Torque and rotational speed FBG-based measurements by sensorized FDM support structure for aerospace applications

This paper presents a fiber Bragg grating (FBG) based sensor integrated into an additively manufactured structural support component for a motor. The sensor embeds two optical fibers each with three FBGS and leverages the linear relationship between strain and torque to estimate the applied torque by monitoring the Bragg wavelength shift of each FBG. While the use of polymers, enabled by fused deposition modeling (FDM), simplifies manufacturing, it introduces short-term creep due to the viscoelastic nature of the material. To mitigate this, polyethylene terephthalate glycol (PETG) was chosen for its superior short-term creep resistance. Additionally, a one-dimensional Kalman filter was implemented during signal processing to minimize creep-related noise. The sensor's design also accounts for torque ripple, a cyclic torque variation related to motor rotation, which allowed the measurement of rotational speed by applying a fast Fourier transform (FFT) to the sensor output and analyzing the dominant frequency. This dual-functionality sensor is tailored for characterizing state-of-the-art toroidal and conventional propellers, offering simultaneous torque and RPM measurements.