Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2000-02-17
2001-09-25
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S239000, C359S305000, C359S314000
Reexamination Certificate
active
06295079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming device, and in particular, relates to a scanning optical unit provided in an image forming device, which scanning optical unit forms an image on a recording medium by scanning, in a main scanning direction, a laser beam which is diffracted by an acousto-optic modulating element (an acousto-optic modulator).
2. Description of the Related Art
An image exposure device, which scans a laser beam to write an image onto a photographic printing paper, is used in a digital laboratory system. The image exposure device is provided with light sources which emit laser beams of the colors of R, G, B. On the basis of color image data, the laser beams emitted from the light sources of the respective colors are modulated, and are illuminated onto a deflector such as a polygon mirror. The laser beam from the deflector is deflected in the main scanning direction and is illuminated onto a photographic printing paper.
The scanning optical unit provided at the image exposure device is provided with a light source unit comprising LDs of the colors of R, G, B, a collimator lens for condensing light, an acousto-optic modulator (AOM), an f&thgr; lens, a cylindrical lens, and the like. The laser beams of R, G, B illuminated from the light source unit are illuminated onto a predetermined point of the polygon mirror, and main scanning is carried out by the laser beam reflected at the polygon mirror being illuminated onto a photographic printing paper.
In a scanning optical unit structured in this manner, the illuminated position of the laser beam is detected by a sensor, and the time at which the main scan starts is determined. The laser beam transmitted through the AOM is diffracted in accordance with the determined time at which the main scan starts.
The sensor that detects the laser beam may be structured so as to receive light which is the laser beam which has been reflected by the polygon mirror and further reflected by a reflecting mirror (Refer to Japanese Patent Application Laid-Open (JP-A) No. 6-202016).
When the laser beam is illuminated onto a peripheral edge portion of this reflecting mirror, flare reflection may occur, and the photographic printing paper may be needlessly exposed due to the flare-reflected laser beam. When the photographic printing paper is needlessly exposed by such flare reflection, the quality of the finish of the recorded image deteriorates.
Attempts have been made to prevent flare reflection in a main scanning optical unit by changing the intensity of light or the direction of diffraction of the light diffracted by the AOM which detects the laser beam by a sensor, such that the laser beam is not illuminated onto a peripheral portion of the reflecting mirror.
However, in the AOM, the laser beam passing through the acousto-optic modulating medium is diffracted by ultrasonic waves which are generated in the acousto-optic modulating medium by the transducer. Therefore, there is a time difference between the time when the ultrasonic waves are generated by the transducer and the time the laser beam is diffracted.
As a result, during the period of time from after the laser beam is detected by the sensor until the AOM is operated, the laser beam may reach a peripheral portion of the reflecting mirror, and flare reflection cannot always be reliably prevented.
SUMMARY OF THE INVENTION
In view of the aforementioned, an object of the present invention is to provide a scanning optical unit in which, by reliably preventing a laser beam from being illuminated onto a peripheral edge portion of a reflecting mirror, deterioration in the finished quality of an image formed on a recording medium such as a recording material due to the laser beam being flare-reflected at the peripheral edge portion of the reflecting mirror can reliably be prevented.
In order to achieve this object, a first aspect of the present invention is a scanning optical unit comprising: an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element diffracts the laser beam by ultrasonic waves inputted by the transducer; main scanning/deflecting means for deflecting, in a main scanning direction of a recording medium, the laser beam which was diffracted by the acousto-optic modulating element; a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the main scanning/deflecting means; and a sensor for determining a main scanning start position by receiving the laser beam reflected by the reflecting mirror, wherein a predetermined region of the recording medium is exposed by the laser beam deflected in a main scanning direction, and a distance, to the transducer from an illuminated position of the laser beam which is a diffracted position of the laser beam within the acousto-optic modulating medium, is set on the basis of a reflected position on the reflecting mirror of the laser beam received by the sensor with respect to a recording medium side end portion of the reflecting mirror, a main scanning speed of the laser beam, and a propagation speed of ultrasonic waves within the acousto-optic modulating medium.
In accordance with the first aspect of the invention, the distance between the transducer and the diffracted position of the laser beam within the acousto-optic modulating medium which diffracts the laser beam, is set on the basis of the propagation speed of ultrasonic waves within the acousto-optic modulating medium, the reflected position of the laser beam detected by the sensor for determining the main scanning start position, and the main scanning speed of the laser beam.
For example, the diffracted position of the laser beam may be set such that the laser beam moving on the reflecting mirror in the main scanning direction does not reach the recording medium side end portion of the reflecting mirror up to the time the diffraction of the laser beam stops, by the transducer being turned off on the basis of the results of detection of the sensor.
In this way, when the laser beam reaches the recording medium side end portion of the reflecting mirror, the laser beam is not illuminated onto the reflecting mirror. Flare reflection caused by the laser beam being illuminated onto the end portion of the reflecting mirror is reliably prevented, and the image formed on the recording medium is not spoiled due to flare reflection.
A second aspect of the present invention is a scanning optical unit comprising: an acousto-optic modulating element including an acousto-optic modulating medium and a transducer which generates ultrasonic waves, and when a laser beam emitted from a laser light source passes through the acousto-optic modulating medium, the acousto-optic modulating element modulates an intensity of the laser beam by ultrasonic waves inputted by the transducer; main scanning/deflecting means for deflecting, in a main scanning direction of a recording medium, the laser beam whose intensity was modulated by the acousto-optic modulating element; an optical system including an f&thgr; lens; a reflecting mirror which is provided outside of an exposure region of the recording medium, and reflects the laser beam from the main scanning/deflecting means; and a scanning optical system including a sensor for determining a main scanning start position by receiving the laser beam reflected at a predetermined position of the reflecting mirror, wherein the recording medium is scanned and exposed by said main scanning/deflecting means and said optical system including the f&thgr; lens, and given that a focal length of the f&thgr; lens is f, the main scanning speed which is the speed at which the laser beam moves on the recording medium is v, the distance between the reflecting mirror and an exposure surface of the recording medium is t, a distance from
Fuji Photo Film Co. , Ltd.
Le N.
Pham Hai C.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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