GBEM is based on the Open EtherCAT Society's SOEM (Simple Open EtherCAT master) project.
GBEM provides a framework to control EtherCAT slaves. It allows you to easily configure a machine (a combination of EtherCAT IO devices and servo and stepper drives) and provides a simple interface through which you can interact with that machine without worrying about the nitty-gritty details of how EtherCAT drives and IO devices work.
- A CiA 402 based state machine framework to control machines and drives
- A configuration structure in which you can define the layout of your EtherCAT network (i.e. the structure of your machine)
- An ability to write your own PLC style functions in the C programming language to control EtherCAT IO
- A simple shared memory interface over which drives and IO can be controlled from your web stack high-level control application
- A signal, synchronous with the fieldbus bus cycle, to trigger the cyclic execution of higher level control functions
- Real-time execution - the lowest achievable cycle times depends on hardware. Typically, 0.5ms, 1ms or 4ms cycles are used
- A code based suitable for use on both Linux and microcontroller targets
- Open Source code base
mkdir build
cd build
cmake ..
make
GBEM needs to have a machine configured. A machine defines the EtherCAT slaves that make up the machine.
See Configuring machines for details on how to do this.
To scan for slaves on an EtherCAT network using network interface eth0:
./GBEM -n -i eth0
To run cyclically using network interface eth0:
./GBEM -c -i eth0
For SOEM documentation see the SOEM github repository.
For the glowbuzzer framework around SOEM (GBEM) see GBEM overivew on the glowbuzzer website.
To swap between pre-configured machine configurations search the code for "MACHINE_SWAP" you will find a #define to toggle. You will need to do this before you compile and run GBEM.
When adding code to support a new drive, you will need to add a library for the new drive and write the required functions. Two CMakeLists.txt files will need to be updated. Also, a few simple changes will need to made elsewhere in the code. Search for the code for "NEW_DRIVE" to find the locations where these changes are needed.
When adding a new machine configuration (that uses existing slave and drive functions), you will not need to write any functions. Small changes are needed to enable the switching between configurations. These can be found by searching for "NEW_MACHINE".
To achieve real-time behaviour, GBEM needs to avoid outputting debug messages to the console.
There are defines available to prevent this. Like #define ENABLE_CYCLIC_MESSAGES 0 in gbem_config.h.
But getting console messages is important when initially getting your slaves/drives working.
Therefore, we recommend:
- using a 4ms cycle time when debugging with various messages enabled and understand the messages will compromise the real-time behaviour
- switching off all messages when you are happy with the behaviour of your machine
Often you will find with drives (apart from superfast linear motors etc.) a 4ms cycle time produces acceptable accuracy/smoothness of motion. But of course you can increase (depending on your hardware) to 2ms or 1ms.