# US 6,724,552 B1 · Magnetic disk apparatus with lower probability of occurrence of read errors due to scratch or the like on magnetic disk surface

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 6,724,552 B1
- Document ID: US6724552B1
- Status: Granted
- Kind: B1
- Application number: 09/416,654
- Filed: 1999-10-12
- Granted: 2004-04-20
- Earliest claimed: 1998-10-14
- Assignees: Alps Electric Co., Ltd.
- Inventors: Takayuki Sugawara; Takahiro Kawauchi; Masahiro Tenpaku; Yoshiyasu Kubota
- Web page: https://patentgrep.com/patent/US6724552B1

## CPC

- G11B 20/1217: {on discs}
- G11B 20/1816: {Testing}
- G11B 27/3027: {used signal is digitally coded}
- G11B 2020/1281: {Servo information}
- G11B 2020/1476: {Synchronisation patterns; Coping with defects thereof}
- G11B 2020/1826: {wherein a defect list or error map is generated}
- 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 magnetic disk apparatus is capable of reading normal data following a read error of a reference signal that has occurred due to a scratch or the like on a disk surface. In the magnetic disk apparatus, if a reference signal (STM) fails to be read at point P, then an elapsed time (Tw) is measured, and a time T2 indicating the difference between a time T1 at which a read gate is supposed to be opened and the time Tw is determined. The read gate is opened after the time T2 has passed, thereby making it possible to properly read data and subject the read data to a decoding process.

## Claims

### Claim 1

A magnetic disk apparatus comprising:
a head for reading recorded information from a disk provided with a servo field and a SYNC area, and a data area following said servo field;
a gate for applying a signal read by said head to a signal processing unit; and
a control unit for controlling said gate;
wherein said control unit carries out control such that said gate is opened after an elapse of a set period of time (T1) as measured from a moment in time at which a reference signal (STM2) in said servo field has been detected from the signal read by said head, and
wherein, if said reference signal (STM2) has not been detected after an elapse of a predetermined period of time (T) following the detection of a preceding reference signal (STM1), said predetermined time (T) corresponding to a period of time within which reference signal (STM2) should have been detected, then said gate is opened after elapse of a period of time corresponding to said predetermined period of time (T) and said set period of time (T1), as measured from a moment in time at which said preceding reference signal (STM1) was detected.

### Claim 2 (depends on 1)

A magnetic disk apparatus according to claim 1, wherein said control unit determines a difference in time (T2), as calculated by subtracting the difference (T1−Tw=T2) between a time (Tw) that has passed after the elapse of said predetermined time (T) and said set period of time (T1), and conducts control for opening said gate at said time (T2) as measured from the elapse of time (Tw).

### Claim 3 (depends on 1)

A magnetic disk apparatus according to claim 1, wherein a magnetic disk is provided with a maintenance area in which a defective sector is registered during a disk inspection, and if said reference signal (STM) is not detected within said predetermined period of time (T), then a sector from which said reference signal (STM) has not been detected is registered as a defective sector in said maintenance area during said disk inspection.

### Claim 4

A magnetic disk apparatus comprising:
a head for reading recorded information from a disk, said disk having a servo field having a reference signal, and a data area following said servo field;
a gate for applying a signal read by said head to a signal processing unit; and
a control unit for controlling said gate;
wherein the gate is opened after the elapse of a first predetermined period of time (T1), being measured from a moment in time at which a reference signal (STM2) in the servo field is detected from the signal read by said head, and
wherein the gate is opened after the elapse of a second predetermined period of time (T3) as measured from a moment in time at which a reference signal (STM1) in an immediately preceding servo field was detected, providing that the reference signal STM2 is not detected within the predetermined time interval T as measured from the occurrence of reference signal STM1, where T3=T+T1.

### Claim 5 (depends on 4)

A magnetic disk apparatus according to claim 4, wherein a magnetic disk is provided with a maintenance area in which a defective sector is registered during a disk inspection, and if said reference signal (STM2) is not detected within said predetermined period of time (T) as measured from the detection of a preceding reference signal, then a sector from which said reference signal (STM2) has not been detected is registered as a defective sector in said maintenance area during said disk inspection.