JPH0441554B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a rotating head type magnetic recording/playback device (hereinafter referred to as
The present invention relates to VTRs (referred to as VTRs), and particularly relates to VTRs that perform noiseless variable speed playback using a video head mounted on an electromechanical transducer. Conventional configuration and its problems Rotating two-head helical scan VTR
Now, one field of images is recorded on a magnetic tape using one track. The recording track is recorded with a constant inclination angle in the longitudinal direction of the magnetic tape, and this inclination angle changes depending on the tape speed. For this reason, when the tape is transported and reproduced at a tape speed different from that during recording, the recording track locus and the scanning locus of the head do not match, resulting in a reproduced image with noise. In order to obtain reproduced images without noise, the head is mounted on an electromechanical transducer (hereinafter referred to as a bimorph) composed of a piezoelectric element, etc., so that the head on-tracks the recording track and performs reproduction scanning. , by applying an appropriate voltage to the bimorph. This applied voltage has a sawtooth waveform as described later, but the level of the applied voltage and the number of sawtooth waves vary depending on the tape speed at the time of reproduction. Conversely, if the tape speed is determined, the applied voltage waveform is determined. The waveform at this time is usually called a preset waveform. This preset waveform is created by a method similar to that seen in the NV-10000 video deck manufactured by Matsushita Electric Industrial Co., Ltd., for example. That is, a sawtooth wave created by counting the capstan FG signal and resetting it with a control signal and a sawtooth wave corresponding to the still locus are combined to form a preset waveform. The feature of this method is that the preset waveform is created using a capstan FG related to tape speed and a control signal. Therefore, even if the tape speed is any suitable speed, a preset waveform can be created according to that speed. A drawback of this method is that it requires a control signal. Therefore, a VTR equipped with a control system that does not use control signals,
For example, a VTR such as an 8mm VTR that records a tracking control pilot signal superimposed on a video signal and controls the level of the crosstalk signal reproduced from each adjacent track to be equal during playback has the above preset. The waveform creation method is not applicable. OBJECTS OF THE INVENTION The first object of the present invention is to create a preset waveform that does not use a control signal, and to create a preset waveform that does not use a control signal, and that can also be used when transitioning to double speed mode, for example from still mode to single speed mode, from single speed mode to double speed mode, etc. The object of the present invention is to provide a method for obtaining reproduced images without noise. Structure of the Invention The present invention includes a magnetic tape, a capstan motor for transporting the magnetic tape, a speed control means for controlling the rotational speed of the capstan motor based on a speed command signal, and a speed control means for generating the speed command signal. A speed command signal generating means, an electromechanical transducer equipped with a rotating magnetic head, a drive means for driving the electromechanical transducer, and a preset signal generating means for generating a preset signal to be supplied to the drive means based on the speed command signal. When the transfer speed of the magnetic tape is transferred from the first transfer speed to the second transfer speed, the speed command signal generation means is configured to generate a waveform at the first transfer speed and the second transfer speed. The transfer speed and the preset signal are changed step by step by outputting a speed command signal that sequentially specifies the speed divided by N (N is a natural number of 2 or more) between the transfer speed and the preset signal. DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a diagram showing the magnetization locus on the magnetic tape of a VTR, where 1 indicates the magnetic tape, arrow 2 indicates the direction of transport of the magnetic tape, and arrow 3 indicates the scanning direction of the magnetic head. A ₁ , A ₂ , A ₃ . . . are magnetization trajectories recorded by the A head and B head having mutually different azimuth angles. When the tape speed during playback is the same as that during recording, the head scans along the trajectory of arrow 4. When the tape is in a stopped state during playback, that is, in a still state, the scanning locus of the head takes the locus shown by arrow 5. FIG. 2 is a diagram for explaining 1/4 slow playback, and A ₁ , B ₁ , A _{2 .} . . are magnetic cutting trajectories recorded by the A and B heads. The magnetic tape is transported in the direction of arrow 6. Trajectory 7 is a still trajectory. When the tape speed during reproduction is set to 1/4 of that during recording, the scanning locus of the head becomes the scanning locus shown by 8 to 23. Consider a field regeneration with an auxiliary head A' dedicated for regeneration. At this time, the azimuth angle of each head A' and B is assumed to be the same as that of the Bi (i=1, 2, 3, . . . ) track. To obtain a noise-free playback image, each head must
