[etherlab-users] Is Ethercat Master Enough to Control Servo

Henry Bausley hbausley at deltatau.com
Thu Sep 13 21:16:43 CEST 2012


   Did you use Graeme Foot's DC patch?  


   I found that without using the slave's clock as a reference there was
always drift even though I have a system with low jitter and my cycles
are performed in kernel mode.  I still don't quite understand why if
someone has a answer let me know.

  Using a scope we monitored the Copley sync0 interrupt and the arrival
of the packet (Thank you for these diagnostic outputs Copley).  You can
see them drifting with respect to one another in the mpeg link. 


   This would manifest itself as a periodic growling noise in the motor
every time the packet would arrive at the same time as the sync
interrupt.  You MAY be able to get away with this in a point to point
application like a pick and place robot, however it would be
unacceptable for machining.

  I found I could never get some amplifiers to properly sync up without
using a slave as the reference clock.  The slave timing does not seem to
modify its self to the master's clock.  Using graeme's patch and
modifying my cycle time based on the slave's clock I was able to get rid
of the drift you see in the scope in the mpeg and the growling noise in
the motor.

  I use xenomai on PPC in kernel mode.  I am not sure how well
RT_PREEMPT  would work but if the slave is used as the reference clock I
think it might have a chance.

On Wed, 2012-09-05 at 09:13 +0300, Raz Ben Yehuda wrote: 
> On Sun, 2012-09-02 at 11:47 +0200, takeshi ikeya wrote:
> > Hi Tahir!
> > I think ENOUGH..
> > If you need quick response, you'd beter use it under RTAI (Linux).
> > 
> I must add that did not find the current design suitable for moving
> servo drives. For this reason I modified etherlab to support slave DC
> bus time ( currently etherlab is App time based).
> > 
> >   takeshi.ikeya at gmail.com

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