胡老师好！

在写作业2（将摄像头和雷达同时加到机器人上）时，使用roslaunch mbot_gazebo view_mbot_with_laser_and_camera_gazebo.launch 指令发生如下报错：
<div>Invalid <param> tag: Cannot load command parameter [robot_description]: command [/opt/ros/kinetic/lib/xacro/xacro –inorder ‘/home/mustar/catkin_ws/src/mbot_gazebo/mbot_description/urdf/mbot_with_laser_and_camera_gazebo.xacro’] returned with code [1]. </div>
<div>Param xml is <param command=”$(find xacro)/xacro –inorder ‘$(find mbot_description)/urdf/mbot_with_laser_and_camera_gazebo.xacro'” name=”robot_description”/>
The traceback for the exception was written to the log file
</div>
<div></div>
<div>我机器人在gazebo的启动文件名是view_mbot_with_laser_and_camera_gazebo.launch ，放在功能包 mbot_gazebo目录下，内容如下：</div>
<div>
<div><launch></div>
<div>    <!– 设置launch文件的参数 –>
<arg name=”world_name” value=”$(find mbot_gazebo)/worlds/playground.world”/>
<arg name=”paused” default=”false”/>
<arg name=”use_sim_time” default=”true”/>
<arg name=”gui” default=”true”/>
<arg name=”headless” default=”false”/>
<arg name=”debug” default=”false”/></div>
<div>    <!– 运行gazebo仿真环境 –>
<include file=”$(find gazebo_ros)/launch/empty_world.launch”>
<arg name=”world_name” value=”$(arg world_name)” />
<arg name=”debug” value=”$(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></div>
<div>    <!– 加载机器人模型描述参数 –>
<param name=”robot_description” command=”$(find xacro)/xacro –inorder ‘$(find mbot_description)/urdf/mbot_with_laser_and_camera_gazebo.xacro'” /> </div>
<div>    <!– 运行joint_state_publisher节点，发布机器人的关节状态  –>
<node name=”joint_state_publisher” pkg=”joint_state_publisher” type=”joint_state_publisher” ></node> </div>
<div>    <!– 运行robot_state_publisher节点，发布tf  –>
<node name=”robot_state_publisher” pkg=”robot_state_publisher” type=”robot_state_publisher”  output=”screen” >
<param name=”publish_frequency” type=”double” value=”50.0″ />
</node></div>
<div>    <!– 在gazebo中加载机器人模型–>
<node name=”urdf_spawner” pkg=”gazebo_ros” type=”spawn_model” respawn=”false” output=”screen”
args=”-urdf -model mrobot -param robot_description”/> </div>
<div></launch></div>
</div>
<div></div>
<div>我launch文件的模型文件mbot_with_laser_and_camera_gazebo.xacro内容如下：</div>
<div>
<div><?xml version=”1.0″?>
<robot name=”arm” xmlns:xacro=”http://www.ros.org/wiki/xacro”></div>
<div>    <xacro:include filename=”$(find mbot_description)/urdf/mbot_base_gazebo.xacro” />
<xacro:include filename=”$(find mbot_description)/urdf/sensors/lidar_gazebo.xacro” />
<xacro:include filename=”$(find mbot_description)/urdf/sensors/camera_gazebo.xacro” /></div>
<div>    <!–雷达的位置–>
<xacro:property name=”lidar_offset_x” value=”0″ />
<xacro:property name=”lidar_offset_y” value=”0″ />
<xacro:property name=”lidar_offset_z” value=”0.105″ /></div>
<div>    <!–相机的位置–>
<xacro:property name=”camera_offset_x” value=”0.17″ />
<xacro:property name=”camera_offset_y” value=”0″ />
<xacro:property name=”camera_offset_z” value=”0.10″ />    </div>
<div>    <!– lidar –>
<joint name=”lidar_joint” type=”fixed”>
<origin xyz=”${lidar_offset_x} ${lidar_offset_y} ${lidar_offset_z}” rpy=”0 0 0″ />
<parent link=”base_link”/>
<child link=”laser_link”/>
</joint></div>
<div>   <!–camera–>
<joint name=”camera_joint” type=”fixed”>
<origin xyz=”${camera_offset_x} ${camera_offset_y} ${camera_offset_z}” rpy=”0 0 0″ />
<parent link=”base_link”/>
<child link=”camera_link”/>
</joint></div>
<div>    <xacro:rplidar prefix=”laser”/>
<xacro:usb_camera prefix=”camera”/>
<mbot_base_gazebo/></div>
<div></robot></div>
</div>
<div></div>
<div>请问究竟是出了什么问题导致报错呢？</div>