Abstract:
A storage phosphor reader. The reader comprises a first roller pair, a cylindrical scan platen, a guide member, and a holding member. The first roller pair transport a storage phosphor medium along a path in a first direction. The cylindrical scan platen supports the medium as it is scanned by a scanner. The guide member is disposed intermediate the first roller pair and the scan platen for guiding the medium to the scan platen. The holding member is disposed downstream of the scan platen for contacting the medium after it is scanned.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a 111A application of Provisional Application Ser. No. 60/444,016, filed Jan. 31, 2003. 
    
    
     FIELD OF THE INVENTION 
     The invention is directed to optical imaging systems, and more particularly to a storage phosphor imaging system. 
     BACKGROUND OF THE INVENTION 
     Storage phosphor imaging systems are known. In one such system, a storage phosphor is exposed to an x-ray image of an object, such as a body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with stimulating radiation. Upon stimulation, the storage phosphor releases emitted radiation of a particular wavelength. To produce a signal useful in electronic image processing, the storage phosphor is scanned, for example, by a laser beam deflected by an oscillating or rotating scanning mirror or by a rotation hologon. The emitted radiation from the storage phosphor is reflected by a collector and detected by a photodetector, such as a photomultiplier, to produce an electronic x-ray image signal. The x-ray image signal can then be viewed as a visual image produced by a softcopy display device, such as a CRT or LCD display, or a hardcopy display device, such as a x-ray film printer (laser printer, CRT printer, thermal printer). U.S. Pat. No. Re. 31,847, issued Mar. 12, 1985, inventor Luckey discloses a storage phosphor system. The reader is often referred to as a computed radiography (CR) reader. 
     The storage phosphor can be disposed on a medium. Such a medium can be flexible, semi-flexible, semi-rigid, or rigid, and can be configured as a sheet or other substantially planar arrangement. When the storage phosphor is being processed/scanned/read/exposed by the storage phosphor processor/reader, it is important that the position of the storage phosphor be controlled so as to not introduce any artifacts in the processed image. 
     Accordingly, there exists a need to control a medium as it is being transported through an optical imaging system. In Applicant&#39;s particular application, there exists a need to control a storage phosphor medium in a storage phosphor reader. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a system and method to control a medium as it is transported through an optical imaging system. 
     Another object of the present invention is to provide such a system and method wherein the medium is configured as a sheet. 
     These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the invention. Other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims. 
     According to one aspect of the invention, there is provided a storage phosphor reader. The reader comprises a first roller pair, a cylindrical scan platen, a guide member, and a holding member. The first roller pair transport a storage phosphor medium along a path in a first direction. The cylindrical scan platen supports the medium as it is scanned by a scanner. The guide member is disposed intermediate the first roller pair and the scan platen for guiding the medium to the scan platen. The holding member is disposed downstream of the scan platen for contacting the medium after it is scanned. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings. 
         FIG. 1  shows a front perspective view of a storage phosphor reader in accordance with the present invention. 
         FIG. 2  shows a front view of a storage phosphor reader of  FIG. 1 . 
         FIG. 3  shows a left side plan view of the storage phosphor reader of  FIGS. 1 and 2 . 
         FIG. 4  shows the scan reader assembly of the storage phosphor reader of  FIG. 3 . 
         FIG. 5  shows the scan reader assembly of the storage phosphor reader of  FIG. 3 . 
         FIG. 6  shows portions of the scan reader assembly of the storage phosphor reader of  FIG. 3 . 
         FIG. 7  shows portions of a flexible sheet medium being transported through portions of the scan reader assembly of the storage phosphor reader of  FIG. 3 . 
         FIG. 8  shows portions of a flexible sheet medium being transported through portions of the scan reader assembly of the storage phosphor reader of  FIG. 3 . 
         FIGS. 9-13  show perspective views elements of the storage phosphor reader of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following is a detailed description of the preferred embodiments of the invention, reference being made to the drawings in which the same reference numerals identify the same elements of structure in each of the several figures. 
     As indicated above, storage phosphor can be disposed on a medium which can be flexible, semi-flexible, semi-rigid, or rigid (i.e., a screen), and can be configured as a sheet or other substantially planar arrangement. For ease of discussion, the present invention will be described with regard to the medium being a flexible sheet. The medium is often referred to as a screen. 
     Referring to  FIGS. 1 and 2  there is shown an exemplary storage phosphor reader  10  in accordance with the present invention. Storage phosphor reader  10  processes images captured on storage phosphor using conventional radiographic equipments. Reader  10  then scans the storage phosphor and converts the latent x-ray image therein into an electrical x-ray image signal that can be viewed. Reader  10  can be operated using a touch screen, generally illustrated in  FIG. 1  as display  12 . 
