Christophe, It's hard to be everything to everyone - regarding howtos and LinuxCNC.
Don't overlook websites like CNCZone.com. They can often times offer specifics for your particular CNC application Knee Mill vs Plasma Cutter vs ? etc. Also, questions such as this are probably better on the EMC Users list rather than the Devel list as you will probably get more replies. Dave On 5/7/2013 1:27 AM, Christophe Grellier wrote: > 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 > > ------------------------------------------------------------------------------ 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
