On Tue, 13 Dec 2011, Tom Easterday wrote: > Date: Tue, 13 Dec 2011 13:06:31 -0500 > From: Tom Easterday <tom-...@bgp.nu> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: Re: [Emc-users] Encoders > > On Dec 13, 2011, at 12:52 PM, Peter C. Wallace wrote: >> On Tue, 13 Dec 2011, Tom Easterday wrote: >> >>> Date: Tue, 13 Dec 2011 11:45:41 -0500 >>> From: Tom Easterday <tom-...@bgp.nu> >>> Reply-To: "Enhanced Machine Controller (EMC)" >>> <emc-users@lists.sourceforge.net> >>> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> >>> Subject: Re: [Emc-users] Encoders >>> >>> Thanks for the info Jon. We are seeing a small (about 0.001) position error >>> just on initial acceleration and deceleration that we cannot account for. >>> It may be due to the encoder. Since this is mainly a plasma machine we will >>> probably live with it. If we need to do better we'll look at replacing the >>> encoders. We now know the string attached to our cheap encoder :-) -Tom >>> >> >> >> Have you tried using FF2 to tune out the lag/lead during accel/decel? >> > > Yes. Peter (working with me) spent a long time playing with FF2. We were > seeing large spikes at first and had FF2 set to 0.007 which helped to lower > it to .002-.003. We then realized we had the Granite Devices input filtering > (which introduces a delay and is documented as doing so) turned on. Turning > that off has allowed us to lower FF2 to 0.000105, not zero but getting there. > The remainder of the delay is now (possibly) coming from the encoder issue > Jon has pointed out. > >> (a jerk limited profile would also help) > > What'd you call me? :-) > > What is a jerk limited profile?
A cubic profile Currently EMC uses a trapezoidal (linear) velocity profile (so parabolic position profile) This means the acceleration profile is a step function. The beginning of this step is whats hard to tune around (as you have found) Jerk is the derivative of acceleration so is infinite with stepped acceleration (the current situation with EMC). By using a cubic profile where the acceleration is ramped (like velocity is now) starts and stops are much "gentler" and contain less high frequency components that make it hard to tune > > -Tom > > > ------------------------------------------------------------------------------ > Systems Optimization Self Assessment > Improve efficiency and utilization of IT resources. Drive out cost and > improve service delivery. Take 5 minutes to use this Systems Optimization > Self Assessment. http://www.accelacomm.com/jaw/sdnl/114/51450054/ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Systems Optimization Self Assessment Improve efficiency and utilization of IT resources. Drive out cost and improve service delivery. Take 5 minutes to use this Systems Optimization Self Assessment. http://www.accelacomm.com/jaw/sdnl/114/51450054/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
