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

Subject: Re: motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm
From: Maren Purves <[email protected]>
To: [email protected]
Date: Wed, 03 Sep 2014 17:10:10 -1000
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: [email protected]
[mailto:[email protected]] On Behalf Of Maren Purves
Sent: Tuesday, September 02, 2014 4:00 PM To: [email protected]
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



Replies:
typo correction, was: Re: motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm Maren Purves
References:
motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm Peter Linardakis
RE: motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm Mark Rivers
Re: motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm Maren Purves
RE: motorApp R6.8 Mclennan PM600 opposite limit datum search mode on linux-arm Mark Rivers

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