Abstract:
The present invention is in the field of electrophotographic printers and copiers. More specifically this invention relates to the fuser apparatus used to fuse an image on a receiving sheet. According to just one aspect of the invention, an apparatus and process for fixing toner images to a receiving sheet is provided. The apparatus may include a fuser having a run condition and an idle condition, the fuser having a fuser roller, a fuser roller heater, and a fuser temperature sensor which inputs to a logic and control system which controls the heating of the fuser roller heater. The fuser roller may be cooled during or after the idle condition, prior to the first receiving sheet entering the fuser. The fuser roller has end portions and a middle portion, and the middle portion may be cooled relative to said end portions. Additional aspects and representative embodiments are described herein.

Description:
RELATED APPLICATIONS 
   This application claims the benefit of prior provisional application Ser. No. 60/459,110 filed Mar. 31, 2003. 

   BACKGROUND 
   The present invention is in the field of electrophotographic printers and copiers. More specifically this invention relates to the fuser apparatus used to fuse an image on a receiving sheet. 
   Most heated roller fusing systems for fixing toner images to a receiving sheet heat a roller called the fusing roller. An unheated pressure roller forms a nip with the fusing roller. The receiving sheet is fed into the nip with an unfixed toner image contacting the fusing roller. The heated fusing roller then ‘fuses’ the image to the receiving sheet. 
   As heat is removed from the fuser roller by several sheets of paper, the temperature sensor tells the heater to turn on full, and the fuser roller end temperatures rise slightly higher than the temperature of the fuser roller at its center. This is because more heat is being removed from the center of the fuser roller (by the receiving sheets) than from the ends. This results in greater thermal expansion at the ends of the fuser roller than at its center. This in turn produces a tentering force that keeps the trail edges of the sheets in tension and prevents wrinkling. 
   After a fuser has been idle for approximately 5 minutes or more, the end temperatures of the fuser roller are slightly lower than the temperature of the middle portion of the fuser roller, due to heat dissipation at the ends. The effect of this temperature profile is that the first few copies (or prints) made have a greater tendency to become wrinkled as they go through the nip because the desired tentering force is insufficient. Tentering is a force that keeps the trail edge of the sheets in cross-track tension as they pass through the fuser in order to minimize wrinkling, i.e. outwardly opposing forces on the sheet in a direction transverse to the direction of motion of the sheet and in the same plane as the sheet. This may be accomplished by providing differential overdrive in the fuser nip. In a prior art device a tentering force is generated with a fuser roll that has a larger outside diameter on the ends than at the center (a “flared” profile). 
   Further, after a fuser has been idle for a few minutes, the first few sheets experience a ‘temperature droop’. That is, the fuser roller temperature decreases as a function of time due to the first few sheets removing heat faster than it can be replenished. This reduces the effectiveness of the image fusing on these first sheets. An apparatus for mitigating thermal droop is disclosed in U.S. Pat. No. 4,963,943, the contents of which are fully incorporated by reference as if set forth herein. 
   Previous fuser roller temperature control devices have focused on maintaining a relatively constant temperature along the axis of the fuser roller. U.S. Pat. No. 5,787,321, by Nishikawa et al discloses a Temperature Controlling Device for a Fixing Unit. The purpose of this device is to prevent overheating of any portions of the fixing (fusing) roller. The control is based on a differential temperature between two sections of the roller, when the differential becomes too great, the cooling fans are either turned on or off. 
   In U.S. Pat. No. 6,532,348, by Allmendinger discloses a Method and Device for Generating and Adjusting Temperature Values in a Fixing Roller of a Toner Image Fixing Unit. The purpose of this device is to allow for homogeneous warming of the fixing roller along its axial length as determined on the basis of a determined core temperature of the fixing roller. 
   A fuser apparatus and method is desired which would create a non-homogeneous temperature along a fuser roller axial length, thus allowing the first sheets passing through to see the same tentering force as the later sheets passing through, thus preventing wrinkling on all the sheets. A method is also desired which would prevent temperature droop, thus allowing the first few sheets to be exposed to the same fuser roller temperature as the later sheets, thereby improving the quality of image fusing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an end view of a fuser according to an aspect of the invention. 
       FIG. 2  is a side view of a fuser roller and cooling device, according to an aspect of the invention. 
       FIG. 3  is a side view of a fuser roller and cooling device, according to an aspect of the invention. 
       FIG. 4  is a side view of an cooling device according to an aspect of the invention. 
       FIG. 5  is a temperature profile according to an aspect of the invention. 
       FIG. 6  is an end view of a fuser according to an aspect of the invention. 