It is necessary for A' and B to on-track on the Bi track for reproduction scanning. For this purpose, it is necessary to mount the reproducing head on the bimorph and displacing the reproducing head in the width direction of the recording track by an amount corresponding to the amount of strut. FIG. 3 shows the amount of displacement, and in the figure, a is a head switching signal (hereinafter referred to as H.sw signal). The numbers 8 to 23 written on the H.sw signal correspond to the respective scanning times 8 to 23 shown in FIG. The waveform shown in Figure 3b shows the voltage applied to the bimorph necessary for on-tracking and reproducing scanning on the B ₁ and B ₂ tracks, with the horizontal axis representing time and the vertical axis representing the voltage applied to the bimorph. It is shown. Here, 1T _P indicates the voltage level applied to the bimorph to obtain a displacement equivalent to one track pitch. Further, the polarity of the applied voltage is shown as positive in the same direction as the tape transport direction and negative in the opposite direction. For example 8
When scanning the head as shown in , if a voltage equivalent to -1/2T _P is applied to the bimol when the head starts contacting the tape, and a voltage equivalent to -5/4T _P is applied to the bimol when the head starts to separate from the tape, the head will move. The recording track _B1 is on-tracked for reproduction scanning. The bimorph applied voltage waveform shown in FIG. 3b is called a preset waveform. The preset waveform shown in FIG. 3 is a waveform necessary for reproducing and scanning the _B1 track during each scan from 8 to 15 in FIG. 2, and the _B2 track during each scan from 16 to 23 in FIG. The preset waveform is a voltage waveform applied to the bimorph that is inevitably determined once the tape speed during reproduction is determined. When playing back at n times speed, for example, the slope amount 24 between 1 field at 1/4 speed is (1-n) T _P ,
That is, 3/4T _P , and the amount 25 that increases per field is nT _P , that is, 1/4T _P. Further, the update amount 26 at the time of track update is (2-n)T _P , that is, 7/4T _P. Here, as a specific numerical example, 1/4
I mentioned double speed, but this idea is generally n
It works at twice the speed. That is, if the tape speed is known, a preset waveform can be created. One method of determining the timing for updating a track is to determine the number of repetitions from the tape speed. For example, at 1/4x speed, the track may be updated every 8 fields. Generally, when the speed is n times faster, it is sufficient to update the track every 2/n fields. Another method is to update the track when the preset voltage exceeds a certain threshold voltage. By simply applying the preset waveform created by the above method to the bimorph, it is possible to make the scanning locus of the head parallel to the longitudinal direction of the recording track, but it is also possible to on-track and perform reproduction scanning on the desired recording track. It is not possible. This is because, for example, when the preset voltage at the H.sw timing shown at 8 in FIG. 3 is applied to the bimorph, the scanning locus of the head is not necessarily the locus of the position shown in FIG. 2, 8. However, this problem
This is a normal tracking problem in which the scanning locus of the head and the scanning locus of the recording track are parallel, but the tracks are misaligned in terms of DC.
Although the details are omitted, in the tracking control method using pilot signals used in 8mm VTRs, etc., the tape feeding phase is adjusted so that the amount of crosstalk from each adjacent track on both sides of the main scanning track is equal. It's in control. Therefore,
By using a preset voltage to make the scanning locus of the head parallel to the recording track, the DC track deviation can be corrected by controlling the tape feeding phase, and as a result, the scanning position at each scanning position shown in Figure 2 can be corrected by controlling the tape feeding phase. At some point, the preset waveform shown in FIG. 3 stabilizes in a corresponding manner. FIG. 4 is a block diagram for performing noiseless special reproduction without using a control signal. In the figure, 27 is a magnetic tape, which is transported by a capstan 28 and a pinch roller (not shown). 29 is a capstan motor, and 30 and 31 are frequency generators (hereinafter referred to as FG) for detecting the rotation speed of the capstan. Circuit 32 is a speed control circuit for the capstan motor, 33
is a drive circuit for the capstan motor, and these circuits control the rotation speed of the capstan motor so that the frequency of the FG is always constant. The capstan motor rotates at a rotation speed corresponding to a speed command signal supplied from the speed command circuit 34. 35 is a magnetic head, and 36 is a bimorph. Magnetic heads and bimorphs are
Although not shown, it is fixed to a rotating cylinder and rotates together with the cylinder. Various signals reproduced from the magnetic head 35 are supplied to a signal processing circuit 37, and a reproduced video signal is taken out to a terminal 38.
