Data storage device with HGSA offset compensation

A data storage device may be configured at least with an actuating assembly that has a head-gimbal suspension assembly (HGSA), first pivot point, and second pivot point. The head-gimbal assembly can be constructed and operated with at least first and second transducers aligned along a longitudinal axis of the head-gimbal suspension assembly. A controller may be adopted to manipulate the head-gimbal suspension assembly about at least one of the pivot points in response to a head-gimbal suspension assembly offset misalignment to compensate for such an offset.

SUMMARY

Assorted embodiments may configure data storage device with at least an actuating assembly that has a head-gimbal suspension assembly (HGSA), first pivot point, and second pivot point. The HGSA can be constructed and operated with at least first and second transducers aligned along a longitudinal axis of the HGSA. A controller may be adapted to manipulate the HGSA about at least one of the pivot points in response to an HGSA offset misalignment.

DETAILED DESCRIPTION

An increase in data bit areal density on a rotating data storage medium provides increased data capacity but also increased complexity for precisely positioning a data transducing means proximal a selected data bit. While position correction for the actuating assembly may be present in the data storage medium, such correction assumes a single, rigid data transducing means. Such an assumption can produce misalignment between data transducing means and a data bit due to the transducing means being offset as a result of microactuation.

Generally, reader-writer offset depends on the skew angle of a transducing head in relation to a data track. Calibration may be done to compensate for the reader-writer offset, but such calibration is static and does not change when the head is on the same data track. Because a co-located microactuator is positioned near the reading and writing transducers on the transducing head, it can induce an additional skew angle that can degrade system performance. The additional skew angle due to co-located microactuation can cause the writing transducer to be off the intended data track and jeopardize the data in adjacent tracks. This offset can be referred to as dynamic reader-writer offset because it varies from sample to sample depending on the microactuator output when the transducing head is on the same data track.

These issues have rendered a data storage device constructed in accordance with assorted embodiments to have at least an actuating assembly that has a head-gimbal suspension assembly (HGSA), first pivot point, and second pivot point with the HGSA having at least first and second transducers aligned along a longitudinal axis of the HGSA. A controller may be adapted to manipulate the HGSA about at least one of the pivot points in response to an HGSA offset misalignment. The ability to compensate for HGSA offset misalignment allows a dual stage actuating assembly to operate with optimized efficiency despite having the first and second transducer aligned.

With the ability to compensate for measured and predicted offset misalignment with manipulation of the HGSA about a pivot point, compensation can be done in real-time both proactively and retroactively without the need for a position error signal to indicate a misalignment. The adaptive nature of the offset misalignment compensation can further optimize data storage device operating efficiency and accuracy in response to changing operating conditions, such as temperature, humidity, vibration, and structural trauma. As such, data throughput and operational bandwidth can be increased in real-time by compensating for offset misalignment so that transducing means more accurately aligns with selected data bits.

FIG. 1generally displays an example data storage system100that can employ offset misalignment compensation in accordance with various embodiments. While not required or limiting, the data storage system100may have any number of data storage devices102that comprise a local controller104and a data transducing system106, such as in a redundant array of independent discs (RAID) or cloud computing environment. The single data transducing system106shown inFIG. 1illustrates how a plurality of magnetic data bits108can be arranged in data tracks110on a data medium112that is controlled by a centrally positioned spindle motor114.

An actuating assembly116can be configured to float a predetermined distance above the data bits108and data medium112on an air bearing118so that at least one transducing head120is suspended over selected data bits108and tracks110. In this way, the local controller104can dictate data access to and from the data medium112by spinning the spindle motor114and articulating the actuating arm122. It should be noted that control of the data transducing assembly106is not limited to the local controller104as various remote computing components can utilize the transducing assembly106across a network124via appropriate communications protocol.

The ability to connect any type, function, and number of computing components to the data storage device102remotely allows for optimized utilization of the data transducing system106. For example, a host126, which may be any number of computing components such as a processor, memory, server, and controller, can operate independently or in conjunction with the local controller104to write and read data to and from the data medium112. In another non-limiting example, the host126may provide temporary cache storage for data that is to be stored in the data storage device102at a scheduled time, such as a low system processing window or prior to system100power down. Through the various system100configurations, data storage can be facilitated with increased data capacity and data access speeds.

