Abstract:
A heat sink roller ( 34 ) is provided as part of a fuser apparatus ( 10 ) to reduce or eliminate thermal transients of a heated fuser roller ( 12 ). The fuser roller ( 12 ) is normally heated to its standby setpoint temperatures. Before the start of a copy run the heat sink roller ( 34 ) is moved to contact fuser roller ( 12 ), causing a temperature gradient due to thermal load placed on fuser roller ( 12 ). Once the run setpoint temperatures are reached, heat sink roller ( 34 ) is removed from contacting fuser roller ( 12 ), and receiver members ( 16 ) are passed through the fuser apparatus. When the last receiver member passes through reproduction apparatus, heat sink roller ( 34 ) moves to once again contact fuser roller ( 12 ) and return it to the standby setpoint temperatures.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to reducing thermal variations during a copy run of a copying device and, more specifically, to heat sinking a fuser roll of a copying device to reduce thermal transients at the start and finish of the copy run.  
       BACKGROUND OF THE INVENTION  
       [0002]     A common problem with almost all internally heated roll fusers of a copying device is the inherent thermal transients that occur throughout a copy run. The major time dependent transient, called temperature droop, occurs at the beginning of the copy run when the fusing unit switches from a standby mode to producing prints at full process speed. The standby power drain of the fuser is typically only a few hundred watts but, depending on the process speed of the copier/printer, the running power usage may be from about 1000 to about 5000 Watts. With an internally heated fuser, a considerable amount of time may be required for the roller elements (the metal core with its external coating) to stabilize to new operating temperatures and thermal gradients. The amount of time required to return to thermal stability will be dependent on the lamp wattage vs. the thermal load of the paper at process speed as well as the amount of thermal mass of the roller elements.  
         [0003]     Thermal transients, called overshoot, may also occur upon completion of the copy run. In this case, when the thermal load of the passing paper is removed, the fuser roll temperature may increase above the operating temperature, even though the fuser unit has switched back to a standby mode. A substantial amount of time may be required for the roller elements to stabilize to new standby temperatures and thermal gradients.  
         [0004]     When these thermal variations are encountered, they will inherently cause variations in the fused copy attributes, such as image permanence and image gloss. The amount of image glass variation within a color machine can easily become unacceptable. It may take, for example, from about 40 to about 50 copies to regain a steady state running and/or standby temperature condition when the thermal load of the paper is added or removed. As a result, these first 40 to 50 copies may be considered waste. Additionally, at the end of a copy run, there may be a delay in starting the next run as the fuser roller returns to a stead state standby temperature.  
         [0005]     U.S. Pat. No. 5,196,894, issued to Merle et al. (Merle) discloses heat sink within a copying apparatus. More specifically, Merle discloses a heat sink member that is maintained substantially below the glass transition temperature of the toner. The heat sink member is used to cool a receiving sheet that has passed through the fuser roll, rapidly cooling the receiving sheet until the toner image and any heat-softenable layer are below their glass transition temperatures (col. 4, lines 45-53). Merle, however, does not address the problem of temperature transients, especially those at the start and finish of a copy run.  
         [0006]     U.S. Pat. No. 5,937,231, issued to Aslam et al. (Aslam) discloses the use of a heat sink roller to control fuser roller temperature droop. The heat sink roller is made of a material having a thermal mass to match the heat take out rate of the nominal fuser operating process (col. 3, lines 60-62). Before the copy process begins, the heat sink roller contacts the fuser roller, removing heat from the fuser roller similar to the heat, which would be removed by copies being fused. When the paper begins to move through the fuser, the heat sink roller is removed, thereby reducing temperature droop. The heat sink roller of Aslam, however, requires a cool down period between uses. For example, if a short run of copies is made, the heat sink roller may not have a chance to cool down to its starting point and, therefore, would not be capable of simulating the heat which be removed by copies being fused. Aslam requires the heat sink roller to be at a relatively uniform starting temperature at the start of each operation. Furthermore, while Aslam may, with the limitations discussed above, help reduce temperature droop, it does not address the problem of overshoot at the end of a copy run. Indeed, Aslam may actually be incapable of correcting overshoot, especially in short copy runs where the heat sink has not had a chance to return to its original ambient temperature.  
