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<== Date ==> <== Thread ==>

Subject: RE: Problem with soft motor record
From: "Rarback, Harvey" <[email protected]>
To: <[email protected]>
Date: Mon, 17 Mar 2008 11:59:04 -0700
	Motor record gurus,

I had written on February 22:

> I have encountered a number of problems with my use of the soft motor
> record.  I am using motor driver version 6.22 (with SLAC modifications for
> RTEMS) on EPICS base 3.14.8.2.  The hardware is an OMS MAXv-8000 motor
> controller along with Kramert 505F SSI encoder readout.
> 
> First the part that works pretty well:
> 
>   One soft motor "RowPhaseMotor" that moves four real EPU girder motors.  We
> have no encoders for these temporary motors and so use motor pulses as our
> position readback.  The soft motor links RDBL, DINP, and STOO seem to behave
> as documented with the exception that "the value specified by DINP is used
> to set the DONE bit in the MSTA field; which in turn sets the DMOV field".
> The DONE bit appears to always be set correctly, but the DMOV field
> sometimes remains at zero after the move.
> 
> Now the problematic part:
> 
>   One soft motor "GapMotor" that moves two real undulator jaws. There are
> absolute linear encoders on the two jaws and I have set a retry count of two
> for both motors because of mechanical imperfections and magnetic deflection
> forces that don't allow reproducible motions.  Each jaw motor/encoder
> combination seems to work ok.  When I try to control these jaws with the
> soft motor, weird non-reproducible things happen:
> 
>   - the DONE bit often stays true throughout the soft motor move
>   - the DMOV field stays false during and after the move
>   - the soft motor will process and move again after both real motor moves
> are finished
>   - sometimes one of the two jaws will start moving without any command.
> 
> I've tried various ways to get the done condition to work, but without
> success.  I would appreciate any suggestions.

I received suggestions to change the soft motor record configuration to:

  - set the LOCK field to "YES".
  - set the NTM (New target monitor) field to "NO".  (BTW the record documentation says the enums for the field are "Yes" and "No", but they are actually "YES and "NO".)
  - add a Gate record which is opened before writing to the first hard motor and then closed when the last motor record is finished and is checked in the value pointed to by DINP.

I implemented these changes, but they did not fix the problems cited above.

What *did* fix the problems were two simple database configuration changes that took me a while to figure out:

  - I removed the backlash distance from the soft motors. In retrospect this is obvious, but I outsmarted myself in calculating this bogus correction.

  - I set URIP to "No" and removed the RDBL link field.  This had the positive effect of eliminating a long delay between the value pointed to by DINP going to 1 and the soft motor record DMOV field going to 1.  A downside is that the record comes up in LINK status after a reboot.  Also since the readback is always zero, this can set the LVIO field to 1, but the record still respects the DLLM and DHLM fields. Since I have other ways to check what should be the motor readback, I can live with these downsides.

I would be glad to hear any other suggestions.

Thanks to Tim Mooney, Ron Sluiter and Emma Shepherd for database configuration suggestions and Stephanie Allison for many code changes.

                               --Harvey Rarback



References:
FW: Problem with soft motor record Rarback, Harvey

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