Abstract:
A printer has a media feed path ( 12 ) for feeding sheets of media ( 14 ), with the path having a side reference edge ( 52 ) for aligning the media. A media transport mechanism feeds the sheets of media at a standard speed and at a reduced speed. A narrow media detector ( 38 ) generates a narrow media signal when sheets of narrow media are fed through the media feed path. A controller ( 68 ) adjusts the media transport mechanism to feed the narrow media aligned with the reference edge at the reduced speed. A method of printing sheets of narrow media in a printer comprises the steps of aligning the narrow media with a reference edge in a media feed path of the printer, sensing when the narrow media are present in the media feed path, and feeding the narrow media through the media feed path at the reduced sheet feeding speed and, particularly with a belt fuser, with increased inter-sheet gap.

Description:
FIELD OF THE INVENTION 
     This invention relates to an electrophotographic printer, and more particularly, to a laser printer for printing narrow media with high throughput that does not overheat the fuser. 
     BACKGROUND OF THE INVENTION 
     An electrophotographic printer prints an image on media, such as sheets of paper, from toner contained in a toner cartridge. A developer roller or sleeve is mounted within the toner cartridge in proximity to a photoconductive drum. The photoconductive drum is charged, and a laser scans the charged photoconductive drum with a laser beam to discharge the surface and form a latent image thereon. The developer roller attracts statically charged toner from the toner container. Toner is transferred from the developer roller to the photoconductive drum to develop the latent image formed on the photoconductive drum. The developed image is then transferred to statically charged sheets of media. The sheets are fed through a heated fuser assembly, where the heat fixes the visible image. 
     Sheets of narrow media, such as envelopes, are aligned with a reference edge in the feed path of the printer. Because the narrow sheets do not extend across the full width of the feed path, the consecutive printing of several sheets of narrow media creates a temperature imbalance in the fuser assembly. The sheets of media, when fed past the fuser assembly to fuse the image to the sheets, remove heat therefrom. Since sheets of narrow media do not extend fully across the width of the fuser assembly, the portion of the fuser assembly away from the reference edge, where the narrow media do not contact the fuser assembly, becomes hotter than the portion adjacent the reference edge, where the narrow media contact the fuser assembly. The fuser assembly can overheat so much after printing several consecutive sheets of narrow media that it becomes damaged. 
     One proposed solution to the problem of the overheating in a fuser assembly with a hot roller has been to make the fuser roller out of very thick material, so that the heat diffuses more evenly across the entire width. This has been unsatisfactory, as the cost of a thick fuser roller is high. This solution, of course, is not applicable to a fuser assembly with a fuser belt. 
     A second proposed solution to the problem of the overheating of the fuser assembly has been the insertion of gaps between the sheets of narrow media. Inter-sheet gaps permit the fuser assembly to equilibrate between sheets. However, this solution has also been unsatisfactory, as the insertion of inter-sheet gaps for all sheets of narrow media dramatically reduces the throughput of the printer. 
     A third proposed solution to the problem of the overheating of the fuser assembly has been to reduce the operating temperature of the fuser assembly and the transport speed. Consequently, all the sheets of media, regardless of width, are fed past the fuser assembly at a very slow speed, so that enough heat is transferred to the media to fuse the image thereto. However, this solution has also been unsatisfactory, as the slow feeding speed for all the sheets of media severely reduces the throughput of the printer. 
     SUMMARY OF THE INVENTION 
     A printer in accord with the present invention overcomes the foregoing problems by determining when narrow media are to be printed, aligning the narrow media with a side reference edge of the media path, lowering the temperature of the fuser assembly and feeding the narrow media through the media path at a reduced speed, and, for certain conditions, increasing the gap between fed sheets. 
     In accord with one aspect of the present invention, a printer comprises a media feed path for feeding sheets of media through the printer, the path including a side reference edge, and a media transport mechanism for feeding the sheets of media at a standard speed and at a reduced speed along the media feed path. A narrow media detector generates a narrow media signal when sheets of narrow media are fed through the media feed path. A controller responds to the narrow media signal and adjusts the media transport mechanism to feed the narrow media aligned with the reference edge at the reduced speed. 
