JPH0740390B2 - 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 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 used 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 due to an error in mounting the CTL playback head, etc. 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 superimposing 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 the system for recording / reproducing information signals to / from a large number of tracks arranged in parallel on the recording medium, the track is recorded in the first area of the track. On the other hand, a pilot signal of a single frequency is recorded 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 control target tracks in the plurality of diagonal tracks, and the second track in the track is recorded.
In the area (1), the pilot signal is recorded so that pilot signals other than the same phase are not recorded at the adjacent positions of both adjacent tracks, and the first area and the second area are mutually adjacent to each other. A guard area having a sufficient length so as not to take adjacent positions and not recording the pilot signal is provided between them, and the pilot signal reproduced from the first area and the second area reproduced at the time of reproduction. Also, a configuration is adopted in which tracking control is performed based on the phase difference from the pilot signal.

[Action]

With the above-described structure, the reference phase of the pilot signal is obtained from the reproduced signal by using the pilot signal reproduced from the second area, so that the band of the recording signal is not limited and the mechanical between the devices is not limited. It has become possible to perform good tracking control without being affected by variations in accuracy.

〔Example〕

An embodiment to which the tracking control method of the present invention is applied will be described below. The embodiment described below is one in which the present invention is applied to a rotary 2 head helical scan type digital VTR.

First, the operation during recording of the digital VTR of this embodiment will be described.

The analog video signal input to the video signal input terminal 1 is digitalized by the analog-to-digital (A / D) converter 2, and further encoded by the encoding circuit 3 to detect redundant data such as error detection, correction code and various additional information. The data is added, converted into a data array suitable for error correction, and supplied to the modulation circuit 4.

In the modulation circuit 4, a signal form suitable for magnetic recording,
For example, so-called mapping coding or the like is performed to convert the signal into a low-frequency component suppressed signal.

In this embodiment, a single frequency pilot signal is superimposed on the band suppressed by the modulation circuit 4, and the single frequency pilot signal and the digital video output from the modulation circuit 4 are output. The addition circuit 5 performs addition with the signal.

Here, the generator of the single frequency pilot signal will be described. In this embodiment, the single frequency pilot signal is a sine wave of about several tens to several hundreds of KHz so as not to adversely affect the digital video signal. The definition of this frequency will be described later.

This sine wave is obtained by reading the data stored in the ROM table 14. The relationship between the address data input to the ROM table 14 and the output data is shown in FIG. As shown in the figure, if the data input to the ROM table 14 is sequentially changed from 0 to N-1 (15 in this example) at regular intervals, data corresponding to the stepwise waveform as shown in the figure is generated. This data is digital-analog (D /
A) A single frequency sine wave can be obtained by converting the signal into an analog signal by the converter 15 and removing harmful harmonics by the LPF 16. Since the ROM table 14 generates data corresponding to one cycle of a sine wave in N steps of 0 to N-1, when the address data is N / 2, N / 4, the phase is π, π / 2. It will be. Therefore, the required pilot signal frequency is f _P
Then, the address may be updated every 1 / (N × f _P ) seconds.

In FIG. 1, reference numeral 11 is an oscillator for generating a clock signal having a frequency of N × f _P , and this clock is counted by a counter 12 having a maximum value N-1 (4 bit counter when N = 16). The output data of the counter 12 is passed through the adder 13 to RO
It is supplied to M14 as address data.

Next, the control of the phase of the pilot signal will be described. For example, if the phase of the output of the ROM 14 is to be shifted by π / 2, it is clear from the above description that the N / 4 address should be shifted. Therefore, the constant data generator 17 is 0, N / 4, N / 2, 3N / 4
4 data are generated in parallel, and these 4 data are selectively supplied to the adder 13 by the data selector. As a result, four kinds of single-frequency pilot signals whose phases are shifted by π / 2 can be output from the ROM 14.

