JPH0668860B2 - Tracking control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking control method, and more particularly, to a tracking control method in a system for recording / reproducing information signals for a large number of tracks arranged in parallel on a recording medium. It is about.

[Conventional technology]

In recent years, it has become more frequent to digitize various information signals and record / reproduce them in the system as described above. On the other hand, the band of the digitalized information signal is extremely wider than that of the analog information signal, and accordingly, it is necessary to perform high-density magnetic recording or the like, and, for example, the track pitch cannot be widened.

On the other hand, if a tracking error occurs during reproduction of the digital information signal, the probability of occurrence of a code error increases significantly. Although this may be corrected by using a so-called error correction code or the like, it is not preferable to improve the correction capability of the error correction code because it increases redundancy. Therefore, improving the tracking accuracy in this type of system is a major theme.

On the other hand, as a conventional tracking control method in this type of system, a control signal (CTL) having a frequency corresponding to the track pitch at the end of the tape-shaped recording medium is used.
Is recorded at a fixed head, and is reproduced to obtain a tracking error signal by phase comparison with a reference signal (CTL method). A pilot signal having four different frequencies is sequentially recorded as an information signal for each track. A method (four-frequency system) has been used in which a tracking error signal is obtained by superimposing recording and comparing the reproduced pilot signal levels from both adjacent tracks of the control target track during reproduction.

[Problems to be solved by the invention]

However, in the CTL method, tracking control is not performed based on the information obtained from the recording track, so, for example, when the linearity of the track is impaired or when the CTL playback head installation error occurs, Therefore, an accurate tracking control signal may not be obtained.

Further, in the 4-frequency system, the problem of the CTL system can be solved, but since four kinds of pilot signals are superimposed on the information signal, the band of the information signal is limited. Especially in the case of digital signals, the lower end of the recording band
Since it extends to about 100 KHz, it is impossible to superimpose four kinds of frequencies.

The present invention has been made in view of the above-mentioned problems, and by simply superposing one type of pilot signal, a tracking error with respect to a recording track can be accurately detected, and a stable and accurate track can be obtained at any position of the track. It is an object of the present invention to provide a novel tracking control method capable of obtaining a king error signal and performing good tracking control accordingly.

[Means for solving problems]

For such a purpose, in the tracking control method of the present invention, in a system for recording / reproducing information signals to / from a number of tracks arranged in parallel on a recording medium, the track is divided into a plurality of areas. In the first region, a pilot signal of a single frequency is applied to the plurality of regions so that the phases of both adjacent tracks are shifted in the opposite directions by the same amount with respect to the phases of the controlled tracks in the plurality of tracks. With respect to the second predetermined area dispersedly arranged, the pilot signal having only a single phase is recorded in at least a part of the tracks, and at the time of reproducing the information signal, the phase of the pilot signal reproduced from the first area is recorded. , Tracking control is performed based on the phase difference from the pilot signal reproduced from the second area.

[Action]

With the above-mentioned structure, the reference phase of the pilot signal can be stably obtained from any part of the track by using the pilot signal reproduced from the second region, so that the reference signal generated from the first region is generated. Since the amount of phase shift of the pilot signal always indicates the tracking error accurately, it is possible to perform extremely good tracking control.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

5 (A) and 5 (B) are diagrams showing the head structure of a digital VTR as an embodiment of the present invention. Ha, Hb, Hc, Hd in the figure
Are rotating video heads, each on cylinder 1
It is installed with a 90 ° phase difference. Also head
Ha and head Hc each have an azimuth angle of + θ °, and head H
b and head Hd each have an azimuth angle of −θ °.

The magnetic tape 2 is wound around the cylinder 1 over an angular range of 180 ° or more, and a digital video signal for one field is sent to the heads Ha, Hb, Hc, H while the cylinder 2 makes one rotation.
It shall be recorded on the four tracks formed by d. Therefore, at this time, the cylinder 2 rotates 60 times per second, and each stock is formed in 1/120 second.

