U.S. patent application number 12/395557 was filed with the patent office on 2009-09-10 for optical scanning apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Shin Mogi.
Application Number | 20090226213 12/395557 |
Document ID | / |
Family ID | 41053737 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090226213 |
Kind Code |
A1 |
Mogi; Shin |
September 10, 2009 |
OPTICAL SCANNING APPARATUS
Abstract
A scanning optical apparatus includes an optical box
accommodating a deflection device for scanningly deflecting a laser
beam emitted by a light source and an optical part for directing
the laser beam toward a member-to-be-scanned; a cap mounted to the
optical box; a sealing member extending from the cap, wherein the
sealing member is made of a material exhibiting easier deformation
than the cap, and is contacted to a wall of the optical box in a
deformed state.
Inventors: |
Mogi; Shin; (Kashiwa-shi,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
41053737 |
Appl. No.: |
12/395557 |
Filed: |
February 27, 2009 |
Current U.S.
Class: |
399/132 |
Current CPC
Class: |
G02B 27/0006 20130101;
G03G 15/04036 20130101; G03G 2215/0132 20130101; G03G 15/0435
20130101; B41J 2/473 20130101 |
Class at
Publication: |
399/132 |
International
Class: |
G03G 16/00 20060101
G03G016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2008 |
JP |
2008-057079 |
Claims
1. A scanning optical apparatus comprising: an optical box
accommodating a deflection device for scanningly deflecting a laser
beam emitted by a light source and an optical part for directing
the laser beam toward a member-to-be-scanned; a cap mounted to said
optical box; a sealing member extending from said cap; wherein said
sealing member is made of a material exhibiting easier deformation
than said cap, and is contacted to a wall of said optical box in a
deformed state.
2. A scanning optical apparatus according to claim 1, wherein said
sealing member has an elastic coefficient which is larger than that
of said cap.
3. A scanning optical apparatus according to claim 1, wherein said
sealing member is provided on said cap by insertion molding.
4. A scanning optical apparatus according to claim 1, wherein the
material of said sealing member is thermoplastic elastic material,
and said cap has an inlet for permitting molten thermoplastic
elastic material to enter at the time of the insertion molding, and
a flow path for guiding the molten thermoplastic elastic material
supplied through said inlet so that sealing member is molded so as
to contact the wall of said optical box when said cap is mounted to
said optical box.
5. A scanning optical apparatus according to claim 1, wherein said
sealing member forms an acute angle relative to the wall.
6. A scanning optical apparatus according to claim 5, wherein said
sealing member has a thickness which is smaller in a free end
portion than in a base portion.
7. A scanning optical apparatus according to claim 5, wherein a
thickness of said sealing member in a range of 1/3 length from the
free end is not more than 1/2 of the thickness in the base
portion.
8. A scanning optical apparatus according to claim 5, wherein said
sealing member presses against the wall is not more than 100 gf per
1 cm of a circumferential length of sealing member.
9. A scanning optical apparatus according to claim 5, wherein said
sealing member has a volume resistivity R which satisfies,
1.times.10.sup.6 .OMEGA.cm.ltoreq.R.ltoreq.1.times.10.sup.10
.OMEGA.cm.
10. A scanning optical apparatus according to claim 1, wherein said
sealing member includes a base portion extending from said cap and
a contact portion contacting to the wall, and the contact portion
is bent toward the wall from the wall.
11. A scanning optical apparatus according to claim 10, wherein
said contact portion has a thickness which is larger than that of
said base portion.
12. A scanning optical apparatus according to claim 11, wherein
said sealing member has a volume resistivity R which satisfies,
1.times.10.sup.6 .OMEGA.cm.ltoreq.R.ltoreq.1.times.10.sup.10
.OMEGA.cm.
Description
FIELD OF THE INVENTION AND RELATED ART
[0001] The present invention relates to an optical scanning
apparatus for scanning the surface of an image bearing member with
a beam of laser light. More specifically, it relates to an optical
scanning apparatus mountable in an image forming apparatus, for
example, an electrophotographic copying machine, a printer, a
facsimile machine, and a multifunction image forming apparatus made
up of a combination of the preceding apparatuses.
[0002] First, referring to FIG. 12, an example of a conventional
optical scanning apparatus mountable in an image forming apparatus,
such as an electrophotographic copying machine, a printer, a
facsimile machine, and a multifunction image forming apparatus made
up of a combination of the preceding image forming apparatuses,
will be described.
[0003] The optical scanning apparatus shown in FIG. 12 generally
has a light source unit 30a and a cylindrical lens 30b. The light
source unit 30a is made up of a semiconductor laser, a collimator
lens, etc., and emits a beam of laser light, which is a parallel
beam of light. The cylindrical lens 30b focuses, in terms of the
secondary scanning direction, the beam of laser light emitted by
the light source unit 30a semiconductor laser. The optical scanning
apparatus also has a rotational polygonal mirror 33 (polygon
mirror), a lens 34, and a lens 41. The polygon mirror 33 deflects
the beam of laser light emitted by the light source unit 30a, in
such a manner that the beam of laser light moves in a manner to
scan the peripheral surface of an electrophotographic
photosensitive member 10 (which hereafter will be referred to as
"photosensitive drum 10"). The lenses 34 and 41 focus the beam of
laser light on the peripheral surface of the photosensitive drum 10
while the beam of laser light is deflected in the above described
manner. The polygon mirror 33, lenses 34 and 41, mirror 51, etc.,
which are optical components, are disposed in an optical box 2.
Further, after the polygon mirror 33, lenses 34 and 41, mirror 51,
etc., are disposed in the optical box 2, a lid (unshown) is
attached to the optical box 2 to hermetically seal the optical box
2.
[0004] The beam of laser light emitted by the semiconductor laser
of the optical unit 30a is focused on the reflective surfaces of
the polygon mirror 33 by the cylindrical lens 30b. As the beam of
laser light is focused on the reflective surface of the polygon
mirror 33, it is deflected in a manner to scan the peripheral
surface of the photosensitive drum 10 through the lenses 34 and 41.
As the beam of laser light is transmitted through the lenses 34 and
41, it is focused on the peripheral surface of the photosensitive
drum 10 while being moved in the manner to scan the peripheral
surface of the photosensitive drum 10 in the direction parallel to
the axial line of the photosensitive drum 10 (which hereafter may
be referred to simply as primary scan direction).
[0005] Since the beam of laser light is moved, while remaining
focused on the peripheral surface of the photosensitive drum 10, in
the primary direction while the photosensitive drum 10 is rotated
in the direction perpendicular to the axial line of the
photosensitive drum 10 (which hereafter may be referred to simply
as secondary scan direction), an electrostatic latent image is
formed on the peripheral surface of the photosensitive drum 10.
[0006] In order to obtain a high quality image with the use of an
image forming apparatus equipped with an optical scanning
apparatus, such as the one described above, it is important that
the optical components, more specifically, the polygon mirror 33,
lenses 34 and 41, mirror 51, etc., are not soiled. Thus, in order
to prevent the optical components from being soiled, the optical
scanning apparatus is structured so that it is difficult for the
dusts to enter the apparatus. For example, an ordinary optical
scanning apparatus is provided with such a sealing member that is
placed between the optical box 2 and the lid for the optical box 2
to prevent dusts from entering the optical box 2 through the gap(s)
between the optical box 2 and lid.
