JPH07101492B2 - Tracking device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tracking device in a VTR (Video tape recorder) or the like.

[Prior art]

In recent years, in a helical scan type rotary head type VTR or the like, a video track in which a video signal is recorded when a tape is played at a speed different from that during recording such as so-called still reproduction or high-speed search reproduction (hereinafter referred to as special reproduction). For the purpose of accurately scanning the magnetic field, a rotating magnetic head used for special reproduction is attached to a transition means such as an electro-mechanical conversion element typified by a bimorph element, and even during variable speed reproduction, a predetermined amount corresponding to the tape speed during reproduction is determined. A control system has been proposed in which the above-mentioned shift means is controlled by a pattern signal, and the rotary head accurately scans the recording track to obtain a good noise-free video signal. As described above, as a tracking device for controlling the rotating head by generating a predetermined pattern signal, for example, Japanese Patent Laid-Open No. 56-
The one disclosed in Japanese Laid-Open Patent Publication No. 54633 or Japanese Laid-Open Patent Publication No. 56-149876 is known.

FIG. 1 is a block diagram of a pattern signal generating circuit in a conventionally known tracking device as described above.
The operation time chart is shown in FIG.

In FIG. 1, reference numeral 1 is a still pattern generation unit, and 2
The circuit is divided into two systems corresponding to one rotating head. The still pattern is a two-headed helical scan type VTR, in which the reproducing head accurately traces the recording track when the tape is stopped and the still reproduction is performed. It refers to the pattern of the applied signal. The oscillator 2 generates a pulse signal having a predetermined frequency (for example, 300 Hz), and this pulse signal is input to the cp terminals of the counters 3 and 4 and counted. The counters 3 and 4 are reset in accordance with a 30 Hz rectangular wave signal (30PG) synchronized with the rotation of the head, which is also used as a switching signal for the reproducing rotary head from the input terminal 5. The outputs of these counters 3 and 4 are the D / A converter respectively.
D / A conversion (digital-analog conversion) is performed by 6, 7 and input to adders 8, 9 as a still pattern. Generally 2
In the case of a head-helical scan type VTR, if the tape speed during playback is set to n times that during recording,
The recorded video track and the trajectory of the rotating head rotating on a predetermined rotating surface are (n-1) track pitches (at intervals between recording tracks at the end point when the deviation amount at the start point is 0). Hereinafter referred to as TP). That is, the above still pattern is for shifting the head by -1 TP from the start point to the end point of the track. Therefore, on the other hand, it is necessary to obtain a pattern signal that shifts the head nTP from the start point to the end point of the track. The inclination of the pattern signal is proportional to the tape speed. Therefore, a pulse (FG pulse) having a frequency related to the rotation of the capstan is used to form this pattern signal. The above-mentioned FG pulse is input to the cp terminal from the input terminal 11 of the counter 10 and is counted. The counter 10 is reset when a control signal (CTL) reproduced by a fixed head from the end of the video tape is input from the input terminal 12. Since one CTL is recorded for every two fields, the output of this counter 10 is for shifting the head by 2TP immediately before resetting. By doing so, the output of the counter 10 becomes a pattern signal having a difference of nTP per field, D / A converted by the D / A converters 13 and 14, and input to the adders 8 and 9. It An adder 8 to which such a pattern signal is added,
From 9 to the output terminals 17 and 18 through the low range filters 15 and 16,
Signals as shown in FIGS. 2 (h) and 2 (i) are output, and control is performed so that the two rotary heads constantly scan the video track in the on-track state. Note that (a) to (i) of FIG. 2 show signal waveforms of respective parts of FIG. A method has also been proposed in which the reset timing of the counter 10 is synchronized with 30 PG so as to prohibit the shift in the middle of the field (2 TP in the figure) as shown in FIGS. 2 (h) and (i).

However, in the above tracking device, a control signal (CTL) separately recorded on the video track is used in order to reset the counter 10 which outputs a voltage according to the reproduction speed. In a VTR of a tracking system in which a predetermined pilot signal is superposed and recorded on a video signal which generally accompanies high-density recording, and the above-mentioned CTL for performing tracking using this pilot signal is not recorded. There was a problem that it could not be used.

