JPH0312381B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a magnetic recording and reproducing device, and particularly in a magnetic recording and reproducing device that uses a rotating magnetic head to record and reproduce data, such as a video tape recorder, the present invention relates to a magnetic recording and reproducing device that uses a rotating magnetic head to record and reproduce data. The present invention relates to a magnetic recording and reproducing device that performs playback and still playback. [Prior Art] A method for performing noise-free slow playback and still playback in a conventional magnetic recording and reproducing apparatus that uses a control track on a magnetic tape to record and play back control signals to control the running of the magnetic tape. One example was as follows. That is, the tape drive during slow playback is an intermittent drive that repeats running and stopping, and during still playback, the intermittent drive is performed once or several times and then stopped. In this method, the positional relationship between the recording track and the rotating magnetic head when the tape is stopped must be within a range where no noise appears on the playback screen. Therefore, in this method, the control signal played during tape running is used as track position information, and by controlling the amount of tape running after the control signal is detected, the tape is stopped at a position where no noise appears on the screen. . Figure 1 shows the conventional control method as described above, so Figure 1a shows the torque applied to the capstan motor, Figure 1b shows the tape speed, and Figure 1c shows the control signal. ing. The tape is accelerated from time t ₀ to t ₁ and then runs at a constant speed. When a control signal is detected at time _t2 , braking is started after a delay time ( _t3 - _t2 ), and at time _t4 , when the tape speed is approximately zero, braking is stopped and the tape stops. Here, (t ₃ −t ₂ ) is called a tracking delay time, and by increasing or decreasing this time, the tape feeding amount is increased or decreased. In conventional video tape recorders, this tracking delay time is usually adjustable by the user using a variable resistor, so that it can be set at the position where the reproduced image is best, that is, at the optimum tape stop position. As described above, in conventional video tape recorders, the user must adjust the tracking delay time, that is, the optimum tape feed amount during slow playback or still playback, which is extremely troublesome. This invention was made to solve the above problems, and it is a magnetic recording system that allows the magnetic tape to be constantly fed to a stop position where no noise appears on the screen without making any manual adjustments. The purpose is to provide a playback device. [Means for Solving the Problems] A magnetic recording and reproducing device according to the present invention performs slow playback and still playback by controlling the running of a magnetic tape intermittently through acceleration, constant speed, braking, and stopping. The magnetic recording and reproducing apparatus is provided with a pilot signal recording and reproducing means, a magnetic tape stop position detecting means, and a magnetic tape constant speed running time changing means. The pilot signal recording/reproducing means is a continuous four-way magnetic tape.
First, second, third, and fourth pilot signals having different frequencies are sequentially recorded and reproduced along with the video signal on each of the four video tracks, with one video track as one cycle. The magnetic tape stop position detecting means outputs a signal indicating how far the magnetic tape stop position is from one end of one cycle during reproduction and when the magnetic tape is stopped. The constant speed running time changing means for the magnetic tape changes the time during which the magnetic tape is run at a constant speed during slow playback and still playback in accordance with the output of the stop position detection means. Further, the magnetic tape stop position detection means includes first and second comparison means, head switching signal output means, and third comparison means. The first comparison means compares the amplitudes of the first and third pilot signals included in the reproduction signal from the pilot signal recording and reproduction means to form a first comparison output. The second comparison means compares the amplitudes of the second and fourth pilot signals included in the reproduction signal from the pilot signal recording and reproduction means to form a second comparison output. The head switching signal output means outputs a head switching signal for switching the rotating magnetic head included in the pilot signal recording/reproducing means. The third comparing means detects the position of the magnetic tape when the magnetic tape is being reproduced and the magnetic tape is stopped, based on the outputs of the first and second comparing means and the head switching signal. [Operation] In the present invention, slow playback and still playback are performed by intermittently controlling the running of the magnetic tape through acceleration, constant speed, braking, and stopping. At this time, the amount of feed of the magnetic tape is controlled to a desired value by changing the constant speed running time of the magnetic tape based on the output of the magnetic tape stop position detection means. In addition, the detection of the stop position of the magnetic tape is performed by the first
and based on the amplitude comparison output of the third pilot signal, the amplitude comparison output of the second and fourth pilot signals, and the head switching signal. [Embodiments of the Invention] The above objects and other objects and features of the invention will become more apparent from the detailed description given below with reference to the drawings. FIG. 2 is a diagram schematically showing the positional relationship between the magnetic tape and the magnetic head. First, the relationship between the video track on the magnetic tape surface and the running locus of the magnetic head will be explained with reference to FIG. FIG. 2 shows the relationship between video tracks 2a, 2b, 2c, and 2d on the magnetic tape 1 and a magnetic head 3a (the magnetic head 3b is not shown) when the magnetic tape 1 is stopped. The magnetic tape 1 is inserted into the magnetic head 3 in the direction shown by arrow A.