[0007] However, with the scanning optical apparatus of Japanese
patent 3352332, the sealing member is compressed between the
optical box and the cap, and therefore, the rigidity of the sealing
member is increased by the compression. Then, the optical box or
the cap is deformed by the high rigidity portion, or the elasticity
of the sealing member is not high enough to accommodate the
deformation of the optical box or the cap, with the result of
liability of deforming the optical box or the cap. Because of this,
the scanning laser beam may deviates on the photosensitive
drum.
[0008] Japanese Laid-open Patent Application Hei 06-273682 proposes
a solution to this problem, wherein a close-contact rib is extended
from the cap, and the rib is closely contacted to the side wall of
the optical box with elastic deformation.
[0009] In this apparatus, the close-contact rib is integrally
molded with the cap. The material of the cap exhibits a property of
uneasy deformation in order to enhance the rigidity of the optical
box. Since the close-contact rib is integral with the cap, the
close-contact rib exhibits the property of uneasy deformation.
Although the close-contact rib deforms elastically when it is
mounted to the optical box, the close-contact rib applies a force
to the side wall and/or the cap because of its property. This would
result in deformation of the optical box.
SUMMARY OF THE INVENTION
[0010] The present invention was made in consideration of the above
described problem. Thus, the primary object of the present
invention is to provide an optical scanning apparatus, the sealing
member of which can keep the optical box of the apparatus
satisfactory reliably sealed without causing the optical box of the
apparatus to deform.
[0011] According to an aspect of the present invention, there is
provided a scanning optical apparatus comprising an optical box
accommodating a deflection device for scanningly deflecting a laser
beam emitted by a light source and an optical part for directing
the laser beam toward a member-to-be-scanned; a cap mounted to said
optical box; a sealing member extending from said cap; wherein said
sealing member is made of a material exhibiting easier deformation
than said cap, and is contacted to a wall of said optical box in a
deformed state.
[0012] The further features of the present invention will become
apparatus from the following description of exemplary embodiments
(with reference to the attached drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a sectional view of an electrophotographic
full-color printer as an example of an image forming apparatus in
which an optical scanning apparatus in accordance with the present
invention is mountable, and shows the general structure of the
image forming apparatus.
[0014] FIG. 2 is a sectional view of the optical scanning apparatus
in the first preferred embodiment of the present invention, and
shows the general structure of the apparatus.
[0015] FIG. 3 is a sectional view of one of the end portions of the
optical scanning apparatus in the first preferred embodiment of the
present invention, and shows the optical box, lid, and sealing
member of the apparatus.
[0016] FIG. 4 is a schematic drawing of one of the top corner
portions of the optical box, and shows the amount of the sealing
member deformation.
[0017] FIG. 5 is a combination of a perspective view of the sealing
member, and the lid to which the sealing member has been attached,
as seen from below, and a plan view of one of the corner portions
of the optical box.
[0018] FIG. 6 is a sectional view of the insert molding machine in
the first preferred embodiment, and shows the general structure of
the machine.
[0019] FIG. 7 is a perspective view of the optical box and lid of
the optical box, as seen from above.
[0020] FIG. 8 is a sectional view of the sealing member shaped in
such a manner that its cross section is in the form of a thin
wedge.
[0021] FIG. 9 is a graph which shows the relationship between the
amount of displacement of the tip of the sealing member and the
amount of pressure applied to the inward surface of the lateral
wall of the optical box.
[0022] FIG. 10(a) is a perspective view of a combination of a
modified version of the sealing member in the preferred embodiment
and a modified version of the lid in the preferred embodiment, and
shows the structures thereof, whereas FIG. 10(b) is a perspective
view of a combination of another modified version of the sealing
member in the preferred embodiment, and another modified version of
the lid in the preferred embodiment, and shows the structures
thereof.
[0023] FIGS. 11(a-1) and 11(a-2) are schematic perspective and
sectional drawings, respectively, of another modified version of
the sealing member in the preferred embodiment, and another
modified version of the lid in the preferred embodiment, and shows
the gap filling portion of the sealing member, whereas FIG. 11(b)
is a schematic drawing of yet another version of the sealing member
in the preferred embodiment, another version of the lid in the
preferred embodiment, and a modified version of the optical box in
the preferred embodiment, and shows the structures thereof. FIG. 12
is a perspective phantom view of an ordinary conventional optical
scanning apparatus, and shows the general structure of the
apparatus.
[0024] FIGS. 13A, 13B and 13C illustrate a bent type sealing member
according to a third embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Hereinafter, the optical scanning apparatuses in accordance
with the present invention will be described in more detail with
reference to the appended drawings.
Embodiment 1
[0026] FIG. 1 is a sectional view of an electrophotographic
full-color printer, as an example of an image forming apparatus, in
which the optical scanning apparatus in accordance with the present
invention is mountable. It shows the general structure of the image
forming apparatus. FIG. 2 is a sectional view of the optical
scanning apparatus in this preferred embodiment of the present
invention. It shows the general structure of the apparatus.
(General Structure of Image Forming Apparatus)
[0027] First, referring to FIG. 1, the electrophotographic
full-color printer, as an example of an image forming apparatus, in
which the optical scanning apparatus in accordance with the present
invention is mountable, will be described. The image forming
apparatus 100 in this embodiment is of a so-called tandem type. It
has four image forming portions (PY, PM, PC, and PK), which are
disposed in tandem in a straight line.
[0028] The image forming apparatus has: an image forming portion
PY, which is for forming yellow images; an image forming portion
PM, which is for forming magenta images; an image forming portion
PC, which is for forming cyan images; and an image forming portion
PK, which is for forming black images. The four image forming
portions PY, PM, PC, and PK are disposed in a straight line with
the presence of preset intervals.
[0029] Each of the image forming portions PY, PM, PC, and PK has:
the photosensitive drum 10 (10Y, 10M, 10C, or 10K) as an image
bearing member. In the adjacencies of the peripheral surface of
each of the photosensitive drums 10Y, 10M, 10C, and 10K, a primary
charging device 11 (11Y, 11M, 11C, and 11K, respectively) for
uniformly charging the peripheral surface of the photosensitive
drum 10 is disposed. Also disposed in the adjacencies of the
peripheral surface of each of the photosensitive drums 10Y, 10M,
10C, and 10PK is a developing apparatus 12 (12Y, 12M, 12C, and
12BK, respectively) for developing the electrostatic latent image
formed on the photosensitive drum 10 by the optical scanning
apparatus (which will be described later), into a toner image
(image formed of toner). The developing apparatuses 12Y, 12M, 12C,
and 12BK contain yellow, magenta, cyan, and black toners,
respectively.
[0030] Further, an intermediary transfer belt 15, and transfer
rollers 14 (14Y, 14M, 14C, and 14K) for transferring the toner
image on the photosensitive drum 10, from the photosensitive drum
10 to the intermediary transfer belt 15, are disposed in the
adjacencies of the peripheral surface of the photosensitive drum
10. The intermediary transfer belt 15 is disposed so that it is on
the top side of each of the photosensitive drums 10Y, 10M, 10C, and
10K). It is supported by a secondary transfer roller 16a and a pair
of tension rollers 16b and 16c, remaining stretched by the rollers.
The aforementioned four primary transfer rollers 14Y, 14M, 14C, and
14K are disposed on the inward side of the loop which the
intermediary transfer belt 15 forms. The four transfer rollers 14Y,
14M, 14C, and 14K are enabled to be pressed against the peripheral
surfaces of the photosensitive drums 10Y, 10M, 10C, and 10K,
respectively, with the presence of the intermediary transfer belt
15, as an intermediary transferring member, between the transfer
rollers 14Y, 14M, 14C, and 14K and photosensitive drums 10Y, 10M,
10C, and 10K, respectively.
