JPS6118254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to automatic tracking adjustment when reproducing a magnetic tape on which sequentially inclined magnetic tracks are formed by a rotary head, and the scanning locus during reproduction of the rotary head always follows the magnetic recording. The objective is to obtain a high-quality reproduction signal by matching the track.

For example, regarding automatic tracking adjustment during playback in a magnetic recording and playback device that has a rotary head capable of recording and playback and forms sequentially inclined magnetic tracks on a magnetic tape, the scanning trajectory of the rotary head during playback is The objective is to always accurately match the magnetic recording track and obtain a high quality reproduction signal.

Conventionally, in this type of recording and reproducing apparatus, the main Due to the longitudinal expansion and contraction of the magnetic tape, the scanning locus of the rotating head and the recording tape pattern do not match during playback.
Therefore, it has been difficult to obtain a high quality reproduction signal. In addition, in recent years, as the recording density of magnetic recording has become higher, the above-mentioned effects tend to become even more significant.

Therefore, it becomes increasingly difficult to consistently obtain high-quality reproduction signals. This can be explained using a diagram as follows. During recording, data is recorded on the tape T in a recording track pattern TP as shown by the solid line in FIG. If, for example, the tape expands and contracts during playback due to changes in temperature, humidity, etc., compared to when it was recorded, the recorded track pattern TP will be the track pattern shown by the broken line in Figure 1 as each track bends.
T′P, which causes distortion generally called S-shaped distortion. However, since the rotary head scans the magnetic tape during playback as well as during recording, along the track pattern TP in Figure 1, the rotary head output can only be obtained from the shaded area in Figure 1. The quality of the reproduced signal deteriorates. When the recording density is high, the amount of this S-shaped distortion may be larger than the track width, and in that case, the reproduction output of the rotating head is hardly obtained in some places, and the reproduction signal is It becomes unusable for practical purposes.

The present invention provides that the reproduction output of the rotary head during reproduction includes relative position information of the rotary head with respect to the magnetic recording track.For example, if the scanning trajectory of the rotary head during reproduction deviates from the magnetic recording track, the reproduction output of the rotary head will This system is characterized by focusing on the fact that magnetic fields change, and by using the playback output of the rotary head to control the position of the rotary head, the scanning trajectory of the rotary head during playback always matches the magnetic recording track. be.

Therefore, it is of course possible to control the relative position of the rotary head with respect to the magnetic recording track using the reproduction output of the conventional rotary head, but the following example will be explained here. For example, a rotary main head and a rotary auxiliary head provided at a specific position are provided as the rotary head, and the positions of both the rotary main head and the rotary auxiliary head are controlled by the playback output of the rotary auxiliary head during playback. It is also possible to do so.

In such an example of the present invention, an auxiliary rotary head is provided adjacent to a conventional rotary head for recording and reproducing to detect the degree and direction of deviation of the reproducing track from the recording track, and the output of the auxiliary head is used to detect the degree and direction of deviation of the reproducing track from the recording track. , the installation position of the playback head is instantaneously changed so that it scans the recording track curved in an S-shape more accurately during playback, in order to always obtain a high-quality playback signal. It is ideal for density recording rotating head type video tape recorders. First, the principle of the present invention in this case will be explained.

The above-mentioned rotary assistant head is rotated so that when the main head is completely on the recording track, the rotary assistant head is placed only half on the track of the main head. The head is attached at a position shifted in the longitudinal direction by one-fourth of the rotation period of the head, or by the sum of n periods (n: an integer). Therefore, if, for example, on an azimuthally recorded tape pattern,
The recording track (tape pattern) is shown in
TP), if the rotary main head H is completely raised during reproduction, the output of the rotary auxiliary head N will be half of its maximum output. If the main head H at the time of reproduction is shifted to the left with respect to the recording track as shown in FIG. 2B, the output of the rotational compensation head H will be larger than that shown in FIG. 2A. On the other hand, if the main rotary head H is shifted to the right as shown in FIG. 2c, the output of the auxiliary rotary head H will be smaller than that shown in FIG. 2a. Therefore, it is detected whether the output of the rotary auxiliary head h is larger or smaller than half of its maximum output, and the positions of the rotary main head H and the rotary auxiliary head h are simultaneously variably controlled depending on the amount of the difference. If the output of the rotary compensation head h is always set to half of its maximum output, the main head can always faithfully scan the recording track during reproduction, and a high quality reproduction output can be obtained.

