JPH0836811A - Tracking controller - Google Patents

Abstract

(57) [Summary] [Purpose] The read head is controlled at the trace position where the error rate is low. [Structure] The error correction circuit 16 detects and corrects an error in reproduced data and outputs an error detection signal to an error measurement circuit for each area 20. The circuit 20 measures the error detection signal from the circuit 16 for each area in the longitudinal direction of the track, and outputs the error number information for each area to the gain adjusting circuit 22.
The circuit 22 weights the output of the circuit 20 with a gain designated by the servo circuit 38 and supplies the weighted output to the circuit 38. The circuit 38 sets the gain of the circuit 22 in the range of 0 to 1.0,
It is zero at the start of the tape, and then increases with time. The ATF error processing circuit 24 generates a tracking error signal from the pilot signal component of the reproduction RF signal. The circuit 38 controls the rotation of the capstan motor 32 according to the outputs of the circuits 22 and 24 so that the error rate for each area becomes low as a whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking control device, and more particularly to a tracking control device that causes a head to follow a track obliquely recorded on a tape-shaped recording medium.

[0002]

2. Description of the Related Art There are mainly two reproduction tracking systems for home video tape recorders or video cassette recorders. In the first method, a fixed magnetic head is provided in a part of the tape path to record a control signal (CTL signal) on a dedicated track at the time of recording, and at the time of reproduction, the CT reproduced from this dedicated track.
The L head causes the reproducing head to follow the track, which is called the CTL method. In the second method, at the time of recording, a plurality of types (usually 4 types) of pilot signals having a relatively low frequency are multiplexed with a main signal (usually a video signal) so that the frequencies are cyclically different for each track. Are recorded at the same time, and at the time of reproduction, a tracking error signal (ATF error signal) is obtained by comparing the frequencies of the pilot signal reproduced at the same time as the main signal and the pilot signals reproduced from the adjacent tracks on both sides by crosstalk. To get the playback head to follow the track.
It is called the F method.

[0003]

SUMMARY OF THE INVENTION Recently, home video
Also for tape recorders, the demand for higher image quality and digitization is increasing, and a format with a narrower track pitch is being developed and researched so that more information can be recorded and reproduced. In reproducing a narrow track, it is extremely important to improve the accuracy of linearity in the longitudinal direction of the track. For example, in the case of a track with a pitch of 10 μm, the linearity must be kept below 3 μm. This is close to the limit of machine accuracy, and is a serious problem in terms of productivity and cost.

There is also known a technique in which an actuator for displacing the rotary head in a direction intersecting the rotation direction is provided, and the rotary head follows the bend even if the track bends to some extent. This technique is effective for improving the tracking performance, but the rotating drum has a very complicated structure and becomes extremely expensive.

An object of the present invention is to provide a tracking control device having a high trackability to track non-linearity.

Another object of the present invention is to provide a tracking control device suitable for a helical scan type digital recording / reproducing device.

[0007]

SUMMARY OF THE INVENTION A tracking control device according to the present invention uses an error detecting means for detecting an error in reproduction information from a recording medium, and the number of errors detected by the error detecting means. Of area-specific error number counting means for counting a predetermined area of a recording unit having a predetermined size, and position control means for controlling the position of the reproducing head with respect to the recording unit according to the output of the area-specific error number counting means. Is characterized by.

For example, the recording medium is a tape-shaped recording medium, and the recording unit of the predetermined size is a track.

Preferably, the area-by-area error number counting means measures the number of errors detected by the error detecting means for an area-by-area error number measuring means for a predetermined area of a recording unit of a predetermined size of the recording medium. And weighting means for weighting the measurement result of the area-specific error number measuring means. Further, it is provided with control means for controlling the weighting amount in the weighting means so as to increase with the lapse of time after starting the recording medium.

[0010]

By the above means, the tracking of the reproducing head can be controlled so that the error rate for each area of the recording unit of a predetermined size (for example, a track of a magnetic tape) becomes low as a whole. As a result, it is possible to control the tracking of the reproducing head at an optimum position in view of the error rate.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic block diagram of an embodiment of the present invention applied to a digital tape recorder. Reference numeral 10 is a reproducing head, 12 is a reproducing amplifier for amplifying the output of the reproducing head 10, 14 is a demodulation circuit for digitally demodulating the output (reproducing RF signal) of the reproducing amplifier 12, 16
Is an error correction circuit that detects and corrects the output data of the demodulation circuit 14, and 18 reproduces the output data of the error correction circuit 16 (time axis separation of video data and audio data, decompression of compressed data, and analogization). , A playback processing circuit that outputs a playback video signal and a playback audio signal.

