JPS618777A - Magnetic recording and reproduction system - Google Patents

Abstract

PURPOSE:To reduce readout errors of data due to the influence of pressing, a tape run flaw, dissidence of linearity, etc., and to shorten the readout completion time of retrieval data by recording retrieval data having the same contents at plural dispersed positions on the same track. CONSTITUTION:A track T1 on a video tape 1 is assigned to a chapter 1-1, T2 to a chapter 1-2, and so on T-16 to a chapter 3-4. Retrieval data C1-1 on the chapter 1-1 is recorded on, for example, the track T1 at four positions ar proper intervals respectively. Similarly, data C1-1-C3-4 are recorded on other tracks. The track T1 is scanned firstly and data C1-1 shown by No.1 when read out without any error is written in a memory. If data No.1 is an error, data C1-2 indicated by No.2 is read and written on the memory when having no error. Thus, readout errors of data due to the influence of pressing, a tape run flaw, dissidence of linearity, etc., are reduced and the readout completion time of inspection data is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a data recording method for a magnetic recording/reproducing device, and more particularly to a recording method for search data in a VTR or the like.

[Prior art 1 Helical scan type VTR (for example, 1/2 inch, 8
In a moving image and still image retrieval device using a video recording medium (mm), a chapter number corresponding to the start address of the video to be searched is usually recorded in the recording track at the beginning of the magnetic tape.

FIG. 2 shows a conventional recording method for this type of search data, in which the search data is recorded at a specific position on a video track formed by a rotating head of a VTR, for example, in 15 horizontal sections (from the switching position of the rotating head). 15H) One chapter worth of data is recorded in the second column.

The magnetic tape on which such search data is recorded is
When set to TR, the search device sequentially reads the search data on the magnetic tape before searching, records the first address corresponding to the chapter number in the device's internal memory, such as the reel stand counter value of a VTR, and enters the standby state. becomes. The search device inputs a chapter number from the outside, indexes the corresponding start address on the memory, fast-forwards the magnetic tape to the start address, and puts the VTR into playback mode or still image mode from the start address. Search for the desired image by
Cueing is being performed. Such a search device, especially a simple search device, uses error detection (parity, CR, etc.) in search data.
However, since it does not have an error correction function (cross interleaving, Reed-Solomon, etc.), data loss occurs due to dropouts and the like that exist in magnetic recording media.

Therefore, in the conventional search data recording method, the same search data is recorded in, for example, eight consecutive recording tracks. That is, the search data for chapter 1-1 is recorded on consecutive tracks T1 to T8, and the search data for chapter 1-2 is recorded on the recording track T9.
- T17, and the search data for chapter 3-4 was similarly recorded in recording tracks Tn-B to Tn. This prevented chemical dropout.

However, in such a conventional search data recording method, when the number of chapters becomes enormous due to the inclusion of still images, it takes a long time to read the search data.

For example, to read 256 chapters on a current 1/2 inch VTR, approximately 34 seconds are required in 8-track continuous recording mode.

In addition, in VTRs, as shown by X in Figure 3, there is an effect of a difference in adhesion between the leader tape and the magnetic tape, commonly known as ``slip'', and errors in reading data at the beginning of the tape occur near the middle. It is known that it is about 20 times worse than that, and there is a possibility of a collective data error 1) in this area.

Such dropouts and data reading errors are caused by
In the case of video information, it is visually compensated by a dropout compensation circuit, but in the case of search data, it cannot be compensated, resulting in a data error.

Furthermore, a data error also occurs if there are scratches or tape folds on the magnetic tape.

In addition, if there are scratches or cracks on the guide rollers for tape running, etc., as shown in Figure 4, linear scratches Y will be formed on the base surface of the magnetic tape, which will be transferred to the magnetic surface, and each video The possibility of collective data errors occurs on certain horizontal sections of the track.

In the case of video information, it is visually compensated by a dropout compensation circuit, but in the case of search data, data errors1)
This results in data loss.

The video track of a VTR has a certain degree of curvature due to the precision of the mechanism travel adjustment. Usually, VH
8, approximately 1 for a track pitch of 58 μI11.
It is said that there is a bend of about 0 μI.

In the case of compatible playback where the first VTR records and the second VTR plays back, there is a mismatch in the bending of the tracks of the two VTRs, that is, a mismatch in linearity, resulting in a mismatch in the scanning of the recording track of 20 μm, which is twice that length, and the playback video head. In some cases,

Figure 5 shows this situation, with the largest discrepancy occurring at A in the figure. Incidentally, FIG. 5(a)(1)) shows that point A has moved as a result of turning the tracking volume for compatible playback.

