JPS59156085A - Head switching signal generating device of vtr - Google Patents

Abstract

PURPOSE:To adjust switching timing of a rotary head automatically by comparing saw-tooth waveform level having wave height corresponding to rotation speed of the rotary head and waveform level obtained by sample holding the peak value of the waveform and voltage dividing the hold output according to the number of rotary head. CONSTITUTION:Output side of a saw-tooth wave generating circuit 10 is connected to an inversional terminal of a comparator 13. The comparator 13 makes voltage divided output of a voltage dividing circuit 12 reference input and makes saw-tooth wave output of the saw-tooth wave generating circuit 10 comparative input, and compares the two inputs. A head switching signal forming circuit 8 switches to the first rotary head H1 side at timing by which output of high level is given from the comparator 13, and forms the first head switching signal that enables driving of the first rotary head during continuation of output of the high level. Further, it switches to the second rotary head H2 side at timing by which output of low level is given, and forms the second head switching signal that enables driving of the second rotary head H2 during continuation of the low level output.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for generating a signal for switching a plurality of signal recording/reproducing rotary heads provided in a video tape recorder (VTR) when the rotary heads for recording and reproducing signals are sequentially switched and driven. Regarding the generating device.

-G is a helical scan type rotating 2-head VT.
In R, as shown in Fig. 1, two rotating heads H1° are installed in the cylinder 1 via the head bar 2 at a distance of 1800 mm, and the cylinder 1v' is rotated about half a circumference along its slit. The video tape 3 is wound around the video tape 3, and one rotary head H,, H2i'l running on the video tape 3 is in a driving state, and the other rotary head H,, H2 is rotating alternately so that it is in a non-driving state. The heads H, , H, are switched and driven.

In order to detect the timing of such head switching, conventionally, the detection magnetic pole 4, which is interlocked with the rotation of the rotary heads H, H2, is connected to the cylinder 1@1. When the detection magnetic pole 4 passes, a drum tack pulse (DTP) is generated.
) A detection coil 5 is provided opposite the magnetic pole 4 to generate a pulse voltage. By the way, if the detection magnetic pole 4 and coil 5 are deviated from their normal mechanical mounting positions, it becomes impossible to accurately detect the timing of head switching. For this reason, conventionally, a first mono multivibrator 6 is provided on the output side of the detection coil 5, and mechanical installation errors can be electrically adjusted by controlling the time constant of this mono multivibrator 6. I'm trying to make it possible. Also, V
In addition to changing the running speed of the videotape 3, the TR has the rotating head
There is a device in which the rotational speed of the rotary head is also changed in order to correct the shift in the period of the horizontal synchronizing signal when the 3.degree. head scans the signal recording track of the video tape 3. In the special playback mode of this type of VTRK, since the rotational speed of the rotating heads H, H2 changes, the rotating heads H, H,
, H2 must be adjusted, but in the conventional system, a second mono multivibrator 7 is provided, and the time constant of this mono multivibrator 7 is controlled to adjust the head switching signal of the head switching signal forming circuit 8. It regulates the formation of 9 is a head drive circuit, and 1o is a head changeover switch circuit. However, in this type of adjustment, it is difficult to accurately determine the time constant in accordance with the head switching timing, making it difficult to perform accurate head switching adjustment.

The present invention has been made in view of the above circumstances, and when changing the rotational speed of the rotating head in the special playback mode, the switching timing of the rotating head is automatically adjusted to follow this change. The purpose is to do so.

In order to achieve such an object, the present invention creates a sawtooth waveform having a peak value corresponding to the rotational speed of the rotating head, samples and holds the peak value of this waveform, and converts this hold output into the number of rotation nodes. The levels of each waveform formed by corresponding voltage division are compared, and each rotary head is switched and driven based on the comparison output.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 2 is a circuit diagram of this embodiment, and parts corresponding to those in FIG. 1 are given the same reference numerals. The VTR of this embodiment has a cylinder 1 shaped like a tea caddy.

Inside this cylinder 1, two rotating heads H, , H2 are arranged. Cylindrical rotating heads H, + H2 (ri) are arranged 180° apart by being fixed to each end of the head bar 2. This head par 2 is fixed to the shaft of a head motor (not shown) in the center of the cylinder 1. The cylinder rotating heads H, H2 are slightly exposed to the outside of the cylinder 1 through the slit around the cylinder 1, and are brought into contact with the video tape 3.The video tape 3 is inserted along the outer circumference of the cylinder 1. 1. As a result, when the rotary heads H, , H2 rotate half a turn, the video signal is recorded on the video tape 3 as a diagonal trunk, and the recorded video signal is also played back. The arrow A indicates the running direction of the videotape 3, and the arrow B indicates the running direction of the videotape 3.
indicates the rotation direction of the rotary heads H, , H2.

