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How about a smart laser?

Posted by kd6hq 
How about a smart laser?
February 02, 2018 06:38PM
Lets say that I have built a 10W laser. I would like to be able to change the drive current
allowed by the laser thru G-code. The reason being, engraving with a 2.5W laser looks
a lot different than engraving the same picture with a 10W laser. Having a diode driver
board that is programmable thru G-code could make it possible. So then after the engraving
you could change the power of the laser and then cut the material with the same laser.
What say you, design wizards? smileys with beer

Edited 1 time(s). Last edit at 02/02/2018 06:45PM by kd6hq.
VDX
Re: How about a smart laser?
February 02, 2018 07:03PM
... with the blue 445nm-diodes I'm engraving and cutting with the same current, but different pulse-widths, set by G-code.

For engraving with a 2W- or 3,5W-diode the pulse-lengths are something between 5 to 30 microseconds (depends on material and color), moving speeds up to 50mm/s ... for cutting more like 50 to 300 microseconds pulse-widths and slower speeds of around 20 to 2mm/s (depending too on material, colour and thickness) ...


Viktor
Re: How about a smart laser?
February 02, 2018 08:22PM
My problem is that I do not understand enough about electronics to fully understand what you are saying.
This is what I'm thinking but I am not sure if it is correct. If I am using a 2W diode and a current setting of 1.5A.
If I then use a gcode setting of S130 a pulse-length of say 12 microseconds is produced. Lets say a power
output of 0.8W is produced. If I then send a signal of S192 then a pulse length of say 17 microseconds is produced.
This results in a power output of 1.2W. Now I change the diode and I'm now using a 5W diode and a current of 3A.
Now if I use the same S130 and S192 signals because of the higher base current a higher power output will be produced.
The result of which will be a deeper engraved burn in the material. So how is using the pulse length being used to
change the current setting? The only thing I see is that a higher power is be obtained because of a longer pulse length not
because of a higher current setting. What I'm thinking is this. Lets say that I have a 10W. diode using 4.5A. So I do an
engraving in wood. What I find is that in some places the wood has burned thru and I have some very small holes where
the S gcode in the area the over 200. However if I use a 2W. diode the same area is dark as it should be but I do not
get the burned thru holes. So if I can use the 10W. diode at a lower current level, say 1.5A. I can do the engraving so it will look good.
Now that the engraving part is done, I can increase the current level, say 4.5A. and do a one pass cut instead of a multiple pass cut
of the material.

Please help me understand this better.
VDX
Re: How about a smart laser?
February 03, 2018 01:32PM
... first, you won't find a "blue 10Watt diode" - there are 6Watt diodes available, but with bigger beam-diameter and worse beam than with te 2W and 3,5W diodes, it won't be as precise or efficient as the "weaker" ones. Either you use beam shaping (double prism) optics with the 6Watt diodes (what's pretty expensive), or they won't give the expected results ...

There are many "10 Watt" diodes at alibaba, but this is a "fake"! - they state only the electrical drawn power, not the optical output!

So actually search for a good clamped 2W diode for finer engraving or a 3,5W diode for slightly better cutting.

Then the pulse-width has to be adjusted for the diode power and material anyway, so this is one of the "variables" you have to set for proper engraving or cutting.

This "variables" are:
- max. power
- focus diameter (power + focus diameter = energy density)
- pulse width (not PWM sequence, so only one pulse per position!)
- pulses per Millimeter
- overlapping of pulses (if the spot diameter is bigger than the distance between "pulses")
- speed (combined too with overlapping will result in deeper cuts)

All of them, optimal combined, will give a reliable result.


If someone want to "cheat" this complex combination by using analogue power controlling (not pulsing), then the software has to calculate all the "speed vs. energy" params to get even burning per line ... or the lines will be burnt more at start and end ...


Viktor
Re: How about a smart laser?
February 03, 2018 06:40PM
I understand the part about the efficiency factor of the diodes. Same way with the old time tubes.
Transmitting tubes (transistors) are rated at the input power for the same reason. "It sounded
better", but most have an efficiency factor somewhere around 55%. So a 100W tube (transistor)
would actually only produce about 55W.

Have you described how you set up the extruder to function like this and another post ?
If so may I have the link please as I'm not sure what to search for.
Also what control program do you use? Is there one that allows you control all these
factors or do you have to change the firmware when you change material types?
VDX
Re: How about a smart laser?
February 03, 2018 07:18PM
... for some of the "simpler" laser engravers I'm using Pronterface and Marlin4Due as firmware.

When using the STEP pin of the Extruder, then the pulse parameter can be set as "pulses per mm" in the firmware and as E-parameter in the G-code. The software will then calculate the correct "pulses per mm" and only output them with "G1" moves, but not for "G0" moves.

When using X- and Y-STEP pulses of the controller, then the pulses per mm are depending on the actual microstep resolution. "Laser ON" is then an output pin, I'm setting to HIGH for activating the laser or to LOW for moving XY without pulsing/firing the laser.

For defining the pulse-length I'm using an Arduino Pro Mini in the laser-driver - it reads an analogue voltage, I'm setting per potentiometer while rebooting it. The voltage is set from 0V to +5V and will result in pulse times from 5µs to 300µs (or another span for different lasers and applications) ...


Viktor
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