1. Field of the Invention
The present invention relates to a helical scan type recording apparatus capable of recording data as inclined tracks onto, e.g., a tape-shaped recording medium, and a recording method therefor.
2. Description of Related Art
Magnetic recording systems of a helical scan type have hitherto been used extensively by, e.g., computer data systems or the like in order to back up data stored in their hard disk.
To accommodate errors during recording/reproduction, some magnetic recording systems use a method wherein data is recorded by adding thereto an error correction code (ECC) which can correct erroneous data, so that, e.g., even when trouble occurs in part of their recording/reproducing system, the data can be recorded correctly (Japanese Unexamined Patent Application Publication No.2001-273096). Some other magnetic recording systems deploy an error correcting device which can record or reproduce data, e.g., even when one of a plurality of helical scan type recording heads fails (Japanese Unexamined Patent Application Publication No. H10-21657).
Here, a helical scan type magnetic recording system will be outlined. In the helical scan system, a magnetic tape 100 is wrapped at an angle around a rotary head drum 101 as shown in, e.g., FIG. 7. Under this condition, the tape 100 is moved so that the head drum 101 rotates in the direction of the arrow, whereby a head scans at the angle with respect to the tape running direction. In this way, tracks are formed on the tape 100 by recording data at angles with respect to the tape running direction, or data is read from such tracks, as shown in FIG. 8.
Furthermore, the above-mentioned helical scan system adopts so-called azimuth recording. In azimuth recording, a pair of heads is used with their gaps slanted at different azimuth angles A and B, respectively, to alternately form on the magnetic tape 100 a track TkA depicting a recording pattern at the azimuth angle A and a track TkB depicting a recording pattern at the azimuth angle B, as shown in FIG. 8.
To reproduce data from a track recorded by such azimuth recording as mentioned above, a reproducing head 102A corresponding to the track TkA is used, and a reproducing head 102B is used for the track TkB recorded at the azimuth angle B as shown in FIG.9. In this way, signals produced in adjacent tracks can suppress themselves from affecting each other as noise owing to the azimuth effect, whereby a higher density recording can be implemented.
As one data reproducing technique in the helical scan technology, a tracking servo system is widely known in the art, in which the thus formed tracks are read through single scanning performed by a reproducing head. As shown in, e.g., FIG. 10, the tracking servo system controls a reproducing head 102 to keep the head constantly right on a track Tk so that all the data recorded on the track Tk will be read by causing the single head 102 to scan only once.
Thus, the tracking servo system gathers error information, e.g., by comparing a block-based scanning time with a pre-defined reference value in each track Tk, and the scanning position of the reproducing head 102 is controlled based on the error information to maintain the so-called “just tracking state” (Japanese Unexamined Patent Application Publication No. H09-245394).
As another reproducing technique in the helical scan technology, a non-tracking (NT) system is known in the art. In the NT system, data is scanned during reproduction at a track density twice as much as that of the recording period. Two reproduced signals are obtained on the average per track, and the better one is used for the data reproduction.
FIG. 11 conceptually shows the relationship between recorded tracks and reproducing heads in a NT system. Note that a description is given only of reproduction of azimuth tracks A in FIG. 11, and a description of azimuth tracks B will be omitted. Here, the tracking servo system as a reproducing technique would use reproducing heads 103 and 105 to scan tracks TkA-1 and TkA-2 to reproduce data, respectively. On the contrary, the NT system, which scans data during reproduction at a track density double as that of during recording, would cause a reproducing head 104 to intervene for scanning between the scanning operations performed by the reproducing heads 103 and 105.
In an example shown in FIG. 11, the track TkA-1 is scanned by the heads 103 and 104, and both heads provide effective reproduced signals for the track TkA-1. In this case, however, a comparison between the heads 103 and 104 indicates that the head 103 overhangs the track TkA-1 wider and, in addition, is less likely to near the track TkA-2 next to the adjacent track of the track TkA-1. Therefore, the reproducing head 103 will provide a more satisfactory reproduced signal. And only a correctly read portion of the thus reproduced signal is re-arranged to provide stream data. Such an NT system requires neither accurate tracking servo nor accurate scanning angle with respect to tracks, thus making the system free from mechanical tolerances, for example.