Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1998-11-13
2001-06-12
Hudspeth, David (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C369S044240, C369S112040
Reexamination Certificate
active
06246535
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to systems and methods for tracking movement of a magnetic tape, and more specifically, to optical servo head assemblies that can transmit and receive light patterns suitable for monitoring an optical servo track carried on a magnetic tape to sense and detect lateral movement of the tape.
BACKGROUND OF THE INVENTION
Digital tape-recording remains a viable solution for storage of massive amounts of data. Conventionally, at least two approaches are employed for recording of digital information onto magnetic recording tape. One approach calls for moving the tape past a rotating head structure which records and plays back user information from discontinuous transverse tracks. Interactive servo systems are employed to synchronize rotation of the head structure with travel of the tape. Another approach is to draw the tape across a non rotating head at a considerable linear velocity. This approach is sometimes referred to as linear “streaming” tape recording and playback.
Increased data storage capacity, and retrieval performance, is being required of all commercially viable mass storage devices and media. In the case of linear tape recording a popular trend is toward multi head, multi-channel fixed head structures with narrowed recording gaps and track widths so that many linear tracks may be achieved on a tape medium of predetermined width, such as one-half inch width tape. Tape substrates are also being made thinner, with increased tape lengths being made possible in small diameter reel packages.
Because of relatively high linear tape velocity, and because tape substrates continue to be made progressively thinner, guiding tape past a tape head structure along an accurate invariant linear path has proven to be difficult problematical. One error phenomena is known as “lateral tape motion” or “LTM” LTM is a major source of tracking errors in linear tape recording. One approach to minimizing LTM tracking errors is to provide a multi-roller tape guide structure, such as the type described in commonly assigned U.S. Pat. No. 5,414,585, entitled Rotating Tape Edge Guide, the disclosure thereof being incorporated herein by reference. While this approach has provided a viable “open loop” solution to LTM, with the advent of new head technologies, such as magneto-resistive read heads, and new higher coercivity recording media, track widths may be very small, and many additional tracks may be defined on the tape. Unfortunately, a limiting factor is LTM, and at some track width dimension and track density, it is not possible to follow the tape accurately enough to provide reliable performance.
One proposed solution for preventing errors arising from LTM is set forth in the above-identified patent application entitled “Multi-Channel Magnetic Tape System Having Optical Tracking Servo.” As disclosed therein, an optical servo mechanism can be employed to track and monitor lateral motion of a magnetic tape relative to a recording head. To this end, the magnetic tape can be provided with an optically detectable servo track that can be detected by an optical pick up head that projects a beam of light onto the servo track and detects light reflected back from the servo track. This optical servo system provides a mechanism that can employ narrow servo tracks that can be detected by a beam of light to provide fine positioning information for aligning a recording head with a magnetic track that has a known spatial relationship to the optically detectable servo track also recorded onto the magnetic tape.
Today, optical pick-up heads exist for reading optical tracks recorded onto CD ROMS. However, these existing systems typically include multiple component lens assemblies that are employed for focusing a light generated by a light source onto the optical servo track of the CD ROM. Although these multiple component optical assemblies can work well, they often require the optical pick up head to have a focal length that is too long to allow for employment with a magnetic recording head, which benefits from close proximity to the magnetic recording media. Additionally, these multicomponent lens assemblies can add to the weight of the optical pick up head, which is undesirable in an application where the pick up head is to be moved in real time with the changing position of a servo track. Additionally, the lens assemblies can add to the expense of manufacture, requiring careful alignment of the lens components to provide an optical path and focal point of desired parameters.
Accordingly, there is a need in the art to provide an optical pick up head, or optical servo head, that is light weight, easy to manufacture, and provides a focal length that is suitable for use with a magnetic recording head that benefits from close proximity to the recording media.
SUMMARY OF THE INVENTION
The systems and methods described herein provide optical servo heads capable of transmitting and receiving at least one beam of light that can be employed for sensing the presence of an optically detectable servo track that is recorded onto a recording media, such as a magnetic tape. In one embodiment, the optical servo head comprises a semiconductor device that emits and receives a diffracted pattern of laser light, and a lens assembly that focuses the emitted light to a spot size, or spot sizes, suitable for detecting the optically detectable servo track that has been placed onto the recording media. The lens assembly can include a spherical lens element that is disposed between two walls, each of the walls having an aperture extending therethrough. The apertures and the spherical lens cooperate to focus the emitted light into a pattern that is suitable for detecting the optical servo track, and cooperate to focus light reflected back from the servo track onto a photo-detector device that can generate a signal that is representative of the presence of reflected light having impinged on the optical servo track.
The systems and methods described herein provide optical servo heads that employ a focusing assembly with reduced complexity, a short focal length and which are sufficiently compact and lightweight to be employed with a servo mechanism that operates to move the optical servo head in real-time. Additionally, the employment of a spherical lens eliminates the need to carefully align conventional lens elements, and thereby reduces the cost of manufacturing.
Other objects and advantages of the invention will, in part, be obvious, and, in part, be shown from the following description of the systems and methods shown herein.
REFERENCES:
patent: 3997715 (1976-12-01), Elliott
patent: 4570191 (1986-02-01), Di Stefano et al.
patent: 4816939 (1989-03-01), Ford et al.
patent: 5218595 (1993-06-01), Lehureau et al.
patent: 6084740 (2000-07-01), Leonhardt et al.
Cappabianca Leo
Chen Hong
Gulbankian Richard
Panish Joseph
Saliba George A.
Habermehl James L
Hudspeth David
Quantum Corporation
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