An error measuring circuit for each area 20 measures the error number information detected by the error correction circuit 16 for each area dividing the track into a plurality of sections in the longitudinal direction.
Is a gain adjustment circuit for weighting the measurement result of the area-specific measurement circuit 20 with a designated weight.

Reference numeral 24 is an ATF error processing circuit which extracts a pilot signal component from the output of the reproduction amplifier 12 and outputs a tracking error signal indicating a tracking error amount.

Reference numeral 26 is a drum motor for rotating the rotary drum, 28 is a motor drive circuit for driving the drum motor 26, and 30 is a rotation signal of the drum motor 26. A drum rotation detection circuit that outputs an FG signal, 32 is a capstan motor that rotates a capstan that runs a video tape, and 3
4 is a motor drive circuit for driving the capstan motor 32, 36 is the rotation of the capstan motor 32,
It is a capstan rotation detection circuit that outputs an FG signal indicating the rotation speed.

Reference numeral 38 indicates the rotational speed and rotational phase of the drum motor 26 by the motor drive circuit 28 according to the outputs of the gain adjustment circuit 22, the ATF error processing circuit 24, the drum rotation detection circuit 30 and the capstan rotation detection circuit 36. A servo circuit for controlling and controlling the rotation speed of the capstan motor 32 by the motor drive circuit 34. The servo circuit 38 also controls the gain (weighting amount) of the gain adjusting circuit 22. The details will be described later. The servo circuit 38 actually comprises a microcomputer.

Before describing the operation of FIG. 1, the relationship between the reproduction RF level and the reproduction data error rate in the case of digital recording will be briefly described. FIG. 2 shows the relationship between the reproduction RF level and the error rate. In digital recording and reproduction, generally, if the reproduction RF level is above a certain level, the reproduction signal quality is not affected. For example, as shown in FIG.
If the level is above a suitable threshold (eg 50%),
The error rate of the reproduced data is usually a low value that can be satisfied Eth
However, when the reproduction RF level becomes lower than the threshold value, the error rate sharply increases. In the case of the characteristics shown in FIG. 2, the reproduction RF level may be 50% or more.

FIGS. 3 and 4 show the relationship between the trace locus and the reproduction RF level when the reproduction head traces a track slightly bent at the start end. FIG. 3 shows a case in which the reproducing head slightly deviates from the track at the beginning of the track, but traces substantially at the middle of the track, and FIG. 4 shows a case of tracing the beginning and middle of the track on average. Show. 3 (1) and 4
(1) shows the trace locus of the reproducing head with respect to the track, and FIGS. 3 (2) and 4 (2) show changes in the reproducing RF level with respect to the longitudinal direction of the track.

A plurality of areas A are arranged in the longitudinal direction of the track.
1, A2, A3, A4, A5, etc. are classified, and the reproduction RF level is considered in each area. In the case of FIG.
Although the reproduction RF level is less than 50% at the beginning of the track (a part of the area A1), it rapidly increases and maintains a high level after the area A2. In the case of FIG.
Even in the area A1 at the beginning of the track, the reproducing head traces the track with a sufficiently wide width, so that the reproducing RF level becomes equal to or higher than the threshold value (50%), and the areas A2 and A thereafter.
In 3 and so on, the reproduction RF level is lower than that in the case of FIG. 3, but is a sufficient level in view of the error rate.

From FIG. 3 and FIG. 4, rather than simply reducing the off-track amount of the reproducing head from the track,
Tracking should be controlled so that the reproduction RF level is above a predetermined level over the entire track.
In the present embodiment, focusing on this point, the error rate of the reproduction data,
In particular, referring to the error rate distribution in the track longitudinal direction, the tracking of the reproducing head is controlled so that this error rate distribution becomes low over the entire track.

The operation of FIG. 1 will be described in detail. The output of the reproducing head 10 is amplified to a predetermined level by the reproducing amplifier 12 and applied to the demodulation circuit 14 and the ATF error processing circuit 24. The demodulation circuit 14 demodulates the output of the reproduction amplifier 12, the error correction circuit 16 detects an error in the output of the demodulation circuit 14, corrects the error within the range of the correction capability, and outputs the error-corrected data to the reproduction processing circuit 18. At the same time, an error detection signal (for example, a pulse signal in which one pulse rises each time an error is detected) is output to the area-based error measurement circuit 20. The reproduction processing circuit 18 separates the reproduction data from the error correction circuit 16 on the time axis, expands and analogizes it,
It outputs a reproduced video signal and a reproduced audio signal.

