WO2000062283A1

WO2000062283A1 - Leading dummy head in a helical scan recorder

Info

Publication number: WO2000062283A1
Application number: PCT/US2000/010006
Authority: WO
Inventors: Ranier M.L. Zollner
Original assignee: Exabyte Corporation
Priority date: 1999-04-14
Filing date: 2000-04-14
Publication date: 2000-10-19
Also published as: AU4241100A

Abstract

A helical scan tape drive (30) which transduces information relative to magnetic tape (31) using an active head set mounted on a rotating scanner (84). A non-transducing body, comparably configured to a transducing head, is mounted upstream from the active head set (82) in a direction of scanner rotation. The mounting of the non-transducing body serves to stabilize a head-to-tape interface at the active head set, resulting in an essentially uniform signal amplitude from a head in the active head set, including a leading or trailing head in the active head set. Even over wide ranges of tape tension, scanner speeds, and tape thickness, the amplitude of the read/write signal for both the leading and trailing heads are 'flat' and steady. In one embodiment, the non-transducing body is a dummy head (80).

Description

LEADING DUMMY HEAD IN A HELICAL SCAN

RECORDER

BACKGROUND

This application claims the benefit and priority of United States provisional patent application Serial No. 60/129,231, filed April 14, 1999, which is incorporated by reference herein in its entirety.

1. FIELD OF THE INVENTION

The present invention pertains to helical scan recording on magnetic tape, and particularly to rotating drum and head structure of a helical scan recorder.

2. RELATED ART AND OTHER CONSIDERATIONS

In magnetic recording on tape using a magnetic tape drive, relative motion between a head unit (typically with both a write element and a read element) and the tape causes a plurality of tracks of information to be transduced with respect to the tape. The magnetic tape is typically housed in a cartridge which is loaded into the tape drive. The tape extends between a cartridge supply reel and a cartridge take-up reel. The tape drive typically has a supply reel motor for rotating the cartridge supply reel and a take- up reel motor for rotating the cartridge take-up reel.

After the cartridge is loaded into the tape drive, the tape is extracted by mechanisms in the drive so that a segment of the tape is pulled from the cartridge and into a tape path that travels proximate the head unit. The extraction mechanisms take the form of tape guides which are mounted on trolleys. During the extraction operation, trolley motors move the trolleys along a predefined trolley path, so that the tape guides which surmount the trolleys displace the tape into the tape path as the trolleys travel along the trolley path. When the trolleys reach the full extent of travel along the trolley path, the tape is proximate the head unit. Thereafter the tape can be transported past the head unit, e.g., by activation of a capstan and/or the supply reel and take-up reel motors, depending upon the particular type of transport mechanisms employed.

In a helical scan arrangement, as the magnetic tape is transported the magnetic tape is at least partially wrapped around a rotating drum so that heads (both write heads and read heads) positioned on the drum are contiguous to the drum as the drum is rotated. One or more write heads on the drum physically record data on the tape in a series of discrete stripes oriented at an angle with respect to the direction of tape travel. The data is formatted, prior to recording on the tape, to provide sufficient referencing information to enable later recovery during readout by one or more read heads.

Examples of helical scan tape drives are shown, inter alia, in the following US patents (all of which are incorporated herein by reference): US Patent 4,835,628 to Hinz et al.; US Patent 4,843,495 to Georgis et al.; US Patent 5,065,261 to Hughes et al.; US Patent 5,068,757 to Hughes et al.; US Patent 5,142,422 to Zook et al.; and US Patent 5,602,694 to Miles et al. (which discloses a capstanless helical scan tape drive).

Prior art helical scan tape drives can have a plurality of heads mounted on the rotating drum. In some embodiments, plural write heads and plural read heads are provided on the cylindrical side wall of the drum, often in pairs. For example, a pair of write heads may situated relatively close together on one side of the drum, while at an approximately 180 degree angle from the write heads a pair of read heads are mounted in close proximity to one another. Typically, a stripe recorded by a first write head is read back by a first read head, and similarly a stripe recorded by a second write head is read back by a second read head.

To increase data capacity and transfer rate in the helical scan tape drive, thinner tapes (media thickness) and higher head-to-tape speeds are used. With these thinner tapes and higher scanner speeds (e.g., higher drum rotation speeds), an unstable head- to-tape interface on a leading head of a head pair occurs. Experiments varying tape tension, head protrusion, head rubbing width, and upper drum design show little effect in fixing the problem. What is needed, therefore, and an object of the present invention, is a stable head-to-tape interface on a leading head of a head pair.

