| 摘要 |
The temperature difference between an internal temperature and an external temperature which are detected by an internal temperature sensor and an external temperature sensor, respectively, is calculated. If the internal temperature is lower by not less than predetermined degrees than the external temperature and, hence, condensation on the surface of each optical component within a laser writing unit is highly likely, a motor is driven to rotate a polygonal mirror. During its operation the motor generates heat, which in turn transfers from a flange portion directly to a housing while heating air around the laser writing unit. Further, air within the housing is stirred by rotation of the polygonal mirror. In this way the temperature of the entire laser writing unit is raised.
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