It works very much similar to running them with an analog input. The encoder feedback can also be handy for double checking the tuning of your servo drives.
You simply disconnect the position feedback from the stepgen and use the feedback from the encoders to connect to the PID and the joint position-fb. You will need to tune the feedback loop, P=1000 will no longer be valid, and will likely have to be significantly less (guess 1/2-2/3) Todd Zuercher P. Graham Dunn Inc. 630 Henry Street Dalton, Ohio 44618 Phone: (330)828-2105ext. 2031 -----Original Message----- From: andrew beck <[email protected]> Sent: Monday, February 10, 2020 4:46 PM To: Enhanced Machine Controller (EMC) <[email protected]> Subject: Re: [Emc-users] closing the loop in linuxcnc with a 7i76 mesa card and step direction control [EXTERNAL EMAIL] Be sure links are safe. Actually all I want to do is be able to home to index. Which I might be able to do now. As my servo can output a encoder Z pulse. And I want to have linuxcnc remember where it is if I disable the servos. That is now a massive deal but I get a bit sick of continously homing the machine every time I push the E stop in and disable power to servos. It would be nice to have the encoders still counting once the servos are disabled. ( drives would still be on just not running a PID loop.) And yes I was wondering what trying to run a PID loop on a position servo loop causes. Regards Andrew On Tue, Feb 11, 2020, 2:14 AM andy pugh <[email protected]> wrote: > On Mon, 10 Feb 2020 at 10:30, andrew beck <[email protected]> > wrote: > > On the back burner though I want to > "close the loop" back into linuxcnc with a 7i84 mesa card I think. > Has anyone done that before with a step direction control system? > > What do you anticipate gaining from bringing the encoders back to LinuxCNC? > > If this is a stepper system (it's not clear without inbox-mining) then > a PID will naturally attempt to run the motors faster, with the > reverse of the hoped-for result. > It is probably possible to simultaneously reduce the feed rate with > adaptve feed and then attempt to recover the lost steps, but I don't > know if anyone has tried that. > > If it is a step-servo system then the drives will already be doing all > that they can. You won't gain much from bringing the motor encoder > data in to LinuxCNC. > However, you might be able to gain accuracy by adding linear scales to > the system, and using the feedback from them to modify the motor > position commands. > > -- > atp > "A motorcycle is a bicycle with a pandemonium attachment and is > designed for the especial use of mechanical geniuses, daredevils and > lunatics." > — George Fitch, Atlanta Constitution Newspaper, 1912 > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
