Image forming with synchronized control

Details Image forming with synchronized control Image forming with synchronized control

1999-10-27

2003-11-04

Pham, Hai (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S234000, C347S248000, C347S250000

Reexamination Certificate

active

06642949

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus and method for forming a color image on a recording medium using recording agents of a plurality of colors.
2. Related Background Art
A laser beam printer (LBP) is a well known example of present-day conventional image forming apparatuses that use color image data for printing. When one type of laser beam printer is used to print a color image, for each of the colors that are to be printed a main scan means employs a laser beam, which uses a rotary polyhedron mirror, to expose a photosensitive member and to form on the member a latent image composed of a series of scan lines for a specific individual color. Then, again for each of the colors, the latent image is developed by using either a magenta (M), a cyan (C), a yellow (Y) or a black (BK) color developer to form an individually colored image that, subsequently, is transferred to a recording sheet, securely held on a transfer drum, on which all the individually colored images are superimposed, one on the other. Another type of color image apparatus temporarily transfers images for individual colors from a photosensitive member to an intermediate transfer member, superimposing the images thereon, and collectively transfers the color images from the intermediate transfer member to a recording sheet.
For these apparatuses, the photosensitive member and the transfer drum, and the intermediate member, if used, are moved at a constant speed in the direction (the sub-scan direction) perpendicular to the main scan direction, while an optical system scans an original document at the same speed.
When, at each revolution, the photosensitive drum, the transfer drum or the intermediate drum generates a sub-scan start reference signal, in synchronization with this signal, the optical system initiates the scanning of an original document, and a CCD (charge-coupled device) begins to read line data. Similarly, in synchronization with the sub-scan start reference signal, data for each color are recorded on a recording sheet held on the transfer drum, or on the intermediate member. In this manner, the timing for the data reading and for the data writing are synchronized.
For the additional image forming apparatus that transfers individually colored images to a photosensitive drum, superimposing them thereon, and collectively transfers the resultant image to a recording sheet, to prevent deterioration of the quality of a color image, which occurs when the positions are shifted at which images are read for the individual colors, a method that controls the position at which an image for each color is read is important.
According to a conventional reading position control method, rotation precision is increased for a polygon motor that generates, as a reference for main scan sync control, a main scan start reference signal (hereinafter referred to as a BD (beam detect) signal), and a drum motor that generates, as a reference for sub-scan sync control, a photosensitive drum rotation position signal (hereinafter referred to as a sub-scan start reference signal (an ITOP (image top) signal)). In addition, the drum motor and an optical motor that drives an original reader for scanning an original document are controlled at the same speed.
FIG. 12
is a diagram showing an example arrangement of a system for driving a polygon motor and a drum motor in a conventional image forming apparatus.
In
FIG. 12
, a photosensitive drum
1301
is rotated via a drive belt
1308
by a photosensitive drum drive motor
1307
. A polygon motor
1302
rotates a polygon mirror
1303
that, for each line of a document, scans, the face of the photosensitive drum
1301
with a beam emitted by a laser
1304
and transmitted via a lens
1305
.
A PLL (phase-locked loop) circuit
1310
drives the polygon motor
1302
at a constant speed based on a reference clock received from an oscillator
1311
, and a PLL circuit
1309
drives the photosensitive drum drive motor
1307
at a constant speed based on a reference clock received from an oscillator
1312
. The rotations of the polygon motor
1302
and of the photosensitive drum drive motor
1301
are matched in consonance with the precision of the frequencies generated by the oscillators
1311
and
1312
.
With this arrangement, since the photosensitive drum
1301
and the polygon motor rotate at a controlled, constant speed, the ITOP signal, which is synchronized with the rotation of the photosensitive drum
1301
, and the BD signal, which is synchronized with the rotation of the polygon motor
1302
, are produced at predetermined frequencies.
Therefore, the conventional image forming apparatus employs the ITOP signal to control the original document scan start timing for the optical system, and the line data reading start timing and the image writing timing for a three-line sensor (hereinafter referred to as CCD), so that the reading positions for individual colors correspond. It should be noted that the CCD includes a light accumulation unit for acquiring, as data, light reflected from an original document that is being scanned, and a transfer unit for outputting, as writing data, the data that are acquired by the light accumulation unit.
An explanation will now be given, while referring to
FIGS. 13
to
16
A and
16
B, for an example original document reading method employed by the conventional image forming apparatus.
FIG. 13
is a timing chart for explaining the line data fetching process performed by the CCD of the conventional image forming apparatus.
In
FIG. 13
, a CCD light accumulation/transfer control signal (hereinafter referred to as a control signal) is synchronized with a BD signal. Light is accumulated (line data are fetched) for a predetermined time period during an interval in which the control signal is at level H, and then, the accumulated line data are transmitted to the transfer unit during an interval in which the control signal is at level L. During the next light accumulation period, line data are output as writing data by the transfer unit at a delay, relative to the line accumulation process, of one line (one BD cycle).
Specifically, the control signal is synchronized with the BD cycle to repeat the light accumulation process (a level H interval) and the data transmission process (a level L interval).
First, at interval (1), during which the control signal is at level H, the CCD accumulates data for an original document that is being currently scanned by the optical system, i.e., “reading data 1” in FIG.
13
. Then, at interval (2), during which the control signal is at level L, the CCD transfers the data acquired at interval (1) to the transfer unit.
At interval (3), during which the control signal goes to H again, data are accumulated for the original document that is currently being scanned by the optical system, i.e., “reading data
2
” in
FIG. 13
, and the “reading data 1”, which were transmitted to the transfer unit, are output as “writing data 1”. The same process is repeated at interval (4) and the following intervals, and in synchronization with the BD signal, each line of the original document is read and the writing data are output.
FIG. 14
is a timing chart for explaining the original document reading timing for the conventional image forming apparatus, in which is shown a BD signal, and ITOP signals, the read data and the write data for a first and a second color.
In
FIG. 14
, the BD signal, which is a main scan start reference signal, is generated at cycle T in synchronization with the rotation of a polygon motor. The ITOP signal, which is a drum rotation position signal, is generated at an arbitrary time during a BD signal cycle.
When the ITOP signal is changed from level H to level L, the optical system begins scanning, and the CCD initiates the fetching of line data, synchronized with the generation of the next BD signal. The scanning speed of the optical system and the rotation speed of the photosensitive drum are indicated by “V”.
Now, the reading/writing operation fo

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