Patent Publication Number: US-7583468-B2

Title: Method and apparatus of dual stage servo control with dual control paths and decoupling feedback for track following in a hard disk drive

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is a continuation in part of U.S. application Ser. No. 10/886,171, filed Jul. 6, 2004, now U.S. Pat. No. 7,009,803, the specification of which is hereby incorporated by referenced in its entirety. 

   TECHNICAL FIELD 
   The present invention relates to the control of a hard disk drive, in particular, to the servo mechanism and method, controlling a voice coil motor and a micro-actuator, positioning a read-write head in a hard disk drive. 
   BACKGROUND OF THE INVENTION 
   Hard disk drives contain one or more magnetic heads coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Typically, magnetic heads have a write element for magnetizing the disks and a separate read element for sensing the magnetic field of the disks. The read element is typically constructed from a magneto-resistive material. The magneto-resistive material has a resistance that varies with the magnetic fields of the disk. Heads with magneto-resistive read elements are commonly referred to as magneto-resistive (MR) heads. 
   Each head is embedded in a slider. The slider mechanically couples to an actuator arm by a head suspension assembly. The head suspension assembly includes a load beam connected to the actuator arm by a spring or hinge coupling. The slider attaches to a flexure arm and the flexure attaches to the load beam to form a head gimbal assembly (HGA). The head gimbal assembly includes the head suspension assembly, the flexure and the slider. Each head gimbal assembly is swaged to the actuator arm through its base plate. The actuator arms rigidly couple to a voice coil motor that moves the heads across the surfaces of the disks. 
   Information is stored in essentially radial tracks that extend across the surfaces of each disk. Each track is typically divided into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks and to different sectors of each track. 
   A suspension interconnect extends along the length of the flexure and connects the head to a preamplifier. The suspension interconnect typically includes a pair of conductive write traces and a pair of conductive read traces. 
   The Tracks Per Inch (TPI) in hard disk drives is rapidly increasing, leading to smaller and smaller track positional tolerances. The track position tolerance, or the offset of the magnetic head from a track, is monitored by a signal known as the head Positional Error Signal (PES). Track Mis-Registration (TMR) occurs when a magnetic head loses the track registration. TMR is often a statistical measure of the positional error between a magnetic head and the center of an accessed track. 
   Today, the bandwidth of the servo controller feedback loop, or servo bandwidth, is typically around 1.1 KHz. Extending servo bandwidth, increases the sensitivity of the servo controller to drive the voice coil actuator to ever finer track positioning. Additionally, it decreases the time for the voice coil actuator to change track positions. Extending servo bandwidth is difficult, and has not significantly improved in years. 
   However, as track densities increase, the need to improve track positioning, and servo bandwidth, increases. One answer to this need involves integrating a micro-actuator into each head gimbal assembly. These micro-actuators are devices typically built of piezoelectric composite materials, often including lead, zirconium, and titanium. The piezoelectric effect generates a mechanical action through the application of electric power. The piezoelectric effect of the micro-actuator, acting through a lever between the slider and the actuator arm, moves the magnetic head over the tracks of a rotating disk surface. 
   The micro-actuator is typically controlled by the servo-controller through one or two wires. Electrically stimulating the micro-actuator through the wires triggers mechanical motion due to the piezoelectric effect. The micro-actuator adds fine positioning capabilities to the voice coil actuator, which effectively extends the servo bandwidth. The single wire approach to controlling one micro-actuator provides an AC (alternating current) voltage to one of the two leads of the piezoelectric element. The other lead is tied to a shared ground. The two wire approach drives both leads of one micro-actuator. 
   There are two approaches to integrating the micro-actuator into a head gimbal assembly. The first embeds the micro-actuator between the slider and the load beam, creating a co-located micro-actuator. The second embeds the micro-actuator into the load beam, creating a non co-located micro-actuator. The non co-located micro-actuators tend to consume more power, requiring higher driving voltages than the co-located micro-actuators. 
   A problem arises when integrating micro-actuators into hard disk drives with multiple disk surfaces. Each of the micro-actuators requires its leads to be controlled by the servo-controller. These leads are coupled to wires, which must traverse the bridge flex or the long tail portion of the suspension to get to the main flex circuit. The bridge flex circuit provides electrical coupling to the leads of the micro-actuator. 
   The main flex circuit constrains many components of the actuator arm assembly within a voice coil actuator. If the shape or area of the main flex circuit is enlarged, changes are required to many of the components of the actuator arm assembly and possibly the entire voice coil actuator. Changing many or most of the components of an actuator arm assembly, leads to increases in development expenses, retesting and recalibrating the production processes for reliability, and inherently increases the cost of production. 
   The existing shape and surface area of the main flex circuit has been extensively optimized for pre-existing requirements. There is no room in the main flex circuit to run separate control wires to each micro-actuator for multiple disk surfaces. This has limited the use of micro-actuators to hard disk drives with only one active disk surface. 
   SUMMARY OF THE INVENTION 
   The invention controls a magnetic head following a track in a hard disk drive. The magnetic head is positioned by a micro-actuator and a voice coil motor. 
