JPH04366457A - Tracking device - Google Patents

Abstract

PURPOSE:To make the tracking speed of a tracking device higher and stable at the time of variable-speed reproduction and, at the same time, to stabilize the tracking speed even when the device is provided with a guide band by providing a means which detects a tracking error from the difference between pilot signals of both adjacent tracks of a main track. CONSTITUTION:Reproduced signals inputted from an input terminal 41 are inputted to a pilot detector 4 through preamplifier 1, LPF 2, and AGC 3 and each component of pilot signals is extracted. Then the difference between the pilot signals selected by means of switches 5 and 6 is taken through envelope detection circuits 7 and 8 and a subtracter 9. A switch 18 selects the difference signal at the time of normal reproduction and the integrated result of the difference signal at the time of variable-reproduction and outputs the selected signals as a tracking error signal from a terminal 42. In other words, tracking control is performed by using the difference between the pilot signals of both adjacent tracks when reproduction is made in a variable-reproduction mode and a main track when reproduction is made in an SP mode. Therefore, high-speed, stable, and high-performance tracking control can be realized without deteriorating the S/N.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a tracking device such as a helical scanning type magnetic recording/reproducing device.
The present invention relates to a tracking device using a ``finding'' method.

0002

2. Description of the Related Art FIG. 2 shows an example of the configuration of a conventional ATF type tracking device using four-frequency pilot signals. First, the four-frequency pilot signal will be briefly explained here.

As shown in FIG. 2, on the magnetic tape 1, pilot signals f1 to f4 are sequentially recorded on each track, superimposed on recording information. These four-frequency pilot signals each have a source vibration of 378 fH (fH: horizontal synchronizing signal frequency of television signal = 15.734 kHz).
It is a signal with a frequency divided into /58, 1/50, 1/36, and 1/40, f1≒6.5fH, f2≒7.5fH
, f3≈10.5fH, f4≈9.5fH. Therefore, the pilot signal frequency difference between adjacent tracks on the magnetic tape is always fH or 3fH. (Strictly speaking, 16.407kHz, 16.521kHz
kHz or 46.145kHz, 46.209kHz
Z, but for convenience of explanation, they will be written as fH and 3fH. ) For example, when the magnetic head 2 is scanning the f2 track shown in FIG. 2, the frequency difference between the f1 pilot signal of the preceding adjacent track and the f2 pilot signal of the scanning track is fH,
The frequency difference between the f3 pilot signal of the trailing adjacent track and the f2 pilot signal of the scanning track is 3fH. The operation of a conventional tracking device using four-frequency pilot signals will be explained below.

In FIG. 2, 20 is a magnetic tape, 21 is a magnetic head, 1 is a preamplifier, 2 is an LPF (low pass filter), 3 is an AGC amplifier (automatic gain control amplifier),
29 is a balanced modulator, 32 is a frequency divider, 33 is a clock generator, 30 and 31 are BPFs (band pass filters), 3
4 is a switch, 7 and 8 are envelope detectors, 9 is a subtracter, 28 and 35 are input terminals, 22 is a capstan,
23 is a motor, 24 is a CFG (capstan FG) sensor, 25 is a capstan speed control system, 26 is an addition circuit,
27 is a motor driver.

