On 20 September 2011 16:01, craig <[email protected]> wrote: > 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?
Two different idea have been conflated here. Andrew was suggesting altering the motor max-acceleration as a function of motor speed to allow for the fact that steppers have less torque available to acceleration with the faster they are spinning. Bryce then brought in the subject of Jerk control, which is a different subject. To answer your question: as the acelleration changes sign, the reaction force on the machine frame changes direction. So the whole frame goes from being loaded to the left, to being loaded to the right, and will swing back-through the neutral position, and out the other side, then wobble back and forth for a while before settling to a new position. You can feel the same effect if you try standing on the Tube (or on a bus) as it comes to a halt. The acceleration as the train brakes to a halt instantaneously goes to zero as the speed hits zero. And all the passengers who are braced against the force stumble. You will find that when driving a car you unconciously feather off the braking as you come to a halt. That is manual (well, podial, I suppose) jerk control. -- atp "Torque wrenches are for the obedience of fools and the guidance of wise men" ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
