Electrophotography – Image formation – Exposure
Reexamination Certificate
2002-04-29
2004-12-28
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Exposure
C399S214000
Reexamination Certificate
active
06836633
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This document claims priority to Japanese Patent Application No. 2001-132597 filed in the Japanese Patent Office on Apr. 27, 2001, and Japanese Patent Application No. 2001-132594 filed in the Japanese Patent Office on Apr. 27, 2001. The entire contents of those applications are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., including the optical scanning device.
2. Discussion of the Background
Generally, an optical scanning device of a flatbed scanner type that scans an image of an original document immovably set on a contact glass includes first and second moving carriages that move in a sub-scanning direction at a speed ratio of two to one. The first moving carriage carries a light source that irradiates an image surface of an original document with light and a first mirror that reflects the light reflected from the image surface of the original document. The second moving carriage carries at least one of a second mirror and a third mirror that reflects the light reflected from the first mirror.
The above-described optical scanning device employs a wire driving system in which the first and second moving carriages are driven via driving wires wired at both sides of the first and second moving carriages, respectively.
Alternatively, the above-described optical scanning device may employ a belt driving system in which the first and second moving carriages are individually driven via timing belts. Specifically, stepped pulleys including large-diameter pulleys and small-diameter pulleys are respectively arranged at both sides of the first and second moving carriages. Each diameter of the small-diameter pulleys is one-half that of the large-diameter pulleys.
Two pairs of endless-belt-like long and short timing belts are respectively spanned around the stepped pulleys including the large-diameter pulleys and small-diameter pulleys at both sides of the first and second moving carriages, i.e., four timing belts are provided in total. The both sides of the first moving carriage are respectively fixed to portions of the two long timing belts, and the both sides of the second moving carriage are respectively fixed to portions of the two short timing belts. With the above-described construction, the first and second moving carriages are individually driven via the long and short timing belts, respectively.
The above-described wire driving system has disadvantages as follows:
(1) The wiring of driving wires is so complicated that assembly work may not be easily accomplished. Therefore, auto-assembly of an optical system of a scanning device may be difficult to perform.
(2) In order to prevent driving wires from being tangled, a predetermined tension is necessary to be applied to the driving wires. Because of complicated wiring of the driving wires, many pulleys are required to rotatably support the driving wires. For example, at least two pulleys are required at one side of the moving carriages. Due to the tension applied to the driving wires, the force in the radial direction is exerted on each of the pulleys. In this case, a ball bearing is often used for each of the pulleys to reduce a load on the pulley, driving the cost of the device higher.
Next, an example of a background optical scanning device employing the above-described belt driving system will be described referring to FIG.
15
. As illustrated in
FIG. 15
, long timing belts
116
,
117
extending in a sub-scanning direction are respectively arranged at both sides of a first moving carriage
104
in a main scanning direction. Further, short timing belts
118
,
119
extending in the sub-scanning direction are respectively arranged at both sides of a second moving carriage
105
in a main scanning direction.
The timing belt
116
is spanned around a set of timing belt pulleys
120
,
121
, and the timing belt
117
is spanned around another set of timing belt pulleys
122
,
123
. Further, the timing belt
118
is spanned around a set of timing belt pulleys
124
,
125
, and the timing belt
119
is spanned around a set of timing belt pulleys
126
,
127
. The timing belt pulleys,
120
and
124
, are intercoupled each other, and the timing belt pulleys,
122
and
126
, are intercoupled each other. A drive shaft
128
connects the timing belt pulleys,
120
and
124
, and the timing belt pulleys,
122
and
126
. One end of the drive shaft
128
is connected to a driven pulley
129
. The driven pulley
129
is connected to a drive pulley
132
of a drive motor
131
via a timing belt
130
.
End portions
133
of the both sides of the first moving carriage
104
in the main scanning direction are respectively attached to the timing belts,
116
and
117
. Further, end portions
134
of the both sides of the second moving carriage
105
in the main scanning direction are respectively attached to the timing belts,
118
and
119
, such that the second moving carriage
105
is arranged parallel to the first moving carriage
104
spaced at a predetermined distance. The end portions
133
of the first moving carriage
104
and the end portions
134
of the second moving carriage
105
are moved in the sub-scanning direction along guide rails
113
.
A driving force of the drive motor
131
is applied to the timing belt pulleys,
120
,
122
,
124
, and
126
, via the drive shaft
128
, thereby rotating the timing belts,
116
,
117
,
118
, and
119
, and moving the first and second moving carriages
104
,
105
in the sub-scanning direction. In this optical scanning device, each diameter of the timing belt pulleys,
124
and
126
, is set to be one-half that of the timing belt pulleys,
120
and
122
. Thereby, the first and second moving carriages
104
,
105
move at a speed ratio of 2 to 1.
The assembly work of the above-described optical scanning device employing the belt driving system may be more easily accomplished than the optical scanning device employing the wire driving system. However, in the above-described background optical scanning device employing the belt driving system, from the theoretical point of view, the first and second moving carriages
104
,
105
may not move at a speed ratio of 2 to 1, because the two types of the timing belts,
116
,
117
, and the timing belts,
118
and
119
, undergo speed variations due to engagement errors and decentering of the timing belt pulleys. In this case, the distance between a lens and an original document is minutely changed, causing deterioration of scanned images.
Further, in the above-described background optical scanning device employing the belt driving system, a predetermined tension needs to be applied to each of the timing belts,
116
,
117
,
118
, and
119
, to convey the driving force of the drive motor
131
to the first and second moving carriages
104
,
105
. In the above-described construction of the background optical scanning device, the drive shaft
128
is subject to the tensions of the timing belts,
116
,
117
,
118
, and
119
, so that relatively large radial forces are exerted on bearings that rotatably hold the drive shaft
128
, and radial forces are also exerted on the four driven timing belt pulleys,
120
,
122
,
124
, and
126
, resulting in a high drive load condition.
Moreover, in the above-described background optical scanning device employing the belt driving system, because the first and second moving carriages
104
,
105
are coupled to the drive motor
131
via the timing belts,
116
,
117
,
118
, and
119
, when the operational condition of the drive motor
131
is switched, for example, between rotation and halt, forward rotation and reverse rotation, etc., the forces in the direction of hindering the movements of the timing belts,
116
,
117
,
118
, and
119
, are typically produced due to the inertial forces of the first and second moving carriages
104
,
105
. As a result, the a
Bannai Kazunori
Fujioka Tetsuya
Ricoh & Company, Ltd.
Tran Hoan
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