Optimisation of Body-ground Contact for Augmenting Whole-Body Loco-manipulation of Quadruped Robots

Abstract

Legged robots have great potential to perform locomanipulation tasks, yet it is challenging to keep the robot balanced while it interacts with the environment. In this paper we study the use of additional contact points for maximising the robustness of locomanipulation motions. Specifically, body-ground contact is studied for enhancing robustness and manipulation capabilities of quadrupedal robots. We propose to equip the robot with prongs: small legs rigidly attached to the body which ensure body-ground contact occurs in controllable point-contacts. The effect of these prongs on robustness is quantified by computing the Smallest Unrejectable Force (SUF), a measure of robustness related to Feasible Wrench Polytopes. We apply the SUF to assess the robustness of the system, and propose an effective approximation of the SUF that can be computed at near-real-time speed. We design a hierarchical quadratic programming based whole-body controller that controls stable interaction when the prongs are in contact with the ground. This novel concept of using prongs and the resulting control framework are all implemented on hardware to validate the effectiveness of the increased robustness and newly enabled loco-manipulation tasks, such as obstacle clearance and manipulation of a large object.

Optimizing Dynamic Trajectories for Robustness to Disturbances Using Polytopic Projections

“…Adapting the results from [11], we find a practically efficient way to simultaneously optimize the robustness metric and the affine relationship prescribing it. These results go beyond earlier adaptations in robotics by [12], as those, like our work relying on LP, were not suitable for use in a trajectory optimization setting.…”

“…Their scheme does not require an explicit description of the projection and works by combining Fourier-Motzkin elimination with techniques from adjustable robust optimization. The scheme was adapted for robustness computations in robotics in [12], where the SUF were estimated for static configurations. However, despite an improvement over exact computation, due to the computational complexity of their formulation it was not previously possible to consider trajectory optimization of full system dynamics and maximization of robustness based on dynamic polytopes at the same time.…”

Dynamic Legged Manipulation of a Ball Through Multi-Contact Optimization

“…Legs of a quadrupedal robot are used for both manipulation and locomotion in [14], wherein the legs statically manipulate a box by holding it on both sides. In other words, two legs function as two manipulators and they do not simultaneously achieve manipulation and locomotion tasks.…”

Circus ANYmal: A Quadruped Learning Dexterous Manipulation with Its Limbs

“…For multi-legs robots such as hexapod robots, four limbs are used balancing while the other two limbs are manipulating objects [15]- [18]. Another solution is to add additional support legs to the quadrupedal robot to maximize the robustness of loco-manipulation [19]. Compared to dual-limbs manipulation, the most extreme idea is to synthesize all the limbs for manipulation.…”