Abstract: The present invention may be regarded as a disk drive comprising a disk having a plurality of data tracks and at least one reserved track. At least one of the data tracks for recording user data along a circumferential path offset from the centerline of the data track, and the at least one reserved track for recording data track micro-jog values along a circumferential path substantially aligned with the centerline of the reserved track.

Abstract: The invention provides magnetic disks with the ability for consecutive tracks to be read or written continuously, removing the traversal of the gap between tracks which degrades bandwidth delivery performance. The invention includes a disk surface formatted with tracks, and sectors within these tracks, which vary in radius. The ending radius of a sector differs significantly from its starting radius. The ending radius of the last sector of one track is very close to the starting radius of its successor track, providing a spiral arrangement of tracks, each possessing a fixed number of sectors, and supporting continuous accessing of successive tracks.

Abstract: An information handling system, such as a disc drive, includes a base, a disc stack rotatably attached to the base, and an actuator assembly movably attached to the base. A region of the disc stack is identified as a parking band, and when power is not provided to the disc drive, the actuator assembly is held in a parked position within the parking band by a magnetic latch. The magnetic latch is overcome during a powerup process by a voice coil motor coupled to the actuator. Other regions of the disc stack are associated with various functions performed by the voice coil motor as the actuator passes over such regions.

Abstract: A disk device that has displacement of servo signals in the circumference direction and radius direction between a plurality of disks, prevents a drop in performance due to the displacement when the heads are switched. To deal with the displacement in the circumference direction, the sector numbers on the disk are converted by a table for each head. Also the servo gate time is corrected by the table according to the eccentricity of the disk, so the servo signal detection accuracy improves. Also to deal with the displacement in the radius direction, the track numbers on the disk are converted by the table using the difference value based on the reference head.

Abstract: An error amplifier for use in a disk drive actuator system having an actuator motor for radially positioning a transducing head with respect to a rotatable disk is newly designed to enable full implementation as an integrated circuit. The error amplifier includes a switched-capacitor proportional-integral controller for comparing first and second differential input signals representing a respective actual current and commanded current for driving the actuator motor, and providing a differential output signal. A transconductor-capacitor filter is connected to filter the differential output signal of the switched-capacitor integrator, and provides a motor control signal to control the actuator motor.

Abstract: An NRRO compensation circuit controls a head position in a disc drive. The circuit has a first frequency circuit providing a first output corresponding to NRRO and a first characteristic sensing circuit that senses the first output and that generates a first control output that adjusts a first NRRO compensation gain. A first control circuit included in the NRRO compensation circuit receives the first control output and the first NRRO compensation gain and provides a first NRRO compensator output.

Abstract: A device for generating synchronous numeric signals, including a reference generating device supplying a reference signal and a first timing signal, both having a reference frequency; and a timed generating device supplying a synchronized signal having the reference frequency. The device further includes a synchronization stage generating a second timing signal having a first controlled frequency correlated to the reference frequency, and phase synchronization pulses having the first frequency and a preset delay programmable with respect to the first timing signal.

Abstract: A method of enhancing the thermal stability of gray codes is disclosed. The gray code block in a servo area is recorded with a combination of two different magnetization directions. When the two different magnetization directions are expressed as “+” and “−”, the information “1” is recorded as “++−−” or “−−++” with the information “0” recorded as “+−+−” or “−+−+”. Since the filter for gray code demodulation is provided with a perpendicular recording mode, the servo area does not use long-wavelength signals that are susceptible to thermal demagnetization. As a result, thermal stability is enhanced.

Abstract: A head position control method controls the speed of the head using the position and the speed detected from the servo information on the disk and directly detects the head speed. The speed detection pattern is assigned to the servo area of the disk, and the speed of the head is detected at the frequency of the regeneration signal. Therefore the speed of the head can be directly detected at the timing of the servo reading. By this, information on the head speed can be obtained with less error. Since there is no delay in the speed detection, the phase margin of the control system increases and stability improves.