         [0007]     As can be seen, there is a need for an improved heat sinking fuser roll that reduces thermal transients, including droop and overshoot, without requiring the operator to wait between copy runs.  
       SUMMARY OF THE INVENTION  
       [0008]     As will be discussed in more detail below, one method to avoid fuser thermal variations during the course of a copy run may be to provide a thermal load to the fuser roll surface just prior to a copy run and establish temperatures and thermal gradients within the fuser roll elements (core and coating) typical of the steady state values they will obtain within the copy run. This thermal load can then be removed as the first unfused copy enters the fuser. Thus, the fuser roll surface will not have any temperature variations during the copy run, resulting in each and every copy/print being fused to an identical level.  
         [0009]     In one aspect of the present invention, a mechanism for controlling temperature transients in a heated fuser roller of a reproduction apparatus includes a heat sink roller movable between a first position and a second position, the first position being separated from the fuser roller and the second position being in contact with the fuser roller; and a coolant inside the heat sink roller, the coolant selected to provide a contact heat load on the fuser roller when the heat sink roller is in contact with the fuser roller, the contact heat load being similar to a receiver member heat load on the fuser roller that would otherwise occur when a receiver member is passed through the fuser roller and an image is fused thereupon.  
         [0010]     In another aspect of the present invention, a mechanism for controlling temperature transients in a heated fuser roller of a reproduction apparatus includes a heat sink roller movable between a first position and a second position, the first position being separated from the fuser roller and the second position being in contact with the fuser roller; a coolant inside the heat sink roller, the coolant selected to provide a contact heat load on the fuser roller when the heat sink roller is in contact with the fuser roller, the contact heat load being similar to a receiver member heat load on the fuser roller that would otherwise occur when a receiver member is passed through the fuser roller and an image is fused thereupon; an input tube for flowing the coolant into the heat sink roller; and an output tube for flowing the coolant out from the heat sink roller; wherein the coolant is virgin water from a water supply; the virgin water is fed to the heat sink roller through the input tube; and the virgin water passes through the heat sink roller and passes through the output tube to a wastewater drain.  
         [0011]     In yet another aspect of the present invention, a fuser, for a reproduction apparatus, for permanently fixing a marking particle image to a receiver member, the fuser includes a heated fuser roller operating at a setpoint temperature; a heat sink roller movable between a first position and a second position, the first position being separated from the fuser roller and the second position being in contact with the fuser roller; and a coolant inside the heat sink roller, the coolant selected to provide a contact heat load on the fuser roller when the heat sink roller is in contact with the fuser roller, the contact heat load being similar to a receiver member heat load on the fuser roller that would otherwise occur when a receiver member is passed through the fuser roller and an image is fused thereupon.  
         [0012]     In a further aspect of the present invention, a reproduction apparatus for permanently fixing a marking particle image to a receiver member includes a heated fuser roller operating at a setpoint temperature; a heat sink roller movable between a first position and a second position, the first position being separated from the fuser roller and the second position being in contact with the fuser roller; and a coolant inside the heat sink roller, the coolant selected to provide a contact heat load on the fuser roller when the heat sink roller is in contact with the fuser roller, the contact heat load being similar to a receiver member heat load on the fuser roller that would otherwise occur when a receiver member is passed through the fuser roller and an image is fused thereupon.  
         [0013]     In still a further aspect of the present invention, a method for reducing thermal transients in a heated fuser roller operating at a setpoint temperature includes providing a heat sink roller movable between a first position and a second position, the first position being separated from the fuser roller and the second position being in contact with the fuser roller; filling the heat sink roller with a coolant; moving the heat sink roller into the second position at the start of a copy run; allowing the fuser roller to reach the setpoint temperature; moving the heat sink roller to the first position; and passing at least one receiver member through the fuser roller to fuse an image thereupon.  
         [0014]     The reduction of thermal transients according to present invention has several advantages over conventional copying methods. First, thermal transients that occur throughout the copy run, especially those at the beginning and the end of the copy run, may be reduced or eliminated. Further, heat sink recovery time between copy runs may be reduced or eliminated with the method and apparatus of the present invention. Moreover, the copy runs may be successfully run without waste copies at the beginning of the run due to variations in image permanence and image gloss because of fuser roll temperature transients.  
