JPH02312048A - Rotating head type reproducing device - Google Patents

Abstract

PURPOSE:To correct a tracking error in a short time and simultaneously to prevent a reproduced image from fluctuating by controlling tracking with the aid of a synchronous detection servo in the starting period of a capstan motor and with the aid of an envelope servo in an ordinary period. CONSTITUTION:In the starting period of the capstan motor 4, a phase error signal Ss formed by the synchronous detection servo is supplied to an addition circuit 16 and integrated. Then, a speed reference is corrected by detecting the direction and the absolute value of a speed error. Next, when an envelope level ENV is detected, the ENV is changed corresponding to the scanning extending to plural tracks which is executed by rotating heads 1a and 1b at the starting period of the motor 4 and a maximum value without the dislocation of the track is detected. At this time, the tracking is controlled by switching a servo system to an envelope servo system. A switching circuit 14 is controlled corresponding to the muting period of the reproducing signal of a VTR.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotary head type reproducing device, and particularly to a tracking control device.

(Summary of the Invention) The present invention provides a rotary head type reproducing device in which a rotary head scans diagonal tracks formed on a tape to reproduce a video signal. The envelope signal of the reproduced RF signal which is wobbled by the signal and reproduced by the rotating head is synchronously detected by the wobbling signal, and the first
A tracking control signal is generated, a second tracking control signal is generated based on the level of the envelope signal, and tracking control is performed using the first tracking control signal in the rising period after the mode transition, and tracking control is performed using the first tracking control signal after the rising period. In the steady period, switching is made to perform tracking control using the second tracking control signal,
Tracking deviation can be effectively corrected without using a tracking signal.

(Prior Art) A rotary head type VTR requires tracking control so that the head can correctly scan the diagonal tracks formed during recording during reproduction. One method of tracking control is to record a control signal with a frequency of 30 Hz formed from a vertical synchronization signal separated from the recorded video signal in the longitudinal direction of the tape during recording, and during playback, the reproduced control signal and the head It is known to control the tape running speed so that the rotational phase has the same relationship as during recording.

This method of using control signals for tracking requires a head for recording and reproducing the control signals, and also requires a track extending in the longitudinal direction for the control signals, which increases cost and increases the recording density. There was a problem that hindered improvement.

In addition, the 8mm VTR has four types of frequencies fl, f2, etc. as shown below. f3. The pilot signal of f4 is sequentially recorded together with the video signal, so that the pilot signals of both adjacent tracks and the pilot signal of the track of interest have a frequency difference of fh (horizontal frequency) and 3fh.

fl=6.5fh 'q102.5k)lzf 2=
1. 5fh':119. 0kHzf3=10
．． 5fh! :1165゜2kHzf4""9.5f
h' When reproducing at 1148.7 kHz, a tracking error is detected by comparing the levels of the frequency difference components (fh, 3fh) between the crosstalk components from both adjacent tracks and the local pilot signal in the reverse order from the recording time.

As described above, the process of switching the frequency of the pilot signal for each track and comparing the levels of frequency difference components has the problem of complicating the circuit configuration.

In order to solve the above-mentioned problems, a tracking control method that does not require special signals for control such as control signals or pilot signals has been proposed. The synchronous detection method is one of these tracking control methods. In this synchronous detection method, the envelope of the reproduced RF signal is wobbled by wobbling the capstan with a low-frequency sine wave signal, and this reproduced RF signal is Tracking error information can be obtained by synchronously detecting the signal.

An envelope method has been proposed as another tracking control method that does not require a special signal for tracking control. The envelope method is a method in which the level of the envelope of the reproduced RF signal is monitored and tracking is controlled so that this level becomes the maximum.

[Problem to be solved by the invention]

The synchronous detection method is not easily affected by deviations in tape speed;
In addition, it has the advantage that the control operation starts quickly, and on the other hand,
The wobbled tape causes uneven rotational speed of the drum, which increases jitter in the reproduced video signal and causes the reproduced image to shake.

The envelope method has the advantage of not having the problem of generating jitter, but on the other hand, it is easily affected by speed deviations (and
If the maximum value of the envelope level is not known, the operation will be unstable, so it is difficult to perform good tracking control when the capstan motor starts up.

Accordingly, an object of the present invention is to provide a rotary head type reproducing apparatus that takes advantage of the respective advantages of the above-mentioned synchronous detection method and envelope method.

