Patent Publication Number: US-2015086231-A1

Title: Fuser Assembly with Automatic Media Width Sensing and Thermal Compensation

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. §119, this application claims the benefit of the earlier filing date of Provisional Application Ser. No. 61/883,036, filed Sep. 26, 2013, entitled “Fuser with Automatic Paper Width Sensing and Thermal Compensation,” the content of which is hereby incorporated by reference herein in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     REFERENCE TO SEQUENTIAL LISTING, ETC 
     None. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to controlling a fuser assembly in an electrophotographic imaging device, and particularly to maintaining temperature levels in the fuser assembly to allow for multiple media widths to print at full speed without overheating any portion of the fuser assembly. 
     2. Description of the Related Art 
     In an electrophotographic (EP) imaging process used in printers, copiers and the like, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over an outer surface. An electrostatic latent image is formed by selectively exposing the uniformly charged surface of the photosensitive member. Toner particles are applied to the electrostatic latent image, and thereafter the toner image is transferred to a media sheet intended to receive the final image. The toner image is fixed to the media sheet by the application of heat and pressure in a fuser assembly. The fuser assembly may include a heated roll and a backup roll forming a fuser nip through which the media sheet passes. Alternatively, the fuser assembly may include a fuser belt, a heater disposed within the belt around which the belt rotates, and an opposing backup member, such as a backup roll. 
     In a belt fusing system, an endless belt surrounds a ceramic heater element. The belt is pushed against the heater element by a pressure roller to create a fusing nip. To be able to fuse the widest media that the printer is designed to print, the length of the heating region is typically about the same width or slightly longer than the width of the widest media supported by the printer. The fusing heat is typically controlled by measuring the temperature of the heating region with a thermistor held in intimate contact with the ceramic heater element and feeding the temperature information to a microprocessor-controlled power supply in the printer, which in turn applies power to the heater element when the temperature drops below a first predetermined level, and which interrupts power when the temperature exceeds a second predetermined level. In this way, the fuser is maintained within an acceptable range of fusing temperatures. 
     When a to-be-printed media sheet has a width narrower than the width of the widest media supported by the printer, overheating problems may occur because the media sheet removes heat from the fuser only in the portion of the fuser contacting the media. As the portion of the fuser beyond the width of the media sheet does not lose any heat to the media sheet, such portion of the fuser becomes hotter than the portion contacting the media sheet and can be damaged due to high temperature. 
     Since excessive thermal energy accumulated at the portion of the fuser not contacting the media (hereinafter “non-media portion”) during narrow media printing can cause damage to the fuser, it is desirable to control the amount of thermal energy accumulated at the non-media portion to be below a certain level so that the fuser will not be damaged. To control the thermal energy accumulated at the non-media portion of the fuser, prior attempts used sensors and/or user-provided information to detect media width. If the media width is less than the full width, process speed is typically reduced and/or the interpage gap is increased to limit the overheating of the non-media portion. By doing so, however, throughput of the printer is reduced when printing media sheet sizes that are less than the widest supported media size leading to reduced performance levels. 
     Further, as machine speeds increase, the tolerable range of media width variation at full speed becomes smaller. For example, in the case of printers operating at 60 ppm and above, a media width difference of 3-4 mm may be enough to cause problematic overheating in the small portion of the fuser beyond the media. In other example cases, printers are equipped with letter width or A4 width heaters. However, if the heater width does not match the media width, problems may occur. For example, printers designed for letter width media and operating at 60 ppm or greater may cause the non-media portion of the fuser to overheat if A4 width media is used. Conversely, if letter width media is used in a printer designed for A4 width media, toner that is on the portion of the letter width media beyond the A4 edge may not be sufficiently fused. 
     Accordingly, there is a need for an improved system for controlling thermal energy in a fuser assembly. 
     SUMMARY 
     Embodiments of the present disclosure provide systems for controlling temperature of portions of a heater of a fuser assembly that would allow for an image forming device to operate substantially at full speed regardless of the width of a media being fused and without user intervention. 
     In one example embodiment, a fuser assembly for an electrophotographic imaging device includes a housing, an endless belt rotatably positioned about the housing and having an inner surface, a backup roll disposed substantially against the endless belt proximal to an outer surface thereof so as to form a fuser nip with the belt, and a heater disposed substantially within the housing. The heater includes a substrate and at least one resistive trace disposed along a surface of the substrate, running a length of the substrate and generating heat for fusing toner to a sheet of media when a current is passed therethrough. The heater further includes at least three conductors for passing current through the at least one resistive trace. The at least three conductors include a first conductor connected to a first end portion of the at least one resistive trace, a second conductor connected to a second end portion of the at least one resistive trace, and a third conductor connected to the at least one resistive trace at a first location between the first end portion and the second end portion of the at least one resistive trace. A temperature sensor is disposed on the substrate to sense a temperature thereof at a location that is offset from the first location for generating a signal having a value that is based upon the sensed temperature. Circuitry is communicatively coupled to the temperature sensor and the first and third conductors for comparing the signal generated by the temperature sensor with a predetermined value. Based upon the comparison, the circuitry selects between the first conductor and the third conductor for passing current through the at least one resistive trace. 
