Using robot with closed loop structure in Moveit

ROS1
urdf

asked 2021-07-23 06:38:00 -0600

robotUrdf
11 ●1 ●2 ●2

updated 2021-07-24 19:22:45 -0600

jayess
6155 ●26 ●85 ●92

How can I define the following robot in URDF to use it with move it

Image :

image description

Update:

image description

I might not phrase my question properly, my apologies. I know how to export from Solidworks to URDF. My issue is that Moveit only accepts tree type of structure and do not accept closed structure due to the URDF limitation. If I set the link in the image to mimic, what should I do to the upper link to make it move correctly, i.e the motion should be according to the four-bar linkage, where the upper-link motion will be close to linear motion with slight rotation.

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I have uploaded your image, I have given you enough karma that you can now be able to upload an image by yourself.

Ranjit Kathiriya ( 2021-07-23 10:48:49 -0600 )edit

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Thanks @Ranjit

robotUrdf ( 2021-07-24 06:06:54 -0600 )edit

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@robotUrdf In the future, please update your question to provide more information instead of using an answer

jayess ( 2021-07-24 19:23:36 -0600 )edit

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answered 2021-07-23 12:29:17 -0600

AndyZe

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updated 2021-07-23 14:40:20 -0600

I believe the way to handle this is to set one of the actuators in the parallel structure as a "mimic joint" in the URDF. Then the robot will be seen as a regular serial manipulator, as far as MoveIt is concerned.

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I might not phrase my question properly, my apologies. I know how to export from Solidworks to URDF. My issue is that Moveit only accepts tree type of structure and do not accept closed structure due to the URDF limitation. If I set the link in the image to mimic, what should I do to the upper link to make it move correctly, i.e the motion should be according to the four-bar linkage, where the upper-link motion will be close to linear motion with slight rotation.

robotUrdf ( 2021-07-24 06:06:14 -0600 )edit

Let's say the joints in the four bar linkage are called J_a, J_b, J_c, J_d.

J_b has the same angle as J_a, right? So set it as a mimic joint of J_a.

J_d has the same angle as J_c, right? So set it as a mimic joint of J_c. Now it's a serial manipulator as far as MoveIt knows. Or am I missing something?

AndyZe ( 2021-07-27 08:40:25 -0600 )edit

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answered 2021-07-23 11:11:49 -0600

Ranjit Kathiriya
1624 ●18 ●148 ●46

updated 2021-07-23 11:14:13 -0600

Hello @robotUrdf,

There is a couple of solution.

a. Creating Urdf by yourself:

You need to create a Urdf file, For creating that you can take help from Urdf tutorials. Before you do that You need to have all links of your robot into STL file and DAE (Note: Optional Just for visualization purpose).

Then you have to join each link with another link as given in the above tutorials tutorial.

b. Let's assume that you are having this robot file of Solidworks and you can directly export your Solidworks file to urdf. This link has steps to export urdf from SW.

http://wiki.ros.org/sw_urdf_exporter https://www.youtube.com/watch?v=Uz6KP...

Note: If you have a Solidworks file then go with the (b) point solution. It will be easier for you.

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I might not phrase my question properly, my apologies. I know how to export from Solidworks to URDF. My issue is that Moveit only accepts tree type of structure and do not accept closed structure due to the URDF limitation. If I set the link in the image to mimic, what should I do to the upper link to make it move correctly, i.e the motion should be according to the four-bar linkage, where the upper-link motion will be close to linear motion with slight rotation.

robotUrdf ( 2021-07-24 06:06:21 -0600 )edit

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Using robot with closed loop structure in Moveit

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