On Mon, 1 Nov 2010, Jon Elson wrote: > Date: Mon, 01 Nov 2010 00:13:36 -0500 > From: Jon Elson <el...@pico-systems.com> > Reply-To: EMC developers <emc-developers@lists.sourceforge.net> > To: EMC developers <emc-developers@lists.sourceforge.net> > Subject: Re: [Emc-developers] pid with derivative inputs > > Well, after an AMAZING amount of fooling around with barely one page of > code, I finally > have MOST of the velocity estimation working in the ppmc driver. I'm > still not sure it is right, though. > > One quirk, which I think is inherent in the way that HAL component > encoder.c works, > and which I copied, > is that a dithering encoder gets the wrong velocity. The first count of > the dither gets > the right velocity, as there was no movement for some time before. The > second count, > if immediately following the first one, cancels out the movement, but it > gets twice the > velocity, as these are seen as two counts in a short period of time. I > suppose you could look > back two servo periods, and if the position delta between now and n-2 is > zero, then velocity > should be zero in that case. > > Maybe I implemented the code wrong. Under some conditions it seems like > it might be an > improvement, but it is not as smooth as I had hoped for. Now, maybe the > problem is the > servo I am using for tuning is so jittery (as it does not yet use the > velocity info) that it creates > a lot of these dithery counts. > > Jon
One good sanity check on the velocity output is to setup your hardware step generator for quadrature mode and set a constant velocity but randomly changing directions(and ~infinite acceleration). Another good test is just a slow velocity ramp. The advantage is the the hardware doesnt have the quirks of a real encoder/motor. For example, quadrature phase error (signals not at exact 90 degrees) will limit the improvement that a simple, all edge time stamp can bring. > > ------------------------------------------------------------------------------ > Nokia and AT&T present the 2010 Calling All Innovators-North America contest > Create new apps & games for the Nokia N8 for consumers in U.S. and Canada > $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing > Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store > http://p.sf.net/sfu/nokia-dev2dev > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
