One of the not so quiet revolutions taking place in the 3d printer
landscape over the last couple years is called input shaping, something
probably done best in the cards like Peter Wallace makes.
A simplified explanation is fitting an accelerometer to to tool head,
the exciting each axis it turn withe an audio sweep of a small
amplitude, sweeping from 10 Hz to about 250 Hz while measuring the
resulting movement with an adxl345 recording the data it outputs for
each of the axises tested. Since a 3d printer works in slices, the z
axis is generally much slower on the 3d printer, so is left out in some
versions.
This data is then run thru a forrier or butterfly transform to develop a
compensating acceleration curve that does not effect the overall speed,
but does reduce the fine detail or boost it, to essentially cancel the
machines natural vibrations. On a 3d printer, given enough heat to
supply the head with continuous hot plastic, the use of this
compensation has taken the 3d printer from 50 or 60mm/second maximum
speeds to 200 mm/second over the last 2 years. I can now buy a printer
with this built into its OS for under $1000.
There is one obstacle, most 3d printers do not have an interpreter that
knows about G2/G3 and its ilk, so most slicer's converts those to tiny
straight line moves that look like a circle in plastic.
This is done in the default interpreter, Marlin, but is done better by
klipper in the better printers but can be reflashed into 99% of the
controller cards out there just like we can do with Peters cards.
This interpreter runs on the controller cards, often stm32 based cards
that sell for, in the ones BTT makes for $59 for a low end octopus card,
which can drive up to 8 motors, 5 fans, 3 heaters and all our limit/home
switches and probing gizmo's. Some of these even include the G2/G3
stuffs. These cards are nearly all designed to handle nema-17 motors at
24 vols and maybe 3 amp max motors, but one line of the octopus family
of cards has a separate motor supply input that assumes 60 volt rated
drivers so even those tiny motors can be moved at amazing speeds.
Top that with signal stealing plugins that fit the driver socket of
these boards I'm rebuilding 2 bigger printers with nema-17 versions of
the closed loop servo/steppers with optical encoders that use drivers
like we use with linuxcnc, 2m542 sized stuff, but now rated for 90 volts
and up so they can be driven at unreal speeds w/o losing home. The PID
is in the driver, linuxcnc just tells them what to do and they do it.
And if they can't do it, they will tell linuxcnc, stopping it by linking
that signal into the F2 of linuxcnc. Doing the stop quick enough on my
Sheldon the I can position a chuck jaw in the way, and jog a carbide
chipped tool into that jaw at 20mm a second, it hits the jaw, the driver
shuts off the motor drive at the same time it tells linuxcnc to stop,
the release of the motor drive lets it spring back away from the jaw by
10 thou or so. The carbide chip is not damaged and the chuck jaw is not
marked. Tested many times, but has never occurred wile running a job on
either machine where I've put those motors. No PID's in the lathe
config, no PID's in the 6040 config. Its all in the much smarter
drivers. They use the PID error to control the motor current so if
conditions are low load, very little current or motor heating, but it it
hits something, it will use every amp the supply has to prevent a step
loss, so home is maintained under downright abusive conditions. In
short, they Just Work and work well. I'm so sold I have 3 more motors,
drivers, and higher voltage power supplies to convert the G0704's other
3 main axises to them, the A axis already is. With the PID's in the
drivers, there will only be one PID left in the G0704 when I'm done, in
the spindle circuit.
It is the "input shaper" thing I think could improve the finish linuxcnc
can do, effectively driving the machine to cancel its vibrations as it
changes speed and directions. Doing it at ridiculous speeds. And that
pays the bills in a for profit shop.
Something to investigate, for 3.1 maybe?
Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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