Patent Document

FIELD OF EMBODIMENTS 
     Embodiments of the invention may relate generally to hard disk drives and more particularly to a technique for cleaning recording heads in operation. 
     BACKGROUND 
     A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator. A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium. 
     Modulated or poor writing is one cause of failure with HDDs. There are numerous conditions that can cause poor writing, whereby the written data pattern is so poor in quality that the data is impossible to read back and, consequently, the user can lose data. Thus, consistent quality writing is a fundamental attribute of reliable HDDs. 
     Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. 
     SUMMARY OF EMBODIMENTS 
     Embodiments of the invention are directed toward a technique for cleaning a recording head slider in-situ, or in-drive during operation. By periodically performing a series of full stroke seek (FSS) operations, liquid contaminants that may have migrated to the head slider are flung from the slider. Consequently, head-disk spacing may be stabilized and data write operations improved. 
     According to embodiments, the series of FSS operations are performed at predetermined intervals, and for a predetermined period of time. However, the series may be interrupted by a client request, and continued thereafter, so as not to affect the operational status of the HDD. 
     Embodiments discussed in the Summary of Embodiments section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section. Furthermore, no limitation, element, property, feature, advantage, attribute, or the like expressed in this section, which is not expressly recited in a claim, limits the scope of any claim in any way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a plan view illustrating a hard disk drive, according to an embodiment; and 
         FIG. 2  is a flowchart illustrating a method for cleaning a recording head slider, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Approaches to cleaning a recording head are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
     Physical Description of Illustrative Operating Environments 
     Embodiments may be used in the context of a hard disk drive (HDD), or other data storage device, self-cleaning recording head. Thus, in accordance with an embodiment, a plan view illustrating an HDD  100  is shown in  FIG. 1  to illustrate an exemplary operating environment. 
       FIG. 1  illustrates the functional arrangement of components of the HDD  100  including a slider  110   b  that includes a magnetic-reading/recording head  110   a . Collectively, slider  110   b  and head  110   a  may be referred to as a head slider. The HDD  100  includes at least one head gimbal assembly (HGA)  110  including the head slider, a lead suspension  110   c  attached to the head slider typically via a flexure, and a load beam  110   d  attached to the lead suspension  110   c . The HDD  100  also includes at least one magnetic-recording medium  120  rotatably mounted on a spindle  124  and a drive motor (not visible) attached to the spindle  124  for rotating the medium  120 . The head  110   a  includes a write element and a read element for respectively writing and reading information stored on the medium  120  of the HDD  100 . The medium  120  or a plurality of disk media may be affixed to the spindle  124  with a disk clamp  128 . 
     The HDD  100  further includes an arm  132  attached to the HGA  110 , a carriage  134 , a voice-coil motor (VCM) that includes an armature  136  including a voice coil  140  attached to the carriage  134  and a stator  144  including a voice-coil magnet (not visible). The armature  136  of the VCM is attached to the carriage  134  and is configured to move the arm  132  and the HGA  110 , to access portions of the medium  120 , being mounted on a pivot-shaft  148  with an interposed pivot-bearing assembly  152 . In the case of an HDD having multiple disks, the carriage  134  is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. 
     An assembly comprising a head gimbal assembly (e.g., HGA  110 ) including a flexure to which the head slider is coupled, an actuator arm (e.g., arm  132 ) and/or load beam to which the flexure is coupled, and an actuator (e.g., the VCM) to which the actuator arm is coupled, may be collectively referred to as a head stack assembly (HSA). An HSA may, however, include more or fewer components than those described. For example, an HSA may refer to an assembly that further includes electrical interconnection components. Generally, an HSA is the assembly configured to move the head slider to access portions of the medium  120  for read and write operations. 
     With further reference to  FIG. 1 , electrical signals (e.g., current to the voice coil  140  of the VCM) comprising a write signal to and a read signal from the head  110   a , are provided by a flexible interconnect cable  156  (“flex cable”). Interconnection between the flex cable  156  and the head  110   a  may be provided by an arm-electronics (AE) module  160 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The AE  160  may be attached to the carriage  134  as shown. The flex cable  156  is coupled to an electrical-connector block  164 , which provides electrical communication through electrical feedthroughs provided by an HDD housing  168 . The HDD housing  168 , also referred to as a base, in conjunction with an HDD cover provides a sealed, protective enclosure for the information storage components of the HDD  100 . 
     Other electronic components, including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  140  of the VCM and the head  110   a  of the HGA  110 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  124  which is in turn transmitted to the medium  120  that is affixed to the spindle  124 . As a result, the medium  120  spins in a direction  172 . The spinning medium  120  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  110   b  rides so that the slider  110   b  flies above the surface of the medium  120  without making contact with a thin magnetic-recording layer in which information is recorded. 
     The electrical signal provided to the voice coil  140  of the VCM enables the head  110   a  of the HGA  110  to access a track  176  on which information is recorded. Thus, the armature  136  of the VCM swings through an arc  180 , which enables the head  110   a  of the HGA  110  to access various tracks on the medium  120 . 
