JPH0664792B2 - Automatic tracking device for magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic tracking device for a magnetic recording / reproducing apparatus, and more particularly to a signal reproduced from a recording track of a magnetic recording medium (for example, a magnetic tape) by a rotary magnetic head. The present invention relates to an automatic tracking device for a magnetic recording / reproducing device that automatically controls a tracking phase based on a change in amplitude.

[Prior Art] Tracking in a video tape recorder (VTR), for example, means that when the recorded information on a magnetic tape (hereinafter, also simply referred to as a tape) recorded by a rotating magnetic head is reproduced, it is rotated to the same position as a recording track. Refers to sliding the magnetic head.

FIG. 4 (a) shows an FM envelope waveform as the output of the rotary magnetic head, and FIG. 4 (b) shows the FM envelope waveform of FIG. 4 (a).
The detection waveform which carried out AM detection of the envelope is shown. Further, FIG. 5 (a) shows the increase / decrease of the FM envelope detection waveform when the tracking phase is changed, and FIG. 5 (c) shows the waveform of FIG. 5 (a) sampled in FIG. 5 (b). The waveform when quantized by a pulse is shown. The conventional automatic tracking control method will be described below with reference to FIGS. 4 and 5. The output from the rotary magnetic head is amplitude-detected (see FIG. 4 (b)), and the tracking phase of the servo circuit is changed to change the head trace at the time of reproduction with respect to the recording track of the rotary magnetic head. ) Waveform. Next, for example, a microcomputer determines the level of the output of the rotary magnetic head when the tracking phase changes at each sampling time shown in FIG. 5 (b) to create a quantization pattern shown in FIG. 5 (c). When the converted level is increasing, the tracking phase is moved in the positive direction, and conversely, when the level is decreasing, the tracking phase is reversed to search for the maximum point H (see FIG. 5 (c)). Was there.

[Problems to be Solved by the Invention] For example, in a stationary VTR, two video heads placed at 180 ° intervals are switched for each field and 2
Create video in field 1 frame, and also C-VH
In the S system movie or the like, four video heads placed at intervals of 90 ° on the rotating drum are sequentially switched to record and reproduce to create an image. In the conventional automatic tracking method in which FM envelope detection level differences are compared on a field-by-field basis and tracking is changed to find the maximum value, if there is an output level difference between video heads or a step is generated between each head. , The tracking convergence value is different for each field, and especially in the case of C-VHS etc., the convergence value is different for each field for a maximum of 2 frames, so the FM envelope changes, the image S / N is different, and automatic tracking is performed. There was a problem that the state where it did not converge continued.

The present invention has been made in order to solve the above-mentioned problems, and it is a level difference between video heads used, a step or a used tape, which is frequently demagnetized, and a compatibility recorded by another device. It is an object of the present invention to provide an automatic tracking device capable of always obtaining a stable and accurate tracking convergence value for a tape having poor performance.

[Means for Solving Problems] An automatic tracking device of a magnetic recording / reproducing apparatus according to the present invention has two or four rotary magnetic heads on a rotary drum, and sequentially records on a magnetic tape field by field. In an automatic tracking device of a magnetic recording / reproducing device for controlling a tracking phase of a rotary magnetic head with respect to a recorded track, a detecting means for detecting an FM reproduction signal sequentially reproduced from the recording track by the rotary magnetic head, and an FM. The minimum level recording track position searching means for searching the recording track position where the output level of the detecting means is the lowest in the two frames of the reproduction signal, and the optimum tracking phase in the recording track searched by this minimum level recording track position searching means. And an optimum tracking phase searching means for searching.

