JPH061577B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a magnetic recording / reproducing apparatus (hereinafter referred to as VTR).
In particular, the present invention relates to a VTR that performs tracking control using a pilot signal recorded by being superimposed on a video signal.

[Prior Art] FIG. 3 is a schematic block diagram showing a configuration of a conventional VTR that performs tracking control using a pilot signal.

First, the structure of the conventional VTR tracking control means will be described with reference to FIG. In the figure, the magnetic head 8 is provided on a rotating head drum (not shown). The magnetic head 8 rotates as the head drum rotates, and obliquely scans a magnetic tape (not shown). The head switch signal input to the head switch signal input terminal 1 representing the switching timing of the rotary magnetic head is
It is provided to the environmental frequency generator 2 and the switch 18.
The environmental frequency generator 2 sequentially generates a pilot signal in response to the leading edge and the trailing edge of the head switch signal.

During recording, the video signal is input to the video signal input terminal 4,
After being superimposed on the above pilot signal, it is amplified via the recording amplifier 5. The changeover switch 6 is connected to the REC side, and the output of the recording amplifier 5 is supplied to the magnetic head 8 via the rotary transformer 7 and recorded on the magnetic tape.

On the other hand, at the time of reproduction, the changeover switch 6 is changed over to the PLAY side, and the video signal including the pilot signal read by the magnetic head 8 is inputted to the reproduction amplifier 9 through the rotary transformer 7 and the changeover switch 6 to be amplified. . The output of the regenerative amplifier 9 is given to the low pass filter 10,
A pilot signal component is extracted from the reproduced signal. This pilot signal component and the aforementioned pilot signal that is sequentially generated by the circulating frequency generator 2 during reproduction (hereinafter referred to as the carrier signal during reproduction, and its frequency is referred to as f _CR ) are input to the mixer 11 and the frequency between the two signals is input. A signal component having a frequency corresponding to the difference is output. The output of the mixer 11 is simultaneously given to a bandpass filter 12 having a 16 kHz passband and a bandpass filter 13 having a 46 kHz passband. The signal passed through the bandpass filter 12 is envelope-detected by the detector 14, and its output is given to the subtractor 16. On the other hand, the signal passed through the bandpass filter 13 is envelope-detected by the detector 15, and the output thereof is also given to the subtractor 16. The output of the subtractor 16 is a signal of the same polarity by the switch 18 that switches in response to the head switch signal, or a signal of the opposite polarity through the inverting amplifier 17, which is input to the sample hold circuit 19 and the sampling pulse. The tracking error signal output terminal 2 is sampled and held by the sampling pulse input from the input terminal 20.
It is output to 1.

FIG. 4 is a diagram showing video cracks formed on the magnetic tape 22 in the longitudinal direction thereof and pilot signals recorded on the respective video tracks so as to be superimposed on the video signals.

Next, the operation of the cracking control means of the VTR shown in FIG. 3 will be described with reference to FIG. During recording, the circulating frequency generator 2 responds to the leading edge and the trailing edge of the head switch signal to generate pilot signals of _four different frequencies f ₁ , f ₂ , f ₃ , f ₄ by switching them field by field. .
These four frequencies are, for example, f ₁ = 102 kHz and f ₂ = 118 k when recording an NTSC video signal.
Hz, f ₃ = 164kHz, as in f ₄ = 148kHz, the frequency difference between f ₁ and f ₂ alpha is equal to the frequency difference between f ₄ and f _3, and f ₄
The frequency difference between f ₂ is set to a value close to twice α. These pilot signals are superposed on the video signal and, as shown in FIG. 4, a video track inclined in the longitudinal direction is formed on the magnetic tape 22 by the magnetic head 8 and recorded in the field order. In FIG. 4, video tracks F ₁ , F ₂ , F ₃ , F ₄ represent that pilot signals of frequencies f ₁ , f ₂ , f ₃ , f ₄ are recorded, respectively.

At the time of reproduction, the magnetic head 8 reads a signal from the video track on the magnetic tape 22, and the reproduction signal is input to the reproduction amplifier 9 via the rotary transformer 7 and the changeover switch 6 and amplified. The output of the reproduction amplifier 9 is given to the low-pass filter 10, and the pilot signal component contained in the reproduction signal is extracted.

Here, for example, as shown in FIG.
Considering a case where the video track F ₁ on the magnetic tape 22 is tracked by the magnetic head 22, the pilot signal components detected by the magnetic head 8 include the pilot signal of frequency f ₁ superimposed on the video track F _1. In addition, a pilot signal superimposed on both adjacent video tracks (video track F ₂ and video track F _{4 in} the example of FIG. ₄ ) due to side read effect, crosstalk, etc. is also included. The magnitude of the pilot signal detected from these adjacent video tracks increases as the amount of positional deviation of the magnetic head 8 from the center of the tracked video track increases. When tracking the video track F ₁ , the above-mentioned pilot signal component extracted by the low-pass filter 10 and the carrier signal of the frequency f _CR = f ₁ generated by the circulating frequency generator 2 are input to the mixer 11. adjacent video tracks frequency _{F 2} of the pilot signal f ₂ = 118kH
The signal component having a frequency of 16 kHz, which is the difference between z and the frequency f _CR = f ₁ = 102 kHz of the carrier signal, and the frequency f ₄ = 148 kH of the pilot signal of the other adjacent video track F _4.
A signal component having a frequency of 46 kHz, which is the difference between z and the frequency f _CR = f ₁ = 102 kHz of the carrier signal, is obtained. These 16 kHz and 46 kHz signal components are separately extracted by a band pass filter 12 having a 16 kHz pass band and a band pass filter 13 having a 46 kHz pass band. The output of the bandpass filter 12 is the detector 1
4, the envelope detection is performed, and the output level indicates the amount of positional deviation of the magnetic head 8 to the adjacent video track F ₂ on the right side. On the other hand, the output of the bandpass filter 13 is envelope-detected by the detector 15, and the output level thereof represents the amount of positional deviation to the adjacent video track F ₄ on the left side of the magnetic head 8.
By passing both of these outputs through the subtractor 16, the amount of displacement of the magnetic head 8 from the center of the video track F ₁ can be obtained.

However, when the magnetic head 8 is tracking the video track F ₁ or F ₃ and when the magnetic head 8 is tracking the video track F ₂ or F ₄ , the frequency difference between the left and right adjacent video tracks is opposite. Therefore, the output of the subtractor 16 has the opposite polarity. Therefore, it is necessary to reverse the polarity of the output of the subtractor 16 when the magnetic head 8 tracks the video track F ₂ or F ₄ by providing the inverting amplifier 17 for inverting the polarity and switching the switch 18 by the head switch signal. There is.

The output of the switch 18 fluctuates within one track period due to the bending of the video track or the bending of the scanning track of the magnetic head, and becomes an electrical disturbance. Therefore, the sample hold circuit 19 samples and holds each track at a fixed position on the track. And output.

In this way, the tracking error signal output terminal 21
A signal having a voltage corresponding to the amount of displacement of the magnetic head 8 from the center of the video track is output to
This signal is fed back to the capstan motor to form a servo control system for tracking.

[Problems to be Solved by the Invention] Since the conventional VTR tracking control device is configured as described above, when there is a head step or a reproduction level difference between the two magnetic heads, the tracking error signal is 2 It varies between tracks and becomes an electrical disturbance of 30Hz.
Further, when there is a reproduction level difference between the four frequencies of the reproduction pilot signal, the tracking error signal fluctuates among the four tracks and becomes an electrical disturbance of 15 Hz. These electrical disturbances cause fluctuations in the tape running speed. In order to eliminate such fluctuations in the tape running speed due to electrical disturbance, the tracking error signal may be sampled and held for every two tracks or four tracks to flatten the tracking error signal that changes between tracks. However,
In such a method, there is a new problem that the sample-hold cycle becomes long, the response band of the capster servo system becomes low, and the pull-in of tracking at the start of reproduction is delayed.

