JPH0531223B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a magnetic recording and reproducing apparatus, and more particularly to a magnetic recording and reproducing apparatus that performs tracking control using a four-frequency tracking method.

Background technology Conventional magnetic recording/reproducing device (hereinafter referred to as VTR)
In this case, during recording, a pulse signal (hereinafter referred to as CTL signal) corresponding to the rotation of the drum is sent to a control track provided along the edge of the magnetic tape.
is recorded, and tracking control is performed by controlling the tape speed so that the phase of this CTL signal coincides with the drum phase during playback. However, recently proposed 8mm
When high-density recording information is attempted, such as in a VTR, the running speed of the magnetic tape as a recording medium generally becomes low and the track pitch becomes narrow. In such a case, in a magnetic flux responsive fixed head, the S/N ratio of the reproduction control signal deteriorates as the running speed of the magnetic tape decreases, causing a problem that it is difficult to ensure sufficient tracking accuracy. For this reason, in an 8mm VTR, four pilot signals having different frequencies and a predetermined relationship are sequentially superimposed on an information signal and recorded, and during playback, tracking is performed using the pilot signals read as crosstalk from adjacent tracks. A so-called four-frequency tracking method is used for control. This is because the pilot signal is played by a rotating head and is therefore less dependent on tape speed.

In this 8 mm VTR, it is expected that a signal level fluctuation of about 12 dB will occur in the reproduced pilot signal due to variations in the reproduction sensitivity of the rotary head, the combination of tape type and head, fluctuations in recording level, etc. This fluctuation in the signal level of the reproduced pilot signal causes the gain of the servo loop that performs tracking control to fluctuate, causing problems such as not only accurate position control but also failure of servo pull-in.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic recording and reproducing apparatus that can perform good tracking control by eliminating problems caused by fluctuations in the signal level of a reproducing pilot signal caused by variations in the reproducing sensitivity of a rotating head. The goal is to provide the following.

The magnetic recording/reproducing apparatus according to the present invention outputs a plurality of pilot signals including a pilot signal for tracking control so that the peak level of the pilot signal obtained from a recording track being scanned by a rotating head becomes a predetermined level. The configuration includes an amplifying means for amplifying the signal.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, a speed detection signal having a frequency corresponding to the rotational speed of a capstan motor 1 as a transfer means is supplied to a speed detector 2 and a phase difference detector 3. This speed detection signal is output from a pickup (not shown) that detects the magnetic flux of a magnet (not shown) fixed to the rotating shaft of the capstan motor 1, for example. Speed detector 2
consists of an F/V (frequency/voltage) converter that generates a voltage according to the frequency of the speed detection signal, for example,
The configuration is such that the output of this F/V converter is used as a speed error signal. The output of this speed detector 2 becomes one input of the adder 4. The added output of the adder 4 becomes a rotation control signal for the capstan motor 1 via the driver 5. The phase difference detector 3 is supplied with a head switching signal SWP obtained from a reference signal generating circuit 6 which receives as input the output of a transfer generator (not shown) fixed to the rotating drum motor. The phase difference detector 3 is configured to output a phase error signal corresponding to the phase difference between the head switching signal SWP and the speed detection signal. The output of this phase difference detector 3 is sent to an adder 4 via a switch S1 that is turned on during recording.
This is another input. The head switching signal SWP is also supplied to a four-frequency signal generating circuit 8. The four-frequency signal generating circuit 8 generates 6.5f H, 7.5f _H , 10.5f _H and 10.5f _H , respectively, each time the state of the head switching signal SWP changes.
It is configured to sequentially output four signals f ₁ to f ₄ of 9.5f _H (f _H is the horizontal synchronization frequency). The output of this 4-frequency signal generation circuit 8 is added and synthesized as a pilot signal by an adder 9 with an information signal, such as an FM signal containing video information and audio information, and then output to a pair of rotary heads via a changeover switch S2 during recording. A and B are applied to record on the magnetic tape T as a recording medium. In addition, if the pilot signal
Assuming that f ₁ , f ₂ , f ₃ , f ₄ are recorded in this order,
For example, if f ₁ is recorded immediately before moving to the recording pause state, the 4-frequency signal generating circuit 8 starts recording from f ₂ in the above order when moving from the recording pause state to the recording state. The tracking control pilot signal is designed to maintain continuity.

Further, the error output of the 4F error detector 11, which is an error detector based on the 4-frequency tracking method, is provided as another input to the adder 4 via a switch S3 that is turned on during reproduction.

