JPH054737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetic recording and reproducing apparatus (VTR) which sequentially records and reproduces signals on a magnetic tape running by a rotating head as a recording locus inclined with respect to the longitudinal direction of the magnetic tape. This invention relates to a rotational position detection device for detecting the rotational position of the rotary head in the invention.

Conventional structure and its problems In recent years, VTR recording technology has improved, and
As shown in Publication No. 2724, a technology has been developed that uses the same rotating head to record time-compressed audio PMG signals in a separate area, instead of recording and reproducing only video signals using a rotating video head. There is.

The rotational position detection signal of the rotary head in a conventional VTR is generated by a rotation detecting means (hereinafter referred to as PG) installed at the bottom of a rotary cylinder in which the rotary head is installed. Moreover, there is only a video signal on the recording/playback trajectory drawn by the rotating head, so
Set the PG position to the beginning of the video signal (near the vertical synchronization signal) and output the head switching signal (hereinafter referred to as
HSW) was created and used as a switching signal for 2-head recording and playback.

However, when adding an area for recording audio signals on an extension of the recording/reproducing trajectory, a signal for detecting the leading position of the audio signal is also required. This will be explained using FIGS. 1 to 4. Figure 1 shows the conventional general
This is the head trajectory on the VTR magnetic tape, and 1
is the magnetic tape, arrow 2 is the running direction of the tape, and arrow 3 is the scanning direction of the head. 2 head type VTR
In this case, the two heads A and B alternately scan the tape and record and reproduce recording trajectories A and B alternately.
Based on this, Figure 2 shows the HSW creation process with time plotted on the horizontal axis. The recording and playback trajectories of the A head and B head are shown as a, and the PG signal that detects the beginning of the video signal recorded by these heads is shown as b.
The HSW signal created by PG is shown in c. On the other hand, FIG. 3 shows a case where audio is recorded in a predetermined area on the recording/reproducing trajectory of the head in the same way as video, and FIG. 3 shows the trajectory of the head on the magnetic tape. dA and dB are the trajectories of the audio PCM drawn by the A head and B head, respectively. Based on this, the HSW creation process is shown in the fourth section with the time axis on the horizontal axis.
As shown in the figure. 4 shows the recording/reproducing trajectory of the A head and B head when audio is recorded together with the video signal. Fourth
As can be seen from Figure 4a, in order to record audio, a PG signal for detecting the beginning of the audio signal is also required, and in the end four PG signals as shown in Figure 4b are required. FIG. 4c is a signal for detecting a PCM area created from the PG signal in FIG. 4b, and d is an HSW signal for reproducing an image as in FIG. 2c. In this way, in order to record not only images but also audio on the same recording/reproducing locus of the same rotating head, a signal for detecting the location where the images are recorded is additionally required. With this configuration, the PG is
Increases from one to four. However, since PGs are normally set after fine adjustment, an increase in the number of PGs is very inconvenient as the number of points to be adjusted during VTR manufacturing increases.

Therefore, as a method to overcome the above problem, a method can be considered in which a clock is used, the clock is counted, and each position is detected based on the counted number. This will be explained using FIG. 5. Similarly to FIG. 4, the horizontal axis is taken as the time axis, and the recording and reproducing trajectories of the A head and B head are shown in a. b is the 4th PG signal
The number has been reduced from four in Figure b to one. this one
Based on the PG signal, clocks with a constant frequency are counted by a predetermined value from this position, and the clock is delayed for a predetermined time, and the total of P ₁ , P ₂ , P ₃ , and P ₄ is 4.
It makes two pulses. This is shown in FIG. 5c, and the positions of these four pulses are the positions indicating the head of the PCM signal and the position indicating the head of the image, which correspond to c in FIG. 4. Similarly to d in FIG. 4, d is an HSW signal for switching images.
The method of counting clocks is effective because it not only allows accurate position determination, but also reduces the number of adjustment points by using only one PG. However, although this method is accurate, it is only applicable when the rotational speed of the rotary cylinder is always constant, such as in recording mode or normal playback mode. This method is not suitable for the following reasons when the speed of the rotating cylinder changes from that during recording, such as in a special playback mode in which playback is performed at a tape speed different from the tape speed during recording. This will be explained using FIG. 6. Figure 6a shows PG with the time axis on the circumference.
With reference to the signal, the pulses P ₁ , P 2 , P ₂ , in FIG.
FIG. 6 is a diagram in normal playback and recording modes in which positions P ₃ and P ₄ are allocated on the circumference. usually
In VTR, the length of time corresponding to the length of the circumference in these modes is 2/ _v ( _v is the frequency of the vertical synchronization signal), and it is always P _{1 to 1} with the PG signal as the reference.
The angular relationship of P ₄ remains constant. However, if the speed of the rotating cylinder changes during playback, the relationship between the angles P ₁ to _{P 4} will collapse.
For example, in slow playback mode,
As shown in the figure, the rotating cylinder is controlled to rotate more slowly than in the normal reproduction mode. Therefore, the time corresponding to the length of the circumference is shorter than 2/ _v seconds. At this time, four signals to be detected
Among P ₁ to _{P 4} , P ₂ to _{P 4} are counted by a clock and the time is constant, so
Each angle will be smaller than the one shown in the figure.
On the other hand, for example, in double speed playback mode,
As shown in FIG. 6c, the rotating cylinder is controlled to rotate faster than in the normal playback mode, so the time corresponding to the length of the circumference is longer than 2/ _v seconds. Of the four signals to be detected at this time, _P2 to _P4 are counted by a clock and time is constant, so they each have a larger angle with respect to the PG signal than in FIG. 6a. In this way, in the special playback mode, an angular error occurs in the signal to be detected compared to during normal playback. This angular error can be tolerated within a certain range, but outside of that it seriously affects image and sound quality. For example, if an angular error occurs in the P ₂ or P ₄ signals in the special mode as described above, these signals create a HSW signal, so the head can be switched at the correct position on the recording/playback trajectory of the head. I become unable to do so. The allowable range of this angular error is the overlap part ₄ of the images recorded by the two heads, which is the broken line part in Figure _5a . A gap occurs. Regarding audio, _P1 is synchronized with the PG signal, so there is no problem, but _P3 has the risk of destroying the PCM area due to angular errors.

