Abstract:
A temperature controlled apparatus comprising: an object having a surface and being rotatable about an axis; an electrical heater assembly thermally coupled to the surface of the object; a temperature sensor assembly mounted on the object for sensing the temperature of the object surface and for producing temperature signals representative of the sensed temperatures; a microprocessor non-rotatably mounted with respect to the rotatable object; an optical communication link for transmitting the temperature signal to the microprocessor; and a temperature control assembly, non-rotatably mounted with respect to the rotatable object for controlling the flow of electrical power to the heater in response to control signals from the microprocessor as a function of the transmitted temperature signals.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to apparatus for controlling temperature and, more particularly, to apparatus for controlling the temperature of moveable, electrically heated objects and, preferably, rotatable, electrically heated drums. 
     BACKGROUND OF THE INVENTION 
     Photothermography is an established imaging technology. In photothermography, a photosensitive media is exposed to radiation to create a latent image which can be thermally processed to develop the latent image. Devices and methods for implementing this thermal development process are generally known and include contacting the imaged photosensitive media with a heated platen, drum or belt, blowing heated air onto the media, immersing the media in a heated inert liquid and exposing the media to radiant energy of a wavelength to which the media is not photosensitive, e.g., infrared. Of these conventional techniques, the use of heated drums is particularly common. 
     A common photosensitive media usable in these imaging processes is known as a photothermographic media, such as film and paper. One photothermographic media has a binder, silver halide, organic salt of silver (or other reducible, light-insensitive silver source), and a reducing agent for the silver ion. In the trade, these photothermographic media are known as dry silver media, including dry silver film. 
     In order to precisely heat exposed photothermographic media, including film and paper, it has been found to be desirable to use electrically heated drums. In apparatus employing this technique, a cylindrical drum is heated to a temperature near the desired development temperature of the photothermographic media. The photothermographic media is held in close proximity to the heated drum as the drum is rotated about its longitudinal axis. When the temperature of the surface of the heated drum is known, the portion of the circumference around which the photothermographic media is held in close proximity is known and the rate of rotation of the drum is known, the development time and temperature of the photothermographic media can be determined. Generally, these parameters are optimized for the particular photothermographic media utilized and, possibly, for the application in which the photothermographic media is employed. 
     In order to achieve a high quality-image in the photothermographic media, very precise development parameters must be maintained. Generally, the circumference of the drum over which the photothermographic media travels will not vary significantly. Also, the rate of rotation of the drum, or the transport rate of the photothermographic media through the thermal processor, can be rather precisely maintained. However, it is generally more difficult to control and maintain the temperature of the surface of the drum. 
     In addition, other factors also contribute to inaccurate processing. The closeness of the proximity which the photothermographic media is held to the drum partially determines the temperature at which the emulsion in the photothermographic media is heated. Further, the presence of foreign particles between the drum and the photothermographic media can interrupt the flow of heat from the drum to the photothermographic media which can affect image quality. 
     Because many factors affect image quality, one of which is the temperature at which the photothermographic media is developed, the preciseness at which the surface temperature of the drum can be maintained is important to thermal processing of photothermographic media. 
     The temperature of the drum depends upon many factors. These include the rate at which heat is delivered to the drum, the thermal conductivity and the thermal mass of the drum, the thermal mass of the photothermographic media, the rate, i.e., the number of sheets (if sheet photothermographic media is used) of photothermographic media being processed, the ambient temperature, whether thermal processing is just beginning or whether the thermal processing is in the middle of a long run. 
     In addition, heated drums are used extensively in various other material processing applications. Examples include calendaring, laminating, coating and drying. 
     Typically, heat is delivered to such drums through the use of electrical resistance heating elements. Since the heated drum is rotating during thermal processing and since it is a desirable to deliver electrical power to the electrical resistance heating elements during rotation of the drum, is desirable to be able to deliver electrical power from a stationary power source, e.g., the standard AC line, to the moving, rotating drum. Electrical power may be delivered to the drum through the use of slip rings coupled to the drum. 
     In addition, to precisely control the temperature of the electrically heated drum there should be a means to sense the temperature of the drum and a means to control the electrical power applied to the electrical resistance heaters in response to the signal from the temperature sensor. 
     While temperature control techniques and apparatus are common, the use of such techniques and apparatus on movable objects or rotating drums is make more difficult by movement of the object of the rotation of the drum. 
     One solution has been to locate all temperature sensing and control techniques on the movable object or rotating drum. In the case of a rotating drum, analog temperature control techniques have been used by incorporating a circuit board containing the analog circuitry on or near the rotating drum allowing the circuit board to rotate along with the drum. While this technique minimizes the difficulty of communicating temperature sensing information and control information between the drum and the analog circuitry, it makes it more difficult to interface to the analog control circuitry or to change or adjust the temperature or control algorithm. 
