Exposure apparatus
In an exposure apparatus employing an over filled optical system, the light quantity distribution on a scanning plane is kept nearly constant for a plurality of scanning light quantities. It selects the light quantity of the light beam irradiated onto the photosensitive body from a plurality of levels, and sets the light quantity selected. According to the light quantity, it selects one of a plurality of correction current profiles, and supplies a light source with a current passing through the correction based on the correction current profile selected. Since the light quantity of the light beam irradiated onto the photosensitive body is corrected by the correction current, the light quantity of the light beam on the photosensitive body becomes nearly constant in the scanning direction.
1. An exposure apparatus comprising:
a light source for emitting a light beam with a light quantity corresponding to an amount of current supplied thereto;
a rotating polygon mirror with a plurality of reflection planes, the rotating polygon mirror configured to rotate in such a manner that the light beam emitted from the light source and reflected off a reflection plane of the plurality of reflection planes scans a photosensitive body;
a beam magnifying unit for expanding the light beam emitted from the light source in a manner that the light beam is irradiated onto the rotating polygon mirror with a beam width exceeding a width of the reflection plane of the rotating polygon mirror in a scanning direction;
a setting unit for setting a target light quantity of the light beam irradiated onto the photosensitive body according to the light beam irradiation duration per unit pixel; and
a current supplying unit for, if a first target light quantity is set by the setting unit, supplying the light source with first correction current such that a light quantity of the light beam irradiated onto the photosensitive body is substantially constant in a main scanning direction and, if a second target light quantity is set by the setting unit, supplying the light source with second correction current such that the light quantity of the light beam irradiated onto the photosensitive body is substantially constant in the main scanning direction.
2. The exposure apparatus as claimed in claim 1 , wherein the current supplying unit comprises:
a D/A converter;
a designating unit for designating a number of transfer data or transfer clock on the basis of the target light quantity set by the setting unit;
a data supplying unit for transferring correction current profile data corresponding to the first or second correction current set by the setting unit to the D/A converter in response to the information designated by the designating unit; and
a current circuit for supplying current to the light source according to the output of the D/A converter, the output being obtained in response to the correction current profile data transferred from the data supplying unit.
3. The exposure apparatus as claimed in claim 2 , wherein, if the target light quantity is relatively small, then the number of transfer data is larger or the transfer clock is smaller than those in a case where the target light quantity is relatively large.
4. An image forming apparatus comprising:
a light source for emitting a light beam with a light quantity corresponding to an amount of current supplied thereto;
a rotating polygon mirror with a plurality of reflection planes, the rotating polygon mirror configured to rotate in such a manner that the light beam emitted from the light source and reflected off a reflection plane of the plurality of reflection planes scans a photosensitive body;
a beam magnifying unit for expanding the light beam emitted from the light source in a manner that the light beam is irradiated onto the rotating polygon mirror with a beam width exceeding a width of the reflection plane of the rotating polygon mirror in a scanning direction;
a setting unit for setting a target light quantity of the light beam irradiated onto the photosensitive body according to the light beam irradiation duration per unit pixel; and
a current supplying unit for, if a first target light quantity is set by the setting unit, supplying the light source with first correction current such that a light quantity of the light beam irradiated onto the photosensitive body is substantially constant in a main scanning direction and, if a second target light quantity is set by the setting unit, supplying the light source with second correction current such that the light quantity of the light beam irradiated onto the photosensitive body is substantially constant in the main scanning direction.
5. The image forming apparatus as claimed in claim 4 , wherein the current supplying unit comprises:
a D/A converter;
a designating unit for designating a number of transfer data or transfer clock on the basis of the target light quantity set by the setting unit;
a data supplying unit for transferring correction current profile data corresponding to the first or second correction current set by the setting unit to the D/A converter in response to the information designated by the designating unit; and
a current circuit for supplying current to the light source according to the output of the D/A converter, the output being obtained in response to the correction current profile data transferred from the data supplying unit.
6. The image forming apparatus as claimed in claim 5 , wherein, if the target light quantity is relatively small, then the number of transfer data is larger or the transfer clock is smaller than those in a case where the target light quantity is relatively large.