Re: [CAD_CAM_EDM_DRO] Re: stepper vs. servo

Hi Tony,

I have to disagree with this. Steppers aren't like mechanical ratchets,
they are springy. As a simple demonstration put a pointer on the pulley
of a stepper, power up the stepper and try to turn it by hand. It will
move slightly, long before you apply enough torque to make it jump a
step. This always happens when you apply a load to a stepper. It is a
known quantity so you design around it. When you design a servo based
system you have to decide what is an acceptable following error and then
set up the encoder resolution + gearing to suit.

Les

> It is worth remembering that with a servo system, if the motor is moving,
> it is doing so *because* there is a discrepancy between the current
> position and the position that it is required to be in. So with a servo
> system, the only time you know that there is no positional error is when
> the motor is stopped. As you increase the load that the motor has to shift
> (e.g., by increasing depth of cut), the size of any positional error will
> tend to increase.
>
> In contrast, with a stepper-based system, as long as the system doesn't
> lose steps (i.e., as long as the motors are sized correctly for the applied
> load), there is no change in the accuracy of the system as the load is
> increased.
>
>
> Regards,
> Tony
>