Disk drive measuring stroke difference between heads by detecting a difference between ramp contact

Information

  • Patent Grant
  • 9355666
  • Patent Number
    9,355,666
  • Date Filed
    Monday, June 8, 2015
    9 years ago
  • Date Issued
    Tuesday, May 31, 2016
    8 years ago
Abstract
A data storage device is disclosed comprising a plurality of disk surfaces including a first disk surface and a second disk surface. A first head is actuated over the first disk surface, and a second head is actuated over the second disk surface. A ramp is located proximate an outer diameter of the disk surfaces. A stroke difference between the first and second heads is measured by moving the first and second heads toward the ramp and detecting when the heads contact the ramp.
Description
BACKGROUND

Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.



FIG. 1 shows a prior art disk format 2 as comprising a number of servo tracks 4 defined by servo sectors 60-6N recorded around the circumference of each servo track. Each servo sector 6i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 6i further comprises groups of servo bursts 14 (e.g., N and Q servo bursts), which are recorded with a predetermined phase relative to one another and relative to the servo track centerlines. The phase based servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations. A position error signal (PES) is generated by reading the servo bursts 14, wherein the PES represents a measured position of the head relative to a centerline of a target servo track. A servo controller processes the PES to generate a control signal applied to a head actuator (e.g., a voice coil motor) in order to actuate the head radially over the disk in a direction that reduces the PES.





BRIEF DESCRIPTION OF THE DRAWINGS


FIG. 1 shows a prior art disk format comprising a plurality of servo tracks defined by servo sectors.



FIGS. 2A and 2B show a data storage device in the form of a disk drive according to an embodiment comprising a plurality of disk surfaces wherein a head is actuated over each disk surface by a voice coil motor (VCM).



FIG. 2C shows top and bottom heads according to an embodiment each comprising a slider coupled to a suspension and a lift tab at the distal end of the suspension for contacting the ramp.



FIG. 2D is a flow diagram according to an embodiment wherein the heads are moved toward a ramp and a stroke difference between the heads is measured based on when the ramp contact occurs.



FIG. 3A shows an embodiment wherein the heads are moved from an inner diameter of the disk to the ramp.



FIG. 3B shows an embodiment wherein the heads are moved from a radial location identified by a reference track to the ramp.



FIG. 4A shows a head according to an embodiment comprising a write element, a read element, and a touchdown sensor.



FIG. 4B is a flow diagram according to an embodiment wherein an interval for each head to contact the ramp is measured after calibrating a repeatable seek trajectory.



FIG. 4C illustrates a difference between measured ramp contact intervals for first and second heads which represents the radial offset between the first and second heads.



FIG. 5A is a flow diagram according to an embodiment wherein while moving the heads toward the ramp a back electromotive force (BEMF) voltage generated by the VCM is sampled/stored and then post-processed to estimate a distance of movement for each of the heads.



FIG. 5B illustrates an example BEMF voltage signal generated by the VCM while moving the heads toward the ramp, and the corresponding touchdown signals when each head contacts the ramp.



FIG. 6A shows an embodiment wherein the control circuitry toggles between evaluating a first contact signal generated by the first head and a second contact signal generated by the second head.



FIG. 6B is a flow diagram according to an embodiment wherein the control circuitry real-time detects when each head contacts the ramp in order to disable the touchdown sensor, and then post-time detects when each head contacts the ramp by post-processing the stored sample sequence of the contact signal.



FIG. 7A shows an embodiment wherein the control circuitry processes a measured repeatable runout (RRO) of a reference track to servo a first head at a substantially fixed location as the disk rotates, and then measures a stroke (or stroke difference) by moving the first and second heads toward the ramp from the fixed location.



FIG. 7B shows an embodiment wherein the control circuitry measure a stroke (or stroke difference) multiple times by moving the first and second heads toward the ramp from a reference track starting from different rotation angles of the disk.





DETAILED DESCRIPTION


FIGS. 2A-2C show a data storage device in the form of a disk drive according to an embodiment comprising a plurality of disk surfaces including a first disk surface 161 and a second disk surface 162. A first head 181 is actuated over the first disk surface 161, and a second head 182 is actuated over the second disk surface 162. A ramp 20 is located proximate an outer diameter of the disk surfaces. The disk drive further comprises control circuitry 22 configured to execute the flow diagram of FIG. 2D wherein a stroke difference between the first and second heads is measured (block 28) by moving the first and second heads toward the ramp (block 24) and detecting when the heads contact the ramp (block 26).


In the embodiment of FIG. 2A, each disk surface may comprise servo data such as a plurality of servo sectors that define a plurality of servo tracks, wherein data tracks may be defined relative to the servo tracks at the same or different radial density. The control circuitry 22 processes a read signal 30 emanating from a head to demodulate the servo sectors and generate a position error signal (PES) representing an error between the actual position of the head and a target position relative to a target track. The control circuitry 22 filters the PES using a suitable compensation filter to generate a control signal 32 applied to a voice coil motor (VCM) 34 which rotates an actuator arm (e.g., 36A) about a pivot in order to actuate the heads radially over the disk surfaces in a direction that reduces the PES. The servo sectors may comprise any suitable head position information, such as a track address for coarse positioning and servo bursts for fine positioning. The servo bursts may comprise any suitable pattern, such as an amplitude based servo pattern or a phase based servo pattern.


Each head (e.g., first head 181) at the distal end of the actuator arm may comprise any suitable components. In the embodiment shown in FIG. 2C, each head comprises a slider (e.g., first slider 381) coupled to a suspension, wherein the suspension comprises a lift tab (e.g., first lift tab 401) at the distal end of the suspension for contacting the ramp 20. In one embodiment, the stroke difference between the heads may provide information about certain manufacturing defects of the disk drive. For example, the stroke difference may indicate a manufacturing defect in the ramp 20 (e.g., a tilt), or a manufacturing defect in the actuator arm and/or suspension (e.g., a tilt). The stroke difference may also reflect a defect in one or more of the disks, such as a vertical offset relative to the ramp 20, a tilt in one or more of the disks, or a warping/wobbling of one or more of the disks. These and other manufacturing defects may cause each head to contact the ramp 20 at different times during an unload operation due to the stroke difference between the heads as measured from a reference location. In one embodiment, the measured stroke difference between the heads may exhibit a particular signature corresponding to each type of manufacturing defect. Accordingly, in one embodiment the signature of the measured stroke difference may be used to discard or rework defective disk drives, and/or used as feedback to modify and improve certain manufacturing processes.



FIG. 3A illustrates an embodiment wherein the control circuitry 22 rotates the head stack assembly shown in FIG. 2B until it presses against an inner diameter crash stop so that the heads are positioned at a starting reference position near the inner diameter of the disk surfaces. The control circuitry 22 then rotates the head stack assembly in the opposite direction so that the heads moves toward the ramp 20. While moving the heads toward the ramp 20, a first interval is measured until the first head 181 contacts the ramp 20. The control circuitry 22 then rotates the head stack assembly back until it again presses against the inner diameter crash stop, and then performs the same operation in order to measure the second interval for the second head, and so on for each head. After measuring the interval for each head, the control circuitry 22 may evaluate the intervals in order to measure the stroke difference between the heads.


