Data storage device adjusting seek profile based on seek length when ending track is near ramp

Description

BACKGROUND

Data storage devices such as 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 6₀-6_N recorded around the circumference of each servo track. Each servo sector 6_i 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 6_i 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 data 12 and 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 tracks defined by servo sectors.

FIG. 2A shows a data storage device in the form of a disk drive comprising a head actuated over a disk and a load/unload ramp.

FIG. 2B is a flow diagram according to an embodiment wherein when seeking the head a seek length from a starting track to an ending track, control circuit is configured to adjust a seek profile when the seek length is greater than a first threshold and the ending track is within a second threshold of a load/unload ramp.

FIG. 3A illustrates a “no man's land” area of a phase plane that is avoided during seek operations to avoid damaging the head during an emergency unload operation according to an embodiment.

FIG. 3B shows the entire seek space for the disk drive, including the seeks wherein the seek profile is adjusted to avoid the “no man's land” area illustrated in FIG. 3A.

FIG. 4 is a flow diagram according to an embodiment wherein the seek profile may be adjusted by enforcing a minimum latency for the seek profile, or by decreasing a deceleration slope for the seek profile, or by employing any other suitable technique.

DETAILED DESCRIPTION

FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a head 16 actuated over a disk 18 comprising a plurality of tracks 20, and a load/unload ramp 22. The disk drive further comprises control circuitry 24 configured to execute the flow diagram of FIG. 2B, wherein when seeking the head a seek length from a starting track to an ending track (block 26), the control circuit 24 is configured to adjust a seek profile (block 32) when the seek length is greater than a first threshold (block 28) and the ending track is within a second threshold of the load/unload ramp (block 30). The control circuitry 24 executes the seek based on the adjusted seek profile (block 34).

In the embodiment of FIG. 2A, the disk 18 comprises a plurality of servo tracks 20 defined by servo sectors 36₀-36_N, wherein data tracks are defined relative to the servo tracks at the same or different radial density. The control circuitry 24 processes a read signal 38 emanating from the head 16 to demodulate the servo sectors 36₀-36_N 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 24 filters the PES using a suitable compensation filter to generate a control signal 40 applied to a voice coil motor (VCM) 42 which rotates an actuator arm 44 about a pivot in order to actuate the head 16 radially over the disk 18 in a direction that reduces the PES. The servo sectors 36₀-36_N 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.

When the disk drive is powered down or in an idle mode, the head 16 is parked on the load/unload ramp 22 which in the embodiment of FIG. 2A is mounted so as to extend over an outer edge of the disk 18. When the disk drive is powered on, the disk 18 is spun up to an operating speed and the head 16 is “loaded” from the ramp 22 over the spinning disk 18. If a power failure occurs, the control circuitry 24 may execute an emergency “unload” operation wherein the head 16 is retracted toward and then onto the ramp 22. In one embodiment, the momentum of the disk 18 spinning generates a back electromotive force (BEMF) voltage across the windings of a spindle motor that rotates the disk 18, and this BEMF voltage may be used to drive the VCM 42 to execute the unload operation. In one embodiment, if a power failure occurs during a normal seek operation while the head is seeking toward the ramp 22 and the head 16 is within a threshold distance from the ramp 22 when the power failure occurs, the emergency unload operation may be unable to control the speed of the head 16 as it approaches the ramp 22, resulting in damage to the head 16 when it contacts the ramp 22.

