Abstract: A notch filter for a disk drive servo system is disclosed having selectable filtering capability. Different servo notch filters for different heads in the actuator head stack are provided. The notch filters may be selected to remove different resonant modes associated with the different disk drive heads. Each of the plurality of notch filters is tuned to remove a resonant frequency associated with at least one magnetic head of the disk drive. In operation, a notch filter is selected to remove a resonant frequency associated with a magnetic head commanded to write or read data to or from the disk drive. The notch filter system includes a multiplexor for controlling the selection of the notch filters. The multiplexor receives commands from a servo processor to control the selection of a notch filter. Different notch filters can be utilized, including series tapped notch filters or parallel notch filters.

Abstract: The present invention is a method and apparatus for preventing a write operation to a storage medium of a data storage system in response to a shock event which excites the component modes of the data storage system. In accordance with the invention, an apparatus is provided which determines the occurrence of a shock event which causes post-shock movement of the transducer resulting from excitation of one or more of the component modes of the data storage system, measures the movement of the transducer for at least a predetermined period of time after the shock event, and prevents the write operation until the movement of the transducer is less than a predetermined threshold throughout this predetermined period of time.

Abstract: A computer disk drive unit having a control system that uses a separate velocity profile for read seeks and for write seeks is disclosed. Appropriate velocity profiles are provided according to whether a seek operation is a read seek operation or a write seek operation. The control system includes a memory for storing an initial velocity profile and a processor for determining whether a read seek operation or a write seek operation is to be performed. The processor obtains the initial velocity profile from memory to produce a read velocity profile or a write velocity profile. The processor multiplies the velocity profile obtain from the memory by a predetermined constant to derive the read velocity profile when the processor determines that a read operation is to be performed. Then the processor repositions the head according to the write velocity profile or the read velocity profile.

Abstract: In a hard disk drive, a head actuator periodically is caused to undertake a calibration seek such that the power amplifier that energizes the head actuator is saturated. The predicted distance moved by the head during the calibration seek is compared to the actual distance moved, and the ratio of the two distances is then used to determine the saturation current of the power amplifier. For a subsequent seek, if the saturation current is less than the current requested for the subsequent seek, the saturation current is input into the head position prediction model. Otherwise, the requested current is used.

Abstract: Real-time gain control calibration is provided for each frequency of a disk drive storage system using dual-frequency, dual-burst position error sensing (PES) signals. Automatic and independent gain control for each PES servo burst frequency component is achieved with an automatic gain control (AGC) mapping that determines the approximate head position and performs an appropriate gain calibration for each servo burst frequency or with sector by sector normalization performed for each PES signal sample. For the AGC mapping, calibration is performed either with calibration tracks or with an in situ method. Both mapping and normalization methods provide accurate automatic gain calibration during signal readback.

Abstract: A method and apparatus for writing binary servo data into the servo bursts contained on the storage medium of a storage device. The binary servo information may include track identifying information such as a track number, cylinder number, head number, sector number, index and/or SID. A burst includes T time slots, each slot comprising one cycle of the servo burst frequency, and the servo data to be written comprises X bits of binary data. Each one-bit of the servo data is represented as a slot containing a transition, and each zero-bit is represented as an empty or null slot. In this manner, the present invention provides a highly bit-efficient scheme for representing digital servo data. A high quality PES signal is assured by writing the binary servo information in such a manner as to guarantee a threshold number of transitions per burst as required for accurate peak-hold detection.

Abstract: A magnetic disk storage system uses multiple-frequency position error sensing (PES) patterns and produces track identification information from the PES signal by detecting changes in relative servo pattern bursts of the multiple-frequency servo pattern. The number of tracks that can be identified with a multiple frequency, dual burst servo pattern is defined by each unique combination of servo pattern bursts. The system can provide accurate track-to-track position control even without gray code information, so long as timing marks or other orienting position information is available. A quad burst servo pattern is used for greater numbers of track types by selecting two dual burst patterns with different numbers of identified track types.

Abstract: A data recording disk file having multiple actuators mounted on a common pivot axis, one of the actuators having fewer arms and lower inertia characteristics than the other. A servo system separately drives each of the actuators for seek repositioning, the lower inertia actuator having a higher performance than the other. A controller selectively records one type of data on the data surfaces associated with the lower inertia actuator, and records all other data on the other data surfaces, thereby providing a disk drive with increased performance appropriate to the data stored on the surfaces associated with the lower inertia actuator. A removable locking pin may be provided which extends through corresponding holes in each of the actuators for maintaining the actuators precisely positioned with respect to each other so that servo information may be written on each of the surfaces in a single process. Additionally, one of the actuators may be provided with a shorter stroke than the other actuators.

Abstract: A method and apparatus for improving data integrity and density in an array of disk drives by synchronizing spindles prior to correcting for repeatable runout (RRO). The invention includes a drive control circuit for controlling synchronization, initiating runout cancellation calibration, and granting customer use of the disk drives. In a further aspect of the invention, rotation of the spindles is monitored for changes. The drive control circuit initiates resynchronization and recalibration of the runout cancellation for the disk drives in response to receiving an indication from the rotation detector that rotation of at least one of the spindles in the disk drives has changed. Initially, or after a change is detected, one of the disk drives is selected as a master and a synchronization signal is routed to each of the disk drives from the selected master drive for synchronizing the spindles in the disk drives.