   Each embodiment of the invention operates as two control paths. The micro-actuator control path includes the micro-actuator control generating a micro-actuator control signal based upon a micro-actuator direction. A version of the micro-actuator control signal stimulates the micro-actuator. The voice coil motor control path includes the following. The voice coil motor control generates a version of the voice coil control signal, which is amplified based upon a tuning gain to stimulate the voice coil motor. These control paths are decoupled by a decoupling feedback filter, which uses the version of the micro-actuator control signal to create the decoupling feedback signal. 
   A first embodiment of the invention uses the voice coil motor control path with notch filtering. The version of the voice coil control signal is notch one filtered to remove at least one significant excitation resonance to create a notch filtered voice coil control signal. Amplifying the notch filtered voice coil control signal based upon a tuning gain stimulates the voice coil motor. 
   A second embodiment of the invention uses the voice coil motor control path and the micro-actuator control path with notch filtering. The version of the voice coil control signal is notch one filtered to remove at least one first significant excitation resonance to create a notch filtered voice coil control signal. Amplifying the notch filtered voice coil control signal based upon a tuning gain stimulates the voice coil motor. The version of the micro-actuator control signal is notch two filtered to remove at least one second significant excitation resonance to create a notch filtered micro-actuator control signal. The notch filtered micro-actuator control signal stimulates the micro-actuator. 
   A third embodiment of the invention uses the micro-actuator control path with notch filtering. The version of the micro-actuator control signal is notch two filtered to remove at least one second significant excitation resonance to create a notch filtered micro-actuator control signal. The notch filtered micro-actuator control signal stimulates the micro-actuator. 
   A fourth embodiment of the invention uses the voice coil motor control path and the micro-actuator control path without notch filtering. Amplifying the voice coil control signal based upon a tuning gain stimulates the voice coil motor. The micro-actuator control signal stimulates the micro-actuator. 
   A track following command, with the PES removed, directs the micro-actuator control. The voice coil motor control is directed by the track following command, with both the PES and the decoupling feedback signal removed. The PES signal is the additive effect of both the voice coil motor and the micro-actuator to position the magnetic head near the track being followed. 
   As used herein, a notch filter removes a narrow band from around at least one rejection frequency of the notch filter input signal to generate its output signal. The notch filter removes at least one significant excitation resonance of the servo system from the output of the voice coil motor control. In certain embodiments the significant excitation resonance may be outside the bandwidth of the voice coil control path and/or the micro-actuator control path. 
   Various embodiments provide the decoupling feedback filter, one or more notch filters and tuning gain to effectively shape the amplitude and phase of at least the voice coil motor control path in the frequency domain. These tools aid in shaping and separating the two control paths, which increases the reliability and performance of the hard disk drives using the invention. 
   Preferably, the servo-controller digitally supports the elements of the invention. The method of the invention may preferably be implemented to include the program system of the servo-controller residing as program steps in an accessibly coupled memory. 
   The invention includes optimizing an implementation within the hard disk drive. The optimization may be part of the manufacturing process for the hard disk drive. The invention includes the hard disk drive as the product of that manufacturing process. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which: 
       FIG. 1A  shows a prior art dual stage servo control system; 
       FIG. 1B  shows a first embodiment of the invention as a control signal flow within a hard disk drive; 
       FIG. 1C  shows a second embodiment of the invention as a control signal flow within a hard disk drive; 
       FIG. 1D  shows a third embodiment of the invention as a control signal flow within a hard disk drive; 
       FIG. 1E  shows a fourth embodiment of the invention as a control signal flow within a hard disk drive; 
       FIG. 2  shows a block diagram implementing the control signal flow of  FIGS. 1B to 1E ; 
       FIG. 3  shows a preferred refinement of  FIG. 2  showing the sharing of a micro-actuator stimulus signal among multiple micro-actuators; 
       FIG. 4A  shows the relationship between of the voice coil motor and actuator assembly traversing a rotating disk surface while following a track; 
       FIG. 4B  shows a typical spectrum for a contemporary hard disk drive with several significant excitation resonances; 
       FIG. 5  shows a simplified diagram of the voice coil motor and actuator assembly of a hard disk drive as in  FIGS. 1B to 4A ; 
       FIG. 6A  shows implementing the method operating the first embodiment of  FIG. 1B  as the program system of  FIG. 2 ; 
       FIG. 6B  shows implementing the method operating the first embodiment of  FIG. 1C  as the program system of  FIG. 2 ; 
       FIG. 6C  shows implementing the method operating the first embodiment of  FIG. 1D  as the program system of  FIG. 2 ; 
       FIG. 6D  shows implementing the method operating the first embodiment of  FIG. 1E  as the program system of  FIG. 2 ; 
       FIG. 7A  shows a detail flowchart of  FIGS. 6A and 6B  supporting the amplifying of  FIGS. 1B and 1C ; 
       FIG. 7B  shows a detail flowchart of  FIGS. 6A and 6B  supporting the notch one filtering of  FIGS. 1B and 1C . 
       FIG. 7C  shows a detail flowchart of  FIG. 7A  providing a version of the notch filtered voice coil control signal of  FIGS. 1B ,  1 C and  9 D. 
