Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Synchronizing moving-head moving-record recorders
Reexamination Certificate
1994-02-09
2001-02-13
Nguyen, Hoa T. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Synchronizing moving-head moving-record recorders
C360S077120, C360S075000
Reexamination Certificate
active
06188535
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to magnetic recording, and in particular to an apparatus for recording and reading data on magnetic tape in the form of a sequence of arcuate tracks which are transverse to the longitudinal axis of the magnetic tape.
The standard configuration of an information storage subsystem for a modern computer installation includes internal and direct access memory. Typically, the information storage subsystem also includes a magnetic tape drive for backup storage of information in the internal and direct access components. Two important trends in storage technology are found in the miniaturization of all storage subsystem components, and a significant increase in the information storage capacity of the internal and direct access components. The tape drive component has been miniaturized by accommodation of the quarter inch tape cartridge which has emerged as a standard in the industry. However, the storage capacity (areal density) of the tape drive has not kept pace with the increased capacities of the other storage components. Accordingly, there is an urgent need to increase the amount of information which can be recorded on a magnetic tape, which can only be realized by increasing the density of information which is stored on the tape.
Most commercially important magnetic tape drive systems are based on the reel-to-reel transport of magnetic tape past a fixed recording/reading location where a stationary single- or multiple-track head is positioned. Recording and playback in such a system is done longitudinally with respect to the tape by moving the tape on its longitudinal axis past a record/playback location where a head mechanism is located. In a stationary head tape drive, the head mechanism consists of a plurality of transversely-aligned heads which are fixedly positioned with respect to the tape during record and playback. Information is placed on the tape in the form of a plurality of parallel, longitudinally-extending tracks; the areal density of information stored on the tape is increased by reducing the dimensions of the heads and the inter-head spacing on the head mechanism. However, small head size and minimal inter-head spacing demand great precision in the manufacture of head components. As a result, the manufacturing tolerances of the tape drive, primarily the mechanical tolerances of the head assemblies, have become increasingly stringent and more difficult and expensive to achieve. Of course, the proliferation of heads is reflected in additional read and write channel electronics for each head which also adds to the expense of these drives.
As is known, in the video recording art, modern high-capacity, high-quality tape drives employ head mechanisms which rotate magnetic heads with respect to a moving tape. The high rotational speed of the “rotary head” recorders steps away from the requirement in stationary head technology for a plurality of transversely-aligned heads and associated electronics and, therefore, obviates the problems attendant with manufacture and assembly of stationary head mechanisms. Servoing is employed in the dominant classes of rotary head tape drives to align rotating heads with tracks on the tape. The servoing techniques developed for these classes of tape drives enhance head/track alignment and result in substantial reduction in track width and inter-track spacing. Consequently, rotary head tape drives enjoy a significant advantage over stationary head tape drives in areal density.
The most widely employed rotary head technology is known as transverse linear or “helical” scanning technology. In transverse linear scanning, one or more transducers (heads) are mounted on the side cylindrical surface of a head carrier drum which is rotated on an axis parallel to, but spaced from, the longitudinal path of tape travel. A succession of linear tracks is laid down transverse to the longitudinal axis of the tape. In helical scan video recorders, a tape is wrapped around a tilted drum on whose outer surface are mounted (usually two) heads. The resulting tracks are substantially straight, but have an angle to the longitudinal axis of the tape. In helical scanning, servoing information included in the tracks or in separate servo tracks is used to vary the speed of the scanner and tape in order to align the tracks with the heads.
Upon an initial consideration, helical scanning would, therefore, promise to provide an increase in areal density which would match the amplified storage capacity of the internal and direct access components of a computer storage subsystem. However, the application of helical scanning to magnetic tape drives for computer systems is limited by two significant factors. First, the tape drive mechanism must have a means for closely engaging the tape and the side cylindrical surface of the head carrier. As is known, head/tape engagement mechanisms in helical scan tape drives are large, complex, and relatively slow acting. They would, therefore, add significantly to the size of a tape drive and to the difficulty and expense of manufacture and would require a significant amount of time to change a tape cartridge. The second drawback of helical scan tape drives is that the head/tape engagement mechanism imposes a high-pressure contact between head and tape, resulting in increased wear on the head parts and decreased lifetime of tapes.
Another type of rotary head technology has been described in which the heads are mounted near the periphery of a circular planar surface and rotated thereon about an axis passing through the center of the circular surface and through the plane of a longitudinally-moving tape. This rotary head technology results in the writing of a sequence of arcuately-shaped tracks which are transverse to the longitudinal axis of the tape. Use of an arcuate scanning tape drive implies an inherently small and simple head/tape interface in which the planar circular transducer-bearing surface is brought against the plane of the longitudinally-moving tape. This interface does not require the elaborate engagement mechanisms of helical scanning tape drives in which the tape is either wound around a tilted drum or conformed to a portion of the curved surface of a straight drum. However, two significant limitations and one erroneous perception have kept this technology from being widely used. The two limitations include the lack of an adequate servoing scheme and the absence of an acceptable low-pressure head/tape interface mechanism. The misperception is that arcuate scanning provides an inherently low storage density.
Prior art arcuate scanning tape drives are described, for example, in: U.S. Pat. No. 2,750,449 of Thompson, et al; U.S. Pat. No. 2,924,668, of Hoshino, et al; U.S. Pat. No. 3,320,371 of Bach; U.S. Pat. No. 4,636,886 of Schwarz; U.S. Pat. No. 4,647,993 of Schwarz, et al; and U.S. Pat. No. 4,731,681 of Ogata. The arcuate scanning mechanism and technique described in the Thompson et al patent concerns a low speed, low density audio recorder for logging communications on two-inch wide tapes Servoing is not considered, probably because the tracks are wide, information density is low, and the signal can be tracked manually during playback. This appears to be the case as well in the Hoshino and Bach references. The rotary head recording systems of Schwarz and Schwarz et al are evidently directed to high data rate applications in which a high head rotation velocity maximizes data density at moderate tape speeds; the Ogata reference describes a magnetic recording playback apparatus in which the relatively high rotational velocity of a head with respect to a tape is used to advantage in the recording of high frequency video signals; none of these references discloses a servoing technique.
The failure of these prior art arcuate scanning references to consider servoing is significant. In fact, head track alignment in arcuate scanning is a difficult challenge because of the geometry of the arcuately scanned tracks. At the edges of the scan, the tracks converge, while in the midd
Crosby James C.
Lemke James U.
Manildi A. Bruce
Spatafore Charles J.
Baker & Maxham
Lemke James U.
Nguyen Hoa T.
Wong K.
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