a and 3b run in the direction shown by arrow B, the track width of the video tracks 2a to 2d is T, the head width of the magnetic heads 3a and 3b is W, and the track pitch in the longitudinal direction of the magnetic tape 1 is P. . The traveling trajectories of the magnetic heads 3a, 3b are expressed using the traveling trajectories 4a, 4b, 4c at the lower end, upper end, and center of the magnetic heads 3a, 3b.
It should be noted that pilot signals _f1 to _f4 are sequentially recorded on the video tracks 2a to 2d by being multiplexed with the video signal, and the video tracks 2a and 2c and the video tracks 2b and 2d are recorded by the same magnetic head, respectively. , these two magnetic heads have different azimuths from each other. At positions close to both ends of the magnetic tape 1, there are switching points 5a,
5b are set respectively. The stop position of the magnetic tape 1 is set by the magnetic heads 3a, 3.
Center travel locus 4c of b and switching point 5
Now, with the longitudinal direction of the magnetic tape 1 as the X coordinate, the zero point is the point where the center of the video track 2d' (the track one track before the video track 2a) intersects the switching point 5a. do. The stop position of the magnetic tape 1 shown in FIG. 2 is at x=0.9p. video track 2a
.about.2d are recorded periodically with respect to the pilot signals f ₁ to f ₄ with four tracks as one period, so by using the pitch p, all stop positions can be represented by x=0 to 4p. The pilot signals f ₁ to _{f 4} are signals each having a different constant frequency in a frequency range lower than that of the reduced conversion color signal, and between the mutual frequencies |f ₁ −f ₂ |
≒｜f ₃ −f ₄ ｜=f _A , |f ₁ −f ₄ ｜≒｜f ₂ −f ₃ ｜=f _B , f _A
It is a signal of approximately 100kHz to 200kHz that satisfies the condition ≠f _B. For example, f ₁ , f ₂ , f ₃ , f ₄ are 102kHz in order,
118kHz, 164kHz, and 148kHz are proposed. Further, the frequency difference f _A and f _B are several tens of kHz (16 kHz and 46 kHz, respectively, in the above example). As mentioned above, since the pilot signals f ₁ to _{f 4} have lower frequencies than the video signals, the influence of the azimuth effect of the magnetic heads 3a and 3b is small, and reproduction is possible even with magnetic heads having an azimuth different from that during recording. be. Regarding the stop magnetic tape 1 as described above, the third
Figure a shows the stop position of the magnetic tape 1, i.e. x=
1.9p, the reproduction track widths T ₁ and T ₃ of the video tracks 2a and 2c traced by the magnetic heads 3a and 3b during one field period are shown. Here, the playback track width means the width of the overlapping portion between the magnetic head and the video track. In the figure, the horizontal axis is the time t normalized by one field time t _f , where t/t _f =0 and 1 indicate when the centers of the magnetic heads 3a and 3b pass through the switching points 5a and 5b, respectively. corresponds to the time it takes to Further, in the figure, the head ends W of the magnetic heads 3a and 3b are designed to be 1.6 times the track width T.
FIG. 3b shows the reproduction track widths T ₂ and T ₄ of the video tracks 2b and 2d at the same magnetic tape stop position as in FIG. 3a. In the same figure,
At the time of t/t _f =0.9, the values of the reproduction track widths T ₂ and T ₄ match, and the magnitude relationship is reversed. As can be seen from the exemplified FIGS. 3a and 3b, there are two reproduction track widths T ₁ , T ₃ and T ₂ , depending on the magnetic tape stop position.
