Abstract:
A method for extending the operating life of a fuser used in an electrophotographic imaging apparatus is disclosed. A control algorithm monitors the number of substrates processed over the lifetime of the fuser and adjusts the fusing temperature of the fuser to compensate for changes occurring in the nip forming members of the fuser. The useful lifetime of the fuser is extended while fusing quality is maintained. A corresponding fuser assembly is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electrophotographic devices and, more specifically, to techniques for extending fuser life. 
     BACKGROUND OF THE INVENTION 
     In electrophotography, an imaging system forms a latent image by exposing select portions of an electrostatically charged photoconductive surface to laser light. Essentially, the density of the electrostatic charge on the photoconductive surface is altered in areas exposed to a laser beam relative to those areas unexposed to the laser beam. The latent electrostatic image thus created is developed into a visible image by exposing the photoconductive surface to toner, which contains pigment components and thermoplastic components. When so exposed, the toner is attracted to the photoconductive surface in a manner that corresponds to the electrostatic density altered by the laser beam. The toner pattern is subsequently transferred from the photoconductive surface to the surface of a print substrate, such as paper, which has been given an electrostatic charge opposite that of the toner. The substrate then passes through a fuser that applies heat and pressure thereto. The applied heat causes constituents including the thermoplastic components of the toner to flow onto the surface and into the interstices between the fibers of the substrate. The applied pressure produces intimate contact between toner and fibers and promotes settling of the toner constituents into these interstitial spaces. As the toner subsequently cools, it solidifies adhering the image to the substrate. 
     The fuser typically includes cooperating fusing members that form a nip area capable of delivering heat and pressure to the substrate passing through the nip. Exemplary nip forming members include a fuser roll and a backup roll, a fuser roll and a backup belt and a fuser belt and backup roll. A heat source associated with one or both of the nip forming members raises the temperature of the fusing members at the nip area to a temperature required by a particular fusing application. As the substrate passes through the nip area, the toner is adhered to the substrate by the pressure between the nip forming members at the nip area and the heat resident in the fusing region. 
     Successful adherence of the toner to the substrate, known as fusegrade, is determined by fusing parameters including temperature, pressure and time in the nip area. Poor fusegrade, resulting in poor adhesion of the toner to the substrate, may be caused by insufficient temperature, pressure or time in the nip area. Moreover, excessive temperature, pressure or time in the nip area may cause damage to the toner image known as image mottle. Excessive temperature, pressure or time in the nip area may also cause the toner to stick to the fusing members rather than the substrate. For example, the toner may peel from the substrate and stick to the fuser members, a condition known as hot offset, or the toner with substrate attached may wrap about a fusing member. 
     In order to achieve proper fusegrade, the fuser parameters should ideally be maintained within an operating window defined between parameter values that result in poor fusegrade and parameter values that may result in image mottle, hot offset and/or wrap. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, a method of controlling a fusing temperature in a fuser assembly is provided. The method may comprise setting a temperature setpoint value to a predetermined initial value, setting a fusing temperature to correspond with the temperature setpoint value at least during fusing operations, providing a predetermined count threshold corresponding to a substrate count event, counting a number of substrates conveyed through the fuser assembly defining a substrate count, comparing the substrate count to the predetermined count threshold and performing a temperature compensation if the substrate count corresponds to the predetermined count threshold. 
     Performing a temperature compensation if the substrate count corresponds to the predetermined count threshold may comprise adjusting the temperature setpoint value to a compensated temperature setpoint value and adjusting the fusing temperature to correspond with the compensated temperature setpoint value. The compensated temperature setpoint value may be configured to extend the operating life of the fuser assembly. 
     In accordance with another aspect of the present invention, a fuser assembly within an image forming apparatus having a paper path along which substrates travel through the image forming apparatus is provided. The fuser assembly may comprise a fusing member, a backup member cooperating with the fusing member to form a fusing region at a nip therebetween for fusing images onto substrates passing through the nip and a heating structure associated with at least one of the fusing member and the backup member for heating the fusing region to a fusing temperature at least during fusing operations. The fusing temperature may correspond to a temperature setpoint value and the temperature setpoint value may be set to a predetermined initial value. 
     The fuser assembly may further comprise a conveying structure for conveying substrates along the paper path into the nip, a substrate detector for determining a number of substrates passing through the nip and a controller for controlling the fusing temperature. The controller may count the number of substrates passing through the nip defining a substrate count. The controller may compare the substrate count to the predetermined count threshold and perform a temperature compensation if the substrate count corresponds to the predetermined count threshold. 
     The temperature compensation may adjust the temperature setpoint value to a compensated temperature setpoint value and may adjust the fusing temperature to correspond to the compensated temperature setpoint value. The compensated temperature setpoint value may be configured to extend the operating life of the fuser assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the preferred embodiments of the present invention can best be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals, and in which: 
         FIG. 1  is a diagrammatic side view of an electrophotgraphic printer illustrating an image forming apparatus, a substrate conveying structure and a fuser assembly; 
         FIG. 2  is a block diagram of an aspect of the present invention illustrating a fuser assembly, a controller and a storage device; 
         FIG. 3  is a flow chart illustrating how an aspect of the present invention may be practiced; 
         FIG. 4  is a flow chart illustrating how another aspect of the present invention may be practiced; and 