The interval required for each head to contact the ramp 20 may be measured relative to any suitable reference point. FIG. 3B illustrates an embodiment wherein the heads may be moved starting from a radial location on one of the disk surfaces (e.g., the first disk surface 161) which may be defined by suitable reference servo data, such as a reference servo track 42 defined by servo sectors. In one embodiment, the reference servo track 42 may be written to the first disk surface 161 prior to servo writing the disk surface with, for example, servo sectors that define concentric servo tracks as shown in FIG. 1. Alternatively, the reference servo track 42 may comprise one of the concentric servo tracks after having servo written the first disk surface 161. In one embodiment, the control circuitry 22 positions all of the heads at the reference position by servoing the first head 181 over the first disk surface 161 until the first head 181 is positioned over the reference servo track 42. The control circuitry 22 then moves all the heads toward the ramp 20 while evaluating a suitable contact signal generated for one of the heads that indicates when the head has contacted the ramp 20.


In one embodiment, when moving all the heads relative to a reference point on the first disk surface 161, the first disk surface 161 may comprise any suitable servo data disbursed at any suitable frequency on the first disk surface 161. For example, the first disk surface 161 may comprise multiple reference servo tracks (such as reference servo track 42 in FIG. 3B) that are spaced radially across the disk surface. When the first head 181 is moved toward the ramp 20, the periodic servo data written on the first disk surface 161 may be read by the first head 181 in order to adjust a seek trajectory for the heads during the seek toward the ramp 20. In this embodiment, the interval for each head to contact the ramp 20 may be measured relative to the last reference point read from the first disk surface 161. In one embodiment, the servo data on the first disk surface 161 may comprise a spiral track, wherein a reference point may be generated each time the head crosses the spiral track. In yet another embodiment, the servo data written on the first disk surface 161 may comprise a full set of servo written concentric servo tracks such as shown in FIG. 1, wherein the reference point for measuring the interval may be the last concentric servo track detected on the first disk surface 161 before each head contacts the ramp 20.


Any suitable contact signal may be generated in order to detect when one of the heads contacts the ramp 20. For example, in one embodiment the read signal emanating from the head may indicate when the head contacts the ramp 20. In another embodiment illustrated in FIG. 4A, each head may be fabricated with a suitable write element 44, a suitable read element 46, and a suitable fly height sensor or touchdown sensor 48 (e.g., a capacitive or magnetoresistive element) for generating a contact signal that may indicate when each head contacts the ramp 20. In yet another embodiment, the disk drive may employ a suitable microactuator (e.g., a piezoelectric actuator) for actuating each head over the respective disk surface in fine movements, wherein the microactuator may actuate the head in any suitable manner, such as by actuating a suspension relative to the actuator arm, or actuating the head relative to the suspension. In one embodiment, the control circuitry 22 may be configured to sense a contact signal generated by the microactuator which may indicate when the head contacts the ramp 20.


In one embodiment, the control circuitry 22 may evaluate the ramp contact signals generated by all of the heads concurrently while moving the head stack assembly toward the ramp 20 in a single pass. In alternative embodiment, the control circuitry 22 may evaluate the ramp contact signal generated by a single head which requires the head stack assembly to be moved toward the ramp in multiple passes (one pass for each head). This embodiment is understood with reference to the flow diagram of FIG. 4B wherein first a repeatable seek trajectory is calibrated for moving the heads from the reference point toward the ramp (block 50). Any suitable technique may be employed to calibrate the repeatable seek trajectory, such as by performing multiple seeks from the reference point to the ramp 20 and adjusting the seek trajectory (e.g., acceleration, constant velocity, and deceleration segments) until the seek time becomes substantially constant. In one embodiment, when calibrating the repeatable seek trajectory, the seek time is evaluated for a single head, such as the first head 181 in the embodiments of FIG. 3A or FIG. 3B, wherein the seek time may be measured as the interval between the beginning of the seek until the first head 181 contacts the ramp 20. In another embodiment, the first disk surface 161 may comprise reference servo data, such as one or more concentric servo tracks or a spiral track. When calibrating the repeatable seek trajectory, the seek trajectory may be adjusted each time the first head 181 crosses over the reference servo data. In this embodiment, the interval for each head to contact the ramp 20 may be measured relative to the last reference point on the first disk surface 161 during the seek before the heads contact the ramp 20.


After calibrating the repeatable seek trajectory at block 38, an index i is initialized to the first head (block 52) to select the first head to measure the first interval required to move the head from the reference point until contacting the ramp. The selected head is then moved to the reference point (block 54) and then moved toward the ramp (block 56) while measuring the ith interval until the ith head contacts the ramp (block 58). The index i is incremented (block 60) and the flow diagram repeated for the next head until an interval has been measured for each head. The relative stroke difference between the heads is then measured based on the measured intervals (block 62).



FIG. 4C illustrates a first interval (t1) measured for the first head 181 and a second interval (t2) measured for the second head 182. Referring to the example of FIG. 2C, a manufacturing defect as described above may cause the second head 182 to contact the ramp sooner than the first head 181, and therefore the second interval (t2) is shorter than the first interval (t1). The difference between the first interval (t1) and the second interval (t2) represents the stroke difference between the first head 181 and the second head 182. In one embodiment, the difference between the intervals may be converted into a physical distance based on the seek trajectory used to move the heads toward the ramp 20, or in an embodiment described below, based on a back electromotive force (BEMF) voltage generated by the VCM 34 which represents the velocity of the heads over the intervals.


In one embodiment, while moving the heads toward the ramp 20 the control circuitry 22 may sample a contact signal generated by one or more heads as well as sample the BEMF voltage generated by the VCM. After the heads have been unloaded onto the ramp 20, the control circuitry 22 may post-process the contact sample sequence and the BEMF sample sequence in order to measure the stroke for the corresponding head. An example of this embodiment is shown in the flow diagram of FIG. 5A wherein prior to moving the heads (or while moving the heads) a touchdown sensor in at least one head is enabled (block 64). While moving the heads toward the ramp 20, the contact signal generated by the touchdown sensor is sampled and stored as a contact sample sequence, and the BEMF voltage generated by the VCM is sampled and stored as a BEMF sample sequence (block 68). After the heads have been unloaded onto the ramp (block 72), the BEMF sample sequence is filtered using a suitable non-causal filter (block 74) in order to attenuate noise in the BEMF sample sequence so as to provide a more accurate velocity measurement of the head. The contact sample sequence for each head and the filtered BEMF sample sequence are then post-processed to measure the stroke difference between the heads (block 76).



FIG. 5B illustrates an example first contact sample sequence 781 generated for the first head and a second contact sample sequence 782 generated for a second head, as well as a BEMF sample sequence 80 generated by sampling the BEMF voltage of the VCM. In this embodiment, the first and second contact sample sequences 781 and 782 were generated concurrently (or interleaved) and therefore both contact sample sequences correspond to the same BEMF sample sequence 80. FIG. 5B illustrates how the BEMF voltage of the VCM may vary while moving the heads toward the ramp, and therefore integrating the BEMF sample sequence over the intervals before contact provides a relatively accurate estimate of the distance traveled by each head even though the velocity of the heads may vary over the intervals. Referring again to the example of FIG. 5B, integrating the BEMF sample sequence over the interval between the ramp contact 821 of the first head and the ramp contact 822 of the second head provides a measurement of the stroke difference between the heads. In one embodiment, post-processing the BEMF sample sequence 80, such as by filtering the BEMF sample sequence with a non-causal filter to reduce noise, provides a more accurate estimate of the velocity over the interval, thereby improving the stroke difference measurement.



