Re: [CAD_CAM_EDM_DRO] Lead screw twist... some musings

"Heuver, Brad (B.R.)" wrote:

> If the screw does twist from the torque required to drive the table,
> and the encoder is on the motor end, the table will now be out of position
> by the amount of the twist (times the pitch of the screw). Only when the
> load is removed, and the windup is taken back out of the system, will the
> table be in the position the controller thinks it is in.
> If the encoder is mounted on the end of the shaft opposite the
> motor, (the end that is not twisted), it will more accurately measure the
> actual position of the table, as the lead screw will not be under load from
> the ball nut to the encoder. I understand the potential for resonances, and
> other nasties with this system, but doesn't it have the inherent advantage
> of more accurately telling the control where the table is under a heavily
> loaded cut?

Accuracy is of no use in an inherently unstable system. As soon as the
phase of the response is more than 180 degrees out of phase with the
driving signal, massive oscillations will build up until either something
breaks or some overload limit is tripped.

Jon