Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Utility Patent
1999-05-18
2001-01-02
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S237000, C347S133000, C250S370150
Utility Patent
active
06169563
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image recording apparatus for recording an image, and in particular, to an image recording apparatus suitable for a proof making apparatus (Direct Digital Color Proof: DDCP) outputting color proofs (a sample for proofreading) with a halftone dot image.
In making color printed matters, in some cases it is performed at the stage of original films color proofreading, in which color proofs are prepared using each of the color-separated halftone dot original films which are separated into a Y-print, an M-print, a C-print, and a BK-print (black or India ink color), so that it may be checked if there is no mistake in the layout of the original films, no mistake in the colors, no mistake in the letters, and so forth, to confirm the finish of the prints before final printing plates are prepared on the basis of the color-separated halftone dot original films.
In recent years, the preparation of color proofs has been carried out using the DDCP (direct digital color proof) method. As one of the techniques in the DDCP method, a silver halide photosensitive material is exposed to a light beam composed of a combination of a plurality of lights having different wavelengths such as R, G, and B to make the dots for the respective colors Y, M, C, and BK develop colors, on the basis of the halftone clot image data of the respective color-separated halftone dot originals.
As a technique other than the DDCP method, there is known technique in which color proofs are prepared by transferring images of the respective colors through the ink pigment transfer process from the respective ink sheets of Y, M, C, and BK onto the same kind of paper sheets as used in printing.
The development of colors in the respective dots for Y, M, C, and BK in printing is determined by the colors of inks of the respective colors. On the other hand, in a silver halide color photosensitive material, the development of colors in the respective dots for Y, M, C, and BK determined by the color development in the photosensitive layers. That is, in a silver halide color photosensitive material, the development of colors in the photosensitive layers is determined by the light emission quantity of the recording light source.
As the above-mentioned recording light source, there has been known a light source using a plurality of laser beams in order to make the recording speed high. As for the laser beams, it is often the case to use a gas laser; and further, in the method of obtaining a plurality of laser beams, a beam splitting optical element has been used.
In recent years, from the view point of cost reduction and owing to the stability established for laser diodes, there has been brought into practice a method in which a plurality of laser beams are formed by arranging a requires number of elements of laser diodes.
The modulation speed of each laser diode has been suppressed at a low level as a result of using plural diodes in view of the transmitting speed of the image data. On the other hand, for the purpose of recording an image with a stable quality, correction has been carried out for the decrease of emission intensity owing to the deterioration of laser diodes with the passage of time, or for the decrease of the beam intensity of the laser beam reaching to the photosensitive material through the optical system.
In the future, it is thinkable that the transmission speed of image data will be improved with the progress of technology, and it is easily judged that the increase of the recording speed in image recording will be required more and more. On this occasion, it will be necessary to make the modulation speed of laser diodes high, and in order to secure a high response speed, it will be required to keep the laser diodes in the state of emitting light at a low level (by applying a bias voltage) even when the image data of pixels for the laser diodes does not form a dot image during image recording period.
However, it raises a problem that, in correcting beam intensity, if each of the laser diodes is always in the light emitting state at a low level, measurement of beam intensity with a high precision can not be made owing to the influence of the light leakage from a laser diode among a plurality of laser diodes other than the target laser diode which is the object of correction, and the precision of correction is made to be lowered.
Further, in conventional image recording apparatus, it has been made a practice that an initial operation of every portion of the apparatus is performed after turning on the power source, and the control of the light emission quantity of the recording light source is carried out at the timing when the initial operations are finished.
The above sequence is shown schematically in FIG.
20
. The abscissa is the passed time t after the turning-on of the power source and the ordinate is the light emission intensity P of a semiconductor laser. The light emission intensity gets increased after the turning-on of the power source and enters in a nearly stable state after the light emission intensity reaches to the maximum value.
Regardless of this light emission characteristic, in conventional general image recording apparatus, it has been made a practice that the light emission intensity is measured at the timing when the initial operations of the apparatus are finished, and the driving current is adjusted so as to obtain a predetermined light emission intensity. For example, this timing when the initial operations are finished corresponds to t
1
in the case of FIG.
20
.
However, as shown in
FIG. 20
, the light emission intensity reaches to the maximum value after the turning-on of the power source, and enters into the nearly stable state after decreasing by a certain quantity. Accordingly, if the adjustment of the light emission intensity is carried out in the neighborhood of the maximum value, the light emission quantity is made to be decreased from several per cent to 10% when the laser diode is brought into the state of actual use.
Further, owing to the atmosphere of the environment where the image recording apparatus is used, sometimes the temperature in the neighborhood of the light source varies. In such a case too, the light emission intensity of the recording light source varies. Moreover, when the temperature in the neighborhood of the light source varies, deviation occurs in the optical system such as a lens and a mirror, the deviation also being produced in the optical axis and the focus, resulting in the variation of the beam intensity, and further, in the variation of the light quantity used in image recording.
Further, lately, some image recording apparatus are continuously used for 24 hours without stopping. In such cases, the apparatus are continuously used with the light emission intensity adjusted only once at the time of turning-on of the power source. As a result, there is a high possibility that the light emission intensity will enter a state that is different from that at the time of its adjustment.
As stated in the above, if the light emission intensity of the recording light source varies, the desired range of variation of the light emission intensity (for example, to the extent of 2 to 3%) can not be maintained, and high-fidelity color proofs are difficult to prepare.
SUMMARY OF THE INVENTION
This invention has been made in view of the above-mentioned problems, and it an object of this invention is to provide an image recording apparatus using a plurality of laser diodes, wherein high-speed writing is possible and wherein measurement of the beam intensity of each of said laser diodes can be performed with a high precision. Further, it is another object of the invention to provide an image recording apparatus having a laser diode, wherein correction of the beam intensity of each of said laser diodes can be performed with a high precision.
The above-described objects are accomplished by the following structures.
I. An image recording apparatus, comprises
an optical unit having a plurality of laser diodes;
a driving c
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
Le N.
Pham Hai C.
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