Data storage device reducing seek power consumption

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 6 0 - 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 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.

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

FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a disk comprising a plurality of tracks, a head, and an actuator configured to actuate the head over the disk.

FIG. 2B is a flow diagram according to an embodiment wherein after determining an adjusted seek time, an adjusted coast velocity and an adjusted coast time are determined based on the adjusted seek time and a power consumption of the seek.

FIG. 3A shows a driving current profile for the actuator based on a nominal seek time to seek the head from a first track to a second track on the disk.

FIG. 3B shows a driving current profile for the actuator according to an embodiment based on an adjusted seek time and based on a root-mean-square (RMS) power consumption of the seek.

FIG. 3C shows a driving current profile for the actuator according to an embodiment based on an adjusted seek time and based on a mean power consumption of the seek.

FIG. 4A illustrates an observed driving current profile according to an embodiment that is based on the adjusted coast velocity and the adjusted coast time.

FIG. 4B illustrates an observed velocity profile according to an embodiment that is based on the adjusted coast velocity and the adjusted coast time.

FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a disk 16 comprising a plurality of tracks 18 , a head 20 , and an actuator 22 configured to actuate the head 20 over the disk 16 . The disk drive further comprises control circuitry 24 configured to execute the flow diagram of FIG. 2B wherein an adjusted seek time to seek the head from a first track to a second track is determined (block 26 ), and an adjusted coast velocity and an adjusted coast time of the seek is determined based on the adjusted seek time and a power consumption of the seek (block 28 ) when a driving current applied to the actuator is substantially constant during at least one of an acceleration time and a deceleration time of the seek.

In the embodiment of FIG. 2A , a plurality of concentric servo tracks are defined by embedded servo sectors 30 0 - 30 N , wherein concentric data tracks 18 are defined relative to the servo tracks at the same or different radial density, and each data track comprises a plurality of data sectors (not shown). The control circuitry 24 processes a read signal 32 emanating from the head 20 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 24 filters the PES using a suitable compensation filter to generate a control signal 34 applied to a voice coil motor (VCM) 22 which rotates an actuator arm 36 about a pivot in order to actuate the head 20 radially over the disk 16 in a direction that reduces the PES. The control circuitry 24 may also generate a control signal applied to a microactuator (not shown) in order to actuate the head 20 over the disk 16 in fine movements. Any suitable microactuator may be employed, such as a piezoelectric actuator. In addition, the microactuator may actuate the head 20 over the disk 16 in any suitable manner, such as by actuating a suspension relative to the actuator arm, or actuating a slider relative to the suspension. The servo sectors 30 0 - 30 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 executing an access operation (write/read operation), the control circuitry 24 generates a driving current applied to the actuator (e.g., VCM 22 ) in order to seek the head 20 from a current track to a target track. The time required to perform the seek (seek time) depends on the driving current profile, which determines an acceleration, coast velocity, and deceleration profile of the seek. That is, the faster the acceleration/deceleration and the higher the coast velocity, the less time required to perform the seek. FIG. 3A shows a model of a nominal driving current profile applied to the actuator during a seek resulting in a nominal seek time T. The nominal driving current profile of FIG. 3A comprises a substantially constant acceleration segment (+a 1 ) for time t, a coast velocity for coast time t c , and a substantially constant deceleration segment (−a 1 ) for time t. If the seek is controlled based on the nominal driving current profile shown in FIG. 3A , the head 20 may arrive at the target track early such that there may be a rotational latency of the disk 16 before the target data sector reaches the head 20 . In addition, performing the seek based on the nominal driving current profile shown in FIG. 3A may consume more power than needed. Accordingly, in one embodiment the power consumption of a seek may be reduced by adjusting the seek time (e.g., increase the seek time by adding the rotation latency of a nominal seek) and then adjusting the coast velocity and the coast time based on the adjusted seek time and a power consumption of the seek.

The parameters of the nominal driving current profile of FIG. 3A may be defined by the following equations:

2* t+t c =T

a 1 *t*t c +a 1 *t 2 =S

V c =a 1 *t   (1)

where S represents the seek distance and V c represents the coast velocity. In an embodiment wherein the power consumption of the seek is based on root-mean-square (RMS) power, the seek power may be represented as:

P= 2* a 1 2 *t   (2)

and from equation (1) the seek power may be minimized by minimizing:

P = 2 * S 2 t * ( T - t ) 2 ( 3 )

The seek power based on the above equation (3) may be minimized based on:

∂ P ∂ t = - 2 * S 2 ⁡ ( T - 3 * t ) t 2 * ( T - t ) 3 ( 4 )

From equation (4), the optimal time for the acceleration/deceleration time t may be represented as:

t op = T 3 ( 5 )

The resulting minimum seek power consumption may be represented as:

P op = 27 * S 2 2 * T 3 ( 6 )

the resulting optimal driving current magnitude may be represented as:

a op = 9 * S 2 * T 2 ( 7 )

and the resulting optimal coast time may be represented as:

The above equations (1) through (8) derive the parameters for the optimal driving current profile when performing a seek operation based on the nominal seek time T as shown in FIG. 3A . If the seek time is increased by adding available rotational latency to the seek time, the adjusted seek time may be represented as:

T 2 =T+t la   (9)

where t la represents the available rotational latency of a nominal seek. Accordingly, when the seek time is adjusted to the new seek time T 2 , the optimal parameters of the driving current profile that will minimize the seek power consumption may be derived as follows. From equation (1), the coast velocity may be represented as:

V c = 2 * S T + t c ( 10 )

and the driving current magnitude represented as:

a 1 = 4 * S T 2 - t c 2 ( 11 )

