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Author: Jordi Pages < jordi.pages@pal-robotics.com >

Maintainer: Jordi Pages < jordi.pages@pal-robotics.com >

Support: tiago-support@pal-robotics.com

Source: https://github.com/pal-robotics/tiago_tutorials.git

Playing pre-defined upper body motions

Description: Tutorial on how to play back pre-defined upper body motions with TIAGo using the play_motion package.

Keywords: play_motion, joint_trajectory_controller, motion planning

Tutorial Level: BEGINNER

Purpose

The purpose of this tutorials is to show how to run pre-defined upper body motions with TIAGo. This is pretty easy by using the play_motion package, which enables executing simultaneous trajectories in multiple groups of joints.

Pre-requisites

First make sure that the tutorials are properly installed along with the TIAGo simulation, as shown in the Tutorials Installation Section.

Execution

First open two consoles and source the public simulation workspace as follows:

• cd /tiago_public_ws/
  source ./devel/setup.bash

Launching the simulation

In the first console launch for example the following simulation

• roslaunch tiago_gazebo tiago_gazebo.launch public_sim:=true end_effector:=pal-hey5 world:=empty

Gazebo will show up with TIAGo in an empty world.

When the simulation is launched, the play_motion action server is automatically launched and the motions defined in tiago_motions_pal-hey5_schunk-ft.yaml have been loaded in the ros parameter server.

In order to see the names of the motions defined run the following instruction in the second console:

• rosparam list | grep  "play_motion/motions" | grep "meta/name" | cut -d '/' -f 4

For TIAGo equipped with the Hey5 hand the following motions are available in the public simulation:

• close
  close_half
  do_weights
  gun_hand
  head_tour
  home
  inspect_surroundings
  offer
  open
  pick_from_floor
  pinch_hand
  point
  pregrasp_weight
  prepare_grasp
  reach_floor
  reach_max
  shake_hands
  thumb_up_hand
  unfold_arm
  wave

The relevant information of a motion, i.e. the wave motion, is stored in the following parameters:

• /play_motion/motions/wave/joints
  /play_motion/motions/wave/points

In the case of the wave motion the joints parameter specifies which joints intervene in the motion:

• rosparam get /play_motion/motions/wave/joints

[arm_1_joint, arm_2_joint, arm_3_joint, arm_4_joint, arm_5_joint, arm_6_joint, arm_7_joint]

which denotes that in order to execute this motion the group of joints of the arm will be used.

The joint trajectory, i.e. timed sequence of positions (see http://wiki.ros.org/joint_trajectory_controller for details), that composes this motion can be retrieved as follows

• rosparam get /play_motion/motions/wave/points

- positions: [0.06337464909724033, -0.679638896132783, -3.1087325315620733, 2.0882339360702575,
    -1.1201172410014792, -0.031008601325809293, -2.0744261217334135]
  time_from_start: 0.0
- positions: [0.06335930908588873, -0.7354151774072313, -2.939624246421942, 1.8341256735249563,
    -1.1201355028397157, -0.031008601325809293, -2.0744261217334135]
  time_from_start: 1.0
- positions: [0.06335930908588873, -0.7231278283145929, -2.9385504456273295, 2.2121050027803877,
    -1.1201355028397157, -0.031008601325809293, -2.0744261217334135]
  time_from_start: 2.0
- positions: [0.06335930908588873, -0.7354151774072313, -2.939624246421942, 1.8341256735249563,
    -1.1201355028397157, -0.031008601325809293, -2.0744261217334135]
  time_from_start: 3.0

Each row of positions denote the position that each joint has to attain at the given time with respect to the start of the motion.

Playing motions

As said, the play_motion is an action server. In order to run a motion the following graphical action client can be used for melodic:

• rosrun actionlib axclient.py /play_motion

and for noetic:

• rosrun actionlib_tools axclient.py /play_motion

In the GUI the name of the motion to run must be filled. The skip_planning is set by default to False, which means that the transition to the first position of the joint trajectory will use planning to prevent collisions. The remaining of the trajectory is always executed without planning as it is responsibility of the programmer to define a safe trajectory. Set skip_planning to True only if you are sure that it is safe to reach the first positions in the trajectory from the current kinematic configuration of the robot.

By pressing the SEND GOAL button the request will be sent to /play_motion Action Server and the motion will start executing as shown in the pictures.

An example of motions execution for the titanium version of TIAGo is shown in the following video:

C++ and Python action clients

In tiago_tutorials/run_motion there are play_motion action clients in C++ and Python.

The usage of the C++ action client node is as follows

• rosrun play_motion run_motion wave

where the argument is the name of the motion. If no motion is given the list of available motions will be printed out.

The Python action client node is run as follows

• rosrun play_motion run_motion_python_node.py home