Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2003-07-11
2004-12-28
Vannucci, James (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C430S569000, C430S363000, C430S383000
Reexamination Certificate
active
06836076
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority-under 35 USC 119 from Japanese patent applications, No. 2002-210113, No. 2002-210114 and No. 2002-210115, the disclosure of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure device. Particularly, the invention relates to an exposure device including a plurality of kinds of light-emitting elements with different light-emitting spectra, which are placed at intersections of matrix electrodes, for performing superior in gradation reproducibility.
2. Description of the Related Art
An organic EL (Electro-Luminescent) element, which employs a fluorescent organic substance for a light-emitting layer thereof, can be easily manufactured compared with other types of light-emitting elements. The organic EL element enables to manufacture a thin, light-weight light-emitting element. Owing to such features, the organic EL elements have been researched and developed to use them as elements for thin display. In recent years, high-performance organic EL elements comparable to light-emitting diodes (LEDs) have been developed in terms of light-emitting luminance, efficiency and durability. Consequently, the application of such organic EL elements has been studied to an exposure device for exposing photosensitive materials such as silver halide photosensitive material.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2000-103114 has disclosed an exposure device using organic EL elements. As shown in
FIG. 8
, element rows, each formed by arranging a plurality of organic EL elements
80
for emitting lights with respective colors of red (R), green (G) and blue (B) in a main scanning direction for the respective colors, are grouped into sets of three RGB colors. Such sets (2 sets in
FIG. 8
) are arranged in the sub-scanning direction. In
FIG. 8
, each alphabet (R/G/B) that represents its corresponding color is put to the ends of respective symbol in order to discriminate between the organic EL elements
80
of the respective RGB colors.
In this exposure device, each of the light rays of RGB colors is applied to the same position of a photosensitive material once every sub-scanning process so that a full color latent image is formed on the photosensitive material. Moreover, an unillustrated control circuit controls the light-emission intensity and light-emission time of each organic EL element. A predetermined exposure gradation is achieved for each of the RGB colors. For example, assuming that exposure gradations of m-steps are available for each color, the number of possible color developments of this exposure device is represented by m
3
. Thus, in order to obtain multiple color developments, the number m of exposure gradations is required to increase. For example, in order to increase the number of exposure gradations in exposure control in the pulse-width modulation system and pulse number modulation system, the minimum pulse time width needs to be smaller.
It is difficult to control the driving current of the light-emitting element such as organic EL elements with high precision by using a fine pulse time width, from the viewpoint of control precision of the control circuit. Moreover, when the organic EL element is used as a light-emitting element, even if the pulse time width of the driving current is controlled with high precision, the response speed of the organic EL element does not properly follow the pulse. Thus, it is difficult to increase the number of exposure gradations. Furthermore, even with the exposure control in the intensity modulation system, it is difficult to control the driving current in fine steps with high precision. In other words, conventionally, when the respective light-emitting elements constituting the exposure device are gradation-modulated in multiple stages so as to carry out exposing processes, the number of exposure gradations is limited.
The control circuit controls the light-emitting intensity and light-emitting time of each organic EL element. A predetermined exposure gradation is achieved for each of the RGB colors. For example, assuming that exposure gradations of m-steps are available for each color, the number of possible color developments of this exposure device is represented by m
3
. Thus, in order to obtain multiple color developments, the number m of exposure gradations needs to increase. For example, in order to increase the number of exposure gradations in exposure control in the pulse-width modulation system and pulse number modulation system, the minimum pulse time width needs to be smaller.
Each photosensitive material has a different sensitivity to each of light rays of the respective colors. Thus, with respect to a color having a low sensitivity, an exposing process is required to be with a higher light-emitting intensity. In this case, the service life of the light-emitting element having a color that requires a high light-emitting intensity tends to become particularly shorter compared with the light-emitting element with the other colors. Thus, the service life of the exposure device is limited by the light-emitting element having the shortest service life. When the photosensitive material is a silver halide photosensitive material, the sensitivity to red light is lower than the sensitivity to green light or blue light in the order of not less than one digit. Thus, the light-emitting intensity of the red color light-emitting element needs to increase. Consequently, the shorter the service life of the light-emitting element of red color becomes, the shorter the shorter service life of the exposure head will become.
Generally, the greater the number of element rows becomes, the more the light-emitting intensity can reduce on a time average basis and the more reliable the exposure device will become. In contrast, the exposure device will become larger, resulting in degradation in the production yield and an increase in costs. This means that the total number of the element rows has an appropriate upper limit. Thus, the reliability of the entire exposure device is demanded to improve while maintaining the total number of the element rows in a fixed value.
For example, assuming that exposure gradations of m-steps are available for each color, the number of possible color developments of this exposure device is represented by m
3
. In order to obtain multiple color developments, the number m of exposure gradations needs to increase. For example, in order to increase the number of exposure gradations in exposure control in the pulse-width modulation system and pulse number modulation system, the minimum pulse time width needs to be smaller.
Each photosensitive material has a different sensitivity to each of light rays of the respective colors. Thus, with respect to a color having a low sensitivity, an exposing process needs to be with a higher light-emitting intensity. Here, the service life of the light-emitting element having a color that requires a high light-emitting intensity tends to become particularly shorter compared with the light-emitting element with the other colors. Thus, the service life of the exposure device is limited by the light-emitting element having the shortest service life. When the photosensitive material is a silver halide photosensitive material, the sensitivity to red light is lower than the sensitivity to green or blue light in the order of not less than one digit. Thus, the light-emitting intensity of the red color light-emitting element needs to increase. Consequently, the service life of the light-emitting element of red color becomes shorter and the service life of the exposure head becomes shorter.
SUMMARY OF THE INVENTION
The present invention has been devised to meet the above-mentioned demands. An object of the invention is to provide an exposure device capable of increasing significantly the number of exposure gradations exceeding the conventional limit.
Another object of the invention is to reduce the light-emitting intensity of
Sughrue & Mion, PLLC
Wu Jimmy
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