GearHeads Forum

Hi Art,

Every indication is that PWM is invertible and there are check boxes to that effect within the 57CNC config. but I spent a good 2 hours trying and it defeated me.
I have now had time to test my hardware solution and it works just fine for me (I was initially concerned about using a transistor in this manner with possible tri-state logic but all is well).

Tweakie.

Tweaky:

Yeah, its probably fine, any lag you see may be Auggies fault, its a tricky thing to try to linearize the pwm over the
accel period so it can appear a bit laggy. The config settings of min and max power can help as
they set the actual start power point(  you set to the PWM power at which laser actually starts
coming out, this can be pretty high on some laser, or low on others. ), this helps in the linear aspect of the accel power correction.

Art

I have just tried some vector cutting as a test of the varying PWM with velocity. My test Gcode is approx. 50/50 arc?s and straight lines so should be a good test.
The results were not quite what I was expecting?
At a maximum set feed-rate of 6000 I was only achieving a max. of 30% PWM but at a maximum set feed-rate of 500 then I was achieving a max. of 100% PWM.
At first sight it appears that the PWM duty cycle is reducing as velocity increases ? the exact opposite of what I was expecting.

I am wondering if I have screwed something up in my software settings somewhere ?

Tweakie.

Hi Tweak:

  Well, its hard to say. But, let me explain how that works.
Lets say you have set a max speed of 6000. Whenever the head is moving
in a G1, it computes the speed for that ms by the number of steps it will
take during that ms ( on each axis so vectored to a directional speed. ).

  So if, just like the days of M3's CV modes, you command a speed which
the head doesn't truly reach, the speed will never hit 100%. If I run RoadRunner
for example, and the max speed it hits is 340mm/sec due to speed/accel/Jerk
constraints in the run, and I have commanded 1000 as a feedrate, the max PWM
during that run at its fastest point will be 34%. Commanding a higher feedrate will
further lower the laser power reached.

  So in a vectored mode, the feedrate commanded is a master setting of top
power as well as speed by virtue of end resultant speed. What I do is a test run in air,
note the speed actually reached, and command that as the max feedrate.
In this way it does hit 100%.

  Trouble is, it may only hit 100% in a straight away and less than that in any other area.
The laser meanwhile is adjusting for max power on a 0-100% scale on actual feedrate
divided into the max feed-rate commanded.

  Now, we also run into a problem of linearity, most lasers are not linear in power,
most specially at very low power. You can for example get 0% until a PWM of 15%
or even 40% on some lasers. They seem to vary widely in this, glass tube lasers
usually have this at a high number as the turn on point is a bit high.

  SO in the config ( from memory) is a dual setting, min power and max power pwm.
This should be set for the lowest power to be the point of turn on. The highest may be set
for a safety ( I recommend 95% or so) as the highest the laser will go to. It may be set to
100 for many lasers, but some co2's are recommended not to go beyond 27ma or so
, so the setting is there to restrict it to that 27ma , you'd need to know what pwm sets it to
27ma is all ( trial and error will often suffice.).

  If the low is set too low, the start of a line will go away as the laser wont turn on till it reaches
a pwm of the laser plasma start point. The high setting as I say, is simply a safety milli-amp limit
for your laser.

  This can be important in variable accel power because as it slows to zero speed, the power ramp
will reflect the minimum turn on power to be zero, not actual pwm of zero. SO make sure you play
with those adjustments and command a feedrate that you can actually reach, not a feedrate that's
unreachable.

  I noted last time I used this ( to cut out a vine in paper ) that it needs a bit of work, it works but
I found it hard to tune the power/feedrate curve. I plan this winter to add a better way of calibrating
the power/speed curves so one can more easily find the sweet spot for a cut. My thought is that it'd
be better to allow a user to set a speed curve designed for that cut or machine.

  Because this can be hard to tune, there is a button on the laser panel to turn off this speed
correction. Its labeled "DistCor" and will turn off the acceleration checking. This will give you selected
power whenever it moves. This , of course, leads to burning in corners and slow area's just like my co2 laser
does when run from its firmware instead of Auggie.

  Most co2 laser engravers take care of this with speed, they try to do a constant speed as much as they can
and allow for burning too much on corners and slow areas. As they have low mass heads they can do a pretty
good job of constant speed most of the time. My laser is high mass, I have to use anti-jerk control
for smoothness and this is why distcor exists.  I have to use acceleration and jerk limiting, and this makes
full power lasing on vectors difficult. When tuned in by selecting proper feed and such the vectors seem to
work fine.

