Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Utility Patent
1998-09-03
2001-01-02
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S233000, C347S116000, C372S023000, C372S020000
Utility Patent
active
06169562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image exposure apparatus, and particularly to an image exposure apparatus in which, based on image data, at least three types of emitted light having different wavelengths are irradiated onto a photosensitive material, thereby forming a latent image on the photosensitive material.
2. Description of the Related Art
In recent years, an image exposure apparatus, which effects scan and exposure of a photographic printing paper by using a light source which emits laser light, has been used widely for writing an image in a digital laboratory system or the like, in which an image recorded on a photographic film is recorded on a photographic printing paper (i.e., a photosensitive material).
Such a conventional image exposure apparatus includes light sources which emit laser light of colors red (R), green (G), and blue (B), respectively. Laser light is modulated for each of the colors R, G, and B based on color image data and deflected by a deflector such as a polygon mirror in a main scanning direction, and simultaneously, the photographic printing paper is conveyed in a sub-scanning direction. The laser light is further transmitted through an f&thgr; lens to allow an image to be scanned and exposed onto the photographic printing paper, and a color image is thus recorded on the photographic printing paper.
The conventional image exposure apparat us thus causes laser light emitted from the light sources to be transmitted through the f&thgr; lens, and therefore, there exists a drawback in that the laser lights of each of the colors have different scanning lengths on an exposure surface, due to chromatic aberration of the f&thgr; lens, thereby causing displacement of color. The chromatic aberration mentioned herein refers to the fact that, since the refractive index of a glass (a lens) varies so as to correspond to the magnitude of a wavelength of light, the position and size of an image formed by a ray of light other than a paraxial ray change due to the wavelength of light.
In order to solve the above-described drawback, for example, Japanese Patent Application Laid-Open (JP-A) No. 9-11538 discloses that improvement in image quality is achieved in such a manner that the respective scanning lengths of the laser lights of the colors a re made to coincide with one another by adjusting the time interval (cycle) at which pixels are written for each laser light, and the write starting position set by each laser light is made to coincide.
Further, as a conventional art in addition to the above, there exists a method for manufacturing and using a lens (achromatic lens) for correcting chromatic aberration of the laser light of all three colors of R, G, and B.
However, in the above-described publication (JP-A No. 9-11538), the time interval at which the pixels are written is adjusted for each laser light, and therefore, a circuit having a complicated structure, such as a phase locked loop circuit formed by an integrator, a phase comparator, a voltage-controlled oscillator, and the like is necessary, thereby resulting in an increase in the cost of the entire apparatus.
In the method for manufacturing and using an achromatic lens for correcting chromatic aberration of laser light of all three colors of R, G, and B, a great deal of adjustment and a large number of processes are required when the achromatic lens is manufactured, thereby resulting in the cost of the entire apparatus increasing in the same manner as described above. Further, conventionally, the main scanning wavelength is approximately 210 mm, and when the main scanning wavelength is made longer (for example, 254 mm), laser light passes through the peripheral portion, having a large aberration, of an f&thgr; lens. In this case, it is difficult to optically correct the color aberration.
SUMMARY OF THE INVENTION
The present invention has been devised to solve the above-described drawbacks, and an object thereof is to provide an image exposure apparatus which can prevent the occurrence of color displacement at a low cost.
In order to achieve the above-described object, there is provided an image exposure apparatus according to a first aspect, which comprises at least three kinds of light sources each of which emits a light of a different wavelength, deflecting device which deflects at least three kinds of emitted light emitted by the light sources in a predetermined scanning direction, a scanning lens which is disposed so that the at least three kinds of emitted light deflected by the deflecting device can be transmitted therethrough and which allows each chromatic aberration of two kinds of emitted light from among the at least three kinds of emitted light to have substantially the same characteristics, clock generating device for generating a scanning clock for the two kinds of emitted light and a scanning clock for emitted light other than the two kinds of emitted light, each frequency of the scanning clocks being determined in advance so that the two kinds of emitted light and the emitted light other than the two kinds of emitted light have substantially the same scanning lengths on an exposure surface, and modulating device which modulates the two kinds of emitted light based on image data and the scanning clock for the two kinds of emitted light, and also modulates the emitted light other than the two kinds of emitted light based on image data and the scanning clock for the emitted light other than the two kinds of emitted light.
According to the first aspect of the present invention, at least three kinds of light sources emit light of different wavelengths and the three or more kinds of emitted light are deflected by the deflecting device in a predetermined scanning direction. As a result, main scanning of the three or more kinds of emitted light is effected. Subsequently, the three or more kinds of emitted light deflected by the deflecting device are transmitted through the scanning lens in which each chromatic aberration of the two kinds of emitted light from among the three or more kinds of emitted light has substantially the same characteristic, and arrives at an exposure surface of a photosensitive material such as a photographic printing paper, thereby allowing scan and exposure of laser light. At this time, the above-described two kinds of emitted light are modulated by the modulating device based on image data and the scanning clock for the above-described two kinds of emitted light, and the emitted light other than the two kinds of emitted light is modulated based on image data and the scanning clock for the emitted light other than the two kinds of emitted light.
The scanning clock for the above-described two kinds of emitted light and the scanning clock for the emitted light other than the two kinds of emitted light, which are used for the scan and exposure, are generated by the clock generating device in such a manner that the frequency of each of these scanning clocks is determined so that the two kinds of emitted light and the emitted light other than the two kinds of emitted light have substantially the same scanning lengths on the exposure surface.
As described above, according to the image exposure apparatus of the first aspect of the present invention, the scanning lens in which each chromatic aberration of the two kinds of emitted light is of the substantially same characteristic is used to allow the two kinds of emitted light to have substantially the same scanning lengths on the exposure surface, and the frequency of each of the scanning clock for the two kinds of emitted light and the scanning clock for the emitted light other than the two kinds of emitted light is determined so that the two kinds of emitted light and the emitted light other than the two kinds of emitted light have substantially the same scanning lengths on the exposure surface, thereby resulting in the respective scanning lengths of all emitted light being made substantially coincident with one another in a simple manner. Accordingly, as compared with
Fuji Photo Film Co. , Ltd.
Le N.
Pham Hai C.
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