Handling Gripper Width with Mimic Joints

[HarisCavkic]

Hi Pinocchio team,

I’m currently working with a gripper that uses mimic joints to define finger motion, and I’m trying to determine the correct procedure to: 1. Compute the gripper width from the current (mimicked) joint value. 2. Compute the required joint value given a target gripper width.

Is this functionality treated as part of FK/IK in Pinocchio, or is there a different recommended approach for dealing with mimic joints in this context? I couldn’t find an example in the documentation or demos that covers this specific case.

Any guidance or pointers would be greatly appreciated!

Kind regards, Haris

[jorisv]

Hello @HarisCavkic,

Mimic joints are handled by pinocchio for FK et jacobian computation. So you should be able compute IK for a robot with mimic joints.

The following file show how to use mimic joints in Pyhon: https://github.com/stack-of-tasks/pinocchio/blob/devel/examples/mimic_dynamics.py From urdf parser you have to use the following argument: mimic=True If you create your model manually you can use transformJointIntoMimic or buildMimicModel functions

There is one constraints: Mimicking joint should have an higher index than mimicked joint.

When you have a working model with mimic joint, you can use a standard IK algorithm