Abstract: Disclosed herein is a self-servo writing method that uses the head of a disk drive to write servo data on a disk-shaped medium. This method calculates an accurate position offset between the read-head element and write-head element incorporated in the head, by using the positioning servo data and measuring servo data that are recorded on the disk-shaped medium.

Abstract: An information storing device and an information processing device having a memory for registering a plurality of working modes at recording/reproduction and a switching circuit for selecting one of the plurality of working modes, which select the optimum working mode automatically or by an instruction of an operator according to power supply capacity of a device of higher rank to effect recording/reproduction.

Abstract: A digital servo controller generates a control signal from an analog observation signal using an output equation, state equation or a transfer function, and performs high precision servo-control with an inexpensive configuration. In a digital servo which executes an output equation yd[k]=C·x[k]+D·ud[k] and state equation x[k+1]=A·x[k]+B·ud[k]. The digital servo comprises a digital processor which outputs the second term D·ud[k] of the output equation by an analog circuit, and outputs the first term C·x[k] earlier for Ts/2. The digital servo also has a digital processor which executes the direct term of the output equation at period Ts/N (N is a 2 or higher natural number), which is 1/N of the basic operation period Ts, and updates the first term with the same delay time as the average delay time Ts/(2N) of the direct term.

Abstract: A disk drive provides head position information as position status variables to a host. The position status variables are derived from information formatted on a disk and processed by a media controller for storage in a position register set. The position information includes both radial and circumferential position references. The disk drive is connected to the host over a host interface which enables the position information to be stored automatically in a host memory so that the host can scan the position information to determine an optimum order of data transfer commands to be sent to the disk drive. A method for selecting a next command to transmit to a disk drive employs the position variables to optimize the command selection. In an alternative method, a host selects a command to be executed by one of an array of disk drives and then determines the disk drive to receive the command based on position information variables which have been stored and updated by the disk drives in the array.

Abstract: An RW offset setting method which includes recording a test pattern by a write head, reading the test pattern by a read head, measuring an amplitude of a read back signal at each tracking position, finding an approximate expression of a profile of the measured amplitude, finding a tracking position, and finding a RW offset based on this tracking position, setting a RW offset for all tracks in the disk device based on the RW offsets about the plurality of tracks to be measured. A read data error recovery method that includes the steps of determining an off-track direction where the amplitude increases, searching an off-track position where the amplitude becomes a local maximum, measuring the amplitude at each off-track position reading data recorded in the data sector.

Abstract: An apparatus and method for compensating actuator arm oscillation induced by resonance mode excitation during a seek in a disc drive data handling system. The actuator arm supports a head adjacent a recording surface, and a servo loop controls the position of the actuator arm. A frequency of actuator arm oscillation is identified, after which a seek is initiated to move the head from an initial track to a destination track on the recording surface. A position error signal (PES) is generated to indicate position of the head relative to the destination track, and a compensation signal is generated by a filter based on the PES and the frequency of oscillation of the actuator arm. The compensation signal is adapted to remove a component of the PES arising from the actuator arm oscillation, and is applied to the servo loop as the head is settled onto the destination track.

Abstract: Apparatus and method for positioning a head adjacent tracks on a recording surface in a disc drive. A servo control circuit includes a multi-mode servo position error signal (PES) demodulator circuit having an operand generator which outputs operand values from decoded servo position data transduced by the head from the disc surface, and a PES generator which generates a PES indicative of head position with respect to the disc surface in accordance with a selected PES mode from a population of mutually exclusive PES modes each derived from a different combination of selected operand values. A programmable servo processor outputs a current adjustment signal to adjust the current applied to an actuator motor in relation to the PES and a desired position. The servo processor selectably configures the PES generator for each track so that different PES modes are used for different tracks.

