Facsimile and static presentation processing – Natural color facsimile – Scanning
Reexamination Certificate
1999-01-11
2001-11-20
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Natural color facsimile
Scanning
C358S501000, C358S481000
Reexamination Certificate
active
06320682
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus of a single pass color system (hereinafter referred to as SPC) in which color forming processes for plural colors are conducted while an image carrier makes one turn, and in particular, to an image forming apparatus wherein plural images each being of a different color can be superposed without positional deviation.
As an image forming apparatus of an SPC system in which the number of copies per a unit of time is increased, there has been proposed, for example, an image forming apparatus wherein four sets (equivalent to four colors) each being composed of a scorotron charger, a scanning optical system and a developing unit which are arranged at prescribed intervals around an image carrier (a photoreceptor drum or a photoreceptor belt) in its rotational direction are arranged, and a transfer unit, a separating unit, a cleaning unit and a fixing unit are further provided so that image forming processes for plural colors may be conducted while the image carrier makes one turn.
In the image forming apparatus of an SPC system wherein plural scanning optical systems are arranged around an image carrier in its rotational direction, it is necessary to prevent deviation in the main scanning direction or in the sub-scanning direction by correcting with various sensors mounted around the image carrier.
However, there are deviation in the mounting positions for various sensors and dispersion in exposure width in the main scanning direction for each color, and these are further subjected to the change with time. As a result, it has been impossible to prevent positional deviation in the main scanning direction or in the sub-scanning direction among plural images each being of a different color.
SUMMARY OF THE INVENTION
In view of the aforesaid technical problems, an object of the invention is to provide an image forming apparatus capable of conducting highly accurate positioning in the main scanning direction and in the sub-scanning direction on a real time basis for plural images each being of a different color.
The invention solving the problems mentioned above is represented by the following structures.
An apparatus for forming multi-color image, comprises:
a rotatable image carrying member having a peripheral surface;
a plurality of image forming means each having a charging device, a scanning exposure device and a developing device so that the plurality of image forming means form the multi-color image during a single rotation of the image carrying member on the peripheral surface;
each scanning exposure device of the plurality of image forming means including a beam generator and a polygonal mirror and controlled such that the polygonal mirror is rotated at the same rotational speed as that of the other scanning exposure devices and a beam scans the peripheral surface in an axial direction of the image carrying member;
a first sensor for detecting the beam passing at a start reference position on the peripheral surface and for outputting a start reference signal;
a second sensor for detecting the beam passing at an end reference position on the peripheral surface and for outputting a stop reference signal;
measuring means for receiving the start reference signal and the stop reference signal sequentially for each scanning exposure device and for measuring a time between the start reference signal and the stop reference signal; and
control means for controlling a frequency of clock pulses to transmit image signals for each scanning exposure device on the basis of the measured time of each scanning exposure device.
Further, the object of the present invention may be attained by the following preferable structures.
Structure (1) An image forming apparatus which conducts image forming processes for plural colors while an image carrier makes one turn, and has therein a start position locating sensor that detects a position to start writing on the surface of the image carrier, an end position locating sensor that detects a position to end writing on the surface of the image carrier, an image forming member composed of a scanning optical system which conducts raster scanning by controlling so that the rotational speed of a polygon mirror may be the same, a charging unit and a developing unit, all arranged around the image carrier in its rotational direction, a time measuring means that measures an interval of time between a detection signal from at least one of the start position locating sensor and the end position locating sensor and an index signal from an index sensor provided on the scanning optical system, and a timing control means that controls exposure timing of the scanning optical system based on measured time coming from the time measuring means.
In the image forming apparatus stated above, it is possible to conduct positioning of an image for each color by controlling exposure timing by the use of at least one of the result of detection of the start position and the result of detection of the end position.
Structure (2) The image forming apparatus of Structure (1) wherein the time measuring means measures time between a detection signal from the start position locating sensor and a detection signal from the end position locating sensor, and there is provided a clock frequency control means which controls the clock frequency for image processing for exposure based on measured time coming from the time measuring means.
In the image forming apparatus stated above, it is possible to conduct positioning in the main scanning direction on an image of each color accurately for each pixel, because a clock frequency for image forming is controlled based on the time of main scanning between the start position and the end position.
Structure (3)The image forming apparatus of Structure (1) wherein a detection window means composed of either a reflection member or a transmission member is provided on the surface of the image carrier, and the start position locating sensor and the end position locating sensor conduct detection by receiving light from the detection window means.
In the image forming apparatus stated above, it is possible, due to the detection window means provided on the surface of the image carrier, to conduct positioning of an image in the main scanning direction and the sub-scanning direction by using scanning light of image forming.
Structure (4) The image forming apparatus of Structure (1) wherein a detection window means composed of either a reflection member or a transmission member is provided on the surface extended from the surface of the image carrier, and the start position locating sensor and the end position locating sensor conduct detection by receiving light from the detection window means.
In the image forming apparatus stated above, it is possible, due to the detection window means provided on the surface of the image carrier, to conduct positioning of an image in the main scanning direction and the sub-scanning direction by using scanning light of image forming, and to utilize the surface of the image carrier effectively.
Structure (5) The image forming apparatus of Structure (1) wherein there is provided a detection window means composed of either a reflection member or a transmission member wherein an edge of the main scanning starting side is not in parallel with that of the main scanning ending side, and the timing control means controls timing in the sub-scanning direction in accordance with a signal width obtained from the portion where the edge of the main scanning starting side and that of the main scanning ending side both of the detection window means are not in parallel with each other.
In the image forming apparatus stated above, it is possible to detect deviation of plural colors in the main scanning direction and the sub-scanning direction by the use of the detection window means having the edges which are not in parallel with each other.
Structure (6) The image forming apparatus of Structure (1) wherein there is provided a detection window means composed of
Azumai Mitsuo
Takaki Kouichi
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Grant II Jerome
Konica Corporation
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