On Thursday 11 April 2013 00:58:10 cogoman did opine: > On 04/10/2013 07:18 AM, Javier Ros wrote: > > Is apparently a stepper motor that is controlled as a brushless. > > Essentially a stepper is a brushless. This needs a encoder, probably > > one with a index pulse correctly positioned, > > so that the electronics can compute the switching accurately. > > > > This means, even if the control of the drive looks like a STEP DIR > > control, internally there are position and current loops, > > theoretically such a drive could offer, velocity and > > current control (I've not checked for the above reference). > > > > The only limitations seem to be related to control at hih rpms, > > performance degrades in comparison with brushless. I would say that > > this is related to the higher pole count of the steeper, > > If you were to design one of these from the ground up, since position > would be verified from a 10,000 step encoder, and the stepper would be > run as a type of servo motor, the stepper driver would function much > differently. It would generate commutation from the encoder, then it > would drive a current into one coil to draw the motor towards the > commanded position. PID would decide how hard to hit the motor by the > difference between commanded position and current encoder position. > Since this works like a servo and not a stepper with feedback, the > stepper motor could be designed with less steps per rev. less steps per > revolution would require less soil current reversals, and would allow > the motor to step faster. If a 1mH coil standard stepper could be driven > to 3000 RPM, one with 100 steps per rev instead of 200 could be driven > at 6000 RPM. One with 50 steps per rev could be driven at 12000 RPM. The > control circuit would have to do some tricky math to keep cogging to a > minimum, but it's likely possible to make a very fast but still accurate > stepper system this way. > Somebody thinking "outside the box", and making perfect sense. The only fly in the soup is the 10,000 step encoder, and servicing it at 200 rpS to get that 12,000 rpms, which would need to be able, if software, to do the whole control loop at a 2 megacycle rate. The best we've been able to do in software is less than 100 kilohertz at the relatively simple job of just issuing steps to the motor. These atom boards can do 50, but are hugely more comfortable running at about 47 kilohertz.
To do the whole control loop at 2 megahertz to get that 12,000 rpm would need dedicated hardware that could do this in much less than .5 microseconds. I won't say its impossible, but I don't believe we have the 'state of the art', nor do "we" represent a sufficient economic incentive to do that as a chip design. At least not in the next calendar year. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> divorce, n: A change of wife. A pen in the hand of this president is far more dangerous than a gun in the hands of 200 million law-abiding citizens. ------------------------------------------------------------------------------ Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