[0031] Further, there are a drum cleaning apparatuses 13 (13Y, 13M,
13C, and 13K) for removing the residual toner on the photosensitive
drums 10 (10Y, 10M, 10C, and 10K, respectively) in the adjacencies
of the peripheral surfaces of the photosensitive drums 10Y, 10M,
10C and 10K, respectively. Further, there is an optical scanning
apparatus 1, as an exposing apparatus, which is disposed below the
primary charging devices 11Y, 11M, 11C, and 11K and developing
apparatuses 12Y, 12M, 12C, and 12K.
[0032] The photosensitive drum 10, primary charging device 11,
developing apparatus 12, cleaning apparatus 13, etc., of each of
the image forming portions P may be integrally disposed in a
cartridge which is removably mountable in the main assembly 10A of
the image forming apparatus 100. Each of the photosensitive drums
10Y, 10M, 10C, and 10k is an organic photosensitive member which is
negatively chargeable. It has an aluminum drum as the substrate,
and a photoconductive layer placed on the peripheral surface of the
aluminum substrate. It is rotated by a driving apparatus (unshown)
in the direction indicated by arrow marks (clockwise direction in
FIG. 1) at a preset process speed.
(Optical Scanning Apparatus)
[0033] Next, the optical scanning apparatus in this embodiment will
be described with reference to FIG. 2, which is an enlarged
sectional view of the optical scanning apparatus 1 used by the
color image forming apparatus 100 of the tandem type, which was
described with reference to FIG. 1. FIG. 2 shows the general
structure of the optical scanning apparatus 1.
[0034] Referring to FIG. 2, the optical scanning apparatus 1 has an
optical box 2, which is roughly in the form of an ordinary
rectangular box. The optical box 2 is provided with a lid 3, which
is for covering the opening 2A of the optical box 2 to airtightly
seal the optical box. The lid 3 is provided with windows 8 through
which the photosensitive drums 10 are exposed, one for one. Each
window 8 is in the form of a long and narrow rectangular slit. The
window 8 is covered with a piece of glass 18 for preventing dusts
from entering the optical box 2, while allowing the beam of laser
light to be projected out of the optical box 2.
[0035] Next, the optical scanning apparatus 1 in this embodiment
will be described regarding its internal structure.
[0036] Referring again to FIG. 2, the optical scanning apparatus 1
has a deflecting device 31, as a means for deflecting light, which
is made up of a polygon mirror 33 and a brushless motor 32.
[0037] The beam of laser light emitted from a light source
(unshown) is projected onto the deflecting device 31 through a
collimator lens (unshown) and a compound cylindrical lens
(unshown). The deflecting device 31 deflects the beam of laser
light, which corresponds to black "color" K and cyan color C, by
its right side, and the beam of laser light, which corresponds to
magenta color M and yellow color M, by its left side.
[0038] Also referring to FIG. 2, the optical system for the black
color K and the optical system for the cyan color C are in the
right portion of the optical scanning apparatus 1 relative to the
deflecting device 31, whereas the optical system for the magenta
color M and the optical system for the yellow color Y are in the
left portion of the optical scanning apparatus 1 relative to the
defective device 31. The four optical systems are independent from
each other, and are positioned in the light path which is behind
the deflective device 31. Each optical system is made up of
focusing lenses, deflective mirrors, etc., and is disposed in a
manner to stand in the light path of the deflecting device 31. As
the beam of laser light is deflected by the deflecting device 31 in
the manner of scanning the peripheral surface of each of the
photosensitive drums 10 (10Y, 10M, 10C, or 10K), it is focused on
the peripheral surface of each photosensitive drums 10 by the
corresponding optical system, while being moved in the manner of
scanning the peripheral surface of the photosensitive drum 10.
[0039] More specifically, each of the abovementioned optical
systems has such optical components as a pair of first focusing
lenses 34 and 35, four second focusing lenses 41, 42, 43, and 44,
eight deflective mirrors 51, 52, 53, 54, 55, 56, 57, and 58. The
first focusing lenses 34 and 35 and the second focusing lenses 41,
42, 43, and 44 are for correcting the beam of laser light in the
f-.theta. factor. Further, the second focusing lenses 41, 42, 43,
and 44 have also the function of keeping the beam of laser light
focused on the peripheral surface of the photosensitive drum 10
while the beam of laser light is moved in the secondary scanning
direction.
[0040] Next, the image forming process of the image forming
apparatus in this embodiment will be described. First, an image
formation start signal is outputted. As the signal is outputted,
the photosensitive drums 10Y, 10M, 10C, and 10K of the image
forming portions PY, PM, PC, and PK begin to be rotationally driven
at the predetermined process speed, while being uniformly charged
by the primary charging devices 11Y, 11M, 11C, and 11K,
respectively, to the negative polarity. The optical scanning
apparatus 1, that is, an exposing apparatus, projects the beam of
laser light while modulating the beam of laser light with the
external image formation signals, which correspond to each of the
monochromatic color images (or image) into which an intended image
has been separated. As a result, an electrostatic latent image is
effected on the peripheral surface of each of the photosensitive
drums 10Y, 10M, 10C, and 10K.
[0041] Then, a development bias, which is the same in polarity as
the polarity to which the photosensitive drum 10Y was charged, is
applied to the electrostatic latent image on the photosensitive
drum 10Y. As a result, the electrostatic latent image on the
photosensitive drum 10Y develops into a yellow toner image (toner
image formed of yellow toner). This toner image is transferred
(primary transfer) onto the intermediary transfer belt 15 (which is
being driven) by the transfer roller 14Y (to which primary transfer
bias (positive), which is opposite in polarity to toner, is being
applied), in a primary transfer portion T1Y, which is between the
peripheral surface of the photosensitive drum 10Y and the
peripheral surface of the transfer roller 14Y. The processes for
forming the monochromatic images of the other colors are the same
as the above described process for forming the yellow monochromatic
image. The monochromatic color toner images on the photosensitive
drums 10, one for one, are transferred in layers onto the
intermediary transfer belt 15.
[0042] Then, the toner images on the intermediary transfer belt 15
are transferred onto a recording medium (sheet of recording medium,
for example) in a second transfer portion T2 while the recording
medium is conveyed through the secondary transfer portion T2, in
synchronism with the toner images. Then, the toner images on the
recording medium are thermally fixed to the recording medium by a
fixing device 25, which is on the downstream side of the secondary
transfer portion T2 in terms of the recording medium conveyance
direction. Then, the recording medium is discharged into a delivery
portion 27 (delivery tray).
[0043] Meanwhile, the toner particles remaining on the peripheral
surface of each photosensitive drum 10, that is, the toner
particles which were not transferred onto the intermediary transfer
belt 15 in the primary transfer portion T1, are removed from the
photosensitive drums 10Y, 10M, 10C, and 10K, by drum cleaning
apparatuses 13Y, 13M, 13C, and 13K, respectively. As for the toner
particles, or the like, remaining on the intermediary transfer belt
15 are removed and recovered, by a belt cleaning apparatus
(unshown).
[0044] The optical scanning apparatus 1 exposes each of the
photosensitive drums 10Y, 10M, 10C, and 10K by deflecting the beam
of laser light in such a manner that the beam of laser light scans
the peripheral surface of each photosensitive drum 10. As a result,
an electrostatic latent image is formed on the peripheral surface
of each of the photosensitive drums 10Y, 10M, 10C, and 10K, which
have just been charged by the primary charging devices 11Y, 11M,
11C, and 11K, respectively. The electrostatic latent images formed
on the photosensitive drums 10Y, 10M, 10C, and 10K, one for one,
reflect the information of the intended image.
