JPS5818827B2 - Servo system of magnetic recording/reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo system applied to a magnetic recording and reproducing apparatus that performs recording and reproduction by scanning a magnetic tape in a helical manner using a rotating dodeo head.

This type of magnetic recording/reproducing device has a function for recording and reproducing by running the magnetic tape at a certain standard speed (hereinafter referred to as "standard mode"), and a function for recording and reproducing by running the magnetic tape at a certain standard speed (hereinafter referred to as "standard mode"), and a function for recording and reproducing by running the magnetic tape at a certain standard speed (hereinafter referred to as "standard mode"). It is equipped with a function to run a magnetic tape for recording and playback (hereinafter referred to as "low speed mode"), and also allows a magnetic tape recorded in one mode to be mutually played back in another mode. Some have a still mode in which the tape is stopped and played back.

In the standard mode, the rotational phase of the video head is determined by comparing the sampling pulse obtained from the vertical synchronization signal separated from the input video signal or the control signal recorded in advance with the slope wave obtained from the phase detection pulse indicating the rotational state. This is done by controlling the oscillator according to the voltage difference.

Further, in the low-speed mode, a reference voltage is generated, and the oscillator is fixed at a substantially constant level using the reference voltage, thereby maintaining the rotation of the video head.

When recording in low-speed mode, the speed of the magnetic tape is reduced to 1/n (n is a positive even number) of the standard mode, and one field of information is sampled for every n fields of the video signal. So-called skip recording is performed.

When recording in low speed mode, control signals are recorded on the magnetic tape in advance so that playback can be performed in standard mode.

In the standard mode, the prerecorded control signal uses a pulse generated every other time of the vertical synchronization signal, but in the low speed mode, the pulse generated every (2rr-1) times of the vertical synchronization signal is recorded by a fixed head.

A detailed example of a device that performs recording and playback using this method is as follows:
“Television Technology 1975 1” published by Denshi Gijutsu Publishing Co., Ltd.
It is also described in pages 115 to 122 of ``Ren Endi Ji Special Issue (Video Technical Guide)''.

However, when the control signals recorded in this manner are used during reproduction, the following problems occur.

When a magnetic tape recorded in the low speed mode is played back in the standard mode, the video head scans between adjacent image recording tracks, and thus scans across the unrecorded guard band.

As a result, a noise band appears prominently in each field of the reproduced signal, making the reproduced reimage difficult to see.

Further, a similar phenomenon occurs when a magnetic tape recorded in the standard mode is stopped and reproduced by detecting a control signal.

Such a phenomenon can be explained in FIGS. 1 and 2.

FIG. 1 shows recording tracks 1, 2, . . . on a magnetic tape recorded in low speed mode. . . 6 is shown in the standard mode.

■-■ are the recording positions of vertical synchronization signals on recording tracks 1°2, . . . 6, and albl, cl and a2t
b2. c2 indicates the recording position of the leading edge and trailing edge of a control signal consisting of pulses with a period of % of the vertical synchronizing signal, and during playback, the leading edge al.

The signal parts b, , cl are used.

Also, arrow A is the scanning direction of the video head, and arrow B is the scanning direction of the video head.
is the running direction of the magnetic tape.

Now, if this magnetic tape is scanned and reproduced in standard mode by a video head that rotates in synchronization with the reproduced control signal, the video head will move recording tracks 1, 2, and so on.・・・
- 6 means scanning routes 10 and 20 shown by diagonal lines with different slopes.

That is, the video head tracks recording tracks 1, 2, . ...
6, the S/N ratio decreases in parts where the scanning ratio is large, and noise panning appears on the playback screen.

FIG. 2 shows a state in which recording tracks 1'+2'l, . . . , 6' on a magnetic tape recorded in the standard mode are reproduced in the still mode.

If the leading edge a'1 of the control signal is detected and the magnetic tenip is stopped, the video head reproduces and scans the path 0', so the scanning ratio of the guard band increases, and the same noise band as mentioned above occurs. appear on the screen.

The present invention aims to improve the above-mentioned phenomenon, and its basic idea and an example of a circuit for implementing the same will be described later in comparison with a conventional system.

Conventionally, when recording in standard mode, a pulse was obtained using a vertical synchronization signal separated from a composite video signal, and this pulse was recorded as a control signal.

At this time, the rotation servo of the video head obtains a sampling pulse with a small pulse width that is delayed by 2 tv (TV: vertical synchronization) with respect to the leading edge of the pulse whose frequency is divided by i.
This has been done by controlling the oscillator using the error voltage generated by comparing the slope part of the trapezoidal wave obtained from the pulse from the rotational phase detector.