     The screen can be mounted in an x-ray cassette. An example of such a cassette is disclosed in U.S. Pat. No. 5,943,390, issued Aug. 24, 1999, inventors Wendlandt et al. and U.S. Ser. No. 08/087,990 (Kodak Docket No. 85921) provisionally filed on Feb. 3, 2003 as Provisional Application U.S. Ser. No. 60/444,462, both being commonly assigned and incorporated herein by reference. Such cassettes can be of varying sizes. 
     Once the radiology technologist exposes a body part to an x-ray which is storage as a latent image on the screen, the cassette is loaded into reader  10  at a supply area or receiving station  14 . Receiving station  14  is shown in  FIG. 1  as a load platform. Scanning is then initiated, for example, by pressing a start button on touch screen  12 . 
     Referring now to  FIG. 3 , inside reader  10 , using means known to those skilled in the art, the screen is extracted from the cassette and moved along a path P in a direction A through a scan reader assembly disposed in a scan area  16  wherein the screen is scanned. 
     The storage phosphor used to hold the latent image can be erased and used repeatably. Therefore, once a portion of the screen has been scanned, it is erased by being moved through an erase assembly disposed in an erase area  18  wherein it is erased by exposure to light which removes the remnants of the image. Once the entire screen has been scanned and erased, the direction of the screen is reversed and the screen is returned to the cassette. Alternatively, the screen can be erased as the screen is being returned to the cassette (i.e., when traveling in the direction reverse to direction A). 
     Referring now to  FIGS. 3 through 9 , as indicated above, the screen is extracted from a cassette  15  and moved along a path P in a direction A. Transport means known to those skilled in the art can be employed to transport the screen along path P. For Applicant&#39;s particular application, a first pair of rollers  19   a,   19   b  has been found suitable. Roller  19   a  is fixed and is driven. Roller  19   b  is a pressure roller. It is not fixed and is biased in a direction toward drive roller  19   a.  With this configuration, first roller pair  19   a,   19   b  form a nip which provides for the transport of the screen along path P. 
     Rollers  19   a,   19   b  move the screen along path P to scan area  16 . Typically, in a computed radiography (CR) reader, the laser beam is scanned in a scanline over the surface of a storage phosphor screen, for example, by a reciprocating galvanometer mirror or polygon rotating mirror, in a fast scan direction while the screen is transported under the scanline in a slow scan direction. 
     Scan area  16  includes a laser scanning optical system for use in a computed radiography scanning system (or any other similar scanning system). Such a laser scanning optical system are well known to those skilled in the art, for example, as disclosed in U.S. Ser. No. 07/761,858 (Kodak Docket No. 85919) provisionally filed on Dec. 19, 2003 as U.S. Provisional No. 60/444,014, commonly assigned and incorporated herein by reference. The laser scanning optical system can includes a laser diode which produces a laser beam shaped by shaper lens elements. A reciprocating galvonometer mirror can be employed to produce a laser beam scan line  17  in a fast scan direction (noted by arrow B in  FIG. 9 ). The scan line is directed onto a scan platen  20 . Scan platen  20  establishes an imaging region for a storage phosphor transported in a slow scan direction over platen  20 . As shown in  FIG. 6 , scan platen  20  has a cylindrical surface and is recessed in a channel  22  of guide plate  24 . The surface of scan platen  20  locates the screen at the focal point F of the scanning laser beam during the reading process. 
     The screen is held against the surface of scan platen  20  by it stiffness as it is bent in a cantilever mode from the first roller pair  19   a,   19   b.  A roller  26 , herein referred to as hold down roller  26 , is disposed proximate path P to contact the screen downstream of first roller pair  19   a,   19   b  to promote contact of the screen on scan platen  20 . As such, hold down roller  26  is arranged to hold down the screen, promoting a cantilever load. 
     A further transport means is disposed downstream of hold down roller  26  to continue the transport of the screen along path P. For Applicant&#39;s particular application, a second pair of rollers  29   a,   29   b  has been found suitable. Roller  29   a  is fixed and is driven. Roller  29   b  is a pressure roller. It can be biased in a direction toward drive roller  29   a.  With this configuration, second roller pair  29   a,   29   b  forms a nip which provides for continued transport of the screen along path P. Once the screen enters the nip of the second roller pair, the transport of the screen is controlled by the second roller pair. 
     Image artifacts might occur with the transfer of control of the transport of the screen from the first roller pair to the second roller pair. To reduce the formation of such image artifacts, in a preferred embodiment pressure roller  29   b  of the second roller pair is preferably initially held open (i.e., spaced from drive roller  29   a ) by moving pressure roller  29   a  away from drive roller  29   b  while the leading edge of the screen moves between the rollers of the second roller pair. Once the leading edge has entered the area between the rollers, pressure roller  29   b  is gently moved toward drive roller  29   b  to form a nip to transport the screen along path P. By this means, the screen is introduced into the second roller pair so as to minimize the formation of an artifact resulting from speed changes in the screen as it enters a closed roller pair. 
