Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
2001-03-12
2004-02-24
Ngo, Hoang (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C399S107000
Reexamination Certificate
active
06697589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrophotographic imaging apparatus, and, more particularly, to a latch mechanism securing the fuser unit in the apparatus.
2. Description of the Related Art
In the electrophotographic process commonly used in printers and the like, an electrostatic image is created on photosensitive material such as a belt or a roll. Tiny marking particles, called toner, are applied to the electrostatic image on the photosensitive material. In a monochrome printer, toner is applied in a single station, as only black toner is used. However, in a color printer, separate application stations are provided for black, magenta, yellow and cyan toners. The toner image is then transferred to the desired media, which may include paper, cardstock, envelopes, transparencies or the like. The applied toner image is not, however, permanent until the toner particles are fixed to the receiving media.
To permanently adhere the toner to the media, the media with the toner image thereon is passed through a fuser unit, in which heat and pressure are applied to the toner image. The heat causes constituents of the toner to flow into the pores or interstices between fibers of the media. Pressure in the fuser promotes settling of the toner constituents into these voids. As the sheet exits the fuser, the toner is cooled and solidified, adhering the image to the media.
A commonly used fuser assembly is a roll fuser, which includes two rolls nipped together, with at least one of the rolls being internally heated. The non-heated roll, or back-up roll, is urged against the hot roll, to form a fuser nip through which the media passes.
As a result of the conditions present in the fuser, including high temperature and high pressure, components of the fuser system may have a life span shorter than other machine components, and shorter than the expected life of the base machine. Therefore, it is expected and required that the fuser or various components thereof will be replaced periodically during the useful life span of the machine. To ease replacement of the expired fuser components, various components are unitized, that is the replaceable components are included in a single unitary assembly having a frame and mounting structures compatible with receiving assemblies and structures in the base machine. When replacement is required, locking components are released, the expired fuser unit is removed, a replacement fresh fuser unit is installed and the locking components are re-engaged.
In past fuser designs, it is known for replacement of the fuser to be a service event performed by trained maintenance personnel. However, with more refined unitization of components, and the standardization of life expectancy for various components of the fuser unit, it is desirable that fuser units be designed to be replaced by the customer. Such units are referred to as a CRU or customer replaceable unit. In designing a CRU, it is necessary that the unit be removed and inserted into the base machine easily and accurately, and that it be sufficiently robust to take reasonable amounts of abuse from an untrained installer. Further, it is essential that the CRU be accurately and easily positioned relative to mating components of the base machine when latched into the base machine. Mating drive gears, paper guides and the like must relate accurately and precisely, to minimize misalignment and allow the machine to perform reliably. Even slightly misaligned gears can wear significantly in a short period of time, and fail prematurely. Misaligned paper paths can cause paper jams.
Although computer equipment, such as a printer, is packaged for shipment in a strong shipping container, with packing material limiting movement of the equipment in the container, the containers can be dropped, bumped or jostled during handling and delivery. Even though the printer housing is stabilized within the container, if the container is dropped, a shock can be transmitted to the internal components of the printer. In new office layouts, cubicles, workstations and the like are frequently moved and rearranged. Computer and printing equipment also must be portable and capable of rearrangement and moving. Printers have become smaller, lighter and more easily and conveniently moved. However, equipment may be moved by untrained personnel, even the user, and during a move a printer can be jarred while being transported from one location to another. Therefore, it is essential that a fuser CRU be adequately secured in the housing to withstand a relatively jarring event, such as if the printer is bumped or dropped.
Known latching schemes for fuser CRUs include conventional screws, thumb screws, levers and ninety degree latches. While most of these latching schemes work adequately to retain the fuser in the machine housing, each has drawbacks in design or use. The major drawback of a plain screw latching scheme to retain the fuser in the housing is that the customer is required to use a tool for detaching the expired unit and attaching the replacement unit to the machine. For any customer performed service, it is desirable to eliminate the need for tools, as appropriate tools may not be conveniently available and untrained personnel performing the service may not be comfortable or skilled in using the required tool.
A drawback to the use of plain screws and thumb screws in the latching schemes for fuser CRUs is the possibility of stripping or damaging the threads during use. The untrained user may over-tighten either a conventional screw or a thumb screw, particularly if the user selects a powered driver for operating the screw. Further, screw assemblies often include the use of a metal insert in a plastic part, and insertion of the screw may result in detachment of the metal and plastic components. If threads or inserts are damaged, the fuser will not be located or restrained adequately. Further, if conventional or thumb screws in different parts of the CRU are not similarly tightened, the fuser may skew and bind during insertion or operation. For these and other reasons, neither conventional screws nor thumb screws are desirable latching schemes for fuser CRUs.
Both levers and ninety degree latches are more intuitive and less prone to assembly problems than conventional screws or thumb screws. A drawback to the use of levers and ninety degree latches in latching schemes for fuser CRUs is the size and cost of the lever system or ninety degree latch. To achieve adequate mechanical advantage for levers and latches, to minimize the effort required to perform the latching process, the levers and latches must have a reasonably long length from a pivot or fulcrum point to the force application position. The length or size of the lever or latch systems often take valuable space in the machine, working against the desire to make printers smaller and more compact. Further, if the latch mechanism is to restrain the fuser during a drop event, the strength requirements for the lever or latch mechanism can become relatively expensive. To reduce cost, it is known to use plastic latches in combination with metal tabs on the machine frame to restrain the fuser. However, drawbacks to this solution include the requirement that the customer lift the relatively heavy CRU fuser over the tabs in the machine in order to remove the fuser, and to install the new fuser, which can be awkward and non-intuitive. The user can be confused as to how to properly perform the operation. The need to consult a user manual is undesirable, as the user manual may become separated from the machine, and many users will not willingly take the time to consult written instructions. Further, the tolerances from the formed tab on the machine base to the fusers mating components are substantial, making it difficult to control the fuser final resting position.
Therefore, what is needed is a fuser latch system that is intuitive and easy to operate, both for disengagement and reengagement of fuser CRUs, and which accurately positions the CR
Dunning Gordon Robert
Horrall Paul Douglas
Rush Edward Alan
Brady John A.
Lexmark International Inc.
Ngo Hoang
Taylor & Aust PC
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