JPH0373930B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tracking device for a helical scan rotary head video tape recorder (hereinafter referred to as VTR).

Structures of conventional examples and their problems In recent years, in video signal magnetic recording and reproducing apparatuses or video signal magnetic reproducing apparatuses using magnetic tapes such as VTRs, so-called auto tracks have been developed for the purpose of accurately scanning recorded tracks during playback. King devices began to be introduced. This auto-tracking device is capable of providing reproduced images without noise bands in special playback modes such as slow playback, still playback, fast playback, and reverse playback that play back at a speed different from the tape running speed during recording. It is possible. Such auto-tracking devices usually connect the magnetic head for video signal reproduction with electricity.
A control system is constructed in which the magnetic head is attached to a mechanical transducer and a driving voltage corresponding to the track deviation is applied to the electro-mechanical transducer to accurately bring the magnetic head onto the recording track. In such a tracking device, as information in the reproduction signal, a signal (hereinafter referred to as a pilot signal) whose frequency periodically differs for each recording track is superimposed and recorded with the video signal during recording, and during reproduction, Adjacent to the front and back of the recorded track to be played,
A method has been proposed in which a positional deviation between a recording track and a magnetic head is detected by detecting and comparing the amount of crosstalk of pilot signals in recording tracks having different frequencies.

Various methods have been proposed for creating a tracking error signal using pilot signals, ranging from one type to four types of pilot signals.Here, we will introduce a method using four types of pilot signals. This will be explained using an example. FIG. 1 shows a diagram of its principle. 1 is a magnetic tape that runs in the direction of arrow A, and 10 is a magnetic head that runs in the direction of arrow B. 101 to 108 are recording tracks (video tracks) on which one field of a video signal is recorded as a predetermined unit, and 101, 103, 105, 1
Each track of 0.07 is recorded with a video head having a first azimuth angle (denoted as A azimuth);
Each track 102, 104, 106, and 108 is recorded with a video head having a second azimuth angle (denoted B azimuth). On the other hand, 10
f ₁ for the track 1,105, f 2 for the track 102,106, and f ₂ for the track 103,107.
On the tracks f ₄ , 104 and 108, pilot signals of different frequencies of f ₃ are sequentially _and periodically superimposed and recorded with the video signal, and these
The four frequencies of f ₄ are, for example, 6 times a certain frequency f ₀ ,
The frequency shall be set to 7 times, 9 times, and 10 times. FIG. 1a shows a state in which the magnetic head 10 is scanning a recording track 103, and a pilot signal of f ₄ (=10f ₀ ) has been superimposed and recorded on the track 103, and it is in a completely on-track state. Therefore, the crosstalk amounts of the pilot signals of f ₂ (=7f ₀ ) and f ₃ (=9f ₀ ) are at almost the same level. FIG. 1b shows a state in which the magnetic head 10 is mistracked forward with respect to the recording track 103 (with the tape traveling direction being forward), and the crosstalk level of the pilot signal becomes f ₂ > f ₃ . ing. FIG. 1c shows a state in which the magnetic head 10 is mistracked backward with respect to the recording track 103, and the crosstalk level of the pilot signal is f ₂ <f ₃ . During reproduction, pilot signal components (f ₁ to _{f 4} ) are extracted from the reproduced RF signal using a filter (in the state shown in Figure 1a, f ₄ >
f ₂ , f ₃ > f ₁ and f ₂ = f ₃ ), the signal has the same frequency as the pilot signal recorded on the track to be reproduced, and is generated by the reference signal generator. When the difference frequency between the reference signal (f ₄ in Fig. 1) and the reproduced pilot signal is obtained by inputting the signal (hereinafter referred to as the reference signal) to the multiplier, |f ₁ −f ₄ |= |6f ₀ −10f ₀ |=4f ₀ ... |f ₂ −f ₄ |=|7f ₀ −10f ₀ |=3f ₀ ... |f ₃ −f ₄ |=|9f ₀ −10f ₀ |=f ₀ ... |f ₄ −f ₄ |=|10f ₀ −10f ₀ |=0 ... Among these, by extracting f ₀ and 3f ₀ using a band pass filter (BPF) and comparing them, the recorded track to be reproduced can be determined. Mistracking can be detected. In other words, in Figure 1b, the amount of crosstalk at f ₂ increases, so the level of 3f ₀ > the level of f _0. In Figure 1c, the amount of crosstalk at f ₃ increases, so the level of 3f ₀ < the level of f ₀ . Become a relationship.

