Optical printer

Details Optical printer Optical printer

1999-09-28

2002-09-03

Mathews, Alan A. (Department: 2851)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S225000, C355S032000

Reexamination Certificate

active

06445403

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an optical printer apparatus capable of relatively moving on a sensitized sheet to expose it with given timing, thereby forming an image, and more specifically, to a technique for controlling the exposure timing of the optical printer apparatus.
BACKGROUND ART
Disclosed in Japanese Patent Application Laid-open No. 2-169270 is an optical printer apparatus in which an optical head is relatively moved on a sensitized sheet to form an image on the sensitized sheet. This optical printer apparatus will now be described with reference to FIG.
16
.
A sensitized sheet
60
is driven at constant speed in the direction of arrow Z with respect to the optical head
10
by means of feed rollers
70
. The optical head
10
comprises a white light source
20
for radially emitting white light, a cylindrical lens
30
for linearly converging the white light on the sensitized sheet
60
, a three-color separation liquid crystal shutter
40
, and a liquid crystal shutter
50
.
The three-color separation liquid crystal shutter
40
is composed of three shutters
40
r
,
40
g
and
40
b
that linearly extend in the width direction (spreading direction) of the white light from the cylindrical lens
30
. These three shutters
40
r
,
40
g
and
40
b
are driven independently of one another, and are provided individually with color filters that transmit red (R), green (G), and blue (B) light beams, respectively.
The liquid crystal shutter
50
includes a plurality of pixels that are arranged in the same direction as the lengthwise direction of the shutters
40
r
,
40
g
and
40
b.
The following is a description of a method for forming an image on the sensitized sheet
60
by means of the apparatus shown in FIG.
16
.
The optical printer apparatus receives gradated color image data, controls the shutters
40
r
,
40
g
and
40
b
in accordance with the image data, and exposes the surface of the sensitized sheet
60
, thereby forming the image thereon. After the shutter
40
r
opened, the shutter
40
g
opens for a predetermined time, and after the shutter
40
g
opened, the shutter
40
b
opens for a predetermined time, to transmit the white light. This predetermined time is just equal to a period of time during which the sensitized sheet
60
moves for a distance X in FIG.
16
.
Thus, the sensitized sheet
60
is exposed to the red light beam (R), which is first transmitted through the shutter
40
r
, for the distance X in its moving direction (direction Z). Then, the shutter
40
r
is closed, while the shutter
40
g
opens. Since the sensitized sheet
60
is moved for the distance X by this time, that portion of the sensitized sheet
60
which has already been exposed to the light beam R is exposed again to the green light beam (G) that is transmitted through the shutter
40
g
. When the sensitized sheet
60
further moves for the distance X, thereafter, the portion already exposed to the light beams R and G is exposed in like manner to the blue light beam (B) that is transmitted through the shutter
40
b
. By repeating these processes of operation in the feeding direction of the sensitized sheet
60
, an image of full-color display can be obtained.
In a direction perpendicular to the feeding direction of the sensitized sheet
60
, an image is formed by means of the liquid crystal shutter
50
.
Referring now to
FIG. 17
, there will be described exposure timing for the formation of an image by means of the conventional optical printer apparatus shown in FIG.
16
.
In
FIG. 17
, it is supposed, for ease of illustration, that the sensitized sheet
60
is stationary and the optical head
10
moves in the direction of arrow Z. In order to indicate the color, R, G or B, of the light beam to which the sensitized sheet
60
is exposed, moreover, the sensitized sheet
60
is divided into three layers for convenience. Exposure of the sensitized sheet
60
to the light beam R is represented by the hatching on the first layer from the top, among the aforesaid three layers. Likewise, exposure to the light beam G and exposure to the light beam B are represented by hatching the second and third layers, respectively. It is, to be understood that
FIG. 17
never illustrates the fact that the actual sensitized sheet
60
is composed of those three layers.
Sections {circle around (
1
)} to {circle around (
6
)} individually represent pixels in the moving direction (direction Z in
FIG. 17
) of the optical head. The width of each pixel is represented by X in FIG.
17
.
Item (a) of
FIG. 17
shows a state in which the light beam R starts to be radiated so that the optical head
10
exposes the section {circle around (
3
)} on the sensitized sheet
60
thereto. As this is done, the light beams G and B are not radiated. Then, the optical head
10
radiates the light beam R as it moves at uniform speed for the distance X (equal to the pixel width) in the direction of arrow Z. The exposure of the section {circle around (
3
)} to the light beam R terminates when the position of (b) of
FIG. 17
is reached.
The moment the optical head
10
comes to the position of (b) of
FIG. 17
to finish the radiation of the light beam R, the optical head
10
starts to radiate the light beam G for the section {circle around (
3
)}, as shown in (c) of FIG.
17
. The section {circle around (
3
)} has already been exposed to the light beam R, as described above. Then, the optical head
10
radiates the light beam G as it moves at uniform speed for the distance X in the direction of arrow Z. The exposure of the section {circle around (
3
)} to the light beam G terminates when the optical head
10
comes to the position of (d) of FIG.
17
.
The moment the optical head
10
comes to the position of (d) of
FIG. 17
to finish the radiation of the light beam G, the optical head
10
starts to radiate the light beam B for the section {circle around (
3
)}, as shown in (e) of FIG.
17
. The section {circle around (
3
)} has already been exposed to the light beams R and G, as described above. Then, the optical head
10
radiates the light beam B as it moves at uniform speed for the distance X in the direction of arrow Z. The exposure of the section {circle around (
3
)} to the light beam B terminates when the optical head
10
comes to the position of (f) of FIG.
17
.
As described above, the section {circle around (
3
)} of the sensitized sheet
60
is exposed to the light beams R, G and B in a series of processes of operation shown in (a) to (f) of FIG.
17
. This series of operation processes will hereinafter be referred to as an exposure cycle. In a second exposure cycle subsequent to this cycle, the section {circle around (
6
)} is exposed, as shown in (g) of FIG.
17
.
In the conventional optical printer, as described above, a full-color image can be formed on the sensitized sheet
60
by continuously repeating the aforesaid exposure cycles.
According to the conventional optical printer apparatus arranged in this manner, however, the image pitch or spacing between images is equal to a maximum exposure distance (mentioned later), as mentioned before, so that the position of the section {circle around (
3
)}, which is situated at a distance 2X from the exposed section {circle around (
3
)}, is exposed between the first and second exposure cycles, as shown in (g) of FIG.
6
.
Thus, according to the conventional optical printer apparatus, the image involves an unexposed portion (i.e., sections {circle around (
4
)} and {circle around (
5
)} that is twice as long as the exposure distance X between the exposure cycles, resulting in lowered resolution and image quality.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an optical printer apparatus, capable of printing high-resolution, high-quality color images free from unexposed portions.
In order to achieve the above object, an optical printer apparatus according to the present invention comprises an optical head, capable of radiating a plurality of color light beams while moving relatively to a sensitized material, an

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