Data storage device having multirate excitation and notch filter calibration based on error cancellation - Patents.com

Abstract

To provide a data storage device enhancing fine control of an actuator system and preventing instability in a servo control loop.SOLUTION: An actuator mechanism control system 300 comprises: one or more disks; an actuator mechanism configured to position one or more heads proximate to one or more disk surfaces of the one or more disks; and one or more processing devices comprising a closed-loop multi-rate error rejection transfer function (mrETF) control system configured to control the actuator mechanism. The one or more processing devices are configured to: output a multi-rate excitation to at least one multi-rate notch filter of the actuator mechanism control system; detect a frequency response of the actuator mechanism in response to the multi-rate excitation; and calibrate the at least one multi-rate notch filter of the actuator mechanism control system, based at least in part on the detected frequency response of the actuator mechanism.SELECTED DRAWING: Figure 3

Description

[Background technology]

[0001] A data storage device such as a disk drive comprises a disk and a head connected to a distal end of an actuator arm that 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 wedges or servo sectors. The servo sectors comprise head positioning information (e.g., track addresses) that is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.

[0002] FIG. 1 shows servo wedges 60-66 recorded around the circumference of each servo track. N 1 shows a prior art disk format 2 with multiple radially spaced concentric servo tracks 4 defined by servo wedges 6. A number of concentric data tracks are defined about the servo tracks 4, and the data tracks may have the same or a different radial density (e.g., tracks per inch (TPI)) as the servo tracks 4. Each servo wedge 6 i comprises a preamble 8 for storing a periodic pattern that allows proper gain adjustment and timing synchronization of the read signal, and a synchronization mark 10 for storing a special pattern used for symbol synchronization to the servo data fields 12. The servo data fields 12 store coarse head positioning information, such as a servo track address, that is used to position the head over a target data track during seek operations. Each servo wedge (e.g., servo wedge 64) further comprises a group of phase-based servo bursts 14 (e.g., N and Q servo bursts), which are recorded at a predetermined phase with respect to each other and with respect to the servo track centerline.

[0003] The coarse head positioning information is processed to position the head over a target data track during seek operations, and the servo bursts 14 provide fine head positioning 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, the PES representing the measured position of the head relative to the centerline of the target servo track. A servo controller processes the PES to generate control signals that are applied to one or more head actuators to actuate the head radially over the disk in a direction that reduces the PES. In some examples, the one or more head actuators may comprise a voice coil motor and one or more fine actuators. Summary of the Invention

[0004] Various examples disclosed herein provide a data storage device such as a hard disk drive having a control circuit that can calibrate a notch filter based on a generated multi-rate excitation. In various examples, the control circuit can inject a multi-rate excitation into an actuator control system (single actuator or multi-actuator), identify a resonant frequency in response to the multi-rate excitation, and use the detected resonant frequency in response to the multi-rate excitation to calibrate an error rejection transfer function (ETF) peak detection, including a multi-rate error rejection transfer function (mrETF). This may include detecting a true resonant frequency above the Nyquist frequency of the system, as distinguished from an alias frequency response below the Nyquist frequency. The hard disk drive control circuit in the examples of the present disclosure may enable the application of a notch filter that is custom calibrated for a particular disk drive, thereby improving fine control of the actuator system, facilitating high data density, and preventing instabilities in the servo control loop, among other advantages.

[0005] Various exemplary aspects relate to a data storage device comprising one or more disks, an actuator mechanism configured to position one or more heads proximate one or more disk surfaces of the one or more disks, and one or more processing devices comprising an actuator mechanism control system configured to control the actuator mechanism, the one or more processing devices configured to output a multi-rate excitation to at least one multi-rate notch filter of the actuator mechanism control system, detect a frequency response of the actuator mechanism in response to the multi-rate excitation, and calibrate the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism.

[0006] Various exemplary aspects relate to a method. The method includes outputting, by one or more processing devices, a multi-rate excitation to at least one multi-rate notch filter of an actuator mechanism control system configured to position one or more heads proximate one or more disk surfaces of a data storage device. The method further includes detecting, by the one or more processing devices, a frequency response of the actuator mechanism in response to the multi-rate excitation. The method further includes calibrating, by the one or more processing devices, the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism.

[0007] Various exemplary aspects relate to one or more processing devices comprising means for outputting a multi-rate excitation to at least one multi-rate notch filter of an actuator mechanism control system configured to control an actuator mechanism, the actuator mechanism being configured to position one or more heads proximate to one or more disk surfaces. The one or more processing devices further comprise means for detecting a frequency response of the actuator mechanism in response to the multi-rate excitation. The one or more processing devices further comprise means for calibrating the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism.

[0008] Various additional aspects are illustrated in and will become more apparent from the accompanying drawings and the following description. [Brief description of the drawings]

[0009] Various features and advantages of the techniques of the present disclosure will become apparent from the following description of specific examples of those techniques and as illustrated in the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed on illustrating the principles of the technical concepts. In the drawings, like reference characters may refer to the same parts throughout the different views. The drawings depict only illustrative examples of the present disclosure and are not limiting in scope. [Figure 1] 1 illustrates a prior art disk format that includes multiple radially spaced concentric servo tracks defined by servo wedges recorded around the circumference of each servo track. [Figure 2A] 1A-1D show conceptual block diagrams of top and side views of a data storage device in the form of a disk drive according to an aspect of the present disclosure. [Figure 2B] 1A-1D show conceptual block diagrams of top and side views of a data storage device in the form of a disk drive according to an aspect of the present disclosure. [Figure 2C]1 shows a flowchart of an exemplary method that a control circuit of a disk drive may implement or execute in controlling operation of the disk drive, including calibrating at least one multi-rate notch filter of an actuator mechanism control system based at least in part on a detected frequency response of the actuator mechanism, in accordance with an aspect of the present disclosure. [Diagram 3] 1 illustrates an actuator mechanism control system with a closed-loop multi-rate error rejection transfer function (mrETF) control system according to an example of the present disclosure. [Figure 4] 13 shows a graph illustrating combinations of frequencies of excitation signals that an actuator mechanism control system may use to measure and calibrate an mrETF, according to an example of the present disclosure. [Diagram 5] 13 shows a graph illustrating certain relative frequency constraints on an excitation signal that an actuator mechanism control system may use to measure and calibrate an mrETF, according to an example of the present disclosure. [Figure 6] 13 shows a set of graphs illustrating the frequency response of a microactuator transfer function, a notch filter transfer function, an mrETF, and a single-rate ETF both before and after calibration of a multi-rate notch filter, in accordance with an example of the present disclosure. [Figure 7] 1 illustrates a coupled closed-loop multi-actuator track following control system for controlling multiple actuators including a primary actuator (e.g., VCM), milliactuators, and microactuators, according to an example of the present disclosure. [Figure 8] 1 illustrates a decoupled closed-loop multi-actuator track following control system according to an aspect of the present disclosure. [Figure 9] 1 illustrates a flowchart of a method for calibrating a notch filter based on a response of an actuator system to a multi-rate excitation and induced mrETF, according to an embodiment of the present disclosure. [Figure 10] 13 shows a flowchart of another method for calibrating a notch filter based on a derived mrETF, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 2A and 2B show conceptual block diagrams of a top view and a side view of a data storage device in the form of a disk drive 15 according to an embodiment of the present disclosure. The disk drive 15 comprises a control circuit 22, an actuator arm assembly 19, and a number of hard disks 16A, 16B, 16C, 16D ("hard disks 16"). FIG. 2C shows a flow chart of an exemplary method 80 that the control circuit 22 of the disk drive 15 may implement or perform in controlling the operation of the disk drive 15 according to an embodiment of the present disclosure, including operations involving outputting a multi-rate excitation to a multi-rate notch filter of an actuator control system, and detecting a multi-rate resonant frequency response of one or more actuators controlled by the actuator control system in response to the multi-rate excitation. The control circuit 22 may perform such operations to calibrate the multi-rate notch filter of the actuator control system based at least in part on the detected mechanical resonant frequency response of the actuator according to an embodiment of the present disclosure.

[0011] The actuator arm assembly 19 includes a primary actuator 20 (e.g., a voice coil motor ("VCM")) and a number of actuator arms 40 (e.g., a top actuator arm 40A as seen in the perspective views of FIGS. 2A and 2B). Each of the actuator arms 40 includes a suspension assembly 42 at its distal end (e.g., a top suspension assembly 42A included in the top actuator arm 40A in the views of FIGS. 2A and 2B). In some examples, each suspension assembly 42 may include one or more additional fine actuators.

[0012] Each of the actuator arms 40 is configured to suspend one of the read / write heads 18 ("heads 18") proximate to a corresponding disk surface 17 (e.g., head 18A suspended by actuator arm 40A over a top corresponding disk surface 17A, head 18H suspended by bottom actuator arm 40H over a bottom corresponding disk surface 17H). Other examples may include any of a wide variety of other numbers of hard disks and disk surfaces, and other numbers of actuator arm assemblies, primary actuators, and fine actuators, other than, for example, one actuator arm assembly 19 and one primary actuator 20 in the examples of Figures 2A and 2B. Thus, according to various examples, the actuator arm assembly 19 includes one or more actuators to form an actuator mechanism configured to position one or more heads proximate to one or more disk surfaces of one or more disks.

[0013] In various examples, disk drive 15 may be considered to perform or execute functions, tasks, processes, methods, and / or techniques, including aspects of exemplary method 80, in terms of its control circuitry 22 performing or executing such functions, tasks, processes, methods, and / or techniques. Control circuitry 22 may comprise and / or take the form of one or more driver devices and / or one or more other processing devices of any type, and in various examples may implement or execute functions, tasks, processes, methods, or techniques by executing computer-readable instructions of software or firmware code on a hardware structure configured to execute such software or firmware code. Control circuitry 22 may also, in various embodiments, implement or execute functions, tasks, processes, methods, or techniques by hardware circuitry that implements or executes such functions, tasks, processes, methods, or techniques by the hardware structure itself, without any operation of software.

[0014] The control circuitry 22 may include one or more processing devices and one or more modules that constitute device drivers that are specifically configured to drive and operate a particular device. Such device drivers may include one or more head drivers configured to drive and operate the head 18. The device drivers may be configured as one or more integrated components of one or more large scale circuits, such as one or more power large scale integrated (PLSI) chips or circuits, and / or as part of the control circuitry 22, in various examples. The device drivers may also be configured as one or more components within other large scale integrated circuits, such as system-on-chip (SoC) circuits, or as more or less standalone circuits that may be operably coupled to other components of the control circuitry 22, in various examples.

[0015] The primary actuator 20 may perform macro primary actuation of a number of actuator arms 40, each of which may suspend one of the heads 18 above and in proximity to a corresponding disk surface 17 of the disk 16. Although the positions of the heads 18, e.g., heads 18A and 18H, are shown in Figure 2A, heads 18 are generally positioned very close to the disk surface and are too small to be seen when drawn to scale in Figures 2A and 2B.

[0016] The exemplary disk drive 15 of Figures 2A and 2B includes four hard disks 16. Other examples may include any number of disks, such as only one disk, two disks, three disks, or five or more disks. The hard disks 16 are also known as platters, and their disk surfaces may also be referred to as media or media surfaces. The four hard disks 16 include eight disk surfaces 17A, 17B, 17C, 17D, 17E, 17F, 17G, and 17H ("disk surfaces 17"), with one disk surface 17 on each side of each hard disk 16 in this illustrative example. The actuator assembly 19 suspends the heads 18 of each actuator arm 40 over and adjacent to a corresponding disk surface 17, enabling each of the heads 18 to write control features and data to and read control features and data from a respective adjacent disk surface 17. In this sense, each head 18 of each actuator arm 40 interacts with a corresponding disk surface 17.

[0017] The term "disk surface" may be understood to have the ordinary meaning that one of ordinary skill in the art has. The term "disk surface" may be understood to include both the very outer surface layer of the disk and the volume of disk material below the outer surface layer, which may be considered in terms of atomic depth, or (in a very simplified model) the number of atoms deep from the surface layer of atoms that the material is susceptible to physical interaction with the head. The term "disk surface" may include, for example, the portion of the disk material susceptible to interaction with a read / write head in disk drive operations such as control write operations, control read operations, data write operations, and data read operations.

[0018] In the embodiment of Figures 2A and 2B, each disk surface, for example disk surface 17A as shown in Figure 2A, includes a plurality of control features. The control features include servo wedges 321-32 that define a plurality of servo tracks 34. N, where the data tracks are defined relative to the servo tracks 34 and may be of the same or different radial density. The control circuit 22 processes a read signal 36 emanating from each head, for example head 18A, to read from the disk surface 17A and to control the servo wedges 321-32. N 1 to generate a position error signal (PES) representative of the error between the actual position of the head and the target position relative to the target track. A servo control system or actuator mechanism control system 30 within control circuitry 22 filters the PES from the servo wedge using an appropriate compensation filter to generate control signals 38 that are applied to actuator arm assembly 19, including controlling actuator 20, which acts as a primary actuator and rotates actuator arm assembly 19 about an axial pivot to effect a primary actuation of the head radially over disk surface 17 in a direction that reduces the PES, and in various examples to control any fine actuators. Control circuitry 22 may also apply control signals to, and receive sensor signals from, any of the various components of head 18 and / or disk drive 15, in various examples.

[0019] In the example of Figures 2A and 2B, the actuator arm assembly 19 rotates the actuator arm 40 about a common pivot. In another example, the first actuator arm assembly and / or VCM and the second actuator arm assembly and / or VCM, or other type of primary actuator, may each be configured to actuate a respective actuator arm assembly or set of multi-actuator arms, for example, about a separate pivot mounted at a different circumferential position around the disk. In other examples, three or more actuator arm assemblies or primary actuators or multi-actuators may be used, which may be actuated about a common pivot or may be included in a plurality of multi-actuators mounted at different circumferential positions around the disk. Thus, the actuator arm assembly 19 and / or any of these other examples may constitute and / or comprise an actuator mechanism in various examples.

[0020] The control circuit 22 comprises an actuator mechanism control system 30 configured to control the actuator mechanism. The actuator mechanism control system 30 may comprise, be included in, or be associated with a servo control system. In performing the exemplary method 80 of FIG. 2C (aspects of which are further described below with reference to additional figures), the actuator mechanism control system 30 and / or other elements of the control circuit 22 may be configured to perform one or more internal operations, such as issuing one or more commands to other components of the disk drive 15, receiving information from one or more other components of the disk drive 15, and / or generating one or more driver currents for output to system components of the disk drive 15. In particular, the control circuit 22 may output a multi-rate excitation to at least one multi-rate notch filter of the actuator mechanism control system (82). The control circuit 22 may detect (84) a resonant frequency response of the actuator mechanism in response to the multi-rate excitation. The control circuit 22 may further calibrate (86) the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism. Control circuitry 22 may further implement additional operations, methods, and techniques according to various aspects, including as further described herein.

[0021] The disk drive control circuit 22 processes one or more read signals from one or more heads to demodulate the servo sector signals into a position error signal (PES). The actuator mechanism control system 30 of the disk drive control circuit 22 includes at least one compensation filter and at least one notch filter that filters the PES as part of the generation of actuator control signals (single actuator control signals or multi-actuator control signals), which may include at least one VCM control signal that is applied to at least one VCM, thereby rotating an actuator arm assembly about a pivot to position one or more heads radially over one or more disks in a direction that reduces the PES. Disk drives that use one or more fine actuators, such as milliactuators and / or microactuators in addition to VCMs, may have additional complexities in their resonant frequencies and the need to filter out such resonant frequencies.

[0022] The notch filter attenuates one or more resonant frequency peaks of the servo system. The notch filter may be calibrated in various examples, such as at an initial notch filter calibration during the manufacturing process, and at other times, such as in an in-field notch filter calibration update process. The calibration may be useful to address and filter one or more actual resonant frequencies of an individual drive, which may have individual variations for each individual disk drive due to the sensitive dependence of mechanical resonant frequencies on the precise specifications of the engineering design and the slight but realistic deviations in the individual end products of the manufacturing process from the ideal. The control circuitry may ideally calibrate the notch filter to attenuate the resonant frequencies while minimizing the impact on the PES, maximizing the useful PES, thereby maximizing the accuracy achieved with the head on the disk surface, maximizing the achieved data density, data input / output rate, and / or other performance characteristics.

[0023] The notch filter calibration performance may be measured using a quality metric defined with reference to the gain of an error rejection transfer function (ETF) for tracking the target track. The maximum peak gain of the error rejection transfer function for tracking the target track may indicate the maximum quality for the notch filter calibration. The error rejection transfer function may be defined in terms of a frequency response that operates to attenuate tracking errors to a command input, for example, as may be measured in decibels per kilohertz. Hard disk drives have an inherent limit on the sampling frequency of the PES, defined by the density of the servo sectors. The inherent limit on the sampling frequency of the PES involves an inherent Nyquist frequency equal to half the sampling frequency, and therefore an inherent aliasing effect. Such an inherent aliasing effect may essentially confuse conventional frequency detection, causing alias frequencies below the Nyquist frequency to be detected instead of the true resonant frequency above the Nyquist frequency, and aliasing to the detected alias frequency. This confusing detection of alias frequencies tends to be particularly problematic in systems incorporating fine actuators (e.g., milliactuators and / or microactuators), which by their nature (e.g., smaller dimensions, lower mass, lower structural strength and stiffness) may inherently have resonant frequencies that are substantially higher than the resonant frequencies of the primary actuators and much higher relative to the sampling frequency of the PES and therefore relative to the Nyquist frequency.

[0024] The disclosed methods, systems, and devices implement novel solutions to these challenges by, among other novel advantages, enabling direct measurement of ETF peaks, including mrETFs, above the Nyquist frequency as a quality metric of notch filter rejection performance without the confusion caused by aliasing, and distinguishing true ETF peak resonant frequencies. This may be particularly useful in multi-actuator systems that use VCMs as primary actuators, but also use fine actuators, such as milliactuators and / or microactuators, whose components and motions are much smaller and finer, and whose resonant frequencies can be significantly higher, more likely to be above the Nyquist frequency.

[0025] The system according to the present disclosure, in various aspects, allows the ETF peaks above the Nyquist frequency to be directly measured as a quality metric of the notch filter rejection performance. In various examples of the present disclosure, the actuator mechanism control system may inject a multi-rate sinusoidal excitation at the multi-rate notch filter input (or output) and use the resulting excitation noise of the multi-rate sinusoid for control feedback and calibration. The frequency response from the injected multi-rate sinusoidal excitation to the sinusoidally added signal corresponds to the multi-rate error rejection transfer function ("mrETF") for frequencies above the Nyquist frequency. Thus, the mrETF can be used to distinguish ETF peaks due to resonances above the Nyquist frequency, allowing the multi-rate notch filter to be applied reliably to the actual resonance frequency, regardless of whether it is below or above the Nyquist frequency. Thus, the disclosed system, in various examples, may evaluate the ETF peak with the actual frequency of resonance above the Nyquist frequency as a quality metric for the notch filter calibration, and customize the multi-rate notch filter to have a notch frequency tuned to match the actual mechanical resonance frequency measured by the actuator mechanism control system of the control circuit in the calibration process. The disclosed system, in various examples, may provide further novel advantages, such as improving the target for tracking the ETF and reducing non-repeatable error (NRRO) errors.

[0026] 3 illustrates an actuator mechanism control system 300 with a closed-loop multi-rate error rejection transfer function (mrETF) control system according to an example of the present disclosure. In this example, the actuator mechanism control system 300 injects a single-rate sinusoidal excitation 304 (dp) into a summing module 308 to be summed with a state target signal 302 minus a state estimator output 306 (which incorporates feedback from the actuator mechanism 336 via a state estimator 340). The resulting output of the summing module 308 is a single-rate tracking error 310. The actuator mechanism control system 300 inputs the single-rate tracking error 310 to a single-rate controller 312, which outputs to an N-fold upsampler 316, thereby generating an N-fold upsampler output 322. The actuator mechanism control system 300 also injects the multi-rate sinusoidal excitation 324 (dm) into a summing module 328, which is summed with the N-fold upsampler output 322, thereby outputting a multi-rate compensation filter input 330 (MR input). There is a single-rate error rejection transfer function (ETF) that is the transfer function from the single-rate sinusoidal excitation 304 (dp) to the single-rate tracking error 310, and a multi-rate error rejection transfer function (mrETF) that is the transfer function from the multi-rate sinusoidal excitation 324 (dm) to the multi-rate compensation filter input 330 (MR input). The multi-rate compensation filter input 330 is input as an input to a multi-rate compensation filter 332 that comprises a multi-rate notch filter. The multi-rate compensation filter 332 generates a multi-rate actuator control signal 334 that the actuator mechanism control system 300 outputs to the actuator mechanism 336 to control the actuator mechanism 336.

[0027] The frequency response from the injected multirate sinusoidal excitation 324 (dm) to the multirate sinusoidal excitation added signal, i.e., N-times upsampler output 322, may correspond to a multirate error rejection transfer function (mrETF) for resonant frequencies above the Nyquist frequency. The actuator mechanism control system 300 may identify the resonant frequencies before starting or as part of the calibration of the mrETF peak detection. To directly measure the mrETF peaks above the Nyquist frequency as a quality metric of the notch filter rejection performance, the actuator mechanism control system 300 may inject the multirate sinusoidal excitation 324 at the input of the multirate notch filter, e.g., at the input of the multirate compensation filter 332 comprising the multirate notch filter. The frequency response from the injected sinusoidal excitation to the sinusoid added signal (N-times upsampler output 322) may correspond to the error rejection for frequencies above the Nyquist frequency (multirate ETF or mrETF). Thus, actuator mechanism control system 300 may use the mrETF to distinguish ETF peaks having frequencies above the Nyquist frequency, thereby enabling actuator mechanism control system 300 to calibrate and apply, for example, a multi-rate notch filter included in multi-rate compensation filter 332 to the actual resonant frequency regardless of the Nyquist frequency or aliasing effects.

[0028] Thus, the multirate resonant frequency response of the actuator mechanism 336 may be based at least in part on a multirate error rejection transfer function (mrETF) or may exhibit a multirate error rejection transfer function (DF). The actuator mechanism control system 300 may output a multirate control input to at least one multirate notch filter included in the multirate compensation filter. The multirate control input may be based at least in part on the mrETF, which is a measure of the error transfer from the multirate sinusoidal excitation 324 and thus, in this example, is based at least in part on the multirate excitation. Calibrating the at least one multirate notch filter may include calibrating based at least in part on the mrETF, as described further below.

[0029] The multi-rate control input may further be based at least in part on a closed-loop control signal of the actuator mechanism control system, such as in this example in the form of an N-fold upsampler output 322 that is summed with the multi-rate excitation 324 to generate a multi-rate compensation filter input 330 (MR input) that is based at least in part on the single-rate excitation 304. That is, the actuator mechanism control system 300 may be further configured to output the single-rate excitation 324 to the single-rate compensation filter 312 of the actuator mechanism control system 300, such that the multi-rate compensation filter input 330 (MR input), which is based at least in part on the multi-rate excitation 304, is further based at least in part on the output of the single-rate compensation filter 312.

[0030] Figure 4 shows a graph 400 illustrating combinations of frequencies of excitation signals in the form of sine waves that the actuator mechanism control system 300 may use to measure and calibrate mrETFs, according to examples of the present disclosure. Although Figure 3 shows a representation of a single sine wave after the multi-rate sine wave excitation 324 (dp), the actuator mechanism control system 300 may generate, superimpose, or combine multiple such sine waves for multi-rate excitation, as shown in Figure 4. The actuator mechanism control system 300 may combine any of a number of sine waves (shown at 401) having any of a wide range of frequencies and amplitudes into an overall multi-rate excitation or multi-rate excitation signal (shown at 411), subject to certain constraints such as avoiding saturation of the control system and avoiding frequencies that alias to mutually shared common alias frequencies below the Nyquist frequency. Thus, outputting a multi-rate excitation may include the actuator mechanism control system 300 outputting a plurality of excitations having a plurality of different frequencies to at least one multi-rate notch filter 332 included in a multi-rate compensation filter of the actuator mechanism control system 300. In various examples, an actuator mechanism control system 300 outputting a plurality of excitations having a plurality of different frequencies may include an actuator mechanism control system 300 outputting one or more substantially sinusoidal excitations. The actuator mechanism control system 300 may output any of a wide variety of excitations, which may be decomposed into at least sinusoidal excitations and thus, in various examples, form a multi-rate excitation equivalent to a plurality of sinusoidal excitations.

[0031] The actuator mechanism control system 300 may calculate the mrETF by performing a fast Fourier transform (FFT) of the multi-rate servo control loop response including the multi-rate sinusoidal excitation 324 (dm) and the multi-rate notch filter input / compensation filter input 330 (MR input) at the frequency of the multi-rate sinusoidal excitation 324. As a result, using multiple frequencies in the measurement may allow for reducing the measurement time of the mrETF in various examples. The actuator mechanism control system 300 may also perform a single frequency injection in some examples. The actuator mechanism control system 300 may perform a Fourier transform of the multi-rate sinusoidal excitation and the single-rate or multi-rate servo control loop response in various examples. The actuator mechanism control system 300 may further select the amplitude per frequency of the multi-rate excitation such that selecting the amplitude per frequency includes selecting an amplitude per frequency that avoids causing signal saturation in the actuator mechanism control system.

[0032] FIG. 5 illustrates a graph showing certain relative frequency constraints for excitation sine waves that an actuator mechanism control system may use to measure and calibrate mrETF, according to an embodiment of the present disclosure. In FIG. 5, the PES sampling frequency is shown as Fs and the Nyquist frequency is shown as Fnyq=0.5Fs. As shown in FIG. 5, in this example, Band0 is 0-0.5Fs, Band1 is 0.5Fs-Fs, Band2 is Fs-1.5Fs, and Band3 is 1.5Fs-2Fs. Before outputting the multi-rate excitation, the actuator mechanism control system 300 may be configured to select multiple frequencies for the multi-rate excitation, where selecting multiple frequencies for the multi-rate excitation includes selecting multiple frequencies above the Nyquist frequency that are below the Nyquist frequency, i.e., do not alias to the same common alias frequency f0 in Band0. As described above, the actuator mechanism control system 300 may select the frequencies to be added for a single measurement, subject to the constraint that the signal amplitude after summation of multiple sinusoidal excitations does not cause signal saturation within the actuator mechanism control system 300, and as shown in FIG. 5, selected frequencies in bands above the Nyquist frequency (e.g., Band1, Band2, Band3 defined by multiples of the Nyquist frequency, which is half the sampling frequency defined by sampling servo sectors on the disk surface) should not alias to a corresponding alias frequency f0 in Band0 below the Nyquist frequency.

[0033] In some examples, the actuator mechanism control system 300 outputting a plurality of excitations having a plurality of different frequencies may include an actuator mechanism control system 300 that sequentially outputs the excitations having a plurality of frequencies, and detecting a frequency response of the actuator mechanism may include sequentially detecting a frequency response of the actuator mechanism to the excitations having a plurality of frequencies. In various examples, the actuator mechanism control system 300 outputting a plurality of excitations having a plurality of different frequencies may include an actuator mechanism control system 300 that adds the excitations having a plurality of frequencies into a simultaneous multi-rate excitation and outputs the simultaneous multi-rate excitation, as shown in FIG. 4. Detecting a frequency response of the actuator mechanism may include the actuator mechanism control system 300 detecting a frequency response, including a multi-rate and / or single rate frequency response, of the actuator mechanism to the simultaneous multi-rate excitation.

[0034] In some examples, detecting a frequency response of the actuator mechanism in response to the multi-rate excitation may include determining a multi-rate error rejection transfer function (mrETF) based at least in part on the multi-rate excitation and / or determining a single-rate error rejection transfer function (single-rate ETF). Determining the mrETF may include the actuator mechanism control system 300 performing a fast Fourier transform of the multi-rate sinusoidal excitation and the multi-rate notch filter input. Determining the mrETF may also include, in various examples, the actuator mechanism control system 300 performing a single frequency excitation injection and performing a Fourier transform of the multi-rate sinusoidal excitation response and the single-rate or multi-rate servo control loop response.

[0035] 6 illustrates a set of graphs showing the frequency response of a microactuator transfer function, a notch filter transfer function, an mrETF, and a single-rate ETF both before (601) and after (651) calibration of a multi-rate notch filter, according to an example of the present disclosure. Graph 601 illustrates the amplitude per frequency 611 of the resonance of an example microactuator plant rising to a sharp peak at the resonant frequency 615, and the amplitude per frequency 621 of the multi-rate notch filter filtering before calibration, such that the filtering by the multi-rate notch filter is flat to zero across frequency (before calibration). After calibration, as shown in graph 651, based on the mrETF, the amplitude per frequency 671 of the multi-rate notch filter filtering is shaped with a negative amplitude per frequency centered around the filtering peak corresponding to the microactuator plant resonant frequency 615, thereby demonstrating the effectiveness of the mrETF as a performance metric to serve as a basis for calibrating a notch filter. The resonant frequency of any individual microactuator plant may vary significantly from other individual unit manufacturing batches of the same design and same manufacturing batch based on minute physical differences in the end product, and yet the process of the present disclosure may effectively calibrate the microactuator plant based on its own individual detected mrETF. Different microactuators may thus have a variety of different resonant frequencies, and the calibration process according to the present disclosure may result in shaping the amplitude per frequency of filtering for the multi-rate notch filter to be centered in each case on the detected resonant frequency of the individual microactuator.

[0036] FIG. 6 also shows the mrETF per frequency before calibration (680) and the mrETF per frequency after calibration (690), as well as the single-rate ETF per frequency before calibration (692) and the single-rate ETF per frequency after calibration (696). As shown in FIG. 6, the mrETF per frequency near the resonant frequency (681) before calibration undergoes rapid fluctuations indicating a rapidly different multi-rate error rejection transfer function for frequencies near the resonant frequency. However, after calibration, the mrETF per frequency near the resonant frequency (691) is substantially flattened and smoothed. Similarly, the single-rate ETF per frequency near the alias frequency (693) before calibration undergoes rapid fluctuations in magnitude per frequency indicating a rapidly different single-rate error rejection transfer function for frequencies near the alias frequency. However, after calibration, the single-rate ETF per frequency exhibits substantially reduced magnitude fluctuations per frequency near the alias frequency (697). This shows that the actuator mechanism control system of the present disclosure, in this example, after being calibrated by the techniques of the present disclosure, can achieve substantially more reliable error cancellation transfer across frequency in both the mrETF and single-rate ETF.

[0037] 7 illustrates a coupled closed-loop multi-actuator track-following control system 700 for controlling multiple actuators including a primary actuator 791 (e.g., VCM), a milliactuator 761, and a microactuator 731, in accordance with an example of the present disclosure. Thus, the closed-loop multi-actuator track-following control system 700 functions as an actuator mechanism control system for a system having three types of actuators: a primary actuator 791, a milliactuator 761, and a microactuator 731. The closed-loop multi-actuator track-following control system 700 includes an actuator control subsystem for each of the three actuator types: a primary actuator control subsystem 771, a milliactuator control subsystem 741, and a microactuator control subsystem 711.

[0038] The microactuator control subsystem 711 and milliactuator control subsystem 741 each include a respective gain circuit, namely, a microactuator gain circuit 712 and a milliactuator gain circuit 742. The actuator control subsystem for each actuator includes a single rate compensation filter 714, 744, 744, respectively (C s* ), N-times upsamplers 716, 746, 776, a summing module that receives and sums the N-times upsampler outputs and respective multirate excitations 718, 748, 778, each respective multirate excitation receiving a respective actuator-specific mrETF to thereby generate a respective actuator-specific multirate compensation filter input 721, 751, 781, a multirate compensation filter 722, 752, 782 including a multirate notch filter, (C m* Each respective multi-rate compensation filter 722, 752, 782 receives a respective multi-rate compensation filter input 721, 751, 781 and generates a respective actuator control output, which the respective multi-rate compensation filter 722, 752, 782 outputs to a respective actuator 731, 761, 791.

[0039] In various examples, the at least one multi-rate notch filter is included in a multi-rate compensation filter, such as multi-rate compensation filters 722, 752, 782. Because each multi-rate compensation filter 722, 752, 782 comprises a multi-rate notch filter, each of the multi-rate compensation filters 722, 752, 782 may be referred to interchangeably as a multi-rate notch filter for purposes of this specification, with the understanding that each of the multi-rate compensation filters 722, 752, 782 is a multi-rate compensation filter that comprises a multi-rate notch filter that may be calibrated by the methods, processes, techniques, devices, and systems of the present disclosure.

[0040] The resulting performance responses, including the excitation responses of all three actuator types 731, 761, 791, may be summed by a summing module 797 and output to a state estimator 798. The state estimator 798 may output the state estimator output 799 to a summing module 704 along with a control target input 701 in a feedback loop to generate a common shared tracking error 706 that is used as an input to each of the actuator control subsystems 711, 741, 771 for each of the actuators 731, 761, 791, in this example.

[0041] The gain circuits 712, 742 (Gu, Gm) for the microactuator 731 and milliactuator 761 can be set to either on or 0 to activate or deactivate control for the microactuator 731 and milliactuator 761. If neither the microactuator gain circuit 712 nor the milliactuator gain circuit 742 are set to 0, the closed loop multi-actuator track following control system 700 operates as a triple stage actuator (TSA) servo. If either the microactuator gain circuit 712 or the milliactuator gain circuit 742 are set to 0, the closed loop multi-actuator track following control system 700 operates as a dual stage actuator (DSA) servo. If both the microactuator gain circuit 712 and the milliactuator gain circuit 742 are set to 0, the closed loop multi-actuator track following control system 700 operates as a single actuator servo (e.g., VCM).

[0042] A separate mrETF value is defined for each actuator type: the microactuator mrETF is defined as the transfer function from the microactuator multirate excitation 718 (dmu) to the microactuator multirate compensation filter input 721 (uAin), the milliactuator mrETF is defined as the transfer function from the milliactuator multirate excitation 748 (dmm) to the milliactuator multirate compensation filter input 751 (mAin), and the primary actuator mrETF is defined as the transfer function from the primary actuator multirate excitation 778 (dmv) to the primary actuator multirate compensation filter input 781 (vcmin).

[0043] The closed-loop multi-actuator track following control system 700 is an illustrative example of a control system for multiple actuators, such as a primary actuator and at least one fine actuator (e.g., a milliactuator and / or a microactuator). In various examples according to the present disclosure, the actuator control system may be configured to control the primary actuator and at least one fine actuator. For example, the control system may be configured to control a primary actuator and a milliactuator; a primary actuator and a microactuator; a primary actuator, a milliactuator, and a microactuator (as shown in the example of FIG. 7); a primary actuator, a milliactuator, a microactuator, and one or more additional fine actuators; two or more primary actuators, which may have a shared axis of rotation or may be located at independent locations around the circumference of the disk 16, and which control independent actuator arm assemblies, which in some examples may include one or more fine actuators on each arm of each actuator arm assembly, or may be other configurations in various examples.

[0044] In various examples, references to milliactuators, microactuators, or fine actuators may generally refer to one milliactuator, microactuator, and / or other fine actuators on each actuator arm of an actuator arm assembly that are controlled by a single primary actuator and that are included in the actuator arm assembly and configured to individually control each head suspended and controlled by the actuator arm assembly. Thus, for example, multi-actuator track following control system 700 may control a single primary actuator that controls the actuator arm assembly, and may control one milliactuator and / or one microactuator on each actuator arm of the actuator arm assembly, which in turn controls each head of the actuator arm assembly.

[0045] Thus, the multi-actuator track following control system 700 comprises at least one multi-rate notch filter in that it comprises a primary actuator multi-rate notch filter 782, and at least one fine actuator multi-rate notch filter, which in this example comprises a milliactuator multi-rate notch filter 752 and a microactuator multi-rate notch filter 722. Outputting the multi-rate excitation may include outputting a primary actuator multi-rate excitation 778 to a primary actuator control subsystem 771 of the multi-actuator track following control system 700 comprising a primary actuator multi-rate notch filter 782, and outputting at least one fine actuator multi-rate excitation, e.g., actuator multi-rate excitation 751, 721, to at least one fine actuator control subsystem, e.g., milliactuator control subsystem 741 and microactuator control subsystem 711, of the closed loop multi-actuator track following control system 700 comprising at least one fine actuator multi-rate notch filter, e.g., a multi-rate compensation filter 752 and a multi-rate compensation filter 722, respectively.

[0046] Detecting a frequency response of the actuator mechanism in response to the multi-rate excitation may include detecting a frequency response of the primary actuator 791 and detecting a frequency response of at least one fine actuator, e.g., milliactuator 761 and microactuator 731. For example, as in the example of FIG. 7, the multi-actuator track following control system 700 may detect a frequency response of the multi-actuator track following control system 700 and the actuators 791, 761, 731 in response to the multi-rate excitation. This may include the multi-actuator track following control system 700 detecting a frequency response of the primary actuator 791 in response to the primary actuator multi-rate excitation 778, detecting a frequency response of the milliactuator 761 in response to the milliactuator multi-rate excitation 748, and detecting a frequency response of the microactuator 731 in response to the microactuator multi-rate excitation 718.

[0047] The control circuit 22 or its multi-actuator track following control system 700 may calibrate at least one multi-rate notch filter of the multi-actuator track following control system 700 based at least in part on the detected frequency responses of the actuator mechanism, i.e., one or more actuators of the system, in this example the primary actuator 791, the milliactuator 761, and the microactuator 731. This may include the multi-actuator track following control system 700 calibrating the primary actuator multi-rate notch filter 782 of the multi-actuator track following control system 700 based at least in part on the detected frequency response of the primary actuator 791, and calibrating at least one fine actuator multi-rate notch filter based at least in part on the detected frequency response of the at least one fine actuator, such as by, in the example of FIG. 7 , calibrating the milliactuator multi-rate notch filter 722 based at least in part on the detected frequency response of the milliactuator 761, and / or calibrating the microactuator multi-rate notch filter 752 based at least in part on the detected frequency response of the microactuator 731. In some examples, calibrating at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism may therefore include calibrating a primary actuator multi-rate notch filter 782 of the multi-actuator track following control system 700 based at least in part on the detected frequency response of the primary actuator 791, calibrating a milliactuator multi-rate notch filter 752 based at least in part on the detected frequency response of the milliactuator 761, and calibrating a microactuator multi-rate notch filter 722 based at least in part on the detected frequency response of the microactuator 731.The calibration may be based at least in part on the frequency response of each actuator 791, 761, 731 detected via feedback through a state estimator 798, in this example as shown in Figure 7. Outputting the multi-rate excitation may include the multi-actuator track following control system 700 outputting a primary actuator multi-rate excitation 778 to a primary actuator control subsystem 771 comprising a primary actuator multi-rate notch filter 782, outputting a milliactuator multi-rate excitation 752 to a milliactuator control subsystem 741 comprising a milliactuator multi-rate notch filter 752, and outputting a microactuator multi-rate excitation 718 to a microactuator control subsystem 711 comprising a microactuator multi-rate notch filter 722.

[0048] 7, the primary actuator control subsystem 771, the milliactuator control subsystem 741, and the microactuator control subsystem 711 share a common input in the form of a tracking error output 706 by a summing module 704 based on a target signal 701 corrected by a state estimator feedback 799. The primary actuator control subsystem 771, the milliactuator control subsystem 741, and the microactuator control subsystem 711 thereby form a coupled system in this example. Thus, in this example, the primary actuator control subsystem 771 and at least one fine actuator control subsystem 741, 711 share a common input in the form of a tracking error output 706. In other examples, the primary actuator control subsystem 771, the milliactuator control subsystem 741, and the microactuator control subsystem 711 may be separated and may have separated inputs, as described below.

[0049] Figure 8 illustrates a decoupled closed-loop multi-actuator track-following control system 800 in accordance with an aspect of the disclosure. The multi-actuator track-following control system 800 includes many of the same configurations and elements as the multi-actuator track-following control system 700 of Figure 7, along with additional configurations and elements as shown in Figure 8 and described herein. Whereas in the example of Figure 7, the primary actuator control subsystem 771, milliactuator control subsystem 741, and microactuator control subsystem 711 are coupled and share a common input in the form of the tracking error output 706, in the example of Figure 8 the various actuator control systems 871, 841, 811 are decoupled and have different inputs.

[0050] In particular, the output of the microactuator control subsystem 811 is coupled to a microactuator estimator 832 which estimates or emulates the response from the microactuator 731 and is coupled to an input to a milliactuator control subsystem 841 by a summing module 834 which sums the tracking error output 806 and the emulation output 833 of the microactuator estimator 832. Thus, the input to the milliactuator control subsystem 841 incorporates the error tracking 806 of the recent performance of the entire multi-actuator system as well as the most recent or near simultaneous mrETF based control signal for the microactuator 731. Similarly, the output of the milliactuator control subsystem 841 is coupled to a milliactuator estimator 862 which is coupled to an input to a primary actuator control subsystem 871 by a summing module 864 which sums the emulation output 833 of the microactuator estimator 832 and the summing output 835 of the summing module 834 which sums the tracking error output 806 and the emulation output 863 of the microactuator estimator 832. Thus, the input to the primary actuator control subsystem 871 incorporates error tracking of the recent performance of the entire multi-actuator system, as well as the most recent or near simultaneous mrETF-based control signals for both the microactuator 731 and the milliactuator 761.

[0051] Thus, the milliactuator control subsystem 841 controls the milliactuator 761 based in part on an emulation of the microactuator 731, and the primary actuator control system 871 controls the primary actuator 791 based in part on an emulation of both the microactuator 731 and the milliactuator 761. In various other examples, in general, any two or more actuator control systems may be separate, and the output of at least one fine actuator control subsystem may be coupled to a fine actuator estimator, which may be coupled to an input to at least one further fine actuator control subsystem and to the primary actuator control subsystem.

[0052] 9 illustrates a flowchart of a method 900 for calibrating a notch filter based on a response of an actuator system to a multi-rate excitation and induced mrETF, according to an embodiment of the disclosure. One or more processing devices, such as may be included in the control circuit 22 and / or closed-loop multi-actuator track following control systems 700 and / or 800 of FIGS. 7 and 8 , may implement, execute, and / or embody the method 900 in various examples. The parameters of the multi-rate notch filter may be one or more frequencies, e.g., ω n and ω d and one or more damping ratios of at least one or more zeros and one or more poles of the multirate notch filter, e.g., δ n and δ d In this example, the frequency ω n and ω d defines the frequency band of the notch, and the damping ratio δ n and δ d defines the zeros and the damping ratio of the poles. Thus, in this example, the parameters of the notch filter in continuous time are the frequency and damping ratio parameters ω n , ω d , δ n , δ dThe actuator control subsystem of the control circuit 22 may calculate the notch coefficients by discretization.

[0053] Method 900 includes receiving, by one or more processing devices, parameters of a multi-rate notch filter (902); determining, by the one or more processing devices, coefficients for the multi-rate notch filter based at least in part on the parameters of the multi-rate notch filter and applying, by the one or more processing devices, the coefficients to a servo control loop (904); measuring, by the one or more processing devices, a multi-rate error cancellation transfer function (906); determining, by the one or more processing devices, whether a peak of the multi-rate error cancellation transfer function is greater than a multi-rate error cancellation transfer function threshold (908); and in response to determining, by the one or more processing devices, that the peak of the multi-rate error cancellation transfer function is not greater than the multi-rate error cancellation transfer function threshold, measuring the multi-rate error cancellation transfer function peak. 9, modifying parameters of the multi-rate notch filter based at least in part on δ, thereby modifying the peaks of the multi-rate error cancellation transfer function to be not greater than the multi-rate error cancellation transfer function threshold (910); after modifying the parameters, repeating, by the one or more processing devices, measuring the multi-rate error cancellation transfer function (912) and repeating the determining whether the peaks of the multi-rate error cancellation transfer function are greater than the multi-rate error cancellation transfer function threshold (914); determining, by the one or more processing devices, whether more profiles are available in response to determining that the peaks of the multi-rate error cancellation transfer function are not greater than the multi-rate error cancellation transfer function threshold (916); n and δ d Different damping ratio δ n and / or δ d and smaller δ n and / or δ which may be larger dand repeating the parameter modification (918), and storing, by the one or more processing devices, the modified parameters of the multi-rate notch filter in response to the peak of the multi-rate error rejection transfer function not being greater than the multi-rate error rejection transfer function threshold (or in response to not having more profiles available) (920). Thus, the one or more processing devices of the multi-actuator track following control system may calibrate the multi-rate notch filter with respect to the mrETF in various examples.

[0054] FIG. 10 illustrates a flowchart of another method 1000 for calibrating a notch filter based on a derived mrETF, according to an embodiment of the disclosure. The method 1000 of FIG. 10 is similar to the method 900 of FIG. 9 and extends thereto to include all of the subject matter of the method 900 shown in FIG. 9 and described above, plus additional elements. As with the method 900, in the example of FIG. 10, the frequency ω n and ω d may define the frequency band and damping ratio of the notch, and the damping ratio δ n and δ d defines the damping ratio of the poles and zeros. As in the example of Figure 9, the parameters of a notch filter in continuous time are the frequency and damping ratio parameter ω n , ω d , δ n , δ d The actuator control subsystem of control circuit 22 may calculate the notch coefficients including the discretization. Method 1000 also adds a process for determining information regarding the exact resonant frequency early in the notch filter calibration process. This may overcome, in some instances, a lack of prior knowledge of where the resonant frequency is, including when the first notch filter profile is above a particular width and depth to the resonance.

[0055] In particular, method 1000 of Figure 10 extends method 900 of Figure 9 to further include determining a plant target frequency of a target controller path for filter calibration (1002), identifying a resonant frequency having a maximum peak gain at the plant target frequency (1004), and modifying one or more frequencies included in parameters associated with frequency bands of the multi-rate notch filter (1006) prior to determining coefficients for the multi-rate notch filter based at least in part on parameters of the multi-rate notch filter. Thus, one or more processing devices of a multi-actuator track following control system may calibrate the multi-rate notch filter with respect to the mrETF, including instances where the notch filter parameters are not fully characterized prior to beginning the calibration process.

[0056] In another specific illustrative example that has undergone experimental testing and validation, a microactuator control subsystem of the control circuit 22 for controlling a microactuator of a triple stage actuator (TSA) can apply a narrow notch filter for the microactuator yaw mode, and the microactuator notch filter can be designed with a design goal for a flat gain reduction of -40 decibels (dB) in the notch filter calibration range from 54 kHz to 62 kHz. The notch filter candidate prepared for applying the customization can have a 20 dB larger gain reduction at the target frequency and a width of 5500 Hertz (Hz) at 10 dB gain reduction. The microactuator control subsystem can perform servo ETF validation using yaw frequency boundary samples. In testing, the TSA mrETF target for tracking error was improved from 0.25 dB to 0.75 dB at frequencies below 10 kHz with calibration according to examples of the present disclosure. Implementations of the present disclosure can also reduce non-repeatable error (NRRO) errors, among other advantages.

[0057] Any suitable control circuitry, such as any suitable integrated circuit or integrated circuits, may be used to implement the flow diagrams in the above examples. For example, the control circuitry may be implemented in a read channel integrated circuit, or may be implemented in a component separate from the read channel, such as a data storage controller, or certain operations described above may be performed by the read channel and other operations may be performed by the data storage controller. In some examples, the read channel and the data storage controller may be implemented as separate integrated circuits, and in some examples, the read channel and the data storage controller may be fabricated in a single integrated circuit or system on chip (SoC). In some examples, the control circuitry may include a suitable preamplifier circuitry implemented as a separate integrated circuit, integrated into the read channel or data storage controller circuitry, or integrated into the SoC.

[0058] In some examples, the control circuitry may comprise a microprocessor that implements instructions operable to cause the microprocessor to perform one or more aspects of the method, process, or technique illustrated in the flow diagram and described herein with reference thereto. The executable instructions of the present disclosure may be stored on any computer-readable medium. In some examples, the executable instructions of the present disclosure may be stored on a non-volatile semiconductor memory device, component, or system external to the microprocessor, or may be integrated with the microprocessor in an SoC. In some examples, the executable instructions of the present disclosure may be stored on one or more disks and loaded into a volatile semiconductor memory when the disk drive is powered on. In some examples, the control circuitry may comprise logic circuits, such as state machine circuits. In some examples, at least some of the flow diagram blocks may be implemented using analog circuits (e.g., analog comparators, timers, etc.). In some examples, at least some of the flow diagram blocks may be implemented using digital circuits or a combination of analog and digital circuits.

[0059] In various examples, one or more processing devices may comprise or be configured with control circuitry as described herein and / or may perform one or more of the functions of the control circuitry as described herein. In various examples, the control circuitry, or one or more other processing devices performing one or more of the functions of the control circuitry as described herein, may be abstracted away from physical proximity to disks and disk surfaces. The control circuitry, and / or its one or more device drivers, and / or one or more processing devices of any other type performing one or more of the functions of the control circuitry as described herein, may in various examples be part of or in proximity to a rack of multiple data storage devices or a stand-alone product comprising multiple data storage devices, part of or in proximity to one or more physical or virtual servers, part of or in proximity to one or more local area networks or one or more storage area networks, part of or in proximity to a data center, or hosted on one or more cloud services.

[0060] In various examples, the disk drive may include a magnetic disk drive, an optical disk drive, a hybrid disk drive, or other types of disk drives. Some examples may include electronic devices such as computing devices, data server devices, media content storage devices, or other devices, components, or systems that may include storage media and / or control circuitry as described above.

[0061] The various features and processes described above may be used independently of each other or may be combined in various ways. All possible combinations and subcombinations are within the scope of the present disclosure. In some implementations, some method, event, or process blocks may be omitted. The methods and processes described herein are not limited to any particular order, and the blocks or states associated therewith may be performed in other orders. For example, the tasks or events described may be performed in an order other than that specifically disclosed, or multiple may be combined into a single block or state. The example tasks or events may be performed in series, parallel, or in another manner. Tasks or events may be added to or removed from the disclosed examples. The example systems and components described herein may be configured differently than described. For example, elements may be added, removed, or rearranged compared to the disclosed examples.

[0062] Although certain exemplary embodiments are described herein, these embodiments are presented by way of example only and do not limit the scope of the invention disclosed herein. Thus, nothing in the above description is intended to imply that any particular feature, characteristic, step, module, or block is required or essential. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Various omissions, substitutions, and changes in the form of the methods and systems described herein may be made without departing from the spirit and scope of the present disclosure.

[0063] Method 80, and other methods of the present disclosure, may include other steps or variations in various other embodiments. Any or all of method 80 and other methods of the present disclosure may be performed or embodied in hardware and / or performed or executed by a controller, CPU, FPGA, SoC, measurement and control multiprocessor system on a chip (MPSoC), which may include both a CPU and FPGA, and other elements together in one integrated SoC, or other processing or computing devices that process executable instructions in controlling other associated hardware, devices, systems, or products in performing, implementing, or embodying various subject matter of the methods.

[0064] Thus, data storage systems, devices, and methods that implement and embody the novel advantages of the present disclosure are shown and described herein in various fundamental aspects and various selected exemplary applications, architectures, techniques, and methods for implementing and embodying the novel advantages of the present disclosure. Those skilled in the relevant art will be fully equipped by this disclosure to understand, and make informed reductions to the implementation of, a wide range of further applications, architectures, techniques, and methods for the novel advantages, techniques, methods, processes, devices, and systems encompassed by the present disclosure and the claims that follow.

[0065] As used herein, the statement "at least one of A, B, and C" is intended to mean "either A, B, C, or any combination of A, B, and C." The description of the disclosed examples is provided to enable those skilled in the relevant art to understand how to make or use the subject matter of the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art based on this disclosure, and the general principles defined herein may be applied to other examples without departing from the spirit or scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0066] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and various changes may be made in the form, construction, and arrangement of the elements without departing from the disclosed subject matter or sacrificing all or any of its material advantages. The described forms are merely illustrative, and the following claims encompass and include a wide range of embodiments, including a wide range of examples that encompass any such changes in the form, construction, and arrangement of the elements as described herein.

[0067] Although the present disclosure has been described with reference to various examples, it will be understood that these examples are illustrative and that the scope of the present disclosure is not limited thereto. All subject matter described herein is presented in the form of illustrative, non-limiting examples, and not as exclusive implementations, whether or not explicitly called out as examples for purposes of illustration. Many variations, modifications, and additions are possible within the scope of the examples of the present disclosure. More generally, the examples according to the present disclosure are described in the context of specific implementations. Functions may be separated or combined in separate blocks or described in different terms in various examples of the present disclosure without departing from the spirit and scope of the present disclosure and the following claims. These and other variations, modifications, additions, and improvements may be included within the scope of the present disclosure, as defined in the following claims.

Claims

1. 1. A data storage device, comprising: One or more disks; an actuator mechanism configured to position one or more heads proximate one or more disk surfaces of the one or more disks; one or more processing devices comprising an actuator mechanism control system configured to control the actuator mechanism; the one or more processing devices: outputting a multi-rate excitation to at least one multi-rate notch filter of the actuator mechanism control system; detecting a frequency response of the actuator mechanism in response to the multi-rate excitation; configured to calibrate the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; the one or more processing devices are further configured to output a multirate control input to the at least one multirate notch filter, the multirate control input being based at least in part on a multirate error rejection transfer function; the multi-rate error rejection transfer function is based at least in part on the multi-rate excitation; The data storage device, wherein calibrating the at least one multi-rate notch filter includes calibrating based at least in part on the multi-rate error rejection transfer function.

2. A data storage device, One or more disks; an actuator mechanism configured to position one or more heads proximate one or more disk surfaces of the one or more disks; one or more processing devices comprising an actuator mechanism control system configured to control the actuator mechanism; the one or more processing devices: outputting a multi-rate excitation to at least one multi-rate notch filter of the actuator mechanism control system; detecting a frequency response of the actuator mechanism in response to the multi-rate excitation; configured to calibrate the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; The at least one multirate notch filter: a primary actuator multirate notch filter; at least one fine actuator multi-rate notch filter.

3. 3. The data storage device of claim 1, wherein outputting the multi-rate excitation comprises outputting a plurality of excitations having a plurality of different frequencies to the at least one multi-rate notch filter of the actuator mechanism control system.

4. outputting the plurality of excitations having a plurality of different frequencies includes sequentially outputting substantially sinusoidal excitations having a plurality of frequencies; 4. The data storage device of claim 3, wherein detecting the frequency response of the actuator mechanism comprises sequentially detecting a frequency response of the actuator mechanism to the excitation having the plurality of frequencies.

5. A data storage device, comprising: One or more disks; an actuator mechanism configured to position one or more heads proximate one or more disk surfaces of the one or more disks; one or more processing devices comprising an actuator mechanism control system configured to control the actuator mechanism; the one or more processing devices: outputting a multi-rate excitation to at least one multi-rate notch filter of the actuator mechanism control system; detecting a frequency response of the actuator mechanism in response to the multi-rate excitation; configured to calibrate the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; outputting the multi-rate excitation includes outputting a plurality of excitations having a plurality of different frequencies to the at least one multi-rate notch filter of the actuator mechanism control system; outputting the plurality of excitations having the plurality of different frequencies; adding a substantially sinusoidal excitation having multiple frequencies to the simultaneous multi-rate excitation; and outputting the simultaneous multi-rate excitations; A data storage device, wherein detecting the frequency response of the actuator mechanism includes detecting a frequency response of the actuator mechanism to the simultaneous multi-rate excitation.

6. Further, detecting the frequency response of the actuator mechanism in response to the multi-rate excitation includes determining a multi-rate error rejection transfer function based at least in part on the multi-rate excitation; 6. The data storage device of claim 5, wherein determining the multi-rate error rejection transfer function comprises performing a Fourier transform of the simultaneous multi-rate excitation and at least one of a single-rate servo control loop response, a multi-rate servo control loop response, and a multi-rate notch filter input.

7. the one or more processing devices are further configured to select a plurality of frequencies for the multi-rate excitation prior to outputting the multi-rate excitation; 6. The data storage device of claim 5, wherein selecting the multiple frequencies for the multi-rate excitation comprises selecting multiple frequencies above the Nyquist frequency that do not alias to alias frequencies below the Nyquist frequency.

8. 6. The data storage device of claim 5, further comprising: selecting an amplitude per frequency for the multi-rate excitation, wherein selecting the amplitude per frequency comprises selecting an amplitude per frequency that avoids causing signal saturation in the actuator mechanism control system.

9. the one or more processing devices:

6. The data storage device of claim 1, further configured to output a single-rate excitation to the single-rate compensation filter of the actuator mechanism control system such that a multi-rate compensation filter input based at least in part on the multi-rate excitation is further based at least in part on an output of the single-rate compensation filter.

10. further comprising: outputting the multi-rate excitation; outputting a primary actuator multi-rate excitation to a primary actuator control subsystem of the actuator mechanism control system comprising the primary actuator multi-rate notch filter; and outputting at least one fine actuator multi-rate excitation to at least one fine actuator control subsystem of said actuator mechanism control system comprising said at least one fine actuator multi-rate notch filter.

11. The data storage device of claim 10 , wherein the primary actuator control subsystem and the at least one fine actuator control subsystem share a common input.

12. 11. The data storage device of claim 10, wherein an output of the at least one fine actuator control subsystem is coupled to a fine actuator estimator that is coupled to an input to the primary actuator control subsystem.

13. detecting the frequency response of the actuator mechanism in response to the multi-rate excitation; Detecting a frequency response of a primary actuator; and detecting a frequency response of the at least one fine actuator; calibrating the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; calibrating the primary actuator multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the primary actuator; and calibrating the at least one fine actuator multi-rate notch filter based at least in part on the detected frequency response of the at least one fine actuator.

14. 1. A method comprising: outputting, by one or more processing devices, the multi-rate excitation to at least one multi-rate notch filter of an actuator mechanism control system, the actuator mechanism control system configured to position one or more heads proximate to one or more disk surfaces of a data storage device; detecting, by the one or more processing devices, a frequency response of an actuator mechanism in response to the multi-rate excitation; calibrating, by the one or more processing devices, the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; the one or more processing devices are further configured to output a multirate control input to the at least one multirate notch filter, the multirate control input being based at least in part on a multirate error rejection transfer function; the multi-rate error rejection transfer function is based at least in part on the multi-rate excitation; The method, wherein calibrating the at least one multi-rate notch filter includes calibrating based at least in part on the multi-rate error rejection transfer function.

15. A method comprising: outputting, by one or more processing devices, the multi-rate excitation to at least one multi-rate notch filter of an actuator mechanism control system, the actuator mechanism control system configured to position one or more heads proximate to one or more disk surfaces of a data storage device; detecting, by the one or more processing devices, a frequency response of an actuator mechanism in response to a multi-rate excitation; calibrating, by the one or more processing devices, the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; outputting the multi-rate excitation includes outputting a plurality of excitations having a plurality of different frequencies to the at least one multi-rate notch filter of the actuator mechanism control system; outputting the plurality of excitations having the plurality of different frequencies; adding a substantially sinusoidal excitation having multiple frequencies to the simultaneous multi-rate excitation; and outputting the simultaneous multi-rate excitations; Detecting the frequency response of the actuator mechanism detecting a frequency response of the actuator mechanism to the simultaneous multi-rate excitation.

16. The method of claim 15, further comprising: detecting the frequency response of the actuator mechanism in response to the multi-rate excitation.

16. The method of claim 15, further comprising: determining a multi-rate error rejection transfer function based at least in part on the multi-rate excitation, wherein determining the multi-rate error rejection transfer function comprises performing a Fourier transform of the simultaneous multi-rate excitation and at least one of a single-rate servo control loop response, a multi-rate servo control loop response, and a multi-rate notch filter input.

17. A method comprising: outputting, by one or more processing devices, the multi-rate excitation to at least one multi-rate notch filter of an actuator mechanism control system, the actuator mechanism control system configured to position one or more heads proximate to one or more disk surfaces of a data storage device; detecting, by the one or more processing devices, a frequency response of an actuator mechanism in response to a multi-rate excitation; calibrating, by the one or more processing devices, the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; The at least one multirate notch filter: a primary actuator multirate notch filter; at least one fine actuator multi-rate notch filter.

18. One or more processing devices, means for outputting a multi-rate excitation to at least one multi-rate notch filter in an actuator mechanism control system configured to control an actuator mechanism, the actuator mechanism being configured to position one or more heads proximate to one or more disk surfaces; means for detecting a frequency response of the actuator mechanism in response to the multi-rate excitation; means for calibrating the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; means for outputting a multirate control input to the at least one multirate notch filter, the multirate control input being based at least in part on a multirate error rejection transfer function; the multi-rate error rejection transfer function is based at least in part on the multi-rate excitation; calibrating the at least one multi-rate notch filter includes calibrating based at least in part on the multi-rate error rejection transfer function; One or more processing devices, where outputting the multi-rate excitation includes outputting a plurality of excitations having a plurality of different frequencies to the at least one multi-rate notch filter of the actuator mechanism control system.

19. One or more processing devices, comprising: means for outputting a multi-rate excitation to at least one multi-rate notch filter in an actuator mechanism control system configured to control an actuator mechanism, the actuator mechanism being configured to position one or more heads proximate to one or more disk surfaces; means for detecting a frequency response of the actuator mechanism in response to the multi-rate excitation; means for calibrating the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; outputting the multi-rate excitation includes outputting a plurality of excitations having a plurality of different frequencies to the at least one multi-rate notch filter of the actuator mechanism control system; outputting the plurality of excitations having the plurality of different frequencies; adding a substantially sinusoidal excitation having multiple frequencies to the simultaneous multi-rate excitation; and outputting the simultaneous multi-rate excitations; One or more processing devices, wherein detecting the frequency response of the actuator mechanism includes detecting a frequency response of the actuator mechanism to the simultaneous multi-rate excitation.

20. One or more processing devices, comprising: means for outputting a multi-rate excitation to at least one multi-rate notch filter in an actuator mechanism control system configured to control an actuator mechanism, the actuator mechanism being configured to position one or more heads proximate to one or more disk surfaces; means for detecting a frequency response of the actuator mechanism in response to the multi-rate excitation; means for calibrating the at least one multi-rate notch filter of the actuator mechanism control system based at least in part on the detected frequency response of the actuator mechanism; The at least one multirate notch filter: a primary actuator multirate notch filter; at least one fine actuator multi-rate notch filter;

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