FIG. 2 shows how the magnetic head sequentially changes tracks and scans as the magnetic tape 1 runs from the state shown in FIG. 1a. Figure 2a shows the state updated by one track from Figure 1a, and the reference signal oscillator outputs f ₃ (=9f ₀ ), and the crosstalk component of the pilot signal from the adjacent track and the reference signal The difference frequency with f ₃ is
From the front: |f ₄ −f ₃ |=|10f ₀ −9f ₀ |=f ₀ ... From the back: |f ₁ −f ₃ |=|6f ₀ −9f ₀ |=3f ₀ ... The magnetic head 11 in FIG. 2a has a second azimuth angle (referred to as B azimuth) different from that of the magnetic head 10 in FIG. 1a. FIG. 2b shows a state updated by one track further from FIG. 2a, the reference signal is f ₁ (=6f ₀ ), and the difference frequency between the pilot signal and the reference signal is:
From the front ｜f ₃ −f ₁ ｜=｜9f ₀ −6f ₀ ｜=3f ₀ …… From the back ｜f ₂ −f ₁ ｜=｜7f ₀ −6f ₀ ｜=f ₀ …… Similarly, Fig. 2 In c, from the front |f ₁ −f ₂ |=|6f ₀ −7f ₀ |=f ₀ ... From the back |f ₄ −f ₂ |=|10f ₀ −7f ₀ |=3f ₀ ... like this Obtain the frequencies of f ₀ and 3f ₀ due to the crosstalk of pilot signals from adjacent tracks,
This is compared in level and used as the tracking error voltage of the magnetic head.

FIG. 3 is a block diagram of a circuit that generates a tracking error voltage. Reference numerals 10 and 11 are the above-mentioned magnetic heads, 12 and 13 are head amplifiers that amplify the RF signal, and a low-pass filter (hereinafter referred to as LPF) 14 is used to generate the RF signal. Extract only the pilot signal component from the signal. 15 is a reference signal generator consisting of an oscillator that generates reference signals f ₁ to _{f 4} in synchronization with the rotation of the magnetic heads 10 and 11, and inputs the pilot signal and the reference signal to a multiplier 16 to obtain the above formula The difference frequency components between the reference signal and each pilot signal are taken out, and among these, the f ₀ and 3f ₀ components are passed through band pass filters (hereinafter referred to as BPF) 17 and 18, and then filtered into a detector (hereinafter referred to as DET). 19,
After double-wave rectification in 20, smoothing is performed in LPFs 21 and 22, and level comparison is performed in a comparator 23 consisting of a differential amplifier. Reference numeral 24 denotes an inverting amplifier with an amplification factor of 1, which allows the magnetic head 10 (A azimuth) and the magnetic head 11 (B azimuth) to update and scan the track as shown in FIG. 1a and FIGS. 2a, b, and c. When doing so, in Figure 1a and Figure 2b, 3f ₀ from the front, f ₀ from the rear,
In FIGS. 2a and 2c, the crosstalk components of the pilot signal f ₀ from the front and 3f ₀ from the rear are obtained alternately for each field, so the output obtained from the comparator 23 is inverted by the inverting amplifier 24. This is for correcting by switching the switch 25 using a head switching pulse (a rectangular wave that switches between high and low for each field) synchronized with the rotational phase of the rotating magnetic heads 10 and 11 to obtain a tracking error voltage.

