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Trajectory filter failing for coordinated arms movement

asked 2011-07-26 11:26:52 -0600

Jonathan Realmuto gravatar image


I am working on coordinated motions with two 7 dof arms. I'm using diamondback. Currently, I am running only simulations via gazebo. I have been able to expose some basic move_arm functionality to two arms by creating an appropriate planning group and by using one joint_trajectory_action controller for handling control of both arms. I am using a JointPlanner via the RRT planner from ompl:

  planner_type: JointPlanner
    - RRTkConfig2 
  projection_evaluator: joint_state

    type: kinematic::RRT  
    range: 0.75

Filter setup:

service_type: FilterJointTrajectoryWithConstraints
    name: unnormalize_trajectory
    type: UnNormalizeFilterJointTrajectoryWithConstraints
    name: cubic_spline_short_cutter_smoother
    type: CubicSplineShortCutterFilterJointTrajectoryWithConstraints
    params: {discretization: 0.01}

The problems is on some coordinated movements, which bring the two arms close together, the trajectory filter doesn't seem to be constraint aware and it is removing parts of the plan which allow for collision free movement. So, in the end the arms are "colliding" with each other. I say "colliding" because they actual just pass through each other. Using rviz I can see the ompl RRT planner (prior to the filter) plans a collision free trajectory. But, after the trajectory filter snips alot of extra movement out the arms "collide". The "collisions" that happen are usually relatively minimal, i.e. just the tips of the end effectors pass through each other. I have tried different discretization values, but this doesn't help. I can increases the link padding, and this fixes the problem, but too much padding is unacceptable for our applications.

  1. Why is the trajectory filter eliminating parts of the plan that allow for collision free movement?

  2. What changes can I make to the filter or planner to stop this from happening? Are their other filters that are more appropriate for my application?

  3. Why is gazebo allowing "collisions", i.e. letting the arms pass through each other, as opposed to having them stop each other?

Any advice is much appreciated.


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Which robot are you doing this with? On the PR2, separate links define the tip of the hand. If you are not including all the links in your collision operations properly, you will get this error. When you have collisions, can you check which two links are colliding?
Sachin Chitta gravatar image Sachin Chitta  ( 2011-08-01 04:46:51 -0600 )edit
We are using a custom robot. On Friday, my lab visited Rice and disgust the problem with the Kavraki Lab. Ioan Sucan suggested this may be a current limitation of the trajectory filter, since we are planning with multiple tips. From my understanding, much work is been done to expand arm_navigation, and maybe this is something you guys can look further into.
Jonathan Realmuto gravatar image Jonathan Realmuto  ( 2011-08-01 05:02:58 -0600 )edit
The two end effectors are "colliding".
Jonathan Realmuto gravatar image Jonathan Realmuto  ( 2011-08-01 05:04:11 -0600 )edit
I can email you a video, if you would like.
Jonathan Realmuto gravatar image Jonathan Realmuto  ( 2011-08-01 05:04:54 -0600 )edit
Would you be able to post or send us (a) your URDF (b) your planning configuration and launch files and (c) your gazebo launch files and environment? We can try and duplicate this with the tools on our end then.
Sachin Chitta gravatar image Sachin Chitta  ( 2011-08-02 09:55:11 -0600 )edit
Sorry for the delay Sachin. My lab has an upcoming demo, and I been incredibly busy preparing. As soon as this demo is over I will send you everything, so you can look at it (2 weeks max). Thank you.
Jonathan Realmuto gravatar image Jonathan Realmuto  ( 2011-08-05 05:16:30 -0600 )edit

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answered 2011-09-02 11:27:55 -0600

kwc gravatar image

no activity in > 1 month, closing

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Asked: 2011-07-26 11:26:52 -0600

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Last updated: Sep 02 '11