     In accord with another aspect of the present invention, a printer system comprises a media feed path for feeding sheets of media through the printer, the path including a reference edge, and a media transport mechanism for feeding the sheets of media at a standard speed and at a reduced speed along the media feed path. A narrow media detector generates a narrow media signal when sheets of narrow media are fed through the media feed path. A programmed microcomputer responds to the narrow media signal and adjusts the media transport mechanism to feed the narrow media aligned with the reference edge at the reduced speed. 
     An advantage of a printer in accord with this invention is that sheets of narrow media are printed without damaging the printer even though use of a side reference edge adds to heat stress at the fixing mechanism when fixing narrow media. 
     Another advantage of a printer in accord with this invention is that sheets of narrow media are printed without overheating and damaging the fuser assembly. 
     A further advantage of a printer in accord with this invention is that narrow media are printed with a high printer throughput. 
     A still further advantage of the present invention is that it can be used in a printer with a fuser assembly having either a hot fuser roller or a fuser belt. 
     Other objects and advantages of the invention will be readily perceived from the following description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The attached drawings illustrate preferred embodiments of the invention, in which: 
     FIG. 1 is a cutaway, diagrammatic side view of an electrophotographic printer; 
     FIG. 2 is a diagrammatic plan view of a fuser roller in the printer of FIG. 1; 
     FIG. 3 is a schematic diagram of the data flow in the printer of FIG. 1; 
     FIG. 4 is a block diagram of the electrical circuitry of the printer of FIG. 1; and 
     FIG. 5 is a flowchart illustrating programs used in the circuit of FIG.  4 . 
     FIG. 6 is illustrative of a belt fuser. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, and initially to FIG. 1 thereof, an electrophotographic printer  10  includes a media feed path  12  for feeding sheets of media  14 , such as paper, from a media tray  16  past a photoconductive drum  18  and a fuser assembly  20  to an output tray  22 . The fuser assembly  20  may be a nip roller fuser formed by a fuser roller  24 , which is heated to a relatively high temperature to fuse particles of toner to the sheets of media  14 , a backup roller  26 . U.S. Pat. No. 5,860,051 to Goto et al. is illustrative of a belt fuser. It will be appreciated that fuser assembly  20  could also be of the belt fuser type (see FIG.  6 ), in which a polyamide belt  24   a  passes over a ceramic heater  24   b  with the media  14  in a nip between belt  24   a  and a backup roller  26   a . Special media, such as envelopes, transparencies or checks, are fed into the media feed path  12  from an external, front-option tray  28 , sometimes referred to as a multi-purpose tray. Envelopes may also be fed from a separate, external tray (not shown). The photoconductive drum  18  forms an integral part of a replaceable toner cartridge  30  inserted in the printer  10 . A printhead  32  is disposed in the printer  10  for scanning the photoconductive drum  18  with a laser beam  34  to form a latent image thereon. The laser beam  34  places a spot of light on a facet of a rotating polygonal mirror  36 , which then redirects the laser beam  34  so that it ultimately sweeps of “scans” across a “writing line” on the photoconductive drum  18 , thereby creating, in a black and white laser printer, a raster line of either black or white print elements, also known as “pels.” The polygonal mirror  36  typically has six or eight facets, and each one-sixth or one-eighth rotation of the polygonal mirror  36 , respectively, creates an entire swept raster scan of laser light that ultimately becomes a writing line on a sheet of media  14 . The operation of the printhead  32  is more fully described in U.S. Pat. No. 5,877,798 to Clarke et al., also assigned to the assignee of the present application. 
     In the illustrated embodiment, the printer  10  has a narrow media sensor  38  located downstream, as viewed from the direction of flow of the media  14 , from the photoconductive drum  18  and the fuser assembly  20 . The narrow media sensor  38  detects the presence of sheets of narrow media in the media feed path  12 . The narrow media sensor  38  could alternatively be located upstream from the photoconductive drum  18 , as indicated in phantom  38 ′. A plurality of rollers  40 ,  42 ,  44 ,  46 ,  48  function in a known manner to transfer the sheets of media  14  from the media tray  16  or multi-purpose tray  28  through the media feed path  12 . 