[0045] At this time, the characteristic features of the optical
scanning apparatus 1 in this embodiment will be described. The
revolution of the polygon mirror 33 of the optical scanning
apparatus 1 is 20,000-30,000 rpm. Since the polygon mirror 33 is
rotated at such a high speed, the sealed optical box becomes
nonuniform in internal pressure. As a portion (portions) of the
internal space of the optical box, which is adjacent to the gap(s)
in the optical box 2 and lid 3, becomes lower in pressure than the
ambience of the optical box 2, the ambient air flows into the
optical box. As the ambient air flows into the optical box 2, the
dusts or the like floating in the ambient air enters the optical
box along with the ambient air, and soil the optical components,
that is, the abovementioned polygon mirror, lenses, mirrors,
etc.
[0046] In order to prevent this problem, the optical box is
provided with an elastic sealing member, which is placed between
the optical box and lid to prevent the intrusion of the dusts or
the like into the optical box. As the material for this sealing
member, an elastic substance, such as thermoplastic elastomer, is
used.
[0047] Here, "thermoplastic elastomer" includes all the polymers
which are as elastic as vulcanized rubber at a temperature level at
which they are used, and which can be melted by increasing their
temperature so that they can be molded, as is generally defined.
For example, it includes polyester elastomers, olefin elastomers,
styrene elastomers, and the like. However, it is not elastomers
alone that can be used as the material for the sealing member 5.
That is, any substance can be used as the material for the sealing
member 5, as long as it is elastic and a sealing member formed
thereof can satisfactorily seal the optical box. This embodiment
uses a thermoplastic elastomer as the sealing member 5. Therefore,
the sealing member 5 more easily deforms than the cap 3. The
elastic coefficient of the sealing member 5 is larger than the
elastic coefficient of the cap 3. The sealing member 5 is provided
by an insertion molding, as will be described hereinafter.
[0048] Generally speaking, the higher in density is elastomer, the
harder it is. Thus, the sealing member 5, which is formed of
elastomer, suffers from the following problem. That is, if screws
or the like fasteners are used to attach the lid to the optical
box, with the presence of the sealing member 5 between the lid and
optical box, the sealing member 5 is compressed as the screws or
the like are tightened. As the sealing member 5 is compressed, it
increases in density, and therefore, it increases in hardness,
because it is formed of elastomer. Thus, as the screws or the like
are tightened, the sealing member 5 having been increased in
hardness by the tightening of the screws or the like causes the
optical box and/or its lid to deform. As a result, the optical
scanning apparatus 1 changes in the path of the beam of laser
light.
[0049] Hereafter, therefore, an optical scanning apparatus
airtightly sealed with a sealing member capable of keeping the
optical box airtightly sealed without causing the optical box of
the optical scanning apparatus 1 to deform, will be described.
(Sealing Member)
[0050] Next, referring to FIGS. 3-10, the characteristic features
of a sealing member in accordance with the present invention will
be described using the sealing member 5 in this embodiment. FIG. 3
is a sectional view of one of the corner portions of the optical
box 2 of the optical scanning apparatus 1 in this embodiment, and
shows the optical box 2, its lid 3 and sealing member 5. FIG. 4 is
a schematic drawing of the corner portion of the optical box 2
before the attachment of the lid 3 to the optical box 2, and shows
the state of the optical box 2, lid 3, and sealing member 5 before
the attachment of the lid 3. FIG. 5 is a combination of a plan view
of the optical box, and a perspective view of the lid 2 as seen
from below. Further, FIG. 6 is sectional view of an insert molding
machine, and shows the general structure of the molding machine.
FIG. 7 is a perspective view of the optical box 2 and lid 3 of the
optical scanning apparatus 1, as seen from above, before the
attachment of the lid 3 to the optical box 2. FIG. 8 is a sectional
view of the sealing member shaped so that its cross section looks
like that of a thin wedge. FIG. 9 is a graph which shows the
relationship between the amount of pressure applied to the sealing
member 5 and the amount of the displacement of the tip of the
sealing member 5. FIGS. 10(a) and 10(b) are partially perspective
and partially cross sectional views of a combination of one of the
modified versions of the sealing member 5 and lid 3 in the
preferred embodiment, and a combination of another modified
versions of the sealing member 5 and lid in the preferred
embodiment.
[0051] Referring to FIG. 5, the sealing member 5 is attached to the
inward surface of the lid 3 of the optical box 2 in such a manner
that it extends along the edge of the lid 3. Next, referring to
FIG. 3, the sealing member 5 is shaped so that after the attachment
of the lid 3 to the optical box 2, it extends to the inward surface
21 of the lateral wall of the optical box 2 from the sealing member
attachment portion 20 of the lid 3. That is, the sealing member 5
is structured (shaped) so that in terms of its cross section, the
center line Ox of the wedge-like portion 5A of the sealing member 5
(FIGS. 4 and 8) has an angle of .alpha. relative to the inward
surface 21. More specifically, the sealing member 5 is shaped so
that after the attachment of lid 3 to the optical box 2, the angle
.alpha. between the center Ox and the inward surface 21 of the
lateral wall of the optical box 2 is acute. Thus, after the
attachment of the lid 3 to the optical box 2, the sealing member 5
remains in contact with the inward surface 21 in such a manner as
to continuously presses on the internal surface 21 across the
entirety of the horizontal circumference of the optical box 2.
Therefore, even if dusts or the like contaminants inwardly passes
through the gap(s) between the lid 3 and optical box 2, it is
prevented from entering all the way into the main portion of the
internal space of the optical box 2.
[0052] Normally, the sealing member 5 is shaped so that the angle
.alpha. is in a range of 10.degree.-60.degree.. If the angle
.alpha. is no more than 10.degree., the amount of pressure which
the sealing member 5 generates as it presses on the internal
surface 21 is insufficient for the sealing member 5 to keep the
optical box 2 airtightly sealed. On the other hand, if the angle
.alpha. is no less than 60.degree., the amount of pressure which
the sealing member 5 generates as it presses on the internal
surface 21 is likely to be large enough to cause the optical box 2
to significantly deform. Therefore, it is not desired to shape the
sealing member 5 so that its angle .alpha. is no less than
60.degree..
[0053] That is, in this embodiment, the sealing member 5 is
attached to the lid 3 of the optical box 2 as described above.
Therefore, it does not occur that the sealing member 5 is pinched
between the lid 3 and optical box 2. Thus, it does not occur that
the sealing member 5 is deformed by being pinched between the lid 3
and optical box 2.
[0054] Next, referring to FIGS. 3-5, the gist of the method, in
this embodiment, for attaching the lid 3 to the optical box 2 will
be described. First, referring to FIG. 4, the lid 3 is to be
positioned so that the sealing member 5 comes in contact with the
internal surface 21 of the lateral wall of the optical box 2 across
the entirety of the horizontal circumference of the optical box.
Then, the lid 3 is to be placed in contact with the optical box 2
by being pressed in such a manner that the sealing member 5 is
pushed all the way into the optical box 2 while remaining in
contact with the internal surface 21. Then, the lid 3 is to be
fastened to the optical box 2 by putting the screws 23 (fasteners)
through the screw holes 26 and 27 and tightening them.
