It is good to hear about your experiences with the different ways to control the motor. I tend to overthink and make things more complicated than necessary sometimes. But just as a point of clarification, industrial servo drives typically have 3 loops in cascade for position control. The inner loop is regulating the current to the motor (which is in an ideal machine, proportional to the torque). the next loop is a velocity loop and in the past tachometers were used for feedback. In modern drives, if the position is sampled fast enough then its derivative can be used for velocity feedback. Finally there is the position loop. Since my professional background experience has been with these drives with the 3 cascaded loops, I was going down that path for what I was looking for, but now since a number of you have said the "torque mode" method work well I will pursue that route as it is a lot easier for me to do.
I think I am going to attempt to figure out what the parameters of my motor are and make a model to simulate my control loop. For hobby stuff I think LTspice may be good to model and simulate. Perhaps in the future I can update you on the result of my simulation and progress if my retrofit. Regards, John Figie On Wed, Nov 25, 2020 at 11:31 AM Les Newell <les.new...@fastmail.co.uk> wrote: > I have used both and personally prefer a single torque loop. My lathe > runs a 7i80 in torque mode. The router uses velocity mode analog Bosch > drives with tachos. The mill runs Yaskawa drives that were configured in > velocity but now I run in torque mode. > > It is easier to tune the outer loop in velocity mode however you then > also need to tune the inner loop (if that isn't already configured in > the drive). Additionally with velocity mode using analog control you > nearly always have dither. The machine will hunt between encoder counts. > With a single torque loop you can configure one encoder count of > deadband. Once the axis reaches position the motor just stops. > > On the mill I originally used velocity mode as that is what it used > before the retrofit. However the dither drove me mad. In the end I > switched to torque mode and achieved far lower following errors at speed > combined with zero dither. > > Velocity mode used to be pretty much essential on older controls as they > did not have a very fast servo loop. LinuxCNC's 1kHz loop is good enough > to run torque mode for nearly any normal machine. > > Les > > On 25/11/2020 13:48, Todd Zuercher wrote: > > I think I'll disagree with Andy a bit on this. While the minimum > following error I could achieve with a single torque vs dual loops in > Linuxcnc was about the same. The tuning was much easier, and I believe > that my drives are running much cooler (not working as hard dithering) > using the dual loops. It is a bit like comparing balancing a pencil on > end on your finger vs a broom handle, the longer one is much easier to > balance. > > > > > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
