Controlling a write inhibit threshold based on vibration

A disk drive can include a data storage disk, a head, an acceleration sensor, and a controller. The head is configured to write data on the disk. The acceleration sensor generates an acceleration signal that is indicative of acceleration of the disk drive. The controller determines when the disk drive is being subjected to a vibration condition determination. The controller can inhibit writing of data through the head onto the disk based on comparison of the acceleration signal to the threshold value.

FIELD OF THE INVENTION

The present invention generally relates to digital data storage devices and, more particularly, to a disk drive that selectively inhibits writing of data to tracks on a disk in the disk drive, and related methods.

BACKGROUND

Disk drives are digital data storage devices that can enable users of computer systems to store and retrieve large amounts of data in a fast and efficient manner. A typical disk drive includes a plurality of magnetic recording disks that are mounted to a rotatable hub of a spindle motor and rotated at a high speed. An array of read/write heads is disposed adjacent surfaces of the disks to transfer data between the disks and a host computer. The heads can be radially positioned over the disks by a rotary actuator and a closed loop servo system, and can fly proximate the surfaces of the disks upon air bearings.

A plurality of nominally concentric tracks can be defined on each disk surface. A preamp and driver circuit generates write currents that are used by the head to selectively magnetize the tracks during a data write operation and amplifies read signals detected by the head from the selective magnetization of the tracks during a data read operation. A read/write channel and interface circuit are connected to the preamp and driver circuit to transfer the data between the disks and the host computer.

The servo system can operate in two primary modes: seeking and track following. During a seek, a selected head is moved from an initial track to a destination track on the corresponding disk surface. Thereafter, the servo system enters the track following mode wherein the head is maintained over the center of the destination track until another seek is performed.

Read and write operations may be performed during track following mode. In order to reduce the occurrence of off-track writes (i.e. writing while the head is located more than a threshold distance from the center of the desired track), the servo system tracks the position of the head by means of a position error signal that is fed back to the servo system. The servo system moves the head in response to the position error signal in an attempt to minimize the position error signal.

In addition to responding to signals from the servo system, the position of the head is affected by operational shock and/or vibration of the disk drive. For example, vibration and/or shock may be transmitted to the disk drive through the frame or housing in which it is mounted. In particular, operational shock may result in large position errors over short periods of time. If the position error signal exceeds a fixed threshold level, data writing may be inhibited until the position error signal is reduced below the threshold level and/or a predetermined number of disk rotations has occurred. Some disk drives include a shock sensor that outputs a shock signal which indicates the occurrence and magnitude of a shock that the disk drive is experiencing. Although inhibiting writes based on a position error threshold and shock signal threshold is implemented in some disk drives, off-track writes may occur at an unacceptable rate if the threshold values are too high. In contrast, if the threshold values are too low, the data throughput of the disk drive may be significantly impaired.

SUMMARY

In some embodiments of the present invention, a circuit includes a controller that determines when a disk drive is being subjected to a vibration condition and varies a write inhibit threshold for the disk drive in response to the vibration condition determination.

In some further embodiments, the controller lowers the write inhibit threshold when the disk drive is not being subjected to a vibration condition, and raises the write inhibit threshold when the disk drive is being subjected to a vibration condition. By lowering the write inhibit threshold in the absence of a vibration condition, the controller may be able to detect and inhibit writing in response a lower level shock condition that may otherwise not be detected if the write inhibit threshold were maintained at a higher level.

Some other embodiments of the present invention are directed to related methods of controlling writing in a disk drive in response to a controllable write inhibit threshold.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.

It will be understood that, as used herein, the term “comprising” or “comprises” is open-ended, and includes one or more stated elements, steps and/or functions without precluding one or more unstated elements, steps and/or functions. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that, although the terms first, second, etc. may be used herein to describe various steps, elements and/or regions, these steps, elements and/or regions should not be limited by these terms. These terms are only used to distinguish one step/element/region from another step/element/region. Thus, a first step/element/region discussed below could be termed a second step/element/region without departing from the teachings of the present invention.

The present invention may be embodied in hardware (analog and/or discrete) and/or in software (including firmware, resident software, micro-code, etc.). Consequently, as used herein, the term “signal” may take the form of a continuous waveform and/or discrete value(s), such as digital value(s) in a memory or register.

The present invention is described below with reference to block diagrams of disk drives and operations according to various embodiments of the invention. It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. Like numbers refer to like elements throughout the description of the figures.