However, the miniaturization of the physical size of the data transducing system106can pose operating difficulties that can jeopardize the integrity of stored data and performance of the data storage device102.FIG. 2is a top view block representation of a portion of an example data storage device130that can experience operational difficulties. As shown, the disk stack portion132of the data storage device130has at least one recordable medium134that is accessed by an actuating assembly136to access data bits138that are resident in predetermined data tracks140.

With the increase in data bit areal density, the width of a data track140along the X-Y plane is reduced, which positions data bits138of adjacent data tracks140perilously close. Such an increase in data bit density can correspond with increased risk of inadvertent data bit138access and erasure as well as increasing the precision necessary for data transducer142alignment with a selected data track140. The incorporation of servo sectors144on the data storage medium134can provide overhead operational data, like error correction code and position error signals, that can indicate misalignment of the data transducer142and a data track140. The actuating assembly136can be configured to interpret the servo sectors144to articulate a voice coil motor146and microactuator148to independently and concurrently translate the actuating arm150and head-gimbal suspension assembly (HGSA)152and correct for indicated transducer142misalignment.

The use of overhead operational data in the servo sectors144can allow for transducer142misalignment correction, but such correction is retroactive and relies on the transducer142passing subsequent servo sectors144to further correct or verify alignment. With the data storage medium134spinning at several thousand rotations per minute, such misalignment correction can be conducted with negligible degradation of data bit access performance. However, the reduction in data track140size in concert with increased data bit138areal density has rendered multiple transducing means to be aligned along the longitudinal axis of the actuating assembly136in what can be characterized as a co-located HGSA.

FIGS. 3A and 3Brespectively display block representations of an example HGSA portion160of a data storage device being operated in different conditions according to assorted embodiments.FIG. 3Aillustrates an HGSA162connected to a microactuator164via a dimple166co-located with a transducing head that has at least one data reader176and writer178. The dimple166allows the HGSA162to pitch and roll on an air bearing to access data bits from a data track168. It is contemplated that the microactuator164can provide a selectively articulable pivot point in an unlimited variety of manners, none of which is required or limiting. In yet, various embodiments configure the microactuator164with a slider170positioned between piezoelectric elements172that can respond to control signals to pivot the HGSA162about the dimple166, as shown inFIG. 3B.

The ability to selectively control the microactuator164allows minor misalignment between the HGSA164and the centerline174to be corrected in real-time to increase the accuracy and performance of data bit accesses from the data track168. That is, the microactuator164can move a data reader176and data writer178into alignment with the data track centerline174to compensate for a track misregistration (TMR)180. Construction of the HGSA162with a co-located microactuator arrangement in which the longitudinal axis182bisects both the data reader176and writer178can allow the HGSA162to better compensate the TMR180and be able to access data from smaller data tracks168.

However,FIG. 3Billustrates how microactuation of the co-located HGSA164can produce unwanted offset θ as a function of the separation distance184between the data reader176and writer178in combination with the degree of rotation of the HGSA longitudinal axis186about the dimple166. In other words, activation of the co-located microactuator164can tilt the HGSA longitudinal axis186that bisects both the data reader176and writer178from alignment along the longitudinal axis182of the actuating arm to a new orientation that is offset from the actuating arm longitudinal axis182by θ. The ability to articulate the microactuator164can provide precise adjustment of the position of the HGSA162to the data track centerline174, as shown in comparison ofFIGS. 3A and 3B.

However, the precision afforded by the microactuator164concurrently produces offset misalignment between the data reader176and writer178that can position one or more of the transducing means to encroach on adjacent data tracks, which can jeopardize data integrity and data storage device reliability.FIG. 4provides another block representation of an example HGSA portion190of a data storage device that can produce a transducer192offset θo. It can be appreciated that the actuating assembly portion190of illustrated inFIG. 4has a single line representing various portions of an actuating assembly, such as assembly136ofFIG. 2, but is in no way limiting to the possible configurations that can be used to position a transducer192proximal a selected data bit resident on a rotating data storage medium.

