Experimental Physics and
Industrial Control System

First, it could be a result of auto-saving both MRES and SREV.  MRES
and UREV/SREV are two different methods of configuring the same thing;
i.e., motor resolution.  Only one method (either MRES or the pair
UREV/SREV) should be auto-saved.  I prefer MRES, so I suggest you
remove SREV from the list.

Second, although the motor record supports configurations where the
sign of MRES and ERES are different, OMS controllers do not.
The following is from the "Known Problems" section of the README
file distributed with the motor record,

4) With R5-3 of the motorRecord, negative encoder resolutions (ERES) are
supported. This allows the user to change the sign of ERES rather than
reverse encoder wires when the motor and encoder direction are
reversed.

There is a peculiarity with the OMS controller boards when they are
configured with MRES and ERES of opposite polarity. Since both the
commanded and feedback positions are set with the same command (LP),
the user must enter the opposite polarity when setting the OMS motor
controllers position.

For example, if MRES is positive and ERES is negative and the user
wants to set the current position to 10.00 inches, then -10.00 must be
entered in the VAL or DVAL field.

Hope this helps,
Ron

Using the EPICS motor record (for OMS MaxV) under R3.14.8.2, I am
experiencing some odd behaviour on IOC reboot and autosave.

I have some systems driving XY stages. The X axis behaves perfectly on
reboot (and restore), but the Y axis does not.
The observation is that, on IOC reboot, all Y axis motor record fields
'appear' to have restored correctly, but on driving the axis (in either
direction) the direction sense is inverted. The Y axis differs from the
X axis, in that the direction is inverted (due to gearing), so the motor
record is initialised with positive MRES, positive DIR, but negative ERES.

On setting UEIP to 'No', 'home' the axis, then set UEIP to 'Yes', the
direction sense is corrected an the axis behaves as expected.

My autosave files refer to the following motor record fields:
0.req:
DVAL OFF

1.req:
DIR DHLM DLLM TWV SREV MRES ERES RRES VBAS VELO ACCL BDST BVEL BACC RDBD
EGU RTRY UEIP URIP DLY PREC DISA DISP FOFF OFF FRAC OMSL JVEL JAR

The startup script makes the following calls before iocInit():
set_pass0_restoreFile("0.sav")
set_pass0_restoreFile("1.sav")
set_pass1_restoreFile("1.sav")

Motor parameters:
MRES: 0.00005
UREV: 0.01
ERES: -0.00002
DIR:  'Pos'

I have tried issuing the DBI command (to invert the output direction at
the MaxV card), whilst setting DIR to 'Neg', but this swaps the
associated limit switches! So, not a solution.

Is anyone aware of known issues in this area? I seem to recall something
about negative ERES values being mentioned in the past, but unable to
find any references.

Ian Gillingham
Diamond Light Source

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References:

Motor record direction sense inverted after IOC reboot & autosave Ian Gillingham

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