On 19/01/16 10:33, Gene Heskett wrote: > Something that has not been mentioned here is that a real error because > the stepper has lost a full step or more because it is being asked for > step movement faster than it can maintain lock. > > When that occurs, generally the motor stops/locks, and thestepper > generator must be stopped and re-started from a low speed and the > controlled acceleration re-applied. But if its a multiaxis move, there > will be a jog in whats supposed to be a straight line unless the whole > machine is stopped while the errored axis is getting back into position. > It would be a good idea to stop the errored axis at the caught up > position, then restart the whole move so that it can proceed along the > selected co-ordinate path, but because it errored at the selected speed, > the new speed ought to be 10% slower until that move is completed.
I'll cut the other comments and just concentrate on the basic problem with a couple of older closed loop options. The Microproto DSLS3000 is sold as a closed loop stepper driver, which works because the driver is only half stepping, and the 'closed loop' simply continues to apply power until it detects that the motor has moved. The problem with that is that if each step takes longer you have to have an interface back to the 'pulse generator' to slow it down. The Microproto 'fix' for that is simply to remember how many steps it needs and keep moving until the the right number have happened ... how ever long it takes ... you see the problem, and the axies can be up to 200 steps adrift before the fault signal fires. In theory LinuxCNC could be configured to monitor the buffering and slow down pulses, but I don't think anybody has added that as yet. On Mach3 it ends up with rounded corners as the change of direction happens before the first move finishes. The newer 'closed loop' motors are essentially using the same approach, but rather than simply applying the same power for longer, they apply a lot more power so as to try and avoid having to wait for the motor to catch up. What I am not sure about as yet is just how effective that is and just what the lag can be between a step pulse and the final positioning. The DSLS3000 approach is sold as a speed improvement with security that the axis has moved, but once the mill is actually cutting one has to drop below the open loop speeds anyway. Yes in free air one can move between cuts quicker, but the characteristics of the closed loop process have to be taken care of when setting feed rates. -- Lester Caine - G8HFL ----------------------------- Contact - http://lsces.co.uk/wiki/?page=contact L.S.Caine Electronic Services - http://lsces.co.uk EnquirySolve - http://enquirysolve.com/ Model Engineers Digital Workshop - http://medw.co.uk Rainbow Digital Media - http://rainbowdigitalmedia.co.uk ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