A simplified diagrammatic representation of a disk drive, generally designated as10, is illustrated inFIG. 1. The disk drive10includes a disk stack12(illustrated as a single disk inFIG. 1) that is rotated by a spindle motor14. The spindle motor14is mounted to a base plate16. An actuator arm assembly18is also mounted to the base plate16. The disk drive10is configured to store and retrieve data responsive to write and read commands from a host device. A host device can include, but is not limited to, a desktop computer, a laptop computer, a personal digital assistant (PDA), a digital video recorder/player, a digital music recorder/player, and/or another electronic device that can be communicatively coupled to store and/or retrieve data in the disk drive10.

The actuator arm assembly18includes a head20(or transducer) mounted to a flexure arm22which is attached to an actuator arm24that can rotate about a pivot bearing assembly26. The head20may, for example, include a magnetoresistive (MR) element and/or a thin film inductive (TFI) element. The actuator arm assembly18also includes a motor28, such as a voice coil motor (VCM), which radially moves the head20across the disk stack12. The spindle motor14and actuator arm assembly18are coupled to a controller, read/write channel circuits, and other associated electronic circuits30which are configured in accordance with at least one embodiment of the present invention, and which can be enclosed within one or more integrated circuit packages mounted to a printed circuit board (PCB)32. The controller, read/write channel circuits, and other associated electronic circuits30are referred to below as a “controller” for brevity. The controller30may include analog circuitry and/or digital circuitry, such as a gate array and/or microprocessor-based instruction processing device.

Referring now to the illustration ofFIG. 2, the disk stack12typically includes a plurality of disks34, each of which may have a pair of disk surfaces36. The disks34are mounted on a cylindrical shaft and are rotated about an axis by the spindle motor14.

The actuator arm assembly18includes a plurality of the heads20, each of which is positioned to be adjacent to a different one of the disk surfaces36. Each head20is mounted to a corresponding one of the flexure arms22. The VCM28operates to move the actuator arm24, and thus moves the heads20across their respective disk surfaces36. The heads20are configured to fly on an air cushion relative to the data recording surfaces36of the rotating disks34while writing data to the data recording surface responsive to a write command from a host device or while reading data from the data recording surface to generate a read signal responsive to a read command from the host device.

FIG. 2further illustrates tracks and sectors on the disks34. Data is stored on the disks34within a number of concentric tracks40(or cylinders). Each track40is divided into a plurality of radially extending sectors42. Each sector is further divided into a plurality of data sectors defined between adjacent servo spokes. The servo spokes are used to, among other things, accurately position the head20so that data can be properly written onto and read from a selected track. The data sectors are where non-servo related data (i.e., host device data) is stored and retrieved.

FIG. 3illustrates exemplary servo information73that may be stored in at least some of the servo spokes within the radial sectors42. The servo information73can include a DC erase field100, a preamble field102, a servo address mark (SAM) field104, a track number field indicated by its least significant bits (LSBs)106, a spoke number field108, an entire track number field110which may be recorded in at least one of the servo spokes, and a servo burst field112of circumferentially staggered radially offset servo bursts (e.g., A, B, C, D servo bursts).

FIG. 4is a block diagram of a portion of the controller30of the disk drive10shown inFIG. 1that is communicatively connected to a host device60and configured to operate in accordance with some embodiments, and associated methods thereof. The controller30can include a data controller52, a servo controller53, a read write channel54, a buffer55, and an acceleration sensor56. Although the controllers52and53, the buffer55, the read write channel54, and the acceleration sensor56have been shown as separate blocks for purposes of illustration and discussion, it is to be understood that their functionality described herein may be integrated within a common integrated circuit package or distributed among more than one integrated circuit package. The head disk assembly (HDA)56can include a plurality of the disks34, a plurality of the heads20mounted to the actuator arm assembly18and positioned adjacent to different data storage surfaces of the disks34, the VCM28, and the spindle motor14.

Write commands and associated data from the host device60are buffered in the buffer55. The data controller52is configured to carry out buffered write commands by formatting the associated data into blocks with the appropriate header information, and transferring the formatted data from the buffer55, via the read/write channel54, to data sectors along one or more tracks on the disk34identified by the associated write command.

The read write channel54can operate in a conventional manner to convert data between the digital form used by the data controller52and the analog form conducted through the heads20in the HDA56. The read write channel54provides servo positional information read from the HDA56, such as from the exemplary servo information73ofFIG. 3, to the servo controller53. The servo positional information can be used to detect the location of the heads20in relation to target data sectors on the disks34. The servo controller53can use target data sectors from the data controller52and the servo positional information to seek the heads20to an addressed track and data sector on the disk34, and to attempt to maintain the heads20aligned with the track while data is written/read on one or more identified data sectors.