FIG. 3A is a phase plane representing a position of the head 16 and a velocity of the head 16 during a seek operation. A seek profile may be defined in the phase plane from a starting track to an ending track (in this example the ending track is the first track near the ramp 22), wherein the control circuitry 24 may generate the control signal 40 applied to the VCM 42 so that the position/velocity states follow the seek profile. As illustrated in FIG. 3A, in one embodiment the shape of the seek profile, including an amplitude of a coast velocity, may depend on the seek length. FIG. 3A also shows a boundary line 45 that defines a “no man's land” area 46 in the phase plane where the head 16 may be damaged if the position/velocity states are within this area during a seek operation and a power failure occurs requiring an emergency unload. Accordingly, in one embodiment the seek profile for seeking the head from a starting track to an ending track is adjusted (e.g., before or during a seek operation) so that the position/velocity states avoid the “no man's land” area 46 shown in FIG. 3A. Referring to the example seek profiles shown in FIG. 3A, the seek profile 48A does not extend into the “no man's land” of the phase plane and so the seek profile 48A need not be adjusted. However, seek profiles 48B and 48C do extend into the “no man's land” and so in one embodiment these seek profiles are adjusted to avoid this area of the phase plane.

In one embodiment, whether the seek profile needs adjusting and the extent of the adjusting is determined based on the seek length as well as the distance that the ending track of the seek is from the load/unload ramp 22. An example of this embodiment is illustrated in FIG. 3B which is a seek space showing all possibilities of the starting track and the ending track for any given seek (the x-axis represents the starting track and the y-axis represents the ending track). The diagonal line 50 represents a zero length seek due to the starting track being equal to the ending track. The diagonal line 52 represents a constant length seek due to the distance between the starting track and ending track being equal as both the starting track and ending track shifting away from the ramp 22. The area 54A of the seek space shown in FIG. 3B defined by line 54B represents the seek lengths and the ending tracks near the ramp 22 where the seek profile needs adjustment to avoid the “no man's land” shown in FIG. 3A. For example, the point 56 of the seek space which is in area 54A represents a particular ending track (y-axis) for a seek length defined by the corresponding starting track (x-axis). If the ending track is shifted away from the ramp 22 by the delta (Δ) shown in FIG. 3B, the point 56 would shift out of the area 54 so that no adjustment to the seek profile would be needed. Accordingly, in one embodiment the seek profile is adjusted based on the delta (Δ), wherein the adjustment may be proportional or any other suitable function of the delta (Δ).

FIG. 4 is a flow diagram according to an embodiment for determining when an adjustment to the seek profile is needed to avoid the “no man's land” of FIG. 3A. When seeking the head (block 58) from a starting track (st) to an ending track (et), the starting track (st) is compared to a first threshold track (s0) (block 60), wherein the first threshold track (s0) is shown in the example of FIG. 3B. If the starting track (st) of the seek is less than the first threshold track (s0), then the seek length will always be short enough so that the seek profile will avoid the “no man's land” of FIG. 3A, and therefore no adjustment to the seek profile is needed. If the starting track (st) of the seek is greater than the first threshold track (s0) at block 60, then the starting track (st) is compared to a second threshold track (s1) (block 62), wherein the second threshold track (s1) is shown in the example of FIG. 3B. If the starting track (st) is greater than the second threshold track (s1) at block 62, then the starting track (st) is set equal to the second threshold track (block 64). If the inequality shown in block 66 is true (where e0 is a third threshold track shown in FIG. 3B), it means an adjustment to the seek profile is needed (block 68) in order to avoid the “no man's land” of FIG. 3A. The seek profile may be adjusted at block 68 in any suitable manner that will result in the seek profile avoiding the “no man's land” of FIG. 3A, such as by enforcing a minimum latency for the seek profile (which may decrease the coast velocity of the seek profile), or by decreasing a deceleration slope for the seek profile, or by employing any other suitable technique. The seek is then performed at block 70 using either the unadjusted or the adjusted seek profile.

As described above, in one embodiment a parameter of the seek profile may be adjusted at block 68 of FIG. 4 based on the delta (Δ) between the ending track (et) of the seek and the line 54B representing the border of the adjustment area 54A shown in FIG. 3B. The adjustment to the seek parameter may be proportional to the delta (Δ), or any other suitable function of the delta (Δ). In one embodiment, the “no man's land” area 46 shown in FIG. 3A may be determined based on the amount of power that may be provided by the BEMF voltage of the spindle motor during an emergency unload operation.

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.