BRIEF SUMMARY OF THE INVENTION

A helical scan tape drive which transduces information relative to magnetic tape using an active head set mounted on a rotating scanner. A non-transducing body, comparably configured to a transducing head, is mounted upstream from the active head set in a direction of scanner rotation. The mounting of the non-transducing body serves to stabilize a head-to-tape interface at the active head set, resulting in an essentially uniform signal amplitude from a head in the active head set, including a leading or trailing head in the active head set. Even over wide ranges of tape tension, scanner speeds, and tape thickness, the amplitude of the read/write signal for both the leading and trailing heads are "flat" and steady. In one embodiment, the non-transducing body is a dummy head.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

Fig. 1 is a schematic view of a tape drive according to the present invention, the tape drive being connected to a host.

Fig. 2 is a diagrammatic view of a tape path of the tape drive of Fig. 1.

Fig. 3 is a top view of a portion of a scanner according to the present invention for use in the tape drive of Fig. 1.

Fig. 4A through Fig. 4D are oscilloscope images showing a decrease in signal amplitude on a leading head in a drum configuration not having the leading dummy head of the present invention. Fig. 5A through Fig. 5D are oscilloscope images showing signal amplitude in accordance with the present invention wherein the leading dummy head is provided.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

Fig. 1 shows a SCSI bus 20 which connects a host computer 22 and a first embodiment of a SCSI target storage device, particularly tape drive 30. In the illustrated embodiment, tape drive 30 is shown as a generic helical scan tape drive which transduces information on/from tape 31. Tape drive 30 includes a SCSI controller 32 which is connected to SCSI bus 20. Data bus 34 connects SCSI controller 32 to buffer manager 36. Both SCSI controller 32 and buffer manager are connected by a bus system 40 to processor 50. Processor 50 is also connected to program memory 51 and to a data memory, particularly RAM 52.

Buffer manager 36 controls, e.g., both storage of user data in buffer memory 56 and retrieval of user data from buffer memory 56. User data is data from host 22 for recording on tape 31 or destined from tape 31 to host 22. Buffer manager 36 is also connected to formatter/encoder 60 and to deformatter/decoder 62. Formatter/encoder 60 and deformatter/decoder 62 are, in turn, respectively connected to write channel 70 and read channel 72. Write channel 70 is connected via write amplifier 74 to plural recording element(s) or write head(s) 80; read channel is connected via read amplifier 76 to plural read element(s) or read head(s) 82.

Those skilled in the art will appreciate that write channel 70 includes various circuits and elements including a RLL modulator, a parallel-to-serial converter, and write current modulator. Similarly, the person skilled in the art understands that read channel 72 includes a data pattern and clock recovery circuitry, a serial-to-parallel converter, and, an RLL demodulator. These and other aspects of tape drive 30, including servoing, error correction, are not necessary for an understanding of the invention and accordingly are not specifically described herein.

As shown generally in Fig. 2, four write heads 8O1 - 80₄ and four read heads 82ι - 82₄ are situated on a peripheral surface of rotating scanner 84. The four write heads 80ι - 80₄ are referred to as active heads, and together the four write heads 801 - 80₄ form an active head set. Similarly, the four read heads 82ι - 82₄ are referred to as active heads, and together the four read heads 82ι - 82₄ also form an active head set. The four write heads 80ι - 80₄ are grouped in pairs, e.g., a first write head pair 80_ - 80₂ and a second write head pair 80₃ - 80₄. Similarly, the four read heads 82₁ - 82₄ are grouped in pairs, e.g., a first write head pair 821 - 82₂ and a second write head pair 82₃ - 82₄. Tape 31 is wrapped around scanner 84 such that the heads 80 and 82 follow helical stripes 86 (see Fig. 1) on tape 31 as tape 31 is transported in a direction indicated by arrow 87 from a supply reel 90 to a take-up reel 92.

Supply reel 90 and take-up reel 92 are typically housed in an unillustrated cartridge or cassette from which tape 31 is extracted into a tape path that includes wrapping around scanner 84. Supply reel 90 and take-up reel 92 are driven by respective reel motors 94 and 96 to transport tape 31 in the direction 87. Reel motors 94 and 96 are driven by transport controller 98, which ultimately is governed by processor 50. Operation and control of the tape transport mechanism of this second type of tape drive including reel motors 94 and 96 is understood by the person skilled in the art with reference, for example, to United States Patent Application SN 08/337,620 for METHOD AND APPARATUS FOR CONTROLLING MEDIA LINEAR SPEED IN A HELICAL SCAN RECORDER, filed November 10, 1994 and incoφorated herein by reference.

Since scanner 84 rotates at a high rotational speed, the relative velocity between the heads 80, 82 and tape 31 is very high. A hydrodynamic air film is created between the scanner 84 and tape 31. To increase data capacity and transfer rate of the recording device, thinner tapes (for example 7.0 and 5.5 μm thickness) and higher scanner rotation speeds (e.g., from about 3,000 RPM to about 9,000 RPM) are used. With these thinner tapes and higher scanner rotational speeds, an unstable head-to-tape interface on a leading head of each head pair has been noticed.

To stabilize the air film, the present invention provides a non- transducing (e.g., non-recording, non-reproducing) dummy head in front of the leading head of an active head set. For example, as shown in Fig. 2 and Fig. 3, a dummy non-recording head 80₀ is provided before the four write heads 801 - 80₄, and a dummy non-reading head 82₀ is provided before the four read heads 821 - 82₄. The dummy non-reading head 82₀ is situated upstream from the leading read head 82_! , the leading read head 82_! being the first head to contact the tape as the scanner 84 rotates in the direction shown by arrow 204. All heads, including the transducing heads and the dummy head, are mounted to a base plate 200 on an upper drum 202 of the scanner 84 in the manner illustrated for the write head side of scanner 84 as shown in Fig. 3. As understood by those skilled in the art, scanner 84 includes both a lower drum and an upper drum 202.

The provision of the dummy heads 80₀ and 82₀ of the present invention results in an improved read/write signal. The configuration of the present invention is much less sensitive to variations in tape tension, scanner rotational speeds, and tape thickness. Moreover, the present invention results in a consistent, flat read write signal over the entire recorded track.

Attesting to the advantages stated above, Fig. 4A - Fig. 4D and Fig. 5A - Fig. 5D are renderings of oscilloscope images taken with a tape tension of 12g, and a tip projection of 20 μm. Fig. 4A through Fig. 4D are renderings of oscilloscope images showing a decrease in signal amplitude on a leading head in a scanner configuration not having the leading dummy head of the present invention, while Fig. 5A through Fig. 5D are oscilloscope images showing signal amplitude in accordance with the present invention wherein the leading dummy head is provided. As evident by a comparison of Fig. 5A - Fig. 5D with the corresponding respective Fig. 4A - Fig. 4D, the present invention has no decrease in signal amplitude in view of addition of the dummy head. That is, the signal in Fig. 5A - Fig. 5D has an equal amplitude (e.g., is "flat") over the entire time that the heads are in contact with the tape.

As used herein, terms such as "dummy head" and "non-transducing head" refer to any comparably configured body whose placement in accordance with the present invention provides the advantages of the present invention, e.g., the stabilized head-to- tape interface at the active head set. "Active head set" refers to a set of heads which are employed for transducing (including reproduction) of information.

Many configurations for placement of the leading dummy head are contemplated by the present invention. In the illustrated embodiment, the dummy heads are mounted to a same base plate as the active (e.g., transducing) heads. However, such need not necessarily be the case, as in other embodiments the dummy heads could be mounted to their own base plate, which in turn would be mounted separately to the scanner upper scanner.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A helical scan tape drive which transduces information relative to magnetic tape using an active head set mounted on a rotating scanner, the improvement comprising a non-transducing body comparably configured to a transducing head, the non-transducing body being mounted upstream from the active head set in a direction of scanner rotation for stabilizing a head-to-tape interface at the active head set.

2. The apparatus of claim 1, wherein provision of the non-transducing body results in an essentially uniform signal amplitude from a head in the active head set.

3. The apparatus of claim 1, wherein provision of the non- transducing body results in an essentially uniform signal amplitude from a leading or trailing head in the active head set.

4. The apparatus of claim 1, further comprising a base plate mouned to the scanner, and wherein both the active head set and the non-transducing body are mounted on the base plate.

5. The apparatus of claim 1, wherein the non- transducing body is a dummy head.

6. A helical scan tape drive which transduces information relative to magnetic tape, the drive comprising: a rotating scanner; an active head set mounted on the rotating scanner for transducing the information relative to the magnetic tape; a tape transport system for transporting the magnetic tape proximate the rotating scanner; a non-transducing body comparably configured to a transducing head, the non- transducing body being mounted upstream from the active head set in a direction of scanner rotation for stabilizing a head-to-tape interface at the active head set.

7. The apparatus of claim 6, wherein provision of the non- transducing body results in an essentially uniform signal amplitude from a head in the active head set.

8. The apparatus of claim 6, wherein provision of the non- transducing body results in an essentially uniform signal amplitude from a leading or trailing head in the active head set.

9. The apparatus of claim 6, further comprising a base plate mouned to the scanner, and wherein both the active head set and the non-transducing body are mounted on the base plate.

10. The apparatus of claim 6, wherein the non- transducing body is a dummy head.