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Significance of jerk limits

asked 2019-05-06 04:14:42 -0500

Pulkit123 gravatar image

Hi

I am working with Ubuntu 16.04 and ROS Kinetic. I am doing motion planning for my 7 dof manipulator arm. I tried incorporating jerk limits in my config file but didn't see much change in the trajectory.Can someone please help me where the jerk limits are used in the planning pipeline ??

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answered 2019-05-06 04:54:42 -0500

gvdhoorn gravatar image

updated 2019-05-06 04:55:46 -0500

Can someone please help me where the jerk limits are used in the planning pipeline ??

If with "planning pipeline" you are referring to MoveIt using the default OMPL planner, then the jerk limits are not used at all there. In fact, no limits other than position limits are used, as OMPL is a kinematic planner only and does not take dynamics into account (at least: not as it's used by MoveIt) and MoveIt setups the planning (ie: search) space for OMPL using the joint limits.

Limits on the dynamics are only taken into account at the end of planning pipeline, namely the "time-parameterisation". OMPL delivers a path, time-parameterisation turns it into a trajectory.

There are currently three options for time-parameterisation provided with MoveIt:

  1. Iterative Parabolic Time Parameterization (IPTP)
  2. Iterative Spline Parameterization
  3. Time-optimal Trajectory Generation (using TOTG by Tobiaz Kunz (paper)

There is some discussion on the various options on the Time Parameterization page in the MoveIt tutorials.

Afaik, none of those take jerk limits into account.

I tried incorporating jerk limits in my config file but didn't see much change in the trajectory.

Afaik, that is to be expected. See my earlier comments.


Note that there are planners that could take dynamics into account while planning (something like STOMP or CHOMP, optimisation based) but those are by default not used and they might require some additional setup and configuration.

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The jerk information is used by several controllers from ros_control. MoveIt reuses the config file format, so that's why the keys are there.

gvdhoorn gravatar imagegvdhoorn ( 2019-05-06 05:21:47 -0500 )edit

Could you please mark the question as answered by ticking the checkmark (✓) to the left of the answer if you feel it has been answered? Thanks.

gvdhoorn gravatar imagegvdhoorn ( 2019-07-11 02:04:32 -0500 )edit

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Asked: 2019-05-06 04:14:42 -0500

Seen: 47 times

Last updated: May 06