         FIG. 5  is a flow chart illustrating how another aspect of the present invention may be practiced. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     According to an aspect of the present invention, an operating lifetime of a fuser assembly for use in an electrophotographic imaging apparatus may be extended by counting a number of fusing operations performed by the fuser assembly and adjusting a fusing temperature when a predetermined number of fusing operations have been performed. The fusing temperature may be adjusted to a higher temperature or to a lower temperature and the adjustment may be made at one or more predetermined counting events during the lifetime of the fuser assembly. Moreover, the changes to the fusing temperature may be selected so as to maintain the fusing temperature within a predefined temperature operating window. The fusing temperature adjustments may be selected, for example, to compensate for changes that occur in fuser components as a result of use. 
     Referring now to  FIG. 1 , a color electrophotographic (EP) printer  10  is illustrated including four image forming stations  12 ,  14 ,  16 ,  18  for creating yellow (Y), cyan (C), magenta (M) and black (K) toner images. Each image forming station  12 ,  14 ,  16  and  18  includes a laser printhead  20 , a toner supply  22 , a rotatable photoconductive (PC) drum  24  and a developing assembly  56 . A uniform charge is provided on each PC drum  24 , which is selectively dissipated by a scanning laser beam generated by its corresponding printhead  20 , such that a latent image is formed on each PC drum  24  according to a bitmap image file of an associated one of the CYMK color image planes. The latent image formed on each PC drum  24  is then developed during an image development process via the corresponding toner supply  22  and developing assembly  56 , in which electrically charged toner particles are transferred to the surface of each PC drum  24  in a pattern corresponding to the latent image formed thereon. 
     Each image forming station also includes an electrically biased transfer roller  26  that opposes its corresponding PC drum  24 . An intermediate transfer member (ITM) belt  28  that is common to each image transfer station travels in an endless loop and passes through a nip defined between each PC drum  24  and its corresponding transfer roller  26 . The toner image developed on each PC drum  24  is transferred during a first transfer operation to the ITM belt  28  by an electrically biased roller transfer operation. In this regard, each PC drum  24  and its corresponding transfer roller  26  constitutes a first image transfer station  32  that transfers its corresponding one of the yellow, cyan, magenta or black toner images to the ITM belt  28 . 
     At a second image transfer station  34 , a composite toner image, i.e., the registered yellow (Y), cyan (C), magenta (M) and black (K) toner images, is transferred from the ITM belt  28  to a substrate  36 . The second image transfer station  34  includes a backup roller  38 , on the inside of the ITM belt  28 , and a transfer roller  40 , positioned opposite the backup roller  38 . Substrates  36 , such as paper, cardstock, labels, envelopes or transparencies, are fed from a substrate supply  42  to the second image transfer station  34  so as to be in registration with the composite toner image on the ITM belt  28 . Structure for conveying substrates from the supply  42  to the second image transfer station  34  may comprise a pick mechanism  42 A that draws a top sheet from the supply  42  and a speed compensation assembly  43 . The composite image is then transferred from the ITM belt  28  to the substrate  36 . A conveying structure  37  conveys the substrate  36  to a fuser assembly  48 , where the toner image is fused to the substrate  36 . The substrate  36  including the fused toner image continues along a paper path  50  until it exits the printer  10  into an exit tray  51 . 
     The paper path  50  taken by the substrates  36  in the printer  10  is illustrated schematically by a dot-dashed line in  FIG. 1 . It will be appreciated that other printer configurations having different paper paths may be used. Further, a duplex unit (not shown) for printing on both sides of the print media and one or more additional media supplies or trays, including manually fed media trays, may be provided. 
     The fuser assembly  48  in the illustrated embodiment includes a fuser hot roller  70  or fusing roller defining a heating member, and a backup member  72  cooperating with the hot roller  70  to define a nip for conveying substrates  36  therebetween. The hot roller  70  may comprise a hollow metal core member  74  covered with a thermally conductive elastomeric material layer  76 . The hot roller  70  may also include a polyperfluoroalkoxy-tetrafluoroethylene (PFA) sleeve (not shown) around its elastomeric material layer  76 . A heating element  78 , such as a halogen tungsten-filament heater, may be located inside the core  74  of the hot roller  70  for providing heat energy to the hot roller  70  under control of a controller  80 . The heating element  78  may comprise a filament that provides an end boost along a predetermined portion adjacent at each end of the heating element  78  to provide a greater heat output adjacent the ends than at a central portion of the heating element  78 . It should be understood that the illustrated embodiment is not limited to a particular mechanism or structure for heating the hot roller  70  and that any known means of heating a roller may be implemented within the scope of this invention. 
     The backup member  72  may comprise any structure for cooperating with the hot roller  70  to create a nip whereby a substrate passing through the fuser assembly  48  is pressed into engagement with the hot roller  70 . The illustrated backup member  72  comprises a belt backup member. However, it should be understood that the backup member  72  may comprise other nip forming structures including, without limitation, a cooperating backup roller. Additionally, a second heating element may be associated with the backup member  72 . 
     The controller  80  may comprise a microprocessor, a discrete logic array or other device controlling arrangement. The controller  80  may be provided to control various aspects of the printer systems and components, including the fuser assembly  48 . Additionally, the controller  80  may be utilized to control the fusing temperature utilized by the fuser assembly  48  in such a way as to extend the life of the fuser assembly  48  as will be described in greater detail herein. 
     Referring now to  FIG. 2 , a block diagram  100  illustrates an exemplary fuser assembly  48 A and control arrangement according to various aspects of the present invention. The fuser assembly  48 A represents another exemplary fuser arrangement that may be utilized in an electrophotographic apparatus, such as the printer  10 , as will be described in greater detail below. 
     As illustrated, the fuser assembly  48 A comprises a fusing member  110  and a backup member  112  defining a nip  114  therebetween through which substrates  36  pass. A distance  116  in a process direction P between the fusing member  110  and the backup member  112  within which temperature and pressure are applied to the substrate  36  defines a fusing region  118 . As illustrated in  FIG. 2 , the backup member  112  is a backup roller rather than the belt backup member  72  shown in  FIG. 1 . A first heating element  120  is associated with the fusing member  110  and a second heating element  122  may be optionally associated with the backup member  112 . Together, the first heating element  120  and the optional second heating element  122  comprise a heating structure  124 . The heating structure  124  is under the control of the controller  80  as will be described more thoroughly herein. 