Next, a specific example will be described in which an embodiment of the present invention is applied to an azimuth recording helical scan rotating two-head type video tape recorder. FIG. 3 is an example of a block diagram of the above application example. In this example, two rotating main heads (hereinafter referred to as main heads) 1
There are 6 and 18, but their operations are the same, so here we will discuss the pair of main head 16 and rotary auxiliary head (hereinafter referred to as auxiliary head) 17.
Note that an auxiliary head 19 is provided for the main head 18. The main head 16 and the auxiliary head 17 are provided so as to have the relative positional relationship of the main head H and the auxiliary head h in FIG. This corresponds to the case where the center of the auxiliary head 17 is located at one end of the recording track to be reproduced of the main head 16, but the auxiliary head 17 is located at the center of the recording track of the main head 16 to be reproduced. Of course, the center may be located at either end of the recording track that is shifted by an integral multiple of the rotation period of explain.

In FIG. 3, the outputs from the auxiliary and main heads 17 and 16 are first applied to amplifiers 1 and 7, and after being amplified to an appropriate level, amplitude detectors 2 and 8
By detecting the waveform at , and passing it through low-pass filters 3, 4, and 9, a DC voltage proportional to the outputs of the main, auxiliary, and main heads 17, 16 is obtained. Here, the low-pass filter 3 has a relatively short time constant so that amplitude fluctuations in the output of the compensation head 17 can be detected faithfully. On the other hand, the low-pass filter 4 is a filter having an extremely short charging time constant and an extremely long discharging time constant in order to obtain the maximum output of the auxiliary head 17 mentioned above. In general, in a helical scan rotating two-head type video tape recorder, the maximum output (considered to be approximately the maximum output) of the auxiliary head 17 is detected by the aforementioned low-pass filter 4 while the rotation speed reaches a specified number from the beginning of playback. and can be retained.
The outputs of the low-pass filters 3 and 4 are applied to a differential amplifier 5 to extract a voltage proportional to the difference between the instantaneous output of the complementary head and half of the maximum output of the complementary head 17.
In the example shown in FIG. 3, the differential amplifier 5 is configured with two power supplies, plus and minus, so that when the output of the low-pass filter 3 is equal to half the output of the low-pass filter 4, it is zero volts, and when it is larger than that, it is zero volts. Negative voltage, when it is small, positive voltage is obtained. This output is applied to the drive amplifier 6 and amplified to a level that can also drive the head control element 15. This head control element 15 is capable of moving both the main and auxiliary heads 16 and 17 in the direction of adjacent tracks with respect to the recording track to be reproduced. It is sufficient that the relative position with respect to the recording track to be reproduced can be controlled; for example, it is possible to control the movement of the main and auxiliary heads 16 and 17 in a direction that has a component in the direction of the rotation axis, especially in the direction of the rotation axis itself. Anything that can be done can be put to practical use.

Here, a bimorph, which is a type of piezoelectric element, is used as the head control element 15, and the main and auxiliary heads 16 and 17 are provided in a fixed relationship to realize the above-mentioned movement control.

It goes without saying that the head control element 30 is provided with the main and auxiliary heads 18 and 19 in the same manner as the head control element 15 is provided with the main and auxiliary heads 16 and 17. By grounding one of the two electrodes of this element 15 and connecting the other to the output of the drive amplifier 6, one pole of the bimorph can have a positive or negative polarity depending on the position of the auxiliary head 17. Since a voltage is applied, if a control voltage is output that causes the compensation head 17 to shift to the left with respect to the recording track, the compensation head 17
If the polarity of the bimorph is adjusted so that the bimorph moves to the right, the auxiliary head 17 will scan a position 90 degrees off from the recorded track, and as a result, the reproduction scanning locus of the main head 16 can be made to match the recorded track. can. By the way, the output characteristics of the complementary head 17 corresponding to the displacement of the bimorph 15 in this application example are shown in _FIG . Indicated by dotted line O ₂ and dashed line O ₃ . From now on, the final operating points P ₁ and P ₂ will be the intersection of _the straight lines O ₁ and O ₂ in FIG. The output will become zero. Therefore, in the block diagram of Fig. 3, when it is pulled toward P ₂ , it is detected and
A circuit is provided to shift the operating point toward _P1 .
That is, in FIG. 3, the output from the main head 16 is amplified to an appropriate level in addition to the regenerative amplifier 7, and after detection by the amplitude detector 8, the output is proportional to the regenerated output of the main head 16 by the low-pass filter 9. Take out the DC voltage. This output is applied to a comparator 10 which outputs only when the input is zero. on the other hand,
The output of the low pass filter 4 which obtains the maximum output of the compensation head 17 and the output of the low pass filter 3 which obtains the instantaneous output are applied to another comparator 11. This comparator 11 is
The output is obtained only when the output of the low-pass filter 3 becomes equal to half the magnitude of the output of the low-pass filter 4. If the outputs of the comparators 10 and 11 are ANDed by 12, the position of _P2 in FIG.
If you activate the output and delay or advance the phase of the playback control signal by 180 degrees, you will get the result shown in Figure 4.
The principle of determining the scanning positions of the main and auxiliary heads 16 and 17 during high-quality reproduction when cP ₂ moves to P ₁ is a well-known technique and will therefore be omitted here. In addition, 24, 25, 2
6, 27 are auxiliary heads 17, 19, main head 16,
18 is an input of a reproduction control signal, and 29 is a reproduction control signal output.

