Patent Application
20080088965
Described is a hard disk drive that includes a voice coil motor and a micro-actuator. The micro-actuator is controlled by a servo that utilizes a micro-actuator controller and a corresponding micro-actuator transfer function. The servo enters a mode to self-determine at least one transfer function coefficient of the micro-actuator controller.
Referring to the drawings more particularly by reference numbers,
The disk drive 10 may include a plurality of heads 20 located adjacent to the disks 12. As shown in
Referring to
The hard disk drive 10 may include a printed circuit board assembly 38 that includes one or more integrated circuits 40 coupled to a printed circuit board 42. The printed circuit board 40 is coupled to the voice coil 32, heads 20 and spindle motor 14 by wires (not shown).
The hard disk drive may include one or more micro-actuators 44 that are coupled to the suspension arms 26 and heads 20. By way of example, the micro-actuators 44 may include piezoelectric elements. The micro-actuators 44 can provide fine movement of the heads 20.
The read/write channel circuit 58 is connected to a controller 64 through read and write channels 66 and 68, respectively, and read and write gates 70 and 72, respectively. The read gate 70 is enabled when data is to be read from the disks 12. The write gate 72 is enabled when writing data to the disks 12. The controller 64 may be a digital signal processor that operates in accordance with a software routine, including a routine(s) to write and read data from the disks 12. The read/write channel circuit 58 and controller 64 may also be connected to a motor control circuit 74 which controls the voice coil motor 36, spindle motor 14 and micro-actuator 44 of the disk drive 10. The controller 64 may be connected to a non-volatile memory device 76. By way of example, the device 76 may be a read only memory (“ROM”) that contains instructions that are read by the controller 64.
Each sector of a disk track typically has servo bits A, B, C and D as shown in
The position error signal is provided to a voice coil motor controller 102 and a micro-actuator controller 104. The controllers 102 and 104 generate output signals uc and um that are provided to the voice coil motor and micro-actuator illustrated as a dual actuator stage 106. The output y contains components relating to the movement of the voice coil motor yc and micro-actuator ym.
The output of the micro-actuator can be defined by the following equation:
y
m
=A[λ cos((2π/N)k)+β sin((2π/N)k)] (2)
where;
A=amplitude.
λ=transfer function coefficient.
β=transfer function coefficient.
The transfer function coefficients may vary between heads. Additionally, the coefficients may change with temperature and time. It is therefore desirable to periodically update the transfer function coefficients. This can be done for example, during an idle mode of the disk drive.
The output signal ŷm can be defined by the equation:
ŷ
m
[k]=â[k] cos((2π/N)k)+{circumflex over (b)}(k)sin((2π/N)k)] (3)
It can be seen by inspection that equation (3) is similar in form with equation (2) where â[k] corresponds to λ and {circumflex over (b)}[k] corresponds to β.
â[k] and {circumflex over (b)}[k] can be defined by the following estimating equations:
â[k]=â[k]+gε cos((2π/N)k) (4)
{circumflex over (b)}[k]={circumflex over (b)}[k]+gε sin((2π/N)k) (5)
where;
g=a known gain value which is a negative number.
ε=is the output of adder 110.
k=an increment of time.
An excitation signal having the following equation can be provided to the system:
u
m
=A cos((2π/N)k) (6)
The excitation signal is fed through the feedback loop of the gain identifier 108 and the adder 110. When the error function ε goes to zero in the feedback loop the sine and cosine terms in equations (4) and (5), respectively, go to essentially zero. At this point â[k] and {circumflex over (b)}[k] are essentially constant and approximate the transfer function coefficients λ and β, respectively. The transfer function coefficients λ and β are then stored and used in the servo system shown in
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
