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

Subject: Re: Insertion Devices Control and EPICS
From: Allan Honey <ahoney@keck.hawaii.edu>
To: tech-talk@aps.anl.gov
Date: Fri, 12 Dec 2003 09:52:55 -1000 (HST)
> Date: Fri, 12 Dec 2003 08:42:33 -1000 (HST)
> From: Nick Rees <n.rees@jach.hawaii.edu>
> X-X-Sender: npr@mahina
> To: tech-talk@aps.anl.gov
> Subject: Re: Insertion Devices Control and EPICS
> MIME-Version: 1.0
> List-Help: <http://www.aps.anl.gov/epics/tech-talk/index.php>
> 
> On Fri, 12 Dec 2003, Rok Sabjan wrote:
> 
> > First let me remind everyone on the problem. We have two (or more) 
> > motors which we would like to move synchronously. This means to 
> > guarantee the movement will start and end at the same time. This is 
> > extremely important when changing the gap of an insertion device.
> 
> We don't make much use of the OMS system - we tend to use serial line
> motor controllers (but they are starting to come with ethernet addresses
> as well). Typically we separate setting the next demand and the move
> command into separate instructions. If we set demands on multiple axes
> before a move instruction the axes move synchronously under hardware
> control.  Otherwise the moves are (of course) asynchronous.
> 
> Just a thought.
> 
> -- 
> Nick Rees
> 
Just to expound upon Nick's thoughts a little.
There are some of the serial motor controllers that use RS-485,
thereby allowing a 'star' interconnection configuration. Some
of those controllers also allow commands that are not targeted
to a specific controller to be acted upon by all controllers. This 
provides very close synchronization of motion, assuming the update 
rate is not too high. I assume this is also true for controllers 
that are connected to ethernet, albeit, I have not researched that 
at all.

Also, in my opinion, for many applications the PMAC solution is overkill!
We use many PMACs with the KECK interferometer, in a lot of cases they 
are used for discrete positioning of optical elements (not tracking). 
All for the sake of consistency?

AH




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