在ROS中开始自主机器人仿真 - 3 建立自己的自主机器人URDF模型

要建立自己的自主机器人，首先，必须要建立自己的机器人模型，URDF（Unified Robot Description Format）模型。

Part 3 建立机器人URDF模型

机器人URDF模型主要由两个文件组成：.xacro 是主文件，包含URDF项，包括关节，连杆；.gazebo包含gazebo的具体信息以便在gazebo中仿真。
例子请见：How to Build a Differential Drive Simulation

以下工程的源码下载地址请见：
http://download.csdn.net/download/ziqian0512/9816156

使用方法主要包括以下三个部分：

rviz查看机器人

roslaunch neurobot_description neurobot_rviz.launch

gazebo 仿真

groslaunch neurobot_gazebo neurobot_world.launch

控制机器人运动

rostopic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 0.1
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0"

如何一步步设计自己的工程请见以下部分的详细说明：

1. 创建工程

catkin_create_pkg neurobot_description

2. 差分驱动模型

neurobot_description/urdf/
├── macros.xacro   帮助简化的宏
├── materials.xacro  材料说明
├── neurobot.gazebo gazebo具体信息
└── neurobot.xacro URDF 主文件

在neurobot.xacro中添加chassis, wheels,

添加chassis

  <link name='chassis'>
    <pose>0 0 0.1 0 0 0pose>

    <inertial>
      <mass value="15.0"/>
      <origin xyz="0.0 0 0.1" rpy=" 0 0 0"/>
      <inertia
          ixx="0.1" ixy="0" ixz="0"
          iyy="0.1" iyz="0"
          izz="0.1"
      />
    inertial>

    <collision name='collision'>
      <geometry>
        <box size=".4 .2 .1"/>
      geometry>
    collision>

    <visual name='chassis_visual'>
      <origin xyz="0 0 0" rpy=" 0 0 0"/>
      <geometry>
        <box size=".4 .2 .1"/>
      geometry>
    visual>


    <collision name='caster_collision'>
      <origin xyz="-0.15 0 -0.05" rpy=" 0 0 0"/>
      <geometry>
        <sphere radius="0.05"/>
      geometry>
      <surface>
        <friction>
          <ode>
            <mu>0mu>
            <mu2>0mu2>
            <slip1>1.0slip1>
            <slip2>1.0slip2>
          ode>
        friction>
      surface>
    collision>

    <visual name='caster_visual'>
      <origin xyz="-0.15 0 -0.05" rpy=" 0 0 0"/>
      <geometry>
        <sphere radius="0.05"/>
      geometry>
    visual>

    <collision name='caster_front_collision'>
      <origin xyz="0.15 0 -0.05" rpy=" 0 0 0"/>
      <geometry>
        <sphere radius="0.05"/>
      geometry>
      <surface>
        <friction>
          <ode>
            <mu>0mu>
            <mu2>0mu2>
            <slip1>1.0slip1>
            <slip2>1.0slip2>
          ode>
        friction>
      surface>
    collision>

    <visual name='caster_front_visual'>
      <origin xyz="0.15 0 -0.05" rpy=" 0 0 0"/>
      <geometry>
        <sphere radius="0.05"/>
      geometry>
    visual>

  link>

添加差分驱动轮子

  <link name="left_wheel">
    
    <collision name="collision">
      <origin xyz="0 0 0" rpy="0 1.5707 1.5707"/>
      <geometry>
        <cylinder radius="0.1" length="0.05"/>
      geometry>
    collision>
    <visual name="left_wheel_visual">
      <origin xyz="0 0 0" rpy="0 1.5707 1.5707"/>
      <geometry>
        <cylinder radius="0.1" length="0.05"/>
      geometry>
    visual>
    <inertial>
      <origin xyz="0 0 0" rpy="0 1.5707 1.5707"/>
      <mass value="5"/>
      <inertia
        ixx=".1" ixy="0.0" ixz="0.0"
        iyy=".1" iyz="0.0"
        izz=".1"/>
    inertial>
  link>

添加hinges链接wheels和chassis

  <joint type="continuous" name="left_wheel_hinge">
    <origin xyz="0 0.15 0" rpy="0 0 0"/>
    
    <child link="left_wheel"/>
    <parent link="chassis"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="10000" velocity="1000"/>
    <joint_properties damping="1.0" friction="1.0"/>
  joint>

  <joint type="continuous" name="right_wheel_hinge">
    <origin xyz="0 -0.15 0" rpy="0 0 0"/>
    
    <child link="right_wheel"/>
    <parent link="chassis"/>
    <axis xyz="0 1 0" rpy="0 0 0"/>
    <limit effort="10000" velocity="1000"/>
    <joint_properties damping="1.0" friction="1.0"/>
  joint>

要实现自主导航还需要添加camera和laser，有了激光器和摄像头我们才能让机器人去感知外部世界。

添加camera

  <link name="camera">
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="${cameraSize} ${cameraSize} ${cameraSize}"/>
      geometry>
    collision>

    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="${cameraSize} ${cameraSize} ${cameraSize}"/>
      geometry>
      <material name="green"/>
    visual>

    <inertial>
      <mass value="${cameraMass}" />
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <box_inertia m="${cameraMass}" x="${cameraSize}" y="${cameraSize}" z="${cameraSize}" />
      <inertia ixx="1e-6" ixy="0" ixz="0" iyy="1e-6" iyz="0" izz="1e-6" />
    inertial>
  link>