As described above, an auxiliary head that rotates integrally with the conventional rotary head to detect the bending of another recording track is provided, and its output also controls the mounting position of the head, so that any bending of the recording track can be followed. Therefore, a high quality reproduction signal can always be obtained. Furthermore, since an auxiliary head, which is completely separate from the main head, is used to detect the control signal, in the case of a video tape recorder, there is no effect on the reproduced image.

In addition, as described above, the playback output of the rotary head (or the rotary head itself if a rotary assistant head is not provided, or the rotary assistant head if a rotary assistant head is provided) corresponds to the recording track to be reproduced. While it includes positional information, it is possible to experimentally obtain in advance the output that would be obtained if the rotary head was exactly along the recording track to be reproduced. Information corresponding to the output obtained when the track is precisely along the recorded track to be reproduced is determined in advance, and rotation is performed in a direction in which the information regarding the reproduction output obtained during actual reproduction matches this information. It is also possible within the scope of the present invention to form a feedback loop that controls the position of the head, or the rotating main head and the rotating auxiliary head, and it goes without saying that various other modifications are possible within the scope of the idea of the present invention. It is. As described in detail above, according to the present invention, since the reproducing head scans according to the curvature of the recording track during reproduction, a high quality reproduction signal can always be obtained. This is extremely effective in putting the recorder into practical use.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the changes in the recorded track recorded in azimuth and the recorded track deformed during reproduction, Fig. 2 is a diagram showing the relationship between the output of the auxiliary head and the curvature of the recorded track, and Fig. FIG. 4, a block diagram of an application of the invention, shows the characteristics of the main head, auxiliary head and head fixing elements. T is the tape, TP is the recording track pattern recorded azimuthally, and the scanning trajectory of the head during playback, T'P is the modified recording track pattern during playback, H is the rotating main head, and h is the rotation. Auxiliary heads, 1, 7, 20, 21 are regenerative amplifiers, 2, 8
is an amplitude detector, 3, 4, and 9 are low-pass filters, 5 is a differential amplifier, 6 is a drive amplifier, 10 and 11 are comparators, 12 is an AND circuit, 13 is a latch circuit, and 14
is a reproduction control signal phase variable circuit, 15,3
0 is bimorph, 16, 18 is main head, 17,
19 is an auxiliary head, 22 is a head switching pulse generation circuit, 23 is a reproduction control signal amplifier, 24,
Reference numerals 25, 26, and 27 are inputs from each head 16, 17, 18, and 19, 28 is an input of a reproduction control signal, and 29 is an output of a reproduction control signal.

Claims (1)

[Claims] 1. In an apparatus for reproducing a magnetic tape on which magnetic tracks with different azimuth angles are recorded alternately by a pair of rotating main heads without a guard band,
A pair of rotary compensation heads having mutually different azimuth angles are arranged such that the center of the rotary compensation head is located at the edge of the magnetic track of the main rotary head, or the center of the rotary compensation head is positioned in the width direction of the magnetic track of the main rotary head. A head that is arranged so that the center of the rotary compensation head is located on the edge of the track that is shifted by an integral multiple of the width, and that allows the positions of the rotary main head and the rotary compensation head to be varied in the width direction of the track. The automatic tracking adjustment is mounted on a control element, detects the level of a reproduction signal of the rotary compensation head, and controls the head control element so that the reproduction signal level is kept constant at a predetermined level. Device.