1. Technical Field
The present application relates generally to an electrophotographic imaging device and more particularly to a fuser for an electrophotographic imaging device.
2. Description of the Related Art
In the electrophotographic (EP) imaging process used in printers, copiers and the like, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over an outer surface. An electrostatic latent image is formed by selectively exposing the uniformly charged surface of the photosensitive member. Toner particles are applied to the electrostatic latent image and thereafter the toner image is transferred to the media intended to receive the image. The toner is fixed to the media by a combination of heat and pressure applied by a fuser.
The fuser may include a belt fuser that includes a fusing belt and an opposing backup member, such as a backup roll. The belt and the backup member form a nip therebetween. The media with the toner image is moved through the nip to fuse the toner to the media. Belt fusers allow for “instant-on” fusing where the fuser has a relatively short warm up time thereby reducing electricity consumption. Fusing speed is a function of the width of the fuser nip and the belt surface temperature, among other things. A fuser with a relatively wide nip is able to fuse toner to media moving at higher speeds through the nip than a comparable fuser with a relatively narrow nip. Further, a fuser with a higher belt surface temperature is able to fuse toner to the media faster than a fuser with a lower belt surface temperature. Higher fusing speeds in turn lead to higher print speeds.
Fusers in laser printers are designed to bond toner to the entire width of media by using heat and pressure. In most fusers, heat is generated by either by a halogen lamp or a ceramic heater. In the case of the halogen lamp fuser, heat is transferred radiantly from the lamp to the black coated inside of an aluminum tube. For monochrome printers, the aluminum tube may have a release layer of either a perfluoroalkoxy (PFA) or polytetrafluoroethylene (PTFE) coating. For color printers, the aluminum tube may be first coated with silicone rubber and then a perfluoroalkoxy (PFA) sleeve. In the cases of the fuser with ceramic heater, heat is transferred conductively from the ceramic heater to either a polyimide tube with a PFA and/or PTFE release layer (for a monochrome fuser), a stainless steel tube with a PFA and/or PTFE release layer (also a monochrome fuser), or a stainless steel tube with a silicone layer and a PFA sleeve (for a color fuser). The release layer coated surface of these tubes applies the heat to the surface of the media that has toner. The pressure is produced by a rubber coated steel or aluminum shaft that is pressed against the coated tube. The media passes between the coated tube and the rubber coated steel shaft. The rubber coated steel shaft typically has a PFA sleeve placed over the rubber coating. This rubber coated steel shaft is commonly called a backup roll. The length of the heating region is typically about 2 to 3 mm longer than the widest media that the laser printer is designed to print. An overheating problem occurs when narrow media is printed in the laser printer. In regions of the fuser nip where the media does not pass through the fuser, the tube and backup roll become very hot and may be damaged due to the high temperature.
In particular, in this case heat generated by the ceramic heater is not removed from those regions of the fuser nip which fail to contact media sheets passing through the nip. The heat generated in such regions heats the tube and the backup roll as a result. Because laser printers are designed to have a very small first copy time, the thermal mass of the heater and of the tube is very small. Because of the small thermal mass, the axial heat conduction from hot regions of the tube and heater to cooler regions is very small. This causes the amount of heat to build up relatively rapidly in the heater and tube in such fuser nip regions not contacting the passing media sheets. The heat build up is not significant for fuser nip regions contacting the media sheets because energy is removed from the system by the sheets and toner fixing. In addition, to achieve the very small first copy time and fix the toner to the media, the backup roll surface needs to become very hot without conducting heat to the steel or aluminum shaft. This is achieved because the rubber is a thermal insulator. However, this also means the heat conducted away from the coated tube and heater by the backup roll in regions not contacting the media sheets is very small.
One other possible mechanism to remove heat from the coated tube and backup roll in such overheating fuser nip regions is by convection into the air. Unfortunately, the amount of heat removed by convection is very small because in order to meet the very small first copy time, the heat lost to the air is minimized by enclosing the coated tube and backup roll in plastic covers to keep the air still. However, the plastic covers are designed to act as a heat insulating surface, thereby providing little if any opportunity to reduce heat to the overheating fuser nip regions via air convection.
A current solution to prevent overheating is to reduce the velocity of the media sheets traveling through the laser printer and increase the distance between media sheets. Reducing the velocity of the media allows the temperature of the coated tube to be reduced. The reduced temperature produces less heat in the overheating regions. The distance between sheets is increased so that, with the reduced media velocity, the time between media sheets becomes large enough for the small heat conduction to cool the overheating regions and prevent overheating. As the media widths become smaller, the amount of time needed to cool the overheating fuser nip regions becomes larger because the size of such regions becomes larger. The overall result of increasing sheet spacing between narrow media is that narrow width media is printed very slowly. For example, existing laser printers may reduce printing speeds for some media sheets of a print job more than 50%.
Accordingly, it will be appreciated that an efficient belt fuser with enhanced heating performance is desired.
Example embodiments of the present disclosure overcome at least some of the shortcomings in prior fuser heaters and thereby satisfy a significant need for a fuser heater for effectively controlling heat within the fuser. According to an example embodiment, there is shown a heating member for a fuser of an electrophotographic imaging device, including a panel of positive thermal coefficient (PTC) material having a first surface and a second surface; and first and second conductor members. The PTC material exhibits a first electrical resistance within a predetermined range of operating temperatures and a near exponential increase in resistance at temperatures greater than the predetermined temperature range. The first conductor member is electrically coupled to the first surface of the panel of PTC material and the second conductive member is electrically coupled the second surface thereof so that the first and second conductive members support a voltage differential to be placed across the panel of PTC material. Application of an AC voltage between the first and second conductive members results in the PTC material having a temperature falling within the predetermined temperature range.
When used in an electrophotographic device, the fuser heating member provides the temperature falling within the predetermined temperature range so that the electrical resistance of the PTC material is at about the first electrical resistance. Passing media sheets through the fuser that are substantially narrower than the fuser nip width causes the portion of the fuser nip region which does not contact the sheets to increase in temperature. If such temperature increase is sufficiently beyond the predetermined temperature range, the electrical resistance of the PTC material increases substantially exponentially within the portion of the fuser nip region which does not contact the media sheets. This increase in electrical resistance within the portion of the fuser nip region not contacting the media sheets results in the temperature of the PTC material corresponding to such portion of the fuser nip region to decrease. This temperature decrease of the PTC material corresponding to the portion of the fuser nip region not contacting the media sheets serves to stabilize the material at around a temperature level greater than the temperature of the fuser nip region that contacts the media sheets but less than a temperature which may adversely affect the performance or longevity of the fuser components.
The above-mentioned and other features and advantages of the various embodiments, and the manner of attaining them, will become more apparent and will be better understood by reference to the accompanying drawings, wherein:
The following description and drawings illustrate embodiments sufficiently to enable those skilled in the art to practice it. It is to be understood that the subject matter of this application is not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The subject matter is capable of other embodiments and of being practiced or of being carried out in various ways. For example, other embodiments may incorporate structural, chronological, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The scope of the application encompasses the appended claims and all available equivalents. The following description is, therefore, not to be taken in a limited sense, and the scope of the present application as defined by the appended claims.
Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings.
Panel member 402 may be, for example, shaped as a rectangular prism having substantially the same rectangular cross section along its length L402. As shown in
Conventional ceramic fabrication processes may be utilized to produce the doped barium titanate composition of panel member 402. Example processes may include tape casting, roll compaction, slip casting, dry pressing and injection molding. Though the selection of a particular process may be based upon a number of factors, tape casting is believed to include economic benefits over some other processes for the production of fuser heating elements for electrophotographic imaging devices.
