Dynamic magnetic information storage or retrieval – Head – Head accessory
Reexamination Certificate
1999-10-26
2002-09-17
Hudspeth, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Head accessory
Reexamination Certificate
active
06452744
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic record/playback apparatus for recording or reproducing a digital signal with respect to a magnetic tape.
In recent years, a combination camera/digital video tape recorder for home use and a stationary digital video tape recorder for home use for recording a digital video signal and a digital audio signal have come on the market.
As a recording system for such digital video tape recorders, a so-called DV format (IEC 61834 helical scan digital video tape cassette recording system using 6.35 mm magnetic tape for consumers (525/60, 625/50, 1125/60, and 1250/50 systems) is known. In the DV format, the tape to be used is 6.35 mm (=¼ inch), which is smaller than the tape width of a video tape to be used in a related art recording system for an analog video tape recorder (e.g., 8-mm format: IEC 60843 helical scan video tape cassette recording system using 8-mm magnetic tape for consumers). In spite of such a smaller tape width, the DV format has an advantage such that a signal to be recorded is compressed and a recording density is increased to thereby allow longer-period recording with a higher image quality as compared with the related art recording format.
There is no compatibility between the DV format and the related art recording format for the analog video tape recorder (e.g., 8-mm format). However, if a signal in the DV format can be recorded/reproduced on/from the wider video tape to be used in the related art analog recording system, the recordable/reproducible period can be further increased with a higher image quality maintained. Further, if such recording/reproduction of a DV-format signal on/from the video tape to be used in the related art recording system is allowed, existing resources including the production facilities and parts of video tape for use in the related art recording system can be effectively used.
A magnetic record/playback apparatus adapted to the format of an 8-mm analog video tape recorder, for example, includes a rotary drum unit having a rotating drum (upper drum) and a fixed drum (lower drum). The rotational speed of the rotating drum is set to 1800 rpm, for example. The outer circumferential surface of the rotating drum is formed with a groove extending in a direction of rotation of the rotating drum. In this kind of magnetic record/playback apparatus, it is important to ensure a suitable RF output waveform. It is known that in rotating the rotating drum to record/playback a signal on/from a magnetic tape by using a magnetic head, the thickness of an air film generated by rotation of the rotating drum has a large influence on whether or not a suitable RF output waveform can be obtained. In this respect, the groove is formed on the outer circumferential surface of the rotating drum to limit the thickness of the air film.
However, if the rotational speed of the rotating drum is changed to 4500 rpm, for example, to record a DV-format signal in the 8-mm format magnetic record/playback apparatus, the thickness of the air film is necessarily increased to cause a problem that a suitable RF output waveform cannot be obtained.
Further, the rotating drum has a magnetic record/playback head for recording/reproducing information on/from an analog video tape and an erase head for erasing information recorded on the analog video tape. Accordingly, the magnetic record/playback head and the erase head are rotated with rotation of the rotating drum. During rotation of the rotating drum, the magnetic record/playback head and the erase head come into contact with the analog video tape to record/playback information on/from the analog video tape or erase information recorded on the analog video tape.
Particularly, in the case that the analog video tape is a coated tape or the like having a high coercive force (Hc), information can be well recorded/reproduced by using the erase head.
To record/playback or erase a DV-format signal by using the rotating drum of a related art 8-mm format magnetic record/playback apparatus, the rotational speed of the rotating drum must be changed from 1800 rpm for analog recording to 4500 rpm for digital recording.
When the rotational speed of the rotating drum is increased as mentioned above, the magnetic record/playback head and the erase head mounted on the rotating drum are also rotated at a higher speed. As a result, the frequency of contacts of the magnetic record/playback head and the erase head with the analog video tape is increased to cause an increase in wear of each head.
In particular, since the erase head precedes the magnetic record/playback head in one revolution of the rotating drum to come into contact with the analog video tape, the wear of the erase head becomes greater than that of the magnetic record/playback head. Such a difference in worn condition between the erase head and the magnetic record/playback head shortens the service life of the magnetic record/playback apparatus.
To eliminate such a difference in worn condition between the erase head and the magnetic record/playback head, it may be proposed to add a dummy head to the rotating drum. By addition of the dummy head, a contact force between the erase head and the analog video tape can be adjusted to reduce the wear of the erase head. However, the addition of the dummy head to the rotating drum causes an increase in cost.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a magnetic record/playback apparatus which can obtain a suitable RF output waveform and can stabilize tape running both in the DV format and in the analog video tape recorder format.
It is another object of the present invention to provide a magnetic record/playback apparatus which can. reduce a difference in worn condition between a magnetic record/playback head and an erase head with a simple configuration to thereby extend the service life of the magnetic record/playback apparatus.
In accordance with an aspect of the present invention, there is provided a magnetic record/playback apparatus for continuously recording at least two tracks of data conforming to a digital recording format applied to a first magnetic tape having a first tape width onto one track formed on a second magnetic tape having a second tape width larger than the first tape width, and for reproducing the data from the second magnetic tape, comprising a fixed drum; and a rotating drum adapted to be rotated relative to the fixed drum, the rotating drum having a magnetic head for recording the data onto the second magnetic tape and for reproducing the data from the second magnetic tape; the rotating drum having an outer circumferential surface formed with a plurality of grooves extending in a direction of rotation of the rotating drum, each of the grooves having a width of 0.21 mm±0.02 mm.
As mentioned above, the plural grooves each having a width of 0.21 mm±0.02 mm are formed on the outer circumferential surface of the rotating drum so as to extend in the direction of rotation of the rotating drum. Accordingly, the thickness of an air film formed between the outer circumferential surface of the rotating drum and the magnetic tape during rotation of the rotating drum can be limited to a suitable value both in the case that the rotational speed of the rotating drum is relatively low and in the case that it is relatively high. As a result, a suitable RF output waveform can be ensured and stable running of the magnetic tape can also be ensured.
If the width of each groove is less than 0.19 mm, the thickness of the air film cannot be limited to a suitable value in recording data conforming to the digital recording format, so that it is difficult to ensure a suitable RF output waveform and stable running of the tape cannot be ensured. Further, the use environment is limited (especially at high temperatures), and the service life is reduced (due to a difference in worn condition between the heads).
If the width of each groove is greater than 0.23 mm, a suitable thickness of the air film cann
Endo Junya
Kiko Masahiro
Ochiai Mutsuko
Tamaru Yoshio
Castro Angel
Frommer William S.
Frommer & Lawrence & Haug LLP
Hudspeth David
Ryan Matthew K.
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