不久前，师弟问了我一个问题：“师兄，我要控制一个机器人在仿真环境下运动，需要学什么，或者从哪里入手呢？“

这个问题不是那么好回答，urdf——Gazebo——ros_control——MoveIt，这是我在很久后才能给出的一个答案。那么之前我是怎么做仿真的呢？

1. 借助Arbotix舵机接口来仿真

之前是在学习《ros by example volume 2 》的时候，接触到一个rbx2_bringup 的package，仿照着里面的https://github.com/pirobot/rbx2/blob/indigo-devel/rbx2_bringup/launch/pi_robot_with_gripper.launch 文件写了一个关于youbot的关节的，另外加上一些static_tf转换。

内容如下

<launch>
   <!-- Make sure we are not using simulated time -->
   <param name="/use_sim_time" value="false" />
 
   <!-- Launch the arbotix driver in fake mode by default -->
   <arg name="sim" default="true" />
 
    <!-- If using a real controller, look on /dev/ttyUSB0 by default -->
   <arg name="port" default="/dev/ttyUSB0" />
 
   <!-- Load the URDF/Xacro model of our robot -->
   <param name="robot_description" command="$(find xacro)/xacro.py '$(find youbot_description)/robots/youbot.urdf.xacro'" />
   <param name="use_gui" value="true"/>
 
   <node name="rviz" pkg="rviz" type="rviz" />
 
<!--   <include file="$(find urdf_tutorial)/launch/display.launch" />-->
 
   <!-- Bring up the arbotix driver with a configuration file appropriate to the robot -->
   <node name="arbotix" pkg="arbotix_python" type="arbotix_driver" clear_params="true" output="screen">
      <rosparam file="$(find rbx2_bringup)/config/fake_youbot_arbotix.yaml" command="load" />
      <param name="sim" value="$(arg sim)" />
      <param name="port" value="$(arg port)" />
   </node>
 
   <!-- Run a separate controller for the one sided gripper -->
   <node name="right_gripper_controller" pkg="arbotix_controllers" type="gripper_controller" output="screen">
      <rosparam>
         model: dualservo
         min_opening: 0.0
         max_opening: 0.009
         invert_left: false
         invert_right: false
         center_left: 0.0
         center_right: 0.0
         pad_width: 0.015
         finger_length: 0.04
         joint_left: gripper_finger_joint_l
         joint_right: gripper_finger_joint_r
      </rosparam>
   </node>
 
   <!-- Publish the robot state -->
   <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher">
       <param name="publish_frequency" type="double" value="20.0" />
   </node>
 
<!--   <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" />-->
 
   <!-- Start all servos in a relaxed state -->
   <node pkg="rbx2_dynamixels" type="arbotix_relax_all_servos.py" name="relax_all_servos" unless="$(arg sim)" />
 
   <!-- Load diagnostics -->
   <node pkg="diagnostic_aggregator" type="aggregator_node" name="diagnostic_aggregator" clear_params="true" unless="$(arg sim)">
      <rosparam command="load" file="$(find rbx2_dynamixels)/config/dynamixel_diagnostics.yaml" />
   </node>
 
   <node pkg="rqt_robot_monitor" type="rqt_robot_monitor" name="rqt_robot_monitor" unless="$(arg sim)" /><!-- Unless value evaluates to false then include tag and its contents，inverse with if  -->
 
<!--   http://wiki.ros.org/tf#static_transform_publisher-->
<!--yaw is rotation about Z, pitch is rotation about Y, and roll is rotation about X frame_id child_frame_id-->
   <!-- Run a static transform between /base_link and /base_footprint needed for SLAM -->
  <node pkg="tf" type="static_transform_publisher" name="wheel_link_fl2base_link" args="0.228 0.158 -0.034 0 0 0 /base_link /wheel_link_fl 100" />
  <node pkg="tf" type="static_transform_publisher" name="wheel_link_fr2base_link" args="0.228 -0.158 -0.034 0 0 0 /base_link /wheel_link_fr 100" />
  <node pkg="tf" type="static_transform_publisher" name="wheel_link_bl2base_link" args="-0.228 0.158 -0.034 0 0 0 /base_link /wheel_link_bl 100" />
  <node pkg="tf" type="static_transform_publisher" name="wheel_link_br2base_link" args="-0.228 -0.158 -0.034 0 0 0 /base_link /wheel_link_br 100" />
 