     Second roller pair  29   a,   29   b  is spaced sufficiently from hold down roller  26  and the scan beam so as to allow the screen to conform to the surface of scan platen  20  by virtue of gravity before entering second roller pair  29   a,   29   b.    
     Image artifacts due to the trail edge exiting the first roller pair is minimized by positioning the first roller pair close to the scanning laser beam, thereby causing the artifact to be close to the edge of the image, in area where the image will not be read by the user. In addition to it&#39;s proximity to scan platen  20 , pressure roller  19   b  of the first roller pair is slowly separated from drive roller  19   a  of the first roller pair after the second roller pair assumes drive control of the screen. 
     Preferably, first roller pair  19   a,   19   b  is angled by an angle α such that a leading edge of the screen encounters/contacts a screen guide  28  (disposed on guide plate  24 ) and is bent upward until it passes over a cylindrical locating surface of scan platen  20 . This surface locates the screen at the focal point F of scanning laser beam  17  during the reading process. The screen is held against the surface of scan plate  20  by its stiffness as it is bent in a cantilever mode from the first roller pair. This is best shown in  FIGS. 7 and 8  wherein the leading edge of the screen exists the nip of first roller pair  19   a,   19   b.  By introducing angle α, the leading edge is directed toward screen guide  28 . As shown in  FIGS. 7 and 8 , screen guide  28  is an angled surface (shown here as an inclined plane) directed toward scan platen  20 . The leading edge of the screen contacts screen guide  28  and appears to slide along screen guide  28  until is reaches scan platen  20 . Once the leading edge of the screen contact scan plate  20 , the screen loses contact with screen guide  28 . 
     Suitable angles for angle α might range from 1 degree to 10 degrees. For Applicant&#39;s particular embodiment, an angle of 4 degrees was employed. 
     As shown in  FIGS. 7 and 8 , screen guide  28  is separate and spaced from scan platen  20 . However, those skilled in the art might consider screen guide  28  and scan platen  20  as a unitary element. For example, an inclined surface abutting an arc, or alternatively, a cylinder having a relatively large radius. 
     To further promote the directing of the leading edge toward screen guide  28 , the cassette can be angled relative to the first roller pair. For example, as shown in  FIG. 8 , cassette  15  might be angled at an angle β from horizontal. Suitable angles for angle β might range from 5 degrees to 10 degrees. For Applicant&#39;s particular embodiment, an angle of 8 degrees was employed. 
     The present invention provides for the maintaining of the positional location of the screen relative to the scanning beam focal length during the scanning process. More particularly, it is the cantilever loading of the screen against scan platen  20  that accomplishes this. The load is applied by the angle of the first roller pair relative to scan platen  20  for the early portion of the scan. During the latter portions of the scan, after the second roller pair engages the screen and the first roller pair is disengaged, hold down roller  26  provides the load for the trailing edge of the screen. 
     Shielding the entrance of a light collector  30  from light is important to the operation of reader  10 . In addition to the a light lock cover, a unique screen path was developed to choke off any light emitted from the erase station. It is this “hump” shape, located between hold down roller  26  and the second roller pair, that accomplishes this task. The screen weaves it&#39;s way through the changing elevations. With such an arrangement, no light can make it to the collector entrance. 
     The first and second roller pairs might be elastomeric. Skew control can be an issue in elastomeric roller systems. Dynamic skew (continuous change) can be managed by the utilization of low density foam pressure rollers and a unique pressure delivery system. To manage skew, the forces delivered to each end of the pressure rollers is preferably closely matched. Referring to  FIGS. 10-13 , the present invention preferably employs a cable/pulley system (element  33  is a lift cable assembly for the first roller pair), which can be located under the assembly, and a single tension spring  32 , 34  (first roller pair, second roller pair, respectively) to provide equalized loads to each end of the pressure rollers. Other elements shown in these figures include a lift cable  40  for the first roller pair, a drive pulley  42  for the first roller pair, a pressure cable  44  for the first roller pair, a cam  46  for the first roller pair, cam drive components  48  for the first roller pair, cam drive components  50  for the second roller pair, and a motor  52 . 
     The invention has been described in detail with particular reference to a presently preferred embodiment, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein. 
     PARTS LIST 
     
         
           10  storage phosphor reader 
           12  touch screen display 
           14  receiving station 
           15  cassette 
           16  scan area 
           17  scanning laser beam 
           18  erase area 
           19   a - 19   b  rollers 
           20  scan platen 
           22  channel 
           24  guide plate 
           26  roller 
           28  screen guide 
           29   a - 29   b  rollers 
           30  light collector 
           32 , 34  single tension springs 
           33  lift cable assembly 
           40  lift cable 
           42  drive pulley 
           44  pressure cable 
           46  cam 
           48  cam drive components 
           50  can drive components 
           52  motor