Experimental Physics and
Industrial Control System

Mark Rivers <[email protected]> · Tue, 2 Sep 2014 21:06:39 +0000

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

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System