Electrophotography – Diagnostics – Document handling
Reexamination Certificate
2002-07-25
2004-03-09
Chen, Sophia S. (Department: 2852)
Electrophotography
Diagnostics
Document handling
C250S559400, C399S009000, C399S081000
Reexamination Certificate
active
06704523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet detecting apparatus that detects the presence or absence of a sheet, and more specifically relates to a sheet detecting apparatus attached to a sheet conveying path of an image forming apparatus such as a copying machine or a printer.
2. Related Background Art
Conventional image forming apparatuses mainly adopt mechanical detection methods as sheet detecting means attached to their sheet conveying paths. As a representative example of the mechanical detecting methods, there has been used a method of a mechanical sensing lever type shown in FIG.
15
. With the mechanical sensing lever type method, a lever
201
is arranged so as to block a sheet conveying path.
How the sheet detection of the mechanical sensing lever type is performed will be described. When a leading end portion
30
of a sheet passing through a sheet conveying path presses a part of the lever
201
and the lever
201
is rotated, the lever
201
cuts off a light flux of a photocoupler
202
arranged in proximity to the lever
201
. Then, immediately after the sheet has passed therethrough, the lever
201
returns to its original position (indicated by a solid line) due to a force generated by a spring or the like.
When the light flux of the photocoupler
202
is cut off, there is generated a signal for detecting a sheet (there is not shown a signal generating portion). With the generated signal, it becomes possible to detect the presence or absence of a sheet.
However, there is exerted an influence of the counteraction of a spring or the like when the lever
201
returns to its original position, so that there occurs chattering. This chattering results in the increase of a time consumed to detect the trailing end of a sheet with precision. In particular, when a sheet is conveyed at high speed and with precision at constant intervals, it is required to detect the leading end and trailing end of the sheet with precision. As a result, the chattering exerts an enormous influence.
In order to detect the trailing end of the sheet with precision without receiving the influence of the chattering caused with the mechanical detection method, there has been used a detection method that uses an optical sensor. There have mainly been known two types of optical sensors: a reflection type optical sensor shown in FIGS.
16
A and
16
B and a transmission type optical sensor shown in FIG.
17
.
The former reflection type optical sensor has a construction where a light emission element
2154
and a light reception element
2155
are placed on the same substrate and a reflection sheet
205
is affixed to a side opposite to the substrate with a conveying path therebetween, as shown in FIG.
16
A. When a sheet
30
does not pass over an optical sensor, irradiation light of the light emission element
2154
is reflected by the reflection sheet and the reflection light is received by the light reception element
2155
. While the sheet
30
is passing over the optical sensor, the irradiation light (reflection light) is cut off as shown in
FIG. 16B
, thereby detecting the sheet.
However, there is a case where erroneous detection is caused by the reflection from the sheet. In order to prevent the erroneous detection, it is required to take measures such as the improvement of the accuracy of the conveying position of each sheet to prevent variations of the position of each sheet or the employment of a condensing lens or the like.
The latter transmission type optical sensor has a construction where the light emission element
2154
and the light reception element
2155
are arranged at positions opposing to each other with the sheet conveying path therebetween, as shown in FIG.
17
.
The presence of absence of a sheet is detected by the cutting off of the irradiation light
212
of the light emission element
2154
by the sheet
30
. As a result, there occurs no erroneous detection due to the reflection from the sheet
30
, but it is required to install the optical sensor with the high accuracy of relative positions on a light emission side and a light reception side.
In recent years, as a modification of the reflection type or transmission type optical sensor, there has been used an optical sensor shown in
FIGS. 18A and 18B
that combines the advantage of the reflection type with the advantage of the transmission type. This optical sensor has a construction where the light emission element
2154
and the light reception element
2155
are mounted on the same substrate
2152
and the axis of light irradiated from the light emission element
2154
and the axis of light received by the light reception element
2155
are set so as to be parallel through the refraction by a prism
2202
or the like. With this construction, it becomes possible to widen the allowable range of the installation accuracy concerning the light emission element
2154
and the light reception element
2155
and also to reduce the influence of the reflection of the sheet
30
.
As shown in
FIG. 18A
, irradiation light from the light emission element
2154
is refracted twice by a prism
2202
at an incident angle of 45° to planes
2203
and
2204
and then is received by the light reception element
2155
. While the sheet
30
is passing, the light is cut off and therefore the sheet
30
is detected (FIG.
18
B).
In the case of a sheet detection method using an optical sensor, the brightness is increased in accordance with the increase of a current flowing to the light emission element
2154
, so that it becomes possible to increase the dynamic range for the sheet detection and to improve the accuracy of the sheet detection. However, if a larger current than is necessary flows to the light emission element
2154
, this leads to the reduction of a life span. In contrast to this, if the dynamic range of the optical sensor is set so as to be narrow in consideration of the reduction of the life span, there is increased the influence of stains on a sheet or the sensor, which means that there is a probability that erroneous detection is caused.
With the sheet detection method using an optical sensor, the adjustment of a light quantity of the optical sensor is an important problem. It is required to perform an appropriate initial adjustment when the optical sensor is installed. However, even if the initial adjustment is performed, a light emission portion or a light reception portion becomes dirty due to paper powder of a sheet, dusts adhering to the sheet, or the like, which means that it is required to perform the adjustment of a light quantity at regular intervals or at irregular intervals. As to the timings at which the light quantity adjustment is performed, the intervals between them are set in conformance with light quantity reduction degree due to the speed, specifications, use application, and the like of an image forming apparatus.
Here, a conventional method of adjusting the light quantity of an optical sensor will be described with reference to
FIGS. 19A and 19B
.
FIG. 19A
is a graph concerning the adjustment of a light quantity of an optical sensor that is carried out when an image forming apparatus is produced or when the optical sensor is replaced by a serviceman.
The reference symbol Vin represents an application voltage applied to a light emission element of an optical sensor. The reference symbol Vout represents an output voltage obtained by converting the quantity of light received by the light reception element of the optical sensor. When a predetermined voltage is applied to the light emission element of the optical sensor, the light reception element outputs a voltage through a voltage conversion circuit. If the output voltage obtained as a result of this operation is equal to or higher than a preset threshold value Vh, the value is set as a control voltage and the light quantity adjustment is ended.
When there is applied Vin
1
, an output voltage becomes equal to or higher than the threshold value Vh like in the case of A
1
shown in FIG.
19
A. Therefor
Fukushi Kenji
Isemura Keizo
Kurahashi Masahiro
Morita Tetsuya
Nakagawa Atsushi
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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