     A similar technique, employed by Systek, Minneapolis, Minn. utilizes rotating temperature control circuitry and additionally provides a technique for the communication of sensed temperature information from the rotating drum/control circuitry and the communication of adjustment parameters from the user of the thermal processor utilizing the drum to the rotating drum/control circuitry. A ring of a plurality of light emitting diodes are arranged in a generally circular pattern on one end of the drum/control circuitry. A single light emitting diode is positioned on a stationary board near to that one end of the rotating drum/control circuitry. A light sensor is located on the rotating drum/control circuitry on the one end of the axis or rotation. Similarly, a second light sensor is located on the stationary board. Each light sensor is adapted to sense the duty cycle modulated pulse train of the corresponding light emitting diode(s) on the opposite member. Interference in light transmission is minimized by having each pair of light emitting diodes and sensors act at a different frequency. For example, one pair could operate in the visible spectrum and the other pair could operate in the infrared spectrum. 
     However, the Systek system is limited to the reading of rather coarse temperature sensing information. Further, all of the temperature control loop circuitry is entirely located on the rotating drum/control circuitry board. Thus, any intelligence built into the temperature control loop must be able to be contained on the rotating drum/control circuitry board, limiting the power and options available. 
     Another solution is described in U.S. Pat. No. 5,580,478, issued Dec. 3, 1996, inventors Tanamachi et al. This U.S. Patent discloses a method of synchronously transmitting frequency modulated signals corresponding to each heating zone&#39;s temperature via a bi-directional infrared optical link from the movable heated object to a stationary microprocessor system. The microprocessor then transferred heater control information back across the bi-directional optical link to the movable heated object. These signals controlled the application of power to the appropriate heater via solid state relays mounted on the movable object. 
     There is thus a need for a less complex temperature control system for a rotatable heated drum. 
     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 a temperature controlled apparatus comprising: 
     an object having a surface and being rotatable about an axis; 
     an electrical heater assembly thermally coupled to said surface of said object; 
     a temperature sensor assembly mounted on said object for sensing the temperature of said object surface and for producing temperature signals representative of the sensed temperatures; 
     a microprocessor non-rotatably mounted with respect to said rotatable object; 
     an optical communication link for transmitting said temperature signal to said microprocessor; and 
     a temperature control assembly, non-rotatably mounted with respect to said rotatable object for controlling the flow of electrical power to said heater in response to control signals from said microprocessor as a function of said transmitted temperature signals. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The invention has the following advantages. 
     1. The surface of a temperature controlled heated movable object and rotatable heated drum is maintained at a very accurate temperature by accurately communicating precisely sensed temperature information from the moving object/drum and by sending precisely timed power to the heaters in the moving object/drum. 
     2. Higher processing power and more sophisticated temperature control techniques are achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a portion of a thermal processor utilizing a rotatable, electrically heated drum. 
     FIG. 2 is a cross-sectional view of the drum shown in FIG.  1 . 
     FIG. 3 is a high level block diagram of an electronic temperature control apparatus constructed in accordance with the present invention. 
     FIG. 4 is a block diagram of a processor communication board utilized in the temperature control apparatus of FIG.  3 . 
     FIG. 5 is a block diagram of a rotating board utilized in the temperature control apparatus of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the present invention provides a temperature controlled heated movable object/rotatable heated drum and an apparatus for controlling the temperature of a rotatable heated movable object/heated drum. Very accurate temperature at the surface of the object/drum can be maintained due, in part, to the ability to accurately communicate precisely sensed temperature information from the movable/rotatable object/drum and to send precisely timed power to the heaters in the movable/rotatable object/drum. This allows a portion of the temperature control loop circuitry to be located on a stationary object which, in turn, allows the use of higher processing power and more sophisticated temperature control techniques. 
     More particularly, the present invention provides a temperature controlled, electrically heated drum. A cylindrical drum has a surface and is rotatable on an axis. An electrical heater is thermally coupled to the surface of the cylindrical drum. A temperature control mechanism, non-rotatably mounted in conjunction with the cylindrical drum and electrically coupled to the electrical heaters through slip rings, controls the temperature by controlling the flow of electricity to the electrical heaters in response to control signals from the non-rotatably mounted microprocessor. A temperature sensor mechanism, rotatably mounted in conjunction with the cylindrical drum and electrically coupled to the temperature sensor, senses the temperature of the surface of the cylindrical drum and produces temperature signals indicative thereof. A microprocessor, non-rotatably mounted with respect to the cylindrical drum, controls the temperature of the electrically heated drum by generating the control signals in response to the temperature signals. An optical mechanism, coupled to the temperature control means, the temperature sensor means and rotating microprocessor means, optically couples the temperature signals from the rotating temperature sensor means to the non-rotating microprocessor means. 
