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Author Topic: Galvo Lasers  (Read 468 times)
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ArtF
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« on: March 07, 2018, 11:23:55 AM »

Hi All:

   I figured Id start a topic on Galvo's and laser. Ive been wanting one since I watched a youtube
video on one years ago. I started collectin g parts 2 years ago, and reading all I could on the subject. There isnt much info out there in truth, so Ill make a video of my machine when its working ( or not) and post this topic in hopes it helps the next person to decide to make one.
  Ive learned a lot in the last couple years on the topic, but Im still wandering in a barren
wildernes s in terms of knowing what I need to I think.

  Most galvo's are analogue devices ( -10 to 10 vdc ) or ( +-5vdc). Mine is a cambridge tech galvo from Ebay. ( normally about $1000, but I bid 300 and got one. ). I figured I needed a good one, I think now I was wrong and a $100 set from Ebay probably would have been fine. I have no interest in writing code to drive an analogue device though, so I made a conversio n
from analogue to Step/Dir so the galvos could be driven by Mach3, or, in this case Auggie.

  This costs about $80 to do , it requires a Arduino DUE, and an ArmFly analogue DAC board
which puts out +-10vdc ( a version is available for +-5vdc as well.  ). . It takes a few other cheap component s like a voltage level converter for the DUE to be run by the 5 volt step/dir
from the pokeys CNC57 ( which is my breakout board for this machine. ).

  Other than that a few cheap power supplies, and a set of gold mirrors to replace the galvos
original mirrors for yag. Mirrors run around $50.00 and the power supplies for it all around the
same I think.

  I added a Z stage for a movable table, I had one laying around so I havent a clue what that costs and this table is really overkill for the applicati on.

  For the laser, Im using a SynRad FireStar V40, Ive tested it at 48watts output. This was a real bargain at about $600.00 with shipping, it came with power supply, expander lens and laser pointer incorpora ted. The seller didnt know if it worked, I took a chance and it turned out it
had a very dirty mirror in the mixer for the pointer.

  The laser is the largest cost, the rest can be done fairly reasonabl y if one doesnt go overboard
on the galvo or Z stage as I did. The second most expensive thing is the Theta lens. This flattens the field as Ill explain later in update as to how it all works. Im waiting on the Lens now, it cost about $300 from China and hasnt yet arrived. All else is working well and Auggie drives
the pointer around very quickly. Speed is very adjustabl e in the arduino firmware which is a pretty simple program that just takes step/direction from the PoKeys and converts it to analogue commands for the armfly board. ( Which incidentl y is about $30.00).

  So I ll use this thread to answer any questions if anyone comes along who wants to play
in galvos with co2 or UV lasers. Prices are dropping fast for UV lasers so a galvo driven
engraver, while in the past out of reach for a hobbiest, is getting to a reasonabl e spot.

Heres 3 photos on my unit so far, from left, top and front.
  Ill let you know how it all works out. Smiley

Art


* laserTop.jpg (3184.76 KB, 4128x2322 - viewed 54 times.)

* laserFront.jpg (2625.91 KB, 4128x2322 - viewed 36 times.)

* side.jpg (2360.03 KB, 4128x2322 - viewed 41 times.)
« Last Edit: March 07, 2018, 11:27:34 AM by ArtF » Logged
tweakie
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« Reply #1 on: March 08, 2018, 02:58:41 AM »

Excellent work Art, I am really looking forward to following your progress.

Tweakie.
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ElevenCubed
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« Reply #2 on: March 19, 2018, 02:30:28 PM »

Way cool!  Saw your quick video on YouTube.

What size is the "Aggie" text you burn in the video?

I did some playing a year or so ago on galvos and steppers as galvos.

Old post: http://gearotic.com/ESW/FavIcons/index.php?topic=1621.0

Have you noticed any pincushio n effects in our scans?  I was seeing exponenti al pincushio n effects even through my f-theta lens.  The lens did correct quite a bit but even within the focal length specs I as getting pincushio ning.  I never could tell if it was an artifact from my stepper style setup or if it was something that would show up if I was using real galvos.

Thanks
Brian

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ArtF
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« Reply #3 on: March 19, 2018, 05:23:12 PM »

Brian:

  Thanks, its a fun device and Im still learning its secrets.

 Your pincusion is probably due to linearity of the stepper. The mirrors actually
track with linearity correctio n as a theta function I suspect in addition to the lens.
While the lens flattens the focal plane, the motion of how many degrees to move
per step I think changes as a function of the theta of the total angle.
  .1 degrees from zero is less distance at center than at the edges. Youd need to make
a correctio n table based on that to get rid of the pincushio n. I used good galvos, but I
suspect cheap laser light show ones at 65 bucks a set probably woudl have worked fine
as I only move one step at any time up to 100Khz rate.

  I opted for a 175 x 175 lens for initial use. But my galvo was for yag so after changing
the mirros and lens, the lens if too far from the mirrors, this shrinks me to 125x125
which appears quite flat over the entire field. Top speed is about 60 meters per minute.