On the other hand, a pilot signal for tracking control which is recorded superimposed on the video signal is taken out via the signal processing circuit 37 and sent to the phase error creation circuit 39.
is supplied to The circuit 39 outputs a phase error signal corresponding to the difference between the crosstalk signals reproduced from each adjacent track located on both sides of the main scanning track. The error signal is fed to a speed control circuit to control the tape advance phase. The circuit 41 is a preset waveform generating circuit, which generates the previously explained preset waveform based on the speed command signal. in fact,
Signal processing can be performed using a microprocessor or the like. The circuit 40 is a phase error processing circuit, and is a circuit for extracting a phase error signal corresponding to, for example, a track bend from the phase error signal supplied from the circuit 39. Since the circuit 40 is different from the main purpose of the present invention, its details will be omitted. The output of the phase error processing circuit 40 and the preset waveform output from the circuit 41 are combined and passed through a bimorph drive circuit 42 to drive the bimorph. With the above configuration, special playback at n times speed without noise is possible. Next, noiseless reproduction at the time of mode transition in double-speed reproduction, which is the object of the present invention, will be explained. Figure 5 shows the recorded magnetization locus, with A ₁ , B ₁ , A ₂ ,
... is the recorded magnetization locus. Reference numeral 42 indicates a head scanning locus during still operation, and numerals 43 to 46 indicate head scanning loci during 1x speed. FIG. 6 shows a preset waveform necessary for the head scanning shown in FIG. In the same figure, a is
This is the H.sw signal, and figure b is the preset waveform.
The symbols 42 to 46 above the H.sw signal indicate the same time timings as the scanning trajectory symbols shown in FIG. Note that this time as well, we will explain this as field playback. At the time of transition to the double speed mode, for example, when the current state is the still mode and the next reproduction is performed in the single speed mode, the preset waveform becomes the waveform shown in FIG. 6b.
That is, in the figure, the still state is repeated for three fields, and after the timing indicated by 43, the normal reproduction state is entered. At this time, since it is field playback, it is necessary to apply a voltage to the bimorph so that the A' head scans the Bimorph.
In FIG. 6, the time when the H.sw signal is High is the period in which the A' head scans, and a preset voltage equivalent to _1TP is applied. When the still mode or 1x speed mode continues for a long time in the same state, a noise-free reproduced image can be obtained, but when transitioning from the still mode to the 1x speed mode, the preset voltage shown in Figure 6 must be set to bimorph. Even if the voltage is applied, it is not possible to obtain a reproduced image without noise. This is because the tape transport speed does not change instantaneously from the still state to the 1x speed mode. FIG. 7 is a diagram showing the rise characteristics of tape speed. In the figure, the still state is repeated until time _t1 , and after time _t1 , the mode changes to 1x speed mode. At this time, the preset waveform is output as shown by a solid line 47, with the tape speed instantaneously becoming 1x speed. However, the actual tape speed is
It shows a rising characteristic as indicated by a broken line 48. Therefore, between _t1 and t(2), the solid line 47 and the broken line 48
A noise corresponding to the difference between the two appears on the screen. In order to solve this problem, it is possible to match the rise of the preset waveform with the rise of the tape speed, but by reading the instantaneous tape speed,
It is actually difficult to output a preset waveform corresponding to this. Therefore, a method can be considered in which the rise characteristics of the tape speed are investigated in advance and a preset waveform is output that roughly matches the characteristics, but this method has the following drawbacks. First, when the running load of the tape changes due to changes in environmental conditions, changes over time, etc., the amount of deviation from the set value becomes a problem. Second, the rise characteristics from still to 1x speed are different from the rise characteristics from 1x to 2x speed, or the rise characteristics are different in the cue direction and review direction even from the same still at 1x speed or -1x speed. , it can only cope with a certain limited number of double speed mode changes. The present invention is a method for solving the above-mentioned drawbacks, and that method is to increase the tape speed command by a constant speed of 1x speed or less, and move to the next tape in a substantially stable state in each mode. Figure 8 shows 1/4 from still mode to 1x speed mode.