       FIG. 8A  shows a detail flowchart of  FIGS. 6A and 6D  further performing the decoupling feedback filtering of  FIGS. 1B and 1E ; 
       FIG. 8B  shows a detail flowchart of  FIG. 6A and 6D  further supporting the decoupling feedback filter of  FIGS. 1B ,  1 E,  6 A,  6 D, and  8 A; 
       FIG. 8C  shows a detail flowchart of  FIG. 6A and 6B  further supporting the notch one filtering of  FIGS. 1B and 1C ; 
       FIG. 9A  shows a flowchart extending the method to optimize the parameter collection of  FIG. 9B ; 
       FIG. 9C  shows details of an embodiment of the decoupling filter parameters of  FIG. 2 ; 
       FIG. 9D  shows details of an embodiment of the voice coil driver of  FIG. 2 ; 
       FIG. 9E  shows details of an embodiment of the decoupling feedback buffer of  FIG. 2 ; 
       FIG. 9F  shows details of an embodiment of the first notch filter parameter collection of  FIG. 2 ; 
       FIG. 10A  shows a detail flowchart of  FIGS. 6B and 6C , supporting the decoupling feedback filtering of  FIGS. 1C and 1D  of the notch filtered micro-actuator signal to create the decoupling feedback signal; 
       FIG. 10B  shows a detail flowchart of  FIGS. 6B and 6C  further supporting the decoupling feedback filter of  FIGS. 1B ,  1 C,  6 A,  6 D, and  8 A; 
       FIG. 10C  shows a detail flowchart of  FIGS. 6B and 6C  further supporting the notch two filtering of  FIGS. 1C and 1D ; and 
       FIG. 10D  shows the notch two parameter collection  1630  of  FIGS. 2 and 9D . 
   

   DETAILED DESCRIPTION 
   The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes presently contemplated by the inventors for carrying out the invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein. 
     FIG. 1A  shows a prior art dual stage servo control system for a hard disk drive. The PES signal  142  is removed  100  from the track following command  102  to create the micro-actuator direction  104 . The micro-actuator direction  104  stimulates the micro-actuator control signal and plant  130  to create the micro-actuator effect  132 . The micro-actuator effect  132  is removed  110  from the micro-actuator direction  104  to create the voice coil motor direction  112 . The voice coil motor direction  112  stimulates the voice coil motor control and plant  120  to effect  122  the position of the magnetic head. The magnetic head position is sensed as the Position Error Signal (PES)  142 , which is the additive result  140  of the voice coil motor effect  122  and the micro-actuator effect  132 . 
   Each embodiment of the invention operates as two control paths. The micro-actuator control path generates a version of the micro-actuator control signal stimulating the micro-actuator. The voice coil motor control path includes the following. The voice coil motor control generates a version of the voice coil control signal, which is amplified based upon a tuning gain to stimulate the voice coil motor. These control paths are decoupled by a decoupling feedback filter, using the version of the micro-actuator control signal to create the decoupling feedback signal. 
     FIGS. 1B to 1E  show four embodiments of the invention. Each embodiment of the invention operates as two control paths. The micro-actuator control path includes the micro-actuator control  250  generating a micro-actuator control signal  252  based upon a micro-actuator direction  204 . A version of the micro-actuator control signal stimulates the micro-actuator  310 . The voice coil motor control path includes the following. The voice coil motor control  220  generates a voice coil control signal  222 . A version of the voice coil control signal is amplified  240 , based upon a tuning gain  244 , to create the tuned voice coil control  242 . The tuned voice coil control  252  stimulates the voice coil motor  300 . These control paths are decoupled by a decoupling feedback filter  260 , which uses the version of the micro-actuator control signal to create a decoupling feedback signal  262 . 
     FIG. 1B  shows the first embodiment of the invention, which uses the voice coil motor control path with notch filtering. The voice coil control signal  222  is notch one filtered  230  to remove at least one first significant excitation resonance to create a notch filtered voice coil control signal  232 , which is the version of the voice coil control signal. Amplifying  240  the notch filtered voice coil control signal  232  is based upon a tuning gain  244 , creating the tuned voice coil control  242 . The micro-actuator control signal  252  is the version of the micro-actuator control signal, which stimulates the micro-actuator  310 . 
     FIG. 1C  shows the second embodiment of the invention, which uses the voice coil motor control path and the micro-actuator control path, both with notch filtering. The voice coil control signal  222  is notch one filtered  230  to remove at least one first significant excitation resonance to create a notch filtered voice coil control signal  232 , which is the version of the voice coil control signal. Amplifying  240  the notch filtered voice coil control signal  232  is based upon a tuning gain  244 , creating the tuned voice coil control  242 . The micro-actuator control signal  252  is notch two filtered to remove at least one second significant excitation resonance to create a notch filtered micro-actuator control signal  256 . The notch filtered micro-actuator control signal  256  stimulates the micro-actuator  310 . 
     FIG. 1D  shows the third embodiment of the invention, which uses the micro-actuator control path with notch filtering. The voice coil control signal  222  is amplified  240 , based upon a tuning gain  244 , to stimulate  242  the voice coil motor  300 . The micro-actuator control signal  252  is notch two filtered to remove at least one second significant excitation resonance to create a notch filtered micro-actuator control signal  256 . The notch filtered micro-actuator control signal  256  stimulates the micro-actuator  310 . 
