Exposing unit having first and second fixing members

Details Exposing unit having first and second fixing members Exposing unit having first and second fixing members

2001-06-25

2003-04-08

Lee, Susan S. Y. (Department: 2852)

Incremental printing of symbolic information

Electric marking apparatus or processes

Electrostatic

C347S152000, C347S263000, C399S126000, C399S177000

Reexamination Certificate

active

06545693

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposing apparatus.
2. Related Background Art
Referring to the accompanying drawings, description will be made of a method for positioning an exposing unit
12
′ relative to a photosensitive body in a conventional exposing apparatus.
FIG. 10
is a perspective view descriptive of a photosensitive drum
11
′ and an exposing unit
12
′.
FIG. 11
is a diagram descriptive of a side surface.
Base members
23
′ and
24
′ are fixed to a front side plate
21
′ and a rear side plate
22
′ of a main body, respectively. Focusing pins
31
′ and
32
′ which serve as members for supporting the exposing unit
12
′ are mounted on the base members
23
′ and
24
′ respectively so as to be movable in a depth direction (y direction).
Engaging portions of the base members
23
′,
24
′ and the focusing pins
31
′,
32
′ are threaded, whereby heights of the focusing pins
31
′ and
32
′ from the base members
23
′ and
24
′ are changed when the focusing pins
31
′ and
32
′ are turned. The exposing unit
12
′ is mounted on two front and rear pedestals
31
a
′ and
32
a
′ of the focusing pins. When the focusing pins
31
′ and
32
′ are rotationally adjusted as described above, the pedestals
31
a
′ and
32
a
′ of the focusing pins are displaced in a height direction, whereby a position of the exposing unit
12
′ is adjusted in the depth direction.
For locking and rattling prevention, a bonding agent is preliminarily coated over entire circumferences of the threaded portions of the focusing pins
31
′ and
32
′ which are engaged with the base members
23
′ and
24
′. Furthermore, tips of the focusing pins
31
′ and
32
′ are slotted so that these pins can be rotationally adjusted with a screwdriver.
Two positioning run-through holes are formed at both ends of the exposing unit
12
′. On the other hand, shaft forms are disposed on the pedestals of the focusing pins
31
′ and
32
′. A round hole
121
′ and an elongated round hole
122
′ which are run-through holes are fitted over shaft root portions
31
b
′ and
32
b
′ of the focusing pins respectively. Accordingly, the exposing unit
12
′ is positioned on a plane coordinate system (x-z coordinate system). Then, the exposing unit
12
′ is fixed to the pedestals
31
′
a
and
32
′
a
of the focusing pins by urging the exposing unit using elastic fixing means (not shown) in a direction indicated by an arrow A in FIG.
11
. Positioning and fixing of the exposing unit
12
′ are thus completed.
Description will be made here of why the exposing unit
12
′ is elastically fixed. An optical inconvenience such as curving of a scanning line may be produced when the exposing unit is deformed. When the exposing unit is fixed firmly with screws, the exposing unit may be deformed due to screw tightening torques during fixing or due to thermal expansion when a temperature rises in the exposing apparatus. When the exposing unit
12
′ is mounted on the main body only by a weight of the exposing unit without being fixed, on the other hand, the exposing unit may be broken during transit or an image may be ununiform due to vibrations at an image forming time, whereby, the exposing unit
12
′ is practically unusable. The exposing unit
12
′ is therefore elastically fixed to the main body of the exposing apparatus to prevent the above described problems.
However, the above described conventional positioning method poses a problem that the method allows a depth of the exposing unit to be deviated as described below.
Fitting plays are reserved in a radial direction between the run-through holes
121
′,
122
′ and the shaft root portions
31
b
′ and
32
b
′ which are fitting parts. This is because the exposing unit cannot be mounted as a matter of course when no gap remains. Furthermore, the fitting plays serve not to restrict span changes on sides of the main unit and the exposing unit due to thermal expansion caused by the above described temperature rise in the exposing apparatus, thereby preventing a stress from being produced in the exposing unit.
Furthermore, axial lines of the front and rear focusing pins
31
′ and
32
′ are usually not in parallel with each other, but inclined due to tolerances of parts such as a main body frame. Fitting lengths are therefore set rather short so that the exposing unit
12
′ can be mounted.
No optical problem is posed even when the exposing unit is statically deviated in the x direction and the z direction within the range of the fitting play. However, inclination of the exposing unit poses a problem of a deviation (inaccuracy) of a depth. A cause for the depth deviation is classified into (1) tilting of the exposing unit and (2) poor reproducibility of a positional relation between a jig and the exposing unit.
First, description will be made of “depth deviation due to tilting of the exposing unit”. When an external force is exerted to the exposing unit, the exposing unit is inclined, thereby changing an optical path length. A concrete example of exerted external force is a stress produced by an electric line bundle (between the exposing unit and the main body) or the like.
Referring to
FIGS. 12A
,
12
B,
13
A and
13
B, description will be made of the tilting of the exposing unit and the change of the optical path length.
FIG. 12A
is a sectional view of the focusing pin
31
′ of the exposing unit
12
′ and
FIG. 12B
is an optical diagram in a regular condition corresponding to FIG.
12
A. Furthermore,
FIG. 13A
is a diagram showing a condition where the exposing unit is inclined and
FIG. 13B
is an optical diagram in an inclined condition corresponding to FIG.
13
A.
Rays emitted from light emitting means
201
′ in the exposing unit
12
′ are imaged by a lens array
202
′ used as imaging means onto a surface of the photosensitive drum
11
′ which is an electrophotographic photosensitive body. A regular optical path length L
1
shown in
FIG. 12B
is 10 mm.
On the other hand, a diameter d of the run-through holes
121
′,
122
′ and the shaft root portions
31
b
′,
32
b
′ has a nominal value of 4 mm, and the fitting plays have a diameter of 20 &mgr;m. A fitting length b is set at 1.6 mm. Furthermore, the pedestal
31
a
′ has a radius R
1
of 4.5 mm. When the exposing unit
12
′ is inclined relative to the focusing pins, an inclination angle &THgr;
1
is 0.7 degrees at maximum.
In
FIGS. 13A and 13B
, an external force is exerted in a direction indicated by an arrow B. The exposing unit
12
′ is inclined around a point C in contact with the pedestal
31
a
′ of the focusing pin which functions as a rotating fulcrum. In the inclined condition, an optical path length L
2
is 10.06 mm. That is, a depth deviation of 60 &mgr;m is produced.
This depth deviation is geometrically reduced by shortening a radius R
1
of the pedestal
31
a
′. However, the radius cannot be shortened easily since the shortening of the radius produces a defect to make a mounted condition of the exposing unit dynamically unstable, whereby an image may be uneven (ununiform) due to the vibrations.
Then, description will be made of “depth deviation due to poor reproducibility of the positional relation between the jig and the exposing unit”.
FIG. 14
is a diagram descriptive of a mounted condition of jig units
99
′ relative to the focusing pins
31
′ and
32
′, and
FIG. 15
is a diagram descriptive of a mounted condition of the exposing unit
12
′ relative to the focusing pins
31
′ and
32
′. A section of a front side of the exposing unit
12
′ is shown on a left side and a section on a depth side

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