Abstract:
A method and an apparatus for detecting unacceptable items in objects, such as in luggage, wherein a detector apparatus, functioning as a second detector stage is divided into a lower testing stage and a higher testing stage. In the lower testing stage, the coordinates of the object location are determined, and subsequently, a diffraction apparatus is moved to this location in the higher testing stage. In particular, X-ray diffraction can be employed to determine the explosive material of the item in the object. The diffraction apparatus comprises a collimator/detector arrangement, which is disposed to be adjusted height-wise and laterally in the higher testing stage, with a laterally-adjustable X-ray source, which is synchronized with the collimator/detector arrangement. The collimator/detector arrangement preferably has only one collimator and one detector. The collimator preferably has a conically-expanding ring slot, which simulates a predetermined angle Θ M  of a scatter radiation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a continuation of U.S. application Ser. No. 09/645,484 filed Aug. 25, 2000, which is incorporated herein by reference.  
         [0002]    This application is related to concurrently filed U.S. Applications (Attorney Docket No. 31659-152914A, Attorney Docket No. 31659-152916A and 31659,152918A) and which are continuations of respective U.S. application Ser. Nos. 09/645,485, 09/645,486 and 09/645,487, each filed Aug. 25, 2000, the subject matter of each such application being incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The invention relates to an apparatus and a method for detecting unacceptable items in objects such as luggage.  
         BACKGROUND OF THE INVENTION  
         [0004]    To assure safety in air travel, for example, it is necessary to check luggage for unacceptable items, particularly explosive agents or materials, by employing the most modern technical equipment. In the process, an object (luggage) typically passes through one or more stages. The first stage usually comprises a fast X-ray system designed to handle the large volume of luggage items to be tested. If a piece of luggage contains materials that cannot be clearly identified, an additional test is performed in a second stage.  
           [0005]    As disclosed in German Patent DE 44 06 956 C2, for an accelerated check in the second, or higher, stage, a plurality of coordinates of the regions that were not unambiguously determined in the lower, first stage is detected distinctly by a computer and transmitted to the second or higher stage.  
           [0006]    The method of X-ray diffraction can be employed, particularly in the search for explosive materials. In this method, X-ray radiation that has been scattered by the crystal structure of an item is measured and compared to the characteristic energy spectra of, for example, various explosive materials. These measured energies give an indication of the presence of an explosive material and additionally information about the explosive material in the object.  
           [0007]    German published patent application DE 195 10 168 A1 discloses an apparatus designed for this purpose. In this case, a fanned X-ray beam is generated at the X-ray source by means of a screen or aperture, and is then radiated onto a test region of a material to be tested. Slot-shaped collimators are disposed symmetrically around the axis of the central X-ray beam, specifically in a plane that extends perpendicular to the fan plane of the X-ray, on the side of the test region opposite the X-ray source. A plurality of detectors performs the evaluation over the entire X-rayed test region.  
           [0008]    European published patent application EP 0 354 045 A2 also discloses an apparatus and a method in which a fanned X-ray beam is generated. This fanned beam radiates through the object to be tested, and is diffracted at the lattice structure of the object, with the diffraction being recorded as an energy spectrum by a plurality of detectors.  
           [0009]    U.S. Pat. No. 4,956,856 discloses a further apparatus. In this case, a narrow X-ray beam(pencil beam) is generated and directed, by means of a rotating roller having a spiral-shaped slot, at an object to be X-rayed. The pencil beam passes through the slot transversely to the object to be tested.  
           [0010]    German published patent application DE 41 01 544 A1 discloses the use of a primary beam having a small cross section in an X-ray device. Here, a plurality of detectors and a concentric collimator arrangement detects the scatter radiation generated from the primary beam.  
           [0011]    A drawback of the aforementioned apparatuses is that the entire piece of luggage must always be sampled or scanned in order to ascertain all unacceptable luggage items.  
           [0012]    An arrangement for generating an expanded X-ray bundle is known from German published patent application DE 41 30 039 A1. A screen arrangement used for this purpose comprises two limiting bodies, which are oriented relative to one another such that they limit a space corresponding to the shape of the ray bundle. This arrangement serves to increase the surface impacted by the X-ray.  
         SUMMARY OF THE INVENTION  
         [0013]    It is an object of the invention to provide a method for fast, automatic detection of unacceptable luggage items inside a detection apparatus, and an apparatus for executing the method.  
           [0014]    The above object generally is achieved according to a first aspect of the present invention by a method for detecting an unacceptable item in an object, in which method comprises: in a lower testing stage in a detection apparatus, the object is scanned with x-rays to detect any unacceptable item, the location of the unacceptable item is determined in the object, with the location including at least first and second dimensional coordinates of the object, and the location is stored and transmitted to a higher testing stage of the detection apparatus. In the higher testing stage, the unacceptable item is directly tested at the determined location, with the direct testing comprising x-ray diffraction analysis.  
