Abstract: Another aspect of the present invention will now be explained. The comb-filter repetitive controller design of the present invention effectively eliminates periodic disturbances of a known period in the position measurements of the disc drive servo system. This is accomplished by merging the averaging ability of the frequency-domain batch process approach into the time-efficient repetitive control approach. An embodiment of the present invention uses a comb-filter incorporated with a real-time repetitive controller based on the real-time filtering concept. This comb-filter design adds the ability of separating the RRO and NRRO component from the PES during the real-time WI-RRO compensation process. This approach at least minimizes the incapability of the real-time repetitive control approach to identify the RRO component beforehand. Because the RRO component can be extracted even under a noisy PES condition using the present invention, the learning gain can be increased.

Abstract: A system and method for attenuating the effect of rotational vibration on the positioning of the read/write head in a disc drive. The rotational acceleration of the disc drive body is sensed and applied to an adaptive filter that produces a feedforward signal designed to offset the effects of the rotational vibration. The adaptive filter adjusts its parameters based on the rotational acceleration signal, the position error signal of the servo system, and a transfer function relating the actual position signal to the feedforward signal. The plant estimate of the transfer function relating the actual position signal to the feedforward signal is determined off-line and stored for use by the adaptive filter in adjusting its parameters during operation.

Abstract: Apparatus suppresses seek-induced vibration in a disc drive. The apparatus is responsive to a selected bang-bang command to provide an operating signal to the actuator, such as a voice coil motor, representing the selected bang-bang command with damped amplitudes of dominant vibration mode frequencies of the selected bang-bang command. One example of the apparatus is a finite impulse response filter having a discrete transfer function of C(1+al1z−l+al2z−l·2+ . . . +alrz−l·r), where C is a constant, al1, al2, . . . alr represent impulse amplitudes at spaced positions within a sample period and z−l·1, z−l·2, . . . z−l·r represent delay components at the respective spaced positions. In a preferred embodiment, the finite impulse response filter employs a pole-zero cancellation technique to damp amplitudes of selected frequencies.

Abstract: An equalization filter for counteracting the effects of unwanted resonance modes and noise in the VCM plant. The filter comprises a transfer function derived from a function of the actual VCM plant response and an ideal response, for which the servo controller is designed. The response of the combined equalization filter and the actual VCM plant response substantially adheres to the ideal response. The disc drive includes firmware operable to generate one or more equalization filters for each of one or more heads.

Abstract: A method is provided for identifying a transfer function used to regulate a response of a positioning system. The method includes identifying data representing a desired frequency response for a transfer function. A first function of one order is generated based on the identified data. A second function of a larger order than the order of the first function is also generated based on the identified data. A transfer function based on one of the first function or second function is then selected and used to regulate the response of the positioning system.

Abstract: An apparatus and method of correcting for written-in repeatable run-out in a disc drive having a servo loop for positioning a head over a rotating disc is provided. The rotating disc has at least one data track and servo information recorded in a plurality of servo fields along the data track. An initial written-in repeatable run-out compensation value for each servo field is computed as a function of a position error signal generated for each servo field during a first revolution of the disc. The initial written-in repeatable run-out compensation value for each servo field is then injected into the servo loop during another revolution of the disc. A compensated position error signal for each servo field is computed as a function of the initial written-in repeatable run-out compensation value for each servo field. A refined written-in repeatable run-out compensation value for each servo field is then computed as a function of the compensated position error signal for each servo field.

Abstract: The present invention incorporates an add-on adaptive feedforward controller into the existent track-following servomechanism of a dual-actuator disc drive to suppress the disturbance caused by mechanical interaction of the two actuator assemblies to thereby enhance the positioning accuracy at track following. The control signal fed into the power amplifier of one actuator is also used as the input signal of an adaptive controller in the other one. In an illustrative embodiment, the information is fed into an adaptive LMS filter. The output of the adaptive filter is then used as a feedforward signal to coordinate the head position with the desired track position. By matching the unknown disturbance dynamics with a filtered-x LMS (least mean square) adaptation algorithm, the output of the feedforward controller is able to cancel the disturbance from mechanical interaction, and thereby realizes the necessary fast, accurate head positioning.

Abstract: A method and system for providing plant variation compensation for a microactuator in a dual-stage servomechanism of a disc drive. The method includes performing indirect adaptive filtering to identify plant variation in the microactuator, and tuning a compensator for the microactuator based on the plant variation. The indirect adaptive filtering can be performed using a two-stage process, including a first stage of adaptive modeling for the dual-stage servomechanism and a second stage of generating an indirect mode-reference inverse for the microactuator. A combined process can alternatively be employed. The microactuator can be a piezoelectric microactuator which forms a PZT system. The dual-stage servomechanism also includes a coarse actuator such as a voice coil motor.