Re: preventing changing an EPICS motor's commanded position

[Maren Purves via Tech-talk <tech-talk at aps.anl.gov>]

Suggestion from the dark past:

Can you just not give the people who you don't want to change the position a user interface that doesn't  have the option?

(I remember somebody cringing at one of our user interfaces where you could change the setpoint of a temperature controller, which we sometimes used quite intentionally and that  person saying wouldn't it be dangerous if that happened by accident (like somebody clicking the wrong button) and all I could reply to that was that it had never happened.)

Aloha,

Maren Purves
Head of Instrument and Telescope Software
East Asian Observatory / JCMT

On Tue, Oct 3, 2023 at 8:20 AM Goetze, Kurt via Tech-talk <tech-talk at aps.anl.gov> wrote:

Hi Ray,

 

“motor.db” loads a bo record, “$(P)$(M)_able”, that the motor record’s SDIS field points to.

 

We use this to enable/disable the motor record.  When disabled, writes to the motor record’s .VAL field are not allowed.

 

Kurt

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Matt Newville via Tech-talk
Sent: Tuesday, October 3, 2023 10:06 AM
To: Peterson, Kevin M. <kmpeters at anl.gov>; Gregory, Ray <gregoryrd at ornl.gov>; tech-talk at aps.anl.gov
Subject: Re: preventing changing an EPICS motor's commanded position

 

Ray, 

 

Perhaps what you're looking for is simply to set the Motor Record low and high limits to the drive value you want to maintain.  

You could also set the SPMG field to 0 or 'Stop'.  That would allow someone to change the VAL field (which is what you said you wanted to not allow), but it will prevent the Motor from actually moving until SMPG is changed back to 2 or 'Go'.   Both of these use the exposed interface to the Motor Record, so in principle can be changed at any time.   But they are also not uncommon things to do for motors that you want to not accidentally move. 

 

 

 

On Tue, Oct 3, 2023 at 8:17 AM Kevin Peterson via Tech-talk <tech-talk at aps.anl.gov> wrote:

Ray,

Can you provide more details about what "disabling the axis" means?  The
behavior of the motor record's CNEN field, which is labeled "Torque" on
the motorx_all screen, is controller dependent; for some controllers
CNEN enables/disables drive power, for other controllers CNEN switches
between open and closed loop control, and some drivers do nothing when
CNEN is changed.

Kevin

On 10/2/23 12:32, Gregory, Ray via Tech-talk wrote:
> Hi,
>
> How can I prevent changing an EPICS motor record’s commanded position
> (.VAL field) without disabling the axis?
>
> Thank you,
>
> Ray
>
> Ray Gregory
>
> Oak Ridge National Laboratory
>

 

--

--Matt Newville <newville at cars.uchicago.edu> 630-327-7411