       FIG. 7  is a cross-sectional view of a cooling nozzle according to an aspect of the invention. 
       FIG. 8  is a cross-sectional view of a cooling nozzle according to an aspect of the invention. 
   

   DETAILED DESCRIPTION 
   Various aspects of the invention are presented in  FIGS. 1–6  which are not drawn to scale and in which like components are numbered alike. According to one aspect of the invention, the thermal response of the fuser with sheets being fed through the fuser is simulated in the fuser prior to feeding sheets through the fuser. The thermal response may be simulated in a manner that minimizes thermal droop, or it may be simulated in a manner that maintains a tentering force, or it may be simulated in a manner that accomplishes both. According to a further aspect of the invention, the thermal response of the fuser with sheets being fed through the fuser is controlled to maintain a desired tentering force. The desired tentering force may be varied based on sheet width, or sheet heat absorbing capacity, or sheet stiffness, or combinations of these (all combinations thereof being included within the purview of the invention). 
     FIG. 1  shows a fuser  5  which includes a fuser roller  10  and a pressure roller  20 . The fuser  5  further has a fuser roller heater  12 , and a fuser temperature sensor  14 , which inputs to a logic and control system  40  which controls the heating of the fuser roller heater  12 . The fuser  5  has a run condition, and an idle condition. The fuser roller  10  and the pressure roller  20  form a nip  30 . A receiving sheet  50  is considered to have entered the fuser  5  when it has entered the nip  30 . The heater  12  may be electrothermal, radiative, convective, or other heat source suitable for fusing images, internal or external to the fuser roller, the particular type of heat source not being critical in the practice of the invention. 
   According to an aspect of the invention, an improved method of operation of a fuser  5  for fixing toner images to a receiving sheet  50  comprises cooling the fuser roller  10  during or after the idle condition, prior to the first receiving sheet  50  entering the fuser  5 , such that the fuser roller  10  is cooled enough to cause the logic and control system  40  to activate the fuser roller heater  12 . By cooling the fuser roller  10 , and activating the fuser roller heater  12  prior to the arrival of the first receiver sheet  50 , the fuser run condition is simulated. This helps prevent thermal droop because it eliminates the lag time between the arrival of the first receiving sheet  50  and the activation of the fuser roller heater  12 . 
   There are many ways in which the fuser roller may be cooled. One such way is blowing a gas, such as air, onto the fuser roller  10 , or drawing a gas, such as air, over the fuser  10 . Another way would be to have a cooling or heat sink roller  15  in contact with the fuser roller  10  (see  FIG. 6 ). Although these cooling methods are detailed, this does not limit the invention to these cooling methods, as any appropriate cooling method is within the purview of this invention. 
     FIGS. 2–4  detail a cooling method of directing a cooling fluid at the fuser roller  10 . According to an aspect of the invention, the fuser roller  10  has end portions  11  and a middle portion  16 , and the cooling is directed at the fuser roller middle portion  16 . In this example, that means the fluid is directed onto the fuser roller middle portion  16 . According to a further aspect of the invention, the fuser roller end portions  11  may be cooled independently, or in conjunction with the fuser roller middle portion  16 . For example, the temperature of the end portions  11  may tend to increase as time progresses from a beginning of the run condition, so the end portions  11  may be cooled during the run condition relative to the beginning of the run condition in order to prevent overheating. 
   In a further aspect of the invention, the fuser roller  10  is cooled for a predetermined amount of time. According to a further aspect of the invention, the fuser roller or just the middle portion  16  is cooled after the run condition, for example to prevent an over-temperature condition. In any of the embodiments of the invention, only the middle portion  16  may be cooled, although both the end portions  11  and the middle portion  16  are cooled. 
   Referring now  FIG. 7 , a cross-sectional view of a cooling nozzle  100  is presented having a lengthwise dimension extending perpendicular to the sheet. Nozzle  100  comprises nozzle sides  102  and an adjustable element  104  adjacent one or both of the nozzle sides  102 . At the position shown in  FIG. 7 , the nozzle  100  blows cooling fluid through an area  106 , as indicated by arrows  108 . Moving the adjustable element  104  in the direction of arrow  110  (new position shown in dashed lines) increases the area through which cooling fluid blows, indicated by area  112 . Moving the adjustable element  104  in the direction of arrow  114  (new position shown in dashed lines) decreases the area through which cooling fluid blows, indicated by area  116 . An array of adjustable elements  104  may be provided adjacent each other in the lengthwise direction and independently controlled in order to alter the flow of cooling fluid according to a lengthwise distribution. 