In FIG. 2, a reproduced signal detected by a magnetic tape 20 from a magnetic head 21 is sufficiently amplified by a preamplifier 1 and then supplied to an LPF 2. LPF2
Then, after suppressing high-frequency components such as video or audio information that are unnecessary for tracking control, the reproduced pilot signal is
C amplifier 3 to an appropriate level and balanced modulator 2.
Supply to 9. The balanced modulator 29 multiplies the reproduced pilot signal by the local pilot signal supplied from the clock frequency divider circuit 32, and converts the pilot signals of both adjacent tracks into frequencies of fH and 3fH. For example, when the magnetic head 21 is scanning the f2 pilot signal track as shown in FIG. 2, the clock frequency dividing circuit 32 selects the local pilot signal f2 according to the control signal SEL supplied from the input terminal 28. has been done. In this case, the reproduced pilot signal includes pilot signals f1, f2, f of the scanning track and both adjacent tracks.
3 is included. Therefore, the output of the balanced modulator 29 is f
It has frequency components of 2±f1 and f3±f2. Note that the f2 pilot signal of the scanning track becomes zero beat by multiplication. The output of this balanced modulator 27 is fH-B
The signal is supplied to the PF 30 and the 3fH-BPF 31, and the frequency components of f2-f1≈fH and f3-f2≈3fH are extracted, respectively. Here, looking at the fH and 3fH signals, the fH signal is the frequency-converted f1 pilot signal of the preceding adjacent track, and the 3fH signal is the frequency-converted f3 pilot signal of the trailing adjacent track. Therefore, fH signal level and 3fH
By comparing the signal level with the signal level, the track position scanned by the magnetic head 21, that is, the tracking phase can be detected. fH-BPF30 and 3fH-B
The fH signal and 3fH signal extracted by the PF 31 are supplied to the envelope detection circuit 7 or 8 via the switch 34. The switch 34 is switched at the cycle of track scanning by a control signal HSW (head switch pulse) supplied from an input terminal 35. This switch 34 is used to cancel out the relationship between the pilot signal of the preceding/following track and the frequency-converted fH/3fH signal, which changes from track to track. For example, in the state shown in FIG. 2, the pilot signal of the preceding truck is converted to an fH signal as described above, and the pilot signal of the trailing truck is converted to a 3fH signal. However, when the magnetic head 21 is scanning the f3 pilot signal track, the local pilot signal supplied to the balanced modulator 29 is f3, and therefore the f2 pilot signal reproduced from the preceding track is f3 - f2 ≒ 3fH, and the f4 pilot signal reproduced from the trailing rack is f
4-f2≒fH, so in the case of Fig. 2 above, the pilot signal of the leading/trailing track and the frequency-converted fH
/3fH signal relationship is reversed. As a result of the above, the fH and 3fH signals switched at the track scanning period are supplied to the envelope detection circuit 7 or 8, respectively. Envelope detection circuits 7 and 8 detect envelope levels of the fH and 3fH signals and supply them to a subtraction circuit 9, respectively. Subtraction circuit 9 has fH and 3f
The level of the H signal is subtracted and a subtracted output, that is, a tracking error signal, is supplied to the adder circuit 26. The adder circuit 26 adds the tracking error signal and the speed error signal supplied from the capstan speed control circuit 25 and supplies the result to the motor driver 27. The motor driver 27 supplies power to the capstan motor 23 according to the sum signal of the tracking error signal and the speed error signal, and drives the capstan 22. This causes the capstan 22 to run on the magnetic tape 20 at a predetermined speed and phase. Note that the capstan speed control circuit 25 measures the period of the CFG signal generated in proportion to the rotation of the capstan 22, and outputs the difference from the target period to the addition circuit 26 as a speed error signal. Further, the clock frequency divider circuit 32 that generates the local pilot signal divides the frequency of the clock supplied from the clock generation circuit 33, and divides the clock frequency from f1 to f4 at the track scanning period according to the control signal SEL supplied from the input terminal 28.
local pilot signals are generated sequentially. Also, A.G.
The C amplifier 3 keeps the level of the reproduced pilot signal constant so that the tracking error signal does not change significantly due to level fluctuations of the reproduced pilot signal.

In the above example, a balanced modulator is used to detect the pilot signal of the adjacent track based on the beat component, but the configuration shown in FIG.
Bandpass filters 36 to 39 corresponding to each frequency of 4
A similar tracking control can be achieved by detecting each frequency component, selecting an appropriate predetermined filter using the switch 40, and detecting the pilot components of both adjacent tracks of the main track to be scanned.

[0007] The above explanation has been given regarding normal speed reproduction, but variable speed reproduction can also be realized using similar means. For example, in the device described in Japanese Patent Publication No. 3-8154, the difference between the pilot signals of both adjacent tracks of the main track, or the difference between the pilot signals of the main track and the adjacent track, is determined using a sampling pulse according to the speed ratio. A method of fixing the position of the noise band by sampling and tracking the position is proposed.

