Product

• Lotem^® 800 Quantum
• Lotem 800 II Family running TH2 exposure head with V1.03b or newer firmware

Symptoms

• Edge detection and registration errors
• Lower sum readings at the edge of the plate than in the center
• Focus learn problems

Background

Plates, such as Spectratech, with untrimmed edges or poor emulsion coating, often have much lower focus sum readings at the home edge than in the center of the plate. The low sum often leads to edge detection and registration issues. To compensate, TH2 head firmware V1.03b and higher uses a lower surface reflectivity during edge detection than it uses during regular imaging. This lower reflectivity, edge sr, increases the focus beam output. This allows us to correctly locate the edge position, without affecting normal imaging.

The procedure below outlines how to calculate and set edge sr for different types of media.

Procedure

To calculate the edge sr value, complete the following steps:

1. Ensure that the TH2 head is running firmware V1.03b or higher.
2. Determine what type of media you have. For most media, proceed to step 3, below. For media that are exposed by high focus laser beam power, proceed to step 4, below. For very reflective media, proceed to step 4, below.
3. For most media, set the focus beam to produce the maximum output power by using an edge sr value of 0.011.
   Skip to step 5, below.
4. On sensitive or highly-integrating media, high focus laser power may inadvertently expose the media during edge detection. On very shiny media, such as the Applause plate, high focus laser power may cause the focus sum signal to decrease. For these media types, find the current sr value by typing:
   Th2>>set med X sr (X = media index)
   Once you have determined sr, calculate edge sr using this equation:
   edge sr = sr / 1.2
5. Once you have determined the correct edge sr value, enter it by typing:
   Th2>>set med X edgesr Y
   (X = media index; Y = edge sr value)

Notes:
Check the image offset for each media type whose edge sr = 0.011. If required, adjust the Sshift parameter, so that the image will be centered in the middle of the plate. In general, you can expect a shift of approximately 140 microns towards the home edge of the plate.

Technical contact(s)

Content owner: Itai Peperovich
See the Escalation page for escalation contacts.

Date submitted

11 Feb 2004