Patent ID: 11923728
Assignee: WAYMO LLC
Field: Measurement (Instruments)
Classification: CPC G  H | IPC G  H

Claim 9:
10. A method of mitigating post-calibration error in a brushless DC motor comprising:
generating a first magnetic field that interacts with a second magnetic field generated by four or more poles of a magnet ring mounted to a first platform such that the first platform rotates about a shaft on a common axis of rotation relative to a second platform mounted to the shaft;
receiving, from a magnetic field sensor connected to the second platform, data indicative of characteristics of the second magnetic field, wherein the second magnetic field is generated by the four or more poles of the magnet ring;
based on the data received from the magnetic field sensor, determining a measured signal;
determining a nominal signal, wherein the nominal signal is indicative of a characteristic field pattern;
determining a difference signal between the measured signal and the nominal signal, wherein the difference signal comprises a phase shift between the measured signal and the nominal signal, wherein the phase shift includes an amplitude that is proportional to an amount the shaft supporting the first platform and the second platform migrates away from the common axis, and wherein there is no difference signal when the shaft is in line with the common axis;
removing a sinusoidal component from the difference signal to determine a phase fingerprint signal;
determining, based on the phase fingerprint signal, a position of the poles of the magnet ring on the first platform, wherein the position includes spacing between a plurality of respective boundaries between neighboring poles of the four or more poles; and
applying the difference signal to the data received from the magnetic field sensor, wherein applying the difference signal comprises subtracting the difference signal from the measured signal.