# US 7,411,758 B1 · Disk drive servo control using spirals

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- Number: US 7,411,758 B1
- Document ID: US7411758B1
- Status: Granted
- Kind: B1
- Application number: 11/337,360
- Filed: 2006-01-23
- Granted: 2008-08-12
- Earliest claimed: 2006-01-23
- Assignees: Marvell International Ltd.
- Inventors: Man Cheung; Perry Neos
- Web page: https://patentgrep.com/patent/US7411758B1

## CPC

- G11B 5/59688: {Servo signal format patterns or signal processing thereof, e.g. dual, tri, quad, burst signal patterns}
- G11B 5/59661: {Spiral servo format}
- G11B 5/59666: {Self servo writing}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

A servo control system includes a peak detection module that detects peak times of spiral signals generated by reading spirals prewritten on a magnetic medium. The servo control system includes a control module that determines positions of the spirals based on the peak times, stores the positions of the spirals, seeks and tracks the spirals using the positions, and writes servo on the magnetic medium based on the positions of the spirals.

## Claims

### Claim 1

A servo control system, comprising:
a peak detection module that detects peak times of spiral signals generated by reading spirals prewritten on a magnetic medium; and
a control module that determines positions of said spirals based on said peak times, stores said positions of said spirals, seeks and tracks said spirals using said positions, and writes servo on said magnetic medium based on said positions of said spirals,
wherein said control module radially seeks by changing an expected peak time for one of said spirals based on at least one of an offset and a spiral correction value and by translating a resultant peak time into a radial distance, and
wherein said offset is indicative of radial seek direction.

### Claim 2 (depends on 1)

The servo control system of claim 1 wherein said control module measures an actual time from one of a reference servo mark and a peak of one of said spiral signals to a peak of an adjacent spiral signal.

### Claim 3 (depends on 1)

The servo control system of claim 1 wherein said control module calculates an expected time from one of a reference servo mark and a peak of one of said spiral signals to a peak an adjacent spiral signal.

### Claim 4 (depends on 1)

The servo control system of claim 1 wherein said control module generates a difference between an actual time and an expected time from one of a reference servo mark and a peak of one of said spiral signals to a peak of an adjacent spiral signal.

### Claim 5 (depends on 4)

The servo control system of claim 4 wherein said control module generates N of said differences, where N is an integer greater than 1, and uses an average of said N differences as a correction value to determine a position of said one of said spirals.

### Claim 6 (depends on 1)

The servo control system of claim 1 wherein said control module radially seeks by changing said expected peak time by a seek-step time for one of said spirals.

### Claim 7 (depends on 1)

The servo control system of claim 1 wherein said control module tracks said spirals by inferring radial distance from time based on said resulting time.

### Claim 8 (depends on 1)

The servo control system of claim 1 further comprising a timing window generator that generates a timing window to scan said spiral signals.

### Claim 9 (depends on 8)

The servo control system of claim 8 wherein said peak detection module determines a half-integral point of integral values and detects one of said sub-windows that corresponds to said half-integral point.

### Claim 10 (depends on 1)

The servo control system of claim 1 wherein said peak detection module counts time of one of said spiral signals relative to a reference servo mark.

### Claim 11 (depends on 10)

The servo control system of claim 10 further comprising a timing window generator that generates a timing window, wherein said peak detection module divides said timing window into multiple sub-windows and calculates integral values of amplitudes of one of said spiral signals in each of said sub-windows.

### Claim 12 (depends on 11)

The servo control system of claim 11 wherein said peak detection module selects a half-integral point of said integral values and detects one of said sub-windows that corresponds to said half-integral point.

### Claim 13 (depends on 12)

The servo control system of claim 12 wherein said peak detection module counts time from said one of said sub-windows to said reference servo mark to determine said peak time.

### Claim 14 (depends on 1)

The servo control system of claim 1 further comprising a phase error detection module that detects a phase error signal.

### Claim 15 (depends on 14)

The servo control system of claim 14 wherein said phase error detection module selects a first time stamp that differs from a second time stamp by a time that is substantially equal to a predetermined time.

