Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-10-12
2003-11-25
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06654197
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to disc drive data storage systems. More particularly, the present invention relates to identifying the dynamics of a drive.
BACKGROUND OF THE INVENTION
Disc drives read and write information along concentric tracks formed on discs. To locate a particular track on a disc, disc drives typically use embedded servo fields on the disc. These embedded fields are utilized by a servo subsystem to position a head over a particular track. The servo fields are written onto the disc when the disc drive is manufactured and are thereafter simply read by the disc drive to determine position. A servo system samples the position of the read/write head relative to a particular track at a particular sampling rate and adjusts the position of the head.
In a typical servo system, the actual position of the read/write head relative to a given track is sensed and compared to the desired position of the head. A position error signal (PES) indicative of the difference between the actual and desired positions is provided to a servo controller. Based on the value of the position error signal, the servo controller provides a servo control signal to a power amplifier that amplifies the servo control signal and provides it to a voice coil motor. The voice coil motor is coupled to an actuator that moves in response to the application of the amplified control signal to the voice coil motor. An actuator arm that holds the read/write head is coupled to the actuator. In this way, the servo controller controls the positioning of the read/write head relative to a particular track on the disc surface.
Thus, a disk drive mechanical structure is composed of multiple mechanical components that are pieced together to form the final disk drive assembly. Each of these components has various resonant modes that if excited by an external energy source will cause the part to physically move at the natural frequencies of oscillation for the component in question. This movement can occur in a bending mode, a twisting mode or a combination of the two. If the component is highly undamped (i.e. the resonance is high amplitude, narrow frequency band) it will tend to oscillate with a minimal external driving energy. This oscillation results in physical motion of the data head, causing off track errors and potential fly height problems. These oscillations are often referred to as resonances.
If resonances occur in a disk drive, they can severely limit drive performance, both in seek mode and track-follow mode. However, the effects of the resonant vibrations of the drive can be attenuated if the resonance characteristics are known to some degree of accuracy. The ability to identify resonance characteristics both in the factory and in the field will be very important as drives are developed to have more sophistication in calibration and field adaptation.
The present invention provides a solution to this and other problems and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
The present invention relates to identifying the dynamics of a drive.
One embodiment of the present invention is directed to a method of identifying the resonance characteristics of a disc drive. Pursuant to the method, a repetitive excitation signal is applied to the actuator assembly. The repetitive excitation signal has a period substantially equal to a positive integer multiple of a period of revolution of the disc. The position of the read/write head relative to a target track on the disc surface is sensed. The sensed position of the read/write head is compared to a desired position of the read/write head and a position error signal indicative of the difference between the sensed position and the desired position is generated. The position error signal is time averaged over multiple revolutions of the disc to obtain an averaged repetitive position error signal. The resonance characteristics of the drive are determined based on a correlation of the averaged repetitive position error signal with respect to the repetitive excitation signal.
Another embodiment of the invention is directed to a disc drive that includes an actuator assembly, sensing means, a comparator, an excitation signal generator and a processor. The actuator assembly operates in a servo loop to position a read/write head relative to a data track on a disc surface. The sensing means senses the position of the read/write head relative to a track on the disc surface. The comparator compares the sensed position of the read/write head to a desired position of the read/write head and generates a position error signal indicative of the difference between the sensed position and the desired position. The excitation signal generator generates a repetitive excitation signal having a period substantially equal to a positive integer multiple of a period of revolution of the disc. The excitation signal generator applies the repetitive excitation signal to the actuator assembly. The processor time averages the position error signal to obtain an averaged repetitive position error signal. The processor then determines the resonance characteristics of the drive based on a correlation of the averaged repetitive position error signal with respect to the repetitive excitation signal.
REFERENCES:
patent: 5465183 (1995-11-01), Hattori
patent: 5995317 (1999-11-01), Ottesen
patent: 6292324 (2001-09-01), Ho et al.
patent: 6377417 (2002-04-01), Ahn
patent: 6417982 (2002-07-01), Ottesen et al.
Hudspeth David
Seagate Technology LLC
Westman Champlin & Kelly P.A.
Wong K.
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