Behavioral Architecture with Real Simualtion

ROS architecture for a robot moving into a simulated arena. The robot has 3 behaviors:

• Play
• Sleep
• Normal

The user can interact with the robot by moving the ball

Software architecture and states diagrams

Software architecture

The architercture is composed by 5 components:

• Ball: simulate a user that move the ball into the arena

• Ball detection: detect the green ball

• Robot controller: control the robot toward a target position

• Command manager: implement robot behaviors through a FSM

• Simulation: simulate the robot and the enviroment

State diagram

The finite state machine is composed by 3 state (robot behaviors):

• PLAY: the robot follows the ball and when the ball is stationary, it rotates its head 45 degrees to the left and 45 degrees to the right. Back in position, the robot follows the ball

• NORMAL (initial state): robot moves in a random ways

• SLEEP: robot goes to home position, it stays there for a certain time and then goes to NORMAL state

ROS messages and parameters

The messages are:

• PoseStamped: robot or ball target position
• Pose: position reached by the robot or the ball
• String: radius and center of the ball
• Int: radius and center of the ball
• CompressedImage: images received from the camera
• Twist: robot velocities

The parameters are:

• home_pos_x,home_pos_x: define the home position in the map (double)
• map_x,map_y: define the dimensions of the map (integer)
• min_delay_ball,max_delay_ball: define the min and max delay for sending the random position of the ball (double)
• min_transition_play_normal,max_transition_play_normal: define the min and max delay to trasit between PLAY and NORMAL (integer,suggested values:80-400)
• min_transition_normal_sleep,max_transition_normal_sleep: define the min and max delay to trasit between NORMAL and SLEEP (integer)
• min_sleep_delay,max_sleep_delay: define the min and max delay for the SLEEP state (double)
• min_dis_ball_delay,max_dis_ball_delay: define the min and max delay for disappearing the ball (int)
• min_clock_head_delay,max_clock_head_delay: define the min and max delay for keeping the head in the -45° position
• min_countclock_head_delay,max_countclock_head_delay: define the min and max delay for keeping the head in the 45° position
• min_head_delay,max_head_delay: define the min and max delay for keeping the head in the 0° position

Packages and files

There are 3 packages:

• Sensoring: contains the command.py and ball_detector.py files used to move the ball and detect it
• Robot control: contains the robot_controller.py file used to move the robot toward a target position
• Command manager: contains the command_manager.py file that implements the FSM of robot behaviors.
• Simulation: contains all the files necessary for running the simulation

Installation and running

In order to run this software, the following prerequisities are needed:

• ROS Noetic
• smach
• gazebo
• gazebo ros control

Before running the software, you must have all files as executable otherwise you can make them executable with the following command

cd <your_workspace>/src/Behavioral-Architecture-with-Real-Simulation
chmod +x sensoring/src/*
chmod +x robot_control/src/*
chmod +x manager/src/*

To run the software

cd <your_workspace>
catkin_make
source devel/setup.bash
cd src/Behavioral-Architecture-with-Real-Simulation
roslaunch launch_file.launch

Working hypothesis and environment

The robot is a pet that interact with a human who moves the ball into an a simulated arena. The arena is a 7x7 grid. Target position of the robot and the ball belong to the arena. The robot has 3 behaviours: PLAY,NORMAL,SLEEP. The PLAY behaviour will start only if the robot sees the ball. The ball is green and is very big with respect to the robot in order to detect it. The home position can be initialize before starting the simulation and cannot be changed during the execution. The word "someTimes" is inteded as number of cycles for which it is executed a piece of code. The ball has no collisions.The ball is considered stationary when the robot is close to it and is stopped.

System's features

• Specify different dimensions of the arena
• It is possibile to define different delays for the simulation
• It is possibile to define different position of the "home" inside the arena before start the simulation
• It is possible to visualize the states transition in the shell
• The robot will notify if it will reach the target position and it is possibile to visualize it in the shell (the position that the robot has reached)
• The robot can perceives the ball even if it is moving in the NORMAL state
• It is possibile to see the camera of the robot in a separated window with the possibility to see a circle around the detected ball
• It is possible to make the ball disappear simply by moving it under the ground
• All the delays are random values between the defined ranges
• The robot ignores the ball when it is in the SLEEP state
• The robot can follow the ball well when it starts to exit the robot's field of view quickly enough thanks to the choice of a good gain for angular velocity
• The robot starts to rotate, for a certain period of time, to look for the ball when it loses it before passing to the NORMAL state

System's limitations

• Slight wheelies of the robot when it passes from NORMAL to PLAY state
• Shaking of the camera due to the joint of the head
• Very slight wheelies of the robot when it starts to move torward a position during NORMAL behavior
• When the ball moves close to the robot but it is stationary, the robot moves its head
• Robot shaking while following the ball
• Since the PLAY-NORMAL transition is implemented as a number of cycles, if the range is small (e.g. 1-10), the transition will be fast (use suggested range or different values)

Possible technical improvements

• Fine tune the PID values for the head joint
• Adopt an incremental gain solution in order to avoid robot wheelies and allow very fast ball following
• Keeping this robot geometry, adopt a control solution that allows you to follow the ball without shaking
• Add collision properties to the ball
• Adopt a different mechanism to understand if the ball is stationary or not
• Implement the transition mechanism between PLAY and NORMAL with a timer

Author and contact

Simone Voto - [email protected]