Mirror installation in an optical device

Structure and method for mirror installation in an optical device such as a laser beam scanning device. An installation reference surface and a support surface are formed to be faced to but spaced apart from each other. The mirror is installed between the above two surfaces in such a manner that the reflection surface of the mirror contacts the installation reference surface. An elastic element is inserted and press-fitted between the rear surface of the mirror and the support surface so as to push the mirror against the installation reference surface. Thus, the mirror is stably held between the installation reference surface and the support surface with accurately positioning the reflecting surface of the mirror.

BACKGROUND OF THE INVENTION 
The present invention relates to a mirror installation in an optical 
device, and more particularly to the installation structure and the 
installation method of a reflection mirror in a light scanning device. 
In the prior arts, one of well known is a laser beam scanning device 
employed in, for instance, a laser printer. In the laser scanning device, 
a deflecting means is provided for scanning a predetermined area with a 
laser beam which is emitted, for example, from a fixed semiconductor 
laser. 
The deflecting means has at least one deflecting surface which is 
perpendicular to a light passage of the laser beam emitted from the laser. 
The deflecting means is controlled to change an angle of its deflection 
surface with respect to the emitted laser beam so that a relative 
reflection angle against the emitted laser beam can be continuously 
changed. 
In the laser printer employing the above scanning device, it is necessary 
to synchronize the modulation of the laser beam with its scanning 
operation, and so a photo-sensor is usually arranged at an edge zone of 
the beam scanning area to take timing of the beam modulation. 
The photo-sensor is, however, often located at a position which is out of 
the beam scanning area due to requirements for effective arrangements of 
related parts and so on, and a reflecting mirror is instead placed at the 
edge zone of the beam scanning area for directing the beam to the 
out-placed photo-sensor. 
The mirror has conventionally been installed in the device, for example, by 
means of a leaf spring 9 and a tapping screw 10 as illustrated in FIG. 7, 
wherein reference numerals 7c and 8 indicate a reflecting mirror and a 
mounting wall formed on a housing case 2,. respectively. 
With this installation, the rear side surface of the reflection mirror 7c 
first abuts the installation wall 8 and then urged and fixed thereto by 
the leaf spring 9 and the tapping screw 10. Accordingly, installing work 
is troublesome and time-consuming. Further, mirror surface would incline 
due to roughness of the rear surface of the mirror and/or to uneven 
thickness of the mirror, which influences timing of the modulation of the 
laser beam. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide improved 
structure and method for installation of a mirror in an optical device, 
capable of avoiding the aforementioned disadvantages, and of guaranteeing 
easy and quick nevertheless accurate installation of a mirror even though 
the rear surface of the mirror is roughly treated and/or if the thickness 
of the mirror is uneven. 
For the above purpose, in accordance with the present invention, there is 
provided a mirror installation structure comprising: a front installation 
wall provided at the predetermined position, said first installation wall 
having a front surface facing toward an optical path of said scanning 
device and a reverse surface formed opposite side of the front surface, 
said reverse surface being finished as an installation reference surface; 
a rear support wall provided to be spaced from the installation reference 
surface and to face with each other, said mirror being installed in such a 
manner that a reflection surface of the mirror is located to contact with 
the installation reference surface of the front installation wall; and an 
elastic element being inserted and press-fitted between the mirror and the 
rear support wall so as to securely hold and bias the mirror toward the 
installation reference surface. 
The elastic element may be constituted as having a plurality of spring 
pieces, each of which is formed by cutting a part of the metallic plate 
into a U-shaped configuration and bending the cut part outward. 
The elastic element may be constituted as additionally having at least one 
bent flange on the top portion of the elastic element for preventing the 
mirror from falling out. 
The elastic element may alternately be constituted by being folded to be 
approximately U-shaped configuration so as to be press-fitted between the 
mirror and the rear support wall. 
