Patent ID: 6833856
Filing Date: 2004-12-21
Classification: G02B,G06K,H04N

Abstract:
An image forming apparatus comprising:a light beam generating device configured to generate a light beam; a light beam modulating device configured to modulate the light beam in accordance with an image signal at a prescribed write clock frequency; a light beam deflecting device configured to rotate by a prescribed rotation number and deflect the light beam so as to scan an image carrier in a main scanning direction; a pair of light beam detecting devices configured to detect the light beam, said pair of light beam detecting devices being separately positioned in the main scanning direction; a time difference determining device configured to determine a time period elapsing from when the light beam is detected by a first of said pair of light beam detecting devices to when the light beam is detected by a second of said pair of light beam detecting devices, said time difference determining device generating a time difference signal at an optional timing of image formation; a comparing device configured to compare the time difference signal with a reference time difference signal representing preferable magnification so as to recognize magnification error of the light beam in the main scanning direction; a magnification correcting device configured to correct the magnification error by changing the prescribed write clock frequency and the prescribed rotation number to prescribed levels based on a result of a comparison between the time difference signal and the reference time difference signal by said comparing device; and a visualizing device configured to visualize an image formed on the image carrier after the magnification error is corrected, wherein said time difference determining device determines a time difference by counting clock pulses after lowering a light beam deflection speed of said light beam deflecting device to a prescribed speed.