Experimental Physics and
Industrial Control System

<[email protected]> · Thu, 12 Aug 2010 15:48:40 +0100

Hi Dirk,

At Diamond our main motor controllers are the Delta Tau VME Turbo PMAC 2
and (more recently) the Delta Tau Geobrick LVM (which has an ethernet
interface). We've also got quite a few Newport XPSs.

All three controllers have similar capabilities. They are actually
overkill for most of what we do, but using the same controller for most
axes (Delta Tau) simplifies the support structure. We mainly use the
Newport XPS for Newport diffractometers, and a few other specific
applications.

The Delta Tau Geobrick is basically a PMAC2 with integrated amplifiers
in a 4U rack mount box. We currently have/deploying close to 100 of
these on several beamlines both in operation and being built. On most
beamlines they have proven very stable, but we have a number of
problems:

1) Some susceptibility to noise. For example, we're currently awaiting
new firmware from Delta Tau to fix a problem that always affects axis 2.
It spontaneously changes it's amplifier configuration so it thinks it's
a servo drive rather than a stepper.

2) On one beamline we have had a large number of controller watchdogs.
This was never tracked down, and eventually we either replaced the
Geobricks or simplified the software running on them. We still have this
problem occasionally.

3) Initially there were a faulty Geobricks being delivered to us
(10-20%). I'm not sure if this is still an issue though.

In general it's a reliable and stable controller. However the software
interface is very difficult to use, and the documentation is large and
complex. But over time we have built up our experience in using it, and
our group now has several experts on PMAC coordinate systems and
developing controller based 'PLC's.

The Newport XPS has similar capabilities to the Delta Tau Geobrick. It's
also a similar form factor - 4U, ethernet, integrated amplifiers. The
amplifiers are easily removable (unlike the Geobrick). And, in general,
it's a better build quality. But we've also had a number of problems
with this:

1) The main software interface to it (apart from an Epics driver) is a
web server. This has been unreliable and frequently crashes.

2) Unexplained controller reboots.

3) Axes losing their homed status and going 'uninitialized'.

4) Corrupt data when gathering data during a trajectory scan.

And several others (enough to prompt us to create a separate document
about them). 

However, the software interface is orders of magnitude easier to use
than the Delta Tau PMAC. To Newport's credit they have put a lot of
effort into making the software intuitive and easy to set up. For
standard Newport stages it's even easier with the 'ESP' type, which can
tell the controller what type of stage it is and auto-configure the
controller to drive it. We have found this useful when setting up
temporary sample stages for example.

I'm sure some of the problems we have had are down to electrical noise
issues on beamlines. We sometimes find it hard to reproduce problems in
the lab. Some of the problems we have worked around, and some not.

By far the most reliable controller we have used on beamlines is the VME
Delta Tau PMAC. However, the newer ethernet based systems are much
easier to set up, are cheaper, and easier to interface to. But I think
it's a fair to say it is still a developing technology. 

We mostly use Linux soft IOCs to talk to our ethernet controllers.

If you decide to go down the Geobrick route, I can ask our motion team
to give you more details on the hardware and tuning aspects. I mainly
deal with the EPICS drivers and controller based programs. 

Cheers,
Matthew

> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Dirk Zimoch
> Sent: 12 August 2010 14:48
> To: EPICS
> Subject: Motion controls alternatives to MAXv?
> 
> Hi all,
> 
> I am looking for an alternative to our current MAXv motion controller 
> solution.
> 
> Can anyone tell me about experiences with
> 
> * DeltaTau pmac
> * Newport XPS
> * Galil
> * other systems?
> 
> Dirk
> 
> 

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System