The present invention has been made in order to solve the above problems, and provides a VTR tracking control device that can reduce fluctuations in the running speed of a tape without delaying the pull-in of tracking at the start of reproduction. The purpose is to provide.

[Means for Solving Problems] A VTR according to the present invention detects a tracking error signal based on a pilot signal extracted from a reproduction signal, and the tracking error signal and the tracking error signal sample-held by a switching means. And are selectively switched to output.

[Operation] In the present invention, the switching means outputs the tracking error signal as it is at the time of pulling in reproduction and tracking, and switches so as to output the sampled and held tracking error signal in the steady reproduction state. Is performed quickly, and in a steady reproducing state, fluctuations in the tape running speed due to electrical disturbance are reduced.

[Embodiment] FIG. 1 is a schematic block diagram showing the structure of a VTR according to an embodiment of the present invention. The embodiment shown in FIG.
It is similar to the conventional VTR tracking control device shown in FIG. 3 except for the following points. That is, the switch 18
Is output to the sample hold circuit 19 and also to one input terminal of the newly provided changeover switch 23. The output of the sample hold circuit 19 is input to the other input terminal of the changeover switch 23. The output of the changeover switch 23 is switched by a control signal input from the control signal input terminal 24 and output to the tracking error signal output terminal 21.

FIG. 2 is a timing chart for explaining the operation of the embodiment shown in FIG. 2A shows the head switch signal input from the head switch signal input terminal 1, FIG. 2B shows the output of the changeover switch 18, and FIG. 2C shows the sampling pulse input. Terminal 2
2 shows the sampling pulse input from 0, and FIG. 2 (d) shows the output of the sample hold circuit 19.
FIG. 6E shows a control signal input from the control signal input terminal 24 (the changeover switch 23 is switched to the output side of the changeover switch 18 at the high level, and the changeover switch 23 is changed to the output side of the sample hold circuit 19 at the low level. Switch)
2 (f) shows the tracking error signal output to the tracking error signal output terminal 21.

The operation of the embodiment of FIG. 1 will be described below with reference to the timing chart of FIG. Note that, here, a case will be described in which the tracking error signal is sampled and held every two tracks after a certain period of time from the start of reproduction.

For a certain period at the start of reproduction, the control signal input from the control signal input terminal 24 is at high level, and the changeover switch 23 is changed over to the output side of the changeover switch 18.
Therefore, the tracking error signal output terminal 21 outputs the tracking error signal as it is without being sampled and held. After that, the control signal is changed to the low level, and the changeover switch 23 is changed over to the output side of the sample hold circuit 19. Therefore, the sample-hold circuit 19 is connected to the tracking error signal output terminal 21.
The tracking error signal sampled and held for every two tracks is output by. The period during which the control signal input from the control signal input terminal 24 is at a high level is set to a sufficient amount of time for pulling in tracking after the start of reproduction.

As described above, the tracking error signal is output as it is without being sample-held for a certain period at the start of reproduction,
Tracking is quickly pulled in. After that, since the tracking error signal is sampled and held and output for every two tracks, there is a head step or a reproduction level difference between the two magnetic heads, and the changeover switch 18
Even if there is a change in the output of the track 2 between the two tracks, this change is removed by the sample hold circuit 19 and is not included in the output of the tracking error signal output terminal 21. Therefore, the tracking error signal output does not include the electric disturbance due to the above fluctuation, and does not cause the fluctuation of the tape speed.

In the above embodiment, the sampling period of the sample hold circuit 19 is shown every two tracks.
Sampling cycle every 4 tracks or 4 × N (N
May be for each track. However, when the level of the reproduced pilot signal is ideal, a step of the tracking error signal does not occur between the tracks, so naturally it is sufficient to sample and hold each track.

