Clear explanation. Thank you, Jon. I will try to make a page on the wiki, with your answers, if you're OK.
Christophe Le 07/05/2013 04:31, Jon Elson a écrit : > Christophe Grellier wrote: >> - What is a stepper motor or a servo ? In french, a "moteur" can be a >> stepper motor, a handrill motor, or even a car engine. Those are quite >> different things. >> > A stepper motor has fixed positions built into it, and will move to a > particular > position when commanded. Feeding it more power will just make it > hold that position more rigidly. It is normally used with no position > sensing > device. A servo motor generally moves smoothly when power is > applied, and will move faster when more power is applied. It must be > used with a position sensing device, as feeding power to the motor gives > you no idea how much it has actually moved, due to variations in > inertia and friction. >> - What are these pulses you are talking about ? >> - Why the pulses need to have a good speed and "rythm" ? >> > A stepper motor responds a bit like a mass with a spring attached. > With the winding current in a particular pattern, it will fall into > "magnetic lock" every four full step positions. If the loads are > excessive, or sudden speed changes are commanded, the motor > can jump from one locked position to another. If the step timing > is not continuous, it can be hard for the magnetics in the motor > to follow the apparent sudden changes in the speed of the > electrical poles, and these jumps become more likely. >> - Why does Linuxcnc need a realtime kernel, while Mach3 can run on a >> stock Windows install ? >> > Mach uses a realtime driver that attempts to do the same thing, for a > very small part of the Mach system. It runs into many of the same > problems with interrupt latency. >> - What is the difference between software stepgen and hardware stepgen ? >> - Is one better than the other ? >> > Ragged step timing makes it hard for the stepper motors to follow the > desired movement. If the timing jitter exceeds some amount depending > on mass, stiffness, the motor and the stepper drive, the motor will skip > steps of fall out of sync completely, leading to a stalled motor for the > rest > of the movement. it will pull back into sync when the commanded move > comes to a stop, leaving the machine at a different position than commanded. > Software step generation has a fundamental limit on the precision of > timing of the steps. For instance, the interrupt period on the base thread > in a LinuxCNC system might be 20 us. The equivalent time is 100 ns > on the Pico Systems Universal Stepper Controller board, or 200 times > finer resolution. The 20 us granularity of step timing is not such a great > deal at modest speeds, but if you need to produce step pulses at > 10,000 per second (rather fast for full-step drives) then the 20 us > granularity means that the next faster or slower speed is a 20% jump > in speed. So, acceleration and deceleration at 10K steps/second > is quite coarse. With our step generator at the same speed, the granularity > is only 1 part per thousand, which the motor will never notice. > > Jon > > ------------------------------------------------------------------------------ > Learn Graph Databases - Download FREE O'Reilly Book > "Graph Databases" is the definitive new guide to graph databases and > their applications. This 200-page book is written by three acclaimed > leaders in the field. The early access version is available now. > Download your free book today! http://p.sf.net/sfu/neotech_d2d_may > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers > ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. This 200-page book is written by three acclaimed leaders in the field. The early access version is available now. Download your free book today! http://p.sf.net/sfu/neotech_d2d_may _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
