GearHeads Corner

Hi:

  Well, heres an example, ( not great but first try) of a photo
in a new mode in auggie that increases discreet power levels
to more than 255, so one can have a distinct power per each grey scale.

  This is a coarse 1mm dot pattern.


  I raised my lens closer to the mirrors and now have 170x170 or so
as a field.

Art

Looking good Art.

That is exactly the halftone technique required for Impact Magnet images on metals so could be a very useful future addition to Auggie's  capabilities.

Tweakie.

Hi Tweaky:

  This is done with a new command effect. The Command
G04P1 is a 1 second delay. The Command G04P.005R50 is a laser shot
for .005seconds at 50% power. This is in normal operation.
But, if in Augment Mode ( an Augment image is loaded), the command
is ignored if the X,Y is outside the image, and modified if X,Y is in the image
to a time from .001 at power 1 (tickle) to a max power of .005 ( from the P
parameter) and the power varied from 1-99% all based on image density.

  The command while in an image then sets max power and time both. This changes
the actual power per shot from 1ms at 0-100% to 0-max ms at 1-100%, which means
a great more grey scales or magnet power levels per strike.The algorithm will deduce
both power and time to arrive at a scaled valule of both that fits the image density
at that pixel. Soon it will supersample the image data to get sub pixel densities from
surrounding areas of the pixels density.

  Also, Vexx has been changed to allow a "FastPost" of any drawing to a quick
Gcode file ( G0,G1,G2,G3 ) of any drawing group selected. Auggie then can
use that file for general vector work.

  This means one can do a pattern Gcode in Vexx for a quick paste into any
augment file to change the pattern of the burn, this allows for other than
raster or circle patterns in the image burn. 

  These changes should all be in the next release. Auggie too will be updated as
it also has the distance correction changed to be much more accurate at smoothing
out corners, accel and decel zones for power linearity. Not perfect yet, but getting
much closer. the old dist correction was sometimes causing a dot at the start of motion.

Sorry for my slow updates lately, but the galvo project has a lot to learn from. :)

Art

Thanks for the explanation Art. I can't say that I fully understand but I am learning.  ;D

Tweakie.

Tweaky:

I should probably have written something about power and photos before. There is a
relationship between speed and power to be considered in doing any photo. Auggie
can only change power for each waypoint, which in a Pokeys is 1ms. So we have
only 1000 chances per second to change power level. If a laser were to do a 500
ms sweep across a raster line, we have a resolution of only 500 pixels really.
  So sweep speed is really a tradeoff of resolution and speed. Worse, we have only
100 power levels in a Pokeys in waypoint changes. Thats 95 with tickle levels taken
out. If you slide requested power to 50%, thats only really 45 differing levels. Tonal
scale will then suffer if not using as high as possible a power, but that means to not burn
one has to go faster, and that limits the resolution. Its all quite a fine balancing act to
get good tonal balance.
  I see only two ways to fix this to get the most realistic photo possible in an
engraving. First we need more levels of power. Say.. 1000 to choose from. The new
mode stops at each point and uses time, so making 1000 levels isnt hard if one
considers both power and time that power is applied in ms. This means if one uses
50% power, then you still have 500 levels of that 50% so the tonal variation would
still be maximized ( the photo only has 255 levels itself..without using supersampling
of the image data... more on that later if everything else works out. ).

  Energy accumulation is another way, multiple scans using different power per pixel
on each scan to create an accumulated power that achives a higher tonal range per pixel
datum. This is almost the same as stopping at each pixel, but a bit harder to calculate
the end energy effect, though the calculation of each pass for energy is trivial as a
calculated sum.

  Im finding in my testing that too much laser power is an issue, you go too slow
and you burn, too fast and you lose resolution due to the 1ms limit. If I limit
to 6% power to get a good grey scale, thats only 6 levels in reality, I need
100% power to get 100 levels of grey..but then Id burn. This is all a system of
tradeoffs. Im thinking to maximize performance, a multipass energy summing
calculation for total energy per pixel over X passes would make the most sense for the
highest tonal range in a photo. Or at least thats what the math and testing is telling
me. Testing continues. :)

Art

 

 

Hi Art,

I don?t know if this is relevant to your thinking but?

I have hardware control over my maximum laser output power.
With the DC excited laser Auggie has full software control over ~5%  to 100% of the power which I have set. I can adjust this hardware maximum power setting on-the-fly and this enables me to easily set the maximum burn for any selected axis speed (my currently available maximum is 6,000 mm/min.).
My RF laser uses my equivalent of the Synrad UC2000 to control it?s maximum output power. I have not yet tried it with Auggie image reproduction as I suspect that PWM frequency conflicts may be difficult to overcome without synchronisation but that is something I will investigate further as time permits.

If only there were more hours in a day.  ;)

Tweakie.

Tweaky:

>>With the DC excited laser Auggie has full software control over ~5%  to 100% of the power which I have set. I can adjust this hardware maximum power setting on-the-fly and this enables me to easily set the maximum burn for any selected axis speed (my currently available maximum is 6,000 mm/min.).

Ahh, that may explain your very nice results. No matter your power level max, you always have
100 slices of that power. With the RF laser only being PWM controlled, it lowers very much
my # of slices. Ill work to overcome that with multipass which is the only way I can see to
do that.

  Youd still be affected by the speed though, time across in ms being equal to the end resolution.
To do a 4k image using all its data, woudl take a 4 second sweep time really.. Thats one
long raster. :)

Art

Tweaky:

    In dwelling on your comments it occures to me I probably
should just add an Arduino that does nothing other than
control the PWM incoming pulses as a % of max. I think
Ill do that and have a "Power Scaling " hardware pot on the
engraver end. I could let Auggie run at 100% then and get full
scale on any power as a function of % scaling desired.

  Arduinos are cheap. :)

Art

Hi Art,

To me, that sounds like the way to go.

Tweakie.

  Downside to that I guess is it would add a 200us delay in the laser power stream...

Ill Dwell on it... :)

Art

Hi Art,

That is the way of life - "nothing is ever simple and there is always a catch".

More electronics but could you perhaps introduce an equal delay in the axis movement ?

Tweakie.

Ill have to give it more thought. Ironically I put in a laser
delay in Auggie for servos that are slow to react, but I hadnt
considered the inverse.

Art

First try at a single pass 3d , 1.5" round. Took less than a minute.
  Not great detail, but its small on pine..

Art

Looking good.

Tweakie.

Art,

Do you have a link to your Arduino code used for the DAC signal conversion?

Saw your youtube video and want to give this build a try with my diy style galvo motors.

Thanks
Brian