Light beam scanning system with motor and vibration isolating means

A light beam scanning system in which the vibration of a rotating multi-face mirror and a high-speed motor which constitute the light beam scanning means of the system is prevented from being transmitted to other optical components of the system by mounting the rotating multi-face mirror and the high-speed motor on the optical component mounting board through the medium of vibration isolators.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved light beam scanning system. 
Light beam scanning systems are comprised of a light beam scanning means 
constituted of a high-speed motor and a rotating multi-face mirror 
together with other optical components including, for example, one or more 
condenser lenses. Such a light beam scanning system is, for example, 
employed in a light-beam scanning type recording device for scanning a 
beam of light modulated by the information to be recorded over a recording 
material. 
2. Description of the Prior Art 
In conventional light-beam scanning type recording devices, however, it has 
been necessary for accomplishing high-resolution recording at high speed 
to rotate a large multi-face mirror at a high rotational velocity. For 
example, when a 24-faced rotating mirror is used at a duty ratio of 70% to 
record 4 frames per second, 2,000 lines per frame, 2,600 resolution points 
per line, it is, when the distance between opposite-facing faces of the 
rotating mirror is made 120 mm, necessary to rotate the mirror at about 
20,000 rpm. When the rotating multi-face mirror is rotated at such a high 
speed, there inevitably occurs a weight unbalance in the light scanning 
system due to imprecisions introduced at the time of fabrication of the 
rotating multi-faced mirror and the motor and at the time of attachment of 
the multi-faced mirror to the shaft of the motor. The existence of such an 
unbalance, no matter how slight, will give rise to vibration in the 
rotating multi-face mirror. The presence of such vibration in the rotating 
multi-face mirror itself does not, however, necessarily cause jitter in 
the image since its effect can be eliminated by the use of a linear 
encoder insofar as the beam incident upon and reflected by the rotating 
multi-face mirror is a collimated beam at least within the scanning 
surface. The problem is, however, that the light beam scanning means is 
mounted on a common optical component mounting plate together with the 
aforementioned condenser lenses and other optical components so that any 
vibration in the light beam scanning means is passed on to the other 
optical elements. As a consequence, these optical components introduce 
jitter into the light beam which jitter shows up in the image produced. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a light beam scanning 
system wherein vibration which may occur in the light beam scanning means 
is prevented from inducing vibration in the other optical components of 
the light beam scanning system. 
The light beam scanning system of the present invention is characterized in 
that its light beam scanning means is mounted on the optical component 
mounting plate via vibration isolation means, whereby the vibration of the 
light beam scanning means is not transmitted to the other optical 
components. 
Various other objects, features and advantages of the present invention 
will be more apparent by reference to the following detailed description 
of preferred embodiments thereof taken in conjunction with accompanying 
drawing as follows:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIG. 1, there is shown a perspective view schematically 
representing a light beam recording system incorporating the light beam 
scanning system of the present invention. The optical system of this light 
beam recording system is constructed so as to first combine a recording 
laser beam for scanning a recording material and a reading laser beam for 
scanning a form and a linear encoder, to then subject the combined beam to 
two-dimensional deflection, and to thereafter separate the combined beam 
and cause the recording laser beam to scan the recording material and the 
reading laser beam to scan the form and the linear encoder. 
In FIG. 1, the recording laser beam, as indicated by the reference numeral 
2, is produced by a laser beam source 1 which may, for example, be an 
argon ion laser that emits blue and green laser beams. The recording laser 
beam 2 transits through a light modulator 3 where it is amplitude 
modulated in accordance with a video signal and then passes through a 
dichromic mirror 4. 
On the other hand, the reading laser beam as indicated by numeral 6, is 
produced by a laser beam source 5 which may, for example, be a helium-neon 
laser that emits a red laser beam. The reading laser beam 6 is reflected 
by a mirror 7, and then by the dichromic mirror 4 to be combined with the 
recording laser beam 2 and travel along the same path therewith. 
The nature of the dichromic mirror 4 is such that it passes the blue and 
green light beams and reflects the red light beam. 