The T ₄ relationship has a unique magnitude relationship. Figure 4 shows the magnitude relationship of the reproduction track widths T ₁ and T ₃ and the magnitude relationship of T ₂ and T ₄ in one field period with respect to the stop position x of the magnetic tape based on the above definition. be. Here, O<x<
The area of p is X ₁ , the area of p≦x≦2p is X ₂ , 2p<x
Let the region <3p be X ₃ and the region 3p≦x≦4p be X ₄ . As is clear from the figure, the reproduction track widths T ₁ and T ₃ and T ₂ and T ₄ during one field period are
When comparing the sizes of the sets, in any region from X _{1 to} It is possible to determine which of the regions X ₁ , X ₂ , X ₃ , and X ₄ the tape stop position x is located in. For example, when comparing playback track widths T ₁ and T ₃ , always
If T ₁ is always greater than or equal to T ₃ , the magnetic tape stop position x is in area X ₂ , and if T ₁ is always less than T ₃ , the magnetic tape stop position x is in area X ₄ . Alternatively, the stop position
It is also possible to determine which region of X ₁ to _{X 4} it is in. However, in FIG. 4, in area X ₂ ,
At the timings of (x=p, t=t _f ) and (x=2p, t=O), the playback track width becomes T ₁ =T ₃ , and (x=p, t=O) and (x=2p , t=
_f ), the reproduction track width becomes T ₂ =T ₄ . Also in region X ₄ , (x=3p, t=t _f ) and (x
= 4p, t = O), the playback track width is T ₁ = T ₃
and (x=3p, t=O) and (x=4p, t
= t _f ), the playback track width becomes T ₂ =T ₄ . Here, since the pilot signals f ₁ , f ₂ , f ₃ , and f ₄ are written superimposed on the video track, the reproduction track widths T ₁ , T ₂ , T ₃ , and T ₄ are the widths of the magnetic head 3.
Pilot signal included in the reproduced signals of a and 3b
It has a proportional relationship with the amplitude of f ₁ , f ₂ , f ₃ , and f ₄ respectively. The stop position detection device described below uses the proportional relationship between the playback track width and the amplitude of the pilot signal as described above, and the stop position of the magnetic tape 1 as explained using FIGS. 2, 3, and 4. The position of the magnetic tape is detected using the reaction relationship between x and the reproduction track widths T ₁ , T ₂ , T ₃ , T ₄ . FIG. 5 shows the relationship between the stop position x of the magnetic tape and the time t _x at which the magnitude relationship between the reproduction track widths T ₁ and T ₃ or T ₂ and T ₄ is reversed. In addition,
t _x is the time when the starting point of the field is set to 0. What this figure 5 means is that each area
Within X ₁ to X ₄ , t _x /t _f differs depending on the stop position, and in any of the areas X ₁ to X ₄ , the relationship between the stop position and t _x /t _f in the area is the same. It means being expressed. Therefore, if the same reference voltage is generated in any region as shown in Figure 5 and the reference voltage value at t _x is extracted, the position within the region can be determined by the extracted voltage value. You can also know. In this way, it is possible to know the exact stop position of the magnetic tape by not only knowing whether the magnetic tape is in one of areas _X1 to _X4 but also by knowing the position within that area. Note that when the stop position x is x=P, 2P, 3P, or 4P, there is no point at which the magnitude relationship of the reproduction track widths is reversed, so in this case, from the relationship shown in Table 1, the value of x is It is possible to detect whether it is P, 2P, 3P, or 4P. This Table 1 provides supplementary explanation for the case where x in FIG. 4 has the above-mentioned four values. From this table, it can be determined that x=P, for example, if there is no reversal of the reproduction track width and T ₁ ≧T ₃ and T ₂ ≦T ₄ .

