JPS6322673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a still image reproducing device, and in particular, for example, in a VTR or the like using two rotating magnetic heads with different azimuth angles, when a still image is reproduced, a recording track on a magnetic tape and two magnetic heads are used. The present invention relates to a still image reproducing device that removes noise bands that occur on a screen depending on the relative positional relationship with the locus of the image.

In a magnetic recording/reproducing device that reproduces recorded signals by sequentially scanning tracks recorded obliquely with respect to the longitudinal direction of a magnetic tape using two rotating magnetic heads having different azimuth angles, the running of the magnetic tape is When a still image is reproduced by stopping the recording head, noise bands may occur depending on the relative positional relationship between the recording track and the locus of the reproduction head.
This will be explained with reference to FIG.

FIG. 1 is a diagram showing the relationship between the formation state of a video track when an image signal is recorded on a magnetic tape and the locus of a reproducing head during still image reproduction. The magnetic tape 1 includes a first tape having a predetermined azimuth angle.
The recording tracks 2a, 2b, 2c are recorded by the heads of
is formed. Furthermore, tracks 3a, 3b, and 3c are formed on the magnetic tape 1 by second heads having an azimuth angle different from that of the first head. Note that the recording tracks 2a to 2c thus formed can be reproduced only by the first head, and the recording tracks 3a to 3c can be reproduced only by the second head.

Now, the track widths of the recording tracks 2a, 2b, 2c are equal to the track widths of the recording tracks 3a, 3b, 3c, the width of the first head is almost equal to the width of each track, and the width of the second head is equal to the width of each track. It should be slightly wider than the width. For example, when the first and second head trajectories during still image playback are in the states shown by trajectories 4a and 4b, respectively, the portion where the reproduction level of the image signal by the first or second head decreases is the track. Located at the edge. Therefore, no noise band appears on the TV screen. However, when the first and second head trajectories are in the state shown by trajectories 5a and 5b, respectively, the position at which the playback level by the first head decreases is away from the top or bottom of the magnetic tape 1 and is centered. It's nearby. Therefore, a noise band 22 appears in the center of the television screen 21 as shown in FIG. That is, when the first head performs reproduction, the first head extracts the signals of the reproduced portion 6b and the reproduced portion 6a as it follows the trajectory 5a, but at the transition point 1.
At 0, the signal level is almost lost, so the reproduced signal is not sufficient as an image signal and appears as noise on the screen.

A method for eliminating noise bands caused by the above-mentioned causes is to read out some signal from the magnetic tape, such as a control signal recorded at a position different from the image signal, when transitioning from normal playback to still image playback, and then After confirming the method of stopping the capstan shaft for feeding the magnetic tape in the longitudinal direction at a predetermined time and that the noise band is out of the position corresponding to the vertical blanking period, it is necessary to continuously drive the capstan shaft with a predetermined width once or twice. Performed several times on the capstan shaft drive mode motor for tape feeding,
There is a way to push the noise band out of the screen. However, in the former method, the position of the control signal varies depending on the characteristics of the recording device as well as the variations in the characteristics of the capstan drive motor, so there is no guarantee that a noiseless still image will be obtained when the tape is stopped. Furthermore, in the latter method, tape feeding is often repeated several times in order to remove noise from the screen, which takes a long time and has the drawback of making the viewer conscious of the presence of noise.

Therefore, the inventor of the present invention has already proposed a still image reproducing device that can remove noise bands in an extremely short time by running the tape only once. Since the present invention is directed to improving such a still image reproducing device that has already been proposed, the general structure and principle of this background art will be explained first, and the problems to be solved will be explained.

