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 ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
