Patent US4881136A successfully refreshed from Google Patents.
US4881136A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for detecting minute defects on magnetic disk by monitoring both amplitude decrease and phase shift of a reproduced signal
Assignee: Hitachi Ltd
•
Filing: 1986-11-07
•
Granted: 1989-11-14
•
Expires: 2006-11-07
Abstract
Abstract Because of increase in data recording density on a magnetic disk in recent years, a minute defect which posed no problem in the past exerts adverse influence upon the recording and reproducing characteristics. An object of the present invention is to provide a method and an apparatus for detecting minute defects on a magnetic disk. In order to achieve this object, the present invention was made on the basis of the recognition that a large defect on the magnetic disk largely decreases the amplitude of the reproduced signal and shifts its phase, whereas a small defect does not decrease the amplitude of the reproduced signal so largely but causes a phase shift. Therefore, defects on the magnetic disk are detected by monitoring the amplitude decrease and phase shift of the reproduced signal.
Inventors
- 👤 Kazuhisa Shiraishi
- 👤 Kazuo Nakagoshi
- 👤 Takuji Ogawa
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 18:20
CPC Classifications
G; G11; G11B; G11B20/00; G11B20/10; G11B20/18; G11B20/1816
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
128 words
A method for detecting defects on a recording medium, comprising the steps of: recording onto the recording medium an amplitude signal corresponding to data to be written and coded in accordance with a 2-7 RLLC coding technique, the amplitude signal having a frequency which minimizes the peak value of the second derivative thereof within the frequency band of the amplitude signal; reproducing the amplitude signal recorded on the recording medium; detecting intervals of peak points of said reproduced amplitude signal; detecting the peak-to-peak amplitude at each peak pint of said reproduced amplitude signal; and determining a defect on the recording medium when said peak-to-peak amplitude is smaller than a predetermined value or the interval between said peak points of said amplitude signal is outside of a predetermined range.
Claim 2
Independent Claim
128 words
A method for detecting defects on a recording medium, comprising the steps of: recording onto the recording medium an amplitude signal corresponding to data to be written and coded in accordance with a 2-7 RLLC coding technique, the amplitude signal having a frequency which minimizes the peak value of the second derivative thereof within the frequency band of the amplitude signal; reproducing the amplitude signal recorded on the recording medium; detecting intervals of peak points of said reproduced amplitude signal; detecting the peak-to-peak amplitude at each peak pint of said reproduced amplitude signal; and determining a defect on the recording medium when said peak-to-peak amplitude is smaller than a predetermined value or the interval between said peak points of said amplitude signal is outside of a predetermined range.
Claim 3
Dependent Claim
21 words
A method for detecting defects on a recording medium according to claim 1, wherein said recording medium comprises a magnetic disk.
Claim 4
Dependent Claim
21 words
A method for detecting defects on a recording medium according to claim 1, wherein the amplitude signal is a continuous signal.
Claim 5
Independent Claim
175 words
An apparatus for detecting defects on a recording medium, comprising: means for generating an amplitude signal having a frequency which minimizes the peak value of the second derivative thereof within the frequency band of said amplitude signal as a signal for recording onto said recording medium; signal recording means for recording said amplitude signal coded by data to be written in accordance with a 2-7 RLLC coding technique onto said recording medium; signal reproducing means for reproducing said amplitude signal recorded on said recording medium; amplitude detecting means for detecting a peak-to-peak amplitude at a peak point of said amplitude signal reproduced by said signal reproducing means; interval detecting means for detecting an interval in phase direction between peak points of said amplitude signal reproduced by said signal reproducing means; determination means for determining a defect on the recording medium when an amplitude width shorter than a predetermined amplitude width is detected by said amplitude detecting means and when a peak interval different from a predetermined peak interval is detected by said interval detecting means.
Claim 6
Independent Claim
175 words
An apparatus for detecting defects on a recording medium, comprising: means for generating an amplitude signal having a frequency which minimizes the peak value of the second derivative thereof within the frequency band of said amplitude signal as a signal for recording onto said recording medium; signal recording means for recording said amplitude signal coded by data to be written in accordance with a 2-7 RLLC coding technique onto said recording medium; signal reproducing means for reproducing said amplitude signal recorded on said recording medium; amplitude detecting means for detecting a peak-to-peak amplitude at a peak point of said amplitude signal reproduced by said signal reproducing means; interval detecting means for detecting an interval in phase direction between peak points of said amplitude signal reproduced by said signal reproducing means; determination means for determining a defect on the recording medium when an amplitude width shorter than a predetermined amplitude width is detected by said amplitude detecting means and when a peak interval different from a predetermined peak interval is detected by said interval detecting means.
Claim 7
Dependent Claim
77 words
An apparatus according to claim 4, wherein said amplitude detecting means includes a level detection circuit for comparing the peak-to-peak amplitude of said reproduced amplitude signal with a predetermined reference level, and wherein said interval detecting means includes a peak detection circuit for detecting the peak signal of the reproduced amplitude signal and a discrimination circuit for discriminating the peak signal detected by said peak detection circuit by means of a discrimination window having a predetermined width.
Claim 8
Dependent Claim
14 words
An apparatus according to claim 4, wherein said amplitude signal is a continuous signal.
References Cited (Backward Citations)
US3659195A
Cited
US3562635A
Cited
US3686682A
Cited
US3761905A
Cited
US3826975A
Cited
US4142215A
Cited
US4394695A
Cited
JPS5921730A
Cited
DE3238077A1
Cited
US4656420A
Cited
US4754222A
Cited
US4604660A
Cited
US4612586A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-11-13 | 1993-05-15 | 1993-11-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-11-13 | 1997-05-15 | 1997-11-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-11-13 | 2001-05-15 | 2001-11-14 | $7700.00 | Window Closed / Lapsed |