Photocopying – Projection printing and copying cameras – Multicolor picture
Reexamination Certificate
1999-09-15
2001-08-14
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Multicolor picture
C355S069000, C355S077000, C355S079000, C355S084000, C355S088000, C358S501000, C358S515000, C358S530000
Reexamination Certificate
active
06275281
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus capable of forming a multi-color image by superposing in succession color component images formed according to the image information of respective color components, and a controlling method for such image forming apparatus.
2. Related Background Art
For printing color image data, there is conventionally known a color image forming apparatus, such as a laser beam printer (LBP), adapted to form a color image by forming a latent image, line by line, on a photosensitive member utilizing main scanning means such as a rotary polygonal mirror which scans the photosensitive member with a laser beam, then forming an image of each color component by developing the latent image with the developer of each color component such as magenta (M), cyan (C), yellow (Y) or black (Bk), and transferring the images of respective color components in superposed manner onto a sheet fixed on a transfer drum.
There is also known an apparatus in which the images of respective color components, formed in succession on the photosensitive member, are transferred in superposed manner on an intermediate transfer member and the color images on the intermediate transfer member are collectively transferred onto the sheet.
In such apparatus, the photosensitive member and the transfer drum or the intermediate transfer member are driven at a constant speed in a direction (sub scanning direction) perpendicular to the main scanning direction, and the superposed image transfer, color by color, onto the sheet on the transfer drum or onto the intermediate transfer member is conducted in synchronization with a sub scanning start signal generated at each rotation of the photosensitive drum, the transfer drum or the intermediate transfer member.
There is also known an apparatus capable of forming images of respective color components in superposed manner on the photosensitive member and collectively transferring such images onto the recording sheet.
In such conventional color image forming apparatus as described in the foregoing, in order to prevent deterioration in the image quality of the color image resulting from the aberration in the superposing position of the color images, the method of controlling the positions of the respective color images in superposition plays an important role.
As an example of such position controlling method, there is proposed a method of employing such a configuration that the number of the sub scan start signal (ITOP signal) generated during a rotation of the photosensitive member or the intermediate transfer member and that of the main scan recording line signal (BD signal) synchronized therewith become an integer (cf.
FIG. 9B
) thereby synchronizing the rotation of the motor driving the photosensitive member or the intermediate transfer member and that of the scanner motor for effecting the main scanning.
FIGS. 9A and 9B
are schematic views showing main scanning lines formed on the photosensitive member or the intermediate transfer member in the conventional image forming apparatus.
Referring to
FIGS. 9A and 9B
, there is shown an image bearing member
901
such as a photosensitive member or an intermediate transfer member, which will be represented by a photosensitive member in the following description. An ITOP sensor
802
generates a sub scanning start signal (ITOP signal) by detecting a sensor flag
803
provided in a predetermined position on the lateral face of the photosensitive member
801
at each rotation thereof.
FIG. 9A
shows a case where the number of the main scanning start signal (BD signal) obtained during a rotation of the photosensitive member
801
and that of the main scan recording line signals synchronized therewith becomes “n+(½)” (n being an integer), and illustrates the positions of the main scan recording line signal in the first, second, . . . , (n−1)th, n-th lines of a first rotation and in the first line in a second rotation.
As shown in
FIG. 9A
, during a rotation of the photosensitive member
801
, namely during the generation of the ITOP signal, the main scan recording line signal is generated by “n+(½)”, so that the first line in the first rotation and the first line in the second rotation are mutually displaced by ½ line corresponding to the fraction.
In the conventional image forming apparatus, in order to avoid such displacement between the first and second rotations, there is proposed such a configuration that the number of the main scan start signal (BD signal) generated during a rotation of the aforementioned photosensitive member or intermediate transfer member and that of the main scan recording line signal synchronized therewith become an integer, as exemplified in FIG.
9
B.
FIG. 9B
shows a case where the number of the main scanning start signal (BD signal) obtained during a rotation of the photosensitive member
801
and that of the main scan recording line signals synchronized therewith become n (n being an integer), and illustrates the positions of the main scan recording line signal in the first, second, . . . , (n−1)th, n-th lines of a first rotation and in the first line in a second rotation.
As shown in
FIG. 9B
, during a rotation of the photosensitive member
801
, namely during generation of the ITOP signal, the main scan recording signal is generated by n (integer), so that the first line in the first rotation and the first line in the second rotation mutually overlap without aberration.
In the following there will be explained, with reference to
FIGS. 10 and 11
, a method of synchronizing the rotation of the motor for driving the photosensitive member or the intermediate transfer member and that of the scanner motor for effecting the main scanning, in the conventional image forming apparatus.
A first method consists of dividing the frequency of the main scanning start signal (BD signal), generated along the rotation of the scanner motor, and utilizing thus obtained signal as the reference clock signal for the motor for driving the photosensitive member or the intermediate transfer member. In the following there will be explained an example of such configuration.
FIG. 10
shows the configuration of a conventional image forming apparatus, corresponding to the first method described above.
Referring to
FIG. 10
, a photosensitive member
901
is rotated, through a driving belt
908
, by a photosensitive member driving motor
907
. A scanner motor
902
is controlled at a constant revolution by a PLL circuit
910
, based on a reference clock signal supplied from an oscillator
911
, and rotates a polygonal mirror
903
. The polygonal mirror
903
deflects a laser beam emitted by a laser
904
, thereby line scanning the surface of the photosensitive member
901
.
A beam detecting sensor (BD sensor)
906
is positioned in a non-image area on the scanning line of the laser beam, and generates a main scanning start signal (BD signal) in each scanning line of the laser beam, namely in synchronization with the rotation of the scanner motor. A PLL circuit
909
effects constant-speed control of the photosensitive member driving motor
907
, utilizing the BD signal, generated by the BD sensor
906
, as the reference clock signal. In this manner the rotation of the scanner motor
902
and that of the photosensitive member driving motor
907
can be synchronized.
A second method consists of utilizing a common clock signal as the reference clock signal for the motor for driving the photosensitive member or the intermediate transfer member and that for the scanner motor effecting the main scanning. In the following there will be explained an example of such configuration.
FIG. 11
shows the configuration of a conventional image forming apparatus, corresponding to the second method described above.
Referring to
FIG. 11
, a photosensitive member
1001
is rotated, through a driving belt
1008
, by a photosensitive member driving motor
1007
. A scanner motor
1002
is controlled at a cons
Adams Russell
Brown Khaled
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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