 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light beam scanner for deflecting a
light beam with a light deflector, and more particularly to a light beam
scanner for two-dimensionally scanning a fixed sheet with a light beam.
2. Description of the Prior Art
Light beam scanners including light deflectors such as galvanometer
mirrors, rotating polygonal mirrors, and hologram scanners for deflecting
a light beam to two-dimensionally scan a sheet have found wide use in
various scanning recording apparatus, scanning readout apparatus, and the
like. The two-dimensional scanning of the sheet has heretofore been
effected by mechanically transferring the sheet in one direction for
sub-scanning thereof while one-dimensionally deflecting the light beam in
a direction substantially normal to the foregoing direction for main
scanning of the sheet. For two-dimensionally scanning the sheet in this
manner, it is important that the sheet being scanned be transferred at a
stable speed in said one direction, i.e., the sub-scanning direction. If
the sheet being scanned were not transferred highly accurately at a
constant speed, it would be scanned irregularly by the light beam, and
image information read out, for example, from the sheet during scanning
thereof would be distorted. Therefore, the sheet has conventionally been
transferred in the sub-scanning direction by a high-precision motor which
can feed the sheet highly accurately at a low speed in one direction.
However, since such a high-precision motor is expensive, the cost of the
entire light beam scanner is substantially increased. Some sheets to be
scanned by a light beam tend to flex out of complete flatness while they
are being transferred. To allow such sheets to be transferred completely
flatwise, it has been one practice to employ an attracting means such as a
suction box within an endless belt which supports a sheet thereon and to
activate the attracting means for holding the sheet in intimate contact
with the endless belt to keep the sheet flatwise against accidental
displacement while being transferred accurately at a constant speed. Use
of such an attracting means in addition to the high-precision motor has
resulted in a further increase in the cost of manufacture of the light
beam scanner.
The space provided for the transfer of a sheet in the light beam scanner
has to be of a size in the sub-scanning direction which is at least twice
the length of the scanned area of the sheet in the sub-scanning direction.
As a consequence, it has been difficult to reduce the size of the light
beam scanner, and the relatively large light beam scanner is not suitable
for use in a limited space.
SUMMARY OF THE INVENTION
In view of the aforesaid drawbacks of the conventional light beam scanner,
it is an object of the present invention to provide a light beam scanner
which is small in size and can be manufactured inexpensively.
According to the present invention, a sheet to be scanned is fixedly
supported on a cylindrical surface, and is two-dimensionally scanned by a
light beam which is emitted from a light source and deflected by a main
scanning light deflector while at the same time the light source and the
main scanning light deflector are being angularly moved. More
specifically, a light beam scanner of the invention comprises a support
means for supporting a sheet to be scanned on a cylindrical surface, a
light source for emitting a light beam, a main scanning light deflector
disposed at the axis of curvature of the cylindrical surface for
deflecting the light beam from the light source toward the cylindrical
surface to scan the sheet on the cylindrical surface with the light beam
in a main scanning direction substantially parallel to the axis, and a
sub-scanning means for angularly moving the light source and the main
scanning light deflector about the axis to scan the sheet on the
cylindrical surface with the light beam in a sub-scanning direction normal
to the main scanning direction.
Since the sheet is fixed and scanned in the sub-scanning direction by
angularly moving the light source and the main scanning light deflector,
no need arises for a high-precision motor such as has heretofore been
employed to transfer the sheet in the sub-scanning direction, or for an
attracting means such as has been used to hold the sheet on an endless
belt. Therefore, the light beam scanner of the present invention is
smaller in size and can be manufactured inexpensively.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description when
taken in conjunction with the accompanying drawings in which a preferred
embodiment of the present invention is shown by way of illustrative
example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a light beam scanner according to the
present invention; and
FIG. 2 is a transverse cross-sectional view of a radiation image
information readout device employing the principles of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a light beam scanner according to the present invention. A
light beam 2 emitted from a light beam source 1 such as a laser beam
source is converted by a beam expander 3 into a light beam having a
suitable beam diameter. The expanded light beam 2 is then applied to a
main scanning light deflector 4 comprising a galvanometer mirror which
reflects and deflects the light beam 2 in the direction of the arrow A. A
scanning lens 5 in the form of a f.theta. lens is disposed in the optical
path of the light beam 2 as it is reflected and deflected by the
galvanometer mirror 4. The laser beam source 1, the beam expander 3, the
galvanometer mirror 4, and the f.theta. lens 5 jointly constitute an
optical system which is housed in a hollow cylindrical member 6, thus
providing an angularly movable optical unit 7. A motor 8 is coupled to one
axial end of the cylindrical member 6 while a bearing 9 is mounted on the
other axial end of the cylindrical member 6. The cylindrical member 6 is
angularly moved by the motor 8 in the direction of the arrow B, and so are
the optical components as described above which are housed in the
cylindrical member 6. The galvanometer mirror 4 is positioned on the
optical axis of the optical unit 7 for deflecting the light beam 2 in a
direction substantially parallel to the optical axis of the optical unit
7. The cylindrical member 6 has an axial slit 6A defined in a cylindrical
wall thereof within the optical path of the light beam 2 as deflected by
the galvanometer mirror 4. Therefore, the light beam 2 which is deflected
by the galvanometer mirror 4 passes out of the optical unit 7 radially
outwardly through the slit 6A.
