> 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 > Hi Jon, Everything you say is correct. In a pure open loop system I also agree with Mariss that micro-stepping is really more about dealing with resonance issues rather than positioning. Where things have changed is the with the capabilities of the high speed DSP processors to monitor phase current and encoder position.
The TXM24C-1G (Size 23, 117 oz-in) with a 28V supply I have running on my bench is amazing to watch. And like a servo it needs a certain amount of tuning of the PI variables in order to make it work right. I'm using it in a constant velocity mode with CANOpen control so I can't compare to the step/dir versions. But with a 5000 line encoder built in there is no doubt they are doing some pretty special software especially since they claim quadrature performance of 20,000 lines per rev. The reason my client is looking at this rather than a brushless servo is the length of the entire motor/encoder is less than the half the power DC servo. So a 60 oz-in motor w/o encoder won't fit. A 120 oz-in step/servo does. The motor is rated up to 3600 RPM. And without anything on the 10mm shaft I've spun it up to 3600 RPM. And then almost burned my fingers trying to stop it spinning. And this puppy is expensive with the CANOpen interface. John Dammeyer ------------------------------------------------------------------------------ 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
