Optical scanning device, image forming apparatus having the same, and method therefor

An image forming apparatus comprising:

• a photoconductive body;
• and
• an optical scanning device comprising:
• a light emitter configured to emit a first light beam and a second light beam;
• a motor;
• a polygon mirror configured to, when driven to rotate by the motor, periodically deflect the first light beam and the second light beam emitted by the light emitter, and form, on an object to be scanned, a first scanning line by the first light beam and a second scanning line by the second light beam;
• a sensor configured to output a first signal in response to detection of the first light beam deflected by the polygon mirror, and output a second signal in response to detection of the second light beam deflected by the polygon mirror;
• and
• a controller configured to:
• control the light emitter to emit the first light beam in accordance with a first pattern, the first pattern being such a waveform pattern as to repeat a cycle that includes a first time period during which the first signal output from the sensor has a voltage value of a first level, and a second time period during which the first signal output from the sensor has a voltage value of a second level lower than the first level, the cycle being shorter than a longest light-incident time period that is a longest time period during which the first light beam deflected by the polygon mirror is allowed to be continuously incident onto the sensor;
• control the light emitter to emit the second light beam in accordance with a second pattern that is different from the first pattern, the second pattern including a third time period during which the second signal output from the sensor has a voltage value of a third level higher than the second level;
• discriminate between the first signal output from the sensor in accordance with the first pattern and the second signal output from the sensor in accordance with the second pattern;
• identify a first moment at which the sensor has output the discriminated first signal according to the first pattern, and a second moment at which the sensor has output the discriminated second signal according to the second pattern;
• and
• determine a moment to start forming, on the object, the first scanning line by the first light beam, based on the identified first moment, and determine a moment to start forming, on the object, the second scanning line by the second light beam, based on the identified second moment.

A method adapted to be implemented on a control device coupled with an optical scanning device comprising:

• a light emitter configured to emit a first light beam and a second light beam;
• a motor;
• a polygon mirror configured to, when driven to rotate by the motor, periodically deflect the first light beam and the second light beam emitted by the light emitter, and form, on an object to be scanned, a first scanning line by the first light beam and a second scanning line by the second light beam;
• a sensor configured to output a first signal in response to detection of the first light beam deflected by the polygon mirror, and output a second signal in response to detection of the second light beam deflected by the polygon mirror,
• the method comprising:
• controlling the light emitter to emit the first light beam in accordance with a first pattern, the first pattern being such a waveform pattern as to repeat a cycle that includes a first time period during which the first signal output from the sensor has a voltage value of a first level, and a second time period during which the first signal output from the sensor has a voltage value of a second level lower than the first level, the cycle being shorter than a longest light-incident time period that is a longest time period during which the first light beam deflected by the polygon mirror is allowed to be continuously incident onto the sensor;
• controlling the light emitter to emit the second light beam in accordance with a second pattern that is different from the first pattern, the second pattern including a third time period during which the second signal output from the sensor has a voltage value of a third level higher than the second level;
• discriminating between the first signal output from the sensor in accordance with the first pattern and the second signal output from the sensor in accordance with the second pattern;
• identifying a first moment at which the sensor has output the discriminated first signal according to the first pattern, and a second moment at which the sensor has output the discriminated second signal according to the second pattern;
• and
• determining a moment to start forming, on the object, the first scanning line by the first light beam, based on the identified first moment, and determining a moment to start forming, on the object, the second scanning line by the second light beam, based on the identified second moment.