〔Purpose〕

The present invention has been made focusing on the above problems,
A first rotary head fixed on the rotary surface; and a second rotary head provided in a phase different from that of the first rotary head and capable of shifting in a direction orthogonal to the rotary surface by a shift means, A first signal indicating a difference in inclination that varies depending on a tape speed between a scanning locus of the second rotary head and a track using the reproduction output from the first rotary head;
Controlling the displacement means using a second signal indicating a scanning locus of the rotary head when reproducing a still image and a third signal indicating a difference between a scanning start point of the rotary head and a track at the time of scanning start. The present invention provides a tracking device capable of performing accurate tracking for all reproduction speeds with or without CTL.

[First Embodiment] FIG. 3 is a schematic diagram showing the structure of a video head according to a VTR as an embodiment of the present invention. In the figure, 19a,
Reference numeral 19b is a rotating video head for recording (first rotating head) fixed on the rotating surface, and 20a and 20b are recording heads 19a, 1.
A rotary video head for reproduction (second rotary head) provided at a phase different from that of 9b, 21 is an electro-mechanical conversion element as a displacement means for displacing the reproduction heads 20a, 20b in the rotational axis direction. The recording heads 19a and 19b precede the reproducing heads 20a and 20b by 90 °, and their azimuths are formed again in the same manner (see FIG. 4).

FIG. 5 shows the positional relationship between the head and the recording track pattern on the tape during reproduction of the video head having the above structure. When the reproducing heads 20a, 20b are not displaced, the recording heads 19a, 19b having the same azimuth again are located at a position 90 ° ahead of the direction of rotation of the cylinder (not shown) in the semi-track pitch with respect to the recording tracks on the tape. It is in a displaced position. This positional relationship is always constant regardless of the tape reproducing speed. Therefore, the preceding recording head 19
The phase difference between the reproduction heads 20a and 20b and the recording track during special reproduction can be known from the reproduction output envelopes a and 198b. In addition, the reproduction head by the electro-mechanical conversion element 21
The displacement amount of 20a, 20b is the tape speed (playback speed)
Therefore, it can be determined by using a signal synchronized with the rotation of the capstan that drives the tape, for example, the FG pulse described above. The preceding first rotary head can also be used as a normal reproducing rotary head, for example.

Next, a circuit for generating the pattern voltage applied to the electromechanical conversion element 21 based on the reproduction output from the recording heads 19a and 19b will be described.

FIG. 6 is a block diagram showing the pattern voltage generating circuit.
In the figure, 22 is an amplifier that amplifies the reproduction output from the recording head 19a or 19b, 23 is a detection circuit that detects the output from the amplifier 22, 24 is a comparator that compares the output value from the detection circuit 23 with a certain set value, Reference numeral 25 is a counter for counting FG pulses, which is reset according to the output signal of the comparator 24. 26 and 27 are counters for counting FG pulses, 30PG
Capture data in sync with. Reference numerals 28 and 29 are D / A converters for D / A converting the outputs of the counters 26 and 27, 30 is an oscillator, and 31 is a counter for counting the output of the oscillator 30, which is reset in accordance with the output signal of the comparator 24. Reference numerals 32 and 33 are counters that count the output of the oscillator 30, and take in data in synchronization with 30PG. 34 and 35 are the outputs of counters 32 and 33
D / A converters for A conversion, 36 and 37 adders, and 38 and 39 output terminals.

