Non-contact revolution measurement by the magnetic field intensity from axes

A new method to measure and/or estimate the angle, angular velocity and acceleration of axes of rotary machinery, that are neither exposed nor artificially marked for measurement purposes is presented. Axes made from magnetic materials like iron are always magnetized in their production processes and the periodic change in the magnetic field intensity is observed when measured near the rotating axis even if it is housed. First, the magnetic field intensity for one period is measured by a highly sensitive magnetic sensor and memorized in a memory storage as a template pattern. The angle of the axis is estimated by comparing the currently measured magnetic field intensity and that in the template pattern. Application of observer techniques to a state variable equation of a triple integrator system that relates the angle, the angular velocity and the angular acceleration leads to the estimated values of these variables. Validity of the measurement and/or estimation method was examined by applying it to various rotating axes