1. Field of the Invention
The present invention relates to a servo routine of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface 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.
Each sector may have also a servo field 5 located adjacent to a data field 6. The servo field 5 contains a plurality of servo bits A, B, C and D that are read and utilized in a servo routine to position the head 7 relative to the track. By way of example, the servo routine may utilize the algorithm of ((A-B)-(C-D)) to create a position error signal (“PES”). The PES is used to create a drive signal for the voice coil motor to position the head on the track.
To access data at different disk tracks the drive enters a seek routine. During a seek routine a requested address location is provided and a corresponding seek time and drive current is calculated to drive the voice coil motor and move the heads to the desired location. The drive current provided to the voice coil motor typically has a sinusoidal waveform. The time derivative of the voice coil motor acceleration curve (“jerk”) is discontinuous. This discontinuity can create unwanted mechanical vibration that increases the seek time of the heads and the access time of the drive. It would be desirable to provide a drive current waveform that does not have discontinuities in the voice coil motor jerk profile.
A hard disk drive that contains a servo circuit that controls a voice coil motor. The servo circuit provides a driving current to the voice coil motor that has a sinusoidal waveform with two harmonic frequencies.
Described is a hard disk drive that includes a voice coil motor controlled by a servo circuit. The servo circuit provides a sinusoidal driving signal that has two different harmonic frequencies. The dual harmonic waveform creates a voice coil motor jerk profile (derivative of acceleration) that is continuous. The continuous jerk profile reduces vibration and seek time of the drive.
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 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 servo circuit 100 includes a Sinusoidal Wave Generator 110 that generates a sinusoidal signal that has two different harmonic frequencies
and
The See Trajectory Calculator 108 outputs position x*(t), velocity v*(t) and current u*(t) trajectories using the Fourier coefficients and two harmonic sinusoidal waveform. The trajectories x*(t), v*(t) and u*(t) may be expressed as follows:
where the Fourier coefficients can be expressed as:
where ka is an acceleration constant of the voice coil motor 36.
The Seek Trajectory Calculator 108 computes the trajectory utilizing equations (1)-(6). The relationship between the seek length xsk and the seek time tsk can be expressed as follows, where Ka is an acceleration constant of the voice coil motor:
The output of the Current Amplitude Calculator 104 can be defined as:
The current trajectory u(t) is provided to the voice coil motor to move the heads to the desired track. The servo system may include a state estimator for feedforward control of the system. The estimator 112 may provide position ŵ(t), velocity v*(t) and torque ŵ(t), estimates to adders 114, 116 and 118 and multiplied by gain coefficients Kp 120 and Kv 122.
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.
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