JP2754731B2 - Rotating head type playback device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary head type reproducing apparatus, and particularly to a tracking control apparatus.

[Summary of the Invention]

According to the present invention, in a rotary head type reproducing apparatus in which a rotary head scans an oblique track formed on a tape and reproduces a video signal, the speed of a capstan motor is wobbling with a signal of a predetermined frequency, The first tracking control signal is generated by synchronously detecting the envelope signal of the reproduced RF signal reproduced by the rotating head by the signal for wobbling, and is formed based on the reproduced vertical synchronization signal from a predetermined position of the rotating head. A second tracking control signal is generated according to a time difference up to a predetermined signal gated by the window pulse. During a rising period after the mode transition, tracking control is performed by the first tracking control signal,
In the steady period after the rising period, the switching is performed so that the tracking control is performed by the second tracking control signal, and the tracking deviation can be satisfactorily corrected without using the tracking signal.

[Conventional technology]

In a rotary head type VTR, tracking control is required so that the head can correctly scan an oblique track formed during recording during reproduction. As one method of tracking control, a control signal with a frequency of 30 Hz formed from a vertical synchronizing signal separated from a recording video signal in the longitudinal direction of the tape at the time of recording is recorded, and at the time of reproduction, the reproduced control signal and the head signal are recorded. There is known one that controls the tape running speed so that the rotation phase has the same relationship as during recording.

In the system using the control signal for tracking, a recording and reproducing head for the control signal is required, and a track extending in the longitudinal direction for the control signal needs to be provided, which is costly.
There is a problem that the improvement in recording density is hindered.

In an 8 mm VTR, the following four types of frequency f
The pilot signals of 1, f2, f3, and f4 are sequentially recorded together with the video signal, and the pilots and signals of both adjacent tracks and the pilot signal of the target track have frequency differences of fh (horizontal frequency) and 3fh.

f1 = 6.5fh ≒ 102.5kHz f2 = 7.5fh ≒ 119.0kHz f3 = 10.5fh ≒ 165.2kHz f4 = 9.5fh ≒ 148.7kHz During playback, the crosstalk components from both adjacent tracks and the local pilot signal in the reverse order of the recording The tracking error is detected by comparing the levels of the frequency difference components (fh, 3fh).

As described above, the process of switching the frequency of the pilot signal for each track and comparing the level of the frequency difference component has a problem that the circuit configuration is complicated.

In order to solve the above-mentioned problem, a tracking control method which does not require a special control signal such as a control signal or a pilot signal has been proposed. The synchronous detection method is one of the tracking control methods. In this synchronous detection method, the envelope of the reproduced RF signal is wobbling by wobbling the capstan with a low-frequency sine wave signal, and the reproduced RF signal is converted to the sine wave signal. , The tracking error information is obtained.

As another tracking control method that does not require a special signal for tracking control, a synchronization signal timing detection method has been proposed. In the synchronous signal timing detection method, a specific horizontal synchronizing signal (or a pilot signal added to a recording video signal for tracking) by a window pulse having a width of ± 1 / 2H (H: horizontal cycle) formed from a reproduced vertical synchronizing signal. ) Is extracted, and a time difference between a reference time at which the rotary head passes a predetermined position and a time at which a specific horizontal synchronizing signal is reproduced is detected, and the direction and amount of the track deviation are determined from the time difference.

[Problems to be solved by the invention]

The synchronous detection method has the advantage that it is hardly affected by the deviation of the tape speed and that the control operation starts quickly.On the other hand, the wobbling tape causes the drum rotation speed to become uneven, and the jitter of the reproduced video signal increases. However, there is a disadvantage that the reproduced image fluctuates. The synchronous signal timing detection method has an advantage that the circuit configuration is simple because it is hardly affected by the deviation of the tape speed and does not require a detection circuit or the like. However, the synchronization signal timing method needs to compare the time difference between the reference time and the gated horizontal synchronization signal with the reference time difference for each tape. If this reference time difference cannot be detected correctly, good tracking control is performed. There are difficult disadvantages.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a rotary head type reproducing apparatus which makes use of the advantages of the synchronous detection method and the synchronous signal timing method.

