Full-Range Cartesian-Decoupled Impedance Control for Physical Human-Robot Interaction with Series-Elastic Space Robots

Effective physical human-robot interaction in space exploration is built on a foundation of admittance and impedance-controlled manipulators. Series-elastic actuators enable these manipulators to render compliant behaviors that are ideal for safe and responsive interaction. However, the cascaded control architectures commonly used in space robotics enforce a strict bandwidth hierarchy, requiring low-level position or torque control loops to operate significantly faster than high-level admittance or impedance loops. This constraint limits achievable performance by preventing the manipulator from expressing the full range of its potential impedance behaviors. Leveraging recent advancements in spaceflight computing, we present a non-cascaded, state-space full-state feedback control architecture that removes the bandwidth hierarchy requirement. This approach enables simultaneous realization of stiff, compliant, and natural impedance behaviors across multiple Cartesian degrees of freedom, a capability we call Full-Range Cartesian-Decoupled Impedance Control. The approach is validated in simulation on a three-degree-of-freedom NASA Valkyrie upper-arm testbed with series-elastic joints. Comparative experiments with a conventional cascaded controller demonstrate a wider stable impedance range, expanding the spectrum of safe human-robot collaboration behaviors for future space missions.