Each electrode 404 may be mechanically, thermally and electrically coupled to a distinct major surface 402a. For example, electrodes 404 may be attached to panel member 402 using a ceramic glass cement or other adhesive. A width W404 and length L404 of electrode 404 may be sized to extend substantially along the fuser nip region in a paper feed direction and a direction substantially orthogonal thereto, respectively. In one example embodiment, the length L404 of electrode 404 may be between about 200 and about 230 mm, and in an example embodiment may be between about 208 mm and about 222 mm. Width W404 of each electrode 404 may be between about 5 mm to about 20 mm, and in one example embodiment may be between about 6.5 mm to about 15 mm. Each electrode 404 may be coupled to at least one wire or the like for providing a voltage across panel member 402.
As shown in
Because heater housings, tubular belts and backup rolls of fuser assemblies are well known, such components will not be discussed in detail herein for reasons of simplicity.
Conductors 404 of heating element 400 may be coupled, either directly or indirectly, to an AC power source 510 which may be controlled by a controller 512. In this way, an AC voltage, such as a 120 v or 240 v, may be applied across panel member 402.
The operation of fuser assembly 500 will now be described. During a fusing operation, backup roll 506 rotates about its axis, which causes belt 504 to rotate due to contact with backup roll 506. An AC voltage from AC power source 510 is applied across panel member 402, which causes a certain current to flow between conductors 404 and heat to be generated by panel 402 as a result. The voltage across panel member 402 may fall within temperature range TR having little variation in electrical resistivity.
Referring to
Further, heating element 700 may include a protective layer 706 disposed over a second side 704b of substrate 704, as shown in
Operation of a fuser assembly having heating element 700 follows the operation of fuser assembly 500 described above. An AC voltage applied across sections 702 creates a temperature falling within a predetermined operating range, such as temperature range TR, for the fuser assembly. When narrower media sheets S are passed through the fuser assembly, regions of the fuser belt and corresponding backup roller increase in temperature, which increases the temperature of sections 702 adjacent thereto. The increase in temperature of such sections 702 above the predetermined temperature range TR and into the portion of the electrical resistance-temperature curve corresponding to an approximately exponential relationship, results in an increase in the electrical resistivity of sections 702 having increased temperatures. The increase in resistivity causes the amount of current through and hence the temperature of such sections 702 to decrease, thereby serving to stabilize the temperature of the sections 702 at a steady state temperature value that is less than a temperature that would otherwise be experienced. As a result of experiencing reduced temperatures, the belt and backup roller will not substantially overheat and become damaged.
Heating element 800 may further include electrodes 820 which extend along length L of panel member 810. As shown in
The intermediate transfer member 18 is formed as an endless transfer belt supported about a plurality of support rollers 36. During image forming operations, transfer member 18 moves in the direction of arrow 38 past the plurality of image forming stations 20y, 20c, 20m, and 20k for printing with yellow, cyan, magenta, and black toner, respectively. Each image forming stations 20y, 20c, 20m, and 20k applies a portion of an image on the transfer member 18. The moving transfer member 18 conveys the image to a print media at the second transfer area 22.
The media tray 14 is positioned in a lower portion of the main body 12 and contains a stack of media. The media tray 14 is removable for refilling. Pick mechanism 16 picks print media from top of the media stack in the media tray 14 and feeds the print media into a primary media path 40. The print media is moved along the primary media path 40 and receives the toner image from the transfer member 18 at the second transfer area 22.
Once the toner image is transferred, the print media is conveyed along the primary media path 40 to the fuser assembly 500, having heating elements 400 or 700. The fuser assembly 500 fuses the toner to the print media and conveys the print media towards the exit rollers 26. Exit rollers 26 either eject the print media to the output tray 28, or direct it into the duplex path 32 for printing on a second side of the print media. In the latter case, the exit rollers 26 partially eject the print media and then reverse direction to invert the print media and direct it into the duplex path 32. A series of rollers in the duplex path 32 return the inverted print media to the primary media path 40 upstream from the second transfer area 22 for printing on the second side of the media. The image forming apparatus 10 also includes a controller 42 that provides instructions to the imaging device 10 for performing imaging.
The foregoing description of multiple embodiments has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the application to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is understood that the subject matter of the present application may be practiced in ways other than as specifically set forth herein without departing from the scope and essential characteristics. It is intended that the scope of the application be defined by the claims appended hereto.