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Disable collisions between specified links and Octomap

asked 2019-05-16 12:35:29 -0500

pwalczykk gravatar image

Hi all,

I am using a manipulator with a suction gripper to pick up objects from the clutter. Planning scene and picking items are visible to the depth camera. I am using MoveIt! with occupancy_map_monitor plugin to generate Octomaps and plan / verify trajectory against potential collisions.

The problem occurs during the picking when I actually want to enter a collision between the suction cup and picked item. I do not want to disable collision check or clear Octomap completely for grasping, as some other collisions might occur.

My current solution involves additional prismatic joint in URDF, controlled via "/joint_states" topic. This joint can "extend" or "compress" suction cup collisions... But this solution seems to be an overkill, and might not scale for another purpose.

I tried to find a simpler solution, such as temporary disabling collisions between specified URDF link and Octomap, but I could not find any. Maybe someone knows a better way?

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You can probably do this using planning_scene::PlanningScene::getAllowedCollisionMatrixNonConst() and then configuring collision checking for your suction cup link and the octomap.

See also Programatically disable self-collision checking on move_group? in the old moveit Google group.

gvdhoorn gravatar image gvdhoorn  ( 2019-05-16 13:53:40 -0500 )edit

Great thanks for quick response!

#1 As I understand, AllowedCollisionMatrix allows me to disable/enable collision check between specified links. But can Octomap be treated as a link?

#2 Solution presented on moveit group cuts some parts of Octomap that collides with newly added scene object. But Octomap is updated only with some pre-defined frequency.This way I always have to wait until next update before planning movement. This introduces "expensive" delay between collision update request and planning.

pwalczykk gravatar image pwalczykk  ( 2019-05-16 15:26:10 -0500 )edit

IIUC, the moveit group discussion discusses the collision matrix approach as the first option.

re: octomap as link: the matrix actually contains information about collision objects. Every link in your urdf (with geometry) is considered a collision object. The octomap -- although dynamically added -- is also a collision object (a single one iirc).

I didn't post this as an answer as it's been a while since I've worked with this, but this is what I remember.

gvdhoorn gravatar image gvdhoorn  ( 2019-05-17 03:29:40 -0500 )edit

Thanks again gvdhoorn. For the next few weeks, I will not be able to dive deeper into this problem. But I will share a better solution if I find it.

pwalczykk gravatar image pwalczykk  ( 2019-05-23 08:11:46 -0500 )edit

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answered 2019-05-23 08:09:20 -0500

pwalczykk gravatar image

For now, I finished with a solution that moves the link I want to disable from collision check 999.0 meters from the robot :) I know it is not very elegant but works exactly as I wanted. It is also really easy to implement. All I needed was a prismatic joint with 0-999 range and a node that constantly publishes JointState message for this "dummy" joint - 0 or 999.

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Asked: 2019-05-16 12:35:29 -0500

Seen: 949 times

Last updated: May 23 '19