Optical scanning apparatus, method of controlling amount of light, and image forming apparatus

An image forming apparatus comprising:

• an image carrier;
• a charging unit which charges said image carrier;
• an optical scanning apparatus for irradiating an image carrier with a light beam emitted from a light source, said optical scanning apparatus forming an electrostatic latent image by scanning the surface of the image carrier with a light beam that conforms to image information;
• a developing unit which forms a developer image by developing the electrostatic latent image;
• a transfer unit which transfers the developer image to printing paper;
• and
• a fixing unit which fixes the transferred developer image to the printing paper,
• wherein said optical scanning apparatus includes:
• an approximation formula determination unit which determines an nth-order approximation formula and an mth-order approximation formula (where n and m are natural numbers and m>n holds), which represent the sensitivity characteristic of the image carrier along the main-scanning direction thereof, from sensitivity data representing the sensitivity of each area obtained by dividing the surface of the image carrier into a plurality of areas;
• a sensitivity correction value determination unit which determines a sensitivity correction value, which is a correction value of sensitivity in each area, from the nth-order approximation formula and mth-order approximation formula;
• and
• a bias current controller which controls a bias current, which is applied to the light source, in accordance with the sensitivity correction value,
• wherein the surface of the image carrier is divided into P-number of columns in the main-scanning direction and Q-number of rows in the sub-scanning direction, thereby dividing the surface into a total of P×Q areas;
• said approximation formula determination unit includes a part which, with regard to each row of the Q-number of rows, determines the nth-order approximation formula and the mth-order approximation formula from each item of sensitivity data of P-number of areas along the main-scanning direction;
• and
• said sensitivity correction value determination unit includes:
• a part which, with regard to each area, calculates a difference value between the corresponding nth-order approximation formula and the mth-order approximation formula;
• a part which, with regard to each column of the P-number of columns, calculates an average value of the difference values regarding Q-number of areas belonging to each column;
• a part which determines the mth-order approximation formula from the calculated P-number of average values and calculates a first maximum value from the mth-order approximation formula determined;
• a part which divides the sensitivity data of each area by the respective first maximum value, thereby calculating a correction coefficient in the main-scanning direction;
• a part which, with regard to each row of the Q-number of rows, calculates a second maximum value from the corresponding nth-order approximation formula;
• a part which divides the sensitivity data of each area by the respective second maximum value, thereby calculating a correction coefficient in the sub-scanning direction;
• and
• a part which, with regard to each area, adds the correction coefficient in the main-scanning direction and the correction coefficient in the sub-scanning direction, thereby calculating the sensitivity correction value.