Product

• Lotem^® 400
• Lotem 800
• Lotem XL

Background

The objective of the elevation test is to find the correct elevation angle of the optical head. When the elevation angle is correct, all 24 or 48 beams along the V groove are in focus. Incorrect elevation results in a different optimal focus value for beams from one side of the V groove to the other. Incorrect elevation can cause an image shift of about 1 mm around the drum and banding, as well as uneven density within the 24/48-beam swath. Correct elevation is pre-set at the factory and rarely needs to be adjusted. Plate fly-off or other physical damage to the otpic tube may disrupt the elevation angle, requiring it to be readjusted.

Elevation does not depend on plate type, size or thickness. The test and adjustment (if needed) can be performed on any plate the customer uses.

Procedure

This procedure includes the following:

• Elevation Test
• Adjustment

Elevation Test

Two focus tests are exposed on the same plate. The first focus test uses only the first five beams while the second test uses only the last five beams. If the elevation angle is correct, the optimal focus value will be the same (+/- 10 microns) for both tests.

1. Focus tests are best run with reduced intensity.
2. To find the best intensity for this test with a particular plate emulsion, find the intensity threshold, as follows:
   • Using an intensity range between 0 and the default value, run an intensity test.
   • Unload the plate.
   • Find the minimum intensity that exposes the plate, then select an intensity one or two steps higher for running the Focus tests.

Or

• For a 48-beam machine, change the First_Expose_Laser_Active to 43.
6. Offset the image around the drum by 250 mm.
7. From the Brisque, run the second focus series at res 100. Make sure to use the same range and increments as before.
8. Process the plate. If the elevation is correct, the best focus value for both series will be the same. If the best focus value is more than a 10-micron difference between the two tests, follow the adjustment procedure below.
9. Remember to re-enable all lasers in the Lotem.

Adjustment

1. Loosen all three of the telescope screws (front and rear screws), as shown below. Make sure to loosen the rear silver screws, and not the small black set screws.

2. Remove the focus limit block on the carriage.

3. On the left side of the carriage (from where you just removed the focus limit block), insert the elevation jig under the telescope tube. Make sure the telescope and the surface of the jig are evenly aligned and fit snuggly together.

4. Tighten the three screws that were loosened in step one.
   Note: The two screws in the jig limit how far the jig goes under the telescope.
5. Remove the jig and reinstall the focus limit block.
6. Move the Focus motor to the home position (HP).
7. Using the tombstone jig, check the lens and drum clearance.
   Note: If you do not have a tombstone jig, the clearance should be 11.5 mm from the drum to the lens protector.
8. Perform the Focus motor procedure as a check to ensure that moving the focus motor to its maximum distance will not put the optics on a collision path with the grippers.
9. Run the elevation test. If adjustment is needed, calculate the amount of adjustment required, as follows:

Use groups of 5 diodes, as indicated in the following examples:

• Diodes 43-47 (20-24) Group A, have a best focus value of 135.
• Diodes 0-4 Group B, have a best focus value of 95.
10. To calculate how much to change the elevation, subtract the best focus value for diodes 43-47 Group A from the best focus value for diodes 0-4, Group B; then divide the result by 2. If the result is negative, you need to lower the rear of the telescope tube by that many microns. If the result is positive, you need to raise the back of the telescope tube by that many microns.

When B-A=C and C is a negative value, you need to lower the back of the telescope tube. When B-A=C and C is a positive value, you should raise the back of the telescope tube.

To reiterate: If A is greater than B, lower the rear of the tube. If A is less than B, raise the rear of the tube.

11. Install the elevation measuring jig on the back of the telescope tube, as shown below.

12. Set the dial indicator to a known zero position.
    Note: Do not loosen the front screw again during the procedure. (When the front screw is loosened again, the front of the telescope drops down and upsets the adjustment.)
13. Adjust the telescope tube position by the amount calculated in step 10. When you have made the adjustment, tighten the two rear screws and then remove the elevation measuring jig.
14. Run another elevation series, as described above to confirm the result.
15. When you are satisfied with the elevation result, re-enable all the lasers.

Technical contact(s)

Itai Peprovich
See the Escalation page for escalation contacts.

Date submitted

dd May 2003