Abstract:
A storage phosphor reader apparatus reads exposed storage phosphors. The reader includes an outer frame assembly including a cassette handling assembly, located on the upper part of the outer frame assembly, for handling vertically oriented cassettes; an inner frame assembly; a first set of vibration isolators for mounting the inner frame assembly on the outer frame assembly, so as to minimize vibrations caused in the outer frame assembly from being transmitted to the inner frame assembly; a storage phosphor scanning assembly; and a second set of vibration isolators for mounting the scanning assembly on the inner frame assembly, so as to minimize vibrations caused in the inner frame assembly frame from being transmitted to the scanning assembly.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates in general to computed radiography imaging systems and more particularly to a computed radiography storage phosphor reader having improved vibration isolation  
       BACKGROUND OF THE INVENTION  
       [0002]     Computed Radiography (CR) is a well established method of radiographic imaging used in the health care environment. The CR system involves exposing a storage phosphor contained in a cassette to x-radiation of a body part to produce a latent radiographic image in the storage phosphor. The cassette is presented to a storage phosphor reader where the storage phosphor is extracted from the cassette, scanned (read) with a stimulating radiation beam to produce a stimulated radiation image which is converted to an electronic (digital) image which can be stored, displayed, transmitted, or output on film. After the latent image has been scanned, the storage phosphor is erased to remove noise and any residual image, and the storage phosphor is replaced in the cassette ready for reuse.  
         [0003]     The scanning system typically uses a laser to energize the storage phosphor. Light energy is released from the storage phosphor and collected using multifaceted, mirrored surfaces, which direct the light energy into photodetectors that amplify the signal. The scanning operation is very sensitive to vibration and impacts, which cause relative movement between the laser and storage phosphor, between the storage phosphor and the light collector, and vibrations around the constant velocity drive system, which moves the storage phosphor past the scanning laser. Such vibrations can result in undesirable image degradation which can affect the diagnostic quality of the radiographic image. In a known storage phosphor reader, vibration isolation is accomplished by separating the scanning assembly from the outer frame and from an upper cassette handling assembly by supporting the scanning assembly separately on the floor.  
         [0004]     U.S. Pat. No. 4,833,325, issued May 23, 1989, inventors Torii et al., discloses an image readout apparatus in which stimulable phosphor sheets are transported along a horizontal path through an image readout system. Vibro-isolating light shield members are interposed between the image readout mechanism and a casing, which are individually supported on a floor. Vibro-isolating members are also disposed between a conveyor system for delivering a stimulable phosphor sheet and an optical system for applying the stimulating light to the stimulable phosphor sheet.  
         [0005]     U.S. Pat. No. 4,417,260, issued Nov. 22, 1983, inventors Kawai i.e. al., discloses an image scanning system in which the optical components for scanning a stimulating light beam across a recording medium and the mechanical components for moving the recording medium through the system in a horizontal direction are all mounted on a single frame which in turn is mounted by way of a vibrating insulator on an outer frame structure.  
         [0006]     U.S. Pat. No. 5,440,146, issued Aug. 8, 1995, inventors Steffen et al., discloses a radiographic image reader wherein a photoreceptive medium is transported horizontally through the reader and an optics module is supported on a support stand by kinematic mounts.  
         [0007]     U.S. Pat. No. 6,739,768 B2, issued May 25, 2004, inventors Johnke et al., discloses an apparatus for processing photographic material horizontally transported through the apparatus. A housing and a processing station are each independently mounted through their own oscillation-damping connection to a common support base.  
         [0008]     None of these patents address the problem of vibration isolation in apparatus in which a storage phosphor is vertically transported through a scanning and erase process.  
       SUMMARY OF THE INVENTION  
       [0009]     According to the present invention, there is provided an apparatus directed to overcoming these problems.  
         [0010]     According to one aspect of the present invention there is provided a storage phosphor reader apparatus comprising: an outer frame assembly including a cassette handling assembly, located on the upper part of said outer frame assembly, for handling vertically oriented cassettes; an inner frame assembly; a first set of vibration isolators for mounting said inner frame assembly on said outer frame assembly, so as to minimize vibrations caused in said outer frame assembly from being transmitted to said inner frame assembly; a storage phosphor scanning assembly; and a second set of vibration isolators for mounting said scanning assembly on said inner frame assembly, so as to minimize vibrations caused in said inner frame assembly frame from being transmitted to said scanning assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.  
         [0012]      FIG. 1  is a perspective view of a storage phosphor reader incorporating the present invention.  
         [0013]      FIG. 2  is an exploded perspective view of the reader of  FIG. 1  showing no cassettes mounted on the cassette handling assembly.  
         [0014]      FIGS. 3 and 4  are perspective and exploded perspective views of the reader of  FIG. 1  showing cassettes of different sizes loaded onto the cassette handling assembly.  
