JPH056725B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a recording device that performs magnetic recording, such as a video tape recorder (VTR).

BACKGROUND ART AND PROBLEMS The recording current of a video signal in a VTR, for example, is adjusted to an optimum value during manufacture, but this optimum value changes over time, for example due to wear of the video head. That is, as the head wears down, the recording efficiency increases and the optimum recording current decreases.

On the other hand, the actual recording current tends to increase due to a decrease in head impedance due to head wear, and the synergistic effect of these causes video recording to result in an excessive current. As a result, as is well known, problems such as deterioration of C/N, overmodulation, and increase in crosstalk occur.

In addition, in the so-called deep recording method, in which the audio signal is FM modulated and recorded in the deep layer of the magnetic layer, and the video signal is recorded in the surface layer, the deep FM audio signal region is eroded due to excessive video storage current, and the audio signal is There was also the risk of S/N deterioration and phenomena such as so-called sound and blur caused by FM.

OBJECTS OF THE INVENTION In view of these points, the present invention is intended to ensure that recording is always performed using an optimal recording current with a simple configuration.

SUMMARY OF THE INVENTION The present invention supplies a predetermined signal to another head that is in the same state of wear as the first head, detects the impedance of the other head, estimates the wear state of the first head, and estimates the wear state of the first head. This is a recording device that corrects the recording current for one head, and with this, recording can always be performed using the optimum recording current with a simple configuration.

Embodiment FIG. 1 shows a case in which the present invention is applied to a VTR that performs so-called deep recording of audio signals.

In the figure, a video signal supplied to an input terminal 1 is supplied to a recording circuit 2 that performs FM modulation of a luminance signal, low frequency conversion of a chroma signal, etc., and the formed recording signal is transmitted through normally on switches 3 and 4. The signal is supplied to the recording amplifier 5. Further, resistors 6 and 7 are provided in parallel with the switches 3 and 4, respectively. Then, the signal from the recording amplifier 5 is transmitted to the rotary transformer 8.
The signal is supplied to the rotating recording heads H _V1 and H _V2 via the tape T and recorded on the tape T.

Also, the audio signal supplied to input terminal 9
The signal is supplied to a recording circuit 10 that performs FM modulation, etc., and the formed recording signal is supplied to rotary recording heads H _A1 and H _A2 via a recording amplifier 11 and a rotary transformer 12, and is recorded on a tape T.

In this case, the heads H _A1 and H _A2 are the heads H _V1 and H _V2
The heads H _A1 and H _A2 record the FM audio signal deep into the magnetic layer of the tape T, and then the heads H _V1 and H _V2 record the recorded video signal deep into the magnetic layer. recorded on the surface.

These heads H _V1 , H _V2 , H _A1 , and H _A2 are usually mounted on the same rotating drum at the same time, and contact with the tape T etc. is performed in exactly the same way, and problems such as wear occur in the same way. Conceivable.

Furthermore, from the output signal of the recording amplifier 11, the head
Changes in impedance of H _A1 and H _A2 can be detected. In other words, the output signal of amplifier 11 is
Since it is an FM signal, the amplitude is constant, and it can be considered to be a substantially constant current. Therefore, the potential at the output end of the amplifier 11 is initially approximately constant as shown in FIG. 2, but as the head impedance decreases due to wear of the head, the potential also decreases in proportion to the impedance.

Therefore, the potential at this output end is supplied to a clamp circuit 13, and the median value is clamped to a predetermined level, for example, and this signal is peak-detected by a peak detection circuit 14. This peak-detected signal is supplied to comparators 15 and 16, and the voltage dividing circuit 1
Reference voltages of V ₁ and V ₂ (V ₁ >V ₂ ) from V 7 are supplied to comparators 15 and 16 .

As a result, the comparator 15 outputs a signal when the peak voltage falls below _V1 , and the comparator 16 outputs a signal when the peak voltage falls below _V2 . These signals turn off the switches 3 and 4, respectively.

Therefore, in this device, when the head impedance decreases due to head wear, the comparator 15 outputs an output when the head impedance drops to a predetermined value.
Switch 3 is turned off. As a result, the input signal to the recording amplifier 5 is attenuated by the resistor 6, and the recording current is reduced. Furthermore, the wear of the head progresses,
When it drops to the next predetermined value, comparators 15 and 1
6 are both output, and switches 3 and 4 are both turned off. As a result, the input signal to the recording amplifier 5 is further attenuated by the resistors 6 and 7, and the recording current is further reduced.

In other words, correction is performed so that the recording current is always close to the optimum value, thereby eliminating the risk of a decrease in the FM audio signal or deterioration of the video signal.

In this case, since detection and correction are performed simultaneously during recording, followability is good and there is no need to perform a check before starting recording.

Note that when the output of the recording amplifier 5 is detected and corrected, oscillation may occur due to positive feedback.

In addition, in the circuit described above, recording of audio signals is deep recording, and the recording current is originally large due to saturation recording, and the output of the recording amplifier 11 has a strong constant current characteristic, so the above-mentioned correction is applied to the recording amplifier 11. There is no need to do so.

Furthermore, in the above circuit, two comparators were provided to perform stepwise correction in three stages, but in this case, the output of the peak detection circuit 14 is supplied to the gain control terminal of the recording amplifier 5 to perform continuous correction. It's okay. On the other hand, there are cases where it is sufficient to use only one tape and perform two levels of correction.

Further, the above-mentioned comparator is provided with some hysteresis to prevent chattering.

Further, in the above-described example, the detection was performed using a head for deep recording, but if such a head is not available, a dummy head for detection may be provided.
When using this dummy head, detection is performed by passing a frequency signal outside the recording band, or positive feedback is applied to the signal system of the dummy head to oscillate it.
The frequency of the oscillation signal may be discriminated to detect a change in the resonance point due to a decrease in impedance.

Alternatively, by using a pair of rotating heads, a signal is sent to the other head while one head is recording, and this signal is used to detect changes in impedance to correct the recording current of one head. .
This may be done for each other. In this case, it is necessary to provide a recording amplifier for each head.

Effects of the Invention According to the magnetic layer, it has become possible to always perform recording with an optimal recording current with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an example of the present invention, and FIG. 2 is a diagram for explaining the same. 1 and 9 are input terminals, 2 and 10 are recording circuits, 3,
4 is a switch, 5 and 11 are recording amplifiers, 6 and 7 are resistors, 8 and 12 are rotary transformers, 13 is a clamp circuit, 14 is a peak detection circuit, 15 and 1
6 is a comparator, 17 is a voltage dividing circuit, H _V1 , H _V2 ,
H _A1 and H _A2 are recording heads, and T is a tape.

Claims (1)

[Claims] 1. A first magnetic head for supplying a first FM modulation signal and recording the signal on a magnetic tape, and a second FM head for recording the signal on a magnetic tape.
a second magnetic head having wear characteristics equivalent to the first magnetic head for supplying a modulation signal to record the signal on the magnetic tape, and detecting changes in impedance of the second magnetic head. . A recording device that estimates the wear state of the first magnetic head and corrects the recording current of the first magnetic head based on this estimation. 2. In claim 1, the first magnetic head is a surface head that records a main signal on the surface layer of the tape magnetic layer, and the second magnetic head precedes the first magnetic head. A recording device characterized in that the recording device is a deep layer head for recording sub-signals in the deep layer of the tape magnetic layer.