Detection of instantaneous torque using the magnetostrictive effect in a practical ferromagnetic shaft

A method is presented by which instantaneous torque can be detected from a practical ferromagnetic shaft using magnetic head type pickups. The method assumes the linearity for the torque sensor. The output of the torque sensor is sampled per 2π/N radian, from which corresponding zero level is subtracted and then multiplied by a coefficient to correct sensitivity fluctuation. The coefficients for N sampling points are inversely proportional to the sensitivity at each sampling point. The coefficients were estimated from the sensitivities measured at M points (M<<N). Demonstrations are presented to show the usefulness of the method, using a S45C carbon steel shaft with no heat- treatment. Nominal carbon content of S45C material is about 0.42%~0.48%, after JIS Handbook. Peak-to-peak flucluation in zero level and that in sensitivity wereoriginally about 30/FS(FS=10Nm) and 10%~15%, respectively. After application of the method, total error was reduced within ± 3%/FS when M=8 and N=250.