  <node pkg="tf" type="static_transform_publisher" name="caster_link_fl2base_link" args="0.228 0.158 -0.034 0 0 0 /base_link /caster_link_fl 100" />
  <node pkg="tf" type="static_transform_publisher" name="caster_link_fr2base_link" args="0.228 -0.158 -0.034 0 0 0 /base_link /caster_link_fr 100" />
  <node pkg="tf" type="static_transform_publisher" name="caster_link_bl2base_link" args="-0.228 0.158 -0.034 0 0 0 /base_link /caster_link_bl 100" />
  <node pkg="tf" type="static_transform_publisher" name="caster_link_bf2base_link" args="-0.228 -0.158 -0.034 0 0 0 /base_link /caster_link_br 100" />
 
</launch>

它加载的yaml文件内容如下

port: /dev/ttyUSB0
baud: 115200
rate: 20
sync_write: True
sync_read: True
read_rate: 20
write_rate: 20
 
joints: {
#    wheel_joint_fl: {id: 1, neutral: 512, max_speed: 684, min_angle: 0, max_angle: 360, invert: False},
#    wheel_joint_fr: {id: 2, neutral: 512, max_speed: 684, min_angle: 0, max_angle: 360, invert: False},
#    wheel_joint_bl: {id: 3, neutral: 512, max_speed: 684, min_angle: 0, max_angle: 360, invert: False},
#    wheel_joint_br: {id: 4, neutral: 512, max_speed: 684, min_angle: 0, max_angle: 360, invert: False},
    
    wheel_joint_fl: {id: 1, neutral: 512, max_speed: 684, invert: False},
    wheel_joint_fr: {id: 2, neutral: 512, max_speed: 684, invert: False},
    wheel_joint_bl: {id: 3, neutral: 512, max_speed: 684, invert: False},
    wheel_joint_br: {id: 4, neutral: 512, max_speed: 684, invert: False},
    
    arm_joint_1: {id: 5, neutral: 512, max_speed: 684, min_angle: -169, max_angle: 169, invert: False},
    arm_joint_2: {id: 6, neutral: 512, max_speed: 684, min_angle: -65, max_angle: 90, invert: False},
    arm_joint_3: {id: 7, neutral: 512, max_speed: 684, min_angle: -151, max_angle: 146, invert: False},
    arm_joint_4: {id: 8, neutral: 512, max_speed: 684, min_angle: -102.5, max_angle: 102.5, invert: False},
    arm_joint_5: {id: 9, neutral: 512, max_speed: 684, min_angle: -167.5, max_angle: 167.5, invert: False},
    
    gripper_finger_joint_l: {id: 10,neutral: 512, max_speed: 684, invert: False},
    gripper_finger_joint_r: {id: 11,neutral: 512, max_speed: 684,  invert: False}
}
#http://wiki.ros.org/arbotix_python
controllers: {
   #  Pololu motors: 1856 cpr = 0.3888105m travel = 4773 ticks per meter (empirical: 4684) WheelRadius_[meter] = 0.0475 EncoderTicksPerRound = 4000
    base_controller: {type: diff_controller, base_frame_id: base_link, base_width: 0.38, ticks_meter: 4684, Kp: 50, Kd: 0, Ki: 20, Ko: 50, accel_limit: 1.0 },
    arm_controller: {type: follow_controller, joints: [arm_joint_1, arm_joint_2, arm_joint_3, arm_joint_4, arm_joint_5], action_name: arm_1/arm_controller/follow_joint_trajectory}
# rbx2/rbx2_dynamixels/config/arbotix/pi_robot_with_gripper.yaml  
#    arm_controller: {type: follow_controller, joints: [right_arm_shoulder_pan_joint, right_arm_shoulder_lift_joint, right_arm_shoulder_roll_joint, right_arm_elbow_flex_joint, right_arm_forearm_flex_joint], action_name: arm_1/arm_controller/follow_joint_trajectory}
}
启动后，运行起来的节点图