         [0015]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description, and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which:  
         [0017]      FIG. 1  shows a schematic view of a fuser roll with a cooler roll according to an embodiment of the present invention;  
         [0018]      FIG. 2  shows a schematic view of one embodiment of the heat sink of the present invention;  
         [0019]      FIG. 3  shows a schematic view of another embodiment of the heat sink of the present invention;  
         [0020]      FIG. 4  shows a schematic view of yet another embodiment of the heat sink of the present invention;  
         [0021]      FIG. 5  shows a graph of temperature vs. time of the fuser roll core and surface during a copy run; and  
         [0022]      FIG. 6  shows a graph of temperature vs. time of the fuser roll core and surface, as well as the cooler roll surface as a cooler roll contacts the fuser roll. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is defined by the appended claims.  
         [0024]     Broadly, the present invention provides a fuser roll that includes a heat-sink in order to avoid temperature transients that occur during a copy run. A heat-sinking roller may be applied to the fuser roll, prior to the copy run, to mimic the thermal load of the paper during a copy run. The fuser roll can draw more power to maintain a proper surface temperature. Once the fuser roll surface reaches a steady state, the heat sink may be removed and the paper may be fed through the apparatus. Because the fuser roll can draw sufficient power to handle the thermal load of the paper (which, prior to the copy run, this thermal load was mimicked by the heat sink), thermal droop at the start of the copy run may be reduced or eliminated.  
         [0025]     Referring to  FIG. 1 , there is shown a schematic drawing of a reproduction fuser apparatus  10  according to an embodiment of the present invention. Fuser apparatus  10  may include a fuser roller  12  in nip relation with a pressure roller  14 . A receiver member  16 , such as a sheet of paper, may be fed from a feeder belt  18 , between the rotating fuser roller  12  and pressure roller  14 , and out to a downstream transport belt  20 .  
         [0026]     Fuser roller  12  may include a core  22  and a fusing blanket  24  that is, for example, cylindrically shaped, and supported on core  22 . Blanket  24  may be made of a rubber material particularly formulated to be heat conductive or heat insulative, depending on whether the fuser heat source is located within core  22  or in juxtaposition with the periphery of blanket  24 . In the illustrated embodiment of the present invention, the heat source is an internal heater lamp  26 . Therefore, blanket  24  may preferably be a heat conductive rubber material, allowing the surface temperature to quickly adjust to changes in heat output of heater lamp  26 .  
         [0027]     A conventional oiler mechanism  28  may selectively apply an oil to blanket  24  of fuser roller  12  to substantially prevent offsetting of the marking particle image to fuser roller  12 . Additionally, a conventional cleaning mechanism  30  may wipe the surface of fuser roller  12  to remove excess offset preventing oil and other contaminants which could degrade the quality of the image fused to receiver member  16 .  
         [0028]     Pressure roller  14  may have an outer surface  32  that may form a pressurized nip with fuser roller  12 . Pressure roller  14  may be made of metal, such as aluminum or steel, optionally coated with a suitable surface coating (not shown) to substantially prevent offsetting of the marking particle image to pressure roller  14 . One example of a suitable surface coating may be Teflon.  
         [0029]     A heat sink roller  34  can have a longitudinal axis substantially parallel with a longitudinal axis of fuser roller  12 . The heat sink roller  34  may be moveably mounted between a first position (indicated by dotted line  34   a  in  FIG. 1 ), where heat sink roller  34  is separated from fuser roller  12 , and a second position (indicated by the solid line  34   b  in  FIG. 1 ), where heat sink  34  contacts the surface of fuser roller  12 , thereby placing a contact heat load on fuser roller  12 . Heat sink roller  34  may preferably mimic the thermal capacity of the paper that would be passing through fuser roll  12  during a copy run. That is, heat sink roller  34  may remove substantially the same heat as a nominal image bearing receiver member  16  being fused at the nominal process speed and fusing setpoint temperature.  
         [0030]     When the reproduction machine is in standby mode (that is, no reproduction request has been made), the surface fuser roller  12  may be heated to a predetermined standby setpoint temperature. To maintain this standby setpoint temperature, low energy output, for example, from about 300 to about 500 watts, is needed from internal heater lamp  26 . In this state, the temperature at the core of fuser roller  12  will only be slightly above the standby setpoint temperature of the surface of fuser roller  12 .  