FIG. 4 is a block diagram of a circuit that processes a tracking error voltage to create an electrical signal that causes an electro-mechanical conversion element to track a predetermined track;
FIG. 5 is a waveform diagram of each block of the circuit shown in FIG. 4. The tracking error voltage proportional to the tracking error is sent to sample and hold circuits (hereinafter referred to as SH) 26 and 27 and analog switches 28 and 29, and S.H 26 and 27 are connected to the head switching circuits shown in FIG. 5a. The tracking error voltage (FIG. 5b) is sampled and held using the sampling pulse A (FIG. 5c) or the sampling pulse B (FIG. 5d) obtained at the pulse timing. The low level period of the head switching path is a period during which the magnetic head 10 of the A channel is in contact with the magnetic tape 1, and is a non-contact period during which the magnetic head 11 of the B channel is not in contact. The high level period is a period in which the magnetic head 11 is in contact and the magnetic head 10 is not in contact. Fifth
To explain only the A channel in the figure, the tracking error voltage D sampled by the pulse C of the sampling pulse A is held during the tape contact period of the magnetic head 10, while the analog switch 28 is closed between terminals b and c. Therefore, the tracking error voltage is output as is as shown in output A shown in Figure 5e, and the LPF3
0 and is amplified until the voltage can drive the electro-mechanical transducer 34 in the drive circuit 32, and the tracking error voltage proportional to the tracking error between the recording track and the magnetic head 10 is reduced, that is, the voltage is applied to the recording track. The magnetic head 10 is controlled to be on-track. Next, during the non-contact period of the magnetic head 10, the analog switch 2
8, the terminals a and c are closed, and the tracking error voltage sampled by S.H26 is input to the LPF 30 via the analog switch 28.
Even with the time constant of the LPF 30, the output of the LPF 30 approaches the sampling error voltage t as shown in FIG. 5e. This voltage G is equal to the voltage D. The same applies to the B channel, and the structure is such that the initial positions of the electro-mechanical transducers 34 and 35 are memorized during the tape contact period of the magnetic heads 10 and 11, and returned to the memory positions during the non-contact period. . In FIG. 4, 76 is a sampling pulse generator.

To summarize, a pilot signal is extracted from the reproduced signals obtained by the magnetic heads 10, ₁₁ , and the recording track to be _reproduced and the magnetic head 10, 11 as a tracking error voltage, and processes and amplifies this tracking error voltage so that the tracking error voltage decreases. , 35 constitutes a closed loop feedback control system.

Next, the operation of the control system (special reproduction function) when the magnetic tape 1 is reproduced at an arbitrary tape speed different from the recording speed will be explained. In the above control system, the electro-mechanical conversion elements 34 and 35 record a pilot signal having the same frequency as the reference signals f ₁ to f ₄ generated from the reference signal generator 15 even at an arbitrary tape speed different from that during recording. On-track and scan the closest track. 6th
In the figure, the magnetic tape 1 is run arbitrarily and the reference signal is
This is an explanatory diagram of the movement of the magnetic head 10 when it is fixed at _f1 , and in a to d, the initial position of the magnetic head 10 (the shaded area) is on-tracked to the nearest track 105 where the pilot signal _f1 was recorded. .
At e and f, as the magnetic tape 1 runs, the _f1 track closest to the initial position of the magnetic head 10 becomes the track 109, and is tracked onto this track.

FIG. 7 is an explanatory diagram for explaining field reproduction, showing the track pattern and the movement of the magnetic head 10. As the reference signal for field reproduction, one of the pilot signals recorded on the odd-numbered tracks or the even-numbered tracks in the figure is selected. Here we have odd tracks, i.e.
The case where f ₁ and f ₄ are sequentially switched and used is shown. The order in which the reference signals are switched differs depending on the content of the special playback mode; for example, in the case of 1/3 slow playback, the same odd-numbered track may be scanned three times, and then the next odd-numbered track is selected. .

FIGS. 8b to 8d show the drive signal waveforms applied to the electro-mechanical conversion elements 34 and 35 during 1/3 slow mode, and if the switching timing of the reference signals f ₁ and f ₄ is appropriate, the waveforms shown in FIG. The average voltage is close to 0 (zero), but if the switching timing is inappropriate (switching timing is early or late), a positive or negative DC voltage component is applied as shown in c and d. Electrical-mechanical conversion element 3
Among them, it is generally considered undesirable to continue applying a DC voltage to a piezoelectric element, such as a bimorph, in terms of the life of the element and deterioration of sensitivity. Note that FIG. 8a shows a head switching pulse.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks, and aims to provide a tracking device that can prevent the application of DC voltage to electro-mechanical conversion elements.

