Product

• Lotem^® 400
• Lotem 400 Xpose
• Lotem 200K

Background

The objective of performing a laser uniformity test is to enable calibrating the laser intensity for all 12 or 24 lasers so that they are uniform.

Note: Test results do not depend on the plate type, size, or thickness, so this test can be performed on any plate type that the customer uses.

Requirements

Confirm that the device is calibrated according to the following tests:

• Focus Calibration Test
• Elevation Adjustment
• Intensity Calibration Test
• Resolution Calibration Test
• Delay Calibration Test

Procedure

1. Load a plate.
2. In Lotem Controler, change the Laser Factor From Host Enable parameter value to 0:
1. In the hardware tree, select Others and then right-click Lotem 400V.
2. In the Properties: 400V dialog box, double-click +EXPOSE.
3. Change the Laser Factor From Host Enable parameter value to 0, and then click Apply.
3. Open the Lotem Calibration dialog box:
• For Lotem 400 Xpose—on the Xpose Utilities panel, double-click LotemCalib.
• For Lotem 400—proceed as follows:
1. In Brisque, on the CDE panel, double-click Devices.
2. In the Output Device Handling dialog box, select Plate Setter > Lotem > Lotem400.
3. On the Operation panel, select Lotem Calibration.
4. In the Lotem Calibration dialog box (example shown for Lotem Xpose), in the Calibration Type list, select Laser Uniformity.
   
5. Select the plate type:
• For Lotem Xpose—in the Current Plate type dropdown list
• For Lotem 400—in Media
6. Define the Plate Policy:
• Load plate—Automatically loads a new plate before the test begins. If you clear this option, an already-loaded plate is used, and you can reuse a plate for additional calibration tests.
• Unload plate—Automatically unloads the plate after the test. You must load another plate for additional tests. If you clear this option, you can reuse the plate for additional calibration tests.
7. Define the Image Offset values:
   • Horizontal offset—the value around the drum in mm
   • Vertical offset—the value along the drum in mm
   If you use the same plate for several tests, use different offset values for each test.
   Note: The (0,0) offset coordinate is located at the upper-left corner of the plate.
   
8. In the Test Resolution list, select 100.
9. In the Intensity factor values area, type 0 in both the From and the To boxes.
10. In the Number of steps list, select 1.
11. Click Test to initiate the laser uniformity test according to the settings.
12. Develop the plate and examine the results. The results appear on the plate in a column of 12 squares for Lotem 400 small, and 24 squares for Lotem 400 non-small.
13. Use a densitometer to measure the dot percentage of each square.
14. Calculate the average of all the measurements.
15. Find the square whose measurement is closest to the average value, and define the dot percentage of this square as the target dot percentage.
16. Define the factor for each diode, as follows:
    0.5(Target dot % - measured dot %).
    Then round off this value to the closest integer. For example:
    • If the target dot % is 55 and you measured a dot % of 46.5 for diode #0, the calculated factor value for this diode is
      (55-46.5)/2=4.25
      In the factor table, the value for diode #0 is 4.
    • If the target dot % is 55 and you measured a dot % of 60.6 for diode #1, the calculated factor value for this diode is
      (55-60.6)/2=-2.8
      In the factor table, the value for diode #1 is -3.
    Note: Write down the factors and save them.
17. After calculating all the diode factors, type these values in the factor table, as shown, and then click Apply.
    
    If the results are not satisfactory, continue with step 19.
18. Repeat the test as described in steps 10 to 12, and write down the factor for each diode.
19. Repeat step 18, and 19 if required.
20. For each diode, analyze the previous dot % measurment, the factor you gave it, and the current dot % measurement. Use these three factors to calculate a better estimate, as shown in the following table:
    

    	Diode #0	Diode #1
    Target dot % in first test	55.0
    Dot % in first test	46.5	60.6
    Factor for second test	4	-3
    Target dot % in second test	58
    Dot % in second test	60.3	61.0
    Factor for third test	3	-5

    
    The factors for the third test are calculated as follows:
    • For diode #0, the dot % in test 2 is higher than the target dot % in test 2. Therefore, the factor was decreased from 4 to 3.
    • For diode #1, the dot % in test 2 is still higher than the target dot % in the second test, so the factor is changed from -3 to -5.
    After performing several tests, you should succeed in bringing the dot % measurements for the diodes to within ±2%.

Technical contact(s)

Content owner: Mario Amir
See the Escalation page for escalation contacts.

Date submitted

18 Dec 2003