[Operation] The automatic tracking device of the magnetic recording / reproducing apparatus according to the present invention searches for the optimum tracking phase using two frames as a reference unit, so that the reproduction output level changes for each field or for each frame. Stable images can be obtained without automatic tracking again.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.
In the figure, an FM reproduction output is obtained by sliding a video head 2 mounted on a rotary drum 1 on a magnetic tape 3. The FM reproduction output is amplified by the preamplifier 4, then converted to a DC voltage by the amplitude detection circuit 5, digitized by the A / D conversion circuit 6, and supplied to the microcomputer 7. On the other hand, in order to correctly position the video head 2 on the magnetic tape 3, the control signal head 8 reads the control signal recorded on the magnetic tape 3 and supplies it to the servo circuit 9. Further, the rotation phase information output from the PG head 10 for detecting the drum rotation phase is supplied to the servo circuit 9. In response to a command from the microcomputer 7, the servo circuit 9 operates the capstan motor 11 and the drum motor 12 by the capstan motor drive circuit 13 and the drum motor drive circuit 14, respectively, based on the control signal and the PG head signal. The drive is performed and the speed and phase are adjusted so as to adjust the positions of the video head 2 and the magnetic tape 3.

Next, the optimum tracking phase search operation, which is a feature of the above embodiment, will be described in detail below. In the following description, an optimum tracking phase search operation in a C-VHS VTR will be described as an example.

FIG. 2A shows a reproduction output pattern of a tape recorded by the C-VHS method. 1 for normal VHS
The same head output is repeated for each frame, but C-V
In the HS system, since the video is sequentially recorded by the video head placed on the rotating drum at 90 ° intervals, the same head output is repeated every two frames. First, the microcomputer 7 reads the detection output voltage at the reproduction output level shown in FIG. 2 (b) in synchronization with the sampling pulse for each time T shown in FIG. In this embodiment, it exists in the channel CH4). Next, the microcomputer 7 searches for the optimum tracking value at the position where the lowest level value A is detected.
This search operation is shown in the flowchart of FIG.

In FIG. 3, the microcomputer 7 first sets an initial value of the tracking phase, for example, to a value t ₀ (see FIGS. 2 (d) and 2 (e)) at which optimum tracking can be obtained with a standard tape when starting the optimum tracking phase search. ,
The servo circuit 9 is controlled so that the tracking phase of the video head 2 with respect to the recording track of the tape 3 becomes this value t ₀ (steps S1 and S2). The above value t ₀
Are fixedly set in advance in the VTR.

Next, the microcomputer 7 controls the servo circuit 9 to change the tracking phase by a unit amount (Δt) (step S3). Along with this, the detection voltage value of the FM reproduction output changes into a mountain shape as shown in FIG. 2 (e).
The microcomputer 7 determines the maximum detection voltage value at this time.
Hmax is detected (steps S4 to S7). The tracking phase tmax when the maximum detected voltage value Hmax is obtained may be determined as the optimum tracking value, but in this embodiment, the processes of the following steps S8 to S16 are further performed to calculate the optimum tracking value t _OPT . I am trying.

That is, the microcomputer 7 shifts the tracking phase by a unit amount in the positive direction, and when the detection output voltage value of the reproduction output becomes a value (Hmax-r) obtained by subtracting a preset value r from the maximum detection voltage value Hmax. Tracking phase ta
Is detected (steps S8 to S11). Then, the microcomputer 7 shifts the tracking phase by a unit amount in the negative direction, and the detection output voltage value of the reproduction output is a value (Hmax) obtained by subtracting the predetermined value r from the detected maximum detection voltage value Hmax.
The tracking phase tb when -r) is reached is detected (steps S12 to S15). Then, the microcomputer 7 detects the tracking phase ta detected as described above.
And an intermediate value (ta + tb) / 2 between tb and tb is set as the optimum tracking phase t _OPT (step S16). Since the optimum tracking phase is calculated in this way, it is possible to accurately detect the optimum tracking phase even when the peak of the peak of the detection output voltage when the tracking phase changes is flat or when there are multiple peaks. it can.