           [0015]    The above object additionally achieved according to a second aspect of the invention by an apparatus for detecting an unacceptable item in an object, which apparatus comprises: a detection apparatus having a lower testing stage, a higher testing stage, and a computer, wherein the lower testing stage includes a first X-ray source, a detector device, a transport device for an object disposed between the source and detector device and extending between the lower and higher testing stages, and a marking device, with the detector and marking device being connected to the computer, and wherein the higher testing stage is located downstream from the lower testing stage and comprises a diffraction apparatus, with the diffraction apparatus being adjustably positionable in the higher testing stage and being connected to the computer  
           [0016]    The concept underlying the invention is to split the scanning process, and pre-scan a piece of luggage to be tested in a lower testing stage of the detection apparatus, so that, in a higher testing stage, the luggage item(s) classified as unacceptable in each location/point or a plurality of locations/points ascertained in the lower testing stage and described by two or three coordinates can be purposefully detected. Thus, the entire piece of luggage no longer needs to be sampled. This multi-step process saves time and exposes the object to a lower dose of radiation. In the higher testing stage, the described location(s) assists (assist) in the detection of the material type through X-ray diffraction. An airport, for example, thus has at its disposal an effective tool for quickly, simply and automatically testing luggage at the second or higher stage.  
           [0017]    This is due to the fact that a point is first determined in the lower testing stage, from a belt or object position and a detector that detects the luggage item, and then is probed by a diffraction apparatus located in the higher testing stage.  
           [0018]    The diffraction apparatus preferably comprises a collimator/detector arrangement, which is mounted to be adjusted height-wise and transversely in the higher testing stage, and a conveying element, e.g., a belt, which adjusts or moves the item in the longitudinal direction. The luggage item is scanned at this determined point through X-ray diffraction. To this end, the collimator/detector arrangement and the X-ray source can be adjusted to operate synchronously. Accordingly, the collimator/detector arrangement is preferably mounted to be adjusted in height relative to the X-ray source.  
           [0019]    If two coordinates are known, the diffraction apparatus can be used to scan the luggage item for the third coordinate, or, if the three coordinates are known, the item is only measured at this point. Thus, the diffraction apparatus is set either to the belt position determined as the X coordinate, and adjusted vertically and laterally in the beam path, or it is set directly into this point.  
           [0020]    The height-adjusted collimator/detector arrangement preferably comprises an adjustable round-slot collimator in the form of a conical jacket with a detector located behind  
           [0021]    In addition, the exact spatial position and dimensions of the unacceptable item in the luggage can be determined, namely in its X, Y and Z coordinates, in the higher testing stage.  
           [0022]    In a further step, additional information can be obtained for identifying the material. For this purpose, the round-slot collimator has a central, blind-bore-like opening, in which two different, spatially-separate detector devices are disposed one behind the other, the devices being used in a known manner to determine the average atomic number of the item located in the primary beam.  
           [0023]    The lower and higher testing stages are preferably located in a common detection apparatus of the second stage. 
       
    
    
       [0024]    The invention is described in detail by way of a preferred embodiment, with reference to the drawing.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a simplified representation of the X-raying of an object with items in an X-ray tunnel of a lower testing stage of a detection apparatus.  
         [0026]    [0026]FIG. 2 is a schematic representation of the apparatus of the invention, in a higher testing stage.  
         [0027]    [0027]FIG. 2 a  illustrates a preferred collimator/detector arrangement for the apparatus of FIG. 2.  
         [0028]    [0028]FIG. 2 b  illustrates the functioning principle of the detection apparatus of FIG. 2.  
         [0029]    [0029]FIG. 3 is a perspective representation of the detection apparatus comprising the parts shown in FIGS. 1 and 2.  
         [0030]    [0030]FIG. 4 is a further representation of the collimator/detector arrangement from FIG. 2.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    In a first (or lower) detection stage of a detection arrangement, not shown in detail, a piece of luggage  5  (object) is tested for security-relevant material that the object  5  may contain. If a suspicious object is detected, this object  5  enters a second (or higher) detection stage for further testing and assessment of the material of suspicious luggage items (items)  6  and/or  7 . These stages are known to be spatially separated from one another.  
         [0032]    In the illustrated example, this second stage, in which the material is determined, is the primary focus.  
         [0033]    Preferably, two testing stages  30 . 1  and  30 . 2  are located inside the second detection stage (detection apparatus  30 ), with  30 . 1  being the lower testing stage and  30 . 2  being the higher testing stage.  
