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Reflexxes-Based Joint Trajectory Generator

Sending Commands

Commands can be sent to this generator in four ways:

  1. As an Eigen::VectorXd of joint positions to be achieved as fast as possible.
  2. As a ROS trajectory_msgs::JointTrajectoryPoint message to be achieved as fast as possible.
  3. As a ROS trajectory_msgs::JointTrajectory to be achieved according to the segment times.
  4. Via the ROS actionlib interface.

Eigen::VectorXd Streaming (Orocos only)

  • Acquisition Time: Immediately, subject to the dynamic limits.
  • Preemption: Preempts current trajectory.

JointTrajectoryPoint Message (Orocos/ROS)

  • Acquisition Time: Immediately, subject to the dynamic limits.
  • Preemption: Preempts current trajectory.

JointTrajectory Message (Orocos/ROS)

When receiving a sensor_msgs/JointTrajectory message, this controller aims to mimic the "classic" PR2 JointTrajectoryController behavior. This behavior is summarized as follows. Additionally, we add the notion of "flexible" points which the controller will try to achieve as quickly as possible subject to the controller's dynamic limits.

  • Acquisition Time: The time at which the trajectory is acquired depends both on the timestamp of the header as well as the time_from_start members of each JointTrajectoryPoint

    • header.stamp == 0.0: Begin pursuing the new trajectory immediately.
    • header.stamp < NOW: If any of the new trajectory points are to be acquired before the current trajectory, preempt the current trajectory and begin pursuing them imediately.
    • header.stamp > NOW: If any of the new trajectory points are to be acquired before points in the current trajectory, insert the new points into the trajectory and begin pursuing them at the future time. All points in the current trajectory after that time will be removed.

  • Preemption: Preempts currently-buffered trajectory segments which beginafter

    • header.stamp == 0.0: Preempt the current trajectory.
    • header.stamp < NOW: Preempt the current trajectory.
    • header.stamp > NOW: Continue the current trajectory.

For each point, if the time_from_start is zero, then the controller will consider it's completion time "flexible." This means that it will execute it subject to the velocity, acceleration, and jerk limits given to the controller. This is useful if your high-level trajectories should be executed as quickly as possible subject to these limits.

JointTrajectoryAction (ROS only)

This component will advertise an actionlib interface on a topic named COMPONENT_NAME/action of time control_msgs::FollowJointTrajectoryAction. This can be used with any ROS actionlib interface, and it has the same semantics as publishing a trajectory_msgs::JointTrajectory message.