JPS6036949Y2 - video tape recorder - Google Patents

Description

[Detailed description of the invention] The present invention is a video tape recorder that uses video magnetic tape recorded in the American and Japanese television standards to be viewed on European standard television receivers and monitors. It is related to.

The American and Japanese television standard system has 52 scanning lines.
The number of scanning lines is 5 lines/second and the number of fields is 60 lines/second, whereas in the European standard system, the number of scanning lines is 625 lines/second and 50 lines/second.

In addition, both standard systems can be applied to any television receiver or monitor by adjusting the heirs of horizontal synchronization and vertical synchronization.

Furthermore, there are also television receivers that automatically switch between these settings.

Therefore, the tapes recorded in the United States and Japan were brought to Europe using a videotape recorder (rVTR).
It is called J.

), it is thought that it will be possible to play it on ordinary European television receivers.

However, in reality, there are the following problems.

When recording one field's worth of signals on a track on a magnetic tape by helical scanning with two heads arranged at 180 degrees, the head rotation speed should be set at 30 Hz for the American and Japanese standard systems. There is.

On the other hand, the European standard system uses 25 Hz.

Therefore, when playing a tape recorded in the United States or Japan in Europe, the VT used in Europe
All you have to do is change the rotation speed of the R head from 25Hz to 30Hz.

However, in general, VTRs are driven by motors that are synchronized with the power supply frequency, so if the head, like the cap screen and reel stand, is also rotated by the same motor, the pulley in the motor transmission mechanism must be replaced. It's very troublesome.

This project was proposed in order to solve these problems.The motor used to rotate the head of a VTR is dedicated, and the rotation speed can be easily changed by slightly changing the constants of the servo circuit. , and can provide an operation with less mistracking.

In addition, recent European color television receivers and monitors are equipped with NT switching circuits for PAL signals.
Automatically or manually stop when receiving SC signal,
Some devices are now available that can also play NTSC signals.

Therefore, these receivers and monitors and the proposed VTR
By combining this, it becomes possible to playback tapes recorded in NTSC in color in Europe.

Furthermore, in the present invention, the rotational speed can be changed only by changing the constants of the servo system, so it is easy to switch not only manually but also automatically by detecting the recorded content on the tape and switching.

In general, a helical scanning type VTR has two magnetic heads on the outer periphery of a rotating disk or rotating cylinder at a 180° angle.
It is fixed in position.

A servo system that rotationally controls a rotating body of a rotating disk or a rotating cylinder generates a pulse (hereinafter referred to as a "tack pulse") in synchronization with the rotation of a motor that drives the rotating body.

), this pulse forms a trapezoidal wave with a slope part set with a predetermined phase relationship and time constant, and during recording, the phase of this trapezoid is compared with the pulse obtained from the vertical synchronization signal, and during playback, a magnetic The control pulses recorded on the tape and the trapezoidal wave are phase-compared, and the rotation of the motor is controlled using an error voltage based on the phase difference.

This operation process can be explained using the circuit diagram of FIG. 1 and the waveforms of FIG. 2, which are shown as an embodiment of the present invention.

In FIG. 1, the operation during recording will first be explained.

Reference numeral 101 denotes a terminal to which a vertical synchronizing signal (see FIG. 2) separated from the video signal in the recording system circuit diagram is applied.

The vertical synchronizing signal is applied to the down converter 102 and becomes a rectangular wave having a frequency 172 times the vertical frequency.

One of the outputs of the downgrader 102 (the opening in FIG. 2) is recorded on a control track on the magnetic tape by a control head 103 via a recording/reproduction changeover switch SWo.

Further, the other output of the down converter 102 (see FIG. 2) is applied to a switch circuit 104.

There is a differentiation circuit on the input side of the switch circuit 104, and a second
The square wave in the figure is differentiated and only the negative pulse (2 in Figure 2) is passed.

The pulse thus passed through the switch circuit 104 is applied to the tracking multivibrator 105, triggering the monostable multivibrator and generating the asymmetric rectangular wave shown in FIG. 2(e).

The duty cycle of this circuit 105 can be adjusted by a variable resistor VR□ for tracking during reproduction.

The asymmetrical rectangular wave extracted from this (FIG. 2(e)) is applied to the correction circuit 106.