FIG. 6A illustrates an embodiment wherein while moving the first head and the second heads toward the ramp, the control circuitry 22 configures a multiplexer 84 to toggle between evaluating a first contact signal 861 generated by the first head 181 and a second contact signal 862 generated by the second head 182. The stroke difference between the first head and the second head is then measured based on when the first contact signal 861 indicates contact with the ramp 20 and when the second contact signal 862 indicates contact with the ramp 20. This embodiment expedites measuring the stroke difference by interleave processing the contact signals from at least two heads (e.g., top and bottom heads) while moving the heads toward the ramp. In other embodiments, the control circuitry may further expedite the process by toggling between three or more heads during a single move of the heads toward the ramp. Also in these embodiments, measuring the stroke for two or more heads during a single move of the heads toward the ramp may increase the accuracy of the measurements (as compared to measuring the stroke for each head over different move operations that may experience different disturbances).


In one embodiment, the stroke difference for each head may be measured relative to the stroke of a reference head (e.g., the first head 181). For example, in one embodiment the stroke difference may be measured relative to a reference head and a target head each time the heads are moved toward the ramp. Accordingly this embodiment requires N−1 move operations in order to measure the stroke difference for N−1 target heads relative to a reference head (where N is the total number of heads).


In an embodiment that employs a touchdown sensor 48 to generate the contact signal, the touchdown sensor 48 may be damaged (e.g., due to electrical overstress) if it remains enabled while the head slides along the ramp 20 after contacting the ramp 20 during the unload operation. Accordingly, in one embodiment the touchdown sensor 48 may be disabled after contact with the ramp 20 is detected, thereby helping to prevent damage to the touchdown sensor 48. The touchdown sensor 48 may be enabled/disabled in any suitable manner, such as by enabling/disabling a bias signal (e.g., voltage or current) applied to the touchdown sensor 48.


This embodiment is understood with reference to the flow diagram of FIG. 6B wherein after enabling one or more touchdown sensors (block 88), the head are moved toward the ramp (block 90). While moving the heads toward the ramp, one or more contact signals generated by the touchdown sensors are sampled to generate contact sample sequence(s) (block 92). The contact sample sequence(s) are evaluated in real-time to detect whether the corresponding head has contacted the ramp (block 94). When the head contacting the ramp is real-time detected, the corresponding touchdown sensor is disabled (block 98), wherein in one embodiment the touchdown sensor is disabled after a margin delay (block 96) that ensures enough samples of the contact signal are taken. In an embodiment wherein two or more contact signals are evaluated during a single move toward the ramp, the process is repeated from block 94 to detect ramp contact and disable the touchdown sensor for the other heads. After the heads have been unloaded onto the ramp (block 100), the contact sample sequences are evaluated to post-time detect when each head actually contacted the ramp (block 102). That is, in one embodiment the post-time detection algorithm at block 102 is more accurate than the real-time detection algorithm at block 94.


In one embodiment, the control circuitry 22 may be configured to real-time detect one of the heads contacting the ramp based on a left peak function (LPF):







L





P






F


(
n
)



=





i
=

1
+
D



M
+
D





(


x
n

-

x

n
-
i



)

2


M






where xn represents a sample of the contact sample sequence at time n, M represents a smoothing factor, and D represents a transient exclusion offset. In one embodiment, the real-time detection of the head contacting the ramp occurs when:

LPF(N)>G2

where N represents the point of contact within the contact sample sequence and G represents a minimum jump in the contact sample sequence before and after the ramp contact.


In one embodiment, control circuitry 22 may be configured to post-time detect one of the heads contacting the ramp based on a left peak function (LPF) and a right peak function (RPF):







L





P






F


(
n
)



=







i
=
1

M



(


x
n

-

x

n
-
i



)


M






and





R





P






F


(
n
)



=





i
=
1

M



(


x
n

-

x

n
+
i



)


M







where xn represents a sample of the contact sample sequence at time n, and M represents a smoothing factor. In one embodiment, the post-time detection of the head contacting the ramp occurs when a difference between LPF(n) and RPF(n) reaches an extremum (minimum or maximum).


In one embodiment, at least one of the disk surfaces (e.g., the first disk surface 161) comprises a plurality of eccentric tracks due, for example, to a non-centric alignment of the disks when clamped to a spindle motor. In one embodiment, the control circuitry 22 is configured to measure a repeatable runout (RRO) of a reference track representing the eccentricity of the reference track. The RRO of the reference track is processed to servo the first head at a substantially fixed location as the disk rotates. An example of this embodiment is illustrated in FIG. 7A wherein the first disk surface 161 may comprise an eccentric reference track 104. The RRO for this servo track 104 may be measured, for example, by evaluating the PES when servoing on the reference servo track 104. The control circuitry may then cancel the measured RRO from the PES so that the heads may be moved toward the ramp 20 from a fixed location 106 as the disk rotates. That is, the heads may be moved from a substantially concentric servo path 106 such as shown in FIG. 7A so that the heads move from essentially the same fixed location toward the ramp 20 regardless as to the rotation angle of the disk.


In another embodiment illustrated in FIG. 7B, the control circuitry 22 may be configured to measure the stroke difference between, for example, the first and second heads multiple times by moving the first and second heads toward the ramp 20 from a reference location 108 starting from different rotation angles of the disk. For example, in one embodiment the measured stroke difference between top and bottom heads may vary relative to the rotation angle of the disk due, for example, to a warping/wobbling of the disk.


In another embodiment, the control circuitry may measure the stroke of each individual head by moving the heads toward the ramp 20 from the reference location 108 multiple times starting from different rotation angles of the disk such as shown in FIG. 7B. The difference in the measured stroke of each head relative to the rotation angle of the disk may be processed, for example, to measure the eccentricity of each disk (i.e., the in-plane runout of the disk such as shown in FIG. 7A). In another embodiment, the control circuitry may measure the stroke of each individual head at different rotation angles of the disk by moving the heads toward the ramp 20 starting from a fixed location 106 such as shown in FIG. 7A (i.e., after canceling the RRO of the eccentric reference track 104). In this manner, the difference in the stroke measurement for each head relative to the rotation angle of the disk may be processed, for example, to measure the vertical runout of the disk due, for example, to warping/wobbling of the disk.


Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC.


In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.


In various embodiments, a disk drive may include a magnetic disk drive, an optical disk drive, etc. In addition, while the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives, solid state drives, hybrid drives, etc. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.


The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.


While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.