Structure of the Invention In order to achieve the above object, the tracking device of the present invention uses a rotating magnetic head to track video signals.
A magnetic recording and reproducing device that records and reproduces data on a magnetic tape as a group of inclined non-continuous recording tracks,
At the time of recording, pilot signals for reproduction tracking control of four different frequencies are superimposed on the video signal and recorded sequentially on each track, and at the time of reproduction, the recording track that is to be reproduced is reproduced from the adjacent recording tracks before and after it. A tracking device that controls the relative positional deviation between a recording track and a rotating magnetic head by detecting a tracking error voltage based on the level difference of a crosstalk signal of a pilot signal, and is used to detect each recording track to be reproduced during reproduction. a reference signal generating circuit that generates a reference signal having the same frequency as the pilot signal superimposed on the video signal; a switching means that generates a frequency switching timing signal for the reference signal for each recording track; An electro-mechanical transducer that displaces the mechanical position of the head in a direction substantially perpendicular to the width direction of the recording track; and an electrical signal corresponding to the tracking error voltage is supplied to the electro-mechanical transducer for recording. feedback control means for causing the track to track the rotating magnetic head;
control means for controlling the switching means so that the DC voltage component of the electric signal supplied to the electro-mechanical conversion element is minimized; The configuration uses a signal obtained by frequency-dividing the capstan FG signal generated from a frequency generator synchronized with the phase, and the frequency division ratio of this capstan FG signal is used as the DC voltage component of the electrical signal waveform supplied to the electro-mechanical conversion element. This configuration is configured to change according to the situation.

That is, the present invention generates a reference signal switching timing signal (hereinafter referred to as a pseudo control signal) in accordance with the DC component of the drive voltage when applying a drive voltage to an electro-mechanical conversion element such as a bimorph. The electro-mechanical transducer is designed so that no direct current voltage is applied to it, and it is possible to prevent the sensitivity of the electro-mechanical transducer from decreasing and extend its life.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 9 is a schematic configuration diagram of a VTR. Magnetic heads 40 and 41 are attached to electromechanical conversion elements 42 and 43, and these and rotational phase detection magnets 44 and 45 are connected to a rotating disk 46. They are integrally rotated by a DC motor 47. A rotational phase detector 48 is installed corresponding to the magnets 44, 45. DC motor 4
The output signal of the frequency generator 49 and the output signal of the oscillation circuit 50 attached to the DC motor 7 are supplied to a disk control circuit 51, which controls the rotational speed and rotational phase of the DC motor 47. The magnetic tape 52 is driven by a capstan 53 and a pinch roller 54 in the direction of the arrow. Capstan 53 is pulley 5
5. Driven by a DC motor 58 via a belt 56 and a pulley 57. The DC motor 58 is controlled by a capstan control circuit 59. 60 is a frequency generator attached to the DC motor 58;
The output is amplified by a capstan FG amplifier 61.
Reference numeral 62 denotes a tracking error control circuit, which has a circuit configuration that combines the circuits shown in broken lines in FIGS. 3 and 4. Since the function is clear from the description of the conventional example, the description thereof will be omitted here. The part surrounded by the broken line N is the main part of the present invention, in which two channels of driving voltage (before amplification) of the electro-mechanical conversion elements 42 and 43 are connected to the MIX circuit 6.
3 and extract the DC voltage component using LPF64. 65 is a pseudo control signal generation circuit which divides the output of the capstan FG amplifier 61 to obtain a pseudo control signal, and changes the frequency division ratio according to the DC voltage component.
As will be described in detail later, the pseudo control signal switches the oscillation frequency of the reference signal generator 66 at the timing with the head switching pulse. In FIG. 9, 71 is a head switching pulse generation circuit, 72 and 73 are drive circuits, and 74 and 75 are head amplifiers.

Figure 10 shows a specific example of the circuit enclosed by the broken line in Figure 9, with resistors R ₁ and R ₂ and capacitor C ₁ .
A MIX circuit 63 and an LPF 64 are formed, and a DC voltage component is output to the line. Resistors R ₃ to R ₅ and operational amplifiers 67 and 68 form a comparator circuit with two threshold values (voltage values at points wo and wa), and when the voltage at line becomes higher than point wo, the operational amplifier 67 The output is at a high level; if it is lower than point W, the output of the operational amplifier 68 is at a high level, and if it is an intermediate value between points W and W, the outputs of the operational amplifiers 67 and 68 are both at a low level. A frequency divider (counter) 69 divides the output of the capstan FG amplifier 61, and the frequency division ratio is changed by changing the preset value of the counter using the logic circuit 70 based on the output values of the operational amplifiers 67 and 68. There is. 66 is a reference signal generation circuit.

