JP2678307B2 - Tracking detection device in magnetic recording / reproducing device - Google Patents

Description

The present invention relates to a tracking detection device in a magnetic recording / reproducing apparatus, and more particularly to a magnetic recording / reproducing apparatus such as a VTR (video tape recorder) having four heads. The same head scans the same recording track at the time of recording and at the time of reproduction, that is, it is detected whether or not the heads match, and when it is detected that they do not match, control can be performed so that they match. Then, the occurrence of jitter is minimized.

[Prior Art] Generally, in a VTR, a head scans a video signal in a direction intersecting the running direction of a magnetic tape to record a video signal and reproduce the video signal. VHS type stationary VTRs are usually equipped with the above two heads.

By the way, as a VHS type voltable VTR compatible with the above-mentioned stationary VTR, the diameter of the head cylinder equipped with the head is reduced for downsizing, and the magnetic tape is attached to the cylinder over about 270 °. It is known that the cylinder is equipped with four heads. An outline of such a VTR is shown in FIG. In FIG. 3, reference numeral 1 is a head cylinder, 2 is a magnetic tape wound on the cylinder over about 270 °, and R ₁ , L1, R2 and L2 are attached to the cylinder 1 at 90 ° intervals. The positions of the individual heads are shown. R1 and R2 have the same azimuth, L1 and L2 have the same azimuth, and R1, R2 and L1 and L2 have different azimuths. The arrow T indicates the traveling direction of the magnetic tape 2.

FIG. 4 shows recording tracks recorded on the magnetic tape 2 by the VTR having the four heads as described above, and R1, L1, R2 and L2 are the positions R described in FIG.
The recording tracks recorded by the heads at 1, L1, R2, and L2 are shown, and (R1), (L1), (R2), and (L2) are the above-mentioned positions.
The recording tracks reproduced by the heads at R1, L1, R2, and L2 are shown. 4A shows the case where the same recording track is scanned by the same head during recording and reproduction, that is, when the heads match, and FIG. 4B shows the head where azimuths match. However, this is the case when recording / reproducing with different heads. In any of these cases, the video signal can be reproduced, but if the heads do not match at the time of recording and at the time of reproduction, there will be more jitter and the image quality will deteriorate as compared with the case where they match. Therefore, it is preferable that the heads match during recording and during reproduction. The arrow T indicates the traveling direction of the magnetic tape 2.

For this reason, conventionally, the recording is performed along the running direction of the magnetic tape by the frame when the heads at the positions R1, L1 in FIG. 3 perform recording and the frame when the heads at R2, L2 perform the recording. The duty of the control pulse to be made different is detected, the duty of the reproduction control pulse is detected at the time of reproduction, and it is determined whether the head coincides with that at the time of recording.
When the heads are not aligned, the capstan motor is accelerated to advance the phase of the reproduction control pulse, and the acceleration of the capstan motor is stopped when the head advances by one frame.

[Problems to be Solved by the Invention] Conventionally, in order to determine whether or not the head at the time of reproduction matches that at the time of recording as described above, a head switching pulse and a pulse obtained by dividing this by 1/2 are used. The duty of the reproduction control pulse was detected with respect to the phase reference determined by, but this required a special microcomputer.

The present invention provides a tracking detection device in a magnetic recording / reproducing device capable of determining whether or not the reproducing head coincides with the recording time by a simple and inexpensive device that does not require the dedicated microcomputer described above. The purpose is to provide.

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, in a magnetic recording / reproducing apparatus having four heads, the duty of a control pulse during recording is changed to a head switching pulse for switching the heads. High level of pulse divided by
At the time of recording and at the time of reproduction, the low-level modulation is performed, and at the time of reproduction, the portion of the difference between the above-mentioned two kinds of modulated duty is compared with the above-mentioned frequency-divided pulse and a signal indicating the comparison result is sampled. It was made possible to detect whether or not the heads match with.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a tracking detection device, and FIG.
The figure is a time chart for explaining the operation of the tracking detection apparatus of FIG.

In FIG. 1, reference numeral 3 is an input terminal for inputting a reproduction control pulse, 4 is an input terminal for inputting a pulse obtained by dividing the head switching pulse by 1/2, 5 is a mono-multivibrator, and 6 is an exclusive logic. A sum gate, 7 is a D flip-flop, 8 is an output terminal thereof, R and C are resistors and capacitors forming a differentiating circuit, and these are connected as shown.

The operation of the tracking detection device configured as described above will be described with reference to FIG.