In addition, when reproducing something recorded in standard mode in standard mode, a pulse corresponding to the leading edge of the control signal at the time of recording is emitted from above the magnetic tape, and a sampling pulse with a small pulse width (delayed by 2 tv) is then generated. The rotational phase of the video head has been controlled by controlling the oscillator using the error voltage generated by forming the trapezoidal wave and comparing it with the slope of the trapezoidal wave, as in recording.

Furthermore, when recording in low-speed mode, a control signal is recorded on the magnetic tape so that the positional relationship is similar to that when recording in standard mode, and the rotational phase of the video head is controlled when playing back in standard mode. It is used for.

In contrast, in the present invention, this is carried out as follows.

. (1) Recording and playback in standard mode When recording in standard mode, the vertical synchronization signal separated from the composite video signal is stored for a certain period of time t.

(<2 tv), and each frequency-divided pulse is recorded as a control signal in the same manner as in the conventional method.

Also, the rotational phase of the video head during recording is 1/2 of this
It is controlled by an error voltage obtained by comparing the sampling pulse, which comes at a position where the leading edge of the frequency-divided pulse is delayed by 2 tv tl, and the slope part of the trapezoidal wave.

As a result, the rotational phase during recording is controlled by pulses having the same phase relationship as in the prior art.

Next, when reproducing a magnetic tape recorded in the standard mode in the standard mode, a reproduction pulse corresponding to the leading edge of the control signal delayed by t is obtained, and then delayed by 2tvt1. A sampling pulse is generated and compared with the slope of the trapezoidal wave to control the rotational phase of the video head in the same way as during recording.

Therefore, the results of recording and reproducing operations in the standard mode will be performed normally without any change from conventional methods.

(2) Reproducing standard mode recording in still mode The pattern diagram shown in FIG. 3 was recorded in standard mode.

The recording position of the control signal is delayed by tl from the conventional position.

If the magnetic tape is stopped by detecting the pulse obtained from the leading edge b1 of the control signal (a waveform obtained by differentiating the control signal during recording) in order to still reproduce the information on recording track 3, the magnetic tape will move t from the conventional stopping position. , it will stop after a long delay.

At this time, if the video head scans the recording track 3' as shown in path 20', a satisfactory still reproduced image can be obtained.

(3) Recording and reproduction in low speed mode When recording in low speed mode, the control signal records a pulse obtained by dividing the frequency of the vertical synchronizing signal by 1/(211-1), as in the conventional case.

The rotational phase of the video head is determined in the same manner as in the prior art based on a sampling pulse generated at a position delayed by 2 tv from the vertical synchronizing signal.

When reproducing low-speed mode recording in low-speed mode, the rotational phase of the video head is controlled by the output of an oscillator based on a reference voltage, and is controlled independently of the control signal on the magnetic tape.

Therefore, the recording and reproducing operations in the low-speed mode can achieve the predetermined purpose without changing the delay t1 of the vertical synchronizing signal.

(4) Reproducing low-speed mode recording in standard mode The pattern diagram shown in FIG. 4 was recorded in low-speed mode, and is substantially the same as that in FIG. 4.

When reproducing this in the standard mode, a pulse based on the leading edge al lbl IC1 of the control signal is made into a sampling pulse delayed by 2 tv tl by the standard mode servo circuit and compared with the slope part of the trapezoidal wave.

By doing so, the rotational phase of the video head is 2t.
The sampling pulse delayed by v-tl is used as a reference, and in other words, the video head rotates at a phase that is tl ahead of the phase when standard mode recording is reproduced in standard mode.

At this time, the video head scans paths 10, 20, and 30, and a satisfactory playback screen is obtained without crossing the guard band.

The delay time t for operating as described above may be determined so that the scanning paths of the video head in the standard mode, low speed mode, and still mode intersect at the center of the recording track.

FIG. 5 is an explanatory diagram for determining this condition, where θ1 is the angle formed by the scanning path of the video head and the tape running direction in the low speed mode or still mode.

Further, θ2 is the angle formed between the scanning path of the video head and the tape running direction in the standard mode, and t is the angle formed by dropping a perpendicular line from the midpoint of the recording track onto the line V-v indicating the position of the recording vertical synchronization signal. Show distance.

P is the pitch between tracks.

Let tx be the distance at which the video track path intersects the ■-■ line in both modes, that is, the distance the magnetic tape travels in the standard mode with respect to time t1, then t t θ-θ□ △θ Ax2□-□2t・□γt・-・ tanθt tanθ2 θ1・θ2 θ2
'.