[0008]

[Problems to be Solved by the Invention] During variable speed playback, there is a method for detecting the difference between pilot signals of both adjacent tracks of the main track (both adjacent methods) and a method for detecting the difference between the pilot signals of the main track and the adjacent tracks (adjacent method). ), each has the following characteristics: Figure 4 shows the detection characteristics of both methods. The horizontal axis represents the longitudinal direction of the tape, and the vertical lines indicate track boundaries. Further, f1 to f4 represent pilot signals recorded on each track. The upper row shows the difference f2-f4 between the pilot signals of both adjacent tracks when f1 is the main track, and the lower row shows the difference f1-f4 between the pilot signals of the adjacent tracks. The double-adjacent method originally uses minute crosstalk components, so it is disadvantageous in terms of S/N, but the error signal exhibits linear characteristics over the entire region. on the other hand,
In the adjacent method, a pilot signal is detected directly from the track being scanned by the head, so a signal with a high S/N ratio can be obtained, and therefore the servo gain can be increased. However, as shown in FIG. 4, at a position shifted by two tracks, the crosstalk component almost disappears, so the detection sensitivity decreases. For this reason, there is a problem in that if the shifter is in the position shown by A in FIG. 4 when shifting to the variable speed reproduction mode, it takes a long time until the phase is locked.

Next, the second problem will be explained. For example, 8mm VT using ATF tracking control.
The track width in standard (SP) mode of R is approximately 20 μm,
In the long-time (LP) mode in which the recording time is doubled, the distance becomes about 10 μm, which is half that. When using heads for both SP and LP modes, if you match the track width of SP mode, L
During P mode playback, crosstalk components from adjacent tracks increase, which is advantageous in terms of tracking, but crosstalk of low-frequency conversion color signals also increases, which causes image quality deterioration. Therefore, from the viewpoint of image quality, it is better to match the track width of the LP mode. However, in this case, when recording and reproducing in SP mode as shown in FIG. 5, unrecorded areas (guard bands) are formed between tracks. This causes a problem in that the crosstalk component of the pilot signal for tracking decreases, the S/N of the detection signal decreases, and tracking becomes unstable. SUMMARY OF THE INVENTION An object of the present invention is, first, to provide a high-speed and stable tracking device during variable speed reproduction, and second, to provide a stable tracking device even for tapes having guard bands.

0010

[Means for Solving the Problems] In order to achieve the first object, a first means for detecting a tracking error from a difference between pilot signals of both adjacent tracks of a main track, and pilot signals of two adjacent tracks. A second means for detecting a racking error from the difference between The structure was designed to switch to the second method. Also,
In order to achieve the above-mentioned second objective, there is a third means for detecting and sampling the pilot signal of the main track, and determining the difference from the previous sample value as a tracking error, and for determining the mode of the recorded signal. For SP mode signals, the third means is used to perform so-called mountain climbing control, and for LP mode signals, the first means is used to apply tracking servo. .

[0011]

[Operation] When transitioning to the variable speed reproduction mode, tracking is performed using a method that uses both adjacent pilots with stable detection characteristics, thereby shortening the time until the phase is locked. After locking, stable tracking control is possible by using the difference between adjacent tracks with high detection sensitivity. Further, when performing SP mode reproduction with a narrow head, tracking control is performed using a pilot signal of the main track. As a result, S/
Since it is not affected by the deterioration of N, good control can be achieved.

0012

Embodiment A first embodiment of the present invention will be described below with reference to FIG. Reference numeral 41 denotes an input terminal from the magnetic head, which inputs a reproduced signal to the pilot detector 4 via the preamplifier 1, LPF 2, and AGC 3. The pilot signal detector 4 is composed of a BPF shown in FIG. 3, for example, and has f1 to f4.
Extract each component of After the pilot signals selected by switches 5 and 6 are detected by envelope detection circuits 7 and 8, a difference is obtained by a subtracter 9. The switch 18 outputs this difference signal during normal playback, and integrates the difference signal during variable speed playback.
, and output it as a tracking error signal from the terminal 42. The switching control signals for the switches 5 and 6 are generated by the following configuration. A head switch pulse (HSW) from a terminal 43 is multiplied by a multiplier circuit 11 and counted by a quaternary counter 12. The multiplication value is controlled according to the playback speed by a signal from a controller such as a microcomputer. The counter output is converted into a switch control signal by decoding circuits 13 and 14. However, the decoding circuit 13 switches the switches 5 and 6 so as to extract the pilot signals of both adjacent tracks of the main track, and the decoding circuit 14 switches the switches 5 and 6 so as to extract the pilot signals of the main track and the adjacent tracks. 6, decode each one to switch. 19 is a circuit that determines whether phase control is locked; 40 is a controller that controls switches 15 and 16 in accordance with phase lock information and playback speed.

The details of the operation of this embodiment will be explained using FIGS. 6 and 7. FIG. 6 shows a track pattern in which four-frequency pilot signals are sequentially recorded, where the horizontal axis is the longitudinal direction of the tape and the vertical axis is the scanning period of the magnetic head. Further, 1 to 4 in the track pattern represent pilot signals f1 to f4. During playback at normal speed, scanning is performed from point A to point B in the figure. As an example of variable speed playback, track patterns during five times speed playback are shown by A to C in the figure. Further, the operating waveforms at this time are shown in FIG. A is HSW,
B is the reproduced video signal, C is f1, D is f2, E is f3, F
are respective pilot signal components of f4. Generally n
When playing back at double speed, (n-1) x 2 noise bands are generated, but if phase control is applied as shown by the solid line in Figure 7, one of the noise bands will be generated during the vertical blanking period. The number of noise bands on the screen can be minimized. Waveform G in FIG. 7 shows a signal obtained by taking the difference between the pilot signals of both adjacent tracks of the main track as a phase control means. Among the encircled numbers, the upper part indicates the pilot input to the + side of the arithmetic unit, and the lower part indicates the number of the pilot input to the - side. In an optimal state, the difference signal G becomes symmetrical about 0V. Therefore, if the difference signal G is integrated, it becomes 0V. Next, the waveforms of each pilot when tracking is shifted as shown by the dotted line in FIG. 6 are shown by dotted lines in FIGS. 7C to 7F. At this time, when the difference signal is integrated, it becomes a waveform H, which does not become 0 when integrated. This deviation from 0V may be used as a tracking error signal.

Next, a case will be described in which a difference between pilots of adjacent tracks is calculated. The difference signal between adjacent tracks is shown in waveform I in FIG. Similar to waveform G, the encircled numbers indicate inputs to the arithmetic unit. In this case too, if the phase is optimal,
The integral output becomes 0. Further, waveform J shows a case where there is a track deviation. Although the integrated output results in a tracking error as in the both adjacent methods, the difference output for the same amount of tracking deviation is larger in this method and the S/N is higher.

In the lock determination 17, for example, the tracking error signal is compared with a predetermined level, and if the tracking error signal becomes smaller than the predetermined value, it is determined that the tracking error signal is locked. Immediately after shifting to the variable speed reproduction mode, the switches 5 and 6 are controlled to take the difference between both adjacent tracks, and after phase locking, the switches 5 and 6 are controlled to take the difference between the pilots of the adjacent tracks. As a result, the phase can be pulled in quickly, and stable control can be achieved after the phase is pulled in. Note that the means for generating control signals for the switches 5 and 6 is as follows:
The computer is not limited to what is shown in FIG. 1, and for example, a microcomputer may be used. Also, in the above explanation, the difference signal was integrated to obtain the tracking error signal, but once the speed ratio is determined, the position where the difference signal crosses 0V during normal tracking is uniquely determined, so this zero-crossing point should be sampled and held. A similar effect can be obtained as a racking error signal.

A second embodiment of the present invention will be explained using FIG. 8. In this embodiment, a signal recorded in SP mode is tracked by a pilot signal of the main track, and a signal recorded in EP mode is tracked by pilot signals of both adjacent tracks. First, tracking using the pilot signal of the main track during SP mode playback will be described. The switch 5 switches f1, f2,
The pilot signal is sequentially switched to f3 and f4. After this is detected by the envelope detection circuit 7, the subtraction circuit 9,
It is input to the sample hold circuit 51. Although the sampling period of the sample-and-hold circuit is not particularly determined, for example, a case where the period is one field will be explained here. The switch 52 is controlled by the SP/LP discrimination circuit described later, but in the case of SP mode, the switch 52 is controlled by the sample hold circuit 5.
Select output 1. Therefore, the calculator 9 outputs the difference between the pilot signal of the current field and the pilot signal of one field before. Using this differential output, so-called hill-climbing control is performed and tracking control is applied.

During LP mode reproduction, the switches 5 and 6 select pilot signals on both sides of the main track, and the switch 52 selects the output of the envelope detector 8. This performs normal tracking control using both adjacent components.

Next, the SP/LP discrimination circuit will be explained. A signal with one specific frequency among the four-frequency pilot signals is used as a discrimination signal, and after envelope detection is performed, it is compared with a predetermined reference value. The operation will be explained using the waveform diagram shown in FIG. A is the HSW, B to D are the output waveforms of the comparator 53, B is when a signal recorded in SP mode is played back in SP mode, C is when a signal is played back in LP mode, and D is recorded in LP mode. When the signal is reproduced in LP mode, E is the waveform when reproduced in SP mode. When the recording mode and the reproduction mode match, the period of the comparator output is 4 fields (waveforms A and D). When a tape recorded in SP mode is played back in LP mode, the period is 8 fields because the tape feed speed is slow. In the opposite case, there will be 2 fields. Therefore, SP/LP mode can be determined by measuring the period of the comparator output.

According to this embodiment, even if the head is used in both the SP and LP modes and the head width is narrower than the track width in the SP mode, the crosstalk components of the pilot signals from both adjacent tracks are reduced. Good tracking can be achieved by switching to tracking using the pilot of the main track. Furthermore, the essence of the present invention is to switch the tracking method depending on the mode, and the method for determining the mode and the tracking method are not limited to those described above.

[0020]

As explained above, according to the present invention, when reproducing in variable speed reproduction mode, the difference between pilot signals of both adjacent tracks with high stability is used in the pull-in stage,
After the pull-in, tracking control is performed using the difference between the pilot signals of adjacent tracks with high S/N ratios, so that high-speed and stable tracking control is possible. Furthermore, when reproducing in SP mode with a narrow head, high-performance tracking can be achieved without deterioration of S/N by performing tracking control using the main track.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the invention.

FIG. 2 is a block diagram of a conventional example of a tracking device.

FIG. 3 is a block diagram of a conventional example of a tracking device.

FIG. 4 is a detection characteristic diagram of a pilot signal.

FIG. 5 is a track pattern diagram.

FIG. 6 is a track pattern diagram during variable speed reproduction.

FIG. 7 is an operation waveform diagram of the first embodiment.

FIG. 8 is a block diagram of a second embodiment of the invention.

FIG. 9 is a waveform diagram of the SP/LP discrimination circuit.

[Explanation of symbols]

4...Pilot signal detection circuit, 7, 8...envelope detection circuit, 9...Subtraction circuit, 17...integrator circuit, 19...Phase lock detection circuit, 51...sample hold circuit, 55...SP/LP discrimination circuit.

Claims (2)

[Claims] Claims: 1. A magnetic recording medium in which pilot signals of four frequencies are sequentially and cyclically recorded on tracks formed by helical scanning, the pilot signals are detected during playback, a tracking error signal is generated, and tracking control is performed. In an apparatus for detecting a phase difference, the apparatus includes: a first means for detecting a difference between pilot signals of both adjacent tracks of a main track to be scanned by a magnetic head; a second means for detecting a difference between pilot signals of the main track and the adjacent track; and a means for detecting that the lead-in is completed, and when reproducing at a tape feed speed different from that during recording, the first means is used until the lead-in, and the second means is used to detect the tracking error signal after the lead-in. A tracking device characterized by generating. 2. A magnetic recording medium that has a magnetic head that performs recording and reproduction in multiple modes with different tape feeding speeds, and in which pilot signals of four frequencies are sequentially and cyclically recorded on tracks formed by helical scanning. In a device that detects the pilot signal during playback, generates a tracking error signal, and performs tracking control, the device includes means for determining a recording mode during playback, and means for detecting a pilot signal of a main track to be scanned by a magnetic head. , a first means for sampling a pilot signal of the main track and detecting a signal difference between samplings, and a second means for detecting a difference between pilot signals of both adjacent tracks of the main track, and a tape feed rate. A tracking device characterized in that the first means performs tracking control during reproduction in a fast recording mode.