     Information is stored on the medium  120  in a plurality of radially nested tracks arranged in sectors on the medium  120 , such as sector  184 . Correspondingly, each track is composed of a plurality of sectored track portions (or “track sector”), for example, sectored track portion  188 . Each sectored track portion  188  may be composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, which is information that identifies the track  176 , and error correction code information. In accessing the track  176 , the read element of the head  110   a  of the HGA  110  reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  140  of the VCM, enabling the head  110   a  to follow the track  176 . Upon finding the track  176  and identifying a particular sectored track portion  188 , the head  110   a  either reads data from the track  176  or writes data to the track  176  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
     An HDD&#39;s electronic architecture comprises numerous electronic components for performing their respective functions for operation of an HDD, such as a hard disk controller (“HDC”), an interface controller, an arm electronics module, a data channel, a motor driver, a servo processor, buffer memory, etc. Two or more of such components may be combined on a single integrated circuit board referred to as a “system on a chip” (“SOC”). Several, if not all, of such electronic components are typically arranged on a printed circuit board that is coupled to the bottom side of an HDD, such as to HDD housing  168 . 
     References herein to a hard disk drive, such as HDD  100  illustrated and described in reference to  FIG. 1 , may encompass a data storage device that is at times referred to as a “hybrid drive”. A hybrid drive refers generally to a storage device having functionality of both a traditional HDD (see, e.g., HDD  100 ) combined with solid-state storage device (SSD) using non-volatile memory, such as flash or other solid-state (e.g., integrated circuits) memory, which is electrically erasable and programmable. As operation, management and control of the different types of storage media typically differs, the solid-state portion of a hybrid drive may include its own corresponding controller functionality, which may be integrated into a single controller along with the HDD functionality. A hybrid drive may be architected and configured to operate and to utilize the solid-state portion in a number of ways, such as, for non-limiting examples, by using the solid-state memory as cache memory, for storing frequently-accessed data, for storing I/O intensive data, and the like. Further, a hybrid drive may be architected and configured essentially as two storage devices in a single enclosure, i.e., a traditional HDD and an SSD, with either one or multiple interfaces for host connection. 
     Introduction 
     As discussed, modulated or poor writing is one cause of failure with HDDs, and there are numerous conditions that can cause poor writing. One mechanism found to cause modulated writing is relatively large accumulations of contaminants, such as oil or other liquid droplets, on failing heads. When a liquid droplet is entrained on a head the head becomes prone to large spacing fluctuations, especially when the liquid bridges the media. If this happens during a writing event, the written data pattern will be so poor in quality that data is typically lost. Non-limiting examples of sources of liquid that may be found to contaminate the head slider include a liquid component of pivot bearing oil, condensation from outgassing of HDD components and aerosols (i.e., air solutions), disk lube pickup, corrosion byproducts, and the like. 
     Method for Cleaning a Recording Head 
       FIG. 2  is a flowchart illustrating a method for cleaning a recording head slider, according to an embodiment. The process depicted in  FIG. 2  may be implemented in an electronic component such as a hard disk controller (HDC), according to an embodiment, or in a system-on-a chip (“SOC”), according to another embodiment. Hard-disk controllers are typically implemented as integrated circuit (IC) boards and, therefore, can be designed in many different architectures of electronic circuitry. Further, modern HDC&#39;s often take the form of an SOC. An SOC is an IC that integrates essentially all components of an electronic system into a single chip. An SOC may contain digital, analog, mixed-signal, and other functions, all on a single chip substrate. 
     The process logic corresponding to the process of  FIG. 2  may be implemented as firmware instructions (e.g., executable logic, or program of instructions) stored in memory and executed by a processor, such as a CPU or an MPU, constituent to or outside of the electronic component, or as analog or digital hardware circuitry constituent to the electronic component. The location of the logic corresponding to the method for cleaning a recording head may vary from implementation to implementation and is not limited to implementation within any particular electronic component. Rather, the logic may be implemented in other electronic components constituent to a hard disk drive storage device besides the HDC, as long as the component is effective in commanding, initiating operation of, or driving the voice coil motor/actuator. 
     At block  202 , a series of full stroke seek (FSS) operations is periodically performed. A full stroke seek operation refers to a HDD seek profile in which the voice coil motor operates to move the head slider a full stroke across the surface of the disk, i.e., generally, from a maximum inner diameter (ID) location of the disk to a maximum outer diameter (OD) location of the disk, or vice versa. A series of FSS operations functions to fling or cast any liquid particulate and/or contaminant from the head slider, thereby cleaning the head slider of any such undesirable particulate or contaminant. Furthermore, the series of FSS operations may function to clean the disk surface of liquid droplets, adsorbing liquid from the disk surface such as by way of slider-droplet collision and/or suction, and eventual removal from the head slider by way of flinging. Note that in addition to a series of true full stroke seeks, a series of “long seeks” could be implemented to perform a similar function of flinging liquid contaminants from the head slider, where a “long seek” could be shorter than a FSS but greater than an average seek length that services client requests, where an average seek length is typically optimized/minimized, for example, by command queuing, performance-enhancing algorithms, routines, and the like. 
     According to an embodiment each seek operation from the series of FSS operations is performed as quickly or as fast as possible within the operational capability of the actuator system, thereby promoting the efficacy of the technique. According to an embodiment the series of FSS operations may be asymmetric in that the ID-to-OD seek operation is performed as quickly as possible within the operational capability of the actuator system while the return OD-to-ID seek operation is performed slower, at less than the maximum operational capability of the actuator system. Such a variation may increase the likelihood that the entrained liquid that is flung from the head slider is flung in the direction toward or away from the disk OD, e.g., outside of the access band (useable area) of the disk and/or to the outer sidewall of the HDD, rather than depositing the entrained liquid toward the disk ID where it is likely to reflux back into the access band region. 
     For example and according to embodiments, a series of FSS operations is performed for a period of about five (5) seconds about every thirty (30) minutes or so. According to embodiments, to further ensure a clean head slider, a series of FSS operations is also performed for a period of about sixty (60) seconds upon powering up the disk spindle motor, and/or after a prolonged period of the slider being parked on a load/unload (LUL) ramp. Note that the duration and period associated with the head cleaning FSS operations, i.e., the schedule, may vary from implementation to implementation. However, the foregoing embodiments have shown to be effective at removing liquids entrained on the head slider, as well as rendering the disk surfaces effectively cleaned free of liquid droplets. 
     While some HDDs are configured to perform a full stroke seek at spin-up (i.e., when the spindle motor is powered on), generally as a quick check that all the head stack assemblies are operational, in the field HDDs are often used in a regime in which they are powered up and then left on indefinitely. Thus, these HDDs have a long but light duty cycle in which the HDD is maintained in an idle state for a majority of the time. Therefore, empirical evidence points to the conclusion that the full stroke seek upon spin-up is not sufficient to clean the head slider of contaminants, as does the procedure described in reference to  FIG. 2 . 
     According to an embodiment, the cleaning procedure is interruptible. Thus, if a client request (e.g., a data read or write request) is received at block  204 , then the series of full stroke seek operations is interrupted at block  206  in response to the one or more client request, in order to fulfill the client request. At block  208 , upon completion of the one or more client request, performance of the series of FSS operations is continued. Thus, the performance of the system is not affected by execution of the procedure, which is effectively transparent to the user experience. 
     Customization and “Intelligence” 
     There are a number of alternative ways in which the approach to in-situ cleaning of recording heads may be implemented. For example, the technique described in reference to  FIG. 2  may be implemented to be customizable, e.g., in the factory and/or by the customer/user. Customer control may be implemented through the use of mode pages, which are used to set operational settings on an HDD via changeable parameters. Thus, if customers want to override execution of the routine for certain of their customers, then the capability to do so is built into the programmed routine. 
     Additionally, certain “intelligence” may be programmed into the routine embodying the foregoing technique. For a non-limiting example, the type of seek operations that an HDD performs is monitored and the routine is either executed or not executed accordingly. Thus, if the normal HDD usage is identified as including a certain number, duration, or cycle of full stroke seeks, for example, then the routine may be at least temporarily overridden. For another non-limiting example, write operations may be audited with immediate verify operations (after, e.g., every 100th write operation) and if any hint of weakened/light modulated writing is found (e.g., as indicated by soft errors), then the routine may be elevated in priority. For yet another example, if the problem of contaminant migration to the head slider is found to occur primarily only after a certain number of operational hours, then execution of the routine may be deferred until that certain number of operational hours is met. 
     Extensions and Alternatives 
     Depending on the configuration of the device in which the foregoing embodiments may be implemented, various alternatives may be available for implementation. For one non-limiting example, if the HDD of interest is configured with a secondary actuation system then the secondary actuation system may be used to augment the foregoing embodiments, such as by performing a full stroke seek with the primary actuator coupled with a full stroke of the secondary actuator. Furthermore, with the relatively high amplitude and frequency that are typically associated with a secondary actuator, one may obtain an ultrasonic cleaning effect by modulating the secondary actuator at maximum or near maximum actuation capabilities, in conjunction with the primary actuator or independent of the primary actuator. For another non-limiting example, if an HDD of interest is configured with a thermal fly-height control (TFC) system then the TFC system may be used to augment the foregoing embodiments, such as by performing a full stroke seek with the primary actuator coupled with a vertical modulation of the slider via the TFC system. 
     In the foregoing description, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Therefore, various modifications and changes may be made thereto without departing from the broader spirit and scope of the embodiments. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 
     In addition, in this description certain process steps may be set forth in a particular order, and alphabetic and alphanumeric labels may be used to identify certain steps. Unless specifically stated in the description, embodiments are not necessarily limited to any particular order of carrying out such steps. In particular, the labels are used merely for convenient identification of steps, and are not intended to specify or require a particular order of carrying out such steps.

Technology Category: 3