Patent ID: 8610754
Filing Date: 2013-12-17
Classification: G02B,G03G,G06K

Abstract:
1. An image forming apparatus comprising: a laser-light generating section configured to generate laser light; a polygon mirror configured to deflect the laser light; a polygon motor configured to rotatably drive the polygon mirror; a light sensor configured to generate a detection signal upon receiving the laser light deflected by the polygon mirror; a rotation sensor provided at the polygon motor and configured to generate a rotation signal in synchronization with rotation of the polygon motor; a mirror-rotation-signal generating section configured to generate a mirror rotation signal in synchronization with rotation of the polygon mirror, based on the detection signal; a motor-rotation-signal generating section configured to generate a motor rotation signal in synchronization with rotation of the polygon motor, based on the rotation signal; a phase-difference measuring section configured to measure a phase difference between the motor rotation signal and the mirror rotation signal; a prediction-signal generating section configured to generate a prediction signal that is delayed from the motor rotation signal by the phase difference; a switching section configured to switch a control mode between: a mirror control mode in which the mirror rotation signal is used to control a rotational speed of the polygon mirror; and a prediction control mode in which the prediction signal is used to control the rotational speed of the polygon mirror; and a motor driver configured to drive the polygon motor in the control mode selected by the switching section; wherein, when printing is performed on both sides of a sheet, the switching section is configured to control the polygon motor in the prediction control mode during a period after printing is finished on one side of the sheet and before printing is started on another side of the sheet; and wherein, when the control mode is switched from the mirror control mode to the prediction control mode, the motor driver is configured to control the laser-light generating section to stop generation of the laser light subsequent to switching of the control mode from the minor control mode to the prediction control mode.