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moveit getJacobian

asked 2018-12-12 02:59:57 -0500

Mike Ferenduros gravatar image

Hi! I had a problem with moveit's computeVariableVelocity, which I tracked down to a weird Jacobian matrix in my model. The robot has X, Y and Z prismatic joints, then a Z revolute. But with the joint-states all zeroed out, I'm getting a jacobian

  1.304  0.31889  0.41454        0
  -0.03  0.97173 -0.06256    0.575
0.19219  0.23349  2.48029        0
      0        0        0        0
      0        0        0        0
      0        0        0        1

which looks very wrong in a bunch of ways (not least, 1m of Z joint movement turns into 2.4m of worldspace Z!). Only the final revolute joint looks right.

Stepping into getJacobian, things seem to go wrong around line 1161:

joint_transform = reference_transform * getGlobalLinkTransform(link);
joint_axis = joint_transform * static_cast<const robot_model::PrismaticJointModel*>(pjm)->getAxis();

When I hit this line, getGlobalLinkTransform returns a valid matrix that includes translation. There's nothing in reference transform to cancel this out, so prismatic axis gets rotated and translated, and joint_axis ends up totally wonky.

Is there something wrong with my RobotModel here? Am I misunderstandingt the Jacobian?

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If you feel this is an issue with MoveIt, I would suggest to report it over at ros-planning/moveit/issues.

If you do, please try to include a reproducable example or nr of steps. That will greatly simplify debugging.

gvdhoorn gravatar image gvdhoorn  ( 2018-12-12 03:06:21 -0500 )edit

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answered 2018-12-12 03:27:16 -0500

Mike Ferenduros gravatar image

Turns out it was indeed a moveit bug, fixed last month.

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Thanks for reporting back.

gvdhoorn gravatar image gvdhoorn  ( 2018-12-12 03:36:06 -0500 )edit

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Asked: 2018-12-12 02:59:09 -0500

Seen: 657 times

Last updated: Dec 12 '18