This shows the tape rise characteristics when the speed is shifted in steps of double speed. In the same figure, the still state is maintained until _t3 . When a command is received from an operation switch etc. to change to 1x speed mode at time _t3 , the speed control circuit of the capstan motor initially receives the command to change to 1/4x speed,
After a certain period of time, approach 1x speed in stages, such as 2/4, 3/4, and 4/4. In FIG. 8, a solid line 49 represents the rise characteristic of an ideal tape speed, and the preset voltage is output in accordance with the speed instruction indicated by 49. The broken line 50 is the actual tape speed rise characteristic. Even when the speed is increased by 1/4 times, there is a difference between the ideal and the actual speed. However, at this time no noise appears on the screen. because,
As is clear from Figure 2, still trajectory 7 and 1/4
There is no big difference from the scanning trajectory 8 at double speed. Therefore, when the tape is stopped, the preset waveform is 1/4
Even if the speed is equivalent to double speed, the reproduction output does not decrease enough to cause noise during the transition period. This also applies to the transition from 1/4x speed to 2/4x speed, and the same can be said for the next step. In FIG. 8, _t4 is the timing at which the speed changes from 1/4 times to 2/4 times, and _t5 represents the timing at which the speed changes from 2/4 times to 3/4 times. The time of one step, for example, the time between _t3 and _t4 , may be set to a time during which the tape speed is approximately stable in that mode.
According to experiments, the time required for one step is 1
A frame (1/30 second) is sufficient. Therefore,
The time it takes to shift from still mode to 1x speed mode is 4/30 seconds even if the speed is changed in steps of 1/4x, which poses no practical problem. The first feature of this method is that it is less susceptible to load fluctuations during tape running. because,
If you choose a time at which the tape speed is stable for each step even under the expected maximum load, the deviation between the actual tape speed rise characteristics and the ideal characteristics within each step will be reduced by noise as described above. This is because it does not appear on the screen. The second feature is that the same concept can be applied when shifting from any double speed mode to any other double speed mode. For example, when changing from 1x speed to 3x speed, 1/4
If the tape speed is changed for each double speed, no noise screen will appear when switching to double speed mode. In this example, each step has been explained as a 1/4 speed step, but it is clear that it may be a 1/8 speed step or a 1/2 speed step, and the setting can be made according to the equipment. Next, an example of a specific circuit configuration for varying the tape speed at each predetermined step will be described with reference to FIG. The means for changing the tape speed in constant steps can be realized by means for sequentially changing the frequency of the capstan FG signal in constant frequency steps. The method is to control the FG signal so that the frequency obtained by dividing the capstan FG signal by D is equal to the step frequency.
A capstan FG signal with a frequency of ×D is obtained,
By changing the frequency division ratio D by 1, the capstan
This is means for changing the frequency of the FG signal by the step frequency. Note that in this example, the capstan
Instead of using the FG signal as it is, use a PLL circuit to generate a fixed multiple.
Multiply by D ₁ and set the division ratio to D ₂ to obtain a capstan FG signal with a frequency of (reference frequency x D ₂ /D ₁ ), and change D ₂ by 1 to change the step frequency (reference frequency / D ₁ ). A means of changing the capstan FG frequency is used. Multiplying D by ₁ prevents the frequency obtained by dividing the FG signal from becoming extremely low. Also, assuming that the standard tape speed is obtained when D ₂ = D ₁ , the reference frequency is the FG frequency at the standard tape speed. It can be done. In FIG. 9, a capstan FG signal having a frequency proportional to the tape feeding speed is inputted from a terminal 51. The circuit 52 is a phase comparison circuit, the circuit 53 is a low-pass filter, the circuit 54 is a voltage controlled oscillation circuit, and the circuit 55 is a frequency dividing circuit. In this example, a 1/16 frequency dividing circuit is taken as an example. Circuit group 56 of circuits 52 to 55
constitutes a PLL circuit (Phase Locked Loop), and in this example, the capstan FG signal is multiplied by 16. The circuit 57 is a variable frequency dividing circuit, and the frequency dividing ratio is set according to instructions from the speed command circuit 64. The speed command circuit 64 receives speed command information obtained from an operation button or the like from a terminal 65 after once passing through the system control section. For example, when the current state of the operation button is in stop mode and you next press the operation button for triple speed mode, the system control section interprets that the operation button has been pressed and sends the speed command circuit 64 to the triple speed mode. The stop mode speed command information that was being sent before the operation button was pressed is changed to triple speed mode. At this time, the speed command circuit 64 does not specify a frequency division ratio corresponding to 3 times the speed from the current stop command all at once, but increases the frequency by 1/16 times and sequentially increases the frequency division ratio to 2/1.
