Cirrus Logic Inc.

Louis Supino

Paul M Romano

Christopher Thomas Settje

James M Graba

German S O Feyh

Jim Graba

German S Feyh

Larry D King

Hao Huang

Francis H Reiff

Shuangxia Zhu

A discrete-time sliding mode controller (SMC) controls the motion of a read head actuated over a disk storage medium during tracking operations. The discret-time SMC comprises a linear signal generator for generating a linear control signal, and a sliding mode generator for generating a sliding mode signal. These signals are combined and applied to a voice coil motor (VCM) for positioning the read head over a particular data track recorded on the disk. The linear signal generator and the gain (c&Ggr;) &Dgr; are designed such that once the sliding mode variable &sgr; crosses the sliding line the first time, it will cross the sliding line in every successive sample period resulting in a zigzag motion about the sliding line wherein &sgr; changes sign at every sample period. The switching action and resulting chatter of the sliding mode controller are minimized by adjusting the width of the boundary layer through appropriate selection of predetermined constants &Dgr; and &lgr;. The boundary layer can be made arbitrarily small so as to better approximate and thereby attain the benefits of continuous time SMC. In addition, the required control effort is minimized while still providing adequate immunity to parameter variations and external load disturbances.

Disk storage system employing a discrete-time sliding mode controller for servo control

Servo circuitry for counting tracks on an optical storage medium is disclosed. The servo circuitry is comprised of a differential phase detector and a digital phase-locked loop. The differential phase detector receives four signals from a quad-photodetector and correlates the four signals into a first correlation signal and a second correlation signal. The digital phase-locked loop receives an adjustable amplification value along with the positive correlation signal and the negative correlation signal. The digital phase-locked loop generates a track count signal based on the adjustable amplification value, the positive correlation signal, and the negative correlation signal. The track count signal represents track crossings on the optical storage medium. The digital phase-locked loop advantageously has an adjustable bandwidth based on the amplification value. The servo circuitry count tracks on both CDs and DVDs.

Servo circuitry for counting tracks on an optical storage medium

Servo circuitry for correlating signals using a correlation data structure is disclosed. The servo circuitry is comprised of a setup system coupled to a correlation system that contains the correlation data structure. The setup system receives four signals and converts the signals to digital values. The correlation system takes the digital values and enters them into the correlation data structure. The correlation data structure yields a correlation value based on the digital values. The servo circuitry advantageously yields the correlation value that is a function of all four signals using the correlation data structure.

Servo detection using a correlation data structure for concurrent processing of quad signals

A discrete-time sliding mode controller (SMC) controls the motion of mechanical apparatus such as a read head in a disk storage system. The overall control effort is generated by combining a linear control effort with a discrete-time sliding mode control effort generated by switching between gains in order to drive the system's phase states toward a sliding line trajectory. An estimate of a reference is generated and added to the control effort, thereby providing an approximation of the derivative of the reference signal. Estimating the reference signal may be performed by various methods, depending on whether the reference is known, unknown but repeatable, or completely unknown and non-repeatable. A least-mean-square (LMS) algorithm is employed to estimate the reference signal by computing coefficients of a function which minimizes a particular system parameter. If the reference is an unknown, repeatable sinusoid, such as the runout signal in a disk storage device, the coefficients of a synthesized sinusoid may be determined by minimizing the position error phase state. Alternatively, the coefficients of the synthesized sinusoid may be determined by minimizing the sliding mode variable &sgr;,which defines the position of the system phase states relative to the sliding line. For references that are unknown and non-repeatable, an estimate of the derivative of the reference signal is computed, weighted, and added to weighted derivatives of the estimate, where the weights or coefficients of this function are also determined by minimizing the sliding mode variable &sgr;,.

Reference estimator in a discrete-time sliding mode controller

Adaptive discrete-time sliding mode controller

A quadrature signal generator for optical disk storage devices is disclosed comprising a differential phase detector (DPD) implemented as an adaptive length dual arm correlator. A photo diode generates a light beam for irradiating the optical disk during read operations, and a pair of diagonal signals S1 and S2 are generated by adding a pair of respective quadrants of a four-quadrant photodetector which detects the light beam reflected from the disk. The phase offset between the diagonal signals represents the centerline offset of the light beam from the centerline of a data track recorded on the optical disk. A first and second position error signals (PES) are generated by computing the difference and sum between a positive and negative correlation of the diagonal signals S1 and S2, otherwise referred to as a dual arm correlation (DAC) ##EQU1## where .DELTA. is the correlation offset and L is the correlation length. In the present invention, the correlation length L is programmably adjusted relative to the t rack crossing velocity such that the correlator outputs a substantially constant number of correlations per track crossing, which facilitates generating a quadrature signal for use in counting track crossings during seek operations.

