Safety assurance of a head-foot steered wheelchair via structured STPA decomposition

Abstract

This work applies Systems-Theoretic Process Analysis (STPA) as an initial step toward the safety assurance of a wheelchair equipped with a head-foot steering interface designed for individuals with severe motor impairments. Modeling the system’s control structure—particularly the human–machine interaction—is challenging and often leads to cascaded control loops that make the analysis time-consuming and susceptible to oversight. To address this complexity, we propose separating the analysis into two complementary parts: a human-centric loop that examines user behavior, and a computer-centric loop that focuses on sensors, actuators, and control logic. This division preserves critical human interaction considerations while streamlining the safety assessment and supporting a more robust design of the wheelchair system.