Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-11-09
2003-02-25
Hilten, John S. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S259000
Reexamination Certificate
active
06525760
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for exposing an image recording medium, such as a thermal printing plate.
DESCRIPTION OF THE PRIOR ART
FIG. 1
is a side view of a conventional single beam internal drum imagesetter. A laser
1
generates a laser beam
2
which is directed onto an angled reflective surface
3
of a spinning mirror
4
. The spinning mirror
4
is rotated by a motor
5
which is mounted on a carriage (not shown). The carriage (not shown) is driven parallel to the axis of a drum
7
by rotation of a lead screw
6
. Items
3
-
6
are housed inside the drum
7
. One or more image recording plates (not shown) are mounted on the inner surface of the drum
7
. To expose the image recording plates on the drum
7
, the motor
5
moves along the axis of the drum
7
, and rotates the spinning mirror
4
about the axis of the drum
7
whereby the reflected laser beam
8
exposes a series of circumferential scan lines.
As can be seen in
FIG. 2
, which is an end view of the apparatus shown in
FIG. 1
, during the lower 80° of its revolution, the reflected laser beam
8
is blocked by the carriage
136
. This creates a shadow area
9
which prevents the scanner from exposing a full 360° of the drum
7
and reduces the speed and efficiency of the system. The angle of the area outside the shadow area
9
is conventionally known as the “drum angle”.
A known way of improving on the efficiency and scanning time of the system of
FIG. 1
is to add a second spinner and a second laser as illustrated in FIG.
3
.
FIG. 3
illustrates the lower half
10
of a cylindrical drum. A first mirror
11
and a second mirror
12
are mounted at 180° to each other on a common shaft
13
which is rotated by a motor (not shown). A first laser
14
is directed at the spinning mirror
11
, and a second laser
15
is directed at the spinning mirror
12
. The distance between the reflective surfaces of the spinning mirrors
11
,
12
is equal to half the length of the drum. The laser
14
directs image radiation to the mirror
11
during one half cycle to expose a line on the upper half of the drum. The laser
15
t directs image radiation to the mirror
12
during the next half cycle to expose another line on the upper half of the drum. The process continues until the right-hand spinner
12
has exposed the right-hand upper quarter of the drum, and the left-hand spinner
11
has exposed the left-hand upper quarter of the drum. Therefore the entire upper half of the drum can be exposed in half the time when compared with the system of FIG.
1
. In addition the overall efficiency is increased since the lower half of the drum (which includes the shadow area
9
) is not exposed.
A problem associated with the system of
FIG. 3
is that two lasers
14
,
15
are required. The cost of lasers can be very high.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention there is provided apparatus for exposing an image recording medium, the apparatus comprising a radiation source; a switch comprising an input arranged to receive radiation from the radiation source, and a plurality of imaging outputs, wherein the switch selectively routes the radiation received at the input to a selected one of the imaging outputs; and means for directing the radiation from each imaging output onto the image recording medium to expose the image recording medium.
In accordance with a second aspect of the present invention, there is provided a method of exposing an image recording medium, the method comprising generating radiation in a radiation source; inputting the radiation to a switch having a plurality of imaging outputs; routing the radiation during a first period to one or more selected ones of the imaging outputs; routing the radiation during a second period to one or more different selected ones of the imaging outputs; and exposing the image recording medium with radiation, from the or each selected imaging output.
The present invention provides a routing device which enables a single radiation source to be used in a scanner of the type illustrated in FIG.
3
. This results in a much simplified system with reduced cost.
The radiation which exposes the image recording medium is generally encoded with image information to expose a desired pattern of pixels. The radiation may be encoded downstream of the routing device, for instance with an acousto-optic modulator. Preferably however the radiation which is input to the routing device is already encoded, for instance by suitable control of the radiation source. Typically the radiation source inputs radiation in the form of a series of pulses to the routing device. This enables pixels to be exposed on the image recording medium with short, high power pulses, resulting in low thermal leakage.
In a preferred embodiment the radiation source comprises an optical amplifier having a pump energy source. The average power of the optical amplifier can then be conveniently adjusted by adjusting the power input by the pump energy source. The pump energy source may input electrical pump energy into the amplifier, but preferably the pump energy source comprises a radiation source such as an array of laser diodes.
The radiation source may be operated in a continuous wave mode as illustrated schematically in
FIG. 4. A
power source (not shown) provides a power signal on input line
16
. When switch
17
is closed the laser cavity
18
outputs a laser beam
19
. A problem with continuous wave mode is that the laser beam
19
cannot have a power any greater than the power on input line
16
. This is a particular problem in thermal printing imagesetters where high laser power may be required.
Therefore preferably the radiation source is operated in pulsed mode, as illustrated schematically in FIG.
5
. In this case a power source provides a power signal on input line
20
which is input continuously to the laser cavity
21
. The laser cavity
21
stores the energy from input line
20
until switch
22
is closed to release the energy in the form of a high power pulsed laser beam
23
. As a result, the power of the pulsed laser beam
23
can be higher than the power on input line
20
. This enables pixels to be exposed on the image recording medium with short, high power pulses, resulting in low thermal leakage.
An example of a suitable radiation source is shown in FIG.
6
.
FIG. 6
illustrates a fibre amplifier of the type described in WO95/10868. The fibre amplifier comprises a fibre
30
having a Erbium-Ytterbium doped single-mode inner core
31
and a multi-mode concentric outer core
32
. A single mode seed laser
33
directs an encoded laser beam
34
into the inner core
31
. Pump radiation is provided by a pump source
35
(an array of multi-mode laser diodes) which is coupled, transversely with respect to the optical axis of the fibre
30
, to the outer core
32
. The method of coupling the pump source
35
to the fibre
30
is described in detail in WO96/20519. Pump radiation from the pump source
35
propagates through the outer core
32
and couples to the amplifying inner core
31
, and pumps the active material in the inner core
31
. Thus the fibre optic amplifier provides a highly amplified encoded output beam
36
at the wavelength of the encoded laser beam
34
.
The fibre optic amplifier illustrated in
FIG. 6
is primarily designed for use in telecommunications in which the encoded input laser beam
34
will not be off for a significant length of time. If the seed laser
33
is off for an extended period, the fibre
30
continues to accumulate energy from the pump source
35
, and as a result the fibre
30
will go into spontaneous emission. This problem is common to all pulsed laser sources and as a result pulsed laser sources are generally not used in imaging applications where the laser may be off for an extended period of time.
In order to solve this problem, the apparatus preferably further comprising an energy dump; and means for directing the radiation from the radiation source either to the energy d
Feggins K.
Fujifilm Electronic Imaging Limited
Hilten John S.
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