FIG. 3 is a diagram showing an overall schematic configuration of a magnetic recording and reproducing device using a still image reproducing device, which is the background art of the present invention. The first magnetic head A and the second magnetic head B draw loci shown by dotted lines 30 and perform a helical scan on the magnetic tape 1. The outputs of these magnetic heads A and B are given to a signal recording/reproducing device 31. This signal recording and reproducing device 31 reproduces the signals given from the magnetic heads A and B into the original video signal, and outputs the signal to the subsequent monitor circuit (not shown).
give to Further, the signal recording/reproducing device 31 includes a dropout detection circuit 31a. The dropout detection circuit 31a includes, for example, a level detection circuit, and derives a dropout detection signal X when the level of the reproduced signal falls below a predetermined value. That is, the dropout detection circuit 31a derives the dropout detection signal X when the level of the reproduction signal decreases due to the cause explained in FIG. 1 or when the reproduction level decreases due to scratches on the magnetic tape 1 or the like. Further, the rotating shafts of the magnetic heads A and B are directly connected to a motor 35, and this motor 35 is driven by a drive circuit 33. Furthermore, two magnets are attached to the rotating shafts of heads A and B. A position detection head PG is placed near this magnet, and its output is sent to the position detection device 32.
given to. That is, this position detection device 32
The rotational position of the magnet and therefore the playback position of heads A and B are detected. The output of the position detecting device 32 is used as a switching signal between the outputs of the magnetic heads A and B to the signal recording and reproducing device 31.
and is also provided to the drive circuit 33. On the other hand, the capstan motor 36 is driven by the drive circuit 34. The magnetic tape 1 is inserted between the capstan shaft 37 of the capstan motor 36 and the pinch roller 38. That is, the running of the magnetic tape 1 is based on the capstan shaft 37.
This is done by rotating the

The still image reproducing device 39 is given a still image reproducing command signal Z from a system control device (not shown) (a device that reads key operations on the keyboard and derives various command signals), and operates according to this command signal Z. Start. Further, the still image reproducing device 39 is supplied with a dropout detection signal X during reproduction from a dropout detection circuit 31a. Furthermore, the still image playback device 39 includes a position detection device 32.
A head switching signal Y is applied from. The still image reproducing device 39 derives drive signals M and N based on the dropout detection signal X and the head switching signal Y, and supplies them to the motor drive circuit 34.

Here, Fig. 4 a and b, Fig. 5 a to c
The principle of the still image reproducing device 39 will be explained with reference to .

FIG. 4a shows the waveform of the switching signal Y between the first head A and the second head B. In FIG. In addition,
When the switching signal Y is high level, the first head A
On the other hand, when it is at a low level, it is a reproduction period by the second head B. Further, FIG. 4b shows the waveform of the dropout detection pulse X corresponding to the noise band on the television screen. In order to move the position of this dropout detection pulse You will get a static screen that does not appear. When the tape 1 is stopped from the normal tape running state, the time difference between the rising time 42 of the dropout pulse X and the immediately following switching time 41 from the second head B to the first head A is the magnetic tape It changes depending on the position where No. 1 stops, that is, the position where a noise band occurs on the screen. Therefore, in order to eliminate the noise from the screen by driving the capstan shaft once, the pulse width applied to the capstan shaft driving DC motor 34 may be increased or decreased in accordance with the time difference.

Here, FIGS. 5a to 5c are diagrams showing characteristics when a general DC motor is caused to perform a stepping operation. Note that FIG. 5a shows a drive command signal for the motor, and FIG. 5b shows a switching signal for power running and reverse braking.
Further, FIG. 5c shows the relationship between the time T1 and the rotation angle θ of the DC motor when the DC motor is caused to perform a stepping operation, assuming that the power running time is T1 and the reverse braking time is T2. As can be seen from Figure 5c,
If T1 is less than the predetermined time T0, the DC motor will not operate due to static friction torque of the motor shaft. Further, in the operating range, a substantially linear relationship is established between the rotation angle θ and T1. That is, assuming that T ₁ :T ₂ is constant and equal to 100, the rotation angle θ of the DC motor becomes larger as the travel time T1 becomes longer.

Therefore, based on the dropout detection signal By appropriately processing the signals, a drive command signal M for the capstan motor 35 (see FIG. 5a) and a switching signal N for forward reverse braking (see FIG. 5b) are created. The rotation angle of the capstan motor 36 and therefore the running distance of the magnetic tape 1 can be controlled via the drive circuit 34, and the noise band can be removed from the TV screen by running the magnetic tape 1 only once. Can be removed.

