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Laser modulation signal?
« on: March 06, 2013, 11:19:03 PM »
Hello,

I am playing around with a 1W laser to cut 0.005" Mylar in order to make SMT solder paste stencils... That Laser circuit is something I'm cobbling-up, it's not a manufactured item... that said, I need to pulse the laser on/off at some interval (yet unknown) that will be proportionate to the feed/speed/movement of the table... as the table speeds-up/runs/slows-down/stops.

I have a modulator that will toggle the laser on/off at a fixed rate (and I suppose that will be ok) however, if I could get a PWM signal from MACH (proportionate with the movement of the table noted above) *this* would be optimum. The modulator accepts TTL input to toggle.

Can any one suggest how this might be done from a MACH3 point-of-view?

This may be a very simple thing, but I am a software developer, not a machinist, and *not* very familiar with MACH3... if anyone can make a suggestion, that would be great!

Also, is there a standard way of turning the laser on and off from a G Code perspective? In the case of a Laser... is the Laser on/off using the Spindle on/off codes? (I suppose it doesn't matter, but I would like to hold to convention).

Thank you for any help/suggestions with this!

-charlie




 

Offline Dan13

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Re: Laser modulation signal?
« Reply #1 on: March 07, 2013, 12:52:17 AM »
Hi Charlie,

For switching the laser ON and OFF there are the M10Px and M11Px commands. See this thread for details:

http://www.machsupport.com/forum/index.php/topic,23636.0.html

For the feed proportional PWM thing your asking, it cannot be done with the parallel port, but the Smooth Stepper offers this feature.

Dan

Offline Tweakie.CNC

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Re: Laser modulation signal?
« Reply #2 on: March 07, 2013, 02:28:46 AM »
Hi Charlie

A lot of experimental / pioneering work is being done by others using low powered (1 Watt) diode lasers in this thread http://hobbycncart.com/forum/63-151-12937-16-1362353174

Because the rate of burn (apparent laser power) can be varied by changing axis speed there are currently two software programs being developed which will create the required Mach3 GCode from a BMP image. Your solder mask could be considered an image so it is more than likely that it could be produced by this method and without the need for PWM control.

Just a thought.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Laser modulation signal?
« Reply #3 on: March 07, 2013, 09:24:07 AM »
Thank you for the replies!

Dan: Can you provide more info on how this is setup in MACH3?

Tweakie: The Stencil starts-out as a GERBER file that gets converted to DXF. These are vector files, I believe I'd loose too much resolution going to a raster image to suite the apps (unless they support GERBER or DXF).

Since the laser is so low power, I'd like to toggle it full power at some interval that varies with speed - I am not against creating my own circuit from a PIC... maybe OR'ing the STEP signals on X and Y, running this through a lowpass filter to create a DC voltage (table speed indicator...) then use that to vary the frequency of a PWM signal that is set to make the best cut... this signal would trigger the modulator to pulse the laser at a desired frequency and vary the pulse accordingly to the speed of the table.

Not sure if I'm on the right track... (?)  ???

-charlie
Re: Laser modulation signal?
« Reply #4 on: March 07, 2013, 10:13:47 AM »
Charlie,
Probably letting my ignorance show here, but why do you need to vary the power with axis speed if you are only cutting with vector files?  Wouldn't you only need to toggle the laser on and off to cut the vectors?

I guess I am puzzled over why the varying axis speed rather than fixed speed.

Regards,
John Champlain
Re: Laser modulation signal?
« Reply #5 on: March 07, 2013, 10:33:39 AM »
Hi John,

This may only be my ignorance as I have never worked with a Laser cutting application before. The SMT Stencil needs to be accurate with a very good/sharp edge. Since the unit I am attempting to utilize is only 1W (and I consider this very low power for a cutting application) I wanted to utilize "full power" in the cut.

In order to dial-in the fine edge I require, I felt that I would need to pulse the laser so the material does not burn. I've run this buy the vendor that sourced the laser diode and optics and he concurred.

I need to go through (at least) 0.005" material, and I don't believe anything but full power will accomplish this...

I noticed that my table (and I assume any table) ramps up/down with speed... furthermore, I want to be able to set speed in my G Code... I'd like to build a "follower" circuit that will vary the laser pulses, such that the pulses are uniform across speed changes... this would require some varying signal to come from MACH3 (easiest) or the Mill itself to trigger the Laser.

As I admitted, I have no Laser experience, but theoretically, if I need a desired cut *depth* without burning, I'd need to pulse the 1W Laser rather than varying the output.... but, I'm open to new, more experienced thinking.

Thoughts?
-charlie
Re: Laser modulation signal?
« Reply #6 on: March 07, 2013, 11:02:59 AM »
Just switching the laser on at the beginning and off at the end of you vector cuts should do the job. That's what I'm currently doing on my 40W laser. The laser head is likely to be very light compared to a CNC mill so acceleration should be high and you'd have minimal ramp up. I'd try this first before going for a more complicated solution.

If you do want to make sure that the laser power doesn't vary with speed then you probably want to go with a fixed number of pulses per inch (or mm). This is an interesting discussion about this. I basically involves counting the pulses Mach3 outputs to the stepper driver. There's some trigonometry involved for diagonals/curves but essentially it's "fire the laser for a fixed time every N" steps.
http://www.buildlog.net/blog/2011/12/getting-more-power-and-cutting-accuracy-out-of-your-home-built-laser-system/
Re: Laser modulation signal?
« Reply #7 on: March 07, 2013, 11:49:44 AM »
Thanks Fred27, I'll give it a look.
-charlie

Offline Dan13

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Re: Laser modulation signal?
« Reply #8 on: March 07, 2013, 01:48:03 PM »
Charlie,

If you meant the PWM, then it has nothing to do with Mach3. What provides this is the Smooth Stepper external controller, which does it locally in its hardware. With the parallel port you cannot do this.

Anyway, as mentioned by others above, I would guess that you may not really need this for the things you're looking to do.

Dan
Re: Laser modulation signal?
« Reply #9 on: March 07, 2013, 03:06:38 PM »
Charlie,
I never tried to burn Mylar, but I have tried other similar films.  I think that you might find that it will melt and shrink where touched by the laser.  Have you tested it?
Regards,
John
Champlain