[0055] Next, referring to FIG. 4, designated by a referential sign
.DELTA.K is the amount of the deformation which occurs to the
sealing member 5 when the lid 3 is attached to the optical box 2.
In the case of this embodiment, the pressure which the sealing
member 5 applies to the inward surface 21 of the lateral wall of
the optical box 2 is nothing but the pressure which is generated by
the deformation of the sealing member 5 itself. Thus, the amount of
the pressure which the sealing member 5 applies to the internal
surface 21 is proportional to the amount .DELTA.K of deformation of
the sealing member 5 (more specifically, amount of displacement of
tip of sealing member 5), being therefore not substantial. In other
words, the pressure which keeps the sealing member 5 pressed upon
the inward surface 21 comes from the elastic deformation of the
sealing member 5.
[0056] A conventional optical scanning apparatus structured so that
its sealing member formed of elastomer is placed between its
optical box and lid thereof suffers from the following problem: As
the screws are tightened to keep the optical box airtightly sealed,
the sealing member between the optical box 2 and lid 3 is
compressed, that is, it is deformed. This deformation of the
sealing member 5 causes the optical box 2 and lid 3 to deform.
[0057] In comparison, in the case of the above described optical
scanning apparatus 1 in this embodiment, its sealing member 5 is
not compressed by the optical box 2 and lid 3 even when the screws
for attaching the lid 3 to the optical box 2 are tightened.
Therefore, unlike the optical box of a conventional optical
scanning apparatus, the optical box 2 of the optical scanning
apparatus in this embodiment does not suffer from the deformation
attributable to the sealing member deformation.
[0058] Further, the sealing member 5 in this embodiment remains in
contact with the inward wall 21 while remaining deformed by an
amount which corresponds to the amount .DELTA.K. Therefore, the
sealing member 5 continuously presses on the inward surface 21.
Thus, the material for the sealing member 5 is selected from among
the elastomers which are low enough in resiliency for the sealing
member 5 formed thereof, not to cause the optical box 2 to deform.
Further, the optical box 2 designed so that the sealing member 5 is
attached to such areas of the lid 3 that do not cause the sealing
member 5 to deform the optical box.
[0059] Next, referring to FIG. 3, the sealing member 5 is shaped so
that it cross section is in the form of a roughly triangular narrow
wedge (which hereafter may be referred to as wedge 5A) (FIGS. 3 and
4). Incidentally, the sealing member 5 is shaped so that it is
roughly uniform in cross section, being wedge shaped, across the
entirety of the horizontal circumference of the lid 3.
[0060] As described above, the sealing member 5 of the optical box
2 of the optical scanning apparatus in this embodiment is shaped,
and also, is attached to the lid 3, in such a manner that after the
attachment of the lid 3 to the optical box 2, the sealing member 5
holds an angle relative to the internal surface 21 of the lateral
wall of the optical box 2.
[0061] Next, referring to FIGS. 6 and 7, the method for
manufacturing the sealing member 5, more specifically, the reliable
method for molding a sealing member which is accurate in shape and
also, is strong enough to ensure that the optical box 2 remains
satisfactorily sealed, will be described.
[0062] FIG. 6 is a schematic sectional view of the insert molding
machine for manufacturing the sealing member 5 in this embodiment,
and shows the structure of the machine. This insert molding machine
is provided with: a mold 60 for molding the sealing member 15; a
mold 61 for holding the lid 3; a mold 62 having gates through which
the molds 60 and 61 are filled with thermoplastic elastomer; and a
mold 62 having a gate through which the molds 60 and 61 are filled
with the thermoplastic elastomer. As the molds 60, 61, 62 and 63
are put together, the entirety of the gate 25 (elastomer passage),
through which the elastomer flows into the combination of the molds
60 and 61, are completed.
[0063] Referring to FIG. 6, first, the lid 3 is positioned in the
mold 61. Then, the melted elastomer is poured into the combination
of the molds 60 and 61. As the melted elastomer is poured, its
flows through the holes 26, with which the lid 3 is provided as
shown in FIG. 7. Then, the elastomer is cooled. As the elastomer
cools, the sealing member 5 is formed on the lid 3 so that it will
remain attached to the lid 3 as shown in FIG. 5.
[0064] The insert molding machine for forming the sealing member 5
in this embodiment is structured to ensure that after the molds 60,
61, 62 and 63 are put together the thermoplastic elastomer flows
through the lid 3, that is, the component to which the resultant
sealing member 5 will remain attached, during the processing of
molding the sealing member 5. However, when the molds 60, 61, 62,
and 63 are separated at the end of the molding process, the
elastomer passage 25 is made up of the gates (25), with which the
molds 62 and 63 are provided, is broken up at the interface between
the lid 3 and mold 62. Therefore, the portions of the sealing
member 5, which are in the holes 26 of the sealing member 5,
through which the elastomer was poured into the combination of the
molds 60 and 61 to form the sealing member 5, are not smooth across
their surfaces on the outward side of the lid 3. However, the tip
portion (functional portion) of the sealing member, 5 that is, the
opposite end of the sealing member 5 from its outward end, are
entirely smooth enough to reliably keep the optical box 2
airtightly sealed.
[0065] Since the mold for manufacturing the sealing member 5 in
this embodiment is structured as described above, the molding
pressure can be applied in the direction to ensure that the lid 3
and resultant sealing member 5 remain airtightly in contact with
each other, and therefore, the body of elastomer conforms in shape
to the molding surface of each mold. Further, the sealing member 5
is molded so that several portions of the sealing member 5 remain
in the through holes 26 of the lid 3. That is, the several portions
of the sealing member 5, which were molded by the through holes 26
of the lid 3 are integral with the lid 3, improving thereby the
sealing member 5 in terms of the airtightness between the lid 3 and
sealing member 5. Further, the portions of the sealing member 5,
which are in the holes 26 of the lid 3, function like the roots of
a plant, ensuring that the sealing member 5 remains stable in
shape.
[0066] As described above, the sealing member 5 is molded in such a
shape that ensures that after the attachment of the lid 3 to the
optical box 2, the sealing member 5 extends to the inward surface
21 and remains in contact with the inward surface 21. Next,
referring to FIG. 8, this shape (structure) of the sealing member 5
will be described in more detail. One of the characteristics of the
sealing member 5 in this embodiment is that it is relatively thin
at its tip 5a and thick at its base 5b. The amount of pressure
which the sealing member 5 applies to the inward surface 21 is
changed by the change in the amount .DELTA.K by which the tip of
the sealing member 5 is displaced. In terms of the amount of the
change which is caused, by the displacement of the tip of a sealing
member, to the amount of pressure applied to the inward surface of
the optical box by the sealing member 5, a sealing member whose tip
portion is the same in thickness as its base portion is greater
than a sealing member whose tip portion is thinner than its base
portion. As long as a sealing member remains in contact with the
inward surface of the lateral wall of the optical box, the dusts or
the like contaminants can be prevented from entering all the way
into the optical scanning apparatus. Therefore, it is not desired
to give a sealing member such a shape that causes the sealing
member to keep on pressing the inward surface 21 by an
unnecessarily large amount of force while it is remaining in
contact with the inward surface.
[0067] Therefore, the sealing member 5 in this embodiment is shaped
so that its base portion 5b is greater in thickness than its tip
portion 5a.
[0068] FIG. 9 is a graph which shows the effects which the change
in the thickness of the sealing member 5 has upon the amount of the
pressure applied to the inward surface 21 by the sealing member 5.