         [0031]     When a reproduction job is requested, heat sink roller  34  may be moved from its first position (not contacting fuser roller  12 ) to its second position (contacting the surface of fuser roller  12 ). On contact, heat sink roller  34  may create a contact heat load to immediately start to remove heat from fuser roller  12 , thus simulating a receiver member heat load caused by heat being removed when copies are fused by fuser roller  12 . This initial contact between heat sink roller  34  and fuser roller  12  may cause a surface temperature droop from the steady state standby setpoint temperature of fuser roller  12 . To compensate for this temperature droop on the surface of fuser roller  12 , internal heater lamp  26  may be supplied greater power, thereby causing the core of fuser roller  12  to increase. Therefore, a radial thermal gradient may be created in fuser roller  12  substantially equal to the radial thermal gradient, which would be created by copy fusing to sheets of paper. Heat sink roller  34  may remain in operative contact with fuser roller  12  until the surface temperature of fuser roller  12  returns at or near its steady state setpoint temperature. As an example, heat sink roller  34  can remain in operative contact with fuser roller  12  until the surface temperature of fuser roller  12  is within about 5 to about 20° F., and more preferably within about 3 to about 10° F., of its steady state temperature.  
         [0032]     Once fuser roller  12  reaches its steady state temperature following contact with heat sink roller  34 , the fuser roller  12  is ready to begin a copy run. When the first sheet of receiver member  16  is fed through fuser roller  12 , heat sink roller  34  can return to its first position (not contacting fuser roller  12 ) and remain there until copy production run is complete. When the copy run is complete, heat sink roller  34  can return to its second position (contacting fuser roller  12 ), thereby eliminating overshoot that would otherwise result in the temperature of the surface of fuser roller climbing above the steady state temperature. The copy run may be considered complete when the last receiver member passes through fuser roller  12 . Heat sink roller  34  may also return to its second position (contacting fuser roller  12 ) during a temporary error condition, such as being out of paper, out of ink, or the like, during a copy run. The application of heat sink roller  34  to fuser  12  during such an error condition may result internal heat lamp  26  providing output similar to that provided during the copy run. This may result in the surface temperature of fuser roller  12  remaining relatively constant, even after the copy job is resumed.  
         [0033]     In one embodiment of the present invention, coolant, such as water, may flow through input tube  36 , pass through heat sink roller  34 , and out to waste through output tube  38 . Coolant temperature, coolant flow rate, loading amount (nip width between fuser roller  12  and heat sink roller  34 ), and rotation speed of the rollers may be adjusted so that heat sink roller  34  mimics the thermal capacity of the paper that would run through fuser roll  12  during a copy run. For example, a heavy bond paper, having a higher thermal capacity, would require a heat sink roller  34  that would draw more energy from fuser roller  12 , as compared to a lightweight paper.  
         [0034]     Referring to  FIG. 2 , there is shown an alternate embodiment of the heat sink roller  34  of the present invention. Instead of flowing virgin water through heat sink roller  34  and out to the waste as in the embodiment of  FIG. 1 , in this alternate embodiment of the present invention, coolant—such as water, ethylene glycol, silicon oil, or the like—may be circulated through a radiator  40  via input tube  36  and output tube  38 . Radiator  40  may also include a fan  42  to help maintain the coolant at ambient temperature.  
         [0035]     Referring to  FIG. 3 , there is shown yet another alternate embodiment of the heat sink roller  34  of the present invention. Instead of flowing virgin water through heat sink roller  34  and out to the waste as in the embodiment of  FIG. 1 , in this alternate embodiment of the present invention, coolant—such as water, ethylene glycol, silicon oil, or the like—may be circulated through a reservoir  44 . Reservoir  44  may be a simple holding tank for storing the coolant. Reservoir  44  may be sized appropriately to cool heat sink roller  34  in an amount sufficient to mimic paper thermal load during operation while preventing significant heating of the coolant itself.  
         [0036]     Referring to  FIG. 4 , there is shown still another alternate embodiment of the heat sink roller  34  of the present invention. Instead of flowing virgin water through heat sink roller  34  and out to the waste as in the embodiment of  FIG. 1 , in this alternate embodiment of the present invention, coolant—such as water, ethylene glycol, silicon oil, or the like—may be sealed within heat sink roller  34  via a cap  46 . The internal volume of heat sink roller  34  and the coolant may be selected to cool heat sink roller  34  in an amount sufficient to mimic paper thermal load during operation while preventing significant heating of the coolant itself.  
