Re: motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm

[Maren Purves <m.purves@jach.hawaii.edu>]

Sorry, meant to reply last night ...

Mark, you clearly have a point there. For me "hard limit" means
"end stop". Yes, it is the end of travel, but I always understood
that in a more physical way, and without necessarily switches
involved at that position - asunder normal circumstances, while
homing or not, the mechanism should never travel that far unless
the actual datum switch is broken. While I don't see it as the 'job'
of the motor record to prevent going further than is allowed the
programmer using the motor record ought to have some idea (as in:
there ought to be specs) how much further they should allow a
mechanism to go once a datum switch opens or closes.

I think we have opened another can of worms about different
languages spoken in different environments here.

Thanks,
Maren

On 09/02/14 11:06, Mark Rivers wrote:
> When I said "hard limit" I am referring to the "end of travel" switch
> that many linear actuators use.  Normally the motor controller will
> stop motion in that direction when this switch is hit.  But some
> motor controllers also use that switch as part of the homing
> sequence.  They won't move past it, but they will hit it to help
> figure out where the motor is.
>
> I am saying that if the motor driver software reports to the motor
> record that the switch has been hit during the homing sequence that
> the motor record should not take any special action.  Device
> protection is handled by the controller, not by the motor record.
>
> The same goes for software limits.  Because by definition the
> position information is potentially meaningless during a homing
> operation (because the controller does not yet know the motor
> position) the motor record should not take any special action if the
> reported position is outside the software limits.
>
> Mark
>
>
> -----Original Message----- From: tech-talk-bounces@aps.anl.gov
> [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Maren Purves
> Sent: Tuesday, September 02, 2014 4:00 PM To: tech-talk@aps.anl.gov
> Subject: Re: motorApp R6.8 Mclennan PM600 opposite limit datum search
> mode on linux-arm
>
> On 09/01/14 03:55, Mark Rivers wrote:
> > Hi Peter,
> >
> > I think the problem is that the motor record should ignore both
> > soft limits and hard limits during a homing sequence.  Soft limit
> > violations are expected because the controller does not yet know
> > where the motor is, and hard limits are also to be expected
> > because sometimes the homing operation involves hitting the limit
> > switch, as in your case.
> >
> > I have had problems with the motor record stopping a motor when a
> > soft limit is exceeding during a homing operation too, but I
> > believe that has been fixed in a recent release.
>
> Hi Mark,
>
> I have one problem here: in my book the term "hard limit" means that
> you can't physically move past that point without breaking
> something, it is a physical end stop. (I have heard of that
> happening. That particular telescope was out of commission for
> several weeks) Datum switches should be a reasonable distance away
> from soft limits, and hard limits should be further away from the
> datum switches than that. Obviously, circular mechanisms may or may
> not have these limitations, but linear ones always do.
>
> ??
>
> Maren