FIG. 11 shows the oscillation frequency switching timing of the reference signal generation circuit 66, where 9 is a head switching pulse, and the reference signal is generated at the edge of the head switching pulse following the pulse of the pseudo control signal shown in b. The oscillation frequencies f ₁ and f ₄ of the circuit 66 are switched. This is to prevent the magnetic heads 40, 41 from updating the track in the middle of the field and to obtain a clear screen. Also, the reason why the oscillation frequency is only f ₁ and f ₄ and not f ₂ and f ₃ is to realize field reproduction.
This is clear from the explanation of FIG.

Figure 12 shows how the pseudo control signal changes depending on the line potential in Figure 10. In this way, the circuit within the broken line N changes the frequency division ratio as the voltage increases relative to around 1/2Vcc. A control loop is formed in which the DC voltage applied to the electro-mechanical conversion elements 42, 43 decreases as the voltage increases, and the DC voltage applied increases as the voltage decreases.

Effects of the Invention As explained above, according to the present invention, it is possible to minimize the harmful DC voltage component of the voltage waveform supplied to an electro-mechanical conversion element such as a bimorph. It is possible to prevent a decrease in the sensitivity of the element and extend its life.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of the relationship between the position of the magnetic head and the crosstalk of the pilot signal recorded on the track, and Figure 3 is a circuit block diagram of a circuit for obtaining a tracking error voltage from the pilot signal in a conventional device. 4 is a circuit block diagram of a circuit that obtains a drive voltage waveform applied to an electro-mechanical conversion element from a tracking error voltage in a conventional device. FIG. 5 is a waveform diagram of each part of the circuit shown in FIG. 4. and FIG. 7 is an explanatory diagram showing the relationship between the reference signal and the recording track on-tracked by the magnetic head;
Figure 8 is a drive waveform diagram of the electro-mechanical conversion element, Figure 9
12 show an embodiment of the present invention, FIG. 9 is a schematic configuration diagram, FIG. 10 is a main circuit diagram, and FIGS. 11 and 12 are waveform diagrams of various parts of the circuit shown in FIG. 10. It is. 40, 41...Magnetic head, 42, 43...Electro-mechanical conversion element, 52...Magnetic tape, 60...
...Frequency generator, 61...Capstan FG amplifier, 62...Tracking error control circuit, 63
...MIX circuit, 64 ...Low pass filter, 6
5... Pseudo control signal generation circuit, 66...
Reference signal generation circuit, 67, 68... operational amplifier,
69... Frequency divider, 70... Logic circuit, 71...
...Head switching pulse generation circuit.

Claims (1)

[Claims] 1. A magnetic recording and reproducing apparatus that records and reproduces video signals as a group of inclined discontinuous recording tracks on a magnetic tape using a rotating magnetic head is equipped with a pilot signal for reproduction tracking control at four different frequencies during recording. is superimposed on the video signal and recorded sequentially on each track, and during playback, tracking errors occur due to the level difference in the crosstalk signal of the pilot signal reproduced from the recording track adjacent to the recording track before and after the recording track to be reproduced. A tracking device that detects voltage to control relative positional deviation between a recording track and a rotating magnetic head, and uses a reference having the same frequency as a pilot signal recorded superimposed on a video signal on each recording track to be reproduced during reproduction. a reference signal generation circuit that generates a signal;
switching means for generating a frequency switching timing signal of the reference signal for each recording track; and electro-mechanical conversion by displacing the mechanical position of the rotating magnetic head in a direction substantially perpendicular to the width direction of the recording track. a feedback control means for causing the rotary magnetic head to track the recording track by supplying an electric signal corresponding to the tracking error voltage to the electro-mechanical conversion element; control means for controlling the switching means so that the DC voltage component of the signal is minimized;
A tracking device configured to use a signal obtained by frequency-dividing an FG signal, and changing the frequency division ratio of the capstan FG signal according to a DC voltage component of an electric signal waveform supplied to an electro-mechanical conversion element.