         [0037]     While the above embodiments and the Example below described heat sink roller  34  using a liquid coolant, such as water, the invention is not meant to be so limited. For example, a gaseous coolant, such as air, may be circulated through input tube  36 , into heat sink roller  34 , and out through output tube  38 , as shown in  FIG. 1 . Air flow and temperature may be chosen such that application of heat sink roller  34  onto fuser roller  12  mimics a heat draw similar to the paper being fed through the copier/printer.  
       EXAMPLES  
       [0038]     Referring to  FIGS. 1 and 5 , fuser roller  12 , having an internal heating lamp  26  with a maximum output of about 3000-5000 W, was sitting in standby, at a constant steady state temperature as shown at time 34:00.0 in  FIG. 5 . In this state, fuser roller  12  had a small thermal gradient across blanket  24 . Heat sink roller  34  was at its first position, not in contact with fuser roller  12 . Receiver members  16  were then introduced between fuser roller  12  and pressure roller  14  at full process speed. The outer surface of fuser roller  12  initially experienced a very large droop downward, as can be seen at a time of about 36:00.0. After about two minutes, the surface of fuser roller  12  returned to a steady state temperature. The copies/prints made during this three-minute period may not be of acceptable quality due to image gloss variation.  
         [0039]     The magnitude of the droop seen in  FIG. 5  is mainly governed by the heat-give-up-ability (conductivity/diffusivity) of blanket  24  and the dwell time with the input media (receiver member  16 ). The power of internal heating lamp  26  has little to do with the magnitude of this variation. During the copy run, internal heating lamp  26  must not only supply energy to receiver member  16 , but also supply additional energy to heat the roller elements (aluminum core  22  and elastomer blanket  24 ) such that the surface of fuser roller  12  returns to its steady state control point.  
         [0040]     Referring now to  FIGS. 1 and 6 , the same fuser roller  12  used for the graph shown in  FIG. 5 , having an internal heating lamp  26  with a maximum output of about 3000-5000 W, was sitting in standby, at a constant steady state temperature as shown at time 46:04.8 in  FIG. 6 . In this state, fuser roller  12  had a small thermal gradient across blanket  24 . Heat sink roller  34 , filled with water similar to the embodiment shown in  FIG. 4 , was at its first position, not in contact with fuser roller  12 . At approximately time 46:30.0, heat sink roller  34  was moved from its first position to its second position, making contact with fuser roller  12 . The outer surface of fuser roller  12  initially experienced a very large droop downward, as can be seen at a time of about 46:48.0. After about three minutes, the surface of fuser roller  12  returned to a steady state temperature. At this point in time, receiver members  16  may now be fed through fuser roller  12  while heat sink roller  34  returns to its first position, not contacting fuser roller  12 . The paper now being fed through fuser roller  12  may cause little or no temperature droop, thereby resulting in each and every copy being of the same copy quality and image gloss.  
         [0041]     As shown in the graph of  FIG. 6 , the surface temperature of heat sink roller  34  increases slightly during the time that heat sink roller  34  is in contact with fuser roller  12 . It is desirable to minimize this temperature rise within heat sink roller  34 , thereby reducing the amount of time necessary for heat sink roller  34  to return to its original state between copy runs. One approach to minimizing this temperature rise is to use a coolant with a higher heat capacity, such as mineral oil or silicon oil, and/or to use a larger volume of coolant. Another approach to minimizing this temperature is to use a flowing coolant, as described above, and as described in the embodiments of  FIGS. 1 through 3 .  
         [0042]     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.  
       Parts List  
       [0000]    
       
           10  fuser apparatus  
           12  fuser roller  
           14  pressure roller  
           16  receiver member  
           18  feeder belt  
           20  receiver belt  
           22  core  
           24  blanket  
           26  internal heater lamp  
           28  oiler mechanism  
           30  cleaning mechanism  
           32  hard outer shell  
           34  heat sink roller  
           36  input tube  
           38  output tube  
           40  radiator  
           42  fan  
           44  reservoir  
           46  cap