SOMANET EtherCAT Drive Cyclic Position/Velocity/Torque Control Demo

This simple demonstration shows how to control your motor using SOMANET EtherCAT DC-Drive from a Linux PC. Only Cyclic Synchronous Position, Velocity and Torque control modes (CSP, CSV, CST) are included with a simple linear profile generator. The CSP, CSV and CST control modes are designed to achieve a desired motion trajectory by using various motion profiles and closing the control loop over EtherCAT. The slave controller is taking the generated position, velocity or torque setpoints at a fixed time interval (1ms) as a controller input and will be following them.

Hardware setup

A minimal requirement for running this application is having the complete SOMANET stack assembled consisting of a SOMANET Core C2X, SOMANET COM-EtherCAT and a SOMANET Drive module. The stack should be powered via the SOMANET Drive board. An example of a stack consisting of the SOMANET COM-EtherCAT, SOMANET Core C2X and SOMANET Drive 1000 boards is shown below. In this case the SOMANET Drive 1000 board can be supplied with 12 - 24 V DC power source. Please refer to the corresponding Drive board hardware documentation and also motor specifications to select the proper supply voltage. For the best experience please make sure that your stabilized DC power supply is capable of delivering more than 2 Amperes of power for low power motors (up to 100W) and more than 10A for high power motors (up to 1kW). Please mind that at high motor accelerations starting current may be as high as 10 times the nominal.


Hardware Setup for SOMANET Cyclic Positioning Control with EtherCAT Demo

To setup the system:

  1. If you don’t have the stack assembled, assemble it as shown in the image above. Make sure to connect the IF2 side of the SOMANET Core module to the Drive board and COM side to the Core Debug Adapter (see markings on the Core module)
  2. Connect the xTAG Adapter to the Core Debug Adapter.
  3. Connect the xTAG to host PC.
  4. Connect the motor supplied with the kit as shown in the image below.
  5. Connect the Drive board to a 24 V DC power supply.
  6. Connect one side of the Ethernet cable to the node and plug the RS-45 connector to your PC.
  7. Switch on the power supply. If everything is connected properly, drained current should not exceed 150mA.

Connecting the motor and cables to your kit

Build the application

  1. You need the EtherCAT master IgH EtherLab to be installed on your system to build the application.

  2. You need the ncurses library installed on your system to build the application. There is probably a package existing for you linux distribution. It’s the libncurses-dev package on Ubuntu:

    $ sudo apt-get install libncurses5-dev
  3. The app also needs libreadsdoconfig which is in sc_sncn_ethercat_drive/examples/libreadsdoconfig

  4. Navigate with the terminal to the application directory sc_sncn_ethercat_drive/examples/app_demo_master_cyclic an run make to build the app.

Run the application

When the application has been compiled, the next step is to run it on the Linux PC. Before doing that, make sure that the SOMANET EtherCAT stack is running a proper motor control software for the EtherCAT slave side

  1. Make sure your EtherCAT Master is up and running. To start the Master on a Linux machine, execute the following command:

    $ sudo /etc/init.d/ethercat start
  2. Make sure your SOMANET node is accessible by the EtherCAT master by typing:

    $ ethercat slave

    The output should indicate a presence of the SOMANET node and pre-operational state if the slave side software is running:

    0  0:0  PREOP  +  CiA402 Drive
  3. Set all the parameters for you motor in the sc_sncn_ethercat_drive/examples/app_demo_master_cyclic/sdo_config/sdo_config.csv file This is a Comma Separated Values formatted file. The parameters are in the format:

    index, subindex,      axis 1,      axis 2,      axis 3,      axis 4,      axis 5,      axis 6
  4. Navigate with the terminal to the application directory on the hard disk. The compiled binaray is in the bin folder. Then execute the application. Use the -o flag if you want to enable sdo parameters upload from the sdo_config.csv file:

    bin/app_demo_master_cyclic -o
  5. The application will display the actual position, velocity and torque of each connected slaves. You can then switch to CSP, CSV or CST mode by pressing p, v or t and set a target value by typing a number and press enter:

    Slave  0: Torque control            0
              Position            6406599 | Velocity       9 | Torque    18
    > 100
  6. You can stop the selected slave with s (stop all the slaves with ss). Quit the app with q. And change the selected slave with the up and down keyboard arrows (the current selected slave is highlighted). If a slave in fault state you need to acknowledge the fault with a to reset it.


The application provides the following command line arguments

  • -h print this help and exit
  • -o enable sdo upload
  • -v print version and exit
  • -d enable debug display
  • -s <speed> profile velocity in rpm
  • -a <acceleration> profile acceleration in rpm/s
  • -t <torque acceleration> profile torque acceleration
    in 1/1000 of rated torque per second
  • -c <file> SDO config filename

The application is a ncurses graphical console application. It uses simple commands to switch between CSP, CSV and CST modes and send a target position, velocity or torque:

  • up | down arrows: select slave
  • p | v | t: switch to CSP | CSV | CST operation mode
  • [number]: set target (depends on the opmode)
  • r: reverse target
  • s: disable operation, ‘ss’ to stop all the slaves
  • d: enable debug display
  • m: enable manual mode
  • c[dec number] | o[dec number]: manually set the controlword | opmode
  • a: acknowledge fault
  • q: quit

The commands are also printed is the app.

Examine the code

  • The master is initialized with ecw_master_init.
  • Then we read the number of slaves with ecw_master_slave_count. Is is used later to loop through all the slaves.
  • If enabled we uploads the sdo parameters with write_sdo_config using the parameter parsed from the sdo_config.csv file.
  • The master is started with ecw_master_start
  • The rest is initialisation of various data structures used by the app. The profiler settings are initialized using values from the command line arguments.
Main loop:

To be able to handle multiple slave all the functions of the main loop are executed for each slaves using a for loop with the slave count parameter. So each slave is handled independently. Only the commands entered by the user apply to only the selected slave. The selected slave is known by using the select local variable which is changed using the up and down arrows.

  • In the main loop the communication with the slave is done with ecw_master_cyclic_function.
  • The pdo values are read and write with pdo_handler.
  • The display_slaves function display the slaves data (position, velocity, torque) and state.
  • cs_command is managing the console commands. It will change the opmode, the selected slave and initialize the profiler when a new target is entered.
  • state_machine_control is an important function. It manages the slave state machine to switch to the opmode selected by the user. It basically puts the slave in SWITCH_ON_DISABLED state when switching the opmode and in OP_ENABLED state to enable the operation after the opmode is set.
  • target_generate generates a new position, velocity or torque target for each loop using the profiler.