Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2002-09-17
2004-04-06
Nolan, Jr., Charles H. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C271S193000, C400S636000
Reexamination Certificate
active
06715872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to sheet conveying devices and image forming apparatuses including the sheet conveying devices.
2. Description of the Related Art
Inkjet image forming apparatuses using full-line print heads capable of performing high-speed, high-quality printing on sheets are known in the art. In image forming apparatuses of this type, sheet conveying devices are commonly used in which conductive electrodes charge a conveyor belt for conveying a sheet with electricity so that an electrostatic force is generated and the sheet is thereby retained and conveyed by the conveyor belt.
An example of a known sheet conveying device will be described below with reference to
FIGS. 3
,
4
, and
6
.
FIG. 3
is a plan view showing the construction of a conveyer belt, and
FIG. 4
is a sectional view of the conveyer belt shown in
FIG. 3
cut along line IV—IV.
FIG. 6
is a side view showing the construction of a known sheet conveying device.
A known sheet conveying device includes a sheet-retaining unit
36
which serves as an electrode unit for retaining a sheet, a conveyor belt
31
which conveys the sheet while retaining it, and an electricity-supplying unit J which applies a voltage to the sheet-retaining unit
36
to generate an attractive force.
The conveyor belt
31
is an endless belt driven by a driving roller
34
and is disposed around a conveying roller
32
and a pressure roller
35
which are driven rollers. A belt motor (not shown) serves as a driving source of the driving roller
34
. The conveyor belt
31
includes the sheet-retaining unit
36
, a base layer
36
c
, and a surface layer
36
d
. The sheet-retaining unit
36
is formed of electrode plates
36
a
and electrode plates
36
b
formed of a conductive metal, electricity-receiving members
36
e
1
disposed at an end of the electrode plates
36
a
, and electricity-receiving members
36
e
2
disposed at an end of the electrode plates
36
b.
FIG. 3
is a plan view of the conveyor belt
31
. As shown in the figure, the electrode plates
36
a
and the electrode plates
36
b
are alternately arranged in a comb-like pattern.
More specifically, the electrode plates
36
a
and the electrode plates
36
b
extend in a direction crossing a sheet-conveying direction C, that is, the direction in which the conveyor belt
31
conveys a sheet, or in a direction approximately perpendicular to the sheet-conveying direction C. In addition, multiple electrode plates
36
a
and multiple electrode plates
36
b
are alternately formed on the conveyor belt
31
in the sheet-conveying direction C. All of the electrode plates
36
a
and the electrode plates
36
b
are formed in the same length, and are arranged parallel to each other such that the ends thereof are aligned.
The electricity-receiving members
36
e
1
formed of a conductive material are disposed at one end of the electrode plates
36
a
arranged on the conveyor belt
31
. In addition, the electricity-receiving members
36
e
2
formed also of a conductive material are disposed at an end of the electrode plates
36
b
opposite to the end at which the electricity-receiving members
36
e
1
are disposed. The thickness of the electricity-receiving members
36
e
1
and
36
e
2
, that is, the vertical size thereof in
FIG. 4
, is set larger than the thickness of the electrode plates
36
a
and
36
b
. In addition, top surfaces of the surface layer
36
d
and the electricity-receiving members
36
e
1
and
36
e
2
are made approximately even so that the top surfaces of the electricity-receiving members
36
e
1
and
36
e
2
face outwards from the top surface of the surface layer
36
d
(that is, so that the top surfaces of the surface layer
36
d
and the electricity-receiving members
36
e
1
and
36
e
2
are in the same plane). The size of the electricity-receiving members
36
e
1
and
36
e
2
in the sheet-conveying direction C is 1 cm, and electricity can be supplied, or eliminated, to/from the electrode plates
36
a
and
36
b
via different paths.
In addition, the electrode plates
36
a
and
36
b
are protected between the base layer
36
c
and the surface layer
36
d
in an area in which an attractive force for retaining the sheet is generated.
The base layer
36
c
and the surface layer
36
d
are formed of a synthetic resin such as polyethylene, polyamide, a fluorocarbon resin including polyvinylidene fluoride (PVDF), polycarbonate, and polyimide. In addition, the volume resistivity of the base layer
36
c
is set in the range of 10
12
to 10
17
&OHgr;cm, and that of the surface layer
36
d
is set in the range of 10
9
to 10
13
&OHgr;cm.
The electricity-receiving members
36
e
1
and
36
e
2
are formed of, for example, a conductive synthetic resin containing carbon, silver, a conductive paste containing copper powder, whose volume resistivity is 10
−1
to 10
5
&OHgr;cm.
In addition, the top surfaces of the surface layer
36
d
and the electricity-receiving members
36
e
1
and
36
e
2
are coated with a fluorocarbon resin, etc., so that water repellency thereof increases.
The known electricity-supplying unit J shown in
FIG. 6
includes an electricity-supplying electrode
52
′ which extends in the sheet-conveying direction C, a pair of electricity-supplying brushes
51
′ disposed at the bottom of the electricity-supplying electrode
52
′, and a supporter
53
′ which retains the electricity-supplying electrode
52
′ and the pair of electricity-supplying brushes
51
′.
The pair of electricity-supplying brushes
51
′ extend parallel to each other at positions directly above the electricity-receiving members
36
e
1
and the
36
e
2
such that they are in contact with the electricity-receiving members
36
e
1
and
36
e
2
, respectively. One of the electricity-supplying brushes
51
′ applies a positive voltage to the electrode plates
36
a
via the electricity-receiving members
36
e
1
, and the other electricity-supplying brush
51
′ applies a negative voltage to the electrode plates
36
b
via the electricity-receiving members
36
e
2
.
When a voltage is applied to the electrode plates
36
a
, an electric force is generated in the direction shown by the arrows in
FIG. 4
, so that electric flux lines are obtained. Then, an attractive force is generated at the top surface of the conveyor belt
31
due to the voltage difference between the electrode plates
36
a
and the electrode plates
36
b
, and the sheet is retained on the conveyor belt
31
by the attractive force.
However, in the sheet conveying device which is constructed as shown in
FIG. 6
, even when a sheet cannot be normally conveyed and no sheet is ready in an image-forming operation, or even when the conveyor belt is stained with ink, etc., and the stain is transferred to the paper, such an abnormal state cannot be detected. Accordingly, there is a risk in that the image-forming operation will be performed even though the sheet is absent, so that the surface of the conveyor belt will be stained. In addition, there is also a risk in that the operation of supplying electricity to the sheet-retaining unit cannot be performed effectively because of the stain on the surface of the conveyor belt, so that the sheet cannot be retained with a sufficient attractive force.
In order to detect the situations in which the sheet is absent or the conveyor belt is stained, a sheet detecting unit and a belt stain detecting unit are both required. However, this leads to an increase in costs.
SUMMARY OF THE INVENTION
The present invention can provide a sheet conveying device in which a stain on the surface of a conveyor belt and the presence/absence of a sheet on the conveyor belt can be detected with a simple construction, and can provide an image forming apparatus including the sheet conveying device.
According to the present invention, a sheet conveying device used for conveying a sheet includes an endless conveyor belt which includes an endless conveyor belt which includes an electrode unit for ret
Nolan, Jr. Charles H.
Tran Ly T
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