Robust Grasping by Bimanual Robots with Stable Parameterization-Based Contact Servoing

Robots with bimanual morphology usually possess higher flexibility, dexterity, and efficiency than those only equipped with a single arm. The dual-arm structure has enabled robots to perform various intricate tasks that are difficult or even impossible to achieve by unimanipulation. In this article, we aim to achieve robust bimanual grasping for object transportation. In particular, provided that stable contact is the key to the success of the transportation task, our focus lies on stabilizing the contact between the object and the robot end-effectors by employing the contact servoing strategy. To ensure that the contact is stable, the contact wrenches are required to evolve within the so-called friction cones all the time throughout the transportation task. To this end, we propose stabilizing the contact by leveraging a novel contact parameterization model. Parameterization expresses the contact stability manifold with a set of constraint-free exogenous parameters where the mapping is bijective. Notably, such parameterization can guarantee that the contact stability constraints can always be satisfied. We also show that many commonly used contact models can be parameterized out of a similar principle. Furthermore, to exploit the parameterized contact models in the control law, we devise a contact servoing strategy for the bimanual robotic system such that the force feedback signals from the force/torque sensors are incorporated into the control loop. The effectiveness of the proposed approach is well demonstrated with the experiments on several representative bimanual transportation tasks.