JPS5823658B2 - Trucking Seigiyosouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking control device suitable for use in tracking servo of a VTR.

Some conventional rotary magnetic head type VTRs are designed to perform tracking servo together with rotary servo, capstan servo, etc. of the rotary head.

A tracking servo is used to accurately scan a rotary head over a recording track during reproduction, and FIG. 1 shows an example of a conventional tracking servo circuit.

When recording a video signal on a magnetic tape, a pulse signal is recorded on a CTL rack as a control signal (hereinafter referred to as a CTL signal) for each field in accordance with the number of rotations of a rotary head.

During VTR playback, this CTL signal is sent to CTL playback head 1.
The signal is reproduced by the frequency divider 2 to become a 60 Hz pulse signal, which is further frequency-divided by the frequency divider 2 to become a 30 Hz CTL signal.

This 30 Hz CTL signal is then delayed by approximately half a cycle of the rotating head by a delay circuit 3 such as a monomulti, and
Furthermore, the delay time is adjusted by the variable delay circuit 4, and the second
This signal becomes the CTL signal shown in Figure A, and this signal is transmitted to the gate circuit 5.
is added as a gate signal to

On the other hand, during reproduction of a VTR, the head 6at6b of a pulse generator, for example, is taken out according to the rotation of the rotary head.
The 60 Hz signal (hereinafter referred to as the PG multiplied signal) is frequency-divided by the frequency divider 7 to become the 30 Hz PG multiplied signal shown in FIG. 2B.

Based on this 30Hz; PG multiplied signal, the trapezoidal wave generation circuit 8
As a result, a 30 Hz trapezoidal wave signal shown in FIG. 2C is obtained.

This trapezoidal wave signal is sampled in the gate circuit 6 by the delayed CTL signal.

The magnitude of this sampled voltage EO corresponds to the phase difference between the CTL signal and the rotating head, and this voltage is held in the holding circuit 9.

If the rotating head is correctly scanning the recording track when the CTL signal and the PG multiplied signal have the relationship shown in FIG. 2A and B, the DC output voltage of the holding circuit 9 will be a trapezoidal wave The sampling voltage Eo of the signal is used as a reference, and increases or decreases according to the phase difference.

The DC output voltage including this variation then passes through a low-pass filter 10 to become a brake voltage, which is applied to the brake coil 11 of the rotary head drive motor.

In such a tracking servo circuit, since the reference voltage Eo differs depending on the magnetic tape, this Eo is
It is necessary to set o.

Conventionally, to make this setting, for example, while looking at the screen, manually adjust the variable delay circuit 4 to move the position of the CTL signal, and then, when the screen is in the best condition,
It was assumed that the phases of each signal had the relationships shown in FIG. 2, A, B, and C.

The present invention is capable of automatically setting the reference voltage EO, and by moving the relative position between the recording track of the recording medium and the reproduction head, the maximum amplitude of the reproduction signal is detected and held. Then, by moving the relative position in the opposite direction, the amplitude of the reproduced signal is detected, and this amplitude is compared with the maximum amplitude held above, and the relative position when the two match is set as the control standard. This is a dot.

The present invention will be explained below with reference to the drawings.

First, the principle of the present invention will be explained.

In the tracking servo circuit shown in Fig. 1 mentioned above, if the rotary head advances by the PG times signal τ, the phase of the trapezoidal wave signal also advances by τ as shown in Fig. 2, but at this time, the phase is not sampled by the CTL signal. The voltage becomes the reference voltage EO.

Similarly, if the PG multiplied signal is delayed by τ, the position of the trapezoidal wave signal will also be delayed by τ as shown in FIG. 2E, and the voltage sampled at this time will also be EO.

In such a case, the rotary head will be controlled based on the wrong phase, and the screen will be in its worst condition at this time.

Therefore, in such a servo circuit, the maximum lead and maximum delay are set to τ, and the phase variable range of the CTL signal by the variable delay circuit 4 is set to ±τ.

