JPS62183049A - Tracking servo restoring method - Google Patents

Abstract

PURPOSE:To decrease the servo recovery time by closing a tracking servo when the synchronizing signal detection level of a track to be traced reaches a prescribed level or above so as to restore a tape feed speed command giving nearly the half speed of the normal reproducing speed to the normal speed. CONSTITUTION:When the synchronizing signal detection level reaches a prescribed level or below, a processing section 19 brings a tape speed command VCMD to nearly a half speed of the tape feeding speed at the normal reproduction, generates a switching signal CHS to make a switch 20 open the tracking servo loop and superimposes a prescribed offset voltage V0 on the voltage VCMD. Thus, the capstan motor is driven at the speed being nearly a half of the normal speed. When an address is traced at a track TB actually to a track TA to be traced while the servo is disabled at a time T1, a recognized track number is coincident with a number traced actually at the time T2 to apply the track servo. Then the processing section 19 allows the switch 20 to close the servo loop thereby bringing the tape speed command to the normal speed command.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a tracking servo recovery method, particularly for a tracking servo that includes a synchronization signal and a pilot signal in each track (recording the = sign and restoring the current track). The present invention relates to a tracking servo recovery method when the servo becomes disabled in a tracking servo that detects pilot signal levels before and after and controls the longitudinal position of a head on a magnetic tape based on the difference between the levels.

<Prior art> A digital audio tape device (R-DAT) that rotates a head obliquely in the longitudinal direction of a magnetic tape, digitally records audio data on the magnetic tape with the head, and reads and reproduces the audio data from the magnetic tape. There is a device (called a device).

The rotating head configuration used in such an R-DAT device is
It has approximately the same structure as the rotary head in a VTR. That is, as shown in FIG. 3, two recording/reproducing heads HDI and HD2 are arranged on a rotary body RB at an interval of 1800 mm from each other, and the traveling locus of each head HDI and HD2 on the magnetic tape MT surface is The relative positional relationship between the magnetic tape and each head is determined so as to be inclined with respect to the longitudinal direction of the magnetic tape MT. And the rotating body RB
Each time the head MDI, ) (D2) rotates 180°, each head MDI (D2) alternately contacts the magnetic tape MT for 90° each time, so that audio data is recorded on the magnetic tape or audio data is read from the magnetic tape. FIG. 4 is an explanatory diagram of recording patterns recorded on the magnetic tape MT, where TI and T2 are patterns recorded by the heads HDI and HD2, respectively, vt is the tape speed, and vh is the head rotation speed.

Now, in order to accurately read and reproduce audio data recorded in the Kakoro R-DAT device, it is necessary for each head to correctly trace the recording track during reproduction. Therefore, the audio data (PCM data) of each track
A tracking servo signal (called an ATF signal) including a synchronization signal and a pilot signal is recorded before and after the
Tracking servo is performed using the ATF signal. That is, after detecting the synchronization signal on the current track, the rotary head detects the level of the pilot signal recorded on each of the preceding and following tracks, and controls the position of the rotary head in the longitudinal direction of the tape based on the level difference. and trace it on the track.

FIGS. 5 to 7 are explanatory diagrams of such a tracking servo method.

Four consecutive tracks TA, TB as shown in FIG.
, TC, TD as one set, and PCM of each track.
ATF signals with different patterns are recorded before and after the data. Note that tracks TA and TC were recorded by the first head, and tracks TB and TD were recorded by the second head. In the ATF signal, f
l is the 130.67KHz pilot signal, f2
is 522.67K for the 1st and 3rd tracks) (z synchronization signal, f3 is 784.0KHz for the 2nd and 4th tracks)
f4 is the synchronization signal of f, , f2. This is a 1,568 MHz erase signal that separates f.

Now, if the head traces on the second track TB, the synchronization signal will be f3. The head is on the second track T
If a synchronizing signal f is detected after a predetermined time after starting the trace of B, the head is immediately moved to detect the pilot signal f1 recorded in the previous track TA and its detection level L1 is memorized. Also, after a predetermined period of time has elapsed, the synchronization signal detection unit detects the pilot signal recorded on the rear track TC and similarly stores its detection level L2.

