Run the VM

Follow the instructions inPerform Co-Simulation between Simulink and Gazeboto download the virtual machine (VM) with Gazebo.

露台的世界

This example uses a world given in the VM,differentialDriveRobot.world, as a simple ground plane with default physics settings. The world uses a Pioneer robot with the default controllers removed, so that the built-in controllers do not compete with torques provided from Simulink. The Pioneer robot is available in default Gazebo installs. The Gazebo plugin references the plugin required for the connection to Simulink, as detailed inPerform Co-Simulation between Simulink and Gazebo.

Double-click theGazebo Differential Drive Roboticon.

选择,在终端运行这些命令:

cd /home/user/src/GazeboPlugin/export export SVGA_VGPU10=0 gazebo ../world/differentialDriveRobot.world

If the Gazebo simulator fails to open, you may need to reinstall the plugin. SeeInstall Gazebo PluginManuallyinPerform Co-Simulation between Simulink and Gazebo.

Model Overview

Open the model:

open_system('GazeboDifferentialDriveControl')

The model has four sections:

Gazebo Pacer

This section establishes the connection to Gazebo. Double-click theGazebo Pacerblock to open its parameters, and then click theConfigure Gazebo network and simulation settingslink. This will open a dialog.

Specify theIP Addressfor your VM. By default, Gazebo connects on the14581port. Click theTestbutton to verify the connection to Gazebo.

If the test is not successful, make sure to check the instructions inPerform Co-Simulation between Simulink and Gazeboand ensure that Gazebo is properly configured and the associated world is up and running.

Gazebo Sensor Outputs

The sensor outputs read sensor data from Gazebo and passes it to the appropriate Simulink blocks. An XY graph plots the current robot position, and pose data is saved to the simulation output.

TheRead Gazebo Sensorssubsystem extracts the robot pose and wheel sensor data. The pose data are thexy-coordinates and a four-element quaternion for orientation. The wheel speeds are computed based on rate of change of the wheel positions as they rotate.

Mobile Robot Control

TheMobile Robot Controlsection accepts a set of target waypoints, current pose, and the current wheel speeds, and outputs the wheel torques needed to have the robot follow a path that pursues the waypoints.

There are three main components.

ThePure Pursuitblock is a controller that specifies the vehicle speed and heading angular velocity of the vehicle needed to follow the waypoints at a fixed speed, given the current pose.

TheSet Wheel SpeedMATLAB Function block converts vehicle speed and heading angular velocity to left and right wheel speed, using the kinematics of a differential drive robot:

${\stackrel{\dot{}}{\varphi }}_{\mathit{L}}$and ${\stackrel{\dot{}}{\varphi }}_{\mathit{R}}$are the left and right wheel speeds, $\mathit{v}$is the vehicle speed, $$is the vehicle heading angular velocity, $\mathit{d}$is the track width, and $\mathit{r}$is the wheel radius. Additionally, this MATLAB® Function includes code to throttle the wheel speed. Since thePure Pursuitblock uses a fixed speed throughout, inside the MATLAB Function block, there are two if-statements. The first slows the velocity at a rate proportional to the distance to the goal when the robot is within a certain distance threshold. The second if-statement stops the robot when it is within a tight threshold. This helps the robot to come to a gentle stop.

Finally, thePioneer Wheel Controlsubsystem converts the desired wheel speeds to torques using a proportional controller.

Actuator Torque Commands

The last section of the model takes the torque commands produced by the controller and sends it to Simulink using blocks from theGazebo Co-Simulation Library.

Inside each of the subsystems in this block, aBus Assignmentblock is used to assign the joint torque to the correct joint.

For example, inside theLeft Wheel Gazebo Torque Commandsubsystem, shown above, aGazebo Blank Messagewith theApplyJointTorquecommand type is used to specify the bus type. The model and joint name are provided by theGazebo Select Entityblock, which is linked to the joint associated with the left wheel in the Gazebo world,left_wheel_hinge. The torque is applied for the entire step time, 0.01 seconds, specified in nanoseconds since these inputs must be provided as integers. The output of the bus is passed to aGazebo Apply Commandblock.

Simulate the robot

To run the model, initialize the waypoints and set the sample time:

waypoints = [0 0; 4 2; 3 7; -3 6]; sampleTime = 0.01;

ClickPlaybutton or use thesimcommand to run the model. During execution, the robot should move in Gazebo, and anXY Plotupdates the pose observed in Simulink.

The figures plot the set of waypoints and the final executed path of the robot.