This invention relates to a light beam scanning apparatus which simultaneously scans and exposes a single photosensitive drum by use of, for example, a plurality of laser beams to form a single electrostatic latent image on the photosensitive drum and an image forming apparatus such as a digital copying machine and laser printer using the same.
Recently, in order to enhance the image forming speed, a digital copying machine of a multi-beam system, that is, a system which emits a plurality of laser beams and simultaneously scans the plurality of laser beams to draw a plurality of lines has been developed.
The above digital copying machine of the multi-beam system includes a plurality of semiconductor laser oscillators which emit laser beams, a polygon rotating mirror which reflects the laser beams emitted from the plurality of semiconductor laser oscillators to the photosensitive drum to scan the laser beams on the photosensitive drum, and an optical system unit used as a scanning apparatus and mainly configured by a collimator lens and f-xcex8 lens and the like.
As the scanning apparatus, there is provided an apparatus which delays the sync clock by a constant period of time by use of a delay line to control the exposure position in the scanning direction (main scanning direction) of the light beam (U.S. Pat. No. 6,208,367).
In the above invention, the sync clock is delayed by a constant period of time by use of the delay line, but in this case, there is a possibility that the duty ratio will vary and there occurs a problem that the reliability is lowered.
An object of this invention is to provided a light beam scanning apparatus and image forming apparatus which enhance the reliability and can always precisely control the exposure position in the scanning direction (main scanning direction) of the light beam.
In order to attain the above object, a light beam scanning apparatus according to an aspect of the present invention comprises light emitting means for emitting a light beam, scanning means for reflecting the light beam emitted from the light emitting means to a to-be-scanned surface to scan the to-be-scanned surface by use of the light beam, light sensing means arranged on the to-be-scanned surface or in an equivalent position thereof, for sensing the light beam which is used to scan the to-be-scanned surface by the scanning means, sync signal output means for delaying an output of the light sensing means by a delay amount which is controllable, image forming range setting means for setting an image forming range of the light beam while the sync signal output from the sync signal output means is used as a reference, and control means for controlling the sync signal output means and image forming range setting means to set the image forming range of the light beam to a preset position.
Further, an image forming apparatus according to another aspect of the present invention which is an image forming apparatus which scans and exposes an image carrying body by use of a light beam to form an image on the image carrying body comprises light emitting means for emitting a light beam, scanning means for reflecting the light beam emitted from the light emitting means to the image carrying body to scan the image carrying body by use of the light beam, light sensing means arranged on the image carrying body or in an equivalent position thereof, for sensing the light beam which is used to scan the image carrying body by the scanning means, sync signal output means for delaying an output of the light sensing means by a delay amount which is controllable, image forming range setting means for setting an image forming range of the light beam while the sync signal output from the sync signal output means is used as a reference, and control means for controlling the sync signal output means and image forming range setting means to set the image forming range of the light beam to a preset position.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.