| 摘要 |
PURPOSE:To obtain images of high quality for a long time and to extend the life of a laser printer or the like by measuring always the extent of surface shake of a polygonal mirror during operation and adjusting a prepressure so that said extent is within a prescribed value range if the measured value exceeds prescribed value. CONSTITUTION:When a polygonal mirror 1 is rotated by a motor 2, an area S between electrodes is changed, and the electrostatic capacity C between the mirror 1 and a sensor electrode 4 is changed because an inter-electrode gap (g) is changed by surface shake of the mirror 1. Consequently, an electric charge Q stored in the capacity C is changed, and the quantity of electricity corresponding to a variation DELTAQ flows as a current. This variation is changed in accordance with the change of the area S and the gap (g). In a ball bearing prepressure adjusting mechanism part 3, the measured signal of the extent of surface shake is used as a prepressure adjusting signal. If the extent of surface shake exceeds the prescribed value, the prepressure adjusting signal is generated to drive a solenoid 14. A pinion 13 is moved thereby to change the position where a rack 12 and the pinion 13 are engaged with each other. Thus, the extent of surface shake is so adjusted that it is within the prescribed extent range. |