Reference numeral 20 denotes a rotary phase detector that detects the phases of the rotary heads Ha and Hb for recording and reproducing, and generates a rectangular wave signal (hereinafter referred to as PG) that indicates the switching timing of the recording and reproducing heads. The counter 12 is reset by the timing pulse indicating the timing of the edge of this PG output from the edge detector 21, that is, the heads Ha and Hb are reset at the timing when the tracing of each recording track is started. Meanwhile, counter 19
Is a 2-bit counter that counts this timing pulse, and the output data is shifted each time the timing pulse is input, that is, every time the track is changed, and accordingly, the data selector 18 is 0 → N / 4 → N. Change the output data as / 2 → 3N / 4 → 0 .... With the above configuration, the head Ha, Hb
The phase of the pilot signal supplied to the adder 5 via the H-side terminal of the switch 55 is sequentially shifted by .pi. / 2 at the timing at which the track tracing is started.

Here, the operation timing of the switch 55 will be described with reference to FIG. In FIG. 3, 0, π / 2, π, 3π / 2 indicate the phase of the pilot signal recorded in each track. Also, the shaded portion in the figure indicates the portion where the pilot signal is not recorded.

In FIG. 3, X ₁ indicates the amount of track shift between adjacent tracks, and the length in the longitudinal direction of the track where the pilot signal is not recorded corresponds to this amount of track shift. Further, when the head attempts to trace toward the upper right in FIG. 3, the length of the pilot signal recording portion up to the portion where the pilot signal is not recorded also corresponds to the track shift amount.

The control of the switch 55 for recording the pilot signal as shown in FIG. 3 will be described with reference to the timing chart of FIG. The edge detection pulse of PG (shown as i in FIG. 5) (ii in FIG. 5) is a mono-multivibrator (MM) 5
It is supplied to 2,53 and outputs as shown in FIGS. 5 (iii) and (iv) are obtained. The period indicated by τ in FIG. 5 indicates the stable period of the MM53, and this period corresponds to the period in which the heads Ha and Hb trace the tape 10 for the above X ₁ minutes. The stable period of the MM52 is 2τ, and the exclusive OR circuit (EXOR) 54 obtains a pulse having a high level for a period of τ as shown in FIG. 5 (v). The switch 55 is connected to the H side when the output pulse (v) of the EXOR 54 is at the high level, and is connected to the L side when the output pulse (v) is at the low level. No pilot signal is supplied to 5.

The pilot signal and the digital video signal formed as described above are frequency-multiplexed by the adder 5, and the head is passed through the recording amplifier 6, the recording (R) side terminal of the recording / reproducing switching switch 7, and the head switching switch 8. It is recorded on the magnetic tape 10 by Ha and Hb. Head switch 8
Is controlled by the PG mentioned above.

Although it has been described that the initial phase of each track shifts for each track according to the above-described method of generating a pilot signal, in order to maintain this relationship over the entire track, with respect to the shift amount X _{1 of the} adjacent track. It is assumed that the frequency of the pilot signal, the number of revolutions of each head and the feeding speed of the tape are determined so that the recording wavelength of the pilot signal becomes a fraction of an integer. In order to facilitate the operation of the reproducing system described later, if the period required for recording one track is 1 / f _T , the frequency of the pilot signal (f _P ) is f _P = f _T × (i + 1/4) ( i
Is an integer).

Next, the operation during reproduction will be described.

The pilot signal and the digital video signal reproduced from the heads Ha and Hb during reproduction are supplied to the reproduction amplifier 31 via the P side (reproduction side) terminals of the head switching switch 8 and the switch 7, and are amplified and then amplified by the low pass filter (LPF). ) 32 and high-pass filter (HPF) 33.

In HPF33, the digital video signal is separated and demodulation circuit 3
It is digitally demodulated at 4 and input to the decoding circuit 35.
In the decoding circuit 35, the processing and error correction corresponding to the above-mentioned encoding circuit 3 are performed, and the reproduced digital video signal is D /
Supply to the A converter 36. The video signal analogized by the D / A converter 36 is output from the output terminal 37 as a reproduced video signal.