     A portion of a thermal processor utilizing a rotatable electrically heated drum  10  is illustrated in FIGS. 1 and 2. Such a thermal processor may be used to process medical diagnostic quality dry silver film. Cylindrical drum  10 , mounted on frame  11 , is rotatable around axis  12 . Optionally, exterior surface  14  of drum  10  may be coated with silicone layer  15 . Also, optionally, exterior surface  14  of drum  10  is divided into separately controlled heating zones  16 ,  18 ,  20 . Since the edges of surface  14  of drum  10  may cool more than the central portion of surface  14 , a central zone  16  is controlled independently of edge zones  18  and  20 . Photothermographic media (not shown) is held in close proximity of exterior surface  14  and drum  10  over a portion of the circumference of drum  10  by means of holding down rollers (not shown). With a known temperature of exterior surface  14  of drum  10 , typically 252 degrees Fahrenheit, a known rotational rate, and a known portion of circumference of surface  14  over which the photothermographic media passes, a known development temperature and dwell time can be achieved. After heated development, a cooling system  22  cools the photothermographic media to a temperature below development temperature. The cooled media is then transported to an output tray. 
     As shown in FIG. 2, cylindrical drum  10  is constructed from aluminum having a diameter, for example, of 8 inches (20.32 centimeters) and with a hollow interior and shell thickness for example, of 0.25 inches (0.635 centimeters). Mounted on the interior surface  34  of drum  10  are electrical resistance heaters  36 ,  38  and  40  adapted to heat zones  16 ,  18 ,  20 , respectively. Exterior surface  14  of drum  10  may have a very delicate silicone coating  15 , so temperature measurement of the drum is done internally in order not to damage the surface coatings. Mounted on the interior surface  34  of drum  10  are temperature sensors  42 ,  44  and  46  adapted to sense the temperature of zones  16 ,  18  and  20 , respectively. 
     The temperature of exterior surface  14  is maintained across drum  10  and from sheet to sheet of photothermographic media to within .+−0.0.5 degrees Fahrenheit in order to produce diagnostic quality images. 
     A high level block diagram of the major components of the temperature control circuitry is illustrated in FIG.  3 . Since drum  10  is rotating, communication to electrical resistance heaters  36 ,  38  and  40  is done by way of slip ring assembly  67  which is mounted on one end of cylindrical drum  10  and which rotates at the same rate as drum  10 . As shown in FIG. 3, circuit board  48  is optically coupled by stationary mounted optical receiver  50  positioned to optically cooperate with rotating circuit board  48 . One way communication occurs over optical communications link  66  from the rotating board to the non-rotating processor communication board  52  through optical receiver  50 . Rotating circuit board  48  rotates with drum  10  to communicate temperature information from the three drum heated zones  16 ,  18 ,  20  to software located on processor communications board  52  via link  66  to optical receiver  50 . Processor communications board  52  contains a microprocessor whose software interprets the coded temperature information from the three heater zones  16 ,  18 ,  20  and converts it to actual zone temperatures. The software then closes the control loop by calculating via a heater control algorithm whether the heater corresponding to the sensed temperature in a particular zone should be turned on or off. The microprocessor then turns on a solid state relay to apply power to the appropriate heater through slip ring assembly  67  A-E. 
     More detail of the function of the processor communication board  52  is shown in FIG. 4. 120Vac from source  70  of the imager in which drum  14  is mounted is brought in to the board  52  to power the processor heaters and supply 12Vac to power the rotating board. The 12Vac is supplied via step down transformer  100 . There are three solid state relays  101 ,  102  and  103  which control power to each of the three drum heaters  36 ,  38  and  40  under control of microprocessor  104 . Coded 12 bit digital temperature data is supplied to the microprocessor  104  from each of the three temperature sensors  42 ,  44 ,  46  via optical link  66  and optical receiver  50 . Communication to the rest of the imager is through the  12 C interface  105 . New software can also be downloaded via the communications system. Interface  105  also includes an RS 232  communications port for service of the processor control system. 
     Referring now to FIG. 5, there is shown in greater detail the electrical components disposed on the rotating drum  10 . Slip rings  67  A-D supply controlled 120Vac power to resistance heaters  36 ,  38  and  40 . 12Vac power is also supplied via slip ring  67 E to bridge rectifier and filter  200  to produce a dc voltage supplied to +5V regulator  202 . +2.5V precision voltage reference  204  and precision voltage divider chain  206  provide d. c. voltages to Analog to Digital Converter  208  and current sources  210 - 216 . Current sources  210 ,  212  and  214  are respectively coupled to temperature sensors  46 ,  44 ,  42 . The temperature signals from sensors  42 ,  44 ,  46  are applied to analog mux  218  which is controlled by rotating microprocessor  220 . Mux  218  supplies the temperature signals serially to A to D converter  208  which converts them to digital signals which are communicated over optical communications link  66  by microprocessor  220  and infrared LED  222 . 
     While the preferred embodiment has been described in relation to a thermal processor having a rotatable heated drum, the temperature control apparatus has usefulness in other application involving heated movable objects requiring precise temperature control. 
     Thus, it can be seen that there has been shown and described a novel apparatus for controlling the temperature of and a movable, electrically heated object. It is to be recognized and understood, however, that various changes, modifications and substitutions in the form and the details of the present invention may be made by those skilled in the art without departing from the scope of the invention as defined by the following claims. 
     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 
                 drum 
               