  So turn off DistCor and you should get full selected power during any ms of motion, kinda like Mach3's on/off
P commands without having to enter them. You can also slide the laser power slider even during a run for
fine correction.

  Lastly, the accel/jerk limits play a part as they control just how slow youll have to go in corners. If you adjust
Jerk Limits upwards, you make it faster on the curves, this is a hard one to tune, some may have jerk set to 5000,
I set mine quite frequently to 500,000 depending on what type of work Im doing on it.  It takes some experimenting
during a vector run to find your best jerk setting if your using DistCor to smooth out power.

  So this winter Ill be looking into better ways to smooth this out, perhaps with user settable speed/power curves
for better control of end power in various situations.  YaNvrNo is my main laser tester, and we both noticed that
vectors take some tuning to do and speed curves we discussed as a way of getting a better result.

  So, lots to play with there, turn off DistCor though and a vector cut is much easier and works more like the
normal engraver does and should mimic M3's P modes for on/off.

Yell if you dont have a DistCor button, Im pretty sure I put it in the release, its on my panel..


Let me know how you make out,

Art




 

 

 

 
 

Hi Art,

Many thanks for the extremely detailed explanation. I had spotted the Distance Correction button but had no idea of it?s purpose or function. Once you mention it then it is obvious that I could not get anywhere near to the 6000 set feed-rate thus the reduced PWM ? it all makes sense now ? thanks again.

I am just loving the ?AUGS? button and Auggie?s variable PWM laser power control together with the ?S curve? Accel / Decel and motion from the 57CNC. My machine is loving it as well ? much quieter and smoother in operation which is certainly kind to all the mechanicals.  My 8 bit photo reproduction is going to be heading to new levels  ;D

Tweakie.

Hi, Tweakie!

Is this with the same Tweakie CNC/laser I had the privilege of visiting some years back?  Pictures?

Kirk

Hi Kirk,

Yes indeed sir, it's the same machine although there have been a few changes and additions. The machine is mainly used for rotary engraving and the laser was just added as an extra but it works as a multi-purpose machine. Check out the pictures etc. on my website for the deja-vu 

Tweakie.

Sweet image.

  Glad your having fun with it and its running well for you. Auggies 6th order motion
should make almost any machine happy mechanically, the heavier it is, the happier
it will be. I havent found the planner to be quite perfect, it seems to labour under
some types of code, though I do find tuning the Jerk clears it up normally.

  Small segment code is probably the worst torture for this type of planner, unlike Mach3,
Auggie has to create a continuous start to stop segment before it starts to move, it
updates the complete line from current position to new positions as they are added
and figures out the jerk and motion waveform again from start to end to make sure
added moves that allow higher speeds due to distance can increase that speed.

  This means in short line code the entire future motion profile may be recalculated
hundreds of times per second as the lines are added and depending on speed
through that motion. The Jerk calculations are a huge part of this, and can tax a
system, so if you find it stuttering or anything, increase the Jerk, youll find that
usually smooths it out, its a balance that can be hard to find that works for all code.

  One other note, the Aug button can create both 2d and 3d laser engravings, the 3d is
made by using a grey scale depth image, (they can be created by saving a grey scale
image of an STL display). Nothing the Aug button does actually changes Auggies
operation, it does all the things it needs to do in the GCode file, so by looking
at the weird additions to your GCode you can get an idea of how the Aug button
works, and how you can do the same things in your own GCode. GCode commands
are available to load binary image data , vary power for it, adjust the power in
stages related to depth for multi-pass 3d work, and to reset the variables that
control such things. Its kinda like Mach3's P words for laser power on/off,
but on steroids. Take note that for engravings the Gcode is loading a data file
that is the same name as the Gcode file. The data file is just a binary format of
a normal grey scale image.

  If you need to shut down a long image run, pause it at the end or start of a line.
Auggie will reload and get you setup to the right spot when you restart with a continue
button press after restarting the program the next day.

Just a couple notes to consider as you learn the program. 

Art

Thanks to YNN for posting the depth map image on his website - I had to give it a try.

Tweakie.

, I have a few of those hanging about..

This is to Certify that ___TWEAKY___ has
achieved the required prerequisites and is hereby
granted a Baccalaureate degree in Auggie CNC
from the University of Gearotic. May God have
mercy  on his soul.


Congrats..
Art