The 4F error detector 11 is supplied with an RF signal read from the magnetic tape T by the rotary heads A and B during reproduction via a changeover switch S2. 4F
In the error detector 11, the RF signal is amplified by a preamplifier 12, and then a low-pass filter 13 removes high-frequency components to extract four pilot signals _f1 to _f4 . These pilot signals f ₁
~ _f4 passes through variable gain amplifier 14 and then mixer 15
and is supplied to the bandpass filter 16. The bandpass filter 16 has frequency characteristics such that, for example, only the pilot signal _f1 is selectively passed. The output of this band filter 16 is the peak hold circuit 1
7 is supplied. The signal is supplied to a peak hold circuit 17. The peak level of the pilot signal f ₁ output from the band filter 16 is held by the peak hold circuit 17 and supplied to the sample hold circuit 18 . The output of the sample and hold circuit 18 is supplied to a control signal generation circuit 19. The control signal generation circuit 19 is configured to output a signal having a level corresponding to the signal held in the sample and hold circuit 18 as a control input of the variable gain amplifier 14.

On the other hand, the reproduced pilot signals f ₁ to _{f 4} supplied to the mixer 15 are mixed with the output of the four-frequency signal generating circuit 8. The f _H and 3f _H components are extracted from the output of the mixer 15 by band filters 21 and 22, respectively, and then supplied to detectors 23 and 24. The detectors 23 and 24 output voltages corresponding to the signal levels of the f _H and 3f _H components, and are applied to the positive and negative input terminals of the comparator 25, respectively. The output of the comparator 25 is directly connected to the signal switching circuit 26.
At the same time, it is applied to the other input terminal of the signal switching circuit 26 via the inverting amplifier 27. A head switching signal SWP is applied to a control input terminal of the signal switching circuit 26.
The output of the comparator 25 and the output of the inverting amplifier 27 are selectively derived from the signal switching circuit 26 and become the output of the 4F error detector 11.

As shown in FIG. 2, the rotating heads A and B are fixedly attached to the drum H at 180 degrees apart with respect to the rotating shaft so that they rotate together. The drum H is rotationally driven in synchronization with a vertical synchronization signal of an input video signal or a signal obtained by frequency-dividing an internal reference signal (for example, 3.58 _MHZ subcarrier).
The magnetic tape T is transported along the rotating heads A and B by a capstan motor 1 at a speed corresponding to the number of rotations of the rotating heads A and B, and as shown in FIG. At the same time as the track is formed, pilot signals are sequentially recorded in the order of f ₁ , f ₂ , f ₃ , and f ₄ . Track A in FIG. 3 corresponds to rotary head A, and track B corresponds to rotary head B. In FIG.

The frequencies of the four pilot signals _f1 to _f4 , which are frequency multiplexed and recorded together with video information etc. on these recording tracks, are each _6.5fH . , 7.5f _H , 10.5f _H , 9.5f _H (f _H
is the horizontal synchronization frequency), so the following relationship holds true.

｜f ₁ −f ₂ ｜=｜f ₃ −f ₄ ｜=f _H ……(1) ｜f ₂ −f ₃ ｜=｜f ₁ −f ₄ ｜=3f _H ……(2) These four pilots The frequency of the signal is
100KH _Z to 160KH _Z , and there is almost no loss due to azimuth, so the pilot signal is not only recorded on the recording track being scanned by rotary head A or B, but also on the two tracks adjacent to this recording track. The two recorded pilot signals are also reproduced as crosstalk. The level of this crosstalk is then approximately proportional to the width of the rotating head in contact with the adjacent track. Therefore, the relative position in the vertical direction of the recording track of the rotary head to the recording track can be detected based on the difference in signal level between the two pilot signals reproduced as crosstalk.

Now, each recording track has a pilot signal f ₁ ,
Since f ₂ , f ₃ , and f ₄ are sequentially recorded in the order, if the pilot signal recorded on the recording track that rotary head A or B is in contact with is f ₁ , the pilot signal is recorded on the two adjacent tracks. The pilot signals recorded in are _f4 and _f2 . And mixer 15
The f _H component and 3f _H component in the output of are f ₂ and 3f H component, respectively.
It corresponds to _f4 . Therefore, when the output of the comparator 25 is at a positive level, the signal level of the _f2 component is large, that is, the rotary head is displaced relative to the recording track in the direction opposite to the tape running direction. Further, when the output of the comparator 25 is at a negative level, the signal level of the _f4 component is large, which means that the rotary head has shifted in the tape running direction with respect to the recording track.