     FIG. 2 illustrates the fuser roller  24  and a reference edge  50  of the media feed path  12 . Sheets of narrow media  14 , such as envelopes, shown in phantom on FIG. 2, are left justified and aligned with the reference edge  50  as they are fed through the media feed path  12 . In one particular embodiment, the fuser roller  24  was slightly wider than 8½inches, so that it could accommodate full-width media, such as U.S. letter size paper and A4 paper. The narrow media sensor  38  was located between two edges  52 ,  54  of the fuser roller  24 , at approximately three-quarters of the distance from the edge  52 , corresponding to the lateral position of the reference edge  50 , to the opposite edge  54  of the fuser roller  24 . The narrow media sensor  38  can be located at different positions across the width of the media feed path  12 . An exit sensor  56  is located adjacent the narrow media sensor  38  and detects the presence of any sheet of media  14  as it leaves the fuser assembly  20 . 
     It will be appreciated that the printer  10  can print different widths of narrow media  14 . In the preferred embodiment, the narrow media were classified into three categories, with each category having similar characteristics vis å vis the heating of the fuser assembly  20  when several sheets are consecutively printed. One category of narrow media is envelopes. A second category of narrow media is very narrow media. Very narrow media are media that the narrow media sensor  38  detects as narrow. Examples of very narrow media are A5 size paper and 3″×5″ index cards. A third category of narrow media is nearly narrow media. Nearly narrow media are media that have a width between very narrow media and normal media. Nearly narrow media engage the narrow media sensor  38 , but do not extend the full width of the fuser roller  24 . Nearly narrow media are determined by the standard paper sizes detected within the paper tray  16 . Examples of nearly narrow media are B5 size paper and executive size paper. 
     It will be recognized that other categories of media width for narrow media can be utilized with the present invention, with each category determined by the width of the media and the temperature characteristics of the fuser assembly  20  in printing them, and that the categories of media widths discussed hereinbefore are the preferred embodiment. 
     Turning now to FIG. 3, a print job is sent to the printer  10  from a variety of sources, such as, for example, a networked personal computer running a word processing program, and is identified in the drawing as being supplied from input data ports  60 . Each print job contains the image to be printed, and may contain additional information about the job, such as the media size and the media source. For example, a print job for an envelope may contain, in addition to the name and address to be printed, information indicating that the job is to be printed on a special size of media, i.e., an envelope. The media source information contained in the print job may specify which tray is to be used to supply the media to be printed. 
     A print job flows from the input data ports  60  to a raster image processor (RIP)  62 , where the print job is rasterized to form a bitmap suitable for printing on the sheets of media  14 . The bitmap from the raster image processor  62  is supplied to a print engine  64  for printing on the sheets of media  14 . The RIP  62  supplements the job information contained in the print job received from the input data ports  60 . 
     Referring to FIG. 4, the raster image processor (RIP)  62  sends the bitmap through an interconnect card  66  to an engine controller  68 . The engine controller  68  acts as a controller and data-manipulating device for the various hardware components within the print engine  64 . The engine controller  68  includes a programmed microcomputer  70 , a flash memory  72  and a random access memory (RAM)  73 , for storing programs to be run thereon. In the preferred embodiment, the programmed microcomputer  70  was a Toshiba TMP90CM38 microcontroller. Other devices, such as a hard drive  74 , can be connected to the RIP  62  via one of the integrated network adapters  76 ,  76 ′,  76 ″ and the interconnect card  66 . A low voltage power supply (LVPS)  78  supplies the engine controller  68  and the RIP  62  with power via the interconnect card  66 . 