As explained above, when the disk drive10is subjected to shock and/or vibration, the heads20may be forced off-track. In particular, operational shock may result in large position errors over short periods of time. To avoid writing on an incorrect track(s) while the heads20are being forced off-track (e.g., to avoid loss of data and/or adjacent track erasure), the data controller52is configured to inhibit writing while the disk drive10is being subjected to a sizable shock condition and/or vibration condition.

The data controller52determines when to inhibit writing based on an acceleration signal generated by the acceleration sensor56. The acceleration sensor56is configured to generate an acceleration signal that is indicative of acceleration of the disk drive10. The acceleration sensor56may include, for example, one or more accelerometers, piezoelectric devices, and/or other devices.

In some embodiments, the data controller52determines when the disk drive is being subjected to a vibration condition and/or a shock condition based on the acceleration signal from the acceleration sensor56. The data controller52inhibits writing of data through the head20onto the disk34based on comparison of the acceleration signal to a threshold value. For example, the data controller52can inhibit writing of data when a magnitude of the acceleration signal exceeds the threshold value. The data controller52also varies the threshold value based on the determination of whether the disk drive10is being subjected to the vibration condition. The data controller52may enable resumption of writing of data when the magnitude of the acceleration signal falls below the threshold value, after expiration of a defined write inhibit time (e.g., after the head20reads a defined number of servo spokes), and/or when the head20has returned to its nominal position over the track.

The data controller52can lower the threshold value when the disk drive10is not being subjected to a vibration condition, and can raise the threshold value when the disk drive10is being subjected to a vibration condition. By lowering the threshold value in the absence of a vibration condition, the data controller52may be able to detect and react to a lower level shock condition that may otherwise not be detected if the threshold value were maintained at a higher level. Because lower level shock conditions may therefore be detected, the data controller52may be able to inhibit writing during such lower level shock conditions and may, therefore, avoid erroneous off-track writing and loss of data and/or allowing other erroneous operation of the disk drive10. By raising the threshold value during the occurrence of a vibration condition, the data controller52may avoid detecting and reacting to too many shock/vibration conditions, which may otherwise unnecessarily reduce the data input/output throughput of the disk drive10.

The data controller52can also be configured to distinguish between occurrence of a vibration condition and occurrence of a shock condition, and can respond differently to those two different types of conditions. Because a shock condition typically lasts for a much briefer time than a vibration condition, the data controller52may enable resumption of the writing of data through the heads20more quickly following occurrence of a shock condition following occurrence of a vibration condition. Accordingly, the disk drive10may resume normal operation more quickly following a properly identified shock condition, rather than waiting a longer delay time that may be defined based on an expected longer lasting vibration condition.

The data controller52may distinguish between occurrence of a vibration condition and occurrence of a shock condition based on characteristics of the acceleration signal and/or based on characteristics of position error signals generated by the heads20reading servo information from the disks34.

In some embodiments, the data controller52may determine that a vibration condition is occurring when a magnitude of the acceleration signal exceeds the threshold value for a least a threshold length of time, and may determine that a shock condition is occurring when the magnitude of the acceleration signal exceeds the threshold value for less than the threshold length of time, because shock conditions typically have a shorter duration than vibration conditions.

The data controller52may alternatively or additionally determine that a shock condition is occurring when the magnitude of the acceleration signal exceeds a shock threshold value that is greater than the threshold value, and may otherwise determine that a vibration condition is occurring (without a shock condition) when the magnitude of the acceleration signal exceeds the threshold value but is less than the shock threshold value.

The data controller52may alternatively or additionally determine that a shock condition is occurring when a position error signal, which is generated by a selected head20reading servo information from an associated disk34, exceeds a threshold position error signal while the magnitude of the acceleration signal exceeds the threshold value, and may similarly determined that a vibration condition (without a shock condition) is occurring when the position error signal is less than the threshold position error signal.

By distinguishing between occurrence of a vibration condition from occurrence of a shock condition, the data controller52may raise the threshold value in response to determining that a vibration condition is occurring while a shock condition is not occurring, and may leave the threshold value unchanged when both a vibration condition and a shock condition are simultaneously occurring. The data controller52may raise the threshold value during a vibration condition because of an ability of the disk drive10to compensate for vibration, and may maintain the threshold value as-is during a shock condition because of a substantially reduced ability of the disk drive10compensate for shock.

