Light deflecting device

A light deflecting device for deflecting a light beam comprises a rotational mirror having two reflecting surfaces for reflecting the light beam, a rotational mirror mounting portion, biasing means for urging the rotational mirror against the mounting portion, and driving means for rotating the mounting portion.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a light deflecting device for use in a laser beam 
printer, a bar code reading apparatus or the like and a device for 
regulating such device. 
Heretofore, in light deflecting devices for deflecting a light beam, 
rotational polygon mirrors rotatable in one direction have been widely 
used because of the stability of their speed of rotation and their 
scanning speed. 
However, where such a rotational polygon mirror is used as the light 
deflecting device of a scanning optical apparatus, there is a problem that 
the deflecting-scanning surface or the reflecting surface thereof tilts 
from a plane perpendicular to the ideal main scanning surface to be formed 
by a scanning beam deflected thereby. 
A means for solving such a problem is, for example, one as disclosed in 
Japanese Laid-Open Patent Application No. 63-188112 (corresponding U.S. 
Application Ser. No. 149,020 filed on Jan. 27, 1988 (now U.S. Pat. No. 
4,915,465) and corresponding EP Application No. 88101263 filed on Jan. 28, 
1988 and published on Aug. 17, 1988 under EP Publication No. 0278332). 
That is, the opposed portions of a cylindrical metallic member are cut 
into parallel flat surfaces and these two surfaces are used as reflecting 
surfaces for deflecting and scanning a light beam. This rotational mirror 
is mounted so that the two parallel reflecting surfaces may be parallel to 
the direction of inclination of the mounting flange surface of the 
rotational mirror and thereby the above-mentioned tilt of the reflecting 
surface of the rotational mirror by the inclination of the mounting flange 
surface may not occur, whereby the irregularity of the pitch of scanning 
lines on a surface scanned by a scanning beam may be minimized. 
By this method, it is made unnecessary to use an expensive special optical 
system for correcting the above-mentioned tilt (a so-called tilt 
correcting optical system) which has heretofore been required. 
However, the inclination of the mounting flange surface of the rotational 
mirror is generally very small and it is difficult to detect the direction 
of this inclination. Accordingly, it is also difficult to assemble the 
rotational mirror with the reflecting surface of the rotational mirror and 
the direction of inclination of the mounting flange surface being made 
parallel to each other. Also, even if the direction of inclination is 
detected at all, there is irregularity during assembly and therefore, it 
is nearly impossible to assemble a great quantity of rotational mirrors 
always with good accuracy. 
So, in order to reliably achieve a construction in which the reflecting 
surface of the rotational mirror and the direction of inclination of said 
mounting flange surface are made parallel to each other, it is an object 
of the present invention to provide a light deflecting device having 
structure which can be regulated so that the direction of inclination of 
the mounting flange surface and the reflecting surface of the rotational 
mirror may reliably become parallel to each other after the rotational 
mirror is incorporated into the light deflecting device, and a regulating 
device therefor. 
To achieve the above object, the light deflecting device according to the 
present invention is of such a construction that by biasing means, the 
rotational mirror is urged against the mounting surface of a rotational 
mirror mounting portion rotatable by a rotational mirror driving motor and 
the rotational mirror can be separated from the mounting surface against 
the biasing force of the biasing means and when so separated, the 
rotational mirror and the mounting surface can rotate relative to each 
other. 
Accordingly, after the rotational mirror has been incorporated into the 
device, the phase relation between the rotational mirror and said mounting 
surface can be regulated and the rotational mirror can be reliably brought 
into a state in which the reflecting surface thereof becomes parallel to 
the direction of inclination of said mounting surface. 
In a regulating device in such a light deflecting device, the rotary shaft 
of the driving motor can be fixed by a clamp portion to thereby fix the 
mounting surface of the rotational mirror mounting portion and the 
rotational mirror can be rotated while being floated up from said mounting 
surface by the pawl of the regulating device, thereby change the phase 
position thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a cross-sectional view of an embodiment of the light deflecting 
device of the present invention. FIG. 2 schematically shows the 
construction of a scanning optical apparatus using the light deflecting 
device shown in FIG. 1. In the figures, the reference numeral 1 designates 
a rotational mirror having its two opposed surfaces cut into flat surfaces 
and worked into mirror surfaces to provide reflecting surfaces 1a for 
deflecting and scanning a laser beam, and the reference numeral 2 denotes 
a driving motor for rotatively driving the rotational mirror 1. A laser 
beam L emitted from a laser source unit 3 including a semiconductor laser 
and a collimator lens is incident on the rotational mirror 1 and is 
deflected and scanned thereby. 