FIGS. 1A and 1B are digital VTs in this embodiment.
FIG. 6 is a diagram for explaining a recording pattern by R. First
In the figure (A), each head Ha, Hb, Hc, Hd shall be traced on the tape 2 in the direction shown by the arrow 3, and p1, p2,
p3 and p4 indicate pilot signals having phases different from each other by 90 °, and the frequency of the bracket pilot signals is a single frequency of about 50 KHz. By the way, here, the phase of each pilot signal is the phase on the tape 2, and when the phase is shifted by 90 ° in the adjacent track, when they are reproduced in the same head, the reproduction phase is shifted by 90 °. Indicates that FIG. 1 (B) is a diagram showing the phase relationship of p1, p2, p3, and p4 as a vector.

Next, the principle of tracking control according to this embodiment will be described with reference to FIGS. 2 (A) and 2 (B). When the pilot signal recorded in the control target track is p1 and the pilot signals recorded in both adjacent tracks are p2 and p4 as shown in FIG. 2 (A), the head is the control target track. On the other hand, in the just-track state, the combined phase vector of the pilot signal reproduced from the head coincides with p1. On the other hand, when the head deviates from the control target track to the track where p2 is recorded, the composite phase of the reproduction pilot signal changes like P _{m1 in} FIG. 2B, and p4 is recorded. When it is shifted to the track side, the composite phase of the reproduction pilot signal is shown in Fig. 2 (B).
Change like P _m2 in.

FIG. 3 is a diagram showing a schematic configuration of the digital VTR of the present embodiment, and FIG. 4 is a timing chart showing waveforms of respective portions in FIG.

The video signal still input from the terminal 10 is processed by a digital signal processing circuit 11 for digital signal processing, and a 1-field video signal is divided into 4 digital signals, which are 1/4 field periods (1/240 seconds). It is output at the timing of each shift. The reference oscillator 13 generates a reference signal that gives the frequency of the pilot signal, and this reference signal is supplied to the phase comparator (PC) 15 via the R side of the switch 14. The voltage controlled oscillator (VC
O) 16 output signal and the reference signal are phase-compared, and the comparison output controls the VCO via the low-pass filter (LPF) 17 and the R side of the switch 18.

By the way, the frequency of this reference signal is such that the wavelength is a fraction of the shift amount of adjacent tracks due to the diagonal formation of tracks and an integral multiple of 240 Hz. If a signal having the same frequency as the reference signal is supplied in the same phase, the phase on the tape 2 will be the same between the tracks and throughout the entire track.

The delay circuits (DL) 19, 20, and 21 respectively use the input signal as the reference signal 1
These outputs are for shifting by / 4 wavelength.
The output signals of VCO16 are 90 °, 180 ° and 270 ° phase shifted respectively, and when the output of VCO16 is pilot signal p1, the outputs of DL19,20,21 are p2, p3 and p4 respectively. .

The 4-phase PG generator 25 is the rotary cylinder 5 in FIG. 5 (A).
As shown in FIGS. 4 (a), (b), (c) and (d), four kinds of phase pulses (PG) indicating the recording / reproducing timing of each head Ha, Hb, Hc, Hd based on the rotation phase of Occur.
Reference numeral 26 is an 8-multiplier such as a PLL, which generates a signal (shown in FIG. 4 (e)) having a frequency eight times that of PG. This signal (e) controls the switches 22, 23, 24, and as a result, the switch 22 switches the output pilot signal between p1 and p2 eight times during the formation of one track. Similarly, the pilot signals output from the switches 23 and 24 are p1 and p3, p.
Switched between 1 and p4 respectively.

The digital signals of the four systems described above are mixed by the mixers 12a, 12b, 12c,
12d is mixed with the pilot signals generated respectively as described above, and recorded at the heads Ha, Hb, Hc, Hd via the R side of the switches 27a, 27b, 27c, 27d and the switches 28a, 28b, 28c, 28d, respectively. It The switches 28a, 28b, 28c and 28d are the aforementioned PGs, respectively.
It is turned on / off by (a), (b), (c) and (d).

Through the above process, a single frequency pilot signal having a phase as shown in FIG. 1 (A) is recorded together with a digital video signal.

