JPS60136069A - Automatic tracking system - Google Patents

Abstract

PURPOSE:To ensure the satisfactory automatic tracking by always detecting the level of a reproduction RF signal for automatic tracking at a point where the envelope of the reproduction RF signal fed from a magnetic head is maximum. CONSTITUTION:The reproduction signal fed from a reproduction amplifier 16 is supplied to an envelope detecting circuit 322 for detection of the envelope level. This detection output is supplied to the (+) input of an electromagnet comparator 326 as well as to a peak holding P/H circuit 324. Thus the peak of the detection output is held. Then the comparator 326 compares the output of the circuit 322 with the output of the circuit 324, and this comparison output is changed to a low level from a high level every time the output of the circuit 322 is smaller than that of the circuit 324. Then a monostable multivibrator 328 outputs a single pulse for each level change of the output of the comparator 326. This single pulse is used as a pulse signal PK.

Description

[Detailed Description of the Invention] [Technical Field] The present invention particularly relates to monitoring the signal level during reproduction of a reproduction device that reproduces signals such as TV signals that are frequency-modulated and recorded on concentric tracks of a rotating recording medium. The present invention also relates to an automatic tracking method suitable for controlling tracking of a recording track of a reproducing head.

[Prior art]

A device that forms concentric tracks on a rotating recording medium and records and reproduces a still image consisting of one field or one frame of a TV signal on each track has been widely used as a TV signal still image recording method. ing. Figure 1 shows the results when such a conventional magnetic recording method is adopted.
FIG. 2 is an explanatory plan view of a recording format on a recording medium.

2 is a magnetic recording sheet which is a rotating recording medium, and the central axis C
For example, the NTS
In the case of recording and reproducing one field or one frame of a TV signal based on the C system, 3,600 rpm or 1
, 800 rpm. On the other hand, a plurality of concentric tracks 4 are formed on the sheet 2, and one field of the TV signal is modulated by a magnetic head (not shown), such as frequency modulation (hereinafter referred to as FM).
and recorded. Incidentally, the correspondence between the magnetic head and the track 4 on the sheet 2 is realized by placing the magnetic head at a position corresponding to the track on the IfsF and bringing it into contact with the sheet 2. Generally, track access is performed by moving one magnetic head along the line F. A guard band 6 is set between each track 4 to prevent crosstalk between trunks, and generally nothing is recorded on this band.

FIG. 2 is a cutaway side view showing the relationship between the magnetic sheet 2 and the magnetic head 8. FIG. The magnetic head 8 is arranged corresponding to a predetermined track 4 on the magnetic sheet 2. On the other hand, since the magnetic sheet 2 is rotating at a speed of 3,600 rpm or 1.800 rpm, there is a gap between the magnetic head 8 and the magnetic sheet 2. This generates an air flow and contacts the magnetic head 8 through a minute air gap 10 .

According to the magnetic recording and reproducing mode as described above, each track 4
, respectively, one field of the TV signal or one
A still screen for one frame can be recorded and played back.

Now, in such a configuration, in order to obtain a good reproduced signal especially when reproducing a signal, it is necessary to have sufficient contact between the magnetic head 8 and the magnetic sheet 2, and also to It is necessary to be exactly opposite to track 4 on 2. However, in general, when selecting a desired track 4 while moving the magnetic head 8 along @F in Fig. 1, accurate correspondence (hereinafter referred to as tracking) may not be achieved due to mechanical errors, orientation, etc. It is difficult to take. Such a tracking error is likely to occur in the form of a difference in ribbon between the machines even when the machine that records signals on the magnetic sheet 2 and the machine that reproduces the signals are different.

In order to deal with the above-mentioned problems, it is necessary to control the magnetic head 8 by slightly moving it in the direction of arrow A or B to accurately bring the magnetic head 8 on-track.

Such control is generally known as autotracking.

Such auto-tracking is often performed by positioning the magnetic head 8 at a position where the reproduction output of the magnetic head 8 is maximized.

Now, when the magnetic head 8 is moved while rotating the magnetic sheet 2, if the signal is recorded in FM, the waveform of the reproduced RF signal output shown in FIG. 3 is generally obtained.