The reflecting surfaces 1a of the rotational mirror 1 for deflecting and 
scanning the laser beam are substantially flat surfaces and the portions 
1b of the rotational mirror which do not deflect and scan the laser beam 
are curved surfaces. These curved surfaces are arcuate surfaces which are 
centered about the center of rotation of the rotational mirror 1. 
The rotational mirror 1 is mounted on a mounting portion 21 (a mounting 
flange) which lies in the central portion of the rotor 20 of the driving 
motor 2. The mounting portion 21 is constructed integrally with the rotary 
shaft 22 of the driving motor 2. 
The laser beam L deflected and scanned by the rotational mirror 1 passes 
through an imaging lens system 4 endowed with the f.multidot..theta. 
function (the function in which the ideal image height is given by the 
product of the focal length f and the beam incidence angle .theta.), 
whereafter it is imaged on a photosensitive drum 5, which is a surface to 
be scanned, and forms a latent image. 
Further, around the photosensitive drum 5, there are disposed process 
instruments, not shown, such as a primary charger, a developing device for 
causing a developer to adhere to that portion of the photosensitive drum 5 
which has been subjected to exposure and effecting positive development, a 
transfer charger and a cleaner, and printing is effected on paper or the 
like by the known electrophotographic process. 
Even when there is an angle of inclination between the mounting surface of 
the flange 21 and the rotary shaft of the motor 2 (in other words, the 
mounting surface of the flange 21 is inclined from state parallel to the 
ideal main scanning plane to be formed by the scanning beam), the 
reflecting surfaces la of the rotational mirror 1 are made parallel to the 
direction of inclination of the mounting surface of the flange 21 and the 
rotational mirror 1 is mounted so that the reflecting surfaces 1a may not 
be inclined from a state perpendicular to said ideal main scanning plane, 
whereby the unevenness of the pitch of the scanning lines in the sub 
scanning direction which is a direction perpendicular to the main scanning 
plane that ought to occur due to the inclination of the mounting surface 
of the flange 21 can be prevented. 
A construction which makes this possible will now be described in detail. 
In the cross-sectional view of the vicinity of the motor 2 shown in FIG. 
1, the outer periphery of the flange 21 on which the rotational mirror 1 
is mounted is smaller in diameter than the circumscribed circle of the 
rotational mirror 1, and the flange 21 is fixed to the rotary shaft 22 as 
by shrinkage fit or adhesion and is fixed to the rotor 20 by caulking. The 
upper surface of the rotor 20 and the bottom surface of the rotational 
mirror 1 are not in contact with each other. A driving magnet 23 is 
mounted inside the rotor 20, and by electrically energizing a driving coil 
24 disposed in opposed relationship with the magnet 23 and mounted on the 
body portion of the motor 2, the rotor 20 is rotatively driven in 
accordance with a force produced between the magnet 23 and the coil 24. 
This rotative driving is highly accurately controlled by a Hall element or 
the like, not shown. Further, the driving motor 2 is comprised of a 
bearing 25 and a motor case 26 having this bearing, etc. therein. 
The hollow portion of the rotational mirror 1 having its opposed two 
surfaces formed into the reflecting mirror surfaces 1a which is fitted to 
the rotary shaft 22 is greatly chamfered in the edge portions thereof so 
that the fitted portion 100 thereof to the rotary shaft 22 may become as 
small as possible and the rotary shaft 22 and the fitted portion 100 may 
almost be in line contact with each other. That is, design is made such 
that the thickness of the fitted portion in a direction parallel to the 
rotary shaft is remarkably small as compared with the thickness of the 
rotational mirror. 