The circuit 106 is a monostable multi-bibreak triggered by a negative pulse (to FIG. 2) obtained by differentiating an asymmetric square wave (FIG. 2(e)) on the input side.

The function of this circuit 106 is to prevent ringing from occurring at the resonance point of the motor's transfer function, and therefore the bandpass filter 1 passes only the frequency components near the resonance point.
The error voltage is fed back through 18 as described below, and the duty cycle of the output pulse (FIG. 2-g) is controlled.

The output of the circuit 106 (FIG. 2) is the output of the sampling circuit 1
07, and after differentiation, it becomes the waveform shown in Fig. 2 (h).

In the circuit 107, only when the negative part of the differential wave (FIG. 2 H) arrives, a positive pulse (FIG. 2 H) is generated as an output, and this is applied to the phase comparator 108.

On the other hand, the rotational phase detector or tack head 109, 10
The pulses taken out alternately from 9' (Figure 2) are applied to the flip-flop 110, and the 2 pulses with opposite phase relationship are applied to the flip-flop 110.
Different types of rectangular waves are taken out from terminals 111 and 111', respectively, and are used to alternately switch the video information obtained from the two rotary heads during playback, and for other purposes such as AGC.

One of the rectangular waves (shown in Figure 2) is the trapezoidal wave shaping circuit 1.
12, where a trapezoidal wave (see FIG. 2) is generated and applied to the phase comparator 108.

The slope of this trapezoidal wave and the sampling pulse (second diagram)
are compared, and a DC voltage is extracted according to the level difference between the two.

This DC voltage, that is, the error voltage, is determined so that the reference value is when the sampling pulse (Figure 2) is located exactly at the center of the slope of the trapezoidal wave (Figure 2). It is made to be in synchronization with the rotation speed.

The error voltage taken out from the phase comparator 108 is applied to a DC amplifier 113 and processed to the correction circuit 106 through a bandpass filter 118 that passes only frequency components near the resonance point of the motor transfer function.

The error voltage amplified by the DC amplifier 113 is applied to an oscillator 114 consisting of an unstable multivibrator.

The oscillator 114 has an oscillation frequency of 50 Hz in the case of a European type, and its phase is controlled by an error voltage so as to synchronize with the vertical synchronizing signal (FIG. 2A) during recording.

Then, the output of the oscillator 114 (second figure, y) is applied to the synchronous motor M via each amplifier 115, 115'.
Rotate at Hz.

Next, referring to FIG. 1, the operation during reproduction will be explained.

As the magnetic tape runs, the control head 103 takes out the evening pulse (control signal) in FIG. 2 via the switch SWQ.

This pulse is applied to the switch circuit 104 via the amplifier 116, and only the negative component (FIG. 2B) is extracted.

Since the signal waveforms are similar to those shown in FIG. 2, these waveforms will be explained below.

During playback, the running of the tape is the time reference, and if there is a lot of wow and flutter, the control signal will also fluctuate on the time axis, affecting the rotational phase of the motor and increasing the jitter on the screen.

Furthermore, due to uneven rotation of the head motor itself, the rotary head does not faithfully scan the video track on the magnetic tape, causing noise components on the reproduced screen.

For this reason, tracking adjustment is required as described above.

On the other hand, since the tape feeding speed is fixed depending on the standard television system, the cause of variations in the rotation of the head drum is the rotational phase of the rotary head drum.

Therefore, the effect is a change in the phase of the tack pulse as shown by the arrow in FIG.

Among these, if the rotation speed of the rotary head drum does not match the standard television system for playing back from tape, and the motor that drives the rotary head drum is completely out of synchronization, causing a tracking error, switch SW2 The rotational speed of the motor is changed to match the standard television system played from the tape, and at the same time the duty cycle of the tracking multivibrator 105 is adjusted by the 10B voltage given by the variable resistor VRl, and its output is adjusted. The correction is made by changing the frequency of the pulse (FIG. 2(e)) and the trailing edge of the output pulse.

In addition, the time axis fluctuation of the error voltage of the phase comparator circuit 108 is processed by the correction circuit 106 as its output pulse (FIG. 2).
Corrected by changing the trailing edge of

Then, the frequency of the oscillator 114 is changed by the error voltage until the sampling pulse (second figure) driven into the slope part of the trapezoidal wave (Figure 2 w) reaches the center position of the slope, and the rotation of the motor is controlled and synchronized. create a state.

