Re: Geckodrive

There's other exciting stuff that falls out using this method (step
motor, encoder and G100):

Let's say you are doing point-to-point X,Y positioning; maybe you are
drilling holes in a printed circuit board. There are a lot of holes
to drill and time is money so you want to go as fast as you can.

If the axis are servoed to the lead/lag stall angles then the axis
determine their own rate of acceleration and maximum speed. Both will
be the maximum possible given the loads on the motors. Also, the axis
dynamically adapt themselves to changing loads. Change load inertia
and acceleration automatically adjusts, change fritional load and
maximum speed automatically adjusts.

The through-put will be far higher compared to set
acceleration/velocity systems. My unloaded test motor accelerates
from zero to 3,000 RPM in 180 degrees of shaft rotation.

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, art <fenerty@...> wrote:
>
> Hi Chris:
>
> >>> Perhaps I don't understand it based on what you are calling
it. But
> > as far as I know, every motor of every kind can be stalled with
> > enough load on it.
>
> A matter of definition. It is stallable, if the pliers are held
very
> tightly the motor "stalls.", however, it can be called unstallable,
because
> it really isnt stalled at all, the hardware at that point is
calling for no
> movement. (You cant stall a motor that isnt moving..). In actual
fact the
> motor is holding itself at the maximum magnetic moment it can
achieve
> without "clicking" into the next position at which it will lose
position.
>
> The Lead/Lag register in the G100 can measure up to 7 counts off
target.
> So imagine your moving at speed, the lead/lag is zero indicating
the motor
> is not going too fast, nor too slow, the necode agrees 100% with
position.
> SO a person puts their hand out and pushes against the axis's
movement. The
> Lag register at that point counts up to one, indicating that the
encoder is
> now one pulse behind. So the axis output stage , slows slightly to
see if
> the motor then catches up. This catchup is likely because the
torque of the
> motor has just increased a bit due to going slower. This is
additive in
> nature, the more you push, the more the output slows down and the
higher the
> motors torque. The trick here is speed. If the G100 can quickly
enough
> monitor (on a step by step basis) the lead/lag, then it can reduce
the
> ourtput speed quickly anough to produce an output speed correction
that is
> smooth enough to allow the motors torque curve to compensate in a
curve that
> assures fast enough correction time. This produces, for all intents
and
> purposes, an unstallable motor.
>
> It is planned, very shortly, for MachIV to start experimentally
using
> the lead-lag to have "Stall prevention" , since it cannot deal fast
enough
> as a program to produce the unstallable motor, a hardware feature,
I was
> thinking even under normal software control, you can have Lag
determined
> speed vectors. SO as the program sees up to 4 times a secnd the lag
> registers, it should be possible during cutting to adjust the
feedrate to
> ensure the lag stays as close to zero as possible, in the odd event
a person
> has programmed a feedrate too high, or is hitting denser material
in wood
> and such. This "slow adjustment" has a possibility fo allowing for
a small
> correction in feed values in what I would call "Stall prevention"
on the
> application side. Not near as good a solution as Mariss's , but it
may allow
> one addition level of tool bit load smoothing. It'll be an
interesting
> experiment anyway. Im adding in the Lag registers use soon, cuz I
did want
> to play a little bit in that regard.. The functions of the MachIV
trajectory
> planner allow me some flexability n that area to apply corrections
in
> feedraet at intervals of 64ms or so feedrate variations.. A lower
term
> solution than an unstallable stepper, but one that also bears
examination, a
> corralary to a spindle load sensor of sorts..In fact , my plan was
to simply
> use it on the spindle output frequency, and see how it may work on
axis
> movement after that. In other words I intend to use "Lead/Lag" to
regulate
> the load on the spindle
> output.. Im just waiting for the Spindle partition to be ready..
>
>