     In another example embodiment, the at least three conductors further includes a fourth conductor connected to the at least one resistive trace at a second location between the second end portion and the first location of the at least one resistive trace. The circuitry selects between the second conductor and the fourth conductor for passing the current through the at least one resistive trace based upon the comparison. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of the disclosed example embodiments, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of the disclosed example embodiments in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of an image forming device including a fuser assembly according to an example embodiment. 
         FIG. 2  is a cross sectional view of the fuser assembly in  FIG. 1 . 
         FIG. 3  is an illustrative view a heater element of the fuser assembly in  FIG. 2  for a reference-edge feed system according to an example embodiment. 
         FIG. 4  illustrates a control configuration for the heater element in  FIG. 3  according to an example embodiment. 
         FIG. 5  illustrates a control configuration for the heater element in  FIG. 3  according to another example embodiment. 
         FIG. 6  illustrates the heater element for the referenced-edge feed system including two parallel resistive traces according to an example embodiment. 
         FIG. 7  is an illustrative view of the heater element for a center-referenced feed system according to an example embodiment. 
         FIG. 8  illustrates a control configuration for the heater element in  FIG. 7  according to an example embodiment. 
         FIG. 9  illustrates a control configuration for the heater element in  FIG. 7  according to another example embodiment. 
         FIG. 10  illustrates a control configuration for the heater element in  FIG. 7  according to yet another example embodiment. 
         FIG. 11  illustrates the heater element for the center-referenced feed system including two parallel resistive traces according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. Terms such as “first”, “second”, and the like, are used to describe various elements, regions, sections, etc. and are not intended to be limiting. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. 
     Furthermore, and as described in subsequent paragraphs, the specific configurations illustrated in the drawings are intended to exemplify embodiments of the disclosure and that other alternative configurations are possible. 
     Reference will now be made in detail to the example embodiments, as illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  illustrates an image forming device  10  according to an example embodiment. Image forming device  10  includes a first toner transfer area  15  having four developer units  20 , including developer rolls  25 , that substantially extend from one end of image forming device  10  to an opposed end thereof. Developer units  20  are disposed along an intermediate transfer member (ITM)  30 . Each developer unit  20  holds a different color toner. The developer units  20  may be aligned in order relative to the direction of the ITM  30  indicated by the arrows in  FIG. 1 , with the yellow developer unit  20 Y being the most upstream, followed by cyan developer unit  20 C, magenta developer unit  20 M, and black developer unit  20 K being the most downstream along ITM  30 . 
     Each developer unit  20  is operably connected to a toner reservoir  35  for receiving toner for use in a printing operation. Each toner reservoir  35  is controlled to supply toner as needed to its corresponding developer unit  20 . Each developer unit  20  is associated with a photoconductive member  40  that receives toner therefrom during toner development to form a toned image thereon. Each photoconductive member  40  is paired with a transfer member  45  to define a transfer station  50  for use in transferring toner to ITM  30  at first transfer area  15 . 
     During color image formation, the surface of each photoconductive member  40  is charged to a specified voltage by a charge roller  55 . At least one laser beam LB from a printhead or laser scanning unit (LSU)  60  is directed to the surface of each photoconductive member  40  and discharges those areas it contacts to form a latent image thereon. In one embodiment, areas on the photoconductive member  40  illuminated by the laser beam LB are discharged. The developer unit  20  then transfers toner to photoconductive member  40  to form a toner image thereon. The toner is attracted to the areas of the surface of photoconductive member  40  that are discharged by the laser beam LB from LSU  60 . 
     ITM  30  is disposed adjacent to each of developer unit  20 . In this embodiment, ITM  30  is formed as an endless ITM disposed about a drive roller and other rollers. During image forming operations, ITM  30  moves past photoconductive members  40  in a clockwise direction as viewed in  FIG. 1 . One or more of photoconductive members  40  applies its toner image in its respective color to ITM  30 . For mono-color images, a toner image is applied from a single photoconductive member  40 K. For multi-color images, toner images are applied from two or more photoconductive members  40 . In one embodiment, a positive voltage field formed in part by transfer member  45  attracts the toner image from the associated photoconductive member  40  to the surface of moving ITM  30 . 
     ITM  30  rotates and collects the one or more toner images from the one or more photoconductive members  40  and then conveys the one or more toner images to a media sheet at a second transfer area  65 . Second transfer area  65  includes a second transfer nip formed between a back-up roller  70  and a second transfer member  75 . 
     A fuser assembly  80  is disposed downstream of second transfer area  65  and receives media sheets with the unfused toner images superposed thereon. In general terms, fuser assembly  80  applies heat and pressure to the media sheets in order to fuse toner thereto. After leaving fuser assembly  80 , a media sheet is either deposited into an output media area  85  or enters duplex media path  90  for transport to second transfer area  65  for imaging on a second surface of the media sheet. 
