parallel_gripper.cpp

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// Author: Michael Ferguson

#include <pluginlib/class_list_macros.h>
#include <robot_controllers/parallel_gripper.h>

PLUGINLIB_EXPORT_CLASS(robot_controllers::ParallelGripperController, robot_controllers::Controller)

namespace robot_controllers
{

int ParallelGripperController::init(ros::NodeHandle& nh, ControllerManager* manager)
{
  // We absolutely need access to the controller manager
  if (!manager)
  {
    initialized_ = false;
    return -1;
  }

  Controller::init(nh, manager);
  manager_ = manager;

  // Setup Joints */
  std::string l_name, r_name;
  nh.param<std::string>("l_gripper_joint", l_name, "l_gripper_finger_joint");
  nh.param<std::string>("r_gripper_joint", r_name, "r_gripper_finger_joint");

  left_ = manager_->getJointHandle(l_name);
  right_ = manager_->getJointHandle(r_name);

  // Checking to see if Joint Handles exists
  if (!left_)
  {
    ROS_ERROR_NAMED("ParallelGripperController",
                    "Unable to retreive joint (%s), Namespace: %s/l_gripper_joint",
                    l_name.c_str(), nh.getNamespace().c_str());
    return -1;  
  }
  
  if (!right_)
  {
    ROS_ERROR_NAMED("ParallelGripperController",
                    "Unable to retreive joint (%s), Namespace: %s/r_gripper_joint",
                    r_name.c_str(), nh.getNamespace().c_str());
    return -1;
  } 

  // Start action server
  server_.reset(new server_t(nh, "",
                boost::bind(&ParallelGripperController::executeCb, this, _1),
                false));
  server_->start();

  // Get Params
  nh.param<double>("max_position", max_position_, 0.1);
  nh.param<double>("max_effort", max_effort_, 10.0);

  // PID controller for centering the gripper
  if (centering_pid_.init(ros::NodeHandle(nh, "centering")))
  {
    use_centering_controller_ = true;
  }

  // Set default to max
  goal_ = max_position_;
  effort_ = max_effort_;

  initialized_ = true;
  return 0;
}

bool ParallelGripperController::start()
{
  if (!initialized_)
  {
    ROS_ERROR_NAMED("ParallelGripperController",
                    "Unable to start, not initialized.");
    return false;
  }

  if (!server_->isActive())
  {
    ROS_ERROR_NAMED("ParallelGripperController",
                    "Unable to start, action server is not active.");
    return false;
  }

  return true;
}

bool ParallelGripperController::stop(bool force)
{
  if (!initialized_)
    return true;

  if (server_->isActive())
  {
    if (force)
    {
      // Shut down the action
      server_->setPreempted();
      return true;
    }

    // Do not abort unless forced
    return false;
  }

  // Just holding position, go ahead and stop us
  return true;
}

bool ParallelGripperController::reset()
{
  // Nothing to do here
  return true;
}

void ParallelGripperController::update(const ros::Time& now, const ros::Duration& dt)
{
  if (!initialized_)
    return;

  if (use_centering_controller_)
  {
    double position = left_->getPosition() + right_->getPosition();
    double effort = fabs(effort_);
    if (goal_ < position)
    {
      effort = -effort;
    }

    double offset = centering_pid_.update(left_->getPosition() - right_->getPosition(), dt.toSec());

    left_->setEffort(effort - offset);
    right_->setEffort(effort + offset);
  }
  else
  {
    left_->setPosition(goal_/2.0, 0, effort_);
    right_->setPosition(goal_/2.0, 0, effort_);
  }
}

void ParallelGripperController::executeCb(const control_msgs::GripperCommandGoalConstPtr& goal)
{
  control_msgs::GripperCommandFeedback feedback;
  control_msgs::GripperCommandResult result;

  if (!initialized_)
  {
    server_->setAborted(result, "Controller is not initialized.");
    return;
  }

  if (manager_->requestStart(getName()) != 0)
  {
    server_->setAborted(result, "Cannot execute, unable to start controller.");
    ROS_ERROR_NAMED("ParallelGripperController",
                    "Cannot execute, unable to start controller.");
    return;
  }

  // Effort of 0.0 means use max
  if (goal->command.max_effort <= 0.0 || goal->command.max_effort > max_effort_)
  {
    effort_ = max_effort_;
  }
  else
  {
    effort_ = goal->command.max_effort;
  }

  // Set goal position
  if (goal->command.position > max_position_)
  {
    goal_ = max_position_;
  }
  else if (goal->command.position < 0.0)
  {
    goal_ = 0.0;
  }
  else
  {
    goal_ = goal->command.position;
  }

  // Track position/time for stall detection
  float last_position = left_->getPosition() + right_->getPosition();
  ros::Time last_position_time = ros::Time::now();

  ros::Rate r(50);
  while (true)
  {
    // Abort detection
    if (server_->isPreemptRequested() || !ros::ok())
    {
      ROS_DEBUG_NAMED("ParallelGripperController", "Command preempted.");
      server_->setPreempted();
      break;
    }

    // Publish feedback before possibly completing
    feedback.position = left_->getPosition() + right_->getPosition();
    feedback.effort = left_->getEffort() + right_->getEffort();
    feedback.reached_goal = false;
    feedback.stalled = false;
    server_->publishFeedback(feedback);

    // Goal detection
    if (fabs(feedback.position - goal->command.position) < 0.002)
    {
      result.position = feedback.position;
      result.effort = feedback.effort;
      result.reached_goal = true;
      result.stalled = false;
      ROS_DEBUG_NAMED("ParallelGripperController", "Command Succeeded.");
      server_->setSucceeded(result);
      return;
    }

    // Stall detection
    if (fabs(feedback.position - last_position) > 0.005)
    {
      last_position = feedback.position;
      last_position_time = ros::Time::now();
    }
    else
    {
      if (ros::Time::now() - last_position_time > ros::Duration(2.0))
      {
        result.position = feedback.position;
        result.effort = feedback.effort;
        result.reached_goal = false;
        result.stalled = true;
        ROS_DEBUG_NAMED("ParallelGripperController", "Gripper stalled, but succeeding.");
        server_->setSucceeded(result);
        return;
      }
    }

    r.sleep();
  }
}

std::vector<std::string> ParallelGripperController::getCommandedNames()
{
  std::vector<std::string> names;
  names.push_back(left_->getName());
  names.push_back(right_->getName());
  return names;
}

std::vector<std::string> ParallelGripperController::getClaimedNames()
{
  // Claimed == commanded.
  return getCommandedNames();
}

}  // namespace robot_controllers