On Tue, 19 Jan 2016, TJoseph Powderly wrote: > Date: Tue, 19 Jan 2016 07:45:02 -0800 > From: TJoseph Powderly <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: [Emc-users] very low speed motion > > i was reading the step/servo thread > ... this is related but OT > > clear me up on in this... > about very slow motion with steppers and servos > > assuming the minimum position change is .001mm > ( commanded step or feedback unit > so: a single step moves .001" > and any feedback has .001 resolution ) > > when the system gets a command to move another .001mm, > what happens when the velocity requested is .001mm per second? > > in a stepper system, does it go clunk and wait 999millisecss? > (or wait 999 then go clunk, or at 500mSec etc.)? > > in a servo system does it crawl towards the destination over the whole > second? > > do we see important differences if the velocity is reduced by say 10? > or increased by 10? > ( is the motion jerky? > and > does motion stay jerky till velocity and the machine frame dampen it) > > i think any sudden jerks are bad for machining and process control. > > any of the above? > > thx > TomP tjtr33 >
What I think happens in a step /dir system is this: Linuxcnc uses floating point numbers for positions and velocities and these vary in a stepwise manner at the the servo thread period. If you command a move with a .001 mm/sec velocity and a distance of .001 mm the position will be incremented by 10^-6 mm every 1 ms servo thread tic until it reaches .0005 mm (at 500 ms) at which point a step will be generated. Thats is the (nearly) continuous linuxcnc position command is quantized to the output device resolution at the last stage. The exact details may vary depending on the actual hardware/driver For example, the Mesa hardware stepgen has a 16 bit fractional step resolution so the actual quantization/rounding to the physical step level occurs in hardware. > > > ------------------------------------------------------------------------------ > Site24x7 APM Insight: Get Deep Visibility into Application Performance > APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month > Monitor end-to-end web transactions and take corrective actions now > Troubleshoot faster and improve end-user experience. Signup Now! > http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
