Sheet feeding or delivering – Feeding – By means to convey sheet
Reexamination Certificate
2000-11-07
2002-07-30
Ellis, Christopher P. (Department: 3651)
Sheet feeding or delivering
Feeding
By means to convey sheet
C271S034000, C271S132000, C271S283000
Reexamination Certificate
active
06425580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to recording medium transportation apparatus incorporated in an image recording apparatus for example printing an image on a sheet of paper or a similar recording medium. The present invention relates particularly to improved recording medium transportation apparatus employing a belt drive device, with a belt having a surface having a suction force produced by air suction and thus holding a recording medium on the belt to transport the recording medium.
2. Description of the Background Art
Printers and copiers are conventionally known as equipment for example printing an image on a sheet of paper, film or a similar recording medium. Such equipment use a belt drive device as means for transporting a recording medium.
To reliably transport a recording medium on a belt, a recording medium transportation apparatus adopts a configuration adhering the recording medium on the belt. More specifically, a chamber is arranged facing a back surface of the belt. The chamber has a surface facing the belt that is provided with suction holes and it is internally vacuumed to allow the suction holes to provide air suction. Furthermore, the belt is also for example blanked and thus provided with a large number of suction holes. Thus the recording medium is adhered on the belt when a negative pressure is produced in the chamber and each suction hole thus provides air suction. This can prevent the recording medium from displacing on the belt. Thus the recording medium transportation apparatus can reliably transport the recording medium.
However, the transportation apparatus adhering a recording medium on a belt and thus transporting the recording medium cannot provide a uniform negative pressure between the recording medium and the belt. More specifically, that portion of the recording medium close to a suction hole of the belt and therearound adheres to the belt with a large negative pressure, whereas that portion of the recording medium slightly apart from the suction hole of the belt adheres to the belt with an extremely small negative pressure, i.e., the atmospheric pressure. In other words, between the recording medium and the belt a region with an extremely high negative pressure and that with an extremely low negative pressure are alternately provided. As such, the recording medium can disadvantageously have an entire surface receiving a reduced average pressure. Thus the recording medium transportation apparatus does not ensure that it reliably transports the recording medium.
To overcome this disadvantage, Japanese Patent No. 2738532 and Japanese Patent Laying-Open No. 7-304167 disclose transportation apparatus.
The former discloses a transportation apparatus using a belt having a rough surface knurled in a diamond pattern. This can prevent a region of a high negative pressure from existing around a suction hole of the belt. Thus, a uniform negative pressure can act over an entire surface of a recording medium.
The latter discloses a belt formed of a porous film, a meshed sheet or the like to provide a uniform negative pressure over the entirety of an area to be printed.
However, there has not been made any suggestion in optimizing a belt surface roughness to obtain an appropriate action of a negative pressure.
The present inventor has noted a relationship between the force allowing a recording medium to adhere to a belt and the belt's surface roughness, and, with his findings, as provided hereinafter, the present inventor has studied on optimizing a belt surface roughness.
More specifically, if a belt has too rough a surface, too large a space is created between the belt and a recording medium and thus results in a reduced suction resistance. Thus, the chamber has a reduced negative pressure therein and can thus not provide a sufficient level of force adhering the recording medium to the belt. This would result in a high possibility of the transportation apparatus failing to reliably transport the recording medium. In addition, the fine convexities and concavities of the belt surface can be reflected on a front side or image bearing side of the recording medium. Thus an image cannot be formed on a smooth surface or obtain high quality.
In contrast, if a belt has an insufficiently rough surface, then a region with an extremely high negative pressure and that with an extremely low negative pressure alternately exist between a recording medium and the belt, as has been described above, resulting in a reduced average pressure preventing the transportation apparatus from reliably transporting the recording medium.
As such, in order to ensure a sufficient force allowing a recording medium to adhere to a belt to reliably transport the recording medium it is important to set an optimal belt surface roughness.
In particular, for a transportation apparatus intermittently transporting a recording medium, such as ink jet printers, the recording medium insufficiently adhering to the belt would tend to slide on the belt and an image formed on the recording medium can have a significantly degraded quality. As such, for printers of this type it is particularly important to have an optimized belt surface roughness.
To provide an optimally set belt surface roughness, it is also important to carefully set a distance between adjacent suction holes. That is, setting a distance between adjacent suction holes is also an important factor in reliably transporting a recording medium to form an image of high quality.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the above disadvantages and contemplates a recording medium transportation apparatus transporting a recording medium adhered to a belt through air suction, wherein a belt surface roughness and a distance between adjacent suction holes can be optimized to provide a level of force allowing the belt to optimally adhere to the recording medium to transport the recording medium with high precision.
More specifically, the present invention basically provides a recording medium transporting apparatus including a recording medium transporting belt having a suction hole to provide air suction to allow a recording medium to adhere to and thus transported on a surface of the belt. For this recording medium transportation apparatus, an equivalent adhesion diameter (Dx) is represented by:
0.5
×
D
0
2
e
c0
/
c1
≦
Dx
≦
0.95
×
D
0
2
e
c0
/
c1
(
1
)
wherein D
0
represents a diameter of a suction hole and c
0
, c
1
are each a fitting value (c
0
=16.49 and c
1
=6.05), and the aforementioned recording medium transporting belt has a surface roughness (Ra) represented by:
Ra
=
{
Dx
5
/
2
-
(
D
0
/
2
)
5
/
2
c
0
-
c
1
ln
(
2
·
Dx
/
D
0
)
}
1
/
3
(
2
)
with Dx substituted by expression (1).
More specifically, when a suction hole has a diameter D
0
of 1 to 2 mm, the recording medium transporting belt has a surface roughness Ra set to 1.9 to 13.7 &mgr;m.
Furthermore, if a suction hole has a diameter D
0
of 2 to 5 mm, the recording medium transporting belt has a surface roughness Ra set to 3.4 to 29.4 &mgr;m.
As described specifically as above, a belt can have a surface roughness set as appropriate and thus obtain a level of force acting to allow the belt to adhere to a recording medium satisfactorily. Thus the transportation apparatus can reliably transport the recording medium.
Furthermore, the present invention also has a feature providing a setting as described below, to optimize a distance between a center of a suction hole and that of another suction hole adjacent thereto. More specifically, in a recording medium transporting apparatus similar in configuration to the above described transportation apparatus, with a suction hole having diameter D
0
represented by &agr; and a recording medium transporting belt having
Edwards & Angell LLP
Ellis Christopher P.
Ridley Richard
Sharp Kabushiki Kaisha
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