US3723668A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of erasing signals from magnetic discs using dc pulses which persist for one disc revolution
Assignee: Ampex Corp
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Filing: 1970-03-27
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Granted: 1973-03-27
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Expires: 1990-03-27
Abstract
Abstract A method for selectively erasing single tracks of recorded signals from a magnetic disc and reconditioning the medium for re-recording. Erasure is effected by energizing a head with successive pulses of direct current alternating in the direction of current flow at decreasing levels of absolute magnitude, each pulse persisting for the duration of one disc revolution. The method further lends itself to track erasure using a read/write head.
Inventors
- 👤 T Ritchey
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 09:56
CPC Classifications
G; G11; G11B; G11B5/00; G11B5/02; G11B5/024; H; H04; H04N; H04N5/00; H04N5/76; H04N5/78; H04N5/781
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
113 words
A method of erasing recorded signals from a magnetic medium and conditioning the medium for re-recording comprising the steps of: generating a current of a stepped waveform including a plurality of successive current pulses of progressively decreasing levels of constant current alternating in the direction of current flow; and controlling the generation of the pulses included in the stepped waveform of current to have a period coinciding with the time for one revolution of the magnetic disc medium from which magnetically recorded signals are to be erased; and applying the current pulses to transduction means in transductional relationship to a selected track of the disc along which signals to be erased are recorded.
Claim 2
Independent Claim
113 words
A method of erasing recorded signals from a magnetic medium and conditioning the medium for re-recording comprising the steps of: generating a current of a stepped waveform including a plurality of successive current pulses of progressively decreasing levels of constant current alternating in the direction of current flow; and controlling the generation of the pulses included in the stepped waveform of current to have a period coinciding with the time for one revolution of the magnetic disc medium from which magnetically recorded signals are to be erased; and applying the current pulses to transduction means in transductional relationship to a selected track of the disc along which signals to be erased are recorded.
Claim 3
Dependent Claim
43 words
The method of claim 1 further including the step of positioning the transduction means in transductional relationship to the track to be erased for a number of disc revolutions, the number of revolutions coinciding with the number of pulses of the generated waveform.
Claim 4
Dependent Claim
52 words
The method of claim 1 wherein the generation of the pulses is controlled to have the said period by switching the current of the stepped waveform between the opposite directions of current flow in an interval equal to less than one wavelength of the signals to be recorded on the magnetic disc.
Claim 5
Dependent Claim
52 words
The method of claim 1 further including the step of adjusting the number of pulses and their respective levels while the transduction means is in transductional relationship with the selected track to reduce the magnetic remanence to a level less than that which is productive of intolerable distortion in a re-recorded signal.
Claim 6
Dependent Claim
38 words
The method of claim 4 in which the magnitude of the first pulse is adjusted for approximately -60db erasure and the magnitude of the second pulse is adjusted to obtain minimum second harmonic distortion on a re-recorded signal.
Claim 7
Dependent Claim
22 words
The method of claim 4 in which the absolute magnitude of successive pulses is approximately tWo-thirds that of the immediate preceding pulse.
Claim 8
Dependent Claim
81 words
The method of claim 1 further including: the steps of: adjusting the number of pulses and their respective levels while the transduction means is in transductional relationship with the selected track to reduce the magnetic remanence to a level less than that which is productive of intolerable distortion in a re-recorded signal; and positioning the transduction means in transductional relationship to the track to be erased for a number of revolutions coinciding with the number of pulses of the generated waveform.
Claim 9
Dependent Claim
27 words
The method of claim 7 in which the current pulses are applied to the transduction means prior to re-record signals are applied to the same transduction means.
Claim 10
Dependent Claim
44 words
The method of claim 1 further including the steps of: detecting a tachometer mark in rotational registry with a particular circumferential position of the magnetic disc; and initiating the generation of the waveform of current in response to the detection of the tachometer mark.
Claim 11
Dependent Claim
67 words
The method of claim 9 in which the tachometer mark is located on the magnetic disc in a time related relation with a zone of the magnetic disc in which no information is recorded, and the waveform of current is generated to have its transitions between opposite directions of current flow occur while the erase transduction means is in a transductional relationship with the magnetic disc zone.
Claim 12
Dependent Claim
37 words
The method of claim 10 further including the step of initiating the recording of information along the erased disc track outside of said disc zone after the erased current pulses have been applied to the transduction means.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-03-26 | 1976-09-25 | 1977-03-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-03-26 | 1980-09-25 | 1981-03-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-03-26 | 1984-09-25 | 1985-03-27 | $7700.00 | Window Closed / Lapsed |