Stall prevention/MachIV/Automated Setup

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
> >>
> >
> >
> >
> >
> >
> >
> > Addresses:
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