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NOTE: This package is unreleased at this point, the documentation is for Willow Garage internal use only.

Overview

This package contains the move_arm_head_monitor node, which is designed primarily for use by move_arm, enabling the monitoring of a given arm during its motion. During the monitoring, the head is continuously pointed at locations in space where the arm will be in the future, allowing the detection of obstacles if a head-mounted sensor is set up to provide data to the collision map. On the PR2, this sensor is typically the stereo vision.

Note on Usage

Normally, you will not interact with move_arm_head_monitor directly. It, along with move_arm, should be launched with the appropriate remappings and parameters, and that's it (see Example Usage below). The API details below are given as a reference.

Node Instances

One instance of move_arm_head_monitor allows the monitoring of one arm. The names required for the node to connect to the appropriate services need to be remapped properly based on which arm is to be monitored.

ROS API

The move_arm_head_monitor node connects to ROS services for querying arm state and calculating forward kinematics, and to the point head action server. It provides two action servers, one to look at a target location on a given link, and one to monitor a given link.

ROS Parameters

The move_arm_head_monitor node does not take any parameters, as all required information is passed in through the action goal at the start of monitoring. It might be desirable to change this in the future.

Required Services

The move_arm_head_monitor node requires two external services and one action server. In a launch file, the names below should be remapped to the appropriate service or action server, such as the ones recommended.

head_controller_actionserver (pr2_controllers_msgs/PointHeadAction)

  • The point head action server. On the PR2, typically /head_traj_controller/point_head_action
trajectory_query_service (pr2_controllers_msgs/QueryTrajectoryState)
  • The trajectory query service for the arm this node is monitoring, used to get the joint positions in the future. On the PR2, typically /x_arm_controller/query_state
forward_kinematics_service (kinematics_msgs/GetPositionFK)
  • The forward kinematics service for the arm this node is monitoring, used to calculate the coordinates of the monitored point in the future. On the PR2, typically /pr2_xxxx_arm_kinematics/get_fk

Action API

Two action servers are provided. The first action can be used to look at a target location on a given link at a certain time, without starting to monitor. This is useful when we want to make sure the head is pointed at the arm before motion starts (NOTE: this action could be removed and a monitoring goal with a short time used instead). The second action invokes the full monitoring capability. The URL links below don't seem to work, for details on the structure of the goal messages please see the action definitions in the move_arm_head_monitor package.

Action Subscribed Topics

move_arm_head_monitor/look_action/goal (move_arm_head_monitor/HeadLookGoal)

  • A goal for move_arm_head_monitor which defines target link, target (x,y,z) location, etc.
move_arm_head_monitor/monitor_action/goal (move_arm_head_monitor/HeadMonitorGoal)
  • A goal for move_arm_head_monitor which defines all relevant monitoring parameters, such as target link, target (x,y,z) location, monitoring frequency, etc.

Published Topics

Visualization topics
point_head_target_marker (visualization_msgs/Marker)
  • The monitored points where the head is pointed.

Example Usage

To use this node, it must be launched with the correct remappings, and then move_arm needs to be launched also with the appropriate remappings as well as the desired monitoring parameters. Below is an example launch file that can be used to launch the move_arm_head_monitor node for the right arm. The file head_monitor_right_arm.launch in pr2_arm_navigation_actions (trunk) contains this code.

Launch Files

<launch>
  <node pkg="move_arm_head_monitor" type="move_arm_head_monitor" respawn="true" name="head_monitor_right_arm" output="screen">

    <remap from="head_controller_actionserver" to="head_traj_controller/point_head_action" />
    <remap from="trajectory_query_service" to="r_arm_controller/query_state" />
    <remap from="forward_kinematics_service" to="pr2_right_arm_kinematics/get_fk" />
  </node>
</launch>

Below is an example of how the above launch file can be used to launch the move_arm node properly. Note the remaps for head_monitor_action and head_look_action and the various params with with the prefix head_monitor_

<launch>
  <include file="$(find pr2_arm_navigation_actions)/launch/head_monitor_right_arm.launch"/>

  <node pkg="move_arm" type="move_arm_simple_action" output="screen" name="move_right_arm">

    <remap from="robot_description" to="robot_description" />
    <remap from="joint_state" to="joint_states" />
    <remap from="arm_ik" to="pr2_right_arm_kinematics/get_constraint_aware_ik" />
    <remap from="arm_fk" to="pr2_right_arm_kinematics/get_fk" />
    <remap from="filter_trajectory" to="chomp_planner_longrange/filter_trajectory_with_constraints" />

    <remap from="get_trajectory_validity" to="environment_server/get_trajectory_validity" />
    <remap from="get_environment_safety" to="environment_server/get_environment_safety" />
    <remap from="get_execution_safety" to="environment_server/get_execution_safety" />
    <remap from="get_joints_in_group" to="environment_server/get_joints_in_group" />
    <remap from="get_robot_state" to="environment_server/get_robot_state" />
    <remap from="get_state_validity" to="environment_server/get_state_validity" />

    <remap from="head_monitor_action" to="head_monitor_right_arm/monitor_action" />
    <remap from="head_look_action" to="head_monitor_right_arm/look_action" />

    <param name="group" type="string" value="right_arm" />
    <param name="ik_allowed_time" type="double" value="2.0" />
    <param name="trajectory_filter_allowed_time" type="double" value="2.0" />
    <param name="group" type="string" value="right_arm" />
    <param name="controller_action_name" type="string" value="/r_arm_controller/joint_trajectory_action" />

    <param name="head_monitor_link" type="string" value="r_forearm_roll_link" />
    <param name="head_monitor_link_x" type="double" value="0.10" />
    <param name="head_monitor_time_offset" type="double" value="3.0" />
    <param name="head_monitor_max_frequency" type="double" value="3.0" />

    <param name="pause_allowed_time" type="double" value="30000.0" />

  </node>
</launch>

move_arm params

The following params can be given to move_arm to control the monitoring process:

Parameters

~head_monitor_link (string, default: "")
  • The link to monitor. If empty string, no monitoring will be performed.
~head_monitor_link_x (double, default: 0.0)
  • The x offset of the point to monitor in the coordinate frame of the link to monitor.
~head_monitor_link_y (double, default: 0.0)
  • The y offset of the point to monitor in the coordinate frame of the link to monitor.
~head_monitor_link_z (double, default: 0.0)
  • The z offset of the point to monitor in the coordinate frame of the link to monitor.
~head_monitor_max_frequency (double, default: 2.0)
  • The frequency in Hz that the move_arm_head_monitor node tries to maintain for updating the head look position. As the system load increases, the maximum frequency that can be maintained decreases.
~head_monitor_time_offset (double, default: 1.0)
  • The number of seconds to look into the future for determining where to point the head.

Wiki: move_arm_head_monitor (last edited 2010-10-14 01:31:09 by KenConley)