         [0034]    [0034]FIG. 1 depicts the lower testing stage  30 . 1 .  
         [0035]    The object  5  is brought into a known X-ray tunnel  1  of the lower testing stage  30 . 1  of the detection apparatus  30 , not shown in detail. Disposed in the X-ray tunnel  1  are, for example, an L-shaped X-ray detector apparatus  2 , a transport device  3  used also as the reference plane of the horizontal plane and, to the side, an X-ray source  4 . The X-ray source  4  is preferably located above the transport device  3  and opposite the detector apparatus  2 . The object  5  with the items  6 ,  7  to be X-rayed is located on the transport device  3 .  
         [0036]    The detector apparatus  2  comprises a plurality of individual detectors D 1−n , with which the type of material is detected in a conventional manner. For the sake of a clear overview, the detectors D 1−n  are only illustrated over a small region of detector apparatus  2 . For material detection, the X-ray source  4  preferably generates a fanned X-ray beam FX composed of rays FX, to FX n  in a known manner. The fanned beam passes through the X-ray tunnel  1  and the object  5 , preferably with a narrow cross section. The L shape of the detector apparatus  2  and the individual arrangement and orientation of the individual detectors D 1−n  ensure that the X-rays FX 1−n  of the X-ray fan impact each detector D 1−n  at a right angle. A plurality of X-ray fans of various energies and/or directions can also be used in other embodiments.  
         [0037]    If one or more items  6 ,  7  is or are located in the respective beam path a 1−n , of the X-rays FX 1−n , these X-rays FX 1−n  are attenuated due to their interaction with the item. The resultant attenuation is detected by the detectors D 1−n  lying respectively, in the beam paths a 1−n .  
         [0038]    [0038]FIG. 2 schematically illustrates the higher testing stage  30 . 2 . Here, the object  5  on the transport device  3  is preferably transported from the lower testing stage  30 . 1  into the higher testing stage  30 . 2  of the detection apparatus  30 , which has an adjustable diffraction apparatus  10 . This diffraction apparatus comprises a collimator/detector arrangement  11  and an X-ray source  12 . The collimator/detector arrangement  11  is oriented toward an X-ray beam FX′, preferably a primary beam of the X-ray source  12  in the form of a ‘pencil beam’ where the X-ray source is preferably disposed beneath the transport device  3 . The collimator/detector arrangement  11  is mounted to be simultaneously adjusted in vertical and laterally positions(in the Z and Y directions, respectively) by element  13 , not shown in detail here. Parallel thereto, the X-ray source  12  is secured to elements  14 , and can likewise be adjusted laterally in the Y direction. The collimator/detector arrangement  11  and the X-ray source  12  are guided synchronously, with the elements  13  and  14 , for example, linear guides with a spindle drive, being centrally actuated. This can be coordinated by a computer  31 , not shown in detail here.  
         [0039]    [0039]FIG. 2 a  shows a preferred embodiment of the collimator/detector arrangement  11  from FIG. 2 for X-ray diffraction.  
         [0040]    The collimator  15  possesses a round slot  18  in the form of a conical jacket such that, of the scatter radiation originating from the tested point of the object, only the components that fall within a specific angle Θ M  are allowed through. An X-ray-sensitive surface  16 . 1  of a detector  16  located behind the collimator captures this scatter radiation. If the collimator/detector arrangement  11  is intended to perform additional functions (to be explained below), the collimator  15  has a central, blind-bore-like opening  17 .  
         [0041]    [0041]FIG. 2 b  is a simplified representation of the functioning principle of the X-ray diffraction. To attain a primary beam FX′, a screen arrangement  20 , such as an apertured-diaphragm arrangement, is mounted in front of the X-ray source  12 . The transport device  3 , with the object  5  on it, is located above the X-ray source  12 . When the primary beam FX′ impacts a material, the beam is known to be partially deflected as scatter radiation FX″ at the crystal-lattice structure of the material (Bragg&#39;s Law). Accordingly, the crystal structure, and thus the material, can be determined from the energy spectrum obtained with the energy-sensitive detector  16 . In particular, explosive materials can be recognized and distinguished based on their known spectra.  
         [0042]    For the sake of a better overview, the most crucial details from FIGS. 1 and 2 are combined in a perspective view of the detection apparatus  30  in FIG. 3, where the elements  13  and  14  are shown more clearly.  
         [0043]    In the example, only the detection of the item  6  is shown in detail in the various views of FIGS. 1 through 3 in order to present a clear overview.  
