JPH029514B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating head type magnetic recording and reproducing device (hereinafter referred to as a VTR), and particularly relates to an improvement in a method for generating a movable head drive pattern in order to achieve high-speed reproduction without noise. be.

Generally, in a helical scanning VTR, the recorded video track and the video head trajectory do not match during high-speed playback. For this reason, a conventional method has been to attach the video head to a piezoelectric element or the like and match the video track with the trajectory of the video head to obtain good image quality. This method is called auto-tracking using a movable head. . (Hereafter simply referred to as AT). this
AT methods include the absolute phase method, which uses control pulses and the FC signal of the capstan motor, and the pilot signal method, which uses pilot signals recorded at different frequencies for each video track (four types of pilot signals). There are 4 methods (also called 4 methods) because the frequencies are switched sequentially.

Here, the above AT will be explained using four methods as examples.

Figures 1 and 2 respectively show the videotape recording pattern and AT system block diagram for four helical scanning VTR systems. In the figures, 1 is the videotape, 2 is the video track, and 3a and 3b are respectively Video heads 4a and 4b are mounted at opposite ends (180° positions) of a rotating cylinder (not shown) with different azimuths, and 4a and 4b are electro-mechanical devices such as bimorphs with video heads 3a and 3b mounted respectively. A piezoelectric element is used as a displacement transducer, and the video heads 3a, 3b and the piezoelectric elements 4a, 4b create movable heads 40a, 40a, 4b.
40b is configured. The movable heads 40a, 40b can be displaced in a direction perpendicular to the rotating surface of the rotary cylinder. Also, 5
is a head switching signal H-SW for selecting signals from video heads 3a and 3b, 6a and 6b are playback signals obtained by video heads 3a and 3b, respectively, and 7a and 7b are playback signals 6a and 6b, respectively.
8 is a switch circuit for selecting either one of the reproduced signals 6a, 6b, and 50 is an output of the switch circuit 8 which is connected to the movable heads 40a, 4.
This is an error detection device that detects a tracking error of 0b, and in this error detection device 50,
9 is a filter for extracting the pilot signal from the output of the switch circuit 8; 10 is the regenerated pilot signal p; 11 is the carrier signal _CR ; 12 is a balanced mixer for mixing the pilot signal 10 and the carrier signal 11; , 13b are band pass filters, 14a and 14b are amplitude detectors, and 15 is a comparison calculator. In addition, 16 is a movable head 40.
17a and 17b are low-pass filters, and 18a and 18b are time constant switching signals for switching the time constants of the low-pass filters 17a and 17b, respectively. , 19a, 19b are piezoelectric elements 4a, 4b, ie, movable heads 40a, 40b, respectively.
This is a drive amplifier for driving the low-pass filters 17a, 17b and the drive amplifier 19.
A and 19b constitute a drive device 60.

In addition, in Figure 1, the pilot signals recorded with the four helical scanning VTR systems are shown.
₁ , ₂ , ₃ , ₄ are respectively 102KHz, 118KHz, 164KHz,
The frequency is set to 148 KHz, which is sufficiently low compared to the Y signal and C signal, and the frequency difference between adjacent pilot signals is set to a predetermined value of 16 KHz and 46 KHz. Also, pilot signals ₁ and ₃ are on one azimuth (CH-1 head), and pilot signals ₂ and ₄ are on the other azimuth (CH-2 head).
It is superimposed on the video track on the side.

FIGS. 3 to 6 are diagrams for explaining the operation of the AT system block diagram shown in FIG. 4a and 4b show an example of the basic pattern and the waveform of the head switching signal during 5x high-speed playback using the conventional method, respectively. FIG. 5 shows an example of synthesizing the driving pattern from the basic pattern and the error pattern. FIG. 6 shows an example of the configuration of a smoothing low-pass filter and an example of a drive pattern that passes through the filter. In the figure, 20 is a movable head 40.
a and 40b are fixed (called a fixed head trajectory), 21 is a head trajectory on the videotape 1 during normal recording and playback (usually called a head trajectory), and 22 is a velocity vector for the normal playback speed ( 23 is the speed vector for the 5x high speed playback speed, 25 is the head trajectory on the videotape during 5x high speed playback, 25
a is the head trajectory on the videotape during 5x high speed playback of CH-1, 25b is the head trajectory on the videotape during 5x high speed playback of CH-2, and 26a is the CH-1 side during 5x high speed playback. 26b is a basic pattern for driving the movable head on the CH-2 side during 5x high-speed playback, 27 is a stepped basic pattern,
28 is the error pattern, 29 is the basic pattern 27
A movable head drive pattern 3 for driving a movable head formed by combining the error pattern 28 and the error pattern 28
0 is a filter passing drive pattern after the movable head drive pattern 29 passes through the smoothing low-pass filter 17.

