Re: Stall prevention/MachIV/Automated Setup

Used "as is" the lead/lag register gives a direct readout
of "percentage of available torque" being used. It is accurate from
zero speed on up.

Mariss


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "vrsculptor" <vrsculptor@...>
wrote:

>
> Art,
> If you can watch the lag register in the g100 you should be able to
> set axis acceleration and maximum rapid rates as part of a more
> automated setup. These maximums could then be de-rated by a
> percentage entered by you or the user. This would vastly simplify
> setup and may go a long way in reducing lost step reports.
>
> Roger
>
> > 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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