Galvo Lasers

[ArtF]

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 collecting 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
wilderness 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 conversion
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 components 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 application.

 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 incorporated. 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 reasonably 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 adjustable 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 incidently 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 reasonable spot.

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

Art

[tweakie]

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

Tweakie.

[ElevenCubed]

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 pincushion effects in our scans?  I was seeing exponential pincushion effects even through my f-theta lens.  The lens did correct quite a bit but even within the focal length specs I as getting pincushioning.  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

[ArtF]

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 correction 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 correction table based on that to get rid of the pincushion. 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. )

Art

[ElevenCubed]

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 ( ElevenCubed  ;D ).  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

[ArtF]

Interesting, I have never actually seen those laser show galvo's for comparison.
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.
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
tightening 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

[ArtF]

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

[tweakie]

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.

[ArtF]

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

[tweakie]

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

Tweakie.