Distributed Feedback Controllers for Stable Cooperative Locomotion of Quadrupedal Robots: A Virtual Constraint Approach

Abstract

This paper aims to develop distributed feedback control algorithms that allow cooperative locomotion of quadrupedal robots which are coupled to each other by holonomic constraints. These constraints can arise from collaborative manipulation of objects during locomotion. In addressing this problem, the complex hybrid dynamical models that describe collaborative legged locomotion are studied. The complex periodic orbits (i.e., gaits) of these sophisticated and high-dimensional hybrid systems are investigated. We consider a set of virtual constraints that stabilizes locomotion of a single agent. The paper then generates modified and local virtual constraints for each agent that allow stable collaborative locomotion. Optimal distributed feedback controllers, based on nonlinear control and quadratic programming, are developed to impose the local virtual constraints. To demonstrate the power of the analytical foundation, an extensive numerical simulation for cooperative locomotion of two quadrupedal robots with robotic manipulators is presented. The numerical complex hybrid model has 64 continuous-time domains, 192 discretetime transitions, 96 state variables, and 36 control inputs.

Layered Control for Cooperative Locomotion of Two Quadrupedal Robots: Centralized and Distributed Approaches

“…However, the capabilities of cooperative legged locomotion have not been fully explored. In particular, collaborating legged robots can be described by inherently unstable dynamical systems with high dimensionality (i.e., high degrees of freedom (DOFs)), nonlinear, and hybrid nature, and subject to underactuation and unilateral constraints, as opposed to most of the MRSs where the state-of-the-art algorithms have been deployed [39]. This complicates the design of real-time trajectory planning and control approaches, both in centralized and distributed fashions, to guarantee each agent's dynamic and robust stability while addressing the curse of dimensionality and respecting the holonomic and unilateral constraints.…”

Human-Scale Mobile Manipulation Using RoMan

“…Many standard manipulator packages at the time such as Baxter (Fitzgerald, 2013) could not deliver the required force, and industrial arms tended to be too massive. Even today's state-of-the-art commercial robots designed for less structured environments, such as Vision 60 (Akbari Hamed et al, 2020) and Spot (Bouman et al, 2020), are less forceful than humans. 3.…”

“…Examples include the Packbot (Yamauchi, 2004), Vision 60 (Akbari Hamed et al, 2020), and Spot (Bouman et al, 2020).…”