Quadrature signal generator using an adaptive length dual arm correlator

An optical disc storage system comprises a sliding mode controller for actuating an optical read head assembly over an optical disc during focus capture, focus tracking, track seeking and centerline tracking. The sliding mode controller is a non-linear control system which operates by switching between positive and negative feedback in order to force certain phase states (such as the read head's position error and velocity) to follow a predetermined phase state trajectory. Sliding mode control provides improved compensation to parametric variations, external load disturbances and other transients such as, for example, the focus capture transient. Furthermore, the sliding mode positive and negative feedback gains need only be within a predetermined range, thereby allowing gain values of 2.sup.n which significantly reduces the complexity and cost of the gain multipliers.

Optical disc drive comprising switching gains for forcing phase states

In an optical disk storage device, a differential phase detector is disclosed for generating a position error signal independent of the frequency content of the recorded data. A pair if diagonal signals S1 and S2 are generated by adding a pair of respective quadrants of a four-quadrant photodetector, where the phase offset between the diagonal signals represents the position error of the pit image as it passes over the photodetector. The position error is determined in the present invention by computing the difference between a positive and negative correlation of the diagonal signals S1 and S2, otherwise referred to as a dual arm correlation (DAC) ##EQU1## where .DELTA. is the correlation offset and L is the correlation length. In the preferred embodiment, the correlation offset .DELTA. is adaptively adjusted to maximize the correlation between S1 and S2. In this manner, the position error estimate is substantially insensitive to the frequency content of the recorded data. Furthermore, this method extends the position error over a range of plus or minus one-half a track, which facilitates generating a quadrature signal for use in counting track crossings during seek operations.

Differential phase error detector using dual arm correlation for servo

A trellis sequence detector is disclosed for detecting a quadrature servo signal in optical disk storage devices. The quadrature servo signal is generated in discrete time and comprises two sinusoidal signals phase offset by 90 degrees. The sampling frequency of the quadrature signal is controlled relative to the track crossing velocity so as to produce a fixed number of samples per period of the sinusoid (i.e., per track crossing). In the embodiment disclosed herein, the sampling of the sinusoidal signals is controlled such that there are eight samples per track crossing. The eight samples are associated with a state transition diagram and corresponding trellis diagram which define the operation of a trellis sequence detector. The trellis sequence detector processes the actual samples of the quadrature signal to determine an estimated quadrature sequence closest to the actual samples of the quadrature signal. In this manner, spurious pulses in the actual quadrature signal are filtered out which significantly enhances the performance of the servo system.

Trellis sequence detector for detecting a quadrature servo signal in

In an optical disk storage device wherein user data is demodulated from a light beam reflecting off data pits in tracks of an optical disk storage medium, a quadrature seek signal is generated indicative of the light beam crossing tracks of the optical disk during a seek operation. The quadrature seek signal is generated from a discrete-time tracking error signal (TES) and a discrete-time RF baseband signal. The discrete-time TES is generated according to the mode of operation, compact disk (CD) or digital video disk (DVD). In CD mode the TES is generated as the difference between E and F tracking photodiodes, and in DVD mode the TES is generated using a discrete-time differential phase detector (DPD). To generate the discrete-time RF baseband signal, the RF data signal (generated as the sum A+B+C+D of a four quadrant photodiode) is sampled at the channel rate and the RF data samples passed through a discrete-time envelope detector. The envelope detector extracts a discrete-time RF baseband signal which represents the light beam's location with respect to a track centerline. The discrete-time TES and baseband signals are synchronized and converted into binary square waves which form a quadrature seek signal (four transitions per track) for counting track crossings and for determining the radial seek direction.