[Means to solve the problem]

In the present invention, in a rotary head type reproducing apparatus in which the rotary heads la and lb scan diagonal tracks formed on the tape 3 to reproduce video signals, the speed of the capstan motor 4 is adjusted to a predetermined frequency. Signal Sw
A first tracking control circuit 9 generates a tracking control signal by synchronously detecting the envelope signal Se of the reproduced RF signal reproduced by the rotary heads 1a and 1b using the wobbling signal Sw.
and a second tracking control circuit 10 that generates a tracking control signal based on the level ENV of the envelope signal Se. During the rising period after the mode transition, the first tracking control circuit 9 performs tracking control, and during the rising period. In the later steady period, the second tracking control circuit 1
Circuit 25 that switches to perform tracking control at 0
are provided.

(Function) When the operation mode of the VTR changes from stop to playback, the synchronous detection servo is used during the start-up period of the capstan motor 4, and the envelope servo is used during the steady period. Therefore, the tracking error is corrected in a short time by the synchronous detection servo, and the problem of wobbling of the reproduced image does not occur.

[Example] The present invention will be described below with reference to the drawings. This description will be given in the following order.

a, Overall configuration of an embodiment, Synchronous detection servo system C, Envelope servo system d, Modification a, Overall configuration of an embodiment In FIG. 1, 1a and tb are frame frequencies (3
The rotating heads are shown mounted at opposing spacing of 180° on a drum rotating at 0 Hz). Rotating head 1a and lb
The extending directions of the differential gaps are shifted by a predetermined angle, and so-called inclined azimuth recording is performed. 2 shows a drum motor that drives the drum, and the magnetic tape 3 is fed at a predetermined speed with the magnetic tape 3 being wound around the circumferential surface of the drum at a winding angle slightly larger than 180°. The winding angle of the magnetic tape 3 can be adjusted to 2 if necessary.
100 and the PC during the overlap period.
M audio signals may be recorded. Reference numeral 4 indicates a capstan motor for feeding the magnetic tape 3, and a rotation detector 5 for generating a detection signal FC corresponding to the rotational frequency and rotational phase of the capstan motor 4 is provided.

The reproduced signals from the rotating rads la and 1b are converted into a one-channel reproduced RF signal by a reproduction switching circuit (not shown), and are taken out to an output terminal 7 via a reproduction amplifier 6, and are also supplied to an envelope detection circuit 8. be done. An envelope signal Se of the reproduced RF signal is obtained from the envelope detection circuit 8, and this envelope signal Se is supplied to a synchronous detection servo circuit 9, an envelope servo circuit 10, and a maximum value detection circuit 11.

The synchronous detection servo circuit 9 is supplied with the sine wave signal SW for wobbling generated by the signal generation circuit 12 via the phase correction circuit 13, and the synchronous detection servo circuit 9 receives the sine wave signal Sw and the envelope signal Se. is synchronously detected, and a phase error signal Ss for tracking control having a polarity and level according to the tracking deviation is formed by the synchronous detection. The phase correction circuit 13 is provided to compensate for a delay until the capstan motor is modulated by the sine wave signal Sw. Envelope servo circuit 1
0, a tracking control signal is formed according to the level ENV of the envelope signal Se. Maximum value detection circuit 1
1 is the maximum value M of the level ENV of the envelope signal Se
AX is detected, and the detected maximum value MAX is supplied to the envelope servo circuit IO. The envelope servo circuit 10 has an envelope signal level ENV of the maximum value MA.
A tracking control signal is formed so that

A phase error signal SS from the synchronous detection servo circuit 9 is supplied to one input terminal 15a of the switch circuit 14. A tracking control signal from the envelope servo circuit 10 is supplied to the other input terminal 15b of the switch circuit 14. The tracking control signal selected by the switch circuit 14 is supplied to an adder circuit 16 and added to the speed error signal.

The switch circuit 14 is controlled by the output signal of the AND game 17. The output signal of the timing generation circuit 18 and the output signal of the timing generation circuit 19 are supplied to the AND gate 17 .

The output signal of the speed reference correction circuit 20 is supplied to the timing generation circuit 18 . The phase error signal Ss formed by the synchronous detection servo circuit 9 is integrated, and the integrated value is supplied to the speed reference correction circuit 20.

This integral value corresponds to the speed deviation (referred to as speed deviation) between the recording and reproducing speeds of the magnetic tape 3.

