Low Level Controllers¶

MoveIt has access to many different controllers through a plugin interface inside the MoveItControllerHandler class. The MoveItControllerManager class is one of the options that is used to interact with a single ros_control node. MoveItControllerManager reads what controller(s) to use from a controllers.yaml file.

Here we will walk through configuring MoveIt with the controllers on your robot. We will assume that your robot offers a FollowJointTrajectory action service for the arms on your robot and (optionally) a GripperCommand service for your gripper. If your robot does not offer this we recommend the ROS control framework for easily adding this functionality around your hardware communication layer.

YAML Configuration¶

The controllers.yaml configuration file is located in the robot_moveit_config/config directory of your MoveIt robot config package. This specifies the controller configuration for your robot. Here’s an example file for configuring a FollowJointTrajectory action controller for the panda_arm and a GripperCommand gripper controller for its hand:

controller_list:
 - name: panda_arm_controller
   action_ns: follow_joint_trajectory
   type: FollowJointTrajectory
   default: true
   joints:
     - panda_joint1
     - panda_joint2
     - panda_joint3
     - panda_joint4
     - panda_joint5
     - panda_joint6
     - panda_joint7
 - name: hand_controller
   action_ns: gripper_action
   type: GripperCommand
   default: true
   parallel: true
   joints:
     - panda_finger_joint1
     - panda_finger_joint2

There are many different parameters that can be used for different types of controllers.

FollowJointTrajectory Controller Interface¶

The parameters are:

name: The name of the controller. (See debugging information below for important notes).
action_ns: The action namespace for the controller. (See debugging information below for important notes).
type: The type of action being used (here FollowJointTrajectory).
default: The default controller is the primary controller chosen by MoveIt for communicating with a particular set of joints.
joints: Names of all the joints that are being addressed by this interface.

GripperCommand Controller Interface¶

The parameters are:

name: The name of the controller. (See debugging information below for important notes).
action_ns: The action namespace for the controller. (See debugging information below for important notes).
type: The type of action being used (here GripperCommand).
default: The default controller is the primary controller chosen by MoveIt for communicating with a particular set of joints.
joints: Names of all the joints that are being addressed by this interface.
command_joint: The single joint, controlling the actual state of the gripper. This is the only value that is sent to the controller. Has to be one of the joints above. If not specified, the first entry in joints will be used instead.
parallel: When this is set, joints should be of size 2, and the command will be the sum of the two joints.

Optional Allowed Trajectory Execution Duration Parameters¶

For each controller it is optionally possible to set the allowed_execution_duration_scaling and allowed_goal_duration_margin parameters. These are controller-specific overrides of the global values trajectory_execution/allowed_execution_duration_scaling and trajectory_execution/allowed_goal_duration_margin. As opposed to the global values, the contoller-specific ones cannot be dynamically reconfigured at runtime. The parameters are used to compute the allowed trajectory execution duration by scaling the expected execution duration and adding the margin afterwards. If this duration is exceeded the trajectory will be cancelled. The controller-specific parameters can be set as follows

controller_list:
 - name: arm_controller
   action_ns: follow_joint_trajectory
   type: FollowJointTrajectory
   allowed_execution_duration_scaling: 1.2
   allowed_goal_duration_margin: 0.5

Create the Controller launch file¶

Now, create the controller launch file (call it robot_moveit_controller_manager.launch.xml where robot is the name of your robot as specified when you created your MoveIt robot config package).

Add the following lines to this file:

<launch>
 <!-- Set the param that trajectory_execution_manager needs to find the controller plugin -->
 <arg name="moveit_controller_manager" default="moveit_simple_controller_manager/MoveItSimpleControllerManager" />
 <param name="moveit_controller_manager" value="$(arg moveit_controller_manager)"/>
 <!-- load controller_list -->
 <rosparam file="$(find robot_moveit_config)/config/controllers.yaml"/>
</launch>

MAKE SURE to replace robot_moveit_config with the correct name of your MoveIt robot config package.

Now, you should be ready to have MoveIt talk to your robot.