Abstract: A system and method for determining the velocity and/or position of a coil driven actuator arm without the aid of servo signals. A sample-hold unit is used to measure no-motion coil voltage in the voice motor coil while applying a predetermined coil current. Then, while the same magnitude (opposite direction) current is applied to move the actuator arm, the coil voltage is measured. The coil voltage is reduced by the measured no-motion coil voltage, producing a measurement of back-emf. The back-emf may be amplified by a predetermined factor to yield an estimation of velocity, and this amount may be integrated to provide a gauge of relative actuator arm position.

Abstract: A servo control system and method for accurately controlling the actuator in a rotatable storage device by adjusting a corrective control signal according to the mode of operation of the actuator and the direction of actuator movement. During track following the corrective control signal is adjusted by a first factor determined by the ratio of a nominal force or torque factor to the actual force or torque factor at the current radial actuator position. When the actuator is seeking in a first direction, the corrective control signal is adjusted by a second factor determined by adjusting the first factor by a first amount, K.sub.fwd. When seeking in the reverse direction, the corrective control signal is adjusted by a third factor determined by adjusting the first factor by a second amount, K.sub.rev. K.sub.fwd incorporates measured variations in force or torque factor when the actuator is moving in the forward direction. Similarly, K.sub.

Abstract: Disclosed is a digital control servo system for read/write head positioning in data recording disk files of the type which use voice coil motor (VCM) actuators for positioning the head, with improved modelling of the servo system in saturated seek mode. The VCM has a characteristic torque factor which varies in accordance with a predetermined relationship to head position and with age and temperature, and the servo system drives the VCM in a saturated seek mode at a maximum level of current which has a low frequency variation due primarily to temperature change. The servo system computes an estimated VCM control representing the VCM current, computes estimates of the state of the VCM including head position and velocity, and computes from an algorithmic model, predictions of head position and velocity. The improved modelling changes the algorithmic model to reflect the actual torque factor of the VCM and actual maximum level of current in saturated seek mode rather than nominal torque factor and VCM current.

Abstract: An apparatus, system and method are described for generating a continuous and linear position signal generated from stitched position error signal (PES) components, for use by a servo control system in positioning a transducer with respect to a storage surface. Continuity is achieved by providing a normalization stage in the servo control loop for correcting discontinuities at the stitch points with minimal impact to the PES zero-crossing points. According to a first preferred embodiment normalization is applied using an algorithm determined by the width of the read transducer. According to a second preferred embodiment, normalization is selectively applied near the stitch points of the PES components, but is not applied at their zero-crossing points. In another preferred embodiment, a first normalization algorithm is applied near the stitch points, and a second normalization algorithm is applied at the zero-crossing points.

Abstract: Method and apparatus are disclosed for a data recording disk file having a head module with separate side by side read and write transducers for optimizing the switching of the head between reading information and writing information on the same track or cylinder. A function generator defines at least one control function for a servo control signal to drive an actuator to move the head module the approximate distance between the side by side write and read transducers, optimized to minimize the time between write and read, and optimized to move the head module the approximate distance between the side by side read and write transducers at the timing best suited to minimize the write transition time.

Abstract: A system and method for determining the velocity and/or position of a coil driven actuator arm without the aid of servo signals. A sample-hold unit is used to measure no-motion coil voltage in the voice motor coil while applying a predetermined coil current. Then, while the same magnitude (opposite direction) current is applied to move the actuator arm, the coil voltage is measured. The coil voltage is reduced by the measured no-motion coil voltage, producing a measurement of back-emf. The back-emf may be amplified by a predetermined factor to yield an estimation of velocity, and this amount may be integrated to provide a gauge of relative actuator arm position.

Abstract: Disclosed is a data recording disk file having multiple actuators mounted on a common pivot axis, one of the actuators having fewer arms and lower inertia characteristics than the other. A servo system separately drives each of the actuators for seek repositioning, the lower inertia actuator having a higher performance than the other. A controller selectively records one type of data on the data surfaces associated with the lower inertia actuator, and records all other data on the other data surfaces, thereby providing a disk drive with increased performance appropriate to the data stored on the surfaces associated with the lower inertia actuator. A removable locking pin may be provided which extends through corresponding holes in each of the actuators for maintaining the actuators precisely positioned with respect to each other so that servo information may be written on each of the surfaces in a single process.

Abstract: A gray code is provided for use with disk servo track identification encodement that preserves the gray code property of only a single digit changing state between two numbers in the code sequence and also preserves magnetization between code numbers while only requiring a single bit for encoding each code value by recording a single pad bit before the gray code bits. By proper selection of the sign of the pad bit and the gray code numbering sequence, the gray code encodement scheme uses n+1 code bits for an n-bit gray code. The efficiency of the gray code encodement can be enhanced by splitting the track identification number to be recorded into multiple fields and then recording only the low order bits sufficient to identify a track within the maximum estimated error of the servo head on every track and otherwise alternating the high and low middle order bit fields with the low order bit field. A run-length limiting feature also can be provided.