Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Reexamination Certificate
1998-06-25
2001-09-25
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
C358S496000, C358S498000, C358S444000, C358S465000
Reexamination Certificate
active
06295140
ABSTRACT:
BACKGROUND
1. Field
This present application generally relates to a document reading apparatus for document readers, copy machines, facsimile machines and other machines used to replicate an original image. More particularly, the present application relates to a document reading apparatus having a white platen roller which is used for shading correction.
2. Description of the Related Art
Document reading apparatus used, for example, in copy machines, facsimile machines and document readers (or scanners), typically obtain a reference measurement prior to scanning one or more original documents in order to compensate for shading variations in the original documents. This compensating process is known as shading correction.
One type of conventional document reading apparatus which has a contact-type image sensor and provides shading correction is disclosed in Japanese Laid-Open Patent Application No.4-183166. This apparatus has a white platen roller which makes contact with the contact-type image sensor at a document reading position. The document is read when it is transported in a state pinched between the contact-type image sensor and the white platen roller.
One drawback to such document reading apparatus is that the outer peripheral surface of the white platen roller becomes dirty due to contact between the roller and the document. That is, the white platen roller collects dust or other debris due to the contact between the roller and documents. As a result, if the contact-type image sensor reads the dirty portion of the white platen roller it is difficult to carry out accurate shading correction.
Another type of document reading apparatus that provides shading correction is described in Japanese Laid-Open Patent Application No.2-70170. This apparatus also uses a white platen roller and a contact-type image sensor. In this document reading apparatus the white platen roller is rotated to different positions and at each position a reference white signal is measured by the image sensor. The output of the contact-type image sensor (i.e., each reference white signal) is stored and compared to each previously stored reference white signal by a comparison circuit. If a newly measured reference white signal is greater than the stored one, the new reference white signal is stored. Thus, a maximum reference white signal is maintained in memory, and the maximum reference white signal is used for shading correction.
Typically, the white platen rollers are manufactured with metallic molds
101
a
and
101
b
, seen in
FIG. 1
b
, which when joined create crevices ‘M’. These crevices create burrs on an outer peripheral surface of the rollers, as shown in
FIG. 1
a
. The burrs ‘C’ are typically created on opposite sides of the circumference of the white platen roller
100
.
If the contact-type image sensor reads near a burr on the white platen roller, the output of the image sensor will reflect a problem that is similar to the case where dirt on the white platen roller is read, which may result in inaccurate shading correction.
Further, most document reading apparatus use a motor is used to move or rotate the white platen roller. When the motor is actuated electrical noise is typically generated and radiates within the document reading apparatus. Therefore, if the contact-type image sensor reads the white platen roller while the motor is energized, the electrical noise may mix with output of the image sensor and affect the white reference data which may result in inaccurate shading correction.
SUMMARY
The present application provides a document reading apparatus that reads original documents and includes a white platen roller, an image sensor and a controller. The white platen roller and image sensor are positioned at an image reading portion of the apparatus, and are used to feed and read an original document for subsequent reproduction. The white platen roller and image sensor are also used to generate white reference data that is used by the controller for shading correction. Generally, the image sensor reads the white platen roller and outputs signal characteristic data after reading the white platen roller. The signal characteristic data is then fed to the controller. The controller controls the reading of the white platen roller so that the image sensor reads the white platen roller a predetermined number of times. The controller also controls the movement of the white platen roller so that a motor used to move the white platen roller is de-energized when the image sensor reads the white platen roller. The controller receives the output signal characteristic data from the image sensor and compares the read output signal characteristic data to pre-existing signal characteristic data to determine if an abnormality exists in the read output signal characteristic data. When an abnormality is determined, the read output signal characteristic data is not used as white reference data, but when no abnormality is determined the controller stores in memory the output signal characteristic data as white reference data.
The pre-existing output signal characteristic data may be user entered data stored in memory, or the pre-existing output signal characteristic data may be output signal characteristic data from an earlier reading of the white platen roller by the image sensor.
Preferably, the image sensor includes comprises an array of photoelectric cells and the output signal characteristic data for each cell in the array includes a bit location and a signal amplitude.
The present application also provides a method for reading an original document with a document reading apparatus. The method includes reading a white platen roller in an image reading portion and generating first output signal characteristic data, storing the first output signal characteristic data, energizing a motor used to move the white platen roller and feeding the original document, de-energizing the motor before the original document reaches the image reading portion, reading a different portion of white platen roller in an image reading portion and generating second output signal characteristic data, comparing the first and second output characteristic data, and storing the first or second output signal characteristic data as white reference data based on a result of the comparing.
REFERENCES:
patent: 5107350 (1992-04-01), Omori
patent: 5644409 (1997-07-01), Irie et al.
patent: 270170 (1990-03-01), None
patent: 4183166 (1992-06-01), None
Cooper & Dunham LLP
Lee Cheukfan
Ricoh & Company, Ltd.
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