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 ferromagnetic shaft using magnetic-head-type pickups. The method assumes linearity of the torque sensor. The output of the torque sensor is sampled per 2π/N radian, from which the 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 are estimated from the sensitivities measured at M points (M≪N). The usefulness of the method has been demonstrated using an S45C carbon steel motor shaft with no heat treatment. The nominal carbon content is about 0.42%~0.48%. Peak-to-peak fluctuations in zero level and sensitivity were originally about 30%/FS (FS=10 Nm) and 10%~15%, respectively. After application of the method, the total error was reduced to within +3%/FS for M=8 and N=250