Abstract:
The present invention is directed to a method and apparatus relating to the thermal management of an image fixing device such as establishing the temperature of a component that engages with the image fixing device in an image forming apparatus.

Description:
FIELD OF INVENTION 
   The present invention relates to establishing temperatures in an image forming apparatus. The image forming apparatus may include printers, including laser or electrophotographic printers and inkjet printers, copiers, faxes, all-in-one devices, or multifunctional devices. 
   BACKGROUND 
   An imaging apparatus, such as a printer, copier, fax machine, all-in-one device or a multifunctional device may include an image fixing device to fix a developing agent, such as toner, to media. The image fixing device may include a heating device such as a fuser. The fuser may have a heat source and a number of rollers or a belt and a roller that may form a nip for the media to pass through. The heat source and the rollers and/or belt may provide heat and/or pressure to the toner that may soften the toner so that the toner may adhere to the media. Improper control of temperature may lead to print defects such as low grade fusing defects, hot offset defects or paper stalls. 
   SUMMARY 
   The present invention is directed at managing the temperature in an image forming apparatus. For example, the present invention is directed to a method and apparatus relating to the thermal management of an image fixing device such as controlling the temperature of a component that engages with the image fixing device in the image forming apparatus. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Features and advantages of the present invention are set forth herein by description of embodiments consistent with the present invention, which description should be considered in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a side view of an exemplary embodiment of an image fixing device. 
       FIGS. 2 ,  3   a  and  3   b  provide a flow chart of an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention relates to the management of temperature in an image fixing device. For example, the present invention provides an article and method for the thermal management of a heating device in an image forming apparatus. An exemplary embodiment of an image forming apparatus may include printers, including laser or electrophotographic printers and inkjet printers, copiers, faxes, all-in-one device, or multifunctional devices. 
     FIG. 1  illustrates one exemplary image fixing device  110 . Any image fixing device that requires temperature management is applicable to the present invention. The image fixing apparatus may include a pressure roller  112 , a heating device  122  and belt or film  132 . The pressure roller  112  may include a number of configurations. For example, the pressure roller  112  may include a shaft portion  116 . The shaft portion  116  may be formed from steel, aluminum, or other metallic or plastic materials. Covering the shaft portion may be a polymeric layer  118 , such as a rubber or elastic layer. The polymeric layer  118  may be formed from silicon rubber or other thermoplastic or thermoset materials. Such materials may have thermal conductivities of about 0.1-4.0 watts/meter-Kelvin (W/mK). 
   Covering the polymeric layer  118  may be an additional layer or sleeve  120 . The additional layer  120  may incorporate low energy material such as polytetrafluoroethylene (PTFE), perfluoroalkoxytetrafluoroethylene, fluorinated ethylene propylene (FEP), fluoroelastomers and other fluoropolymers and combinations of fluoropolymers and other materials. The pressure roller  112  may be driven by a motor M in communication with the pressure roller  112 . 
   The heating device  122  may include a number of components. For example, the heating device may include a heater substrate  124 , which may include one or more segments. The substrate may be composed of ceramic material. Furthermore the substrate may be electrically insulative, have a high thermal conductivity, a high heat resistance and/or a low thermal capacity. The heating device may also include one or more heat-generating electrical resistors  126 . The resistors may extend along the length of the substrate  124 . A temperature detecting element  128  may be included in the heating device  122 . The temperature detecting element  128  may include a thermistor or a thermostat. The temperature detecting element  128  may be mounted in contact with the substrate member  124  and in one embodiment may be mounted on a surface of the substrate member  124  opposite an electrical resistor  126 . 
   The heating device may communicate with a processor C. The processor may be a microprocessor or other processor located within the printing device or within the fixing device  122 . The heating device may be fixed to a holder  130 . A thin layer of electrical insulation such as glass (not shown) may cover the electrical resistors  126 . A belt or film  132  may surround the heating device  122 . 
   In one embodiment, the belt  132  may be an idling belt as the belt may be rotated by the pressure roller  112 . The belt  132  may be composed of a relatively high heat resistant and durable material such as polyimide. The belt  132  may also be an endless tube and may be between 40-100 microns in thickness. The belt  132  may also include an outer layer (not illustrated) incorporating a relatively low surface energy material such as polytetrafluoroethylene (PTFE), perfluoroalkoxytetrafluroethylene, fluorinated ethylene propylene (FEP), fluoroelastomers and other fluoropolymers and combinations of fluoropolymers and other materials. 