Further provided, according to this invention, is a method for installing a 
mirror in an optical device, comprising the steps of: forming an 
installation reference surface and a support surface, said installation 
reference surface and said support surface being faced to but spaced apart 
from each other; placing said mirror in such a manner that the reflection 
surface of said mirror is contacted said installation reference surface; 
and inserting and press-fitting an elastic element between the rear 
surface of said mirror and said support surface so as to push the mirror 
against the installation reference surface, whereby said mirror is stably 
held between the installation reference surface and the support surface 
with accurately positioning the reflecting surface of the mirror. 
The above, and other objects, features and advantages of the present 
invention will become apparent from the following detail description which 
is to be read in conjunction with the accompany drawings.

DESCRIPTION OF THE EMBODIMENTS 
Hereinafter, the embodiments of the present invention are explained in 
detail by referring to accompanying drawings. 
FIG. 1 is a plan view showing principal parts of a laser beam scanning 
device embodying the invention, which is applied, for example, to a laser 
printer. 
The illustrated laser beam scanning device comprises a housing case 2 and 
various optical components mounted thereon. The optical components are a 
laser unit 3 for emitting laser beam carrying optical image information, a 
light deflection means 4 for deflecting the emitted laser beam, a pair of 
f.theta. lenses 5a and 5b for making constant a scanning speed of the 
laser beam on an image-forming surface X, a correction lens 6 for 
correcting astigmatism and so on caused by manufacturing errors of the 
f.theta. lenses 5a and 5b and so on, a reflecting mirror 7c for reflecting 
the laser beam, and a horizontal-sync signal generating unit 7 including a 
photo-sensor 7a which receives the beam reflected by the reflecting mirror 
7c. 
The laser unit 3 is constituted, not shown but as well known in the art, by 
a semi-conductor laser which is electrically ON/OFF controlled, a 
collimator lens for converting a light generated by the semi-conductor 
lens into a beam-shaped parallel luminous flux (i.e., laser beam), and so 
on. 
The light deflection means 4 is constituted by a polygonal mirror 4a and a 
motor 4b for rotating the polygonal mirror 4a at high revolutional speed. 
The correction lens 6 comprises a cylindrical lens and the like, and 
arranged between the laser unit 3 and the light deflecting means 4. The 
position of the correction lens 6 is adjusted along the optical axis 
indicated by the arrow in FIG. 1 so as to correct astigmatism and so on of 
the f.theta. lenses 5a and 5b. 
The horizontal-sync signal generating unit 7 comprises, besides the 
photo-sensor 7a, a signal output member 7b which generates and outputs 
horizontal-sync signal when the beam reflected by the reflection mirror 7c 
incidents upon the photo-sensor 7a. The horizontal-sync signal output from 
the signal output member 7b is transmitted to a controller, not shown, 
which regulates ON/OFF operation of the laser unit 3. 
The reflection mirror 7c is installed in the device as illustrated in FIG. 
1 and more particularly in FIGS. 2 through 4. 
That is, near one end of the beam scanning area, provided is a front 
installation wall 11 which is horizontally protruded from a rear support 
wall 12 formed on the housing case 2. 
The front installation wall 11 has a generally U-shaped figure, and is 
provided with a front-reverse surface 11a which is finished as an 
installation reference surface. The installation reference surface is 
accurately formed to stand vertically but to oblique at a predetermined 
angle with respect to the laser beam LB deflected by the deflection means 
4 (the polygonal mirror 4a). 
Behind the front installation wall 11, the reflection mirror 7c is 
installed in such a manner that a front reflection surface of the 
reflection mirror 7c contacts the front-reverse surface 11a of the front 
installation wall 11. 
The height of the front installation wall 11 is designed to be lower than 
that of the reflection mirror 7c, so that the reflection mirror 7c 
protrudes above the front installation wall 11. Thus, the deflected laser 
beam LB can be reflected on the front-reflection surface of the mirror 7c 
protruding above the front installation wall 11. 