As mentioned above, signals based on the European standard system are normally recorded or played back.

Here, when a magnetic tape on which American and Japanese standard signals are recorded is reproduced, the VTR is switched by the following operation.

For example, when the frequency is set to 50Hz by a variable resistor VH2 in the oscillator 114, the switch SW
2 to the contact N side, the variable resistor VR3 is connected in parallel.

Therefore, the oscillation frequency can be changed from 50Hz to 60H by the voltage determined by the parallel connection of variable resistors VR2 and VR3.
It can be changed to z.

In this case, the variable resistors VR2 and VR3 can be considered to be inserted in the path of the above-mentioned error voltage.

As the frequency changes, the frequency of the trapezoidal wave also changes, but at this time, the slope of the trapezoidal wave has a certain time width set by a predetermined time constant, and this time width remains constant regardless of the frequency change. Since the frequency is constant, when the frequency changes, the duty ratio of the trapezoidal wave will also change.

Then, as the frequency changes, the phase relationship between the tack pulse, which is the reference signal of the trapezoidal wave, and this slope part cannot maintain the state before the frequency change, so they are taken out from the control head 103 and subjected to phase comparison. The sampling pulse position with respect to the sampling pulse (second diagram) applied to the oscillator 108 is disturbed, and the error voltage does not reach the desired value.
14 is incorrectly controlled.

As a result, the rotating head no longer accurately tracks the recording track.

Therefore, in order to eliminate this problem, the 10B voltage applied to the variable resistor VR1 for tracking adjustment via the resistor R
2.

If the playback information is changed in this way, switch SW □
, SW2 may be switched together to change the frequency and correct mistracking.

In FIG. 1, a circuit is provided which automatically performs the means for switching the switch SW and SW2.

Since the control signal is half the frequency of the vertical synchronization signal, it is 25 Hz in the European standard system, and 30 Hz in the American and Japanese standard systems.

Therefore, the locked oscillator 2 oscillates the control signal (see FIG. 2) reproduced by the control head 103 at a frequency of 25 Hz via the buffer 201.
02, oscillation will occur when the control signal is 25 Hz, but oscillation will stop when the control signal is 30 Hz.

The output of the locked oscillator 202 is rectified and applied to a control circuit 203 such as a Schmitt circuit.

The circuit 203 generates a positive control voltage when there is an output from the locked oscillator 202, and is at zero level when there is no output from the oscillator 202.

This control voltage operates the relay 204 and switches SW
1. The contact of SW2 is switched.

Note that it is also possible to configure the relay 203, switches sw, sw, etc. with electronic switching circuits.

As described above, the present invention is extremely practical as it allows tapes recorded with video signals of different formats to be played back on a single VTR.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a servo system circuit of a VTR according to an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the general operation of the circuit shown in FIG. M... Motor for rotating head, 105...
・Tracking multivibrator, VR□・・・・・・
・Variable resistor for tracking adjustment, SWl...
Constant change switch, 114...Oscillator, VH
2 and VH3... variable resistor for setting the oscillation frequency, SW2... switch for changing the oscillator constant, 201... buffer, 202...
...Track oscillator, 203...Control circuit, 204...Relay.

Claims (1)

[Scope of utility model registration request] A rotary head for recording video signals for one field on one track of a magnetic tape by helical scanning, means for generating a rotational phase signal of the rotary head, and a frame (or field) based on a control signal reproduced from the magnetic tape. means for obtaining a periodic signal; adjustable first delaying means for performing tracking adjustment by delaying the frame (or field) periodic signal; and further delaying the signal delayed by the first delaying means. a second delay means configured to obtain a delay amount exceeding a frame (or field) period in total; and a rotational phase signal of the rotary head and a second delay means.
means for controlling the oscillation frequency of an oscillator according to an error signal obtained by phase comparing the output signals of the delay means; a rotary head drive motor whose rotation speed is determined according to the oscillation frequency of the oscillator; a first switch for changing the amount of delay required by the delay means; a second switch for changing the center frequency of the oscillator; The magnetic tape is switched so that the format recorded on the magnetic tape and the format during playback are the same for each of the television standard formats having different numbers of scanning lines and fields per unit time. video tape recorder.