Enzymatic numerical P system - robot control using the Robot Operating System (ROS)

This package is a flexible robot controller that uses enzymatic numerical P systems (ENPS) as base model. It allows the user to control ROS-compatible robots with great flexibility thanks to the use of ROS launch files.

This package depends on the pep.py script from the PeP repository Python2 version. The pep.py script must be placed in the src folder.

Connection with ROS

This package uses ROS Parameters to define the connection between the controller and ROS, as shown in the diagram below:

More specifically, starting from a skeleton launch file such as:

<launch>
    <arg name="pep_input_file" default="$(find pep_controller)src/pep_input/hello_world.pep"/>
    <arg name="loop_rate_hz" default="10"/>

    <group ns="constants">
        <param name="kP" value="10" />
    </group>

    <group ns="input_dev">
        <group ns="range">
            <param name="prox0" value="proximity0" />
            <param name="prox1" value="proximity1" />
        </group>
    </group>

    <group ns="output_dev">
        <group ns="cmd_vel">
            <group ns="linear">
                <param name="linear_x" value="x" />
                <param name="linear_y" value="y" />
                <param name="linear_z" value="z" />
            </group>
            <group ns="angular">
                <param name="angular_x" value="x" />
                <param name="angular_y" value="y" />
                <param name="angular_z" value="z" />
            </group>
        </group>
    </group>

	<node pkg="pep_controller" type="pep_controller.py" name="pep_control" output="screen">
        <param name="pepInputFile" value="$(arg pep_input_file)"/>
        <param name="loopRateHz" value="$(arg loop_rate_hz)"/>

        <!--remap the cmd_vel output topic to that expected by epuck_driver-->
        <remap from="cmd_vel" to="mobile_base/cmd_vel"/>
	</node>

	<!--<node pkg="rviz" type="rviz" name="rviz" />-->

</launch>

one would be able to use the following ENPS objects in the ENPS system defined in pep_input/hello_world.pep:

• kP always receive the constant value 10, before the start of each simulation step. Even if the value is consumed by the system, the controller will always restore it to its set value before each simulation step.

• prox0 and prox1 that receive the most recently received value from proximity sensors (sensor_msgs/Range) with ROS topics /proximity0 and /proximity1 respectively.

  • The values are received and stored in the associated P object before the start of each ENPS simulation step.

• the current value of linear_x, linear_y, linear_z, angular_x, angular_y, angular_z would be used to compose a new geometry_msgs/Twist messsage.

  • The message is published immediately after the end of the simulation step;

ROS compatibility

The package is designed to use the following topics:

• INPUT:

  • sensor_msgs/Range (see launch/leader_follow_distance.launch)
  • sensor_msgs/Imu (see launch/drone_p_controller.launch)
  • TF library translation/rotation (see launch/leader_follow_tf.launch)
  • any std_msgs/Int32 numerical (single value topic) (see signal_receive in launch/led_sync.launch)
  • crazyflie GenericLogData (see crazyflie_ros) available in the crazyflie branch (see launch/crazyflie_pi_waypoint_height.launch)

• OUTPUT:

  • geometry_msgs/Twist in both its complete 6 DOF form (see launch/leader_follow_tf.launch) and a 2-DOF form for use on differential-drive robots (see launch/leader_follow_distance.launch)
  • any std_msgs/UInt8MultiArray value; used here for the cmd_led topic available for the e_puck driver LEDs.
  • any std_msgs/Int32 numerical (single value topic) (see signal_broadcast in launch/led_sync.launch)
  • crazyflie Hover (see crazyflie_ros) available in the crazyflie branch (see launch/crazyflie_pi_waypoint_height.launch)

The package was tested on ROS Indigo on Ubuntu 14.04.

Authors

Andrei George Florea, Cătălin Buiu

Department of Automatic Control And Systems Engineering,

Politehnica University of Bucharest

Bucharest, Romania.