Next, the operation will be explained.

First, control of the movable head during playback at normal speed will be explained.

Now, as shown in Figure 4b, the video head 3
Switching signal H-SW5 for switching between a and 3b is “H”
It is assumed that the video head 3a is in the recording/playback state at this time. That is, the video heads 3a and 3b are placed on the CH-1 side and CH-2 side, respectively. It is also assumed that the video head 3a is tracing the video track 2a on which the pilot signal ₁ is recorded.
At this time, pilot signals ₂ and ₄ recorded on adjacent tracks are mixed into the reproduced signal 6a as a crosstalk signal. This reproduction signal 6a is amplified by a reproduction amplifier 7a, passes through a switch circuit 8,
The signal is input to a filter 9 that selectively passes the pilot signal, thereby obtaining a reproduced pilot signal P10. This reproduced pilot signal p10 includes pilot signal ₁ and pilot signals ₂ and ₄ as crosstalk.

Next, transfer carrier signal _CR 11 to pilot signal _1.
Set to the same frequency as the above reproducing pilot signal.
p10 and this carrier signal _CR11 are input to the balanced mixer 12. Then, the output of this balanced mixer 12 has a frequency component of | ₁ − ₄ | = 46KHz and | ₁
− ₂ | = 16KHz frequency component is generated. Then, each of the above components is extracted by a first band pass filter 13a and a second band pass filter 13b whose center frequencies are set to 16 KHz and 46 KHz, respectively, and these components are transferred to the first detection circuit 14a and the second band pass filter 13b. The detection circuit 14b converts the signal into a DC level, and the comparator 15 compares each level. At this time, if the output of the first detection circuit 14a is larger than the second detection circuit 14b, it means that the video head 3a is biased towards the video track side where the pilot signal ₂ is recorded. A movable head drive pattern for correcting the offset is generated by a pattern generation circuit 16 composed of a microcomputer, etc., and the movable head drive pattern is filtered by a low-pass filter 17a to an extent that the piezoelectric element 4a does not generate abnormal vibrations. It is smoothed and supplied to the piezoelectric element 4a via the piezoelectric element drive amplifier 19a.

As a result, the balance of the amount of crosstalk between the pilot signals from the adjacent tracks played back by the video head 3a changes, and a servo loop is formed.
Auto tracking is performed in this way.

Furthermore, auto-tracking is performed on the CH-2 side by almost the same operation. In addition,
Although the explanation is omitted here, the video head 3a,
The capstan motor control system is also operating at the same time to reduce the signal for correcting the offset of the motor 3b.

Next, control of the movable head during high-speed reproduction will be explained.

In FIG. 3, the video track 2 is connected to the trajectory 20 of the video head 3a or 3b and the video tape 1.
The head locus 21 during normal reproduction can be expressed as a composite vector of the velocity vector V _s →22 corresponding to the movement of the head. Therefore, as long as the video tape 1 is moving at the same speed _Vs as during recording, the head trajectory 21 remains parallel to the video track 2 during normal playback. However, if the moving speed of videotape 1 increases five times, the corresponding velocity vector becomes 5V _s → 23, so 5 as a composite vector
A double-speed high-speed playback head trajectory 25 is obtained. Also,
These head trajectories 25 become head trajectories 25a and 25b on the video tape 1, but in order to obtain good signals, the piezoelectric elements 4a and 4b are displaced so that the video heads 3a and 3b become head trajectories 25a and 25b during normal playback.
Must match 1.

Here, if the negative direction is to displace the video heads 3a and 3b vertically upwards (in the upper right direction in FIG. 3) with respect to the rotating surface of the rotating cylinder, then
The basic patterns P _N 26a, 26b for the head trajectories 25a, 25b in FIG. 3 are as shown in FIG. However, this basic pattern P _N 26a,
Since the waveform 26b is actually synthesized by a microcomputer or the like, it is a stepped waveform 27 as shown in FIG. Figure 5 shows one such example.
The field is divided into eight parts.

However, since the piezoelectric element 4a has a hysteresis characteristic, accurate tracking cannot be performed using only this basic pattern P _N 27. Therefore, for example, by adding the error pattern EM _N (t)28 to the basic pattern P _N 27 in FIG. 5, the driving pattern D _N (t) is created.
29, thereby moving the movable heads 40a, 40b.
I like to drive. That is, the drive pattern D _N (t) in frame t is expressed as D _N (t)=P _N +EM _N (t) (N=1 to 2M, 2M is the number of divisions). Also, the error pattern EM _N (t)
is expressed as the error E _N (t) to E _N (t) = E _N (t-1) + E _N (t-1), and the contents are updated and stored in memory every frame t.