         [0015]      FIG. 5  is a diagrammatic view of an embodiment of the present invention.  
         [0016]      FIG. 6  is a diagrammatic, perspective view of the outer frame assembly of the reader of  FIG. 1  showing three low frequency vibration isolators for mounting an inner frame assembly.  
         [0017]      FIG. 7  is a diagrammatic perspective view of the inner frame assembly of the reader of  FIG. 1  showing four higher frequency vibration isolators for mounting the scanning assembly.  
         [0018]      FIG. 8  is a diagrammatic perspective view showing the inner frame assembly tipped back looking under to three isolator jackstuds that support the inner frame assembly.  
         [0019]      FIG. 9  is a diagrammatic perspective view showing the inner frame assembly mounted on the outer frame assembly.  
         [0020]      FIG. 10  is a diagrammatic perspective view of the scanning assembly which includes the optical system and scanning system.  
         [0021]      FIG. 11  is a diagrammatic, perspective view of the scanning assembly mounted on the inner frame assembly.  
         [0022]      FIG. 12  is a diagrammatic, perspective view of the scanning assembly, inner frame assembly, and outer frame assembly assembled together.  
         [0023]      FIGS. 13 and 14  are perspective, diagrammatic views showing the Frame Locker mounted to the outer frame assembly and the scanning assembly.  
         [0024]      FIGS. 15-19  are diagrammatic views showing details of the Frame Locker.  
         [0025]      FIGS. 20-22  are diagrammatic views showing the cam plate in greater detail.  
         [0026]      FIGS. 23-25  are diagrammatic views showing the Frame Locker in the engaged position.  
         [0027]      FIGS. 26-28  are diagrammatic views showing the Frame Locker in the disengaged position. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     In general, a storage phosphor reader incorporating the present invention is provided with three main frame assemblies, an outer frame assembly, an inner frame assembly, and a scanning assembly. A cassette handling assembly is part of an upper frame assembly supported by the outer frame assembly. The outer frame assembly also supports the inner frame assembly which in turn supports the scanning assembly. Vibration isolation between the scanning assembly and the outer frame assembly is accomplished by using two levels of isolation. One level is between the outer frame assembly and the inner frame assembly and the other level is between the inner frame assembly and the scanning assembly.  
         [0029]     Referring now to the Figures, there is shown an embodiment of the present invention. As shown in  FIGS. 1-4 , storage phosphor reader  10  includes a housing  12  having a cassette handling assembly  14  on the upper part thereof. Cassette handling assembly  14  includes a load side  15  having several cassette loading locations  16  and an unload side  17  having several cassette unloading locations  18 . The cassettes on side  15  contain exposed storage phosphors to be read by reader  10 , whereas the cassettes on side  17  contain storage phosphors that have been read and erased and are ready for reuse.  FIGS. 3 and 4  show cassettes  20  of different dimensions vertically mounted on the load side  15  of cassette handling assembly  14 . Reader  10  is also provided with a central slot  22  at which cassettes  20  are sequentially positioned by assembly  14  for scanning. A start button  24  is provided at the front of reader  10 .  
         [0030]      FIG. 5  diagrammatically shows an embodiment of the present invention. As shown, reader  10  includes outer frame assembly  30 , an inner frame assembly  32 , and a scanning assembly  34 . The outer frame assembly  30  also supports an upper frame assembly  36  having cassette handling assembly  14 . Outer frame assembly  30  is mounted on wheels  31  for ease of movement of reader  10 . Inner frame assembly  32  is supported on outer frame assembly  30  by a first set of low frequency vibration isolators  38 . Scanning assembly  34  is mounted on inner frame assembly  32  by a second set of higher frequency vibration isolators  40 . Scanning assembly  34  includes a laser and associated optics, a reciprocating galvo mirror for scanning the laser beam, and a storage phosphor positioning system including a very smooth motion lead screw drive with feedback controls to position a storage phosphor relative to the scanning laser beam. In an implementation of reader  10 , the natural frequency of the scanning assembly  34  mounted on isolators  40  to inner frame assembly  32  is approximately 12 Hz in the axial direction and approximately 21 Hz in the radial direction.  
         [0031]      FIGS. 6-12  show in greater detail the present invention.  FIG. 6  shows outer frame assembly  30  as a generally rectangular structure having three low frequency vibration isolators  38  mounted on a base plate  50  for mounting inner frame assembly  32 . Isolators  38  are rubber isolators with internally molded compression springs. Isolators  38  are positioned such that the entire weight of the inner frame assembly  32 , including the weight of scanning assembly  34 , is equally distributed among them. This equal distribution of weight aids in maintaining an equal amount of creep of each isolator.  
