Experimental Physics and Industrial Control System
Some options:
Use the hardware capability in the OMS card -
Requires modification to driver, device support and record
support. Perhaps write an undulator record that accesses
this synchronized move in the modified driver.
Modify the driver support to wakeup the database on each
readback. The driver reads the motor position at 30 Hz. If
there was analog input device support that posted this
event, database logic could be used to wake up at 30 Hz
while the motor is moving and verify that the difference
in the gaps is constant or within tolerance. A stop to the
motors if they are starting to diverge would occur within
40 msec. This would be a minimal change to the device
support and driver and may still meet the requirements.
Bob
On Fri, 12 Dec 2003 13:38:17 +0100
Rok Sabjan <[email protected]> wrote:
Hello everyone!
I'm trying to prepare a proposal for ID control system at
Diamond. During that time I have been asking some people
some questions how this is currently managed in EPICS. To
my surprise I found out that there was no clear way to
solve this problem. I had a discussion with Tim Mooney
and we were thinking of some possible solutions for the
biggest problem - synchronous motor movement under EPICS.
We have developed some suggestions, but I think it is
time to broaden the discussion to tech-talk. There may be
more people interested in such solutions and there are
probably some people with some experience on the matter.
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.
One may suggest that we should just wire the signal lines
together (hardware solution) and use one signal line to
control multiple motors, but we also want to move these
motors independently. We may implement some logic (using
FPGA or some other programmable logic) to multiplex this
one signal line in one operation mode and use multiple
signals for different motors in some other mode.
The OMS VME58 card, which is normally used in EPICS for
motion control, supports such synchronized moves, but
this is (to my knowledge and experience) not supported
via EPICS motor record and device support. We should also
provide some kind of sync record, which would take
control of correspondent motor records (when instructed
to do so) and would then perform the synchronized moves.
Needless to say, there are a lot of design choices to
identify and make on the behaviour of this record.
This mail is intended to identify people who have common
interest for such a development in EPICS community.
Definitely, we will have to make some modifications to
the existing motor software if we decide to go through
with any of these ideas. The idea is to make a general
EPICS solution for such situations.
Cheers,
Rok
Bob Dalesio
[email protected]
410 557 0297 Maryland
505 667 5643 Los Alamos (New Number)
505 699 1632 Cell Phone
505 667 6087 Our Secretary (Lisa Marie)
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