> On 3/25/2016 5:29 PM, Nicklas Karlsson wrote: > >>>>> As someone mentioned before a the an axis/joint may/will run away > >>>>> in case of an encoder failure. > >>>>> > >>>>> It would be possible to detect an encoder failure by comparing > >>>>> output signal with encoder signal. A velocity signal may be > >>>>> integrated and do not allow to wander to much or an encoder error > >>>>> will be detected. A torque signal would be worse. > >>>> An encoder that fails into runaway (motion erroneously detected > >>>> when none is occurring) or that fails into stop (no motion detected > >>>> when motion *is* occurring) will both result in a following error, > >>>> precisely for the reason you say above: linuxcnc compares the > >>>> commanded position with the feedback position from the encoder. > >>>> > >>>> > >>>> -- Sebastian Kuzminsky > >>> No if no motion is detected and there is a small error linuxcnc will > >>> output a signal to correct it and machine start to move. Since no > >>> feedback is detected integrator will turn up speed and machine run > >>> away. > >> Are you describing a scenario where the signals from the encoder are not > >> getting to LinuxCNC? So it always looks to linuxcnc like there is no > >> motion happening, no matter what's actually happening in the motion > >> hardware? > >> > >> In that situation, if LinuxCNC is "at rest" and not commanding any > >> motion, it's true that any small PID output will be applied forever, > >> with no change in the feedback, and the motor will run away. > >> > >> And you're suggesting to look at the PID output, and if it's commanding > >> motion but the encoder is reporting no motion, then trigger some sort of > >> "hardware malfunction" estop? > >> > >> That sounds like it would work. > >> > >> > >> -- > >> Sebastian Kuzminsky > > Yes I am suggesting comparing the PID output and encoder input. > > > > > > Nicklas Karlsson > > > > I think that could only be a problem with torque mode servo drives. > If you are using velocity drives the most that can happen is that the > drives drift away. But even in those conditions > I always seem to get a following error that drops the enable to the > drives and shows a fault on the screen. > > Dave
Torque or velocity driver make no difference, without encoder it run away as soon it is touched form it's perfect position. Nicklas Karlsson ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785351&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