On the other hand, the LPF 32 is for separating the pilot signal, and the separated pilot signal is supplied to the phase comparator 38 and compared in phase with the signal output from the voltage control generator (VCO) 60.

The VCO 60, the phase comparator 38, the LPF 59, and the gate circuit 58 are PLs for generating a signal (hereinafter referred to as a reference arbitration pilot signal) serving as a reference for detecting the phase of the reproduction pilot signal.
It constitutes an L circuit, and the operation of this PLL circuit will be described below. The gate circuit 58 gates the output of the phase comparator 38 only when the output (iii) of the MM53 described above is at a high level. Here, when the output (iii) of the MM53 is at a high level, the heads Ha and Hb are reproducing the pilot signal recorded immediately before the unrecorded portion of the pilot signal in FIG. The reproduction pilot signal is not affected by the pilot signals recorded in the adjacent tracks.
Therefore, this reproduction pilot signal indicates the phase reference of the pilot signal recorded in the track. Therefore, in this PLL circuit, a reference signal which is phase-synchronized with the pilot signal gated by the gate circuit 58 is generated.

By the way, there is no problem when a circuit having an extremely fast response is used as this PLL circuit, but in this embodiment, the frequency f _{P of the} pilot signal is (1/4 + i) f _T ) and the center frequency of the VCO 60 is f _{P as described above.} By matching with, even if the VCO60 performs a free run, the phase of the referral spirott signal is automatically shifted by π / 2 for each track.
Therefore, the phase error gated by the gate circuit 58 is only due to the mechanical error of the device, and can be sufficiently tracked even if the response speed of the PLL circuit is slow to some extent.

The tracking control using this reference allot signal will be described below.

Now, as the phase of the referral spirott signal output from the VCO 60 changes from 0 → π / 2 → π → 3π / 2, the control target track has a phase of 0 → π / 2 → π → 3π / 2 in sequence. This is a track in which the pilot signal is recorded. The phase comparator 38 detects the phase difference between the reproduced pilot signal and the reference all-spray signal from the region showing most of the track, and uses this as a tracking error signal via the gate circuit 57 to the capstan motor control circuit 39. To control the rotation of the capstan 40 and perform tracking control. This gate circuit 57 is a phase comparator when the signal (vii) obtained by inverting the output of the MM51 (shown in FIG. 5 vi) by the inverter 56, which is triggered by the output pulse (ii) of the aforementioned edge detector 21, is high level. Gate the output of 38. Since the stable period of MM51 is set to 3τ, only the phase error signal indicating the tracking error is supplied from the gate circuit 57 to the capstan motor control circuit 39.

Here, the state of tracking control according to the present embodiment will be described with reference to FIG.
This will be described with reference to FIGS. (A), (b), (c) and (d).
Assuming that the track whose recorded pilot signal has a phase of 0 is the control target track, the phase of the reproduction pilot signal when the reproduction head is on this control target track is the vector Ba of FIG. 4 (a). As shown, it matches the phase of the reference array signal. The head trace position at this time is shown in FIG. 3a.

Next, as shown in FIG. 3b, assuming that the reproduction head is at a position shifted 1/2 track to the right side of the figure with respect to the control target track, the phase of the reproduction pilot signal is shown in Bb of FIG. 4 (b). As described above, it becomes a composite vector of the pilot signal of phase 0 and the pilot signal of phase π / 2, and has a phase difference of θb (π / 4) with respect to the referral spirott signal. Assuming that the running direction of the tape is the direction shown in FIG. 3Y, the phase comparator 38 supplies a page level signal corresponding to the magnitude of this θb to the capstan motor control circuit 39 to change the rotation speed of the capstan 40. Reduce it to try to bring the regeneration head closer to the control target track.

