3.1 机器人系统设计

机器人定义与组成

执行机构
驱动系统
传感系统
控制系统

机器人系统构建

执行机构的实现

机器人底盘、电机、舵机

驱动系统的实现

电源子系统，电机驱动子系统、传感器接口

内部传感系统的实现

机器人里程计、惯性测量单元（IMU）

控制系统的实现

外部传感系统的实现

常用传感器的ROS驱动可参考：http://wiki.ros.org/Sensor

URDF机器人建模

Unified Robot Description Format,统一机器人描述格式
ROS中非常重要的机器人模型描述格式

<link>

描述机器人某个刚体部分的外观和物理属性
尺寸、颜色、形状、惯性矩阵、碰撞参数等
<visual>:描述机器人link部分的外观参数
<inertial>:描述link的惯性参数
<collision>:描述link的碰撞属性

<joint>

描述机器人关节的运动学和动力学属性
包括关节运动的位置和速度限制
根据关节运动形式，可以将其分为六种类型：

关节类型	描述
continuous	旋转关节，可以围绕单轴无限旋转
revolute	旋转关节，类似于continuous，但是有旋转的角度极限
prismatic	滑动关节，沿某一轴线移动的关节，带有位置极限
planar	平面关节，允许在平面正交方向上平移或旋转
floating	浮动关节，允许进行平移、旋转运动
fixed	固定关节，不允许运动的特殊关节

<calibration>:关节的参考位置，用来校准关节的绝对位置
<dynamics>:描述关节的物理属性，例如阻尼值、物理经摩擦力等，经常在动力学仿真中用到。
<limit>:描述运动的一些极限值包括关节运动的上下限位置、速度限制、力矩限制等；
<mimic>:描述该关节与已有关节的关系
<safety_controller>:描述安全控制器参数

<robot> URDF顶层标签

实践：

1.创建一个机器人建模的功能包

catkin_create_pkg mbot_description urdf xacro //功能包名一般为：机器人名字_description

urdf:存放机器人模型的URDF或xacro文件
meshes:防止URDF中引用的模型渲染文件
launch:保存相关启动文件
config:保存rviz的配置文件

2.创建一些文件夹

在mobot_description功能包中添加一些文件夹

3.创建launch文件

创建launch文件

文件内容如下：

注意：

joint_state_publisher:发布每个joint（除fixed类型）的状态，而且可以通过UI界面对joint进行控制
robot_state_publisher:将机器人各个links、joints之间的关系，通过TF的形式，整理成三维姿态信息发布