Next, in Figure 3, the delayed 30 shown in Figure A
Hz CTL signal (same as in Figure 2A),
Create a sawtooth wave signal as shown in figure B, and also
τ from the TL signal.

Assume that a gate signal as shown in C in the same figure is generated with a delay of 1.

Furthermore, the PG signal from the pulse generator at this time is delayed to produce a PG□ signal as shown in the same figure, which is matched in phase with the gate signal.

Assume that the CTL signal is now at the position relative to the trapezoidal wave signal in the second diagram, that is, the maximum advance τ position, and control is being performed.

This state continues until the first and second CTL signals in FIG. 3A, and the level of the sawtooth signal with respect to the position of the gate signal during this period is El.

Next, from this state, this C between the 3rd to 7th CTL signal
When the phase of the TL signal is suddenly delayed by 2τ, that is, when the state shown in the second diagram is changed to the state E, the phase of the gate signal is also delayed by 2τ, as shown by the dotted line in FIG. 3C.

The level of the sawtooth signal with respect to the position of this delayed gate signal changes from E1 to E2.

Accordingly, based on the principle shown in Fig. 1, the phase of the PG1 signal is controlled to match the gate signal and is changed as shown by the dotted line in Fig. 3, but there is a certain time delay due to the transient response of the servo loose. For example, the CTL signal coincides with the gate signal at the sixth point in time.

Until the above PG1 signal matches the gate signal, the first
The brake control voltage of the servo circuit in the figure is El.

However, during this time it passes through a point where the correct control reference voltage Eo is obtained, and at this passing point a, the rotary head scans the entire width of the recording track, so the reproduction output is as shown in Fig. 3E. The maximum value Ep is obtained as follows.

After this, if the CTL signal and gate signal are suddenly advanced by 2τ to return to the second state, the PG1 signal will follow this and return to its original position after a certain time, and during this time the playback output of the rotating head will be The maximum output Ep is reached again at point b in FIG. 3E.

Therefore, the initial maximum voltage Ep at point a is held, and then the maximum voltage Ep at point b is detected and compared in level with the held voltage at point a, and at this time, the sawtooth wave sampled by the gate signal is If the voltage of the signal is used as the tracking control voltage, the control reference point can be automatically determined depending on the magnetic tape of the seed.

Next, an embodiment of the tracking control device according to the present invention based on the above-mentioned principle will be described with reference to FIG.

In FIG. 4, 12 is a tracking servo circuit similar to that in FIG.

Reference numeral 13 denotes a sawtooth wave oscillator, which is used to obtain the sawtooth wave signal shown in FIG. 3B in synchronization with the CTL signal from the delay circuit 3.

14 is τ.

The gate signal shown in Figure 3C is obtained using a delay monomulti.

15 is a 2τ delay monomulti, which obtains a gate signal delayed by 2τ as shown by the dotted line in FIG. 3C.

SL is a switch for switching between the two gate signals, and 16 is a gate circuit which samples the sawtooth wave using the gate signal.

17 is a holding circuit for holding the sampled voltage.

S2 is a switch that is closed for a predetermined time until a control reference point is set, and 18 is a delay circuit for obtaining the PG signal shown in the third diagram.

19 is a video signal detection circuit which obtains the envelope signal shown in FIG. 3E from the video signal reproduced by the rotary head.

A gate circuit 20 samples the envelope signal using the gate signal.

A holding circuit 21 holds the sampled voltage.

S3 is a switch that is closed for a predetermined time, and 22 is a peak holding circuit that holds the peak voltage Ep at point a in FIG. 3E.

23 is a comparison pulse generation circuit which compares the voltage at point a and the voltage at point b and generates one gate pulse when both have the same value.

A gate circuit 24 samples the sawtooth signal using the gate pulse.

A holding circuit 25 holds the sampled voltage.

S4 is a switch which is switched from contact a to contact after a predetermined time, and this movable contact is connected to the delay time control terminal of the variable delay circuit 4.

Next, the operation of the above configuration will be explained.

When starting the VTR, switches S1 and S4 are closed to the contact a side, and switches S2. S3 is closed.

When the rotating head is rotated to run a magnetic tape (both not shown), the 60 Hz CTL signal reproduced by the head 1 is divided into 30 Hz by the frequency divider 2, and further delayed for a predetermined time by the delay circuit 3. So, 30Hz in Figure 3A
This becomes the CTL signal.

Based on this CTL signal, the sawtooth wave oscillator 13
The sawtooth wave signal shown in Figure B is oscillated, and the next stage gate circuit 16
Add to.

Also, the above CTL signal is a mono multi-14 signal with τ.

3, resulting in the gate signal shown in FIG. 3C.

This gate signal causes the gate circuit 16 to sample the voltage E1 shown in FIG. 3B, and this voltage E1 is applied to the holding circuit 1.
7 and is applied to contact a of switch S4.

On the other hand, the servo circuit 12 performs the servo control described with reference to FIG. 1, and at this time, the voltage E1 is applied to the variable delay circuit 4 from the contact point of the switch S4.

As a result, the rotary head is rotated at approximately the maximum advance, and the delay circuit 18 outputs the PG1 signal shown in the third diagram.

The above states correspond to the second to second states of the CTL signal in FIG.

Next, when the switch S1 is switched to contact from the above state and the monomulti 15 is connected, the CTL signal applied to the gate circuit 16 is suddenly delayed by 2τ, so this gate circuit 16
The voltage sampled at changes from El to E2 (3rd
Figure B).

This voltage E2 is the contact a of the holding circuit 11 and switch S4.
The rotary head also attempts to be delayed by 2τ by being applied to the variable delay circuit 4 via the servo circuit 12, but due to the transient response of the servo circuit 12, the delay becomes 2τ after 1 to 2 seconds.

Along with this, the PG1 signal also moves as indicated by the dotted line in Figure 3-C during the 1 to 2 seconds mentioned above, and passes through point a in Figure 3E during this time.

At this time, the envelope signal of the video signal from the detection circuit 19 sampled by the PG1 signal has a maximum value Ep.
This voltage Ep is held by the peak holding circuit 22.

Then, when the switch S1 is switched to contact a again and the monomulti 14 is connected, the voltage E1 is applied to the variable delay circuit 4.

Following this, the rotating head and PG1 signal are again 1 to 2.
during which the PG1 signal is
The maximum value Ep is sampled again when passing the point.

This voltage Ep is applied to the comparison pulse generation circuit 23 via the holding circuit 21, and the peak held voltage E at point a is
compared with p.

When the voltages at point a and point b are equal, this comparison pulse generation circuit 23 outputs a gate pulse, and the gate circuit 24
is opened and the voltage level E of the sawtooth voltage from the sawtooth oscillator 13 at this point.

is sampled and held in the holding circuit 25.

At this time, if the switch S4 is switched to contact, the holding voltage Eo is applied to the variable delay circuit 4, so that the CTL signal, the PG multiplied signal and the trapezoidal wave signal follow the rotating head and the PG multiplied signal. The relationships shown in FIGS. A, B, and C are established, and the servo circuit 12 is able to perform servo operation with a correct control reference point set.

After this, the switch S3 is opened and the holding voltage E of the holding circuit 25 is maintained.

is continuously applied to the variable delay circuit 4, so that
The servo circuit 12 can perform servo operations while always setting a correct control reference point.

5A, B, C, D, and E show the operation timing of each switch 81 to S4 in the above operation, and FIG.
As a start signal, for example, the above-mentioned reference voltage E is applied to the VTR.

Either provide a push button to automatically determine the operation and generate it by pressing the push button, or use a pulse that starts the VTR and indicates that the servo circuit 12 has operated, such as a video muting OFF pulse. I can do it.

Further, the timing of the switch S□ can be determined by, for example, determining the time for the servo to follow using a monomulti, and operating this monomulti using the start signal to operate the switching element.

Also, switch S2. S3. S4 can be switched by inverting the flip-flop with a start signal and operating the switching element.