     Image forming device  10  is depicted in  FIG. 1  as a color laser printer in which toner is transferred to a media sheet in a two step operation. Alternatively, image forming device  10  may be a color laser printer in which toner is transferred to a media sheet in a single step process—from photoconductive members  40  directly to a media sheet. In another alternative embodiment, image forming device  10  may be a monochrome laser printer which utilizes only a single developer unit  20  and photoconductive member  40  for depositing black toner directly to media sheets. Further, image forming device  10  may be part of a multi-function product having, among other things, an image scanner for scanning printed sheets. 
     Image forming device  10  further includes a controller  95  and an associated memory  97 . Memory  97  may be any volatile and/or non-volatile memory such as, for example, random access memory (RAM), read only memory (ROM), flash memory and/or non-volatile RAM (NVRAM). Alternatively, memory  97  may be in the form of a separate electronic memory (e.g., RAM, ROM, and/or NVRAM), a hard drive, a CD or DVD drive, or any memory device convenient for use with controller  95 . Though not shown in  FIG. 1 , controller  95  may be coupled to components and modules in image forming device  10  for controlling same. For instance, controller  95  may be coupled to toner reservoirs  35 , developer units  20 , photoconductive members  40 , fuser assembly  80  and/or LSU  60  as well as to motors (not shown) for imparting motion thereto. It is understood that controller  95  may be implemented as any number of controllers and/or processors for suitably controlling image forming device  10  to perform, among other functions, printing operations. 
     With reference to  FIG. 2 , fuser assembly  80  includes a fuser housing  98  which mounts a heat transfer member  100  and a backup roll  105  cooperating with the heat transfer member  100  to define a fuser nip N for conveying media sheets therein. The heat transfer member  100  may include a housing  110 , a heater element  115  supported on or at least partially in housing  110 , and an endless flexible fuser belt  120  positioned about housing  110 . Heater element  115  has a length that extends substantially perpendicular to a media feed direction and may be formed from a substrate of ceramic or like material to which one or more resistive traces are secured which generate heat when a current is passed therethrough. Heater element  115  may further include at least one temperature sensor, such as a thermistor, coupled to the substrate for detecting a temperature of heater element  115 . It is understood that heater element  115  alternatively may be implemented using other heat generating mechanisms. 
     Fuser belt  120  is disposed around housing  110  and heater element  115 . Backup roll  105  contacts fuser belt  120  such that fuser belt  120  rotates about housing  110  and heater element  115  in response to backup roll  105  rotating. With fuser belt  120  rotating around housing  110  and heater element  115 , the inner surface of fuser belt  120  contacts heater element  115  so as to heat fuser belt  120  to a temperature sufficient to perform a fusing operation to fuse toner to sheets of media. 
     Fuser assembly  80  may be configured for fusing toner to media sheets of different widths. With reference to  FIG. 3 , three different media sheets M1, M2, and M3 having different widths relative to a reference edge RE are shown, with media sheet M1 representing a widest supported media and media sheet M3 representing a narrowest supported media. In accordance with an example embodiment of the present disclosure, fuser assembly  80  may be controlled to selectively heat portions of the length of heater element  115  to desired fusing temperature levels depending on the width of a sheet of media passing through the fuser nip N such that the heated portion substantially matches with the media width in order to prevent overheating at non-media portions. For example, to perform a fusing operation to fuse toner to media sheet M1, a length L1 of heater element  115  corresponding to the width of media sheet M1 may be energized to generate sufficient amount of heat along length L1 for fusing toner. Likewise, in order to fuse toner to media sheets M2 and M3, lengths L2 and L3 of heater element  115 , respectively, may be energized to generate sufficient amount of heat therealong for fusing toner. In this way, only portions of the heater element  115  contacted by the sheet of media passing through the fuser nip N are heated at fusing temperature levels such that non-media portions are substantially kept from accumulating excessive thermal energy that may otherwise cause overheating and damage to the fuser assembly  80 . 
     Referring now to  FIG. 4 , a control configuration, which can be used for controlling the temperature of heater element  115  in order to avoid overheating at non-media portions, is illustrated according to an example embodiment. Heater element  115  may include a substrate  125 . Formed on a surface of substrate  125  is a resistive trace  130  extending from a first end portion  130 A to a second end portion  130 B across the length of substrate  125  and capable of generating heat when provided with electrical power. Substrate  125  and resistive trace  130  may be coated with a protective layer, such as a glass layer, which contacts the inner surface of fuser belt  120 . Heater element  115  further includes a plurality of conductors  135  connected to resistive trace  130 . Fusing temperature may be controlled by measuring the temperature of the substrate  125  with a temperature sensor  140  held in contact therewith and feeding the temperature information to controller  95  which in turn controls a power supply  145 , such as an AC power supply, of imaging forming device  10  to apply power to heater element  115  based on the temperature information such that the fuser is maintained within an acceptable range of fusing temperatures. Temperature sensor  140  may be disposed on a side of heater element  115  opposite the surface along which resistive trace  130  is disposed. 
