User Program - While at the Beamline - EPICS and Motion Controls
The lower level of GM/CA control system is constituted by EPICS
input-output controllers (IOC). Generally we have two VME-type IOC per
beamline, one embedded IOC for bimorph mirrors power supplies, and
Linux IOC providing frame acquisition with area detectors (Eiger-16,
Pilatus3-6m or Rayonix-300 depending on beamline). The electronics
installed at the beamlines and controllable via EPICS includes: Turbo
PMAC2 VME intelligent motion controllers by Delta Tau, SIS3801
Multichannel scaler, Joerger VS64 latching scaler, Systran DAC128
digital to analog converter, Acromag IP330 analog to digital converter,
AVME9440 Digital I/O, XY542 combined DAC/ADC, Keithley-428 Current
Amplifier, Canberra NIM modules (556 AIM, 9635 ADC, 2016 AMP/TCA) for
Our main EPICS development platform is Redhat Enterpise
Linux and the VME IOC are operational under VxWorks.
The core of the whole control system are Turbo PMAC2
motion controllers that we made
availvable in EPICS. The advantages of these controllers are (see
the picture below):
- Distributed controls allowing to place parts of the controller
called Macro Stations close to motors (only two fiber links have
to be layed instead of dozens of cables running from the control
rack into endstation).
- Support for virtually any type of motor -- steper, servo,
brushless servo, piezo, and so on. We only need one type of
motion controller for all three beamlines.
- Support for many types of encoders, so that all motors including
steppers can be encoded thus enhancing controls reliability.
- Support for coordinated motions: controller can synchronize
motion of several motors on the fly.
- Option for 24-channel digital I/O that allows to synchronize
motion with other beamline events
- Programmability allowing to write custom motion trajectories and
custom servo cycles.
Using these controllers we implemented on-the-fly scans for beamline
alignment. The scans are partially based on an open-source FastScans
project formerly carried by Elena Kondrashkina and Sergey Stepanov
while they were employed at BioCAT.
The package consists of a number of programs witten in C language with
user-friendly GUI frontend developed in Java.
As illustrated by the scan plot, the actual motion time of the
shutter is about 12.5 ms and the beam blocking occurs within 2.5
> JBluIce - EPICS source distribution