PicoMotor control system using EPICS and Python

• Overview

• Installation

  • EpicsCA

  • EPICS IOC

  • Generating db file, MEDM screens and autoBurt file

Overview

In CLIO, Picomotors are used everywhere. In this page, how to control those Picomotors through EPICS is explained. There are a few scripts and configuration files to make the EPICS-Picomotor system work in harmony. The list of scripts and files involved are shown below.

This system mainly consists of two programs. One is an EPICS IOC, named k1pico, which holds PVs (or channels) used to communicate with Picomotors. This IOC resides in /cvs/cds/kami/target/k1pico. The IOC can be started by running startk1pico command.

Another part of the system is a daemon script called pmepics.py. This script connects to those PVs provided by k1pico and wait for changes. Once it detects a change in one of the PVs, it takes an appropriate action, such as changing the speed of a motor, or start/stop motor rotation, etc. Therefore, users can control Picomotors by changing the values of those PVs, either through MEDM or command line tools.

For example, K1:PICO-MC_END_PIT_SPD is used to set the speed (pulses/sec) of the Picomotor for MC end mirror pitch. Another example is K1:PICO-MC_END_PIT_FWD. If pmepics.py detects a change in this channel, it starts or stops the rotation of the Picomotor depending on the value of this channel. If it is 1, the Picomotor starts moving. If it is 0, the motor stops.

The way pmepics.py controls the Picomotors are somewhat hidden from users. However, it is worth explaining the mechanism here since it will helpful to understand the syntax of pmepics.conf.

||autoBurt.req||This is a Burt request file for the IOC k1pico||

Installation

We assume that EPICS base is installed in /cvs/cds/kami/lib/epics/base.

EpicsCA

Download EpicsCA version 2 (not 3 yet) from below:

http://cars9.uchicago.edu/~newville/Epics/Python/

Extract it in /cvs/cds/kami/lib/epics/.

Set appropriate environmental variables (these are actually set by .cshrc, so you shouldn't have to be bothered).

LD_LIBRARY_PATH=/cvs/cds/kami/lib/epics/base/lib/linux-x86_64
EPICS_BASE=/cvs/cds/kami/lib/epics/base
EPICS_EXTENSIONS=/cvs/cds/kami/lib/epics/extensions
EPICS_HOST_ARCH=linux-x86_64

Run

python setup.py build

You may need to install development files for python, if these are not installed yet.

Run

python setup.py install

as root. Be sure to source /home/controls/.cshrc to set the environmental variables.

EPICS IOC

We want to have a dedicated IOC for the PicoMotor controller. Actually, this section gives you a general procedure to make a generic IOC.

Make a directory in /cvs/cds/kami/target. In this example, we create /cvs/cds/kami/target/k1pico.
Run the following commands in the created directory:

/cvs/cds/kami/lib/epics/base/bin/linux-x86_64/makeBaseApp.pl -t example k1pico
/cvs/cds/kami/lib/epics/base/bin/linux-x86_64/makeBaseApp.pl -i -t example k1pico

example is the name of a template. example is a good template to start. k1pico is the name of your IOC. Usually, we want to start it with k1.

Type make in the directory. The EPICS build system will compile an IOC.

Modify db/*.db file. Then go to iocBoot/iock1pico and run st.cmd.

Now, for the PicoMotor controller, we have to put pmepics.db in the db/ directory. This file is automatically generated by pmGenDbMedm.py script. Then you have to add a line like the following to iocBoot/iock1pico/st.cmd.

dbLoadRecords("db/pmepics.db", "site=K1")

Run the IOC by typing

cd /cvs/cds/kami/target/k1pico/iocBoot/iock1pico
./st.cmd

Generating db file, MEDM screens and autoBurt file

pmGenDbMedm.py is a python script to automatically generate an EPICS db file, MEDM screens and an autoBurt request file.

The usage is:

pmGenDbMedm.py -c pmepics.conf

The syntax of pmepics.conf is explained at the beginning of the file as comments.