> >> 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. > > > > > It will not detect a following error if the failed encoder > is on an axis that does not have any motion commanded at > that time. This may not cause a catastrophic runaway on > some systems like Mesa and Pico Systems analog velocity > controlled servos with tachometers, but a slow creep toward > the limits. Some other systems might have an integrator > that will just keep winding up without feedback. > > Old Allen-Bradley controls generated an absolute velocity > analog signal from the encoder, and compared that to the > absolute value of the tach signal. If the tach came out 20% > above the encoder-derived value, it caused an E-stop.
20% is used before for other reasons. For a velocity output compared with encoder feedback it should work. With some averaging of course. > This > was in the days of incandescent lamps in the encoders, so > these errors did occur. They also used 4-sensor encoders, > where they had a separate optical sensor for the A and the > A-not signals. (Same for B and B-not.) These 4 signals > went to Xor gates that made sure the A and A-not and B and > B-not were complementary. If A and A-not were equal for > more than a few us, that caused an E-stop. This detected a > failed lamp. I guess this signal both equal also could work for other cases like connector problem but these signals are usually not available in linuxcnc so it is not possible to care about them at this level. > Jon 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
