Data storage device employing spindle motor driving profile during seek to improve power performance

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional U.S. Patent Application Ser. No. 62/160,564, filed on May 12, 2015, which is hereby incorporated by reference in its entirety.

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 track 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 track 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.

The disk 2 is typically rotated by a spindle motor at a high speed so that an air bearing forms between the head and the disk surface. A commutation controller applies a driving signal to the windings of the spindle motor using a particular commutation sequence in order to generate a rotating magnetic field that causes the spindle motor to rotate. Prior art disk drives have typically controlled the commutation of the windings by measuring a zero-crossing frequency of a back electromotive force (BEMF) voltage generated by the windings of the spindle motor. Prior art disk drives may also utilize the BEMF voltage generated by the spindle motor as a power source during power failure to assist with power down operations, such as unloading the head onto a ramp.

BRIEF DESCRIPTION OF THE DRAWINGS

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 head actuated over a disk, and a spindle motor configured to rotate the disk.

FIG. 2B is a flow diagram according to an embodiment wherein during a seek operation to seek the head a seek length, an amplitude of the periodic driving voltage applied to the windings of the spindle motor is adjusted according to a driving profile corresponding to the seek length, wherein the driving profile compensates for a power disturbance during the seek operation.

FIG. 3 shows control circuitry according to an embodiment comprising a spindle control block, a commutation controller, commutation logic, and a voltage regulator configured to generate a power voltage for powering the spindle motor based on a supply voltage received from a host.

FIG. 4A illustrates an example of a power disturbance during a seek operation due to a voice coil motor (VCM) moving the head to a target track.

FIG. 4B illustrates an example driving profile for adjusting the amplitude of the periodic driving voltage applied to the windings of the spindle motor to compensate for the power disturbance during the seek.

FIG. 5A illustrates an example of a power disturbance during a seek operation due to a voice coil motor (VCM) unloading the head onto a ramp.

FIG. 5B illustrates an example driving profile for adjusting the amplitude of the periodic driving voltage applied to the windings of the spindle motor to compensate for the power disturbance during the seek (unload operation).

FIG. 6A shows a data storage device in the form of a disk drive according to an embodiment comprising a head actuated over a disk, a spindle motor configured to rotate the disk, and a non-volatile semiconductor memory (NVSM).

FIG. 6B is a flow diagram according to an embodiment wherein during a seek operation to seek the head a seek length, an amplitude of the periodic driving voltage applied to the windings of the spindle motor is adjusted according to a driving profile corresponding to the seek length, wherein the driving profile compensates for a power disturbance due to accessing the NVSM during the seek operation.

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, and a spindle motor 20 configured to rotate a disk 18, wherein the spindle motor 20 comprises a plurality of windings. The disk drive further comprises control circuitry 22 configured to execute the flow diagram of FIG. 2B, wherein the windings of the spindle motor are commutated based on a commutation sequence while applying a periodic driving voltage 24 to each winding (block 26). During a seek operation to seek the head a seek length (block 28), an amplitude of the periodic driving voltage 24 is adjusted according to a driving profile corresponding to the seek length (block 30), wherein the driving profile compensates for a power disturbance during the seek operation. A seek operation may include a track seek operation where the head is moved from one track to another, an unload operation where the head is moved from the disk to the ramp, and a load operation where the head is moved from the ramp to the disk.

In the embodiment of FIG. 2A, the disk 18 comprises a plurality of servo sectors 32₀-32_N that define a plurality of servo tracks 34, wherein data tracks are defined relative to the servo tracks at the same or different radial density. The control circuitry 22 processes a read signal 36 emanating from the head 16 to demodulate the servo sectors 32₀-32_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. A servo control system in the control circuitry 22 filters the PES using a suitable compensation filter to generate a control signal 38 applied to a voice coil motor (VCM) 40 which rotates an actuator arm 41 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 32₀-32_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 (FIG. 1).