[Table] FIG. 6 is a block diagram of a stop position detection device used in one embodiment of this explanation. First, the configuration of the main parts in FIG. 6 will be explained. A reproduction signal of the rotating magnetic heads 3a, 3b including a pilot signal is inputted from an input terminal 28. This reproduced signal is given to balanced modulators 6a and 6b.
A pilot signal _f1 input to an input terminal 29 is given to the balanced modulator 6a, and this pilot signal
A beat signal of frequency f _A or f _B (hereinafter referred to as beat signal f _A or f _B ) is formed between f ₁ and pilot signals f ₂ and f ₄ included in the reproduced signal. The output signal of the balanced modulator 6a is input to band filters 7a and 7b whose center frequencies are set to the frequencies f _A and f _B of the beat signal, respectively, and the output signal of the balanced modulator 6 a
The beat signal component included in the output signal of is separated. The separated beat signals f _A and f _B are respectively detected by detectors 8 a and 8 b into signals having corresponding amplitudes, and are applied to the input terminal of a comparator 9 a to compare the levels between the two input signals. be done. Comparator 9
a provides a high level or low level signal to the pulse generator 10a based on the comparison result. The pulse generator 10a generates positive pulses at the rise and fall of the input signal and applies them to the trigger terminal T of the D-type flip-flop 11a. Moreover, the input terminal 30 is connected to the other balanced modulator 6b.
The pilot signal f ₂ input to is given. Then, the balanced modulator 6b generates a beat signal f A or _{f B} between the pilot signals f ₁ , f ₃ and the pilot signal f ₂ included in the reproduced signal, and this beat signal f _A
Or f _B is band filter 7c and 7d, detector 8c
and 8d to the comparator 9b. Comparator 9b
The output of is applied to the pulse generator 10b, which generates a positive pulse and applies it to the trigger terminal T of the D-type flip-flop 11b. A head switching signal H.Sw is input to the input terminal 31. This head switching signal H.Sw is applied to a trigger terminal T of a D-type flip-flop 18 via a pulse generating circuit 17. A detection command is input to the input terminal 32, and this detection command is applied to the reset input terminals of the D-type flip-flops 11a, 11b and 18 as a reset signal. The output of the D-type flip-flop 18 is input to a triangular wave generating circuit 19 which generates a triangular wave signal. The triangular wave signal generated by the triangular wave generating circuit 19 is given to a sample hold circuit 22. Sample hold circuit 2
2 will be explained in detail in the operation explanation below, but
The output of the AND gate 21 is used as a sampling pulse to sample and hold a triangular wave signal. FIG. 7 is a timing diagram for explaining the operation of the device shown in FIG. 6. Next, the specific operation of the stop position detection device will be explained with reference to FIGS. 2 to 7. As shown in FIG. 7a, time t=
Assume that a stop position detection command is issued at t ₀ . Before this time, the D-type flip-flop 11
A, 11b and 18 are in a reset state, and their respective output terminals Q are at a low level.
The balanced modulator 6a generates a signal using the second and fourth pilot signals f ₂ and f ₄ among the four pilot signals included in the reproduced signal, and a pilot signal f ₁ of constant amplitude that is input separately. Each frequency outputs a signal containing the beat signals f _A and f _B as described above. Here, the amplitudes of the beat signals f _A and f _B match the amplitudes of the pilot signals f ₂ and f ₄ included in the reproduced signal. The above-mentioned reproduced signal is obtained by amplifying the signal reproduced by the rotating magnetic heads 3a and 3b and then passing it through a filter having the pilot signals f ₁ , f ₂ , f ₃ and f ₄ in its passband. In this case, there is an advantage that there is no undesirable influence from video signals or the like. Band filters 7a and 7b separate and detect beat signals f _A and f _B from the output of balanced modulator 6a, respectively, and detectors 8a and 8b output the amplitudes of the respective signals. The outputs of the detectors 8a and 8b are input to a comparator 9a, and the magnitudes thereof are compared.
Similarly, the balanced modulator 9b has the first and third
beat signals f A , f _B are output based on the pilot signals f ₁ , f ₃ and the separately input pilot signal f ₂ , and the band filters 7c, _7b output the beat signals f _A , f _B
Separate. The detectors 8c and 8d detect the beat signal f _A ,
The amplitude of f _B is output and compared by comparator 9b. In this case, the beat signals f _A and f _B are pilot signals whose amplitudes are included in the reproduced signal.