     After a toner image has been transferred to a substrate  36  as previously described with reference to  FIG. 1 , the substrate  36  is conveyed to the nip  114  by a conveying structure  37  as described with reference to  FIG. 1 . The toner image comprises unfused toner containing pigment components and thermoplastic components. When the substrate  36  passes through the nip  114 , the heat applied to the toner causes constituents including the thermoplastic components in the toner to melt and flow onto the surface and into interstices between the fibers of the substrate  36 . The applied pressure produces intimate contact between toner and fibers and promotes settling of the toner constituents into these interstitial spaces. As the toner subsequently cools, it solidifies adhering the image to the substrate  36 . 
     Successful adherence of the toner to the media, known as fusegrade, is determined substantially by the temperature applied to the toner, the pressure applied between the toner image and the substrate surface while the toner is heated and the time that the temperature and pressure are simultaneously applied, i.e., the time in the fusing region  118 . If the temperature or pressure applied to the toner is insufficient or the time that the toner spends in the fusing region  118  is too little, the toner may not properly adhere to the substrate, resulting in poor fusegrade. On the other hand, if the temperature or pressure applied to the toner is excessive or the time that the toner spends in the fusing region  118  is too long, the toner may stick to the fusing members rather than the substrate  36 . This may cause the toner to peel from the substrate  36  and adhere to the fusing members, a condition known as hot offset. Should the toner adhere sufficiently to both the substrate and the fusing member, the substrate may wrap around the fusing member. Additionally, excessive temperature, pressure or time in the fusing region  118  may damage the toner image, resulting in image mottle. 
     Fusegrade may be correlated with fusing temperature. As such, in order to achieve proper fusegrade while avoiding image mottle, hot offset and wrap, the fusing temperature may be maintained within a predetermined temperature range, also referred to herein as a temperature operating window. For example, the temperature operating window may define a fusing temperature range that extends from a relatively low temperature just suitable to achieve proper fusegrade to a relatively high temperature that achieves proper fusegrade and avoids image mottle, hot offset and wrap, etc. 
     Fusegrade may also be correlated with nip pressure times the square of the time in the fusing region  118 . The pressure exerted on the toner is determined substantially by the force applied between the fusing member  110  and the backup member  112  divided by the distance  116  that defines the fusing region  118 . The pressure may vary between different points in the fusing region  118 . 
     As illustrated in  FIG. 2 , the fusing member  110  may comprise a hollow metal core  126  surrounded by a thermally conductive elastomeric layer  128 . Similarly, the backup member  112  may comprise a hollow metal core  130  surrounded by a thermally conductive elastomeric layer  132 . Alternatively, the backup member  112  may comprise any structure for cooperating with the fusing member  110  such that a compressive pressure is applied to opposite sides of the substrate  36  as it is conveyed through the nip  114 . 
     Because one or both of the fusing member  110  and the backup member  112  is compliant at least in the thermally conductive elastomeric layers  128  and  132 , respectively, the outer portion of one or both of the fusing member  110  and the backup member  112  deforms in the fusing region  118  defined by the distance  116 . For a given pressure between the fusing member  110  and the backup member  112 , the amount that the fusing member  110  and/or the backup member  112  deforms will vary substantially in accordance with the hardness of the compliant portions of the fusing member  110  and the backup member  112 . 
     The distance  116  corresponds to the amount of deformation that occurs in the fusing member  110  and the backup member  112 . As a result, the distance  116  varies in accordance with the hardness of the fusing member  110  and the backup member  112 . In this fashion, the distance  116  is increased as the hardness of the fusing member  110  and the backup member  116 , i.e., the nip forming members decreases. Conversely, the distance  116  decreases as the hardness of the nip forming members increases. 
     The time that the temperature and pressure are applied to the toner, i.e., the time in the fusing region  118 , is a function of the distance  116  and the velocity of the substrate  36  as it is conveyed through the nip  114 . As previously mentioned, the distance  116  corresponds to the shape and hardness of the fusing member  110  and the backup member  112  and the force applied therebetween. Thus, for a given substrate velocity, the time that the toner spends in the fusing region  118  corresponds to the hardness of the fusing member  110  and the backup member  112 . 
     The compliant portions of the fusing member  110  and the backup member  112  may be harder when new, i.e., at a beginning of fuser life, and may soften with age as a result of repetitive turning under pressure. As a result, the distance  116  may be smaller at the beginning of fuser life and may increase as the fuser assembly ages and the nip forming members soften. The increase in the distance  116  results in a corresponding increasing in time that substrate  36  spends in the fusing region  118  if the substrate velocity remains constant. For this reason, fusegrade may be lower at the beginning of fuser life and may improve with use. Thus, it may be practical to select a fuser operating temperature high enough to achieve adequate fusegrade at the beginning of fuser life. Subsequently, as the nip forming members age and soften, resulting in an increase in the distance  116  and a corresponding increase in the time that the substrate  36  spends within the fusing region  118 , it may be unnecessary to operate the fuser assembly at the same high temperature in order to achieve adequate fusegrade. 
     In one example, fusing temperature may refer to the temperature to which the fusing member  110  is regulated. The fusing member may be in contact with a substrate surface upon which an un-fused toner image has been deposited. Backup member temperature may refer to the temperature to which the backup member  112  may be regulated if the backup member  112  is separately heated. Alternatively, backup member temperature may refer to the surface temperature of the backup member  112  if the backup member  112  is heated by contact with the heated fusing member  110  and is not otherwise heated. Backup member temperature may normally be lower than fusing temperature. 
     The fusing member  110  and the backup member  112  in the fuser assembly  48 A illustrated in  FIG. 2  have a useful lifetime that is inversely related to fuser operating temperature, hereinafter fusing temperature. The lifetime of the fusing member  110  may correspond to the fusing temperature to which the fusing member  110  is exposed and the lifetime of the backup member  112  may correspond to the backup member temperature to which the backup member  112  is exposed. For example, in accordance with an application of the Arrhenius model in the context of evaluating the effect of temperature on the fuser assembly  48 A, it has been observed that the operating life of a fusing member such as fusing member  110  may be extended by a factor of two for every 7 to 10 degree C reduction in fusing temperature. 
