1. Field of the Invention
The present general inventive concept relates to an electrophotographic image forming apparatus, and a scanning method thereof, and more particularly, to an electrophotographic image forming apparatus including a light scanning device to scan a plurality of light beams, and a scanning method thereof.
2. Description of the Related Art
A conventional image forming apparatus such as a laser printer forms an image by scanning a light beam onto a photosensitive drum by using a light scanning device to form an electrostatic latent image thereupon, developing the electrostatic latent image by using toner, and transferring the developed toner image onto a printing medium. In order for a light scanning device to scan a light beam onto a photosensitive drum with a correct timing, a synchronization signal detection unit to detect a horizontal synchronization signal of a scanned light beam is required.
Conventionally, in order to produce a color image, a light scanning device scans a plurality of light beams by using one or two polygonal rotating mirrors. In this case, light sources are arranged in such a way that light beams are incident on a polygonal rotating mirror in a vertically symmetrical manner with respect to a center of the polygonal rotating mirror. For example, when a single polygonal rotating mirror is used, light sources are arranged in such a way that light beams of two colors are incident on each of right and left portions of the polygonal rotating mirror with respect to a center of the polygonal rotating mirror. When two polygonal rotating mirrors are used, light sources are arranged in such a way that light beams of a single color are incident on each of right and left portions of the polygonal rotating mirrors with respect to centers of the polygonal rotating mirrors. In a light scanning device including a single polygonal rotating mirror, a conventional synchronization signal detection unit detects a horizontal synchronization signal by using two beam detecting sensors. In a light scanning device including two polygonal rotating mirrors, a conventional synchronization signal detection unit detects a horizontal synchronization signal by using four beam detecting sensors. Such detected horizontal synchronization signals are transferred to a printer video controller (PVC). A PVC transmits video data to a laser diode drive (LDD) in a light scanning apparatus according to a transferred horizontal synchronization signal, and a light source driver controls a power on and/or off of light sources according to the video data so as to emit a light beam.
When a plurality of beam detecting sensors corresponding to a plurality of light beams are present, material costs and likelihood of failure are increased due to the relatively large number of components, and sensitivities of the beam detecting sensors are differently changed due to a changed in temperature, or detection surfaces of the beam detecting sensors may be non-uniformly changed, (e.g., contaminated). Thus, synchronization signal detecting timings of the beam detecting sensors become slightly different from each other, and image quality may deteriorate.