This corresponds to the magnitude of the amplitudes of f ₁ and f ₃ . When the stop position of the magnetic tape 1 is x = 2.5P, the detector 8
The outputs of a to 8d change as shown in FIG. 7 c to f. At this time, the output of the comparator 9a is always at a high level as shown in FIG.
After the output values of 8d match, the time point when the magnitude relationship is reversed (for example, at time t=
t ₂ ) and at the start of the field (e.g. 7th
In the figure, it is reversed at time t=t ₁ ). Incidentally, FIG. 7b shows a head switching signal for switching between the rotating magnetic heads 3a and 3b. Now, in synchronization with the inversion of the output of the comparator 9b at t= _t1 , the pulse generator 10b generates a pulse of positive polarity, and this pulse triggers the D-type flip-flop 11b, and the data terminal D
The high level signal input to the output terminal Q is outputted to the output terminal Q. On the other hand, the output terminal Q of the D-type flip-flop 11a remains at low level. At this time, the first and second output terminals 33, 3
The output signals O ₁ and O ₂ generated at the output terminal 4 are both at high level. In the embodiment shown in FIG. 6, information indicating which of the regions X1 to _X4 the rotating magnetic heads 3a and _3b are located (i.e., the rough stop position of the magnetic tape) is provided by the output signal _O1 shown in Table 2. , determined by the combination of O ₂ . Therefore, the output signal O ₁ ,
If both _O2 levels are high, it is determined that the magnetic tape stop position is in area _X3 .
In this way, in the embodiment shown in FIG.
The approximate stopping position of the magnetic tape can be determined from the binary information of O ₁ and O ₂ . Next, a method for more accurately determining the stopping position of the magnetic tape, rather than by area, will be explained with reference to FIGS. 6 and 7. Even in that case, the aforementioned output signals O ₁ and O ₂ are necessary, and by obtaining a signal indicating the position in the area represented by these output signals O ₁ and O ₂ , the reflective The exact stopping position can be determined. In FIG. 6, the output of the exclusive OR circuit 14b goes from a high level to a low level in synchronization with the point in time when the values of the outputs of the detectors 8c and 8d match and their magnitude relationship is reversed, as shown in FIG. 7l. Flip to level. The pulse generator 15b generates positive pulses in synchronization with the rise and fall of the output of the exclusive OR circuit 15b. As mentioned above, since the output terminals Q of the D-type flip-flops 11a and 11b are at low level and high level, respectively, the NAND circuit 20
outputs the output of the above-mentioned pulse generator 15b as is. Output terminal Q of D-type flip-flop 18
is synchronized with the rise or fall of the first head switching signal H.Sw (Fig. 7b) after the detection command is output, that is, in Fig. 7, time t =
When t ₁ , it changes from low level to high level,
Thereafter, the low level and high level are repeated with two fields as one cycle. The triangular wave generating circuit 19 is the seventh
As shown in Figure P, the potential increases from Va at a constant rate of increase (Vb - Va)/ _tf in synchronization with the rise of the Q terminal output of the D-type flip-flop 18, and as the Q terminal output mentioned above falls. The potential changes from Vb synchronously.
