Seagate Technology Incorporated

Lockheed Martin Corporation

Maxtor Corporation

Syquest Technology, Inc.

Ministor Peripherals International Limited

Ich V Pham

Mark A Pajdowski

Duc T Phan

David M Drouin

Gopal Vasudevan

Samuel George Williams

Johnny Si-Pau Pong

Evelyn Howard

Fidencio Mederos

Franz J Dierkes

An adaptive optics system comprises a beamsplitter configured to divide an incoming beam with an aberrated wave front into a first input beam and a second input beam, a microelectromechanical system configured to reflect the first input beam onto an image plane, and a self-reference wave front generator configured to spatially filter the second input beam to form a reference beam, and to interfere the reference beam with the first input beam on the image plane to form a hologram. The system further comprises an imaging device configured to capture an image of the hologram on the image plane, and one or more processors. The one or more processors are configured to perform the steps of Fourier transforming the captured image to generate a transform including a first object image, a conjugate object image, and an auto-correlation image, truncating the transform to exclude the conjugate object image and the auto-correlation image, inverse Fourier transforming the truncated transform to generate amplitude and phase information about the aberrated wave front, generating control signals for mitigating aberrations in the aberrated wave front via phase conjugation based on the amplitude and phase information, and providing the control signals to the microelectromechanical system.

High performance adaptive optics with a reconstructed coherent wave front

An adaptive optics system is provided. The system includes a light source, a pair of deformable mirrors and a detection module. The light source is configured to provide an outgoing beam. The outgoing beam has an amplitude and a phase. The first deformable mirror is configured to reflect the outgoing beam and adjust its associated amplitude. The second deformable mirror is configured to reflect the outgoing beam reflected from the first deformable mirror and adjust its associated phase. The detection module is configured to detect an incoming beam and the reflected outgoing beam from the second deformable mirror and generate certain signals. The signals are used to control the first and second deformable mirrors such that the amplitude of the outgoing beam is the same as that of the incoming beam and the phase of the outgoing beam is opposite that of the incoming beam.

Amplitude and phase controlled adaptive optics system

A method and apparatus for reducing seek acoustics in a disk drive using a variable-bandwidth low-pass filter is provided. The variable-bandwidth low-pass filter is used to adaptively shape a control signal supplied to a VCM for moving a head relative to a disk surface during a seek operation. The bandwidth of the variable-bandwidth low-pass filter is dependent upon head position relative to a target track.

Method and apparatus for reducing seek acoustics using a variable-bandwidth low-pass filter

A data recording disk file includes rotatable disks with concentric data tracks thereon. The data disk file includes servo information recorded on at least one of the disks, at least one head for reading the servo information during rotation of the disk, and a voice coil motor (VCM) attached to the head for positioning the head relative to the data tracks. A servo is driven by signals read from the head to control the VCM. The servo includes a processor employing an estimator model for estimating the parameters of the VCM and for generating, from the estimated parameters and the servo information, a digital control signal. The digital control signal is converted to an analog control signal. The control signal is applied to a power amplifier which generates an input current for use by the VCM. The processor provides solely a single estimator model which operates in both saturated mode and linear mode depending on the magnitude of the digital PES. In the processor, a discrete model is formed by using a linear continuous model in which the effect of the back electromotive force (emf) is implicitly added into the model, and the current rise time in the VCM is ignored. The processor employs an adaptive estimator model which adjusts its calculations based on both calibrated overall servo gain and the VCM torque constant. The processor also employs a technique used during calibration to identify the average VCM torque constant. The processor employs a technique used during calibration to identify head offsets. The servo includes a short seek and head switch technique which adaptively adjusts the estimator position, the feed forward durations and magnitude based on the identified head offsets.

Disk file head positioning servo system incorporating adaptive saturated

A method for applying an optimal seeking technique to a disk file with excessive repeatable runout includes a method of modifying a control signal for a rotary actuator arm of a disk drive. The control signal is modified during track seeking by adding a runout state that is calculated each time a servo sector of a target data track on a surface of a disk is sampled by read/write heads carried by the actuator arm. A calibration algorithm can be used during track following to determine runout magnitude and runout phase at various preselected calibration tracks on the surface of the disk. A seeking algorithm can be implemented to compensate for the relative runout magnitude and phase variations between present and target tracks.