> Thanks,
> Art
> www.artofcnc.ca
>
> Videos And Support Forums http://www.machsupport.com
> Users Map: http://www.frappr.com/machsupport
> ----- Original Message -----
> From: "lcdpublishing" <lcdpublishing@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Saturday, April 29, 2006 8:34 AM
> Subject: [CAD_CAM_EDM_DRO] Re: Geckodrive
>
>
> > Perhaps I don't understand it based on what you are calling it.
But
> > as far as I know, every motor of every kind can be stalled with
> > enough load on it. So, is it "Unstallable" in the sense the motor
> > cannot be stopped?
> >
> > Or is it just closing the loop?
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> > <mariss92705@> wrote:
> >>
> >> Sorry for the cross posting but it's been a stellar day here.
This
> >> has to do with the "Unstallable Step Motor Project" that may be
of
> >> interest to some:
> >> -----------------------------
> >> Hi,
> >>
> >> The very crux of the G100 project is to have PID servoed step
> > motors
> >> that cannot be stalled under load. The G100 hardware was designed
> > with
> >> this goal in mind; that is why it has 6 encoder input channels,
one
> >> for
> >> each axis. I have recently made/found the time to work towards
this
> >> goal.
> >>
> >> Before anyone asks "When will it be done?", don't. It will be
done
> >> when
> >> it's done. A lot of steps, work and time stands between what has
> > been
> >> recently accomplished and a finished product.
> >>
> >> The goal: Imagine you are doing 3-D contouring (X,Y,Z) when
someone
> >> decides to sit on your gantry. An ordinary open-loop stepper or
> > servo
> >> motor would stall/fault-out and that would be that.
> >>
> >> Now imagine the overloaded X-axis servo-stepper would just slow
> > down
> >> under this load. The other axis (Y,Z) would slow down as well,
> > keeping
> >> their speed ratios with the overburdened X-axis. The 3-D
contouring
> >> path would be strictly maintained albeit at a much reduced speed.
> > Once
> >> your friend got off of the gantry, speed would pick up to where
it
> > was
> >> before. Your work would not be ruined.
> >>
> >> How would this be done? Your step motors would be mounted with
> >> encoders. The G100 would sense 1 or more motors are about to
stall
> >> (develop a phase lag of 1.8 degrees). The G100 would slow them
down
> >> and
> >> back up the speed-torque curve to where more "grunt" (torque) was
> >> available.
> >>
> >> Steppers have the unique characteristic of having a speed-torque
> > curve
> >> where the slower you go, the more torque that is available. Can't
> > do
> >> that with a regular servomotor.
> >>
> >> OK. That's the goal; that's the picture in my mind. Here's what
has
> >> been done by today:
> >>
> >> I have a G100 driving a G201 running a step motor at 3,000 RPM
> > (NEMA
> >> 23, 3A/phase, 24VDC). Open-loop, you so much as look at it and it
> > will
> >> stall. A flea landing on the shaft would stall it open-loop. I
> > take a
> >> pair of pliers and clamp down on a wet paper towel folded over
the
> >> motor shaft and all I get is steam. The motor will not stall. It
> > slows
> >> down under load but it delivers 50W to the paper towel/pliers
> > combo to
> >> make said steam. It goes all the way down to zero RPM without
> > losing
> >> position.
> >>
> >> I ease up on the pliers and the motor is back up to 3,000 RPM
> >> lickedly-
> >> split, gives a chance for the boiling-hot paper towel to cool
off.
> > Not
> >> a step has been lost; you just can't kill the motor (stall it).
> >>
> >> This is just the first step (though a very important one) to
> > integrate
> >> the unstallable feature into a working CNC firmware. There are
many
> >> problems this feature presents.
> >>
> >> Just right now, having it do what it does, has me totally stoked.
> > It,s
> >> so cool, jerk down on the pliers, motor slows down. Instruments
say
> >> it's delivering 95%+ of all it has to give at all speeds. Let up
> > and
> >> bing-boom-bam, 3,000 RPM again. Just can't kill it no matter
what I
> >> do;
> >> very fine Friday nite indeed.
> >>
> >> Before you ask #2: Yes, it will traslate into all step motors of
> > all
> >> sizes at all supply voltages at all speeds.
> >>
> >> Mariss
> >>
> >
> >
> >
> >
> >
> >
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