This relationship will be explained in more detail below using FIG. 7. FIGS. 7a and 7b are diagrams for determining the angular error in the slow playback mode by comparing the normal playback mode and the slow playback mode by taking time in the horizontal axis direction. Figure a is a diagram of normal mode, with 1 in 2/ _v seconds based on the PG signal.
b indicates slow playback mode, and the rotating cylinder is controlled to rotate slowly for 2/ _v +T seconds (T
>0) indicates one rotation. In normal playback mode, a detection signal detected at an angle α° with the PG signal at a certain time t is at an angle β° with the PG signal at the same time t in slow playback mode.
Detected with Therefore, it can be said that the angular error in slow reproduction mode is α°−β°>0. Calculating α°=360°×t/2/ _v , β°=360°×t/2/ _v +T. Therefore α°−β°=360°×t×(1
/2/ _v −1/2/ _v +T).

From the above formula, a certain slow playback mode (T is fixed)
It can be seen that the farther the detected position signal is from the PG signal, the larger the value of t becomes, and the larger the angular error becomes. Next, FIGS. 7c and 7d are diagrams for determining the angular error in the double-speed playback mode by taking time in the horizontal axis direction and comparing the normal playback mode and the double-speed playback mode. c is a diagram of normal playback mode, with 2/2
It shows that it rotates once every _v seconds, and d is double speed playback mode, the cylinder is controlled to rotate quickly, and 2/ _v - T seconds (T >
0) indicates one rotation. A detection signal that is detected at an angle α° with respect to the PG signal at a certain fixed time t in the normal playback mode is detected at an angle r° with the PG signal at the same time t during double-speed playback. Therefore, it can be said that the angular error in the double speed playback mode is r°−α°>0. When calculated, α°
=360°×t/2/ _v , γ°=360°×t/2/ _v −T
.

Therefore, γ°−α°=360°×t×(1/2/ _v −T− 1/2/ _v ).

According to the above formula, in a certain double-speed playback mode (T is fixed), the farther the detected position signal is from the PG signal, the faster t becomes.
It can be seen that the value of becomes larger and the angular error becomes larger. From the above, it can be seen that in either mode, an angular error occurs in the detection signal in the special mode, and furthermore, this angular error changes in magnitude depending on the detection position. Generally, T, which is related to the speed change of the rotating cylinder in the same mode, is minute, and therefore this value has little effect on the angular error. However, the influence of t on the detection position cannot be ignored, and it can be said that this value influences the value of the angular error.

From the above, the method of using one PG is
Although it is possible to include a sufficient angle error within a certain tolerance range for P ₂ in Figure 6a, P ₃ and
P ₄ may exceed the allowable range. On the other hand, in order to prevent these from exceeding the allowable range, it is necessary to reduce T, which is related to the speed change of the rotating cylinder, and the range in which special reproduction can be performed is therefore limited.

OBJECTS OF THE INVENTION The present invention provides an apparatus for generating a rotational position detection signal for a rotary cylinder, which reduces the angular error in the special mode at any of the four detection positions.

Structure of the Invention In order to solve the above-mentioned problems, the present invention has four
In order to create 2 position detection signals, 2 PG
The purpose is to use the outputs of PG and count clock signals based on these PG outputs to generate the other two position detection signals.