This/Linda111! A magnetic pole 4 for head switching timing detection, which rotates integrally with the rotary heads H, H2, is attached to l. A detection coil 5 that faces this magnetic pole 4 and induces a DTP voltage when this magnetic pole 4 passes
is installed. In the figure, the mounting positions of the magnetic pole 4 and the coil 5 are shown schematically for convenience of explanation. Therefore, a DTP voltage is induced in the detection coil 5 every time the rotation knobs H, , H2 rotate once. This DTP voltage is applied to the mono-multivibrator 6 as a trigger voltage for the mono-multivibrator 6. The output waveform of the mono-multivibrator 6 has a rising speed according to its time constant, and by controlling this time constant, the error in the mechanical attachment position between the magnetic pole 4 and the coil 5 can be electrically adjusted. .

The output of the monochrome multivibrator 6 is given as a trigger signal to a sawtooth wave generation circuit 10 and a peak sample and hold circuit 11. The sawtooth wave generation circuit 10 generates a sawtooth wave output having a peak value corresponding to the input period of the trigger signal, that is, the rotational speed of the rotary head, while the peak sample/hold circuit 11 outputs a sawtooth wave having a peak value corresponding to the input period of the trigger signal, that is, the rotational speed of the rotary head. It is designed to sample and hold and generate this hold output. On the output side of the peak sample and hold circuit 11, there is provided a circuit 12 for dividing this output into voltages corresponding to the number K of rotating heads (two in this embodiment). This voltage dividing circuit 12 includes a resistor 121 having the same resistance value,
122 are connected in series, and the connection point C is connected to the non-inverting terminal of the comparator 13. The output side of the sawtooth wave generating circuit 10 is connected to the inverting terminal of the comparator 13. This comparator 13 uses the divided voltage output of the voltage dividing circuit 12 as a reference input, uses the sawtooth wave output of the sawtooth wave generation circuit 10 as a comparison input, and compares the power of both people.
When the divided voltage output is larger than the sawtooth wave output, a high level output is derived, and when the divided voltage output is smaller than the sawtooth wave output, a low level output is derived. The output of the comparator 13 is given to the head cut signal forming circuit 8. This head switching signal forming circuit 8 switches to the first rotary head H1 side at the timing when a high level output is given from the comparator 13, and makes the first head switch possible to drive the first rotary head H1 while the high level output is maintained. Forms a signal, and also switches to the second rotary head horse side at the timing when a low level output is given, and forms a throat switching signal to the second rotary head horse that enables driving of the second rotary head horse while the low level output is maintained. do. The illustrated switching of the head switching circuit 10 is based on the first head switching signal. In this switch changeover, head drive circuit 9 td, g 1 rotation head H1 (f
tn, and the first rotating head H1
It is shown that the device can record and reproduce signals on the video tape 3.

Next, the operation will be explained with reference to the signal waveforms of each part shown in FIG. In FIG. 3, A is the waveform of the DTP signal generated by the detection coil 5, and B is the waveform of the mono multivibrator 6.
C is the waveform of the output signal S2 of the sawtooth wave generation circuit 10 and the waveform of the output signal S3 of the sawtooth wave generation circuit 10, and
1 and the waveform of the output signal S4 of the voltage dividing circuit 12 and the voltage dividing signal S of the voltage dividing circuit 12.
The waveform of No. 5 is shown.

D shows the waveform of the output signal S6 of the comparator 13.

As is clear from each waveform diagram, if the rotational speed of the rotary heads H1, H2 decreases due to the special playback mode, for example,
Both forces of comparator 13 S3. The level of S5 also changes following this speed change. Therefore, the period of head switching timing is automatically adjusted in accordance with the rotational speed of the rotary head.

FIG. 4 is a circuit diagram of another embodiment, and FIG.

Portions corresponding to those in FIG. 2 are given the same reference numerals.

What should be noted in this embodiment is that it is a four-rotary head system in which there are a total of four rotary heads, designated H, H2, Tow, and H4.

This third. The fourth rotating head holder is fixed to the end of the H4 head dobber 2'. 1st. The head par 2 to which the second rotating head H1° horse is fixed and the head par 2' are structured to rotate together. Each rotating head H1~
H4 is arranged in the cylinder 1 with a 90° interval maintained between the two head pars 2 and 2'. The videotape 3 is wound around the outer periphery of the cylinder 1 to an extent that it slightly exceeds seven turns of the cylinder 1. The rotary head rotates, and the time for one rotation of the rotary head is set to be one field of the video signal. What should be further noted in this embodiment is that the voltage dividing circuit 12 is
It is constructed by connecting four resistors 121 to 124 in series, each having the same resistance value, and each connection point c,
, c2. c3 is each comparator 13°13', 13
" is connected to the non-inverting terminal of each converter (lator 13.
The inverting terminals of 13' and 13" are commonly connected to the sawtooth generating circuit 1.
0 output side. 14 is a DTP signal controlled by the head switching signal forming circuit 8.
This is a pulse gate circuit that controls the passage of signal S1.