Next, the difference between levels Ll and L2 is calculated. Note that when the head HD2 is located at the center of the second track TB as shown in FIG. 6(A), L1=L2 and the level difference becomes zero, and as shown in FIG. 6(B), the head HD2 is located at the center of the second track TB.
When the head HD2 is shifted toward the front track TA side, Ll>L2, and when the head HD2 is shifted toward the rear track TC side, as shown in FIG. 6(C), Ll<L2.

If the voltage applied to the capstan motor is increased or decreased based on the level difference between Ll and L2 (Ll-L2), the tape moving speed will be increased or decreased. For example, in the case shown in FIG. 6(C), the tape moving speed Vt increases and the head HD2 is moved toward the track center, and in the case shown in FIG. 6(B), the tape moving speed decreases. Similarly, the head HD2 is moved toward the center of the track. Then, each head accurately traces each track by the above tracking servo.

By the way, in this tracking servo method,
Some scratches on the tape or other causes may cause the head to deviate significantly from the current track, in which case tracking servo is no longer possible. If this tracking servo disabled state continues, the head will naturally be unable to trace the track correctly, making it impossible to reproduce accurate audio. From the above, it is necessary to promptly detect that the servo has become disabled, and control so that the servo is enabled again.

For this reason, the synchronization signal detection level is monitored, and when it falls below a predetermined threshold level, recovery control is executed so that servo is disabled and servo becomes possible again.

And tracking servo recovery control is synchronous 4M
When the signal detection level becomes below a predetermined threshold level, the tracking servo loop is opened and a predetermined offset voltage is superimposed on the tape feed speed command value.

That is, when the servo is disabled, the capsun motor is rotated slightly slower or faster than the normal speed, and the relative speed of the head to the tape in the longitudinal direction of the tape is decreased or increased. As a result, the position of the head in the track width direction moves sequentially. For example, if we focus only on the first track TA of each set of four consecutive tracks, the position of the head 11 in the track width direction will be as shown in FIGS. 7(A) to (D) due to the above control. Moving.

Therefore, someday the head will trace a track that it really needs to trace, and at this time, the synchronization signal detection level will exceed a predetermined level, so the servo will be closed and the tracking servo will be restarted.

The processing section monitors which track number of the four 1-racks TA-TD (referred to as +-rack numbers) the head should currently trace as follows. That is, at the start of playback, the head is moved to the first track TA.
Since the alignment is performed upward, every time a track is scanned after alignment, for example, every time a head switching signal is generated,
By updating the track number, the current track number to be traced can be monitored. Therefore, depending on whether the synchronization signal detection level of the track that the processing unit recognizes as the one to be traced is higher than a predetermined level, servo is disabled.
You can judge when servo recovery is complete.

Figure 8 is an explanatory diagram of the servo recovery operation when the tape feed speed is slightly increased to recover the servo after the servo becomes disabled, and (A) of the figure shows the tracks that the processing section recognizes as those to be traced. The number CB in the figure is the track number actually traced by the head. Note that even if the servo becomes disabled, the head rotational speed does not change, so the alternating cycle of the track numbers shown in the diagram (A) is constant.

Now, in the state where servo becomes impossible at time t1,
Assuming that the processing unit recognizes the track TA and is actually tracing the track TD, at time t2
At this point, the recognized track number and the track number actually being traced match, and tracking servo becomes possible from that time.

<Problem that the invention seeks to solve> However, in the conventional method, it takes a considerable amount of time (for example, 1 to 2 seconds) to recover the tracking servo, and during this time, the audio output is interrupted, resulting in skipping, which causes sound quality deterioration. It has become.

From the above, an object of the present invention is to provide a tracking servo recovery method that can shorten the time required for tracking servo recovery.

Means for Solving the Problems> FIG. 1 is a block diagram of essential parts of a tracking servo device according to the present invention.

11 is a head, 12 is a reproduction amplifier, 13 is a low-pass filter, 14 is an envelope detector, 15 is a first sampling and holding circuit, 16 is an adder, 17 is a second sampling and holding circuit, 18 is a synchronization signal detection section, 1
9 is a processing section, 20 is a switching section, 21 is an offset voltage setting section, 22 is an adder, and 23 is a tape feed control section.

Effect> The synchronization signal detection unit 18 detects the synchronization signal of the track that the processing unit 19 currently recognizes as being to be traced by the head.

When the synchronization signal detection level falls below a predetermined threshold level, the processing unit 19 considers that servo is impossible and sets the tape feed speed command value VCM D to 1/2 of the speed command value during normal playback. . In addition, processing section 1
9 is an offset voltage (■) which is set by the switching unit 20 to open the tracking servo loop and by the offset voltage setting unit 21. The tape feed speed command V. Superimpose at 1°.

By reducing the tape feed speed to 1/2, the track number to be traced and the track number actually being traced match in a short time. As a result, since the synchronization signal detection level becomes equal to or higher than the predetermined level, the processing section 19
;ej, closes the tracking servo and sets the tape feed speed command value V. Set M(+ to normal playback speed and restart tracking servo.

<Embodiment> FIG. 1 is a block diagram of a tracking servo device according to the present invention.

11 is a head (actually there are two, but only one is shown); 12 is a head output; in other words, a playback amplifier that amplifies the playback signal; 13 is a pie-foot signal f included in the playback signal; The low-pass filter 14 is an envelope detector, which outputs an envelope signal indicating the envelope of the pyrond signal output from the low-pass filter 13.

A first sampling and holding circuit 15 samples and holds the output of the envelope detector 14. 16 is an adder, and sampling and holding circuit 1
The difference between the hold value stored in the envelope detector 5 and the output value of the envelope detector 14 is calculated and output. 17 is the second
This is a sampling and hold circuit for storing the difference calculated by the adder 16.

18 is a synchronization signal detection section, 19 is a processing section, and the synchronization signal detection section 18 detects four consecutive tracks (TA-TD).
...) as the first, second, third, and fourth tracks from the front, the track number of the next track to be traced is input from the processing unit 19, and a synchronization signal corresponding to the track number is input. (f or f,) and inputs the detection signal to the processing unit 14, and also detects whether the synchronization signal is above a predetermined threshold level and similarly inputs the detection signal to the processing unit 14.
Enter 9. The processing unit 19 (a) generates a head switching signal HC generated every half rotation of the head;
(b) Generates sampling signal S1 and holds pilot signal level L1 of the previous track for sampling and holding times #!
15, (cl) generates the sampling signal S2 at a predetermined time and outputs the adder 16, in other words, the pilot 4M of the previous track.
The difference between the level L1 of the first track and the pilot signal level L2 of the next track is stored in the sampling and hold circuit 17. The tape feed speed during normal playback is set to 1/2, the tracking servo loop is opened, and a constant offset voltage is set to vc.
l. (When the e+ synchronization signal level reaches a predetermined second level or higher, the tracking servo loop is closed and the tape speed command is set to the normal playback speed.

20 is a switching unit, and 21 is a constant offset voltage V.

The switching unit 20 opens the tracking servo loop and outputs the offset voltage v0 in response to the switching signal CH3 from the processing unit 19.

22 is an offset voltage V. and tape speed command vo,.

23 is a tape feed control section.

The operation shown in FIG. 1 will be explained below. Note that the processing section 19 issues a tape speed command V to the tape feed control section 23 in accordance with the normal playback speed. ,,. is output, and the tape is moved at the playback speed by the king servo.

Now, move the head 11 over the second track TB (see Figure 5).
If the data should be traced, the processing unit 19 notifies the synchronization signal detection unit 18 of this fact.

The synchronization signal detection unit 18 recognizes whether the synchronization signal is f2 or f3 based on the notified track number. In this case, since it is the second track, the synchronization signal is f. When the head 11 starts tracing the second track TB, the signal read by the head 11 is input to the low-pass filter 13 and the synchronization signal detection section 18. be done.

The low-pass filter 13 passes the pilot signal f1 included in the reproduced signal and outputs it to the envelope detector 14, and the envelope detector 14 generates an envelope signal enveloping the pilot signal.

Further, the synchronization signal detection section 18 detects the synchronization signal f3 and inputs the synchronization detection signal to the processing section 19.

When the synchronization detection signal is input, the processing section 19 immediately generates the sampling signal S1 and sends it to the envelope detector 14.
In other words, the detection level of the pilot signal f recorded on the previous track (first track) TA is stored in the sampling and hold circuit 15.