     As previously discussed, the time spent within the fusing region  118  may increase with fuser life due to softening of the nip forming members, resulting in improved fusegrade. As a result, it may be possible to operate the fuser assembly  48 A at a reduced fusing temperature at some point later in the lifetime of the fuser assembly  48 A while still maintaining adequate fusegrade. By taking advantage of the improvement in fusegrade that may occur due to the softening of the nip forming members with age, it may be possible to extend the operating lifetime of the components of the fuser assembly  48 A by reducing the fusing temperature at one or more point(s) in the lifetime of the fuser assembly  48 A without producing unacceptable fusegrade. 
     For example, for a fusing member  110  comprising a metal core  126  surrounded by an elastomeric layer  128 , failures generally occur first at the interface between the elastomeric layer  128  and the metal core  126  or within the elastomeric layer  128  because the temperature is highest at these points during fusing operations. By reducing the fusing temperature at some point in the lifetime of the fuser assembly  48 A, it may be possible to avoid, postpone or otherwise mitigate such occurrences. 
     As another illustrative example, the hardness of the nip forming members may decrease sufficiently during the lifetime of the fuser assembly  48 A such that the distance  116  of the fusing region  118  increases enough that the time spent in the fusing region  118  is sufficient to cause hot offset, image mottle or wraps if the fusing temperature remains constant over the lifetime of the fuser assembly  48 A. In this case it may not be possible to establish a single temperature range that will assure adequate fusegrade while avoiding hot offset, image mottle and/or wraps over the entire operating lifetime of the fuser assembly  48 A. As a result, it may be necessary to lower the fusing temperature at some point during the lifetime of the fuser assembly  48 A in order to maintain the fusing temperature within the temperature operating window as previously defined. By maintaining the fusing temperature within the temperature operating window so as to avoid hot offset, image mottle and/or wraps it may be possible to operate the fuser assembly  48 A beyond a point in fuser life where such conditions might otherwise necessitate maintenance or repair, and a functional life of the fuser assembly  48 A may be extended. 
     As yet a further illustrative example, certain materials sometimes used in fuser nip forming members may harden rather than soften with use. For example, a fuser nip forming member having a soft silicone rubber layer may harden during use as a silicone oil within the rubber is driven out due to repetitive turning under pressure at elevated temperature. As another example, a fuser nip forming member having a rubber layer that is not fully cured may harden during use as the rubber continues to cure when it is exposed to elevated temperature during fusing operations. As the nip forming member hardens, the distance  116  decreases, and the substrate  36  spends less time in the fusing region  118 . In this situation, fusegrade generally decreases over the lifetime of the fuser assembly  48 A. In order to maintain adequate fusegrade, the fusing temperature may be raised at one or more point(s) during the lifetime of the fuser assembly  48 A. Though the higher fusing temperature may decrease the life of the nip forming members as previously discussed, it may be possible to maintain adequate fusegrade beyond a point in fuser life where fusegrade would otherwise become unacceptable if the temperature were not increased. In this fashion, the functional life of the fuser assembly  48 A may be extended. 
     The controller  80  is communicably coupled to the fuser assembly  48 A. The controller  80  may comprise a microprocessor, microcontroller, discrete logic array or other controlling arrangement. The controller  80  includes a fuser temperature control module  134  communicating with one or more power switching devices (not shown) connected to the heating structure  124 . In this fashion, the fuser temperature control module  134  may cause the power switching device or devices (not shown) to energize the first heating element  120  and/or the second heating element  122  either individually or in conjunction causing the fusing temperature to increase. Conversely, the fuser temperature control module  134  may cause the power switching device or devices (not shown) to de-energize the first heating element  120  and/or the second heating element  122  allowing the fusing temperature to decrease. 
     The controller  80  also includes a substrate count module  138 . The substrate count module  138  is configured to count a number of substrates  36 , passing through the fuser assembly  48 A. The substrate count module  138  may communicate with a substrate detector in the fuser assembly  48 A or elsewhere in the printer  10 . The substrate detector may comprise an optoelectronic substrate detector, an electromechanical substrate detector, a paper pick mechanism, a bump sensor, a software implemented substrate detector within the controller  80  or other suitable means for detecting substrates approaching the fuser assembly  48 A. In this fashion, a total number of substrates  36  that have passed through the fuser assembly  48 A, defining a substrate count, may be compiled. 
     For example, the substrate detector may comprise an optical interrupter having a mechanical flag that is moved out of an optical path when a substrate  36  is conveyed past the substrate detector. One or more substrate detectors may be provided in a substrate path in the printer  10 . Any such substrate detector may communicate with the controller  80  for purposes of counting the number of substrates  36  passing through the fuser assembly  48 A. 
     As another example, a substrate detector may be located in the printer  10  in a location in the substrate path where substrates  36  that have passed through the fuser have entered a duplex paper path provided to allow the printer  10  to convey the substrate  36  through the image transfer station  34  a second time such that the substrate  36  may be printed on an opposite side. Because the substrate  36  passes through the fuser assembly  48 A a second time to fuse a toner image on the opposite side but passes through a substrate detector located in the duplex paper path only once, the substrate count module  138  of the controller  80  may add two to the substrate count to account for two fusing operations corresponding to a fusing operation to fuse a toner image on each side of the substrate  36 . 
     A media type module  142  is also provided within the controller  80 . The media type module  142  is configured to determine a media type of the substrate  36  that is to be fused in the fuser assembly  48 A. The media type module  142  may acquire media type information from a media type sensor, an operator control panel, a print driver module, or a print data stream. The fuser temperature control module  134  may control the fusing temperature of the fuser assembly  48 A in accordance with the media type as determined by the media type module  142 . Furthermore, a unique substrate count corresponding to a total number of substrates  36  of each of a plurality of media types that have passed through the fuser assembly  48 A may be compiled by the substrate count module  138 . 