First, the process of detecting the deviation between the reproduction heads 20a and 20b and the recording track will be described. As mentioned above, the recording head 19
The reproduction output from a or 19b can correspond to the phase difference between the reproduction heads 20a and 20b and the recording track. Therefore, the playback output from the recording head 19a or 19b is
After amplification by 22, the detection circuit 23 performs detection, AGC (gain control) is performed, and the comparator 24 compares with a predetermined set level. This level differs depending on the head width, etc., but here, for the sake of simplicity, the head width is equal to the track pitch, the set level is set to 1/2 of the maximum output, and the output of the comparator 24 is high level when it is above the set value. Shall be By setting in this way, the comparator 24
The rising or falling timing of the output of the
It is the same as the on-track time of 20a and 20b. (If the tape speed during recording is 1, the rising timing coincides with the on-track when n> 1, and the falling timing coincides with the on-track when n <1. Here, the case of n> 1 is taken as an example. Next, in order to detect the deviation from that timing, the capstan FG corresponding to the tape speed is counted and a triangular pattern is created.
Then, assuming that the reset of the counter 25 is performed at the rising edge of the output signal of the comparator 24, and the FG pulse counts n (for example, 5) for one track pitch, the scanning start points of the reproduction heads 20a, 20b. The difference between the recording track and the recording track is the output of the counter 25.
It can be detected by sampling with the switching pulse of a and 20b, that is, 30PG described above. Therefore, by loading the output of the counter 25 into the counters 26 and 27 in synchronism with the output of 30 PG and further loading the FG pulse into the counters 26 and 27, it is possible to know the necessary displacement amount of the reproduction heads 20a and 20b. Then, the outputs of the counters 26 and 27 are D / A converted and input to the adders 36 and 37. At that time, the average value of the voltage applied to the electromechanical conversion element 21 is set to 0 by shifting the reference level by 2 track pitches.
It can approach (V). But the counter 26,2
The output signal from 7 is a signal proportional to the tape speed (N), and the control signal (voltage signal to the electro-mechanical element 21) for displacing the reproducing heads 20a, 20b is the tape speed (N-1). Must be a proportional signal. Therefore, still pattern signals are added to correct the outputs of the D / A converters 28 and 29. This still pattern signal is
Since it needs to be constant regardless of tape speed,
It is obtained from the output of the oscillator 30. The oscillator 30 oscillates by m during one field of the switching pulse (30PG) of the reproduction heads 20a and 20b (for example, m = 5 in the case of 300 Hz). This oscillation signal is counted by the counter 31.
This counter 31 is reset by the output signal of the comparator 24. Then, the output of the counter 31 is taken into the counters 32 and 33 in synchronism with 30PG, and is set as a complement value of the deviation amount of the scanning start points of the reproduction heads 20a and 20b. Further, by incorporating the outputs of the oscillator 30 into the counters 32 and 33, it is possible to obtain the correction value from the scanning start point. And counter 3
D / A conversion of the output of 2,33, and the above-mentioned D / A converter 28,29
It is possible to obtain the control signals of the reproduction heads 20a and 20b by inputting them to the adders 36 and 37 and adding them together with the uncorrected signal from. In this way, even during special reproduction, accurate tracking can be performed without the reproduction heads 20a and 20b crossing adjacent recording tracks. In addition, in FIG. 7, 3. of each part (b) to (l) of FIG.
The timing chart and the signal waveform diagram at the time of 5 times reproduction are shown.

In the above circuit, the counter circuit is divided into two series corresponding to the number of heads. This is because when the response of the electromechanical conversion element 21 is not fast, the reset timing is a head switching pulse (30PG). This is because the head must be shifted a little before the input, and the head will move during the reproduction unless it is divided into two series.

FIG. 8 is a diagram showing the positional relationship between the loci (representing the head center) of the reproduction heads 20a and 20b and the recording tracks at the time of the 3.5 × reproduction shown in FIG. The solid line in the figure shows the center of the A track, the broken line shows the center of the adjacent B track, and the shaded part shows the parts of the reproduction heads 20a, 20b to be displaced. As can be seen from this figure, accurate tracking can be performed for all variable speed reproduction speeds by the control signal obtained from the output terminal of FIG.

Further, although FIG. 7 shows the case of reproduction in the forward direction, in the case of reproduction in the reverse direction, the polarities of the D / A converters 28 and 29 in FIG.
It is sufficient to use a signal obtained by inverting the output of.

Next, a detailed circuit configuration of this embodiment will be described with reference to FIG. In FIG. 9, the same components as those in FIG. 6 are designated by the same reference numerals and the description thereof will be omitted. 40 in FIG. 9
Is a counter for counting FG pulses, which is reset according to the output signal of the comparator 24. 41 is the oscillator 30
Is a counter that counts the output of
Is reset according to the output signal of. 42 is a D / A converter that performs D / A conversion on the output of the counter 40, 43 is a D / A converter that performs D / A conversion on the output of the counter 40, 44 is an adder, and 45 is the output of the adder 44 that rises by 30 PG , A sample and hold circuit that samples and holds at the falling edge. 46 and 47 are oscillators 3 respectively
This counter counts the output of 0 and is reset by 30PG. 48 and 49 are the outputs of counters 46 and 47, respectively.
It is a D / A converter for conversion. 50 and 51 are counters for counting FG pulses, respectively, which are reset by 30PG.
52 and 53 are D / A converters for D / A converting the outputs of the counters 50 and 51, respectively, and 54, 55, 56 and 57 are adders.