The undulation of the signal envelope curve is caused by the contact relationship between the magnetic sheet 2 and the magnetic head 8 being the same time T of the magnetic sheet 2.
Although this may be due to slight differences among the above, the biggest cause is that the magnetic sheet 2 has an orientation, and the output level changes due to the orientation with the magnetic head gap 10. Therefore, Level detection for auto-tracking is preferably performed at a fixed rotational position of the magnetic sheet 2, and may be performed, for example, at a point Tx in FIG. 3.

FIG. 4 is a block diagram of a conventional auto-tracking device constructed from the above viewpoint. Note that here, one field of TV is recorded on one recording track of the magnetic sheet 2.
Assume that the signal is recorded. In the figure, the motor 12 constitutes a drive source for rotating the magnetic sheet 2 at a speed of It has a function of controlling the phase and speed of the motor 12 based on the rotational position control signal 4 (PG multiplication signal) of the pulse. Incidentally, in order to control the phase of the magnetic sheet 2 with the servo circuit 14, the phase detector PG from 13
It is necessary to compare it with a signal corresponding to one field period of the double signal TV signal, and for this purpose the signal VD is supplied.

Preamplifier 16 amplifies the signal read from magnetic head 8. Further, the reproduced signal processing circuit 1B demodulates the reproduced RF signal from the preamplifier 16 and generates a TV multiplied signal V.
Send as S. On the other hand, in order to position the magnetic head 8 at a position where the reproduced RF signal from the preamplifier 16 is maximized, the auto-tracking control circuit 20 controls the displacement of the head composed of an electro-mechanical transducer such as a bimorph via the amplifier 22. The element 11 is controlled to control the position of the magnetic head 8 with respect to the track. Note that 15 is a head moving mechanism for moving the head 8 step by step in the radial direction of the sheet 2 together with the displacement element.

By the way, the auto tracking control circuit 20
The point at which the level of the F signal is detected is VD in this example.
At one point determined based on the timing of the signal,
This is one predetermined location during one rotation of the magnetic sheet 2. Then, the auto-tracking control circuit 20 compares the level of the reproduced RF signal at each predetermined point while slightly moving the magnetic head 8 for each rotation of the magnetic sheet 2, using a method generally referred to as a ``mountain climbing control method''. , always RF
The magnetic head 8 is positioned at a position where the reproduced signal is maximized.

FIG. 5 shows a block diagram of a specific example of the track control circuit shown in FIG. 4.

The reproduced RF' signal from the reproduced preamplifier 16 is input to an envelope detection circuit 202, where its envelope is detected. This envelope output is input to a first sample and hold circuit (hereinafter referred to as S/H circuit) 204 to which the VD signal is applied as a sampling pulse, where it is sampled and held at the timing of the VD signal.

The output of this 18th/H circuit 204 is the voltage comparator 2
10 (g) input and the 28th/H circuit 206 at the next stage. The 28th/H circuit 206 receives the first delayed VD signal, which is obtained by delaying the v0 signal by T-t below the period of the VD signal in the first delay circuit 208, as a sampling pulse. The output of the first s/H@ path 204 is sampled and held with a delay of Tt from the sampling timing of the output of the envelope detection circuit 202 by the circuit 204. The output of the 28th/H circuit 206 is applied to the input of the comparator 210. Comparator 210 is sl, 28th/'H circuit 204, 206
Compare the outputs of '1st s/H circuit 2n4tB≧2nd
When the 8/H circuit 206 outputs 1, its output becomes high, and otherwise it becomes 4. The output of the comparator 210 is given to the count mode selection input of an up/down counter (hereinafter referred to as UDc) 212. When this mode setting input is high, the UDC 212 is in up count mode, and when it is low, it is in down count mode. The VD signal is used as the count pulse of the UDC 212 by the second delay circuit 214.
11 (However, a second delayed VD signal delayed by it (T, tl) is given.The count output of the UDC 212 is converted to an analog voltage by a D/A converter (hereinafter referred to as D/A C) 216. After that, it is applied to the amplifier 22.