     Also included in the controller  80  is a fuser temperature compensation module  144 . The fuser temperature compensation module  144  is configured to compensate the fusing temperature of the fuser assembly  48 A in accordance with the substrate count as will be described more thoroughly herein. 
     A storage device  146  is connected to the controller  80 . The storage device  146  may comprise NVRAM or any other suitable storage for non volatile storage of program and data information for use by the controller  80 . For example, the previously mentioned plurality of substrate counts corresponding to different media types may be stored in the storage device  146 . 
     In accordance with an aspect of the present invention, the fuser temperature control module  134  may operate the fuser assembly  48 A at a predetermined initial fusing temperature, hereinafter a temperature setpoint, for example, 175 degrees Centigrade (C), when fusing toner images on a substrate  36  comprising 20 lb. (75 g/m 2 ) plain paper. The fuser assembly  48 A may be expected to fuse 120,000, 20 lb. plain paper substrates  36  while maintaining adequate fusegrade before replacement of the nip forming members may be recommended. In order to extend the lifetime of the fuser assembly  48 A the fuser temperature compensation module  144  may adjust the temperature setpoint downward by, for example, 3 degrees C to 172 degrees C, after a total of 15,000, 20 lb. plain paper substrates  36  have been fused. The reduction in the temperature setpoint and the corresponding reduction in fusing temperature contributes to an extension of the operating lifetime of the fuser assembly  48 A during the period of the fuser lifetime after the initial 15,000 substrates  36  have been fused. It may not be necessary to make any further adjustments in fusing temperature over the remaining lifetime of the fuser assembly  48 A. 
     In accordance with another aspect of the present invention, the fuser temperature compensation module  144  may adjust the temperature setpoint downward a first time to 172 degrees C. after a total of 15,000, 20 lb. plain paper substrates  36  have been fused as previously described. Subsequently, the fuser temperature compensation module  144  may adjust the fusing temperature by a second predetermined amount, for example, by −4 degrees C. from the initial setpoint value to 171 degrees C, after a total of 30,000, 20 lb. plain paper substrates  36  have been fused. The second reduction in the temperature setpoint contributes to an extension of the operating lifetime of the fuser during the period of the fuser lifetime after the initial 30,000 substrates  36  have been fused. Further, the temperature setpoint may be adjusted by a third amount, for example, by −5 degrees C from the initial setpoint value to 170 degrees C, after a total of 40,000, 20 lb. plain paper substrates  36  have been fused. The third reduction in the temperature setpoint contributes to an extension of the operating lifetime of the fuser during the period of the fuser lifetime after the initial 40,000 substrates  36  have been fused. Still further, the temperature setpoint may be adjusted by a fourth amount, for example, by −6 degree C from the initial setpoint value to 169 degrees C, after a total of 50,000, 20 lb. plain paper substrates  36  have been fused. The fourth reduction in the temperature setpoint contributes to an extension of the operating lifetime of the fuser during the period of the fuser lifetime after the initial 50,000 substrates  36  have been fused. 
     The above adjustment examples are presented by way of illustration and not by way of limitation. In practice, other temperature setpoint adjustment amounts may be made. Moreover, the substrate count events corresponding to temperature adjustments may be different than the above example. Still further, additional or fewer adjustments may be made. The implemented adjustments may be based, for example, upon factors such as the particular components and component characteristics of the particular fuser assembly and of the particular substrates and fusing requirements of particular applications. 
     Though the preceding discussion refer to substrates  36  comprising 20 lb. plain paper sheets, the present invention is not limited to such material and is applicable to any media type to which toner images may be fused, e.g., card stock, labels, envelopes, transparency stock, heavier or lighter weight paper, etc. For example, 110 lb. card stock may require a higher initial fusing temperature than 20 lb. plain paper. The fuser assembly  48 A in accordance with the principles and concepts of the present invention may operate at the higher fusing temperature when fusing images onto substrates  36  comprising 110 lb. card stock. The fuser assembly  48 A may then operate at an adjusted fusing temperature after a predetermined number of substrates  36  comprising 110 lb. card stock have been fused in order to extend the operating lifetime of the fuser assembly  48 A. The temperature adjustment amount may be determined empirically and may be a greater or lesser adjustment than the temperature adjustment previously discussed with respect to 20 lb. plain paper substrates  36 . Furthermore, the number of temperature adjustments performed over the lifetime of the fuser assembly  48 A may be more or fewer than the number of adjustments made when processing 20 lb. plain paper substrates  36 . 
     In yet another aspect of the present invention, the substrate count module  138  may compile a plurality of substrate counts corresponding to a total number of substrates  36  of a plurality of different media types that have passed through the fuser assembly  48 A. When the media type module  142  determines that a substrate  36  about to be fused by the fuser assembly  48 A is of a specific media type, the controller  80  may set the temperature setpoint to a specific value corresponding to a fusing temperature corresponding to the specific media type. The fuser temperature control module  134  may now control the heating structure  124  such that the fusing temperature corresponds to the temperature setpoint corresponding to the specific media type. Further, the fuser temperature compensation module  144  may adjust the temperature setpoint upward or downward when the specific substrate count corresponding to the specific media type to be fused corresponds with a predetermined substrate count value as previously described. In this way, the fuser temperature control module  134  may now adjust the fusing temperature in accordance with the compensated temperature setpoint. As previously described, the temperature setpoint may be adjusted once or a plurality of times during the lifetime of the fuser assembly  48 A and the fusing temperature may be adjusted downward or upward as a result. 
     According to an aspect of the present invention, substrates  36  comprising media types that are rarely fused by the fuser assembly  48 A may have little effect upon the operating life of the fuser assembly  48 A, and the temperature compensation module  144  may ignore compensating the temperature setpoint when such substrates are fused. 
     In yet another aspect of the present invention, a temperature compensation table may be provided. An exemplary temperature compensation table is shown below: 
     