         [0044]    As the object  5  enters the lower testing stage  30 . 1 , a marking device, not shown in detail here, reads a first belt or position mark X 1  into a memory of a computer  31 ; the mark characterizes the beginning of the object  5 . The marking device can be, for example, a light barrier. As the object  5  is transported further, additional belt positions are written into the memory, for example through pixel counting. In the detection of the item  6 , a so-called initial belt position X AG  is entered into the memory. In addition to the determined belt positions, the signals of the detectors D 266-275 , which record the attenuation, and the associated beam paths a 1−n , are read into the memory, or a further memory, of the computer  31 .  
         [0045]    From these stored data, a location G M  of the item  6  is determined in the image processing according to special criteria. This location can be described, for example, by two coordinates, with the X coordinate being determined from the initial belt position X AG  and the Y coordinate being determined from the detecting detector D 270 =G AA . The beam path a 270  associated with this detector D 270  is likewise stored. In the description of a location point G M  in three spatial coordinates, for example, with the use of an additional radiation direction and an additional detector arrangement in the lower testing stage  30 . 1 , the center point of the X-rayed surface of the item  6  located in the beam path FX 1−n , which results from X GM , Y GM  and Z Gm , is determined. This is also read into the memory of the computer  31 , and the result is stored there.  
         [0046]    The computer  31  transmits these data to the higher testing stage  30 . 2  of the detection apparatus  30 .  
         [0047]    In the higher testing stage, the diffraction apparatus  10  is now moved to the coordinates of the location or location point G M , which were transmitted from the lower testing stage  30 . 1  to the higher testing stage  30 . 2 .  
         [0048]    If two coordinates of the location G M  are known, the diffraction apparatus  10  is preferably moved into the initial belt position X AG  determined for the item  6 . The collimation/detector apparatus  12  is subsequently moved parallel to the direction a 270 , that is, synchronously in the vertical and lateral directions, with the scatter radiation that was generated in the item along the line a 270  being detected in an energy-selective manner. The X-ray source is accordingly moved synchronously in the lateral direction.  
         [0049]    The energy-sensitive signals are stored in one or more temporally-sequential energy spectra, which also permits a spatial distinction among the measured materials along the line a 270 .  
         [0050]    In the computer  31 , these spectra are compared with known energy spectra in a known manner. This comparison serves to identify the material, particularly an explosive material.  
         [0051]    If the location point GM determined by the lower testing stage is known in three spatial coordinates, the item  6  is conveyed into the predetermined belt position X GM , and the collimator/detector arrangement  11  and the X-ray source  12  of the diffraction apparatus  10  are brought into the location point G M  such that, in this point G M , the scatter radiation FX″ of the X-ray source  12 , which is deflected at the crystal lattice of the item  6 , is captured through the round slot  18  of the collimator  13 . In this case, it is not necessary to perform an additional adjustment for determining the type of material.  
         [0052]    It is also possible to combine the coordinate information from the lower testing stage and the additional spatial information from the higher stage, possibly expanded by numerous measuring sweeps, and thus determine the volume and the precise spatial position of the item  6  in the object  5 .  
         [0053]    [0053]FIG. 4 illustrates an advantageous embodiment of the round-slot collimator  15 . A central, blind-bore-like opening  17  is preferably integrated into the collimator  15 . Disposed in the opening  17  are a first detection device  21  and, behind it at a defined distance, a second detection device  22 . The first detection device  21  is embodied as a detector for relatively lower X-ray energies, and the second detection device  22  is embodied as a detector for relatively higher X-ray energies. The collimator  15  can additionally be used, for example, to perform a conventional material detection through the determination of the average atomic number of the material of the item  6 . The combination of this average atomic number and the determined energy spectrum can provide an improved identification of the material of the item  6 . This is of particular significance if the item  6  contains a highly-absorbent material. Often, lower energies of the central beam FX′ are absorbed in the material, so the corresponding lines of diffraction are missing in the measured energy spectrum. This absence can be reported to the computer  31  with the additional determination of material, and considered in the comparison for the evaluation.  
         [0054]    These detection devices  21 ,  22  can also perform a precise spatial orientation (adjustment) of the collimation/detection arrangement  11  relative to the X-ray source  12 . The adjustment itself is effected without an object  5  being located between the collimation/detection arrangement  11  and the X-ray source  12 .  
         [0055]    Of course, modifications are possible within the scope of the concept of the invention.  
         [0056]    For example, the testing stages  30 . 1  and  30 . 2  can be separate, so the describing coordinates can be determined in the lower testing stage as the first stage, then transmitted to the higher—here, the second—stage; it must be ensured that the correct position of the coordinates determined in the first stage is transmitted to the second stage.  
         [0057]    Other diffraction apparatuses  10  can also be used, such as those described in the state of the technology, in which case the diffraction apparatus  10  must be adjustable, as disclosed in the description.  
         [0058]    The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.