     FIG. 1E  shows the fourth embodiment of the invention uses the voice coil motor control path and the micro-actuator control path without notch filtering. The voice coil control signal  222  is amplified  240 , based upon a tuning gain  244 , to stimulate  242  the voice coil motor  300 . The micro-actuator control signal  252  is the version of the micro-actuator control signal, which stimulates the micro-actuator  310 . 
     FIGS. 1B to 1E  show the direction of the micro-actuator control  250  and the voice coil motor control  220 . The track following command  202 , with the PES  272  removed  200 , creates the micro-actuator direction  204 , which directs the micro-actuator control  250 . The voice coil motor control  220  is directed  212  by the track following command  202 , with both the PES  272  and the decoupling feedback signal  262  removed. 
     FIGS. 1B to 1E  show the removal  200  of first the PES  272 , followed by the removal  210  of the decoupling feedback signal  262 . The invention also includes removal of the decoupling feedback signal  262  followed by the removal of the PES  272  to create an essentially equivalent stimulus  212  of the voice coil motor control  220 . The invention also includes the concurrent, essentially simultaneous, removal of both the decoupling feedback signal  262  and the PES  272  to create an essentially equivalent stimulus  212  of the voice coil motor control  220 . One skilled in the art will recognize that these alternatives are essentially equivalent and within the scope of the claimed invention. 
     FIGS. 1B to 1E , and  4 A, show the PES  272  as the additive result  270  of the effect  302  of the voice coil motor  300  and the effect  312  of the micro-actuator  310  positioning the magnetic head  500  near the track  18 . 
   As used in  FIGS. 1B and 1C , as well as else herein, a notch one filter  230  removes a narrow band from around at least one rejection frequency of the notch filter input signal  222  to generate its output signal  232 . The notch one filter  230  removes at least one first significant excitation resonance of the servo system from the output  222  of the voice coil motor control  220 . The invention includes the notch one filter removing more than one rejection frequency in certain preferred embodiments. 
   As used in  FIGS. 1C and 1D , as well as elsewhere herein, a notch two filter  280  removes a narrow band from around at least one rejection frequency of the notch filter input signal  252  to generate its output signal  256 . The notch two filter  280  removes at least one second significant excitation resonance of the servo system from the output  252  of the micro-actuator control  250 . The invention includes the notch two filter removing more than one rejection frequency in certain preferred embodiments. 
   Various combinations the decoupling feedback filter  260 , the notch one filter  230 , the notch two filter  280 , and the amplifier  240 , of  FIGS. 1B to 1E , provide the tools to effectively shape the amplitude and phase of at least the voice coil motor control path in the frequency domain. These tools aid in shaping and separating the two control paths, which increase the reliability and performance of the hard disk drive  10 . The first embodiment employs the decoupling feedback filter  260 , the notch one filter  230 , and the amplifier  240 , as shown in  FIG. 1B . The second embodiment employs the decoupling feedback filter  260 , the notch one filter  230 , the notch two filter  280 , and the amplifier  240 , as shown in  FIG. 1C . The third embodiment employs the decoupling feedback filter  260 , the notch two filter  280 , and the amplifier  240 , as shown in  FIG. 1D . The fourth embodiment employs the decoupling feedback filter  260  and the amplifier  240 , as shown in  FIG. 1E . 
     FIGS. 1B to 2  show the micro-actuator stimulus  252  provided to one micro-actuator  310 .  FIG. 3  shows the micro-actuator stimulus  252  provided to multiple micro-actuators,  310 - 316 .  FIG. 3  shows a further preferred embodiment, providing the micro-actuator stimulus  252  in parallel to each of the micro-actuators  310 - 316 .  FIGS. 2 and 3  show a single wire approach to stimulating the micro-actuator(s). In certain, sometimes preferred, circumstances, the micro-actuators may include a second lead presented a common signal, often ground. In certain other circumstances, the micro-actuators may be stimulated  252  by a two wire signal. 
   In many circumstances, the micro-actuators may preferably include at least one piezoelectric device. However, one skilled in the art will recognize that at least one of the micro-actuators may include an electrostatic device and/or an electromagnetic device. While these alternatives are potentially viable and of use, the remainder of this discussion will focus on piezoelectric based micro-actuators. This is to simplify the discussion, and is not meant to limit the scope of the claims for this invention. 
     FIG. 2  shows a block diagram implementing the control signal flow in the hard disk drive  10  of  FIG. 1B . The embedded disk controller Printed Circuit Board (PCB)  100  uses a program system  3000 , a collection of buffers  1600 - 1580 , and parameters  1590 - 1630 , interacting through the servo-controller  1030 . These components act together. The voice coil driver  500  simulates  244  the voice coil  32  of the voice coil motor  300 . At least one piezo driver  1010  stimulates  252  at least one micro-actuator  310  to position a magnetic head  500 . 
   The buffers  1600 - 1580  of  FIG. 2  may be used by the relevant operations of the invention to store one or more items. Examples may include input buffers such as the PES sample buffer  1600 , the voice coil motor control input buffer  1610 , and the micro-actuator control signal input buffer  1614 . Example output buffers may include the voice coil motor control output buffer  1612  and the micro-actuator control signal output buffer  1618 . There may be buffers which act to store intermediate values, such as the micro-actuator intermediate buffer  1616 . There may also be buffers which act to store both input and output buffers, such as the decoupling feedback buffer  1550 . 