6, 3/16, . . . , 48/16 (=3) Frequency division ratios corresponding to double speeds are sequentially output. Now, the multiplier of the multiplier circuit is
16 times, when the reference frequency for comparison in the speed error detection circuit is set to the FG frequency at standard tape speed,
The speed command circuit 64 sequentially increases the frequency division ratio of the variable frequency divider 57 to 1, 2, 3, . The speed can be increased in steps of 1/16 of the FG frequency. Such operations can be easily performed using a microcomputer. As a concrete method, a fixed value (1 in this example) is set for each timer interrupt of the microcomputer.
For example, by executing a program that adds up to 48 and stops the addition when the added value becomes equal to 48, it is possible to sequentially increase the speed up to 3 times. Circuit 58 is a speed error detection circuit, and variable frequency divider circuit 5
This is a circuit that outputs a voltage value (speed error voltage) according to the frequency difference between the frequency of the signal output from 7 and the reference frequency held internally, and specifically,
For example, Natonal Technical Report
It is constructed using the AN6341 speed error detection circuit described in Feb.1978P125. The phase error voltage already explained using FIG. 4 is supplied from the terminal 59,
Superimposed on the speed error voltage. Therefore, the speed error detection circuit 58 outputs a voltage that controls both the speed error and the phase error, and the tape speed is controlled including the phase. The circuit 60 is a variable amplifier circuit and corrects the loop gain of the control system. In the control system shown in FIG. 9, the frequency of the capstan FG signal changes depending on the rotation speed of the motor, but by appropriately setting the frequency division ratio of the variable frequency divider circuit, In a control system that controls the input signal so that it always has a constant frequency,
The speed error voltage of the speed error detection circuit is inversely proportional to the rotation speed of the capstan. For example, if the speed error voltage in the 1x speed mode is used as a reference, the speed error voltage at 1/2x speed is doubled, and at nx speed it becomes 1/n. Therefore, a loop gain correction circuit is required to stabilize the control system at any rotation speed. In the case of the control system of this example, it has already been stated that the loop gain is inversely proportional to the rotation speed of the capstan motor. Therefore, the same signal can be used as the frequency division command signal of the variable frequency division circuit and the command signal for gain correction, and this is also one of the features of the present invention. circuit 63
is a D/A conversion circuit, which converts a signal corresponding to the speed command signal into an analog signal, and supplies the analog signal to the gain correction circuit. A circuit 61 is a drive circuit for a capstan motor, and a reference numeral 62 is a capstan motor that determines the tape feeding speed. Table 1 shows
The frequency division ratio D ₁ of the PLL frequency divider circuit, the frequency division ratio D ₂ of the variable frequency divider circuit, and the rotation speed N of the capstan motor
is shown. When dividing ratio D ₂ is set to 16,
The multiplication value of the PLL circuit and the frequency division value of the variable frequency divider circuit cancel each other out, and a signal with the same frequency as the capstan FG signal is input to the speed error detection circuit, thereby stabilizing it. This time is the 1x speed mode. When the frequency division ratio of the variable frequency divider circuit is set to 1, in order for the frequency of the signal input to the speed error detection circuit to be the same as the frequency of the capstan FG signal at 1x speed, the capstan motor must be It needs to rotate at 16x speed. In other words, speed control can be performed at 1/16 times the speed. Other rotational speeds can be set in the same way, and Table 1 shows an example where the rotational speed is varied in steps of 1/16 times from 1/16 times speed to 7 times speed. Therefore, by using the speed control circuit shown in FIG. 9, it is possible to perform the variable speed every n times as already explained using FIG.

[Table] In this example, the explanation has been given of a direction in which the speed increases, such as from still to 1x speed, but it is obvious that the invention can also be applied to a direction in which the speed decreases, such as from 1x speed to still. In this case, the tape transport speed may be decreased step by step. Effects of the Invention According to the present invention, by controlling the tape speed stepwise at every n times speed when changing to the double speed mode, it is possible to obtain a reproduced image without noise even when changing to the double speed mode. Moreover, if the method of the present invention is used,
Differences in environmental changes and double speed mode commands, that is, 0 to 1
Changes in tape running load due to differences in commands such as double speed and 1x to 3x speed can also be fully absorbed. Further, if the speed control circuit of the present invention is used in combination with a conventional single-frequency speed control circuit, speed control can be performed at 1/16 times the speed, for example.
Furthermore, the speed control circuit of the present invention has the advantage that the command signal to the variable frequency dividing circuit and the loop gain correction command signal can be the same signal.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the recording magnetization locus of a VTR and the scanning locus of the head during reproduction, and Fig. 2 is a diagram showing the relationship between the scanning locus of the head and the recording magnetization locus during field 1/4 speed reproduction. Figure 3 shows field 1/4
A diagram showing the head switching pulse and the voltage waveform applied to the bimorph during double-speed playback, FIG. 4 is a specific configuration diagram for performing noiseless n-times speed playback in one embodiment of the present invention, and FIG. 5 is a still trajectory and 1
A diagram showing the relationship with the head scanning locus during double speed playback,
Figure 6 shows the head switching pulse and bimorph applied voltage waveform when transitioning from still mode to 1x speed mode, and Figure 7 shows the ideal tape speed when transitioning from still mode to 1x speed mode. Figure 8 is a diagram showing the ideal characteristic and actual tape rise characteristic when the tape speed is controlled every n times speed step, and Figure 9 is a diagram showing the rise characteristic and actual rise characteristic when the tape speed is controlled every n times speed step according to the present invention. FIG. 2 is a block diagram showing an example of a speed control circuit for controlling a capstan motor. 5... Steel locus, 30, 31... Capstan FG, 36... Bimorph, 52... Phase comparison circuit, 53... Low pass filter, 57... Voltage controlled oscillation circuit, 56... PLL circuit.

Claims (1)

[Claims] 1. A magnetic tape, a capstan motor for transporting the magnetic tape, a speed control means for controlling the rotational speed of the capstan motor based on a speed command signal, and a speed control means for controlling the rotation speed of the capstan motor based on a speed command signal. A speed command signal generating means, an electromechanical transducer equipped with a rotating magnetic head, a drive means for driving the electromechanical transducer, and a preset signal to be supplied to the drive means are generated based on the speed command signal. and a preset waveform generating means for generating a magnetic tape, and when the transfer speed of the magnetic tape is shifted from the first transfer speed to the second transfer speed, the speed command signal generating means has a preset waveform generating means that A magnetic device characterized by outputting a speed command signal that sequentially specifies a speed divided by N (N is a natural number of 2 or more) from the transfer speed, and changing the transfer speed and the preset signal in steps. Recording and playback device. 2. The speed control means includes a multiplier that inputs and multiplies an FG signal having a frequency proportional to the transport speed of the magnetic tape, a variable frequency divider that divides and outputs the output signal of the multiplier, and a variable frequency divider that divides and outputs the output signal of the multiplier. speed error detection means for outputting a speed error voltage according to the value of the difference between the frequency of the output of the speed error detection means and a reference frequency; variable gain means for amplifying the output signal of the speed error detection means; A motor driving means is provided for accelerating and decelerating a capstan motor in response to the amplified and reduced speed error voltage to be output, and the frequency division ratio of the frequency dividing means is specified by the output signal of the speed command signal generating means. In addition, by changing the gain of the variable gain means and setting the loop gain substantially constant, the FG frequency is controlled to be set in steps of (reference frequency/multiplication number). The magnetic recording and reproducing device according to item 1.