Thinking out loud and sharing some info and musing on PPI and laser response

Lasers
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Thinking out loud and sharing some info and musing on PPI and laser response :

I have been thinking about PPI for some time due to its purported power efficiency for cutting. The K40 @30-40 watts has plenty of power for engraving but marginal power for cutting IMO.

The PPI method purports to extend the tubes life. Then again some think it will shorten it.

I want to play with PPI [like i need another project]:.
…
How to implement with a smoothie:
I imagine an Arduino placed in series with the smoothie and the Laser Powers ‘L’ control signal? Maybe some hardware help on a shield? Or maybe all hardware?
I would simply “AND” the PPI pulse with the PWM signal from smoothie going to ‘L’ … I think.

Simple approach:
I wonder why (haven’t thought about this enough) you couldn’t just “AND” a fixed 3ms pulse stream with the ‘L’ signal to create a cheap modulated approach to PPI. You would turn this on and off for vector cutting. I assume this will not work as you need to know the feed rate?
…
Whoops:
On a related note. For some time I have been wondering what the lasers dynamic response is. I have imagined it to be in ms not us as the gas has to ionize. I have it on my list of tests.
From a below reference it states that the laser will not respond fully to pulses less than 2-3ms ?? This value is useful to know in that PWM frequencies that allow a pulse of less than 3ms won’t be outputting the power we expect.

Example: of the PWM period is 20us then a 10% DF setting will result in a pulse of 2us. If I recall the typical period setting in the smoothie configuration is 20us??

…Should the period be set to 20,000us (20ms)?
That is 50hz…?
Am I missing something?
How am I off by 3 orders of magnitude …???
…
Links:

http://www.buildlog.net/blog/2011/12/getting-more-power-and-cutting-accuracy-out-of-your-home-built-laser-system/

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Why use an Srduino for the 3ms pulse - just set up a 3ms signal and a simple and gate Don, then you get the same result - No? I suppose it could be cheaper with Arduino?

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@greg_greene YES!, that was what I meant in the “Simple Approach” above.

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Kewl !

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@greg_greene the answer may be that when you change speeds the power in the cut changes with a fixed pulse? But in reality are you changing speed that dramatically when vector cutting? You accelerate at the start and then decelerate at the end of a cut.

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Yes, vector cutting is at a set speed, with the possible exception if the laser takes a finite time to come up to the power level - but that would be very minimal if at all. I would think, the variation in material density would cause a more notable level in cut efficiency than that.

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@greg_greene then the simple approach may work :).

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Yeah, it would be a good place to start - simpler is better ! :slight_smile: and also more easily spread throughout the community