Re: [CAD_CAM_EDM_DRO] Re: Helical Couplings

Backlash is not the same as torsional windup. Any coupling between the
motor and the inertia with too low torsional stiffness can be modeled as a
3rd or 4th order linear dynamic equation. The solution to the control
equation is to accepted lower performance, lower accelerations, and
sometimes lower accuracy. Backlash is not a linear problem and cannot be
resolved using typical control theory (PID or standard state space).

All of the above is just a bunch of technobabble. The only important thing
to keep in mind is that the backlash problem is LOTS different than a
springy transmission with no slop. Both issues are serious problems for
control, and both are best resolved mechanically.

BTW: helical couplings can create the springy transmission problem, not the
backlash problem. In order to reduce the problem, both shafts mounted in a
helical coupling need to be very stiff against both lateral and thrust
forces. Most motor bearings expect lateral forces and are not fitted with
thrust bearings.

G. Jackson


At 11:50 AM 2/18/01 -0700, you wrote:

>By that reckoning...technically speaking...there's no such thing as a zero
>backlash coupling. If you apply enough torque even a solid bar will twist.
>You can even deform (or break) the bar by this method. I've done in many
>times.
>
>Smoke
>
>
>>But you need to watch out for the windup. If the coupling is not stiff