The rotational mirror 1 is controlled from above and urged against the 
flange 21 by a resilient member 11 (biasing means) such as a star-shaped 
spring. Thus, a frictional force works between the bottom surface of the 
rotational mirror 1 and the mounting surface of the flange 21, whereby the 
rotational mirror 1 is fixed to the flange 21, and the rotor 20, the 
flange 21, the rotary shaft 22, the rotational mirror 1, etc. rotate as a 
unit. In the upper portion of the resilient member 11, a fixing member 12 
for the purpose of tightening or the like is fixed to the rotary shaft 22 
and holds down the resilient member 11 between itself and the upper 
surface of the rotational mirror 1 
A method of regulating the rotational mirror 1 so that the reflecting 
surfaces 1a thereof may be parallel to the direction of inclination of the 
surface of the flange 21 after assembly will now be described with 
reference to FIGS. 3 and 4. FIG. 3 illustrates a method of regulating the 
phase position of the rotational mirror, and FIG. 4 is a graph showing the 
relation between the phase position of the rotational mirror and the 
amount of unevenness of pitch. 
FIG. 4 shows the amount of unevenness of the pitch of the scanning lines 
when the phase of the rotational mirror 1 arbitrarily mounted on the 
surface of the flange 21 (the position of the rotational mirror 1 relative 
to the flange 21 as it is represented in terms of the angle of rotation 
about the rotary shaft 22 with the arbitrary mounted position as the 
reference) is changed in succession. 
In this figure, the graph approximate to a sine curve indicated by an 
amplitude .delta..sub.2 shows the relation between the amount of 
unevenness of the pitch and the angle of the rotational mirror when only 
the inclination of the surface of the flange 21 is taken into 
consideration. If the tilt of the mirror surface of the rotational mirror 
itself is further added thereto, the O position becomes offset by 
.delta..sub.1 as shown. In this figure, the length from the O position to 
the curve is the amount of unevenness of the pitch, and the maximum amount 
of unevenness of the pitch is .delta.. 
Usually, the inclination of the surface of the flange is greater than the 
tilt of the mirror surface of the rotational mirror and therefore, the 
relation as shown in FIG. 4 is established and it is possible to nullify 
the amount of unevenness of the pitch. However, when the machining 
accuracy and mounting accuracy of the surface of the flange are good and 
the inclination of the surface of the flange becomes smaller than the tilt 
of the mirror surface of the rotational mirror, .delta..sub.2 in the 
figure becomes very small and the amount of unevenness of the pitch will 
not become zero even if the angle of the rotational mirror is changed. 
Here, if the focal length of the imaging optical system is up to the order 
of 100 mm, the tilt of the mirror surface of the rotational mirror will 
pose no problem if the existing machining accuracy is used and therefore, 
the inclination of the surface of the flange can be considered to be the 
main factor of the unevenness of the pitch. 
However, where the focal length of the imaging optical system is greater 
than that indicated above, it is preferable to make the inclination of the 
surface of the flange greater than the tilt of the mirror surface so that 
the relation as shown in FIG. 4 may be brought about. 
An example in which the phase regulation of the rotational mirror 1 is 
automatically effected as by an automatic regulating machine will 
hereinafter be described with reference to FIGS. 1 and 3. 
Since, as previously described, the size of the mounting surface of the 
flange 21 is smaller than the outer peripheral circle circumscribed by the 
curved surface which is the nonreflecting surface 1b of the rotational 
mirror 1, gaps C are formed at two substantially opposed locations between 
the upper surface of the rotor 20 and the bottom surface of the rotational 
mirror 1. In order that such gaps may be formed, the outer periphery of 
the flange 21 may lie inside the outer periphery of the rotational mirror 
1 at least two locations (of course, at one location if it is continuous), 
and the example shown above is merely exemplary. The pawls 61 of an 
automatic regulating machine 60 (shown by hatching to distinguish it from 
the rotational mirror 1, etc.) are inserted into such gaps C, and the 
pawls 61 are urged against the bottom surface of the rotational mirror 1 
to thereby slightly raise the rotational mirror 1 against the biasing 
force of the resilient member 11 and separate it from the mounting surface 
of the flange 21. 