Here, the speed P of the magnetic tape in standard mode is is 60・□, so the time t is, Ko-D It will be given as.

FIG. 6 is a block diagram of a servo circuit of a magnetic recording/reproducing apparatus to which the present invention is applied.

What is essentially different from the conventional circuit is that a new circuit 50 has been added and the delay times of the sections 58 and 63 have been changed.

Motors 90, 93, and 94 are shown in this figure, and motor 90 is a synchronous motor that rotates the video head.

Further, motors 93 and 94 are used to rotate the cap screen and reel, and motor 94 is a synchronous motor that is driven in a standard mode, while motor 93 is a pulse motor that is driven in a low speed mode.

53 is a fixed head for recording and reproducing control signals, and 59a and 59b are detection heads for detecting the rotational phase of the video head.

Switches 56a, 56b, 56c, 56a56e
$- and 56f are switches for setting the standard mode and low speed mode, which are switched in conjunction with each other to set the standard mode and low speed mode.When connected to the contact a side, the standard mode is selected, and when the contact is connected to the closed side, the low speed mode is selected.

The switches 54a and 54b are interlocking switches for setting recording and reproducing operations, and when they are on the contact REC side, the recording operation is performed, and when they are on the contact PB side, the reproducing operation is performed.

Furthermore, the switch 91 is a switch for setting a still mode, and can be switched during low speed mode playback to perform still playback.

The configuration of this circuit will be described below along with its operation.

When recording in standard mode, switch 56a to 56
f is connected to the contact a side, and switches 54a and 54
Connect b to the contact REC side.

Therefore, the pulse motor 93 for low speed mode is separated from the drive source and stopped by the switch 56e, and the magnetic tape is fed by the motor 94.

In this state, the terminal 49 has 6 signals separated from the composite video signal.
The 0 vertical interval signal to which the 0 Hz vertical synchronizing signal (Fig. 7 A) is applied is applied to the delay circuit 50, and becomes the synchronizing signal (Fig. 7 Ex) delayed by a time t, and is converted from a monostable multi-by-break. The voltage is applied to the divide-by-1 circuit 51.

The output of the circuit 51 becomes a 30Hz control signal (FIG. 7C) and is applied to the buffer amplifier 52, switch 56a,
54b, and is recorded on a control track on the magnetic tape by the control head 53.

In addition, the output of the frequency dividing circuit 51 (FIG. 7C) is output from the switch 5
4a to a monostable multi-by-break 58.

This circuit 58 functions to determine the switching phase of the video head during recording, and performs tracking adjustment during playback.

During playback, the duty cycle of the output pulse (Fig. 7 2) can be varied, but during recording, the output pulse with a predetermined duty cycle is sent out in a preset state. has been done.

Next, the output of the circuit 58 is applied to a time base correction circuit 63 including a differentiating circuit and a multi-by-break, and a sampling pulse (see Fig. 7) is taken out.

On the other hand, pulses indicating the rotational phase of the video head are taken out from the detection heads 59a and 59b and sent to the flip-flop 6.
Trigger 0.

This pulse is generated when a pair of video heads is just about to start recording or playback operation.

The flip-flop 60 thereby sends out pulses of opposite polarity, one of which (FIG. 7 H) is given to the trapezoidal wave generating circuit 61, which obtains a trapezoidal wave (FIG. 7) and gives it to the phase comparator 62. It will be done.

The phase comparator 62 compares the slope part of the trapezoidal wave (7th diagram) with the pulse delayed by 2 tv obtained from the vertical synchronization signal, and applies an error voltage generated according to the difference to the oscillator 77 to adjust its output frequency. Controls 480Hz.

The output of the oscillator 77 is divided into 1/8 by a frequency divider 78 to become a 60 Hz pulse, which is then applied to the head motor 90.

Further, the output of the multi-by-break 58 is given to the pulse detection circuit 64, and when the synchronization signal is cut off, the output connects the reference voltage generation circuit 65 to the oscillator 7T, thereby preventing abnormal rotation of the head motor 90. .

As can be seen from FIG. 7, conventionally, the control signal (including the broken line part of FIG. 7 C) is obtained directly from the vertical synchronization signal (FIG. 7 A) and recorded, and the sampling pulse is generated in the circuits 58 and 63. (Fig. 7 G) was obtained.

In contrast, in the present invention, in order to obtain sampling pulses at the same position, a vertical synchronizing signal (see FIG. 7) delayed by a time t1 is generated in advance by a delay circuit 50.