   As alluded to above, the media P may pass from the developer, where a developing agent such as toner may be deposited, to the fixing device. Prior to fixing, the toner Ta may be loose on the media P. The toner and media may enter the nip (N) between the heating device  122  and the pressure roller  112 . The belt  132  may be an idling belt, driven by contact with the pressure roller  112  or alternatively may be driven by driving members, such as motor M. For example, the pressure roller  112  may contact the belt  132  with about 5-20 kilograms of force. Once the media enters the nip N, the toner may be heated and may fuse to the media P, exiting the nip N in a fused state Tc. 
   In one embodiment the processor C, may be capable of interacting with an image fixing device including a heating device and a pressure or back-up roller. The processor may include software, hardware or firmware. When a print job is generated, the processor may recognize that there may be a print job to be printed and may also recognize the type or properties of print job. 
   A print job as referred to herein may be considered information or images, such as text, characters or graphics that may be printed on at least one sheet of media. Individual pages of a print job may be referred to as a print page. Properties of a print job may relate to the types of media chosen for printing, the size of the media, the type of developing agent used in the print job, the number of sheets or pages, etc. For example, a print job or a print page in a print job may be a simplex or duplex print job. A simplex may be referred to herein where images may be printed on only one side of the media. A duplex may be referred to herein where images may be printed on both sides of the media. 
   The processor may also communicate with a temperature detecting element  128 , illustrated in  FIG. 1 , to detect a heating device temperature such as a fuser temperature. This is one form of information that may be sourced from the image forming apparatus. The processor may be capable of determining whether the heating device temperature is relatively warm or cold such by comparing the heating device temperature to a set point. For example, if the heating device temperature is greater than or equal to a given set point, the heating device temperature may be considered warm. If the heating device temperature is less than a given set point, the heating device temperature may be considered cold. The given set point may be any temperature. For example a desired temperature between 50 degrees Celsius and 200 degrees Celsius, and any interval therebetween including 85 degrees Celsius, 100 degrees Celsius, etc, which may be selected for any given print job. Alternatively, the set point temperature may be related to the type of media chosen for the print job or the type of developing agent, toner or whatever particular image forming substance that may used by the printing device, which may be determined when the processor detects the type of print job. 
   Furthermore, the processor may be capable of interacting with the heating device  122  to set or adjust the heating device temperature. The heating device temperature may be set or adjusted according to another source of information, such as the type of media chosen, the image forming substance used, the speed at which the media may pass through the heating device, the pressure that may be applied to the media during heating, etc. As the heating device, which may be a fuser, and which may include a belt, may be in proximity to the pressure roller, and may contact the pressure roller directly or indirectly (such as when media passes through the nip), adjusting the heating device temperature may directly affect the pressure roller temperature. 
   It should be appreciated that as the pressure roller may be composed of a polymeric material, such as an elastomeric or rubber material, the pressure roller may retain a portion of the heat energy transferred to the pressure roller from the heating device. This may be the case when one employs polymeric material which may have a relatively low thermal conductivity. Once media begins to feed through the nip, the media may begin to absorb some of the heat otherwise retained in the pressure roller and the pressure roller temperature may partially decrease. However, the pressure roller may retain an excess amount of heat in certain printing situations. The excess heat may cause, e.g., hot offset defects or papers stalls that may result from the generation of steam caused by vaporization of water (e.g., steam) out of the media. 
   For example purposes only, if a user were to print several short print jobs with relatively small pauses between jobs, the heating device may turn off and cool during the pause and may be forced to ramp back to the printing temperature (without media in the nip) for the next job. Each time the heating device ramps more energy is put into the pressure roller and there may be less opportunity to transfer that energy to the media and there may be a build-up in energy (heat) in the pressure roller. Such repeated ramping to higher printing temperature may cause the temperature in the pressure roller to rise to some undesirable level. 
   By way another non-limiting example, in the case of duplex printing, a time gap may exist between heating the front and back side of the media. The heating device may be turned off during such gap, which then may require that the heating device must ramp to a printing temperature for heating the back side. As a consequence, when the heating device ramps more energy may then be put into the pressure roller and again there may be less opportunity to transfer that energy to the media. This then may provide another exemplary case of build-up of energy (heat) in the pressure roller and the ramping of the heating device may again cause the temperature in the pressure roller to rise to detrimental levels. 
   Returning then to the description of the processor, it should be noted that the processor is capable of maintaining a page count. The page count may be referred to herein as the number of print pages that may have been printed in a print job, or the number of print pages that may have been printed in a number of print jobs printed in succession (i.e. a running total). At the start of a print job, the processor may clear the page count and increment the page count for every page printed. However, there may be cases where a number of print jobs have been printed in succession and the page count may not be cleared between the print jobs. 
   The processor may be further capable of determining whether the motors communicating with the media feeding device M were running when a print job was received. If the motor was still running, it may be possible to skip the step of determining the heating device temperature as one assumption may be made that the heating device is warm. 
