Abstract:
An apparatus for cooling thermally processed media exiting from a thermal processor comprising: a heat conductive member which has first and second opposite sides which is positioned to receive media from a thermal processor, and which removes heat from the heated media as it passes over the first side of the member; and means for removing heat from the member by passing air in contact with and past the second side of the member to remove heat from the member.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to imaging systems and more particularly to an active cooling system for cooling thermally processed media after development by a heated member in an imaging system 
     BACKGROUND OF THE INVENTION 
     Thermally processed media are widely used in a variety of applications, such as in the medical, industrial and graphic imaging fields. For example, medical laser imagers reproduce diagnostic images on thermally processed photothermographic film. After exposure, the film is thermally developed by means of a heated member, such as a rotatable heated drum. Subsequently, the developed media is cooled to prevent over development of the image and to allow a user to hold the media while examining the developed image. 
     During the cooling process, it is important to cool the media uniformly to avoid image artifacts that could interfere with diagnosis. Film cooling is also required to protect various electronics components in the laser imager from overheating. Various active cooling systems have been proposed using forced convection where moving air directly contacts the heated media. (See: U.S. Pat. No. 5,557,388, issued Sep. 17, 1996, inventors Creutzmann et al.; U.S. Pat. No. 3,914,097, issued Oct. 21, 1975, inventor Wurl; U.S. Pat. No. 4,545,671, issued Oct. 8, 1985, inventor Anderson; U.S. Pat. No. 5,221,200, issued Jun. 22, 1993, inventors Roztocil et al.). These systems present problems resulting from uneven cooling which produces image artifacts. 
     A passive cooling system has also been used with great success. As disclosed in U.S. Pat. No. 5,563,681, issued Oct. 8, 1996, inventors Kirkwold et al., and U.S. Pat. No. 5,699,101 issued Dec. 16, 1997, inventor Allen, this system included a plate positioned adjacent the exit of a heated drum processor. In one arrangement, the plate has a first region adjacent the exit from the heated drum of thermally insulative material and a second successive region of thennally conductive material. In another arrangement, the plate has a textured and/or perforated top surface positioned relative to the heated drum so that the media slides on the top surface. Although the passive cooling systems disclosed in the latter two patents are successful for their intended purposes, in laser imager producing film at rates of 160 images per hour or more such systems are unable to handle the substantial increase in heat generated. The high throughput requires the cooling system to absorb proportionately more heat per unit of time, before the film encounters components in the imager that might produce image artifacts by non-uniformly cooling the film. 
     There is thus a need for a cooling system in high throughput laser imagers which maintains excellent image quality by uniformly cooling heated media processed by the laser imager. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a solution to the problems discussed above. 
     According to a feature of the present invention, there is provided an apparatus for cooling thermally processed media exiting from a thermal processor comprising: a heat conductive member which has first and second opposite sides which is positioned to receive media from a thermal processor, and which removes heat from said heated media as it passes over said first side of said member; and means for removing heat from said member by passing are in contact with and past said second side of said member to remove heat from said member. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The invention has the following advantages. 
     1. A laser imager producing thermally processed media can operate at higher throughput, while maintaining excellent image quality. 
     2. The objective of Par. 1 is achieved by maximizing the heat transfer from the media via conduction and isolating the convective heat transfer from the media. 
     3. The invention uses an acceptable input power requirement; occupies a small space; is reasonably easy-to-service components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a laser imager thermal processor incorporating the present invention. 
         FIG. 2  is a side elevational view of the thermal processor of  FIG. 1 . 
         FIG. 3  is an exploded view of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1 and 2  there is shown an exemplary thermal processor of a laser imager incorporating an embodiment of the present invention. As shown, thermal processor  10  includes a main drum assembly  12  having a rotatably mounted heated drum  14  having an outer resilient layer  15 . Drum  14  is heated with an electrical heater  16  applied to the inner surface of drum  14 . The electrical heater is divided into a plurality of electrical heater zones across the width of the drum to minimize optical density variations in the cross media direction. Processor  10  also includes a cooling section  18  according to the invention, densitometer  20 , drive train  22 , chassis member  24 , cover assembly  26  and condensation traps  28 ,  30 . Rollers  32  hold an exposed film in contact with drum  14 . 
     In operation, exposed film is fed by roller pair  34 ,  36  into contact with drum  14 , rollers  32  holding film in contact with heated drum  14 . Drum rotational velocity, drum diameter, and film wrap on drum  14  determine drum dwell time. Thermal processor  10  is configured to process up to 160 images per hour for 35×43 cm. film. 
