REDUCING NOISE IN BACK EMF SENSING FOR DATA STORAGE
Various illustrative aspects are directed to a data storage device comprising: a voice coil motor (VCM) and one or more processing devices, configured to actuate the VCM, switch on measuring a back electromotive force (BEMF) from the VCM for intervals of an initial BEMF measurement that are free of spikes in the initial BEMF measurement, and process a measured BEMF signal from the intervals of the initial BEMF measurement that are free of spikes in a change of current term of the initial BEMF measurement.
Data storage devices such as disk drives comprise one or more disks, and one or more read/write heads connected to distal ends of actuator arms, which are rotated by actuators (e.g., a voice coil motor, one or more fine actuators) to position the heads radially over surfaces of the disks, at carefully controlled fly heights over the disk surfaces. The disk surfaces each comprise a plurality of radially spaced, concentric tracks for recording user data sectors and servo wedges or servo sectors. The servo tracks are written on previously blank disk drive surfaces as part of the final stage of preparation of the disk drive. The servo sectors comprise head positioning information (e.g., a track address) which is read by the heads and processed by a servo control system to control the actuator arms as they seek from track to track.
The coarse head position information is processed to position a head over a target data track during a seek operation, and the 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 the one or more actuators in order to actuate the head radially over the disk in a direction that reduces the PES.
SUMMARYThe following presents a summary relating to one or more aspects and/or embodiments disclosed herein. The following summary should not be considered an extensive overview relating to all contemplated aspects and/or embodiments, nor should the following summary be regarded to identify key or critical elements relating to all contemplated aspects and/or embodiments or to delineate the scope associated with any particular aspect and/or embodiment. Accordingly, the following summary has the sole purpose to present certain concepts relating to one or more aspects and/or embodiments relating to the mechanisms disclosed herein in a simplified form to precede the detailed description presented below.
In some examples, Back Electromotive Force (BEMF) measurements of a Voice Coil Motor (VCM) may be utilized to estimate the velocity of an actuator head, for instance, during Open Loop Boot (OLB) spiral, or when the actuator head is on a ramp. As used herein, the term “OLB spiral” may refer to an initial phase for a disk drive when the first spiral is being written on a blank disk. In some cases, a filter may be employed at the output of a BEMF extraction circuit to reduce the amount of noise entering a circuit used to measure the BEMF. In some circumstances, however, this filter introduces extra noise in the form of transient spikes, adversely impacting the accuracy of the BEMF measurement (hereafter BEMFm). These transient spikes are caused by a rapid change of current term (e.g., a rate of change of current term exceeding a threshold) of the VCM and the inductance of the VCM driven by a power amplifier employing a high bandwidth current feedback. Various aspects disclosed herein are directed to enhancing the accuracy of the BEMF measurement (BEMFm) for data storage devices, such as hard disk drives, among other aspects. In some embodiments, the self-induced noise (i.e., transient spikes) introduced by the filter may be removed using one or more switches at the input of the low pass filter. These switches may be implemented in an analog or a digital manner. Further, these switches may help remove, or at least reduce, the effects of the transient spikes on the BEMF measurement (BEMFm) by preventing the transient spikes from entering the low pass filter. In this way, the BEMFm accuracy and speed is enhanced by reducing the wait time required for the transient spikes to settle, which serves to optimize OLB acceleration and Load Unload (LUL) phases for disk drives, to name two non-limiting examples.
Various illustrative aspects are directed to a data storage device comprising a voice coil motor (VCM) and one or more processing devices configured to actuate the VCM, switch on measuring a BEMF from the VCM for intervals of an initial BEMF measurement that are free of spikes in the initial BEMF measurement and process a measured BEMF signal from the intervals of the initial BEMF measurement that are free of spikes in a change of current term of the initial BEMF measurement.
