Loco-Manipulation with Nonimpulsive Contact-Implicit Planning in a Slithering Robot

TL;DR

The paper tackles loco-manipulation for a snake robot by integrating locomotion and object interaction through nonimpulsive contact-implicit path planning. It develops a full-dynamics model with $M(q)\dot{u} - h(q,u,\tau) = \sum_i J_i^T(q) f_{ext,i}$, models unilateral contacts via normal-cone conditions with Coulomb friction, and uses the Delassus matrix $G = J_c M^{-1} J_c^T$ in a quadratic objective $\min_{f_{ext},u} \tfrac{1}{2} f_{ext}^T G f_{ext} + f_{ext}^T c$ under dynamics and actuation bounds, solved by a time-stepping shooting method. The constrained optimization yields contact forces and joint trajectories that respect gap constraints and kinematic limits. The authors validate the approach with high-fidelity Matlab/Simulink simulations and hardware experiments, demonstrating tasks like lifting, placing, and translating a box on flat surfaces and ramps, and analyzing ground-reaction forces. The work advances loco-manipulation for morpho-functional snakes and points toward real-time, tactile-sensing-enabled planning for robust manipulation in contact-rich environments.

Abstract

Object manipulation has been extensively studied in the context of fixed base and mobile manipulators. However, the overactuated locomotion modality employed by snake robots allows for a unique blend of object manipulation through locomotion, referred to as loco-manipulation. The following work presents an optimization approach to solving the loco-manipulation problem based on non-impulsive implicit contact path planning for our snake robot COBRA. We present the mathematical framework and show high-fidelity simulation results and experiments to demonstrate the effectiveness of our approach.

Figures (9)

• Figure 1: Illustrates COBRA while manipulating the position of a box.
• Figure 2: (Above) Closeup view of the head with actuated fins. (Below) Docking module attached to object for loco-manipulation.
• Figure 3: Full-dynamics model parameters in the object manipulation task considered in this paper
• Figure 4: Snapshots of COBRA lifting a box and placing it on a raised platform.
• Figure 5: Snapshots depict simulation of COBRA lifting a box from a raised platform, placing it on the flat ground, and translating the box to a new location through continuous body-object interactions during slithering motions.