When the reflection mirror 7c is installed in the foregoing manner, a 
reverse surface of the reflection mirror 7c is located to face to the rear 
support wall 12. Then, an elastic element 13 as illustrated in FIG. 3 is 
inserted and press-fitted between the rear support wall 12 and the reverse 
surface of the reflection mirror 7c, as illustrated in FIG. 4. The elastic 
element 13 pushes the reflection mirror 7c toward the installation 
reference surface (the front-reverse surface 11a) on the front 
installation wall 11. Thus, the reflection mirror 7c can be firmly held 
between the front installation wall 11 and the rear support wall 12 
without falling out. 
The elastic element 13 is made of metal plate and the like, and has a 
plurality of spring pieces 13a, 13b, each of which is formed by cutting a 
part of the metal plate in a U-shaped configuration and bending the cut 
part outward. One spring piece 13a is formed at middle of the metal plate 
and bent toward one side. A pair of spring pieces 13b, 13b are formed 
close to the spring piece 13a so as to place the spring piece 13a between 
these spring pieces 13b, 13b. Furthermore, there is provided a stopper 
piece 14 on a top portion of the elastic element 13 for preventing the 
reflection mirror 7c from falling out. The stopper piece 14 is formed to 
be perpendicular to the remaining part of the metal plate and to overlap 
with the upper surface of the reflection mirror 7c when it is inserted and 
press-fitted between the reflection mirror 7c and the rear support wall 
12. The elastic element 13 is inserted until the bottom portion 13e of the 
elastic element 13 reaches to a recessed portion 11b formed on the housing 
case 2. 
Thus, the front-reflection surface of the reflection mirror 7c can be 
pressed to contact the installation reference surface (i.e., the 
front-reverse surface 11a) of the front installation wall 11 by virtue of 
elastic force given by the plurality of spring pieces 13a, 13b of the 
elastic element 13. 
With the above arrangement, the installation of the reflection mirror 7c is 
completed with only one step of press-fitting the elastic element 13. 
In addition, as the placement of the front-reflection surface of the 
reflection mirror 7c is accurately regulated by the front-reverse surface 
11a (i.e., the installation reference surface) of the front installation 
wall 11, the beam detection is not affected by the manufacturing 
dispersions of the reverse surface of the reflection mirror 7c and/or the 
rear support wall 12. 
FIGS. 5 and 6 show another embodiment of the present invention. 
In this embodiment, the elastic element 13A is formed, as illustrated in 
FIG. 5, by being folded to be approximately U-shaped configuration so as 
to fit the clearance between the reflection mirror 7c and the rear support 
wall 12A. The elastic element 13A has a pair of middle portions 18, 18, 
each protruding outward in opposite direction so as to engage with the 
front-reverse surface 11a of the front installation wall 11 and the rear 
support wall 12A. 
Further provided is a hole 15 surrounded by a plurality of rising cut 
pieces 15a, 15a at the bottom portion of the elastic element 13A. At the 
top portion of the elastic element 13A, provided are a pair of 
bent-flanges 16, 16 for preventing the reflection mirror 7c from falling 
out. 
When the reflection mirror 7c is installed, the elastic element 13A is 
inserted and press-fitted between the reflection mirror 7c and the rear 
support wall 12A until the hole 15 is engaged with a pin 17 formed on the 
housing case 2, as illustrated in FIG. 6. 
With the above arrangement, the reflection mirror 7c is firmly held by the 
elastic element 13A to contact the installation reference surface (i.e., 
the front-reverse surface 11a of the front installation wall 11, as is the 
same as the first embodiment. 
As this invention may be embodied in several forms without departing from 
the spirit of essential characteristics thereof, the present embodiment is 
therefore illustrative and not restrictive, since the scope of the 
invention is defined by the appending claims rather than by the 
description preceding them, and all changes that fall within meets and 
bounds of the claims, or equivalence of such meets and bounds are 
therefore intended to embraced by the claims. 
The present disclosure relates to subject matters contained in Japanese 
Utility Model Application No. HEI 2-95484 filed on Sep. 10, 1990, which is 
expressly incorporated herein by reference in its entirety.