Here, the oscillator 30, the counters 46 and 47, and the D / A converters 48 and 49 in FIG. 9 use the reproduction outputs from the recording heads 19a and 19b to measure the tape speed between the scanning loci of the reproducing heads 20a and 20b and the tracks. The first means for generating a first signal indicating a difference in inclination that varies according to the recording heads 19a and 19b, the amplifier 22, the detection circuit 23, the comparator 24, the D / A converter 42,
43, the counters 40 and 41, the adder 44, and the sample and hold circuit 45 constitute a second means for generating a second signal indicating the scanning loci of the reproducing heads 20a and 20b at the time of reproducing the still image, and the counter 50. , 51 and D / A converters 52, 53 constitute a third means for generating a third signal indicating the difference between the scanning start point of the reproducing heads 20a, 20b and the track at the start of scanning. Then, the first signal (the output signals i, m of the D / A converters 48 and 49) and the second signal (the sample hold circuit 45)
Output signal) and a third signal (output signals g, k of the D / A converters 52, 53) to control the conversion element 21 by adders 54-57.

The process of detecting the deviation between the reproducing heads 20a and 20b and the recording track in this structure is the same as that of the circuit of FIG. In other words, depending on the output of the comparator 24, the counter 4
0 and 41 are reset, which is exactly the same as resetting the counters 25 and 31 shown in FIG. Further, in FIG. 9, the outputs of the counters 40 and 41 are first set to the D / A converter.
A signal corresponding to the above-mentioned shift amount is obtained in advance by performing D / A conversion at 42 and 43 and then adding at the adder 44.

Then, this signal is sampled and held by the sample and hold circuit 45 when the head is switched according to 30 PG, so that the signal according to the deviation from the recording track at the start of scanning of each head can be held. This holding signal is added to the still pattern described above by adders 54 and 55, and D / A converters 48 and 49 that have slopes according to tape running speed are added by adders 56 and 57.
By adding it to the output of, the control signal for the transition means such as the electro-mechanical conversion element capable of performing accurate tracking can be obtained.

Even if the reproduction heads 20a and 20b have the same azimuth angle, only one of the still pattern signals to be added is shifted by one track pitch, and a control signal for performing accurate tracking can be obtained.

[Effect]

As described above, according to the present invention, the first head fixed on the rotating surface and the first rotating head are provided at different phases and are displaced in the direction orthogonal to the rotating surface by the displacement means. A second rotary head capable of displaying the difference between the scanning trajectory of the second rotary head and the track, which varies depending on the tape speed, using the reproduction output from the first rotary head. 1 signal, a second signal indicating the scanning locus of the rotary head at the time of reproducing a still image, and a third signal indicating the difference between the scanning start point of the rotary head and the track at the start of scanning. Since the means is controlled, there is an excellent effect that accurate tracking can be performed for all reproduction speeds even if there is no separately recorded control signal on the recording track.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a diagram showing signal waveforms of respective parts shown in FIG. 1, and FIGS. 3 and 4 are diagrams showing a structure of a video head according to the present invention. Figure 5 shows the positional relationship between the head and tape pattern during playback,
FIG. 6 is a block diagram showing the structure of the pattern voltage generating circuit, FIG. 7 is a timing chart and signal waveform diagram of each part shown in FIG. 6, and FIG. 8 is a positional relationship between the locus of the reproducing head and the recording track. FIG. 9 is a block diagram showing the detailed circuit configuration of the first embodiment, and FIG. 10 is a timing chart and signal waveform diagram of each part shown in FIG. 19a, 19b ...... Recording head (first rotating head) 20a, 20b ...... Reproducing head (second rotating head) 21 ...... Electro-mechanical conversion element

Claims (1)

[Claims] 1. A first rotary head fixed on a rotary surface, and a second rotary head provided in a phase different from that of the first rotary head and capable of being displaced in a direction orthogonal to the rotary surface by a displacement means. A second head using a reproduction output from the first rotary head.
Generating a first signal indicating a difference in inclination between the scanning locus of the rotary head and the track, which varies depending on the tape speed.
Means, second means for generating a second signal indicating the scanning locus of the rotary head during still image reproduction, and third signal indicating the difference between the scanning start point of the rotary head at the start of scanning and the track And a control means for controlling the shift means using the first signal to the third signal.