         [0032]      FIG. 7  shows the inner frame assembly  32  with four vibration isolators  40  for mounting scanning assembly  34 .  FIG. 11  shows inner frame assembly  32  mounting scanning assembly  34 , computer  60 , world wide power supply  62 , UPS battery backup  64 , cooling fans, an electrical box  66  containing all the circuit boards. In the implementation of reader  10 , the natural frequency of the complete inner frame assembly is approximately 5 Hz in the axial direction and approximately 3 Hz in the radial direction. The low natural frequency of the inner frame assembly  32  isolates the scanning assembly  34  from external impacts against outer frame assembly  30  and cassette handling impacts from the upper frame. These impacts are contained within the outer frame assembly  30  so it can be moved for service very easily without the need to realign the scanning assembly  34  to the cassette handling assembly  14 .  
         [0033]      FIG. 8  shows inner frame assembly  32  tipped back looking under to see three jack studs  70  that support inner frame assembly  32  on outer frame assembly  30  by screwing into isolators  38 . Jack studs  70  are used during alignment of reader  10  to “dial out” isolator height, isolator stiffness and frame tolerances.  
         [0034]      FIG. 9  shows inner frame assembly  32  mounted on outer frame assembly  30  by isolators  38 . Isolators  40  are shown for mounting scanning assembly  34 .  FIG. 10  shows scanning assembly  34  alone and  FIG. 11  shows scanning assembly  34  mounted on inner frame assembly  32  by isolators  40 .  FIG. 12  shows scanning assembly  34 , inner frame assembly  32 , and outer frame assembly  30  assembled together.  
         [0035]     According to the invention, the design intent is to drive the natural frequency of the inner frame assembly  32  as low as possible in order to provide lower transmissibility of external vibration and impacts. To drive the Natural Frequency down required an isolator with a high load capability and low stiffness. In the implementation of reader  10 , the weight of the inner frame assembly  32  was increased as much as possible by mounting the world wide power supply, UPS battery backup, erase assembly, computer and electrical box on the inner frame assembly  32 . This helped increase the weight of the assembly to 500 pounds. The purpose of the second layer of isolation is to isolate higher frequencies between the inner frame assembly  32  and the scanning assembly  34 . These frequencies were on the order of 50 Hz and higher and came from internal components, such as fans and other electrical devices. As shown and described above, two layers of vibration isolation are used to isolate the scanning system from impacts and vibration. The source of these impacts were both external (customer induced) as well as internal (component vibration). Some external impacts include loading cassettes onto the reader during a phosphor scan, dropping a stack of cassettes to be loaded onto the reader work surface, removing cassettes from the unload side during phosphor scan, bumping the front or sides during phosphor scan, and using the reader controls during phosphor scan. The low frequency vibration isolation was designed to provide the necessary isolation from primarily external impacts and the second layer of vibration isolation was used to provide isolation from primarily internally generated sources.  
         [0036]     One difficulty with employing vibration isolators in a scanning device is that there is the potential of adding a great deal of positional variation between critical subassemblies. This variation is unpredictable due to varying amounts of isolator creep, machine levelness, and frame twist. A function of the cassette handling assembly  14  is to transfer a cassette from the cassette handling assembly to an elevator which moves the cassette vertically to the scanning assembly  34 . This system interface requires repeatable cassette positioning in order for transfer to occur reliably.  
         [0037]     According to a feature of the present invention, a “Frame Locker” (FL) mechanism dynamically locks the scanning assembly  34  to the outer frame assembly  30  during cassette transfer. As shown in  FIGS. 13 and 14 , FL  100  includes a cam follower assembly  101  including rotating cam follower mount  102  and four cam followers  104  mounted on the scan assembly  34  and a locating cam plate  106  mounted on outer frame assembly  30 . During the assembly of reader  10 , the cassette elevator (not shown) is adjusted to the cassette handling assembly  14 . While the adjusted position is temporarily frozen with assembly tooling, the outer frame assembly cam plate  106  is positioned over the scan assembly cam follower assembly  101 . The outer frame assembly cam plate  106  is then rigidly fixed to outer frame assembly  30  and the assembly tooling is removed.  
         [0038]      FIGS. 15-19  show FL  100  in greater detail. FL  100  includes an encoder disc  108  which has four slots  110  used to identify state or position. Encoder disc  108  and cam follower mount  102  are supported on pivot shaft  112  having retaining ring  114 . Shaft  112  is rotatably supported by bearing and shaft housing  116  mounted on FL mount frame  118 . DC motor  120  is connected to shaft  112  via timing belt  122  and pulleys  124  and  126 . Through beam optical sensors  128  and  130  control the FL cam follower positions. Wire tie and base  132  is also provided.  
