how pos/vel_based_pos_traj_controller work?

edit

Hi all,

I am trying to control a real UR5 using the position based controller of ur_modern_driver package, but I have a little problem: when i plan and execute a trajectory through MoveIt the robot achieves the goal not in a clean way (the end-effector passes over the goal and reaches it in a second moment after few oscillations).

• What should I do in order to improve this situation? I know there are some parameters that could be set in the ur5_controllers.yaml file (ur_modern_driver -> config -> ur5_controllers.yaml) but the PID parameters can be set only for velocity_based controller, which I don't use because when I try to use it the robot doesn't move at all! Then here comes another question:

• how can I use vel_based_pos_traj_controller from ur_modern_driver package?

At the moment I am using pos_based_pos_traj_controller, but I don't know how to setup it. Here I copy its yaml code:

pos_based_pos_traj_controller:
type: position_controllers/JointTrajectoryController
   joints:
     - shoulder_pan_joint
     - shoulder_lift_joint
     - elbow_joint
     - wrist_1_joint
     - wrist_2_joint
     - wrist_3_joint
   constraints:
      goal_time: 0.6
      stopped_velocity_tolerance: 0.05
      shoulder_pan_joint: {trajectory: 0.1, goal: 0.1}
      shoulder_lift_joint: {trajectory: 0.1, goal: 0.1}
      elbow_joint: {trajectory: 0.1, goal: 0.1}
      wrist_1_joint: {trajectory: 0.1, goal: 0.1}
      wrist_2_joint: {trajectory: 0.1, goal: 0.1}
      wrist_3_joint: {trajectory: 0.1, goal: 0.1}
   stop_trajectory_duration: 0.5
   state_publish_rate:  125 
   action_monitor_rate: 10

   # state_publish_rate:  50 # Defaults to 50
   # action_monitor_rate: 20 # Defaults to 20
   #hold_trajectory_duration: 0.0 # Defaults to 0.5

The commands I run in order to communicate with real hardware are the followings:

roslaunch ur_modern_driver ur5_ros_control.launch robot_ip:=192.168.0.9

roslaunch ur5_moveit_config ur5_moveit_planning_execution.launch

roslaunch ur5_moveit_config moveit_rviz.launch config:=true

my ubuntu version: 16.04 Ros Kinetic

Thanks in advance to anyone who will help. -Enrico

Edit: this is the error when using /vel_based_pos_traj_controller:

[ WARN] [1530109956.151695655]: Controller /vel_based_pos_traj_controller failed with error code PATH_TOLERANCE_VIOLATED

[ WARN] [1530109956.151808590]: Controller handle /vel_based_pos_traj_controller reports status ABORTED

[ INFO] [1530109956.170454938]: Completed trajectory execution with status ABORTED ...

[ INFO] [1530109956.170689596]: Execution completed: ABORTED

(Actually I have the same kind of error when running pos_based controller, but the execution is done anyway)

this is my controller.yaml when using vel_based_controller:

controller_list:
  - name: /vel_based_pos_traj_controller
    action_ns: follow_joint_trajectory 
    type: FollowJointTrajectory
    default: true
    joints:
      - shoulder_pan_joint
      - shoulder_lift_joint
      - elbow_joint
      - wrist_1_joint
      - wrist_2_joint
      - wrist_3_joint