JPH0438070B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a reproducing apparatus that uses a reproducing head to reproduce an image signal or the like from a record carrier.
The present invention relates to a tracking device that causes a playback head to automatically track recording tracks on a record carrier.

(Prior art) In order to efficiently detect signals when a head carrier supporting the reproducing head is transmitted perpendicularly to the recording track of a record carrier at predetermined pitch intervals during reproduction, the envelope amplitude of the signal detected from the reproducing head is A tracking device has already been proposed in which the reproducing head performs a tracking operation so as to position the read head in the direction where the maximum value is maximized, that is, to position it directly above the recording track of the record carrier.

This tracking device uses a playback head to detect an image signal recorded on a record carrier by frequency modulation, and adds this to a low-pass filter circuit, so that the amplitude of the envelope signal from the low-pass filter circuit is maximized. By detecting the position, it was determined that the reproducing head was located directly above the recording track of the record carrier.

By the way, an image signal consists of a high-brightness part and a low-brightness part depending on the subject, and when such an image signal is frequency-modulated, for example, a high-brightness part is converted to a high frequency, and a low-brightness part is converted to a low frequency. . On the other hand, the frequency characteristics of the reproduction circuit device that reproduces the signal detected from the reproduction head do not necessarily correspond exactly to the frequency characteristics of the signal detected from the reproduction head, and therefore the level of the reproduced signal may vary depending on the reproduction head. It fluctuates due to the influence of the frequency characteristics of the system. As mentioned above, in order to position the playback head directly above the recording track of the record carrier, the change in the amplitude of the envelope signal is used as a judgment criterion and the position is controlled in the direction in which the amplitude increases. If the frequency characteristics of the reproduction system fluctuate, the tracking operation cannot be performed smoothly.

(Objective) The present invention solves the drawbacks of the prior art described above, and provides a reproducing apparatus for reproducing image signals and the like from a record carrier using a reproducing head.
It is an object of the present invention to provide a tracking device whose level is stable even under the influence of the frequency characteristics of a reproduction system and which can obtain a plurality of tracking error detection signals within one vertical period.

(Example) (Figures 1 to 4) Hereinafter, the means taken by the present invention to achieve the above object will be illustrated and explained based on the drawings.

The tracking device of the present invention can be applied not only to disk-shaped or tape-shaped record carriers, but also to magnetic, capacitive, and optical record carriers.

In the following embodiments, a case where the reproducing head is magnetic and the record carrier is disk-shaped will be described.

Fig. 1 shows an embodiment of the tracking device of the present invention, Fig. 2 shows the relationship between the gain characteristics of the bandpass filter, the composite image signal, and the frequency of FM modulation, and Fig. 3 shows the relationship between the horizontal synchronization signal and the frequency of FM modulation. The sampling pulses φ ₁ and φ ₂ formed from this signal are shown,
FIG. 4 shows another embodiment of the invention.

In FIG. 1, numeral 1 is a magnetic reproducing head, and numeral 2 is a preamplifier for detecting a signal recorded on a disc-shaped record carrier (not shown) by the reproducing head 1 and amplifying the signal. 3 is a band pass filter whose frequency vs. gain characteristic is as shown in waveform a in FIG. 2, and passes frequencies near frequency ₁ . To further explain FIG. 2, b is a modulation signal and indicates a composite image signal consisting of horizontal synchronizing signals b ₁ , b ₁ ' and image signal b, and ₁ is a horizontal synchronizing signal b ₁ and b ₁ ' of composite image signal b. ₂ is the carrier frequency corresponding to the white peak _b2 of the image signal b. The aforementioned bandpass filter 3 outputs a band near frequency ₁ corresponding to the sync chip. 4 is an envelope detection circuit which outputs an envelope signal of the output signal from the band pass filter 3 and inputs it to the control circuit 8. A demodulator 5 receives an output signal from a preamplifier 2 that amplifies the reproduction signal detected from the reproduction head 1, demodulates the frequency modulation signal, and converts it into the original image signal. Reference numeral 6 denotes a horizontal synchronization signal separation circuit which extracts only the horizontal synchronization signal from the composite image signal from the demodulator 5. Reference numeral 7 denotes a sampling pulse forming circuit which forms sampling pulses φ ₁ and φ ₂ shown in FIG. 3 b and 3 c from the horizontal synchronizing signal shown in FIG. 3 a, and inputs them to the control circuit 8 as sampling pulses. Since the control circuit 8 receives an envelope signal near the frequency ₁ of the horizontal synchronizing signals b ₁ and b ₁ ', the horizontal synchronizing signal pulses φ ₁ and φ ₂ from the sampling pulse forming circuit 7 are input. Each time, the envelope signal in which the horizontal synchronizing signals b ₁ and b ₁ ' are located is sampled and held from the composite image signal b, and the difference between the two sample and hold values is detected, and the envelope signal from the envelope detection circuit 4 is detected. The reproducing head 1 is displaced in the direction in which the amplitude of the recording head 1 increases, thereby performing a tracking operation. 9 is a piezoelectric element drive circuit, and 10 is a piezoelectric element provided in a head carrier (not shown) on which the reproducing head 1 is mounted. The piezoelectric element driving circuit 9 receives a control signal from the control circuit 8 and sends the head carrier carrying the reproducing head 1 at predetermined pitch intervals in a direction perpendicular to the recording track of the record carrier, and also applies a voltage to the piezoelectric element 10. This mechanical strain is transmitted to a support (not shown) that supports the reproducing head 1, and biases the reproducing head 1 to position it directly above the recording track of the record carrier.