### Claim 16 (depends on 15)

The servo control system of claim 15 wherein said phase error detection module calculates a raw timing error by comparing said first time stamp with an expected time stamp.

### Claim 17 (depends on 16)

The servo control system of claim 16 wherein said phase error detection module calculates a modulus of said raw timing error and generates a phase error signal.

### Claim 18 (depends on 1)

The servo control system of claim 1 further comprising a phase-locked loop (PLL) module that uses a phase error signal generated by a phase error detection module to synchronize a self-servo write (SSW) clock to a reference servo sector (RSS) clock derived from said spiral signals.

### Claim 19 (depends on 1)

The servo control system of claim 1 wherein said control module comprises at least one of said peak detection module, a timing window generator module, a phase-locked loop module, and a phase error detection module.

### Claim 20 (depends on 1)

A hard disk subsystem comprising the servo control system of claim 1 and further comprising:
a hard disk controller that communicates with said servo control system;
a read-write channel that communicates with said hard disk controller; and
an interface that communicates with said hard disk controller.

### Claim 21 (depends on 20)

A hard disk system comprising the hard disk subsystem of claim 20 and further comprising:
a magnetic medium; and
a read-write head that communicates with said hard disk subsystem and that reads and writes data on said magnetic medium.

### Claim 22

A method for servo control, comprising:
detecting peak times of spiral signals generated by reading spirals prewritten on a magnetic medium;
determining positions of said spirals based on said peak times;
storing said positions of said spirals;
seeking and tracking said spirals using said positions;
writing servo on said magnetic medium based on said positions of said spirals; and
seeking radially by changing an expected peak time for one of said spirals based on at least one of an offset and a spiral correction value and by translating a resultant peak time into a radial distance,
wherein said offset is indicative of radial seek direction.

### Claim 23 (depends on 22)

The method of claim 22 further comprising measuring an actual time from one of a reference servo mark and a peak of one of said spiral signals to a peak of an adjacent spiral signal.

### Claim 24 (depends on 22)

The method of claim 22 further comprising calculating an expected time from one of a reference servo mark and a peak of one of said spiral signals to a peak an adjacent spiral signal.

### Claim 25 (depends on 22)

The method of claim 22 further comprising generating a difference between an actual time and an expected time from one of a reference servo mark and a peak of one of said spiral signals to a peak of an adjacent spiral signal.

### Claim 26 (depends on 25)

The method of claim 25 further comprising generating N of said differences, where N is an integer greater than 1, and using an average of said N differences as a correction value to determine a position of said one of said spirals.

### Claim 27 (depends on 22)

The method of claim 22 further comprising seeking in radial position one of said spirals by changing said expected peak time by a seek-step time for said one of said spirals.

### Claim 28 (depends on 22)

The method of claim 22 further comprising tracking said spirals by inferring radial distance from time based on said resulting time.

### Claim 29 (depends on 22)

The method of claim 22 further comprising generating a timing window to scan said spiral signals.

### Claim 30 (depends on 22)

The method of claim 22 further comprising generating a control signal to synchronize said spiral signals to a timing window generated by a timing window generator.

### Claim 31 (depends on 22)

The method of claim 22 further comprising determining a peak time of one of said spiral signals relative to a reference servo mark.

### Claim 32 (depends on 31)

The method of claim 31 further comprising generating a timing window, dividing said timing window into multiple sub-windows, and calculating integral values of amplitudes of one of said spiral signals in each of said sub-windows.

### Claim 33 (depends on 32)

The method of claim 32 further comprising determining a half-integral point of said integral values and detecting one of said sub-windows that corresponds to said half-integral point.

### Claim 34 (depends on 33)

The method of claim 33 further comprising counting time from said one of said sub-windows to said reference servo mark to determine said peak time.

### Claim 35 (depends on 22)

The method of claim 22 further comprising detecting a phase error between time stamps of a plurality of reference servo marks and minimizing said phase error.

### Claim 36 (depends on 35)

The method of claim 35 further comprising selecting a first time stamp that differs from a second time stamp by a time that is substantially equal to a predetermined time.