[Means for solving the problem]

According to the present invention, in the rotary head type reproducing apparatus in which the diagonal tracks formed on the tape 4 are scanned by the rotary heads 1a and 1b to reproduce a video signal, the speed of the capstan motor 5 is adjusted to a predetermined frequency. Signal Sw
A first tracking control circuit 10 for generating a tracking control signal by synchronously detecting the envelope signal Se of the reproduced RF signal reproduced by the rotary heads 1a and 1b with the wobbling signal Sw; A second tracking control circuit 19 for detecting a time difference from a predetermined position of 1a, 1b to a predetermined signal gated by a window pulse formed based on the reproduced vertical synchronization signal, and correcting a tracking error according to the time difference.
During the rising period after the mode transition, the first tracking control circuit 10 performs tracking control, and during the steady period after the rising period, the second tracking control circuit
And a circuit 12 for switching to perform tracking control in 19.

[Action]

In the rising period after the operation mode of the VTR transitions from stop to reproduction, synchronous detection servo is used, and in the steady period, synchronous signal timing servo is used. Therefore, the reference time difference required for the synchronization signal timing servo can be detected by the synchronous detection servo, and the reproduced image does not fluctuate due to wobbling.

〔Example〕

Hereinafter, the present invention will be described with reference to the drawings. This description will be made in the following order.

a. Overall configuration of one embodiment b. Synchronous detection servo system c. Synchronous signal servo system d. Modification a. Overall configuration of one embodiment In FIG. 1, 1a and 1b indicate frame frequencies (30H
The rotating head mounted on the rotating drum at 180 ° is shown in z). In the rotary heads 1a and 1b, the extending directions of the differential gaps of the rotary heads 1a and 1b are shifted by a predetermined angle, and so-called tilt azimuth recording is performed. Reference numeral 2 denotes a drum motor, and reference numeral 3 denotes a rotation detector that generates a detection signal PG corresponding to the rotation phase of the drum motor 2. Further, the magnetic tape 4 is fed at a predetermined speed in a state where the magnetic tape 4 is wound around the drum at a winding angle slightly larger than 180 °. The winding angle of the magnetic tape 4 may be 210
The size may be increased as in ゜, and the PCM audio signal may be recorded during the overlap period. Reference numeral 5 denotes a capstan motor for feeding the magnetic tape 4, and a rotation detector 6 for generating a detection signal FG corresponding to the rotation frequency and rotation phase of the capstan motor 5 is provided.

The reproduction signals from the rotary heads 1a and 1b are not shown,
The signal is converted into a one-channel reproduction RF signal by the reproduction switching circuit and supplied to the FM demodulation circuit 8 and the envelope detection circuit 9 via the reproduction amplifier 7. An envelope signal Se of the reproduced RF signal is obtained from the envelope detection circuit 9, and the envelope signal Se is supplied to the synchronous detection servo circuit 10. The synchronous detection servo circuit 10 is supplied with a wobbling sine wave signal Sw from the signal generation circuit 11. As described later, the synchronous detection servo circuit 10 performs synchronous detection of the envelope signal Se with a sine wave signal Sw for wobbling, so that a polarity corresponding to the direction of the tracking shift and a level for tracking control according to the tracking shift are provided. A phase error signal Ss is formed. The phase error signal Ss from the synchronous detection servo circuit 10 is applied to one input terminal 13 of the switch circuit 12.
Supplied to a.

The reproduced video signal from the FM demodulation circuit 8 is taken out to a terminal 14 and supplied to a reproduction signal processing circuit (not shown) and to a composite synchronization signal separation circuit 15. The composite synchronization signal CSY from the composite synchronization signal separation circuit 15 is supplied to the vertical synchronization signal separation circuit 16 and the AND gate 17. The vertical synchronization signal VSY is separated by the vertical synchronization signal separation circuit 16. This vertical synchronizing signal VSY is supplied to the pulse generation circuit 18, and a window pulse WN for extracting a predetermined horizontal synchronizing signal after the timing of the vertical synchronizing signal VSY is formed. The window pulse WN is supplied to the AND gate 17, and the AND gate 17 outputs a predetermined horizontal synchronization signal Ph.

The horizontal synchronization signal Ph extracted by the AND gate 17 is supplied to the synchronization signal servo circuit 19 and the reference detection circuit 20. The output signal of the rotation detector 3 related to the drum motor 2 is
21 to the drum (rotary heads 1a, 1
A detection signal PG having a phase corresponding to the rotation phase of b) is generated. This detection signal PG is supplied to the synchronization signal servo circuit 19 and the reference detection circuit 20. The synchronization signal servo circuit 19
Synchronous signal timing detection method, where detection signals PG and AN
The time difference Td from the horizontal synchronization signal Ph from the D gate 17 is compared with the reference value Tr detected by the reference detection circuit 20, thereby forming the tracking control signal St. In the synchronous signal servo method, the tracking state may be detected from a pilot signal for tracking control added to a predetermined position in the video signal, instead of the horizontal synchronous signal. The tracking control signal St from the synchronization signal servo circuit 19 is supplied to the input terminal 13b of the switch circuit 12.