This 20μm discrepancy is 0μm in VH8 standard mode.
In other words, the data read error is about 10 times that of the best point, and since the read error continues in the tape running direction, there is a possibility that the search data will be lost.

Furthermore, it is obvious that this point A cannot be specified because it differs depending on the combination of individual VTRs and tracking volume adjustment during compatible playback.

In addition, in FIG. 5, the curvature of the head trajectory is exaggerated compared to the track pitch.

[Objective of the Invention] The present invention reduces the probability of data being lost due to data reading errors due to the effects of ``rolling'', tape running scratches, linearity discrepancies, etc., and further reduces the time required to complete reading of search data. The purpose of this study is to propose a magnetic recording and reproducing method that shortens the time required.

[Configuration of the invention 1 Hereinafter, one embodiment of the present invention will be described.

The embodiment in Figure 1 is 16 chapters from 1-1 to 3-4.
Indicates when there are chapters. Track T1 on videotape 1 is chapter 1-1, and track T2 is chapter 1-1.
2...T16 is assigned to Chapter 3-4.

Then, on each track, for example, Go 1, the search data C1-1 of chapter 1-1 is recorded at four locations separated by appropriate intervals.

The contents of the search data are similar to those shown in FIG. 2, for example. Similarly to the above, distributed search data C1-2 to C3-4 are recorded on other tracks T2...T16, respectively.

Videotape 1 with the search data recorded in this way is
The retrieval device to be set in the ITR first scans the track T1, and when the retrieval data C1-1 indicated by No. 1 is read out without error, it is written into an appropriate memory.

If there is an error in the data at N001, data C1-1 at N002 is read, and if there is no error, this data is written to the memory. Thereafter, the data of all searched chapters are written to the memory in the same manner.

As described above, according to the present invention, since search data is recorded in multiple locations on one track, it is possible to avoid the effects of "degree rolling", tape running scratches, and the trajectory of the recording track and head. It is possible to deal with read errors due to linearity discrepancies, and the time required to read search data can also be shortened.For example, the time required for reading 8 tracks continuously can be reduced to about 1/8.

For example, due to linearity discrepancy, Chapter 1-1-3
Even if all the search data for Nos., 1 and N004 up to -4 are read out incorrectly (the error rate is only about 10 times higher, so this is unlikely to happen), Nos., 2 and No.
3, and even if No. 12 is read erroneously due to the influence of "sleeping", No. 3 remains, so the possibility of missing search data is extremely small. - The distribution of this recording depends on the error rate of the data, but it is desirable to write four or more times on the same track with appropriate distribution.

In addition, in the case of general β and VH3 type helical scan VTRs, two heads are used for normal playback, but these two heads are used for special playback (slow, still), so normally These two head widths are different. −
In the example, the track pitch is 58 μm and the R channel head is 58 μm.

The length of the L channel head is 40 μm. In this case, if the reproduction scan is deviated by 10 μm due to the tracking volume adjustment error, the output of the R head will be (58-10) 158〒83%, and the output of the L head will be (40-10) 15111 = 52%, and R Compared to the head, the reproduction output of the L hand is lower and errors occur more often. In other words, even (odd) numbered chapter data has fewer errors, but conversely, odd (even) numbered chapter data has more errors.

In order to guarantee search data for odd (even) tracks,
By inserting one dummy for the even number of chapter data 16 and continuously recording it on the recording track as 17 chapter data, the first half 16 chapter data and the second half 16 chapter data are different. It is safer and more reliable if the heads used are different. Although the search time is doubled, the reliability of the data is guaranteed by recording each chapter data twice in succession.

[Advantageous Effects of the Invention 1] As detailed above, the same search data of this invention is repeatedly recorded at multiple locations on one video track, so even if the tape is scratched or bent, it cannot be played again. Even if there is an error such as a bend in the trace trajectory of the head, the search data can be reliably detected and there is an advantage that data loss due to the inability to read the data can be prevented.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the search data recording method of the present invention, FIG. 2 is a diagram showing a conventional search data recording method, and FIG. 3 is a diagram illustrating the deformation that occurs on a videotape. , FIG. 4 is a diagram showing an example of scratches occurring on a videotape, and FIGS. 5(a), (1)), and (c) are diagrams showing various states of curvature of the trajectory of the reproducing head. 1...Video tape, T1. T2...T16...Truck, C1-1~C
3-4...Search data.

Claims (1)

[Claims] (1) A magnetic recording and reproducing method characterized by recording search data of the same content in a plurality of distributed locations on the same track.