DATA STORAGE DEVICE CONCURRENTLY CONTROLLING AND SENSING A SECONDARY ACTUATOR FOR ACTUATING A HEAD OVER A DISK
A data storage device is disclosed comprising a voice coil motor (VCM) and a secondary actuator configured to actuate a head over a disk. A control signal is applied to the secondary actuator while processing a sensor signal generated by the secondary actuator. A vibration signal is generated based on the sensor signal, wherein the vibration signal has a cut-off frequency between ten percent and ninety percent of a bandwidth of a control loop for controlling the secondary actuator.
This application is a continuation of U.S. patent application Ser. No. 14/865,858 (Atty. Docket No. T8190), filed on Sep. 25, 2015, entitled “DATA STORAGE DEVICE CONCURRENTLY CONTROLLING AND SENSING A SECONDARY ACTUATOR FOR ACTUATING A HEAD OVER A DISK,” which is hereby incorporated by reference in its entirety
BACKGROUNDData storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
In the embodiment of
The secondary actuator 18 may comprise any suitable elements for actuating the head 20 over the disk 22, such as one or more piezoelectric elements. Further, the secondary actuator 18 may actuate the head 20 in any suitable manner, wherein in the example of
In one embodiment, the secondary actuator 18 may operate as a sensor for sensing vibrations affecting the disk drive. That is, a vibration may cause a rotational displacement of the actuator arm 38 which may induce an electrical response (sensor signal) in the secondary actuator 18. In one embodiment, the sensor signal may manifest on the same electrical lead used to apply the control signal 40 to the secondary actuator 18, and in other embodiments, there may be a dedicated lead coupled to the secondary actuator 18 for conducting the sensor signal. In one embodiment, the sensor signal may be processed to generate a vibration signal representing a vibration affecting the disk drive (magnitude and/or phase). The vibration signal may be used for any suitable purpose, such as for aborting a write operation to prevent an off-track write, or for generating a feed-forward control signal that compensates for the vibration in the servo control loop.
Any suitable control circuitry may be employed to implement blocks 70 and 74 in
In the embodiment of
In one embodiment, the ratio of the current mirror F and the gain K are selected to enable the capacitance C′ of the sensor capacitor 80 to be significantly less than the capacitance C of the secondary actuator 18 (e.g., two times less). In this manner, the capacitor C′ in the sensor capacitor 80 may be fabricated as part of an integrated circuit rather than implemented as a more expensive external capacitor. For example, if the capacitor C′ is fabricated to be approximately two times smaller than the capacitor C of the secondary actuator 18, the current mirror F may be fabricated with an approximately unitary ratio and the gain K adapted to approximately two. In other embodiments, the ratio of the current mirror F and/or the gain K may be selected so that the capacitor C′ of the sensor capacitor 80 may be larger than the capacitor C of the secondary actuator 18.
Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In other embodiments, the control circuitry may be implemented within a suitable preamp circuit, within a power large scale integrated (PLSI) circuit, or within a stand-alone integrated circuit.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry. In some embodiments, the control circuitry may comprise suitable conversion circuitry so that at least some of the operations are implemented in the digital domain, and in other embodiments at least some of the operations are implemented in the analog domain.
In various embodiments, a disk drive may include a magnetic disk drive, an optical disk drive, etc. In addition, while the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives, solid state drives, hybrid drives, etc. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.
Claims
1. A method of operating a data storage device, the method comprising:
- actuating a head over a disk using a voice coil motor (VCM) and a secondary actuator;
- applying a control signal to the secondary actuator and concurrently process a sensor signal generated by the secondary actuator; and
- generating a vibration signal based on the sensor signal and a sensor capacitor, wherein a capacitance of the sensor capacitor is at least two times less than a capacitance of the secondary actuator.
2. The method as recited in claim 1, wherein the vibration signal has a cut-off frequency between ten percent and ninety percent of a bandwidth of a control loop for controlling the secondary actuator.
3. The method as recited in claim 1, wherein:
- a control loop for controlling the secondary actuator has a high-pass response; and
- the vibration signal has a cut-off frequency above a cut-off frequency of the high-pass response of the control loop for the secondary actuator.
4. The method as recited in claim 1, wherein the vibration signal has a cut-off frequency higher than a cut-off frequency of a response of a control loop for controlling the VCM.
5. The method as recited in claim 1, further comprising:
- generating a sensor current proportional to a current applied to the secondary actuator due to the control signal;
- estimating a capacitive voltage of the secondary actuator based on the sensor current; and
- generating the vibration signal based on a difference between the sensor signal and the estimated capacitive voltage.
6. The method as recited in claim 5, further comprising estimating the capacitive voltage of the secondary actuator by applying the sensor current to the sensor capacitor.