     FIG. 4A  shows the actuator assembly  30  following a track  18  of a rotating disk surface  12  in a hard disk drive  10 .  FIG. 5  shows further details of the voice coil motor  300  and an alternative actuator assembly  30 . The actuator assembly  30  of  FIG. 4A  shows one actuator arm  50 , whereas the alternative actuator assembly  30  of  FIG. 5  shows multiple actuator arms  50 - 56 . 
   The actuator assembly  30  of  FIGS. 4A and 5 , includes actuator arms  50 - 56  coupled with voice coil  32 . 
   By way of example,  FIGS. 4A  shows an actuator arm  50  coupled with at least one Head Gimbal Assembly (HGA)  60 . Each HGA  60  couples with at least one slider  90 . Embedded in each slider  90  is a magnetic head  500 , which is positioned to follow a track  18  at a very small distance above the rotating disk surface  12 . 
   In  FIG. 5 , the actuator assembly  30  includes each the actuator arms  50 - 56  coupled with at least one HGA  60 - 66 . Each of the HGAs  60 - 66  are coupled with at least one slider (not shown in  FIG. 5 ). 
   The voice coil motor  300  in  FIG. 5  includes the actuator assembly  30  and the fixed magnet  20 . Stimulating  242  the voice coil motor  300  in  FIG. 1B  further involves stimulating  242  the voice coil  32  in  FIG. 2 . The effect  302  of the voice coil motor  300  includes the interaction of the fixed magnet  20  with the voice coil  32 . The coupling of the voice coil with the actuator arm  50 , and its coupling with the HGA  60 , moves the slider  90 , with its embedded magnetic head  500 , by a lever action. The lever action pivots the actuator assembly  30  by the actuator axis  40  as shown in  FIG. 4A . 
   There are two mechanisms acting to position the magnetic head  500  close to the track  18  in  FIGS. 4A and 5 . The voice coil motor  300  includes the voice coil  32  interacting with a fixed magnet  20 . The interaction of the voice coil  32  pivots actuator assembly  30  through actuator axis  40 . Additionally, the micro-actuator  310  interacts with the HGA  60  and the slider  90  to position the magnetic head  500 . 
   The method of controlling the magnetic head  500  of  FIG. 2  is shown as a flowchart in  FIG. 6  of program steps of the program system  3000 . 
   Preferably, the servo-controller  1030  of  FIGS. 2 and 3 , digitally provides at least some of the elements of the invention. Preferably, the implementation of the method includes the program system  3000  of the servo-controller  1030  residing as the program steps of  FIGS. 6 to 7C  in a servo memory  1040  accessibly coupled  1032  with the servo-controller  1030 . The servo memory  1040  may include any combination of volatile and non-volatile memory. As used herein, volatile memory requires a power supply to maintain its memory states, whereas a non-volatile memory has at least one memory state which persists without a power supply. 
   Some of the following figures show flowcharts of at least one method of the invention, possessing arrows with reference numbers. These arrows will signify of flow of control and sometimes data supporting implementations including at least one program operation or program thread executing upon a computer, inferential links in an inferential engine, state transitions in a finite state machine, and dominant learned responses within a neural network. 
   The operation of starting a flowchart refers to at least one of the following. Entering a subroutine in a macro instruction sequence in a computer. Entering into a deeper node of an inferential graph. Directing a state transition in a finite state machine, possibly while pushing a return state. And triggering a collection of neurons in a neural network. 
   The operation of termination in a flowchart refers to at least one or more of the following. The completion of those operations, which may result in a subroutine return, traversal of a higher node in an inferential graph, popping of a previously stored state in a finite state machine, return to dormancy of the firing neurons of the neural network. 
   A computer as used herein will include, but is not limited to an instruction processor. The instruction processor includes at least one instruction processing element and at least one data processing element, each data processing element controlled by at least one instruction processing element. By way of example, a computer may include a general purpose computer and a Digital Signal Processor (DSP). The DSP may directly implement fixed point and/or floating point arithmetic. 
     FIG. 4B  shows a typical Non-Repeatable Run-Out (NRRO) spectrum of the PES signal for a contemporary hard disk drive with several significant excitation resonances. These significant resonances are labeled  1 B,  1 F,  2 B,  2 F,  3 B,  3 F,  4 B, and  4 F. These resonances are significant because of their affect on the PES signal, which is shown in terms of a percentage fraction of the track pitch, also known herein as track width. 
     FIG. 4B  shows a common form of significant excitation resonance, often occurring when the disk surface bends up or down. Bending is defined in terms of bending modes. For a positive integer k, a bending mode of (k, 0 ) produces k nodal lines running through the disk surface center, creating k peaks and k troughs arranged on the disk surface. Bending mode ( 0 , 0 ) produces no nodal lines, either the entire disk is bent up or bent down. 
   In  FIG. 4B , reference labels  1 B and IF represent the backward frequency and the forward frequency associated with bending mode ( 1 , 0 ). Reference labels  2 B and  2 F represent the backward frequency and the forward frequency associated with bending mode ( 2 , 0 ). Reference labels  3 B and  3 F represent the backward frequency and the forward frequency associated with bending mode ( 3 , 0 ). 