       
         
               
             
               
               
             
               
               
             
           
               
                   
               
               
                 Temperature Compensation Table 
               
             
          
           
               
                   
                 Temperature Compensation Value 
               
               
                 Predetermined Count Threshold 
                 Degrees C. 
               
               
                   
               
             
          
           
               
                    0-14,999 
                 0 
               
               
                 15,000-29,999 
                 −3 
               
               
                 30,000-39,999 
                 −4 
               
               
                 40,000-49,999 
                 −5 
               
               
                   50,000-&gt;50,000 
                 −6 
               
               
                   
               
             
          
         
       
     
     The exemplary temperature compensation table includes a plurality of compensation table records. Each compensation table record includes a predetermined count threshold component and a corresponding temperature compensation value component. The predetermined count threshold corresponds to a substrate count event when the fusing temperature is to be compensated, and the corresponding temperature compensation value indicates the amount of the temperature compensation. As substrates  36  pass through the fuser assembly  48 A, the substrate count module  138  compiles a substrate count corresponding to a total number of substrates  36  that have been fused as previously described. 
     The controller  80  compares the substrate count to the predetermined count threshold values in the temperature compensation table and the fuser temperature compensation component  144  adjusts the setpoint temperature in accordance with the corresponding temperature compensation value from the temperature compensation table. For example, as each substrate  36  is fused in the fuser assembly  48 A, the substrate count module  138  increments the substrate count by one and compares the new substrate count value to the temperature compensation table predetermined count threshold values. In the example above, the fuser temperature compensation module  144  does not adjust the setpoint temperature until the substrate count reaches 15,000 because the temperature compensation table records indicate a temperature compensation value of 0 for all predetermined count threshold values less than 15,000. 
     When the substrate count reaches 15,000 the fuser temperature compensation module  144  adjusts the temperature setpoint by the corresponding temperature compensation value, e.g., −3 degrees C. in the illustrated example. When the substrate count reaches 30,000, the fuser temperature compensation module  144  adjusts the temperature setpoint by the corresponding temperature compensation value, e.g., −4 degrees C. When the substrate count reaches 40,000 the fuser temperature compensation module  144  adjusts the temperature setpoint by the corresponding temperature compensation value, e.g., −5 degrees C. In like fashion, when the substrate count reaches 50,000 the fuser temperature compensation module  144  adjusts the temperature setpoint by the corresponding temperature compensation value, e.g., −6 degrees C. In the illustrated example, the temperature compensation value remains −6 degrees C. for all substrate count values above 50,000. 
     The temperature compensation table may be stored in the storage device  146  where it may be accessed by the controller  80 . The controller  80  may include a table address pointer for specifying which compensation table record to access and the table address pointer may be stored in the storage device  146 . 
     The number of compensation table records and the predetermined count threshold values and corresponding temperature compensation values may be determined empirically by the fuser designers and are not limited to the exemplary compensation table values illustrated above. For example, the temperature compensation table may include more or fewer compensation table records, and other embodiments of the present invention may include different predetermined count and temperature compensation value data than the exemplary temperature compensation table depicted above. For example, the temperature compensation data may be represented in fashions other than offsets from the initial set point value. 
     In another aspect of the present invention, a plurality of temperature compensation tables may be provided. Each of the plurality of temperature compensation tables may correspond to one of a plurality of media types that may be processed by the fuser assembly  48 A. Each of the plurality of temperature compensation tables may include a plurality of compensation table records comprising a predetermined count threshold component and a corresponding temperature compensation value component corresponding to a specific media type. In this fashion, individual temperature compensation tables may be provided comprising predetermined count threshold values and corresponding temperature compensation values to be used when fusing substrates  36  of a plurality of differing media types. A plurality of table address pointers corresponding to each of the plurality of temperature compensation tables may be provided for specifying which compensation table record to access. The plurality of temperature compensation tables and the plurality of corresponding table address pointers may be stored in the storage device  146 . 
     Referring now to  FIG. 3 , a flowchart  300  illustrates process steps implemented by the controller  80  for practicing an aspect of the present invention. The controller  80  may implement the process steps indicated in  FIG. 3  each time a toner image is to be fused to a substrate  36  by the fuser assembly  48 A. The temperature compensation process begins at step  302 . When the controller  80  determines that a substrate  36  is to be fused by the fuser assembly  48 A, the process proceeds to step  304 . 
