Patent Application
20110194867
This invention relates in general to a fuser assembly for an electrographic reproduction apparatus, and more particularly to a fuser assembly including a cooling system for effectively cooling the fuser to regulate the fuser temperature.
Wrinkles and image defects are unwanted side effects often encountered in the use of a heated roller fuser in an electrophotographic printer (EP). In typical commercial reproduction apparatus (electrostatographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fuser assembly for typical electrographic reproduction apparatus includes at least one heated roller, having an aluminum core and an elastomeric cover layer, and at least one pressure roller in nip relation with the heated roller. The fuser assembly rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member and then is permanently fixed to the receiver member.
Wrinkles and image defects can be caused by differential overdrive in the fuser nip. Overdrive is caused by deflection of the incompressible elastomer on either or both the fuser roller and pressure roller when the fusing nip is formed and the rollers are rotated. Differences in elastomeric deflection along the axes of the fuser and pressure roller cause corresponding differences in differential overdrive and thus substrate velocity, which in turn cause wrinkles or image defects. Specifically, when the center of the substrate is driven faster than the edges, the trail edge of the substrate will collapse and form wrinkles as the substrate passes through the fuser nip. When the edges of the substrate are driven faster than the center, the trail edge of the substrate will “slap” up or down and smear the image as the image is fused.
Several methods are used to prevent wrinkles and image defects. One common method is to vary the diameter of the fuser or pressure roller along the roller length to reduce the nominal amount of differential overdrive in the nip. Another method is taught in U.S. Pat. No. 5,406,362, where the force that forms the fuser nip is applied inside the ends of one of the rollers in order to impart a bending moment to one of the rollers which in part counteracts the deflection of the fuser and pressure rollers as the nip forming force is applied.
The problem of differential overdrive and resulting wrinkles and image defects is further complicated by temperature differences along the fuser and pressure roller axis, which in turn cause differences in overdrive due to thermal expansion of the elastomer on at least one of the rollers. In addition, the amount of thermal expansion increases during a print run, as heat is continually applied by the fuser lamp(s) to the rollers. Differential thermal expansion is further varied by the width of the substrate. Narrower substrates, as the substrate passes though the fuser nip, causes the ends of the rollers to increase in temperature and thus thermal expansion, since no heat is removed by the substrate outside its path through the fuser nip. The increased thermal expansion of the ends of the roller(s) increases overdrive on the edges of the paper, causing image defects as described.
Another method of improving axial temperature uniformity in a roller fuser is taught in U.S. Pat. No. 6,289,185, where multiple lamps having different filament lengths are used compensate for differences in substrate width. Still another method is taught in U.S. Pat. No. 7,054,572, where the middle of a fuser roller is cooled prior to a print run, to simulate the removal of heat by the substrates, so that axial roller temperatures and resulting differential overdrive is reduced during a subsequent print run.
These methods are not sufficient to prevent all wrinkles and image defects under all conditions, including changes in ambient relative humidity. These problems are especially evident in certain circumstances, such as when heater rollers having thick walls are used to externally heat the fuser roller because the roller transfers heat so well along the axis of the rollers that lamps of different filament length have only a minimal effect on the temperature differential along the fuser roller. Further problems arise due to a lack of access to the middle of the fuser roller because of the placement of other components such as oilers, skives, temperature sensors and cleaners that are necessary for fuser operation.
This controlled fuser system and related method solves these problems by using strategically placed and controlled fluid directed one of a fuser roller and/or heater rollers such that one or more fusing parameter controls the system, such as cooling air directed at the ends of these rollers based on a receiver sheet width.
The present invention is in the field of electrophotographic printers and copiers. More specifically this invention relates to a temperature controlled fuser apparatus used to fuse an image on a receiving sheet. 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.
Referring now to the accompanying drawings,
The electrographic printer engine P has a series of electrographic printing modules M1, M2, M3, M4, and M5. As discussed below, each of the printing modules forms an electrostatic image, employs a developer having a carrier and toner particles to develop the electrostatic image, and transfers a developed image to a receiver member S. Where the toner particles of the developer are pigmented, the toner particles are also referred to as “marking particles.” The receiver member may be a sheet of paper, cardboard, plastic, or other material to which it is desired to print an image or a predefined pattern. In one embodiment of the invention (not shown) a fusing module is interspaced between at least two of the printing modules.
The electrographic printing modules M(1-5) shown in
The roller fuser assembly 10 includes a fuser roller 12, a pressure roller 14, and other necessary sub-systems and components (not shown). The roller 12 (or both rollers 12 and 14) is heated internally (for example by lamps 16, 18) to preset temperatures and is cooled using a cooling system 20. The fuser roller can be heated in a variety of means including internally and/or externally or even with a non-contact heater, such as an infrared or ultraviolet source of heat. One means of externally heating the fuser roller includes the heating external heat rollers (as shown in
When fusing prints on receiver members S, the rollers 12 and 14 are pressed together to form a nip, and rotation of the rollers drive prints through the nip. In the nip, heat energy stored in the fuser roller 12 is transferred to the prints, and heats up and melts the toner image carried by the receiver member so that the toner is fixed on the receiver member under controlled temperature and pressure conditions.
The fuser roller, as well as the external heater rollers, has end portions and a middle portion. The fuser roller fixes the image on the receiver. The optional one or more external heater rollers are in contact with the fuser roller. In one embodiment one or more nozzles are directed at the fuser roller and/or the external heater rollers, to direct pressurized fluid toward the fuser roller based on fusing parameters. The system also has a controller to control at least a fuser run condition and a fuser idle condition to control the amount of fluid directed through the nozzles to cool the ends of external heater roller(s) relative to the middle portion starting and ending at predetermined times during the fuser run condition as will be discussed in more details below.
In one example if the air flow is initiated at the beginning of a print run in sufficient quantities of cooling air it reduces the temperature increase at the ends of the fuser roller during a print run, and eliminates image defects, even at conditions that generated substantial image defects before addition of the cooling air. The controlled fuser system has to regulate the air temperatures, flow rate, flow pressure and/or a nozzle location since these fusing parameters all effect the cooling rate and final temperature of the fusing roller. For example, the amount and temperature of cooling air that is directed at the heater rollers is at a different temperature since the temperature of the external heater rollers is much higher than that of the fuser roller, and thus it is necessary to remove more heat with a given amount of cooling air at a given temperature, compared to directing the air at the fuser roller.
The controlled fusing system has of two sets of air (or “cooling fluid”) applicators, with a temperature sensor mounted in conjunction with one of the applicators, directed at opposite ends of at least one heater roller of an externally heated fuser. In one type of electrophotographic printer with center paper registration, the two cooling fluid applicators move equally in opposite directions to adjust to different substrate sizes, as determined by a paper supply or sensor in the paper path. In another type of electrophotographic printer with edge paper registration, only one cooling fluid applicator would be required. Cooling fluid (most practically air) flows to the applicators is controlled by a regulator that is controlled by the temperature sensor. In one embodiment the cooling fluid is supplied and is equally split between the two applicators by conventional means.
The configuration of the fuser roller 12 can greatly affect the receiver member release characteristics and heat transfer of the fuser. Generally the fuser roller 12 has a metal core 22, a base cushion 24, and a thin release topcoat 26. A thicker base cushion makes release geometry in the nip area more favorable for the receiver member to be released from the fuser roller 12, but makes the heat more difficult to transfer from the core 22 to the outer surface of the topcoat 26.
In another embodiment of the fuser as shown in
This embodiment helps to preserve the favorable release geometry and improve the heat transfer characteristics, and may have one or more heating lamps 30 inside the heater rollers. The external heating rollers 28 can be metal and thus have high thermal conductivity and can transfer higher amount of heat than other external heating methodologies, such as radiation heating. They are also simple, less expensive, and present less potential fire hazards. However, since the external heating rollers 28 usually have small diameter, it is difficult to provide a large nip between an external heating roller and a fuser roller. This limits the heat transfer rate between an external heating roller 28 and a fuser roller 12. Furthermore, a high force between the external heating roller 28 and the fuser roller 12 may cause wear and damage to the fuser roller topcoat 26. The system is controlled relative to one or more fusing, fuser related parameter that is related to one or more of a print run and printer idle condition, an image formation parameter, a gloss-related parameter, a receiver property or other printing related conditions.
In the embodiment show in
The adjustment of the cooling location, in one example, is made for the various widths of the paper by moving the two nozzles so that the air impinges on the roller. The fluid flow rate would preferably be kept constant. However, if desired, the fluid flow rate could be adjusted for the varying roller lengths to be cooled by varying the pressure applied to the fluid in a predetermined relationship to the length of the roller to be cooled. If desired, the pressure can be proportional to the length of the roller to be cooled. This technique can be used to cool portions of either the fuser roller or the heater roller. Alternatively, the nozzles can also contain adjustable orifices to maintain a constant fluid flow per unit length of the portion of the roller to be cooled. Specifically, the area of the nozzle opened by the orifice should be proportional to the length of the portion of the roller to be cooled.
Cooling must be done from the minimum width specified in the disclosure and extend to at least one inch on either side of the size of the paper being fused. Thus, an 8½ by 11 inch sheet of paper would require that the roller be cooled from a distance of one inch inside the edge of the paper path to at least one inch beyond the edge of the paper path up to the extent of the roller.
One embodiment of the current invention allows the fuser roller to be heated to within 85% of a nominal running temperature. In one example the heater roller is also used to obtain the nominal operating temperatures, which is preset for the specific printing conditions, along the length of the fuser roller so that the fuser roller is heated to one or more temperatures such as approximately 85% of the nominal operation temperature.
The fuser roller temperature control sensor is also shown in the top view. This sensor controls the fuser roller temperature at the center of the fuser roller by varying the duty cycle of the lamps (not shown) located inside the heater rollers, as is common in the art. The reason for showing both temperature control sensors is to differentiate between their functions. The existing sensor in the center of the fuser roller is used for heating the entire fuser roller while the new temperature control sensor near one edge of the fuser roller is used for cooling the ends of the fuser roller.
The temperature control sensor for cooling is shown in the exact same position (along the axis of the fuser roller) as the cooling fluid applicator in this illustration. The temperature control sensor for cooling could also be biased with respect to the cooling fluid applicator within the scope of the invention, but must move axially in conjunction with the cooling fluid applicator.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
This application relates to commonly assigned, copending U.S. application Ser. No. ______ (Docket No. 96117DPS), filed ______, entitled: “SELECTIVE COOLING OF A FUSER” hereby incorporated by reference.