     Conductors  135  generally provide paths for electrical energy from power supply  145  to travel through resistive trace  130 . In the example shown, first conductor  135 A, second conductor  135 B, and third conductor  135 C are connected to resistive trace  130  at different locations thereof. In particular, first conductor  135 A is connected to the first end portion  130 A, second conductor  135 B is connected to the second end portion  130 B, and third conductor  135 C is connected to resistive trace  130  at a location  130 C that is laterally offset from the first end portion  130 A and between the first and second end portions  130 A,  130 B. A temperature sensor  150  is coupled to substrate  125  at a location between the locations at which first conductor  135 A and third conductor  135 C are connected to resistive trace  130  for sensing a temperature of a substrate region corresponding to an edge segment  155  of the length of resistive trace  130 . Temperature sensor  150  may be disposed on the side of heater element  115  opposite the surface along which resistive trace  130  is disposed. 
     In an example embodiment, the location at which first conductor  135 A is connected to resistive trace  130  may correspond to an edge  160  ( FIG. 4 ) of a widest supported media sheet, such as media sheet M1, while the location at which third conductor  135 C is connected to resistive trace  130  may correspond to an edge  165  of a narrower supported media sheet, such as media sheet M2. The location at which second conductor  135 B connects to resistive trace  130  may correspond to the reference edge RE of the media path. Generally, the various locations at which conductors  135  are connected to resistive trace  130  define points at which current enters and/or leaves resistive trace  130  when connected to power supply  145 , as will be explained in greater detail below. 
     One or more of conductors  135  may be selectively coupled to power supply  145  by a control circuit  200  to control the flow of current through resistive trace  130  based on the temperature sensed by temperature sensor  150 . In an example embodiment, control circuit  200  may be contained within fuser assembly  80 . For example, control circuit  200  may be disposed on or within fuser housing  98 . In addition, control circuit  200  may operate independently from controller  95 . In particular, in the embodiment of  FIG. 4 , control circuit  200  operates without receiving control instructions from controller  95 . 
     Control circuit  200  may include a comparator circuit  205  and a switch  210 . As shown in  FIG. 4 , comparator circuit  205  has an input coupled to the output of temperature sensor  150 , a second input (not shown) coupled to at least one reference signal corresponding to one or more predetermined temperature levels, and an output coupled to a control terminal of switch  210 . Comparator circuit  205  receives signals generated by temperature sensor  150  having values that are based upon temperatures sensed thereby, compare the received signals with the at least one reference signal, and generate a signal at its output that is based upon the comparison. Comparator circuit  205  includes hysteresis, as explained in greater detail below. Switch  210  may be, for example, a mechanical switch, an electronic switch, a relay, or other switching device. As shown in  FIG. 4 , switch  210  includes a plurality of conduction terminals, such as a first conduction terminal  210 A, a second conduction terminal  210 B, and a third conduction terminal  210 C so as to be a single pole, double throw type switch, and a control terminal. In the example shown, first conduction terminal  210 A is connected to first conductor  135 A of heater element  115 , second conduction terminal  210 B is connected to a first terminal  145 A of power supply  145 , and third conduction terminal  210 C is connected to third conductor  135 C of heater element  115 . Further, switch  210  is communicatively coupled to the output of comparator circuit  205  and together provide a control mechanism for selecting and controlling a path of current through resistive trace  130  in order to control generation of heat therefrom without overheating. In particular, based on the output of comparator circuit  205 , switch  210  may selectively connect one of the first and third conductors  135 A,  135 C to power supply  145  by switching connection between first and third conduction terminals  210 A,  210 C to second conduction terminal  210 B. A second terminal  145 B of power supply  145  is connected to second conductor  135 B which, in an example embodiment, serves as a common return conductor. 
     In operation, controller  95  may control power supply  145  to provide electrical power to resistive trace  130  via first and second terminals  145 A,  145 B for heating heater element  115  to a target fusing temperature level. Switch  210  may connect first conduction terminal  210 A to second conduction terminal  210 B, as shown in  FIG. 4 , to allow current to flow between first conductor  135 A and second conductor  135 B of heater element  115 . Temperature sensor  150 , positioned proximate to edge segment  155  of resistive trace  130 , may measure the temperature of the region corresponding thereto. Comparator circuit  205  compares the output voltage of temperature sensor  150  to a voltage corresponding to the first predetermined temperature level that is greater than the target fusing temperature level. In an example embodiment, the first predetermined temperature level may correspond to a temperature limit above which damage to fuser assembly  80  may occur. Detecting a voltage corresponding to a temperature that is below the first predetermined temperature level may indicate that the region corresponding to the edge segment  155  of resistive trace  130  is not overheating and/or that the sheet of media passing through the fuser nip N is a widest supported media, absorbing heat across length L1 of heater element  115 . Accordingly, if the sensed temperature remains below the first predetermined temperature level, switch  210  may continue to keep the connection between the first conduction terminal  210 A and second conduction terminal  210 B to allow heating of length L1 of heater element  115  to the target temperature level to accommodate the detected sheet of widest supported media. 