     Film is stripped from drum  14  by stripper  38  which directs the heated film along an exit path over cooling section  18 . Roller pairs  42 ,  44 ,  46 ,  48  and  50 ,  52  transport the film along the exit path to an output tray past densitometer  20 . 
     Referring now more particularly to  FIG. 3 , there will be described in greater detail cooling section  18  according to an embodiment of the present invention. Cooling section  18  includes heat sink  60 , inlet duct  70 , outlet duct  80 , and fan  90 . Heat sink  60  includes a rectangular, extruded tubular part  61  having upper member  62 , lower member  63 , side members  64 ,  65  and internal fins  66 . Part  61  is made of heat conductive material such aluminum, or other metal, heat conductive polymer or the like. The upper side  67  of member  62  is smooth and free of defects to avoid scratching the warm film. 
     Internal fins  66  contact lower side  68  of member  62  and provide maximum surface area for convective heat transfer from member  62  to the air flowing through part  61 . 
     The inlet duct  70  is preferably a blow molded rectangular, tubular plastic part. It directs the cooling air from outside of the front of the imager to the inside of the heat sink, preventing any air flow from occurring near the warm film. 
     The outlet duct  80  is also preferably a blow molded rectangular, tubular plastic part. It directs the cooling air from the heat sink  60  to the fan  90 , preventing any air flow from occurring near the warm film. 
     The fan  90  meets a minimum air flow requirement, in order to provide sufficient cooling and minimize cross-web temperature variation in the heat sink  60 . It draws minimum electrical power. Its form factor is of a reasonable size, which allows it to fit into the space allowed near the imager back panel. The outlet of the fan directs the air through the imager back panel to the rear of the imager. 
     Gaskets  100  are installed in between each part in the active cooling system  18 , to prevent air from leaking out of the cooling system to the volume under the hood. The gaskets  100  that seal the heat sink  60  to the processor chassis are made of closed-cell silicone so that they can withstand the higher temperatures that the heat sink experiences. 
     Important parameters of the cooling section design include the following: 
     Heat Removal Rate 
     The cooling section  18  must remove enough heat from the film to prevent the film from over heating the densitometer  20  and output electronics. The densitometer  20  must remain at preferably less than 75 C. The heat removal rate is primarily determined by two parameters: the efficiency of the heat transfer between the film and the aluminum top plate  62 , and the amount of heat convection from the aluminum plate  62  and fins  66  to the air moving through the box. The design is limited by the convection to the air. 
     Top Plate Material 
     The cooling system top plate  62  is made of aluminum, because aluminum is an excellent heat conductor. At the same time, aluminum is reasonably priced, relative to materials that are better heat conductors than aluminum. It will be understood that other heat conductive materials can be used including other metals, heat conductive polymer or the like. 
     Film Contact Surface Shape 
     The cooling section top plate  62  is flat. 
     Top Plate Surface Coating 
     The top surface  67  of the top plate  62  must be very smooth in order to avoid scratching the film. The top plate  62  preferably uses a Fluoropolymer coating (Perfluoroalkoxy) in order to minimize film scratching. 
     Duct Design 
     The ducts and cooling box are designed to minimize pressure drops that would impeded air flow in the system, thus maximizing the heat removed. Therefore, the design avoids sharp changes in direction and in cross-sectional area through the air flow path. 
     Fan Performance 
     The performance of the cooling section fan must balance many factors. First and foremost, it must provide enough air flow to adequately remove the heat transferred from the film to the top plate. However, it must run on low voltage and draw minimal current, to avoid overloading the electrical system. It must have a lifetime greater than the imager&#39;s lifetime. It must be small enough to fit within the space available between the processor chassis and the back panel. It must be quiet enough to allow the imager to pass the noise specification. It must not produce vibrations that affect the performance of the optics subsystem. 
     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 
     
         
           10  thermal processor 
           12  main drum assembly 
           14  heated drum 
           15  resilient layer 
           16  electrical heater 
           18  cooling section 
           20  densitometer 
           22  drive train 
           24  chassis member 
           26  cover assembly 
           28 , 30  condensation traps 
           32 , 34 , 36  rollers 
           38  stripper 
           42 , 44 , 46 , 48 , 50 , 52  roller pairs 
           60  heat sink 
           61  extruded tubular aluminum part 
           62  upper surface member 
           63  lower member 
           64 , 65  side members 
           66  internal fins 
           67  upper side 
           68  lower side 
           70  inlet duct 
           80  outlet duct 
           90  fan 
           100  gaskets