Lab 4: Interpolation of motion¶

Scope:¶

This laboratory consist of two parts:

• A short introduction.
• Writing your own ROS package.

The task:¶

• Develop the system from the previous laboratory by either copying the package or modyfying it.
• Create ROS node jint that interpolates trajectory in configuration space.
  • The node uses ROS service (Remote Procedure Call - RPC) of type jint_control_srv. You should create this service type.
    • The node jint gets desired joint position and other required parameters (e.g. duration) as input.
    • The node answers interpolation status that can be sent after the interpolation is complete or immediately, if there are errors in the input parameters (e.g. zero or negative duration).
  • The RPC can be executed directly from terminal or by a dedicated node jcmd.
  • After reception of valid command, the node jint publishes interpolated positions on ROS topic and sends it to robot_state_publiher node.
    • At first, use linear interpolation.
    • Next, add more sophisticated method, e.g. trapezoid velocity profile or spline interpolation (please refer to: https://en.wikipedia.org/wiki/Spline_interpolation#Algorithm_to_find_the_interpolating_cubic_spline). You can assume zero velocity at the beginning and at the end of motion.
    • All interpolation modes should be implemented in one ROS node and can be selected in jint_control_srv.
  • Visualize behaviour of the system in RVIZ. Visualize the followed trajectory.
    

• Create a similar ROS node oint, that generates interpolation of a reference frame in Cartesian space.
  • In this task the frame is not related to the robot nor to its end effector.
  • Use pose marker in RVIZ and set its shape as axes.
  • The message sent to RVIZ is of type PoseStamped from geometry_msgs package.
  • At first, interpolate position only and keep orientation constant.
  • Next, interpolate orientation.
  • The command for node oint is sent through ROS service of type oint_control_srv from terminal or from a dedicated node ocmd.
  • Visualize behavior of the system in RVIZ. Draw the trajectory of the frame.
    

• Add wiki page to your repository (the documentation). The page should contain description of source files, instruction for launching and description of tests.
  • On all graphs of structure of the system topics and services should be shown differently.
  • The plots of variables from topics should contain outputs of interpolators. The outputs should be continuous.
• Use separate roslaunch files for:
  • roscore and RVIZ (it should be running until URDF file is modified).
  • The rest of the system.
• Test the system and show it to the tutor.