Electric heating – Heating devices – Combined with diverse-type art device
Reexamination Certificate
2002-02-22
2003-11-18
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with diverse-type art device
C399S329000, C399S334000
Reexamination Certificate
active
06649874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to machines, including laser imaging and printing devices. More specifically, the present invention relates to toner-media fusing units used in laser imaging and printing devices and the use of the user non-perceivable light sources therein.
2. Description of the Related Art
Laser printers and other imaging devices that employ toner transfer and toner fusing technology all rely upon a fusing unit to adhere toner particles, which form the images to some type of media, such as paper. The fusing operation makes the toner-transferred image durable and permanent. Techniques used for toner fusing employ heat and pressure to fuse the toner particles to the media. Current fusing technologies employ a two-roller arrangement that utilize a pressure roller and a heating (or fusing) roller. The two rollers are urged together with a predetermined amount of force. At least one of the rollers is driven to rotate. The combined pressure and rotation of the two rollers pinch and convey the media while heat and pressure serve to fuse the toner particles to the media.
There are two dominant technologies applied in fusing units. Both utilize a pressure roller and fusing roller. Typically, the fusing roller is located relative to the side of the media upon which the toner particles are deposited. Both rollers have a length at least as long as one of the media dimensions. In both technologies, the pressure roller consists of a rigid core, followed by a rubber or rubber-like covering that is coated with a release compound. The release coating prevents residual toner adhering to the fusing film from transferring to the pressure roller and thereby being inadvertently transferred to the back side of the media during subsequent print jobs. The pressure roller brings physical pressure against the fusing roller. The pressure is typically produced using spring force. In operation, toner is deposited on the media, which is usually paper, in advance of the fusing operation. The media is urged toward the pinch point of the pressure roller and fusing roller. The flattened area between the rollers is referred to as the nip of the rollers by those skilled in the art. As the media traverses the rollers, heat and pressure fuse the toner to the page. In a typical letter-sized paper printer, the fusing temperature is in the 150-200° C. range and the force applied to the pressure roller is in the 10-15 kilogram force range for 9 inch pressure rollers.
In the first of the two dominant technologies, a ceramic heating element is used to heat the fusing roller. The ceramic heating element is a resistive heating element that is adhered to a ceramic substrate that has a long and narrow configuration. It produces the required fusing heat. The ceramic heating element is supported by a fixed and rigid support structure, usually fabricated from sheet metal, inside of the fusing roller covering. The ceramic heating element and its support structure do not rotate. The fusing roller is a flexible, tubular shaped structure formed from a suitable fusing roller material. The basic circular shape of the flexible fusing roller/film is maintained by the fixed and rigid support structure and the ceramic heater. The fusing roller covering does rotate in synchronous with the pressure roller. The fusing roller material has certain physical, electrical, and thermodynamic characteristics, which are appreciated by those skilled in the art. In particular, the material possesses good heat transfer characteristics, has a smooth exterior finish so that particles are not captured by its surface, can withstand the heat used in the fusing operation, and has electrostatic and other electrical properties consistent with the general principles of electrostatic toner management. Such principles are understood by those skilled in the art. Mylar, Polyester, and Polyamide materials coated with Teflon and TFE thermoplastics are suitable fusing roller materials, for example. The outer surface of the fusing roller contacts the media at the pinch point with the pressure roller. The ceramic heating element contacts the interior surface of the fusing roller at the same position as the media contacts the exterior surface. The fusing roller material is thin, which is useful to provide good heat transfer characteristics. The dominant heat transfer mechanism in a ceramic heater fusing unit is thermal conduction.
The second of the two dominant fusing technologies employs a bulb heating element instead of a ceramic heating element. The second dominant technology uses the same type of pressure roller. The fusing roller for a bulb heating element employs a rigid metallic tube to form the roller, which may be fabricated from aluminum or other suitable metal. The roller is covered with a fusing film that is adhered directly to the surface of the metallic tube. The fusing film has essentially the same physical, mechanical, and thermodynamic characteristics as the aforementioned fusing roller material. The fabrication process differs because the film is applied to a rigid metal tube. A long light bulb is disposed within the fusing roller tube. The light bulb produces visible light and radiant heat when it is energized. The metallic tube and fusing film rotate, while the bulb heater does not rotate. The light and heat couple to the inside surface of the metallic tube. The principle coupling mechanism is thermal radiation. The metal tube then conducts the heat through the roller to the media as it traverses the pinch point between the fusing roller and the pressure roller. In a letter-sized paper printer, the light bulb heating element is approximately 8-9 inches long and about ¼″ in diameter. The bulb comprises several filaments, each about an inch long.
While both of the ceramic heater and bulb heater fusers perform the desired fusing function in a toner imaging device, there are significant design trade-offs between the two. Bulb heaters are characterized by lower cost, often better robustness and reliability, and longer warm-up times. Ceramic heaters are characterized by higher cost and shorter warm-up times. The brittle nature of ceramic, along with its other mechanical properties, may result in reliability issues in some ceramic heater designs. This is due to the stresses of temperature cycling over many print jobs and the high pressures imparted by the pressure roller onto the ceramic substrate. The desire for low cost and high reliability is an obvious design choice. The desire for short warm-up time involves two concepts. First is the desire to reduce power consumption of the imaging device. The fuser heater draws a large amount of power, so it is very desirable to shut the heat off during idle periods. This implies that the fuser heater must warm-up prior to each printing operation. Thus, there is a desire to produce a short fuser heater warm-up time so that the time duration to the first page output after a printing operation is initialized is as short as possible. This is known as the “time to first page out” by those skilled in the art. In fact, the time to first page out is an important perceptual aspect of the apparent performance of a laser-imaging device in the minds of consumers. Modern ceramic heater fuser devices achieve a time to first page out on the order of 10 seconds from a cold start. Bulb heater fuser devices have times to first page out in the 20-50 second range from a cold start.
Thus, it can be appreciate that there is a need in the art for an apparatus and method that uses lower cost bulb heater fusers while maintaining the performance and low time to first page out of ceramic-based fusers.
Further, as is well known in the art, laser print engines are utilized in a variety of machines, including laser printers, facsimile machines, laser photocopying machines, multi-function peripheral devices, and other business, office and home imaging machines. These machines typically include control panels, indicators and other user interface components, many of
Hewlett--Packard Development Company, L.P.
Pelham Joseph
LandOfFree
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