sim_hw_interface.cpp

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/* Author: Dave Coleman
   Desc:   Example ros_control hardware interface that performs a perfect control loop for
   simulation
*/

#include <ros_control_boilerplate/sim_hw_interface.h>

// ROS parameter loading
#include <rosparam_shortcuts/rosparam_shortcuts.h>

namespace ros_control_boilerplate
{
SimHWInterface::SimHWInterface(ros::NodeHandle& nh, urdf::Model* urdf_model)
  : GenericHWInterface(nh, urdf_model), name_("sim_hw_interface")
{
  // Load rosparams
  ros::NodeHandle rpnh(nh_, "hardware_interface");
  std::size_t error = 0;
  error += !rosparam_shortcuts::get(name_, rpnh, "sim_control_mode", sim_control_mode_);
  if (error)
  {
    ROS_WARN_STREAM_NAMED(name_, "SimHWInterface now requires the following config in the yaml:");
    ROS_WARN_STREAM_NAMED(name_, "   sim_control_mode: 0 # 0: position, 1: velocity");
  }
  rosparam_shortcuts::shutdownIfError(name_, error);
}

void SimHWInterface::init()
{
  // Call parent class version of this function
  GenericHWInterface::init();

  // Resize vectors
  joint_position_prev_.resize(num_joints_, 0.0);

  ROS_INFO_NAMED(name_, "SimHWInterface Ready.");
}

void SimHWInterface::read(ros::Duration& elapsed_time)
{
  // No need to read since our write() command populates our state for us
}

void SimHWInterface::write(ros::Duration& elapsed_time)
{
  // Safety
  enforceLimits(elapsed_time);

  // NOTE: the following is a "simuation" example so that this boilerplate can be run without being
  // connected to hardware
  // When converting to your robot, remove the built-in PID loop and instead let the higher leverl
  // ros_control controllers take
  // care of PID loops for you. This P-controller is only intended to mimic the delay in real
  // hardware, somewhat like a simualator
  for (std::size_t joint_id = 0; joint_id < num_joints_; ++joint_id)
  {
    switch (sim_control_mode_)
    {
      case 0:  // hardware_interface::MODE_POSITION:
        positionControlSimulation(elapsed_time, joint_id);
        break;

      case 1:  // hardware_interface::MODE_VELOCITY:

        // // Move all the states to the commanded set points slowly
        // joint_position_[joint_id] += joint_velocity_[joint_id] * elapsed_time.toSec();

        // v_error_ = joint_velocity_command_[joint_id] - joint_velocity_[joint_id];

        // // scale the rate it takes to achieve velocity by a factor that is invariant to the feedback loop
        // joint_velocity_[joint_id] += v_error_ * VELOCITY_STEP_FACTOR;

        // Naive
        joint_velocity_[joint_id] = joint_velocity_command_[joint_id];
        joint_position_[joint_id] += joint_velocity_command_[joint_id] * elapsed_time.toSec();

        break;

      case 2:  // hardware_interface::MODE_EFFORT:
        ROS_ERROR_STREAM_NAMED(name_, "Effort not implemented yet");
        break;
    }
  }
}

void SimHWInterface::enforceLimits(ros::Duration& period)
{
  // Enforces position and velocity
  pos_jnt_sat_interface_.enforceLimits(period);
}

void SimHWInterface::positionControlSimulation(ros::Duration& elapsed_time, const std::size_t joint_id)
{
  const double max_delta_pos = joint_velocity_limits_[joint_id] * elapsed_time.toSec();

  // Move all the states to the commanded set points at max velocity
  p_error_ = joint_position_command_[joint_id] - joint_position_[joint_id];

  const double delta_pos = std::max(std::min(p_error_, max_delta_pos), -max_delta_pos);
  joint_position_[joint_id] += delta_pos;

  // Bypass max velocity p controller:
  // joint_position_[joint_id] = joint_position_command_[joint_id];

  // Calculate velocity based on change in positions
  if (elapsed_time.toSec() > 0)
  {
    joint_velocity_[joint_id] = (joint_position_[joint_id] - joint_position_prev_[joint_id]) / elapsed_time.toSec();
  }
  else
    joint_velocity_[joint_id] = 0;

  // Save last position
  joint_position_prev_[joint_id] = joint_position_[joint_id];
}

}  // namespace ros_control_boilerplate