In addition, in the figure E, the comparison pulse generation circuit 23 generates the maximum value E at point b.
This shows a gate pulse that is output when p is detected and matches the voltage at point a.

Although the case where the rotation of the rotary head is controlled by the servo circuit 12 has been described above, the present invention can also be applied to the case where a cab stan servo is performed.

The present invention is equipped with a phase comparison circuit 8,4.5 that performs a phase comparison between a reference signal (PG multiplied signal and a reproduction signal), and based on the output of this phase comparison circuit, the relative relationship between the recording track on the recording medium and the reproduction head is determined. The tracking control circuit configured to control the positional relationship includes a sawtooth wave generation circuit 13 that generates a sawtooth wave in relation to the reproduction CTL signal, and a sawtooth wave generation circuit 13 that generates a sawtooth wave in relation to the reproduction CTL signal, and a maximum value Ep of the reproduction signal from the reproduction head and a maximum It has a value holding circuit 20, 22, and an amplitude comparison circuit 23 that compares the amplitude of the output of this holding circuit and the reproduction signal from the reproduction head, and during operation, the sawtooth wave is set at two predetermined points. The gated signal controls the variable delay circuit 4 inserted in the line of the reproduced CTL signal supplied to the phase comparator circuit to determine the relative positional relationship between the recording track and the reproduced track on the recording medium. The maximum amplitude of the reproduction signal from the reproduction head is held by the maximum value holding circuit during shift control in the first direction (advance direction), and the amplitude is forcibly shifted in the second direction (delay direction). During the shift control, the amplitude comparison circuit detects the phase at which the output of the reproducing head becomes maximum, and the amplitude value of the sawtooth wave sampled from the sawtooth wave generation circuit is held based on the detected output, The present invention relates to a tracking device configured to complete its operation by controlling the variable delay circuit using the held amplitude value.

Therefore, according to the present invention, VT
A correct control reference point for the R tracking servo circuit can be automatically set.

[Brief explanation of drawings]

Figure 1 is a conventional tracking servo circuit system diagram, Figure 2 A, B, C, D, and E are waveform diagrams of each part in Figure 1, and Figure 3 A.
, B, C, D, and E are various waveform diagrams for explaining the present invention in detail, FIG. 4 is a circuit system diagram showing an embodiment of the present invention, and FIG. 5 is A, B, C, and D. E is a waveform diagram showing the timing of each switch in FIG. 4. In the symbols used in the drawings, 1 is a CTL reproducing head, 4 is a variable delay circuit, 12 is a servo circuit, 13 is a sawtooth wave oscillator, and 14 is τ. 15 is a 2τ delayed monomulti, 19 is a detection circuit, 22 is a peak holding circuit, and 23 is a comparison pulse generation circuit.

Claims (1)

[Claims] 1. A tracking system that is equipped with a phase comparison circuit that performs a phase comparison between a reference signal and a reproduced CTL signal, and is configured to control the relative positional relationship between a recording track on a recording medium and a reproduction head based on the output of this phase comparison circuit. The control circuit includes a sawtooth wave generation circuit that generates a sawtooth wave in relation to the reproduction CTL signal, a maximum value holding circuit that holds the maximum value of the reproduction signal from the reproduction head, and an output of the holding circuit and the reproduction signal. It has an amplitude comparison circuit that compares the amplitude of the reproduction signal from the head, and during operation, the reproduction CTL signal given to the phase comparison circuit is determined by a signal obtained by gating the above-mentioned sawtooth wave at two predetermined points. A variable delay circuit inserted in the track is controlled to forcibly shift the relative positional relationship between the recording track and the reproduction track on the recording medium, and the first
When controlling the shift in the direction, the maximum amplitude of the reproduction signal from the reproduction head is held by the maximum value holding circuit, and the second
During shift control in the direction of , the amplitude comparison circuit detects the phase at which the output of the playback head is maximum, and the amplitude value of the sawtooth wave sampled by the sawtooth wave generation circuit is held based on this detection output. By controlling the variable delay circuit using this held amplitude value,
A tracking device configured to complete the operation.