While the data controller52is inhibiting writing of data because of a vibration condition, in the absence of a shock condition, the threshold value may become sufficiently increased so that the acceleration signal no longer exceeds the threshold value, which can result in the data controller52enabling resumption of writing of data.

The data controller52may measure statistical characteristics of the acceleration signal, such as an average background level (e.g., mean magnitude), frequency content, number/rate of peaks values, and/or statistical deviation, and may define or otherwise vary the threshold value based on the measured characteristics. Because the servo controller53may compensate for vibration in some frequency bands better than others, the data controller52may define and/or adjust the threshold value based on the measured frequency content of the acceleration signal so as to respond to higher versus lower amounts of frequency content in certain bands. Thus, for example, the threshold value may be initially defined based on measured statistical characteristics of the acceleration signal. The threshold value may be increased while a vibration condition is occurring and a shock condition is not occurring, and may be decreased while neither a vibration condition nor a shock condition are occurring. Accordingly, the threshold value can be dynamically tuned so that the data controller52may identify and respond to lower-level shocks. The data controller52may additionally or alternatively define or otherwise vary the threshold value based on how often writing of data is inhibited responsive to the comparison of the acceleration signal to the threshold value. Thus, for example, the threshold value may be defined or varied to avoid an excessive number of inhibited writes during a defined period of time.

FIG. 5is an exemplary graph that shows variation of write inhibit threshold values in response to vibration and no-vibration conditions and associated detection of shock conditions in accordance with some embodiments of the present invention. Referring toFIG. 5, the write inhibit threshold value may be initially set to level502awhich can be determined during drive design and/or during verification test of the disk drive10, and may be refined during operation, such as based on measured statistical characteristics of the acceleration signal.

The write inhibit threshold value may be regulated (updated) once per calculation period, which may be, for example, once per disk revolution or once per sector42. For example, the write inhibit threshold value may be regulated so as to track variation in samples of the acceleration signal, or the variation in the sampled acceleration signal may be time filter (e.g., averaged) over a time period that may correspond to a sector42and used to regulate the write inhibit threshold value. Accordingly, the write inhibit threshold value may be incrementally varied once per acceleration signal sample, once per defined number of acceleration signal samples, once per sector42, once per disk revolution, and/or at another defined rate which may vary over time.

Before time t1, the disk drive10is not being subjected to a vibration condition and, responsive thereto, the threshold value is maintained at level502a. The level502ais defined to be sufficiently low to enable the data controller52to detect two low-level shock conditions, and, responsive thereto, to assert a write inhibit gate to inhibit writing when the respective acceleration signals504aand504bexceed the threshold value level502a.

At about time t1, the disk drive10is subjected to a vibration condition as indicated by the acceleration signal504c. The data controller52responds to the vibration condition by raising the threshold value to a higher level502c. During the time period t1to t2, the acceleration signal504cbriefly exceeds the threshold value which causes the write inhibit gate to be asserted for a defined time, after which write operations are not inhibited while the acceleration signal504cis less than the increased threshold502c. At time t2, disk drive10is no longer subjected to the vibration condition and the data controller52responds thereto by lowering the threshold value to a lower level502d. Subsequently, the disk drive10is subjected to a shock condition as indicated by the acceleration signal504d, which the data controller52can detect and respond to (e.g., by asserting the write inhibit gate to inhibit writing) because the acceleration signal504dexceeds the threshold value502d.

As illustrated, the duration of assertion of the write inhibit gate while the disk drive10is not subjected to a vibration condition (i.e., before time t1and after time t2) can be substantially less than the duration of the write inhibit gate during the vibration condition (i.e., between times t1and t2). The duration of assertion of the write inhibit gate may be defined so that the data controller52may resume writing data more quickly following occurrence of a shock condition than following occurrence of a vibration condition, because a shock condition typically lasts for a much briefer time than a vibration condition. The length of assertion of write inhibit gate may be determined during drive design, and/or during verification test of the disk drive10, and may be refined during operation.

Although some embodiments of the invention have been described with reference to a disk drive including a dual-stage actuator configuration, the disk drive may in some embodiments include a single actuator.

The foregoing discussion of the invention has been presented for purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings are within the scope of the present invention. The embodiments described hereinabove are further intended to explain the best mode presently known of practicing the invention and to enable others skilled in the art to utilize the invention in such or in other embodiments and with various modifications required by their particular application or use of the invention. It is intended that the appended claims be construed to include the alternative embodiments.