Next, the operation of the apparatus of this embodiment during reproduction will be described.
The switches 27a, 27b, 27c and 27d are connected to the p side, and PG
The switches 28a, 28 are formed by (a), (b), (c), and (d).
By controlling b, 28c, 28d, a reproduction signal can be obtained from each head Ha, Hb, Hc, Hd. The reproduced signals of these four systems are supplied to the reproduced digital signal processing circuit 29, where the original video signal is restored and output from the terminal 30 as a reproduced video signal.

On the other hand, the reproduced signals of the four systems are supplied to the BPFs 31a, 31b, 31c and 31d, respectively, and the pilot signal components are separated. Here, as is apparent from FIG. 1A, the pilot signal reproduced from the areas a1, a3, a5 and a7 is always P1. On the other hand, a multiplier
When the pulse signal (e) output from 26 is at a high level, each of the cuts Ha, Hb, Hc, Hd traces the areas a1, a3, a5, a7. At this time, the switches 32a, 32b, 32c, 32d are set to H level. If connected to the side, the pilot signal input to the adder 33 will be p1. Therefore, the pilot signal output from the adder 33 is the average signal of p1 reproduced from the two heads tracing on the tape. For the phase difference due to head mounting error, add the output of this adder 33 to PC15, LPF
It is smoothed by supplying it to a PLL circuit composed of 17, VCO16. However, in the PC15, since only the error signal during the reproduction of the area where the pilot signal p1 is reproduced is effective,
This is sample-held by a sample hold circuit (S / H) 35. As a result, the VCO 16 obtains the reference signal of p1 in which the variations in the mounting positions of the four heads are smoothed, and the reference signals of p2, p3, and p4 are obtained from the DL19, 20, and 21, respectively.

There is no problem if the response speed of the PLL circuit is extremely fast, but in this embodiment, the frequency _P of the pilot signal is set to be 4n times (n is an integer) the rotation frequency _D of the rotary drum 5, and the VCO 16 is centered. By setting the frequency to _P , V
Even if CO16 runs freely, the reference signal output from the VCO is always p1. Therefore PC15
The phase error obtained in step 1 is only due to the mechanical error of the device, and can be sufficiently tracked even if the response speed of the PLL is slow to some extent.

On the other hand, from the L side terminals of the switches 32a, 32b, 32c, 32d, the head H
A pilot signal is output in which a, Hb, Hc, and Hd are separated from the reproduced signal while tracing the regions a2, a4, a6, and a8. The phase of this pilot signal changes according to the track shift with respect to the control track. Now, if the phase of each pilot signal is in the relationship shown in FIG. 1 (B), when each head is shifted to the right side in FIG. 1 (A) with respect to the control target track, the phase of the reproduced pilot signal is clockwise. It rotates to the left, and when it shifts to the left, it rotates counterclockwise.

Therefore, in the PCs 34a, 34b, 34c, 34d, a tracking error signal can be obtained by phase comparison between the reference pilot signal and the reproduction pilot signal of the control target track.
However, in this case, each of the heads Ha, Hb, Hc, Hd is in the region a2, a4, a respectively.
Since only the error signal during tracing 6, a8 is valid,
A signal indicating this timing (Figs. 4 (f), (G),
(Shown in (h) and (i)) is an inverter 35, an AND gate 3
6a, 36b, 36c, 36d to form gates 37a, 37b, 37c, 37
control d. As a result, only a valid tracking error signal is input to the adder 38, and the output of the adder 38 is supplied to the capstan control circuit 40 via the LPF 39. The capstan control circuit 40 controls the running of the tape 2 by the capstan 41 and the pinch roller 42 in the direction of compensating for the track deviation. Digital VTR of the above embodiment
In that case, since tracking control can be performed only by superimposing a single frequency pilot signal, a wide band of the digital video signal can be taken. Further, since the reference phase for forming this error signal is obtained based on the signals reproduced from various positions in the width direction of the tape, the influence on the tracking error signal by the jitter at the time of reproduction by the rotary head is suppressed to a small level. be able to. Further, since the phase of the pilot signal recorded in the control target track of each head is always the same, the configuration of the switching circuit system when the circuit is constructed can be simplified. Further, since the tracking error signal is formed by using the reproduction signals of all the heads, it is possible to deal with the variation in the mounting position of each head, and it is possible to obtain an extremely good tracking error control signal.