Claims
  • 1. A data storage device comprising: a plurality of disk surfaces including a first disk surface and a second disk surface;a first head actuated over the first disk surface;a second head actuated over the second disk surface;a ramp proximate an outer diameter of the disk surfaces; andcontrol circuitry configured to measure a stroke difference between the first and second heads by moving the first and second heads toward the ramp and detecting when the heads contact the ramp.
  • 2. The data storage device as recited in claim 1, wherein the data storage device further comprises a voice coil motor (VCM) configured to actuate the heads over the disk surfaces, and control circuitry is further configured to: while moving the first and second heads toward the ramp, periodically sample a back electromotive force (BEMF) voltage of the VCM to generate a BEMF sample sequence;after the heads contact the ramp, post-process the BEMF sample sequence to estimate a distance of movement for each of the heads; andmeasure the stroke difference based on the distance of movement for each of the heads.
  • 3. The data storage device as recited in claim 2, wherein the control circuitry is further configured to: post-process the BEMF sample sequence by filtering the BEMF sample sequence using a non-causal filter to generate a filtered BEMF sample sequence; andestimate the distance of movement for each of the heads based on the filtered BEMF sample sequence.
  • 4. The data storage device as recited in claim 1, wherein the control circuitry is further configured to: while moving the first head and the second heads toward the ramp, toggle between evaluating a first contact signal generated by the first head and a second contact signal generated by the second head; andmeasure the stroke difference between the first head and the second head based on when the first contact signal indicates contact with the ramp and when the second contact signal indicates contact with the ramp.
  • 5. The data storage device as recited in claim 1, wherein the first disk surface comprises a plurality of eccentric tracks and the control circuitry is further configured to: measure a repeatable runout (RRO) of a reference track on the first disk surface representing the eccentricity of the reference track;process the RRO of the reference track to servo the first head at a substantially fixed location as the disk rotates; andmeasure a stroke of the first head by moving the first head toward the ramp from the fixed location.
  • 6. The data storage device as recited in claim 5, wherein the control circuitry is further configured to measure a stroke of the first head multiple times by moving the first head toward the ramp from the fixed location starting from different rotation angles of the disk.
  • 7. The data storage device as recited in claim 1, wherein the control circuitry is further configured to measure a stroke of the first head multiple times by moving the first head toward the ramp from a reference location starting from different rotation angles of the disk.
  • 8. The data storage device as recited in claim 1, wherein the first head comprises a first touchdown sensor, the second head comprises a second touchdown sensor, and while moving the first and second heads toward the ramp the control circuitry is further configured to: sample a first contact signal generated by the first touchdown sensor to generate a first contact sample sequence;sample a second contact signal generated by the second touchdown sensor to generate a second contact sample sequence;real-time detect the first head contacting the ramp based on the first contact sample sequence;when the first head contacting the ramp is real-time detected, disable the first touchdown sensor;real-time detect the second head contacting the ramp based on the second contact sample sequence; andwhen contact the second head contacting the ramp is real-time detected, disable the second touchdown sensor.
  • 9. The data storage device as recited in claim 8, wherein the control circuitry is further configured to real-time detect the first head contacting the ramp based on:
  • 10. The data storage device as recited in claim 8, wherein after moving the first and second heads toward the ramp the control circuitry is further configured to: post-time detect the first head contacting the ramp based on the first contact sample sequence; andpost-time detect the second head contacting the ramp based on the second contact sample sequence.
  • 11. The data storage device as recited in claim 8, wherein the control circuitry is further configured to post-time detect the first head contacting the ramp based on:
  • 12. The data storage device as recited in claim 11, wherein the control circuitry is further configured to post-time detect the first head contacting the ramp based on a difference between LPF(n) and RPF(n).
  • 13. The data storage device as recited in claim 12, wherein the control circuitry is further configured to post-time detect the first head contacting the ramp based on when the difference between LPF(n) and RPF(n) reaches an extremum.
  • 14. A method of operating a data storage device, the method comprising: moving first and second heads over respective disk surfaces to generate a contact signal; andmeasuring a stroke difference between the first and second heads by detecting when the heads contact a ramp based on the contact signal.
  • 15. The method as recited in claim 14, further comprising: while moving the first and second heads toward the ramp, periodically sampling a back electromotive force (BEMF) voltage of the VCM to generate a BEMF sample sequence;after the heads contact the ramp, post-processing the BEMF sample sequence to estimate a distance of movement for each of the heads; andmeasuring the stroke difference based on the distance of movement for each of the heads.
  • 16. The method as recited in claim 15, further comprising: post-processing the BEMF sample sequence by filtering the BEMF sample sequence using a non-causal filter to generate a filtered BEMF sample sequence; andestimating the distance of movement for each of the heads based on the filtered BEMF sample sequence.
  • 17. The method as recited in claim 14, further comprising: while moving the first head and the second heads toward the ramp, toggling between evaluating a first contact signal generated by the first head and a second contact signal generated by the second head; andmeasuring the stroke difference between the first head and the second head based on when the first contact signal indicates contact with the ramp and when the second contact signal indicates contact with the ramp.
  • 18. The method as recited in claim 14, wherein the first disk surface comprises a plurality of eccentric tracks and the method further comprises: measuring a repeatable runout (RRO) of a reference track on the first disk surface representing the eccentricity of the reference track;processing the RRO of the reference track to servo the first head at a substantially fixed location as the disk rotates; andmeasuring a stroke of the first head by moving the first head toward the ramp from the fixed location.
  • 19. The method as recited in claim 18, further comprising measuring a stroke of the first head multiple times by moving the first head toward the ramp from the fixed location starting from different rotation angles of the disk.
  • 20. The method as recited in claim 14, further comprising measuring a stroke of the first head multiple times by moving the first head toward the ramp from a reference location starting from different rotation angles of the disk.
  • 21. The method as recited in claim 14, wherein while moving the first and second heads toward the ramp the method further comprises: sampling a first contact signal generated by a first touchdown sensor of the first head to generate a first contact sample sequence;sampling a second contact signal generated by a second touchdown sensor of the second head to generate a second contact sample sequence;real-time detecting the first head contacting the ramp based on the first contact sample sequence;when the first head contacting the ramp is real-time detected, disabling the first touchdown sensor;real-time detecting the second head contacting the ramp based on the second contact sample sequence; andwhen contact the second head contacting the ramp is real-time detected, disabling the second touchdown sensor.
  • 22. The method as recited in claim 21, further comprising real-time detecting the first head contacting the ramp based on:
  • 23. The method as recited in claim 21, wherein after moving the first and second heads toward the ramp the method further comprises: post-time detecting the first head contacting the ramp based on the first contact sample sequence; andpost-time detecting the second head contacting the ramp based on the second contact sample sequence.
  • 24. The method as recited in claim 21, further comprising post-time detecting the first head contacting the ramp based on:
  • 25. The method as recited in claim 24, further comprising post-time detecting the first head contacting the ramp based on a difference between LPF(n) and RPF(n).
  • 26. The method as recited in claim 25, further comprising post-time detecting the first head contacting the ramp based on when the difference between LPF(n) and RPF(n) reaches an extremum.
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/040,960, filed on Sep. 30, 2013, entitled “DISK DRIVE MEASURING RADIAL OFFSET BETWEEN HEADS BY DETECTING A DIFFERENCE BETWEEN RAMP CONTACT,” which is hereby incorporated by reference in its entirety.