In the above configuration, the 18th/H circuit 204 samples the output of the envelope detection circuit 202 in response to the VD signal, and then, after a time 1t, the UDC 21
If the output of the comparator 210 is high at the time when the count pulse (second delayed VD signal) is applied from the second delay circuit 214 to the UDC 212, the UDC 212 is in the up-count mode, so the count pulse causes the UDC 212 to count up. And the count output at this time is D/A C2
16, it is converted into an analog voltage and applied to an amplifier 22. As a result, the head 8 is slightly displaced by the displacement element 11 in a direction approaching on-track. Below, the second
As long as the output of the comparator 210 is high at the time when the second delayed VD signal is output from the delay circuit 214, the above-described operation is repeated.

Note that the head 8 goes too far with respect to the track.

That is, if the displacement is excessive, the comparator 210
Since the output becomes low, the UDC 212 enters a down-count mode, and the second delayed vo signal now counts down by one, and the head 8 is returned to its original position.

The above operations are repeated to maintain the on-track state of the head 8.

6 shows the VD signal and the output timing of 204 to 210°214.

However, according to this method, if there is a dropout at the detection point of the reproduced RF signal or if it corresponds to the lowest position of an envelope that changes at a constant cycle,
Accurate auto-tracking cannot be achieved.

In particular, the sampling point of the reproduced RF signal for good automatic hooking is Ts in FIG. Since prediction is impossible, there is a problem that there is no effective countermeasure method.0 [Purpose] The present invention has been made in view of the above problems. A tracking method that eliminates the drawbacks of the prior art and can perform good autotracking by always detecting the reproduced RF signal level for autotracking at the point where the envelope of We aim to provide the following.

Another object of the present invention is to perform good level detection by controlling the time relationship between the level detection point of the playback signal obtained through the playback head and the playback signal for auto-tracking based on the level of the playback signal. The present invention will be described below with reference to the drawings. FIG. 7 is a block diagram of an embodiment of an auto-tracking device using the auto-tracking method according to the present invention, and the same (equivalent) components as in the block diagram of the conventional example shown in FIG. 4 are designated by the same reference numerals.

Reference numeral 32 denotes a peak detection circuit, which has the function of detecting the peak of the envelope level of the reproduced RF signal output from the preamplifier 16, detects the peak level of the envelope of the reproduced RF signal within one revolution of the magnetic sheet 2, and detects the peak. Outputs pulse signal PK at the time of detection. 34 is a programmable timer counter, and when the preset command CM is input, the VD
The time difference between the signal and the PK signal is stored, and after the preset command CM is cut off, the sampling pulse signal P is generated after the elapse of the previously stored time difference from the time the VD signal is generated.
Output KC. On the other hand, while the preset command CM is being output, the analog gate circuit 24 is turned off, so the input of the reproduction RF signal from the reproduction preamplifier 16 to the tracking control circuit 20 is cut off, and the circuit 20 becomes inactive. .

Then, after the preset command CM is cut off, the analog gate circuit 24 is turned on, so that the tracking control circuit 20 is given a reproduced RF signal to perform tracking control. In this case, the tracking control circuit 20 uses the timer counter 34 as a sampling signal instead of the VD signal.

1, the level of the reproduced RF signal from the preamplifier 16 is detected and sampled and held based on this pulse signal PKC. Based on the above-described hill climbing control method, the auto-tracking control circuit 20 moves the magnetic head 8 slightly in response to the Norse signal P input every rotation of the magnetic sheet 2. Auto-tracking is performed by detecting the level of the reproduced RF signal at the moving position and positioning the magnetic heald 8 at a position where the reproduced RF signal is always at its maximum.

FIG. 8 shows a silk diagram of an example of a combination of the peak detection circuit 32 and programmable timer counter 34 shown in FIG.

First, the peak detection circuit 32 will be explained. The reproduction RF signal from the reproduction preamplifier 16 is applied to the envelope detection circuit 322, where the envelope level is detected. This detection output is the (+) of the weight emparator 326.
) is applied to the input while the peak hold circuit (hereinafter referred to as
P/H circuit) 324, and its peak is held.

