Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-07-17
2004-03-02
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S250000, C347S259000, C359S205100
Reexamination Certificate
active
06700596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical scanning apparatus and an image forming apparatus using the same. More particularly, the present invention relates to an optical scanning apparatus and an image forming apparatus using the same that are suitably applicable to apparatuses such as, for example, laser beam printers or digital copiers employing an electrophotographic process in which image information is formed using signals from a synchronizing-signal detecting means for controlling writing start in the main scanning direction when a beam emitted from a light source means is deflected by a deflection means and then passes through an f⊖ lens in a scanning optical system to optically scan a surface to be scanned and thus to form the image information.
2. Related Background Art
In conventional optical scanning apparatuses such as laser beam printers, a light beam emitted from a light source means is optically modulated according to an image signal. Then the optically modulated light beam is deflected periodically by a deflection means composed of, for instance, a polygon mirror and then is focused in a spot shape on a surface of a photosensitive recording medium by a scanning optical system having the f⊖ characteristics to optically scan the recording medium surface. Thus, the image information is recorded.
FIG. 6
is a perspective view showing main part of a conventional optical scanning apparatus. In
FIG. 6
, a divergent light beam emitted from a light source means
1
in a laser unit
3
is converted into a substantially parallel beam by a collimator lens in the unit
3
. The substantially parallel beam enters a cylindrical lens
4
with its width limited by a stop in the unit
3
. Among the parallel beam that has entered the cylindrical lens
4
, the beam in a plane in the main scanning direction emerges in the unchanged state and that in a plane in the sub-scanning direction is converged, which then form a substantially linear image on a deflecting/reflecting surface
5
a
of a deflection means
5
composed of a polygon mirror.
The light beam (indicated with a broken line) reflected and deflected by the deflecting/reflecting surface
5
a
of the polygon mirror
5
is led onto a recording medium surface (the surface to be scanned)
10
through a scanning optical system
7
having the f⊖ characteristics including two f⊖ lenses
7
a
and
7
b
. The polygon mirror
5
is rotated by a driving means
6
at a substantially constant angular velocity, so that the recording medium surface
10
is optically scanned at a substantially constant velocity. Thus, a latent image is formed using potential difference.
Part (indicated with a solid line) of the light beam reflected and deflected by the deflecting/reflecting surface
5
a
of the polygon mirror
5
passes through the scanning optical system
7
and then its traveling direction is changed by a reflecting mirror (BD mirror )
11
used for synchronization detection. Afterward, the part of the beam is converged on a synchronization detecting means (BD sensor)
13
by a condenser lens (BD lens)
12
used for synchronization detection. Thus, a horizontal synchronizing signal is formed.
In a recent optical scanning apparatus, its scanning optical system having the f⊖ characteristics has been made compact in size with the increase in demand for making the optical scanning apparatus compact in size. Methods of making the scanning optical system compact in size include, for example, increasing the angle of view of the scanning optical system and disposing the f⊖ lens near the polygon mirror.
Methods of reducing the width in the main scanning direction of the f⊖ lens include arranging an optical path for a synchronizing light beam (BD light beam) that is different from one for a scanning beam.
The scanning beam may not be focused at a desired position on the surface to be scanned and thus the image quality may be degraded unless the f⊖ lens is disposed in a predetermined position with high precision. When optical elements are gathered in the vicinity of the polygon mirror to reduce the size of the whole apparatus, the synchronizing light beam and the f⊖ lens physically interfere with each other and thus the synchronizing light beam may be blocked.
On the other hand, Japanese Patent Application Laid-open No. 11-311749 discloses an optical scanning apparatus in which an inclined part for securing an optical path of a synchronizing light beam is provided at an end of an f⊖ scanning optical system as a scanning-beam imaging lens and thus the synchronizing light beam passes by the inclined part to enter a synchronization detecting means.
In Japanese Patent Application Laid-open No. 11-311749, however, due to the formation of the inclined part, the thickness of the imaging/scanning lens is reduced in the inclined part and this causes a problem of stiffness deterioration. In addition, it is difficult to provide a positioning reference in the inclined part. The positioning reference should therefore be provided in a place closer to the optical axis of the imaging/scanning lens relative to the inclined part. As a result, the spacing between the positioning references arranged in the longitudinal direction of the imaging/scanning lens is reduced. This causes the increase in rotational deviation of the imaging/scanning lens.
Furthermore, in Japanese Patent Application Laid-open No. 11-223789, in
FIG. 1
, a laser beam emitted from a laser unit
5
passes through a laser beam transmission hole
11
a
provided in a f⊖ lens
11
, enters a rotary polygon mirror
4
, and then optically scans a photosensitive member surface
9
through the f⊖ lens
11
.
The rotary polygon mirror
4
allows a laser beam that has passed through an inner portion of the f⊖ lens
11
among the laser beam reflected by the rotary polygon mirror
4
to enter a light-receiving element
8
for detecting a synchronizing signal. Thus, a horizontal periodic signal is obtained from the light-receiving element
8
.
SUMMARY OF THE INVENTION
The present invention is intended to further improve the optical scanning apparatuses disclosed in the publications described above. It is an object of the present invention to provide an optical scanning apparatus in which a wide-angle scanning optical system can be used, the scanning optical system can be disposed closely to a deflection means, and the reduction in size of the whole optical scanning apparatus can be achieved easily. It is also an object of the present invention to provide an image forming apparatus using the optical scanning apparatus.
The present invention is intended to solve the problems of stiffness deterioration and increased rotational deviation of the scanning/imaging lens disclosed in Japanese Patent Application Laid-open No. 11-311749.
According to a first aspect of the present invention, there is provided an optical scanning apparatus, characterized in that: the optical scanning apparatus includes: a light source means: a deflection means with a deflecting/reflecting surface, the deflection means deflecting an incident light beam from the light source means by the deflecting/reflecting surface; a scanning optical system including at least one scanning optical element for leading the light beam deflected by the deflection means onto a surface to be scanned and forming an image as a spot on the surface to be scanned; and a synchronization detecting means for obtaining a scanning start position signal with respect to a main scanning direction on the surface to be scanned; and in that the scanning optical element is provided with a light-beam passage for allowing a light beam traveling toward the synchronization detecting means to pass through, the light-beam passage being provided in an inner portion of the scanning optical element located outside an effective portion of the scanning optical element.
According to a second aspect of the present invention, in the first
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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