Further, the processing unit 19 generates the sampling signal S2 after a predetermined time has elapsed after the synchronization detection signal is input, and outputs the envelope detector at that time, in other words, the rear track (
3rd track) Pilot signal f recorded in TC
1 and the level L1 stored in the sampling and holding circuit 15 is stored in the sampling and holding circuit 17. The sampling hold circuit 17 adds the stored difference (=L1-L2) to the adder 22 via the switching section 20 to increase or decrease the tape feeding speed. For example, in the case shown in FIG. 6(C), the tape moving speed Vt
increases to move the head toward the track center, and in the case shown in FIG. 6(B), the tape moving speed decreases to similarly move the head toward the track center. Then, when servo is possible, the above-described tracking servo is performed for each track, and each head accurately traces each track.

Now, if the head deviates significantly from the track to be traced for some reason, the synchronization signal cannot be reliably detected (in other words, the synchronization signal detection level decreases).

When the synchronization signal detection level falls below a predetermined level, the processing unit 19 sets the tape speed command vc0 to 1/2 of the tape feed speed during normal playback, generates a switching signal CH3, and switches the switching device 20. Open the tracking servo loop and set a constant offset voltage v0 to V. M. superimpose it on

This allows the capstan motor to move at approximately 1/1/2 of its normal speed.
The head rotates at a speed of 2, and the relative speed of the head to the tape in the longitudinal direction of the tape decreases. As a result, the position of the head in the track width direction moves sequentially for each track (see FIG. 7).

FIG. 2 is an explanatory diagram of the servo recovery operation according to the present invention,
5A shows the track number to be traced recognized by the processing unit 19, and FIG. 1B shows the track number actually traced by the head.

In a state where servo is disabled at time T, if the track to be traced is TA and track TB is actually being traced, then at time T2 the recognized track number and the track number actually being traced are (track number TC), tracking servo becomes possible from that time.

If the recognized track number and the track number actually being traced match, the synchronization signal level becomes higher than a predetermined second level, so the processing section 19 closes the tracking servo loop by switching the switch 20, and changes the tape speed. Set the command to the normal playback speed.

<Effects of the Invention> According to the present invention, when the synchronization signal detection level of the track currently being traced by the head falls below a predetermined threshold level, the tracking servo loop is opened and a predetermined signal is detected. Input the offset voltage and set the tape feed speed command value to approximately 1 of the normal playback speed.
/2, the time required for tracking servo recovery can be shortened and deterioration of sound quality can be prevented.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts of the tracking servo device according to the present invention, Fig. 2 is an explanatory diagram of the servo recovery operation of the present invention, Figs.
The figure is a schematic explanatory diagram of the R-DAT device, FIGS. 5 to 7 are explanatory diagrams of tracking servo, and FIG. 8 is an explanatory diagram of conventional servo recovery operation. 110. Head, 13...Low pass filter, 14...
Envelope detector, 15.17... Sampling hold circuit, 16... Adder, 18... Synchronization signal detection unit, 19... Processing unit, 20
...Switching section, 21..Offset voltage setting section, 23..Tape feed control section Patent applicant Alpine Co., Ltd. Agent Patent attorney Chiki Saito A3ri
Φ

Claims (1)

[Claims] A set of four consecutive tracks TA, TB, TC, and TD, and tracks TA, TB, and TD that include a synchronization signal and a pilot signal.
A tracking servo signal having a different pattern for each TC and TD is recorded on each track along with audio data, and after detecting the synchronization signal on the current track, the level of the pilot signal recorded on the previous and subsequent tracks is determined by the rotating head. In a tracking servo recovery method for a digital audio tape device in which the position of a rotating head in the longitudinal direction of the tape is controlled based on the level difference, the synchronization signal detection level of the track to be traced by the head is at a predetermined threshold level. When the following occurs, open the tracking servo loop, input a predetermined offset voltage, and set the tape feed speed command value to approximately 1/2 of the normal playback speed, so that the synchronization signal detection level of the track to be traced exceeds the predetermined level. A tracking servo recovery method characterized in that when the tracking servo is reached, the tracking servo is closed and the tape feed speed command value is set to the normal playback speed.