As a result, a control signal (solid line in FIG. 7) is obtained and recorded, and at the same time, the remaining 2 tv tl delay is obtained by circuits 58 and 63.

When reproducing a magnetic tape recorded in the standard mode as described above in the standard mode, the switches 54a and 54b are switched to the PB side.

The pulse taken out from the control head 53 is in the form of a differentiated control signal (FIG. 7C) during recording, and is sent to the multi-by-break 58 via a switch 54b, amplifiers 55A, 55B, and switches 56b, 54a.
give to

Therefore, if tracking adjustment and time axis correction are not taken into consideration, the same sampling pulse as shown in FIG.

The output obtained by comparing this with the trapezoidal wave (seventh diagram) controls the oscillator 77 in the same manner as during recording, and rotates the head motor 90.

The control signal during playback is delayed by t, but it is delayed by 2tv t1 by circuits 58 and 63 and finally becomes a sampling pulse with a delay relationship of 2tv, so the servo circuit works in the same way as during recording.

Also, at this time, the output of the flip-flop 60 is at the terminal 57.
．． 158 to a video signal reproduction system circuit, and is used to alternately switch the outputs of the pair of video heads.

When playing back a magnetic tape recorded in the standard mode in the still mode, the switches 54a and 54b are switched to the PB side, and the switches 56a to 56f are switched to the contact side to first perform playback in the low speed mode. .

That is, the motor 94 stops and the pulse motor 9
The heather is driven.

It is recorded when in low speed mode.

The control signal is not used for rotation of the motors cut off by switch 56b and therefore pulse detector 64
The reference voltage generation circuit 65 is coupled to the oscillator 77.

The oscillator 77 oscillates using a predetermined stable reference voltage and rotates the head motor 90 via the frequency dividing circuit 78.

Also, the output pulse of 480 Hz from the oscillator 77 is controlled by the switch 56.
The pulse motor 93 is connected to the gate circuit 80 via e.
is applied to the drive circuit 92 to rotate the motor 93 at a predetermined speed.

As a result, the magnetic tape runs at a low speed and the video head scans the recording tracks overlappingly, resulting in a reproduced image in slow motion.

When the switch 91 is closed in this state, the first control signal that comes immediately after that is sent to the switch 54b and the amplifier 55A.
and triggers flip-flop 79 via switch 91.

The output of the circuit 79 had previously opened the gate circuit 80, but upon arrival of the control signal it changes to a voltage that closes the gate circuit 80.

As a result, the pulse motor 93 is stopped, and the video head scans the same recording track while the magnetic tape is stopped, thereby reproducing the still image.

In this case, since the magnetic tape is shifted from the conventional recording position of the control signal, it stops later than the conventional stopping position.

As a result, the video head can scan without crossing the guardband.

When the switch 91 is reset, the flip-flop 79 is reset, the gate circuit 80 is opened, and the pulse motor 93 is driven again to perform slow motion reproduction.

When recording in the low speed mode, the switches 54a and 54b are connected to the REC side, and the switches 56a to 56f are switched to the contact side.

In this case, the rad motor 90 is rotated in the same manner as in the standard mode.

Further, the pulse motor 93 is controlled by the oscillator 7 based on a sampling pulse delayed by 2 tv from the vertical synchronization signal.
7 output).

If a pulse obtained by dividing the vertical synchronization signal by 2 is recorded as a control signal during low-speed mode recording, it will be recorded densely on the magnetic tape, which will be inconvenient as the servo circuit will not be able to follow it when playing back in standard mode. .

Therefore, when recording in the low speed mode, the control signal number must be recorded in accordance with the tape speed and by selecting the relative position of the video signal recording track.

Therefore, the output pulse of the flip-flop 60 (FIG. 7H) triggered by the output of the phase detection heads 59a and 59b and the drive pulse of the head motor 90 (FIG. 7N) are used.

That is, send both pulses to the Nant gate 66 7711,
When both pulses are at the low level at the same time, a pulse (see FIG. 7) which becomes bi is obtained and applied to the V4 frequency divider circuit 67.

The divided pulse (Figure 7) is a monostable multi-bibreak 7
2 to obtain a gate signal (see FIG. 7) that sufficiently covers one field of the video signal.

This gate signal is applied to the video signal recording system circuit from the terminal 73 and is used to gate the recording signal for one field, and is also applied to the NAND circuit 74 during which the vertical synchronizing signal (see Fig. 7) is applied. Gate b).

The gated vertical synchronization signal (see FIG. 7) is used as a trigger pulse for the monostable multi-bi break 75, which causes the circuit 75 to generate a pulse (see FIG. 7) as a control signal.