     When fusing toner onto a sheet of narrower supported media while current flows between first conductor  135 A and second conductor  135 B of heater element  115 , the temperature of the portion of heater element  115  corresponding to edge segment  155  may increase more rapidly than the temperature of the length of heater element  115  corresponding to the width of narrower supported media. In an example embodiment, detecting a temperature that exceeds the first predetermined temperature level may indicate that the region corresponding to the edge segment  155  of heater element  115  is overheating due to the sheet of narrower media passing through fuser nip N and absorbing heat energy of heater element  115  only along the length thereof contacted by the media sheet. Accordingly, if the temperature sensed by temperature sensor  150  exceeds the first predetermined temperature level, comparator circuit  205  compares the voltage corresponding to the sensed temperature with the voltage corresponding to the first predetermined temperature level and in response causes its output to switch binary states, which thereby causes switch  210  to disconnect its first conduction terminal  210 A from second conduction terminal  210 B so as to decouple first conductor  135 A from power supply  145 , and to connect third conduction terminal  210 C to second conduction terminal  210 B to couple third conductor  135 C to power supply  145  and thereby cause current to flow between and through third conductor  135 C and second conductor  135 B. In this way, the current flow path is redirected such that only the length of heater element  115  contacted by the narrower media sheet is substantially heated to the target temperature level while preventing overheating at the non-media portion. In other words, a current path through heater element  115  is selected so that only the portion of heater element  115  corresponding to the location of the narrower media sheet is heated as the sheet is passed through fuser assembly  80 . 
     In an example embodiment, comparator circuit  205  may further be configured to compare the voltage corresponding to the temperature sensed by temperature sensor  150  to a voltage corresponding to a second predetermined temperature level that is less than the first predetermined temperature level. The second predetermined temperature level may correspond to a temperature level in which the amount of thermal energy is not sufficient for fusing toner onto a sheet of media. Comparator circuit  205  comparing the voltage corresponding to the sensed temperature to voltages corresponding to both the first and second predetermined temperature levels is accomplished by comparator circuit  205  having hysteresis with switching voltages being the voltages corresponding to the first and second predetermined temperature levels. Comparator circuits having hysteresis are well known in the art such that a detailed description thereof will not be provided for reasons of simplicity. It is understood that the comparator circuits described below include hysteresis. 
     Heat generated by passing current through the portion of resistive trace  130  between and through third conductor  135 C and second conductor  135 B may transfer and/or dissipate in the longitudinal direction of heater element  115  and into edge segment  155 , thereby heating edge segment  155  to some extent. In the event that a sheet of widest supported media is fed into fuser nip N while the current of resistive trace  130  passes through third conductor  135 C, any heat transferred to edge segment  155  from the portion of heater element  115  between second conductor  135 B and third conductor  135 C may be absorbed by the sheet of media which may cause the temperature of edge segment  155  to drop below the second predetermined temperature level. In an example embodiment, detecting a temperature that is below the second predetermined temperature level may indicate that the sheet of media passing through fuser nip N is a widest supported media while heater element  115  is heated for fusing narrower media. If the sensed temperature is below the second predetermined temperature level, comparator circuit  205  may compare the voltage corresponding to the sensed temperature to the voltage corresponding to the second predetermined level and cause its output to change binary states to disconnect its third conduction terminal  210 C from second conduction terminal  210 B and thereby decouple third conductor  135 C from power supply  145 , and to connect first conduction terminal  210 A to second conduction terminal  210 A to couple first conductor  135 A to power supply  145 . This coupling establishes the current of resistive trace  130  to flow through first conductor  135 A and second conductor  135 B. Thus, control circuit  200  selects the current path through resistive trace  130  such that entire length L1 of heater element  115  is substantially heated to the target temperature level to accommodate the sheet of widest supported media. 
     In an alternative example embodiment, control circuit  200  may employ a shunt configuration for switching the current between flowing through first conductor  135 A and flowing through third conductor  135 C. For example, in the embodiment shown in  FIG. 5 , control circuit  200  includes a single pole single throw (SPST) switch  212  having a first conduction terminal  212 A connected to first conductor  135 A and a second conduction terminal  212 C connected to third conductor  135 C, with the control terminal of switch  212  being coupled to the output of comparator circuit  205 . Further, first conductor  135 A and first conduction terminal  212 A are connected to first terminal  145 A of power supply  145 . In this example, switch  212  either connects or disconnects first conduction terminal  212 A to or from second conduction terminal  212 C based on the output of comparator circuit  205 . When switch  212  is open, the current flows through first conductor  135 A and thus through the full length of resistive trace  130  between first conductor  135 A and second conductor  135 B. When switch  212  is closed, the current passes through switch  212  to third conductor  135 C thereby bypassing edge segment  155  and causing current flow between third conductor  135 C and second conductor  135 B. As in the embodiment of  FIG. 4 , comparator circuit  205  may employ hysteresis in which the output of comparator circuit  205  changes state when signals received from temperature sensor  150  exceed or fall below reference signals corresponding to the first and second predetermined temperature levels, respectively. 
     In operation, when passing current through first conductor  135 A (i.e., switch  212  being open for fusing wider media), in the event the temperature sensed by temperature sensor  150  exceeds the first predetermined temperature level (indicating narrower media being fused), comparator circuit  205  compares the voltage corresponding to the sensed temperature with the voltage corresponding to the first predetermined temperature level and causes the output of comparator circuit  205  to change binary state which closes switch  212  so that current is thereafter redirected through third conductor  135 C (for fusing narrower media). In addition, when passing current through third conductor  135 C (i.e., switch  212  being closed for fusing narrower media), in the event the temperature sensed by temperature sensor  150  falls below the second predetermined temperature level (indicating wider media being fused), comparator circuit  205  compares the voltage corresponding to the sensed temperature with the voltage corresponding to the second predetermined temperature level and causes the output of comparator circuit  205  to change binary state which opens switch  212  so that the current is redirected through first conductor  135 A (for fusing wider media). 
