Torque disturbance precompensation for disk drive spindle motors

A method of substantially canceling torque disturbance to the spindle motor that rotates a disk in a disk drive, said disturbance resulting from the change in drag force on the disk and spindle motor produced by the head during radial movement thereof over the disk surface, the movement of the head being produced by the actuator, said method comprising the steps of:

• providing a disk with a disk surface for storing data;
• providing a head for reading data on said disk surface;
• providing a spindle motor for rotating said disk past said head;
• providing an actuator for radially moving said head over said disk surface;
• wherein said head creates a drag on the rotation of said disk and the amount of said drag varies depending upon the radial position of said head over said disk surface;
• defining a plurality of N radial zones on said disk surface, where N is an integer greater than 1;
• providing a table of N torque correction values, each of said values representing a current to be applied to said spindle motor to compensate for head drag at a particular radial zone of the disk surface, each of said values being associated with one of said N radial zones on said disk surface;
• detecting when the movement of said actuator causes said head to move from a first zone to a second zone of said disk surface;
• selecting, after said step of detecting, a particular torque correction value from said table, said particular torque correction value corresponding to said second zone;
• and
• commanding said particular torque correction value to said spindle motor to substantially prevent a change in the velocity of said spindle motor attributable to the change in drag caused by moving said head across said disk surface.

A method of substantially canceling torque disturbance on the spindle motor that rotates a disk in a disk drive, the torque disturbance resulting from the change in drag force produced by the head during radial movement thereof over the disk surface, said spindle motor being controlled by a motor speed control loop, said method comprising the steps of:

• providing a disk with a disk surface for storing data;
• providing a head for reading data on said disk surface;
• providing a spindle motor for rotating said disk past said head;
• providing an actuator for radially moving said head over said disk surface;
• wherein said head creates a drag on the rotation of said disk and the amount of said drag varies depending upon the radial position of said head over said disk surface;
• providing means for controlling the speed of said spindle motor;
• entering a set of initial correction values in a look-up table, said values corresponding to the incremental current required to be applied to said spindle motor to maintain a predetermined velocity when said heads are at a particular radial position over the disk surface relative to a reference position;
• detecting when said head moves from a present radial position to a new radial position over said disk surface;
• selecting, after said step of detecting, from said look-up table the particular correction value corresponding to said new radial position;
• and
• adding said particular correction value to said control loop to precompensate said motor and thereby prevent any change in the velocity of said spindle motor attributable to the change in drag caused when moving said head across said disk surface.

A disk drive for a portable computer, said disk drive having at least one read/write head for writing information to and reading information from at least one magnetic disk rotatable at a constant speed by a spindle motor, said magnetic disk having at least one surface with N radial zones defined thereon, where N is an integer greater than one, said spindle motor supplied with a steady-state current by an amplifier, said constant speed maintained by a control loop comprising:

• a velocity detector for measuring an instantaneous speed of said motor;
• a comparator, coupled to said velocity detector, to contrast said instantaneous speed with said constant speed, said comparator producing an error signal proportional to a discrepancy between said constant speed and said instantaneous speed;
• a compensator for providing said amplifier with an actuating signal proportional to said error signal;
• and
• a memory containing a plurality of N correction values for said steady state current, each of said N radial zones having a corresponding correction value located in said memory;
• means for adding one of said plurality of N correction values to said error signal at a time that substantially prevents a change in motor speed attributable to the change in drag resulting from movement of said at least one read/write head over said at least one magnetic disk.

A disk drive, comprising:

• a disk with a disk surface for storing data;
• a head for reading data stored on said disk surface;
• a spindle motor for rotating said disk past said head;
• means for radially moving said head from a first radial position over said disk surface to a second radial position over said surface;
• wherein, when in operation, said head creates a drag on said disk and the amount of said drag varies depending upon the radial position of said head over said disk surface;
• wherein, when in operation, the change in the drag produced when the radial position of said head changes can create a torque disturbance that changes the rotational velocity of said spindle motor;
• and
• means for substantially preventing a change in the rotational velocity of said spindle motor attributable to a change in drag produced by said head when the radial position of said head over said disk changes.