Product

• Kodak^® Lotem^® 400 FH family
• Kodak Magnus^™ 400 LDA family
• Kodak Magnus 400 II LDA family

Background

Laser intensity is used to expose the plate.

The objective of the intensity test is to find the required laser intensity for optimal exposure at a resolution of 100 dpm, and the drum speed value required to obtain optimal intensity.

During the intensity test, drum speed is a fixed value, while the intensity value varies. In contrast, during the drum speed test, intensity is a fixed value, while the drum speed varies.
Note: Test results depend on the plate type (but not plate size or thickness); you must perform the test on each plate type that the customer uses.

Requirements

Tools:

• Densitometer
• Loupe
• Plates

Prerequisites:

• Focus value obtained in the Focus calibration test

Procedure

This procedure includes the following sections:

• Calibrating intensity
• Selecting the optimal laser intensity and drum speed

Calibrating intensity

1. Load a plate.
2. From the Kodak Xpo^™ palette, select Tools > Calibration. The Plate Sensitivity parameters of the loaded plate are automatically transferred from the Lotem/Magnus 400 Controller software.
   
   
   
   
3. In the Calibrate dialog box, perform the following steps:
   1. In the Calibration Type list, select Intensity.
   2. In the Intensity field, do not change this value until the optimal laser intensity has been determined. See Setting the optimal laser intensity and drum speed.
      Note: To load the last-saved intensity test value, click Get.
      
   3. In the Drum Speed field, type the number of revolutions per minute (rpm) at which you want the drum speed motor to revolve, or perform the test with the last-saved drum speed that appears in this field.
      Note: Accelerated drum speeds require higher intensities than reduced/low drum speeds. The optimal drum speed is the drum speed value that was used to obtain the optimal laser intensity. See Setting the optimal laser intensity and drum speed.
      
   4. Clear the Calculate All Points When Saving check box. This ensures that the working conditions are updated only for the resolution that is currently defined.
   5. In the Test Intensity Values [mW] area, in the From and To fields, type the test range for the laser intensity stepper motor values. For best results, enter a range between 180 mW and 300 mW.
   6. In the Number of Steps list, select the number of exposures to perform for the laser intensity test. For best results, enter a minimum of 10 or 11 steps.
      When you type a step value, the Lotem/Magnus 400 Controller software automatically calculates and displays the size of each step interval in the Size field, using the following formula:
      Step size = (To–From)/(Number of steps –1)
      Note: The interval value provides a quick reference for the platesetter operator, and cannot be changed.
   7. In the Resoluton list, select the resolution used by the customer.
   8. In the Test File list, select the TIF file that you want to use for the drum speed test.
      Note: Test files are predefined; the ones that appear in the list are according to the selected resolution and plate type.
   9. In the Current Plate list, select the plate that you are using for the test.
   10. In the Image Offset fields, type a value in millimeters for the horizontal offset (around the drum), and the vertical offset (along the drum).
       Note: The (0,0) offset coordinate is located at the upper-left corner of the plate.
       If you use the same plate for multiple tests, enter the appropriate offset values for each test.
   11. In the Plate Policy section, select or clear the Load and Unload check boxes that apply to focus test:
       • Load: Automatically loads a new plate before the test begins. To perform multiple calibration tests on the same plate, before you start the next test, clear this check box to reuse the plate.
       • Unload: Automatically unloads the plate after the test. To perform multiple calibration tests on the same plate, before you start the next test, clear this check box.
4. Click Test to start the intensity test.
   Lotem/Magnus Controller performs a series of exposures on the plate, after which you need to process the plate and examine the results.

Selecting the optimal laser intensity and drum speed

1. Visually examine the results, and select the target strip for which the 50% dot area measures 50%.
   
   
   
   

   Measure the density in the solid area. A good density reading should be 0.07 dmin or less, as shown below.
   
   
   
   

   When the intensity is too low, the black imaged lines are almost invisible, while the non-imaged white lines are easily noticeable. Likewise, when the intensity is too high, the black imaged lines are easily noticeable, while the non-imaged white lines are less visible.
   
      
               Low intensity                        High intensity
   

2. In the Intensity field, type the optimal intensity value returned, and click Save.
3. Verify that the new value was saved in the database.
   1. In the Lotem/Magnus 400 Controller software, in the Hardware tree, go to DataBase, and double-click Res Int.
      
      
      
      
   2. In the Resolution/Intensity Tables dialog box, locate the row with the resolution and drum speed that you used for the test and, in the Intensity column, the newly-saved value should appear.
   3. Click Close.
4. If required, repeat the test for other resolutions used by the customer.

Technical contact

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

Date submitted

11 Jun 2008