US Referenced Citations (557)
Number Name Date Kind
4321517 Touchton et al. Mar 1982 A
4353101 Kawai Oct 1982 A
4491885 Morikawa Jan 1985 A
4532802 Yeack-Scranton et al. Aug 1985 A
4591937 Nakarai May 1986 A
4691152 Ell et al. Sep 1987 A
4908723 Ohyama Mar 1990 A
5075805 Peddle et al. Dec 1991 A
5113296 Kaneko May 1992 A
5384675 Crawforth et al. Jan 1995 A
5455723 Boutaghou et al. Oct 1995 A
5485323 Anderson et al. Jan 1996 A
5559648 Hunter et al. Sep 1996 A
5576906 Fisher et al. Nov 1996 A
5668679 Swearingen et al. Sep 1997 A
5754353 Behrens et al. May 1998 A
5761212 Foland, Jr. et al. Jun 1998 A
5781363 Rowan et al. Jul 1998 A
5828522 Brown et al. Oct 1998 A
5831888 Glover Nov 1998 A
5973870 Boutaghou et al. Oct 1999 A
6000282 Ku et al. Dec 1999 A
6005725 Emo Dec 1999 A
6018789 Sokolov et al. Jan 2000 A
6021012 Bang Feb 2000 A
6023386 Reed et al. Feb 2000 A
6065095 Sokolov et al. May 2000 A
6078452 Kittilson et al. Jun 2000 A
6081447 Lofgren et al. Jun 2000 A
6091564 Codilian et al. Jul 2000 A
6092149 Hicken et al. Jul 2000 A
6092150 Sokolov et al. Jul 2000 A
6092412 Flechsig et al. Jul 2000 A
6094707 Sokolov et al. Jul 2000 A
6105104 Guttmann et al. Aug 2000 A
6111717 Cloke et al. Aug 2000 A
6145052 Howe et al. Nov 2000 A
6175893 D'Souza et al. Jan 2001 B1
6178056 Cloke et al. Jan 2001 B1
6191909 Cloke et al. Feb 2001 B1
6195218 Guttmann et al. Feb 2001 B1
6205494 Williams Mar 2001 B1
6208477 Cloke et al. Mar 2001 B1
6223303 Billings et al. Apr 2001 B1
6230233 Lofgren et al. May 2001 B1
6246346 Cloke et al. Jun 2001 B1
6249393 Billings et al. Jun 2001 B1
6249896 Ho et al. Jun 2001 B1
6256695 Williams Jul 2001 B1
6262857 Hull et al. Jul 2001 B1
6263459 Schibilla Jul 2001 B1
6272694 Weaver et al. Aug 2001 B1
6278568 Cloke et al. Aug 2001 B1
6279089 Schibilla et al. Aug 2001 B1
6289484 Rothberg et al. Sep 2001 B1
6292318 Hayashi Sep 2001 B1
6292912 Cloke et al. Sep 2001 B1
6304407 Baker et al. Oct 2001 B1
6310740 Dunbar et al. Oct 2001 B1
6317850 Rothberg Nov 2001 B1
6327106 Rothberg Dec 2001 B1
6337778 Gagne Jan 2002 B1
6369969 Christiansen et al. Apr 2002 B1
6384999 Schibilla May 2002 B1
6388833 Golowka et al. May 2002 B1
6405342 Lee Jun 2002 B1
6408357 Hanmann et al. Jun 2002 B1
6408406 Parris Jun 2002 B1
6411452 Cloke Jun 2002 B1
6411453 Chainer et al. Jun 2002 B1
6411458 Billings et al. Jun 2002 B1
6412083 Rothberg et al. Jun 2002 B1
6415349 Hull et al. Jul 2002 B1
6425128 Krapf et al. Jul 2002 B1
6429989 Schultz et al. Aug 2002 B1
6441981 Cloke et al. Aug 2002 B1
6442328 Elliott et al. Aug 2002 B1
6445524 Nazarian et al. Sep 2002 B1
6449767 Krapf et al. Sep 2002 B1
6453115 Boyle Sep 2002 B1
6470420 Hospodor Oct 2002 B1
6480020 Jung et al. Nov 2002 B1
6480349 Kim et al. Nov 2002 B1
6480932 Vallis et al. Nov 2002 B1
6483986 Krapf Nov 2002 B1
6487032 Cloke et al. Nov 2002 B1
6490635 Holmes Dec 2002 B1
6493173 Kim et al. Dec 2002 B1
6499083 Hamlin Dec 2002 B1
6507450 Elliott Jan 2003 B1
6519104 Cloke et al. Feb 2003 B1
6519107 Ehrlich et al. Feb 2003 B1
6525892 Dunbar et al. Feb 2003 B1
6545830 Briggs et al. Apr 2003 B1
6546489 Frank, Jr. et al. Apr 2003 B1
6549377 Yoshida et al. Apr 2003 B2
6550021 Dalphy et al. Apr 2003 B1
6552880 Dunbar et al. Apr 2003 B1
6553457 Wilkins et al. Apr 2003 B1
6563660 Hirano et al. May 2003 B1
6578106 Price Jun 2003 B1
6580573 Hull et al. Jun 2003 B1
6587293 Ding et al. Jul 2003 B1
6590732 Kitagawa et al. Jul 2003 B2
6594183 Lofgren et al. Jul 2003 B1
6600620 Krounbi et al. Jul 2003 B1
6601137 Castro et al. Jul 2003 B1
6603622 Christiansen et al. Aug 2003 B1
6603625 Hospodor et al. Aug 2003 B1
6604220 Lee Aug 2003 B1
6606682 Dang et al. Aug 2003 B1
6606714 Thelin Aug 2003 B1
6606717 Yu et al. Aug 2003 B1
6611393 Nguyen et al. Aug 2003 B1
6615312 Hamlin et al. Sep 2003 B1
6636377 Yu et al. Oct 2003 B1
6639748 Christiansen et al. Oct 2003 B1
6643088 Kawachi Nov 2003 B1
6647481 Luu et al. Nov 2003 B1
6654193 Thelin Nov 2003 B1
6657810 Kupferman Dec 2003 B1
6661591 Rothberg Dec 2003 B1
6665772 Hamlin Dec 2003 B1
6687073 Kupferman Feb 2004 B1
6687078 Kim Feb 2004 B1
6687850 Rothberg Feb 2004 B1
6690523 Nguyen et al. Feb 2004 B1
6690882 Hanmann et al. Feb 2004 B1
6691198 Hamlin Feb 2004 B1
6691213 Luu et al. Feb 2004 B1
6691255 Rothberg et al. Feb 2004 B1
6693760 Krounbi et al. Feb 2004 B1
6694477 Lee Feb 2004 B1
6697914 Hospodor et al. Feb 2004 B1
6700726 Gillis et al. Mar 2004 B1
6704153 Rothberg et al. Mar 2004 B1
6704156 Baker et al. Mar 2004 B1
6708251 Boyle et al. Mar 2004 B1
6710951 Cloke Mar 2004 B1
6711628 Thelin Mar 2004 B1
6711635 Wang Mar 2004 B1
6711660 Milne et al. Mar 2004 B1
