Electrophotography – Document handling – Original
Reexamination Certificate
1999-07-13
2001-06-12
Beatty, Robert (Department: 2852)
Electrophotography
Document handling
Original
C250S227110, C250S239000
Reexamination Certificate
active
06246859
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensing device and, more particularly, to a sensing device for accurately sensing the presence/absence of a target object by a sensor. The present invention further relates to an original sensing device and, more particularly, to an original sensing device in a copying machine with an automatic document feeder, which accurately senses the presence/absence of originals placed on an original tray when each of the originals stacked on the original tray is moved to a copying machine main body and image information on the original is read.
2. Related Background Art
FIG. 1
is a schematic view showing the main parts of a copying machine as an image forming apparatus having an automatic document feeder with a conventional original sensing device. General functions and operations of the automatic document feeder will be described below with reference to FIG.
1
.
First, a sensor (original sensing device)
103
senses the presence/absence of originals
204
stacked on an original tray
101
of the document. feeder. An output signal from this sensor
103
is input to a copying machine
104
. When an operator operates a copy start switch (not shown) of the copying machine
104
, paper feed rollers
105
,
106
, and
107
and a paper feed belt
108
rotate in the direction of an arrow in
FIG. 1. A
stop blade
109
for preventing multiple sheet feeding separates the lowermost one of the originals
204
and feeds this original
204
to the upper left portion in FIG.
1
. The fed original
204
is conveyed onto an original glass table
122
by the rotation of an original conveyor roller
111
, as a conveyor means which has started rotating in the direction shown by an arrow by the copy start operation, and by the rotation of a press roller
110
and an original conveyor belt
120
which rotate in accordance with the rotation of the original conveyor roller
111
. When the original
204
is set in a predetermined position on the original glass table
122
, the rotation of the original conveyor belt
120
is stopped. Rollers
121
behind the original conveyor belt
120
press the original
204
with appropriate pressure against the original glass table
122
, and the copying machine
104
(details of its optical system are not shown) starts reading an image. When the exposure is complete, the copying machine
104
generates a signal to rotate the original conveyor belt
120
and rollers
141
,
142
, and
143
and deliver the original
204
subjected to the image reading onto the original tray
101
.
FIG. 2
is a schematic view showing the major parts of the conventional original sensing device.
FIG. 3
is a schematic view showing the main components of a projector shown in FIG.
3
.
Referring to
FIG. 2
, a projector
211
has, e.g., a light-emitting diode (LED) as a light source. A light-shielding window member
201
has openings
205
and
206
. A transparent dust cover
202
is placed on this light-shielding window member
201
. Portions
203
on this dust cover
202
are part of an original tray case. The originals
204
are placed on the original tray
101
. A photodetector
212
has a sensor (photosensor). A printed board
213
fixes the projector
211
and the photodetector
212
.
Referring to
FIG. 3
, a light-emitting chip
11
of the LED is usually encapsulated with a transparent resin. A ring-like reflector
12
is placed near this light-emitting chip
11
. When electrodes
15
supply electric power, the whole light-emitting chip
11
emits light, and the reflector
12
reflects a portion of the emitted light beam toward a portion above the light-emitting chip
11
. Since a dome-like lens
14
is placed above the light-emitting chip
11
, the light beam entering this lens
14
slightly decreases the diffusion angle when emerging from the lens
14
and further points upward as a light beam
16
shown in FIG.
3
. On the other hand, light beams entering a cylindrical portion
13
, rather than the lens
14
, are largely refracted because the angle of incidence to the cylindrical portion
13
is large. Consequently, these light beams obliquely point upward as light beams
17
shown in FIG.
3
.
Referring to
FIG. 2
, of the light beams emitted upward from the projector
211
, those passing through the opening
205
in the light-shielding window member
201
illuminate the surface of the original
204
through the transparent dust filter
202
. A curve A in
FIG. 4
indicates the light amount distribution in the illuminated portion on the surface of the original
204
. The illuminating light amount is largest immediately above the light source. Of the light beams reflected by the surface of the original
204
, those transmitted through the dust filter
202
and passing through the opening
206
in the light-shielding window member
201
irradiate the photoelectric surface through a resin lens
21
in the upper portion of the photodetector
212
. A curve B in
FIG. 4
indicates the sensitivity distribution on the surface of the original
204
obtained by the photodetector
212
. The sensitivity is highest immediately above the photodetector
212
.
When the original
204
is placed on the original tray
101
in the above arrangement, light beams from the projector
211
illuminate the surface of the original
204
as indicated by the curves A and B in FIG.
4
. Of reflected light beams from the illuminated portion of the original
204
, those passing through the opening
206
in the light-shielding window member
201
irradiate the photodetector
212
. These light beams are photoelectrically converted by the photodetector
212
and converted into an electrical signal by an electronic circuit (not shown). When the original
204
does not exist on the original tray
101
, no reflected light beams are produced, so neither light beams irradiate the photodetector
212
, nor electrical signal is generated. With this arrangement, the presence/absence of the original
204
on the original tray
101
can be converted into an electrical signal.
In this conventional device, as shown in
FIG. 4
, a portion where the amount of illuminating light from the light source (projector) is largest is different from a portion where the sensitivity of light detection by the photodetector is highest. Therefore, the amount of light entering the photodetector is small even when an original exists on the original tray. To overcome this drawback, one of following means (1), (2), and (3) is conventionally used.
(1) Increase the light emission amount of the light source of the projector to increase the amount of illuminating light to an original.
(2) Raise the sensitivity of the photodetector.
(3) Make the illuminating light amount largest and the sensitivity highest in close positions or in the same position.
Unfortunately, these means have the following problems.
Means (1) requires an expensive light source because a high-output light source is necessary.
Means (2) is readily influenced by external light such as a ceiling illuminating lamp because the sensitivity of the photodetector is raised. Accordingly, light beams sometimes enter the sensor although no original exists on the original tray, and a detection error occurs in some cases.
Means (3) will be described in detail below.
(A) The light source and the sensor can also be inclined with respect to the original tray surface (original surface). If this is the case, however, the light source and the sensor can no longer be fixed on the same plane of one printed board. The use of a plurality of printed boards requires a connector and results in an expensive device. Also, assembly of these parts into the device requires much labor and increases the assembly cost.
(B)
FIGS. 5 and 6
show a conventional device when the countermeasure according to means (3) above is practiced. Referring to
FIGS. 5 and 6
, a condenser lens
221
has a convex section. In
FIG. 5
, light beams from the light-emitting chip of the LED of the projector
211
are fed into the left-hand side, in
FI
Setani Michitaka
Takemura Yukio
Beatty Robert
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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