     In step  304 , the controller may optionally retrieve the current substrate count from the substrate count module  138 . Alternatively, the controller  80  may retrieve the current substrate count from the substrate count module  138  prior to step  304 . The process now proceeds to step  306 . 
     In step  306 , the controller  80  determines if it is appropriate to compensate the temperature setpoint. If the controller  80  determines that temperature compensation is not indicated in step  306  the process proceeds to step  310 . If the controller  80  determines that temperature compensation is appropriate in step  306 , the process proceeds to step  308 . 
     In step  308  the fuser temperature compensation module  144  compensates the temperature setpoint by adjusting the temperature setpoint value to equal a compensated temperature setpoint value. The compensated temperature setpoint value is configured to extend the operating life of the fuser assembly  48 A as previously described. The compensated temperature setpoint value may be retrieved from, for example, a table or other logical arrangement stored in the storage device  146 . The process now proceeds to step  312 . 
     In step  310 , the controller  80  may set the temperature setpoint value to a predetermined initial value. Alternatively, the temperature setpoint value may be set to the predetermined initial value prior to step  310 . The process now proceeds to step  312 . 
     In step  312 , the fuser temperature control module  134  adjusts the fusing temperature of the fuser assembly  48 A to correspond with the temperature setpoint value as determined in step  308  or  310 , at least during fusing operations. The process now proceeds to step  314 . 
     In step  314 , the substrate  36  is fused by the fuser assembly  48 A at a fusing temperature corresponding to the temperature setpoint value as determined in step  308  or  310 . The process now proceeds to step  316 . 
     In step  316  the substrate count module  138  increments the substrate count by one so that the substrate count now corresponds to a total number of substrates  36  fused by the fuser assembly  48 A including the substrate  36  just fused. The substrate count module  138  may store the new substrate count value in the storage device  146 . The process now proceeds to step  318 . 
     Step  318  is an ending step where the process may stop. Alternatively, the process may proceed to step  302  where the process may begin again when the controller  80  determines that another substrate  36  is to be fused by the fuser assembly  48 A. 
     Referring now to  FIG. 4 , a flowchart  400  illustrates process steps implemented by the processor  80  for practicing another aspect of the present invention. The controller  80  may implement the process steps indicated in  FIG. 4  each time a toner image is to be fused to a substrate  36  by the fuser assembly  48 A. The temperature compensation process begins at step  402 . When the controller  80  determines that a substrate  36  is to be fused by the fuser assembly  48 A, the process proceeds to step  404 . 
     In step  404 , the controller  80  sets the temperature setpoint value to a predetermined initial value corresponding to a desired fusing temperature. The predetermined initial value may be determined by the fuser designers and may have been stored in the storage device  146  before the process begins at step  402 . The temperature setpoint value may optionally be stored in the storage device  146 . The process now proceeds to step  406 . 
     In step  406 , the fuser temperature control module  134  controls the heating structure  124  such that the fusing temperature of the fuser assembly  48 A corresponds to the temperature setpoint value at least during fusing operations. The fuser temperature control module  134  may cause the heating structure  124  to raise the fusing temperature of the fuser assembly  48 A to a temperature corresponding to the temperature setpoint value only during a time when a substrate  36  is being fused in the fuser assembly  48 A. Alternatively, the fuser temperature control module  134  may cause the heating structure  124  to raise the fusing temperature of the fuser assembly  48 A to a temperature corresponding to the temperature setpoint value in advance of a time when the substrate  36  is to be fused in the fuser assembly  48 A. The process now proceeds to step  408 . 
     In step  408 , the controller  80  acquires a predetermined count threshold corresponding to a substrate count event when the temperature setpoint value shall be compensated. The predetermined count threshold may be determined by the fuser designers and may have been stored in the storage device  146  before the process begins at step  402 . The process now proceeds to step  410 . 
     In step  410 , the controller  80  acquires the current substrate count from the substrate count module  138 . The process now proceeds to step  412 . 
     In step  412 , the controller  80  determines if it is appropriate to compensate the temperature setpoint value from the predetermined initial value to which it was set in step  404 . The controller  80  may do this by comparing the substrate count to the predetermined count threshold acquired in step  408 . If the substrate count does not correspond to the predetermined count threshold, the process proceeds to step  418 . If the substrate count corresponds to the predetermined count threshold, the process proceeds to step  414 . 
     In step  414  the fuser temperature compensation module  144  compensates the temperature setpoint creating a compensated temperature setpoint value. The compensated temperature setpoint value is configured to extend the operating life of the fuser assembly  48 A as previously described. The process now proceeds to step  416 . 
     In step  416  the fuser temperature control module  134  adjusts the fuser assembly  48 A fusing temperature to correspond with the compensated temperature setpoint value. The process now proceeds to step  418 . 
     In step  418 , the substrate  36  is fused at a fusing temperature corresponding to the temperature setpoint value as determined in step  404  or  414 . The process now proceeds to step  420 . 
     In step  420  the substrate count module  138  increments the substrate count by one so that the substrate count now corresponds to a total number of substrates  36  fused by the fuser assembly  48 A including the substrate  36  just fused. The substrate count module  138  may store the new substrate count value in the storage device  146 . The process now proceeds to step  422 . 