Outputs a signal that decreases toward Va. As shown in FIG. 7 (n to r), the sample and hold circuit 22 uses the output of the AND circuit 21, which is the logical product of the output of the NAND circuit 21 and the Q terminal output of the D-type flip-flop 18, as a sampling pulse to output the output of the triangular wave generation circuit 19. is sampled and held, and the potential V is output. Here, as is clear from the correspondence with FIG. 5, when x=2.5P, the potential V is V=
(Va+Vb)/2. Since the control terminal C of the switch circuit 24 is at a high level, the output of the sample hold circuit 22 connected to the input terminal Ib, that is, the potential V is outputted to the third output terminal 35. The above explanation is for the case where x=2.5P, but if x is in the region _X3 , the embodiment shown in FIG. 6 operates in the same way, and the output signal _O1 becomes high level The output signal O ₂ also becomes high level, and the potential of the output O ₃ is Va + (X-2P) × (Vb-
Va)/P. As is clear from FIGS. 6 and 7, in this embodiment, regardless of the timing at which the stop position detection command is issued, the output signals O ₁ and O ₂ are output one field time after the detection command is issued. As for the output signal _O3 , the above-mentioned stop position information is output after two field times. Stop position x is area X ₁ or area X ₂ excluding x=P, 2P or _area
If it is, compare the outputs of the detectors 8a and 8b or the outputs of the detectors 8c and 8d,
There is a point in time when the magnitude relationship is reversed in either the combination of the outputs of the detectors 8a and 8b or the combination of the outputs of the detectors 8c and 8d, and the output signal O ₁ ,
The signals shown in Table 2 are obtained for O ₂ and O ₃ . Here, x=P, 2P, which was excluded in the above explanation,
The output signal _O3 in the case of 3P and 4P will be explained.
The outputs of comparators 9a and 9b are both fixed at high level or low level and are not inverted, so the Q terminal outputs of D-type flip-flops 11a and 11b both remain at low level. At this time,
The control terminal C of the switch circuit 24 is at a low level, and the input terminal Ia is connected to the third output terminal 35. On the other hand, the input terminal Ia is connected to the output terminal of a second switch circuit 27, which is controlled by the outputs of the comparators 9a and 9b at its control terminal C'. Exclusive
The output of the OR gate 26 is given, and when the output is high level, it is set to the lower side, and when it is low level, it is set to the upper side, and the comparators 9a and 9b are set to the high level or low level according to the relationship explained in Table 1. Since the signal is output, the output of the third output terminal 35 ends up being
For O ₃ , x=P, and for 3P, Va is derived,
In the case of x=2P, 4P, Vb will be derived. Note that the fixed Va and Vb in this case are the resistance R
It is generated by connecting 1, R2, and R3. As described above, the output signal _O3 shown in Table 2 is obtained also at each point of x=P, 2P, 3P, and 4P. To summarize the above explanation, in the embodiment shown in FIG. 6, as shown in Table 2 below, depending on the high level and low level of the output signals O ₁ and O ₂ ,
The stop position x of the magnetic tape 1 is in the areas X ₁ , X ₂ , X ₃ ,
It is possible to detect whether it is in any of X ₄ and further to detect the value of x from the potential of the output signal O ₃ . In the embodiment shown in FIG. 6, the pilot signals f ₁ and f ₂ are used as the reproduction signal and the beat signal, but other combinations, that is, f ₁ and
Similar detection is possible using f ₄ , f ₃ and f ₂ , or f ₃ and f ₄ .

[Table] Note that by taking the beat using a signal formed separately from the reproduced signal in this way, the frequency of the comparison signal can be lowered, and the band filters 7a and 7c and 7b and 7d can each have the same frequency. It gives you the advantage of being able to use things. Furthermore, using the pilot signal as the signal for taking the beat is because the pilot signal itself is prepared in the VTR as a signal to be multiplexed with the video signal and recorded. This has the advantage that there is no need to provide a special oscillation circuit. Furthermore, in the embodiment shown in FIG. 6, _the comparison between pilot signals f ₁ and f ₃ included in the reproduced signal
Although comparisons of f and _f4 are performed in parallel, the same detection is possible even if both are performed sequentially. and,
