Experimental Physics and
Industrial Control System

Emma Shepherd <[email protected]> · Tue, 28 May 2013 08:57:25 +1000

Hi all,

I've stumbled into this issue a couple of times now so I thought it was worth a message to tech-talk.

The .RDBD field of the motor record limits the smallest allowed move - quite often we want to set this very low so that we can do small step moves.  However, in a few cases we also want to use the motor record's retry mechanism by setting .UEIP to 'Yes' and feeding the encoder into .REP (I'm using the tpmac driver which allows you to do this when the encoder is on a different channel).  Because .RDBD is now used as the retry deadband, we need to make it larger since it is not capable of attaining such an accurate position.

It would be better if we could somehow decouple the use of .RDBD in the retry sense from the smallest allowed move.  Have other people run into this and found a solution?  In the meantime I need to keep switching between modes (toggling .UEIP and changing .RDBD appropriately) to allow me to do scans in very small steps followed by a wind-back which uses retries to ensure I'm not losing steps.  It's a bit messy and not ideal.

Of course if we had perfect mechanics we wouldn't need to be doing retries at all, but c'est la vie!

Thanks,
Emma

P.S. I hope I haven't missed a thread on this already, the APS website seems to be down at the moment so I can't check

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System