Further, in the above-described embodiment, the switching switch 23 switches between the tracking error signal which is not sampled and held as it is and the tracking error signal which is sampled and held by the sample and hold circuit 19. The sampling pulse may be switched by using only the sample hold circuit 19 without using. That is, the sampling pulse width is set to duty 1 for a certain period at the start of reproduction.
The output of the change-over switch 18 is allowed to pass through as it is set to 00%, and then the sampling pulse may be changed to the same one as in the above embodiment.

Further, in the above-mentioned embodiment, the case of starting reproduction is shown, but it is also possible to transit from special reproduction such as speed search, still reproduction, slow-motion reproduction, frame-advance reproduction to passing reproduction, and the same effect as in the above-mentioned embodiment. Play.

Furthermore, although the VTR has been described in the above description, the present invention is also effective for other information signal storage devices such as a digital audio signal magnetic recording / reproducing device.

[Effects of the Invention] As described above, according to the present invention, the tracking error signal is output as it is without being sampled and held for a certain period at the time of pull-in, and the sampled and held tracking error signal is output in the steady reproduction state. Since the output is performed, tracking is quickly pulled in, and when there is a head step or a reproduction level difference between the two magnetic heads or a reproduction level difference between the reproduction pilot signals in a steady reproduction state. However, it is possible to eliminate the fluctuation of the tape speed due to these.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a VTR according to an embodiment of the present invention. FIG. 2 is a timing chart for explaining the operation of the embodiment shown in FIG. FIG. 3 shows a conventional VT for performing tracking control using a pilot signal.
It is a schematic block diagram of R. FIG. 4 is a diagram showing a video track and a magnetic head formed on a magnetic tape. In the figure, 2 is a circulating frequency generator, 7 is a rotary transformer, 8 is a magnetic head, 9 is a regenerative amplifier, 10 is a low pass filter, 11 is a mixer, 12 and 13 are band pass filters, 14 and 15 are wave detectors, Reference numeral 19 is a sample and hold circuit, and reference numerals 6, 18 and 23 are changeover switches.

Claims (6)

[Claims] 1. A plurality of rotary magnetic heads are used to superimpose a plurality of pilot signals each having a different frequency on a video signal and sequentially and repeatedly recorded for each video track on a magnetic tape, and are extracted from the reproduced signal at the time of reproduction. A magnetic recording / reproducing apparatus for controlling running of the magnetic tape based on the pilot signal, the pilot signal extracting means extracting the pilot signal from the reproduction signal, and tracking based on the extracted pilot signal. The switching means includes a detection means for detecting an error signal, a sample and hold means for sampling and holding the tracking error signal, and a switching means for selectively switching the tracking error signal and the tracking error sampled and held. , Before playback, before tracking pull-in And it outputs a tracking error signal, a magnetic recording and reproducing apparatus in a steady reproduction state and performs switching so as to output a tracking error signal the sampled and held. 2. The switching means outputs the tracking error signal detected by the detecting means as it is for a certain period at the start of reproduction and a certain period at the time of transition from speed search, still reproduction or slow motion reproduction to normal reproduction. 2. The magnetic recording / reproducing apparatus according to claim 1, wherein the tracking error signal is output and, after the predetermined period of time, the tracking error signal sampled and held by the sample and hold means is output. 3. The magnetic recording / reproducing apparatus according to claim 1 or 2, wherein said sample hold means samples and holds said tracking error signal for each predetermined track and outputs it. 4. The magnetic recording / reproducing apparatus according to claim 3, wherein the sample hold means samples and holds the tracking error signal for each track and outputs it. 5. The magnetic recording / reproducing apparatus according to claim 3, wherein the sample hold means samples and holds the tracking error signal for every two tracks. 6. The magnetic recording / reproducing apparatus according to claim 3, wherein the sample hold means samples and holds the tracking error signal for each track of an integer multiple of 4.