Typewriting machines – Sheet or web – Including friction-feed means
Reexamination Certificate
1999-04-08
2001-10-09
Colilla, Daniel J. (Department: 2854)
Typewriting machines
Sheet or web
Including friction-feed means
C400S645000, C400S645400, C267S180000, C267S272000, C347S104000
Reexamination Certificate
active
06299367
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sheet feeding mechanism in use with an ink jet printer, for example, and more particularly to a sheet feeding mechanism including an object pressing member for pressing a printed sheet.
To print by an ink jet printer, the nozzle orifices of a printhead selectively eject ink drops onto a printing paper in accordance with print information while synchronizing with a relative movement of a printhead relative to a printing paper.
Generally, to feed a printing paper in the printer, the printing paper is nipped by a pair of paper-feed rollers, and one of the paired rollers is rotated.
In the case of the ink jet printer, characters, for example, printed on the printing paper are not fixed. Accordingly, when the printed paper is pressed against the rollers, ink of the printed characters is still wet. The wet ink sticks onto the roller, and is transferred from the roller to the sheet or paper.
An ink jet printer designed to solve the ink sticking problem is disclosed in JP-A-2-41277.
In the ink jet printer, the sheet is held by pressing the medium on the sheet feed roller. Therefore, the ink jet printer indispensably includes a sheet-pressing member having a spur gear with sharp teeth on the shaft.
The sheet-pressing member is designed to act elastically to the spur gear or the shaft, and the thus designed member presses the printing paper against the sheet feed roller.
A contact area where the spur gear is in contact with the paper is small in the ink jet printer using the thus constructed sheet-pressing member. Therefore, no ink transfer to the paper takes place in such a printer.
The sheet-pressing member of the printer takes the form of a bar or a plate, and the thus shaped member, while being bent, presses the sheet against the sheet feed roller.
The sheet-pressing member has a large spring constant, and inevitably suffers from dimensional variations. For this reason, work to properly set a pressing force is very difficult.
Where the pressing force is too large, an excessive load acts on the paper being fed. On the other hand, where it is too small, a sheet feeding force is insufficient. Either case leads to degradation of print quality.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an ink jet printer with a sheet feeding mechanism which imparts an optimum pressing force onto a sheet being transported.
To achieve the above object, there is provided an object pressing member for pressing a sheet being transported along a transport path, the object-pressing member including a pressing portion of large diameter being shaped like an eddy current by spirally coiling an elastic wire.
A sheet feeding mechanism includes a sheet feed roller and a sheet-pressing member disposed so as to press the sheet feed roller, the sheet-pressing member including a pressing portion of large diameter being shaped like an eddy current by spirally coiling an elastic wire.
A printer for printing on a sheet set therein, the printer having a printhead, and a sheet feeding mechanism disposed downward of the printhead when viewed in a sheet feeding direction, wherein the sheet feeding mechanism comprises a sheet feed roller for feeding a sheet printed by the printhead in a predetermined direction; and a sheet-pressing member disposed so as to press the sheet feed roller, the sheet-pressing member including a pressing portion of large diameter being shaped like an eddy current by spirally coiling an elastic wire.
The sheet-pressing member includes a coil spring portion formed by spirally coiling the wire so that the wire rings formed are brought into close contact with one another, and the pressing portion is formed by increasing the diameter of a part of the coil spring portion.
In this case, the pressing portion may be formed by increasing the diameter of the middle of a main body of the coil spring portion.
The pressing portion may be formed by increasing the diameter of both ends of a main body of the compression coil spring.
The sheet-pressing member
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is constructed such that the eddy-current shaped pressing portion (e.g., a flat spiral spring)
23
a
of large diameter flexibly presses the slip sheet S against the sheet feed roller. With this feature, in design, a spring constant of it measured in the pressing direction may be set to be small when comparing with the conventional one.
This fact implies that even if dimensional variation of the manufactured sheet-pressing members
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is relatively large, a variation of pressing forces of the sheet-pressing members, which impart onto the slip sheet S, is reduced.
Thus, the sheet feeding mechanism, an appropriate pressing force may stably be imparted onto the slip sheet S by properly selecting such factors as the effective number of turns and the diameter of the coil portion of the sheet-pressing member, and a material of the sheet-pressing member.
The sheet-pressing member takes an integral form. The feature of the integral form contributes to reduction of the number of required component parts and size reduction, and further easy assembling.
Thus, the sheet feeding mechanism of the invention, which is simple in construction, can stably impart a pressing force of an optimum magnitude onto the sheet while being free from external factors such as assembling accuracy and medium or paper thickness.
The ink jet printer equipped with the thus constructed sheet feeding mechanism succeeds in solving the wet-ink transfer problem in which ink is transferred from the sheet feeding mechanism to a printing paper immediately after it is printed, viz., the paper bearing printed characters, for example, which are still wet since it is not fixed. Further, the printer is capable of stably feeding the printing paper and hence printing at high print quality.
Further, according to the present invention, the printer comprises a printhead for printing characters, for example, on a sheet moving relatively to the printhead by ejecting ink drops through ink discharging orifices; and sheet-pressing members having pressing portions, located near to the discharging orifices, for pressing on the sheet at their positions not in contact with the ink of the characters immediately after printed, the positions being spaced apart from the ink discharging orifices, the sheet-pressing members each including a coil spring portion formed by spirally coiling an elastic wire so that the wire rings formed when coiled are brought into close contact with one another, and each the pressing portion being formed by increasing the diameter of a part of the coil spring portion.
With such a construction, the sheet, even if it is bent, does not come in contact with the nozzle face since it is separated by the sheet-pressing members. Therefore, no ink is transferred to the slip sheet S.
The pressing portions do not come in contact with the printed characters, for example, being still wet on the sheet. Therefore, the printer is free from ink sticking problem arising from the rubbing of the sheet with the sheet-pressing members.
The sheet-pressing members may include pressing portions for pressing down both sides of a region on the sheet immediately after characters, for example, are printed on the sheet.
In the construction, the sheet is pressed down at a plurality of positions by use of the pressing portions, and hence the sheet is reliably held down.
The thus constructed printer may include a wiper means for wiping ink stuck onto the ink discharging orifices while moving relatively to the ink discharging orifices, wherein the sheet-pressing members include pressing portions for pressing down the sheet while being located at positions out of a region including the ink discharging orifices when viewed in the wiping direction of the wiper means.
In the construction, the sheet-pressing members are located at positions out of a region including the ink discharging orifices when viewed in the wiping direction of the wiper means. Therefore, there is no chance that the pairs of the pressing portions of the shee
Hirabayashi Kenichi
Kawakami Hideki
Colilla Daniel J.
Nixon & Vanderhye P.C.
Seiko Epson Corporation
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