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This paper introduces a self-sensing fiber-reinforced pneumatic twisted-and-coiled actuator (FR-PTCA) by integrating a conductive nickel wire, enabling force estimation via inductance feedback. The key finding is a deterministic, low-hysteresis inductance-force relationship at constant pressures, unlike the hysteretic inductance-length behavior. A parametric self-sensing model and a nonlinear hybrid observer, combining an Extended Kalman Filter (EKF) with constrained optimization, are developed to estimate actuator states, achieving force estimation accuracy comparable to external load cells.
Forget external sensors: embedding a simple nickel wire into a pneumatic actuator unlocks surprisingly accurate force sensing via inductance, even with hysteresis.
Fiber-reinforced pneumatic twisted-and-coiled actuators (FR-PTCAs) offer high power density and compliance but their strong hysteresis and lack of intrinsic proprioception limit effective closed-loop control. This paper presents a self-sensing FR-PTCA integrated with a conductive nickel wire that enables intrinsic force estimation and indirect displacement inference via inductance feedback. Experimental characterization reveals that the inductance of the actuator exhibits a deterministic, low-hysteresis inductance-force relationship at constant pressures, in contrast to the strongly hysteretic inductance-length behavior. Leveraging this property, this paper develops a parametric self-sensing model and a nonlinear hybrid observer that integrates an Extended Kalman Filter (EKF) with constrained optimization to resolve the ambiguity in the inductance-force mapping and estimate actuator states. Experimental results demonstrate that the proposed approach achieves force estimation accuracy comparable to that of external load cells and maintains robust performance under varying load conditions.