Here, the error E _N (t) is "0" when the tracking is almost accurate, and "-" when the movable head has a large deflection, where α is a certain pitch.
α”, and when it is small, it takes one of the three values of “α”. For example, in Fig. 5, N = 3 of frame t.
_{Let the} basic pattern, error _pattern , _and drive _pattern in ₃ (t) = P ₃ -α, and if the swing of the movable head is too large, then E ₃ (t) = -α
Therefore, EM ₃ (t+1)=-α-α=-2α,
Driving pattern D ₃ (t+
1) becomes D ₃ (t+1)=P ₃ −2α.

The drive pattern 29 thus synthesized by the movable head drive pattern generator 16 is smoothed by low-pass filters 17a and 17b.

For the sake of simplicity, a straight line or a curved line that can approximate a step-like pattern, that is, an infinite number of divisions, will be used to represent the step-like pattern.

The filter 17a is constructed, for example, as shown in FIG. 6a, and its time constant is switched so that the movable head 40a can swing faithfully to the drive pattern 29 and without causing abnormal vibrations. (The filter 17b is not shown because it is the same as the filter 17a.) That is, the drive pattern 29 in FIG.
In section H, where the video track inside is traced,
The time constant T _H =R _H C is selected so that only SW _H becomes conductive by the time constant switching signal 18a, and the drive pattern 29 can be output faithfully. Similarly, in interval I at the beginning of the forwarding pattern for returning the head to the starting point of the next tracking, only SW _I becomes conductive, and a time constant T _I = R _I C is established to smooth out the sudden change in the pattern. , in interval J in the latter half of the forwarding pattern, only SW _J is in a conductive state, and the time constant T _H of the above intervals H and I, and the time constant T _J between T _I
=R _J C is selected. Therefore, the movable head drive pattern 29 is smoothed by the smoothing filter 17,
Filter passing drive pattern 3 as shown in figure c
0 is obtained, and this filter passing drive pattern 30
is amplified by a drive amplifier 19 to drive the piezoelectric element 4a.

Since the conventional movable head drive pattern is constructed as described above, it is necessary to change the time constant of the smoothing filter, which increases the circuit scale. Furthermore, even if the smoothing is performed using the conventional method, a satisfactory drive pattern is not always obtained, as shown in the filter passing drive pattern 30 in FIG.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional ones. During high-speed playback of a VTR, the forwarding section of the basic pattern, that is, the section where the head returns to the starting point of the next tracking, is smoothed. To this basic pattern, add an error pattern in which the tracking section and forwarding section are symmetrical with respect to the tracking start point to synthesize a movable head drive pattern, and drive the movable head with this. The purpose of the present invention is to provide a magnetic recording/reproducing device which can auto-track a VTR with a very faithful and smooth pattern to the video track, and which can reduce the circuit scale by reducing the number of smoothing filters.

An embodiment of the present invention will be described below with reference to the drawings. An example of the basic pattern of this invention is shown in FIG.
FIG. 8 shows an example of synthesizing a driving pattern from a basic pattern and an error pattern according to the present invention.

In the figure, 31 is a basic pattern, 32 is an error pattern, and 33 is a movable head drive pattern.

Next, the operation will be explained.

First, move the basic pattern P _N 31 between AB in Fig. 7.
The tracking section where the video track is tracked, such as between EF, is linear, and the video head forwarding section between BE is smooth, and each A, B,
Synthesis is performed using the memory of a microcomputer so that points E and F are smoothly connected. Points A, B, E, and F in FIG. 4 correspond to those in FIG. 7, respectively. In this way, the pattern of the video head forwarding section can be freely selected, so the point B in Figure 4,
Acute angles such as point C can be eliminated,
For example, points B and E in FIG. 7 can be made smooth.

However, as shown in FIG. 8, the movable head drive pattern D _N (t) 33 is a combination of the basic pattern P _N 31 and the error pattern E _N (t) 32.
In the driving pattern, when the error pattern in the forwarding section is set to the value of point B as in pattern 32a, it becomes "0" as in pattern 33a and pattern 32b.
If you do so, pattern 32 will appear like pattern 33b.
If the value at point E is set as shown in c, a pattern 33c will be obtained, and a gap will be created at each point where the tracking section changes to the forwarding section. Therefore, if the error pattern EM _N (t) in the video head forwarding section is made to be symmetrical with the next error pattern with respect to the next tracking start point S, as shown in pattern 32d, the gap for the maximum α will be reduced at point B. The generated items will be connected smoothly.

In other words, the video head forwarding section and the next tracking section are combined into one set, and the pattern of each set is divided into 2M, and the error EN(t) is approximately Assume that the error pattern EM _{N (} t) takes one of three values: "0" when tracking is accurate, "-α" when the movable head has a large deflection, and "α" when the deflection is small. EM _N (t)=EM _N (t-1)+E _N (t-1) EM _N (t)=EM _2M-o+1(t) E _N (t)=E _2M-N +1(t) and Then, EM _M (t) = EM _M +1(t) EM ₁ (t) = EM _2M(t-1) +E _2M(t-1) , which is completely equal at the starting point of tracking and also at the end point of tracking. At most “α”
There will be a gap.

According to this embodiment, the driving pattern 33 synthesized from the smooth basic pattern 31 and the error pattern 32 that is symmetrical with respect to the tracking starting point S becomes smooth, and a good tracking operation can be expected. can. Moreover, this makes it easy to form the smoothing filter 17a.

In the above embodiment, only the CH-1 side has been described, but the same applies to the CH-2 side. Also, I explained about 5x high speed playback,
Similar effects can be obtained at other speeds as long as they are integral multiples. The basic pattern is 31 in Figure 7.
It goes without saying that various patterns such as a, 31b, and 31c are possible, and one can freely select one that matches the characteristics of the piezoelectric element. Further, although the four methods have been described, the present invention can of course be applied to a method of obtaining an error pattern from the level of a reproduced video signal. Furthermore, although a piezoelectric element has been described as an example of an electro-mechanical displacement converter, other types such as a moving coil or the like may be used as the electro-mechanical displacement converter.

As described above, according to the present invention, the forwarding section of the basic pattern is smoothed during high-speed playback of a VTR, and the tracking section and the forwarding section of this basic pattern are symmetrical with respect to the tracking start point. Since we added an error pattern to create a movable head drive pattern,
A movable head drive pattern can be generated that is extremely smooth and allows faithful tracking of the video track, and as a result, good tracking operation can be expected. In addition, this makes it easy to create a smoothing filter to prevent abnormal vibrations in actuators such as piezoelectric elements, and if the number of divisions per field is selected to be large enough, the above filter may be able to be removed, reducing costs. It will also be advantageous. Note that these patterns can be easily generated using a microcomputer.
Furthermore, the present invention is more effective than conventional methods because the amplitude of the piezoelectric element increases and the hysteresis increases as the multiple of high-speed reproduction increases.

[Brief explanation of drawings]

Figure 1 is a diagram showing the videotape recording pattern in the four systems, Figure 2 is a block diagram of the AT system,
Figures 3a and 3b are diagrams showing the relationship between the head trajectory and video track during 5x playback, and Figures 4a and 4b are the basic pattern and waveform of the head switching signal during 5x high-speed playback using the conventional method, respectively. A diagram showing
FIGS. 5a and 5b are diagrams for explaining the operation of synthesizing a drive pattern from a basic pattern and an error pattern, and FIGS. 6a, b, and c are examples of the configuration of a conventional smoothing low-pass filter, respectively. A diagram showing a drive pattern before passing through the filter and a drive pattern after passing through the filter, FIG. 7 is a diagram showing a basic pattern of a VTR according to an embodiment of the present invention, and FIGS. 8a, b, and c are diagrams showing an embodiment of the present invention. FIG. 3 is a diagram for explaining a driving pattern synthesis method according to an example. 2...Video track, 3a, 3b...Video head, 4a, 4b...Piezoelectric element (electro-mechanical displacement converter), 16...Movable head drive pattern generator (pattern generator), 40a, 40b...
Movable head, 50... Error detection device, 60...
Drive device, 31... Basic pattern, 32... Error pattern, 33... Drive pattern. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1 At least a pair of movable heads consisting of a video head and an electro-mechanical displacement converter that displaces the video head when an electric signal is applied, and a tracking error of the movable head is determined from a reproduction signal obtained from the movable head. A basic pattern for driving the movable head consisting of a linear tracking pattern for video track tracing and a smoothly changing forwarding pattern for video head forwarding, and an output of the error detecting device. a pattern generating device that generates a movable head drive pattern by combining an error pattern in which a tracking section and a forwarding section are symmetrical with respect to a tracking starting point created based on the pattern;
A magnetic recording/reproducing apparatus comprising: a drive device for applying the movable head drive pattern to an electro-mechanical displacement converter of the movable head.