Next, if the pilot signal recorded on the recording track that the rotary head is in contact with is f ₂ , the pilot signals recorded on the two adjacent tracks are f ₁ and f ₃ , and the mixer 15 The f _H and 3f _H components in the output correspond to f ₁ and f ₃ , respectively. Therefore, in this case, when the output of the comparator 25 is at a positive level, the signal level of the _f1 component is large, which means that, contrary to the above case, the rotating head has shifted in the tape running direction with respect to the recording track. . Further, when the output of the comparator 25 is at a negative level, the signal level of the _f3 component is large, that is, the rotary head is shifted in the direction opposite to the tape running direction with respect to the recording track.

Therefore, the signal switching circuit 26 outputs a head switching signal.
If the output of the comparator 25 and the output of the inverting amplifier 27 are output alternately by SWP, a continuous error signal will be obtained and tracking control will be performed.

Here, a head switching signal as shown in FIG.
It is assumed that the frequency of the output of the four-frequency signal generation circuit 20 changes depending on the SWP as shown in FIG.
At this time, as shown in FIG.
If the reset signal a is supplied when the frequency becomes equal to the frequency _f1 , the output of the peak hold circuit 17 becomes as shown by the solid line in FIG. 5E in the normal reproduction mode. Incidentally, the envelope component of the pilot signal _f1 supplied to the peak hold circuit 17 from the band filter 16 at this time has a waveform as shown by the broken line in FIG. In addition, in the search mode, the band filter 16 outputs a pilot signal _f1 having an envelope waveform as shown by the broken line in FIG. F, and the output of the peak hold circuit 17 becomes as shown by the solid line in FIG. Therefore, as shown in Figure D, the sample signal pulse b is generated immediately before the reset signal a is generated.
If the signal is supplied to the sample and hold circuit 18, the peak level is always held in the sample and hold circuit 18, regardless of the playback mode, as shown in FIG.
The output of the sample and hold circuit 18 is supplied to the control signal generation circuit 19 to form the control input of the variable gain amplifier 14, so that the output of the variable gain amplifier 14 is adjusted so that the peak level of the pilot signal _f1 is equal to a predetermined level. This makes it possible to control the gain.

In the above embodiment, the peak hold circuit 17 is provided before the sample hold circuit 18, but the peak hold circuit 17 is not provided when tracking control is not performed during search operation, double speed playback, slow playback, etc. Can be removed.

Effects As detailed above, the magnetic recording/reproducing apparatus according to the present invention includes an amplifying means for amplifying the pilot signal so that the peak level of the pilot signal obtained from the recording track being scanned by the rotating head becomes a predetermined level. Since it is configured with
Fluctuations in the signal level of the reproduction pilot signal due to variations in the reproduction sensitivity of the rotary head, combinations of tape type and rotary head, fluctuations in recording level, etc. are prevented, and the relative position of the rotary head to the recording medium is accurately determined. This eliminates the problem of inability to perform proper control or deterioration of servo pull-in characteristics, and allows for good tracking control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing a drum on which rotary heads A and B in the apparatus of FIG. 1 are fixed, and FIG. FIG. 4 is a diagram showing a recording track formed on a recording medium by the apparatus shown in the figure, and is a timing chart showing the operation of each part in the apparatus shown in FIG. Explanation of symbols of main parts, 1...Capstan motor, 11...4F error detector, 14...Variable gain amplifier, 16...Band filter, 17...Peak hold circuit, 18...Sample hold circuit, 19...Control signal generation circuit.

Claims (1)

[Claims] 1 at least two rotating heads that rotate integrally; and moving the recording medium along the at least two rotating heads at the rotational speed of the at least two rotating heads so that the at least two rotating heads alternately scan the recording medium. a transporting means for transporting at a corresponding speed, and at the time of recording, a plurality of recording tracks are formed on the recording medium so as to be parallel to each other, and at the same time, the plurality of recording tracks have different frequencies and have a predetermined relationship with each other. The plurality of pilot signals obtained simultaneously from two recording tracks adjacent to one of the plurality of recording tracks being scanned by one of the at least two rotary heads during reproduction. a magnetic field controlling the relative position of the recording track in the vertical direction of the rotary head scanning the recording medium to the recording track so that the signal levels of two of the pilot signals of the recording medium are equal to each other; The recording/reproducing apparatus further comprises amplifying means for amplifying the plurality of pilot signals so that the peak level of the pilot signals obtained from the recording track being scanned by the rotary head reaches a predetermined level. Features of magnetic recording and reproducing device.