Laser Unit The laser unit emits laser beams.

Laser Unit

　

○Purpose: Here we study the control performed by the laser unit.

　

　

1. Outline

The laser unit emits laser beams.

This laser emission is controlled by the DC controller. When the DC controller receives from the main controller image signals (VDO1/VDO1, VDO2/VDO2), it switches the laser control signals (CNT0, CNT1, CNT2) to the print mode, synchronizing them to BD synchronous signals (BD), and emits laser beams.

As a safety precaution, the laser unit prevents any leak of laser beam by laser shutter when the door is open.

The control performed by the laser unit is as follows:

∙ Laser Light ON/OFF Control

∙ Main Scanning Synchronization Control

∙ APC Control

∙ Laser Shutter Control

　

Below is a figure showing the part configuration of the laser scanner system.

1]  Laser Unit

[2]  Polygon Mirror

[3]  BD Mirror

[4]  BD Circuit Board

[5]  Laser Lens

Next, we explain various types of control performed by the laser unit:

　

　

2. Laser Light ON/OFF Control

This control switches the laser beam(s) ON and OFF according to the laser light-emitting mode.

Switching of the light-emitting mode is determined by the combination of the laser control signals (CNT0, CNT01, CNT02) output from the DC controller.

When the DC controller sends its output, the laser control signals, to the laser unit according to the laser's light-emitting mode, the laser unit turns the laser beam(s) ON or OFF according to the light-emitting mode.

　

Laser Control Signals Laser Light Emission Mode Laser Condition Remarks CNT2 CNT1 CNT0 Laser A Laser B 0 1 0 APC Control of Laser A ON OFF 　 0 0 1 APC Control of Laser B OFF ON 　 0 1 1 Laser Forced Shut-Off OFF OFF Mask outside the image region. 1 1 1 Video Signal Input ON/OFF ON/OFF This turns the laser ON or OFF according to the image signals sent from the main controller.

　

　

3. Main Scanning Synchronization Control

This is the control that aligns the starting position of printing in the main scanning direction for each line.

This control is carried out by the DC controller based on the BD synchronous signals (BD) input from the BD circuit board. This unit is equipped with two beams (Laser A and Laser B); however, the BD synchronous signal is put out only for Laser A. The synchronous signal for Laser B is generated inside the DC controller, based on the BD synchronous signal for Laser A.

Next, we explain how data flow in this control.

1) The light of Laser A is detected by the BD circuit board, and the BD synchronous signal of Laser A is output to the DC controller.

2) Based on the input of the BD synchronous signal of Laser A, the DC controller generates the BD synchronous signal for Laser A (BD_A) and the BD synchronous signal for Laser B (BD_B).

3) The image data input from the main controller are written into the line memory of the DC controller. They are then read through the readable signals (RE_A, RE_B) generated based on the BD synchronous signals (BD_A, BD_B) and are transmitted to the laser unit.

1] Synchronous Circuit

　

[2] Delay Circuit

　

[3] Line Memory

　

[4] VDO

　

[5] VDO Signal Processor

　

[6] Laser Unit

　

BD_A/B: BD Synchronous Signals

　

RE_A/B: Readable Signals

The light from Laser B does not enter the BD sensor on the BD circuit board; only the light from Laser A does

4. APC Control

This is the control that corrects the laser volume so that the image density is homogeneous.

This control is performed by the laser driver circuit inside the laser unit. In the interior of the laser diode inside the laser unit, photo diodes are mounted. When the laser diodes emit light, that light is irradiated to the photo diodes, and the volume of the light is converted to voltage and is sent back to the laser driver circuit as feedback. The laser driver circuit then detects the laser volume from the voltage value in the feedback and then makes correction so that the light volume is appropriate.

APC Control is carried out for each line.

　

　

5. Laser Shutter Control

This control is to prevent the laser light from leaking out when the door is open.  It is carried out by both hardware and software.

<Laser Shutter by Hardware>

Inside the laser scanner is a shutter that shuts out the laser light path. Normally the laser light path is not shut off, but when the right door is open, the laser shutter link, connected and interlocked with the right door, causes the laser shutter to go down, blocking the laser light path.

<Laser Shutter by Software>

When the DC controller detects that the door is open, it forces the laser scanner motor and the laser output to be turned OFF.

1] Laser Shutter

　

[2] Laser Shutter Link

　

[3] Laser Unit

On the door being "open":

The door is considered open by the DC controller when either the front cover or the right door is open.

6. Failure Detection

This unit is not equipped with the function to detect the laser unit failure.