EPICS and Motion Controls

The lower level of GM/CA control system is constituted by EPICS. EPICS is an abbreviation for "Experimental Physics and Industrial Control System", a distributed hardware control system widely deployed at the APS and other synchrotron radiation facilities. In EPICS each hardware component is interfaced via a database server called input-output controller (IOC).

GM/CA runs multiple IOC for each beamline:

Two VME-type IOC based on VxWorks real-time operating system providing interface to 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
Embedded IOC for bimorph mirrors power supplies (for X-ray beam focusing),
Linux IOC providing frame acquisition with area detectors (Eiger-16, Pilatus3-6m or Rayonix-300 depending on beamline),
Linux IOC for JBluIce communication, Sample Environment Server, Point and Click Server, CryoJet control, Keithley-428 Current Amplifiers, XIA Falcon DXP, and Canberra NIM modules (556 AIM, 9635 ADC, 2016 AMP/TCA) for fluorescent detector,
Linux IOC for Mono Stabilizer (beamline intensity feedback),
Linux IOC for beamline Equipment Protection system (EPS),
Linux IOC for monitoring consistency of 4 monochromator encoders.

EPICS allows multiple client programs to access the IOC and control hardware in parallel. While our main user interface software is JBluIce, manual and semi-automated procedures, for example interfacing beamline intensity feedback, can be performed with other EPICS tools such as MEDM and CaQtDMscreens, StripTool (time plots) and various automation scripts. Most of relevant EPICS tools are available via the Beamline Controls Toolbar, which can be accessed either from the JBluIce Tools menu, or by opening a terminal window and typing 23i, 23o, or 23b for the 23ID-D, 23ID-B or 23BM beamline respectively, or by pressing the icon on the computer desktop (the color may vary per beamline).

Our main EPICS development platform is Redhat Enterprise Linux and the VME IOC are operational under VxWorks.

The core of the whole control system are Turbo PMAC2 motion controllers that we made available 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 laid instead of dozens of cables running from the control rack into endstation).
Support for virtually any type of motor -- stepper, 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
Programming capability 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 written 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 ms.

> JBluIce - EPICS source distribution