       FIGS. 4 and 5  show heater element  115  having resistive trace  130  formed as a single trace. In another example embodiment, heater element  115  may include a plurality of resistive traces with each trace sized to accommodate a different media sheet size. For example, in  FIG. 6 , heater element  115  includes a first resistive trace  180  and a second resistive  185  having different lengths and extending parallel relative to each other. In this example, first resistive trace  180  has a length corresponding to the width of widest supported media M1, while second resistive trace  185  has a length that is less than the width of the first resistive trace  180  that corresponds to the width of narrower supported media M2. First conductor  135 A is connected to a first end portion  180 A of first resistive trace  180 , second conductor  135 B is connected to both second end portions  180 B,  185 B of first and second resistive traces  180 ,  185 , respectively, and third conductor  135 C is connected to a first end portion  185 A of second resistive trace  185 . Temperature sensor  150  is coupled to substrate  125  at a location between first end portion  180 A of first resistive trace  180  and first end portion  185 A of second resistive trace  185  for sensing the temperature of the region corresponding to difference in lengths between first resistive trace  180  and second resistive trace  185 . Conductors  135 A- 135 C are connected to control circuit  200  and power supply  145  in the same fashion as described with respect to  FIG. 4  or  FIG. 5  such that control circuit  200  may serve to provide the same function of selecting between conductors  135 A and  135 C for passing current through one of first resistive trace  180  and second resistive trace  185  depending on the media width ascertained from the temperature sensed by temperature sensor  150 . Thus, control circuit  200  may automatically control current to flow through first resistive trace  180  when a sheet of widest supported media is being fused, or through second resistive trace  185  when a sheet of narrower supported media is being fused. 
     The above example embodiments have been described with respect to a reference-edge media feed system where one side of the media sheet is in a substantially constant location within fuser assembly  80  regardless of the media width. In another example embodiment, the applications described herein may also be used in center-referenced media feed systems where media sheets move at a center position along the media path and locations of both edges of the media sheet vary with media width. 
     With reference to  FIG. 7  depicting a center-referenced feed system, three media sheets M1, M2, and M3 having differing widths are illustrated with media sheet M1 being the widest and then decreasing in width through media sheets M2 and M3. To perform a fusing operation to fuse toner to media sheet M1, a length L1 of heater element  115  corresponding to the width of media sheet M1 may be energized to generate sufficient amount of heat along length L1 for fusing toner. Likewise, in order to fuse toner to media sheets M2 and M3, lengths L2 and L3 of heater element  115 , respectively, may be energized to generate sufficient amount of heat therealong for fusing toner. In this way, only portions of the heater element  115  contacted by the sheet of media passing through the fuser nip N are heated at fusing temperature levels such that non-media portions along both edges of heater element  115  are substantially kept from accumulating excessive thermal energy that may otherwise cause overheating and damage to fuser assembly  80 . 
     Referring now to  FIG. 8 , a control configuration, which can be used for controlling temperature levels of heater element  115  in a center-referenced feed system, is illustrated according to an example embodiment. Heater element  115  may include a resistive trace  230  extending between a first end portion  230 A and a second end portion  230 B. Heater element  115  further includes a plurality of conductors  235  which are coupled between power supply  145  and resistive trace  230  for providing current thereto. In the example shown, outer conductors include a first conductor  235 A and a second conductor  235 B connected to first and second end portions  230 A,  230 B of resistive trace  230 , respectively. Inner conductors include a third conductor  235 C and a fourth conductor  235 D connected to resistive trace  230  at locations  230 C,  230 D between and laterally offset from respective end portions  230 A,  230 B. In this example, the locations at which first and second conductors  235 A,  235 B are connected to resistive trace  230  may correspond to edges  260 A,  260 B of the widest supported media M1, while the locations at which third and fourth conductors  235 C,  235 D are connected to resistive trace  230  may correspond to edges  265 A,  265 B of the narrower supported media M2. Accordingly, the distance between edges  260 A and  260 B corresponds to length L1 of heater element  115 , while the distance between edges  265 A and  265 B corresponds to length L2 of heater element  115 . 
     A first edge temperature sensor  250 A may be coupled to the substrate of heater element  115  on a side opposite from the surface along which resistive trace  230  is disposed and at a location between the locations at which first and third conductors  235 A,  235 C are connected to resistive trace  230  for sensing a temperature of a region corresponding to a first edge segment  255 A of resistive trace  230 . Additionally or optionally, a second edge temperature sensor  250 B may be coupled to the substrate of heater element  115  at a location between the locations at which second and fourth conductors  235 B,  235 D are connected to resistive trace  230  for sensing a temperature of a region corresponding to a second edge segment  255 B of resistive trace  230  opposite the first edge segment  255 A thereof. 
