🤖 AI Summary
This work addresses the challenge of simultaneously ensuring balance and safety in floating-base robots during continuous physical human–robot interaction, where existing whole-body control methods often suffer from steady-state errors or inflexible joint-space allocation. The authors propose a three-layer control architecture: a centroidal model predictive controller plans contact forces; a priority-driven whole-body controller generates joint torques via contact-consistent nullspace projection; and a Kalman-enhanced moving horizon quadratic program suppresses interaction disturbances in the residual nullspace. A novel covariance inflation mechanism ensures continuity of disturbance estimation across contact switches, achieving zero steady-state error under bounded constant interaction forces. Furthermore, an impedance equivalence theorem is introduced, proving that adaptive task-space impedance behavior can be exactly recovered over an infinite horizon. The method is validated on a 17-DOF bipedal robot and the Unitree G1 humanoid, supporting real-time operation at ≥1 kHz with high precision and minimal steady-state error.
📝 Abstract
Floating-base robots must balance under rigid contact constraints while interacting safely with humans. Existing whole-body control~(WBC) frameworks allocate the full joint space to locomotion or rely on fixed-gain impedance feedback that accumulates steady-state error under sustained physical human--robot interaction~(pHRI) forces. This paper extends the authors' fixed-base two-layer Impedance MPC to floating-base platforms through a three-level architecture: a centroidal MPC plans contact forces over a 500\,ms horizon; a priority-driven WBC layer resolves balance into joint torques through contact-consistent null-space projection; and the residual null space is governed by a receding-horizon quadratic program~(QP) that predicts and rejects pHRI disturbances using a Kalman-augmented state. A contact-consistent feedback linearization reduces the arm end-effector plant to a double integrator with a \emph{constant} state matrix within each contact mode, enabling offline precomputation of the QP cost and ${\geq}1$\,kHz operation. A covariance-inflation protocol preserves the disturbance estimate across contact-mode switches, guaranteeing zero steady-state error under bounded constant pHRI loads, and an Impedance Equivalence Theorem shows the infinite-horizon limit recovers a classical task-space impedance law whose effective mass, damping, and stiffness adapt to posture and contact configuration. Simulations on a 17-DOF biped and the Unitree G1 humanoid validate the design.