               
                   
                  11 
                 frame 
               
               
                   
                  12 
                 axis 
               
               
                   
                  14 
                 exterior surface 
               
               
                   
                  15 
                 silicone coating 
               
               
                   
                  16, 18, 20 
                 controlled heating zones 
               
               
                   
                  22 
                 cooling system 
               
               
                   
                  34 
                 interior surface 
               
               
                   
                  36, 38, 40 
                 electrical resistance heaters 
               
               
                   
                  42, 44, 46 
                 temperature sensors 
               
               
                   
                  48 
                 rotating circuit board 
               
               
                   
                  50 
                 optical receiver sensor 
               
               
                   
                  52 
                 processor communication board 
               
               
                   
                  66 
                 link 
               
               
                   
                  67 
                 slip ring assembly 
               
               
                   
                  70 
                 120 Vac power 
               
               
                   
                 100 
                 transformer 
               
               
                   
                 101 
                 solid state relay 
               
               
                   
                 102 
                 solid state relay 
               
               
                   
                 103 
                 solid state relay 
               
               
                   
                 104 
                 microprocessor 
               
               
                   
                 105 
                 12C and RS232 communication interfaces 
               
               
                   
                 200 
                 bridge rectifier and filter 
               
               
                   
                 204 
                 precision voltage reference 
               
               
                   
                 206 
                 precision voltage divider chain 
               
               
                   
                 208 
                 A to D converter 
               
               
                   
                 210 
                 current source 
               
               
                   
                 212 
                 current source 
               
               
                   
                 214 
                 current source 
               
               
                   
                 216 
                 current source 
               
               
                   
                 220 
                 microprocessor 
               
               
                   
                 222 
                 infrared LED