Debugging Information¶

The FollowJointTrajectory or GripperCommand interfaces on your robot must be communicating in the namespace: /name/action_ns. In the above example, you should be able to see the following topics (using rostopic list) on your robot:

/panda_arm_controller/follow_joint_trajectory/goal

/panda_arm_controller/follow_joint_trajectory/feedback

/panda_arm_controller/follow_joint_trajectory/result

/hand_controller/gripper_action/goal

/hand_controller/gripper_action/feedback

/hand_controller/gripper_action/result

You should also be able to see (using rostopic info topic_name) that the topics are published/subscribed to by the controllers on your robot and also by the move_group node.

Remapping /joint_states topic¶

When you run a move group node, you may need to remap the topic /joint_states to /robot/joint_states, otherwise MoveIt won’t have feedback from the joints. To do this remapping you could make a simple launch file for your node as follows:

<node pkg="moveit_ros_move_group" type="move_group" name="any_name" output="screen">
  <remap from="joint_states" to="robot/joint_states"/>
</node>

Or you can make a subscriber with the correct topic name and then ensure that the starting robot state for your move group corresponds to a correct joints angle by using the call back of this subscriber.

Trajectory Execution Manager Options¶

There are several options for tuning the behavior and safety checks of the execution pipeline in MoveIt. In your moveit_config package edit the trajectory_execution.launch.xml file to change the following parameters:

execution_duration_monitoring: when false, will not throw error is trajectory takes longer than expected to complete at the low-level controller side

allowed_goal_duration_margin: Allow more than the expected execution time before triggering a trajectory cancel (applied after scaling)

allowed_start_tolerance: Allowed joint-value tolerance for validation that trajectory’s first point matches current robot state. If set to zero will skip waiting for robot to stop after execution

Example Controller Manager¶

MoveIt controller managers, somewhat a misnomer, are the interfaces to your custom low level controllers. A better way to think of them are controller interfaces. For most use cases, the included MoveItSimpleControllerManager is sufficient if your robot controllers already provide ROS actions for FollowJointTrajectory. If you use ros_control, the included MoveItRosControlInterface is also ideal.

However, for some applications you might desire a more custom controller manager. An example template for starting your custom controller manager is provided here.

Fake Controller Manager¶

MoveIt comes with a series of fake trajectory controllers that can be used for simulations. For example, the demo.launch generated by MoveIt’s setup assistant, employs fake controllers for nice visualization in RViz. For configuration, edit the file config/fake_controllers.yaml, and adjust the desired controller type. The following controllers are available:

interpolate: perform smooth interpolation between via points - the default for visualization
via points: traverse via points, w/o interpolation in between - useful for visual debugging
last point: warp directly to the last point of the trajectory - fastest method for off-line benchmarking

Fake Controller Yaml File¶

rate: 10 (Hz, used for interpolation controller)
controller_list:
  - name: fake_arm_controller
    type: interpolate | via points | last point
    joints:
      - joint_1
      - joint_2
      - joint_3
      - joint_4
      - joint_5
      - joint_6
  - name: fake_gripper_controller
    joints:
      []

In order to load an initial pose, one can have a list of (group, pose) pairs as follows:

initial:
  - group: arm
    pose:  ready

Controller Switching and Namespaces¶

All controller names get prefixed by the namespace of their ros_control node. For this reason controller names should not contain slashes, and can’t be named /. For a particular node MoveIt can decide which controllers to have started or stopped. Since only controller names with registered allocator plugins are handled over MoveIt, MoveIt takes care of stopping controllers based on their claimed resources if a to-be-started controller needs any of those resources.

Controllers for Multiple Nodes¶

MoveItMultiControllerManager can be used for more than one ros_control nodes. It works by creating several MoveItControllerManagers, one for each node. It instantiates them with their respecitve namespace and takes care of proper delegation. To use it must be added to the launch file.

<param name="moveit_controller_manager" value="moveit_ros_control_interface::MoveItMultiControllerManager" />

开源反馈

有地方需要改进？请在 GitHub page 新开一个 pull request。