The horizontal axis of the graph represents the amount .DELTA.K of
the displacement of the tip 5a of the sealing member 5, and the
vertical axis represents the amount of pressure which the sealing
member 5 applies to the inward surface 21 when the amount of
displacement of the tip 5a of the sealing member 5 is .DELTA.K.
More specifically, the amount of pressure which the sealing member
5 applies to the inward surface 21 means the amount of pressure
which the sealing member 5 applies to the inward surface 21 per
centimeter in terms of the circumferential direction of the sealing
member 5 after the attachment of the lid 3 of the optical box 2.
FIG. 9 shows the results of the actual tests.
[0069] In the tests carried out to obtain the data on which FIG. 9
is based, the thickness of the sealing member 5, that is, the
dimension of the sealing member 5 in terms of the direction
perpendicular to the inward surface 21, that is, the surface on
which the sealing member 5 presses, was set as follows. That is,
the thickness T0 of the base of the sealing member 5 (portion of
sealing member, which is in contact with sealing member attachment
portion 20 of lid 3) was 1.6 mm, and the length Ds of the sealing
member 5, that is, the distance from the intersection between the
center line Ox of the wedge 5A and the sealing member attachment
portion 20 to the tip 5a, was 5 mm. Further, the thickness T1,
which is the thickness of the portion of the wedge 5A, at the point
which is 1/3 of the length Ds from the tip 5a in terms of the
lengthwise direction of the wedge 5A, was no more than 1/2 of the
thickness T0 of the base of the sealing member 5
(T1.ltoreq.(1/2)T0), more specifically, 0.8 mm. Further, the
sealing member 5 was shaped so that it gradually reduces in
thickness from the portion which is T1 in thickness, toward the tip
5a, in such a manner that the thickness T of the tip 5a becomes
roughly 0.5 mm. More specifically, in this embodiment, the tip
portion 5a of the sealing member was made semicircular, and 0.5 mm
in diameter.
[0070] As will be evident from FIG. 9 (graph), when the distance
between the tip of the sealing member 5 and the inward surface 21
of the optical box 2 was changed by 0.1 mm (for example, when
distance was changed from 0.5 mm to 0.6), the amount .DELTA.P2 of
the change which occurred to the amount of pressure applied to the
inward surface 21 by the sealing member 5 was roughly 12 gf per
centimeter in terms of the direction parallel to the horizontal
circumference of the optical box 2.
[0071] In comparison, in the case of the sealing member 5 which was
uniform in thickness from the base to the tip (if T1=T0), the
amount .DELTA.P1 of the change in the amount of pressure applied to
the inward surface 21 by the sealing member 5 was roughly 30 gf per
centimeter, that is, no less than twice that applied by the sealing
member 5 in accordance with the presence invention, under the same
conditions.
[0072] As will be evident from the results of the above described
tests, when the tip portion of the sealing member was displaced,
the sealing member which was uniform in thickness of the wedge 5A
in terms of the lengthwise direction of the wedge 5A (T1=T0) was
excessive in the amount of the change which occurred to the amount
of pressure which the sealing member applied to the inward surface
21. In other words, this sealing member was likely to cause the
wall of the optical box to deform. Obviously, it is possible to
increase the wall of the optical box in thickness. However, the
increase in the thickness of the wall of the optical box results in
the increase in apparatus size, and therefore, is not desired.
[0073] Further, from the standpoint of preventing the wall of the
optical box from deforming, it is desired that the pressure which
the sealing member 5 applies to the inward surface 21 is as small
as possible, as long as the sealing member 5 remains in contact
with the inward surface 21. In this embodiment, therefore, the
amount .DELTA.K of the displacement of the tip 5a of the sealing
member 5 was set to a value no more than 1/6 of the length Ds of
the wedge 5A, in consideration of the shape of the wedge 5A.
Further, based on the rigidity of the optical box 2, the criterial
value for the amount of pressure applied to the inward surface 21
of the optical box 2 by the sealing member 5, below which the
optical box 2 is not deformed by the pressure, was set to be no
more than 100 gf per centimeter in terms of the direction parallel
to the horizontal circumferential direction of the optical box 2.
Further, the sealing member 5 in this embodiment was 61 in the
hardness scale defined by "JIS K7215 HDA".
[0074] FIGS. 10(a) and 10(b) show the combinations of the modified
versions of the sealing member 5 and lid 3 in the preferred
embodiment, one for one. As will be evident from FIGS. 10(a) and
10(b), it is desired that the base portion of the sealing member 5
is embedded in the lid 3; the base 5b of the sealing member is
inward of the lid 3 relative to the inward surface of the lid 3,
more specifically, inward of the sealing member attachment portion
20 of the inward surface of the lid 3. More specifically, the lid 3
in this embodiment is provided with a narrow groove 45, which
extends along the entirety of the circumferential edge of the lid
3. From the standpoint of ensuring that the sealing member 5
remains mechanically stable after the attachment of the lid 3 to
the optical box 2, it is desired that the lid 3 is designed as will
be described next, regarding the groove 45.
[0075] The experiments carried out by the inventors of the present
invention revealed that it is desired that the depth to which the
base portion of the wedge 5A is embedded in the lid 3 is no less
than 1/2 of the thickness T0 of the base of the wedge 5A. The
insertion of the base portion of the sealing member 5 into the
groove 45 ensures that the sealing member 5 remains satisfactorily
attached to the lid 3, because the reactive force to which the
sealing member 5 is subjected as it presses on the inward surface
21 is partially borne by the base portion of the sealing member 5,
which is in the groove 45. It should be noted here that in a case
where the base portion of the sealing member is embedded in the lid
3, TO is the thickness of the wedge 5A at the inward surface of the
lid 3 (FIG. 8).
[0076] Next, referring to FIG. 10(b), instead of providing the lid
3 with the groove 45, simply providing the lid 3 with a supporting
wall 46 for supporting the sealing member 5 by the base portion of
the sealing member 5, can also achieve the same effects as those
described above.
[0077] As described above, the adoption of the characteristic
features of the structure of the sealing member 5 in this
embodiment makes it possible to provide a sealing member which is
stable in the amount of pressure it applies to the inward surface
21 of the optical box 2.
[0078] Further, it is possible to further improve the sealing
member 5 in terms of the airtightness between the inward surface 21
and sealing member 5, by modifying the sealing member 5 in each of,
or combination of, the thickness and length of its wedge 5A, and
its hardness.
[0079] As for the amount of the pressure which the sealing member 5
structured as described above applies to the inward surface 21, it
was judged proper if it was no more than 100 gf per centimeter, for
the following reason.
[0080] If the optical box 2 is deformed by the pressure applied to
the inward surface 21 by the sealing member 5, the deformation
sometimes causes the beam of laser light projected toward the
peripheral surface of the photosensitive drums 10, to deviate by
several micrometers to several tens of micrometers in terms of the
position of the point of the peripheral surface of each of the
photosensitive drums 10, onto which the beam of laser light
focused. Thus, if the amount of the pressure which the sealing
member 5 applied to the inward surface 21 is excessive (which
results in deformation of optical box), it is possible that an
electrostatic latent image is formed on the wrong portion of the
peripheral surface of the photosensitive drums 10.
