How to setup ros control to realize zero control error (Direct feedthrough of reference to output)?

asked 2018-10-29 02:35:24 -0500

maxbaeten
11 ●5 ●5 ●8

updated 2018-10-29 02:41:27 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

Hi guys,

Currently I am using Gazebo to simulate a robot and a rotating table. Therefore i spawn two controllers, a position_controllers/JointPositionController for the single joint rotating table and a position_controllers/JointGroupPositionController for the multi joint arm.

These controllers have as input position and as output position. Does that mean there is a one on one relation with the desired reference to the controller and the output? So the control error is always zero? And if not, How should I configure ros control such that what ever trajectory is sent to the robot it is executed 100% correctly by the gazebo simulated robot? Because in my use case I am currently not interested in simulating physics and low level control I just want to plan motion.

Currently i use the following:

control_params.yaml:

joint_state_controller:
  type: "joint_state_controller/JointStateController"
  publish_rate: 50

joint_table_controller:
  type: "position_controllers/JointPositionController"
  joint: joint_table

joint_manipulator_controller:
  type: "position_controllers/JointGroupPositionController"
  joints: ['joint_track','joint_s', 'joint_l', 'joint_u', 'joint_r', 'joint_b', 'joint_t', 'joint_weld']

Which i load by:

<!-- Spawn controller -->
<node name="controller_spawner" pkg="controller_manager" type="spawner"
    respawn="false" output="screen"
    args="joint_state_controller
          joint_table_controller
          joint_manipulator_controller
          --timeout 50" />

answered 2018-10-29 02:50:28 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

updated 2018-10-29 03:07:33 -0500

These controllers have as input position and as output position. Does that mean there is a one on one relation with the desired reference to the controller and the output?

In your previous question this also came up.

All classes in the position_controllers group are pure passthrough controllers (or forward_command_controller), they do not have any internal PID. From the class' header (here):

This class passes the commanded position down to the joint

Comments

Thanks for your quick and thorough answer. I will have a look at implementing the industrial robot simulator. I did not want to use the fake controller manager since at the end of the trajectory the robot is not staying at the end point.

maxbaeten ( 2018-10-29 03:19:25 -0500 )edit