Speed deviation is likely to occur when the VTR used for recording and the VTR used for reproduction are different sets.

If there is no speed deviation, the phase envelope signal S
The integral value of s is O.

The output signal of the speed reference correction circuit 20 is supplied to the speed error detection circuit 21, and the reference value for detecting speed errors is corrected. The speed error detection circuit 21 includes a rotation detector 5.
Detection signal FG generated from is supplied. Since this detection signal FC has a frequency proportional to the rotational speed of the capstan motor 4, the speed error detection circuit 21
The speed of the capstan motor 4 detected from the period of the detection signal FC is compared with a speed reference to form a speed servo signal. This speed servo signal is supplied to an adder circuit 16. An adder circuit 16 adds the tracking control signal from the switch circuit 14 and the speed servo signal.

A signal indicating that the above-described speed reference correction has been completed is supplied to the timing generation circuit 18, and the timing generation circuit 1
8, a timing signal is generated which becomes high level when the speed reference correction is completed. Further, in the maximum value detection circuit 11, the maximum value M of the envelope level ENV
A signal indicating that the detection of AX has been completed is generated, and this signal is supplied to the timing generation circuit 19. The timing generation circuit 19 generates a timing signal that becomes high level when the detection of the maximum value MAX is completed. Therefore, the output signal of the AND gate 17 changes from low level to high level when the speed reference correction and maximum value MAX detection are completed.

During the rising period of the capstan motor 4 when the operation mode of V 'I' H changes from stop to regeneration, the output signal of the AND gate 17 is at a low level, and the AND gate is in a steady period where tracking control can be performed by the envelope servo. The output signal of gate 17 is at high level. Therefore, in the rising period, the synchronous detection servo circuit 9
Tracking control is performed by the envelope servo circuit 10 during the steady period.

The output signal of the adder circuit 16 is supplied to an adder circuit 24 via a phase compensation circuit 22 and a servo amplifier 23. The phase compensation circuit 22 is provided to control the phase characteristics of the servo loop, and the servo amplifier 24 is provided to control the gain characteristics of the servo loop. The adding circuit 24 is supplied with the wobbling sine wave signal Sw from the signal generating circuit 12 via the switch circuit 25. The switch circuit 25 is turned on during a rising period when the output of the AND gate 17 is at a low level, and turned off during a steady period when its output is at a high level. The output signal of the adder circuit 24 is sent to the drive amplifier 26.
is supplied to the capstan motor 4 via. The capstan motor 4 runs the magnetic tape 3 at a constant speed using a tracking control signal and a speed servo signal so as not to cause a tracking error. In the rising period,
Since the switch circuit 25 is turned on and the sine wave signal Sw is used to drive the capstan motor 4, the rotational speed of the capstan motor 4 is modulated by the sine wave signal Sw. The frequency of the sine wave signal Sw is selected to be low enough to be followed by the capstan motor 4.

In one embodiment of the present invention described above, the portion surrounded by the broken line in FIG. 1 can be a digital configuration using a microcomputer. In the case of microcomputer control, the operation is controlled as shown in the flowchart shown in FIG.

At the time of mode transition (startup of the capstan motor 4) in which the operation of the VTR changes from stop to playback, the phase error signal Ss formed by the synchronous detection servo is supplied to the adder circuit 16, and the synchronous detection servo is started (step 31). )
.

The phase error signal Ss obtained by the synchronous detection servo is integrated (step 32). From this integrated value, the direction of the speed error and its absolute value are detected (step 33). With this detection, the speed reference is corrected. (Step 34).

Next, the envelope level ENV is detected (step 35), and when the capstan motor 4 starts up,
As the rotary heads la and 1b scan across a plurality of tracks, the envelope level ENV changes, and its maximum value MAX, which occurs when there is no track deviation, is detected (step 36), a speed reference. After the correction of MAX and the detection of the maximum value MAX are completed, the servo system is switched from synchronous detection servo to envelope servo (step 37). In the subsequent steady period, tracking is controlled by envelope servo (step 3B). ), VT
The R reproduced video signal is normally muted during the rising period, and the correction of the speed reference and the detection of the maximum value MAX are completed within this meeting period. Therefore, the control of the switch circuit 14 may be performed in correspondence with the muting period.

b. Synchronous detection servo method FIG. 3 shows an example of the synchronous detection servo circuit 9.

