RE: Motor home status

["Pearson, MR (Matthew)" <matthew.pearson@diamond.ac.uk>]

Hi Mark,

Thanks. I agree we should stick with 'at home', especially if a lot of
controllers don't have the 'homed' concept. 
 
With regards to the controllers that do have that concept, should the
drivers use ATHM to mean 'at home'? The PMAC driver currently doesn't,
but the XPS driver does. Do you think we should bring the XPS driver in
line with the PMAC driver? (or vice versa?)

>From the users point of view it's slightly confusing. At Diamond they
are used to seeing motors in a homed state, regardless of position. Our
XPS motors always tend to look 'un-homed', because they've been driven
away from home position. 

> 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.
>

Good point, I forgot about that one.


Cheers,
Matthew

 
> 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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