On Sun, 2011-06-05 at 09:03 -0700, Peter C. Wallace wrote: > On Sun, 5 Jun 2011, dave wrote: > > > Date: Sun, 05 Jun 2011 07:58:52 -0700 > > From: dave <[email protected]> > > Reply-To: "Enhanced Machine Controller (EMC)" > > <[email protected]> > > To: "Enhanced Machine Controller (EMC)" <[email protected]> > > Subject: [Emc-users] synthetic tach > > > > Hi all, > > IRC seems pretty dead this morning so I'll try here. > > > > I seem to remember cradek doing a velocity to dac signal to emulate a > > tach. However I cannot seem to find documentation. > > Board is a 5I20 running hm2 so the velocity signal should be there. > > I just need the hal commands to get started. > > > > I've been using a Keling 750 W servo motor with a 2:1 and a 10 mm pitch > > ballscrew to drive the Z on my Cinci contourmaster. In torque mode I > > have stability problems; I finally ended up getting the following error > > down to about .002 ... pretty bad .. and that is after about 8 hours of > > tuning! This is usable for some things but doesn't do well for > > contours. > > > > Plan 1. go to velocity mode and add a tach. The tach is low output. > > only about 2.5 V/1000 rpm. For some reason I can't get the system > > stable. When enabled it oscillates for a few seconds and faults. > > That is with the analog input at zero (shorted). > > I've moved the tach gain all over the place with no luck so far. > > > > > > Plan 2. add the synthetic tach as per cradek. > > > > Plan 3. install a SEM servo motor with a known tach output. > > The X axis of this machine already has an SEM so I know it will > > work. :-) > > > > I'm open to ideas and opinions. > > > > Dave > > > > Torque mode often requires higher loop bandwidth (as EMCs PID loop now > controls the higher bandwidth velocity portion of the control loop). Have you > tried speeding up your servo thread (to 2 or 4 KHz perhaps). A 1 KHz servo > loop rate with first order hold has about a 300 Hz bandwidth. This may not be > high enough to get the desired loop gain with enough phase margin to make it > stable. > > Also, I assume you aren't tuning a bare motor, this is nearly impossible in > torque mode...
Motor is coupled to the load thru a 2:1 reduction to a 10 mm pitch ballscrew driving a rather light load relative to the power ( 750 w). Mass is about the same as a Bridgeport I spindle arrangement. I certainly can try the faster servo loop. That is probably less pain than having to change the whole mechanical arrangement. The servo amp has a freq response of about 2 - 2.5 KHz. I'll see how much I can push the servo rate. :-) Tnx. Dave > > > > > > > > > > ------------------------------------------------------------------------------ > > Simplify data backup and recovery for your virtual environment with vRanger. > > Installation's a snap, and flexible recovery options mean your data is safe, > > secure and there when you need it. Discover what all the cheering's about. > > Get your free trial download today. > > http://p.sf.net/sfu/quest-dev2dev2 > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > 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. > > > ------------------------------------------------------------------------------ > Simplify data backup and recovery for your virtual environment with vRanger. > Installation's a snap, and flexible recovery options mean your data is safe, > secure and there when you need it. Discover what all the cheering's about. > Get your free trial download today. > http://p.sf.net/sfu/quest-dev2dev2 > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Simplify data backup and recovery for your virtual environment with vRanger. Installation's a snap, and flexible recovery options mean your data is safe, secure and there when you need it. Discover what all the cheering's about. Get your free trial download today. http://p.sf.net/sfu/quest-dev2dev2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