如果用这个仿真，很大程度上是有问题的，虽然也能够让模型动起来，主要是因为Arbotix是针对舵机的，而实际中很多的机器人不只是舵机，也有步进电机等等。我们的KUKA youBot机械臂是步进电机。以前的仿真中主要用的是follow_joint_trajectory action topics。而实际的youbot_driver也会启动这个topic，所以格式方面，仿真中能够用的，实际也可以直接用上，最大的问题是，仿真的参数与实际动作的相似度有有多少，这里是有个很大的问号的。

2. 借助Moveit

关于Moveit之前研究过一段时间，也总结成了三篇博客。点击打开链接

在利用命令roslaunch moveit_setup_assistant setup_assistant.launch 配置好一些config文件后。要控制实际的机器人，我们还得自己设置一个～/catkin_ws/src/moveit_youbot/config/controllers.yaml的配置文件，我的配置如下

controller_list:
  - name: arm_1/arm_controller
    action_ns: follow_joint_trajectory
    type: FollowJointTrajectory
    default: true
    joints:
      - arm_joint_1
      - arm_joint_2
      - arm_joint_3
      - arm_joint_4
      - arm_joint_5
从这里也可以看出，它也是用的Action接口来达到控制的目的的。搜索过一些资料后发现好像还真没其他的配置的方法，基本都是用action来做的。

其实根据youbot实际的Driver

我还尝试过这样的配置，为的是只使用/arm_1/arm_controller/position_command这个topic，而非action。也有网上的资料说那个type是ros_controller的type，而它又是与Gazebo相关的。在这里我设置的是topic 的type

controller_list:
  - name: arm_1/arm_controller/position_command
    type: brics_actuator/JointPositions
    default: true
    joints:
      - arm_joint_1
      - arm_joint_2
      - arm_joint_3
      - arm_joint_4
      - arm_joint_5
~/catkin_ws/src/moveit_youbot/launchyoubot_moveit_controller_manager.launch.xml 则如下： 
<launch>
  <arg name="moveit_controller_manager" default="moveit_simple_controller_manager/MoveItSimpleControllerManager"/>
<!--  <arg name="moveit_controller_manager" default="moveit_ros_control_interface/MoveItControllerManager"/>-->
  <param name="moveit_controller_manager" value="$(arg moveit_controller_manager)"/>

  <rosparam file="$(find moveit_youbot)/config/controllers.yaml"/>

</launch>

貌似也只能使用MoveItSimpleControllerManager了。根据这里的说明点击打开链接。它提供action的接口，绕了个路还是回到了action。也就是这种方式貌似是行不通。

3. Gazebo与ros_control

很久之前学习Gazebo的时候，那个官方tutorial的rrbot，2自由度连杆机器人，结合rqt的一些工具联合调pid，现在依然印象深刻，视频地址点击打开链接。不过当时没太深入，现在随着积累的东西多了，慢慢又会回头看看以前的东西，总有新的收获。而这次则主要是关于ros_control。这里我会先跑一遍官方的例子，然后结合youBot的相关文件来对比说明。

整理了一下，基本上按照这几个地方就好，按照顺序跑一遍：

  1. http://gazebosim.org/tutorials?tut=ros_roslaunch
  2. http://gazebosim.org/tutorials/?tut=ros_urdf
  3. http://gazebosim.org/tutorials?tut=ros_gzplugins
  4. http://gazebosim.org/tutorials/?tut=ros_control