         [0039]      FIGS. 20-22  show the cam plate  106  in greater detail. Cam plate  106  is mounted on frame mount plate  134 . Cam plate  106  has four circular regions  136  used to lock the frame assemblies. Cam plate  106  has four square regions  138  for clearance when the FL  100  is disengaged.  
         [0040]      FIGS. 23-25  show FL  100  in the engaged position. Motor  120  has rotated cam follower mount  102  to a position at which cam followers  104  are aligned with the circular regions  136  of cam plate  106 . An encoder slot  110  is located at the engagement position  140  at engage sensor  130 .  
         [0041]      FIGS. 26-28  show DFL  100  in the disengaged position. Motor  120  has rotated cam follower mount  102  by 45 degrees to a position at which cam followers  104  are in the square regions  138  of cam plate  106 . Cam followers  104  have ample clearance within cam plate  106  so that the scanning assembly is vibrationally isolated from the outer frame assembly during the scanning process. An encoder slot  110  is located at the disengagement position  142  at disengage sensor  128 .  
         [0042]     The geometric mounting locations of the vibration isolators and FL  100  create a system which “hinges” about the isolator positions. When actuated, DFL  100  can relocate the frame assemblies in X, theta X, Y, and theta Y, directions to nearly the original fixtured positions. Directional stiffness of the isolators insures that theta Z is maintained. FL  100  does not control the Z position. The cassette transfer interface is insensitive to Z variations.  
         [0043]     The circular cam profile combined with corner lead-ins and the cam followers creates a highly efficient locating device. This is contrary to a typical locating device such as a pin in hole arrangement.  
         [0044]      FIG. 29  is a diagrammatic view useful in explaining the present invention. As shown, after cassettes have been loaded onto assembly  14  and the start button  24  actuated, sensors (not shown) detect the presence of cassettes. When cassette presence sensor  220  detects a cassette  20  in the position next to slot  22 , a barcode label on the cassette is read by barcode reader  222  which allows the cassette elevator mechanism  224  to be put into the correct position for the particular size cassette to be read. In addition, FL  100  is engaged to align the scanning assembly  34  with the cassette handling assembly  14  on outer frame assembly  30 . Cassette handling assembly  14  positions a cassette  20  containing an exposed storage phosphor  200  at slot  22  and cassette elevator mechanism  224  engages the cassette  20  and brings it down to storage phosphor extractor assembly  206 . The FL  100  insures the proper alignment for the handoff to the elevator mechanism  224 .  
         [0045]     Cassette  20  is now registered against a datum structure and clamps  202 ,  204  hold the cassette in position. FL  100  is disengaged, allowing scanning assembly  34  to be isolated through isolators  38  and  40 . Storage phosphor  200  is extracted from cassette  20  by extractor assembly  206  and transported vertically past laser scanner  208  and erase assembly  210  by drive mechanism  228  at a very constant velocity. After the image has been read and storage phosphor  200  erased, FL  100  is reengaged to bring the scanning assembly in alignment with cassette handling assembly  14 . Drive mechanism  228  causes assembly  206  to reinsert storage phosphor  200  into cassette  20  and latch it. Elevator mechanism  224  delivers cassette  20  to cassette handling assembly  14  in preparation for processing the next cassette.  
         [0046]     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       Parts List  
       [0000]    
       
           10 —storage phosphor reader  
           12 —housing  
           14 —cassette handling assembly  
           15 —load side  
           16 —cassette loading location  
           17 —unload side  
           18 —cassette unloading location  
           20 —cassette  
           22 —central slot  
           24 —start button  
           30 —outer frame assembly  
           31 —wheels  
           32 —inner frame assembly  
           34 —scanning assembly  
           36 —upper frame assembly  
           38 —low frequency vibration isolators  
           40 —higher frequency vibration isolators  
           60 —computer  
           62 —world wide power supply  
           64 —UPS battery backup  
           66 —electrical box  
           70 —jack stud  
           100 —DFL  
           101 —cam follower assembly  
           102 —cam follower mount  
           104 —cam follower  
           106 —cam plate  
           108 —encoder disc  
           110 —slot  
           112 —pivot shaft  
           114 —retaining ring  
           116 —bearing and shaft housing  
           118 —DFL mount frame  
           120 —DC motor  
           122 —timing belt  
           124 ,  126 —pulley  
           128 ,  130 —through beam optical sensor  
           132 —wire tie and base  
           134 —frame mount plate  
           136 —circular regions  
           138 —square regions  
           140 —engagement position  
           142 —disengagement position  
           200 —storage phosphor  
           202 ,  204 —clamps  
           206 —extractor mechanism  
           208 —laser scanner  
           210 —erase assembly  
           220 —cassette presence sensor  
           222 —barcode reader  
           224 —cassette elevator mechanism  
           228 —drive mechanism