Image forming apparatus and control method thereof

An image forming apparatus being configured to change a magnification ratio of an image formed on a printing medium, comprising:

• a light source that outputs a light beam;
• a deflection unit that is driven to rotate and deflect the light beam such that the light beam scans on a photosensitive member;
• a light beam detection unit that detects the light beam deflected by the deflection unit;
• an outputting unit that sets the magnification ratio of the image and outputs a setting signal related to the magnification ratio of the image;
• a first signal generation unit that generates a reference clock signal;
• a second signal generation unit that generates a first divided clock signal, a frequency of which corresponds to a first magnification ratio set by the outputting unit by dividing the reference clock signal;
• a third signal generation unit that generates a second divided clock signal, a frequency of which corresponds to a second magnification ratio set by the outputting unit by dividing the reference clock signal;
• a phase control unit that receives the first divided clock signal and the second divided clock signal and outputs a divided clock signal based on the setting signal outputted from the outputting unit, wherein the phase control unit switches the outputted divided clock signal from the first divided clock signal to the second divided clock signal or switches the outputted divided clock signal from the second divided clock signal to the first divided clock signal when a phase difference between the first divided clock signal and the second divided clock signal becomes a predetermined phase difference after the setting signal outputted from the outputting unit is changed;
• and
• a rotation control unit that controls a rotation speed of the deflection unit based on the divided clock signal outputted from the phase control unit and a detection period of the light beam detected by the light beam detection unit.