   A cross-sectional view of another embodiment, nozzle  200 , is presented in  FIG. 8 . Nozzle  200  comprises a nozzle sides  202  and  204 . Nozzle side  204  is deflectable. A deflecting element  206  is positioned against the nozzle side  204 , and cooling fluid blows through an area  208  as indicated by arrows  210 . The deflecting element  206  may be pressed against the nozzle side  204  which deflects the nozzle side  204  (deflected position shown in dashed lines) and narrows the area through which cooling fluid blows, as indicated by area  212 . The nozzle side  204  is elastic and returns moves with the deflecting element  206  as it is moved back to its original position. An array of deflecting elements  206  may be provided adjacent each other in the lengthwise direction and independently controlled in order to alter the flow of cooling fluid according to a lengthwise distribution. 
   The adjustable element  104  and deflecting element  206  may be independently controlled by any suitable means, for example screws, cams, levers, pneumatics, hydraulics, and electromechanical devices (including solenoids, motors and stepper motors). An array of such control elements may be provided to control a lengthwise array of elements  104  and  206 . 
   Several temperature sensors  14  may be provided along the length of the fuser roller  10 . These various temperatures give a temperature profile of the fuser roller  10 .  FIG. 5  shows one typical fuser roller  10  temperature profile for a fuser  5  during operation. In a further embodiment, the fuser roller  10  would be cooled until the fuser roller  10  achieves a predetermined temperature profile. The logic and control system  40  may then be used to delay the feeding of the first receiving sheet  50  until the fuser roller  10  achieves the predetermined temperature profile. According to another aspect of the invention, the logic and control system is responsive to the temperatures  14  and controls cooling to maintain a desired temperature profile. The desired temperature profile may vary depending upon the size, weight, thickness, stiffness, and heat absorbing capacity of the sheet, these variables as discussed elsewhere herein. 
   In various aspects of the invention, the amount of heat drawn from the fuser roll is varied to achieve a desired result, including minimizing thermal droop and/or maintaining sheet tentering force. For example, receiving sheets  50  can be of various weights. Lighter weight sheets are more likely to wrinkle than heavier weight sheets. Thus lighter weight sheets need the fuser roller ends  11  hotter than do heavier weight sheets to prevent wrinkling. Thus, in a further embodiment of the invention, the heat absorbing capacity of the receiving sheet may be input to the logic and control system  40 , and the logic and control system  40  adjusts the predetermined amount of time that the fuser roller  10  is cooled according to the receiver sheet  50  heat absorbing capacity. According to further embodiments, the heat absorbing capacity of the receiving sheet may be input manually, or by using a look-up table, or by sensing with a sensor, or by sensing the power being drawn by the fuser heat source. For example, heavier-weight sheets and sheets having a higher heat capacity absorb more heat during the fusing process, which could be determined in advance, and be compiled in a look-up table. Depending on the weight of the receiving sheet, the logic and control system  40  can delay the feeding of a first receiving sheet  50  until the predetermined amount of time has passed. According to a further aspect of the invention, the intensity of the fluid flow could be varied as a function of the sheet heat absorbing capacity. In further embodiments, the predetermined time could remain unchanged, and the flow intensity varied as a function of sheet heat absorbing capacity. Further, the temperature of the cooling fluid could also be modulated as a function of sheet heat absorbing capacity. Variations and combinations of these concepts are evident in light of the description provided herein. 
   According to another aspect of the invention, a fuser  5  for fixing toner images to a receiving sheet  50  comprises a fuser roller  10 , wherein the fuser roller  10  has opposing end portions  11 , and a middle portion  16 , a fuser roller heater  12 , a logic and control system  40 , a fuser roller temperature sensor  14 , a source of cooling fluid  60 , and a cooling device  70  for cooling the fuser roller  10 , wherein the cooling device  70  cools the fuser roller middle portion  16 . 
   In a preferred embodiment, the cooling device  70  further comprises a separate cooling device  71  for cooling the end portions  11 , such that the cooling device  70  can cool either the middle portion  16  and/or the end portions  11 . To more effectively simulate the run condition, according to an aspect of the invention, the length of the middle portion  16  is related to the width of the receiving sheet  50 . For example, it may be approximately equal to, less than, or greater than the width of the receiving sheet, the ideal relationship being determined empirically. In a preferred embodiment, the cooling device  70  is adjustable such that as the receiver sheet  50  width changes, the cooling device  70  adjusts to cool the corresponding fuser middle portion  16 . Thus, for 11 inch paper, the middle portion would equal 11 inches, and for 14 inch paper, the middle portion would be 14 inches. This adjustment could be done on the cooling device  70  for example by having various ports available for fluid flow, and closing or opening these port according to the width needing cooling. 