Next, the microcomputer 7 determines whether the detection output voltage H _{OPT at the} optimum tracking phase t _OPT is larger than a preset value n (step S17). This set value n is the permissible level of the visual sense of the video signal. If H _OPT is larger than this set value n, the optimum tracking phase t _OPT is adopted to continue the tracking servo, but if H _OPT is smaller than the set value n, then n is lowered in step S20 and then optimum again. A tracking phase search operation is performed to calculate a proper optimum tracking phase t _OPT even for a tape having a low recording level. When H _OPT is larger than the set value n, the servo circuit 9 performs tracking servo control so that the optimum tracking phase t _OPT phase is maintained. The microcomputer 7 always detects the detection output voltage at the optimum tracking phase t _OPT . The value is monitored (steps S18 and S19). In other words, it determines whether or not lower than a preset value l from the initial reproduction output detection voltage value H _OPT when optimum tracking phase t reproduction output detection voltage value x in _OPT was determined the optimum tracking phase t _OPT If it is not decreased, the tracking servo is continued as it is, and if it is decreased by 1 or more, the search operation for the optimum tracking phase is performed again. For example, tape is another VTR
When the image S / N is deteriorated to the place where the recording is performed and it is necessary to change the tracking phase, the optimum tracking phase detection operation is performed again.

As described above, in the above-described embodiment, the optimum tracking phase of the portion where the detection output voltage has the lowest value is detected within two frames, so that the reproduction output level changes for each field or for each frame. As a result, automatic tracking can be surely converged and a stable image can be always supplied. On the other hand, in the conventional method of detecting the optimum tracking value with one frame as one unit, for example, in the case of FIG. 2, the first half of the first half (channel CH1
And the reproduction output detection voltage value for the optimum tracking phase obtained in CH2) and the reproduction output detection voltage value for the optimum tracking phase obtained in the second frame of the latter half (channels CH3 and CH4) are different values.
When the difference between them is 1 or more, the optimum tracking phase detection operation is repeated for each frame, and automatic tracking does not converge. In this embodiment, such a problem does not occur.

In the above embodiment, the automatic tracking for the video signal has been described, but the present invention is applicable not only to the video signal but also to the automatic tracking of the audio signal.

[Effects of the Invention] As described above, according to the present invention, the optimum tracking value is detected with two frames as one unit.
Regardless of the difference in the pattern on the recording tape between the VHS formats, it is possible to always perform highly accurate and stable tracking control.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a waveform diagram for explaining the optimum tracking phase detecting operation of the embodiment shown in FIG. FIG. 3 is a flow chart for explaining the optimum tracking phase detection operation in the embodiment of FIG. 4 and 5 are waveform diagrams for explaining the conventional tracking control method. In the figure, 1 is a rotary drum, 2 is a video head, 3 is a magnetic tape, 4 is a preamplifier, 5 is an amplitude detection circuit, and 6 is A.
/ D conversion circuit, 7 is a microcomputer, 8 is a control signal head, 10 is a PG head, 11 is a capstan motor, 12 is a drum motor, 13 is a capstan motor drive circuit, and 14 is a drum motor drive circuit.

Claims (3)

[Claims] 1. A rotary drum having two or four rotary magnetic heads for controlling a tracking phase of the rotary magnetic head with respect to recording tracks sequentially recorded for each field on a magnetic tape. In an automatic tracking device of a magnetic recording / reproducing apparatus, a detection means for detecting an FM reproduction signal sequentially reproduced from a recording track by the rotary magnetic head, and an output level of the detection means within two frames of the FM reproduction signal is the lowest. A lowest level recording track position searching means for searching the recording track position, and an optimum tracking phase searching means for searching the optimum tracking phase in the recording track searched by the lowest level recording track position searching means. Automatic tracking device for magnetic recording / reproducing device. 2. The optimum tracking phase searching means reads the output of the detecting means in the recording track searched by the lowest level recording track position searching means by shifting the tracking phase by a unit amount, and the output level of the detecting means. A maximum level detecting means for detecting the level value at which the maximum value becomes maximum, and a tracking phase corresponding to a value obtained by subtracting a preset first predetermined value from the maximum level value detected by the maximum level detecting means. The automatic recording according to claim 1, further comprising: predetermined tracking phase searching means for searching; and calculating means for calculating the optimum tracking phase based on a search result of the predetermined tracking phase searching means. Automatic tracking device for playback device. 3. When the output level of the detecting means at the optimum tracking phase falls from a maximum level value initially detected by the maximum level detecting means by a second predetermined value set in advance, the output level of the detecting means is again set. The second aspect of the present invention is characterized in that the optimum tracking phase is searched.
An automatic tracking device for a magnetic recording / reproducing device according to the item.