Document reader and image forming apparatus capable of reducing line-shaped noise
View Patent ↗A document reading unit constituting an MFP reciprocates a reading glass holder in a direction of a vertical scanning at a low frequency (18 times per second) with use of a crank mechanism including a motor and gears. A stroke length of the reciprocating motion of a reading glass is 9 mm. This structure can make a line-shaped noise less noticeable, because a length of each portion of a line-shaped noise becomes 2.57 mm and a distance between adjacent portions of the line-shaped noise becomes 7.27 mm when a foreign object having a diameter of 100 μm adheres to the reading glass.
1. A document reader that reads a color image of a document via a transparent member while feeding the document, comprising:
a plurality of reading units disposed in a feeding direction of the document; and
a driving unit operable to reciprocate the transparent member in the feeding direction over the reading units,
wherein, when a stroke length of the reciprocating motion of the transparent member is S, and a width in the feeding direction of a reading area of the reading units is W,
W
S
≤
0.9
.
2. The document reader of claim 1 , wherein
W
S
≤
0.3
.
3. The document reader of claim 1 , wherein a velocity of the reciprocating motion varies according to a sine wave.
4. The document reader of claim 1 , wherein
when a linear reading velocity of each reading unit is V, the width of the reading area is W, a frequency of the reciprocating motion is f, a length in the feeding direction of a foreign object adherent to the transparent member is d, and the stroke length of the reciprocating motion is S,
S
≥
(
V
(
W
+
d
)
)
2
9
f
2
W
,
and
S
≥
(
1
1
-
7
f
V
×
W
+
d
W
)
2
.
5. The document reader of claim 1 , wherein
when a linear reading velocity of each reading unit is V, the width of the reading area is W, a frequency of the reciprocating motion is f, and the stroke length of the reciprocating motion is S,
S
≥
V
2
W
9
f
2
,
and
S
≥
(
1
1
-
7
f
V
×
W
)
2
.
6. The document reader of claim 1 , wherein
a linear reading velocity of each reading unit is 177 mm/s, the width of the reading area is 387 μm, a frequency of the reciprocating motion is 18 Hz, and the stroke length is 9 mm.
7. The document reader of claim 1 , wherein
the reading units are three CCD line sensors, which are disposed so that longitudinal directions of the CCD line sensors respectively corresponding to three primary colors are substantially orthogonal to the feeding direction.
8. An image forming apparatus, comprising
a document reader including:
a feeding unit operable to feed a document;
a transparent member;
a plurality of reading units disposed in a feeding direction of the document and operable to read a color image of the document via the transparent member; and
a driving unit operable to reciprocate the transparent member in the feeding direction over the reading units,
wherein, when a stroke length of the reciprocating motion of the transparent member is S, and a width in the feeding direction of a reading area of the reading units is W,
W
S
≤
0.9
.
9. A document reading method performed by a document reader including a transparent member and a plurality of reading units that read a color image of a document via the transparent member, the reading units being disposed in a feeding direction of the document, the document reading method comprising:
a feeding step of feeding the document; and
a driving step of driving reciprocating the transparent member in the feeding direction over the reading units,
wherein, when a stroke length of the reciprocating motion of the transparent member is S, and a width in the feeding direction of a reading area of the reading units is W,
W
S
≤
0.9
.
10. The document reader of claim 1 , wherein to obscure degradation of image quality due to a high-density foreign object,
W
S
≤
0.5
.
11. The image forming apparatus of claim 8 , wherein to obscure degradation of image quality due to a high-density foreign object,
W
S
≤
0.5
.
12. The image forming apparatus of claim 8 , wherein
W
S
≤
0.3
.
13. The document reading method of claim 9 , wherein to obscure degradation of image quality due to a high-density foreign object,
W
S
≤
0.5
.
14. The document reading method of claim 9 , wherein
W
S
≤
0.3
.