Method and Apparatus for Encoder Interpolation

An encoder interpolator comprising:

• input circuitry configured to receive encoder signals from a sinusoidal encoder and sample the encoder signals to obtain sampled signal values;
• processing circuitry configured to:
• calculate positions from the sampled signal values;
• obtain corrected positions by applying corresponding correction values to the calculated positions;
• form extended positions comprising the corrected positions and a current cycle count associated with the encoder signals;
• determine position errors between the extended positions and corresponding estimated positions, as estimated by an included digital state estimator that constrains position estimation according to a mathematical model of a physical system whose position is being tracked by the sinusoidal encoder;
• and
• output circuitry configured to output the extended positions, or a filtered version thereof, for use in monitoring or controlling the position of the physical system;
• wherein, to determine the correction values, said processing circuitry is configured to:
• process the position errors on a running basis to determine the magnitude of one or more harmonic components of the position errors;
• and
• determine the correction values as a function of the determined magnitudes.