The area-by-area error measuring circuit 20 receives an error detection signal from the error correcting circuit 20 to determine an area in the longitudinal direction of the track (for example, area A1 shown in FIGS. 3 and 4).
The number of errors is measured for each of A2, A3, ..., And the error number information for each area is output to the gain adjustment circuit 22. The gain of the gain adjusting circuit 22 is controlled by the servo circuit 38, and the gain adjusting circuit 22 uses the error measuring circuit 2 for each area.
Information in which the number of errors by area from 0 is weighted with a designated gain is supplied to the servo circuit 38.

On the other hand, the ATF error processing circuit 24 extracts a pilot signal component from the output of the reproduction amplifier 12 and outputs a tracking error signal indicating the off-track amount to the servo circuit 38.

In addition to the servo circuit 38, a signal indicating the rotation speed and the rotation phase of the drum motor 26, that is, the rotating drum is supplied from the drum rotation detection circuit 30, and the capstan rotation detection circuit 36 outputs the capstan. Information about the rotation speed of the motor 32, that is, the tape running speed is supplied, and the rotation of the drum motor 26 is controlled via the motor drive circuit 28 so that the information is in a predetermined state. Control the rotation of the capstan motor 32.

The servo circuit 38 further performs tracking / tracking from the ATF error processing circuit 24 for tracking.
The rotation of the capstan motor 32 is controlled as follows according to the error signal and the number of weighted errors by area from the gain adjusting circuit 22. FIG. 5 shows characteristics of weighting by the gain adjusting circuit 22. In the present embodiment, the gain of the gain adjusting circuit 22, that is, the weighting of the number of errors by area is set to zero immediately after the tape is started, and is increased with the lapse of time. FIG. 5 (1) shows an example of weighting, that is, an example of linearly increasing the gain, and FIG. 5 (2) shows an example of increasing the gain nonlinearly (for example, exponential function, power, geometric series) with time. (3)
Shows an example of gradually increasing with time. Figure 5
Then, the horizontal axis represents time and the vertical axis represents the weighting amount of the number of errors by area. In any case, the weight is 0 to 1.0
And becomes constant at 1.0 after a certain period of time.

The reference value of the tracking error signal is corrected according to the number of errors by area thus weighted,
The rotation of the capstan motor 32 is controlled so that the tracking error signal matches the corrected reference value.
That is, normally, the rotation of the capstan motor 32 is controlled so that the tracking error signal becomes equal to a reference value (for example, 2.5 V).
This reference value is shifted to, for example, 2 V or 3 V according to the weighted area-specific error number, and the reproducing head is off-tracked by an appropriate amount according to the area-specific error number.

For example, assuming that the number of errors is 100 and the track width is 1/2 off-track, when the number of errors is 50, the track width is 1/4 of the track width. The weighting being “0” means that the tracking control is executed only by the tracking error signal regardless of the number of errors, and the off-track amount becomes zero. When the number of errors is 100 and the weighting is 0.5, 1/4 of the track width is offtrack, and when the weighting is 1.0, it is 1/2 of the track width.
Only off track.

Details of the tracking control according to the number of errors for each area according to this embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing the track shape and the off-track directions A and B of the reproducing head in the following description. Figure 7
Indicates the error rate of each area A1, A2, A3, A4, A5 of the track and the off-track amount at each stage of the tracking control. In FIG. 7, the horizontal axis represents time, and the vertical axis represents (1) to
(5) shows the error rate for each area, and (6) shows the off-track amount. Here, the error rate threshold Eth is 10 −4.
I tried to ride.

Immediately after the tape is started, the weighting of the number of errors by area becomes 0 to a very small value as described with reference to FIG. 5, and the tracking error signal output from the ATF error processing circuit 24 is used exclusively for tracking. Will be controlled. For convenience of explanation, it is assumed that the gain of the gain adjusting circuit 22 is constant while the reproducing head traces one track. In the example shown in FIGS. 6 and 7, the error rate of the area A1 is the threshold value Eth in the first trace t1.
Below, in other areas A2, A3, A4, A5,
The error rate is equal to or higher than the threshold Eth. Therefore, the servo circuit 38 makes the reproducing head off-track a predetermined amount in the A direction or B direction (B direction in FIG. 7) with respect to the target track. Whether to move in the A direction or B direction first,
Usually determined by the tracking error signal (or initial setting).

Due to the movement in the B direction, the error rate in the area A1 is deteriorated in the second trace t2. Although the error rates of the other areas A2, A3, A4, A5 are also deteriorated, they are still below the threshold Eth. Since the error rate of the area A1 is equal to or greater than the threshold Eth and is worse than the previous time,
The off-track direction of the reproducing head is reversed, and thereafter the reproducing head is off-tracked in the A direction. In the third trace t3, the error rate is the same as that in the first trace t1, and in the trace t4 in which the reproducing head is stepwise moved in the A direction, even if the error rate in the area A1 is equal to or larger than the threshold Eth, Has decreased, and the error rates of the other areas A2, A3, A4, A5 are still below the threshold Eth.

Further, the trace t moved stepwise in the direction A
5, the error rate of the area A1 is less than or equal to the threshold Eth, and the error rates of the other areas A2, A3, A4, A5 are still less than or equal to the threshold Eth. In order to find the optimum trace position where the error rate for each area becomes lower, the step is further moved in the A direction. In the trace t6, the error rate of the area A1 is lower than that of the previous trace t5, and the error rates of the other areas A2, A3, A4, and A5 are high, but still below the threshold Eth.

Further, the trace t moved stepwise in the direction A
7, the error rate of the area A1 is lower than that of the previous trace t6, and the other areas A2, A3, A
The error rates of 4 and A5 are equal to or higher than the threshold Eth.

From these, it can be seen that the optimum trace position is the trace t5 or the trace t6. The servo circuit 38 makes the reproducing head 10 off-track in the B direction this time, and the reproducing head 10 traces the trace t5.
Alternatively, the trace position corresponding to t6 is controlled.

As described above, in this embodiment, the reproducing head is off-tracked so that the error rate of each area is low as a whole. When the reproduction track is partially curved as shown in FIG. 6, the error rate deteriorates in one or a plurality of areas, but attention is paid to continuous areas where the error rate is equal to or higher than the threshold Eth, and Area error rate is threshold Eth
The reproducing head may be off-tracked as follows, but for example, when the reproducing track is meandering, the error rate deteriorates in a plurality of distant areas. In such a situation, the change in the error rate of each area with respect to the off-track position is statistically processed to determine the optimum off-track position.

Further, in the above-mentioned embodiment, although it was explained that one track is optimally traced, since it is usual that continuous tracks are curved in the same shape, the tape travels with the tape running. Then, as described with reference to FIG. 7, the tracking for each continuous track may be controlled according to the number of errors for each area.

In the above embodiment, the off-track is determined by the number of errors (or error rate) in the five areas of the track start portion. However, each area of the entire track or a plurality of selected tracks of the entire track is determined. Obviously, tracking control by the number of errors (or error rate) in the area is also included in the technical scope of the present invention.

According to the above embodiment, when the tape is started, the reproducing head can be controlled to the optimum position with respect to the reproducing track earlier than before.

The technique of controlling the tracking of the reproducing head based on the number of errors (or error rate) for each area is not limited to the magnetic tape for helical scan recording, but also a disk-shaped recording medium (optical disk, magneto-optical disk, floppy disk, etc.).
It can also be applied to disks, hard disks, etc.

[0039]

As can be easily understood from the above description, according to the present invention, the tracking control of the digital recording system can be made more appropriate, the error rate as a whole can be reduced, and the reproduction signal quality can be improved. .

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a reproduction RF level and an error rate.

FIG. 3 is a diagram showing a correspondence between a trace position of a reproducing head and a reproducing RF level.

FIG. 4 is a diagram showing a correspondence between another trace position of a reproducing head and a reproducing RF level.

FIG. 5 is a characteristic diagram of weighting by the gain adjusting circuit 22.

FIG. 6 is a diagram showing a head trace for explaining the operation of the present embodiment.

FIG. 7 is a diagram showing an error rate change in each area and off-track in the trace shown in FIG.

[Explanation of symbols]

 10: playback head 12: playback amplifier 14: digital demodulation circuit 16: error correction circuit 18: playback processing circuit 20: error measurement circuit for each area 22: gain adjustment circuit 24: ATF error processing circuit 26: drum motor 28: motor drive Circuit 30: Drum rotation detection circuit 32: Capstan motor 34: Motor drive circuit 36: Capstan rotation detection circuit 38: Servo circuit

Claims (4)

[Claims] 1. An error detecting means for detecting an error in reproduction information from a recording medium, and the number of errors detected by the error detecting means is counted for a predetermined area of a recording unit of a predetermined size of the recording medium. A tracking control device comprising: an area-based error number counting means; and a position control means for controlling the position of the reproducing head with respect to the recording unit according to the output of the area-based error number counting means. 2. The tracking control device according to claim 1, wherein the recording medium is a tape-shaped recording medium, and the recording unit of the predetermined size is a track. 3. An area-by-area error number measuring means for measuring the number of errors detected by the error detecting means by the area-by-area error number counting means for a predetermined area of a recording unit of a predetermined size of the recording medium. The tracking control device according to claim 1 or 2, further comprising: weighting means for weighting a measurement result of the error count measuring means for each area. 4. The control means for controlling the weighting amount of the weighting means to increase with the passage of time after the recording medium is activated.
The tracking control device according to any one of 1.