Typewriting machines – Including adjustment for optimum printing plane – By adjustment of platen relative to carriage
Reexamination Certificate
1999-02-12
2001-07-17
Yan, Ren (Department: 2854)
Typewriting machines
Including adjustment for optimum printing plane
By adjustment of platen relative to carriage
C400S648000, C400S662000
Reexamination Certificate
active
06261008
ABSTRACT:
The present invention relates to printing devices and more particularly to printing devices with a platen mechanism, and a method of controlling the printing device.
BACKGROUND OF THE INVENTION
In printing devices, such as impact printers, the gap between the print head and the platen is one of the key factors that determine print quality. If the gap is too large, the print head loses its proper distance for printing on the surface of a printing sheet. This results in blur and deformation of printed characters. With ink jet printers, if the gap is excessively large, an error of the ink drop arrival position caused by an error of the ejecting angle is enlarged, so that the print quality is also deteriorated. For this reason, to secure a high print quality, the platen-to-print head gap should be reduced by locating the platen as close to the print head as possible in a state that the platen is opposite the print head.
Typically, a printing sheet is transported from the sheet supply side to a printing region by a transporting mechanism, such as rollers, through a sheet transport path. The height of the inner space within the transport path is large enough to allow the printing sheet to smoothly move therethrough, thereby preventing the sheet from being jammed in the transport path. Accordingly, the printing sheet must be inserted in a narrower gap in the printing region from the large enough transport path. As a result, the leading edge of the sheet hits the platen or a member near to it, possibly causing a paper jam.
One technique to solve the problem is known. This conventional, prior art platen mechanism is illustrated in
FIGS. 8
to
10
. As shown, a platen
81
is disposed opposite a print head
80
, which is horizontally movable. The platen
81
consists of a plate-like member having a length corresponding to a movable range of the print head
80
. The platen
81
is fastened to a support member
83
, which may be turned about a shaft
82
. The support member
83
is mechanically coupled with a solenoid plunger
84
. When driven by the plunger
84
, the support member
83
and hence the platen
81
are moved to and from the print head
80
.
In a print mode of the printer, the platen
81
is moved toward the print head
80
and its end face is positioned in a sheet transport path
85
. Accordingly, a reduced gap G is set up between the platen
81
and the print head
80
(FIG.
9
).
In a sheet insertion mode of the printer in which a sheet is inserted into a printing region (including a portion of the transport path
85
located between the platen
81
and the print head
80
), the platen
81
is retracted from the transport path
85
, and hence its end face is moved apart from the print head
80
and the gap G is increased. Under this condition, the printing sheet P may enter the printing location smoothly or without any interruption.
This conventional platen mechanism suffers from problems. In operation, the entirety of the combination of the platen
81
and the support member
83
is pivoted by the plunger
84
. To keep the gap G constant when the printer is in the print mode, exactness is required for the dimensions of the related parts. In addition, a large space is required between the opening of the transport path
85
and the platen
81
. The moving sheet is frequently caught by the large space, resulting in a paper jam. Finally, the platen
81
needs to be stable when it receives an impact from the print head
80
. To this end, the output power of the plunger
84
must be large.
Another prior art platen mechanism is disclosed in JP-A8-11365. In this prior art, the gap between the print head and the platen is adjusted such that the gap is increased in the sheet insertion mode, and decreased in the print mode. An eccentrically mounted cylindrical platen is rotated to adjust the gap.
In a design where the eccentrically mounted cylindrical platen protrudes beyond the guide wall defining the transport path, the radius of the movement of the cylindrical platen is larger than that of the platen per se, so that a large gap is created between the platen and the guide wall. This large gap can easily catch the leading edge of the printing sheet, causing a paper jam.
There are cases where the leading edge of the printing sheet merely hits the guide wall portion defining the gap, not causing a paper jam. In this case, the transporting speed of the printing sheet is varied. Therefore, when the printer engages in reading information on the sheet or Magnetic Ink Character Recognition (MICR) characters, the speed variation appears as read errors.
SUMMARY OF THE INVENTION
The present invention aims at providing a platen mechanism in use with a printing device which, in the print mode, keeps the gap in the printing region constant, and, in the sheet insertion mode, allows a sheet to smoothly pass the gap without any adverse effect on the sheet transporting speed.
A platen mechanism, disposed opposite a print head, is provided for supporting a recording medium. The platen mechanism includes a guide wall for guiding the recording medium to the print head, a platen which is rotatable about a shaft substantially parallel to the guide wall and has a support portion and a guide portion. When the rotating platen is stopped at a first position where the support portion is opposite the print head, the support portion projects from the guide wall to support the recording medium to the print head. When the rotating platen is stopped at a second position where the guide portion is opposite the print head, the guide portion is substantially continuous to the guide wall to smoothly guide the recording medium being transported. A platen drive mechanism rotates the platen so that the support portion or the guide portion selectively confronts the print head.
With such a mechanical arrangement, when the printing device is in a print mode, the platen is turned to confront the support portion of the platen with the print head, and it serves as a platen. In this case, a force applied from the print head (such as a dot matrix or other impact print head) to the platen may be received by the rotary shaft of the platen. In accordance with the present invention, the platen is immovable and stable printing is ensured. When the printing device is in a medium transporting mode, the recording medium passes through a printing region (including a portion of the transport path located between the platen and the print head), the platen is turned to confront the guide portion of the platen with the print head. In this case, the guide portion is substantially continuous to the guide wall, so that the recording medium being transported is smoothly guided. The result is to prevent a variation of the transporting speed of the recording medium.
The platen mechanism may comprise an urging member which urges the recording medium apart from the print head and supports the recording medium at a predetermined distance from the print head in cooperation with the support portion of the platen. In this case, the guide portion of the platen is preferably positioned apart from the urging member when the guide portion is opposite the print head. With the additional feature, in the print mode, the distance between the recording medium and the print head can be kept constant. Therefore, in the ink jet printer, for example, print quality deterioration caused by a print position variation that is due to the ejecting angle error of the ink drop is eliminated. In the medium transporting mode, the urging member is separated from the guide portion of the platen to open and to provide a large sheet transporting path. Therefore, the recording medium advances without any collision and hence is free from the transporting speed variation caused by the collision of the recording medium. In the platen mechanism, when the guide portion is opposite the print head, the guide portion of the platen matches the ends of the guide wall. The guide portion of the platen is disposed with respect to the guide walls. A minimum gap is present between each end o
Nixon & Vanderhye P.C.
Seiko Epson Corporation
Yan Ren
LandOfFree
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