Note that the P/H circuit 324 is reset by the VD signal. The output of the P/H circuit 324 is output from the emparator 326 (
−) attached to the input. Emparator 326 compares the output of envelope detection circuit 322 and the output of P/H circuit 324, and its output goes from high to low each time the output of detection circuit 11322 is less than the output of P/H circuit 324. Changes to Each time the output of the emparator 326 changes from high to low, a mono multivibrator (hereinafter referred to as MM) 328 outputs a single pulse in response, and this becomes the pulse signal PK.

Next, the programmable timer counter 34 will be explained. An oscillator (hereinafter referred to as 1.08C) 342 generates clock pulses of a predetermined frequency, and a first counter 344 counts these clock pulses.

Note that the first counter 344 is reset by the VD times signal. The AND gate 348 passes the output pulse of the peak detection circuit 32 during the output period of the preset command CM, and this is applied to the latch circuit 346 as a load pulse. The latch circuit 346 responds to this load pulse and latches the current count value of the first counter 344.

The output of the latch circuit 346 is the digital emparator 35
It is given to the eight-person power of 2. On the other hand, the clock pulse from 0SC342 is also counted by the second counter 350,
The count output is applied to the B input of the emparator 352. Note that the second counter 350 is also the same as the first counter 34.
Similar to 4, it is reset by the VD times signal. In the process of the second counter 350 counting clock pulses, the emparator 352 outputs a signal when the count value (8 inputs) matches the output (6 inputs) of the latch circuit 346.
A) B-output changes from high to low. Then, in response to the change in the "A)B" output of the emparator 352 from high to low, the MM 354 outputs a single pulse, which becomes the pulse signal P"KC to the dragging control circuit 20.

That is, in the configuration of the timer counter 34,
While the preset command CM is being output, the time difference between the generation point of the VD double signal and the output point of the pulse signal PK from the peak detection circuit 32 is stored in the latch circuit 346 in the form of a clock number of 08C342, and the command CM is After being disconnected, the memory data in the latch circuit 346 is
This is reproduced in the form of the count time of the second counter 350 until the count value of the counter 350 matches the memory contents of the latch circuit 346.

By adopting the control method described above, the regeneration R
Since it is possible to perform auto-dragging operation using the point where the F signal is maximum, it is possible to perform auto-dragging operation using the point where the F signal is maximum. Auto-tracking can be performed with much higher reliability and better performance than in the case of overlapping.

Note that the sampling point determined by the pulse signal PKC can be modified as appropriate by giving a preset command and resetting the preset value of the timer counter 34.

[Other Examples]

In the above embodiment, the sampling point is matched with the maximum value of the envelope level of the reproduced RF signal. A similar effect can be obtained by providing an arbitrary delay time via a programmable variable delay line t7.

〔effect〕

As described above, according to the present invention, when detecting the level of the reproduced signal for the ζ auto-tracking operation,
Since it is possible to detect the level at a point that has the best S/N ratio and does not overlap the dropout region, it is possible to realize auto-tracking control with excellent reliability and performance.

[Brief explanation of the drawing]

FIG. 1 is a plan view for explaining the recording format on a conventional recording medium, FIG. 2 is a broken side view showing the relationship between the magnetic sheet and the magnetic head, and FIG. 4 is a block diagram of a conventional auto-tracking device, and FIG. 5 is a diagram of the track control circuit 2 of FIG. 4.
6 is a timing chart of each signal, FIG. 7 is a block diagram of an auto-tracking device using a level detection device according to an embodiment of the present invention, and FIG. 8 is a block diagram of one specific example of the present invention. , is a block diagram of an example of a combination of the peak detection circuit 32 and the programmable timer counter 34 of FIG. 7. 2...Magnetic sheet (rotating recording medium) 4.
......Track 6...Guide band 8...Magnetic head 12...Drive motor 14...Servo Control circuit 18...Reproduction signal processing circuit 20...Auto tracking circuit 32...
・Peak detection circuit

Claims (1)

[Claims] In a reproducing device that reproduces a frequency modulated signal recorded on concentric tracks of a rotating recording medium, the point where the maximum value of the envelope of the reproduced signal waveform occurs during one rotation of the rotating recording medium is detected, and from now on, this detection point is used. An automatic tracking method characterized in that tracking control of a recording track of a playback head is performed based on an envelope level.