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What is a good way of storing robot paths and access them?

asked 2019-06-18 01:39:51 -0600

dofrey gravatar image

updated 2019-06-18 09:40:38 -0600

Hi guys

I am writing a controller for a 6DOF robot arm. I am generating paths for the robot to come from the starting point to a desired pose. To do this I do a piecewise polynomial interpolation. Meaning that I first easily interpolate linearly over time between the two points. And then I attach a 6-degree polynomial in the beginning and the end to smoothen the motion. It looks then as follows:

image description

Now I have the problem, that because of numerical issues (at least I think so) or because of time discretization, I got small jumps between the different polynoms:

image description

My idea is now to just filter the paths to get rid of these jumps. For this I need to store the path somehow that I can filter it but I don't really have an idea what is a good way of doing this. How are paths saved for example in MoveIt? Do they save discrete or continuous paths? Is there a way of connecting my polynoms to make it "filterable"?

Thanks for your help!

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Could you please attach your image directly to the question? You have 11 karma, so you should be able to do this.

gvdhoorn gravatar image gvdhoorn  ( 2019-06-18 08:50:23 -0600 )edit

Yes of course. When I posted the question this morning I did not have enough karma yet. Updated my question accordingly.

dofrey gravatar image dofrey  ( 2019-06-18 09:39:46 -0600 )edit

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answered 2019-06-18 13:06:51 -0600

Fundamentally a joint trajectory is a matrix of points and a matching vector of time offsets (in sections from the start of the trajectory) which give each row of the matrix a point in time. You could write these out to a CSV file fairly easily from a ROS node.

However taking a step back I don't think filtering out these glitches is the best idea, they are probably caused by a bug in your code or error in your maths. There is no reason why you shouldn't be able to produce a perfectly smooth (and tangentially continuous) joint trajectory path. So I would concentrate your efforts there, and hopefully you will not need an additional filtering step.

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Thanks. I really found a bug in my code now that fixed the problem. I gave up after multiple days of debugging but took it up now again. Thanks anyways for the information about how trajectories are stored usually. My trajectory I store as a function and not as a matrix of points. I think to publish it in RViz I need to convert my functions then to the matrix form.

dofrey gravatar image dofrey  ( 2019-06-19 06:10:52 -0600 )edit

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Asked: 2019-06-18 01:39:51 -0600

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Last updated: Jun 18 '19