On Fri, 2012-12-07 at 10:35 -0500, Kent A. Reed wrote:
> On 12/7/2012 9:36 AM, Steve Stallings wrote:
> > The paper being referenced can be found here:
> >
> > http://www.nist.gov/manuscript-publication-search.cfm?pub_id=824455
> >
> > In the data cited in this paper the motor speed was 15 revolutions
> > per second (900 RPM) with the motor running in half step mode. This
> > required 6000 steps per second or a 166.66 microsecond step period.
> > The stated jitter for the results of less than 10% torque loss
> > (actually 7.6%) was 3.6 microseconds. This is a jitter of 2.16%,
> > so the loss of torque in percent is approximately 3.5 times the
> > percentage of jitter timing. I have not checked out the derivation
> > of the formulas in the paper, so I will use this as a rule for
> > rough approximation.
>
> And the analysis in the P&S paper was a rough approximation as well. It
> is based on assumptions equivalent to the small-angle assumption in the
> analysis of motion of a pendulum.
>
> Qualitatively, one would expect from the analysis that large jitter
> should lead to missed steps and drop-out. Quantitatively, the
> assumptions of the analysis break down for large values of jitter so one
> can't easily calculate an upper limit.
>
> When I've searched the Internet looking for quantified wisdom I come up
> with precious little. I've had hits on posts by (no surprise) Jon,
> Steve, Mariss Freimanis from way back, but the points made are usually
> very brief and very qualitative. The P&S paper is the only analysis my
> search engines return. I wouldn't be surprised if there are moldering
> master's theses and proprietary reports that aren't being found.
>
> I for one would like to see some documented experiments. I can easily
> rig up a one-motor bench test but I don't have the measurement equipment
> I'd want at my side.
>
> > The motor in the NIST test case was run at a speed that allowed the
> > motor to produce 50% of its holding torque. This is a reasonable value
> > for industrial use. I only wish we could get most users of LinuxCNC
> > and Mach3 to accept such assumptions when setting up their machines.
>
> Yep. We're like farmers-"some is good, more is better."
>
> Regards,
> Kent
>
Actually, maybe some place between the "some is good, more is better"
and the sign behind my wife's desk.
I want it all
I want it now
and
I want it delivered!
:-)
Dave
>
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