The tracking control method of the present invention is not limited to the arrangement of the pilot signals in the above embodiment,
Other arrangements are possible.

6 and 7 are diagrams showing other examples of the phase arrangement of the pilot signal on the tape, respectively, and the meanings of p1, p2, p3 and p4 in the figure are the same as those of FIG. 1 (A). Yes, the blank portion indicates that the pilot signal is not recorded.

The tracks that can be the control target in FIG. 6 are T1, T2, and T.
3, T4, T5, which exist every two tracks as shown in the figure.
Only p1 is recorded in the control target track, and p2 and p4 are recorded in the areas a2, a4, a6 and a8 of both adjacent tracks. That is, the head areas a1, a3, which should trace the control target track,
The reference phase is detected by the reproduced signal from a5, a7, and the area a2,
It is intended to obtain the tracking control signal by the reproduced signals from a4, a6, a8. However, in this case, since the direction of the tracking error signal is inverted for each control target track, the tracking error signal must be appropriately inverted by an inverting amplifier or the like.

In the recording pattern shown in FIG. 7, each track is divided into 10 areas a1 to a10 in the width direction of the tape, and the control target track is T
As shown by a, Tb, and Tc, it becomes every 3 tracks. In this pattern, the period of the recording pattern of the pilot signal is 6 track periods, which is suitable for recording a digital video signal with 6 heads.

Further, in each of the above-described embodiments, the phase difference of each pilot signal on the recording medium is 90 °, but it may be 120 ° or another phase difference.

〔The invention's effect〕

As described above, according to the present invention, a tracking error signal can be obtained stably and accurately at any position of the track without requiring a large band.

[Brief description of drawings]

1 (A) and 1 (B) are diagrams showing recording patterns by a digital VTR as one embodiment of the tracking control method of the present invention, and FIGS. 2 (A) and 2 (B) are embodiments of the present invention. FIG. 3 is a diagram for explaining the principle of tracking control in FIG. 3, FIG. 3 is a diagram showing a schematic configuration of a digital VTR as an embodiment of the present invention, FIG. 4 is a timing chart showing waveforms of respective parts in FIG. FIGS. 6A and 6B are views showing the head structure of a digital VTR as one embodiment of the present invention, and FIGS. 6 and 7 are views showing other examples of the phase arrangement of the pilot signals on the tape. Is. In the figure, 2 is a magnetic tape as a recording medium, 11 is a recording digital signal processing circuit, 12a, 12b, 12c and 12d are adders, 13 is a reference oscillator, 16 is a voltage controlled oscillator, and 19, 20 and 21 are delays, respectively. Circuits, 22, 23, 24 are switches, 25 is a 4-phase PG generator, 26
Is an 8-multiplier, 29 is a reproduction digital signal processing circuit, 34a, 34
b, 34c, and 34d are phase comparators, 38 is an adder, 40 is a capstan control circuit, 41 is a capstan, a1 to a10 are track divided areas, and p1, p2, p3, and p4 are pilot signals, respectively. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinsuke Yamashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Souichi Kashida 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Tamagawa Works of Canon Inc. (72) Mitsuhiro Otokawa 770 Shimonoge, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Inside the Tamagawa Works of Canon Inc. (56) Reference JP-A-58-41469 (JP, A) JP-A-58 -147847 (JP, A) JP 60-173752 (JP, A) JP 63-119058 (JP, A)

Claims (1)

[Claims] 1. A system for recording / reproducing an information signal to / from a plurality of tracks arranged in parallel on a recording medium, wherein a first area among a plurality of areas into which the track is divided has a plurality of tracks among the plurality of tracks. A pilot signal of a single frequency is set for the second predetermined area dispersedly arranged in the plurality of areas so that the phases of both adjacent tracks are shifted by the same amount in opposite directions with respect to the phase of the track to be controlled. The pilot signal having only one phase is recorded in at least a part of the tracks, and when the information signal is reproduced, the phase of the pilot signal reproduced from the first area and the pilot signal reproduced from the second area. A tracking control method for performing tracking control based on the phase difference between the and.