Experimental Physics and
Industrial Control System

"Pearson, Matthew R." <[email protected]> · Wed, 18 Jun 2014 14:08:19 +0000

Hi Emma,

This would be a problem in the pmacAsynMotorPort driver too. I would suggest using an Asyn parameter to control this, defaulting to disabled. It would be easy to add to the model 3 driver. It's a bad idea to disable hardware limits as part of a homing routine, and I imagine it was originally added to get around PMAC limitations. But it sounds like it's possible to avoid it altogether, using the 'flag low' setting.

Cheers,
Matt

On Jun 18, 2014, at 12:16 AM, Emma Shepherd <[email protected]> wrote:

> Hi everyone,
> 
> I've recently come across an issue with the pmacAsynMotor driver that I thought I should share, as the consequences can be quite severe!
> 
> The driver is designed to support homing onto a limit ('flag high'), which requires limits to be disabled (by setting the appropriate bit of ixx24) in order to work.
> 
> Since this is quite a dangerous thing to do, we have been typically setting up homing to capture on the release of the limit instead ('flag low').  However, I've discovered that if you have got the homing direction set incorrectly (e.g. -ve direction when homing off the negative switch), this results in limits being disabled and the motor driving through the switch.
> 
> You can turn off this behaviour by commenting out the #define REMOVE_LIMITS_ON_HOME, but by default this is included so I'm just letting people know in case they are not already aware of it!
> 
> If other people do want to use the feature of disabling limits, I think it would be worth revisiting the driver to make this safer.  For example if the home type is 'flag low', disabling limits should not be necessary, so we could at least check for this case.
> 
> Cheers,
> Emma
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System