joint_group_position_controller.cpp

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 *  Copyright (c) 2008, Willow Garage, Inc.
 *  Copyright (c) 2012, hiDOF, Inc.
 *  Copyright (c) 2013, PAL Robotics, S.L.
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#include <effort_controllers/joint_group_position_controller.h>
#include <pluginlib/class_list_macros.hpp>
#include <angles/angles.h>
 
namespace effort_controllers
{
 
  JointGroupPositionController::JointGroupPositionController() {}
  JointGroupPositionController::~JointGroupPositionController() {sub_command_.shutdown();}
 
  bool JointGroupPositionController::init(hardware_interface::EffortJointInterface* hw, ros::NodeHandle &n)
  {
    // List of controlled joints
    std::string param_name = "joints";
    if(!n.getParam(param_name, joint_names_))
    {
      ROS_ERROR_STREAM("Failed to getParam '" << param_name << "' (namespace: " << n.getNamespace() << ").");
      return false;
    }
    n_joints_ = joint_names_.size();
 
    if(n_joints_ == 0){
      ROS_ERROR_STREAM("List of joint names is empty.");
      return false;
    }
 
    // Get URDF
    urdf::Model urdf;
    if (!urdf.initParamWithNodeHandle("robot_description", n))
    {
      ROS_ERROR("Failed to parse urdf file");
      return false;
    }
 
    pid_controllers_.resize(n_joints_);
 
    for(unsigned int i=0; i<n_joints_; i++)
    {
      const auto& joint_name = joint_names_[i];
 
      try
      {
        joints_.push_back(hw->getHandle(joint_name));
      }
      catch (const hardware_interface::HardwareInterfaceException& e)
      {
        ROS_ERROR_STREAM("Exception thrown: " << e.what());
        return false;
      }
 
      urdf::JointConstSharedPtr joint_urdf = urdf.getJoint(joint_name);
      if (!joint_urdf)
      {
        ROS_ERROR("Could not find joint '%s' in urdf", joint_name.c_str());
        return false;
      }
      joint_urdfs_.push_back(joint_urdf);
 
      // Load PID Controller using gains set on parameter server
      if (!pid_controllers_[i].init(ros::NodeHandle(n, joint_name + "/pid")))
      {
        ROS_ERROR_STREAM("Failed to load PID parameters from " << joint_name + "/pid");
        return false;
      }
    }
 
    commands_buffer_.writeFromNonRT(std::vector<double>(n_joints_, 0.0));
 
    sub_command_ = n.subscribe<std_msgs::Float64MultiArray>("command", 1, &JointGroupPositionController::commandCB, this);
    return true;
  }
 
  void JointGroupPositionController::starting(const ros::Time& time)
  {
    std::vector<double> current_positions(n_joints_, 0.0);
    for (std::size_t i = 0; i < n_joints_; ++i)
    {
      current_positions[i] = joints_[i].getPosition();
      enforceJointLimits(current_positions[i], i);
      pid_controllers_[i].reset();
    }
    commands_buffer_.initRT(current_positions);
  }
 
  void JointGroupPositionController::update(const ros::Time& time, const ros::Duration& period)
  {
    std::vector<double> & commands = *commands_buffer_.readFromRT();
    for(unsigned int i=0; i<n_joints_; i++)
    {
        double command_position = commands[i];
 
        double error;
        double commanded_effort;
 
        double current_position = joints_[i].getPosition();
 
        // Make sure joint is within limits if applicable
        enforceJointLimits(command_position, i);
 
        // Compute position error
        if (joint_urdfs_[i]->type == urdf::Joint::REVOLUTE)
        {
          angles::shortest_angular_distance_with_large_limits(
            current_position,
            command_position,
            joint_urdfs_[i]->limits->lower,
            joint_urdfs_[i]->limits->upper,
            error);
        }
        else if (joint_urdfs_[i]->type == urdf::Joint::CONTINUOUS)
        {
          error = angles::shortest_angular_distance(current_position, command_position);
        }
        else //prismatic
        {
          error = command_position - current_position;
        }
 
        // Set the PID error and compute the PID command with nonuniform
        // time step size.
        commanded_effort = pid_controllers_[i].computeCommand(error, period);
 
        joints_[i].setCommand(commanded_effort);
    }
  }
 
  void JointGroupPositionController::commandCB(const std_msgs::Float64MultiArrayConstPtr& msg)
  {
    if(msg->data.size()!=n_joints_)
    {
      ROS_ERROR_STREAM("Dimension of command (" << msg->data.size() << ") does not match number of joints (" << n_joints_ << ")! Not executing!");
      return;
    }
    commands_buffer_.writeFromNonRT(msg->data);
  }
 
  void JointGroupPositionController::enforceJointLimits(double &command, unsigned int index)
  {
    // Check that this joint has applicable limits
    if (joint_urdfs_[index]->type == urdf::Joint::REVOLUTE || joint_urdfs_[index]->type == urdf::Joint::PRISMATIC)
    {
      if( command > joint_urdfs_[index]->limits->upper ) // above upper limnit
      {
        command = joint_urdfs_[index]->limits->upper;
      }
      else if( command < joint_urdfs_[index]->limits->lower ) // below lower limit
      {
        command = joint_urdfs_[index]->limits->lower;
      }
    }
  }
 
} // namespace
 
PLUGINLIB_EXPORT_CLASS( effort_controllers::JointGroupPositionController, controller_interface::ControllerBase)