On 01/19/2016 10:24 AM, Peter C. Wallace wrote: > > 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. > > But, a stepper motor cannot be expected to move in nm units (or, if it was geared to that level, it would not be able to move at a perceptible rate). So, whatever the microstepping level permits, and whatever the magnetic-spring effects allow, is how small it can move at any time. Microstepping improves smoothness and avoids resonance problems by preventing square wave drive from pumping resonant energy into the rotor. Microstepping also increases resolution by a small amount. But, I am convinced Mariss Freimanis is correct that microstepping more than about 10:1 really provides no benefit. A stepper motor can be modeled as a mass (the rotor and external load) controlled by a spring (the magnetic force on the rotor). Changing the motor coil currents moves the point where the spring is pulling from. Thus, a stepper does NOT have some hard mechanical detents in it. Apply a torque, and the position of the rotor shifts. If you have encoder feedback, the PID system can send a slight shift in position to compensate for this. But, you really don't get a lot of control over it.
Jon ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