As shown, the actuating assembly portion190has a first pivot point194, which may be a voice coil motor in some embodiments, and an actuating arm196that continuously extends from the first pivot point194to a suspension pivot point198. The suspension pivot point198is filled in to illustrate that the point is fixed and the angular orientation of the actuating arm196and suspension200are rigid. Such fixed orientation can have a swaging bias angular offset θsbthat is predetermined to be part of the actuating assembly or is an inadvertent byproduct of manufacturing and assembly of a data storage device. Regardless of the origin of the swaging bias offset θsb, the position of the microactuator pivot point202is separated from the longitudinal axis204of the actuating assembly and can contribute to how much driving bias θdbis to be applied to properly position a transducer192over a selected data bit.

In the event the multiple transducers192present on the HGSA206have negligible separation distance208, such as when the transducers192are placed symmetrically about the longitudinal axis210of the HGSA, each transducer192could be plotted by a single location of the HGSA206in relation to the first194, second198, and third202pivot points. However, the read and write transducers192are each bisected by the longitudinal axis210of the HGSA206and separated by a non-negligible distance208, the respective transducers192will be offset, as illustrated inFIG. 4.

Such transducer192offset cannot be compensated with position error signals and other servo data from a data storage medium due to the position error signal correcting the data reading transducer's position relative to the medium and not the data writing transducer's position. That is, servo data from a data storage medium is read by a transducer192and translated into position correcting information, but the correction of the position of one transducer does not equate to correcting the position of another co-located transducer192due to the transducer offset θoas a function of θsband θdb. Therefore, transducer offset can produce HGSA misalignment that can position a transducer192outside a selected data track and risk inadvertent data access to data bits from adjacent data tracks, which can be especially problematic in two-dimensional and shingled data storage environments where transducer192alignment is paramount to efficient data storage.

Accordingly, transducer192offset and the consequential data track misalignment can be computed and compensated by at least a local controller of a data storage device, such as controller104ofFIG. 1. The controller can proactively and retroactively identify transducer offset and compensate by actively adjusting the microactuation about the microactuator pivot point202and factoring the offset into data access requests, such as two-dimensional and shingled data reads and writes, and future position error signals that identify where the HGSA is relative to a data storage medium. Hence, through the identification of the transducer offset, the actuating assembly190can be calibrated to compensate for the offset distance as a function of θsband θdbfrom the longitudinal axis204of the actuating assembly.

FIGS. 5A and 5Bare block representations of an example actuating assembly220in operation in accordance with assorted embodiments.FIG. 5Aillustrates some of the variables that can be evaluated to compute an offset deviation of a data read transducer222from a longitudinal axis224of the actuating arm226. It is contemplated that the position of the read transducer222can be sensed by conducting one or more dynamic test patterns where non-user data is written to and subsequently read from a data storage medium. However, various embodiments can statically compute the position of the read transducer222and the corresponding offset angle via equation 1:

The offset angle φrcan be used in conjunction with the microactuator228skew angle θsto understand the relationship of microactuator228articulation with read transducer222offset. The microactuator228skew angle θscan be computed via equation 2:

With the ability to compute the offset angle φrand microactuator228skew angle θs, the microactuator228can be tuned to proactively compensate for the offset to ensure the read transducer222is properly positioned relative the actuating arm226. It can be appreciated that the farther the read transducer222is from the microactuator228corresponds to greater HGSA stroke and increased ability to conduct minute microactuator228adjustments about pivot point D to position the read transducer222over a selected portion of an adjacent data storage medium. Although, the position of the read transducer222does not correctly plot the write transducer230as additional offset angle is induced by distance ε.

