JPH0421959A - Tracking control circuit - Google Patents

Abstract

PURPOSE:To shorten time until tracking is turned to an optimum state by detecting a deviating direction immediately when a track on the magnetic tape of a magnetic head is deviated from the center line of the track recorded onto the magnetic tape in advance. CONSTITUTION:Discrimination circuits 10 and 11 respectively output signals 101 and 102 as the results of envelope detection to output signals from a preamplifier 4 and a delay circuit 9 and output discrimination signals 103 and 104 to decide whether the signal reaches a prescribed level or not. When scanning is executed while deviating the center of a magnetic head HA1 to the side of a track Bn-1 from the center line of a track An, a changeover switch 14 is turned to the state of connecting a 14a by detecting that time tS required for the scan of a logic circuit 12 shown by the difference of starting time for the discrimination signals 103 and 104 obtains difference more than the allowable error of prescribed time, and the signal 102 at a level in proportion to the envelope of the reproducing signal of an HB'3 from the discrimination circuit 11 is guided to a driving circuit 15. Thus, the speed of traveling the magnetic tape is increased and the track at the center of the HA1 is controlled to correctly trace the center line of the track An.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a tracking control circuit for a magnetic recording/reproducing apparatus, and particularly to a tracking control circuit for a helical scanning type magnetic recording/reproducing apparatus.

(Prior Art) Conventional tracking control in a helical scanning type magnetic recording/reproducing device will be explained using a VH8 type VTR as an example. FIG. 2 is a schematic diagram of a video track recorded on a magnetic tape and a magnetic head that scans the video track.

A pair of magnetic heads are HA and BIl, and the tracks recorded by each head on the magnetic tape are A and A.

B, (n = 0, 1, 2-).

Here, H.

A) Consider when tracing a rack. The center of H^ is A. It is assumed that tracking is in the best state when tracing on the center line of , and that this best state is reached at the starting point S7 of the trace. The center of HA is the broken line ρ
. The top of the magnetic tape is scanned toward the end point Fl *-1 of track B4-1, but during this time the magnetic tape moves by the length ■ between the tracks in the longitudinal direction, so HA
The center of the magnetic tape is relatively scanned on the broken line ρ1 from S to E. Since pl is equal to the center line of A, then HA is A. This means that the track has been scanned in the best tracking state.

Since each track on a magnetic tape is not necessarily recorded at regular intervals, even if the magnetic tape is fed at a constant speed, the head and the track scanned by the head may deviate from each other.

In FIG. 2, the center of HA changes from ρ1 to ρ during scanning. When the tape is shifted to the side, the center of the HA can be returned to above p by appropriately increasing the tape running speed. Similarly, when the center of HA shifts from ρ1 to the opposite side of 10, the center of HA can be returned to ρ1 by appropriately decreasing the tape running speed.

A pair of magnetic heads HA and HB are usually mounted on a rotating drum in opposite directions in the diametrical direction, and HA or H8 scans the magnetic tape wound around the rotating drum. So...

The magnetic heads HA, H, are attached to a rotating drum via a piezo element, etc., and the mounting height of the magnetic heads HA, H can be changed by applying voltage to the piezo element, so that the center of the magnetic head and the track can be changed. By applying a voltage to the piezo element that is proportional to the amount of deviation from the center line of the piezo element, the best tracking state can be maintained.

As described above, conventional tracking control optimizes the tracking state by controlling the feeding speed of the magnetic tape and the position of the magnetic head on the rotating drum.

(Problems to be Solved by the Invention) In the conventional tracking control described above, tracking deviation is determined based on the magnitude of the envelope of the reproduction signal reproduced by the magnetic head. FIG. 3 shows the relationship between the envelope of this reproduced signal and the tracking error. As is clear from this figure, it is not possible to detect whether the center of the magnetic head has shifted to the right or left with respect to the direction of travel of the magnetic head from the center line of the track only from the size of the envelope of the reproduced signal. . Therefore, the feeding speed of the magnetic tape is slightly increased or decreased, and the direction of the track deviation is detected based on the level change of the envelope 1 of the reproduction signal at that time. Therefore, with conventional tracking control, it takes time to correct the tracking deviation, and when detecting the direction of the tracking deviation, the magnetic tape feeding speed is changed in the direction that increases the tracking deviation, resulting in playback. There were drawbacks such as the signal envelope becoming even smaller. In addition, it is not known whether the current tracking state is the best or not, and the magnetic tape feeding speed must be constantly increased or decreased slightly.

