Accessing the RoNeX data directly from a controller

This tutorial shows how you can access RoNex data directly from a controller at 1kHz.

As input, we use here a potentiometer (a three-terminal resistor with a sliding contact that forms an adjustable voltage divider). And it is connected to the first analogue sampling channel (i.e., index 0) on the General I/O module with the alias “test_ronex”.

Files belonging to this tutorial can be found in the sr_ronex_examples package.

• model/simple_robot.urdf: a description of the robot.
• launch/sr_ronex_simple_controller.launch: a launch file to start the drivers, the controllers, and a few utils.
• config/data_access_controller.yaml: the parameter settings.
• controller_plugins.xml: the plugin settings.

For a detailed desription of how these files are used, please read this tutorial: Working with a joint based robot

The code

Change directories to your sr_ronex_examples package.

roscd sr_ronex_examples/
cd src
pwd

C++ header file sr_ronex_simple_controller.hpp is located inside the include/sr_ronex_examples directory.

#pragma once

#include <ros/node_handle.h>

#include <controller_interface/controller.h>
#include <ros_ethercat_model/robot_state.hpp>
#include <sr_ronex_hardware_interface/mk2_gio_hardware_interface.hpp>
#include <realtime_tools/realtime_publisher.h>
#include <sr_ronex_utilities/sr_ronex_utilities.hpp>

#include <std_msgs/Bool.h>
#include <sr_ronex_msgs/PWM.h>

namespace ronex
{
  class SrRoNeXSimpleController
    : public controller_interface::Controller<ros_ethercat_model::RobotState>
  {
public:
    SrRoNeXSimpleController();
    virtual ~SrRoNeXSimpleController();

    virtual bool init(ros_ethercat_model::RobotState* robot, ros::NodeHandle &n);

    virtual void starting(const ros::Time&);

    virtual void update(const ros::Time&, const ros::Duration&);

    virtual void stopping(const ros::Time&);

  private:
    int loop_count_;

    ronex::GeneralIO* general_io_;
  };
}

C++ source file sr_ronex_simple_controller.cpp is located inside the src directory.

#include "sr_ronex_examples/sr_ronex_simple_controller.hpp"
#include "pluginlib/class_list_macros.h"

PLUGINLIB_EXPORT_CLASS( ronex::SrRoNeXSimpleController, controller_interface::ControllerBase)

namespace ronex
{
SrRoNeXSimpleController::SrRoNeXSimpleController()
  : loop_count_(0)
{
}

SrRoNeXSimpleController::~SrRoNeXSimpleController()
{
}

bool SrRoNeXSimpleController::init(ros_ethercat_model::RobotState* robot, ros::NodeHandle &n)
{
  assert (robot);

  std::string path("/ronex/general_io/test_ronex");
  general_io_ = static_cast<ronex::GeneralIO*>( robot->getCustomHW(path) );
  if( general_io_ == NULL)
  {
    ROS_ERROR_STREAM("Could not find RoNeX module (i.e., test_ronex). The controller is not loaded.");
    return false;
  }

  return true;
}

void SrRoNeXSimpleController::starting(const ros::Time&)
{
  // Do nothing.
}

void SrRoNeXSimpleController::update(const ros::Time&, const ros::Duration&)
{
  double position = general_io_->state_.analogue_[0];
  if (loop_count_++ % 100 == 0)
  {
    ROS_INFO_STREAM( "Position = " << position );
    loop_count_ = 0;
  }
}

void SrRoNeXSimpleController::stopping(const ros::Time&)
{
  // Do nothing.
}

}

The Code Explained

First, we look for General I/O module “test_ronex”.

bool SrRoNeXSimpleController::init(ros_ethercat_model::RobotState* robot, ros::NodeHandle &n)
{
  assert (robot);

  std::string path("/ronex/general_io/test_ronex");
  general_io_ = static_cast<ronex::GeneralIO*>( robot->getCustomHW(path) );
  if( general_io_ == NULL)
  {
    ROS_ERROR_STREAM("Could not find RoNeX module (i.e., test_ronex). The controller is not loaded.");
    return false;
  }

  return true;
}

If the module is found, we repeatedly read the data from the first analogue sampling channel and output it to the console.

void SrRoNeXSimpleController::update(const ros::Time&, const ros::Duration&)
{
  double position = general_io_->state_.analogue_[0];
  if (loop_count_++ % 100 == 0)
  {
    ROS_INFO_STREAM( "Position = " << position );
    loop_count_ = 0;
  }
}

Note that class SrRoNeXSimpleController inherits from the template class controller_interface::Controller

namespace ronex
{
  class SrRoNeXSimpleController
    : public controller_interface::Controller<ros_ethercat_model::RobotState>
  {
  public:
    SrRoNeXSimpleController();
    virtual ~SrRoNeXSimpleController();

Running the code

First, if you are using eth0 instead of eth1, please update the following line in the launch file.

<arg name="ethercat_port" default="$(optenv ETHERCAT_PORT eth1)" />

Now, run terminal in sudo mode.

sudo -s

Launch the controller (it was compiled to a library: libsr_ronex_simple_controller.so).

roslaunch sr_ronex_examples sr_ronex_simple_controller.launch

Now you should to able to see the analogue data on the console.

[ INFO] [1380207765.910351751]: Position = 4095
[ INFO] [1380207765.911347629]: Position = 4095
[ INFO] [1380207765.912353727]: Position = 4095
[ INFO] [1380207765.913331810]: Position = 4095
[ INFO] [1380207765.914350895]: Position = 4095
[ INFO] [1380207765.915329345]: Position = 4095