Abstract:
A media input tray for an imaging device such as a laser printer is configured to heat media disposed in the tray in order to reduce potential curl of the media caused by image processing in the imaging device. In a preferred embodiment, the input tray is configured with a flexible printed circuit having conductive traces for dissipating heat in response to an electric current. The flexible circuit is coupled to a power supply in the imaging device to enable a continuous warming of media in the tray, independent of any imaging operations by the imaging device. A method of image processing includes providing a heating device in a media input tray of an image processing device, and heating the media disposed in the input tray with the heating device such that media curl, caused by image processing operations, is reduced.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to image forming devices and, more particularly, to pre-heating media in an input tray for reducing media curl caused by image processing. 
     BACKGROUND OF THE INVENTION 
     Conventional electrophotographic imaging devices, such as laser printers, facsimile machines or copiers, operate by using a roller or a series of rollers to pull a sheet of media (typically a sheet of paper) from an input tray and to move the media to a registration roller assembly. The registration roller assembly aligns the media so that the edges of the media are parallel to the media path. Once the media is properly aligned, the registration roller assembly passes the media to an optical photoconductor (OPC) surface, such as a drum or belt. The OPC has a latent image on its surface formed by scanning a laser across the surface. A difference in electrostatic charge density is created between the areas on the surface exposed and unexposed to the laser beam. A visible image is developed by toners that are selectively attracted to the OPC surface, either exposed or unexposed to light, depending on the relative electrostatic charges of the OPC surface, development electrode, and the toner. The OPC may be either positively or negatively charged, and the toner similarly may contain negatively or positively charged particles. 
     The media is given an electrostatic charge and passed close to the photoconductor surface. As the media passes close to the photoconductor surface, it pulls the toner from the photoconductor surface onto the media still in the pattern of the image developed from the photoconductor surface. After receiving the image, the media is passed to a fuser. The fuser heats the toner image on the media, bonding the toner to the media. 
     The temperature of the fuser is critical. Rough or thick media requires a higher fuser temperature than smooth or thin media. In either case, if the fuser temperature is too low, toner will not be adequately fused to the media. On the other hand, if the temperature is too high, the toner will be pulled from the media by the fuser and the media may be damaged. Either case results in an undesirable print defect. 
     Notably, over fusing can cause the media to curl, wrinkle, or warp and possibly jam the printer. However, other factors also affect media curl, wrinkle or warping, including composition and weight of the media, moisture content of the media, whether one or both sides of the media is imaged, toner distribution on the media, fusing temperature, fusing configuration (i.e., single or dual heated fuser rollers), ejection speed of the media when leaving the printer, and external environmental factors such as temperature and humidity. For example, media curl is common in environments where air conditioning is unavailable to moderate humid conditions. In such situations, media moisture content is naturally high. As a result, media curl, wrinkle or warping may occur simply due to the moisture being quickly driven off during normal image fusing, even if the printer parameters are optimally established. 
     Many of these factors affect media curl not only in electrophotographic imaging systems but also in ink jet imaging systems. For example, notably, the heavy moisture concentrations in conventional liquid inks causes the inks to soak into conventional paper media and, in combination with ink distribution on the media, causes the media to curl, wrinkle or warp. 
     Accordingly, an object of the present invention is to reduce media curl often caused by conventional image processing techniques and environmental conditions. 
     SUMMARY OF THE INVENTION 
     According to principles of the present invention, a media input tray for an imaging device such as a laser printer is configured to heat media in the tray in order to reduce potential curl of the media caused by image processing in the imaging device. In a preferred embodiment, the input tray is configured with a flexible printed circuit having conductive traces for dissipating heat in response to an electric current. The flexible circuit is coupled to a power supply in the imaging device to enable a continuous warming of media in the tray, independent of imaging operations by the imaging device. 
     According to further principles, a method of image processing includes providing a heating device in a media input tray of an image processing device and heating the media disposed in the input tray with the heating device such that potential media curl, caused by image processing operations, is reduced. 
     Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a page printer embodying the present invention heated media input tray. 
     FIG. 2 is a schematic block diagram of the printer of FIG.  1 . 
     FIG. 3 is a flow chart depicting a preferred method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a perspective view of a page printer  10  embodying the present invention heated media input tray  15 . Although printer  10  is described as an electrophotographic imaging device employing conventional laser imaging technology, it is understood that the present invention heated media input tray  15  is similarly feasible in other media processing apparatus, such as ink jet printers, facsimile machines, and photocopiers. 
     Printer  10  includes an electrophotographic imaging system (not shown) disposed within housing  20 . Printer  10  further includes media input tray  15  for holding media to be image processed by printer  10 , media output bin  25  for holding imaged media that have been image processed by printer  10 , control panel  30 , information display  35 , and power switch  37 . 
     The present invention media input tray  15  is shown in an extended or open position relative to housing  20  so as to receive media therein by a user and so as to more clearly view resistive heating device  40  disposed therein. In a preferred embodiment, heating device  40  is a planar flexible printed wiring substrate, often referred to as a flex assembly or flex circuit, and is disposed adjacent a bottom support member  45  of tray  15 . Alternatively, heating device  40  includes a rigid printed wiring substrate or other resistive heating mechanism. In further alternate embodiments, heating device  40  includes resistive elements formed into (as part of) tray  15  or includes any other mechanism that generates or radiates heat. 
     Flex circuit  40  includes one or more laterally spaced conductive traces  50  (such as aluminum or copper) formed on a flexible non-conductive layer  55  (such as Mylar or polyamide) as is known in the printed circuit art. The conductive traces  50  are electrically coupled to a power supply disposed within housing  20 . Flex circuit  40  is disposed within tray  15  such that sheet media (not shown) rests upon the flex circuit when the media is inserted into the tray for use by printer  10 . In this context, the media when held in tray  15  is warmed and maintained at an elevated temperature by flex circuit  40  before being image processed by printer  10 . Importantly, the elevated temperature reduces curling, wrinkling or warping of the media during image processing by printer  10 . 
     Referring now to FIG. 2, a schematic block diagram of printer  10  is depicted. Here, media input tray  15  is shown having sheet media  105  disposed in sheet stack support member  110  which is biased upward by spring bias  115 . Media  105  rests on top of flex circuit  40  such that conductive warming of the media occurs and a maintaining of the media at an elevated temperature occurs in response to electric current supplied through the resistive electrical traces  50 . Flex circuit  40  is disposed adjacent bottom support member  45  of sheet stack support member  110  in tray  15 . 
     Conductive traces  50  terminate in contacts at an outer edge of flex circuit  40 . The contacts interface with an electrical connector  120  as conventional in the art. Connector  120  couples with receptor  125  which is coupled to power supply  130 . In this configuration, as tray  15  is extended out from within housing  20  (see FIG.  1 ), connector  120  is disconnected from receptor  125  such that power is no longer provided to flex circuit  40 . However, when tray  15  is pushed back into its home position (shown) within housing  20 , connector  120  is guided to properly mate with receptor  125  such that flex circuit  40  is power enabled for heating media  105 . 
     Although not shown, other configurations for transferring power to flex circuit  40  are similarly feasible and contemplated. For example, in an alternate embodiment, a flexible, elongated power cable couples power supply  130  to connector  120 . In this context, as tray  15  is extended out from within housing  20 , the power cable is snaked out along with the tray such that connector  120  remains connected to the power cable so that connection is continuously maintained with flex circuit  40 . Additionally, when tray  15  is pushed back into its home position within housing  20 , the power cable is retracted to not interfere with tray  15 , yet connector  120  remains connected for continuously heating media  105 . 
     Whatever the power connection chosen, in a preferred embodiment flex circuit  40  is continuously powered by power supply  130  regardless of the “on” or “off” status of printer  10  as controlled by power switch  37  (so long as the printer itself is plugged into an external power source as conventional in the art). In this manner, media  105  continuously remains at an elevated temperature, even if the printer is unused for imaging operations for extended periods of time, such as over night. In this context, a low power consumption of ten (10) to twenty (20) watts by flex circuit  40  is preferred. 
     If a continuously heated state is not desired, other power enabling configurations are similarly feasible and contemplated. For example, in an alternate embodiment, the supply of power to flex circuit  40  is controlled in relation to the “on” or “off” status of power switch  37 . In yet another alternate embodiment, the supply of power to flex circuit  40  is governed by firmware resident in memory of printer  10 . For example, upon detecting a power-on cycle for printer  10 , the firmware enables a higher wattage (i.e., about 20 watts) to be supplied to flex circuit  40  for a predetermined amount of time for initial warming of media  105 , after which the wattage is reduced (i.e., to about 10 watts) for the remaining time. Alternatively, numerous other variations of control as enabled by the firmware or other software or hardware are equally feasible. For example, in yet a further embodiment, power to flex circuit  40  is thermostatically governed. 
     Now, the longer the amount of time that media  105  remains in tray  15 , the warmer and more dried it becomes as moisture is driven off, up to the point of elevated temperature saturation. However, obviously, sheets at the top of the stack of media  105  will be slower to warm than sheets at the bottom of the stack. In this context, in an alternate embodiment (not shown), dual flex circuits are utilized to heat not only from the bottom up but also from the top down. Alternatively, flex circuit  40  is disposed so as to be biased only against the top of the stack of media  105 . This embodiment is helpful where the top sheet is picked for processing because it will be the most quickly heated. In any case, this warming and drying of media  105  in tray  15  is especially helpful in environments where external temperatures and humidity factors are high. Again, the less moisture that is absorbed in the media, then the less curl, wrinkling and warping will occur during image processing by the printer. 
     The general operation of printer  10  is described as follows. Media  105  as placed in tray  15  by a user is warmed to an elevated temperature by conductive heat transfer in response to flex circuit  40  being enabled by power supply  130 . Upon initiation of an image transfer operation by printer  10 , feed roller  135  picks top sheet  140  from media stack  105  in input tray  15  and advances it to a pair of transport rollers  145 . Transport rollers  145  further advance sheet  140  through paper guides  150  toward registration rollers  155 . Registration rollers  155  advance sheet  140  to photoconductive drum  160  (of toner cartridge  165 ) and transfer roller  170  where toner is applied as conventional in the art. Sheet  140  then moves through heated fuser rollers  175  where the toner is fused or bonded to the media. Finally, the sheet is passed upward and ejected into output bin  25 . 
     It should be noted here that, in a preferred embodiment, flex circuit  40  is configured to be removably coupled to a bottom portion of tray  15 , such as adjacent bottom support member  45  of sheet stack support member  110  in tray  15 . As such, flex circuit  40  is adaptively fitted into tray  15  as an optional component or accessory. Alternatively, flex circuit  40  is formed into, or as a part of, the bottom portion of sheet stack support member  110 . As such, tray  15 , having flex circuit  40  formed therein, is adaptively fitted into printer  10  as a complete optional component or accessory. 
     Referring now to FIG. 3, a flow chart depicts a preferred method of the present invention. First,  205 , flex circuit  40  is provided in tray  15 . Next,  210 , power is supplied to flex circuit  40  such that conductive traces  50  dissipate heat to media  105  disposed in the tray. Subsequently,  215 , the media is image processed through printer  10 . Consequently,  220 , the media is output to bin  25  with reduced curl, wrinkle or warping, due to the media having been pre-heated in tray  15 . 
     Finally, it will be obvious to one of ordinary skill in the art that the present invention is easily implemented utilizing any of a variety of components existing in the art. Moreover, while the present invention has been described by reference to specific embodiments, it will be apparent that other alternative embodiments and methods of implementation or modification may be employed without departing from the true spirit and scope of the invention.