An envelope signal Se is supplied from the envelope detection circuit 8 to an input terminal 41 . A synchronous detection circuit 43 is connected to the input terminal 41 via a bypass filter 42 . A sine wave signal Sw for wobbling is supplied from an input terminal 44 to the synchronous detection circuit 43 . Synchronous detection circuit 43
The output signal is supplied to a low-pass filter 45, and a phase error signal Ss for tracking control is taken out at an output terminal 46.The 0-phase error signal Ss is supplied to an integration circuit 47, and an integral output for speed reference correction is output. terminal 48
It is taken out.

Since the capstan motor 4 is vibrated by the sine wave sin ωt, the envelope signal Se contains tracking information θ(L), and if sin(ω is 10(t)
)It can be expressed as. From the synchronous detection circuit 43, sin ωtXsin(ωt+θ(t))='/, (
cos (-θ(t))-cos(2ωt+θ(t))
A phase error signal Ss expressed as is obtained. By passing this phase error signal Ss through the low-pass filter 45, twice the frequency component is removed.

Therefore, from the low-pass filter 45, 'Acos(-
A phase error signal Ss represented by θ(t)) is obtained.

Detection of a tracking error by the synchronous detection servo circuit 9 will be described with reference to FIGS. 4 and 5. In FIG. 4A and FIG. 5A, T indicates a part of the track formed on the magnetic tape 3, and H indicates a rotating track la or lb.
shows the scanning trajectory of

During the rising period of the capstan motor 4, the sine wave signal Sw is supplied to the adder circuit 24 via the switch circuit 25, so the rotational speed (tape speed) of the capstan motor 4 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 the diagonally shaded area where the track T and the scanning locus H overlap, a reproduced RF signal is obtained from the track, as shown in FIG. 4B. From the envelope detection circuit 8, Fig. 4C
An envelope signal Se shown in is generated, and the envelope signal Se is passed through the bypass filter 42 to the synchronous detection circuit 4
3. Further, a sine wave Sw for wobbling is supplied to the synchronous detection circuit 43. This sine wave Sw is converted into the pulse signal shown in Figure 4 in the synchronous detection circuit 43 and multiplied by the envelope signal Se, so the synchronous detection circuit 43 generates the output signal shown in Figure 4. do. This output signal is supplied to the one-pass filter 45,
A phase error signal Ss shown in FIG. 4F is generated from the low-pass filter 45. When there is no tracking error,
The phase error signal Ss is zero.

On the other hand, as shown in FIG. 5A, when there is a tracking error (that is, when the center of the track T and the center of the scanning locus H do not coincide), the RF signal shown in FIG. 5B is generated, An envelope signal Se shown in FIG. 5C is obtained. Since this envelope signal Se is multiplied by the pulse signal shown in Figure 5, the synchronous detection output shown in Figure 5 is generated. Therefore, as shown in FIG. 5F, a phase error signal Ss is obtained from the low-pass filter 45, with a polarity corresponding to the direction of the track deviation and a level corresponding to the track deviation.

Phase error signal Ss generated by the synchronous detection servo circuit 9
As shown by the solid line 49a in FIG.
The maximum level is reached when it is equal to p. If there is a deviation in the speed of the magnetic tape 3, a tracking deviation indicated by Δ occurs, as indicated by a broken line 49b in FIG. In order to prevent this deviation from occurring, the speed reference correction circuit 20
is provided.

C. Envelope servo system The envelope servo circuit 10 performs tracking control by utilizing the fact that the envelope level ENV changes in accordance with tracking deviation. The envelope servo method will be explained with reference to FIGS. 7, 8, and 9.

In FIG. 7, the head width and track pitch Wp of the rotary heads 1a and 1b are made equal, and the positional relationship between the scanning position of the rotary head 1a and the track Ta is shown in FIG. 7 and described below. It can take a state.

(2) A state in which a track Tau on the upstream side having the same azimuth as the target track TaO is partially scanned.

(2) A state in which only the upstream track with an azimuth different from the target track TaO is scanned.

(2) A state in which the upstream side of the target track TaO is partially scanned.

IV, ) Target track TaO without racking shift
The state to scan.

(2) A state in which the downstream side of the target track TaO is partially scanned.

(2) A state in which only the downstream track with an azimuth different from the target track TaO is scanned.

(2) A state in which a track Tan on the downstream side having the same azimuth as the target track TaO is partially scanned.