FIG. 3 shows control circuitry 22 according to an embodiment wherein a back electromotive force (BEMF) voltage 42 generated by the windings of the spindle motor 20 may be processed in order to drive the commutation sequence of a commutation controller 44. A spindle control block 46 may process a BEMF signal 48 which may be a square wave representing the BEMF zero-crossings as detected by a BEMF detector 50. The commutation controller 44 may generate a control signal 52 which configures the BEMF detector 50 to detect the zero-crossing of the BEMF voltage generated by each winding as the disk rotates. The commutation controller 44 also generates a control signal 54 applied to commutation logic 56. In the embodiment of FIG. 3, the commutation logic 56 is configured by the control signal 54 to control the state of switches 58 in order to drive the windings with driving voltages +V and −V. The commutation logic 56 may operate in any suitable manner, such as by driving the switches 58 as linear amplifiers that apply continuous-time sinusoidal voltages to the windings. In another embodiment, the commutation logic 56 may drive the switches 58 using pulse width modulation (PWM), such as using square wave PWM, trapezoidal PWM, or sinusoidal PWM. Regardless as to how the windings are driven, the commutation controller 44 generates the control signal 54 so that the windings are commutated at the correct periods, thereby generating the desired rotating magnetic field that causes the spindle motor to rotate. In one embodiment, the spindle control block 46 may generate a control signal 60 that controls the effective amplitude of the periodic driving voltage applied to the windings (continuous or PWM), thereby controlling the speed of the spindle motor 20. A voltage regulator 62 generates a power voltage Vpwr 64 based on a supply voltage 66 received from a host, wherein the power voltage Vpwr 64 is configured to power the spindle motor 20.

In one embodiment, it may be desirable to limit the power consumption of the disk drive, such as by minimizing at least one of an average power consumption, peak power consumption, and root-mean-square power consumption in order, for example, to satisfy the host specified power constraints of the supply voltage 66. As described in greater detail below, the disk drive may exhibit a high power demand during seek operations due to the power consumed by the VCM 40 when rotating the actuator arm 41, including during load/unload operations. Accordingly, in one embodiment the periodic driving voltage applied to the spindle motor 20 may be adjusted according to a driving profile that compensates for a power disturbance during the seek operation, such as the power consumed by the VCM 40. In this manner, the seek operations may be executed with the desired performance without violating the power constraints of the supply voltage 66.

In one embodiment, the total average power loss may be represented as the sum of the power consumed by the voltage regulator 62 (FIG. 3) and the power consumed by the various components of the disk drive:
P_tot=P_supply+P_drive
In one embodiment, the average power consumed by the voltage regulator may be based on the lumped resistance R (e.g., switching FET, inductor, line resistance, and battery):
P_supply=Ri_RMS²P_supply=Ri_RMS².
In one embodiment, the average power consumed by the components of the disk drive P_drive=v_drivei_avg may be represented as:
P_drive=V_pwri_avg
since V_pwr 64 is held substantially constant by the voltage regulator. Therefore, the total average power loss is dependent on the average and RMS drive current:
P_tot=Ri_RMS²+V_pwri_avg
In one embodiment, the drive current may be represented as:

i drive ⁡ ( t ) = P spindle ⁡ ( D A ⁢ ⁢ C ) + P disturbance ⁡ ( t ) V drive
where P_spindle(D_AC) represents the power consumed by the spindle motor at a given amplitude of the driving voltage, and P_disturbance(t) represents a power disturbance during a seek operation, such as the power consumed by the VCM 40 during a seek operation. Accordingly, in one embodiment the amplitude of the driving voltage is adjusted (by adjusting a digital-to-analog converter setting D_AC) according to a driving profile that compensates for the power disturbance during the seek operation.

In one embodiment, the driving profile for the spindle motor is generated so as to minimize the average power consumption during a seek operation. In one embodiment, the driving profile for the spindle motor adjusts the speed of the spindle motor during the seek, but ensures the ending rotation speed of the spindle motor substantially matches the starting rotation speed. In this manner, at the end of the seek operation the disk is rotating at an access rotation speed so that the disk may be accessed (during write/read operations). Accordingly, in one embodiment a power consumption constraint is satisfied while also satisfying the following constraints:

RPM ⁡ ( end ) = RPM ⁡ ( start ) ∂ RPM ⁡ ( end ) ⅆ t = 0 min ⁢ ⁢ DAC < D A ⁢ ⁢ C < max ⁢ ⁢ DAC  i phase  < max ⁢ ⁢ i phase  v phase  < max ⁢ ⁢ v phase
where RPM represents the spindle rotation speed, i_phase represents an amplitude of current flowing through a winding of the spindle motor and v_phase represents an amplitude of the driving voltage across the winding. In one embodiment, the limit values in the above constraints are determined by the disk drive specifications.

In one embodiment, the optimization is done over the disturbance period during the seek operation. All values are represented as a vector of samples for each servo sector (wedge) in the disturbance period. For example, drive current can be represented as:
i_drive=[i_drive(wedge 1),i_drive(wedge 2) . . . i_drive(end wedge)]^T.
Rewriting the above equations using these vectors:
P_tot=Ri_drive^Ti_drive+v_drive^eTi_drive
i_drive=P_spindle+P_disturbance/v_drive

• • e=[11 . . . 1]^T of appropriate length representing the disturbance period.

Gradients:

∂ P _ tot ∂ D A ⁢ ⁢ C = ⁢ ( 2 ⁢ ⁢ R ⁢ ⁢ i drive T + v drive ⁢ e T ) ⁢ ∂ i drive ∂ D A ⁢ ⁢ C ∂ i drive ∂ D A ⁢ ⁢ C = ⁢ 1 / v drive ⁢ ∂ P spindle ∂ D A ⁢ ⁢ C
Spindle Power Model:
P_spindle=i_phase·*v_phase
v_phase=[v_phaseA^Tv_phaseB^Tv_phaseC^T]^T
i_phase=[i_phaseA^Ti_phaseB^Ti_phaseC^T]^T

Gradient:

∂ P spindle ∂ D A ⁢ ⁢ C = i phase ⁢ e T · * ∂ v phase ∂ D A ⁢ ⁢ C + v phase ⁢ e T · * ∂ i phase ∂ D A ⁢ ⁢ C
Spindle Phase Model

v phaseX ⁡ ( t ) = v BEMF , X + R phase ⁢ i phase ⁢ ⁢ X ⁡ ( t ) + L phase ⁢ ⅆ i phase , X ⁡ ( t ) ⅆ t H phase , X ⁡ ( s ) = i phase , X v phase , X - v BEMF , X ⁢ ( s ) = 1 R phase + L phase ⁢ S
h_phase,x(n) is the discrete time impulse response of H_phase,x(s) found using the bilinear transform.

H phase , X = [ h phase , X ⁡ ( 0 ) 0 0 0 h phase , X ⁡ ( 1 ) h phase , X ⁡ ( 0 ) 0 0 ⋮ h phase , X ⁡ ( 1 ) h phase , X ⁡ ( 0 ) 0 h phase , X ⁡ ( end ) … h phase , X ⁡ ( 1 ) h phase , X ⁡ ( 0 ) ]

i phase = H phase ⁡ ( v phase - v phase ⁢ ⁢ 0 ) + i phase ⁢ ⁢ 0 H phase = [ H phase , X 0 0 0 H phase , X 0 0 0 H phase , X ] v phase ⁢ ⁢ 0 = [ v phase ⁢ ⁢ A ⁢ ⁢ 0 T ⁢ ⁢ v phase ⁢ ⁢ B ⁢ ⁢ 0 T ⁢ ⁢ v phase ⁢ ⁢ C ⁢ ⁢ 0 T ] T ⁢ ⁢ Nominal ⁢ ⁢ Phase ⁢ ⁢ Voltage i phase ⁢ ⁢ 0 = [ i phase ⁢ ⁢ A ⁢ ⁢ 0 T ⁢ ⁢ i phase ⁢ ⁢ B ⁢ ⁢ 0 T ⁢ ⁢ i phase ⁢ ⁢ C ⁢ ⁢ 0 T ] T ⁢ ⁢ Nominal ⁢ ⁢ Phase ⁢ ⁢ current

Gradient:

∂ i phase ∂ D A ⁢ ⁢ C = H phase ⁢ ∂ v phase ∂ D A ⁢ ⁢ C
Spindle DAC Model:

v phase = A ⁢ ⁢ D A ⁢ ⁢ C A = Max ⁢ ⁢ DacFF Max ⁢ ⁢ DAC ⁢ 3 ⁡ [ diag ⁡ [ sin ⁡ ( w e ⁢ t + ϕ Torque + ϕ A ) ] diag ⁡ [ sin ⁡ ( w e ⁢ t + ϕ Torque + ϕ B ) ] diag ⁡ [ sin ⁡ ( w e ⁢ t + ϕ Torque + ϕ C ) ] ] ⁢