If at this time, the force of the resilient member 11 becomes too strong, 
the rotational mirror 1 will be distorted and therefore, such structure 
that the amount of float-up of the rotational mirror 1 is made as small as 
possible and moreover the regulating force of the resilient member 11 is 
not much varied by a variation in the amount of float-up is desirable. 
According to the experiment, distortion occurred to the reflecting surfaces 
1a when a load of 5 kg was applied to the rotational mirror 1 and 
therefore, it is necessary that the regulating force or the biasing force 
of the resilient member 11 be less than 5 kg. Accordingly, assuming that 
the amount by which the rotational mirror 1 is floated up to change the 
phase of the reflecting surfaces 1a thereof is of the order of 0.1 to 0.2 
mm, it is necessary to make the deformation stroke required of the 
resilient member 11 small so that even when the rotational mirror 1 is 
floated up, the force applied from the resilient member 11 to the 
rotational mirror 1 may not exceed 5 kg. 
In this manner, there is provided a construction in which the rotational 
mirror can be separated from the mounting surface against the biasing 
means and the rotational mirror and the mounting surface of the rotational 
mirror mounting portion integral with the rotary shaft can rotate relative 
to each other. The pawls are for rotating the rotational mirror relative 
to the rotary shaft while separating the rotational mirror from the 
rotational mirror mounting portion or the flange against the biasing means 
or the resilient member. 
Also, in the present embodiment, that portion 100 of the rotational mirror 
1 which contacts with the shaft or the rotary shaft 22 is made small so 
that the frictional action between the rotational mirror and the shaft 22 
may not become great when the rotational mirror 1 is floated up or when 
the rotational mirror 1 is rotated about the shaft 22 to thereby change 
the phase thereof. As means for reducing such friction, that portion of 
the shaft 22 which is fitted to the rotational mirror may be partly worked 
into a concave portion 220, as shown in FIG. 5, whereby the same effect 
may be obtained. 
FIG. 5 is a cross-sectional view showing another embodiment of the light 
deflecting device of the present invention. 
In FIG. 5, that portion of the rotational mirror which is fitted to the 
rotary shaft is formed more thinly than the thickness of the rotational 
mirror. If the thickness of this portion which is fitted to the rotary 
shaft in a direction parallel to the rotary shaft is small, as in the case 
of the rotational mirror shown in FIG. 1, the frictional action between 
the rotational mirror and the rotary shaft will not become great when the 
rotational mirror is floated up or when the rotational mirror is rotated 
about the rotary shaft to thereby change the phase thereof. Consequently, 
it is preferable that the thickness of the portion which is fitted to the 
rotary shaft in the direction parallel to the rotary shaft be 1/2 or less 
of the thickness of the rotational mirror. 
That is, the hole extending through the body of the rotational mirror 
having reflecting surfaces on the sides thereof has a first diameter and a 
second diameter smaller than the first diameter, and the thickness of the 
portion having the second diameter in a direction substantially parallel 
to said reflecting surfaces is 1/2 or less of the thickness of the body of 
the rotational mirror. 
Simultaneously with the rotational mirror 1 being floated up by the 
automatic regulating machine 60 as described above, one end portion of the 
shaft 22 vertically protruding from the case 26 of the motor 2 is fixed by 
the clamp portion 62 of the automatic regulating machine 60. Thereby the 
shaft 22 is fixed and the position of the flange 21 is fixed. If in this 
case, there is a limitation in the shape of the motor 2 and the shaft 22 
cannot be protruded downwardly, the side portion of the rotor 20 may be 
held or the upper portion of the shaft 22 which protrudes upwardly from 
the fixing member 12 may be held to thereby fix the position of the flange 
21. 
When the rotational mirror is separated from the mounting surface of the 
flange and the position of the mounting surface of the flange is fixed, 
the rotational mirror held by the pawls is rotated relative to the 
mounting surface by a predetermined amount in the direction of arrow A to 
thereby change the phase thereof by a predetermined amount. After the 
phase has been changed by a predetermined amount, the pawls are lowered 
and the rotational mirror is again mounted on the mounting surface of the 
flange, whereafter the fixing of the position of the mounting surface is 
released. Then, the light beam from the light source is deflected and 
scanned by the rotational mirror being rotated and the amount of 
unevenness of the pitch is detected. 
The above-described operation is repeated and the rotational mirror 1 is 
rotated in the direction of arrow A to thereby change the phase thereof 
variously, and the beam is actually deflected and scanned in each phase 
position to find out a phase position in which the unevenness of the pitch 
becomes small, whereupon the regulation is completed. 
FIG. 6 illustrates another method of regulating the phase relation of the 
rotational mirror, and is a view of the rotational mirror as it is seen 
from sideways thereof. 
FIG. 6 shows an embodiment in which a pair of grooves or holes 110 are 
formed in the bottom surface of the rotational mirror 1, and the pawls 61a 
of the automatic regulating machine are caught in these holes 110 and 
thus, it is easy to float up the rotational mirror 1 and change the phase 
thereof. 
FIG. 7 is a view of the rotational mirror of the present invention as it is 
seen from above. 
FIG. 7 shows an embodiment in which a portion of the upper surface of the 
rotational mirror 1 is made into a mirror surface 111 formed with a mark. 
As previously described, there is a relation as shown by the sine curve of 
FIG. 4 between the phase and the amount of unevenness of the pitch and 
therefore, if the phase relation between the flange 21 and the rotational 
mirror 1 can be directly detected, it will become unnecessary to see the 
unevenness of the pitch in each phase position each time and the 
regulation will be completed by only the detection of that phase and thus, 
the regulation can be accomplished more quickly. So, if a position 
detecting sensor, not shown, is installed above the rotational mirror 1 
and the reflected light from the mark 111 of the rotational mirror 1 is 
detected, the phase of the rotational mirror 1 can be detected. In this 
manner, the regulation can be accomplished efficiently in this embodiment. 
The mark 111 shown in FIG. 7 is a mark which indicates the position of the 
reflecting surface of the rotational mirror associated with the position 
of the reflecting mirror, and it is provided on a portion of the upper 
surface which is the other portion than the reflecting surfaces 1a of the 
rotational mirror. Of course, the mark may be provided on the side portion 
of the rotational mirror which is not provided with the reflecting 
surfaces. 
Also, the mark shown in FIG. 7 is an optically detectable mark, but 
alternatively, it may of course be a mechanically, electrically or 
magnetically detectable mark. 
FIG. 8 illustrates another method of regulating the phase relation of the 
rotational mirror, and is a view of the rotational mirror as it is seen 
from above. 
In the example shown in FIG. 8, a position B at which the force of a 
resilient member 11a regulating the rotational mirror 1 from above acts is 
on the upper portion of the rotational mirror 1 which corresponds to the 
portion in which the pawls 61 of the automatic regulating machine are 
engaged with the rotational mirror 1. Thus, it is difficult for the 
distortion by a shearing force to occur to the rotational mirror 1. The 
resilient member 11a in this example, as shown, is of an elongate lozenge 
shape as viewed from above and of a simple angled shape as viewed from 
sideways and therefore, the effective stroke of the spring can be made 
longer than that of the aforedescribed star-shaped spring and the 
reduction in the function of the spring is small and thus, this resilient 
member 11a can be said to have a preferable shape. The resilient member 
11a causes its force to act on the positions on the rotational mirror 
which correspond to the gaps between the upper surface of the rotor on 
which the pawls of the automatic regulating machine lie and the bottom 
surface of the rotational mirror. 
While in the above-described embodiments of the present invention, there 
has been shown a construction in which the rotary shaft, rotor and flange 
of the driving motor are integrally formed by discrete members, they may 
of course be integrally formed by one and the same member. 
By the above-described construction, in the present invention, the 
unevenness of the pitch of the scanning lines can be minimized to that due 
to the other factors than the tilt of the deflecting-reflecting surface 
(for example, that due to the vibration of the device), and this can 
contribute to the high quality of recorded image which has been desired in 
recent years. 
Further, the phase position of the rotational mirror can be regulated after 
assembly and therefore, in every light deflecting device assembled, the 
irregularity during assembly is eliminated and the direction of 
inclination of the surface of the flange and the reflecting surfaces of 
the rotational mirror can be made parallel to each other, and the 
unevenness of the pitch of the scanning lines can be minimized.