Re: [CAD_CAM_EDM_DRO] How do you compare steppers to servos

Les Newell wrote:

>
>> A servo, if you put an arm on it, is probably less capable of holding an
>> exact position, as the encoder would sense motion and try to drive in
>> the opposite direction to correct it, but it would be confused as to how
>> MUCH to drive it.
>>
>
> Not really. The drive system knows that if the motor is only one encoder
> count out, it probably doesn't need to apply much torque to return to
> center, whereas if you are lots of encoder counts out then you need to
> apply more power. Integral helps overcome steady state loads.
>
>

Yes, exactly. The error (commanded position minus actual position) is
measured perhaps
a thousand times a second and the amount of effort to restore the
position to zero error
is sent to the drive. Increasing error commands increasing torque,
decreasing error commands
less torque. A properly tuned servo will strongly resist deflections
from commanded position,
and can be so stiff you'd think there's a brake on the motor. The
tuning of the servo control loop
is so that it WON'T be "confused", but will always apply a controlled
and optimum amount of
torque to resist any outside forces.

Jon