     Conductors  235  may be selectively coupled to power supply  145  by a control circuit  300  to control the flow of current through resistive trace  230  based on the temperature sensed by at least one of the first and second edge temperature sensors  250 A,  250 B. Control circuit  300  may include a comparator circuit  305  having hysteresis as described above, a first switch  310 , and a second switch  315 . Comparator circuit  305  has an input coupled to first edge temperature sensor  250 A and an output coupled to first and second switches  310 ,  315 . If second edge temperature sensor  250 B is used, comparator circuit  305  may have a second input coupled thereto. Comparator circuit  305  may receive signals generated by each of the first and second edge temperature sensors  250 A,  250 B having values that are based upon temperatures sensed thereby, compare the received signals with one or more predetermined values corresponding to one or more predetermined temperature levels, and output a signal based upon the comparison. 
     Each of first switch  310  and second switch  315  includes a plurality of conduction terminals, such as first conduction terminals  310 A,  315 A, second conduction terminals  310 B,  315 B, and third conduction terminals  310 C,  315 C, respectively. First conduction terminals  310 A,  315 A are connected to first and second conductors  235 A,  235 B, respectively, while third conduction terminals  310 C,  315 C are connected to third and fourth conductors  235 C,  235 D, respectively. Second conduction terminal  310 B of first switch  310  is connected to second terminal  145 B of power supply  145  and second conduction terminal  315 B of second switch  315  is connected to first terminal  145 A of power supply  145 . Control circuit  300  may select the conductors  235  for passing current through resistive trace  230  and specifically control current to flow either through first and second conductors  235 A,  235 B or through third and fourth conductors  235 C,  235 D. Comparator circuit  305  actuates first and second switches  310 ,  315  based on the temperature(s) sensed by at least one of the first and second edge temperature sensors  250 A,  250 B in order to control the generation of heat across at least portions of the length of resistive trace  230  to prevent overheating. 
     In operation, controller  95  may control power supply  145  to provide electrical power to resistive trace  230  via first and second terminals  145 A,  145 B for heating heater element  115  to a target fusing temperature level. First switch  310 A is controlled to connect its first conduction terminal  310 A to second conduction terminal  310 B and second switch  315  is controlled to connect its first conduction terminal  315 A to second conduction terminal  315 B to cause current to flow in resistive trace  230  through conductors  235 A and  235 B. First and second edge temperature sensors  250 A,  250 B positioned proximate to the first and second end portions  230 A,  230 B of resistive trace  230  measure the temperature of the regions corresponding to first and second edge segments  255 A,  255 B, respectively. 
     Comparator circuit  305  compares the voltage corresponding to the temperature sensed by one or more of edge temperature sensors  250 A,  250 B to the voltage corresponding to the first predetermined temperature level. If the temperature(s) sensed is less than the first predetermined temperature level, it is indicative of a sheet of media having a width corresponding to media sheet M1 that does not result in overheating, and control circuit  300  may maintain current flow through resistive trace  230  via conductors  235 A and  235 B to accommodate fusing of media sheet M1. If any temperature sensed exceeds the first predetermined temperature level, it is indicative of overheating at regions corresponding to first edge segment  255 A and/or second edge segment  255 B due to narrower media sheet M2 being fused. In response, comparator circuit  305  actuates first and second switches  310 ,  315  which in turn disconnect corresponding first conduction terminals  310 A,  315 A from respective second conduction terminals  310 B,  315 B and connect corresponding third conduction terminals  310 C,  315 C to respective second conduction terminals  310 B,  315 B. Accordingly, a current flow path is established which allows current to flow through resistive trace  230  via third and fourth conductors  235 C,  235 D. In this way, current flow may be controlled to follow a path defined by the inner conductors such that fusing temperature levels may exist only within functional areas of heater element  115  corresponding to the width of the narrower sheet of media M2 while preventing overheating at the non-media portions. 
     In the event that a sheet of media M1 is fed into fuser nip N while the third and fourth conductors  235 C,  235 D are used to provide current through resistive trace  130 , heat of the region corresponding to the edge segments  255 A,  255 B may drop due to heat absorption by the sheet of media at the edges thereof. In an example embodiment, comparator circuit  305  may further be configured to compare the voltage corresponding to the temperature sensed by at least one of the edge temperature sensors  250 A,  250 B to the voltage corresponding to the second predetermined temperature level. If the temperature sensed by one of the edge temperature sensors  250 A,  250 B falls below the second predetermined temperature level, and if the temperature sensed by the other edge temperature sensor  250 A,  250 B is below the first predetermined temperature, the output of comparator circuit  305  changes binary state to actuate first and second switches  310 ,  315  to disconnect corresponding third conduction terminals  310 C,  315 C from respective second conduction terminals  310 B,  315 B and connect corresponding first conduction terminals  310 A,  315 A to respective second conduction terminals  310 B,  315 B. Accordingly, a resistive trace current flow path is established through first and second conductors  235 A and  235 B, respectively, such that the length of heater element  115  corresponding to the width of the sheet of media M1 is heated to the target temperature level to accommodate fusing of the entire width of the sheet of media. 
