Re: Geckodrive

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
> > > >
> > >
> >
>