Abstract: The magnetic disk system in which a disk controller for controlling data reading and writing from and to a plurality of magnetic disk mediums while making magnetic heads seek, said magnetic disk mediums being formatted by a plurality of tracks and sectors into which the tracks are divided in a circumferential direction, includes format selecting means for selecting either a first format of continuing the sector number from a track on a magnetic disk medium to a track on another magnetic disk medium in the same cylinder or a second format of continuing the sector number from a track on a magnetic disk medium to another track on the same recording surface, hence to format the magnetic disk mediums.

Abstract: A system and method for performing read retry operations with respect to an erroneously read data sector is disclosed. The system and method use estimates of bit error rates determined during previous attempts to read data from the sector to determine an optimal distance and direction to move a read transducer for a subsequent read retry of the erroneously data sector.

Abstract: The present invention provides an apparatus and system (300) supplying a regulated voltage of sufficient magnitude to enable de-latching of a head carriage from a latching device. In at least one embodiment, providing a voltage source for the voice coil motor (14) includes a regulator (310) having an input for receiving a first voltage potential and operably configured to provide a second voltage potential to an output selectively coupled to the voice coil motor (14) by a switch (345). A current source (315) is operably configured to provide a predetermined limited current via a pass transistor (325) associated with the regulator is also included. Further included is a capacitor (335) coupled to the regulator output and operably configured for charging by the current source via the current limited pass transistor.

Abstract: Method and apparatus for performing a seek operation to move a data transducing head from an initial track to a destination track on a rotatable recording surface. A servo control circuit operates to sweep the head across the recording surface. Servo data from an intermediary track are transduced to obtain a detected angular position value for the head with respect to the recording surface. When the detected angular position value differs from a predicted angular position value for the head, the servo control circuit initiates an index qualification routine at the conclusion of the seek. The qualification routine involves transducing the servo data from the destination track to verify the accuracy of the predicted angular position value. In this way, the effects of spurious (false) index signals obtained from the servo data transduced during the seek operation are minimized, and unnecessary reinitializations of the servo control circuit are avoided.

Abstract: Oil-retaining configuration in partially filled or fully filled dynamic-pressure bearing system for miniaturized, low-profile spindle motor. A radial bearing section and a magnetically balanced thrust bearing section compose the bearing system. An oil taper seal is configured in between the rotor and the sleeve, radially beyond the radial bearing section, and not axially beyond the thrust bearing section. The taper-seal gap slopes radially inward, flaring with further separation from the rotor undersurface, in a configuration that lengthens the tapered space functioning as, and enlarges the capacity within, the taper-seal area, and that sets up the oil boundary surface oriented sloping radially inward. Centrifugal force during rotation thus acts pressing in on the oil boundary surface, fortifying the sealing strength. The oil-retaining configuration allows for span, between twin constituents provided as the radial bearing section, sufficient for increased conical stiffness even in a reduced-profile structure.

Abstract: With respect to the disk drives provided power from a single power source in a disk drive system, start up power is first supplied to a first start-up group of the disks, preferably comprising all of the master disks, with the size of the group being selected so that the required current does not exceed the capacity of the power source. When the disk drives of the first group have substantially reached steady state, start-up is conducted with respect to a second start-up group of the disk drives so that the current required during start-up for the second group and the current required for steady state drive of the first start-up group does not exceed the capacity of the power source. With respect to each start-up group, the number of disk drives is the maximum integer value and decreases or remains the same with respect to subsequent start-up groups.

Abstract: A number of data pairs, each data pair comprises a write-to-read track misregistration (WRTMR) value and an average position error margin (APE) value, are determined for a data storage device. Each of the data pairs is associated with a unique predetermined non-repeatable runout (NRRO) error in the data storage device. Each of the predetermined NRRO errors is caused by subjecting the data storage device to a unique NRRO error stimulus. An ideal APE margin is then determined for the data storage device by using the data pairs to extrapolate an APE margin corresponding to a WRTMR value of zero.