Reproduction RF in each of the states ■ to ■ shown in FIG.
The envelope level ENv of the signal changes as shown in FIG. 8, with the tracking shift toward the upstream side being in the positive direction. Using the maximum value MAX of the envelope level ENV as a target value, the tape speed is controlled and tracking deviation is corrected. That is, when the tracking is shifted to the upstream side as in the state (■), the arrow Vt-
As shown by arrow Vt+, the magnetic tape 3 is decelerated, and when the tracking is shifted to the downstream side as in the state (2), the magnetic tape 3 is accelerated as shown by the arrow Vt+.

FIG. 9 is a flowchart showing a more specific operation of the envelope servo circuit 10. In the envelope servo circuit 10, for example, it is determined for each field whether the tape running is in an accelerated state, that is, whether the tracking control output CXn of the current field is positive (step 51). Next, the envelope level ENVn of the reproduced RF signal of the current field is compared with the envelope level ENVn-1 of the previous field (steps 52 and 5).
3) Based on the determination results in steps 51, 52, and 53 described above, the tracking state is classified into the following four types, and a tracking control signal is generated according to each state.

When the tape is accelerating and the envelope level ENV is increasing, it is in a tracking state as shown by ■ in FIG. 8, and it can be determined that it is being controlled in a stable direction. Therefore, a positive tracking control command for acceleration is output so that the control continues in the same direction (
Step 54).

When the tape is accelerating and the envelope level ENV is decreasing, it is in a tracking state as shown by ■ in FIG. 8, and it can be determined that the control is in the opposite direction to the stable direction. Therefore, a tracking control command of negative polarity for deceleration is outputted so as to be controlled in a stable direction (step 55).

When the tape is being decelerated and the envelope level ENV is increasing, it is in a tracking state as shown by ■ in FIG. 8, and it can be determined that it is being controlled in a stable direction. Therefore, a negative tracking control command for deceleration is output so that the control continues in the same direction (
Step 56).

When the tape is decelerating and the envelope level ENV is decreasing, it is in a tracking state as indicated by V in FIG. 8, and it can be determined that the tape is being controlled in the opposite direction to the stable direction. Therefore, a royal tracking control command for acceleration is output so that the control is performed in a stable direction (step 57).

An error signal is output in accordance with each of the control commands in steps 54 to 57 (step 58).

d. Modified example Furthermore, it is not limited to mode transition from stop to playback, but also when switching between short time recording mode (SP mode) and long time recording mode (LP mode) in the middle of one tape. The present invention can be similarly applied to transitions at switching points, transitions at splicing points of tapes that are spliced together, and the like.

〔Effect of the invention〕

In this invention, tracking control is performed by the synchronous detection servo during the rising period after the transition of the operation mode of the VTR from the stop state to the playback state, and tracking control is performed by the envelope servo after the rising period. Therefore, tracking can be stabilized in a short time by synchronous detection servo, and in the steady period, envelope servo is performed based on the maximum value detected during synchronous detection servo, so highly accurate control can be achieved. Furthermore, it is possible to prevent the problem of the reproduced image shaking due to wobbling during the steady period.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of this invention, and FIG. 2 is a flowchart used to explain the operation of an embodiment of this invention.
Figure 3 is a block diagram of an example of a synchronous detection servo circuit, Figure 4
Figures 5 and 5 are route maps used to explain tracking error detection using synchronous detection servo, Figure 6 is route map used to explain speed deviation correction, and Figures 7 and 8 are route maps used to explain tracking error detection using envelope servo. The route map used in the explanation and FIG. 9 are flowcharts used in the explanation of the envelope servo. Explanation of main symbols in the drawings la, lb: rotating head, 3: magnetic tape, 4: capstan motor, 8: envelope detection circuit, 9: synchronous detection servo circuit, 10: envelope servo circuit, 14.25: switch circuit .

Claims (1)

[Claims] In a rotary head type playback device in which a rotary head scans diagonal tracks formed on a tape to reproduce video signals, the speed of a capstan motor is wobbled by a signal of a predetermined frequency. a first tracking control means for generating a tracking control signal by synchronously detecting an envelope signal of the reproduced RF signal reproduced by the rotary head with the wobbling signal; a second tracking control means that generates a control signal; during a rising period after the mode transition, the first tracking control means performs tracking control, and during a steady period after the rising period, the second tracking control means performs tracking control; 1. A rotary head type playback device comprising: means for switching to perform tracking control using the means.