[0081] Further, the amount of the deformation of the optical box 2
was extremely small. Thus, it was virtually impossible to
accurately measure the amount of the deformation of the optical box
2. Therefore, in order to determine the acceptable range for the
amount of the pressure applied to the inward surface 21 by the
sealing member 5, that is, the range in which the positional
deviation of the focal point of the beam of laser light, which was
caused by the deformation of the optical box 2, is acceptable,
experiments were carried out to find out the relationship between
the amount of the pressure applied to the inward surface 21 by the
sealing member 5 and the positional deviation of the focal point of
the beam of laser light on the peripheral surface of the
photosensitive drums 10.
[0082] The studies made by the inventors of the present invention
revealed that in the case of an ordinary optical box 2, no more
than 100 gf per centimeter was the range that does not cause the
beam of laser light to significantly deviate in position.
[0083] Further, referring to FIGS. 11(a-1), 11(a-2), and 11(b), it
is possible to modify the above described preferred embodiment in
terms of the structure of the sealing member 5 or both the sealing
member 5 and optical box 2. The sealing member shown in FIGS.
11(a-1) and 11(a-2) is provided with an additional sealing portion
which extends in the outward direction of the optical box from the
base portion of the sealing member so that as the lid 3 is attached
to the optical box 2, the tip portion of the additional sealing
portion is sandwiched between the lid 3 and the optical box 2.
Hereafter, the additional sealing portion of this sealing member
will be referred to as a gap filling elastic portion 37.
[0084] As the lid 3 is attached to the optical box 2, the gap
filling elastic portion 37 fills the gap provided between the
optical box 2 and the lid 3. However, the amount of the stress
generated by the deformation of the gap filling elastic portion 37
can be minimized by shaping the gap filling portion 37 and gap so
that their measurements are roughly 1 mm or so, and also, by
strictly controlling the sealing member manufacturing process in
terms of the measurements of the gap filling portion 37, lid 3 and
optical box 2. Thus, the amount of stress attributable to the
deformation of the gap filling portion 37 is no more than 10 gf per
centimeter in terms of the circumferential direction of the sealing
member. In other words, it is smaller by no less than one place
than the amount of the pressure applied to the optical box 2 by the
sealing member 5. Therefore, the problem that the optical box 2 is
deformed by the deformation of the gap filling portion 37 does not
occur.
[0085] In a case where a part of the inward surface of the lateral
wall of the optical box 2 is slanted as shown in FIG. 11(b), which
is a sectional view of the optical box in another modification of
the preferred embodiment, the sealing member 5, which in this case
is an elastic sealing member 38, is attached to the lid 3 in such a
manner that after the attachment of the lid 3 to the optical box 2,
it remains in contact with the slanted portion 39 of the inward
surface of the wall of the optical box 2. This modified version of
the preferred embodiment is intended to partially modify the
preferred embodiment, from the standpoint of affording more
latitude in designing an optical scanning apparatus, in terms of
the positioning of its components to be disposed in its optical
box. This modified version is also the same as the sealing member
having the gap filling elastic portion 35 in that the amount of the
pressure applied to the inward surface 21 of the lateral wall of
the optical box, and therefore, neither does this cause the optical
box to deform.
[0086] Described above are only two of the modified versions of the
sealing member 5, lid 3, and optical box 2 in the preferred
embodiment. It will be evident, however, that any sealing member
for sealing the optical box of an optical scanning apparatus, and
any structural arrangement for the optical box and lid of an
optical scanning apparatus, are to be regarded as the results of
the modifications of the preferred embodiment of the present
invention, and therefore, are thought to fall within the scope of
the present invention.
[0087] Described next will be the results of the above mentioned
experiments carried out by the inventors of the present
invention.
[0088] The conditions set up for the experiments are as follows:
The length Ds of the wedge 5A was in a range of 3-10 mm, and the
shape of the wedge 5A is such that its thickness T1, that is, the
thickness at the point which is 1/3 the length of the wedge 5A from
the tip of the wedge 5A, was 1/2 the thickness T0, that is, the
thickness of the wedge 5A at its base. Further, the amount .DELTA.K
of the displacement of the top 5a of the sealing member 5 was made
to be no more than 1/6 the length Ds of the wedge 5A. Further,
sealing members which are 25, 40, 61, 75, and 90, respectively, in
hardness are evaluated.
[0089] As for the criterion for the evaluation, the sealing members
5 which were no more than 100 gf per centimeter were evaluated as
the acceptable sealing members.
[0090] The relationship between the thickness T0, or the thickness
of the wedge 5A at its base, and the hardness of the acceptable
(satisfactory) sealing member was as follows:
[0091] T0=0.7-1.8 mm . . . sealing members which were 40, 61, 75,
or 90 in hardness
[0092] T0=1.9-3.0 mm . . . sealing members which were 25, 40, 61,
or 75 in hardness
[0093] T0=3.1-3.8 mm . . . sealing members which were 25, 40, or 61
in hardness
[0094] Regarding the thickness T0 of the base of the wedge 5A of
each of the sealing members listed above, it was no more than
roughly 3 mm. Thus, in consideration of the generous amount of
tolerance in the amount of pressure applied by a sealing member, it
may be determined that the sealing members which are no more than 3
mm in the thickness (T0) at the base of their wedges 5A, and are in
a hardness range of 40-75 are satisfactory with room to spare.
Here, "hardness" means the hardness defined in "JIS K7215 HDA".
[0095] Structuring the optical box of the optical scanning
apparatus as described above while using thermoplastic elastomer as
the material for the sealing member 5 for the optical box makes it
possible to provide an optical scanning apparatus which remains
satisfactorily sealed from dusts or the like contaminants without
suffering from the problem that an optical scanning apparatus is
reduced in performance by the deformation of its optical box.
Embodiment 2
[0096] This preferred embodiment of the present invention will be
described primarily regarding the problem which might occur when
assembling the optical scanning apparatus 1, based on the contents
of the description of the first preferred embodiment of the present
invention given above.
[0097] The abovementioned problem that when the lid 3, to which the
sealing member 5 formed of thermoplastic elastomer has been
attached, is attached to the optical box 2 of the optical scanning
apparatus 1, dusts or the like contaminants enter the optical box.
Thus, hereafter, the means for preventing the dusts or the like
from entering the optical box (optical scanning apparatus) will be
described along with this problem.
[0098] It is sometimes noticed, during the process of attaching the
lid 3 to the optical box 2, that after the formation of the sealing
member 5 on the lid 3 in a manner to be integrated with the lid 3,
fine dusts have adhered to the integral combination of the sealing
member 5 and lid 3.
[0099] These dusts are the dusts which were floating in the ambient
air. Unless some measures are taken, the dusts having adhered to
the sealing member 5 and lid 3 are destined to enter the interior
of the optical box, as the lid 3 is attached to the optical box 2.
Thus, it is possible that the optical components in the optical box
will be soiled by these dusts.
[0100] It is generally thought that dusts is more likely to adhere,
and remain adhered, to an object holding static electricity than an
object holding no static electricity. Thus, it has been known that
one of the effective means for preventing the dusts from entering
the optical box during the process of assembling an optical
scanning apparatus is to reduce, in electrical potential level, the
components of the apparatus known to electrostatically attract
dusts, with the use of a charge removing apparatus, such as an
ionizer, before they are mounted. It is reasonable to think that
this means also effective to prevent dusts from adhering to the
sealing member 5 and/or removing the dusts from the sealing member
5.
[0101] However, these components sometimes increase in charge level
even after the removal of the static electricity by a charging
removing apparatus. That is, it is possible that the components
become charged again with the elapse of time. On the other hand, in
a case where the sealing member is rid of static electricity
immediately before the process of assembling an optical scanning
apparatus, it is impossible to thoroughly remove the dusts having
adhered to the sealing member. Therefore, it is desired that an
optical scanning apparatus is assembled in an ambience in which the
amount by which dusts adheres to its components is as small as
possible.
