Re: Torsion Test Results

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:

>
>
> Mariss Freimanis wrote:
>
> > Hi,
> >
> > Ok, as promised, here's the results of my tests.
> >
> > The short answer is there is no significant difference which end

of

> > the leadscrew the encoder is on.
>
> > The leadscrew simply did not twist enough to make any difference.
> > Pulsed torque 275 oz-in, 3/8" leadscrew, 30" travel.
>
> Fascinating! I'm amazed that you didn't see much twist under
> this setup. Now, one question - did you have a load on that
> leadscrew? (The significant difference between this test and the
> earlier one you reported was the big, heavy wrench on the end
> of the bar, which dramatically enhances the effect. The tiny

rotational

> inertia of the encoder doesn't compare.)
>
> Jon

Hi,

Actually the load was 15lbs of lead. Inertially this was equivalent
to 375 lb load on a 5-pitch screw and 1,500 lbs on a 10-pitch screw.
The leadscrew is 1 turn per inch.

The motor was caused to move the slide back and forth over a 4"
distance. Torque applied was accelerating and decelerating this load.
Peak acceleration was 7G (107 lbs of thrust @ 275 oz-in, 21A motor
current). Torque was measured indirectly using a DC current probe.

This figure will need revision to remove the inertial contribution of
the leadscrew and motor armature, however it should be small when one
compares the motor's moment of inertia against that of the load.

1,000 line encoders were placed at both ends, one on the back of the
motor, the other at the far end of the leadscrew. A phase meter read
both encoders to measure torsion dynamically.

The motor encoder was used to establish a baseline. Then the encoder
cable was plugged into the far encoder.

The load was oscillated first near the motor end, then at the far end
where maximum torsion would occur, and the results compared against
the baseline data.

The first observation was the loop remained stable and the position
error node response was unremarkable compared to the baseline.

The phase meter results were difficult to interpret for the torsional
component. Cyclic errors and residual switching ripple (after 4th
order low-pass filtering) contributed the majority of the output. The
torsional component was visible but difficult to quantify beyond
saying it was less than +/- 1 count.

Mariss