Further, as shown in FIG. 3c, when the reproduction head is at the position shifted by 1/2 track to the left side in the figure with respect to the control target track, the phase of the reproduction pilot signal is also changed to the vector Bc in FIG. 4 (c). As shown, the phase comparator 38 generates a signal of a positive level according to the phase difference θc. In response to this, the rotation speed of the capstan 40 increases, and the reproduction head tries to approach the control target track.

Further, as shown in FIG. 3d, when the reproduction head traces the position shifted by two track pitches from the control target track, the phase of the reproduction pilot signal is Bd in FIG. 4 (d).
As shown in, the phase difference (θd) of the reference signal and the reference signal is obtained, and a large level error voltage is obtained from the phase comparator 38. Even if the rotation speed of the capstan 40 is increased, it may be decreased. Even so, try to bring the regeneration head closer to the control target track.

Next, another embodiment of the present invention will be described. FIG. 6 is a block diagram showing the construction of a digital VTR as another embodiment of the present invention, and FIG. 7 is a diagram showing a recording pattern on a tape by the VTR of FIG. The same components as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 7, the structure is such that the pilot signal of phase 0 is recorded over the predetermined length X ₂ at the beginning of each track, and after recording the pilot signal of phase 0, the length of X ₁ described above is recorded. A portion is provided over which the pilot signal is not recorded.
As a result, as compared with the case of FIG. 1, the period during which the reproduction signal serving as the phase reference of the reference phase pilot signal can be picked up is extended.

First, the structure for performing recording as shown in FIG. 7 will be described with reference to the timing chart of FIG. The stable period of MM53 'is set to the period T (shown in FIG. 7) required for the heads Ha and Hb to trace the distance X ₂ on the tape, and the output of this MM53' controls the data selector 64. It
The data selector 64 selects the output data of the 2-bit counter 19 and the output data of 63 for generating the 2-bit fixed data, and outputs the fixed data when the output of the MM 53 'is at the high level. This fixed data is the data for supplying the constant data corresponding to the pilot signal of phase 0 to the adder 13 by the data selector 18, so that when the output of the MM53 'is high level, the pilot of phase 0 from LPF16. A signal is generated. On the other hand, when the output of MM53 'is low level, the LPF 16 outputs a pilot signal whose phase sequentially changes by π / 2 for each track.

The stable period of MM52 'is set to (T + τ),
As in the case of the figure, the switch 55 'is connected to the L side during the period τ by the output (v) of the EXOR 54', during which the pilot signal is not recorded. In this way, recording is performed according to the recording pattern shown in FIG.

Next, the tracking control operation during reproduction will be described.

The gate circuit 58 uses the output of the MM53 'to output the phase comparator for the period T.
Gate the output of 38. The phase of the pilot signal reproduced from the heads Ha and Hb during this period is 0, and the VCO 60 is intended to generate a reference all-round signal in phase with the pilot signal having the phase 0. At this time, the fixed data output from the data generation circuit 63 is supplied from the data selector 64 to the switch 62, and a signal that is not subjected to the phase shift by the phase shifter 61 is supplied to the phase comparator 38. This causes the VCO 60 to generate a reference 0 phase reference signal. However, in this case as well, the frequency f _P ′ of the pilot signal is jf _T so that the reference signal of phase 0 is output even if the VCO 60 is free running in the same manner as in the embodiment of FIG. (J is an integer), and the center frequency of the VCO is also jf _T.

When the pilot signal reproduced from the remaining portion of the track is supplied to the phase comparator 38 via the LPF 32,
The switch 62 is controlled by the output of the counter 19 and supplies the reference comparator 38 with a reference shift signal which is phase-shifted by 0, π / 2, π, 3π / 2 by the phase shifter 61. As a result, the phase of the reference array signal is 0 → π / 2 →
It changes from .pi..fwdarw.3.pi. / 2, and the output of the phase comparator 38 shows a tracking error as in the case of the embodiment of FIG. Only the effective portion of this tracking error signal is gated by the gate circuit 57, and the capstan motor control circuit 39
Is supplied to. The gate circuit 57 has a stable period (T + 2τ)
It is gated when the inverted signal (vii) of the output (vi) of the MM51 'is high level.

In the embodiment of FIG. 6 as described above, the synchronization pull-in period T of the reference allen pilot signal can be freely set, and a more stable reference allen pilot signal can be generated.

In the digital VTRs of the above two embodiments, good tracking control can be performed and the band of the digital signal can be limited only by superimposing the single-frequency pilot signal on the recording signal. Disappear. Further, since the phase of the reference allotment signal is determined by using the reproduction pilot signal, it is possible to prevent the tracking control from being adversely affected by variations in mechanical precision between the devices.

That is, in the case where the reference alle-spirot signal is formed, for example, only based on the rotation phase of the rotating head, it is possible that this reference alliance pilot signal does not match the reproduction signal of the pilot signal of the control target track, which is the tracking error signal. Although it is concerned that the difference appears, there is no such concern in the above-described two embodiments.

The tracking control system of the present invention is not limited to the above-mentioned embodiment. For example, the reference signal may be recorded every other track for a predetermined part of the track by a similar structure. Can be formed.

〔The invention's effect〕

As described above, according to the present invention, it is possible to perform extremely excellent tracking control irrespective of variations in mechanical accuracy between devices by only recording a single frequency pilot signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of a digital VTR as an embodiment of the present invention, FIG. 2 is a diagram showing the input / output data of the ROM table in FIG. 1, and FIG. 3 is a digital diagram of FIG. FIG. 4 is a diagram showing a VTR recording pattern, FIGS. 4 (a), (b), (c) and (d) are diagrams for explaining tracking control in the digital VTR of FIG. 1, and FIG. 1 is a timing chart for explaining the operation of the VTR shown in FIG. 1, FIG. 6 is a block diagram showing the configuration of a digital VTR as another embodiment of the present invention, and FIG. 7 shows a recording pattern by the digital VTR shown in FIG. FIG. 8 and FIG. 8 are timing charts for explaining the operation of the digital VTR shown in FIG. 5 …… Adder 11 …… Clock oscillator 12 …… Counter 13 …… Adder 14 …… ROM 15 …… D / A converter 16 …… Low-pass filter 32 …… Low-pass filter 38 …… Phase comparator 39 …… Capstan motor control circuit 51,52,53,51 ′, 52 ′, 53 ′ …… Mono multivibrator 55,55 ′ …… Switch 57,58 …… Gate circuit 60 …… Voltage controlled oscillator

Front page continuation (72) Inventor Shinsuke Yamashita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Soichi Kashida 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Canon Inc. Inside the Tamagawa Plant (72) Inventor Mitsuhiro Otokawa 770 Shimonoge, Takatsu-ku, Kawasaki City, Kanagawa Prefecture Canon Inc., Tamagawa Plant

Claims (1)

[Claims] 1. A system for recording / reproducing information signals to / from a plurality of diagonal tracks arranged in parallel on a recording medium, wherein a control target track in the plurality of diagonal tracks is provided for a first area in the track. A pilot signal of a single frequency is recorded so that the phases of both adjacent tracks are shifted in the opposite directions by the same amount with respect to the phase of, and the second area in the track is identical to the adjacent position of both adjacent tracks. The pilot signal is recorded so that a pilot signal other than the phase is not recorded, and the first region and the second region are long enough so as not to be adjacent to each other between adjacent tracks. A guard area in which no pilot signal is recorded is provided between them so that the pilot signal reproduced from the first area and the pad area reproduced from the second area during reproduction. A tracking control method that performs tracking control based on the phase difference from the Ylot signal.