(Means for Solving the Problems) The tracking control circuit of the present invention uses a helical scanning method for magnetic recording and reproducing in which a pair of first and second magnetic heads having different azimuth angles alternately scan obliquely on a magnetic tape. In the tracking control circuit of the apparatus, the second magnetic head has the same azimuth angle and scans the same trajectory as the first magnetic head, and tracks adjacent to the track scanned by the first magnetic head. at least one third magnetic head that reproduces either one; and a delay that delays the reproduction output signal of the third magnetic head by a time equal to the scanning difference between the first magnetic head and the third magnetic head. a detection circuit that detects a tracking deviation based on a time difference between the rise or fall of the output signal of the delay circuit and the reproduced output signal of the first magnetic head; and a control circuit that controls the feeding speed of the magnetic tape.

(Example) Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 1, 2 and 2 are a pair of magnetic heads HA and HA having different azimuth angles, and each reproduction signal is amplified to a predetermined level by preamplifiers 4 and 5, and then a changeover switch 7 63, which is appropriately selected and guided to the demodulator 8 at the subsequent stage, has the same azimuth angle as the magnetic head H, and is placed immediately before the TR head, and is placed on the magnetic tape with the same azimuth angle as the magnetic head HA. This is the third magnetic head HIl' adjusted so as to draw a trajectory.

The reproduced signals of H and '3 are reproduced from racks I to one of the tracks adjacent to the track scanned by the HAI. The delay circuit 9 converts the reproduced signal of H,'3 which has not been amplified to a predetermined level by the preamplifier 6 into H,3.
and HAl pass through the same point on the magnetic tape. Discrimination circuits 10 and 11 output signals 101 and 102 obtained by envelope-detecting the output signals of the preamplifier 4 and delay circuit 9, respectively, and output discrimination signals 103 and 104 that determine whether or not the signals have reached a predetermined level.

Now, as shown in Fig. 4, let's say that the center of HAl is A and B is from the center line of the track. Consider a case where scanning is performed closer to -1 track. At this time, HAl outputs the reproduction signal of track A, H, °3 outputs the reproduction signal of track B, -i, and the envelope of the output signal of the preamplifier 4 and delay circuit 9 is as follows.

As shown in FIGS. 5(b) and 5(d), respectively.

In Figure 4, HAl moves from the start point S7 of the Afi track to the end point E.
While tracing up to 7, H8°3 precedes IA1 by a predetermined distance and scans the same trajectory as HAl, but its output signal is given a delay of the preceding time by delay circuit 9. Therefore, when comparing the output signals of the preamplifier 4 and the delay circuit 9, it is safe to assume that ■-■A1 and Hll''3 are at the same position.

At this time, the discrimination signal 1 output from the discrimination circuit 10.11
．． 03104 is the time t required for the magnetic head to scan by T11 in FIG. 4, as shown in FIGS. 5(e) and 5(f).
8, the rise of the discrimination signal 104 is delayed from the rise of the discrimination signal 103.

On the other hand, if the center of HAl scans closer to the B, l-rack than the center line of the As track in Figure S4, the discrimination signals 103 and 104 are shown in Figures 6 (b) and (c). Thus, the rise of the discrimination signal 104 precedes the rise of the discrimination signal 103 by the time t8 required for the magnetic head to scan by T8 in FIG.

Here, the relationship between the discrimination signals 103 and 104 is shown in FIG.
In the cases shown in e) and (f), the magnetic head is deviated to the left with respect to the traveling direction of the magnetic head in Fig. 4, and as shown in Fig. 6 (b) and (c). In such a case, FIG. 4 shows that the magnetic head is shifted to the right with respect to the traveling direction of the magnetic head. Further, when ts or t8 at the standard interval between adjacent tracks is a predetermined time, if t8 or tll is larger than the predetermined time, it indicates that the interval between adjacent tracks is larger than the standard interval, If t8 or t8 is smaller than the predetermined time, it indicates that the interval between adjacent tracks is smaller than the standard interval.