     The engine controller  68  is connected to an operator panel  80 , which is an input/output interface providing a user with a method to supply the printer  10  with configuration information. In one embodiment, the operator panel  80  was an LCD panel and input buttons. A user can use the operator panel  80  to supply the printer  10  with media information. The operator panel  80  can also display any of a large number of messages to the user, including status messages, e.g. ready/busy, output tray empty, output tray near full, output tray full, and error messages. The engine controller  68  is connected to a high voltage power supply (HVPS)  82 , which supplies high voltages to hardware components, such as the photoconductive drum  18 . A base input tray paper LED indicating a low paper condition  84 , a base input tray paper LED indicating a no paper condition  86 , a paper size sensor  88 , a multifunction paper tray LED indicating a no paper condition  90 , an output tray LED  92  indicating a near full output tray condition, an input sensor LED  94 , which indicates that a sheet of media  14  is about to be printed, and a multipurpose tray (MPT) solenoid  96 , which picks the sheets of media  14  out of the multipurpose tray  28 , are connected to the engine controller  68 . Additional components operated under control of the engine controller  68  include a main fan  98 , a transport motor assembly  100 , and an autocompensator picker motor  102 . A fuser assembly  104 , generally corresponding to the fuser assembly  20  of FIG. 1, operates under control of the engine controller  68 . A fuser on/off signal passes from the engine controller  68  through the interconnect card  66  to the low voltage power supply (LVPS)  78 . There, the on/off signal actuates a triac (not shown), thereby allowing AC current to flow into the fuser lamp or heater inside the fuser assembly  104  (depending on the type of fuser  104  employed in the printer  10 ). An inductor  106  is connected to the fuser assembly  104  and the engine controller  68 . A laser printhead  108  is connected to the engine controller  68  and a top cover switch  110 , which is also connected to the engine controller  68 . 
     A front feeder option  112  is connected to the engine controller  68  through a front feeder option autoconnect connector  114 . As noted hereinbefore, envelopes may be fed from the multi-purpose tray  28  (see FIG.  1 ), or from a separate tray associated with the front feeder option  112 . The printer  10  has an optional output tray  116  and an optional input tray  118  with different options configurable under the control of a software program stored in the engine controller  68 . The output and input trays  116 ,  118  are connected by an output stacker autoconnect connector  120  and a bottom tray option autoconnect connector  122 , respectively, which provide electrical connections to the engine controller  68 . 
     FIG. 5 depicts flowcharts for software programs or subroutines used in the engine controller  68 , and which assist in the operation thereof. In one embodiment, software programs were written in a suitable computer language, such as C, and stored in the flash memory  72 . As will be evident to those of ordinary skill in the art, the engine controller  68  could be replaced by an application specific integrated circuit (ASIC), which would operate as hereindescribed. Additionally, the software programs associated with FIG. 5 could be run on a server and connected to the printer through one of the integrated network adapters  76 ,  76 ′,  76 ″ of FIG.  3 . 
     As shown on Figure 5A, the software program begins at step S 100 , which is associated with the condition when a sheet of media  14  is positioned in the media feed path  12  proximate the narrow media sensor  38 . Program flow then continues at step S 102 , where the program determines whether the sheet of media  14  in the media feed path  12  is known to be an envelope. As discussed in connection with FIG. 3, the program does this by examining the information contained in the print job. If the program determines at step S 102  that the sheet of media  14  is an envelope, program flow continues at step S 104 , where the program increments a count, commonly identified as a meltometer, by an amount corresponding to an envelope. Program flow then continues at step S 106 , where the program sets a flag corresponding to the condition where the last sheet width was an envelope. Program flow then continues at step S 108 . 
     As noted hereinbefore, the engine controller  68  maintains a count, called the meltometer, associated with the temperature of the fuser assembly  20 . The meltometer is incremented or decremented according to the heat properties associated with each sheet of media  14  that the printer prints. When a sheet of media  14  is printed, it feeds past the heated fuser roller  24  (see FIG.  2 ), where the heat from the fuser roller  24  fuses the image to the sheet  14 . In addition to fixing the image to the sheet  14 , this operation removes heat from the fuser roller  24 . Since sheets of narrow media, when aligned with the reference edge  50 , do not extend fully across the width of the fuser roller  24 , the portion of the fuser roller  24  away from the reference edge  50 , where the narrow media do not contact the fuser roller  24 , becomes hotter than the portion adjacent the reference edge  50 , where the narrow media contact the fuser roller  24 . The fuser roller  24  can overheat so much after printing several consecutive sheets of narrow media that it becomes damaged. Different widths of media remove different amounts of heat from the fuser assembly  20  when images are printed thereon, and the value of the meltometer is changed to reflect the sheets that have been printed on the printer  10 , and hence, the temperature of the fuser assembly  20 . It is to be appreciated that the value of the meltometer is not the actual temperature of the fuser assembly  20 , but rather, a numeric representation of the approximate or projected value thereof. The changes in the value of the meltometer are related to the width of the sheets of media  14 , as wider sheets of media  14  absorb greater amounts of heat from the fuser assembly  20  during the printing process, as discussed more fully hereinbelow. 
     If the program determines at step S 102  that the sheet of media  14  is not an envelope, program flow continues at step S 110 , where the program interrogates the narrow media sensor  38  to determine whether the sheet of media  14  is very narrow, that is, whether it does not engage the narrow media sensor  38 . If the program determines at step S 110  that the sheet of media  14  is very narrow, program flow continues at step S 112 , where the program increments the meltometer by an amount corresponding to a sheet of very narrow media. Program flow continues at step S 114 , where the program stores a value to indicate that the input source for the sheet of media  14  is one that contains very narrow media. Program flow continues at step S 116 , where the program sets a flag to indicate that the last sheet width was a sheet of narrow media. Program flow continues at step S 108 . 
     If the program determines at step S 110  that the sheet of media  14  is not very narrow media, program flow continues at step S 118 , where the program determines whether the sheet of media  14  is a sheet of nearly narrow media. As noted hereinbefore, nearly narrow media are media that have a width between very narrow media and normal media. If the program determines at step S 118  that the sheet of media  14  is a sheet of nearly narrow media, program flow continues at step S 120 , where the program increments the meltometer by an amount corresponding to a sheet of nearly narrow media. Program flow continues at step S 122 , where the program sets a flag to indicate that the last sheet width was a sheet of nearly narrow media. Program flow continues at step S 124 , where the program stores a value to indicate that the input source for the sheet of media  14  is one that does not contain narrow media. Program flow continues at step S 108 . 
     If the program determines at step S 118  that the sheet of media  14  is not nearly narrow media, program flow continues at step S 126 , where the program increments the meltometer by an amount corresponding to a sheet of full-width media. Program flow continues at step S 128 , where the program sets a flag to indicate that the last sheet width was a sheet of full-width media. Program flow continues at step S 124 , where the program stores a value in the RAM  73  to indicate that the input source for the sheet of media  14  is one that does not contain narrow media. Program flow continues at step S 108 . 
     At step S 108 , the program tests to determine whether the meltometer is greater than an upper threshold value. If the program determines that the meltometer is greater than the upper threshold value, program flow continues at step S 130 , where the program sets a reduced throughput flag, i.e., a value is stored in the RAM  73  to indicate that subsequent sheets of narrow media are to be fed through the media feed path  12  at a reduced rate. Program flow then continues at step S 132 , where the program has completed its task of looking at the input signals from the narrow media sensor  38 . 
     If the program determines at step S 108  that the value of the meltometer is not greater than the upper threshold value, program flow continues at step S 134 , where the program tests to determine whether the value of the meltometer is less than a lower threshold value. If the program determines at step S 134  that the value of the meltometer is not less than the lower threshold value, program flow continues at step S 132 . If the program determines at step S 134  that the value of the meltometer is less than the lower threshold value, program flow continues at step S 136 , where the program clears the reduced throughput flag. Program flow continues at step S 132 , where the program has completed its task of looking at the input signals from the narrow media sensor  38 . 
     From step S 132  on FIG. 5B, program flow continues at step S 138 , where the program tests to determine whether the reduced throughput flag has been set. If the program determines at step S 138  that the reduced throughput flag has not been set, program flow continues a step S 140 , where the program determines that the narrow media calculations have been completed. If the program determines at step S 138  that the reduced throughput flag has been set, program flow continues at step S 142 , where the program tests to determine whether the reduced throughput flag for the last sheet width should include a setting to indicate a reduced media sheet feeding speed. In a current embodiment, set reduced speed is done for all categories of narrow media except for nearly narrow media being printed in a nip-roller-fuser version of the highest speed printer (35 pages per minute). If the program determines at step S 142  that the reduced throughput flag for the last sheet width should be set, program flow continues at step S 144 , where the program sets the reduced speed flag. Program flow continues at step S 146 . 
     If the program determines at step S 142  that the reduced throughput flag for the last sheet width should not be set, program flow continues at step S 146 . 
     At step S 146 , the program tests to determine whether the reduced throughput for the last sheet width includes a larger inter-sheet gap. In a current embodiment, this set enlarged gap is not done for any narrow media with a nip roller fuser and is done for all categories of narrow media for a belt fuser (except for nearly narrow media with the nip-roller-fuser 35 ppm printer the gap is enlarged, but the speed is not reduced). If the program determines at step S 146  that the reduced throughput for the last sheet width does not include a larger inter-sheet gap, program flow continues at step S 140 . If the program determines at step S 146  that the reduced throughput for the last sheet width includes a larger inter-sheet gap, program flow continues at step S 148 , where the program sets the enlarged gap flag. Program flow continues at step S 150 , where the program sets a value indicating that the selected gap is an increased gap for the last sheet width. Program flow continues at step S 140 , where the program has completed the narrow media calculations. 
     It will be appreciated from the foregoing description that the present invention can be utilized with an enlarged inter-sheet gap to provide additional opportunities for the fuser assembly  20  to cool between consecutive sheets of narrow media. 
     Turning now to FIG. 5C, program flow continues at step S 152 , where the sheet of media  14  is staged to be picked from an input source, such as a particular tray containing envelopes or other narrow media. At step S 154 , the program tests to determine whether the sheet of media  14  is known to be an envelope. If the program determines that the sheet of media  14  is an envelope, program flow continues at step S 156 , where the program tests to determine whether an envelope must always be picked and fed at a reduced speed. In a current embodiment, this is set to require reduced speed only when the fuser is a belt fuser. If the program determines at step S 156  that an envelope must always be picked and fed at a reduced speed, program flow continues at step S 158 , where the reduced speed flag is set. Program flow continues at step S 160 . 
     If the program determines at step S 156  that an envelope need not be picked and fed at a reduced speed, program flow continues at step S 162 , where the program tests to determine whether the sheet of media  14  is known to be very narrow media. If the program determines at step S 162  that the sheet of media  14  is known to be very narrow media, program flow continues at step S 164 , where the program tests to determine whether sheets of very narrow media must always be picked and fed at a reduced speed. However, in a current embodiment, an envelope is the only category of narrow media which is picked and fed at a reduced speed. If the program determines at step S 164  that sheets of very narrow media must always be picked and fed at a reduced speed, program flow continues at step S 158 , where the program sets the reduced speed flag. Program flow continues at step S 160 . If the program determines at step S 164  that sheets of very narrow media are not always picked and fed at a reduced speed, program flow continues at step S 160 . 
     At step S 160 , the program tests to determine whether the reduced speed flag has been set. If the program determines at step S 160  that the reduced speed flag has been set, program flow continues at step S 166 , where the program sets the printer to require the sheet of media  14  to be picked and fed at a reduced speed. Program flow continues at step S 168 , where the program sets the temperature of the fuser assembly  20  to a reduced temperature for the sheet of media  14 . Program flow continues at step S 170 . 
     If the program determines at step S 160  that the reduced speed flag has not been set, program flow continues at step S 172 , where the program sets the temperature of the fuser assembly  20  to a normal (or unreduced) temperature for the sheet of media  14 . Program flow continues at step S 170 . 
     At step S 170 , the program tests to determine whether the enlarged inter-sheet gap flag has been set. If the program determines at step S 170  that the enlarged inter-sheet gap flag has been set, program flow continues at step S 174 , where the program sets the printer  10  to require the sheet of media  14  to be picked and fed with the enlarged inter-sheet gap. Program flow continues at step S 178 , where the program has completed its operations with regard to staging the sheets of media  14  prior to the picking and feeding operation. Accordingly, with a belt fuser, the first envelopes are fed at a reduced speed and temperature, and subsequent envelopes are fed with increased gap by action of steps  148  in response to step S 108  being “yes” when the amount of meltometer count is above the predetermined threshold value. In a current embodiment for the belt fuser, standard speed is 20 pages per minute (ppm), reduced speed is 10 ppm, and reduced speed with inter-sheet gap is 5 ppm. 
     If the program determines at step S 170  that the enlarged inter-sheet gap flag has not been set, program flow continues at step S 176 , where the program sets the printer  10  to require the sheet of media  14  to be picked and fed at the normal inter-sheet gap. Program flow continues at step S 178 , where the program has completed its operations with regard to staging the sheets of media  14  prior to the picking and feeding operation. 
     It will be appreciated from the foregoing that the engine controller  68  has three sources of information about the width of a sheet of media  14  to be printed: the narrow media sensor  38 , the information in the print job as it comes from the raster image processor  62 , and historical data about the media source stored in the RAM  73 . It will be further appreciated that the computer program of FIG. 5 utilizes information from the three sources in operating the printer  10 . In the preferred embodiment, in the calculations performed above, the output from the narrow media sensor  38  overruled any information contained within the print job. In addition, in the calculations performed above, the printing of an envelope overruled any other categorization, such as very narrow media. 
     The primary benefit of reducing the speed at which the sheets of media  14  are fed through the media feed path  12  of the printer  10  is that, at a reduced speed, the operating temperature of the fuser assembly  20  can be reduced. The energy transferred from the fuser roller  24  to the sheet of media  14  is proportional to the fusing temperature and the time spent in contact with the fuser roller  24 . Thus, when the speed at which the sheets of media  14  are fed through the media feed path  12  is reduced, the time each sheet of media  14  spends in contact with the fuser roller  24  is increased, and the fusing temperature can be reduced while providing the same amount of energy for the fusing process properly to occur. Lowering the temperature of the fuser assembly  20  avoids temperature extremes for the fuser assembly  20  when printing narrow media. 
     However, lowering the fusing temperature and accompanying sheet feeding speed for all sheets of media  14  severely reduces throughput of the printer  10 . Hence, in the printer of the present invention, only selected sheets of media  14  are printed at the reduced sheet feeding speed, so that throughput of the printer  10  is greater than the case in which all the sheets of media  14  are printed at the reduced sheet feeding speed. 
     It was found that a single threshold was not sufficient to implement the desired control of the temperature of the fuser assembly  20 . A pair of thresholds, on the other hand, provided an adequate hysteresis. With a single threshold, intermixing different categories of media width resulted in the printer  10  repeatedly switching between the normal sheet feeding speed and the reduced sheet feeding speed. It will be recognized that substantial amounts of time are required to change from one printing speed to another, so that numerous speed changes in rapid succession severely reduce the throughput of printer  10 . The upper threshold (Step S 108 ) was selected so that the precision of the value of the meltometer was maximized without using large amounts of the available memory. The lower threshold (Step S 134 ) was set some distance below the upper threshold to provide an appropriate hysteresis. 
     Many different reduced speeds can be selected to feed the sheets of media  14  through the printer  10 . However, the engine controller  68  must adjust all the speed-related parameters for the printer  10  for each speed selected. These parameters include, for example, gamma correction, laser duty cycle, laser power, and developer voltage. This is very complicated for many different speeds. Since the memory space available in the flash memory  72  for storing the associated parameters is limited, it has not been found to be practical to have a large number of different sheet feeding speeds implemented in the printer  10 . One solution is to limit the different sheet feeding speeds to a small number. In the preferred embodiment, a single speed of about one-half the normal sheet feeding speed was selected as the reduced sheet feeding speed. 
     It is to be appreciated that additional advantages accrue from the selection of a single reduced sheet feeding speed of one-half the normal sheet feeding speed. Video processing for each writing line is comparatively simple for a speed of one-half normal sheet feeding speed. Gamma correction, laser duty cycle, laser power, and developer voltage are also relatively simply handled. 
     Different methods of video processing in the printer  10  can be utilized for one-half normal sheet feeding speed. One method of video processing is to reduce the printhead scanning motor velocity so that each writing line of an image to be printed on a sheet of media  14  will take twice as long as at normal sheet feeding speed. A second method of video processing is to interlace a blank scan with each information-bearing scan during printing. This is sometimes called “skip-a-scan” or “scan-skipping”operation. 
