嗨，我在机器人手臂 urdf 中添加了控制插件，然后创建了启动文件，但是当我运行启动文件 gazebo 和机器人手臂模型打开时，我收到如下错误。我该如何解决这个问题？
[robot_state_publisher-3] Parsing robot urdf xml string.
[robot_state_publisher-3] Error: Error document empty.
[robot_state_publisher-3] at line 71 in /tmp/binarydeb/ros-foxy-urdfdom-2.3.3/urdf_parser/src/model.cpp
[robot_state_publisher-3] terminate called after throwing an instance of 'std::runtime_error'
[robot_state_publisher-3] what(): Unable to initialize urdf::model from robot description
[ros2_control_node-4] terminate called after throwing an instance of 'std::runtime_error'
[ros2_control_node-4] what(): invalid URDF passed in to robot parser
[spawner.py-5] [INFO] [1677069069.554681723] [spawner_joint_state_broadcaster]: Waiting for /controller_manager services
[spawner.py-6] [INFO] [1677069069.580805205] [spawner_joint_trajectory_controller]: Waiting for /controller_manager services
[spawn_entity.py-2] [INFO] [1677069069.734785422] [spawn_entity]: Spawn Entity started
[spawn_entity.py-2] [INFO] [1677069069.735058596] [spawn_entity]: Loading entity XML from file /home/gursel/robotic_arm_ws/install/robotic_arm/share/robotic_arm/urdf/robotic_arm.urdf
[spawn_entity.py-2] [INFO] [1677069069.736418915] [spawn_entity]: Waiting for service /spawn_entity, timeout = 30
[spawn_entity.py-2] [INFO] [1677069069.736653475] [spawn_entity]: Waiting for service /spawn_entity
[ERROR] [gazebo-1]: process has died [pid 4545, exit code 255, cmd 'gazebo -s libgazebo_ros_factory.so'].
[ERROR] [robot_state_publisher-3]: process has died [pid 4549, exit code -6, cmd '/opt/ros/foxy/lib/robot_state_publisher/robot_state_publisher /home/gursel/robotic_arm_ws/install/robotic_arm/share/robotic_arm/urdf/robotic_arm.urdf --ros-args --params-file /tmp/launch_params_302rtmoc'].
[ERROR] [ros2_control_node-4]: process has died [pid 4551, exit code -6, cmd '/opt/ros/foxy/lib/controller_manager/ros2_control_node --ros-args --params-file /tmp/launch_params_wb0x7xnl --params-file /home/gursel/robotic_arm_ws/install/robotic_arm/share/robotic_arm/config/jtc.yaml'].
[spawner.py-5] [INFO] [1677069071.570302266] [spawner_joint_state_broadcaster]: Waiting for /controller_manager services
[spawner.py-6] [INFO] [1677069071.595951515] [spawner_joint_trajectory_controller]: Waiting for /controller_manager services
[spawner.py-5] [INFO] [1677069073.586642702] [spawner_joint_state_broadcaster]: Waiting for /controller_manager services
[spawner.py-6] [INFO] [1677069073.612373454] [spawner_joint_trajectory_controller]: Waiting for /controller_manager services
[spawner.py-5] [INFO] [1677069075.603461546] [spawner_joint_state_broadcaster]: Waiting for /controller_manager services
[spawner.py-6] [INFO] [1677069075.629372887] [spawner_joint_trajectory_controller]: Waiting for /controller_manager services
[spawner.py-5] [INFO] [1677069077.620421456] [spawner_joint_state_broadcaster]: Waiting for /controller_manager services
[spawner.py-6] [INFO] [1677069077.646128433] [spawner_joint_trajectory_controller]: Waiting for /controller_manager services
[spawner.py-5] [ERROR] [1677069079.637362419] [spawner_joint_state_broadcaster]: Controller manager not available
[spawner.py-6] [ERROR] [1677069079.662836259] [spawner_joint_trajectory_controller]: Controller manager not available
[ERROR] [spawner.py-5]: process has died [pid 4553, exit code 1, cmd '/opt/ros/foxy/lib/controller_manager/spawner.py joint_state_broadcaster --controller-manager /controller_manager --ros-args'].
[ERROR] [spawner.py-6]: process has died [pid 4555, exit code 1, cmd '/opt/ros/foxy/lib/controller_manager/spawner.py joint_trajectory_controller -c /controller_manager --ros-args'].
已解决： 问题是 ROS2 版本和启动文件的变化。它适用于 Ubuntu 22.04 Humble，您应该安装所有控制包，例如 joint_trajectory_controller、joint_state_broadcaster、controller_manager、joint-state-publisher-gui，然后编辑您的启动文件。
urdf 解析器无法找到您的 urdf。这可能是由于许多不同的原因。首先，您应该尝试查看您的 urdf 路径是否正确。也许在您的项目中，urdf 位于您未使用 cmakelists 安装的文件夹中。