其中涉及urdf的相关知识，具体参考查看roswiki, http://wiki.ros.org/urdf/XML。

官方package的目录结构如下

这里，我主要是想说说plugin和ros_control，介绍可以看看http://wiki.ros.org/ros_control，开头的那个PPT很不错，可以有个大概了解。

ros_control主要是提供各种controller和Hardware硬件抽象层，而实体机器人或者仿真部件就是其控制的资源，它用来连接它们


下面就结合具体的官方代码来分析下，是如何让仿真中的模型动起来的。首先～/catkin_ws/src/gazebo_ros_demos/rrbot_description/urdf/rrbot.xacro文件定义了两个运动关节的transmission，它的type是：transmission_interface/SimpleTransmission，它的hardwareInterface是：EffortJointInterface

  <transmission name="tran1">
    <type>transmission_interface/SimpleTransmission</type>
    <joint name="joint1">
      <hardwareInterface>EffortJointInterface</hardwareInterface>
    </joint>
    <actuator name="motor1">
      <hardwareInterface>EffortJointInterface</hardwareInterface>
      <mechanicalReduction>1</mechanicalReduction>
    </actuator>
  </transmission>

接着～/catkin_ws/src/gazebo_ros_demos/rrbot_description/urdf/ rrbot.gazebo里有一些传感器的 plugin： libgazebo_ros_control.so， libgazebo_ros_gpu_laser.so， libgazebo_ros_camera.so。hokuyo激光雷达的如下，也就是说即使没有传感器，也可以仿真得到传感器的数据。 
 <gazebo reference="hokuyo_link">
    <sensor type="gpu_ray" name="head_hokuyo_sensor">
      <pose>0 0 0 0 0 0</pose>
      <visualize>false</visualize>
      <update_rate>40</update_rate>
      <ray>
        <scan>
          <horizontal>
            <samples>720</samples>
            <resolution>1</resolution>
            <min_angle>-1.570796</min_angle>
            <max_angle>1.570796</max_angle>
          </horizontal>
        </scan>
        <range>
          <min>0.10</min>
          <max>30.0</max>
          <resolution>0.01</resolution>
        </range>
        <noise>
          <type>gaussian</type>
          <!-- Noise parameters based on published spec for Hokuyo laser
               achieving "+-30mm" accuracy at range < 10m.  A mean of 0.0m and
               stddev of 0.01m will put 99.7% of samples within 0.03m of the true
               reading. -->
          <mean>0.0</mean>
          <stddev>0.01</stddev>
        </noise>
      </ray>
      <plugin name="gazebo_ros_head_hokuyo_controller" filename="libgazebo_ros_gpu_laser.so">
        <topicName>/rrbot/laser/scan</topicName>
        <frameName>hokuyo_link</frameName>
      </plugin>
    </sensor>
  </gazebo>
关于ros_control的plugin也在这个文件中，如下 
  <gazebo>
    <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
      <robotNamespace>/rrbot</robotNamespace>
      <robotSimType>gazebo_ros_control/DefaultRobotHWSim</robotSimType>
    </plugin>
  </gazebo>
关于它们的说明，如下图

Controllers：

  • effort_controllers
    • joint_effort_controller
    • joint_position_controller
    • joint_velocity_controller
  • joint_state_controller
    • joint_state_controller
  • position_controllers
    • joint_position_controller
  • velocity_controllers
    • joint_velocity_controllers
Hardware Interface：
  • joint Command Interfaces
    • Effort Joint Interface
    • Velocity Joint Interface
    • Position Joint Interface
  • Joint State Interfaces
  • Actuator State Interfaces
  • Actuator Command Interfaces
    • Effort Actuator Interface
    • Velocity Actuator Interface
    • Position Actuator Interface
  • Joint Pose Trajectory
  • Differential Drive
  • Skid Steering Drive（Pioneer 3AT for instance）
  • Plannar Move plugin
  • Bumper
  • GPU Laser(e.g. Hokuyo)
  • Block Laser(e.g. Velodyne)
  • Force-torque sensor Interface
  • IMU sensor Interface
ros_control又是和urdf中的transmission相关的，这里有部分解释 http://wiki.ros.org/ros_control 具体语法还可以参考 http://wiki.ros.org/urdf/XML/Transmission 

