Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Drum record
Patent
1988-10-13
1991-01-08
Severin, David J.
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Drum record
360 84, G11B 556, G11B 553
Patent
active
049841165
DESCRIPTION:
BRIEF SUMMARY
Cross-reference to related patents, the disclosures of which are incorporated by reference:
The present invention relates generally to tape heads for oblique-track tape recorders, and more particularly to adjustment of head position to assure that different machines will properly follow the tracks on a particular tape.
BACKGROUND
In oblique-track tape decks, it is necessary that the recorded track be laid down precisely on the magnetic tape, so that magnetic tapes played on various machines of the same system provide the same reproduction. One criterion for this is the distance of video tracks from an edge of the tape used as a reference edge. For precise adjustment of this distance, the head wheel height must be adjustable to within precise tolerances upon initial assembly and upon every replacement of the head wheel.
SCHULEIN/GRUNDIG (German Patent Disclosure Document DE-OS 31 30 801) discloses how to avoid tedious mechanical adjustment of the head wheel height by electrical adjustment, namely adjusting the phase difference between head wheel tachometer pulses and specified image pulses. This method has, however, the disadvantage that, due to the possible shifting of the sampling interval in the circumferential direction of the sampling or scanning device, the mechanical looping of the magnetic tape about the sampling device must be chosen greater than is theoretically necessary. This results in the storage surface on the magnetic tape being generally poorly used.
TAKAHASHI/JVC (U.S. Pat. No. 4,564,876 and German Patent Disclosure Document DE-OS 32 44 215) discloses how to axially slide the head wheel of a rotating magnetic head device to facilitate proper tracking. However, this relates to the shifting of the head wheel in operation, and not to the precise adjustment of the head wheel height in initial or starting condition. Furthermore, in conventional rotating magnetic head devices, the biassing pressure on or among the ball bearings changes, in correspondence with the axial position of the head wheel.
THE INVENTION
It is an object of the present invention to provide a playback device for a oblique-track tape deck, in which the head wheel height can be mechanically set exactly for compatibility without adversely affecting the biassing pressure on the head wheel bearings and without the necessity to select, in view of the head wheel height adjustment, a larger mechanical looping of the magnetic tape about the playback device than is actually necessary for trouble-free playback.
Briefly, this is accomplished by the features recited in the characterizing clause of the main claim.
The playback device of the present invention has the advantage that the head wheel height can be precisely adjusted to within very close tolerances.
A further advantage is that the biassing or pre-tensioning of the ball bearings does not change during the course of the adjustment process.
The features set forth in the dependent claims make possible further extensions and improvements of the scanning device set forth in the main claim. A particular advantage is that the angular extent of looping of the magnetic tape about the playback device is not adversely affected by the head wheel height adjustment mechanism.
DRAWING
An exemplary embodiment of the invention is illustrated in the drawing and further detailed in the following description.
The FIGURE shows a playback device of an oblique-track tape deck in cross-section (without the head wheel).
DETAILED DESCRIPTION
The playback device shown, when operating, is partially helically encircled by a magnetic tape (not shown) which, depending upon the standard chosen, subtends an angle of between 90.degree. and somewhat less than 360.degree.. A playback device with two magnetic heads and a magnetic tape looping of somewhat more than 180.degree. is known from, among others, the MAXEY/BOSCH reference (U.S. Pat. No. 3,516,146=DE-OS 19 30 779).
The playback device of the invention, of which only the lower drum is shown, has a cylindrical outer diameter which is only a little
REFERENCES:
patent: 3179909 (1965-04-01), Cheney
patent: 3516146 (1968-06-01), Maxey
patent: 3995317 (1976-11-01), Schmidt
patent: 4080639 (1978-03-01), Gunschmann
patent: 4156261 (1979-05-01), Wolf
patent: 4564876 (1986-01-01), Takahashi et al.
Hescher Manfred
Wolf Theo
BTS Broadcast Television Systems GmbH
Severin David J.
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