Abstract: There is disclosed a head positioning control system including a feedforward (FF) control system to compensate a disturbance in a disk drive. This system includes an identification unit which executes parameter identification processing to determine a transfer function of the FF controller as well as a control operation. This identification unit updates a transfer characteristic of the FF controller so as to be adapted to a disturbance fluctuation.

Abstract: A disk drive with a plant having an actual plant response G(z) and a servo controller that includes a feed-forward control path that operates with a modeled plant response G0(z) in order to output a feed-forward command effort. The plant includes a transducer that is moveable from a start position to a target position according to a total control effort.

Abstract: A process determines a seek time of an access head of a physical storage disk. The process includes collecting statistical access data on physical storage volumes served by the access head and determining seek times for a set of reference head travel time functions. Each function depends on distances between pairs of the physical storage volumes. The process also includes performing a sum of the determined seek times. Each term of the sum is weighted by an expansion coefficient of a travel time function of the access head with respect to the set of reference head travel time functions.

Abstract: A method of determining a clearance between a magnetic transducer and a magnetic recording medium during a track seeking operation, the magnetic recording medium being moveable with respect to the transducer and including at least a test track and a reference track, which method comprises the steps of: at least partially erasing a predetermined area of the recording medium including at least one test track and one reference track; writing a first series of predetermined magnetic transitions along a spiral trace, formed by seeking operation of the transducer, on the at least one test track in the predetermined area; reading the test track and obtaining a pulse width of signals read back from the test track (test track pulse width) at a predetermined amplitude level; writing a further series of predetermined magnetic transitions identical to the first series on a reference track of the recording medium in the predetermined area; reading the reference track and obtaining, a pulse width of signals read back from

Abstract: A magnetic disk drive system having a write head Hw and a read head Hr which can move over a magnetic disk in a radial direction of the disk and are arranged at a distance from each other. At a predetermined write start timing tWG, it writes measurement information by the write head in a specific sector at a first timing tW, then reads the information by the read head, detects predetermined positional information included in the information, and produces a second timing tDA. The system subtracts the interval between the second timing and the start timing from the interval between the first timing and second timing to measure the write/read head distance time difference in the track direction of the magnetic head unit. The write/read head distance information is used for correction and control of the operation of the magnetic head unit.

Abstract: A data storage device including spindle power control to reduce power consumption. The spindle power control includes a read-write control mode and an idle control mode. In the read-write control mode, the spindle motor is energized to rotate a disc at a fill operating speed for read-write operations and in the idle control mode, spindle speed is reduced to provide an idle power mode. The idle power mode provides a desired or steady state fly height spindle speed so that the head glides above the disc surface during an idle period to reduce power consumption. In illustrated embodiments, the disc includes a dedicated glide zone and the head is positioned in the dedicated glide zone during the idle power mode.

Abstract: A disc drive system and method of screening an actuator resonance includes a servo controller providing a multi-servo zone architecture. The servo controller partitions the disc into a plurality of servo zones. Each of the servo zones has a corresponding servo gain. When an actuator resonance is detected in one of the servo zones, the servo controller reduces the corresponding servo gain of the detected servo zone such that a drive with very low resonance at a certain zone does not affect the servo bandwidth of the other good zones. Accordingly, a drive with very low resonance is prevented from being scrapped. Further, the screening technique allows a drive to have an adequate servo margin for its normal operation after going through a resonance detection test.

Abstract: A zone where a head is positioned is determined in a track to be one of zones 1 to 4 according to a combination of the polarities of phase-A and phase-B detection outputs having different phases, and the positional deviation of the head from the current position to the center of the target track is obtained from the phase-B detection output in the zone. The phase-B detection output is provided with a dead zone corresponding to a range where both detection outputs have a phase-difference error. Therefore, even if the phase difference has an error, the positional deviation of the head is accurately calculated.

Abstract: Techniques are provided herein for reducing vibrations in various modes of a dynamic system. One such technique comprises incorporating vibration limiting and sensitivity constraints into a partial fraction expansion equation model of the system so as to reduce vibrations to specific levels. Another technique comprises shaping a command determined using the partial fraction expansion equation model to produce a desired output. The entire command may be shaped or only selected portions thereof which produce vibrations. Another technique involves commanding in current to produce saturation in voltage. By doing this, it is possible to command voltage switches. The times at which the switches occur can be set to reduce system vibrations. Other techniques are also provided. These include varying transient portions at the beginning, middle and/or end of a move and using Posicast inputs, among others.

Abstract: An active noise canceller outputs a noise pattern learning request signal to a hard disk drive causing the hard disk drive to perform a predetermined operation, receives noise at this moment through a sound-receiving unit, and stores, in a nonvolatile memory unit, a relationship between the noise and a head operation data signal output from the hard disk drive. Based on the operation data signal outputted from the hard disk drive, the active noise canceller generates a noise-canceling sound while making a reference to the above relationship stored in the nonvolatile memory unit. Therefore, the signal processing needs a low degree of response for operating the noise-canceling sound.

Abstract: A method for measuring servo pattern irregularity and other servo information of pre-patterned servo media mounted on a spindle with the center of the pre-pattern tracks off center from the axis rotation of the spindle. An actuator is stepped radially while measuring the PES signals from the servo sectors of at least one highly eccentric track to form a cross track profile of the PES signals for each sector. A mathematical algorithm removes step measurement error from the data. A second mathematical algorithm removes non-repeatable random noise from the data. The amount of phase-in that radially aligns the respective cross track profiles is computed. Servo pattern written-in repeatable runout is determined by unwrapping the phase-in values to form a periodic curve.

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: A method is provided for radially moving a transducer over a storage surface of a rotating data disk including multiple concentric data tracks, for reducing noise generated during a seek operation from a starting track to a destination track on the disk. The transducer is radially moveable relative to said data tracks by an actuator in proportion to an input signal to the actuator, wherein the transducer is initially accelerated away from the starting track to a radial transition location between the starting track and the destination track, and then decelerated toward the destination track from the transition location.

Abstract: An alternative powered evaporative cooler has a squirrel cage fan. A low voltage DC motor is provided to power the squirrel cage fan. A pulley system is coupled to the squirrel cage fan and the low voltage DC motor for transferring energy from the low voltage DC motor to rotate the squirrel cage fan. A low voltage DC power source is provided to power the low voltage DC motor.

Abstract: A disc drive includes a base and a disc rotatably attached to the base. The disc drive also includes an actuator assembly rotatably attached to said base and a device for moving the actuator assembly. The actuator assembly includes a transducer head in a transducing relationship with respect to the disc. The disc drive includes a disc drive controller for controlling movement of the actuator during track follow and track seek operations. The disc drive controller monitors the actuator during seek operations. The disc drive controller further computes a maximum average settle time from the monitored settle times. The dis drive controller further compares the maximum average settle time to a predetermined threshold value, and issues a command signal to adjust seek profile parameters of the disc drive to eliminate resonance in the actuator arm during a seek operation.

Abstract: In an apparatus for recording and/or reproducing information, which reproduces servo information being recorded on a medium and conducts a tracking operation based on the servo information, a power save part conducts a power save operation by reducing an operation clock frequency in accordance with a predetermined process during a tracking operation, during a seek operation, and/or during spindle motor startup.

Abstract: Disclosed is a method of access control for a disk drive whereby an access operation for, particularly, sequentially and alternately executing accesses is supported. A CPU of the present disk drive sequentially and alternately executes accesses to a plurality of data tracks on a disk in response to an access request generated from a host system. During the access operation, the CPU secures time for a look-ahead operation, the time corresponding to the difference between transfer rates. Thus, sequential and alternate access operation in which the number of seek operations can be reduced can be realized.

