Using Eddy Currents Within Magnetostrictive Position Sensors for Velocity Estimation

Absolute long-range as well as high-precision linear position measurement can be accomplished by magnetostrictive position sensors (MPS). The principle of operation of these sensors is based on a time-of-flight (TOF) measurement of a structure-borne sound wave within a magnetostrictive waveguide. In state-of-the-art position is calculated based on the measured TOF and physically related parameters like velocity or acceleration are calculated by numerical derivation. This paper discusses a novel method for real-time simultaneous estimation of position and velocity of a position marker. Related to the position marker's dynamics eddy currents are induced within the MPS housing. The magnetic fields generated by these eddy currents influence the generation of the structure-borne sound wave. Furthermore, this impact is detected and evaluated by digital signal processing and by means of an artificial neural network. Hence, the electrical representation of the detected structure-borne sound wave is digitalized at high speed. The reference or training dataset for the velocity estimation is constructed from recorded datasets itself, without an external velocity reference system (self-training). Using the presented method, the velocity data could be used either as an additional independent parameter for consistency checking (self-diagnostics), or for the improvement of the position measurement by signal fusion (self-optimization).