JPH0481273B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a magnetic recording and reproducing apparatus having a variable speed function by intermittent driving of a magnetic tape. [Background of the Invention] In a rotating head helical scan type magnetic recording/reproducing device, some kind of synchronization signal is recorded on the magnetic tape during recording, and the synchronization signal is reproduced during playback to adjust the rotational phase of the capstan or rotary head cylinder. A servo circuit performs tracking control so that the rotating head correctly traces the video signal recording track on the magnetic tape. As the synchronization signal, a method is used in which a pulse signal of 1/2 period of a vertical synchronization signal, usually called a control signal (abbreviated as CTL), is written at the end of the tape. In the method using this control signal, no matter what speed the magnetic tape is run intermittently, the absolute phase relative to the recording pattern on the magnetic tape is uniquely determined when the CTL signal is detected. For this reason, an intermittent drive variable speed system allows a magnetic tape stopped in a noiseless still state to be instantaneously moved to a noiseless state one frame later by intermittent drive, and this operation is repeated at appropriate time intervals to perform noiseless slow motion. In the CTL system, regeneration could be easily carried out by performing stop control, including reverse braking of the capstan motor, after a predetermined time delay after the detection of the CTL signal. The method described above was for a system that uses CTL signals, but in another servo system that records a synchronization signal superimposed on the video track (abbreviated as the pilot system), the CTL signal is used instead of the CTL signal. It is necessary to obtain a tracking error signal from the level of the reproduction pilot signal during the period and use this information to control the intermittent drive of the magnetic tape. However, unlike normal playback, in which the tracking error signal is passed through a low-pass filter with a sufficiently large time constant and servo control is performed on the average, tracking error signal information is The signal-to-noise ratio is poor;
It has not been possible to achieve noiseless intermittent drive equivalent to the conventional CTL method. [Object of the Invention] It is an object of the present invention to eliminate the drawbacks of the prior art described above, and to eliminate the drawbacks of the conventional CTL even if a regenerated pilot signal is used.
It is an object of the present invention to provide a magnetic recording and reproducing device having a variable speed function using intermittent drive that can perform stop control in a noiseless still state with an accuracy equal to or higher than that using a signal. [Summary of the Invention] In order to achieve the above-mentioned object, the present invention provides the following steps to control the intermittent drive of a magnetic tape by utilizing information during the stop period as effectively as possible.
The reproduced pilot signal converted to digital quantity is
Integration is performed for a predetermined period of time in the field period, and the digital integration processing is performed over a predetermined plurality of fields during the stop period, and the SN ratio corresponding to the amount of deviation from the normal noiseless stop state is calculated based on the total integrated value. A means of producing a good stopping error signal was adopted. [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a magnetic recording and reproducing apparatus according to an embodiment of the present invention. In FIG. 1, 1 is a magnetic tape, 2 is a cylinder motor, 3 is a rotating video head, and 4 is an intermittent drive control circuit 16 that detects the rotational phase of the cylinder and includes a servo circuit to create a head switching signal SW30. 5 is a capstan motor, 6 is a signal circuit for extracting low-frequency components from the video head output, 7 is a tracking error signal processing circuit using a pilot system, and 8 is a pilot signal having the four local frequencies described below. 9 is a local frequency generator 10 and BPF _{1 .}
Mixers 11 and 13 selectively pass a specific pilot frequency difference, respectively.
Bandpass filter (BPF ₂ ) and bandpass filter (BPF ₃ ) that output 3f _H error and f _H error, 12 and 14 are detectors, 15 is a frequency detector, 17 is an AD (analog digital) converter, and 18 is a 19 is an integrator (or accumulator), 20 is a data latch, 21 is a comparator, 22
The circuit for creating these stop error signals is connected to the intermittent drive mode command and head switching signal SW3.
This is a control circuit for controlling based on the timing of zero. Next, see Figure 1, the intermittent drive pattern diagram in Figure 2, and the signal waveform diagram of each part in Figure 3 (the horizontal axis is the time axis).
The operation of an embodiment of the present invention will be explained using FIG. In this example, four types of pilot frequencies f ₁ (6.5f _H ), f ₂ (7.5f _H ), f ₃ (10.5f _H
),
We will explain the method of writing f ₄ (9.5f _H ) to the video track field by field in this order. Here, f _H is the horizontal synchronization frequency. Note that the operation of the pilot system regarding normal recording and playback is well known and will not be described in detail. In Fig. 2, f ₁ , f ₂ , f ₃ , f ₄ , f ₁ , and f ₂ are tracks on which pilot signals have been recorded in advance, and shaded areas A, B, and A are intermittent drives that stop each time. The trajectory of the head is shown, and a and b indicate that the head is moving with intermittent drive. In addition, in this embodiment, A, B,
A...I will explain so-called field stills, which reproduce everything at the same azimuth, but normal frame stills can be considered in the same way. First, it will be explained that a stop error signal corresponding to the amount of deviation from the normal noiseless state in the stop state A can be created with a good S/N ratio as follows. In the intermittent drive mode, the control circuit 22 fixes the local frequency mixed with the reproduced pilot signal PILOT to, for example, _f2 . At position A, the error signals 3f _H error and f _H error obtained from both adjacent tracks during the stop period shown in FIG. 1 are as shown in FIG. 3. Therefore, the difference between 3f _H error and f _H error is SW3
It is considered that the value sampled at the center point of the "L" period of 0 represents the instantaneous stop error signal.
However, as can be seen from Figure 3, this value is extremely
Poor signal to noise ratio. Therefore, in this embodiment, the sampling pulse i is 1
Sampling and AD conversion (by AD converter 17) n times during a predetermined time τ (to remove the effect of switching) of the field (approximately 16.7 ms) period,
An integrator 19 integrates the difference P between the 3f _H error and the f _H error passed through the subtracter 18 . Furthermore, the waveform obtained by integrating this operation over m fields (equivalent to m/2 operations because it is integrated only at "L" of SW30) is Q, and finally, the control circuit 22 data-latches the total integrated value with a latch pulse j. The value latched at 20 is the stop error signal E whose SN ratio has been improved by integrating and averaging. The reason why only one side (here, "L") of SW 30 is integrated is to ignore the fact that differences in conditions such as head width imbalance exist between "H" and "L" of SW 30. Assuming that the noise in the reproduced pilot signal is only a random component, the S/N ratio will be lower than in the case of an instantaneous stop error signal.