If it is performed sequentially, only one comparator is required. As described above, according to this stop position detection device, when playing back and stopping the magnetic tape, the playback signals of four pilot signals f ₁ to f ₄ having different frequencies are multiplexed with the video signal and recorded sequentially in advance. From, the comparison output about the magnitude of f ₁ and f ₃ and f ₂ and
A comparison output for the magnitude of _f4 is generated, and a signal indicating the stop position of the magnetic tape is generated based on these comparison signals and the head switching signal. You can know the location. Here, slow playback and still playback are
It is assumed that two heads having the same azimuth as the heads that recorded the tracks 2b and 2d shown in the figure are used. As is clear from the figure, the optimum tape stop position for stably reproducing the video signal is x
=0.5p, 2.5p. Therefore, after detecting the magnetic tape stop position x by the stop position detection device,
For example, the magnetic tape feed length shown in Figure 8
If the magnetic tape is sent according to the relationship t _x /t _f , then
Noiseless slow playback and still playback can be achieved. In FIG. 8, the line 45 indicates that x is the area X ₁ ,
In the case of X ₃ , the line 46 corresponds to the case where x is in the areas X ₂ and X ₄ , and the point A corresponds to the magnetic tape stop position _x = 1.9p, _t This indicates that the tape length to be sent is 0.6p. FIG. 9 is a schematic block diagram showing one embodiment of the present invention. In the figure, in this example, the sixth
The stop position detecting device 42 shown in the figure, the charging/discharging circuit 41 whose input signals are the acceleration signal that controls the acceleration time of the capstan motor and the output signal _O1 of the stopping position detecting device 42, and the output of the charging/discharging circuit 41 and the output signal _O3 of the stop position detection device 42 as input signals, and a NOR circuit 44 that uses the acceleration signal and the output of the comparator 43 as input signals. In addition, the stop position detection device 42
The detection command given to is a signal that is high level when the magnetic tape is stopped and low level when the magnetic tape is running. Moreover, the output of the NOR circuit 44 is
The signal is applied to a capstan motor drive circuit (not shown) as a constant speed signal for controlling the constant speed running time of the capstan motor. It should be noted that FIG. 9 only shows the structure of the part of the overall VTR structure that is particularly interesting to this embodiment. The configuration of the other parts is almost the same as that of a conventional video tape recorder, so a description thereof will be omitted. FIG. 10 is a time chart for explaining the operation of the embodiment shown in FIG. The operation of the embodiment shown in FIG. 9 will be explained with reference to FIG. 10. In the following description, it is assumed that the stop position x of the magnetic tape is in the area X ₂ or X ₄ (see FIG. 4). As shown in FIG. 10a and d, at time t ₀ ,
The magnetic tape 1 is accelerated for a time (t ₂ −t ₀ ) from a stopped state. At this time, the output of the charging/discharging circuit 41 is
As shown in FIG. 0B, the low potential V ₂ before time t ₀ changes to the high potential V _H in time (t ₁ −t ₀ ). Here,
The variation ranges Va and Vb of V _L , V _H and output signal O ₃ are:
The relationship is V _L < Va < Vb < V _H , and t ₁ < t ₂ . Now, when x is in the area X ₂ or X ₄ ,
The output signal O ₁ of the stop position detection device 42 is at a low level, and at this time, the charging/discharging circuit 41 starts discharging from time t ₂ at the end of acceleration, as shown by the solid line in FIG. 10b. During discharging, let t ₃ and t ₅ be the times when the output of the charging/discharging circuit 41 matches Vb and Va, and let t ₄ be the time when the output matches the potential V of the output signal O ₃ .
As shown in Figure 10c and d, from time t ₂ to t ₄
The magnetic tape is maintained at a constant speed ve until time t6, and then braked until time _t6 , when it comes to a stop. Here,
t ₂ , t ₃ , ve are the shaded parts in Figure 10d, i.e. (t ₂ - _{t 0} ) acceleration of time, (t ₃ - t ₂ ) constant velocity of time, and (t ₅ - _{t 4} ) Assume that the length of the magnetic tape fed by time braking is set to 0.5p. In addition, the charging/discharging circuit 41 (t ₅ −
t ₃ )·ve=p. Therefore, when x is in the regions X ₂ and X ₄ , the braking start time t ₄ changes depending on the potential V of the output signal O ₃ , and the length of the magnetic tape sent between times t ₃ and t ₄ changes. is varied in the range of 0.5p to 1.5p, and the magnetic tape is fed to the optimal stopping position. When the stop position x of the magnetic tape is in the areas X ₁ and X ₃ , as is clear from _FIG .
