Calculating the edge surface reflectivity (edgesr)

Products affected

• Lotem^® 800 Quantum
• Lotem 800 II Family
• Trendsetter^® NEWS

Component

• Thermal 2 exposure head with head firmware version 1.03c or later

When to use this procedure

• After upgrading to Thermal 2 head firmware version 1.03c
• When troubleshooting the following problems on media with untrimmed edges or poor emulsion coating:
  • edge detection and registration errors
  • lower sum readings at the edge of the plate than in the center
  • focus learn problems

Note: On sensitive or highly integrating media, high-focus laser power may inadvertently expose the media during edge detection. On very shiny media, high-focus laser power may cause the focus sum signal to decrease.

Background

Plates 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 focus sum often leads to edge detection and registration issues.

To compensate, Thermal 2 head firmware version 1.03c and later uses a lower surface reflectivity during edge detection than it uses during regular imaging. This lower reflectivity, edge surface reflectivity or edgesr, increases the focus beam output. This allows you to correctly locate the edge position without affecting normal imaging.

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

Procedure

1. Ensure that the Thermal 2 head is running head firmware version 1.03c or later (type the command TH2> ver).
2. Determine what type of media you have. Make sure you have downloaded the correct media technical note (available from the Media site).
3. Enter the correct edgesr value, available from the Media Technical Note. Use the command
   TH2> set med X edgesr # (X = media index, # = edgesr value)

Note: If the tech note is not available, set edgesr to the default value of 0.011.

3. For each media type with edgesr = 0.011, check the image offset.
   Note: If there are any problems with subscan image shifting, especially if there are multiple machines on site, refer to the following procedures:
   • Trendsetters: Geometric Correction: Aligning Multiple MPE Machines in the Field
   • Lotem Quantums: Calculating and Adjusting the M/S Shift Parameters
4. If required, adjust the sshift parameter, so that the image is registered correctly. Adjust the image offset by typing the command:
   set gc sshift X (X = adjustment in microns)
   
   Note: 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