Re: Geckodrive

So, then if the motor does stop rotating, call it what you will if
that isn't what a stall is, what is planned at that point, a fault
condition like on a servo system?




--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
<mariss92705@...> wrote:

>
> To "keep a motor turning no matter what" is clearly impossible; it
> requires infinite power from the motor. Nice mental picture

though.:-)

>
> Slowing down under load is a better option than the alternative;
> having the motor skip steps, desynchronize or fault-out. That is

the

> practical definition of "stalling".
>
> Mariss

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
> <lcdpublishing@> wrote:
> >
> > Mariss, this isn't making any sense, but I think it has to do

with

> > what you call a stall and what I call a stall.
> >
> > To me, a motor is stalled when it no longer rotates. Are you
> saying
> > that your GREX device will keep that motor moving no matter

what?

> >
> > Now unless you have magic powers, this isn't possible. Which

makes

> > me think that your interpretation of stall is different than

mine.

> >
> > Based on your description below, it appears as though the drive
> will
> > slow down the velocity in hopes that the greater torque at low
> speed
> > will overcome the load and allow the motor to rotate again.
> > However, at some point, there will be a load in excess of what

the

> > drive/motor can overcome - resulting in a stalled (Stopped)

motor.

> > Does the GREX then fault or what is planned for this condition?
> >
> > Thanks
> >
> > Chris
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> > <mariss92705@> wrote:
> > >
> > > No, the motor does not stall. It is prevented from doing that

by

> > > monitoring the lag angle and decelerating the rotating

magnetic

> > field
> > > to prevent it from getting more than 1.8 degrees ahead of the
> > rotor.
> > >
> > > The net effect is the motor slows down under heavy load. As it
> > does,
> > > more torque is available as speed drops until a "balance

point"

> is
> > > found where available torque equals load torque.
> > >
> > > Relieve the load torque and the motor accelerates until a new
> > balance
> > > point is found.
> > >
> > > The lead/lag angle register is analogous to the position error
> > summing
> > > node in a classic servo. A step pulse increments this

register,

> > the
> > > encoder count decrements it. The contents of this register is
> > input to
> > > a PID algorithm; the PID algorithm output then modifies the

step

> > pulse
> > > rate to keep the summing node at a desired constant value.
> > >
> > > The lead/lag register also is used to increase the
> > motor's "stiffness".
> > >
> > > An open-loop step motor has +/- 1.8 degrees of stiffness. In
> fact,
> > a
> > > step motor only delivers its rated holding torque when its

shaft

> > is
> > > displaced 1.8 degrees from its no-load position. The servoed
> > response
> > > is to "step into" the load, canceling this error. A 500-line
> > encoder
> > > gives a 10-fold increase in stiffness over an open-loop step
> motor.
> > >
> > >
> > > Mariss
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
> > > <lcdpublishing@> wrote:
> > > >
> > > > Okay, so the motor still stalls like any other stepper

system.

> > > > However, it tolerates the stall and provides feedback to the
> > > > controlling software which would allow for a recovery if in
> fact
> > the
> > > > problem causing the stall is self-correcting?
> > > >
> > > > It sounds neat, yet impossible at the same time. Either

way,

> it
> > > > sounds like it has the potential of allowing higher speed
> > performance
> > > > from stepper systems. Perhaps I should look at this as if

it

> > were in
> > > > an adaptive control system and it would make more sense.
> > > >
> > > > Sounds cool guys.
> > > >
> > >
> >
>