Adaptive compensation for hard disc drive spindle motor manufacturing tolerances

A method for providing commutation timing and speed control to windings of an electrically commutated spindle motor in a circuit having a back emf sense circuit for generating a plurality of zero crossing signals in response to voltages sensed on the windings in a mechanical revolution of the spindle motor, the plurality of zero crossing signals defining a corresponding plurality of zero crossing periods, each zero crossing period comprising a duration of time between successive zero crossing signals the circuit further having a predetermined number of reference frequency periods for each mechanical revolution of the spindle motor, each reference frequency period having corresponding period boundaries, the method comprising the steps of:

• identifying systematic variations in operational speed of the spindle motor, including the steps of:
• determining a plurality of average phase differences, each average phase difference comprising the phase difference between each zero crossing signal and selected period boundaries of the reference frequency periods over a plurality of revolutions of the spindle motor;
• and
• determining a plurality of average zero crossing periods, each average zero crossing period comprising an average duration of each of the plurality of zero crossing periods over the plurality, of revolutions of the spindle motor;
• and
• compensating for the systematic variations in operational speed of the spindle motor, including the steps of:
• generating speed control timing signals in response to the average phase differences and using the speed control timing signals to control the speed of the spindle motor;
• and
• generating commutation timing signals in response to the average zero crossing periods and using the commutation timing signals to commutate the spindle motor.

In a hard disc drive of the type having a multi-phase spindle motor and a back emf sense circuit, the spindle motor having a plurality of commutation frequency periods in a mechanical revolution, a method for compensating for variations in rotational speed of the spindle motor, comprising the steps of:

• quantifying spindle motor rotational speed variations during a learn mode by commutating the spindle motor using back emf sensing, comprising the steps of:
• generating zero crossing signals in response to voltages of the spindle motor;
• generating commutation signals in response to the zero crossing signals;
• and
• using the commutation signals to commutate the spindle motor;
• generating pump signals according to phase differences between the zero crossing signals, and reference pulses at a reference frequency;
• and
• averaging the lengths of the pump signals for each commutation frequency period and storing an associated average length value;
• and
• compensating for the spindle motor rotational speed variations, by generating adaptive pump signals according to phase differences between the zero crossing signals and adapted reference pulses, each adapted reference pulse comprising the reference pulse adjusted by the associated average length value;
• and
• using the adaptive pump signals to control the rotational speed of the spindle motor.

In a disc drive having a multi-phase spindle motor and a back emf sense circuit for providing zero crossing signals in response to voltages sensed from the spindle motor during rotation of the spindle motor, the spindle motor having a plurality of nominal zero crossings associated with each mechanical revolution of the spindle motor, each nominal zero crossing indicating a point in time at which a nominal zero crossing signal would be generated by the back emf sense circuit as a result of operation of the spindle motor without variations in rotational speed, a method for minimizing variations in rotational speed of the spindle motor comprising the steps of:

• identifying a timing error associated with each zero crossing signal within a mechanical revolution of the spindle motor by determining an average phase difference between each zero crossing signal provided by the back emf sense circuit and each associated nominal zero crossing, over a plurality of mechanical revolutions;
• and
• compensating for the timing error associated with each zero crossing signal provided by the back emf sense circuit by using the average phase difference to identify an adaptive zero crossing signal for each zero crossing signal provided by the back emf sense circuit;
• and
• using the adaptive zero crossing signals to control the rotational speed of the spindle motor.

In a disc drive having a multi-phase spindle motor and a back emf sense circuit for providing zero crossing signals in response to voltages sensed from the spindle motor during rotation of the spindle motor, the spindle motor having a plurality of nominal zero crossings associated with each mechanical revolution of the spindle motor, each nominal zero crossing indicative of a nominal zero crossing signal generated by the back emf sense circuit as a result of operation of the spindle motor without variations in rotational speed, an apparatus for minimizing variations in rotational speed of the spindle motor comprising:

• zero crossing error means for characterizing error associated with the timing of each zero crossing signal provided by the back emf sense circuit over a mechanical revolution of the spindle motor, wherein the error is characterized as an average phase difference between each zero crossing signal and each associated nominal zero crossing, over a plurality of mechanical revolutions;
• and
• zero crossing compensation means, responsive to the zero crossing error means, for compensating for the error associated with each zero crossing by using the average phase difference to identify an adaptive zero crossing signal for each zero crossing signal provided by the back emf sense circuit;
• and
• using the adaptive zero crossing signals to control the rotational speed of the spindle motor.