Abstract: A disk storage apparatus includes: an actuator positioning a head with respect to a disk; a drive means driving the actuator; a voltage detection means detecting a voltage signal induced in driving the actuator; a disturbance estimation unit estimating the magnitude of load disturbance exerted on the head from a drive signal and the voltage signal, and outputting a disturbance estimation signal; a filter unit cutting off a high frequency component of the disturbance estimation signal, and outputting a filter signal; a position detection unit producing a position error signal corresponding to a current position of the head; a position control unit producing a position control signal based on the position error signal; and a correction unit outputting the drive signal based on the filter signal and the position control signal, and the apparatus controls stable positioning of the head against a resistance value fluctuation of a drive coil of the actuator and a resistance value change.

Abstract: An apparatus and method for tracking radially-dependent repeatable run-out in a disc drive having a servo loop for positioning a head over a rotating disc is provided. The disc includes multiple tracks. Radially-dependent repeatable run-out control components for at least a subset of the multiple tracks are first determined. Data representative of the radially-dependent repeatable run-out control components for the subset of the multiple tracks is then stored. The stored data representative of the radially-dependent repeatable run-out control components is retrieved before settling on the target track, and subsequently used to follow the selected track.

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: In a magnetic recording device, a control element placed on a flexible wiring board between a control device and first actuators includes a plurality of actuator-driving-signal connecting terminals connected to a plurality of second actuators, an actuator-driving-signal input terminal to which driving voltage for the second actuators is input from the control device, connecting wires for connecting the actuator-driving-signal input terminal to the actuator-driving-signal connecting terminals, signal selection elements incorporated in the connecting wires, and a decoder for selecting one of the signal selection elements so that a specific actuator-driving-signal connecting terminal is connected to the actuator-driving-signal input terminal.

Abstract: A disk drive is provided which uses a disk having a maximal limit cylinder group formed based on an initially recorded servo data before being assembled in a drive body. A CPU sets an actually usable data recording area on the disk by seeking the head in a radial direction over the disk. Further, the CPU allows the generation of a translation table for obtaining a correspondence between inherent physical cylinder address information of an effective cylinder group contained in the set data recording area and logical cylinder address information set to identify the effective cylinder group and allows the translation table to be stored in a memory. The CPU refers to the translation table when, in response to an access request from a host system, control is made to position a head to a target position, and finds physical cylinder address information corresponding to the target cylinder.

Abstract: In order to provide an information recording and reproducing apparatus having a high track density and a high recording density in each of tracks, in which a seeking time is short, a control circuit 21 performs a calculation required for a seeking operation upon receipt of a command of the seeking operation, and then, sets, to (f=fs), a drive pulse frequency f for a tracking control to be supplied to a piezoelectric element based on the calculation result. A drive circuit 23 outputs a drive pulse of the frequency f corresponding to the input drive pulse to an actuator 12, so that a recording and reproducing head 16 is moved near a target track, whereby the seeking operation is completed. In contrast, the control circuit 21 performs a calculation required for a following operation upon receipt of a command of the following operation, and then, sets, to (f=ft, wherein fs>ft), the drive pulse frequency f to be supplied to the piezoelectric element based on the calculation result.

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: The position error signal (PES), representing relative position regarding position information (RRO) previously recorded on a magnetic disk and the magnetic head, is averaged in each servo sector by an averaging unit, and a control input is obtained based on the PES by a phase compensator and the control input undergoes an averaging process in each servo sector by another averaging unit. Convolution integration with respect to the signal data processed by those averaging units is carried out by using a transfer characteristic formed by adding 1 to an open-loop transfer characteristic, which is determined by a magnetic head actuator model and a servo control circuit, to obtain a synchronous vibration estimate. This estimate undergoes a high-pass filtering process of a zero phase error characteristic by the filter unit to remove the vibration component of low frequency band and to thereby obtain a synchronous vibration learned value with high precision.

Abstract: A method and apparatus for resolving a “continuity” problem that occurs when modes are switched in the head positioning control process, and a contradiction exists between a short seek and a long seek.