RE: Motor home status

["Mark Rivers" <rivers@cars.uchicago.edu>]

Hi Matthew,

I think we should stick with the "at home" meaning.  Many (most?)
controllers don't have the concept of "homed" but they do have the
concept of "at home".

> It is arguably more
> useful to have a 'homed' status, rather than 'at home'. Especially
since
> the 'at home' status can be inferred from the position (once it is
homed
> of course).

I don't think you can infer "at home" from the position.  What if the
motor is a stepper with no encoder and it lost steps sometime after
being homed?  It might not really be at home when the position says it
is.

Mark


-----Original Message-----
From: Pearson, MR (Matthew) [mailto:matthew.pearson@diamond.ac.uk] 
Sent: Wednesday, August 13, 2008 4:37 AM
To: Mark Rivers; Ron Sluiter; Joe Sullivan; Tim Mooney; Pete R. Jemian
Cc: tech-talk@aps.anl.gov
Subject: Motor home status


Hi,

At Diamond we're currently using several motor controllers, including
the OMS (58 and MAXv), the Delta Tau PMAC (PMAC2-VME, Geobrick) and the
Newport XPS.

The motor record has a field called ATHM, which is set to 1 when the
motor has hit a home switch.

The OMS and Newport drivers use this field correctly, in that ATHM is
set to 1 when the motor is at home position (and is 0 otherwise).
However, the PMAC driver retains the ATHM status when moving away from
the home position - it actually means 'homed' for this driver, rather
than 'at home'.

Most of the motor control at Diamond is performed using the PMAC driver,
so everyone here has become used to this convention. It is arguably more
useful to have a 'homed' status, rather than 'at home'. Especially since
the 'at home' status can be inferred from the position (once it is homed
of course).

Is it the case that every other driver apart from the PMAC driver obeys
the ATHM status? I was considering changing the XPS driver to bring it
in line with the PMAC driver (for the benefit of our beamline users
mainly). However, if every other motor controller driver out there obeys
ATHM, then changing another one to do something different probably isn't
ideal. In this case, we'll probably just leave it as it is.

Any thoughts on this? Or info on other motor controller drivers?

Regards,
Matthew

Dr Matthew Pearson
Software Systems Engineer
Diamond Light Source Ltd
Diamond House
Chilton, Didcot
OX11 0DE
Tel: +44 (0)1235 778538
(58
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