Long Name:

Applies to:

Description:

By setting the head parameter "vb" to 1, the thermal head will output a diagnostic message for each drum rotation while plotting. This message consists or four numbers which summarize the performance of the autofocus control system for that drum rotation. Please see the enclosed log file for sample output. For each rotation of the drum, the head generates four values:

• 463 -35 422 620 // first drum rotation
• 98 -18 495 619 // second rotation
• 27 22 0 620 // you get the idea...

The first number is a "Figure of Merit" (FOM) for the autofocus control system. It quantifies how well the control system believes it was able to follow the plate profile for that drum rotation. The smaller the number, the better it thinks it did (0 would be perfection). During autofocus learning (as shown above) this value may start out large but it should rapidly decrease. Heads should maintain this value below 100 while imaging.

For the mathematically minded: The head calculates a "focus error" at each sample point using the optical distance sensor output, foffset value, etc. It accumulates a sum of the squares of these errors for all sample points in a given drum rotation. The FOM is this sum divided by the number of sample points.

The second number is the largest "focus error" value which occurred during the drum rotation. If the error magnitude is greater than the "fthresh" threshold, then the head will generate a "Focus error out of range" error message (provided the threshold was exceeded for at least "ferrdur" consecutive sample periods).

The third number is the sample number which produced the peak error indicated by the second number.

The fourth number is the total number of sample points in the drum rotation.

E.g., In the first line given above, the peak error was -35 and it occurred as the 422nd sample out of 620 total samples in the drum.

Type:

Default:

• 0

Range:

• 0 to 32767

Notes:

Partition:

See Also: