Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-02-18
2001-08-28
Brase, Sandra (Department: 2852)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S233000
Reexamination Certificate
active
06281922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image forming apparatus and more particularly to an image forming apparatus comprising an optical scanner for deflecting light beams emitted from a plurality of light sources by a single deflector (for example, a rotating polygon mirror), dividing one scanning line on an image carrier (for example, a photosensitive drum) whose surface moves in a predetermined direction by the deflected light beams, and scanning the light beams over the line in a main scanning direction.
2. Description of the Related Art
Hitherto, an optical scanner for emitting light beams from two light sources, deflecting the two emitted light beams by a polygon mirror, dividing one scanning line on a photosensitive body by the two deflected light beams, and scanning the light beams over the line has been proposed (refer to Japanese Patent Unexamined Publication No. Sho. 63-47718).
The optical scanner scans one light beam over the first half of an image area of the photosensitive body and the other beam over the latter half of the image area of the photosensitive body. The scanning line is thus divided by two light beams and the light beams are scanned, whereby the number of images of the polygon mirror can be increased and the print speed can be improved without upsizing the optical scanner.
By the way, to divide one scanning line by two light beams and scan the light beams, if an image formed by scanning one light beam is assumed to be one panel image, images formed by scanning two light beams are formed as a set of panel images.
The light beams are generated from light sources placed at different positions and arrive at the photosensitive body over different passages. Thus, the placement positions of the light sources, the positions of the parts making up the light sources, the positions of optical systems placed on the passages, and the like are displaced due to external causes such as temperature change, vibration, and shock, and the light beam passage may shift from a predetermined passage.
If the light beam passage thus shifts, a discontinuous image occurs in the joint between panel images formed by scanning the light beams and it is feared that the image quality may be degraded remarkably.
The images formed from light sources on both sides of the joint according to image signals having the same number of clocks may differ in length (namely, a partial magnification difference may occur), and to form a multicolor image, it is feared that a color misregistration may be caused.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an image forming apparatus that can avoid degradation of image quality in a joint if a light beam passage shifts from a predetermined passage or a partial magnification difference occurs.
In order to achieve the above object, according to the invention, there is provided an image forming apparatus comprising: a plurality of light sources each for modulating and emitting a light beam based on image data at an operation speed responsive to a predetermined clock; an optical scanner for deflecting the light beams emitted from the plurality of light sources by a single deflector, dividing one scanning line on an image carrier rotating in a predetermined direction by the deflected light beams, and scanning the light beams over the line in a main scanning direction; a detector for detecting a position displacement amount in a boundary portion of areas over which the light beams are scanned; and a controller for controlling light beam emission start timings from the light sources or clock frequencies corresponding to the light sources so as to eliminate a displacement amount in the main scanning direction if the position displacement amount detected by the detector contains the displacement amount in the main scanning direction, and for controlling the light sources so as to modulate and emit the light beams based on image data of a scanning line shifted as many lines as the number of lines responsive to a displacement amount in a rotation direction of the image carrier If the position displacement amount contains the displacement amount along the rotation direction.
In the image forming apparatus, each of the light sources modulates and emits a light beam based on image data at the operation speed responsive to a predetermined clock. The optical scanner deflects the light beams emitted from the light sources by a single deflector (for example, a rotating polygon mirror), divides one scanning line on the image carrier by the deflected light beams, and scans the light beams over the line in the main scanning direction. Since the image carrier rotates in the predetermined direction (corresponding to a subscanning direction), a plurality of light beams are scanned over the surface of the image carrier.
The detector detects a position displacement amount in the boundary portion of the areas over which the light beams are scanned.
If the position displacement amount detected by the detector contains a displacement amount in the main scanning direction, the controller controls the light beam emission start timings from the light sources or the clock frequencies corresponding to the light sources so as to eliminate the displacement amount in the main scanning direction.
For example, to scan two light beams over the image carrier, one light beam emission start timing is delayed or moved up with respect to the other light beam emission start timing, whereby the scan area over which one light beam is scanned is displaced along the main scanning direction for correcting the displacement amount in the main scanning direction. The clock frequency of one light source may be increased or decreased for changing the width along the main scanning direction of the scan area over which one light beam is scanned, thereby correcting the displacement amount in the main scanning direction.
On the other hand, if the position displacement amount contains a displacement amount along the rotation direction of the image carrier, the controller controls the light sources so as to modulate and emit the light beams based on image data of a scanning line shifted as many lines as the number of lines responsive to the displacement amount in the rotation direction.
For example, to scan two light beams over the image carrier, if the positions of the areas over which the light beams are scanned are displaced three scanning lines along the rotation direction of the image carrier, the controller controls the light sources so as to modulate and emit the light beam based on image data of a predetermined scanning line by one light source and at the same time, modulate and emit the light beam based on image data of the scanning line shifted three lines from the predetermined scanning line by the other light source.
Thus, if position displacement occurs in the boundary portion of the areas over which the light beams are scanned, it can be corrected with accuracy in the main scanning direction and in the rotation direction of the image carrier (subscanning direction) and degradation of image quality in the boundary portion of the areas over which the light beams are scanned can be avoided.
Further, according to the invention, there is provided an image forming apparatus comprising: a plurality of light sources each for modulating and emitting a light beam based on image data at an operation speed responsive to a predetermined clock; an optical scanner for deflecting the light beams emitted from the plurality of light sources by a single deflector, dividing one scanning line on an image carrier rotating in a predetermined direction by the deflected light beams, and scanning the light beams over the line in a main scanning direction; a scan distance detector for detecting a scan distance of each light beam along the main scanning direction within a predetermined time; and a frequency controller for controlling clock frequencies corresponding to the light sources so that the scan distances of the light beams detected by the sc
Brase Sandra
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fuji Xerox Co. LTD
LandOfFree
Image forming apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2441549