Based on the above equations (1) and (3), the seek power consumption may be represented as:

P = 16 * S 2 ( T - t c ) ⁢ ( T + t c ) 2 ( 12 )

To make full use of the rotational latency t la , the coast velocity V c will be reduced with the constraint that the new driving current magnitude a 2 will be smaller than the nominal driving current magnitude a 1 to avoid exciting resonances (i.e., a 2 <a 1 ). From equation (11) the adjusted coast time t c2 may be represented as:

t c2 2 <T 2 2 −T 2 +t c 2   (13)

Another constraint is that the adjusted coast velocity V c2 be less than the nominal coast velocity V c (i.e., V c2 <V c ) and therefore from equation (10) the following condition must be satisfied:

t c2 >t c −t la   (14)

Accordingly, in one embodiment the adjusted coast time t c2 may be represented based on equation (8) as:

t c ⁢ ⁢ 2 = { T 2 3 if ⁢ ⁢ T 2 2 - T 2 + t c 2 ≥ ( T 2 3 ) 2 ⁢ ⁢ and ⁢ ⁢ T 2 3 > t c - t la T 2 2 - T 2 + t c 2 if ⁢ ⁢ ( T 2 2 - T 2 + t c 2 ) < ( T 2 3 ) 2 t c - t la Otherwise ( 15 )

The adjusted coast velocity V c2 may be represented based on equations (10) and (15) as:

V c ⁢ ⁢ 2 = { 3 ⁢ ⁢ S 2 ⁢ ⁢ T 2 if ⁢ ⁢ T 2 2 - T 2 + t c 2 ≥ ( T 2 3 ) 2 ⁢ ⁢ and ⁢ ⁢ T 2 3 > t c - t la 2 ⁢ ⁢ S T 2 + T 2 2 - T 2 + t c 2 if ⁢ ⁢ ( T 2 2 - T 2 + t c 2 ) < ( T 2 3 ) 2 V c Otherwise ( 16 )

The adjusted driving current a 2 may be represented based on equations (11), (15) and (16) as:

a 2 = { a 1 * 9 8 * T 2 - t c 2 T 2 2 if ⁢ ⁢ T 2 2 - T 2 + t c 2 ≥ ( T 2 3 ) 2 ⁢ ⁢ and ⁢ ⁢ T 2 3 > t c - t la a 1 if ⁢ ⁢ ( T 2 2 - T 2 + t c 2 ) < ( T 2 3 ) 2 a 1 * T - t c T 2 - t c + t la Otherwise ( 17 ) FIG. 3B shows an example driving current profile derived using the above equations based on minimizing a RMS power when the nominal seek time T for a given seek operation is increased to seek time T 2 by adding the available rotational latency t la .

In another embodiment, the seek power consumption may be minimized based on a mean power consumption which may be represented as:

P = 2 * a 1 * t T ( 18 )

From equations (1), (11) and (18) the seek power may be represented as:

P = 4 ⁢ ⁢ S T ⁡ ( T + t c ) ( 19 )

Therefore from equation (19), the longer the coast time, the less power will be consumed; however, the constraints of equation (13) and (14) still need to be satisfied. Accordingly, in one embodiment the adjusted coast time t c2 may be represented as:

t c2 =√{square root over ( T 2 2 −T 2 +t c 2 )}  (20)

the adjusted coast velocity V c2 may be represented as:

V c ⁢ ⁢ 2 = 2 ⁢ S T 2 + T 2 2 - T 2 + t c 2 ( 21 )

and the adjusted driving current may be represented as:

a 2 =a 1   (22)

FIG. 3C shows an example driving current profile derived using the above equations based on minimizing a mean seek power when the nominal seek time T for a given seek operation is increased to seek time T 2 by adding the available rotational latency t la .

In one embodiment, the control circuitry 24 may derive the adjusted coast velocity and the adjusted coast time (and optionally the adjusted driving current) based on the above equations using any suitable technique, such as implementing the equations directly, or implementing the results of the equations as a lookup table. In one embodiment, the adjusted driving current profiles such as shown in FIGS. 3B and 3C are a modeled representation of the actual driving current profile generated by the control circuitry 24 during a seek operation. The actual driving current profile may differ based on the servo algorithm employed, which may include a linear controller that forces one or more servo states to follow a servo state profile, and/or a non-linear controller (e.g., a sliding mode controller) which may be implemented, for example, during a settle operation. Accordingly, in one embodiment the adjusted coast velocity and the adjusted coast time (and optionally the adjusted driving current) derived using the above equations may be used to adjust one or more seek parameters of the servo control algorithm so that the resulting seek power is reduced (not necessarily minimized).

FIG. 4A illustrates an actual (observed) driving current profile 38 when executing a seek operation based on the nominal seek time T together with the actual (observed) driving current profile 40 after adjusting at least one seek parameter based on the adjusted seek time T 2 and the corresponding adjusted coast velocity and adjusted coast time as determined from the above equations. FIG. 4B shows a corresponding actual (observed) velocity profile 42 when executing a seek operation based on the nominal seek time T together with the actual (observed) velocity profile 44 after adjusting at least one seek parameter based on the adjusted seek time T 2 and the corresponding adjusted coast velocity and adjusted coast time as determined from the above equations. These figures illustrate that in one embodiment reducing the seek power by adjusting the seek parameter(s) based on the adjusted seek time T 2 and the corresponding adjusted coast velocity and adjusted coast time as determined from the above equations results in a reduced coast velocity and an increased coast time.

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.

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.