The tracking control signal selected by the switch circuit 12 is supplied to the adding circuit 22, and is added to the speed error signal.
The switch circuit 12 is controlled by a control signal generated by the timing generation circuit 23. The detection signal PG and the operation mode signal from the terminal 24 are supplied to the timing generation circuit 23. When the operation mode of the VTR changes from stop to reproduction, this control signal is at a low level in a predetermined rising period immediately after the mode transition, and is at a high level in a subsequent steady period. The input terminal 13a of the switch circuit 12 is selected during the low-level rising period of the control signal, and the input terminal 13b is selected during the high-level steady period.

The output signal of the rotation detector 6 for detecting the rotation speed of the capstan motor 5 is supplied to the amplifier 25. The detection signal FG from the amplifier 25 is supplied to the speed error detection circuit 26. Since this detection signal FG has a frequency proportional to the rotation speed of the capstan motor 5, the speed error detection circuit 26
Then, the speed of the capstan motor 5 detected from the cycle of the detection signal FG is compared with a speed reference to form a speed servo signal. This speed servo signal is supplied to the adding circuit 22. The tracking control signal from the switch circuit 12 and the speed servo signal are added by the adding circuit 22.

The output signal of the addition circuit 22 is supplied to the addition circuit 29 via the phase compensation circuit 27 and the servo amplifier 28. Phase compensation circuit
27 is provided for controlling the phase characteristics of the servo loop, and the servo amplifier 28 is provided for controlling the gain characteristics of the servo loop. The wobbling sine wave signal Sw from the signal generation circuit 11 is supplied to the addition circuit 22 via the switch circuit 30. The switch circuit 30 is turned on during the low level rising period of the output of the timing generation circuit 23, and is turned off during the high level steady period. The output signal of the adding circuit 29 is supplied to the capstan motor 5 via the drive amplifier 31. The capstan motor 5 runs the magnetic tape 4 so that a tracking error does not occur at a constant speed between the tracking control signal and the speed servo signal. In the rising period, the switch circuit 30 is turned on, and the sine wave signal Sw is used for driving the capstan motor 5, so that the rotation speed of the capstan motor 5 is modulated by the sine wave signal Sw. The sine wave signal Sw is a low frequency signal that the capstan motor 5 can follow.

During the low-level rising period of the control signal from the timing signal generation circuit 23, the reproduced video signal is muted, and the reproduced image is not displayed. After the rotation of the capstan motor 5 is stabilized and the detection of the reference time difference Tr is completed, the output signal of the timing signal generation circuit 23 changes to a high level during a steady period in which tracking control can be performed by the synchronization signal servo circuit 19. I do. With this control signal, tracking control is performed by the synchronous detection servo circuit 10 during the rising period, and tracking control is performed by the synchronous signal servo circuit 19 during the steady period.

In the above-described embodiment of the present invention, a portion surrounded by a broken line in FIG. 1 can have a digital configuration using a microcomputer. In the case of the control of the microcomputer, the operation is controlled as shown in the flowchart of FIG. Mode transition in which VTR operation changes from stop to playback (capstan motor 5 rises)
At times, the synchronous detection servo is started by the phase error signal Ss (step 41).

When tracking control is performed by the synchronous detection servo, a time difference Td between a detection signal PG indicating a predetermined rotation position of the rotating drum and a gated horizontal drum signal Ph is detected, and the time difference Td is integrated to obtain a reference value. Is detected (step 42). When the synchronous detection servo is operating, the detected time difference Td is also affected by the wobbling, so the value averaged by integration is used as the reference value Tr. The detected reference time difference Tr is stored in the storage means (step 43).

Next, the envelope level ENV is detected (step 44). After the detection of the reference time difference Tr is completed, the servo system is switched from the synchronous detection servo to the synchronous signal servo (step 45).

