On Tuesday, September 20, 2011 03:45:13 PM craig did opine: > Although my education, long ago, was in physics, I do not really > understand the physics of electric motors. > > Are there reasons to limit the rate of change of acceleration? Every hear of E=MV2? The machine has a mass that must have its velocity changed when you accel or decel it, and the biggest (usually) piece of that mass, because of the 'gear' ratios involved, is the mass in the iron or steel in the motors armature + the mass of the (usually) direct driven screw and the couplings between them.
> for example: Are there reasons that one would not want to go from max > acceleration in one direction to max acceleration is the opposite > direction? > > If so under what circumstances? What kind of motors? A secondary effect when using steppers is that the base_period controls the percentage of the speed that changing the pulse speed by a multiple of the base_period, sounds infinitely variable at low speeds, but as you approach the high end of the range, that difference in the number of base_periods is a lot bigger speed step when the motor is doing 400 rpm than it is when it is doing 10 rpm. There must be sufficient power available for the motor to maintain synch with the steps AFTER it has moved the rest of the machine else its likely stalled very quickly. Stalls = wrecked parts & sometimes broken tooling. Don't ask me how I know. :-) So the accel/decel must take place at a rate the motor can stay within a degree or less of synchronized. This can be boosted by higher voltages from the motor psu, and I believe it is fairly common to use 20 to 40x the nameplate ratings, with the current controls in the drivers to control the actual maximum current, in this manner the inductance of the motor is overcome faster. One can only drive them as fast as the inductance of the motor coils vs the applied voltage allows the rated current to be achieved. Hopefully I haven't screwed this up too badly... > Craig > > On 9/20/2011 6:56 AM, Dave wrote: > > I would think that this would be very hard to implement successfully. > > You are talking about optimizing the acceleration settings to a > > particular motor/drive/load setup. > > > > I can only see this being of a benefit if you were running a fixed > > part with the same cutter over and over again with a undersized or > > poorly sized drive system. If you changed materials or cutters or > > the carriage mass you might have to > > retune everything. > > > > The norm is to make sure that you are not operating your motors that > > close to the edge of their torque curve. > > > > A machine with accels tightly fitted to the motor/drive/load would be > > very unforgiving. > > > > Servos can operate beyond their ratings for short periods of time > > which sometimes makes them more forgiving, especially if you increase > > the the max following error allowed. > > > > Dave > > > > On 9/19/2011 4:02 PM, Andrew wrote: > >> Thinking about decreasing stepper (and servo, to some extent) torque > >> at higher speeds, I just thought that having variable axis > >> acceleration would be perfect. I.e., the highest at lower speeds and > >> lower at higher speeds. Is that ever possible with EMC2? If no, is > >> it hard to implement? > >> > >> Andrew > >> --------------------------------------------------------------------- > >> --------- All the data continuously generated in your IT > >> infrastructure contains a definitive record of customers, > >> application performance, security threats, fraudulent activity and > >> more. Splunk takes this data and makes sense of it. Business sense. > >> IT sense. Common sense. > >> http://p.sf.net/sfu/splunk-d2dcopy1 > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > > ---------------------------------------------------------------------- > > -------- All the data continuously generated in your IT infrastructure > > contains a definitive record of customers, application performance, > > security threats, fraudulent activity and more. Splunk takes this > > data and makes sense of it. Business sense. IT sense. Common sense. > > http://p.sf.net/sfu/splunk-d2dcopy1 > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------ > ------ All the data continuously generated in your IT infrastructure > contains a definitive record of customers, application performance, > security threats, fraudulent activity and more. Splunk takes this data > and makes sense of it. Business sense. IT sense. Common sense. > http://p.sf.net/sfu/splunk-d2dcopy1 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. 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