Parallel Robots - Implementing close kinematic chains

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Closed kinematic chains are not officially supported with URDF, though they are supported with SDF. Here is an example of an SDF model with closed chain. Also, the PR2 gripper has a 4-bar linkage.

We are planning to create a unit test for closed chains, but haven't done it yet.

Building on what is already said, I created a Tutorial on Simple Closed Kinematics Model . Its just to have a starting point for anyone that is interested. It certainly helped me to understand it better and work afterwards on the fantastic tracksdriveplugin and my own projects .

Here I leave you all the files I used, bith open and closed models sdf, their spawn launch files and the spawn sdf launch file:

simple_open_chain.sdf

open_chain_spawn.launch

simple_closed_chain.sdf

spawn_closekinem_example.launch

spawn_sdf_robotdesc.launch

You should be able to have something like this:

Hope this is usefull.

Hi, I'm considering the same thing. In my case several linear actuators are applying forces to the same joint in parallel - some of them spanning only one joint, some even two joints.

As Gazebo7 features a graphical interface, is it possible to create those closed chains graphically? Are the physics engines able to calculate valid solutions?

Thanks!

the closed_loop_plugin can solve the issue that URDF not support Closed loop chains. please refer to : http://wiki.ros.org/action/edit/Angel... or https://github.com/wojiaojiao/pegasus...

URDF doesn't support close kinematic chains but the functionality of the same can be increased via using gazebo tags because sdf does support it . For realising the same kindly refer to pr2's gripper urdf file they have already implemented close kinematic chains in it.

The following tree shows how closed kinematic chain is implemented in pr2 gripper.