Patent ID: 8729889
Filing Date: 2014-05-20
Classification: G01D

Abstract:
1. A method of measuring angular positions based on a magnetic principle of operation, and featuring self-compensation against unwanted deviations of the measurement's output value from a predetermined function of angular position, comprising: a. providing a rotor part containing a rotary magnetic circuit, the magnetic flux through which is generated by a permanent magnet, featuring one or more circular air gaps coaxial with respect to the rotor main rotational axis, the geometry, when referring to a cylindrical coordinate system whose z axis coincides with the rotor main rotational axis, of said circular air gaps being purposely designed with widths which are predetermined functions of azimuth φ, such that the mathematical form of the resulting functions which describe the value of the magnetic field B(φ) along circles contained within said air gaps, said circles being further centred on and perpendicular to the z axis, possess such a rotational symmetry that there exist pairs of fixed locations characterised by pairs of magnetic field values, B1 and B2, having the property that the sum B1+B2 is substantially a constant value, and thereby also independent of the value of the angle of rotation θ of the rotor with respect to said fixed locations, b. providing a plurality of magnetic field probes arranged in pairs for measuring the corresponding pairs of magnetic field values heretofore, the two probes of each pair possessing substantially the same electrical characteristics and belonging either to the known type whose output signal is ratiometric with respect to the supply voltage or to the known type whose output signal is ratiometric with respect to the supply current, d. providing means for coupling the rotor part to the rotary members whose angular position is the ultimate objective of the measurement, while ensuring that the rotor main rotational axis is substantially coaxial, given some unavoidable mechanical tolerances and mounting inaccuracies, with respect to the rotational axis of said rotary members, e. providing, for each of said pairs of magnetic field probes, a signal conditioning and processing electronics realising a compensating feedback loop which will: whereby drifts and deviations from nominal values of those parameters whose variations would otherwise result, in case the compensating feedback loop heretofore were not implemented, in unwanted deviations of the V h1 (θ) or V h2 (θ) output signal values from their respective predetermined functions of θ, and consequently also in corresponding deviations from an otherwise constant value of the V mean value heretofore, will now urge a reaction of the feedback loop resulting in said magnetic field probes' output signal values, V ref B1(θ)/B virtual and V ref B2(θ)/B virtual , being inherently compensated and hence independent of the values of those components of said drifts and deviations from nominal values which affect in the same proportional manner both the numerator and the denominator, said feedback loop reaction having acted to adjust in the same proportional manner the individual gains of the two probes by modifying their common supply, thereby transferring the effects of the drifts and deviations heretofore from said probes' output signal values to the otherwise predetermined constant value of said common supply, value of common supply which thereby naturally contains useful diagnostic information about the nature and extent of said drifts and deviations from nominal values.