   In a typical contemporary disk drive lacking a micro-actuator, the bandwidth of the servo system is often in the range of 1 KHz to 1.1 KHz. In a hard disk drive employing micro-actuators, the bandwidth of the servo system has been reported in excess of 1.8 KHz. 
   The micro-actuator stimulus  252  may preferably, be concurrently provided to more than one micro-actuator, as shown in  FIG. 3 . The micro-actuators  310 - 316  may further preferably be concurrently stimulated in parallel, as shown. 
     FIG. 6A  shows a flowchart of program system  3000  of  FIG. 2  implementing the first embodiment for controlling a voice coil motor  300  and at least one micro-actuator  310  of  FIGS. 1-4A  and  5 . The first embodiment of the invention is shown as two control paths in  FIG. 1B . The first embodiment of the invention uses the voice coil motor control path with notch filtering. The version of the voice coil control signal is notch one filtered to remove at least one significant excitation resonance to create a notch filtered voice coil control signal. Amplifying the notch filtered voice coil control signal based upon a tuning gain stimulates the voice coil motor. 
     FIG. 6B  shows a flowchart of program system  3000  of  FIG. 2  implementing the second embodiment for controlling a voice coil motor  300  and at least one micro-actuator  310  of  FIGS. 1-4A  and  5 . The second embodiment of the invention is shown as two control paths in  FIG. 1C . A second embodiment of the invention uses the voice coil motor control path and the micro-actuator control path with notch filtering. The version of the voice coil control signal is notch one filtered to remove at least one first significant excitation resonance to create a notch filtered voice coil control signal. Amplifying the notch filtered voice coil control signal based upon a tuning gain stimulates the voice coil motor. The version of the micro-actuator control signal is notch two filtered to remove at least one second significant excitation resonance to create a notch filtered micro-actuator control signal. The notch filtered micro-actuator control signal stimulates the micro-actuator. 
     FIG. 6C  shows a flowchart of program system  3000  of  FIG. 2  implementing the third embodiment for controlling a voice coil motor  300  and at least one micro-actuator  310  of  FIGS. 1-4A  and  5 . The third embodiment of the invention is shown as two control paths in  FIG. 1C . A third embodiment of the invention uses the micro-actuator control path with notch filtering. The version of the micro-actuator control signal is notch two filtered to remove at least one second significant excitation resonance to create a notch filtered micro-actuator control signal. The notch filtered micro-actuator control signal stimulates the micro-actuator. 
     FIG. 6D  shows a flowchart of program system  3000  of  FIG. 2  implementing the foruth embodiment for controlling a voice coil motor  300  and at least one micro-actuator  310  of  FIGS. 1-4A  and  5 . The fourth embodiment of the invention is shown as two control paths in  FIG. 1E . A fourth embodiment of the invention uses the voice coil motor control path and the micro-actuator control path without notch filtering. Amplifying the voice coil control signal based upon a tuning gain stimulates the voice coil motor. The micro-actuator control signal stimulates the micro-actuator. 
   In  FIGS. 6A to 6D , operation  2012  supports a micro-actuator control  250 , of  FIGS. 1B to 1E , creating a micro-actuator control signal  252  based upon a micro-actuator direction  204 . The micro-actuator  310  creates the first  312  of the two effects resulting  270  in the magnetic head  500  following the track  18  of  FIG. 4A . 
   In  FIGS. 6A to 6D , operation  2022  supports a voice coil motor control  220 , of  FIGS. 1B to 1E , creating a voice coil control signal  222  based upon a voice coil motor direction  212 . 
   In  FIGS. 6A and 6B , operation  2032  supports the notch one filter  230 , of  FIG. 1B . The notch one filter  230  uses the voice coil control signal  222  to create a notch filtered voice coil control signal  232 . Operation  2032  supports removing at least one first significant excitation resonance in creating the notch filtered voice coil control signal  232 . Examples of the significant excitation resonances are labeled  1 B- 3 F in  FIG. 4B . 
   In  FIGS. 6A and 6B , operation  2042  supports the amplifying  240 , of  FIGS. 1B and 1C . The notch filtered voice coil control signal  232  is amplified  240 , based upon a tuning gain  244 , to create a tuned voice coil control signal  242 . 
   In  FIGS. 6C and 6D , operation  2102  supports the amplifying  240 , of  FIGS. 1D and 1E . The voice coil control signal  224  is amplified  240 , based upon a tuning gain  244 , to create a tuned voice coil control signal  242 . 
   In  FIGS. 1B to 2 , the tuned voice coil control signal  242  stimulates the voice coil motor  300 .  FIG. 2  further shows the tuned voice coil control signal  242  stimulating the voice coil  32 . The voice coil motor  300 , based upon stimulus  242  of the voice coil  32 , creates the second  300  of the two effects resulting  270  in the magnetic head  500  following the track  18  of  FIG. 4A . 
   In  FIGS. 6A to 6D , operation  2052  supports removing  200  the PES  272  from a track following command  202  to create the micro-actuator direction  204 , as shown in  FIGS. 1B to 1E . 
   In  FIGS. 6A and 6D , operation  2062  supports decoupling feedback filtering  260  the micro-actuator control signal  252  to create a decoupling feedback signal  262 , as shown in  FIGS. 1B and 1E . 
   In  FIGS. 6B and 6C , operation  2082  supports notch two filtering  280  the micro-actuator control signal  252  to create the notch filtered micro-actuator control signal  256 , as shown in  FIGS. 1C and 1D . Operation  2082  preferably supports removing at least one second significant excitation resonance in creating the notch filtered micro-actuator control signal  256 . Examples of the significant excitation resonances are labeled  1 B- 3 F in  FIG. 4B . 
   In  FIGS. 6B and 6C , operation  2092  supports decoupling feedback filtering  260  the notch filtered micro-actuator control signal  256  to create a decoupling feedback signal  262 , as shown in  FIGS. 1C and 1D . 
   In  FIGS. 6A to 6D , operation  2072  supports removing  200  the PES  272  and removing  210  the decoupling feedback signal  262  from the track following command  202  to create the voice coil motor direction  212 , as shown in  FIGS. 1B to 1E . 
     FIG. 7A  shows a detail flowchart of operation  2042  of  FIGS. 6A and 6B , supporting amplifying  240  the notch filtered voice coil control signal  232  based upon the tuning gain  244 , as shown in  FIG. 1B and 1C . 
   In  FIG. 7A , operation  2102  supports setting a gain parameter  522 , shown in  FIG. 9D , of an amplifier  520 , based upon the tuning gain  244 , shown in  FIGS. 1B ,  1 C, and  2 . Operation  2112  supports providing the amplifier  520  a version  512  of the notch filtered voice coil control signal  232  to at least partly create the tuned voice coil control signal  522 . 
     FIG. 7B  shows a detail flowchart of operation  2032  of  FIG. 6A and 6B  supporting the notch one filtering  230  of  FIGS. 1B and 1C . 
     FIG. 7C  shows a detail flowchart of operation  2112  of  FIG. 7A  providing the version  512  of  FIG. 9D  of the notch filtered voice coil control signal  232  of  FIGS. 1B and 1C . 
   In  FIG. 7B , operation  2132  supports providing the notch filtered voice coil control signal  232  to a Digital to Analog Converter (DAC)  510 . The output of the DAC  510  at least partly creates the version  512  of the notch filtered voice coil control signal  232  shown in  FIGS. 1B and 1C . 
   In  FIG. 7C , operation  2152  supports providing the notch filtered voice coil control signal  232  to the DAC  510  to at least partly create the version  512  of the notch filtered voice coil control signal  232 . 
     FIGS. 7B and 7C  show essentially comparable operations, performed as part of two separate operations  2032  and  2042 , within the method  3000 . The invention includes both approaches, as well as alternative scheduling of the operations of  FIG. 6A and 6B . 
     FIG. 9B  shows the DAC  510  included in the voice coil driver  500  of  FIG. 2 . One skilled in the art will recognize that the communication  502  with the voice coil driver  500  may include communication integrated into one communication protocol as shown, or may include multiple communication protocols. Such multiple protocols may support separated data communication to a DAC  510  and an amplifier  520 , as well as communication for setting  504  parameters within a voice coil driver  500 . One skilled in the art will also recognize that the DAC output  512  may be further conditioned by a filter, often a RC network, coupled to remove quantization noise. 
     FIG. 8A  shows a detail flowchart of operation  2062  of  FIGS. 6A and 6D  further performing the decoupling feedback filtering  260  of  FIGS. 1B and 1E . Operation  2172  supports calculating a spectrum of the micro-actuator control signal  252  to create at least two spectrum components  1552  and  1554 , as shown in  FIG. 9E . These spectrum components  1552  and  1554  are preferably contained in the decoupling feedback buffer  1550 , residing in the servo memory  1040  as shown in  FIG. 2 . Operation  2182  generates the decoupling feedback signal  262  of  FIGS. 1B and 1E  based upon a first weight  1622  of  FIG. 9C  applied to the first spectrum component  1552  and a second weight  1624  applied to the second spectrum component  1554 . Typically, applying a weight to a spectrum component involves approximating the multiplication of the weight by the spectrum component. The decoupling feedback signal  262  is typically formed from the sum of these applications. 
     FIG. 8B  shows a detail flowchart of operation  2062  of  FIG. 6A and 6D  further supporting the decoupling feedback filter  260  of  FIGS. 1B ,  1 E,  6 A,  6 D, and  8 A. Operation  2202  supports decoupling feedback filtering  260 , based upon a decoupling parameter collection  1620  of  FIG. 2 . The decoupling feedback filter  260  receives the micro-actuator control signal  252  to create a decoupling feedback signal  262 . 
     FIG. 8C  shows a detail flowchart of operation  2032  of  FIG. 6A and 6B  further supporting the notch one filtering  230  of  FIGS. 1B and 1C . Operation  2222  supports the notch one filtering  230 , removing a first notch filter frequency collection  1592  from the voice coil control signal  222  of  FIGS. 1B and 1C  to create the notch filtered voice coil control signal  232 . The first notch filter frequency collection  1592  is shown in  FIG. 9F . 
   Preferably, the first notch filter frequency collection  1592  is contained in the first notch filter parameters  1590  as shown in  FIG. 9F . Preferably, the first notch filter parameters  1590  reside in servo memory  1040  as shown in  FIG. 2 . It may be preferred that the first notch filter frequency collection  1592  include more than one member. 