The operation of the embodiment shown in Fig. 4 will be explained with reference to the signal waveform diagram of each part in Fig. 5. Figure 5 (A) (B) (C)
CD) corresponds to (A), (B), and (C) in FIG. 3, respectively. FIG. 5(A)' shows the waveform of the output signal S of the pulse gate circuit 14, and this output signal Sf triggers the mono multivibrator 6 once every three rotations of H1 to H4. This is given as a signal.This is because the head is switched every time each rotary head makes one revolution, so the rotary head must make three revolutions before the head is switched to drive the same rotary head again. This is because in Fig. 5(C), S
3 and 84 are the respective output waveforms of the sawtooth wave generation circuit 10 and the peak sample/hold circuit 11 as in FIG. 3(C), and s5. sj and s5' are output waveforms at each connection point CI+C2+03 of the voltage dividing circuit 12. The level of the output waveform at each of the connection points C1, C2, and C3 divides the level of the output signal S4 of the peak sample and hold circuit 11 into four equal parts. This quarter is
This is because it is necessary to switch the heads four times to equalize the switching timing of each rotary head and to drive the same rotary head again. In Figure 5 (g)), SH2 is for the second rotating head, and SH3 is for the third rotating head.
To the rotating head, S H is the first rotating head H1
, S H indicates the waveform of each head switching signal from the head switching signal forming circuit 8 for the fourth rotary head H4. Therefore, the same rotary head is switched and driven by the head switching signal from the head switching signal forming circuit 8 once every three rotations. Also,
Even if the rotational speed of the rotary head decreases in the special playback mode and the period of the DTP signal S1 becomes longer as shown in FIG. 4, the peak value and peak sample of the sawtooth wave output S3 will be The hold value of the hold output S also increases. Therefore, the period until the same rotary head is switched again and driven becomes longer, and at the same time, the time during which the same drive head is driven becomes longer. Therefore, no matter how the rotational speed of the rotary head changes, the switching timing of each rotary head is automatically adjusted to follow this change. Note that in FIG. 4, the head changeover switch circuit and head drive circuit are not shown.

Each of the above embodiments has been described applying to a two-rotation head system and a four-rotation head system, but can be similarly applied to a rotary n-head system (where n is the number of bacteria of 6 or more). Needless to say.

As described above, according to the present invention, the sawtooth wave output has a peak value corresponding to the rotational speed of the rotating head, the peak value of this waveform is sampled and held, and the held output is divided corresponding to the number of rotating heads. The level of each waveform generated by the rotation is compared, and each rotary head is switched and driven based on this comparison output, so when the rotation speed of the rotary head is changed in a special playback mode, for example, this change Correspondingly, since the peak value of the sawtooth waveform changes, the level of each waveform obtained by dividing the hold output also changes.

Therefore, as the rotational speed of the rotary head changes, the comparison output that determines the switching timing of the rotary head changes accordingly, and as a result, the switching timing of the rotary head can be automatically adjusted.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional example, FIG. 2 is a circuit diagram of an embodiment of the present invention, FIG. 3 is a signal waveform diagram for explaining the operation of FIG. 2, and FIG. 4 is a circuit diagram of another embodiment. FIG. 5 is a signal waveform diagram for explaining the operation of FIG. 4. 1.../Linda, 3...Video tape, 4...Magnetic pole, 5
...Detection coil, 8...Head switching signal forming circuit, 1
0: Sawtooth wave generation circuit, 11: Peak sample/hold circuit, 12: Voltage dividing circuit, 13: Comparator, H4: Rotating head. Patent applicant: ROHM Co., Ltd. Agent: Kazuhide Okada, patent attorney

Claims (1)

[Claims] +1) A circuit that generates a sawtooth wave having a peak value corresponding to the rotation speed of the rotating head, a circuit that samples and holds the peak value of the output waveform of this sawtooth wave generation circuit, and an output of this sample and hold circuit. a circuit that divides the voltage equally according to the number of rotating heads, a comparator that compares the levels of the output of this voltage dividing circuit and the output of the sawtooth wave generation circuit, and a circuit that forms a head switching signal based on the output of this comparator. A VTR switching signal generator comprising: