Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1998-11-05
2001-01-09
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S129000, C347S232000, C399S167000
Reexamination Certificate
active
06172696
ABSTRACT:
This application is based on an application No. 9-303901 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus, and especially relates to an image forming apparatus provided with a photosensitive drum which is driven by a stepping motor.
(2) Related Art
In an electrophotographic type image forming apparatus, a toner image is formed on a photosensitive drum and the toner image is transferred onto a recording sheet to form an image. To transfer the toner image formed on the photosensitive drum onto the recording sheet with fidelity, a circumferential speed of the photosensitive drum needs to be precisely equal to a transportation speed of the recording sheet. For this reason, in recent years, a stepping motor is used as a driving source of the photosensitive drum for its high performance in braking in comparison with other kinds of motors.
As one example of conventional image forming apparatuses, Japanese Laid-Open Patent Application No. 4-34444 discloses an image forming apparatus which includes a photosensitive drum driven by a stepping motor whose rotational speed is decreased to 1/129 via a reducer composed of pulleys and a belt. Using this conventional image forming apparatus, one scanning line of the electrostatic latent image is formed on the surface of the photosensitive drum every time the stepping motor rotates four steps.
However, with the construction of the conventional image forming apparatus, rotation of the stepping motor is not reliably transmitted to the photosensitive drum due to problems such as the belt skidding on the pulleys or expansion and contraction of the belt. This leads to nonuniformity in rotation of the photosensitive drum and in the distances between the scanning lines, and so causes inconsistency in the print density on the reproduced image.
To address this problem, the photosensitive drum can be directly driven by a stepping motor. However, using the cited image forming apparatus, about 32 scanning lines (obtained by calculating an equation 129/4) of the electrostatic latent image are formed every time the stepping motor rotates one step. As known in general, the rotational speed of the stepping motor during one step is not uniform. Consequently, the distances between the 32 lines are not uniform, and so causes inconsistency in the print density on a reproduced image.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an image forming apparatus, with distances between scanning lines being almost uniform.
The object of the present invention can be achieved by an image forming apparatus made up of: a photosensitive drum;
a stepping motor for directly driving and rotating the photosensitive drum; and an optical unit for scanning the photosensitive drum, which is rotated by the stepping motor, one scanning line at a time using an optical beam to form a latent image on the photosensitive drum, wherein &thgr; (°) indicating a step angle of the stepping motor, p (mm) indicating a distance between scanning lines on the photosensitive drum, and d (mm) indicating a diameter of the photosensitive drum are set so as to satisfy a following equation to make the optical unit scan the photosensitive drum by one scanning line every time the photosensitive drum is rotated n steps by the stepping motor, n being a positive integer: n·&thgr;=(360·p)/(&pgr;·d).
With this construction, the photosensitive drum is scanned by one scanning line every time the photosensitive drum is rotated n steps, so that the distances between the scanning lines are kept almost uniform. This prevents inconsistency in the print density on a reproduced image caused by the nonuniformity in the distances between the scanning lines.
The object of the present invention can be also achieved by an image forming apparatus made up of: an image holding member which is rotatable; a driving source which is directly connected to a rotational shaft of the image holding member to rotationally drive the image holding member; and an optical unit for scanning the image holding member, which is rotated by the driving source, one scanning line at a time using an optical beam to form a latent image on the image holding member, wherein &thgr; (°) indicating a unit moving angle of the driving source, p (mm) indicating a distance between scanning lines on the image holding member, and d (mm) indicating a diameter of the image holding member are set so as to satisfy a following equation to make the optical unit scan the image holding member by one scanning line every time the image holding member is rotated in units of n by the driving source, n being a positive integer: n·&thgr;=(360·p)/(&pgr;·d).
With this construction, the image holding component is scanned by one scanning line every time the image holding component is rotated n·&thgr; degrees, so that the distances between the scanning lines are kept almost uniform. This prevents inconsistency in the density on a reproduced image caused by the nonuniformity in the distances between the scanning lines.
REFERENCES:
patent: 5991576 (1999-11-01), Lee
patent: 4-16966 (1992-01-01), None
patent: 4-34444 (1992-02-01), None
patent: 6-149137 (1994-05-01), None
patent: 6-186239 (1994-07-01), None
Fujikura Teruhiko
Higashi Toshikazu
Takasu Akira
Tamura Tomonobu
Lee Susan S. Y.
McDermott & Will & Emery
Minolta Co. , Ltd.
LandOfFree
Image forming apparatus having photosensitive drum driven by... 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 having photosensitive drum driven by..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus having photosensitive drum driven by... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2516901