This pulse is recorded on the control track by the control head 53 via the buffer amplifier 76, switches 56a and 54b.

This control signal is not delayed by time t1 and is recorded at the same position as the conventional recording relationship, and a time constant is set in the circuit 75 so that it has the same pulse width relationship as the standard mode recording when reproducing the standard mode. is selected.

When reproducing a magnetic tape recorded in the low speed mode in the low speed mode, the switches 54a and 54b are switched to the PB side, and the switches 56a to 56f are on the contact side.

The head motor 90 is rotated by the output of an oscillator 77 determined by the operation of the reference voltage generating circuit 65, and the magnetic tape is run by a pulse motor 93.

That is, this is the same as the intermediate low-speed mode operation described in the case of reproducing standard mode recording in still mode.

However, this place. In this case, the skip recording information will be reproduced.

When reproducing a magnetic tape recorded in the low speed mode in the standard mode, the magnetic tape is driven by a motor 94.

The head motor 90 is controlled and driven by sampling pulses generated based on pulses obtained from recorded control signals.

In other words, since it appears as a pulse whose phase is advanced by time t1 from the control signal during standard mode recording,
The sampling pulse (eighth) given to the phase comparator 62
(alternative to t) also has an advanced phase of t,
As a result, the rotational speed of the oscillator 77 is synchronized in a decreasing direction.

This changes the scan path of the video head and provides an image that does not cross the guardband, as previously discussed.

[Brief explanation of the drawing]

1 and 2 are plan views showing the recording pattern on the magnetic tape and the scanning path of the video head by the conventional servo method, FIGS. 3 and 4 are the same plan views by the method of the present invention, and FIG. An explanatory diagram of the dimensions on a magnetic tape for setting the conditions of the method of the present invention, FIG. 6 is a block configuration diagram of a servo circuit of a magnetic recording/reproducing apparatus to which the present invention is applied, and FIG. FIG. 3 is a timing chart diagram showing waveforms. 1 to 6... Recording track by low speed mode recording, 10.20... Scanning path of video head by standard mode playback, ala2, bl-b2,
cl-c2...Control track, 1'
〜・・・−・Recording track by standard mode 1 recording,
20'... Scanning path of the video head during still mode playback, t,... First delay time, 50
・・・・・・Circuit that delays the vertical synchronization signal by tl, 5
8 and 63...Control, No. 4 2t
v −t A circuit that generates a sampling pulse delayed by 1.

Claims (1)

[Scope of Claims] 1. A standard mode in which a magnetic tape is scanned in a helical manner by a rotating video head, and the magnetic tape is run at a single speed to sequentially record or reproduce continuous fields of video signals; a low-speed recording mode in which the magnetic tape is run at an even-numbered speed, and a field of video signals is sampled and recorded at the same rate as the reduction rate of the tape speed, and the recorded magnetic tape is in a similar low-speed running state. and a still mode in which the mode is stopped and a selected recording field is reproduced, so that the magnetic tape recorded in the standard mode and the low speed mode can be reproduced in both modes. In the standard mode and low speed recording mode, the rotation of the video head is controlled by a vertical synchronization signal or a prerecorded control signal, and in the low speed playback mode and still playback mode, the rotation of the video head is controlled by a predetermined reference voltage. In a magnetic recording/reproducing apparatus which is controlled depending on Repeat the second pulse
obtaining a sampling pulse by delaying it by a delay time of , and controlling a rotational servo of the video head in accordance with an output of a difference obtained by comparing the sampling pulse with a gradient wave obtained from a detection pulse indicating a rotational phase of the video head; When recording in the low-speed mode, pulses obtained without delaying the vertical synchronizing signal are taken out and recorded on the control track according to the field sampling ratio, and the video signal is recorded in accordance with the output of the difference between the gradient wave and the sampling pulse. When reproducing the magnetic tape recorded in the low-speed mode in the standard mode by controlling a rotation servo of a head, the reproduction control signal based on the undelayed pulse is delayed by the second delay time. The rotation servo of the video head is controlled by the output of the difference obtained by comparing the obtained sampling pulse with the gradient wave, and when the magnetic tape recorded in the standard mode is reproduced in the still mode, the first delay is performed. Running on the magnetic tape is stopped at the position where a playback control signal delayed by a certain amount of time is detected, and the scanning path of the video head during all of the playbacks actively straddles between recording tracks on the magnetic tape where video information is recorded. A servo system for a magnetic recording/reproducing apparatus, characterized in that the first and second delay times are set so that the delay time does not occur.