Re: Geckodrive

Yes, I guess it would help during acceleration; it would servo to a
fixed following error then.

Mariss

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

>
> Mariss,
> I rarely disagree with you but there is a big benefit to servo
> systems. Servo systems are torque sensitive during acceleration. If
> I load a 1,000-lb. part on a Bridgeport style machine my preset
> acceleration curve is shot. With an unloaded table I might be able
> (on a good day, with a following wind) do .1 G acceleration on

rapid

> positioning moves. Doubling my table load and maintaining the same
> servo torque probably halves the possible acceleration. Without
> the "unstoppable" I would have to de-tune my system to .05 G to
> always be safe. I don't want to do that, "time is money" and
> acceleration affects the rounding of corners on parts in constant
> velocity mode.
>
> If my G320's fault it is on acceleration, not cutting.
>
> Roger
>
> > Well, it's a motor physics thing. Unlike steppers, servomotors
> have a
> > torque limit independent of speed. Nothing is gained by slowing
> the
> > motor down; if the continuous rated torque 250 in-oz, it's the
> same
> > at 3,000 RPM and at 1 RPM. The only benefit would be if the work-
> load
> > decreases with speed.
> >
> > In a word, if the G100 can monitor the servomotor encoder, it can
> > adaptively slow the servo down if the following error exceeds a
> set
> > threshold.
> >
> > If the overload torque is speed independent (lifting a weight
> against
> > gravity), then the consequence would be a speed reduction to zero
> or
> > reversed direction motion.
> >
> > An apt analogy with which to view step motors is to imagine a
> > constant-speed motor attached to an infinitely-variable gearbox.
> The
> > step pulse frequency modifies the gearbox reduction ratio; double
> the
> > ratio and you get half the speed at twice the torque, etc.
> >
> > You don't get that with servomotors.
> >
> > Finally, give the poor step motor a break.:-) It too is a mighty
> > servomotor deserving of respect when run closed-loop. What is

your

> > servomotor outside a closed-loop? Just an ordinary AC or DC
> utility
> > motor.
> >
> > Mariss
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
> > <polaraligned@> wrote:
> > >
> > > So Mariss, Is your G100 going to have an advantage using it
> > > with a servo system? or is it primarily going to be for
> > > use with steppers. There are a lot of servo guys out there
> > > that need the G100 advantage in there servo systems.
> > > What can a G100 do for a servo system?
> > >
> > > Scott
> > >
> > >
> > >
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> > > <mariss92705@> wrote:
> > > >
> > > > A truly unstallable motor would have to deliver infinite
> power.:-)
> > > >
> > > > I call this "the unstallable step motor project" because of
> its
> > > > practical implications. An open-loop step motor has only two
> > options,
> > > > run or stall. If stalls while work is being done then more
> likely
> > > > than not that work will be ruined.
> > > >
> > > > This is also true for ordinary servo drives. If overloaded,
> they
> > > > develop a following error; if the following error is large
> > enough,
> > > > the drive faults-out and the motor stops. Same result.
> > > >
> > > > The "unstallable" step motor will just slow down when
> overloaded.
> > The
> > > > G100 will slow the other axis motors down by the same ratio
> and
> > your
> > > > work will be unaffected. You may not even notice it until
> after
> > you
> > > > oil your machine.:-)
> > > >
> > > > By this definition the motor is "unstallable" in practical
> terms.
> > > >
> > > >
> > > > Mariss
> > > >
> > > >
> > > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler"
> <eexgs@>
> > > > wrote:
> > > > >
> > > > >
> > > > > It seems there is some confusion because it is not
> unstallable
> > > > because
> > > > > the system can beat any load and carry on regardless rather
> it
> > rolls
> > > > > with the punches. If something loads the motor such that
> it
> > cannot
> > > > > carry on at its current speed it slows to get some more
> > torque. At
> > > > > the limit I guess it will stop but it won't be trying to go
> > anywhere
> > > > > either!
> > > > >
> > > > > I suppose you could say the definition of a stall is for a
> > motor to
> > > > be
> > > > > trying to move when it can't. The unstallable drive knows
> when
> > it
> > > > > needs to slow down to keep moving and ultimately when to
> give
> > up :)
> > > > >
> > > > > Jack, the resonant type stall dues to the mid band stuff it
> not
> > the
> > > > > kind of stalling that is being refered to as far as I can
> > tell. I
> > > > > also beleive that the geckodrives deal with the mid band
> > resonances
> > > > > already.
> > > > >
> > > > > Graham
> > > > >
> > > >
> > >
> >
>