Inverse Kinematics on rviz

asked 2018-08-23 08:38:10 -0500

tony chen
3 ●1 ●1 ●2

Hi,

I am recently working on Fetch robot and motion planning and I have run into such a problem:

Given a serial of pose in work space, the serial of configurations in joint space the IK solver output are not continue (sometime flip).

I have noticed that when you are dragging the interactive marker on the end-effector in rviz, the joints can always be continue. Does anyone have any idea what kind of IK algorithm rviz is using?

Thanks!

answered 2018-08-23 15:49:53 -0500

fergs

13902 ●59 ●157 ●196 http://www.robotandchisel.com

RVIZ doesn't have any IK internally -- I presume you are using the MoveIt configuration to drag the arm with Interactive Markers? If so, the IK is probably the KDL plugin from MoveIt. Just a note though: it does not provide any guarantee that the arm won't "flip" -- you're probably just getting lucky since the Fetch has so many continuous rotation joints.

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Thank you very much for your help!

tony chen ( 2018-08-25 20:15:40 -0500 )edit

Tony, if that answers your question, please click the checkmark next to my answer to accept the answer.

fergs ( 2018-08-25 22:50:12 -0500 )edit

Hi fergs, sorry for asking you again. Do you know any IK plugin in Moveit that can guarantee the continuity of the joint angles? Thanks!

tony chen ( 2018-08-27 06:13:43 -0500 )edit

There really isn't one AFAIK -- that's still an area of active research (for instance, see http://www.roboticsproceedings.org/rs... )

fergs ( 2018-08-27 10:24:01 -0500 )edit

No guarantee, but trac_ik configured with Distance solve type will generally return solutions that are "close" to the current pose of the robot. It doesn't give any guarantees, but it will try.

Edit: that is not the same as 'continuity' of course.