  Ill be making a video to explain about this type of thing once I finish a new photo
engraving routine based on galvo's to increase tones from 100 max in raster, to
1024 shades of grey in the new method. ( If it all works. Smiley )

Art


 
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ElevenCubed
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« Reply #4 on: March 19, 2018, 08:48:27 PM »

The light show galvos found on Ebay that are used by many to do SLA type printing are quite small (mirrors).  Smaller than the raw beam diameter of an 02 laser. 

My o2 setup has a ~5mm raw beam that goes into a 3x making it ~15mm, that's all in front of the f-theta.  My lens is ~8.25" flat field if I remember correctly, it was $$$ spendy.  I thought about gluing the 02 mirrors to the laser show type galvos but the they are just too small (power) to move the large thick 02 mirrors. 

I started to design my own galvo motors (for fun) but got side tracked with another project ( ElevenCub ed  Grin ).  I would totally pick the project back up and had been planning on it at some point.  The motors are simple enough, just a few machined parts and some windings Smiley




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ArtF
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« Reply #5 on: March 20, 2018, 07:20:25 AM »

Interesti ng, I have never actually seen those laser show galvo's for compariso n.
 Your right though, to protect the theta lens and the mirros you want expansion
of the beam. My beam is about 2.5mm expanded X6 to about 14mm.
 
   I used 2mm thick gold mirrors, glued them into the yag galvo stems.  Looks like
quite a job to build those galvos. Look nice though. Smiley
 I paid $265.00 for my theta lens, direct from alibaba. They shipped and I recieved
in less then 2 weeks, so not too bad.

  Ive fixed the dropouts, turns out an arduino's loop() is called after the hardware debugging
module, so by placing it in a while(1) loop, I dont lose any more DAC updates. The debugger
was causing 2ms dropouts.

   Start and stop delays are not really there, the dropouts in start/stop were caused
by my Auggie code that attempts to keep radiation per mm during motion the same. Im
tightenin g the code there and its getting better fast.

  Hope to do more video's soon. Pity about the lightshow galvos, they may
have been a great way to do this cheaper. I paid $300 on a bid for my cambridge tech
set, which is very very fast really. Draws about 6 Amps on a large fast move.

  I could only do this all because the Arduino DUE is 84Mhz, just fast enough for
a dual channel step/direction interface . Earlier Arduino's were far too slow.

  I have to say so far Im impressed . Wont replace a x,y engraver, but can probably do
things the engraver cant.

Art

 
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ArtF
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« Reply #6 on: March 20, 2018, 04:06:16 PM »

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


* buddy.jpg (2705.48 KB, 2322x4128 - viewed 31 times.)
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tweakie
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« Reply #7 on: March 21, 2018, 01:41:05 AM »

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  capabilit ies.

Tweakie.


* halftone.jpg (29.9 KB, 260x310 - viewed 7 times.)
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ArtF
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« Reply #8 on: March 21, 2018, 07:17:31 AM »

Hi Tweaky:

   This is done with a new command effect. The Command
G04P1 is a 1 second delay. The Command G04P.005R 50 is a laser shot
for .005secon ds 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.Th e 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 supersamp le the image data to get sub pixel densities from
surroundi ng 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 correctio n 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 correctio n 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. Smiley

Art

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tweakie
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« Reply #9 on: March 21, 2018, 10:37:44 AM »

Thanks for the explanati on Art. I can't say that I fully understan d but I am learning.  Grin

Tweakie.
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ArtF
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« Reply #10 on: March 21, 2018, 02:19:56 PM »

Tweaky:

 I should probably have written something about power and photos before. There is a
relations hip between speed and power to be considere d 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 resolutio n of only 500 pixels really.
  So sweep speed is really a tradeoff of resolutio n 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 resolutio n. 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..w ithout using supersamp ling
of the image data... more on that later if everythin g else works out. ).

  Energy accumulat ion is another way, multiple scans using different power per pixel
on each scan to create an accumulat ed 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 calculati on of each pass for energy is trivial as a
calculate d 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 resolutio n 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 performan ce, a multipass energy summing
calculati on 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 . Smiley

Art
 
 

 

 
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tweakie
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« Reply #11 on: March 22, 2018, 05:49:29 AM »

Hi Art,

I donít know if this is relevant to your thinking butÖ

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 equivalen t of the Synrad UC2000 to control itís maximum output power. I have not yet tried it with Auggie image reproduct ion as I suspect that PWM frequency conflicts may be difficult to overcome without synchroni sation but that is something I will investiga te further as time permits.

If only there were more hours in a day.  Wink

Tweakie.
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ArtF
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« Reply #12 on: March 22, 2018, 06:49:56 AM »

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 controlle d, 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 resolutio n.
To do a 4k image using all its data, woudl take a 4 second sweep time really.. Thats one
long raster. Smiley

Art
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ArtF
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« Reply #13 on: March 22, 2018, 08:28:48 AM »

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. Smiley

Art
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tweakie
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« Reply #14 on: March 22, 2018, 10:37:15 AM »

Hi Art,

To me, that sounds like the way to go.

Tweakie.
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