Patent Application
20060067752
1. Field of the Invention
The present invention relates generally to electrophotographic imaging devices and, more particularly, to fusers of electrophotographic imaging devices.
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 final permanent image. The toner image is fixed to the media by the application of heat and pressure in a fuser. A fuser may include a heated roll and a backup roll forming a fuser nip through which the media passes. A fuser may also include a fuser belt and an opposing backup member, such as a backup roll.
In color EP imaging, time to first print from cold start is an important factor. If the time to first print is short enough, the printer need not use standby mode, and therefore significantly reduces power usage. The environmental impact of reducing power usage has led to the “Energy Star Program” developed by the “Sustainable Energy Development Authority” (SEDA). SEDA is a New South Wales Government agency that runs in conjunction with the USA Environmental Protection Agency (EPA). These governmental agencies promote the reduction in power usage by setting the Energy Star rating for low power.
Energy Star specifications and a desire for fast first copy times require that fusers be ready for printing from room temperature in seconds, not minutes. Conventional roller fusers are unable to meet this requirement due to large thermal masses. A belt fuser using ceramic or inductive heating heats up very quickly and can be ready for printing within 20 seconds. Normally such belt fusers are used in mid-range mono or low-speed color applications. Either the belt temperature cannot be kept high enough to achieve good fusing quality for high speed printing or the printing speed has to slow down to prevent portions of the belt from overheating.
The empirical test results illustrated in
In current belt fusers, when a print job is initiated and the backup roller is cool, the operating temperature is elevated over the normal steady state temperature by as much as 50° C. The excessively high temperatures required for fusing with a cool/cold backup roller can cause the belt to heat to such a temperature that material failure will occur prematurely and the belt will not meet fuser life requirements. For belts coated with silicone rubber, the primer layer between the base layer and the silicone rubber layer is one typical weak point. Another point of possible failure is between the PFA sleeve and the base/silicone rubber layer, if such a sleeve is used in the belt construction. For polyimide belts, material failure occurs in the form of belt buckling or tearing at the edges.
What is needed in the art is a belt fuser which has an increased thermal extendibility with improved print quality.
To increase belt fuser thermal capability, the present invention provides a belt fuser with a heated backup roll. Using a heated backup roller allows heat to be conducted to media from both sides; reducing fusing temperature requirements of the belt. As the backup roller is maintained at a higher temperature than a non-heated backup roller, belt temperatures for jobs from cool starting conditions need not be excessively high. The fuser belt may be heated with a ceramic or inductive heater, and the backup roll may be heated with a lamp or inductive heater.
The invention comprises, in one form thereof, an electrophotographic imaging device, including a print media transport assembly, and a fuser positioned in association with the print media transport assembly. The fuser includes a first heater assembly; a belt positioned around and adjacent to the first heater assembly; a backup roll positioned in opposition to the first heater assembly on a side of the belt opposite the first heater assembly, the belt and the backup roll defining a fusing nip therebetween; and a second heater assembly positioned in association with the backup roll.
The invention comprises, in another form thereof, a method of operating a fuser of an electrophotographic imaging device, including the steps of: transporting a print medium to the fuser; carrying the print medium through a fusing nip between a belt and a backup member; and heating toner particles on the print medium using a first heater assembly positioned on a side of the belt opposite the print medium, and a second heater assembly positioned in association with the backup roll.
An advantage of the present invention is that the belt fuser and heated backup roll combination provides a higher thermal extendibility to allow the belt fuser to meet high speed printing requirements.
Another advantage is that the belt fuser with heated backup roll reduces paper curl.
Yet another advantage is that the belt fuser with heated backup roll eliminates belt stalls due to water condensation on the backup roll.
A further advantage is that the belt fuser with heated backup roll allows for higher gloss printing at printing speeds of 32 pages per minute or greater.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings and particularly to
Paper transport belt 16 transports an individual print medium to fuser 30 where the toner particles are fused to the print medium through the application of heat and pressure. Fuser 30 includes a first heater assembly 32, flexible belt 34 carried by heater assembly 32, backup roll 36, and a second heater assembly 38. In the embodiment shown, backup roll 36 is a driven roll and belt 34 is an idler belt; however, the drive scheme may be reversed depending upon the application. Belt 34 and backup roll 36 define a fusing nip 40 therebetween.
Referring now to
Referring to
Belt 34 includes a polyimide layer, and optionally may include a metal layer and/or a silicone layer. Belt 34 also preferably includes a release layer in the form of a PFA or PTFE coating, or a PFA sleeve (PFA is a perfluoroalkyl vinyl ether copolymer, and PTFE is polytetrafluoroethylene).
Backup roll 36 has a metallic core and an elastomeric covering, but may be differently configured. Techniques for the general concept of rotatably driving backup roll 36 using gears, belts, pulleys and the like (not shown) are conventional and not described in detail herein.
Second heater assembly 38 is a lamp heater in the form of an incandescent lamp. Second heater assembly 38 has a power level of between approximately 400 to 900 watts, and preferably approximately 600 watts.
Referring to
Referring to
Referring to
During fusing, toner particles are transferred from ITM belt 18 to a print medium. The print medium with toner particles is transferred to fusing nip 40, where heat is applied to one side of the print medium by belt 34 and to the other side of the print medium by backup roll 36. Belt 34 and backup roll 36 are respectively heated by first heater assembly 32 and second heater assembly 38.
Current color belt fusing systems use expensive belts and heating methods, yet still suffer from significant print quality issues. Although time to first print has been reduced dramatically providing quick heating fusing systems, high gloss images cannot be achieved, and significant gloss variation is observed. Also the transmittance on transparencies is poor and could be considered unacceptable. High speeds over 32 ppm have not been achieved in ceramic heated color belt fusing systems. The use of belt fuser 30 with heated backup roll 36 described above provides an instant-on belt fusing system that has increased thermal extendibility.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