### Claim 37 (depends on 36)

The method of claim 36 further comprising calculating a raw timing error by comparing said first time stamp with an expected time stamp.

### Claim 38 (depends on 37)

The method of claim 37 further comprising calculating a modulus of said raw timing error and generating a phase error signal.

### Claim 39 (depends on 22)

The method of claim 22 further comprising using a phase error signal to synchronize a self-servo write (SSW) clock to a reference servo sector (RSS) clock derived from said spiral signals.

### Claim 40 (depends on 1)

The servo control system of claim 1 wherein said control module determines said offset based on an expected peak time, an actual peak timer a spiral to spiral radial distance, and a spiral to spiral circumferential distance.

### Claim 41 (depends on 40)

The servo control system of claim 40 wherein said control module tracks said spirals by determining a radial distance based on said offset.

### Claim 42 (depends on 40)

The servo control system of claim 40 wherein said control module minimizes said offset.

### Claim 43 (depends on 1)

The servo control system of claim 1 wherein said control module determines said offset based on a difference in an expected peak time and an actual peak time and based on a spiral to spiral radial distance divided by a spiral to spiral circumferential distance.

### Claim 44 (depends on 1)

The servo control system of claim 1 wherein said control module determines said spiral correction value based on at least one of an expected time of a spiral without actuator movement and spiral imperfections (A), an observed spiral-to-spiral time with actuator movement and spiral imperfections (C), and a time due to actuator movement (D).

### Claim 45 (depends on 44)

The servo control system of claim 44 wherein said control module determines said spiral correction value based on a difference between C and D.

### Claim 46 (depends on 44)

The servo control system of claim 44 wherein said control module determines said spiral correction value based on a sum of N differences between C and D, where N is a number of spindle revolutions.

### Claim 47 (depends on 44)

The servo control system of claim 44 wherein said control module determines said spiral correction value based on a sum of N differences between C and D, where N is a number of spindle revolutions and based on a difference between the resulting sum and A.

### Claim 48 (depends on 44)

The servo control system of claim 44 wherein said control module tracks said spirals by determining a radial distance based on said spiral correction value.

### Claim 49 (depends on 1)

The servo control system of claim 1 wherein said control module tracks said spirals by inferring radial and circumferential distance based on a speed associated with writing a spiral.

### Claim 50 (depends on 49)

The servo control system of claim 49 wherein said speed includes a spindle speed.

### Claim 51

A servo control system, comprising:
a peak detection module that detects peak times of spiral signals generated by reading spirals prewritten on a magnetic medium; and
a control module that determines positions of said spirals based on said peak times, stores said positions of said spirals, seeks and tracks said spirals using said positions, and writes servo on said magnetic medium based on said positions of said spirals,
wherein said peak detection module determines a peak time of a spiral by integrating spiral signal amplitudes and selecting a half-integral point based on a result of said integration.

### Claim 52 (depends on 51)

The servo control system of claim 51 wherein said peak detection module determines a first time between a reference time and a first start of a timing window, a second time between said first start and said half-integral point, and sums said first time and said second time to determine said peak time.

### Claim 53

The servo control system of claim wherein said peak detection module in determining said second time determines a third time between said first start and a second start of a sub-window of said timing window and a fourth time between said second start and said half-integral point.

### Claim 54

A servo control system, comprising:
a phase error detection module that generates a phase correcting signal;
a phase lock loop module that synchronizes a self-servo write clock to a reference servos sector clock based on said phase correcting signal; and
a control module that seeks and tracks spirals based on said self-servo write clock, and writes servo on said magnetic medium based on said based on said self-servo write clock,
wherein said phase error detection module selects a first time stamp that differs from a second time stamp by a time that is substantially equal to a predetermined time and generates a phase error signal based on said selection.

### Claim 55 (depends on 54)

The servo control system of claim 54 wherein said phase error detection module calculates a raw timing error by comparing said first time stamp with an expected time stamp.

### Claim 56 (depends on 55)

The servo control system of claim 55 wherein said phase error detection module calculates a modulus of said raw timing error and generates a phase error signal.