  11  for identifying the component type for example with the aid of an optical camera and an image recognition algorithm. As a function of the result of the identification, parameters of the measuring/testing device  11  may be adjusted to the respective component type and/or the result of the X-ray investigation may be related to the individual component  12 , for example by means of the serial number. Alternatively, identification of the component type may also be effected from the three-dimensional X-ray image by means of a corresponding recognition algorithm.

Technology Category: 3