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Author Topic: The Laser Project.  (Read 694645 times)
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ART
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« Reply #1030 on: February 14, 2018, 07:57:26 AM »

Tweakie:

  Yes, I try to post in for archival purposes when I can so others following will have some data to find. Laser information can
be hard to find and hard to research.

  (btw: I now have my galvos working as step direction wiring and happily jogging around with Auggie and even homing nicely.. My problems now I think are mainly the damn theta lens, one of those things with very little information to go on. )

Art
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Tweakie.CNC
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« Reply #1031 on: February 14, 2018, 08:18:51 AM »

Quote
My problems now I think are mainly the damn theta lens, one of those things with very little information to go on.

Hi Art,

Not something I would tackle - mathematically correcting for the scale and pincushion distortions sounds like hard work compared to my simple linear engraving work and drinking beer.

I am pleased you have your galvo head working OK I am still thinking along the lines of linear Y axis and galvo X axis but yet to construct the prototype.

Tweakie.
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« Reply #1032 on: February 14, 2018, 09:40:45 AM »

Ive learned quite a bit on the galvo's.. I can see where the real problem is the F-Theta thing. Its
really not that expensive to do the rest. Ive used an arduino to convert step/direction to analogue
values and a DAC to control the galvos. Easy enough, but the pincusion and focus will be the real
challenge.. Ive a lot to learn there..

Art
 
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« Reply #1033 on: February 15, 2018, 01:15:30 AM »

Has anyone done any assessment on how good at depth control one of these lasers are? I'm not talking about $10K priced lasers that definitely can control depth very well. What can you reasonably expect form a cheap CO2 laser?
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Tweakie.CNC
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« Reply #1034 on: February 15, 2018, 01:41:05 AM »

Hi Spandex,

Depth control is a weak point.
Comparative depth and repeatability is generally good but trial & error is usually used to arrive at the correct initial settings.

Tweakie.
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« Reply #1035 on: February 15, 2018, 02:18:09 AM »

Hi Spandex,

Depth control is a weak point.
Comparative depth and repeatability is generally good but trial & error is usually used to arrive at the correct initial settings.

Tweakie.


Sounds workable. Wouldn't it be cool if along with laser cutting, it also had a sensor that gauged depth at the same time! And I'm guessing getting your hands on TOMTOM isn't really possible? I haven't been able to find any links other than his blog:

https://blogs.yahoo.co.jp/tomtchi (need chrome to translate) but there's no links to the plugin.

Another update for the Impact / Laser Engraver plugin (v1.2a).

Image aspect ratio;
I have re-instated the ‘maintain aspect ratio’ function (somehow lost along the way) which is now operated in a slightly different way to which it was originally. There is a new screen button “Calculate Parameters AR” and this automatically sets the vertical (Y Axis) height based on the, user input, horizontal (X Axis) width information and the original image aspect ratio. This new function works alongside the original “Calculate Parameters” function and provides a choice of either locked or free aspect ratio.

Changing the Mach mode of motion;
If the original image detail extends to the vertical sides of the canvas it has been found best to process the engraving in the Exact Stop mode whereas if the image detail stops short of the edges there is a small but significant gain in process speed if Constant Velocity mode is used.
By default the plugin now operates in Exact Stop mode and I have added a new check box “CV mode” so that Constant Velocity can easily be used, as and when required. (Without having to open the Mach General Config page to change the settings there). On exit the plugin returns Mach to CV mode.

I have also updated the PDF file to reflect these changes.

Engraving.dll   http://www.cooperman.talktalk.net/Engraving.dll

Engraving.pdf   http://www.cooperman.talktalk.net/Engraving.pdf

Tweakie.


What is the difference if any between this plugin and DotG?
« Last Edit: February 15, 2018, 02:21:25 AM by Spandex » Logged
Tweakie.CNC
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« Reply #1036 on: February 15, 2018, 02:24:28 AM »

Quote
Wouldn't it be cool if along with laser cutting, it also had a sensor that gauged depth at the same time!

Something for you to design perhaps ?

The Mach3 plugin will reproduce 8 bit images (true shades of grey).
DotG produces 1 bit images (illusion of shade by dot-dithering).

If you contact Tomura directly he will send you a copy of his TomTom plugin.

Tweakie.
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« Reply #1037 on: February 15, 2018, 03:03:27 AM »

Something for you to design perhaps ?

Maybe one day. I can't think of a use for such a contraption for me at the moment. I think trial and error will suit me just fine.

Thanks, will get in touch with him.
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« Reply #1038 on: February 15, 2018, 05:17:28 AM »

Hi Art,

Thought you may be interested in this which is something I had not seen before. It is a 3 axis scan head which can scan very large areas by obviating the requirement for an F-Theta lens system. https://nutfieldtech.com/3xb-3-axis-scan-head/

This pic. is of a Nutfield 3XB. Obviously the beam angle changes dramatically during the scan but the focus remains constant.

Certainly something for me to investigate further.

Tweakie.


* 3axis-scan.jpg (101.89 KB, 1024x678 - viewed 71 times.)
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« Reply #1039 on: February 15, 2018, 08:38:38 AM »

Hi Tweaky:

   Thanks for the photo of the Z axis lens. I was aware of, but hadnt seen one. Synrads newest also uses this, they use a voice coil
lens to move it the required theta distance as the mirrors sweep.  The real problem I think with Galvos is the distance vs focus spot
formulas. For a TEM0 laser like the RF ones, focus size is  (4*wavelength*focal distance) / (PI * inputdiameter). InputDiam is ually around 2-3mm for a co2, but with an expander mine is 12mm or so.

   I have a beam expander to try to get the smallest dot possible. The formula shows how important the expander and focal distance is though. You can double the effective power of a laser by expanding its beam prior to focus or simply by using a smaller focal distance.
So galvos have it rough, to get a 12" field for example if that field requires a 12" focus length,  thats (4 * .01 * 304) / (3.14 * 12mm) = .322 and thats if its a good lens. When a focus gets that large you need alot of power as power reduces 4 times faster than its growth in distance.  Its this balance that Im currently working on as I puzzle out the size matrix I want from my galvo. I always knew smaller focus
distances were better, but till I crunched the numbers I didnt realize just how much better and why.

  When it comes to Depth engraving, I shoot one level, leasure the distance engraved, and then do multiple levels
using that initial test pass's depth as the multiplier for pass depth. It produces 3d images to a very close desired depth I find that way.
Each material being different, its only a guide but allows pretty good 3d.

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