Abstract: An embodiment of the present invention includes a method for driving a voice coil motor in response to signals from a feedback network that senses voice coil motor velocity. The method includes steps of providing a drive signal to an H-bridge for a first interval. At the end of the first interval, the H-bridge is placed in a high impedance state. Following a pause for a second interval during which transient voltages extinguish, a sample and hold circuit is coupled to the voice coil motor. The sample and hold circuit measures a voltage from the voice coil motor that is directly proportional to voice coil motor velocity and thus is directly related to head velocity. After the sample and hold circuit measures the voice coil motor voltage, the input to the sample and hold circuit is disabled. An output signal from the sample and hold circuit is coupled to the feedback network and thus to the H-bridge.

Abstract: An embodiment of the present invention includes a method for driving a voice coil motor in response to signals from a feedback network that senses voice coil motor velocity. The method includes steps of providing a drive signal to an H-bridge for a first interval. At the end of the first interval, the H-bridge is placed in a high impedance state. Following a pause for a second interval during which transient voltages extinguish, a sample and hold circuit is coupled to the voice coil motor. The sample and hold circuit measures a voltage from the voice coil motor that is directly proportional to voice coil motor velocity and thus is directly related to head velocity. After the sample and hold circuit measures the voice coil motor voltage, the input to the sample and hold circuit is disabled. An output signal from the sample and hold circuit is coupled to the feedback network and thus to the H-bridge.

Abstract: Methods and apparatuses are provided to identify and extract a torque ripple signal found in the back-emf signal from an electric motor. The torque ripple signal is used in a feedback control loop to reduce the amount and effects of torque ripple in the motor and the motor system. A motor controller is provided to reduce torque ripple in an electric motor. The motor controller is suitable for controlling the speed or torque or other related parameters associated with the electric motor. A disc drive apparatus for use in information storage and retrieval systems is provided. The disc drive apparatus includes an electric motor, an information storage disc, and a motor controller. A method is provided for reducing the effects of torque ripple in an electric motor by sampling the back-emf signal generated by the electric motor, extracting the torque ripple signal from the back-emf signal, and generating an AC component signal proportional to the torque ripple signal.