The combined light beams 2 and 6 advance to a reflective surface 9 of a 
rotating multi-face mirror 8 being rotated in the direction of arrow 8' at 
a fixed speed (for example, at 20,000 rpm) by a motor M and, after being 
deflected by the reflective surface 9 (this deflection being hereinafter 
referred to as "horizontal deflection"), are passed onto a galvanometer 
mirror 11 by a first light converging optical system 10. The galvanometer 
mirror 11, which is driven in the well-known manner by a saw-toothed wave 
signal to vibrate in the direction indicated by arrow 11', deflects the 
combined light beams 2 and 6 in the direction perpendicular to the 
horizontal direction (this deflection being hereinafter referred to as 
"vertical deflection"). 
For each time the combined light beams 2 and 6 are horizontally deflected 
by one of the reflective surfaces 9 of the rotating multi-face mirror 8, 
they are vertically deflected one unit distance by the galvanometer mirror 
11. As a result of these deflections, the light beams 2 and 6, after they 
are finally separated, perform two-dimensional scanning (hereinafter 
referred to as "raster scanning") by passing along scanning lines on the 
surface of the scanning surface of, for example, a recording material to 
be described later. 
The combined light beams 2 and 6 deflected by the galvanometer mirror 11 
are separated by a dichromic mirror 12. The recording light beam 2 passes 
through the dichromic mirror 12 and is then converged by a second light 
converging optical system 13 and passed on to the surface of a recording 
material 14 where, as a small light spot, it performs raster scanning. 
When one raster of recording (hereinafter referred to as "one frame") has 
been completed on the recording material, the recording material is 
advanced by the distance of one frame by a driving device 15. The 
particular type of driving device 15 employed is appropriately selected in 
accordance with the type of recording material 14 and the recording mode 
(that is, depending on whether the frames are recorded continuously in a 
single row on a roll of recording material or are two dimensionally 
recorded in a form like a microfiche. 
On the other hand, the reading light beam 6 is reflected by a dichromic 
mirror 12 and is then condensed by a third light converging optical system 
and passed on to a half-mirror 17. The portion of the reading light beam 6 
that transmits through the half-mirror 17 advances to the surface of a 
linear encoder 18 where, as a small light spot, it performs raster 
scanning. The remaining portion of the reading light beam 6 that is 
reflected by the half-mirror 17 advances to the surface of a form slide 19 
having a form consisting of lines or characters drawn thereon where, as a 
small light spot, it performs raster scanning. 
The linear encoder 18 is a flat plate having long, narrow transparent 
portions and opaque portions extending in the direction of vertical 
deflection and disposed alternately at equal intervals in the direction of 
horizontal deflection to produce a pattern consisting of many stripes. As 
the reading light beam 6 passes over the surface of the linear encoder in 
raster scanning, it is transmitted by the transparent portions and is 
blocked by the opaque portions. The portions of the beam 6 transmitted 
through the linear encoder 18 are passed through a fourth light converging 
optical system 20 to a light detector 21 which produces a pulse signal A 
each time the light beam 6 passes through a transparent portion of the 
linear encoder 18 and impinges thereon. 
On the other hand, as the reading light beam 6 passes over the surface of 
the form slide 19 in raster scanning, it is transmitted by those portions 
where the form image is present and is blocked by those portions where the 
form image is not present. The portions of the beam 6 transmitted through 
the form slide 19 are passed through a fifth light converging optical 
system 22 to a light detector 23 which produces an ON-OFF signal 
corresponding to the form image. 
The rotating multi-face mirror and the motor M are mounted on an optical 
component mounting plate P (See FIG. 2) together with such other optical 
components as the first and second light condensing optical systems 10 and 
13. Consequently, any vibration generated by the motor M and the rotating 
multi-face mirror 8 when, as mentioned above, they are rotated at 20,000 
rpm is transmitted via the optical component mounting plate P to the first 
and second light converging optical systems 10 and 13, causing the first 
and second light converging optical systems to vibrate as well. 
In the present invention, in order to prevent such vibration of the first 
and second light converging optical systems, the light beam scanning means 
24 comprised of the rotating multi-face mirror 8 and the motor 8 is 
mounted on the optical component mounting plate P through the medium of 
vibration isolating means. 
As vibration insulators suitable for the purpose of this invention, there 
can be mentioned by way of example those of the type which prevent 
transmission of vibration through deformation of the isolator material by 
the energy of the vibration and those of the type which prevent 
transmission of vibration by absorbing the energy of the vibration and 
converting it into heat energy. As examples of the former type there can 
be mentioned leaf-spring and rubber vibration isolators and as examples of 
the latter type there can be mentioned lead-plate and silent alloy-plate 
vibration isolators. 
FIG. 2 is a perspective view of a first embodiment of the present invention 
wherein the light beam scanning means 24 is mounted on the optical 
component mounting plate P through the medium of leaf-spring vibration 
isolators. 
More specifically, the light beam scanning means 24 is mounted on the 
optical component mounting plate P via a mount 25 which comprises a fixing 
plate 26, a bracket 27 for retaining the light beam scanning means 24 and 
leaf-springs 28 by which the fixing plate 26 and the bracket 27 are joined 
to each other. Thus, any vibration produced by the light beam scanning 
means 24 is prevented by the action of the leaf-springs 28 from being 
transmitted from the light beam scanning means 24 to the optical component 
mounting plate P and the other optical components. In this first 
embodiment of the invention, the vibration isolating effect is maximum 
when the leaf-springs 28 are disposed to have their major surfaces 
parallel to the rotating shaft of the light beam scanning means 24. This 
is because the major component of the vibration of the light beam scanning 
means acts perpendicular to the rotating shaft. 
Although most of the vibration of the light beam scanning means can be 
absorbed by the structure shown in FIG. 2, the structure does not permit 
absorption of that component of the vibration which acts perpendicular to 
the plate P, namely, the component acting in the direction in which the 
leaf-springs 28 extend. Where it is found necessary to absorb the vertical 
component as well, the desired results can be obtained by using the second 
embodiment of the invention shown in FIG. 3. In this embodiment of the 
invention, intermediate members 29 (only one shown) are disposed between 
the fixing plate 26 and the bracket 27, with the leaf-springs 28 disposed 
between the fixing plate 26 and the intermediate members 29 and 
leaf-springs 30 disposed between the intermediate members 29 and the 
bracket 27. With this arrangement, any vibration in the direction 
perpendicular to the plate P is effectively absorbed by the leaf-springs 
30. In this second embodiment of the invention, the vibration isolating 
effect is maximum when the leaf-springs 30 have their major surfaces 
parallel to both the rotating shaft of the light beam scanning means 24 
and the plate P. 
FIG. 4 is a side view of a third embodiment of the present invention 
wherein the light beam scanning means 24 is mounted on the optical 
component mounting plate P through the medium of rubber vibration 
isolators. 
More specifically, the light beam scanning means 24 is mounted on the 
optical component mounting plate P by means of bolts 32 which connect the 
bracket 27 retaining the light beam scanning means 24 to the optical 
component mounting plate P through the medium of rubber bushings 31. Thus, 
any vibration produced by the light beam scanning means 24 is prevented by 
the action of the rubber bushings 31 from being transmitted to other parts 
of the scanning system. 
FIG. 5 shows the structure of the rubber bushings 31 in detail. This rubber 
bushing is made by Barry Light Co. and marketed by Showa Wire and Cable 
Co., Ltd. under the brandname of QUITIGHT and consists of a rubber portion 
31a and a nut 31b joined thereto. 
Moreover, although not illustrated in the drawing, the vibration of the 
light beam scanning means 24 can also be prevented from being transmitted 
to the optical component mounting plate P by mounting the light beam 
scanning means on the plate through the medium of vibration isolators made 
of silent alloy plate, lead plate, etc. In such case, the silent alloy 
plate, lead plate etc. is disposed between the bracket 27 and the plate P. 
As has been described above, the light beam scanning system according to 
the present invention is so constructed that vibration arising in the 
light beam scanning means is confined to this means and is prevented from 
being transmitted to the optical component mounting plate on which it is 
mounted so that the vibration does not reach the light converging optical 
systems and other optical components of the light beam scanning system. 
Therefore, when the light beam scanning system of this invention is used 
in a light beam recording system, the characters, symbols etc. formed by 
the recording system through light beam scanning are free of jitter and 
are, as a result, recorded accurately and with a high degree of precision.