Strange Tool Flip in Descartes

asked 2017-07-07 06:31:14 -0500

jbeck28 gravatar image

I've been trying to plan a path through a pretty dense cartesian path, and I've noticed that throughout the trajectory, the tool will occasionally flip 2pi radians. I'm wondering if anyone has any ideas as to why this might be? Here's a link to a video of the problem:

I'm also wondering if there's any way to speed up the visualization, as it takes quite a long time to view the entire simulation.

Thanks in advance, Josh

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joint flips are typically an IK problem. I don't know exactly how you've configured things, but that would be something to check.

gvdhoorn gravatar image gvdhoorn  ( 2017-07-07 07:09:40 -0500 )edit

I have tried using KDL, but I've found that trac ik generally chooses a more natural configuration so I've begun using that. Is there anything in particular I could provide that would help narrow down the cause?

jbeck28 gravatar image jbeck28  ( 2017-07-07 07:14:10 -0500 )edit

I'm surprised this works for you. Descartes used to absolutely require an IKFast plugin (as it needs all solutions for each pose to properly plan). Is that not the case any more?

Also: IKFast solves in microseconds. Trac_IK is millisecondS work.

gvdhoorn gravatar image gvdhoorn  ( 2017-07-07 07:16:15 -0500 )edit

Are you re-using any part of the demo setups, or is this a completely new setup? I think your video shows an IRB 2400, correct? There is a descartes IK plugin for that, no?

gvdhoorn gravatar image gvdhoorn  ( 2017-07-07 07:18:04 -0500 )edit

I didn't realize that IKFast was so necessary. I just changed the solver in kinematics.yaml and it had massively increased success rate. I found that with IKfast it would only be able to plan a path perhaps 20% of the time for the same set of poses, so it also seemed very non-repeatable.

jbeck28 gravatar image jbeck28  ( 2017-07-07 08:45:57 -0500 )edit

I modified a few launch files and made a moveit config for the IRB2400, I mostly reused the second descartes tutorial, just made some changes to parse in a predefined set of poses, and changed which robot to load.

jbeck28 gravatar image jbeck28  ( 2017-07-07 08:46:45 -0500 )edit

I believe there is an ikfast plugin for that robot. Though, with IKFast, don't I need to plan with respect to tool0 instead of my defined toolFrame?

jbeck28 gravatar image jbeck28  ( 2017-07-07 08:47:31 -0500 )edit

There is a descartes specific IKFast plugin for ABB IRB 2400 in ros-industrial-consortium/godel. See godel_irb2400. I'm not sure what the status is. I'd ask on the issue tracker.

gvdhoorn gravatar image gvdhoorn  ( 2017-07-07 08:50:15 -0500 )edit