The logic circuit 12 receives the discrimination signals 1.03 and 104, controls the changeover switch 14, and guides the signal 102 or the output signal 105 of the inverting amplifier 13 to the drive circuit 15. If the relationship between the discrimination signals 103 and 104 is as shown in FIGS. 5(e) and 5(f), and ts is different from the predetermined time by more than the allowable error, the changeover switch 14 is set to the connected state of 14a. . The relationship between the discrimination signals 103 and 104 is shown in FIG. 6(b) and (C
), and if t8 differs from the predetermined time by more than the allowable error, the changeover switch 14 is set to the connected state 14c. ts or 1. If the difference from the predetermined time is within the allowable error, or if the output signal of the delay circuit 9 is less than or equal to a predetermined value, the changeover switch 14 is set to the connected state of 14b.

The output signal 102 of the discrimination circuit 11 is 118 while the HAl is racing the magnetic tape A, tracks 1 to 11.
It takes a value proportional to the envelope of the output signal of °3, and I
(, 2 is B on the magnetic tape. While tracing a track, the HAl immediately before it is A on the magnetic tape.) The envelope of the output signal of H8'3 when tracing the rack (this is proportional to The drive circuit 15 uses the output signal to drive the capstan motor 16 to run the magnetic tape.When the drive circuit 15 receives the signal 102, the capstan motor 16 rotates 'f14f'. is increased, and upon receiving the signal 105, the rotational speed of the capstan motor 16 is decreased.

Therefore, in FIG. 4, when the center of HAl is scanning toward A, B, -+)'' rack from the center line of the track, the discrimination signals 103 and 104 are as shown in FIG.
The waveform becomes as shown in (f), and if the logic circuit 12 detects that ts differs from the predetermined time by more than the allowable error (not shown in FIG. A signal 102 with a level proportional to the envelope of the reproduction signal of H6゛3 is guided to the drive circuit 15, and the running speed of the magnetic tape is increased so that the trajectory of the center of HAI correctly traces the center line of the track A. controlled.

(Effects of the Invention) As explained above, in the present invention, when the trajectory of the magnetic head on the magnetic tape deviates from the center line of the track previously recorded on the magnetic tape, the direction of the deviation can be immediately detected. It takes only a short time to bring tracking to the best state, and when correcting tracking deviation, the tape feeding speed is not changed in a direction that increases the amount of tracking deviation.

Furthermore, since the best point in the tracking state can be detected, it also has the effect that more stable tracking control can be performed in a steady state.

Further, in the embodiment, tracking control is performed by adjusting the feeding speed of the magnetic tape, but the present invention is also effective in a system in which tracking control is performed by adjusting the head mounting height using a piezo element or the like. It is.

Furthermore, the present invention is effective not only for VH3 type VTRs, but also for systems such as β type, 8 nm VTR, or UN I HI format, in which heads with different azimuth angles alternately perform diagonal recording on a magnetic tape. It is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the tracking control circuit of the present invention, FIG. 2 is a diagram showing a schematic diagram when a magnetic head scans a magnetic tape, and FIG. 3 shows tracking deviation amount and reproduction. FIG. 4 is a diagram showing the relationship between the signal envelope size and FIG. 4 is a schematic diagram when the magnetic head scans the magnetic tape. FIG. 5 is a diagram showing the envelope of each output signal and a time chart of the discrimination signal. , FIG. 6 is a diagram showing the envelope of each output signal and a time chart of the discrimination signal. 12.3... Magnetic head, 4, 5.6... Preamplifier, 7, 14... Changeover switch, 8... Demodulator, 9
...Delay circuit, 10.11...Discrimination circuit, 12...
・Logic circuit, 13... Inverting amplifier, 15... Drive circuit, 16... Capstan motor, 17... F
G.

Claims (1)

[Claims] In a tracking control circuit in a helical scanning magnetic recording/reproducing device in which a pair of first and second magnetic heads having different azimuth angles alternately scan obliquely on a magnetic tape, at least one third magnetic head having a corner and scanning the same trajectory as the first magnetic head to reproduce either a track scanned by the first magnetic head or an adjacent track;
a magnetic head, a delay circuit that delays the reproduction output signal of the third magnetic head by a time equal to the scanning difference between the first magnetic head and the third magnetic head, and an output signal of the delay circuit and the A detection circuit that detects a tracking deviation from the time difference between the rise or fall of the reproduction output signal of the first magnetic head, and a control circuit that controls the feeding speed of the magnetic tape according to the tracking deviation detected by the detection circuit. A tracking control circuit comprising: