JPH0249486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a magnetic recording and reproducing apparatus configured to superimpose a pilot signal for tracking control on an information signal to be recorded during recording, and perform tracking control using the pilot signal during playback. This invention relates to a tracking control method for an apparatus, and is characterized by a method of removing noise components that leak into a pilot signal for tracking control during reproduction.

A magnetic head is mounted on an electromechanical transducer such as a piezoelectric element and rotated, and the vertical position of the rotating magnetic head is electrically controlled by applying a control signal to the piezoelectric element to perform playback. Various tracking error detection methods have been proposed for rotary head type magnetic recording/reproducing apparatuses that maintain normal time tracking at all times.

Tracking error detection methods that have been proposed in the past can be roughly divided into: (1) a method using an auxiliary head, and (2) a method in which the playback head is slightly varied in the width direction of the recording track during playback, and the output level obtained at this time. A method (search method) that detects the direction of track deviation from fluctuations. (3) This is a method of recording a pilot signal for detecting track deviation.

The auxiliary head method (1) requires an extra head (for tracking deviation detection) to be mounted accurately on the same piezoelectric element, and also requires an extra rotary transformer and preamplifier to extract the error signal. The disadvantage is that the structure is complicated and the cost is high.

In the method (2), the response speed of the piezoelectric element is limited by the mass of the magnetic head, etc., making it difficult to perform control that sufficiently follows the curvature of the recording track, and the gap angle of the head relative to the longitudinal direction of the recording track.
Azimuth recording method that is not 90° (VHS method)
In the case of the method used in VTRs, etc., when the head is vibrated in the track width direction during playback,
This oscillation appears as a time axis fluctuation of the reproduced signal, so this search method has the drawback of being difficult to use.

Various methods have been proposed for method (3), but they can be roughly divided into 3-1. A method that detects the direction of track deviation by using the difference in the frequency of the pilot signal reproduced from the track.

3-B A method has been proposed in which a pilot signal is recorded intermittently, and during playback, the crosstalk pilot signal levels from both adjacent tracks are detected based on the timing of the pilot signal of the main track to detect the direction of track deviation. It will be done.

In the case of 3-a, it is generally necessary to use three or more types of pilot signal frequencies, which requires a considerable band for recording the pilot signal, which reduces the video signal recording band, and it is necessary to separate three or more types of pilot signals. There are disadvantages such as the need for many narrow band filters and the need for three or more types of pilot signal generation circuits.
Even during playback, interference occurs due to the tracking control pilot signal leaking onto the screen, making the screen difficult to view. Based on the above results, we believe that the best tracking control method is to record the pilot signal intermittently as shown in 3-B above, considering the effects on the screen, time axis fluctuations, cost, etc. It will be done.

Next, a method for recording a tracking control pilot signal, which is the object of the present invention, will be described. 1st
The figure shows the recording positional relationship between the video signal a and the tracking control pilot signal b, and the tracking control pilot signal is used only during the blanking period of the horizontal synchronization signal (hereinafter referred to as H) of the video signal. (hereinafter referred to as the burst pilot signal). In FIG. 2, recording tracks A ₁ , B ₁ ,
It is assumed that A ₂ , B ₂ , A ₃ , B ₃ . are doing). The blacked out area is where the burst pilot signal is recorded every 2H. The frequency p of the burst pilot signal is n×H (n is an integer,
H is horizontal synchronization signal frequency) For example, 8・H≒
126 (KHz) is a simple circuit configuration. Also, the burst pilot signals are recorded adjacent to each other between the tracks recorded on the A head (A track) and the tracks recorded on the B head (B track), and are arranged so that they are not adjacent to each other for each frame. recorded. Furthermore, the phases of the burst pilot signals recorded on the A track are in phase (0
The burst pilot signal recorded on the B track is recorded to have a 0 degree phase and a 180 degree phase every 2H. In the figure, O and π indicate the recording phase of the burst pilot signal. On the contrary, A track
The same effect can be obtained by recording the B track as the same phase (0 degrees) with the phase being 0 degrees and the phase being 180 degrees every 2H. Also, in Figure 2, the magnetic head
It is assumed that the track width T _W of _HD is approximately equal to the track pitch T _P , but is slightly larger. (T _W
Even if the area is slightly narrower than T _P , if the recorded frequency is low, signals from the adjacent area can be reproduced due to leakage magnetic flux. ), and the core width W _C of the magnetic head in contact with the tape is assumed to be W _C <7T _P. Now, assuming that the burst pilot signal is recorded as shown in Fig. 2, the recording track _A3 is
Considering the case where the head reproduces the burst pilot signal, the burst pilot signal reproduced by the A head is connected to a two horizontal scanning period delay line (2H-
DL) 51, the signals shown in FIGS. 4a and 4b are obtained at the output terminal 53 of the adder 52 and the output terminal 55 of the subtracter 54, respectively. In FIG. 4, signals such as A ₃ , B ₂ , and B ₃ represent playback signals from A ₃ , B ₂ , and B ₃ tracks, respectively, and ΔA ₂ , ΔA ₄ , ΔB ₁ , ΔB ₄ , etc.
The reproduced signals from the A ₂ , A ₄ , B ₁ , and B ₄ tracks are shown, but the reproduction level is low.
In other words, this comb filter allows A to be added to the addition side.
Only the signal components recorded by the head are separated so that only the signal components of the tracks recorded by the B head are output to the subtraction circuit.

Since A ₃ >ΔA ₂ +ΔA ₄ in Figure 4a,
The location where the burst pilot signal is recorded on the _A3 track can be identified. Using this identified position as a reference, B ₂ +ΔB ₄ and B ₃ +ΔB ₁ can be separated from the b signal, and since B ₂ ≫ ΔB ₄ and B ₃ ≫ ΔB ₁ (B ₂ and B ₃ are magnetic heads) The output is large because it is applied to the A track, but B ₄ tracks and B ₁ track are 3 times larger than the A ₃ track played by the A head.
Since the track pitches are far apart, the output thereof is relatively small enough)B ₂ +ΔB ₄ B ₂ , B ₃ +ΔB ₁ B ₃ , and B ₂ and B ₃ can be separated. This B ₂
By comparing the size of B3 and _B3 , it is possible to identify whether the A head is shifted to the _B2 side (left side) or _B3 side (right side) when playing the _A3 track. Correct tracking can be achieved by controlling the height position of the A head so that the reproduction signal levels from the _B2 track and the _B3 track are equal. Also, when the B head reproduces the _B3 track, the output of the output terminal 3 of the adder 2 of the comb filter is the fourth one.
By controlling the reproduction signal processing circuit so that the output of the output terminal 5 of the subtracter 4 becomes as shown in FIG. can be set.
In this case, the output of the adder circuit of the comb filter is B.
Only the A head recording track signal component is output to the subtraction circuit.
The track components recorded by the head and B head are separated.

Next, the basic configuration of a reproducing circuit system for obtaining a tracking error signal will be explained using FIGS. 5 and 6. FIG. 5 is a block diagram of the reproducing circuit system, and FIG. 6 shows waveforms at various parts in FIG. In Fig. 5, the signal reproduced from the magnetic head 1 is transmitted to the switch connected to the reproduction side (PB terminal).
It is amplified by a regenerative amplifier 2 via SW1, and its output is passed through a low pass filter 4 (hereinafter referred to as LPF).
and is supplied to terminal 3. Terminal 3 is sent to a video signal processing circuit (not shown). A tracking control pilot signal a (hereinafter referred to as a burst pilot signal) is obtained by the LPF 4. It is assumed that the magnetic head 1 is scanning a recording track _A3 shown in FIG. At this time, the output of the reproduced burst pilot signal as shown in FIG. 6a is obtained. _P1 and _P3 are signals in which the main pilot signal recorded on track _A3 and the error pilot signal (crosstalk component from the adjacent track) recorded on track _B3 are superimposed. Burst pilot signals P ₂ and P ₄ are error pilot signals recorded on track B ₂ . The phase inversion circuit 5 is a circuit for making the phases of the burst pilot signals from the main track to be reproduced the same. In this embodiment, phase inversion is performed on the B track, and when the reproduced burst pilot signal is reproduced on the B track,
The signals are inverted every 2H to obtain signals that are all in phase. Since the reproduction signals of the A track are all reproduced in the same phase, they are not operated when the A track is reproduced. The phase inversion circuit 5 is controlled by obtaining a head switching signal (hereinafter referred to as a switching pulse) supplied from a terminal 6 and a 1/4H signal supplied from a terminal 7 via a NAND circuit 8. The output of the phase inversion circuit 5 is supplied to a 2H delay line 9, and a sum and difference signal is obtained from the pre-delay and post-delay signals. From the obtained sum signal, only the burst pilot signal reproduced from the main track is extracted. Also, as the difference signal, only the error pilot signal reproduced from the adjacent track is extracted. The extracted sum and difference signals are supplied to LPF 10 and LPF 11.
The signals shown in FIG. 6b and c are obtained from the LPF 10 and LPF 11. In Fig. 6b, P _A3 is the burst pilot signal regenerated from the main track _A3 , and P _B2 in Fig. 6c is the track
B ₂ and P _B3 are signals obtained from track B ₃ .
The error pilot signal c is supplied to a peak hold circuit 12, where the peak value is held. The peak value hold circuit 12 is configured to be reset by a reset pulse e every 1H, and the peak value hold circuit 12 outputs a hold value according to the error pilot signal output reproduced every 1H.
(Figure 6d). On the other hand, the output from the LPF 10 is supplied to a sampling pulse shaping circuit 13. The sampling pulse shaping circuit 13 creates sampling pulses f and g delayed by approximately 1/2H period and 1.5H period, respectively, from the pilot signal b reproduced from the main track.
supply to. The error pilot signal d from the peak value hold circuit 12 is sampled and held in the sampling hold circuits 14 and 15, and the error pilot signal d is sampled and held as P B2 and P _B2 of the error pilot signal c.
Each signal corresponding to the playback output of P _B3 is sent to the differential amplifier 16.
supplied to The differential amplifier 16 compares the levels of P _B2 and P _B3 and obtains a signal corresponding to the difference between the two outputs. The signal obtained from the differential amplifier 16 is a signal corresponding to the track deviation. This is because when the magnetic head 1 scans and reproduces the track _A3 shown in Fig. 2, if the magnetic head 1 shifts toward the _B3 track side, the level of the error pilot signal P _B3 reproduced from the track _B3 increases. , and if the scan is shifted to the B ₂ track side, the track B ₂
The level of the error pilot signal P _B2 reproduced from the error signal increases, and the level of the error pilot signal P _B3 decreases. Therefore, if the error pilot signals P _B2 and P _B3 reproduced from tracks B ₂ and B ₃ are controlled to have the same level, the magnetic head 1 can scan on the track A ₃ . As is clear from FIG. 2, when the magnetic head 1 scans the A track and when the magnetic head 1 scans the B track, there is a difference in the track deviation direction of the magnetic head 1 and the level difference between the error pilot signals obtained from both adjacent tracks. The relationship is in the opposite direction. For example, if the magnetic head 1 is
When the track is reproduced and scanned, the track on which the burst pilot signal is recorded at the same position in the track width direction as the burst pilot signal reproduced from the main track A is the track located on the right side of the paper, and the magnetic head 1 is located on the right side of the paper. When the B track is reproduced and scanned, the track in which the burst pilot signal is recorded at the same position as the burst pilot signal reproduced from the main track B at this time is located on the left side on the paper. Therefore A
It is necessary to reverse the polarity of the tracking error signal obtained from the head and the B head. The inversion circuit 17 shown in FIG. 5 is provided for this purpose. The inverted signal and original signal (non-inverted signal) from the inverting circuit 17 are supplied to the switch SW2. The switch SW2 is switched by a head switching pulse from the terminal 18, and the inverted signal and the original signal are alternately outputted, and an output signal h is obtained. This signal h is a tracking error signal, and when the magnetic head shifts to the right with respect to the recording track,
For example, if a higher voltage is obtained when the vehicle is on track, a lower voltage is obtained when the vehicle shifts to the left. The tracking error signal h is separated by gate circuits 19 and 20 into A and B independent error signals i and j. These signals output a tracking error signal only while each head is in contact with the tape, and hold the value of the previous error signal while other heads are in contact with the tape. Circuits 21 and 22 are piezoelectric element drive circuits, and drive piezoelectric elements 23 and 24. With the above configuration, relatively high frequency (1/2
By driving the piezoelectric element according to the tracking signal of H) and controlling the height direction position of the rotary head, auto-tracking control that can follow track curves of several tens of Hz with sufficient gain system can be constructed.

Although a detailed explanation of the recording system has been omitted in this embodiment, a brief explanation of the recording of the burst pilot signal for tracking is as well known.
To record a video signal on a VHS VTR, etc., the video signal is separated into a brightness signal and a chroma signal, and the brightness signal is
Convert to FM modulation, and chroma signal has color subcarrier frequency C (for NTSC signal = 3.579545 [MHz])
Convert the frequency from
Hz) and is recorded superimposed on the above-mentioned FM modulation signal. In this embodiment, a tracking burst pilot signal (in this embodiment, 8.H
≒126 [Hz]), and the above FM
A low frequency conversion color signal is superimposed on the modulated signal, and a burst pilot signal for tracking is further superimposed on the modulated signal and recorded.

The center frequency of the burst pilot signal in the present invention is 8.H≒126 [KHz], but it is a burst-like signal, and the frequency spectrum of the pilot signal is distributed around 126 [KHz] ±120 [KHz]. ing. Therefore, the LPF 4 is set to, for example, 126 [K
Hz), a normal burst pilot signal cannot be extracted because ringing occurs in the extracted burst pilot signal. Therefore, the LPF 4 has a frequency of 250 [KHz] to 300 [KHz].
Hz]. When extracted by an LPF with such a band, the band of the above-mentioned low-frequency converted color signal is 200 [KHz] to 250 [KHz] in the low range.
Hz], it is not possible to completely remove the chroma signal, and it may be mixed into the burst pilot signal. Also, the horizontal synchronization signal of the video signal during playback leaks from around the ground,
There are also cases where noise such as flying in from the air is superimposed on the burst pilot signal. When this noise increases, the peak value is held and the sampling hold is performed as described above, and the period other than the burst pilot signal (between the pilot signal and the next pilot signal because it is a burst type) is used. If noise is present in the burst pilot signal and the noise is larger than the burst pilot signal, the signal may be held at its peak value, causing the above-mentioned tracking control system to malfunction. In addition, when there are multiple recording/reproducing magnetic heads as in this embodiment, level fluctuations due to different reproduction phases from the A and B heads at the time of switching the magnetic heads during reproduction, or the response characteristics of the switching circuit's rise. Due to level changes, etc., fluctuations in the envelope of the switching portion occur, resulting in fluctuations in the level of the burst pilot signal, causing the tracking control system to malfunction as described above. If the tracking control is not performed normally, problems such as a distorted reproduced image or a deterioration of the S/N of the reproduced signal will occur, as is well known. Next, to briefly explain the necessity of the peak value hold circuit 12, as mentioned above, the burst pilot signal is recorded during the blacking period of the horizontal synchronizing signal, and the center frequency of the burst pilot signal is 8·H≒126 [ KHz], therefore the synchronization is about 8 [μS]. Furthermore, the blanking period of the horizontal synchronizing signal is approximately 10 [μS]. Therefore, only one cycle period can be recorded during the blanking period, and recording is performed in bursts of one cycle. Therefore, in order to perform sampling hold without peak value hold, the above period (5 to 10
[μS]). However, as mentioned above, the sampling pulse is formed by the horizontal synchronization signal of the reproduced signal from the main track, and the error signals from both adjacent tracks of the main track are sampled and held, and H jumps may occur for some reason during recording. , A, B with compatible playback
If there is a head indexing (180°) error, etc., the reproduction timing of the error pilot signal will be shifted and the peak value will not necessarily be held. Therefore, the peak value hold circuit 12 described above is installed to lengthen the peak value hold period (approximately 40
(about [μS]), sampling and holding is always performed at the peak value.

The present invention aims to prevent malfunctions caused by changes in the peak value held in the peak value hold circuit 12 due to noise components or level fluctuations of the reproduced signal when switching heads, as described above. An embodiment of the present invention is shown in FIGS. 7 and 8.
In FIG. 7, parts having the same functions as those in FIG. 5 are given the same numbers. In Figure 7, terminal 6 has a head switching pulse (K in Figure 8).
is supplied, and the gate generation circuit 27 generates a gate signal l having a width corresponding to the period (1H to 3H period) in which level fluctuation occurs during head switching in synchronization with the rise and fall of the gate signal.
is made. The output l from the gate generation circuit 27 is supplied to an AND gate circuit 29. terminal 2
A reproduced horizontal synchronizing signal m is supplied from 6 and input to the gate generating circuit 28. The gate generation circuit 28 generates a gate pulse n having the width of the burst pilot signal insertion period in synchronization with the reproduced horizontal synchronization signal.
is created and supplied to the AND gate circuit 29. The AND gate circuit 29 generates an AND gate signal o based on the signals m and n from the gate generators 27 and 28, and supplies it as a control signal to the switch SW3. With such a configuration, when the operation explained in FIG. 5 is performed, the tracking signal a extracted becomes a signal with noise in the vicinity of the head switch a' in FIG. 8 and sections other than the burst pilot signal removed. , malfunctions can be prevented and stable tracking can be achieved.

As described above, the present invention provides a method in which a burst pilot signal recorded intermittently superimposed on an information signal for tracking control is extracted during reproduction, and tracking is controlled by the level of the reproduced burst pilot signal. Since the configuration is such that only the section where the burst pilot signal is inserted is gated to extract the burst pilot signal component, there is no possibility of errors caused by noise occurring outside the section where the burst pilot signal is inserted, and the head In sections where the playback signal level may change significantly near the time of switching, the burst pilot signal is not extracted and is controlled according to the burst pilot signal level before that section, so the head This also eliminates malfunctions caused by reproduction level fluctuations during switching.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the timing relationship of the video signal pilot signal used in the present invention, and Fig. 2 is a diagram showing a portion of the recording pattern of the pilot signal used in the present invention on the magnetic tape and the shape of the magnetic head. 3 is a block diagram showing an example of a comb-shaped filter, and FIG. 4 shows the recording pattern of FIG. 2 when the A ₃ track and B ₃ track are reproduced with the magnetic head shown in FIG. 2. 5 is a block diagram showing the basic configuration of the tracking control method of the present invention. FIG. 6 is an operation waveform diagram of FIG. 5. FIG. 7 is a block diagram showing an embodiment of the present invention. Figure 8 is the seventh
FIG. 3 is an operation waveform diagram of FIG. 1...Magnetic head, 2...Regenerative amplifier, 4,1
0, 11...Low pass filter, 5...Phase inversion circuit, 6, 18...Head switching pulse input terminal, 8...NAND gate circuit, 9...Delay circuit, 12...Peak hold circuit, 13...Sampling Pulse generation circuit, 14, 15... Sample hold circuit, 16... Differential amplifier, 19, 2
0... Gate circuit, 21, 22... Drive circuit.

Claims (1)

[Claims] 1. A video signal is recorded as a plurality of recording track groups on a recording medium, and a pilot signal for tracking control that is intermittently present every two horizontal scanning periods of the video signal is superimposed on the video signal. However, during reproduction, a frequency separating means for separating and extracting only the reproduction pilot signal from the video signal, a first gate signal generation means for generating a gate signal for a fixed period from the reproduction horizontal synchronization signal, and a plurality of a second gate signal generating means for generating a gate signal for a certain period of time from the rising edge and falling edge of a head switching signal for selecting each video signal to be reproduced from a group of recorded tracks; A tracking system that includes a comb filter that separates a pilot signal reproduced from a track and a pilot signal reproduced from each track adjacent to the main track, and a tracking error signal that is created using the output signal of this comb filter. and an error signal generating means, which separates the reproduced pilot signal using the first gate signal and separates the reproduced pilot signal using the first gate signal, and separates the reproduced pilot signal using the first gate signal as the pilot signal inputted to the comb filter. Tracking characterized in that a pilot signal from which a reproduced pilot signal has been removed is used, and as a tracking error signal in the second gate signal generation period, a tracking error signal before the second gate signal generation period is used. control method.