     Step  422  is an ending step where the process may stop. Alternatively, the process may proceed to step  402  where the process may begin again when the controller  80  determines that another substrate  36  is to be fused by the fuser assembly  48 A 
     Referring now to  FIG. 5 , a flowchart  500  illustrates process steps implemented by the controller  80  for practicing another aspect of the present invention. The controller  80  may implement the steps indicated in  FIG. 5  each time a print job is received by the printer  10 . A print job may comprise the printing of one or more substrates  36  of the same or different media type. Beginning at step  502 , the controller  80  is initially in an idle state such as when the printer  10  is initially turned on or when no print jobs have been received by the printer  10 . 
     In step  504 , the process waits until the controller  80  determines that a print job has been received. The process then proceeds to step  506 . 
     In step  506 , the media type module  142  determines which of a plurality of media types the substrate  36  comprises. Indication of a specific media type may be stored in the storage device  146 . The process now proceeds to step  508 . 
     In step  508 , the controller  80  sets the temperature setpoint value to a predetermined initial value corresponding to one of a plurality of media types that may be fused in the fuser assembly  48 A. The predetermined initial value corresponds to a desired fusing temperature for the media type of the substrate  36  about to be fused. The predetermined initial value may be determined by the fuser designers and may have been stored in the storage device  146  before processing begins at step  502 . For example, the predetermined initial value corresponding to the desired fusing temperature for the specific media type may have been stored in a table or other logical arrangement in the storage device  146 . The processing now proceeds to step  510 . 
     In step  510 , the controller  80  fuser temperature control module  134  controls the fuser assembly  48 A heating structure  124  such that the fusing temperature corresponds to the temperature setpoint value as set in step  508  at least during fusing operations. In this fashion, the fusing temperature corresponds to the desired fusing temperature for the media type of the substrate  36  about to be fused. The fuser temperature control module  134  may cause the heating structure  124  to raise the fusing temperature of the fuser assembly  48 A to the temperature corresponding to the temperature setpoint value only during a time when the substrate  36  is being fused in the fuser assembly  48 A. Alternatively, the fuser temperature control module  134  may cause the heating structure  124  to raise the fusing temperature of the fuser assembly  48 A to the temperature corresponding to the temperature setpoint value in advance of a time when the substrate  36  is to be fused in the fuser assembly  48 A. The processing now proceeds to step  512 . 
     In step  512 , the controller  80  determines a temperature compensation value to be used by the fuser temperature compensation module  144  to compensate the temperature setpoint as will be discussed next. The controller  80  may retrieve the temperature compensation value from a temperature compensation table as previously described. For example, the controller  80  may maintain a table address pointer to provide a table address of a temperature compensation table record that includes a predetermined count threshold and a corresponding temperature compensation value. The controller  80  may maintain a plurality of table address pointers corresponding to a plurality of temperature compensation tables, each of which includes a plurality of records including a predetermined count threshold component and a corresponding temperature compensation value component corresponding to a specific media type. Each of the plurality of table address pointers may be stored in the storage device  146 . The process now proceeds to step  514 . 
     In step  514 , the fuser temperature compensation module  144  compensates the temperature setpoint value creating a compensated temperature setpoint value. The compensated temperature setpoint value is a sum of the predetermined initial value to which the temperature setpoint was set in step  508  and the temperature compensation value as determined in step  514 . The compensated temperature setpoint value is configured to extend the operating life of the fuser assembly  48 A. The compensated temperature setpoint value may be stored in the storage device  146 . The process now proceeds to step  516 . 
     In step  516 , the fuser temperature control module  134  controls the fuser heating structure  124  such that the fusing temperature of the fuser assembly  48 A corresponds to the compensated temperature setpoint value. The process now proceeds to step  520 . 
     In step  518 , the substrate  36  is fused at the fusing temperature corresponding to the compensated temperature setpoint value and the process waits until fusing of the substrate  36  is finished. When the fuser assembly  48 A has finished fusing the substrate  36 , the process continues to step  520 . 
     In step  520 , the substrate count module  138  increments the substrate count by one so that the substrate count now indicates a total number of substrates  36  fused by the fuser assembly  48 A including the substrate  36  just fused. The substrate count module  138  may compile and maintain a plurality of individual substrate counts corresponding to a plurality of substrates  36  of a plurality of media types as determined by the media type module  142  and fused in the fuser assembly  48 A. Individual substrate counts for substrates  36  of certain media types that are rarely processed by the printer  10  and fused in the fuser assembly  48 A may not be compiled and maintained. Each of the plurality of substrate counts may be stored in the storage device  146 . Upon completion of step  520 , the process returns to step  504  where the process waits until another print job has been received or another substrate  36  within the same print job is detected. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.