   In one exemplary of the present invention heating device temperature may be regulated and/or the pressure roller temperature may be established based on one or a combination of factors. Such factors may include the heating device temperature prior to printing or at the beginning of a print job, the count of pages that have been printed already, whether the page to be printed may be simplex or duplex or whether the motors for feeding and/or transferring are still running. 
   The processor may therefore utilize a number of look up tables. The look-up tables may also correlate to the above described factors as well as the aspects of the printing device, such as media throughput. For example, where it is determined that the heating device is beginning from a cold start, the heating device may use temperatures from a first table, e.g., a cold-start look up table, that may be relatively high and allow for the pressure roller to heat up. Alternatively, where it is determined that the heating device is beginning from a cold start but more than a predetermined number of pages have already been printed, cooler heating device temperatures may be used as the pressure roller may already be relatively warm. 
   When it is determined that the heating device is beginning from a warm start, the heating device may use temperatures from a second table, e.g., a warm-start look up table that may then keep the pressure roller from overheating. Furthermore, if it is determined that the heating device is beginning from a warm start but there is a low page count, the heating device may be set to warmer temperatures. 
   It should be appreciated therefore, that as referred to herein, the cold-start look up table may include relatively warmer temperatures than the warm-start look up table under comparative conditions of printing. Furthermore, it should be appreciated that there may be more than two look up tables. For example, where a number of heating device states may be identified and printing may start from a number of modes such as cold start, warm start, hot start, etc. or cold start, warm up start, hot start, standby start or power save start. 
   Illustrated in  FIGS. 2 ,  3   a  and  3   b  is an exemplary embodiment of the present invention that illustrates some of the features noted above. For example, the processor may receive a print job and a print page signal may be detected, at  210 . At  211  a determination may be made as to whether the feeding and/or transfer motor have been turned off. If the motors have been turned off, the process may clear the page count at  212 . At  214  the processor may receive input from a temperature detecting element and determine whether the heating device temperature is above or below a set point. If the heating device temperature is above a set or desired temperature then a cold start flag may be cleared at  216  thereby indicating that the heating device is above the set point. If the heating device temperature is below a set or desired temperature, then a cold start flag may be set at  218 . 
   The processor may then increment the page count by 1 at  220 ; however, it should be appreciated that the page count may be incremented at any point in the process. Furthermore, if it has been determined at  211  that the motor have not been turned off, then the process of determining heating device temperature may be skipped and the page count may be incremented directly at  220 . A determination whether the page print is a simplex or a duplex may be made at  222 . If the page is a duplex, then path A may be followed continuing on  FIG. 3   a . If the page is a simplex, then path B may be followed continuing on  FIG. 3   b.    
   For a duplex, illustrated in  FIG. 3   a , a determination may be made whether the cold start flag has been set at  310 . If the cold start flag has not been set, and the heating device is considered warm, then the temperatures may be selected from the cooler temperatures on a warm-start temperature look up table at  320 . If the cold start flag has been set, then the page count may be considered  322 . If the page count is less than a set point number such as 2 at  322  then the temperatures may be selected from a grouping of temperatures in the cold-start temperature look up table at  324 . If the page count is greater than 2 at  322 , then the cold start flag may be cleared at  326  and heating device temperatures may be adjusted to temperatures correlating to a warm-start temperature table at  320 . It should be appreciated that a page count of 2 was chosen as an example only and the page count may vary depending on a number of factors such as the type of media, the type of pressure roller used, the throughput of the media in the printing device, etc. Accordingly, in some situations, at block  322  a page count of any value greater than 1 may be used, including a page count of 4, 7, 10, etc. 
   For a simplex page, referring to  FIG. 3   b , a determination may be made whether the cold start flag has been set at  312 . If the cold start flag has been set, then the processor may select temperatures that are relatively warmer to heat up the pressure roller and set the heating device according to a cold-start temperature look-up table at  330 . If the cold start flag has not been set, then the page count may be determined at  332 . Where the page count is lower than a given number, illustrated in this example as 3, cooler temperatures from the warm-start temperature look up table may be chosen  334 . Where the page count is greater than a given number (e.g. any number greater than 1) the cold start flag may be set at  336  and temperatures may be chosen from a cold start temperature look up table. It should be appreciated that a page count of 3 was chosen as an example only and the page count may vary depending on a number of factors such as the type of media, the type of pressure roller used, the throughput of the media in the printing device, etc. Accordingly, in some situations, at block  332  a page count of any value greater than 1 may be used. 
   The foregoing description is provided to illustrate and explain the present invention. However, the description hereinabove should not be considered to limit the scope of the invention set forth in the claims appended here to.