On Saturday, 16 April 2022 12:13:37 EDT Torsten Curdt via Emc-developers wrote: > > > I can see this to be super useful when there is an external encoder > > > - so linuxcnc is in full control. > > > But what's the benefit with e.g. Servos and Closed Loop Stepper > > > that have their internal encoder and control loop? > > > > Sending out position instead of velocity also work. > > You mean LinuxCNC can be set up to send either - but Mesa has chosen to > use velocity for their integration? > > > Use encoder sending position using external feed back loop for > > position, following error and display also work as usual. > > Could you expand on that? > > I assume with "external feedback loop" you mean the feedback loop of > the servo or CL stepper. > > But this feedback loop decouples the real position from the meant-to-be > position. (expressed in the following error) > And I don't see how the real position could be reported back to > LinuxCNC so it's still in full control of the movement. > ...unless you connect the encoder directly to the Mesa instead of the > Closed Loop Stepper driver. > > > > (Another crazy(?) thought I had was to have an acceleration sensor > > > as > > > incoming feedback. To help with servo parameterization.) > > > > Should help at least then there is elasticity in between motor and > > position feed back. > > Yes, there would be some lag for sure. > But this isn't possible right now, is it? > > Could this be added as a component? > Either to feed into the motion control loop - or just to monitor it? > > > ... > > > > > It feels like sending the velocity commands over ethernet also > > > means some kind of buffering, but I guess the 1kHz feedback loop > > > is the big> > > difference > > > > > here. > > > > NML is for the non real time stuff so no 1kHz feedback loop there. > > I thought Mesa is reporting back the position in a 1kHz feedback loop - > no? >
Yes, but while the huge majority of the stepper systems read the stepgen position as the feedback, this is only valid if the axis has been homed, there is a new tech that I consider an improvement. The usual two phase stepper has no way to notify linuxcnc of a lost step, and that can be and has been a problem. The even newer stepper/servo's, are 3 phase, and have an encoder on the rear of the motor that only feeds the the driver, AND they have a fault output wihich can be used to stop LCNC anytime the steps received by the driver have not been done because the tool has hit something and cannot reach the commanded position. I have 2 of those new 3 phase motors on that Sheldon now, and while its possible for noise to be interpreted as a step, it has not occured. I don't even use PID's, the motors are getting commands directly from motion. And doing EXACTLY what I tell it to do. The only errors are errors I introduced to test the fault stops. Like parking a carbide tool .010" from a chuck jaw and jogging it into the jaw, the chip hits the jaw, the fault triggers, which kills the motor psu's and the spring in the steel or iron bounces back to about .01" clear of the chuck jaw. Pull the tool off the post, re-enable motion, rehome the machine, put the tool back on the post and its ready to do it again. No damage to the carbide chip or the chuck. And I'm very pleased. They are very quiet, the whole machine doing a job is as quiet as it would be with casper the ghost turning the cranks. An advantage they ae not advertising (and should be) for the 3 phase family is the improved power efficiency, the error detected in the driver controls the motor current. 2 phase steppers need full or half power depending on moving or holding, so they can run burn your hand hot. These 3 phaser's run just barely warm at the end of an hours work. If the motor isn't working hard, they run at room temp. If I don't fall over and miss role call first, I'll replace all of my steppers with them in due time. Take care and stay well everybody. Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
