Man I need you to come over here to my shop and show me how to do it on my Cincinnati Arrow 500 LOL. I am not sure really what sort of motor it has but it has been working for some time now with my Hitachi wj200-110LF sensorless vector drive. Spindle orient is the only thing keeping me from a toolchange really. LOL
Pete On Monday, January 25, 2016, Stephen Dubovsky <smdubov...@gmail.com> wrote: > No mixup. I used to work for GE (and Hughes) designing AC induction drives > for mostly traction applications. You can servo **ANY** induction motor. > The only limit to frequency response is the inductance and that can be > solved with high enough bus voltage (DC motors and steppers have the exact > same problem.) There is ZERO residual magnetism needed to get an induction > motor to hold position (even at zero) during closed loop operation. > > Everyone has played w/ a DC motor w/ the rotor terminals shorted out. They > are darn near impossible to turn w/o a large lever. The DC rotor which has > zero power applied, when moved (even a little) through the stators magnetic > field, induces currents in the rotors shorted windings. Sound familiar?? > Apply DC current to an induction motor and it can produce the same magnetic > flux in the gap as the DC motors magnets do. The shorted rotor windings > thing? Yep, thats already taken care of as its how an induction machine > ALWAYS works. The result is the rotor is just as hard to turn as that of a > DC machine. Now neither of these machines hold the exact position open > loop so what do you do... > > Closed loop! Ok, now we put a shaft encoder on both machines. On a DC > servo, when you see the position error you apply voltage. Voltage = > current. Current = proportional to torque. You apply enough until the > resulting torque is enough to both stop the load and move it back to the > commanded position. Servoing it. W/ an AC induction motor, when you see > the position error you apply frequency (the voltage may already be present > just like in the paragraph above.) You can then command any torque at any > shaft speed within the motors torque/speed envelope - it just takes more > calculations;) So you "apply enough until the resulting torque is enough > to both stop the load and move it back to the commanded position." Exact > same result as a DC servo. > > Another way to think of it is look back at the shorted winding example of > the 2nd paragraph. To get the DC motor to hold position w/ shorted > windings, you could slowly move the stator magnets 'backwards' to conteract > the shaft torque and movement. Not too convenient since they are likely > glued in the frame. Bot that **EXACTLY** how an induction motor does it. > Its 'moving' the (virtual) stator magnets to apply torque to the shorted > rotor and hold it in place. > > Most folks who have never done advanced induction control are surprised to > find the torque vs slip curve is both 2 quadrant and symmetric. You can > indeed provide full torque, in either direction, at zero shaft speed (or > any non zero speed). Once you have a predictable way to respond to a force > command (from the PID loop) you can position servo any system. AC > induction, PMSM, DC, hydraulic, etc. doesn't matter. > > Bottom line is that you can servo an induction motor VERY well if you have > a VFD smart enough to do it. > > SMD > > > On Mon, Jan 25, 2016 at 11:09 AM, Dave Cole <linuxcncro...@gmail.com > <javascript:;>> wrote: > > > You are getting your motors mixed up. > > > > Typical AC induction motors suck for positioning. > > > > You are thinking of AC servo motors that use a magnetic rotor. > > They are a totally different animal. > > > > DC servos typically have wound armatures (and brushes) and use magnets > > for the field. > > > > > > ------------------------------------------------------------------------------ > 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 <javascript:;> > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Pete Matos A and N Precision and Fabrication Maryville, Tennessee 865-236-8996 ------------------------------------------------------------------------------ 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
