On Sun, Aug 8, 2010 at 5:33 AM, Andy Pugh <a...@andypugh.fsnet.co.uk> wrote: > On 8 August 2010 04:35, Igor Chudov <ichu...@gmail.com> wrote: > >> Say, I say S3000 and drill. Then I change tool to a tap and say S300 >> and rigid tap. To accomplish that, EMC would actuate SPEED DECREASE >> solenoid and wait until the output speed, as reported by the encoder, >> approximately equals the commanded speed. > > Rigid tapping is where a rather complicated behaviour is likely to be > seen. Assuming the stop and reverse is done by the VFD, as soon as > your varispeed control structure sees the speed dropping is it likely > to try to try to keep the speed up and the two speed control systems > are likely to end up fighting. > > A VFD is a much faster-reacting system than the Varispeed, and less > prone to wear. However, the Varispeed gives increased torque at lower > speeds, so you really should use both. > > You could potentially use the Varispeed as a gearbox, perhaps fitting > a home-made encoder quadrant or disc to some part of the actuator and > then automatically driving it a given position, or having input and > output encoders and settting an absolute speed ratio dependent on > spindle speed request then using a PID and the VFD for fine-tuning, > load compensation etc. > Ideally you would want to do this purely on the basis of the active > "S=" parameter, rather than on the spindle speed output pin, which > varies during rigid tapping moves. I am not aware if this value is > available separately to HAL. > > Anyway, you can operate the solenoids fairly easily using two > comparator functions in HAL. > http://www.linuxcnc.org/docview/html//man/man9/comp.9.html > > loadrt comp names=over,under > . > . > addf over servo-thread > addf under servo-thread > > setp over.hyst 25 > setp under.hyst 25 > > net motion.spindle-speed-out => over.in0 under.in1 > net {whatever your speed signal pin is called} => over.in1 under.in0 > net over.out => {speed reduce pin} > net under.out => {speed increase pin}
Andy, my feeling on the matter, is that your solution is great. I should somehow activate these comparators for a short time after a speed change command (like for 7 seconds) and then disable them afterwards. That way reversing with a VFD, is not a problem. Igor ------------------------------------------------------------------------------ This SF.net email is sponsored by Make an app they can't live without Enter the BlackBerry Developer Challenge http://p.sf.net/sfu/RIM-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