FIG. 5Bdisplays how the position of the write transducer230can be computed using equations 3, 4, and 5 as follows:

While equations 1-5 can be used individually and collectively to plot the position of the read222and write230transducers, various embodiments utilize simplified equation 6 to model the offset between the transducers222and230.

d=ɛ*cot⁡[cos-1⁡(Ww⁢P_2+r2-PO_22⁢Ww⁢P_*r)-θs](Equation⁢⁢6)
The ability to compute the various constituent geometric aspects of the position of the read222and write230transducers allows the actuating assembly220be dynamically and statically modeled before, during, and after operation that may or may not involve access to an adjacent data storage medium. That is, various test patterns may be conducted with the actuating assembly220that allows the position of the read222and write230transducers to be computed in relation to the microactuator228, which may be verified by data bit programming and reading operations to a corresponding data storage medium. Such computed transducer position, and specifically the transducer offset for various microactuator228bias voltages, may then be tuned with respect to the position of the actuator arm226to prevent or correct for transducer misalignment due to the co-located configuration of the microactuator with respect to the transducers about the longitudinal axis224of the actuating assembly220.

The transducer modeling capabilities provided by equations 1-6 are utilized in assorted embodiments to conduct the actuating assembly calibration routine240ofFIG. 6A, which is generally represented by the example actuating assembly250ofFIG. 6B. Step242initially places the actuating assembly250in a single stage mode in which the microactuator pivot point256is fixed and the voice coil motor146translates the HGSA258to align the reader260to a data track. The microactuator pivot point256is selectively articulated by a known static voltage to translate the HGSA258and induce offset misalignment between the read260and write262transducers, as illustrated inFIG. 6B.

Next in step244, routine240uses at least one of equations 1-6 to model the position of the respective transducers260and262for different static microactuator voltages. It should be noted that step244can be carried out in an unlimited variety of manners that may, or may not, include using real-time measured data, such as a position error signal and data bit accessing operation, as well as logged data and data predicted by various prediction algorithms. The various positions of the HGSA258inFIG. 6Billustrate how step244can articulate the microactuator about pivot point256with different voltages to induce greater skew angles and differing amounts of transducer offset.

With the position of at least two different HGSA258positions due to varying microactuator articulation, step246can then use equation 7 to compute any additional transducer offset as a function of actual real-time measured data. That is, at least one real-time measurement, such as microactuator voltage, can be correlated by equation 7 with modeling data from equations 1-7 to provide accurate, actual transducer offset misalignment that can be compensated for efficiently without degrading data storage performance.
f(αo)=Σv=V2v=VpΣt=t2t=tp[δΩM(v,t)−δΩm(v,t,αo)]  (Equation 7)
where αt0is the HGSA misalignment angle, v is voltage applied to the microactuator pivot point256, t is data track location, δΩMis computed from real-time measurement, and δΩmis computed from modeling.

Calculation of the transducer misalignment angle for various microactuator voltages then allows248to calibrate the HGSA misalignment angle α0by minimizing the modeling error, which can be conducted in an unlimited variety of manners. In one example, the modeling error is minimized by repeating steps244and246for an increased number of microactuator voltages and corresponding transducer misalignment angles, as shown by routine240returning to step244after step248. However, such return to step244is not required as step248may minimize the modeling error by evaluating position error signals and bit error rates of the actuating assembly250during operation to refine the misalignment data and the precision of the transducer offset predicted from equation 7. The actuating assembly calibration routine240ofFIG. 6Acan also be applied to optimize the assembly process for reducing the swaging bias in the HGSA in accordance with some embodiments.

The HGSA can consist of several parts that correspond with precise tooling to be able to align the parts to the same axis204. There exists misalignment in HGSA due to swaging bias and microactuator driving signal bias, so the three pivot points194,198and202do not perfectly line up with204. Routine240can provide not only a calibration approach of the misalignment angle (α0) to complete the model for the offset estimator240, but also an in-drive measurement technique to adjust the tooling or assembly process to reduce the misalignment in the HGSA.

As a review, the position of transducers can be predicted using modeling equations 1-6. The predicted position of the transducers can then be tested and correlated to actuating assembly250operation by combining real-time measured data with the modeling results. Such combination of real-time measured data with predicted modeling allows for proactive calibration of microactuator articulation to compensate for the co-located configuration of microactuator being located near, but separated from, the transducers along the longitudinal axis of the HGSA.

FIGS. 7A and 7Brespectively display an example HGSA offset compensation routine270that can be carried out in accordance with some embodiments in association with the example prediction circuitry280ofFIG. 7B. Routine270begins by logging microactuator output from position error signals from a corresponding data storage medium in step272. Step272may further involve data bit programming and reading operations along with the passage of the transducers over servo portions of the data storage medium during the servicing of user data commands as an active or passive measurement. The logged microactuator output is not limited to a particular value, but may have at least the microactuator voltage and HGSA skew angle as part of the logged data.

The logged microactuator output can then be predictively modeled in step274by the output predictor282ofFIG. 7B. The output predictor282can utilize a transfer function to translate the logged microactuator output into actuating assembly controls dictating such output. That is, the output predictor282can utilize logged microactuator data to compute various actuating assembly controls associated with that data, such as voice coil voltage, swaging bias, and HGSA skew angle. With the microactuator output being computed, step276can next predict the additional transducer offset misalignment due to the co-located configuration of microactuator and the transducers via an offset estimator284portion of the prediction circuitry280.

Various embodiments configure the offset estimator284to utilize a mathematical function, such as a polynomial function, to simplify the transducer position and offset models represented by equations 1-6 and to predict the offset distance between the read and write transducers of the HGSA. The offset estimator may further predict the offset misalignment of the transducers as a function of the microactuator voltage and HGSA skew angle. Subsequently, step278of routine270adds the predicted transducer offset to position error signals received from the corresponding data storage medium to compensate for the offset misalignment by altering the amount of actuator articulations, such as voice coil voltage and microactuator voltage, called for by the position error signals.

As a non-limiting example of the operation of routine270and prediction circuitry280, the output predictor282and offset estimator284can predict the amount of transducer offset misalignment for various microactuator skew angles and the resultant compensation can increase or decrease the amount of microactuation or voice coil voltage employed from received position error signals. As such, low microactuator skew angles may not employ offset compensation while high skew angles greatly modify the voltage to the microactuator and the resulting skew angle to ensure both transducers are aligned with a selected data track of a data storage medium.

In some embodiments, routine270can be continually conducted while user data is programmed to a data storage medium to dynamically compensate for changes in actuating assembly conditions, such as vibration, microactuator malfunction, and heat. The ability to precisely predict transducer offset misalignment and continually, routinely, and sporadically evolve the computation of the offset misalignment ensures accurate and efficient data storage performance regardless of the environmental and operational variables like co-located transducers and temperature.

It should be noted that while routine270and prediction circuitry280can be utilized to optimize data storage performance, the various aspects shown inFIGS. 7A and 7Bare not required or limiting. Accordingly, any number of steps can be added, omitted, and modified to accommodate the measurement, prediction, calibration, and compensation of transducer offset misalignment. For example, a step may be added to routine270that provides the offset misalignment prediction to the position error signals of the corresponding data storage medium as a closed-loop that operates similar to shifting the reference input into the feedback control loop for the actuating assembly. Furthermore, a step may be added that provides the offset misalignment prediction to one or more actuator outputs to compensate the offset by a feed-forward control loop.

Even though data storage media can contain sophisticated high-bandwidth servo control that can precisely position a transducer over a designated data bit, the co-located configuration of microactuator and transducers along a longitudinal axis of the HGSA can produce offset misalignment of transducers on the HGSA that degrades data access performance. While the position error controls of the data storage media can correct a single transducer's position relative to a data storage medium, the compensation of co-located configuration of microactuator and transducers can involve the modeling of the position of various transducing means in relation to various actuating assembly pivot points before calibrating the actuating assembly to combine real-time microactuator measurements with the modeled data. Such combination of model and actual measured data allows transducer offset misalignment to modify a microactuator's or voice coil's response to a position error signal to ensure each transducer is positioned over a selected data track of the data storage medium to optimize data access performance and accuracy.