| Revision A |
2.1.5 Printhead Unit (Exposure Section)
The print head unit incorporates a laser diode that emits the laser beam corresponding to the print image data. The spot of the laser beam emitted from the laser diode is shaped in a circle through the collimator lens. Then, it is applied to the heptagonal polygon mirror via the cylindrical lens. The polygon mirror is turned by the polygon motor in the print head unit in the direction as shown by the arrow.
The reflected laser beam by the rotating polygon mirror passes the three lenses, producing a parallel scanning laser beam. The scanning laser beam scans on the PC drum from left to right for producing an electrostatic latent image on the surface of the PC drum.
Collimator Lens |
|
Cylindrical Lens | Laser Diode |
| |
Rotational |
|
direction | SOS Sensor |
| Scanning direction |
Heptagonal Polygon |
|
Mirror |
|
| PC Drum |
Figure 2-19. Printhead Unit Mechanism
Operation of the SOS Sensor
To maintain the printing density constant, it is required to emit a laser beam at constant laser power. To control the laser power to be constant is called APC (Automatic Power Control).
The SOS sensor incorporated in the print head unit is used to detect whether the laser power reaches certain laser power for printing. The SOS sensor is located outside of the printing area. When printing starts, it takes 1 or 2 scans to obtain the SOS sensor output. During printing, the SOS sensor output is monitored in every scanning for controlling the laser power constant.
Operating Principles | Printer Mechanism Operating Principles | 66 |