Method for applying optimal seeking technique to disk file with

A multirate sampled closed-loop digital servo system controls read/write head positioning in a magnetic disc storage device. Using a multirate estimator, positional data embedded in the storage medium is sampled once per sector, and inter-sector positional information is predicted. At least two control signals are provided per sample. The control signals are outputted at a multiple of the measurement sample rate, e.g., twice the sample rate. The estimator estimates head position and velocity, system and DC bias, and accounts for estimator calculation time delay, in the system and in the control updates. Estimated states are based on the measurement, control value, last control value, and last estimated states. Input information used by the estimator includes the digitized sampled position error signal (PES), the Gray code value, the present digital control value, and the last digital control value. At every sample, the present invention calculates the control values based upon estimated read/write head position and velocity, and the absolute position of the target track. Both present and last control values are used for the estimator to compensate for computational delay and for additional system phase lags. To minimize computational delay, the algorithm implementing the estimator and controller requires but one multiplication and one addition are necessary to calculate the control value. Once the heads are moved close to the desired target tracks, the servo operates closed-loop in track-follow mode.

Multirate digital control system for use with a system having a linear

A digital servo control system for controlling a disk file head includes a main control loop at least one head for reading servo information; a voice coil motor (VCM) attached to the head for positioning the head relative to the target track centerline of a track in response to a VCM control signal; means for deriving from the servo information a digital head position error signal (PES); and a processor employing an estimator model for estimating parameters of the VCM and for generating from the estimated parameters and the digital VCM control signal. A secondary control loop receives the PES and provides a compensation signal for repeatable runout (RRO) by providing high open-loop gain near the spindle rotation frequency of said disk. The compensation signal for repeatable runout (RRO) is added to VCM control signal. The secondary control loop includes two states x.sub.a and x.sub.b with state equations x.sub.a (k)=x.sub.b (k-1)-k.sub.1r e(k) and x.sub.b (k)=2 cos .omega.Tx.sub.a (k)-x.sub.a (k-1)-k.sub.2r e(k), where k.sub.1r and k.sub.2r are the feedback coefficients for the states e(k) and e(k-1) respectively and the control signal u(k) is the summation of the VCM control signal and x.sub.a (k-1), which is written as u(k)=VCM control signal+x.sub.a (k-1). A compensation module for repeatable runout error includes: a first feedback scaling block having a gain coefficient of k.sub.2r ; second feedback scaling block having a gain coefficient of k.sub.1r ; a first feedback block having a value of 2 cos .omega.T; a second feedback block having a gain of -1; a first unit delay for delaying x.sub.b (k); a second unit delay for delaying x.sub.a (k); a first summer having an output x.sub.b (k)=2 cos .omega.Tx.sub.a (k)-x.sub.a (k-1)-k.sub.2r e(k); a second summer having an output x.sub.a (k)=x.sub.b (k-1)-k.sub.1r e(k); a third summer for combining the VCM control signal with the output of the second unit delay to provide a modified VCM control signal which includes compensation for repeatable runout.

Digital sector servo incorporating repeatable run out tracking

A method of controlling track seeking and track following of a head in a disk file having servo information recorded thereon to provide a track number and a position error signal (PES). The physical parameters of the disk file are modeled by at least three sets of constants associated with selected numbers of tracks. An actuator is connected to the head by a support arm assembly and is responsive to a control signal for positioning the head. The method comprises, for each servo information sample, the steps of predicting a relative position, velocity, and bias of a data head. It is determined whether the predicted relative data head position corresponds to the selected number of tracks, if not, at least the predicted relative data head position is rescaled to form the predicted relative data head position to correspond to the selected number of tracks of the predicted data head position prior to rescaling. The set of the one of at least three sets of constants is changed to correspond to the selected number of tracks of the predicted data head position prior to rescaling. A measured relative data head position is formed from the track number, the PES and the target track. An error in a relative data head position is estimated. A control signal as a function of the relative position error, the predicted relative position, the predicted velocity, the predicted bias, and the adjusted velocity, of the data head, is generated.

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Ich V Pham