依照官网的解释ros_control会去读取～/catkin_ws/src/gazebo_ros_demos/rrbot_description/urdf/rrbot.xacro中的transmisson条目，每个运动关节都需要一个transmission。

那么这些运动关节是以什么方式运动，或者pid参数是如何设定呢?因此就需要一个配置文件来配置这些。这里名叫～/catkin_ws/src/gazebo_ros_demos/rrbot_control/config/rrbot_control.yaml文件。Hardwareinterface的作用就在这个配置文件中体现了，注意Joint1和Joint2的type

rrbot:
  # Publish all joint states -----------------------------------
  joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50  
  
  # Position Controllers ---------------------------------------
  joint1_position_controller:
    type: effort_controllers/JointPositionController
    joint: joint1
    pid: {p: 100.0, i: 0.01, d: 10.0}
  joint2_position_controller:
    type: effort_controllers/JointPositionController
    joint: joint2
    pid: {p: 100.0, i: 0.01, d: 10.0}

具体的关于启动的文件，都写在launch文件中了，具体来说就是rrbot_world.launch和rrbot_control.launch，内容分别如下

<launch>
 
  <!-- these are the arguments you can pass this launch file, for example paused:=true -->
  <arg name="paused" default="false"/>
  <arg name="use_sim_time" default="true"/>
  <arg name="gui" default="true"/>
  <arg name="headless" default="false"/>
  <arg name="debug" default="false"/>
 
  <!-- We resume the logic in empty_world.launch, changing only the name of the world to be launched -->
  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find rrbot_gazebo)/worlds/rrbot.world"/>
    <arg name="debug" value="$(arg debug)" />
    <arg name="gui" value="$(arg gui)" />
    <arg name="paused" value="$(arg paused)"/>
    <arg name="use_sim_time" value="$(arg use_sim_time)"/>
    <arg name="headless" value="$(arg headless)"/>
  </include>
 
  <!-- Load the URDF into the ROS Parameter Server -->
  <param name="robot_description"
	 command="$(find xacro)/xacro.py '$(find rrbot_description)/urdf/rrbot.xacro'" />
 
  <!-- Run a python script to the send a service call to gazebo_ros to spawn a URDF robot -->
  <node name="urdf_spawner" pkg="gazebo_ros" type="spawn_model" respawn="false" output="screen"
	args="-urdf -model rrbot -param robot_description"/>
 
</launch>

以下的这个lanuch文件是用来启动controller_manager和发布joint states

<launch>
 
  <!-- Load joint controller configurations from YAML file to parameter server -->
  <rosparam file="$(find rrbot_control)/config/rrbot_control.yaml" command="load"/>
 
  <!-- load the controllers -->
  <node name="controller_spawner" pkg="controller_manager" type="spawner" respawn="false"
	output="screen" ns="/rrbot" args="joint_state_controller
					  joint1_position_controller
					  joint2_position_controller"/>
 
  <!-- convert joint states to TF transforms for rviz, etc -->
  <node name="robot_state_publisher" pkg="robot_state_publisher" type="robot_state_publisher"
	respawn="false" output="screen">
    <remap from="/joint_states" to="/rrbot/joint_states" />
  </node>
 
</launch>

上面的这几个文件都是比较通用的，可以当作参考的模板。

以下的这个链接是总的一个关于ROS和Gazebo的系列教程。

http://gazebosim.org/tutorials?cat=connect_ros

=========================================

古月的教程：https://www.guyuehome.com/890