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Author Topic: PWM for laser control issues  (Read 10552 times)
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iggy
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« on: December 23, 2007, 07:34:51 AM »

Hi, I know this topic has come up a couple of times, but I have not been able to resolve my problem with previously posted information, hence this post.

It's a bit long-winded, but I wanted to explain all the background so that the issue makes sense - please bear with me...

Basically, I am trying to control the power output of a CO2 laser using the PWM capabilities of Mach3.
In the ideal case, S commands embedded in the G code would enable me to directly modulate the laser power (e.g. to select between acrylic engrave and acrylic cut in the same job).

I have set Mach3 up based on the information given by Art and others (spindle output enabled, PWM frequency and minimum set, PWM output on step pin of spindle motor output, pulley speeds set up correctly). I have intentionally not enabled the laser option, as this generates a continuous pulse output - my system does not require a constant tickle input.

Now, when I look at the voltage on the spindle motor step output usin an oscilloscope, I do NOT see a smooth PWM signal as I enter Sxx to change the spindle speed. In fact, I only get four discrete states - off, about 30% PWM, about 45%, and about 55%. I know why this is - the manual explains the compromise between kernel speed (100k in this case), PWM base frequency (20kHz input, gets reduced to 16666Hz by Mach on input) and number of possible PWM steps.

I cannot reduce the PWM base frequency, as this directly affects the laser power output and pulse frequency, giving rise to visible discrete spots on the workpiece, which is not acceptable. I also don't want to slow down the x/y speeds (increased processing time).

My problem: I would be very happy with 3 different PWM settings (off, engrave, cut), as long as it is possible to preset the available PWM pulse widths (e.g. 10%, 50%). Is this possible? If so, how?

Thank you very much for any suggestions, and Season's Greetings to all of you out there in MachLand!
Ilya
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iggy
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« Reply #1 on: December 23, 2007, 08:43:25 AM »

In addition to the above, when I use the spindle relay output to control the laser (simple on/off), I always experience a delay (some ms?) between the laser coming on and the table beginning to move, even with all delays set to zero. This leads to a spot at the beginning of every object.
Thanks.
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Ricktron
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« Reply #2 on: January 12, 2008, 11:16:47 AM »

I have the same problem.. And I still looking for a solution..
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iggy
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« Reply #3 on: January 12, 2008, 04:09:51 PM »

Hi, I now have a solution, thanks to Art's patience and wisdom!
Command M11P1 switches output 1 on at the next axis pin transition; M10P1 switches it off at the next transition (you must output something to an axis immediately after this command for it to work - I use z-axis commands to do this, as I do not have a z-axis).

Works beautifully - thanks again, Art!     Cheesy Cheesy
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STRATOTANKER
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« Reply #4 on: March 13, 2008, 08:53:53 PM »

IGGY, could you please elaborate and walk me through tht process of setting up my laser.  it runs and cuts fine, but I always have that delay at the beginning and end of a cut.  I am transitioning from Deskam to Mach3 so there are a lot of things I do not understand.  Thank you for your help.
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iggy
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« Reply #5 on: March 15, 2008, 01:51:02 PM »

Hi STRATOTANKER,

If you give me your email address, I will send you the LazyCam post-processing script I use with an explanation.

Best wishes,
Iggy
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DaveDoesIT
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« Reply #6 on: July 20, 2008, 03:30:32 PM »

Hi STRATOTANKER,

If you give me your email address, I will send you the LazyCam post-processing script I use with an explanation.

Hi Iggy,

I would appreciate the same assistance. I will PM you an email if I may but thought I would post here top keep the thread open.

I have an old Laser engraver and the electronics are dead. It was supposed to only run under win3.1 and I do have the drivers for it. Anyway, I isolated the 25W Laser wiring from the entire thing and applied power. I used a AA battery on the 0-10v intensity and the thing shot a hole in some cardboard in an instant. So far so good.

I am thinking of a couple of Gecko 201 for the existing 6-wire motors. The X and Y motors are tiny so I am sure they are in the 1A or less range so 201 might be overkill.

Dave
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seisops
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« Reply #7 on: November 19, 2008, 08:35:11 AM »

Hi, I now have a solution, thanks to Art's patience and wisdom!
Command M11P1 switches output 1 on at the next axis pin transition; M10P1 switches it off at the next transition (you must output something to an axis immediately after this command for it to work - I use z-axis commands to do this, as I do not have a z-axis).

Works beautifully - thanks again, Art!     Cheesy Cheesy


Dear Iggy,
your idea is interesting but those two commands, control two states (on and off). If we are to implement 3 states (off, engrave and cut) for laser, how can those commands work? Commands M10 and M11 do not exist by default.  What kind of macro did you create?
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jasko
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« Reply #8 on: January 18, 2010, 05:01:26 PM »

Iggy
can you please sent me this LazyCam post-processing script with some explanation because I come on same problem with laser
thanks
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darkfires
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« Reply #9 on: February 14, 2010, 11:44:40 PM »

Hi,

Is there any chance somebody could attach the files needed to do this to the thread ?

I have a laser that I'm trying to solve this issue too


Thanks
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