6715044 Lofgren et al. Mar 2004 B2
6721119 Hassan et al. Apr 2004 B1
6721121 Schreck et al. Apr 2004 B1
6724982 Hamlin Apr 2004 B1
6725329 Ng et al. Apr 2004 B1
6735650 Rothberg May 2004 B1
6735693 Hamlin May 2004 B1
6738205 Moran et al. May 2004 B1
6744772 Eneboe et al. Jun 2004 B1
6745283 Dang Jun 2004 B1
6751402 Elliott et al. Jun 2004 B1
6754027 Hirano et al. Jun 2004 B2
6757481 Nazarian et al. Jun 2004 B1
6771480 Brito Aug 2004 B2
6772281 Hamlin Aug 2004 B2
6781826 Goldstone et al. Aug 2004 B1
6782449 Codilian et al. Aug 2004 B1
6791779 Singh et al. Sep 2004 B1
6792486 Hanan et al. Sep 2004 B1
6799274 Hamlin Sep 2004 B1
6811427 Garrett et al. Nov 2004 B2
6826003 Subrahmanyam Nov 2004 B1
6826007 Patton, III Nov 2004 B1
6826614 Hanmann et al. Nov 2004 B1
6832041 Boyle Dec 2004 B1
6832929 Garrett et al. Dec 2004 B2
6845405 Thelin Jan 2005 B1
6845427 Atai-Azimi Jan 2005 B1
6850443 Lofgren et al. Feb 2005 B2
6851055 Boyle et al. Feb 2005 B1
6851063 Boyle et al. Feb 2005 B1
6853731 Boyle et al. Feb 2005 B1
6854022 Thelin Feb 2005 B1
6862660 Wilkins et al. Mar 2005 B1
6867944 Ryan Mar 2005 B1
6880043 Castro et al. Apr 2005 B1
6882486 Kupferman Apr 2005 B1
6884085 Goldstone Apr 2005 B1
6888831 Hospodor et al. May 2005 B1
6892217 Hanmann et al. May 2005 B1
6892249 Codilian et al. May 2005 B1
6892313 Codilian et al. May 2005 B1
6895455 Rothberg May 2005 B1
6895500 Rothberg May 2005 B1
6898730 Hanan May 2005 B1
6902007 Orr et al. Jun 2005 B1
6910099 Wang et al. Jun 2005 B1
6917489 Lee Jul 2005 B2
6920007 Tominaga et al. Jul 2005 B2
6928470 Hamlin Aug 2005 B1
6931439 Hanmann et al. Aug 2005 B1
6934104 Kupferman Aug 2005 B1
6934713 Schwartz et al. Aug 2005 B2
6937419 Suk et al. Aug 2005 B2
6940873 Boyle et al. Sep 2005 B2
6943978 Lee Sep 2005 B1
6948165 Luu et al. Sep 2005 B1
6950267 Liu et al. Sep 2005 B1
6954733 Ellis et al. Oct 2005 B1
6961814 Thelin et al. Nov 2005 B1
6965489 Lee et al. Nov 2005 B1
6965563 Hospodor et al. Nov 2005 B1
6965966 Rothberg et al. Nov 2005 B1
6967799 Lee Nov 2005 B1
6968422 Codilian et al. Nov 2005 B1
6968450 Rothberg et al. Nov 2005 B1
6973495 Milne et al. Dec 2005 B1
6973570 Hamlin Dec 2005 B1
6976190 Goldstone Dec 2005 B1
6977791 Zhu et al. Dec 2005 B2
6983316 Milne et al. Jan 2006 B1
6986007 Procyk et al. Jan 2006 B1
6986154 Price et al. Jan 2006 B1
6995933 Codilian et al. Feb 2006 B1
6996501 Rothberg Feb 2006 B1
6996669 Dang et al. Feb 2006 B1
7002926 Eneboe et al. Feb 2006 B1
7003674 Hamlin Feb 2006 B1
7006316 Sargenti, Jr. et al. Feb 2006 B1
7009820 Hogg Mar 2006 B1
7019932 Hirano et al. Mar 2006 B2
7023639 Kupferman Apr 2006 B1
7024491 Hanmann et al. Apr 2006 B1
7024549 Luu et al. Apr 2006 B1
7024614 Thelin et al. Apr 2006 B1
7027716 Boyle et al. Apr 2006 B1
7028174 Atai-Azimi et al. Apr 2006 B1
7031902 Catiller Apr 2006 B1
7046465 Kupferman May 2006 B1
7046474 Kuramoto et al. May 2006 B2
7046475 Hosokawa May 2006 B2
7046488 Hogg May 2006 B1
7050252 Vallis May 2006 B1
7054937 Milne et al. May 2006 B1
7055000 Severtson May 2006 B1
7055167 Masters May 2006 B1
7057836 Kupferman Jun 2006 B1
7062398 Rothberg Jun 2006 B1
7068459 Cloke et al. Jun 2006 B1
7075746 Kupferman Jul 2006 B1
7076604 Thelin Jul 2006 B1
7082494 Thelin et al. Jul 2006 B1
7088533 Shepherd et al. Aug 2006 B1
7088538 Codilian et al. Aug 2006 B1
7088545 Singh et al. Aug 2006 B1
7092186 Hogg Aug 2006 B1
7095577 Codilian et al. Aug 2006 B1
7099095 Subrahmanyam et al. Aug 2006 B1
7106537 Bennett Sep 2006 B1
7106947 Boyle et al. Sep 2006 B2
7110202 Vasquez Sep 2006 B1
7111116 Boyle et al. Sep 2006 B1
7113361 Hassan Sep 2006 B2
7114029 Thelin Sep 2006 B1
7120737 Thelin Oct 2006 B1
7120806 Codilian et al. Oct 2006 B1
7126776 Warren, Jr. et al. Oct 2006 B1
7129763 Bennett et al. Oct 2006 B1
7133600 Boyle Nov 2006 B1
7136244 Rothberg Nov 2006 B1
7146094 Boyle Dec 2006 B1
7149046 Coker et al. Dec 2006 B1
7150036 Milne et al. Dec 2006 B1
7155616 Hamlin Dec 2006 B1
7159299 McMunigal et al. Jan 2007 B1
7171108 Masters et al. Jan 2007 B1
7171110 Wilshire Jan 2007 B1
7177111 Gururangan et al. Feb 2007 B2
7190547 Khurshudov et al. Mar 2007 B2
7194576 Boyle Mar 2007 B1
7199960 Schreck et al. Apr 2007 B1
7200698 Rothberg Apr 2007 B1
7203019 Liu et al. Apr 2007 B1
7205805 Bennett Apr 2007 B1
7206497 Boyle et al. Apr 2007 B1
7209310 Tsai et al. Apr 2007 B1
7215496 Kupferman et al. May 2007 B1
7215504 Bennett May 2007 B1
7215771 Hamlin May 2007 B1
7237054 Cain et al. Jun 2007 B1
7240161 Boyle Jul 2007 B1
7249365 Price et al. Jul 2007 B1
7263709 Krapf Aug 2007 B1
7274527 Calfee et al. Sep 2007 B2
7274639 Codilian et al. Sep 2007 B1