2A shows the well-known head switching pulse shown in FIG. 2A, and this pulse is divided in half to become the pulse shown in FIG. (C) is a control pulse whose duty is modulated according to the high level and low level of the pulse shown in (b) at the time of recording, in other words, the duty is changed according to each two levels of the pulse shown in (b) repeated. The control pulse whose duty is modulated according to the modulation, that is, the operation period of any two adjacent heads of the above four magnetic heads and the period other than this period is shown. This control pulse has a duty ratio of M% when it is at a high level and a duty ratio of N% (however, M> N) when it is at a low level. The control pulse modulated in this way is secondly reproduced.
The input terminal 3 described in FIG. 1 is reproduced in the state shown in (f) (when recording and the head match) or (i) (when recording and the head do not match). Is supplied to. The rising of the control pulse supplied to the terminal causes the mono-multivibrator 5 to
Is triggered, and an output pulse having a metastable period N + (M−N) / 2 shown in FIG. 2D is obtained from the mono-multivibrator. The rising edge of this output pulse is shaped into the pulse shown in FIG. 2 (e) by the partial circuit composed of the resistor R and the capacitor C, and this pulse is supplied to the D flip-flop 7 as a sampling pulse.

On the other hand, FIG. 2 (f) supplied to the above-mentioned input terminal 3,
The modulated control pulse shown in (i) is input to the gate 6, and the 1 / 2-divided pulse shown in FIG. 2 (b) is also input to the gate 6. Output pulses shown in (g) and (j) of FIG. 2 are obtained, respectively. This output pulse is the D flip-flop 7 described above.
Is supplied to the output terminal 8 and is latched by the pulse shown in (e), and the output terminal 8 is at a low level (when the heads match) or at a high level (k) (the heads match). If not) output is obtained.

As described above, the present invention has the first and second magnetic heads having the first azimuth angle, and the third and the third magnetic heads having the second azimuth angle different from the first azimuth angle. 4 magnetic heads, the magnetic tapes are sequentially scanned by the magnetic heads in the order of the first magnetic head, the third magnetic head, the second magnetic head, and the fourth magnetic head in a direction intersecting the running direction of the magnetic tapes. A magnetic recording / reproducing apparatus for recording a signal such as a video signal and reproducing the same by recording a control pulse indicating the position of the recording track by the scanning along the running direction of the magnetic tape,
Also, in reproducing this, during recording, the duty of the control pulse is modulated by the high level and low level of a pulse obtained by dividing the head switching pulse for switching the head.
Alternatively, the duty of the control pulse is made different depending on whether the third magnetic head is operating or the second or fourth magnetic head is operating, and the two types of modulated duty described above are reproduced at the time of reproduction. By comparing the portion of the difference between the divided pulse and the signal indicating the comparison result, it is possible to detect whether or not the heads match during recording and during reproduction. It is possible to reliably detect whether or not the heads match with each other with a simple configuration without using an expensive device such as a microcomputer as in the conventional detection device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of FIG. 1, and FIG.
FIG. 4 is a plan view showing an outline of a main part of a conventional VTR, and FIG. 4 is a schematic view showing recording tracks on a magnetic tape of a conventional VTR. 1: Head cylinder, 2: Magnetic tape, 5: Mono multivibrator, 6: Exclusive OR gate, 7: D flip-flop.

Claims (1)

(57) [Claims] 1. A first magnetic head having a first azimuth angle, a second magnetic head, and a third magnetic head having a second azimuth angle different from the first azimuth angle. The first, third, second, and fourth magnetic heads are sequentially scanned by the magnetic heads in a direction intersecting the traveling direction of the magnetic tapes, and the heads record signals such as video signals. Further, in a magnetic recording / reproducing apparatus for reproducing the same, in which a control pulse indicating the position of a recording track by the scanning along the traveling direction of the magnetic tape is recorded and reproduced, at the time of recording, The duty of the control pulse is modulated by the high level or low level of a pulse obtained by dividing the head switching pulse for switching the head to move the first or third magnetic head. The duty of the control pulse is made different depending on whether it is in operation or the second or fourth magnetic head is in operation, and at the time of reproduction, the portion of the difference between the above-mentioned two kinds of modulated duty is divided by the above-mentioned amount. In a magnetic recording / reproducing apparatus, it is possible to detect whether or not the heads match at the time of recording and at the time of reproducing by sampling a signal showing the result of the comparison in comparison with a pulse which has been circulated. Tracking detector.