〔Effect of the invention〕

As explained above, according to the present invention, a CTL signal is not required, and any method that can obtain a tracking error signal using a pilot signal or the like can be used to reduce slow and still speeds due to intermittent drive due to the averaging effect of digital integration. It is possible to realize variable speed playback such as the following with the same or higher accuracy than when using conventional CTL signals.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a magnetic recording/reproducing device according to an embodiment of the present invention, Fig. 2 is a pattern diagram of intermittent drive according to the present invention, Fig. 3 is a signal waveform diagram of each part, and Fig. 4 is a diagram of a stop error signal. FIG. 5 is a block diagram according to another embodiment, and FIG. 6 is a flowchart for explaining the operation of FIG. 5. 7...Tracking error signal processing circuit, 16
...Intermittent drive control circuit, 17, 30...AD converter, 18, 34...Subtractor, 19...Integrator, 20...Data latch, 21...Comparator, 3
1...CPU, 33...Microcomputer.

Claims (1)

[Scope of Claims] 1. Means for intermittently driving a magnetic tape in a rotating head helical scan type magnetic recording and reproducing apparatus that performs tracking by superimposing and recording a pilot signal on a video track, and a means for intermittently driving a magnetic tape, and a reproduction pilot signal during a stop period. and means for fixing the pilot local frequency mixed in the pilot signal to one specific type for a predetermined period;
means for converting the detected reproduction pilot signal into a digital quantity and integrating it for a predetermined time period of one field period; means for performing the integration over a plurality of fields during the stop period; and means for creating a stop error signal corresponding to the amount of deviation from a normal noiseless stop state, and controlling intermittent drive of the magnetic tape in a direction in which the stop error signal approaches zero. Device. 2. The magnetic recording and reproducing apparatus according to claim 1, wherein an integral operation is performed only in one of the even-numbered fields and the odd-numbered fields. 3. A means for fixing the mixed pilot local frequency to one specific type for detecting a tracking error signal, and a means for detecting a tracking error signal, and detecting a signal obtained from both adjacent tracks during a stop period using two predetermined types of bandpass filters from the mixed signal. 3. The magnetic recording and reproducing apparatus according to claim 1, further comprising means for extracting an error signal, and performing differential processing after each of the two types of error signals is digitally converted. 4. The magnetic recording and reproducing apparatus according to claims 1 to 3, characterized in that the specific type of pilot local frequency to be mixed is selected so that the level of the error signal after mixing is not the lowest. .