Abstract:
A spectrometer for measuring the intensity of light, comprises a grating having a major axis, a first entrance aperture aligned with the grating major axis and configured to direct light energy onto the grating, wherein the grating is adapted to produce a focused light beam, a first exit aperture aligned with the grating major axis and configured to accept the focused light beam, a second entrance aperture configured to direct the light energy onto the grating, wherein the second entrance aperture is offset from the grating major axis, and a second exit aperture configured to accept the focused light beam.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention pertains to spectrometer analysis and more particularly to the simultaneous measurement of several spectral properties using a single spectrometer.  
         BACKGROUND OF THE INVENTION  
         [0002]    Optical spectrometers allow the study of a large variety of samples over a wide range of wavelengths. Materials can be studied in the solid, liquid, or gas phase either in a pure form or in mixtures. Various designs allow the study of spectra as a function of temperature, pressure, and external magnetic fields.  
           [0003]    Grating spectrometers, in particular, make use of the diffraction of light from a regularly spaced ruled surface. They disperse the light by a combination of diffraction and interference rather than the refractive index variation with wavelength. The normal operation of a grating is the same as with a prism. The grating is rotated, and wavelength after wavelength passes a field stop and is detected by a sensor. In general, a grating spectrometer operates by focusing the light through an optical system to the field stop. In a classical spectrometer the field stop is a slit. This light is then collimated and passes through a transmission grating or passed to a reflective grating. The dispersed light is then either focused onto a spectral array or through an exit slit to a detector where it can be analyzed. While plane gratings require separate collimating optics, concave gratings combine the function of the grating and collimating optics into a single optical component.  
           [0004]    Near-Infrared (NIR) spectroscopy is one of the most rapidly growing methodologies in pharmaceutical analysis. In particular, NIR is being increasingly used as an inspection method during the packaging process of pharmaceuticals, often augmenting or replacing previously used vision inspection systems. For example, an NIR inspection system can be used to inspect a blister packaging for, among other things, proper filling, physical aberrations, chemical composition, moisture content, and proper package arrangement.  
           [0005]    The use of vision systems as an inspection mechanism is becoming less and less sufficient as the need for more in depth inspection procedures, and near 100% inspection processes, are desired and in many cases required. Of particular note is that vision systems are not capable of performing any sort of chemical analysis of the product being packaged, relying only on a comparison of a visual snapshot of the package to a reference image. A typical vision packaging inspection system “looks” at each individual package to see whether it has the correct number of doses in the pack, i.e. the system looks for missing or overfilled tablet wells. In some cases, physical discrepancies such as cracks or gouges on a tablet, will also cause a rejection of the package. The limitations of these types of vision systems become apparent when they are compared with the capabilities of a spectrometer adapted to function in a pharmaceutical packaging and inspection facility.  
           [0006]    In high speed, large-volume processing, automated spectrometer-based monitoring systems have become indispensable in examining product flow in order to detect irregularities. Since these systems are meant in large part to replace vision systems, accuracy is a critical factor.  
           [0007]    Known spectrometer designs typically incorporate a single entrance slit (field stop) and a single exit slit. The single exit slit typically corresponds to a single detector or other sensor and the measurement system requires a separate spectrometer (including entrance slit, exit slit, and grating) for each required simultaneous spectrum measurement. When multiple simultaneous spectrum measurements are desired, the cost and complexity of a spectrometer system capable of performing such analysis increases dramatically, particularly because of the need for multiple gratings. What is needed is a device and method that provides for multiple and simultaneous spectrum measurements while only requiring a single spectrometer.  
         SUMMARY OF THE INVENTION  
         [0008]    In one aspect, a spectrometer having a reflective grating and the grating having a major axis, a light plate, comprises a plurality of entrance apertures, wherein at least one of the entrance apertures is offset from the grating major axis.  
           [0009]    In another aspect, a spectrometer for measuring the intensity of light, comprises a grating having a major axis, a first entrance aperture aligned with the grating major axis and configured to direct light energy onto the grating, wherein the grating is adapted to produce a focused light beam, a first exit aperture aligned with the grating major axis and configured to accept the focused light beam, a second entrance aperture configured to direct the light energy onto the grating, wherein the second entrance aperture is offset from the grating major axis, and a second exit aperture configured to accept the focused light beam.  
