Re: Geckodrive

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.
>