Viesturs Lācis wrote: > 2010/5/15 Stephen Wille Padnos<[email protected]>: > >> [snip] > Motors will be moving relatively slowly, so loss of torque in high > speeds is not a problem. > I expect that rotary axis will have to hold their existing position > more than do any movement at all and steppers are better in holding > their position than servos without a brake. > I guess I should have said that since a stepper never has more torque than when it's stopped, it will never have extra torque to "catch up" if it falls behind the expected position or speed. > > 2010/5/15 Jon Elson<[email protected]>: > >> Tom Easterday wrote: >> >>> On May 15, 2010, at 9:24 AM, Andy Pugh wrote: >>> >>> >>>> There are people running closed-loop stepper systems. >>>> >>>> >>> Really? I keep getting told you can't do it for various reasons. >>> >>> >>> I would love to see someone's configuration files who has made a closed >>> loop with steppers work. >>> >>> >> The Pico Systems Universal Stepper Controller is a sort of closed loop >> system all the time. The default method is to count the step pulses >> sent out. By flipping a switch for each axis, you can set it to read >> the encoder pulses, instead. >> >> So, in fact, EMC doesn't actually even KNOW whether it is physical >> closed-loop or electronic closed-loop! The only changes in the .ini >> file would be to change the INPUT_SCALE parameter to reflect the encoder >> resolution vs. the step resolution per user unit. >> >> See the configs file directory included in your EMC2 distro under univstep. >> >> Now, the reason you've been told you "can't do that" is because it >> doesn't PREVENT stalls. It WILL detect a stalled motor and cause a >> following error stop. It will also silently fix a single lost step here >> and there caused by setup time violations during direction reversals. >> Some machines suffer from this kind of problem. >> >> Jon >> >> > I (and seems like other EMC users as well) did not know that stepper > motors are used in closed-loop systems. I will try to search for more > information about that Pico Systems Universal Stepper controller. > Thank You for sharing the information? > It's not as common to use steppers in "true" closed loop systems, since they can't catch up once they fall behind. Using a stepper in a system that has feedback that is used only for following error detection is a different story, and is definitely do-able. > Then I have one more question - what are the options to use servo > motors and stepper motors together in one machine? You can use any kind of motor for any joint on the machine. You can also use more than one type of hardware, so for instance you could have a Pico Systems card on one parallel port, use a second parallel port directly, and use a PCI plug-in Mesa card, all at once. > I have 3 servos (2 > on X axis and 1 on Y axis) and currently I am trying to control servo > drives in step/dir mode, which does not seem very clever idea, besides > movement of axis with old, DOS based control system is smoother > (analog +10V/-10V signal is used) than EMC with step/dir mode > performs. I want to add 3 stepper motors on Z, A and B axis > respectively. I already have stepper drivers and motors, so i could > save some money and as I mentioned - i believe that steppers on rotary > axis are better. > Just mix and match them as you like, EMC doesn't care.
- Steve ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
