Patent US3961374A successfully refreshed from Google Patents.
US3961374A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Static magnetic erasing head
Assignee: Sony Corp
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Filing: 1974-09-27
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Granted: 1976-06-01
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Expires: 1994-09-27
Abstract
Abstract A magnetic erasing head for magnetic recording apparatus using a static magnetic field. The erasing head includes at least three magnetic poles all of which are arranged to scan the same recorded track on the tape. The first and third poles have the same polarity while the second pole has opposite magnetic polarity. The first pole is arranged to engage the full width of the track and magnetizes it with one polarity. The second pole faces the upper half of the track and magnetizes it with the opposite polarity. The third pole engages the lower half of the track and magnetizes it with the same polarity as the first pole. After passing by these three poles, substantially one-half of the recording track is magnetized with one polarity and the other half of the track is magnetized with the other polarity so that distortion of output signals is maintained small or eliminated for various magnetic tapes having different coercive force values.
Inventors
- 👤 Nobuyuki Murata
- 👤 Makoto Saito
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 11:16
CPC Classifications
G; G11; G11B; G11B5/00; G11B5/02; G11B5/027; G11B5/03
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
229 words
A magnetic erasing head comprising at least three magnetic poles arranged to engage the recording track of a moving magnetic recording medium, said first magnetic pole extending perpendicular to the direction of such movement and engaging at least the full width of said recording track and providing a static magnetic field sufficient to magnetize said track with a first polarity to a magnetically saturated state, a second magnetic pole engaging substantially one-half of said recording track with one edge of said second pole extending beyond one edge of the recording track, the other edge of said pole being spaced from the centerline of the recording track on the same side as said one edge of the recording track, said second pole providing a static magnetic recording field which is greater than the maximum coercive force of the magnetic recording medium, said second pole having a polarity opposite to that of the first pole, said third magnetic pole engaging the other half of said recording track below said centerline and providing a static magnetic field to said magnetic recording medium which is greater than the minimum coercive force of the magnetic recording medium, said third pole having a polarity the same as the first pole, said first, second and third magnetic poles being spaced in the direction of such movement with said second pole between said first and third poles.
Claim 2
Dependent Claim
229 words
A magnetic erasing head comprising at least three magnetic poles arranged to engage the recording track of a moving magnetic recording medium, said first magnetic pole extending perpendicular to the direction of such movement and engaging at least the full width of said recording track and providing a static magnetic field sufficient to magnetize said track with a first polarity to a magnetically saturated state, a second magnetic pole engaging substantially one-half of said recording track with one edge of said second pole extending beyond one edge of the recording track, the other edge of said pole being spaced from the centerline of the recording track on the same side as said one edge of the recording track, said second pole providing a static magnetic recording field which is greater than the maximum coercive force of the magnetic recording medium, said second pole having a polarity opposite to that of the first pole, said third magnetic pole engaging the other half of said recording track below said centerline and providing a static magnetic field to said magnetic recording medium which is greater than the minimum coercive force of the magnetic recording medium, said third pole having a polarity the same as the first pole, said first, second and third magnetic poles being spaced in the direction of such movement with said second pole between said first and third poles.
Claim 3
Dependent Claim
22 words
A magnetic erasing head as claimed in claim 1, wherein said magnetic poles are disposed on the surface of a head block.
Claim 4
Dependent Claim
34 words
A magnetic erasing head as claimed in claim 1, wherein said magnetic poles are located on the surface of a head block composed of magnetizable material by means of selective magnetization of said block.
Claim 5
Dependent Claim
16 words
A magnetic erasing head as claimed in claim 3, wherein said magnetizable material is barium ferrite.
Claim 6
Dependent Claim
18 words
A magnetic erasing head as claimed in claim 1, wherein said magnetic poles are edges of permanent magnets.
Claim 7
Dependent Claim
37 words
A magnetic erasing head as claimed in claim 1, wherein said magnetic poles are disposed on the surface of a head block, and each magnetic pole is one edge of a permanent magnet confined within non-magnetizable material.
Claim 8
Dependent Claim
15 words
A magnetic erasing head as claimed in claim 6, wherein said non-magnetizable material is brass.
Claim 9
Dependent Claim
17 words
A magnetic erasing head as claimed in claim 1, wherein said magnetic poles are edges of electromagnets.
Claim 10
Dependent Claim
26 words
A magnetic erasing head as claimed in claim 1, wherein said magnetic poles consist of ring-shaped cores having coils thereon to which direct current is supplied.
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) | 1979-06-01 | 1979-12-01 | 1980-06-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-06-01 | 1983-12-01 | 1984-06-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-06-01 | 1987-12-01 | 1988-06-01 | $7700.00 | Window Closed / Lapsed |