Incidentally, even if the reproduced signal level decreases due to scratches on the reproduced magnetic tape 1, dropout is detected. However, the still image playback device 3 as described above
9 cannot distinguish between dropout pulses due to the relative positional relationship between the head and track and dropout pulses due to scratches, etc., so it also operates on dropout pulses due to scratches, etc. The magnetic tape 1 is run to remove from the screen the noise band on the screen corresponding to the dropout pulse caused by the dropout pulse. Therefore, when there are many scratches on the magnetic tape 1, if you run the magnetic tape 1 to remove the noise band from the screen, the noise band due to the next scratch will appear on the screen, and this will repeat. 1 may continue to be run forever.

Therefore, the main purpose of the present invention is to solve the above-mentioned problems, and to prevent the magnetic tape from continuing to run even if there is a scratch on the magnetic tape, and to shorten the time by running the magnetic tape once. An object of the present invention is to provide a still image reproducing device that can remove noise bands.

In summary, when controlling the travel distance of the magnetic tape based on the dropout detection signal and the playback position detection signal in the still image playback mode, the magnetic tape is This prevents the magnetic tape from running repeatedly due to a dropout pulse detection signal caused by, for example, a scratch on the magnetic tape.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 6 is a circuit diagram showing an embodiment of the present invention. In this configuration, the still image reproduction command signal Z is applied to the input terminal 61. In addition, input terminal 6
2 is supplied with the dropout detection signal X. Further, a head switching signal Y is applied to the input terminal 63. These input terminals 61 to 63 are connected to a still image reproduction device 60.

In this still image reproducing device 60, the still image reproducing command signal Z and the dropout detection command signal
is given to the time limit circuit 16 as a means for prohibiting running. This timer circuit 16 is used to gradually attenuate the level of the dropout detection signal X, and is the most significant feature of this embodiment. As will be explained in detail later, this time limit circuit 16 is effective when the magnetic tape 1 has scratches or the like. The output Xa of this time limit circuit 16 is the time difference detection circuit 11 as a noise band position detection means.
given to. Further, the time difference detection circuit 11 includes:
The still image reproduction command signal Z and the head switching signal Y
is given. This time difference detection circuit 11 is a circuit for detecting the time difference between the dropout detection signal X and the head switching signal Y and generating a signal corresponding to the position of the noise band on the television screen. The output H of the time difference detection circuit 11 is given to the time width conversion circuit 12. This time width conversion circuit 1
2 is a time difference detection signal H from the time difference detection circuit 11
This circuit converts the pulse into a pulse with an appropriate time width. The output K of the time width conversion circuit 12 is given to the drive signal generation circuit 13. This drive signal generation circuit 13 is a circuit for generating a motor drive command signal M and a motor reverse braking signal N based on the applied time width conversion pulse K. Outputs M and N of this drive signal generation circuit 13 are given to a capstan shaft drive circuit 34.

7a to 7n and 8a to 8c are waveform diagrams for explaining the operation of the circuit of FIG. 6.

First, with reference to FIG. 7, an explanation will be given of the operation in the case where it is not necessary to take into account the dropout detection signal generated due to scratches on the magnetic tape 1 to be reproduced. In this case, the operation of the still image reproduction device 39 is completed before the effect of the time limit circuit 16 appears, that is, before the level of the dropout detection signal Xa is lowered below the input threshold of the time difference detection circuit 11, so the dropout is detected. It may be considered that the signal X and the output Xa of the time limit circuit 16 are approximately equal. Note that the operation when the magnetic tape 1 has a scratch will be described later.

A dropout detection signal X as shown in FIG. 4b is applied to the input terminal 62. In this case, as described above, the output Xa of the timer circuit 16 becomes approximately equal to the dropout detection signal X, as shown in FIG. 7b. A still image reproduction command signal Z which becomes high level at time t0 is applied to the input terminal 61 as shown in FIG. 7a. Further, a head switching signal Y as shown in FIG. 7c is applied to the input terminal 63. It is assumed that the magnetic tape 1 is stationary, and that the first and second heads A and B running on the magnetic tape 1 are in the positions 5a and 5b in FIG.

As shown in FIG. 7f, before and after time t0,
Assuming that the Q output of the flip-flop 113 is at a low level and the 0 terminal output of the one-shot multivibrator 114 is at a high level as shown in FIG. 7g, the head switching signal Y changes from a high level to a low level at time t1. The state of the output of the time difference detection circuit 11 (see FIG. 7h) does not change even when the time difference detection circuit 11 switches to the current state. As shown in Figure 7b, the time
When the output Xa of the time limit circuit 16 is applied to the time difference detection circuit 11 at t2, the output of the gate 111, that is, the S input of the flip-flop 113 momentarily drops to a low level as shown in FIG. The level becomes high as shown in Fig. 7 f. At the same time, flip-flop 1
The output of the terminal 13 becomes low level, the one-shot multivibrator 114 is activated, and the output of the 0 terminal becomes low level for a predetermined period τ as shown in FIG. 7g. Therefore, this τ period gate 1
Passage of the signal Xa at 11 is prohibited. time
At time t4, the head switching signal Y is inputted again, and the output of the differentiating circuit 115, that is, the R input of the flip-flop 113 falls, and the flip-flop 113 is reset. In response, the Q output of flip-flop 113 changes to low level again. As described above, since the gate 111 is closed during the period from time t2 to τ, this time difference detection device 11 does not function with respect to the new dropout pulse Xa. Also, from time t2
During t4, both inputs of the gate 112 are at a high level, so the output H of the time difference detection circuit 11 is at a low level during this period, as shown in FIG. 7h. That is, the time difference detection circuit 11 outputs a signal H corresponding to the time difference between the rise of the dropout detection pulse Xa and the rise of the switching signal Y immediately after.

The time width conversion circuit 12 is the time difference detection circuit 1 described above.
It operates upon receiving the output H of 1. That is, while the time difference detection signal H is at a high level, the diode 1
Since 26 and 127 are conductive, capacitor 129
The output of the operational amplifier 121 used for integration remains at a constant potential slightly lower than its positive phase input terminal 12a. That is, at this time, the potential at point 12b is lower than the potential at point 12a, so the output of comparator 123 is at a high level, and analog switch 124 is conductive. When the time difference detection signal H changes to low level after time t2, the output of the amplifier 121 quickly increases via the low resistance R1, the diode 128, and the capacitor 129, and the potential at the point 12b also increases. Therefore,
At time t3 when the potential at point 12b exceeds the potential at point 12a, the output of comparator 123 becomes low level, and after time t3, high resistance R2 and diode 12
8 and the amplifier 121 via the capacitor 129
The output voltage of increases. At time t4, the time difference detection signal H becomes high level, so the output voltage of the amplifier 121 gradually decreases via the resistor R3, the diode 126, and the capacitor 129, and after the charge on the capacitor 129 has a characteristic opposite to that shown in the figure. time
At t6, the output of amplifier 121 becomes stationary again. How the output voltage of the amplifier 121 changes during this period is shown in FIG. 7i. Further, the output of the comparator 122 during this period is as shown in FIG. 7j. Therefore, the output of the gate 125, that is, the converted output K of the time width conversion circuit 12 changes as shown in FIG. 7k.

In this way, the output H of the time difference detection circuit 11 is processed by the time width conversion circuit 12 and then converted into an output K having a different time width as shown in FIG. 7k. As a result, the travel time of the capstan motor 35 (time width T1 in FIG. 5b) is determined. Note that the ratio of the time width of the signal K to the time width of the signal H is appropriately determined by the resistance values of the resistors R1, R2, and R3 and the capacitance value of the capacitor 129.

The drive signal generation circuit 13 operates with the output K as an input, and while the output K is at a low level, the output voltage of the amplifier 131 is applied to the resistor R6 and the capacitor 134.
, and gradually decreases when the output K returns to high level. The state of the change in the output of the amplifier 131 is shown in FIG. 7l. On the other hand, the output of the comparator 132 becomes high level only when the output of the amplifier 131 is equal to or higher than a predetermined value. Therefore, the output M of the comparator 132 changes as shown in FIG. 7m. Further, the output N of the gate 133 changes as shown in FIG. 7n.

