Arm Jogging in Real-Time

This tutorial shows how to send real-time jogging commands to a ROS-enabled robot. Some nice features of the jogger are singularity handling and collision checking that prevents the operator from breaking the robot.

Getting Started

This tutorial tests the jogger with a UR5 Gazebo simulation. If you haven’t already done so, make sure you’ve completed the steps in Getting Started.

Clone universal_robot melodic-devel branch into the same catkin workspace from Getting Started:

cd ~/ws_moveit/src

git clone -b melodic-devel https://github.com/ros-industrial/universal_robot

Install any new dependencies that may be missing:

rosdep install -y --from-paths . --ignore-src --rosdistro $ROS_DISTRO

Re-build and re-source the workspace.

cd ~/ws_moveit/

catkin build

source devel/setup.bash

Launch the Gazebo simulation:

roslaunch ur_gazebo ur5.launch

roslaunch ur5_moveit_config ur5_moveit_planning_execution.launch sim:=true

roslaunch ur5_moveit_config moveit_rviz.launch config:=true

In RViz, grab the red/blue/green “interactive marker” and drag the robot to a non-singular position (not all zero joint angles) that is not close to a joint limit. Click “plan and execute” to move the robot to that pose.

Switch to a compatible type of ros-control controller. It should be a JointGroupVelocityController or a JointGroupPositionController, not a trajectory controller like MoveIt usually requires.

rosservice call /controller_manager/switch_controller "start_controllers:
- 'joint_group_position_controller'
stop_controllers:
- 'arm_controller'
strictness: 2"

Launch the jog node. This example uses commands from a SpaceNavigator joystick-like device:

roslaunch moveit_jog_arm spacenav_cpp.launch

If you do not have a SpaceNav 3D mouse, you can publish example jogging commands from the command line with:

rostopic pub -r 100 /jog_arm_server/delta_jog_cmds geometry_msgs/TwistStamped "header: auto
twist:
  linear:
    x: 0.0
    y: 0.01
    z: -0.01
  angular:
    x: 0.0
    y: 0.0
    z: 0.0"

Settings

User-configurable settings of the jog node are well-documented in jog_arm/config/ur_simulated_config.yaml.

Robot Requirements

The jogger streams an array of position or velocity commands to the robot controller. This is compatible with ros_control position_controllers/JointGroupPositionControllers or velocity_controllers/JointGroupVelocityControllers. You can check if these controllers are available for your robot by searching for the controller config file (typically named controllers.yaml). After launching the robot, you can check if any ros_control controllers are available with:

rosservice call /controller_manager/list_controllers

And switch to the desired controller with:

rosservice call /controller_manager/switch_controllers controller_to_start controller_to_stop

NOTE: You can tab-complete to help fill these commands.

Jogging may work on other robots that have a different control scheme but there is no guarantee. It has been tested heavily on UR robots using the ur_modern_driver. The jogger currently does not limit joint jerk so may not be compatible with most heavy industrial robots.

The jogger can publish trajectory_msgs/JointTrajectory or std_msgs/Float64MultiArray message types. This is configured in a yaml file (see config/ur_simulated_config.yaml for an example). Most robots that use ros_control will use the Float64MultiArray type. Some UR robots using older driver versions can require the JointTrajectory message type.

ROS Signals

An rqt_graph of the jogger is shown below (Enlarge by clicking it). Most of these connections can be ignored. The important ones are:

  • jog_arm_server node: Does the core jogging calculations.
  • spacenav_to_twist node: Converts incoming commands from the joystick to Cartesian commands or joint angle commands, depending on which buttons are pressed.
  • tf topic: Carries ROS coordinate frame information. The jogger uses it to transform commands from the joystick’s frame of reference to the robot’s base/planning frame. These frames are configured in config/ur_simulated_config.yaml.
  • joint_states topic: The jogger uses this joint information for calculations.
  • joint_group_position_controller/command topic: This is the outgoing command that causes the robot to move.
../../_images/jogging_rqt_graph.png

Configuring Control Devices (Gamepads, Joysticks, etc)

The jog_arm/config folder contains two examples of converting SpaceNavigator 3D mouse commands to jog commands. spacenav_teleop_tools.launch loads a config file then publishes commands to the jogger on the spacenav/joy topic. It is easy to create your own config file for a particular joystick or gamepad. We welcome pull requests of config files for new controllers.

spacenav_cpp.launch launches a C++ node that does the same thing but with less latency. We do not plan to accept C++ pull requests for more controller types because there is a lot of overhead involved in supporting them.

Integration Testing

There is a Python integration test in test/integration. Run it by:

roscd jog_arm
catkin run_tests --this

Open Source Feedback

See something that needs improvement? Please open a pull request on this GitHub page