Various illustrative aspects are directed to a method of operating a data storage device, comprising actuating by one or more processing devices, a VCM, switching on, by the one or more processing devices, measurement of a BEMF from the VCM for intervals of an initial BEMF measurement that are free of spikes in the initial BEMF measurement, and processing, by the one or more processing devices, a measured BEMF signal from the intervals of the initial BEMF measurement that are free of spikes in a change of current term of the initial BEMF measurement.
Various illustrative aspects are directed to one or more processing devices, comprising means for actuating a VCM, means for switching on measuring a BEMF from the VCM for intervals of an initial BEMF measurement that are free of spikes in the initial BEMF measurement, and means for processing a measured BEMF signal from the intervals of the initial BEMF measurement that are free of spikes in a change of current term of the initial BEMF measurement.
Various further aspects are depicted in the accompanying figures and described below and will be further apparent based thereon.
Various features and advantages of the technology of the present disclosure will be apparent from the following description of particular examples of those technologies, and as illustrated in the accompanying drawings. The drawings are not necessarily to scale; the emphasis instead is placed on illustrating the principles of the technological 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.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
The embodiments described below are not intended to limit the invention to the precise form disclosed, nor are they intended to be exhaustive. Rather, the embodiment is presented to provide a description so that others skilled in the art may utilize its teachings. Technology continues to develop, and elements of the described and disclosed embodiments may be replaced by improved and enhanced items, however the teaching of the present disclosure inherently discloses elements used in embodiments incorporating technology available at the time of this disclosure.
As previously described, in hard disk drives or HDDs, the BEMF measurement (herein referred to as BEMFm) may be used as a way to measure the velocity of an actuator arm (e.g., actuator arm 40 in
In some cases, a BEMF voltage drop is created across the VCM coil, for instance, when the coil is moving in a magnetic field. The voltage across the VCM coil is a function of the BEMF and the impedance of the coil (i.e., both resistive and inductive effects) in response to a VCM current. Specifically, the voltage developed across the VCM coil may include three components, such as a resistive component (e.g., a product of the current, IVCM, provided to the VCM coil by the driver and the VCM coil’s intrinsic resistance, RVCM), an inductance component (LVCM*di/dt), and the BEMF. In some cases, the inductance component may be a transient voltage produced by the VCM coil’s intrinsic inductance. For instance, changes to the VCM current may contribute to voltage drops across the VCM that are not due to the induced BEMF. To differentiate between the various BEMF terms, the following terminology is used herein and elsewhere throughout the disclosure. Specifically, the terms “actual BEMF”, “BEMF”, or “true BEMF” may be used to refer to the actual BEMF voltage drop created across the VCM coil; the terms “measured BEMF”, “ADC filter voltage”, or “BEMFm” refers to the voltage measured at or near the output of the low pass filter (e.g., filter 435 in
Turning now to
Actuator assembly 19 comprises a primary actuator 20 (e.g., a voice coil motor (“VCM”)) and a number of actuator arms 40 (e.g., topmost actuator arm 40A, as seen in the perspective view of
As noted above, the BEMF voltage drop is proportional to VCM velocity. Typically, the true or actual BEMF voltage drop does not spike since the velocity does not spike. For instance, the velocity, which is the integration of acceleration, may not spike as it takes some time to change the velocity. In some circumstances, however, the BEMF measurement (BEMFm) signal may contain spikes because of the way it is extracted (e.g., due to an inaccurate di/dt term or the absence of the di/dt term). Aspects of the present disclosure are directed to enhancing the accuracy of the BEMF measurement (BEMFm) by reducing the effects of the transient spikes on the BEMF measurement. In some examples (82), the control circuitry 22 is configured to control the actuation of the primary actuator (i.e., VCM). Further, the VCM 20 is configured to actuate the head 18 over the disk surfaces 17. The control circuitry 22 is also configured to switch on measuring BEMF (BEMFm) from the VCM 20 for intervals of the initial BEMF measurement, i.e., BEMFm0, that are free of spikes in the initial BEMF measurement (84) and process a measured BEMF signal from intervals of the initial BEMF measurement (BEMFm0) that are free of spikes in a change of current term of the initial BEMF measurement (86). In some cases, a spike comprises rapid changes in the initial BEMF measurement (BEMFm0) over time. As an example, a spike in the BEMFm0 may be defined when a rate of change in the BEMFm0 exceeds a threshold. While not necessary, the threshold may be pre-defined (e.g., above 2 V in < 0.01 ms, above 4 V in < 0.01 ms, less than -2 V in < 0.01 ms, to name a few non-limiting examples). In another cases, a spike in the BEMFm0 comprises rapid changes in the BEMFm0 over time, where the rate of change is relative to a set of bounds on a rate of change for a majority of the BEMFm0 signal. In some cases, if the rate of change for a majority of the BEMFm0 signal is between an upper bound ‘X’ and a lower bound ‘Y’, a spike in the BEMFm0 may be defined when a rate of change in the BEMFm0 is above or below an upper/lower threshold, where the upper and lower thresholds are relative to the upper and lower bounds. Said another way, spikes in the BEMFm0 may be defined by intervals of the BEMFm0 that comprise anomalous rates of change relative to the majority of the BEMFm0 signal.
