Multi-beam optical scanning apparatus and image forming apparatus

摘要

The optical scanning apparatus correctly measures a gap between the laser beams of a plurality of the laser beams even when the scanning speed is changed and when the variation is caused, rightly corrects the variation. Thus, the optical scanning apparatus inputs detection signal BD_IN to the edge detecting unit at timing at which the laser beam is detected. During the enable gating, the count value representing the distance between the head laser beam and the end laser beam is counted in the counting unit. A plurality of speed ratio parameters according to the degree of changes in the scanning speed is input in the selector. The selector selects any one of the speed ratio parameters and multiplies by the count value by the multiplier, it is controlled to obtain the same multiplication result whichever scanning speed may be selected.

主权项

1. An image forming apparatus operable to switch a speed of image forming from one image forming speed to another, comprising:
a photosensitive member; a scanning unit including a light source having a plurality of light emitting elements including a first light emitting element and a second light emitting element, each of which emits laser beams, a polygon mirror configured to deflect the laser beam emitted from each such light emitting element so that the laser beam emitted from each of the light emitting elements scans the photosensitive member, and a sensor configured to output, by receiving the laser beams emitted from the first and second light emitting elements and deflected by the polygon mirror, detection signals respectively corresponding to the first and second light emitting elements, wherein the plurality of light emitting elements are arranged such that the light emitting elements expose respective different positions on the photosensitive member in a scanning direction, and wherein the scanning unit is configured to control the scanning speed of the laser beams to be a speed corresponding to the image forming speed by controlling a rotation speed of the polygon mirror based on scanning speed information; a storage unit configured to store a reference time interval corresponding to a reference scanning speed of the laser beams; a measuring unit configured to:
obtain the scanning speed information representing scanning speed of the plurality of the laser beams,measure a time interval between a first timing and a second timing, wherein the first timing is a timing at which the sensor outputs a detection signal by receiving a laser beam irradiated from the first light emitting element during one scanning period of the laser beam, and the second timing is a timing at which the sensor outputs a detection signal by receiving a laser beam irradiated from the second light emitting element, andcorrect the time interval based on a speed ratio of the reference speed to the scanning speed represented by the scanning speed information; and a control unit configured to compare the corrected time interval with the reference time interval and to control a relative light emitting start timing of the plurality of light emitting elements in one scanning period of the light beams based on a comparison result of the corrected time interval and the reference time interval, wherein the relative light emitting start timing corresponds to the scanning speed represented by the scanning speed information.