In the subsequent steady period, tracking is controlled by the synchronization signal servo (step 46).

b. Synchronous detection servo system FIG. 3 shows an example of the synchronous detection servo circuit 10. An envelope signal Se is supplied from an envelope detection circuit 9 to an input terminal indicated by 51. High-pass filter at input terminal 51
A synchronous detection circuit 53 is connected via 52. Synchronous detection circuit
The sine wave signal Sw for wobbling from the input terminal 54 is supplied to 53 via the phase correction circuit 55. Phase correction circuit 55
Is provided to correct a delay until the speed of the capstan motor 5 is modulated by the sine wave signal Sw. The output signal of the synchronous detection circuit 53 is supplied to a low-pass filter 56, and a phase error signal for tracking control is output to an output terminal 57.
Ss is taken out.

The envelope signal Se includes tracking information θ (t) because the capstan motor 5 is vibrated by the sine wave sin ωt, and can be expressed as sin (ωt + θ (t)). From the synchronous detection circuit 53, a phase error signal Ss represented by sin ωt × sin (ωt + θ (t)) = ｛{cos (−θ (t)) − cos (2ωt + θ (t)} is obtained. This phase error signal Ss is passed through the low-pass filter 56 to remove twice as many frequency components.
From 56, a phase error signal Ss represented by 1/2 cos (-θ (t)) is obtained.

The tracking error detection by the synchronous detection servo circuit 10 will be described with reference to FIGS. 4th
5A, T indicates a part of the track formed on the magnetic tape 4, and H indicates the scanning trajectory of the rotary head 1a or 1b. In the rising period of the capstan motor 5, the sine wave signal Sw is supplied to the addition circuit 29 via the switch circuit 30, so that the rotation speed (tape speed) of the capstan motor 5 is modulated according to the sine wave signal Sw. , A wobbling scanning trajectory H is formed.

FIG. 4 shows the operation when there is no tracking error. In a hatched area where the track T and the scanning locus H overlap, as shown in FIG. 4B, a reproduced RF signal is obtained from the track. From the envelope detection circuit 9, FIG.
The envelope signal Se shown in
Se is supplied to the synchronous detection circuit 53 via the high-pass filter 52. Further, a sine wave Sw for wobbling is supplied to the synchronous detection circuit 53. The sine wave Sw is converted into a pulse signal shown in FIG. 4D by the synchronous detection circuit 53 and multiplied by the envelope signal Se.
The output signal shown in FIG. 4E is generated. This output signal is supplied to the low-pass filter 56, which generates a phase error signal Ss shown in FIG. 4F. When there is no tracking error, the phase error signal Ss is 0.

On the other hand, as shown in FIG. 5A, when there is a tracking error (that is, when the center of the track T does not coincide with the center of the scanning locus H), the RF signal shown in FIG. 5B is generated, The envelope signal Se shown in FIG. 5C is obtained. Since the envelope signal Se is multiplied by the pulse signal shown in FIG. 5D, a synchronous detection output shown in FIG. 5E is generated. Accordingly, as shown in FIG. 5F, a phase error signal Ss having a polarity corresponding to the direction of the track shift and a level corresponding to the track shift is obtained from the low-pass filter 56. The phase error signal Ss formed by the synchronous detection servo circuit 10 becomes 0 when there is no tracking error, increases in response to the tracking error, and reaches the maximum level when the tracking error is equal to the track pitch Wp.

c. Synchronous signal servo method The synchronous signal servo circuit 19 compares the timing of the synchronous signal with a predetermined rotation phase of the rotary head and detects a tracking error. To perform tracking control. Sixth
The formation of the tracking control signal by the synchronous signal servo method will be described with reference to the drawings. FIG. 6A shows a composite synchronizing signal CSYNC separated from the reproduced video signal by the composite synchronizing signal separating circuit 15, and FIG.
6 shows a vertical synchronization signal VSYNC separated from the reproduced video signal. The window pulse WN shown in FIG. 6C is formed by the pulse generation circuit 18 from the vertical synchronization signal VSYNC. The window pulse WN has a pulse width of ± 1 / 2H with respect to the horizontal synchronization signal Ph used for detecting a time difference. The predetermined horizontal synchronizing signal Ph gated by the window pulse WN and the detection signal PG (FIG. 6E) having a phase corresponding to the predetermined rotation phase of the drum shown in FIG. The signal is supplied to the circuit 20, and the time difference indicated by Td in FIG. 6 is detected. When the tracking error is corrected by the synchronous detection servo, the time difference Td becomes the reference value, and thus the integrated value of the time difference Td is detected as the reference value Tr.

The tracking control by the above-described synchronous signal servo method will be described with reference to FIGS. 7 and 8.