     The skip-a-scan operation of the printer  10  can be implemented by different methods. According to one method, the raster image processor  62  alternately supplies the blank scans with the information-bearing scans. According to a second method, the engine controller  68  prints a blank scan by not asking the raster image processor  62  for an information-bearing scan. According to a third method, the control signal for sync pulses for the laser beam  34  is delayed for one cycle, corresponding to one facet of the polygonal mirror  36 . In the preferred embodiment, the engine controller  68  skipped a scan of one facet of the polygonal mirror  36  during the reduced sheet feeding speed operation by delaying the sync pulses for the laser beam  34 . 
     An additional advantage of skip-a-scan operation is that video switching times remain unchanged between the reduced sheet feeding speed and the normal sheet feeding speed, since the printhead scanning motor can operate at the same velocity as at normal sheet feeding speed. A second advantage of skip-a-scan operation is that unique parameters for gamma correction, laser duty cycle, laser power, and developer voltage are not necessarily required. 
     In operation, whenever any sheet of media  14  is printed, the computer program of FIG. 5 adds a value associated with the width category of the media to the meltometer (Steps S 112 , S 120 , and S 126 ). The value of the meltometer is then compared to a pair of thresholds (Steps S 108  and S 134 ). The result of the comparisons determines whether over-temperature compensation of the fuser assembly  20  is invoked, if not currently active (Step S 130 ), or ceased, if currently active (Step S 136 ). 
     Categories of media width that have a tendency to increase the temperature of the fuser assembly  20  are assigned positive weighting factors (Steps S 112 , S 120 , and S 126 ). Positive weighting factors are determined for each category of media width by:        WeightingFactor   =     UpperThreshold   NumSheetsAllowedBeforeCompensationNeeded                            
     Categories of media width that have a tendency to reduce the temperature of the fuser assembly  20  are assigned negative weighting factors (Steps S 112 , S 120 , and S 126 ). Negative weighting factors are determined for each category of media width by:        WeightingFactor   =       UpperThreshold   -   LowerThreshold     NumSheetsAllowedBeforeCompensationNeeded                            
     In some special printing situations, it is advantageous immediately to invoke the reduced sheet feeding speed in order to prevent the fuser assembly  20  from reaching a high temperature. For these specific instances, the reduced sheet feeding speed is invoked when the sheets of media  14  are picked from the tray  16 ,  28 . An example of a special printing situation in which the reduced sheet feeding speed is immediately invoked is the printing of an envelope on a belt-type fuser. Envelopes printed by such a belt-type fuser also require the reduced speed in order to provide sufficient energy to fuse properly. 
     It is to be appreciated that the value of the meltometer is not involved in selecting the reduced sheet feeding speed in special printing situations. However, the present invention does recognize that over-temperature compensation may be appropriate for special printing situations. In the preferred embodiment, if the value of the meltometer exceeds the upper threshold (Step S 108 ) while the reduced sheet feeding speed is invoked, thus indicating that over-temperature compensation is appropriate, an inter-sheet gap is inserted in the printing of the sheets of media  14  to prevent overheating of the fuser assembly  20 . 
     Since the computer program can invoke different over-temperature compensation methods to reduce the temperature of the fuser assembly  20 , e.g. Employing a reduced sheet feeding speed or inserting an inter-sheet gap between consecutive sheets of media  14 , once an over-temperature method is invoked, it remains in operation until the program determines that over-temperature compensation is no longer required. 
     If the value of the meltometer is below the lower threshold value (Step S 134 ), over-temperature compensation is eliminated, and normal sheet feeding operation is resumed. 
     If the printing of the sheets of media  14  is paused, and the temperature of the fuser assembly  20  drops below a reset temperature, the computer program resets the value of the meltometer to an initial, minimal value. 
     For purposes of exemplification, particular embodiments of the invention have been shown and described according to the best present understanding thereof. However, it will be apparent that various changes and modifications in the arrangement and construction of the parts thereof may be made without departing from the spirit and scope of the invention as defined in the appended claims.