andy pugh wrote: > Is there any reason LinuxCNC couldn't use tachometers and glass scales? > > If the tachos go direct to velocity-mode drives then LinuxCNC doesn't > even need to know about them. But there is no fundamental reason why > LinuxCNC can't run a separate velocity loop and position loop given > accurate-enough bipolar analogue inputs. The Mesa 7i87 has 12 bits of > resolution, I wonder if that would be enough? > Sure. The problem with backlash/spring between the motor and linear motion still stands. Tachs on the motor will help stabilize the hunting behavior.
I did some tests when I made my original analog servo amps. I wanted to see how slow it could go before motion started to break up into stick/slip. I got down to .01 IPM, where the tach voltage was calculated to be 7 micro-Volts! (I couldn't measure that.) I don't think a 12 bit ADC could handle that. I am using 16-bit DACs to sent the velocity command to the servo amps. But, the tach would need a dynamic range of nearly 1 million to one to cover the full range of velocities, not even a 16-bit ADC would suffice. The ADC resolution would set a minimum velocity that would be recognized. It would probably be better to derive velocity from a high-resolution encoder than trying to digitize a tach voltage. This is what Fanuc has been doing for almost 30 years, now. Jon Jon ------------------------------------------------------------------------------ Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
