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Create a simple EtherCAT IO network (Implementation Notes)

Description:

Keywords: EtherCAT

Tutorial Level: ADVANCED

Hardware Setup (example)

  1. T61 Thinkpad Laptop (built in Ethernet card)
  2. IO rack: EtherCAT Couper, 8 DI, & 8DO (all Beckhoff)

Beckhoff EtherCAT Drivers

  1. Install OROCOS toolchain for ROS

  2. Install Simple Open !EtherCAT Master (soem) library from source:
    git clone https://github.com/orocos/rtt_soem.git
  3. Make soem by running catkin_make.

  4. Connect EtherCAT device to ethernet port. EtherCAT works over standard ethernet cable. Make a direct connection, I do not think connections through switches work since EtherCAT couplers do not have IP addresses (typcially)
  5. In the soem_core package give the slaveinfo binary root access to socket commands:

     sudo setcap cap_net_raw+ep bin/slaveinfo

    (you might have to install this utility: sudo apt-get install libcap2-bin)

  6. Execute the slaveinfo utility:

     rosrun soem_core slaveinfo <device, typcially eth0>
    When the utility successfully executes a list of connected slaves is printed (this list is generated by auto discovery).
  7. (This step may not be required on the latest soem version) The soem stack has a bug that fails to recognize IO sizes for unknown modules. The following patch fixes the bug (BUG has been submitted). Patch the soem stack with the following:

     diff --git a/soem_master/soem_master_component.cpp b/soem_master/soem_master_component.cpp
     index e166ad0..dc6b460 100644
     --- a/soem_master/soem_master_component.cpp
     +++ b/soem_master/soem_master_component.cpp
     @@ -79,6 +79,8 @@ bool SoemMasterComponent::configureHook()
                  // wait for all slaves to reach PRE_OP state
                  ec_statecheck(0, EC_STATE_PRE_OP, EC_TIMEOUTSTATE);
    
     +          ec_config(FALSE, &m_IOmap);
     +
                  for (int i = 1; i <= ec_slavecount; i++)
                  {
                      SoemDriver
     @@ -89,6 +91,8 @@ bool SoemMasterComponent::configureHook()
                          m_drivers.push_back(driver);
                          log(Info) << "Created driver for " << ec_slave[i].name
                                  << ", with address " << ec_slave[i].configadr
     +                            << ", output bits " << ec_slave[i].Obits
     +                            << ", input bits " << ec_slave[i].Ibits
                                  << endlog();
                          //Adding driver's services to master component
                          this->provides()->addService(driver->provides());
  8. Run rosmake from the soem_master directory to compile in the patch

  9. Edit the test.ops script to start the master up and map OROCOS messages to ROS topics

     import("soem_beckhoff_drivers")
     loadComponent("Master","soem_master::SoemMasterComponent")
     Master.displayAvailableDrivers()
    
     # Default nic is eth0, set if different. e.g.
     #Master.ifname = "eth1"
    
     # Crawls the network and identifies attached devices.  Devices are loaded
     # (if a driver exists) and given names "Slave_1***".  The *** appear to be
     # the module order (at least this is the case for a single rack)
     Master.configure()
    
     # Setting the update period (in seconds).  This determines the rate at which
     # the data is published on the ROS side (setting this value to zero turns
     # off updating
     Master.setPeriod(0.05)
    
     # This stars the Master "task" running.  It will update at the period set
     # above
     Master.start()
    
     # This command remaps OROCOS topics to ROS topics
     stream("Master.Slave_1002.bits", ros.topic("DI"))
     stream("Master.Slave_1003.bits", ros.topic("DO"))
  10. In the ocl package give the deployer-gnulinux binary (called by launch file below) root access to socket commands:

     sudo setcap cap_net_raw+ep bin/deployer-gnulinux
  11. From the command line, launch the master:
     roslaunch soem_master soem_master_test.launch

    The launch file launches orocos and loads the test.ops script.

Other Notes:

  1. Enabling OROCOS Info Logging: export ORO_LOGLEVEL=5 (see The Orocos Component Builder's Manual - Logging)

  2. Orocos messages to/from ROS messages (see rtt_ros_integration_example). Example script call: stream("Master.Slave_1002.bits", ros.topic("DI_bits"))


2018-12-08 12:20