       FIG. 9  illustrates another example embodiment. The embodiment of  FIG. 9  generally uses the control configuration of the embodiment of  FIG. 8 , for controlling temperature levels of heater element  115  in a center-referenced feed system. Similar to the embodiment of  FIG. 5 , however, SPST switch  312  is used to selectively short first conductor  235 A and third conductor  235 C, and SPST switch  317  is used to selectively short second conductor  235 B and fourth conductor  235 D, based upon the output of comparator circuit  305 . During the time the output of comparator circuit  305  causes switches  312  and  317  to be open, thereby causing current to pass through first conductor  235 A and second conductor  235 B for fusing wider media, when the temperature sensed by any edge temperature sensor  250 A and  250 B rises above the first predetermined temperature level (indicating narrower media being fused), comparator circuit  305  compares the voltage corresponding to the sensed temperature with the voltage corresponding to the first predetermined temperature level and causes the output of comparator circuit  305  to change binary state which closes switches  312  and  317 , which thereby causes current of resistive trace  230  to flow through third conductor  235 C and fourth conductor  235 D for fusing narrower media. During the time the output of comparator circuit  305  causes switches  312  and  317  to be closed, thereby causing current to pass through third conductor  235 C and fourth conductor  235 D for fusing narrower media, when the temperature sensed by one of the edge temperature sensors  250 A and  250 B falls below the second predetermined temperature level and if the temperature sensed by the other edge temperature sensor  250 A,  250 B is below the first predetermined temperature (indicating wider media being fused), comparator circuit  305  compares the voltage corresponding to the sensed temperature to the voltage corresponding to the second predetermined temperature level and causes the output of comparator circuit  305  to change binary state which opens switches  312  and  317 , which thereby causes current of resistive trace  230  to flow through first conductor  235 A and second conductor  235 B for fusing narrower media. In the embodiments in which a single comparator circuit  305  receives sensor data from two edge temperature sensors  250 A,  250 B, such as the embodiments illustrated in  FIGS. 8 and 9 , comparator circuit  305  favors fusing narrower media in which resistive trace current is passed through third conductor  235 C and fourth conductor  235 D so that the transition from fusing narrower media to fusing wide media occurs only if neither one of edge temperature sensors  250 A,  250 B has a temperature greater than the first predetermined temperature level. 
     In an alternative example embodiment shown in  FIG. 10 , the first edge segment  255 A and second edge segment  255 B of resistive trace  230  may be equipped with separate control circuits  400 A and  400 B, respectively. Conductors  235  associated with the first and second edge segments  255 A,  255 B and corresponding edge temperature sensors  250 A,  250 B may be connected to corresponding control circuits  400 A,  400 B and power supply  145  in the same fashion as described above with respect to  FIG. 4 . In this example, each control circuit  400 A,  400 B may serve to provide the function of independently switching switches  410 ,  415  using comparator circuits  405 A,  405 B, respectively, to control the flow of current through resistive trace  230 . 
     In another example embodiment, heater element  115  may include a plurality of resistive traces of differing lengths to accommodate multiple media sheet sizes in a center-referenced feed system. For example, in  FIG. 11 , heater element  115  may include a first resistive trace  280  and a second resistive  285  extending parallel relative to each other. In the example shown, first resistive trace  280  may have a length corresponding to the width of media sheet M1, while second resistive trace  285  may have a length corresponding to the width of media sheet M2. Conductors  335 A,  335 B,  335 C and edge temperature sensor  250  may be coupled to a control circuit in a similar manner as described above with respect to  FIGS. 4 and 6  such that the control circuit may serve to provide the same function of controlling current to flow either through first resistive trace  280  when fusing a widest supported media sheet M1, or through second resistive trace  285  when fusing a narrower sheet of media M2. It is further contemplated that in other alternative example embodiments, the aforementioned control circuits used for controlling temperature in center-referenced feed systems may employ the shunt configuration described above with respect to  FIGS. 5 and 9 . 
     Illustrative examples of control configurations have been described using three or four conductors, one or two resistive traces, and a given number of comparator circuits and switches that would accommodate two different media sheet sizes. However, it is understood that a multiplicity of conductors, resistive traces, and any number of comparator circuits or switches may be implemented to accommodate more than two media sheet sizes. 
     With the above example embodiments, one or both edges of the heater element  115  may be equipped with self-controlling segments to prevent overheating the edge segments thereof. Temperature information sensed by temperature sensor(s) at the edge segments may be fed to one or more control circuits which in turn controls the switching of one or more switches to select a current path through and otherwise control the flow of current through the resistive trace and, consequently, control at least portions of the resistive trace to heat to desired temperature levels based on the temperature information. Accordingly, no operator intervention may be needed to configure fuser assembly  80  for the media width being used, and fuser assembly  80  can operate substantially at full speed regardless of which media width is being used. Additionally, since control circuitries are contained within the fuser assembly  80  and since no logic, temperature feedback, or additional interaction/communication is required between the fuser assembly control circuitry and the image forming device controller, any image forming device can be configured as a multiple-media width imaging device by simply removing a traditional single-width fuser and installing a multiple-width fuser equipped with self-controlling segments described herein. 
     The foregoing description of several example embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.