7274659 Hospodor Sep 2007 B2
7275116 Hanmann et al. Sep 2007 B1
7280302 Masiewicz Oct 2007 B1
7292774 Masters et al. Nov 2007 B1
7292775 Boyle et al. Nov 2007 B1
7295395 Koh et al. Nov 2007 B2
7296284 Price et al. Nov 2007 B1
7302501 Cain et al. Nov 2007 B1
7302579 Cain et al. Nov 2007 B1
7317587 Furuhashi et al. Jan 2008 B2
7318088 Mann Jan 2008 B1
7319806 Willner et al. Jan 2008 B1
7325244 Boyle et al. Jan 2008 B2
7330323 Singh et al. Feb 2008 B1
7346790 Klein Mar 2008 B1
7366641 Masiewicz et al. Apr 2008 B1
7369340 Dang et al. May 2008 B1
7369343 Yeo et al. May 2008 B1
7372650 Kupferman May 2008 B1
7380147 Sun May 2008 B1
7391586 Keast Jun 2008 B2
7392340 Dang et al. Jun 2008 B1
7404013 Masiewicz Jul 2008 B1
7406545 Rothberg et al. Jul 2008 B1
7415571 Hanan Aug 2008 B1
7436610 Thelin Oct 2008 B1
7437502 Coker Oct 2008 B1
7440214 Ell et al. Oct 2008 B1
7451344 Rothberg Nov 2008 B1
7471483 Ferris et al. Dec 2008 B1
7471486 Coker et al. Dec 2008 B1
7486060 Bennett Feb 2009 B1
7486466 Hara et al. Feb 2009 B2
7496493 Stevens Feb 2009 B1
7502194 Alexander et al. Mar 2009 B2
7518819 Yu et al. Apr 2009 B1
7526184 Parkinen et al. Apr 2009 B1
7539924 Vasquez et al. May 2009 B1
7543117 Hanan Jun 2009 B1
7551383 Kupferman Jun 2009 B1
7562282 Rothberg Jul 2009 B1
7577973 Kapner, III et al. Aug 2009 B1
7596797 Kapner, III et al. Sep 2009 B1
7599139 Bombet et al. Oct 2009 B1
7599257 Suzuki Oct 2009 B2
7619841 Kupferman Nov 2009 B1
7647544 Masiewicz Jan 2010 B1
7649704 Bombet et al. Jan 2010 B1
7653927 Kapner, III et al. Jan 2010 B1
7656603 Xing Feb 2010 B1
7656763 Jin et al. Feb 2010 B1
7657149 Boyle Feb 2010 B2
7672072 Boyle et al. Mar 2010 B1
7673075 Masiewicz Mar 2010 B1
7688540 Mei et al. Mar 2010 B1
7724461 McFadyen et al. May 2010 B1
7725584 Hanmann et al. May 2010 B1
7730295 Lee Jun 2010 B1
7760458 Trinh Jul 2010 B1
7768776 Szeremeta et al. Aug 2010 B1
7804657 Hogg et al. Sep 2010 B1
7813954 Price et al. Oct 2010 B1
7827320 Stevens Nov 2010 B1
7839588 Dang et al. Nov 2010 B1
7843660 Yeo Nov 2010 B1
7843662 Weerasooriya et al. Nov 2010 B1
7852596 Boyle et al. Dec 2010 B2
7859782 Lee Dec 2010 B1
7869155 Wong Jan 2011 B1
7869164 Shin Jan 2011 B2
7872822 Rothberg Jan 2011 B1
7898756 Wang Mar 2011 B1
7898762 Guo et al. Mar 2011 B1
7900037 Fallone et al. Mar 2011 B1
7907364 Boyle et al. Mar 2011 B2
7929234 Boyle et al. Apr 2011 B1
7933087 Tsai et al. Apr 2011 B1
7933090 Jung et al. Apr 2011 B1
7934030 Sargenti, Jr. et al. Apr 2011 B1
7940491 Szeremeta et al. May 2011 B2
7944639 Wang May 2011 B1
7945727 Rothberg et al. May 2011 B2
7949564 Hughes et al. May 2011 B1
7974029 Tsai et al. Jul 2011 B2
7974039 Xu et al. Jul 2011 B1
7982993 Tsai et al. Jul 2011 B1
7984200 Bombet et al. Jul 2011 B1
7990648 Wang Aug 2011 B1
7992179 Kapner, III et al. Aug 2011 B1
8004785 Tsai et al. Aug 2011 B1
8006027 Stevens et al. Aug 2011 B1
8014094 Jin Sep 2011 B1
8014977 Masiewicz et al. Sep 2011 B1
8019914 Vasquez et al. Sep 2011 B1
8040625 Boyle et al. Oct 2011 B1
8078943 Lee Dec 2011 B1
8079045 Krapf et al. Dec 2011 B2
8082433 Fallone et al. Dec 2011 B1
8085487 Jung et al. Dec 2011 B1
8089719 Dakroub Jan 2012 B1
8090902 Bennett et al. Jan 2012 B1
8090906 Blaha et al. Jan 2012 B1
8091112 Elliott et al. Jan 2012 B1
8094396 Zhang et al. Jan 2012 B1
8094401 Peng et al. Jan 2012 B1
8116020 Lee Feb 2012 B1
8116025 Chan et al. Feb 2012 B1
8134793 Vasquez et al. Mar 2012 B1
8134798 Thelin et al. Mar 2012 B1
8139301 Li et al. Mar 2012 B1
8139310 Hogg Mar 2012 B1
8144419 Liu Mar 2012 B1
8145452 Masiewicz et al. Mar 2012 B1
8149528 Suratman et al. Apr 2012 B1
8154812 Boyle et al. Apr 2012 B1
8159768 Miyamura Apr 2012 B1
8161328 Wilshire Apr 2012 B1
8164849 Szeremeta et al. Apr 2012 B1
8174780 Tsai et al. May 2012 B1
8190575 Ong et al. May 2012 B1
8194338 Zhang Jun 2012 B1
8194340 Boyle et al. Jun 2012 B1
8194341 Boyle Jun 2012 B1
8201066 Wang Jun 2012 B1
8271692 Dinh et al. Sep 2012 B1
8279550 Hogg Oct 2012 B1
8281218 Ybarra et al. Oct 2012 B1
8285923 Stevens Oct 2012 B2
8289656 Huber Oct 2012 B1
8300438 Herbert Oct 2012 B1
8305705 Roohr Nov 2012 B1
8307156 Codilian et al. Nov 2012 B1
8310775 Boguslawski et al. Nov 2012 B1
8315005 Zou et al. Nov 2012 B1
8315006 Chahwan et al. Nov 2012 B1
8316263 Gough et al. Nov 2012 B1
8320067 Tsai et al. Nov 2012 B1
8324974 Bennett Dec 2012 B1
8332695 Dalphy et al. Dec 2012 B2
8339919 Lee Dec 2012 B1
8341337 Ong et al. Dec 2012 B1
8350628 Bennett Jan 2013 B1
8356184 Meyer et al. Jan 2013 B1
8370683 Ryan et al. Feb 2013 B1
8375225 Ybarra Feb 2013 B1
8375274 Bonke Feb 2013 B1
8380922 DeForest et al. Feb 2013 B1
8390948 Hogg Mar 2013 B2
