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urdf conditional limits

asked 2012-02-07 02:08:10 -0500

tbh gravatar image

I was wondering if there was any way to specify a limit in urdf or xacro based on the positions of other joints or perhaps based on another transform entirely. My robot uses parallelograms and triangles in its structure, and while I know this is not 100% urdf compatible, I'm naturally trying to use as much existing code as possible. Anyway, my robot model works relatively well, but my "hacked" urdf joints should have a different "safe" range than their full range. This "safe" range is dependant on either the entire robot state (or at least parts of it) or the base coordinate system. Thanks for your help.

Note: I'm still under the impression that parallel robots are not urdf compatible, but I'd be super happy to know if there is support for them now. This thread says there still isn't, but this thread creates a gripper with parallel links using some undocumented urdf tag called mimic? Any clarification about this is welcome, as well.

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answered 2012-02-07 06:49:53 -0500

David Lu gravatar image

The mimic tag is an enigma that people at Willow seem to be very hushed about. The other thread uses the mimic tag with JointStatePublisher to mimic parallel links, which only works under certain circumstances.

There is no URDF support (as far as I know) for the type of safety constraints you're describing. I would enforce them separately in your control code, or possibly with the collision element.

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answered 2012-02-07 05:50:51 -0500

Wim gravatar image

The urdf only supports tree-like kinematic chains. So parallel robots are not supported. Also, joint limits that depend on the position of other joints are not part of the feature set.

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Asked: 2012-02-07 02:08:10 -0500

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Last updated: Feb 07 '12