DESCRIPTION OF THE EMBODIMENT This will be explained using FIG. 8. a is Figure 6a
The time axis is set on the same circumference as , and each detected position signal P ₁ to _{P 4} in Figure 5c is detected by counting clocks based on two PGs facing each other with a phase of 180°. FIG. 6 is a diagram in playback mode.
The broken lines are the detection positions of P ₂ and P ₄ in the normal state, and correspond to the positions of P ₂ and P ₄ in FIG. 6a.
Similar to FIG. 8a, FIG. 8b shows the detected position signal P ₁ to
FIG. 6 is a diagram in a double-speed playback mode in which _P4 is detected by counting clocks. These two figures require two PGs, which
Since the detection positions of P ₁ and P ₃ are always synchronized with the PG signal, the PCM detection signals P ₁ and P ₃ are accurately detected.
Furthermore, although the detected positions of P ₂ and P ₄ include an angular error, the magnitude of the error is equivalent to that of P ₂ in Figure 6b in slow playback mode for both P ₂ and P ₄ . Moreover, even in the double-speed playback mode, both P ₂ and P ₄ are only large enough to correspond to P ₂ in FIG. 6c. Therefore, the angle error of the HSW signal can be sufficiently suppressed within the tolerance range corresponding to the image overlap, and in other words, the range in which special reproduction can be performed can be sufficiently widened.

Next, FIG. 9 shows the configuration of a specific embodiment of the present invention, and FIG. 10 shows its operating waveform diagram.

In FIG. 9, 10 is a rotating cylinder, 11
a and 11b are rotation detection means (PG) of cylinders facing each other at a phase of 180; 14 is a first switch;
15 is a signal mixing circuit, 16 is a second switch, and 20 is a count circuit.

As the rotary cylinder 10 rotates, the signal shown in FIG. 10a is obtained from the PG 11a and the signal shown in FIG. 10b is obtained from the other PG 11b for each rotation.
Here, if the VTR is in the recording or normal reproduction mode, the second switch 16 is connected to the terminal 17, thereby opening the switch 14 and outputting the signal a from the mix circuit 15. Then, this signal a is inputted to the count circuit 20 as a reset signal, but at this point, the count circuit 20 starts applying the voltage from the terminal 19 until the count value is predetermined by the mode signal sent from the terminal 17. The clock signal is counted and each time the counted value is reached, it is output as shown in Figure 10d.
P ₁ , P ₂ , P ₃ , and P ₄ are output, and four position detection signals P ₁ , P ₂ , P ₃ , and P ₄ are created for one rotation of the cylinder.

Also, when the VTR enters the special playback mode, the switch 16 is connected to the terminal 18, which closes the switch 14 and outputs the signal a from the mixer circuit 15.
A signal c, which is a mixed output of and b, is output. This signal c is input to the count circuit 20 as a reset signal, but at this point the count circuit 2
0 counts up to the count value set by the special playback mode signal sent from terminal 18, and PG1
P ₁ as shown in Fig. 10e by the output a of 1a
and P ₂ ', and P ₃ and P ₄ ' are respectively created using the output b of the PG11b.

Note that, as described above, P ₂ ′ and P ₄ ′ are slightly shifted from their normal positions.

Effects of the Invention As described above, in the present invention, during recording and normal playback, four position detection signals are generated per revolution of the rotary cylinder by the output of one PG, and in special playback mode, four position detection signals are generated by the output of two PGs. Since two position detection signals are created for each half rotation of the rotating cylinder, by providing two PGs, it is possible to ensure that four position detection signals are accurate in recording mode and normal playback mode, and also for special playback. In this mode, four position detection signals with few errors can be generated.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the recording trajectory on the tape of a conventional general VTR, Figure 2 is a diagram showing the phase relationship between the recording trajectory, position detection signal, and head switching signal in the same VTR, and Figure 3 is a diagram showing the recording trajectory on the tape of a conventional general VTR. , a diagram showing the recording trajectory on the tape of a VTR that reproduces a video signal and a P-section CM signal on the same trajectory, and FIGS. 4 and 5 are the same.
Figure 6 shows the phase relationship between the recording trajectory, position detection signal, and head switching signal in a VTR. FIG. 7 is a diagram showing the output position, and FIG. 7 is a diagram showing the angular error of the position detection signal in special playback mode in the same method.
FIG. 8 is a diagram showing the output position of the position detection signal during special playback in the position detection device of the present invention, FIG. 9 is a block diagram showing an embodiment of the position detection device of the present invention, and FIG. 10 is the same operation. It is an explanatory diagram. 10... Rotating cylinder, 11a, 11b... Position detection means, 14, 16... Switch, 15...
Mix circuit, 20... Count circuit.

Claims (1)

[Claims] 1. It has first and second rotation detection means that respectively detect the rotation phase of a rotary cylinder provided with a rotary head at positions where the rotation angle is different by 180 degrees, and the first rotation detection means is used during recording and normal playback. A plurality of rotational position detection signals necessary for one rotation period of the rotary cylinder are generated by the output of the counter circuit generated when each clock signal is counted up to a predetermined count value from the generation of the detection output of the means. and during special playback at a tape speed different from that during recording, when the clock signal is counted up to a predetermined count value from the generation of each detection output of the first and second rotation detection means. A rotational position detection device for a rotary head type magnetic recording/reproducing device, characterized in that a plurality of rotational position detection signals necessary for one rotation period of the rotary cylinder are created based on the generated output of the counter circuit.