FIG. 7 shows a recording pattern formed on the magnetic tape 4, Ta indicates a track formed by the rotary head 1a (+ azimuth), and Tb indicates a track formed by the rotary head 1b (-azimuth). ing. In this example, there is no guard band, the distance between the start ends of two adjacent tracks Ta and Tb is equivalent to a time difference of 1 / 2H, and the recording position of the horizontal synchronization signal is orthogonal to the track. Are aligned in the direction. In FIG. 7, Lr is a line indicating a predetermined rotation phase of the rotary heads 1a and 1b, that is, a phase of the detection signal PG.

A case will be described in which control is performed so that the rotary head 1a scans correctly on the center track Ta in FIG. When there is no track shift, that is, when the scanning locus S0 in which the center of the track Ta matches the center of the rotary head 1a is drawn, the detection signal PG and the horizontal synchronization signal Ph recorded on the track Ta are drawn.
Is equal to the reference value Tr (see FIG. 8). With respect to the state where there is no track shift, the track shift where the scanning locus of the center of the rotary head 1a is shifted to the upstream side of the tape is defined as positive, while the scanning track of the center of the rotary head is shifted to the downstream side of the tape. The track deviation in the state is negative.

As shown by the scanning trajectories S1 and S2, when there is a track shift of ± 1/2 Wp (Wp: track pitch), the time difference is (Tr
± 1 / 4H). Further, as shown by the scanning trajectories S3 and S4, when there is a track deviation of ± Wp, the time difference is (Tr ±
1 / 2H). Accordingly, the relationship between the track deviation and the detected time difference is as shown in FIG. Tracking control can be performed by controlling the rotation speed of the capstan motor 5 according to the detected time difference.

The time difference between the horizontal synchronization signal and the detection signal PG is
The detection accuracy is not limited to one time for one track, but may be detected a plurality of times to increase the tracking accuracy.

The present invention can be applied to a pattern other than the recording pattern shown in FIG. 7, for example, a pattern in which the start end of an adjacent track has a shift of 1H. In a pattern having no guard band and adjacent tracks having a shift of 1H, the width of the window pulse WN is ± 1H.

d. Modified example In addition to the mode transition from stop to playback, when a short recording mode (SP mode) and a long recording mode (LP mode) are switched in the middle of one tape, The present invention is similarly applicable to a case where a transition at a switching point, a transition at a splicing point of a spliced tape, and the like occur.

〔The invention's effect〕

In the present invention, tracking control is performed by the synchronous detection servo during a rising period after the mode transition in which the operation mode of the VTR changes from the stop state to the reproduction state, and after the rising period, tracking control is performed by the synchronous signal servo. Therefore, the reference value Tr for the synchronous signal servo can be detected by the synchronous detection servo.
Since the synchronous signal servo operates using the Tr, highly accurate control can be performed. Further, since the synchronization signal servo is used in the steady period, it is possible to prevent a problem that the reproduced image fluctuates due to wobbling.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a flowchart used to explain the operation of one embodiment of the present invention,
FIG. 3 is a block diagram of an example of a synchronous detection servo circuit, and FIG.
5 and 5 are schematic diagrams used to explain the detection of a tracking error by the synchronous detection servo, FIG. 6 is a timing chart used to describe the synchronous signal servo, and FIGS. 7 and 8.
The figure is a schematic diagram used for explaining tracking control by a synchronization signal servo. Explanation of main symbols in drawings 1a, 1b: rotating head, 4: magnetic tape, 5: capstan motor, 9: envelope detection circuit, 10: synchronous detection servo circuit, 19: synchronous signal servo circuit, 12, 30: switch circuit.

Claims (1)

(57) [Claims] In a rotary head type reproducing apparatus in which a rotary head scans an oblique track formed on a tape to reproduce a video signal, the speed of a capstan motor is wobbled by a signal of a predetermined frequency. First tracking control means for generating a tracking control signal by synchronously detecting an envelope signal of a reproduction RF signal reproduced by the rotary head with the wobbling signal; and reproducing vertical signals from a predetermined position of the rotary head. A second tracking control unit that detects a time difference up to a predetermined signal gated by a window pulse formed based on the synchronization signal and corrects a tracking shift according to the time difference; The tracking control is performed by the first tracking control means, and In the steady period after between, rotary head type reproducing apparatus characterized by comprising a means for switching to perform the tracking control by the second tracking control means.