• • MaxDacFF: Max Spindle DAC FF ADC voltage
  • w_e: electrical frequency [rad/s]
  • φ_Torque: Torque Optimizer Electrical angle

Gradient:

∂ v phase ∂ D A ⁢ ⁢ C = A
Spindle Torque Model:

τ ⁡ ( t ) = k t ⁢ ∑ sin ⁡ ( w e ⁢ t + ϕ phase , X ) ⁢ i phase , X ⁡ ( t ) τ = B ⁢ ⁢ i phase B = k t ⁡ [ diag ⁡ [ sin ⁡ ( w e ⁢ t + ϕ A ) ] ⁢ ⁢ diag ⁡ [ sin ⁡ ( w e ⁢ t + ϕ B ) ] ⁢ ⁢ diag ⁡ [ sin ⁡ ( w e ⁢ t + ϕ C ) ] ] k t = k e , peak ⁢ 60 1000 * 2 ⁢ π * 3 : Peak ⁢ ⁢ phase ⁢ ⁢ Kt ⁢ [ N - m / A ]
Spindle Speed Model:

J ⁢ ⅆ w RPM ⅆ t ⁢ ( t ) = - β ⁢ ⁢ w RPM ⁡ ( t ) + τ ⁡ ( t ) H RPM ⁡ ( s ) = w RPM τ ⁢ ( s ) = 1 β + J ⁢ ⁢ S
h_RPM(n) is the discrete time impulse response of H_RPM(s) found using the bilinear transform.

H RPM = [ h RPM ⁡ ( 0 ) 0 0 0 h RPM ⁡ ( 1 ) h RPM ⁡ ( 0 ) 0 0 ⋮ h RPM ⁡ ( 1 ) h RPM ⁡ ( 0 ) 0 h RPM ⁡ ( end ) … h RPM ⁡ ( 1 ) h RPM ⁡ ( 0 ) ]
w_RPM=H_RPM(τ−τ₀)+w_RPMO

In one embodiment, the above equations may be solved using any suitable numerical computing program (e.g., using MATLAB) so as to satisfy any suitable power consumption constraint, such as minimizing one of the average power consumption, peak power consumption, or root-mean-square (RMS) power consumption of the disk drive during a seek operation as well as satisfy the above constraint that the rotation speed of the spindle motor at the end of the seek substantially match the rotation speed at the start of the seek. In one embodiment, the above equations may be solved to achieve a target weighting of at least two of an average power consumption, a peak power consumption, and a root-mean-square (RMS) power consumption of the data storage device during the seek.

FIGS. 4A and 4B illustrate a solution to the above equations for the driving profile (FIG. 4B) that substantially minimizes the average power consumption of the disk drive for a particular seek length when seeking the head to a target track. As shown in FIG. 4A, the power disturbance (PWR DIST) waveform during the seek is due to the power consumed by the VCM 40 during an acceleration phase, coast phase, and deceleration phase. If the rotation speed of the spindle motor 20 were maintained at the access rotation speed during the seek, the power consumed by the spindle motor 20 as well as the VCM 40 may exceed the constraints on the supply voltage 66. Since the disk 18 is not accessed during a seek (other than to read the servo sectors 32₀-32_N), in one embodiment the rotation speed of the spindle motor 20 is adjusted by the driving profile shown in FIG. 4B in order to reduce the power consumed by the spindle motor 20 during the seek. In the example shown in FIG. 4A, the driving profile brakes the spindle motor 20 so as to extract power from the spindle motor 20 during at last part of the seek (acceleration phase in this example). That is, not only is the power consumed by the spindle motor 20 reduced, in one embodiment the driving profile may cause the spindle motor 20 to generate power for the VCM 40 during at least part of the seek which further reduces the power extracted from the supply voltage 66. In this example, the driving profile shown in FIG. 4B substantially minimizes the average power waveform (AVE PWR) in FIG. 4A.

