Measuring stiction and friction between the heads and discs of a hard disc drive

An apparatus for measuring the maximum static friction force and the kinetic friction force between discs of a disc drive and read/write heads positioned adjacent the discs, wherein the discs are affixed to a rotor of a disc drive spindle motor mounted to a case of the disc drive, the spindle motor having a plurality of windings through which electrical currents are passed to rotate the discs with respect to the case of the disc drive, the apparatus comprising:

• a spin-up motor having a rotatable shaft;
• a motor driver electrically connected to the spin-up motor for passing a motor drive current through the spin-up motor, wherein the motor driver is characterized as being of the type that measures the angular velocity of the spin-up motor shaft and adjusts the motor drive current in relation to the difference between the angular velocity of the spin-up motor shaft and an angular velocity command received by the motor driver;
• disc drive mounting means for mounting the case of the disc drive on the spin-up motor shaft for rotation of the disc drive case about an axis parallel to an axis of the discs of the disc drive;
• an accelerometer mounted on the disc drive mounting means for measuring the angular acceleration of the disc drive case during rotation of the disc drive case by the spin-up motor;
• slip ring means for making electrical contacts to the windings of the disc drive spindle motor and to the accelerometer;
• and
• measurement means, responsive to the motor driver, the accelerometer and the slip ring means, for measuring the static friction force and the kinetic friction force between the discs and the read/write heads in response to the rotation of the disc drive case and voltages induced in the windings of the spindle motor.

A method for determining the maximum static friction force between a disc of a disc drive and a head positioned adjacent the disc, wherein the disc can be rotated about a rotor of a disc drive spindle motor mounted on a case of the disc drive, the spindle motor having a plurality of windings through which electrical currents can be passed to rotate the discs with respect to the case of the disc drive about a disc axis, the method characterized by:

• (a) angularly accelerating the disc drive case at an increasing rate about an axis parallel to the disc axis;
• (b) repetitively measuring the angular acceleration of the disc drive case;
• (c) measuring voltages induced in the windings of the disc drive spindle motor by rotation of the disc relative to the disc drive case concurrently with the repetitive measurement of the angular acceleration of the disc drive case;
• and
• (d) determining the maximum static friction force between the disc and the head from the moment of inertia of the disc and disc drive spindle motor rotor about the disc axis and the angular acceleration of the disc drive case at the onset of relative movement of the disc with respect to the disc drive case.

A method for determining the kinetic friction force between a disc of a disc drive and a head positioned adjacent the disc, wherein the disc can be rotated about a rotor of a disc drive spindle motor mounted on a case of the disc drive, the spindle motor having a plurality of windings through which electrical currents can be passed to rotate the discs with respect to the case of the disc drive about a disc axis, the method characterized by:

• (a) angularly accelerating the disc drive case at an increasing rate about an axis parallel to the disc axis;
• (b) repetitively measuring the angular acceleration of the disc drive case;
• (c) measuring voltages induced in the windings of the disc drive spindle motor by rotation of the disc relative to the disc drive case concurrently with the repetitive measurement of the angular acceleration of the disc drive case;
• (d) determining angular accelerations of the discs relative to the disc drive case corresponding to measured angular accelerations of the disc drive case from the voltages induced in the windings of the disc drive spindle motor;
• and
• (e) determining the kinetic friction force between the discs and the heads from the moment of inertia of the discs and disc drive motor rotor about the axes of the discs and the angular accelerations of the disc drive case and of the discs relative to the disc drive case.