Beam Profiler

[nilay]

Hi,

We have viloet ctp system in multiple plants (Krause). Is there any device (may be named as Beam profiler) to check the laser focus on CtP Plate. In other words: It checks that laser is even across the whole plate and helps in other manner to set the platen (where plate sets from the cassatte) in optimized manner. We could setup the platen if laser focus is little uneven or may be set up the last mirror from where the laser is exposing the plate.
Thanks
Nilay

 

[VladCanada]

Normally that's a "calibration target" file for visual control of different parameters of CTP.
For example: AGFA uses DigiControl Wedge file.
Ask Krause what file they have or recommend to be used for that purposes.

 

[maxon]

Correct. There's a procedure to follow based on the tiff files you have on your harddisk, use maximum plate size if available. A beam profiler will not help much because it characterizes the beam shape and energy distribution not necessarily focus condition and you machines are long depth of field.

 

[BillJ]

you could use any test file with high res focus targets (i.e. starbursts, 1X1 or 2x2 pixel) if you are using them for a reference. The main point is that you check them against a manufacturer's standard. You must also remember that no 2 machines will focus exactly the same. also variances in exposure, plate emulsions, and processing will yield different results. It would be odd for focus to vary on a particular machine. Usually when I have seen a "focus" issue on a violet system, it was caused rarely by a laser failure or much more likely plate load/vacuum issues on the drum or dirty optics.

 

[nilay]

In fact I used the test page which we created. Variation in the exposure is high. I expose on same device and processe the plate on other processor and it is fine. So it is CtP device defect not processor. In that workflow: does beam profiler (linearize laser across the plate) should be useful? By linearizing laser: we know that beam is even on all edge as well as platen/ bed is in correct position. What device need to use for platten calibration (other then bubble device)?

 

[BillJ]

If I understand correctly, you are saying that exposure varies from one side to the other. From what i can tell about the Krause, it is a flat bed. If that is the case, then the laser power would have to vary in the fast scan direction to compensate for change in distance the beam travels from the spinner/galvo mirror and the plate. In the machines I have worked on this is a service function to test and calibrate. You would need to speak with a expert on Krause to know their procedure.

Before you get that involved I would start by checking the optics and see if they are clean. I have seen dirty optics create this type of problem.

 

[maxon]

Variation in the exposure is high. I expose on same device and processe the plate on other processor and it is fine

If you say you expose a plate on the ctp and process in another plate processor and it comes out fine, then why is the platesetter suspect ? I think you have to reconsider everything and start over again. Forget about focus and beam shape, come back to simple things : what do you see on plate ? You mention exposure variation, did you take measurements with a platereader in various area on plate ? Have you exposed a smaller plate and fed it rotated 90 degrees into the processor ? Please explain how did you exactly rule out the processor, also post a relevant photo of a developed plate.

 

[maxon]

... from what i can tell about the Krause, it is a flat bed

Yes he mentioned platen and cassette so I guess it's an LS-Jet ...he's lucky because aligning the optics bed in a commercial granite bed Krause is a complete murder.