A semicylindrical support 10 is disposed around part of the optical unit 7
and has its center of curvature aligned with the axis of angular movement
of the optical unit 7. The semicylindrical support 10 supports a sheet 11
to be scanned on its concave surface confronting the optical unit 7. The
light beam 2 which is reflected and deflected by the galvanometer mirror 4
scans the sheet 11 in the direction of the arrow C (main scanning). At the
same time, since the optical unit 7 is angularly moved about its own axis
in the direction of the arrow B (sub-scanning), substantially the entire
surface of the sheet 11 is two-dimensionally scanned by the light beam 2.
The light beam 2 is caused by the f.theta. lens 5 to scan the sheet 11 at
a constant speed and with a uniform beam spot diameter.
A pair of feed rollers 16A, 16B is disposed on one end 10A of the support
10 for delivering the sheet 11 onto the semicylindrical support 10. The
semicylindrical support 10 has a pair of spaced guide plates 15A, 15B
extending in the sub-scanning direction and projecting inwardly from the
surface of the semicylindrical support 10 for guiding the sheet 11 in the
sub-scanning direction when the sheet 11 is delivered onto the
semicylindrical support 10. Upon rotation of the feed rollers 16A, 16B
about their own axes in the respective directions of the solid-line arrows
D, the sheet 11 is delivered along the guide plates 15A, 15B onto the
surface of the semicylindrical support 10 axially between the guide plates
15A, 15B. The sheet 11 is stopped in position when its leading end engages
a stopper 10B on the end of the support 10 remote from the feed rollers
16A, 16B. With the sheet 11 thus stopped in position, the trailing end of
the sheet 11 is gripped between the feed rollers 16A, 16B. When the
scanning of the sheet 11 is finished, the feed rollers 16A, 16B are
rotated in the opposite directions indicated by the
dotted-line arrows D', respectively, to deliver the sheet 11 off the
support 10. The sheet 11 may be delivered onto and off the support 10, and
positioned in the support 10 by any of various known means. For example,
means for moving the sheet, other than the illustrated feed rollers 16A,
16B, may be employed.
With the aforesaid arrangement of the light beam scanner, the sub-scanning
of the sheet is carried out by angularly moving the light beam source, the
light deflector, and other optical components, without moving the sheet in
the sub-scanning direction. Therefore, the length of the light beam
scanner in the sub-scanning direction may be half the length of the
conventional light beam scanners, and the size of the light beam scanner
is reduced. Since it is much easier to angularly move the optical system
than to transfer the sheet in the sub-scanning direction, the motor 8 and
its associated transmission mechanism (not shown) for angularly moving the
optical system in the sub-scanning direction can be less complex than the
conventional high-precision motor and its associated transmission
mechanism used to transfer the sheet in the sub-scanning direction. The
sheet is immovably and stably supported on the semicylindrical support,
and no attracting means such as a suction box is required for holding the
sheet in position. For the reasons described above, the light beam scanner
is simple in structure and inexpensive to manufacture.
A radiation image information readout device incorporating the principles
of the present invention will be described with reference to FIG. 2.
It is known that when a certain phosphor is exposed to a radiation such as
X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or
ultraviolet rays, the phosphor stores a part of the energy of the
radiation, and that when the phosphor exposed to the radiation is exposed
to stimulating rays such as visible light, the phosphor emits light in
proportion to the stored energy of the radiation. The phosphor exhibiting
such a property is referred to as a "stimulable phosphor".
There has been proposed a radiation image recording and readout system
employing such a stimulable phosphor. More specifically, the radiation
image of an object such as a human body is stored in a sheet of stimulable
phosphor (hereinafter referred to as a "stimulable phosphor sheet" or a
"phosphor sheet"), and then the stimulable phosphor sheet is scanned with
stimulating rays to cause the stimulable phosphor sheet to emit light
representative of the radiation image. The emitted light is then
photoelectrically detected to produce an image information signal that is
electrically processed for generating a radiation image of the human body,
which is recorded on a recording medium such as a photosensitive material
or displayed as a visible image on a CRT. The aforesaid radiation image
recording and readout system is disclosed in Japanese Kokais Nos. 55-12429
and 56-11395, for example
FIG. 2 shows a readout device for reading out radiation image information
in the above radiation image recording and readout system. The readout
device is shown in its transverse cross section and viewed along the axis
of angular movement of an optical unit (described below), the view
illustrating a support on which a stimulable phosophor sheet is placed and
various components in the optical unit.
