Agfa Palladio exposure variances

[Sev]

We have a 4 year old Agfa Palladio platesetter and have recently noticed a large variance in dot values across the width of the plate (Agfa LapV plates). We had some variances to a small degree from the start, but Agfa says this is normal for this machine, and it appeared to be within tolerances. However, it is now well out of tolerance, with at least a ten percent difference in the 50 percent dot, from the gripper edge of the plate to the center of the plate, and then even more differences to the tail of the plate. Would some recalibration help this, along with cleaning the optics, or does this point to possible laser end-of-life? We have cleaned the optics in the past to help eliminate distortions and other exposure issues, and we dont appear to have calibration issues for our press curve, but the inconsistent exposure along the width of the plate shows us concern. Any ideas would be most appreciated.

-Sev

 

[SteveAgfa]

Sev:

I'm not tech support -
but your suggestion to have the optics
cleaned is a good place to start. While
service is there, they might want to take
a look at the rollers in the processor as
well. Is this an automated unit - or a
manual one? If manual - this might
be fog. Again - I'd suggest that a
service call would be the first
place to start.

Regards,

 

[Sev]

Agfa Palladio exposure variances-more test results

Agfa Palladio exposure variances-more test results

We have made a series of exposure tests and have found that we needed to increase the laser intensity. We have the exposures now to the point where the screen values on the plate read very close to the actual input screen values. However, this is only on the tail edge of the plate, and is consistent for about two-thirds of the width of the plate (in the primary scan direction). At that point the screen values drop by a dramatic amount, but it is much less dramatic now, since we have increased the laser intensity. We have also noticed that this difference in screen values is much more pronounced in the mid tone range, but in the highlight and shadow areas it is far less noticeable. The platesetter is fully automatic, so I really doubt there is any fogging. When we do our next maintenance we will pay close attention to the rollers, but I am still leaning toward something is not correct in the optics. Could this be a possibility of a mirror out of alignment, or something along that line?

-Sev

 

[nexcorp]

You need a technician to check and clean the optics - most importantly the polygon which gets dirty/dusty on one side only, hence the problem you are having. Cleaning the polygon is quite a delicate operation so I do not suggest that you try it yourself. If the plates are OK on the grip edge then there is no problem with the laser.

 

[Lukas Engqvist]

Don't ignore chemistry, on our old system we had a circulation pump in the chemistry stop, we were tearing our hair out over laser issues. ofc that was for film so I don't know if is valid.

 

[maxon]

As Lukas said before, check your process conditions: dev circulation and proper brush and rollers pressure adjustments left to right. Expose a smaller plate and feed 90 degrees into the processor see if percentage drift is still the same. If it's not the processor, then optics/polygon most probably (4-yr old palladio, could be some dust inside by now...).

Good luck.

 

[nexcorp]

Yes, try rotating a plate through 90 or 180 degrees before it goes into the processor to see if the problem changes. If so it is the processor. If not it is dust on the polygon which is the most likely cause.

 

[Sev]

Thanks for the responses. The problem was indeed, dust on the mirror. The dust pattern was the same pattern as the exposure problem. Once the optic system was cleaned, the system performed as good as new, with a variance of less than 1 tenth of 1 percent, from edge to edge. Problem solved. The best part of this whole issue is that it forced us to re-establish proper laser exposure values.

-Sev