   It may be preferred that each of the first notch filter collection  1592  members of  FIGS. 8C and 9F  approximate one of the significant excitation resonances  1 B- 3 F as shown in  FIG. 4B . It may further be preferred that at least one of the notch filter frequency collection  1592  members be outside the servo bandwidth of the voice coil motor control path of  FIG. 1B . It may be further preferred that all the first notch filter frequency collection members be outside the servo bandwidth of the voice coil motor control path. It may be further preferred that the first notch filter frequency collection members be within the bandwidth of the micro-actuator control signal path, to minimize interference between the two control paths. 
     FIG. 9A  shows the method of the invention  3000  of  FIG. 2 and 6A  to  6 D, optimizing the implementation within the hard disk drive  10  of  FIGS. 1  B to  4 A. 
   In  FIG. 9A , operation  2252  optimizes a parameter collection  1700 , shown in  FIG. 9B , based upon a spectrum of the PES  272 , as shown in  FIG. 4B , resulting from using the parameter collection  1700 . 
   The parameter collection  1700  of  FIG. 9B  includes various combinations of the tuning gain  244 , the first notch filter parameter collection  1590 , the second notch filter collection  1630 , and the decoupling filter parameter collection  1620 . The tuning gain  244  is shown in  FIGS. 1B and 2 . The first notch filter parameter collection  1590  is shown in  FIGS. 2 and 9F . The decoupling filter parameter collection  1620  is shown in  FIGS. 2 and 9C . The second notch filter collection is shown in  FIGS. 2 and 10D . 
   The first embodiment of the invention shown in  FIGS. 1B and 6A  uses the parameter collection  1700  including the tuning gain  244 , the first notch filter parameter collection  1590 , and the decoupling filter parameter collection  1620 . 
   The second embodiment of the invention shown in  FIGS. 1C and 6B  uses the parameter collection  1700  including the tuning gain  244 , the first notch filter parameter collection  1590 , the second notch filter collection  1630 , and the decoupling filter parameter collection  1620 . 
   The third embodiment of the invention shown in  FIGS. 1D and 6C  uses the parameter collection  1700  including the tuning gain  244 , the second notch filter collection  1630 , and the decoupling filter parameter collection  1620 . 
   The fourth embodiment of the invention shown in  FIGS. 1E and 6D  uses the parameter collection  1700  including the tuning gain  244  and the decoupling filter parameter collection  1620 . 
   By way of example, the optimizing operation  2252  of  FIG. 9A  may include, but is not limited to, a randomized search of the parameter collection  1700 , possibly constrained by feasibility relationships. The randomized search may be augmented by a local search of candidate neighborhoods discovered by the randomized search. 
   The parameter collection  1700  may have more than one instance. Differing operating conditions within the hard disk drive  10  may use differing instances. Such differing operating conditions may involve ambient temperature. 
   The optimizing  2252  of  FIG. 9A  may be part of the process of manufacturing the hard disk drive  10  of  FIG. 1B to 4A , and  5 . The hard disk drive  10 , resulting from the manufacturing process is part of the invention. 
     FIG. 10A  shows a detail flowchart of operation  2092  of  FIGS. 6B and 6C , supporting the decoupling feedback filtering  260  of  FIGS. 1C and 1D  of the notch filtered micro-actuator signal  256  to create the decoupling feedback signal  262 . 
   In  FIG. 10A , operation  2272  supports calculating a spectrum of the notch filtered micro-actuator control signal  256  to create at least two spectrum components  1552  and  1554 , as shown in  FIG. 9E . These spectrum components  1552  and  1554  are preferably contained in the decoupling feedback buffer  1550 , residing in the servo memory  1040  as shown in  FIG. 2 . 
   In  FIG. 10A , operation  2282  generates the decoupling feedback signal  262  of  FIGS. 1C and 1D  based upon a first weight  1622  of  FIG. 9C  applied to the first spectrum component  1552  and a second weight  1624  applied to the second spectrum component  1554 . Typically, applying a weight to a spectrum component involves approximating the multiplication of the weight by the spectrum component. The decoupling feedback signal  262  is typically formed from the sum of these applications. 
     FIG. 10B  shows a detail flowchart of operation  2092  of  FIG. 6B and 6C  further supporting the decoupling feedback filter  260  of  FIGS. 1B ,  1 C,  6 A,  6 D, and  8 A. Operation  2302  supports decoupling feedback filtering  260 , based upon a decoupling parameter collection  1620  of  FIG. 2 . The decoupling feedback filter  260  receives the notch filtered micro-actuator control signal  256  to create a decoupling feedback signal  262 . 
     FIG. 10C  shows a detail flowchart of operation  2082  of  FIG. 6B and 6C  further supporting the notch two filtering  280  of  FIGS. 1C and 1D . Operation  2322  supports the notch two filtering  280 , removing a second notch filter frequency collection  1592  from the micro-actuator control signal  252  of  FIGS. 1C and 1D  to create the notch filtered micro-actuator control signal  256 . The second notch filter frequency collection  1632  is shown in  FIG. 10D . 
     FIG. 10D  shows the notch two parameter collection  1630  of  FIGS. 2 and 9D . The notch two parameter collection  1630  preferably includes the second notch frequency collection  1632 . The second notch frequency collection  1632  preferably includes at least one and often preferably two members. 
   Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.