4.添加rviz配置文件

添加rviz配置文件

内容如下：

Panels:
  - Class: rviz/Displays
    Help Height: 78
    Name: Displays
    Property Tree Widget:
      Expanded:
        - /Global Options1
        - /Status1
        - /TF1
      Splitter Ratio: 0.5
    Tree Height: 541
  - Class: rviz/Selection
    Name: Selection
  - Class: rviz/Tool Properties
    Expanded:
      - /2D Pose Estimate1
      - /2D Nav Goal1
      - /Publish Point1
    Name: Tool Properties
    Splitter Ratio: 0.588679016
  - Class: rviz/Views
    Expanded:
      - /Current View1
    Name: Views
    Splitter Ratio: 0.5
  - Class: rviz/Time
    Experimental: false
    Name: Time
    SyncMode: 0
    SyncSource: ""
Visualization Manager:
  Class: ""
  Displays:
    - Alpha: 0.5
      Cell Size: 1
      Class: rviz/Grid
      Color: 160; 160; 164
      Enabled: true
      Line Style:
        Line Width: 0.0299999993
        Value: Lines
      Name: Grid
      Normal Cell Count: 0
      Offset:
        X: 0
        Y: 0
        Z: 0
      Plane: XY
      Plane Cell Count: 10
      Reference Frame: <Fixed Frame>
      Value: true
    - Alpha: 1
      Class: rviz/RobotModel
      Collision Enabled: false
      Enabled: true
      Links:
        All Links Enabled: true
        Expand Joint Details: false
        Expand Link Details: false
        Expand Tree: false
        Link Tree Style: Links in Alphabetic Order
        back_caster_link:
          Alpha: 1
          Show Axes: false
          Show Trail: false
          Value: true
        base_link:
          Alpha: 1
          Show Axes: false
          Show Trail: false
          Value: true
        camera_link:
          Alpha: 1
          Show Axes: false
          Show Trail: false
          Value: true
        front_caster_link:
          Alpha: 1
          Show Axes: false
          Show Trail: false
          Value: true
        left_wheel_link:
          Alpha: 1
          Show Axes: false
          Show Trail: false
          Value: true
        right_wheel_link:
          Alpha: 1
          Show Axes: false
          Show Trail: false
          Value: true
      Name: RobotModel
      Robot Description: robot_description
      TF Prefix: ""
      Update Interval: 0
      Value: true
      Visual Enabled: true
    - Class: rviz/TF
      Enabled: true
      Frame Timeout: 15
      Frames:
        All Enabled: true
        back_caster_link:
          Value: true
        base_link:
          Value: true
        camera_link:
          Value: true
        front_caster_link:
          Value: true
        left_wheel_link:
          Value: true
        right_wheel_link:
          Value: true
      Marker Scale: 0.200000003
      Name: TF
      Show Arrows: true
      Show Axes: true
      Show Names: true
      Tree:
        base_link:
          back_caster_link:
            {}
          camera_link:
            {}
          front_caster_link:
            {}
          left_wheel_link:
            {}
          right_wheel_link:
            {}
      Update Interval: 0
      Value: true
  Enabled: true
  Global Options:
    Background Color: 48; 48; 48
    Default Light: true
    Fixed Frame: base_link
    Frame Rate: 30
  Name: root
  Tools:
    - Class: rviz/Interact
      Hide Inactive Objects: true
    - Class: rviz/MoveCamera
    - Class: rviz/Select
    - Class: rviz/FocusCamera
    - Class: rviz/Measure
    - Class: rviz/SetInitialPose
      Topic: /initialpose
    - Class: rviz/SetGoal
      Topic: /move_base_simple/goal
    - Class: rviz/PublishPoint
      Single click: true
      Topic: /clicked_point
  Value: true
  Views:
    Current:
      Class: rviz/Orbit
      Distance: 0.791995764
      Enable Stereo Rendering:
        Stereo Eye Separation: 0.0599999987
        Stereo Focal Distance: 1
        Swap Stereo Eyes: false
        Value: false
      Focal Point:
        X: -0.00707128178
        Y: 0.000214380445
        Z: 0.0199916083
      Focal Shape Fixed Size: true
      Focal Shape Size: 0.0500000007
      Invert Z Axis: false
      Name: Current View
      Near Clip Distance: 0.00999999978
      Pitch: 0.305397928
      Target Frame: <Fixed Frame>
      Value: Orbit (rviz)
      Yaw: 0.725397766
    Saved: ~
Window Geometry:
  Displays:
    collapsed: false
  Height: 754
  Hide Left Dock: false
  Hide Right Dock: false
  QMainWindow State: 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
  Selection:
    collapsed: false
  Time:
    collapsed: false
  Tool Properties:
    collapsed: false
  Views:
    collapsed: false
  Width: 1191
  X: 297
  Y: 107

URDF机器人建模
5.1 使用圆柱体创建一个车体模型

.urdf文件内容

对应的rviz图像

5.2 使用圆柱体创建左、右侧车轮

    <joint name="left_wheel_joint" type="continuous">
        <origin xyz="0 0.19 -0.05" rpy="0 0 0"/>
        <parent link="base_link"/>
        <child link="left_wheel_link"/>
        <axis xyz="0 1 0"/>
    </joint>

    <link name="left_wheel_link">
        <visual>
            <origin xyz="0 0 0" rpy="1.5707 0 0" />
            <geometry>
                <cylinder radius="0.06" length = "0.025"/>
            </geometry>
            <material name="white">
                <color rgba="1 1 1 0.9"/>
            </material>
        </visual>
    </link>

    <joint name="right_wheel_joint" type="continuous">
        <origin xyz="0 -0.19 -0.05" rpy="0 0 0"/>
        <parent link="base_link"/>
        <child link="right_wheel_link"/>
        <axis xyz="0 1 0"/>
    </joint>

    <link name="right_wheel_link">
        <visual>
            <origin xyz="0 0 0" rpy="1.5707 0 0" />
            <geometry>
                <cylinder radius="0.06" length = "0.025"/>
            </geometry>
            <material name="white">
                <color rgba="1 1 1 0.9"/>
            </material>
        </visual>
    </link>

完成后的图像

5.3 使用球体创建前后支撑轮

   <joint name="front_caster_joint" type="continuous">
        <origin xyz="0.18 0 -0.095" rpy="0 0 0"/>
        <parent link="base_link"/>
        <child link="front_caster_link"/>
        <axis xyz="0 1 0"/>
    </joint>

    <link name="front_caster_link">
        <visual>
            <origin xyz="0 0 0" rpy="0 0 0"/>
            <geometry>
                <sphere radius="0.015" />
            </geometry>
            <material name="black">
                <color rgba="0 0 0 0.95"/>
            </material>
        </visual>
    </link>


    <joint name="back_caster_joint" type="continuous">
        <origin xyz="-0.18 0 -0.095" rpy="0 0 0"/>
        <parent link="base_link"/>
        <child link="back_caster_link"/>
        <axis xyz="0 1 0"/>
    </joint>

    <link name="back_caster_link">
        <visual>
            <origin xyz="0 0 0" rpy="0 0 0"/>
            <geometry>
                <sphere radius="0.015" />
            </geometry>
            <material name="black">
                <color rgba="0 0 0 0.95"/>
            </material>
        </visual>
    </link>