JPH01144255A - Tracking servo circuit - Google Patents

Abstract

PURPOSE:To reduce an error rate by inserting a circuit to convert the sampling cycle of a tracking error signal at equal intervals into a control loop. CONSTITUTION:The circuit 4 to convert the sampling cycle of the tracking error signal TE1 generated by sampling with an unequal interval and represents the deviation of a head from the center of a track to the equal interval is inserted into the control loop. Therefore, since the mean value goes to a control value assuming that the duty of the tracking error signal TE1 used in the control loop of a tracking servo system is 50%, the center of the head 1 can pass a locus A where the maximum volume of data can be picked up even when the deviation theta of a track angle exists. In such a way, it is possible to draw the locus with a low error rate of the head.

Description

[Detailed Description of the Invention] [Summary] By adding a circuit that converts the sampling period of the tracking error signal to equal intervals, the tracking error can be reduced to O at the center of the track even if there is an inherent deviation in the track angle. to control.

[Industrial application field]

The present invention relates to a tracking servo circuit that minimizes error rate.

[Conventional technology]

In helical scan type tape decks such as R-DAT and VTR, there is often some angular deviation between the center of the recorded track and the center trajectory of the head during playback. This angle deviation is called track angle deviation, and the second
It is represented by θ in the figure.

When there is such a track angle deviation θ,
If a tracking servo circuit such as R-DAT generates a tracking error by sampling at non-uniform intervals, the trajectory of the center of the head becomes ■. Since the head center (3) passes through the center of the track, it is convenient for reducing the error rate. However, due to a principle problem, the tracking servo circuit performs control so that the trajectory is as shown in (2), so the average tracking error is larger than that in (2), and as a result, the error rate increases.

[Problem that the invention seeks to solve]

The conventional tracking servo circuit causes the above-mentioned results.
There is a problem with the processing circuit (ATF circuit) that generates the tracking error signal.

The playback envelope obtained by sequentially scanning the tracks includes a signal (sync) corresponding to the ATF area set before and after the track as shown in Figure 3 (al), so this was detected (b) and (C). ) sink detection pulse D
When the level of the pilot signal (see FIG. 5) is sampled at i and D2, a tracking error signal TEI of dl, which indicates the amount and direction of deviation from the track center in the ATF area, is obtained twice per track.Tracking The servo circuit uses this tracking error signal TEI.
The rotational speed of the drum or capstan is controlled according to the average level of the tape, and the center of the head is controlled to move parallel to the tape running direction.

However, if the sampling period of the tracking error is not constant, a problem will occur if there is a deviation in the track angle. For example, when using a drum with an angle of 90°, the time difference between the sync detection pulses D1 and D2 (approximately 5 ms) and the time difference between the sync detection pulses D2 and Dl (approximately IQms) are different, so the sampling period is not constant. When there is a track angle deviation, when tracing (2) is performed, the tracking error signal device generates a rectangular wave with a duty of 33%. As a result, the average value of the receiving device becomes lower than the level (center value) of the tracking error O, so the head center moves to the position (2) that reduces the tracking error.

The present invention attempts to solve the above-mentioned problems by adding a circuit that converts the sampling period of the tracking error signal to equal intervals (a circuit that converts the duty of the tracking error signal to 50%).

[Means for solving problems]

The present invention provides a tracking servo circuit for a helical scan tape deck that corrects the relative position of the head and the track by using a tracking error signal generated by non-uniform sampling and indicating the deviation of the head from the center of the track. This is characterized in that a circuit for converting the sampling period of the error signal to equal intervals is inserted into the control loop.

[Effect]

If the duty of the tracking error signal used in the control loop of the trunking servo system is 50%, the average value will be the center value, so even if there is a track angle deviation θ as shown in Figure 2, the head center will be The error rate can be kept to a minimum because it follows the trajectory that can collect the most data.

〔Example〕

FIG. 1 is a configuration diagram of main parts showing an embodiment of the present invention, in which 1 is a rotary magnetic head, 2 is a high-frequency amplifier, 3 is an ATF @ path that generates a tracking error signal device, and 4 is an addition according to the present invention. This is a duty conversion circuit.

The ATF circuit 3 includes a sync detection circuit 31 that detects a sync from the ATF area shown in FIG. 5 and generates two types of sampling signals SH1 and SH2, a filter 32 that extracts a pilot signal, and a detection circuit that detects its output. 33, a first sample and hold circuit 34 that samples its output with a first sampling signal SHI, and a difference circuit 35 that takes the difference between the output level of this circuit and the input level.
A second sample and hold circuit 36 is provided that samples the output with a second sampling signal SH2.

The first sampling signal SHI is a general term for the sync detection pulses DI and D2 shown in FIG. 3, and the second sampling signal SH2 is generated with a delay of τ1. Since the pilot signal is obtained when successively passing through the pilot areas of adjacent tracks, if the head center and track center coincide, the first half and the second half will have the same level. However, if there is a discrepancy, it becomes a level difference (
Tracking error) appears as TE. The output TEI of the second sample and hold circuit 36 is a signal indicating the amount of this tracking error in terms of amplitude, as shown in FIG. However, as mentioned above, in the case of a deck with a wrap angle of 90'', the duty is 33%, so this is converted to 50% by the duty conversion circuit 4.

The duty conversion circuit 4 converts the first sampling signal S H
1, a gate 41 extracts only the rear sync detection pulse D2 with a gate pulse D, and a rising drive type monomulti 42 that converts it into a hold signal H with a pulse width τ.
The output TE2 of this hold circuit 43 has a duty of 50% as shown in FIG. This is the trunking error signal converted to .

FIG. 4 shows a tracking servo system incorporating this duty conversion circuit 4, in which 5 is a filter for averaging the level of the tracking error signal TE2, 6 is a drive amplifier, and 7 is a drum motor or capstan motor.

〔Effect of the invention〕

As described above, the present invention has the advantage of being able to draw a gutter trajectory with a low error rate even if there is a track angle deviation.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of main parts showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of track angle deviation, FIG. 3 is an explanatory diagram of a tracking error signal, and FIG. 4 is an overall diagram of the tracking servo circuit of the present invention. FIG. 5 is an explanatory diagram of the sampling signal. Applicant Fujitsu Ten Ltd. Representative Patent Attorney Minoru Aoyagi 1

Claims (1)

[Claims] In a tracking servo circuit of a helical scan tape deck that corrects the relative position of the head and track by using a tracking error signal generated by non-uniform sampling and indicating the deviation of the head from the center of the track, the tracking error signal is A tracking servo circuit characterized in that a circuit for converting a sampling period to equal intervals is inserted into a control loop.