Although as shown in FIG. 4A the driving profile adjusts the rotation speed (RPM) of the spindle motor 20 during the seek (and therefore reduces the power consumption during the seek), the above equations are solved so that the driving profile ensures the ending rotation speed at the end of the seek substantially matches the starting rotation speed at the beginning of the seek. This ensures that at the end of the seek the disk 18 is rotating at the access rotation speed required to access the disk, thereby avoiding any latency (or slipped disk revolutions) that would otherwise occur while waiting for the spindle motor 20 to re-acquire the access rotation speed.

The driving profile shown in the example of FIG. 4B corresponds to a particular seek length; that is, the power disturbance (PWR DIST) waveform shown in FIG. 4A will have a particular shape for each seek length. Accordingly, in one embodiment the above equations are solved for a plurality of different seek lengths and the resulting driving profiles stored in memory (e.g., on the disk 18). When the control circuitry executes a seek having a particular seek length, the corresponding driving profile is retrieved from memory and applied to the spindle motor 20 during the seek. In one embodiment, the driving profile may be generated and stored for a plurality of discrete seek lengths at any suitable resolution, and then intermediate driving profiles may be generated on-the-fly through interpolation.

In one embodiment, the above equations are solved to generate a stepped driving profile, wherein each step (sample value) in the driving profile corresponds to a servo sector on the disk 18. That is, during a seek operation the control circuitry adjusts the amplitude of the driving voltage applied to the spindle motor 20 at each servo sector based on the corresponding step value stored in the driving profile. However, the above equations may be modified to generate the driving profile at a finer/coarser resolution than the servo sector frequency. In other embodiments, the control circuitry may include circuitry for smoothing the amplitude of the driving voltage between the step values specified by the driving profile.

In one embodiment such as shown in FIG. 2A, the control circuitry 22 may load the head 16 from a ramp 68 onto the disk 18 (after the disk is rotating), and then unload the head 16 onto the ramp 68 (e.g., when the disk drive is powered down or idled). In one embodiment, the seek length referred to at block 30 of FIG. 2B may comprise the distance the head 16 travels during a load and/or unload operation. That is, in one embodiment the power disturbance associated with a load and/or unload operation may be known and therefore a driving profile for the spindle motor 20 may be generated based on the above equations in order to achieve any suitable power consumption constraint during the load and/or unload operation. An example driving profile and corresponding power/RPM waveforms for an unload operation is illustrated in FIGS. 5A and 5B.

In the example unload operation shown in FIGS. 5A and 5B, the control circuitry 22 first seeks the head 16 to an outer diameter track, and then unloads the head 16 onto the ramp 68 from the outer diameter track. While the head 16 is served over the outer diameter track, the driving profile shown in FIG. 5B increases the rotation speed of the spindle motor 20 before moving (accelerating) the head 16 toward the ramp 68. In this embodiment, increasing the rotation speed of the spindle motor 20 increases its kinetic energy so that when the head 16 contacts the ramp 68 the resulting spike in the power disturbance shown in FIG. 5A may be compensated by supplementing the power to the VCM 40 from the spindle motor 20 rather than from the supply voltage 66. In one embodiment when executing a seek operation (e.g., an unload operation), the driving profile such as shown in FIG. 5B is configured to increase the rotation speed of the spindle motor above an access speed used to access the disk by at least twice a maximum jitter error, where the maximum jitter error represents the maximum deviation of the rotation speed from the target access speed when accessing the disk. For example, in one embodiment a write operation to the disk may be aborted if the rotation speed deviates from the target access speed by a maximum jitter error of 0.02% of the access speed. Therefore in one embodiment when executing a seek operation (e.g., an unload operation), the rotation speed may be increased by at least 0.04% of the access speed in order to increase the kinetic energy of the spindle motor. The rotation speed of the spindle motor may be increased by any suitable amount, and in one embodiment the rotation speed may be increased by not more than 20% of the access speed.

The driving profile for the spindle motor 20 may be generated by solving the above equations in order to compensate for any known power disturbance in the disk drive. FIG. 6A shows an embodiment wherein the disk drive may comprise a non-volatile semiconductor memory (NVSM) 70, such as a flash memory, which may induce a power disturbance if accessed during a seek operation. Accordingly, in an embodiment illustrated by the flow diagram of FIG. 6B, if the NVSM 70 is accessed during a seek operation (block 72), the driving profile may be generated based on the above equations to compensate for the corresponding power disturbance (block 74) similar to the embodiments described above.

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.