Generating a quadrature seek signal from a discrete-time tracking error

A sliding mode controller is disclosed for controlling a read/write head actuator in a magnetic disk drive storage system wherein a voice coil motor connected to the actuator operates to adjust the position of the read/write head over a selected data track recorded on a magnetic medium. The sliding mode controller comprises an improved technique for reducing chatter associated with the inherent operation of such a controller--rapid switching between gains to force the observable phase states to follow a predetermined phase state trajectory. The sliding mode controller generates a motor control command by multiplying an actuator position error and an actuator position error velocity by respective switching gains. The gains are switched according to a predetermined relationship .sigma. between the phase states and a phase state trajectory. In order to reduce the switching frequency (i.e., chatter), a boundary layer around the phase state trajectory results in hysteresis, causing the gain blocks to switch only after the phase states cross over the boundary line. Further chatter reduction is achieved by generating the motor control signal proportional to an integral of sgn(.sigma.). The cost of the sliding mode controller is reduced by implementing the phase state trajectory .sigma. as a lookup table indexed by a single phase state.

Chatter reduction in sliding mode control of a disk drive actuator

In a storage system using multiple disk drives, the disk drive spindles are rotated at the same frequency and at a predetermined phase relationship. A phase angle, measured as the difference between an index mark recorded on the disk and the disk's read head, is used to control the spindle rotation speed. Each of the disk drives are first independently frequency locked to a target frequency, and once frequency locked, each disk drive is phase locked in relation to one another. In the phase locking process, each disk generates a synchronizing signal for synchronizing the rotation of the disks to a predetermined phase relationship. If any one of the disk drives becomes inoperable (due to a failure or 'hot-swapping'), the other disk drives remain synchronized since the synchronizing signal is not lost.

Masterless spindle synchronization in a multiple disk drive storage

A sliding mode controller is disclosed for controlling the motion of a read/write head actuated by a voice coil motor over a rotating magnetic disk storage medium. The magnetic disk comprises a plurality of concentric data tracks recorded thereon wherein each data track comprises user data and servo data. The sliding mode controller operates by multiplying a head position error phase state and a head position error velocity phase state by respective switching gains to force the phase states to follow a predetermined phase state trajectory. The phase state trajectory can be defined by a single linear segment, a variable linear segment, multiple linear segments over the entire region of excursion, or optimum parabolic acceleration and deceleration segments. Switching logic, responsive to the phase states and a trajectory segment value .sigma., switches between positive and negative feedback gains to drive the phase states toward a current trajectory segment. A .sigma. processing block monitors the phase states to determine when to switch from a current trajectory segment to the next trajectory segment. The resulting servo control system is relatively inexpensive to implement in either software or hardware, and it is substantially insensitive to parametric changes and external load disturbances. Further, it does not require notch filters commonly used in conventional linear controllers to compensate for mechanical resonances.

Sliding mode control of a disk drive actuator for positioning a

A sliding mode controller is disclosed for controlling the motion of a magnetoresistive (MR) read head actuated by a voice coil motor over a rotating magnetic disk storage medium. The magnetic disk comprises a plurality of concentric data tracks recorded thereon wherein each data track comprises user data and servo data. The sliding mode controller operates by multiplying a head position error phase state and a head position error velocity phase state by respective switching gains to force the phase states to follow a predetermined phase state trajectory. The phase state trajectory can be defined by a single linear segment, a variable linear segment, multiple linear segments over the entire region of excursion, or optimum parabolic acceleration and deceleration segments. Switching logic, responsive to the phase states and a trajectory segment value .sigma., switches between positive and negative feedback gains to drive the phase states toward a current trajectory segment. A .sigma. processing block monitors the phase states to determine when to switch from a current trajectory segment to the next trajectory segment. The resulting servo control system is relatively inexpensive to implement in either software or hardware, and it is substantially insensitive to parametric changes, external load disturbances, and non-linearities inherent in controlling MR read heads. Further, it does not require notch filters commonly used in conventional linear controllers to compensate for mechanical resonances.

Sliding mode control of a magnetoresistive read head for magnetic

A sliding mode controller for controlling a read/write head actuator in a magnetic disk drive storage system wherein a voice coil motor connected to the actuator operates to adjust the position of the read/write head over a selected data track recorded on a magnetic medium. The sliding mode controller comprises a technique for reducing chatter associated with the inherent operation of such a controller--rapid switching between gains to force the observable phase states to follow a predetermined phase state trajectory. While tracking the centerline of a selected track, the sliding mode controller generates a motor control command by multiplying an actuator position error and an actuator position error velocity by respective switching gains. When seeking to a new track, the controller reduces switching noise by disabling the actuator position error and generating the motor control signal responsive to the actuator position error velocity alone. The sliding mode controller further comprises an integrator for integrating the actuator position error during tracking in order to compensate for biasing forces that can cause a DC offset from the selected track's centerline.

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Boulder, CO, United States of America

Louis Supino