| 摘要 |
PURPOSE:To stabilize picture quality while maintaining low cost based upon the use of a plastic lens by controlling the output of a laser beam generator according to variation in laser beam diameter, and correcting the beam diameter to a specific value. CONSTITUTION:The laser beam 10 from the laser beam generator is modulated with an image signal X to make a scan on a photosensitive body 5, thereby forming an electrostatic latent image on a printer. The collimator lens 2 and Ftheta lens 4 of a scanning optical system are both constituted by plastic lenses, and when the laser beam is photodetected by a linear image sensor 6 arranged near the no-image part (c) on the photosensitive body 5 through said lenses, the linear image sensor 6 outputs a signal corresponding to the beam 10. This signal is inputted to the control part 11 and compared with the reference value to decide on the diameter of the laser beam, and a semiconductor laser driving circuit 9 is controlled on the basis of the diameter to correct the beam diameter to the reference diameter. |