8390952 Szeremeta Mar 2013 B1
8392689 Lott Mar 2013 B1
8407393 Yolar et al. Mar 2013 B1
8413010 Vasquez et al. Apr 2013 B1
8417566 Price et al. Apr 2013 B2
8421663 Bennett Apr 2013 B1
8422172 Dakroub et al. Apr 2013 B1
8427770 O'Dell et al. Apr 2013 B1
8427771 Tsai Apr 2013 B1
8429343 Tsai Apr 2013 B1
8433937 Wheelock et al. Apr 2013 B1
8433977 Vasquez et al. Apr 2013 B1
8441909 Thayamballi et al. May 2013 B1
8456980 Thayamballi Jun 2013 B1
8458526 Dalphy et al. Jun 2013 B2
8462466 Huber Jun 2013 B2
8467151 Huber Jun 2013 B1
8483027 Mak et al. Jul 2013 B1
8489841 Strecke et al. Jul 2013 B1
8493679 Boguslawski et al. Jul 2013 B1
8499198 Messenger et al. Jul 2013 B1
8514506 Li et al. Aug 2013 B1
8547657 Liu Oct 2013 B1
8554741 Malina Oct 2013 B1
8560759 Boyle et al. Oct 2013 B1
8576509 Hogg Nov 2013 B1
8576511 Coker et al. Nov 2013 B1
8578100 Huynh et al. Nov 2013 B1
8578242 Burton et al. Nov 2013 B1
8582223 Garani et al. Nov 2013 B1
8582231 Kermiche et al. Nov 2013 B1
8589773 Wang et al. Nov 2013 B1
8593753 Anderson Nov 2013 B1
8599512 Hogg Dec 2013 B2
8605379 Sun Dec 2013 B1
8611031 Tan et al. Dec 2013 B1
8611032 Champion et al. Dec 2013 B2
8612798 Tsai Dec 2013 B1
8619383 Jung et al. Dec 2013 B1
8619508 Krichevsky et al. Dec 2013 B1
8619529 Liew et al. Dec 2013 B1
8621115 Bombet et al. Dec 2013 B1
8621133 Boyle Dec 2013 B1
8625224 Lin et al. Jan 2014 B1
8625225 Wang Jan 2014 B1
8626463 Stevens et al. Jan 2014 B2
8630052 Jung et al. Jan 2014 B1
8631188 Heath et al. Jan 2014 B1
8634283 Rigney et al. Jan 2014 B1
8635412 Wilshire Jan 2014 B1
8661193 Cobos et al. Feb 2014 B1
8665547 Yeo et al. Mar 2014 B1
8667248 Neppalli Mar 2014 B1
8670205 Malina et al. Mar 2014 B1
8671250 Lee Mar 2014 B2
8681442 Hogg Mar 2014 B2
8681445 Kermiche et al. Mar 2014 B1
8683295 Syu et al. Mar 2014 B1
8687306 Coker et al. Apr 2014 B1
8687307 Patton, III Apr 2014 B1
8687313 Selvaraj Apr 2014 B2
8693133 Lee et al. Apr 2014 B1
8698492 Mak et al. Apr 2014 B1
8699171 Boyle Apr 2014 B1
8699172 Gunderson et al. Apr 2014 B1
8711500 Fong et al. Apr 2014 B1
8711506 Giovenzana et al. Apr 2014 B1
8711665 Abdul Hamid Apr 2014 B1
8717694 Liew et al. May 2014 B1
8717695 Lin et al. May 2014 B1
8730612 Haralson May 2014 B1
8743502 Bonke et al. Jun 2014 B1
8749911 Sun et al. Jun 2014 B1
8753146 Szeremeta et al. Jun 2014 B1
8755136 Ng et al. Jun 2014 B1
8756361 Carlson et al. Jun 2014 B1
8760782 Garani et al. Jun 2014 B1
8760792 Tam Jun 2014 B1
8769593 Schwartz et al. Jul 2014 B1
8773793 McFadyen Jul 2014 B1
8773802 Anderson et al. Jul 2014 B1
8773807 Chia et al. Jul 2014 B1
8773957 Champion et al. Jul 2014 B1
8780470 Wang et al. Jul 2014 B1
8782334 Boyle et al. Jul 2014 B1
8786976 Kang et al. Jul 2014 B1
8787125 Lee Jul 2014 B1
8792196 Lee Jul 2014 B1
8792200 Tam et al. Jul 2014 B1
8797667 Barlow et al. Aug 2014 B1
8799977 Kapner, III et al. Aug 2014 B1
8817413 Knigge et al. Aug 2014 B1
8817584 Selvaraj Aug 2014 B1
8825976 Jones Sep 2014 B1
8825977 Syu et al. Sep 2014 B1
9064537 Nie et al. Jun 2015 B1
20020012193 Kobayashi Jan 2002 A1
20020071219 Yoshida et al. Jun 2002 A1
20020181139 Weiehelt et al. Dec 2002 A1
20040179289 Suk et al. Sep 2004 A1
20050152060 Gururangan et al. Jul 2005 A1
20050198656 Yamamoto Sep 2005 A1
20050280916 Calfee et al. Dec 2005 A1
20060005403 Calfee et al. Jan 2006 A1
20060028933 Liu Feb 2006 A1
20070076317 Keast Apr 2007 A1
20070230017 Hiller Oct 2007 A1
20070263522 Yamamoto Nov 2007 A1
20080002274 Allen et al. Jan 2008 A1
20080279060 Nishi Nov 2008 A1
20080291564 Tang et al. Nov 2008 A1
20090113702 Hogg May 2009 A1
20100053798 Saga Mar 2010 A1
20100306551 Meyer et al. Dec 2010 A1
20100309574 Bahirat et al. Dec 2010 A1
20110226729 Hogg Sep 2011 A1
20120127614 Arai May 2012 A1
20120159042 Lott et al. Jun 2012 A1
20120275050 Wilson et al. Nov 2012 A1
20120281963 Krapf et al. Nov 2012 A1
20120324980 Nguyen et al. Dec 2012 A1
20130286807 Gao Oct 2013 A1
Non-Patent Literature Citations (7)
Entry
U.S. Appl. No. 11/760,601, filed Jun. 8, 2007, 24 pages.
www.microesys.com/dataStorage/specifications.html.
http://www.microesys.com/pdf/pa2000.pdf, “PA 2000 High Performance Positioning System for Servotrack Writers”, MicroE Systems, PA2000 Rev.S1, 2 pages.
Notice of Allowance dated Feb. 25, 2015 from U.S. Appl. No. 14/040,960, 5 pages.
Office Action dated Nov. 6, 2014 from U.S. Appl. No. 14/040,960, 5 pages.
Office Action dated Aug. 7, 2014 from U.S. Appl. No. 14/040,960, 6 pages.
Office Action dated Apr. 7, 2014 from U.S. Appl. No. 14/040,960, 5 pages.
Continuation in Parts (1)
Number Date Country
Parent 14040960 Sep 2013 US
Child 14733027 US