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Fórum » Only in English » Technologies » CO2 Lasers. (Anything relating to CO2 Lasers can be discussed here.)
CO2 Lasers.
tweakie Dátum/Date: Hétfő, 2015-04-20, 13:19 | Üzenet/Post # 521
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Just by way of a comparison, this is the same image reproduced using a smaller dot size.

Tweakie.

Csatolások/Attachments: 9346454.jpg(167Kb)


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Amatőr Dátum/Date: Hétfő, 2015-04-20, 16:35 | Üzenet/Post # 522
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tweakie, really nice results! What was the raster setting?
I tried to paint my test engravings, but I cannot see the paint color from front.
I made another photo about my test, where the mirror is about 45° under the camera. Here visible what is wrong. The picture is somewhere in the red area, under it there is an old method stipe. The old settings made a deep hole or crater in every pixel, so it is visible from any angle. I think I really need to try to fine adjust the power with pwm.

Csatolások/Attachments: 4996555.jpg(165Kb)


H1i.hu
 
tweakie Dátum/Date: Kedd, 2015-04-21, 06:46 | Üzenet/Post # 523
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Hi Zoltan,

I believe PWM control is the way forward.

When only lightly engraving items the main problem we encounter is that the laser does not fire reliably at low current settings. By
setting the laser current at say 5mA then it will fire reliably but may have too much output power for the engraving job in hand (assuming we have a limit to the maximum feed-rate available).

By using PWM control we can achieve two things…
1) Lower the laser output power at a relatively high tube current setting.
2) Reduce the spot size produced on the surface of the work.
I have tried to explain the principles involved in a bit more detail here; http://hobbycncart.com/publ....-1-0-44

We should now consider the following…
The beam output from our CO2 lasers is not perfect but lets assume for a moment that it is perfect. The beam would be TEM00 (round in section) and exhibit a Gaussian (bell shaped) power distribution graph.
Assuming, for one moment, that the largest diameter of the ‘bell’ is the minimum diameter we can focus our laser beam (10.6 microns) then by carefully controlling the PWM and PRF we can start to use only the maximum power area of
our laser beam (towards the centre of the beam) which, on the power distribution graph, moves up the ‘bell’ towards a smaller diameter.

Now I am not certain that I have explained this very well but the following diagram may help.

Question – Can we produce a ‘dot’, which is smaller in diameter than the wavelength of our laser, on the surface of the work ?

Answer – Yes we can.

Tweakie.

Csatolások/Attachments: 7929760.jpg(26Kb)


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tweakie Dátum/Date: Kedd, 2015-04-21, 06:57 | Üzenet/Post # 524
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Hi Zoltan,

On my mirror engravings the first was dithered to a resolution of 300 d.p.i. and the second to a resolution of 600 d.p.i. both were produced using a feed-rate of 3500 mm/min. with a step-over of 0.15 mm.

Tweakie.


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Amatőr Dátum/Date: Kedd, 2015-04-21, 15:51 | Üzenet/Post # 525
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tweakie, thanks again for useful infos!
I had to look after what is TEM00, but now it is logical how to use the power ditribution for my goal.
I will make a simple pwm circuit, based on 555, I have to order some parts, and test again. I think with pwm when the laser fires more times onto the same pixel it can be more contollable than a sigle shot.


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Amatőr Dátum/Date: Kedd, 2015-04-21, 18:43 | Üzenet/Post # 526
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This afternoon a made some more test, and come out with good results:



On the middle there is a try I made yesterday, on the left the best settings I currently could do. It is visible from angle, white enough, and made with 0,15mm raster. It was terribly hard to find this setting, I was playing in a 10° angle with the potentiometer. A very little change causes an overburned picture, like the right side one. Conclusion for today: it is not impossible to make good picture.
Csatolások/Attachments: 9679756.jpg(292Kb)


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tweakie Dátum/Date: Szerda, 2015-04-22, 05:38 | Üzenet/Post # 527
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Hi Zoltan,

The image on the left is excellent  ok

PWM / PRF control gives better (easier) fine adjustment of the laser output power but it can be tricky to set-up and use properly (I suppose if it was easy then everybody would be doing it).

Tweakie.


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Amatőr Dátum/Date: Szerda, 2015-04-22, 18:31 | Üzenet/Post # 528
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tweakie, thanks!
I think pwm control will work as a fine adjustment over the power setting. Maybe with helipot will be easier, with resistors series on both sides.
What is Your opinion about 6n137? It is fast enough, and have an enable input where I can attach the pwm circuit.


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tweakie Dátum/Date: Csütörtök, 2015-04-23, 12:46 | Üzenet/Post # 529
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Hi Zoltan,

In my opinion the 6n137 will be switching fast enough but I am not sure what circuit you are planning to use.

Tweakie.


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Amatőr Dátum/Date: Csütörtök, 2015-04-23, 16:58 | Üzenet/Post # 530
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tweakie, I'm planning to use a simple PWM circuit, based on 555, where the PWM signal is enables the 6n137 to flow through the firing signals from the PC to the laser's PSU.
Something like this:

Csatolások/Attachments: 1706104.gif(5Kb)


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tweakie Dátum/Date: Szombat, 2015-04-25, 05:25 | Üzenet/Post # 531
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Hi Zoltan,

That should work just fine. My only concern is that you may not be able to obtain the full range of PWM duty cycle (0 - 100%) using a LM555 timer but I have never tried it so have no personal experience with this circuit.

Tweakie.


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Amatőr Dátum/Date: Szombat, 2015-04-25, 09:45 | Üzenet/Post # 532
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tweakie, I was searching the 555 pwm circuits on the net, and You're right, they won't go up to 100%. The idea is that when I need I will switch the 6n137 enable pin to 5V. The only little problem is that the opto inverts the signal. Maybe I have to use a fast inverting gate in series with it. Or is it enough to change the active high/low setting in Mach?

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tweakie Dátum/Date: Szombat, 2015-04-25, 11:50 | Üzenet/Post # 533
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Hi Zoltan,

I would be inclined to just change the active Hi/Low settings in Mach3 but the output signal from your electronics must be high with inputs disconnected (assuming the laser PSU is using an active low input) or Mach3 E-Stop activated. This is a necessary safety precaution to prevent the laser turning on if a wire is disconnected or the PC / Mach3 fails. If changing the Hi/Low setting does not achieve this then, as you have suggested, you will need to incorporate a TTL inverter or similar gate in your circuit.

Tweakie.


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Amatőr Dátum/Date: Szombat, 2015-04-25, 19:20 | Üzenet/Post # 534
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tweakie, it makes a lot of sense. Technically the opposite Mach output signal works, but it's disadvantageous. I rather use an inverter. Thanks a lot!

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Amatőr Dátum/Date: Kedd, 2015-10-27, 17:24 | Üzenet/Post # 535
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Although I learned not to play with food, I had to try this:
Mona Lisa on a banana :)

Csatolások/Attachments: 9198368.jpg(293Kb)


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tweakie Dátum/Date: Kedd, 2015-10-27, 17:35 | Üzenet/Post # 536
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Excellent hands biggrin

Tweakie.


Success consists of going from failure to failure without loss of enthusiasm.
 
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