The operation of the tracking device having such a configuration will be explained.

A detection signal from the reproduction head 1 is amplified by a preamplifier 2, and one of its outputs is applied to a bandpass filter 3, and the other output is applied to a frequency demodulator 5.
Bandpass filter 3 extracts carrier frequencies near frequency ₁ shown in FIG. The reproduction output signal from the reproduction head 1 is vibrated in the left and right directions with respect to the recording track direction, so that it is subject to fluctuations in amplitude level, and the envelope detection circuit 4 outputs an envelope signal. This envelope signal is input to the control circuit 8. On the other hand, the signal converted into the original image signal by the frequency demodulator is input to the horizontal synchronization signal separation circuit 6, and is shown in FIG.
The sampling pulse forming circuit 7 obtains sampling pulses φ ₁ and φ ₂ shown in FIG.
Enter. The control circuit 8 samples and holds the envelope signal in which the horizontal synchronization signals b ₁ and b ₁ ' shown in FIG. 2 are located among the envelope signals from the envelope detection circuit 4 in synchronization with the sampling pulses φ ₁ and φ ₂ , The amplitude values of both are compared, and a control signal is applied to the piezoelectric element drive circuit 9 so as to move the reproduction head 1 in the direction in which the envelope signal from the envelope detection circuit 4 increases.

In the embodiment described above, a bandpass filter 3 that extracts a frequency band near frequency ₁ has been described, but similar effects can be obtained by using a low-pass filter that extracts signals of frequency ₁ or lower.

Also, although the case where sampling is performed using two synchronizing signals, _φ1 and _φ2 , of the horizontal synchronizing signal train is explained, it is not limited to two, and the response speed of the tracking system should be taken into consideration to perform optimal control. It is also possible to obtain a number of sampling pulses within one vertical period and perform sampling using this number.

FIG. 4 shows another embodiment of the present invention, which is different from the one shown in FIG. 1 in that the bandpass filter 3 is omitted, but is similar to the one shown in FIG. 1. The purpose and effect can be achieved. Even without the bandpass filter 3, the sampling pulses φ ₁ and φ ₂ from the horizontal sync signal train shown in FIG. 3a obtained by the horizontal sync signal separation circuit 6 are applied to the control circuit 8, and Since the envelope signal at which the horizontal synchronization signal is located is sampled from the envelope signal from the envelope detection circuit 4, it is not affected by frequencies other than the frequency of the horizontal synchronization signal, and the tracking error is at a stable level with a good S/N ratio. signal can be detected. Particularly, the effect of this embodiment, in which the synchronization signal is placed on the low frequency side, is significant.

In the embodiments shown in FIGS. 1 and 4, the magnetic head is used for reproduction, but when a device that performs recording or reproduction using a single magnetic head is used in the reproduction mode, Of course, the tracking device of the present invention can also be applied to.

(Effects) As explained above, according to the present invention, since the envelope signal of the reproduction signal of the reproduction head is sampled in synchronization with the sampling pulse obtained from the horizontal synchronization signal, the influence of information signals other than the horizontal synchronization signal It is possible to detect multiple signals of only the horizontal synchronization signal part in a composite image signal, etc., which is not affected and is further reproduced, within one vertical period.
Moreover, it is possible to obtain a tracking error signal with a stable level and a good signal-to-noise ratio.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit of an embodiment of the tracking device of the present invention, FIG. 2 is a waveform diagram showing the form of frequency modulation of this embodiment and the gain characteristics of the bandpass filter used in this embodiment, and FIG. The figure is a waveform diagram showing sampling pulses obtained by the horizontal synchronizing signal separation circuit and sampling pulse forming circuit used in the embodiment, where a is a waveform diagram of the horizontal synchronizing signal train, b and c are waveform diagrams of the sampling pulse train, FIG. 4 shows a block diagram of a circuit according to another embodiment of the invention. In the figure, 1 is a reproduction head, 2 is a preamplifier, 3 is a bandpass filter, 4 is an envelope detection circuit, 5 is a frequency demodulator, 6 is a horizontal synchronization signal separation circuit, 7 is a sampling pulse forming circuit, 8 is a control circuit, 9 is a piezoelectric element drive circuit, and 10 is a piezoelectric element.

Claims (1)

[Scope of Claims] 1. A playback head, an envelope forming means for forming an envelope signal from a playback signal of the playback head, a sampling pulse forming means for obtaining a sampling pulse from a horizontal synchronizing signal, and an output signal from the envelope forming means. A tracking device comprising a control means for sampling with a sampling pulse to form a tracking error signal and causing a reproducing head to perform a tracking operation. 2. The tracking device according to claim 1, further comprising a low-pass filter provided upstream of the envelope forming means and passing a frequency component lower than the frequency of the horizontal synchronizing signal of the composite image signal. 3. The tracking device according to claim 1, further comprising a bandpass filter that passes frequency band components of the composite image signal and is provided before the envelope forming means.