7. The method as recited in claim 5, further comprising adapting a gain of the sensor capacitor based on the sensor signal and the estimated capacitive voltage.
8. The method as recited in claim 7, further comprising:
- low pass filtering a difference between the sensor signal and the estimated capacitive voltage to generate a low-pass signal; and
- adapting the gain of the sensor capacitor based on the low-pass signal.
9. The method as recited in claim 1, further comprising generating a feed-forward compensation signal applied to the secondary actuator based on the vibration signal.
10. Control circuitry configured to control a voice coil motor (VCM) and a secondary actuator to actuate a head over a disk, the control circuitry configured to:
- apply a control signal to the secondary actuator and concurrently process a sensor signal generated by the secondary actuator; and
- generate a vibration signal based on the sensor signal and a sensor capacitor, wherein a capacitance of the sensor capacitor is at least two times less than a capacitance of the secondary actuator.
11. The control circuitry as recited in claim 10, wherein the vibration signal has a cut-off frequency between ten percent and ninety percent of a bandwidth of a control loop for controlling the secondary actuator.
12. The control circuitry as recited in claim 10, wherein:
- a control loop for controlling the secondary actuator has a high-pass response; and
- the vibration signal has a cut-off frequency above a cut-off frequency of the high-pass response of the secondary actuator.
13. The control circuitry as recited in claim 10, wherein the vibration signal has a cut-off frequency higher than a cut-off frequency of a response of a control loop for controlling the VCM.
14. The control circuitry as recited in claim 10, further configured to:
- generate a sensor current proportional to a current applied to the secondary actuator due to the control signal;
- estimate a capacitive voltage of the secondary actuator based on the sensor current; and
- generate the vibration signal based on a difference between the sensor signal and the estimated capacitive voltage.
15. The control circuitry as recited in claim 14, further configured to estimate the capacitive voltage of the secondary actuator by applying the sensor current to the sensor capacitor that is proportional to a capacitance of the secondary actuator.
16. The control circuitry as recited in claim 14, further configured to adapt a gain of the sensor capacitor based on the sensor signal and the estimated capacitive voltage.
17. The control circuitry as recited in claim 16, further configured to:
- low pass filter a difference between the sensor signal and the estimated capacitive voltage to generate a low-pass signal; and
- adapt the gain of the sensor capacitor based on the low-pass signal.
18. The control circuitry as recited in claim 10, further configured to generate a feed-forward compensation signal applied to the secondary actuator based on the vibration signal.
19. A data storage device comprising:
- a disk;
- a head;
- a voice coil motor (VCM) and a secondary actuator configured to actuate the head over the disk; and
- control circuitry configured to: apply a control signal to the secondary actuator and concurrently process a sensor signal generated by the secondary actuator; and generate a vibration signal based on the sensor signal, wherein the vibration signal has a cut-off frequency between ten percent and ninety percent of a bandwidth of a control loop for controlling the secondary actuator.
20. The data storage device as recited in claim 19, wherein:
- the control loop for controlling the secondary actuator has a high-pass response; and
- the vibration signal has a cut-off frequency above a cut-off frequency of the high-pass response of the control loop for the secondary actuator.
21. The data storage device as recited in claim 19, wherein the vibration signal has a cut-off frequency higher than a cut-off frequency of a response of a control loop for controlling the VCM.
22. The data storage device as recited in claim 19, wherein the control circuitry is further configured to:
- generate a sensor current proportional to a current applied to the secondary actuator due to the control signal;
- estimate a capacitive voltage of the secondary actuator based on the sensor current; and
- generate the vibration signal based on a difference between the sensor signal and the estimated capacitive voltage.
23. The data storage device as recited in claim 22, wherein the control circuitry is further configured to estimate the capacitive voltage of the secondary actuator by applying the sensor current to a sensor capacitor that is proportional to a capacitance of the secondary actuator.
24. The data storage device as recited in claim 23, wherein the control circuitry is further configured to adapt a gain of the sensor capacitor based on the sensor signal and the estimated capacitive voltage.
25. The data storage device as recited in claim 24, wherein the control circuitry is further configured to:
- low pass filter a difference between the sensor signal and the estimated capacitive voltage to generate a low-pass signal; and
- adapt the gain of the sensor capacitor based on the low-pass signal.
26. The data storage device as recited in claim 23, wherein a capacitance of the sensor capacitor is at least two times less than the capacitance of the secondary actuator.
27. The data storage device as recited in claim 19, wherein the control circuitry is further configured to generate a feed-forward compensation signal applied to the secondary actuator based on the vibration signal.
Type: Application
Filed: Aug 24, 2016
Publication Date: Mar 30, 2017
Inventors: TIMOTHY A. FERRIS (MISSION VIEJO, CA), JAESOO BYOUN (IRVINE, CA)
Application Number: 15/246,332