By sending the length p more than in the case of X ₄ ,
The magnetic tape is fed to the optimum stop position. At this time, the charging/discharging circuit 41 detects that the output signal O ₁ is at a high level, and as shown by the dashed line in FIG. 10b, discharge occurs at the same slope as the solid line from time t ₇ .
Here, it is assumed that t ₇ is set to satisfy (t ₇ −t ₂ )·ve=p. In the above embodiment, the triangular wave generator 19, sample hold circuit 22, charging/discharging circuit 41, etc. in the stop position detection device 42 employs analog signal processing, but digital processing using a clock signal, a counter, etc. It goes without saying that the same function can be achieved by signal processing. In addition, in the above embodiment, a case was explained in which so-called field throw and field still are realized using heads with the same azimuth, but frame throw and frame still using heads with different azimuths can also be realized by the stop position detection device. The constant speed running time of the magnetic tape can be controlled from the output. Further, the magnetic tape may be fed in either a forward direction or a reverse direction, and is therefore applicable to both normal slow playback and reverse slow playback. [Effects of the Invention] As described above, according to the present invention, the stop position of the tape is detected from the pilot signal included in the playback signal, and the constant speed running time during tape feeding is determined according to the result. Therefore, good slow playback and still playback can be achieved without any adjustment. Further, according to the present invention, the amplitude comparison output of the first and third pilot signals and the amplitude comparison output of the second and fourth pilot signals are used for detecting the position of the magnetic tape. Since either of the above two amplitude comparison outputs can be obtained from the rotating magnetic head no matter where the tape stops, the magnetic tape stop position can always be accurately detected.

[Brief explanation of the drawing]

FIG. 1 is a time chart for explaining magnetic tape running control operation during slow playback or still playback in a conventional video tape recorder. FIGS. 2, 3, 4 and 5 are diagrams for explaining the relationship between the stop position of the magnetic tape used in one embodiment of the present invention and the pilot signal included in the reproduced signal. FIG. 6 is a block diagram showing an example of a stop position detection device used in an embodiment of the present invention. FIG. 7 is a time chart for explaining the operation of the stop position detection device shown in FIG. 6. FIG. 8 is a graph for explaining the relationship between the magnetic tape stop position and the feed length.
FIG. 9 is a schematic block diagram showing one embodiment of the present invention. FIG. 10 is a time chart for explaining the operation of the embodiment shown in FIG. In the figure, 1 is a magnetic tape, 2a, 2b, 2
c and 2d are video tracks, 6a and 6b
is a balanced modulator, 7a, 7b, 7c and 7d are bandpass filters, 8a, 8b, 8c and 8d are detectors, 9a, 9b and 43 are comparators, 19
is a triangular wave generation circuit, 22 is a sample hold circuit, 24 and 27 are switch circuits, 41 is a charging/discharging circuit, 42 is a stop position detection device, 44 is a NOR
Shows the circuit.

Claims (1)

[Scope of Claims] 1. In a magnetic recording and reproducing device that performs slow playback and still playback by intermittently controlling the running of a magnetic tape through acceleration, constant speed, braking, and stopping, there is provided the following: With one video track as one cycle, each of the four video tracks receives a video signal as well as a first video signal having a different frequency,
Means for sequentially recording and reproducing second, third, and fourth pilot signals, and determining how far a stop position of the magnetic tape is from one end of the one cycle when reproducing and stopping the magnetic tape. stop position detection means for outputting a signal indicating the stop position detection means; and means for changing the time during which the magnetic tape is run at a constant speed during the slow playback and still playback according to the output of the stop position detection means, the stop position detection means compares the amplitudes of the first and third pilot signals included in the reproduced signal from the recording and reproducing means and determines the first and second pilot signals;
a first comparison means for forming a comparison output of the second and fourth pilot signals included in the reproduction signal from the recording and reproduction means;
a second comparison means for forming a comparison output of the first and second comparison means; a means for outputting a head switching signal for switching the rotating magnetic head included in the recording/reproducing means; A magnetic recording and reproducing apparatus, comprising: a third comparing means for detecting the position of the magnetic tape in a state in which the magnetic tape is reproduced and the magnetic tape is stopped, based on the signal.