           [0010]    As will become apparent to those skilled in the art, numerous other embodiments and aspects will become evident hereinafter from the following descriptions and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The drawings illustrate both the design and utility of the preferred embodiments of the present invention, wherein:  
         [0012]    [0012]FIG. 1 shows a packaging line utilizing a spectrometer-based inspection system;  
         [0013]    [0013]FIG. 2 is a diagrammatic representation of the spectrometer from FIG. 1;  
         [0014]    [0014]FIG. 3 is a diagrammatic representation of a multiplexed input spectrometer constructed in accordance with the present invention;  
         [0015]    [0015]FIG. 3A is a physical representation of a multiplexed input spectrometer constructed in accordance with the present invention that corresponds to the diagram of FIG. 3; and  
         [0016]    FIGS.  4 - 12  are details of a preferred embodiment of a multiplexed input spectrometer constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    [0017]FIG. 1 shows a spectrometer-based tablet inspection system  100 . The inspection system  100 , generally includes a spectrometer head  105  mounted adjacent to or above a conveyer  110 . The spectrometer head  105  has three individual sensors  115   a ,  115   b , and  115   c  and is a substantially self-contained unit that includes a number of individual spectrometers, typically corresponding to the number of individual sensors. Therefore, in the example of FIG. 1, the spectrometer head  105  contains three spectrometers, one linked to each of the sensors  115   a ,  115   b , and  115   c . Depending on the application, a fewer or greater number of sensors/spectrometers can be incorporated into the inspection system  100 . Generally, larger systems become more complex to operate and are more expensive, the individual spectrometers being the largest contributor to the cost and complexity of such an inspection system.  
         [0018]    Positioned on the conveyer  110  is a pharmaceutical packaging unit  132  such as a blister pack, tablet well, ampul, or vial. As the packaging unit  132  passes the spectrometer head  105 , it has already been filled with a product, such as a tablet or capsule  130 , and is ready for inspection. The filling step typically occurs at a prior point in the manufacturing process. Typically, the packaging unit  132 , filled with the tablets  130 , are aligned in one or more rows  135   a ,  135   b , and  135   c . As positioned on the conveyer  110 , each of the rows  135   a ,  135   b , and  135   c  correspond to one of the sensors  115   a ,  115   b , and  115   c . The spectrometer head  105  is aligned so that each of the sensors  115   a ,  115   b , and  115   c  are positioned substantially over a corresponding row  135   a ,  135   b , or  135   c . As the conveyer  110  moves each packaging unit  132  past the spectrometer head  105 , a corresponding packaging unit  132  passes under one of the sensors  115   a ,  115   b , and  115   c . Readings taken by the sensors are fed to the spectrometer head  105  where information about the individual tablets  130  in the packaging unit  132  is analyzed. Defective or otherwise unacceptable packages/tablets are rejected at a subsequent stage in the manufacturing and packaging process. A computer  140  is linked to the spectrometer head  105  and is adapted to analyze the data gathered by the inspection system  100 . Statistical information or other analytical data can be gathered by the computer  140  and sent to an operator for viewing or stored for later review and analysis.  
         [0019]    In known systems, inspection systems are adapted so that each sensor is linked to a separate spectrometer and is therefore capable of only a single spectrum measurement at any given time, i.e. only one tablet can be inspected at a time by each sensor. A sensor must therefore take a separate reading for each tablet (or other product) contained within each packaging unit. FIG. 2 shows a diagrammatic representation of the single sensor  115   a  and its corresponding spectrometer  200 .  
         [0020]    A white light source  205  illuminates the tablet  130  passing on the conveyer  110  and generates reflected light energy  207 . The reflected light energy  207  is collected by the sensor  115   a  and is passed into the spectrometer  200  as incoming light energy  210 . In some applications, and as shown in FIG. 2, a lens  215  focuses the incoming light energy  210  into an outgoing beam  220  which is then directed at a light plate  225  containing an entrance slit  230 . The light plate  225  and entrance slit  230  are aligned with a major axis  235  of a grating  245 . In the example in FIG. 2, the grating  245  is a concave reflective scanning grating mounted on a pivot shaft  250 . Since the grating  245  is mounted on a pivot shaft, it does not require separate collimating optics. Various other types and styles of gratings are also contemplated, such as transmissive gratings or a plane grating coupled with collimating optics. Light energy  240  is passed from the entrance slit  230  and directed at the grating  245 . Light energy  255  that is reflected by the grating  245  is focused at a second light plate  260  that contains an exit slit  265 . By rotating the grating  245  about the pivot shaft  250 , different wavelengths of the light energy  240  are focused onto the exit slit  265 . Mounted behind the exit slit  265  is a detector  275  that preferably includes a photo-cell  280  that is adapted to respond to the light energy  255 . The detector  275  provides a measurement of the light energy  255  that corresponds to a specific physical property of the tablet  130 . However, the measurement of different tablet properties cannot be achieved without moving sensor  115   a  and initiating another measurement. In these arrangements, simultaneous measurement of several tablet properties requires the addition of a separate sensor, spectrometer and grating for each simultaneous measurement desired.  
         [0021]    It is generally understood that spectrometer designs incorporate a single entrance slit aligned with the major axis of the grating. This arrangement is referred to herein as an on-axis alignment and an on-axis entrance slit. Off-axis entrance slits, i.e. entrance slits that are not aligned with the major axis of the grating but are rather offset from the major axis, are known to result in the introduction of aberrations into the spectrum being measured. This degradation in performance is generally not acceptable for analytical measurements that require high precision and accuracy.  
         [0022]    For those applications, however, where precision and accuracy of the raw spectrographic measurement is not a critical factor, the allowable tolerances of the spectral measurement allows for a certain amount of aberrations in the measured spectrum. For example, when accepting or rejecting a group of tablets based on the similarity of that group&#39;s spectrum as compared with the spectrum of known good tablets, such aberrations do not affect the performance of the system or the resulting measurements. Since this type of comparison is relative rather than absolute, the aberrations that perturb the spectrum do not influence the comparison as long as the perturbations are static. Known approaches to tablet inspection require that all spectra are measured with spectrometers having equivalent characteristics and therefore will not tolerate the introduction of these types of aberrations.  
         [0023]    Referring to FIG. 3, a diagrammatic representation of a multiple input spectrometer  300  constructed in accordance with the present invention is shown. The diagram of FIG. 3 is meant only to be a diagrammatic representation of a multiple input spectrometer constructed in accordance with the present invention. For details of the physical layout of a multiple input spectrometer constructed in accordance with the present invention, reference should be made to FIGS.  3 A and  4 - 11 .  
         [0024]    In FIG. 3, a source  305  delivers sampled light energy to the spectrometer  300  via a series of three inputs  310   a ,  310   b , and  310   c . The three inputs focus the light energy from the sample at three corresponding entrance light plates  315   a ,  315   b , and  315   c  each of which includes an entrance slit ( 320   a ,  320   b , and  320   c  respectfully). As shown in FIG.  3 , the entrance light plate  315   b  and its corresponding entrance slit  320   b  are aligned with a major axis  335  of a grating  330 , i.e. it is an on-axis entrance slit. The other two entrance light plates  315   a  and  315   c , as well as the other two entrance slits  320   a  and  320   c , are not aligned with the grating normal axis  335 , rather, the entrance light plates  315   a  and  315   c  and the entrance slits  320   a  and  320   c  are offset from the grating normal axis  335  and are therefore referred to herein as “off-axis” entrance slits. Known spectrometers, the normal line to the grating and the exit slits all fall in the same plane. The normal to the grating is the line that is 90° to the plane defined by the front surface of the grating. In the case of a concave grating, the normal to the grating is a line that is 90° to a plane tangent to the center point (focus) of the grating.  
         [0025]    After the sampled light energy passes through each of the entrance slits  320   a ,  320   b , and  320   c , it is directed as light rays  325   a ,  325   b , and  325   c  onto the grating  330 . The orientation and construction of the grating  330  determines which wavelength of the light is reflected and focused as light rays  345   a ,  345   b , and  345   c . The grating  330  as shown in FIG. 3 is a scanning grating and is thus mounted on a pivot shaft  340 . The wavelength of the sampled light that is reflected as rays  345   a ,  345   b , and  345   c  can thus be altered by rotating the grating through various angles. Each of the light rays described herein are in actuality individual rays of a cone of illumination and are shown as individual rays for ease of illustration and understanding.  
         [0026]    Also positioned within the spectrometer  300  are a series of detectors  360   a ,  360   b , and  360   c . Each of the detectors  360   a ,  360   b , and  360   c  is positioned adjacent an exit light plate ( 350   a ,  350   b , and  350   c  respectively). Each of the exit light plates  350   a ,  350   b , and  350   c  includes an exit slit  355   a ,  355   b , and  355   c . The reflected light rays  345   a ,  345   b , and  345   c  are directed at each of the exit slits  355   a ,  355   b , and  355   c  respectively. Detectors  360   a ,  360   b , and  360   c  are positioned behind each of the exit slits. The detectors function to analyze the light energy that is passed through each of the respective exit slits  355   a ,  355   b , and  355   c . Alternately, each of the detector and exit slit pairs may be replaced with a detector array so that various wavelengths may be measured simultaneously without the need to rotate the grating.  
         [0027]    The three entrance slit/exit slit/detector arrangement of the multiplexed spectrometer  300  can be utilized to analyze three different light energy samples simultaneously (by having three separate inputs to the entrance light plates/entrance slits). Increased throughput in an inspection systems utilizing such an arrangement is thereby realized because three tablets can be inspected simultaneously by a single spectrometer. Since the location of the off-axis entrance slits  320   a  and  320   c  are static, so are the aberrations that are reflected in the spectrum results from the corresponding samples. Since the aberrations are static, the relative spectrum measurements are not influenced and the comparison is not affected.  
         [0028]    [0028]FIG. 3A shows six views of a physical spectrometer constructed in accordance with the present invention that correspond to the diagrammatic representation of the spectrometer  300  from FIG. 3. The left column in FIG. 3A shows three views from behind the entrance and exit slits looking toward the grating and along the optical axis of the grating. The right column in FIG. 3A shows three views from the side of the spectrometer.  
         [0029]    FIGS.  4 - 11  show various details of a preferred embodiment of a multiplexed input spectrometer constructed in accordance with the present invention. With attention to FIGS. 4 and 5, a light plate  400  and a reflective grating  440  are shown. The light plate  400  includes a set of three entrance slits  405 ,  410 , and  415  and a set of three exit slits  455 ,  460 , and  465 . In alternate embodiments, the entrance slits and exit slits may be contained on separate light plates or a greater or fewer number of slits may be provided. Entrance slit  410  and exit slit  460  are on-axis since they are aligned with the major axis  435  of the grating  440 . The remaining entrance and exit slits are off-axis since they are offset from the grating major axis  435 .  
         [0030]    [0030]FIG. 4 shows how light energy is passed from the three entrance slits  405 ,  410 , and  415  to the reflective grating  440 . Line  435  depicts the major axis of the grating. The on-axis entrance slit  410  aligns with the major axis  435 . Light entering the on-axis entrance slit  410  is passed to the reflective grating  440  in a cone of illumination. Light rays  425  are two such rays that comprise this cone of illumination. Light entering the off-axis entrance slit  405  is passed to the reflective grating  440  in a cone of illumination. Light rays  420  are two such rays that comprise this cone of illumination. Light entering the off-axis entrance slit  415  is passed to the reflective grating  440  in a cone of illumination. Light rays  430  are two such rays that comprise this cone of illumination.  
         [0031]    [0031]FIG. 5 shows how light energy is passed from the reflective grating  440  to the three exit slits  455 ,  460 , and  465 . The on-axis exit slit  460  aligns with the major axis  435 . Light is passed from the reflective grating  440  to the on-axis exit slit  460  in a cone of illumination. Light rays  475  are two rays that comprise this cone of illumination. Light is passed from the reflective grating  440  to the off-axis exit slit  455  in a cone of illumination. Light rays  480  are two rays that comprise this cone of illumination. Light is passed from the reflective grating  440  to the off-axis exit slit  465  in a cone of illumination. Light rays  470  are two rays that comprise this cone of illumination.  
         [0032]    FIGS.  6 - 11  show various other views of the grating  440  and the manner in which light rays are passed from the entrance slits to the exit slits. FIG. 6 shows the grating  440  viewed perpendicular to the spectrometer&#39;s optical plane, including the grating at two different rotations,  440   a  and  440   b . FIG. 7 shows the grating  440  viewed from within the spectrometer&#39;s optical plane while showing only the light rays  420 ,  425 , and  430  from the entrance slits. FIG. 8 shows the grating  440  viewed from within the spectrometer&#39;s optical plane while showing only the light rays  470 ,  475 , and  480  from the exit slits. Each of the light rays described herein are in actuality individual rays of a cone of illumination and are shown as individual rays for ease of illustration and understanding. FIGS. 9, 10, and  11  are the views perpendicular to the grating  440  that correspond respectively to FIGS. 6, 7, and  8 . The flat edge  485  of the grating  440  is provided to ensure that the grating is properly oriented when installed in the spectrometer.  
         [0033]    Although the present invention is particularly suited for use in connection with pharmaceutical capsules and tablets, it is to be clearly understood that the principals of this invention as well as the invention itself are applicable to and may be employed in connection with countless different types and kinds of solid discrete particular objects, including solid or multi-colored objects, liquids, powders, and various other substances.  
         [0034]    Although the present invention has been described and illustrated in the above description and drawings, it is understood that this description is by example only and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention. The invention, therefore, is not to be restricted, except by the following claims and their equivalents.