As noted above, the VCM 20 generates a BEMF, where the BEMF is proportional to the velocity of the VCM 20. Accurate measurement of the BEMF facilitates in more accurate control of the VCM 20, which is especially important when there is no servo sector information available (e.g., during OLB phase, when the first spiral is written on the disk; outside servo information area, such as during load-unload or LUL operations), and when detecting the rotational speed of the VCM 20 is the only source of positional information. Since the VCM is associated with an inductance (L), a transient spike in the form of a product of the inductance and a rate of change of current term, such as, but not limited to, the Lm di/dt transient spike, is introduced. In some examples, ensuring that this transient spike is bypassed or prevented from entering the low pass filter, in accordance with aspects of this disclosure (e.g., shown as BEMF extraction circuit 440 in
It should be noted that, as used herein, the term “transient spike” may refer to the di/dt transient spike, or alternatively, the L,*di/dt transient spike. Other types of transient spikes associated with the VCM, or other components of the disk drive (e.g., the spindle motor), are contemplated in different embodiments, and the examples listed herein are not intended to be limiting.
In one embodiment, the servo data (e.g., servo sectors 32) read from the disk surface 17, i.e., in order to servo the head over the disk during access operations, may be self-written to the disk using the control circuitry 22 internal to the disk drive. In some examples, a plurality of spiral servo tracks are first written to the disk surface 17, and then servo sectors 32 are written to the disk while servoing on the spiral servo tracks. In order to write the spiral servo tracks to the disk surface 17, at least one bootstrap spiral track is first written to the disk without using position feedback from servo data (i.e., the actuator or VCM 20 is controlled open loop with respect to servo data on the disk). Before writing the bootstrap spiral track, feedforward compensation is generated by evaluating the BEMFm voltage generated by the VCM 20 during a calibration seek (where the BEMFm voltage represents an estimated velocity of the VCM). The bootstrap spiral track is then written to the disk using the feed-forward compensation. Alternatively, the measured BEMFm can be used for velocity feedback control when writing the OLBs.
In some embodiments, the BEMF voltage (shown as Vbemf within the VCM driver 402 in
As noted above, in some cases, a switch 405 coupled to a low pass filter 435, the low pass filter 435 comprising a resistor (Rfilter 410) and a capacitor (Cfilter), may be opened at the point of VCM DAC update, which allows the transient spike (e.g., Lm di/dt transient spike) to settle. In some cases, the switch 405 is opened by the control circuitry 22. Further, after the transient spike settles (e.g., between 50 to 80 us), the control circuitry 22 closes (or turns on) the switch 405 for regular low pass filtering. In this way, the transient spike from the VCM driver circuit 402 is prevented from entering the low pass filter 435 from the BEMF extraction circuit 440, which serves to reduce noise in the BEMF measurement, i.e., BEMFm. Additionally, or alternatively, by controlling the opening/closing of the switch 405, the low pass filter 435 can more effectively filter out the BEMF sensing noise, as compared to the prior art. In some aspects, controlling the opening/closing of the switch 405 also removes the need to wait for filter setting following the VCM’s transient spike. By controlling the opening/closing of the switch 405, the control circuitry 22 switches on BEMF measurement from the VCM for intervals of BEMFm0 that are free of transient spikes in the BEMFm0. The control circuitry 22 then processes the measured BEMFm signals from intervals of the initial BEMF measurement, BEMFm0, that are free of spikes in a change of current term (e.g., di/dt, L*di/dt) of the BEMFm0 equations (2) and (3).
Further,
Turning now to
Conceptual graph 700-b depicts an example of voltage measurements against time for the low pass filter (e.g., VADCFLT in
As seen in
While not necessary, in some embodiments, the OFF period of the switch (e.g., switch 605 coupled to the low pass filter 612) may be longer than the duration of the VCM transient spike. Alternatively, the OFF period of the switch may be at or around (e.g., slightly longer than, slightly shorter than) the duration of the VCM transient spike. For example, the OFF period of the switch may be at least 90%, at least 95%, at least 110%, at least 120%, etc., of the transient spike duration. In one non-limiting example, the OFF period of the switch (i.e., the duration for which the switch is opened) may be less than 80 µs (e.g., 50 µs, 60 µs, etc.). In one non-limiting example, the control circuitry 22 may calculate an estimate of the BEMF from the VADCFLT 66-b (e.g., shown in graph 700-b), for example, from the VADCFLT 66-b from 80 µs to about 400 µs.
In accordance with another aspect of the present disclosure, the corner frequency of the low pass filter may be selected such that the transient spikes from the VCM 20 can be bypassed after a VCM DAC update. In some cases, the transient spikes may be bypassed (or ignored) by waiting to perform sampling until a low pass filter “OFF period” begins. Next, the ADC filter waveforms (i.e., without the transients) may be read one or more times and averaged (or digitally filtered using any other means). In this way, the ADC filter sample ignores all (or at least a portion of) the effects associated with the VCM transients (e.g., L *di/dt or di/dt transient spikes). While not necessary, in some embodiments, this filtering may be performed in firmware (FW). As shown in
It should be noted that the example scenarios listed herein are not intended to be limiting, and other situations not described herein may lend to rapid changes in VCM current 406. For instance, VCM current 406 may be subject to sharp changes in other situations experienced during normal operation of a disk drive. In some examples, rapid changes in the VCM current 406 may cause VCM voltage spikes (e.g., transient voltage spike 63). The VCM voltage spikes 63 may be calculated as a function of the inductance (L) of the VCM and a rate of change of the measured current term (di/dt). For instance, the VCM voltage spikes 63 may be represented by a L*di/dt term in the BEMF equation. As used herein, the term “transient spikes” may refer to the VCM voltage spikes (e.g., L*di/dt transient spikes), or alternatively, the rate of change of current term transient spikes (e.g., di/dt transient spikes). Currently used techniques for BEMF estimation often ignore the VCM voltage spikes (i.e., the L*di/dt term) in the BEMF estimation equation. According to aspects of this disclosure, in some instances, an L*di/dt term (e.g., non-transient) may be considered in estimating the BEMF. Equations (1)-(3) shown below depict the relation between the BEMF, the VCM voltage, and the L*di/dt term.
Note here that equation (1) represents the relationship between the voltage applied to the VCM and the corresponding current and BEMF. Equations (2) and (3) show how to derive the raw BEMF measurement before low pass filtering, i.e., BEMFm0, from the known motor parameters (Rm and Lm), the current sensing resistor (RS), and the measured variables VRS (i.e., VAOUT-VISENSE, which represents the voltage across RRS) and VVCM (i.e., VISENSE-VBOUT, which represents the voltage across the VCM). Because differentiating a quickly changing current is noisy, prior art techniques simply drop the d(VRS ÷ RS)/dt term in the analog BEMF estimation; In this disclosure, we retain the differentiator term for the BEMFm0, but add the switch 405 to bypass the spiky current change period where the d(VRS ÷ RS)/dt cannot be measured well due to being noisy and/or signal saturations. As a result, the BEMFm, which is the low passed filtered version of BEMFm0, has a negligible (or substantially lower) spike and latency as compared to the prior art. In some aspects of the present disclosure, the control circuitry 22 may utilize a practical differentiator (PD) when implementing equations (2) or (3) and an optional switch to bypass the transient spikes (e.g., transient spike 1172, VCM noise 1171) when filtering the initial BEMF measurement (BEMFm0) to obtain BEMFm. The BEMF estimation may be performed using either analog or digital means. In some cases, the control circuitry 22 samples the voltage across the sensing resistor (e.g., shown as Rs in
As seen,
Any suitable control circuitry may be employed to implement the flow diagrams in the above examples, 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 data storage controller, or certain operations described above may be performed by a read channel and others by a data storage controller. In one example, the read channel and data storage controller are implemented as separate integrated circuits, and in another example, they are fabricated into a single integrated circuit or system on a chip (SoC). In addition, the control circuitry may include a preamp circuit, or a VCM power driver circuit, implemented as a separate integrated circuit, integrated into the read channel or data storage controller circuit, or integrated into an SoC.
In some examples, 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 some examples, they may be stored on a non-volatile semiconductor memory device, component, or system external to the microprocessor, or integrated with the microprocessor in an SoC. In some examples, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In some examples, the control circuitry (e.g., control circuitry 22) comprises suitable logic circuitry, such as state machine circuitry. In some examples, at least some of the flow diagram blocks may be implemented using analog circuitry (e.g., analog comparators, timers, etc.), and in other examples at least some of the blocks may be implemented using digital circuitry or a combination of analog and digital circuitry.
In various examples, one or more processing devices may comprise or constitute the control circuitry as described herein, and/or may perform one or more of the functions of control circuitry as described herein. In various examples, the control circuitry, or other one or more processing devices performing one or more of the functions of control circuitry as described herein, may be abstracted away from being physically proximate to the disks and disk surfaces. The control circuitry, or other one or more processing devices performing one or more of the functions of control circuitry as described herein, may be part of or proximate to a rack of or a unitary product comprising multiple data storage devices, or may be part of or proximate to one or more physical or virtual servers, or may be part of or proximate to one or more local area networks or one or more storage area networks, or may be part of or proximate to a data center, or may be hosted in one or more cloud services, in various examples.
In various examples, a disk drive may include a magnetic disk drive, an optical disk drive, a hybrid disk drive, or other types of disk drive. In addition, 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 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. 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 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 to, removed from, or rearranged compared to the disclosed examples.
While certain example embodiments are described herein, these embodiments are presented by way of example only, and do not limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description implies that any particular feature, characteristic, step, module, or block is necessary or indispensable. 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.
Method 80 and other methods of this disclosure may include other steps or variations in various other embodiments. Some or all of any of method 80 may be performed by or embodied in hardware, and/or performed or executed by a controller, a CPU, an FPGA, a SoC, a multi-processor system on chip (MPSoC), which may include both a CPU and an FPGA, and other elements together in one integrated SoC, or other processing device or computing device processing executable instructions, in controlling other associated hardware, devices, systems, or products in executing, implementing, or embodying various subject matter of the method.
Data storage systems, devices, and methods are thus shown and described herein, in various foundational aspects and in various selected illustrative applications, architectures, techniques, and methods for reducing noise in BEMF sensing for data storage, and other aspects of this disclosure. Persons skilled in the relevant fields of art will be well-equipped by this disclosure with an understanding and an informed reduction to practice of a wide panoply of further applications, architectures, techniques, and methods for reducing noise in BEMF sensing for data storage, and other aspects of this disclosure encompassed by the present disclosure and by the claims set forth below.
As used herein, the recitation of “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 descriptions of the disclosed examples are provided to enable any person skilled in the relevant fields of 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 the present disclosure, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the 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.
The present disclosure and many of its attendant advantages will be understood by the foregoing description, and various changes may be made in the form, construction, and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory, and the following claims encompass and include a wide range of embodiments, including a wide range of examples encompassing any such changes in the form, construction, and arrangement of the components as described herein.
While 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 disclosure is not limited to them. All subject matter described herein are presented in the form of illustrative, non-limiting examples, and not as exclusive implementations, whether or not they are explicitly called out as examples as described. Many variations, modifications, and additions are possible within the scope of the examples of the disclosure. More generally, examples in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined in blocks differently in various examples of the disclosure or described with different terminology, without departing from the spirit and scope of the present disclosure and the following claims. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.
Claims
1. A data storage device comprising:
- a voice coil motor (VCM); and
- one or more processing devices, configured to: actuate the VCM; switch on measuring a back electromotive force (BEMF) from the VCM for intervals of an initial BEMF measurement that are free of spikes in the initial BEMF measurement, free of spikes being indicative of amplitude measurements not exceeding 5% of a peak amplitude of a preceding interval where a spike has occurred; and process a measured BEMF signal from the intervals of the initial BEMF measurement that are free of spikes in a change of current term of the initial BEMF measurement.
2. The data storage device of claim 1, wherein the one or more processing devices are further configured to switch off measuring the BEMF from the VCM for an interval that comprises a spike in a change of current term of the initial BEMF measurement.
3. The data storage device of claim 1, wherein the one or more processing devices are further configured to switch on measuring the BEMF from the VCM for intervals of the initial BEMF measurement that are free of spikes in the change of current term of the initial BEMF measurement, and wherein the change of current term of the initial BEMF measurement is based at least in part on a rate of change of current flowing through the VCM.
4. The data storage device of claim 1, wherein the spikes in the initial BEMF measurement comprise a rate of change of current in the initial BEMF measurement exceeding a threshold.
5. The data storage device of claim 1, wherein the one or more processing devices are further configured to control the VCM to accelerate,
- wherein the spikes in the initial BEMF measurement comprise changes in the initial BEMF measurement during intervals when the VCM is accelerated or decelerated.
6. The data storage device of claim 1, further comprising:
- one or more disks; and
- an actuator arm assembly comprising one or more disk heads and the VCM;
- wherein the one or more processing devices are further configured to control the actuator arm assembly to actuate the one or more disk heads over corresponding disk surfaces of the one or more disks.
7. The data storage device of claim 6, wherein the one or more processing devices are configured to control the actuator arm assembly to write at least one bootstrap spiral track from an inner diameter to an outer diameter of at least one of the one or more disks, and wherein the at least one bootstrap spiral track is written open loop and using at least one of the one or more disk heads.
8. The data storage device of claim 6, wherein the one or more processing devices are configured to control the actuator arm assembly to unload at least one of the one or more disk heads on at least one ramp of the data storage device, and wherein the spikes in the initial BEMF measurement comprise changes in the initial BEMF measurement during intervals when the at least one disk head is unloaded on the at least one ramp.
9. The data storage device of claim 6, wherein the one or more processing devices are configured to control the actuator arm assembly to load at least one of the one or more disk heads from at least one ramp of the data storage device to a corresponding disk surface of at least one disk, and wherein the spikes in the initial BEMF measurement comprise changes in the BEMF during intervals when the at least one disk head is loaded on the corresponding disk surface.
10. The data storage device of claim 1, further comprising:
- a filter circuit; and
- a switch coupled to an input of the filter circuit;
- wherein the one or more processing devices are further configured to control the switch to open during intervals of the initial BEMF measurement that comprise spikes in the change of current term of the initial BEMF measurement to prevent the spikes from entering the filter circuit.
11. The data storage device of claim 10, wherein the one or more processing devices are further configured to control the switch to close during intervals of the initial BEMF measurement that are free of spikes in the change of current term of the initial BEMF measurement.
12. A method of operating a data storage device, comprising:
- actuating, by one or more processing devices, a voice coil motor (VCM);
- selectively switching on, by the one or more processing devices, measurement of a back electromotive force (BEMF) from the VCM for intervals of an initial BEMF measurement in the initial BEMF measurement, based on a measurement of spikes, to reduce spikes in a change of current term of the initial BEMF measurement; and
- processing, by the one or more processing devices, a measured BEMF signal from the intervals of the initial BEMF measurement that have less than or equal to a threshold number of spikes in the change of current term of the initial BEMF measurement.
13. The method of claim 12, further comprising:
- switching off, by the one or more processing devices, measuring the BEMF from the VCM for an interval that comprises a spike in a change of current term of the initial BEMF measurement.
14. The method of claim 12, further comprising:
- switching on, by the one or more processing devices, measuring the BEMF from the VCM for intervals of the initial BEMF measurement that are free of spikes in the change of current term of the initial BEMF measurement,
- and wherein the change of current term of the initial BEMF measurement is based at least in part on a rate of change of current flowing through the VCM.
15. The method of claim 12, wherein the spikes in the initial BEMF measurement comprise a rate of change of current in the initial BEMF measurement exceeding a threshold.
16. The method of claim 12, further comprising:
- controlling, by the one or more processing devices, acceleration of the VCM,
- and wherein the spikes in the initial BEMF measurement comprise changes in the initial BEMF measurement during intervals when the VCM is accelerated or decelerated.
17. The method of claim 12, further comprising:
- controlling, by the one or more processing devices, an actuator arm assembly to actuate one or more disk heads over corresponding disk surfaces of one or more disks;
- writing, by at least one of the one or more disk heads, at least one bootstrap spiral track, wherein the at least one bootstrap spiral track is written open loop;
- controlling, by the one or more processing devices, the actuator arm assembly to unload the at least one disk head on at least one ramp;
- and wherein the spikes in the initial BEMF measurement comprise changes in the initial BEMF measurement during intervals when the at least one bootstrap spiral track is written, the at least one disk is loaded or unloaded, or a combination thereof.
18. The method of claim 12, further comprising:
- opening, by the one or more processing devices, a switch coupled to an input of a filter circuit during intervals of the initial BEMF measurement that comprise spikes in the change of current term of the initial BEMF measurement to prevent the spikes from entering the filter circuit; and
- closing, by the one or more processing devices, the switch during intervals of the initial BEMF measurement that are free of spikes in the change of current term of the initial BEMF measurement.
19. One or more processing devices comprising:
- means for actuating a voice coil motor (VCM);
- means for switching on measuring a back electromotive force (BEMF) from the VCM for intervals of an initial BEMF measurement that are free of spikes in a change of current term of the initial BEMF measurement; and
- means for processing a measured BEMF signal from the intervals of the initial BEMF measurement that are free of spikes in the change of current term of the initial BEMF measurement.
20. The one or more processing devices of claim 19, further comprising means for switching off measuring the BEMF from the VCM for an interval that comprises a spike in a change of current term of the initial BEMF measurement.
21. The one or more processing devices of claim 20, wherein the means for switching off is configured to switch off measuring the BEMF for a period of time at a digital-to-analog conversion (DAC) update of the one or more processing devices.
22. The one or more processing devices of claim 19, further comprising a BEMF extraction circuit and a low pass filter, wherein:
- an output of the low pass filter is provided to the means for processing; and
- the means for switching on comprises one or more switches coupled to (1) an output of the BEMF extraction circuit, and (2) an input of the low pass filter.
23. A data storage device comprising the one or more processing devices of claim 19.
Type: Application
Filed: Mar 14, 2022
Publication Date: Oct 5, 2023
Inventors: Guoxiao Guo (Irvine, CA), Jianbin Nie (Fremont, CA), Triet Tieu (Milipitas, CA), Duc H. Banh (San Jose, CA), Tianyu Jiang (San Jose, CA)
Application Number: 17/693,626