Sheet feeding or delivering – Feeding – Pack holders
Reexamination Certificate
1999-07-22
2001-04-17
Valenza, Joseph E. (Department: 3651)
Sheet feeding or delivering
Feeding
Pack holders
C271S162000, C271S213000
Reexamination Certificate
active
06217018
ABSTRACT:
FIELD OF INVENTION
This invention relates to a sheet feed mechanism for feeding sheet media in a printing device.
BACKGROUND OF THE INVENTION
In printing devices, such as computer printers and plain-paper fax machines, a sheet of media (e.g. paper, transparencies) is transported from an input tray to a printing engine where the sheet receives graphic or text markings. The sheet is then transported into an output tray.
FIG. 1
illustrates a known type of sheet feed mechanism
5
. The input tray
10
accommodates a stack of sheet media
12
, and a pick mechanism comprising a friction roller
14
is employed to pick individual sheets from the stack and advance the sheets along a media path
16
. To effectively transport a media sheet, it is desirable that the sheet does not slide relative to the friction roller
14
surface. It is also desirable that individual sheets be transported in series rather than being one of multiple overlapping sheets. To avoid sliding and multiple-sheet picking, the pick mechanism is configured so that the friction roller applies a normal force N to the media.
The normal force of the friction roller on the media may be achieved by spring-loading the friction roller, or by allowing the weight of the friction roller to act directly on the stack. With the normal force applied, a drive motor rotates the friction roller in an anti-clockwise direction to pick and advance the top-most sheet of the stack. A gear mechanism may be employed to couple the drive motor to the friction roller.
Some friction rollers have a continuous elastomeric surface contacting the media along the roller length. Other friction rollers may include several elastomeric surfaces in parallel (e.g. “tyres”) along the roller length. The friction roller preferably has a high friction surface. To achieve a high friction surface, it is desirable to provide a high coefficient of friction (COF) between the roller and the media sheet. Factors affecting the COF include the base material of the roller surface, adjunct materials added to or modifying the base material, the finish of the surface, and cleaning chemicals applied to the surface during its useful lifetime. A drawback with the friction roller is that over time the COF reduces due to paper fibres, dirt and other contaminants interacting with the roller surface.
FIG. 2
illustrates the sheet feed mechanism of
FIG. 1
with the stack of media exhausted. The media stack may be replenished by manually sliding out the tray
10
in a direction B, adding a fresh stack of paper, and sliding the tray back to its operational position. The replenishing process has a drawback due to the floor of the tray dragging against the friction roller as the tray is slid out. This dragging action forces the friction roller in a clockwise direction opposite to the normal anti-clockwise pick direction of the roller, which in turn can result in permanent damage to the drive motor or the gear mechanism. Sometimes, the dragging action can be so strong as to strip the teeth from the gears of the gear mechanism.
In an attempt to solve the problem of the tray floor dragging against the roller, a known sheet feed mechanism includes a withdrawing mechanism which simultaneously lifts or withdraws the friction roller away from the sheet stack as the tray is withdrawn. However, the applicant has found in practice that users frequently remove the in-tray at excessive speeds, sometimes in order to replenish the media stack before the printer signals a “paper out” error. In these situations, the inertia of the withdrawing mechanism prevents the friction roller from being lifted quickly enough to avoid the dragging action of the tray floor. Accordingly, the motor and gear mechanism can still be damaged. Sometimes, the frictional force produced by the dragging action of the tray floor can actually hold the roller in place against the withdrawing action of the mechanism.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a sheet feed mechanism for feeding sheet media in a printing device, comprising a slidably retractable tray having a floor for supporting a stack of sheet media, and a pick mechanism including a friction roller for picking individual sheets from the stack of sheet media and advancing the sheets along a media path, the pick mechanism being configured such that in use the friction roller applies a compression force on the stack of sheet media to increase the friction force between the friction roller and the top sheet of the stack, whereby upon the stack of media being exhausted, the friction roller applies a compression force directly on the tray floor, characterised in that the tray floor includes a surface adapted to reduce the coefficient of friction between the friction roller and said surface in a region where the friction roller applies the compression force.
A sheet feed mechanism in accordance with the invention has the advantage that compared to existing sheet feed mechanisms, the adapted surface of the tray floor provides a reduced coefficient of friction between the friction roller and the tray floor. This reduced coefficient of friction decreases the frictional force between the tray and the friction roller when the media is exhausted. Thus the drive motor or the gear mechanism are less likely to become damaged if the tray is retracted.
Ideally, the adapted surface of the tray floor is knurled and includes a series of peaks and troughs. Preferably, the adapted surface is ridged with the ridges running in the direction of the friction roller.
A sheet feed mechanism in accordance with the invention also has the advantage that the peaks and troughs in said region of the tray floor provide a suitable abrasive surface for removing paper fibres, dirt and other contaminants built up on the friction roller. This abrasive surface acts on the friction roller as the tray is retracted. Thus, the adapted surface can further restore the high friction surface to the friction roller during operation of the printing device.
Ideally, the tray is slidably retractable from the printer device and the pick mechanism. The sheet media is preferably advanced in a direction generally opposite to the direction in which the tray may be retracted.
In a preferred embodiment, the pick mechanism includes a withdrawing mechanism that releases the compression force of the drive roller as the tray is retracted. Suitably, the pick mechanism includes a drive motor coupled to the friction roller. The pick mechanism may also include a gear mechanism that couples the drive motor and the friction roller. The gear mechanism may comprise a worm gear, and a clutch which decouples the friction roller and the drive motor in the non-pick direction of relative rotation between the friction roller and the drive motor.
In a first embodiment, the ridged surface has a saw-tooth like profile. In a second embodiment, the ridged surface has a triangle-wave like profile. In a third embodiment, the ridged surface has a square-wave like profile.
Ideally, the sheet feed mechanism is incorporated in a printing device, such as a computer printer or a plain-paper fax machine.
REFERENCES:
patent: 5370380 (1994-12-01), Suzuki et al.
patent: 5485991 (1996-01-01), Hirano et al.
patent: 5527026 (1996-06-01), Padget et al.
patent: 5547181 (1996-08-01), Underwood
patent: 5669601 (1997-09-01), Fisher
patent: 5951180 (1999-09-01), Kawaura
patent: 6082002 (2000-07-01), Belon et al.
Chua Ching Yong
Tay See Yek
Tee Ah Chong Johnny
Crawford Gene O.
Hewlett--Packard Company
Valenza Joseph E.
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