   In a further embodiment, the fluid directing device  70  further comprises a fluid directing device for directing the fluid onto the middle portion  76 , and a separate fluid directing device for directing the fluid onto the end portions  71 , such that the fluid directing device  70  can direct the fluid either at the middle portion  16  or at the end portions  11 . This aspect is shown in  FIGS. 3 and 4 , where the fluid directing device for directing the fluid onto said middle portion  76  is a series of holes, slots, or other suitable openings, corresponding to the fuser roller middle portion  16 , and the fluid directing device for directing the fluid onto the end portions  71  is an opening corresponding to the fuser roller end portions  11 . 
   In a steady state run condition, the fuser roller end  11  temperature is greater than the fuser roller middle  16  temperature. This results in greater thermal expansion at the ends  11  of the fuser roller  10 . The expanded, hotter ends  11  of the fuser roller  10  create differential overdrive with respect to the cooler smaller center of the fuser roller  10 , this results in a differential ‘tentering’ force on the receiving sheets  50 . According to a further aspect of the invention, a method of creating a desired tentering force on a receiving sheet  50  in a fuser  5  for fixing toner images to a receiving sheet  50 , comprises cooling the middle portion  16  of the fuser roller  10  prior to the run condition, such that the end portions  11  are hotter than the middle portion  16 . This may be controlled and maintained while sheets are being fed through the fuser, for example during steady state sheet feeding. In a preferred embodiment, the middle portion  16  is approximately equal to the receiver sheet  50  width. This tentering force could further be improved by grinding the fuser roller  10  to the desired optimum shape, such that the ends  11  are slightly expanded with respect to the middle portion  16 , for example in a fusing system having a pressure roll and a fuser roll, by slightly modifying the shape of the fuser roller and/or pressure roller. The variance of pressure, in the form of a gradient of pressure that changes along the direction through the nip that is parallel to the axes of the rolls, can be established, for example, by continuously varying the overall diameter of the fuser and/or pressure roller along the direction of its axis such that the diameter is smallest at the midpoint of the axis and largest at the ends of the axis, in order to give the fuser roller and/or pressure roll a subtle “bow tie” or “hourglass” shape. This causes the pair of rolls to exert more pressure on the receiver sheet in the nip in the areas near the ends of the rolls than in the area about the midpoint of the rolls. This gradient of pressure helps to prevent wrinkles and cockle in the receiver sheet as it passes through the nip. A fuser roller is disclosed in United Patent Application Publication US 2004/0023144 A1, filed Aug. 4, 2003, in the names of Jerry A. Pickering and Alan R. Priebe, the contents of which are incorporated by reference as if fully set forth herein. Alternatively or in combination, the tentering force may also be improved by varying the degree of fuser roller and/or pressure roller bending. 
   According to further aspects of the invention, a roller  10  shape is provided to generate a tentering force for all sheet sizes. A constant temperature may be maintained along the length of the roller  10  by selective cooling along the length of the roller  10 . In addition, a center portion of the roller  10  may receive greater cooling (heat removal) than end portions of the roller  10  prior to sheet feeding, and/or the end portions of the roller  10  may receive greater cooling (heat removal) than the center portion during sheet feeding). 
   According to further aspects of the invention, a desired temperature gradient along the length of the roller  10  is controlled and maintained by controlling cooling (heat removal) along the length of the roller  10 . This temperature gradient may be chosen, in combination with the roller  10  profile, to provide a desired tentering force on the sheets. This temperature gradient may be controlled during feeding of sheets to maintain the desired tentering force on the sheet. Alone or in combination, the temperature gradient, and thus the cooling, may be varied as a function of time to vary from one sheet to the next in order to compensate for the various sheet variables previously described herein. 
   The logic and control  40  may be constructed and programmed according to methods and practices know in the relevant art. In this regard, it is contemplated that those skilled in the art having reference to this specification will be readily able to derive the specific computer program instructions suitable for a given logic and control to carry out the operations described herein, in the appropriate computer language. 
   The concepts disclosed herein may also be applied to the pressure roll  20 , as an alternative, or in combination with applying them to the fuser roll  10 . 
   The various aspects disclosed herein may be used alone or in combination, the invention not being limited to the specific examples presented herein, including the drawings. Numerous variations are possible, and may be evident to persons of ordinary skill in the relevant art, all of which are considered to fall within the purview of the invention.