In addition, in this case, it is necessary to set the ratio of the period T1 from time t5 to t6 to the time T2 from time t6 to t7 so that T1>T2, but this ratio is determined by the resistance between resistors R4 and R5. This is done by adding a difference between the values. The output M of the comparator 132 is given to the motor drive circuit 34 as a drive command signal for the capstan motor 35, and the output N of the gate 133 is given to the drive circuit 34 as a reverse braking signal for the capstan motor 35.

In the motor drive circuit 34, the transistor 341
A drive voltage is applied to the motor, and transistors 342 to 345 switch between forward and reverse rotation. Therefore, during the period T1, the capstan motor 35 is driven in the forward direction, and during the period T2, the capstan motor 35 is reversely braked. Since the ratio of the periods between T1 and T2 is always constant regardless of its absolute value, T1
The amount of rotation of the capstan motor varies depending on the length of the period. Note that during the T2 period, the capstan motor 35 is only decelerated by the amount accelerated during the T1 period, and the length of T2 is selected so that the capstan motor 35 does not rotate in reverse.

As shown in FIG. 7h, the time difference detection circuit 11 operates again at time t9, and its output H becomes low level for a short period from time t9 to time t10.
Accordingly, the output K of the time difference conversion circuit 12 is shown in FIG.
The output of the drive signal generating circuit 13 changes as shown in FIG. 7 m and n. However, since the noise band has already been removed from the screen, the period between times t9 and t10 is narrow, and the motor shaft 37 of the capstan motor 35 does not rotate due to static friction torque. Therefore, the magnetic tape 1 remains stationary. In addition,
An ideal time difference conversion circuit 12 can be obtained by determining the value of the resistor R1 so that the period between times t2 and t3 is approximately equal to the period between times t9 and t10.

In this way, the time width of the output H of the time difference detection circuit 11 changes depending on the position of the noise band, and the time width of the output K of the time width conversion circuit 12 also changes depending on the magnitude of this time width. The time width of this output K determines the drive time of the capstan shaft drive motor 35. Therefore, if the conversion rate of the time width conversion circuit 12 is appropriately selected by adjusting the resistors R2 and R3, the noise band can be erased from the screen with one motor drive.

Next, referring to FIG. 8, an explanation will be given of the operation when the reproducing magnetic tape 1 has a scratch and the timer circuit 16 is effective. In this case, schematically, the timer circuit 16 controls the gate 1 in the time difference detection circuit 11.
The level of dropout detection signal Xa applied to gate 111 is made equal to or less than the input threshold of gate 111 for a predetermined time. As a result, the time difference detection circuit 11
It is determined that there is no dropout detection signal after a predetermined time, and the magnetic tape 1 is not run. Therefore, it is possible to prevent the magnetic tape 1 from stopping forever.

Now, at time t0 as shown in Figure 8a,
It is assumed that a still image reproduction command signal Z is applied to the input terminal 61. In the time limit circuit 16 of FIG.
Capacitor 164, which was charged by the output of inverter 161 before time t0, starts discharging to the output terminal of inverter 161 through resistor 162 after time t0. This discharge causes transistor 16
The base potential of transistor 164 decreases exponentially and conduction begins between the emitter and collector of transistor 164, so the dropout detection signal X is output as a signal Xa whose level has been lowered, as shown in FIGS. Ru. If the level of the signal Xa falls below the input threshold value vx of the gate 111 after a predetermined time T3 after the signal Z becomes high level at time t0, the time difference detection circuit 11 changes the dropout detection signal X to the dropout detection signal X after the predetermined time T3. No action is taken against it. Therefore, if the predetermined time T3 is set to a time sufficient to drive the noise band from the screen when there are no scratches on the tape, it is possible to prevent the magnetic tape 1 from running again due to a dropout detection signal due to scratches, etc. do not have. Note that the predetermined time T3 is appropriately determined depending on the capacitance value of the capacitor 164 and the resistance value of the resistor 162.

In the embodiment shown in FIG. 6, the time limit circuit 16 is used as an example of the travel prohibition means, but instead of this, a circuit that prohibits the application of the dropout detection signal X to the time difference detection circuit 11 after a predetermined period of time may be used. May be used. Such a circuit includes, for example, a one-shot multivibrator whose output goes to a high level when the still image reproduction command signal Z rises and then goes to a low level after a predetermined period of time, and the output of this one-shot multivibrator and dropout detection. Receive signal X as two inputs
It can be configured by AND gate.
Further, as another example of the driving prohibition means, it is also possible to reduce or prohibit the outputs M and N of the still image reproduction device 40 to be lower than the motor operating voltage after a predetermined period of time.

In the embodiments shown in FIGS. 3 and 6, a DC motor is used as the capstan shaft drive motor 35. However, it goes without saying that the present invention can also be applied to brushless motors. In this case, the circuit configuration of the motor drive circuit 34 will be different from that shown in FIG.
The output M corresponds to the motor current command, and the output N
can be easily realized by making it correspond to a forward/reverse switching signal. Furthermore, the present invention is applicable regardless of whether the capstan shaft drive motor 35 is a direct drive motor or a belt drive motor.

As described above, according to the present invention, running of the magnetic tape is prohibited after a predetermined period of time after a still image playback mode command is issued, so even if a dropout occurs due to a scratch on the magnetic tape, for example, it will not occur. With one run, noise bands can be removed from the visible screen in a short time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the formation state of a video track when an image signal is recorded on a magnetic tape and the locus of a reproducing head during still image reproduction. FIG. 2 is a diagram showing noise bands on a television screen. FIG. 3 is a diagram showing an overall schematic configuration of a magnetic recording and reproducing device using a still image reproducing device, which is the background art of the present invention. 4 and 5 are diagrams for explaining the principle of the still image reproducing device 39 shown in FIG. 3. FIG. FIG. 6 is a circuit diagram showing an embodiment of the present invention. 7 and 8 are waveform diagrams for explaining the operation of the circuit of FIG. 6. In the figure, 1 is a magnetic tape, 11 is a time difference detection circuit, 12 is a time width conversion circuit, 13 is a drive signal generation circuit, 16 is a time limit circuit, 31a is a dropout detection circuit, 32 is a position detection circuit, and 36 is a capstan. Motors 39 and 60 represent a still image reproducing device.

Claims (1)

[Claims] 1 Still image reproduction command means for instructing a still image reproduction mode, reproduction position detection means for detecting the reproduction positions of two magnetic heads having different azimuth angles, and a reproduction signal having a level of a reproduction signal. In a magnetic recording/reproducing apparatus, the magnetic recording/reproducing apparatus includes a dropout detecting means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means for detecting dropout detection means.
A still image reproducing device that removes noise bands generated on a screen due to a relative positional relationship with the trajectory of two magnetic heads, wherein a still image reproducing mode is commanded by the still image reproducing mode command means. noise band position detection means for detecting the generation position of the noise band based on a reproduction position detection signal from the reproduction position detection means and a dropout detection signal from the dropout detection means when the noise band is detected; a travel amount control means for controlling the travel amount of the magnetic tape so as to remove the noise band from the screen based on the position detection means; and a still image reproduction mode is set by the still image reproduction mode command means. A still image reproducing device comprising a running prohibition means for prohibiting the running of the magnetic tape after a predetermined time selected to be at least longer than the time required for the running amount control means to remove the noise band after being commanded. 2. The noise band position detection means includes means for prohibiting input of the dropout detection signal when the level of the dropout detection signal is below a predetermined value, and the travel prohibition means is configured to prevent the dropout detection signal from being inputted to the noise band position detection means. Claim 1, further comprising means for attenuating the level of the detection signal to below the predetermined value in the predetermined time.
The still image playback device described in . 3. The travel prohibition means includes means for generating a signal for a predetermined time after the still image playback mode is commanded by the still image playback command means, and detecting the noise band position after a predetermined time based on the predetermined time signal. 2. The still image reproducing apparatus according to claim 1, further comprising means for inhibiting input of said dropout detection signal to said means.