A laser beam 102 emitted from a laser beam source 101 is converted by a
beam expander 103 into a light beam having a suitable beam diameter. The
expanded light beam 2 is then applied to a galvanometer mirror 104 which
deflects the light beam 102 in the direction of the arrow A. After the
deflected laser beam 102 has passed through a scanning lens 105 in the
form of an f.theta. lens, the laser beam 102 goes through a slit 106A
defined in a cylindrical member 106 and scans the surface of a stimulable
phosphor sheet 111 supported on a semicylindrical support 110 in a
direction normal to the sheet of FIG. 2. The laser beam source 101, the
galvanometer mirror 104, and the f.theta. lens 105 are housed in the
cylindrical member 106, thus providing an optical unit 107 capable of
angular movement in the direction of the arrow B. Substantially the entire
surface of the stimulable phosphor sheet 111 is two-dimensionally scanned
by the laser beam 102 by causing the laser beam 102 to scan the stimulable
phosphor sheet 111 (main scanning) and angularly moving the optical unit
107 (sub-scanning). The galvanometer mirror 104 is positioned on the axis
of angular movement of the optical unit 107, and the laser beam 102 is
deflected by the galvanometer mirror 104 in a direction substantially
parallel to the axis of angular movement of the optical unit 107, which is
coaxial with the center of curvature of the semicylindrical support 110.
Other structural, positional, and functional details of the optical unit
107 and the support 110 are the same as those of the optical unit 7 and
the support 10 shown in FIG. 1. The stimulable phosphor sheet 111 is
delivered onto and off the support 110 by means of a pair of feed rollers
116A, 116B disposed at one end of the support 110, and is positioned on
the support 110 by means of a stopper 110B on the opposite end of the
support 110.
The stimulable phosphor sheet 111 is of a nature as disclosed in Japanese
Kokais Nos. 55-12429 and 55-116340, for example. The stimulable phosphor
sheet 111 stores thereon radiation image information of an object which
has been recorded upon exposure to stimulating radiation such as an X ray
that has passed through the object. When the laser beam 102 is applied to
a portion of the stimulable phosphor sheet 111, that portion emits light
in an intensity commensurate with the stored radiation image information.
The emitted light enters a transparent light guide 112 through its
entrance end 112A extending in the main scanning direction and having a
length larger than the interval scanned in the main scanning direction.
The emitted light is then guided by the light guide 112 into a
photomultiplier 113. A filter (not shown) which selectively passes the
emitted light only, but shuts off the stimulating radiation, is interposed
between the joined surfaces of the light guide 112 and the photomultiplier
113. The photomultiplier 113 photoelectrically detects the emitted light
that has passed through the filter and generates an electric signal
representative of the radiation image information recorded on the
stimulable phosphor sheet 111. The electric signal is then processed by an
image information readout circuit, which applies an electric image signal
to an image reproducer such as a CRT or a scanning recorder, so that an
image carried by the electric image signal can be displayed on the CRT or
reproduced as a hard copy by the scanning recorder.
A light collecting mirror 114 is supported on a support base 114A and
positioned in confronting relation to the entrance end 112A of the light
guide 112 across the portion of the sheet 111 which is scanned by the
laser beam 102. The light collecting mirror 114 serves to reflect light
emitted from the scanned portion of the sheet 111 toward the entrance end
112A of the light guide 112 so that the emitted light can efficiently be
supplied to the light guide 112. The light guide 112, the photomultiplier
113, the light collecting mirror 114, and the support base 114A are
fixedly positioned in the cylindrical member 106 for angular movement
therewith, and serve as components of the optical unit 107. Alternatively,
the light collecting mirror 114 may be dispensed with. As another
alternative, the light collecting mirror 114 and the support base 114A may
be replaced with another light guide and another photomultiplier, so that
the light emitted from the sheet 111 can be directed to the two
photomultipliers and electric signals from the photomultipliers can
simultaneously be applied to the image information readout circuit.
In the radiation image information readout device, the main (final) reading
mode in which the stimulable phosphor sheet is two-dimensionally scanned
in the above manner may be preceded by a preliminary read-out mode in
which the stimulable phosphor sheet is scanned by stimulating low-energy
radiation. In the preliminary read-out mode, light is emitted from the
stimulable phosphor sheet upon exposure to stimulating low-energy
radiation so as to obtain information based on which the final readout
gain is adjusted in order to eliminate unwanted effects of varying
conditions in which the image was recorded on the stimulable phosphor
sheet and also to generate a radiation image that can be better observed.
During the preliminary read-out mode, it is possible to angularly move the
optical unit in the direction of the arrow B' (FIG. 2) which is opposite
to the sub-scanning direction in the main reading mode.
With the stimulable phosphor sheet 111 fixed on the semicylindrical support
110, the optical unit 107 is angularly moved to scan the stimulable
phosphor sheet 111 in the sub-scanning mode while the stimulable phosphor
sheet 111 is being scanned in the main scanning mode by the laser beam
102, in the same manner as described with reference to FIG. 1.
The optical components such as the light beam source and the light
deflector need not necessarily be disposed in the cylindrical member, but
may be positioned in other locations provided they are angularly movable
for scanning the sheet in the sub-scanning mode.
The principles of the present invention are also applicable to light beam
scanners for use in image scanning recording devices. The various optical
elements employed in the light beam scanner are not limited to the types
and configurations described above.
Although a certain preferred embodiment has been shown and described, it
should be understood that many changes and modifications may be made
therein without departing from the scope of the appended claims.
* * * * *
|
|
 |
|
 |
Description |
|