[0102] Thus, the inventors of the present invention studied various
means for reducing the amount by which dusts adheres to the
combination of the sealing member 5 and lid 3 of the optical box,
after the molding of the sealing member 5 with the use of the
insert molding machine. Further, the following six substances were
studied as the material used to form the sealing member 5 by insert
molding. These substances are the same as the resinous substance
used as the material for the sealing member 5 in the first
preferred embodiment, except that they are made different in volume
resistivity by dispersing carbon, as electrically conductive
substance, in the resinous substance:
[0103] A: 5.times.10.sup.13 .OMEGA..times.cm in volume resistivity
R
[0104] B: 5.times.10.sup.10 .OMEGA..times.cm in volume resistivity
R
[0105] C: 1.times.10.sup.10 .OMEGA..times.cm in volume resistivity
R
[0106] D: 5.times.10.sup.8 .OMEGA..times.cm in volume resistivity
R
[0107] E: 1.times.10.sup.6 .OMEGA..times.cm in volume resistivity
R
[0108] F: 5.times.10.sup.5 .OMEGA..times.cm in volume resistivity
R
[0109] The measured surface potential levels of these thermoplastic
elastomers were as follows: The surface potential levels of
substances A and B were in a range of roughly 100-1K, and were
unstable. The surface potential levels of the substances C-F were
in a range of roughly 50-100 V. These figures were obtained by
measuring the surface potential levels of the sealing members
formed of these substances, after the sealing members molded by
insert molding were left as it was, following the molding of the
sealing members.
[0110] It is reasonable to think, based on these results, that it
is unlikely for dusts to electrostatically adhere to the sealing
members formed of the materials C-F. However, the materials F was
substantial in the amount of carbon content, and therefore, the
sealing members formed of the material F were inferior in
elasticity, being unable to satisfactorily seal the optical
box.
[0111] Thus, the proper range for the volume resistivity of the
material for the sealing member 5, that is, the range in which the
sealing member formed of any of these materials can satisfactorily
seal the optical box while remaining low in potential level, is
1.times.10.sup.6 .OMEGA.cm.ltoreq.R.ltoreq.1.times.10.sup.10
.OMEGA.cm.
[0112] Further, there were thermoplastic elastomers which were
lower in volume resistivity than those listed above. However, an
optical scanning apparatus is an electric device which internally
holds a motor, a semiconductor laser, and groups of electric
circuit. Therefore, the thermoplastic elastomers which were lower
in volumetric resistivity than those listed above were not taken
into consideration as the material for the sealing member, in fear
of short circuit.
[0113] Further, the substances listed above were easily obtainable,
and were relatively stable in volume resistivity. These materials
have been disclosed in Japanese Laid-open Patent Applications
2003-20411 (title of invention: thermoplastic resinous compounds)
and 2003-277622 (title of invention: compound for charge control,
and method for manufacturing compound).
[0114] It is evident from the detailed description of the preferred
embodiment of the present invention that as long as the volume
resistivity of a material for a sealing member is within the range
of
1.times.10.sup.6 .OMEGA.cm.ltoreq.R.ltoreq.1.times.10.sup.10
.OMEGA.cm,
[0115] the potential level to which the material will be charged is
no more than the criterial value of 100 V. Therefore, it is
reasonable to think that a sealing member formed of this material
is relatively small in the amount of dusts adhesion. Thus, it is
desired that an elastomer with the above described characteristics
is used as the material for the sealing member for an optical
scanning apparatus.
[0116] With the use of a lid provided with a sealing member, such
as those described above, as the lid 3 for the optical box of an
optical scanning apparatus, it is possible to reduce the amount by
which dusts enter the optical scanning apparatus 1 when the optical
scanning apparatus 1 is assembled. That is, the use contributes to
the manufacturing of an optical scanning apparatus (1) which is
superior and stable in writing performance.
Embodiment 3
[0117] Referring to FIGS. 13A, 13B and 13C, a further embodiment of
the present invention will be described. FIG. 13A is a sectional
view of a part of a cap 3 and a different bent type sealing member
131. FIG. 13B is a partial perspective view of the bent type
sealing member 131. FIG. 13C is a partially sectional view
illustrating a state in which the bent type sealing member 131 is
in contact with the inner wall 21 (side wall 21) of the optical
box. The broken line 21a shows a surface of the wall when the inner
wall 21 is offset inwardly.
[0118] The bent type sealing member 131 of this embodiment is
produced, similarly to the first embodiment, by the insertion
molding with a thermoplastic elastomer, wherein the sealing member
131 has a material and rigidity which are different from those of
the cap 3, similarly. The bent type sealing member 131 of this
embodiment is different from the first embodiment in the sealing
material and the cross-sectional configuration. As shown in FIG.
13A, the bent type sealing member 131 includes a base portion 132
extending from the cap 3, and a contact portion 133 extending and
bending from the base portion 132 toward the inner wall 21 of the
optical box. In other words, the bent type sealing member 131 is
constituted by the base portion 132 and the contact portion 133. As
shown in FIG. 13C, the contact portion 133 is contacted to the
inner wall 21 when it caps the optical box 2.
[0119] The contact portion 133 is thinner and longer than in the
first embodiment, and therefore, it is more flexible. With the
higher flexibility of the contact portion 133, the force required
to bend is more even despite the position where it is bent varies
slightly. In other words, the force pressing against the wall is
small, and therefore, the deformation of the inner wall 21 is
small.
[0120] On the other hand, the base portion 132 is relatively thick
as compared with the contact portion 133 to be more difficult to
flex. Because of the larger thickness, in the section, of base
portion 132, when the cap 3 is set to the optical box 2, the
contact portion 133 flexes such that leading side of the contact
portion 133 bends toward the cap 3. By doing so, the dust free
property of the optical box is assured by the bent type sealing
member 131.
[0121] Furthermore, the bent type sealing member 133 provides the
following advantages. The optical box 2 is a mold product, and
therefore, it is influenced by the manufacturing variation of the
metal. That is, as shown in FIG. 13C, the position of the inner
surface of the wall 21 may be offset as indicated by the phantom
line 21a due to the variation in the manufacturing accuracy. Even
in such a case, the leading side of the bent type sealing member
131 compensate for such a variation in a wide range by the bending
as indicated by broken lines. More particularly, the flexibility is
enough to accommodate approx. .+-.0.7 mm deviation of the inner
surface of the inner wall 21 and accommodate .+-.1.5 mm in total
including the manufacturing variation of the cap, so that bent type
sealing member 131 is assuredly contacted to the surface of the
inner wall 21.
[0122] It is desirable that thin long portion in the free end side
of the sealing member has a length of approx. 2-10 mm and a
thickness of approx. 0.2-0.8 mm.
[0123] The thickness of the contact portion 133 may be partly
changed to limit the position of bending when the contact portion
133 contacts the inner wall 21.
[0124] According to this embodiment, even when the position of the
sealing member 131 relative to the inner wall 21 varies, the urging
pressure can be significantly uniform. In addition, it can be
closely contacted to the inner wall 21 assuredly, and therefore,
the dust preventing sealing effect can be assured even under the
influence of manufacturing tolerance.
[0125] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0126] This application claims priority from Japanese Patent
Application No. 057079/2008 filed Mar. 6, 2008 which is hereby
incorporated by reference.
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