  <joint name="camera_joint" type="fixed">
    <axis xyz="0 1 0" />
    <origin xyz=".2 0 0" rpy="0 0 0"/>
    <parent link="chassis"/>
    <child link="camera"/>
  joint>

添加laser

 <joint name="hokuyo_joint" type="fixed">
    <axis xyz="0 1 0" />
    <origin xyz=".15 0 .1" rpy="0 0 0"/>
    <parent link="chassis"/>
    <child link="hokuyo"/>
  joint>

  
  <link name="hokuyo">
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
    <box size="0.1 0.1 0.1"/>
      geometry>
    collision>

    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://neurobot_description/meshes/hokuyo.dae"/>
      geometry>
    visual>

    <inertial>
      <mass value="1e-5" />
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="1e-6" ixy="0" ixz="0" iyy="1e-6" iyz="0" izz="1e-6" />
    inertial>
  link>

3. 添加模型插件

只有添加了模型插件，我们才能编写代码控制机器人的运动，采用信息。插件是模型和代码的桥梁。

在neurobot.gazebo中添加gazebo具体描述信息和插件。

差分驱动

 <gazebo>
    <plugin name="differential_drive_controller" filename="libgazebo_ros_diff_drive.so">
      <legacyMode>falselegacyMode>
      <alwaysOn>truealwaysOn>
      <updateRate>10updateRate>
      <leftJoint>left_wheel_hingeleftJoint>
      <rightJoint>right_wheel_hingerightJoint>
      <wheelSeparation>0.4wheelSeparation>
      <wheelDiameter>0.2wheelDiameter>
      <torque>10torque>
      <commandTopic>cmd_velcommandTopic>
      <odometryTopic>odomodometryTopic>
      <odometryFrame>odomodometryFrame>
      <robotBaseFrame>chassisrobotBaseFrame>
    plugin>
  gazebo>

camera

  <gazebo reference="camera">
    <material>Gazebo/Greenmaterial>
    <sensor type="camera" name="camera1">
      <update_rate>30.0update_rate>
      <camera name="head">
        <horizontal_fov>1.3962634horizontal_fov>
        <image>
          <width>800width>
          <height>800height>
          <format>R8G8B8format>
        image>
        <clip>
          <near>0.02near>
          <far>300far>
        clip>
      camera>
      <plugin name="camera_controller" filename="libgazebo_ros_camera.so">
        <alwaysOn>truealwaysOn>
        <updateRate>0.0updateRate>
        <cameraName>neurobot/camera1cameraName>
        <imageTopicName>image_rawimageTopicName>
        <cameraInfoTopicName>camera_infocameraInfoTopicName>
        <frameName>cameraframeName>
        <hackBaseline>0.07hackBaseline>
        <distortionK1>0.0distortionK1>
        <distortionK2>0.0distortionK2>
        <distortionK3>0.0distortionK3>
        <distortionT1>0.0distortionT1>
        <distortionT2>0.0distortionT2>
      plugin>
    sensor>
  gazebo>

laser

laser的几何信息采用mesh文件hokuyo.dae放在meshes文件夹中，

  
  <gazebo reference="hokuyo">
    <sensor type="gpu_ray" name="head_hokuyo_sensor">
      <pose>0 0 0 0 0 0pose>
      <visualize>falsevisualize>
      <update_rate>40update_rate>
      <ray>
        <scan>
          <horizontal>
            <samples>720samples>
            <resolution>1resolution>
            <min_angle>-1.570796min_angle>
            <max_angle>1.570796max_angle>
          horizontal>
        scan>
        <range>
          <min>0.10min>
          <max>30.0max>
          <resolution>0.01resolution>
        range>
        <noise>
          <type>gaussiantype>
          
          <mean>0.0mean>
          <stddev>0.01stddev>
        noise>
      ray>
      <plugin name="gazebo_ros_head_hokuyo_controller" filename="libgazebo_ros_gpu_laser.so">
        <topicName>/neurobot/laser/scantopicName>
        <frameName>hokuyoframeName>
      plugin>
    sensor>
  gazebo>

gazebo仿真材料信息

  <gazebo reference="chassis">
    <material>Gazebo/Orangematerial>
  gazebo>

  <gazebo reference="left_wheel">
    <material>Gazebo/Bluematerial>
  gazebo>

  <gazebo reference="right_wheel">
    <material>Gazebo/Bluematerial>
  gazebo>

4.机器人控制

终于到了我们可以控制自己建立的机器人了。

在rviz中查看自己的机器人

roslaunch neurobot_description neurobot_rviz.launch

neurobot_rviz.launch 文件如下

<launch>
  <param name="robot_description" command="$(find xacro)/xacro.py '$(find mybot_description)/urdf/mybot.xacro'"/>
  
  <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher">
    <param name="use_gui" value="False"/>
  node>
  
  <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher"/>
  
  <node name="rviz" pkg="rviz" type="rviz"/>
  
launch>

在gazebo中加载机器人并控制机器人运动

依然采用在turtlebot中使用的world场景，加载机器人。

roslaunch neurobot_gazebo neurobot_world.launch

通过如下命令

rostopic list

我们可以找到非常重要的四个topic

/cmd_vel  速度控制命令
/neurobot/camera1/image_raw 图像信息
/neurobot/laser/scan 激光数据
/odom 里程计

使用如下命令便可以控制机器人运动了，fancy。

rostopic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 0.1
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0"

也可以使用我们之前turtlebot中使用的keyboard_teleop.launch 和keyop.launch， 将topic主题映射到/cmd_vel。

References:

How to Build a Differential Drive Simulation

urdf Tutorials