JPS6353624B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tension servo device for stabilizing tape tension in a tape running system such as a VTR when the tape runs at high speed.

Figure 1 shows a known cassette type helical scan type.
This figure schematically shows the tape running system of a VTR.

During normal recording and playback, the tape 4 unwound from the supply reel (hereinafter referred to as S reel) 2 of the cassette 1 advances in the direction of arrow a, and moves from the guide pin 5 to the drum 6 to which a rotating head (not shown) is attached.
The reel is wound around the circumferential surface of the reel, and is further wound onto a take-up reel (hereinafter referred to as T-reel) 3 via a plurality of guide pins 7. With such a VTR, you can fast forward FF or rewind REW while the tape is wound around the drum 6.
You can perform playback while driving at high speed, and cue the desired content while looking at the monitor screen.
Alternatively, a so-called search mode can be set to check the recorded contents of the tape. In general VTRs, when changing the tape speed, the tape speed is controlled by controlling the rotational speed of the capstan in the range of, for example, 1/30 to 5 times the standard speed. However, it is technically very difficult to obtain a speed of five times or more from the capstan at the same time as this exceeds the controllable range of the capstan motor. Therefore, when running the tape at a high speed of 5 times or higher in the search mode described above, the tape should be run at high speed by rotating the reel at high speed with the pinch roller separated from the capstan without using the capstan. I have to.

In this way, the tape can be FF or
When the search mode is performed by REW, it is necessary to maintain the tape tension at predetermined portions of the tape running system shown in FIG. 1, such as the tape outlet and inlet of the cassette 1, the circumferential surface of the drum 6, etc., within predetermined ranges. If the tape tension falls outside of this range, normal image reproduction will not be possible, the tape may become irregularly wound on the reel, and in some cases, the tape may become slack or stretched in the running system, causing the tape to become loose. may be damaged. To prevent this,
The tape tension servo may be applied to maintain the tension in the predetermined portion within a predetermined range. However, while the tape is running, the tape winding diameter on the reel, the friction inside the cassette, the friction caused by the guide pins of the running system, etc. change every moment.
The tape tension at each part changes accordingly, making it extremely difficult to perform stable tension servo operation.

Here, necessary conditions, changing factors, etc. when actually performing tension servo will be explained with reference to FIG. 2, using specific numerical examples. FIG. 2 shows the tape running system in REW search mode, where the T reel 3 is on the supply side, the S reel 2 is on the winding side, and the tape 4 runs in the direction of arrow b.

In the figure, the tension near the tape exit of cassette 1 is T ₁ , the tension near the tape entrance is T ₂ , the drum 6
Let the tension on the circumferential surface be T ₃ . Further, the tape winding diameter including the hub diameter on each reel 2, 3 varies from a minimum of 2 cm to a maximum of 6 cm. The maximum friction torque inside cassette 1 is 500 gcm. This frictional torque includes, for example, friction caused by a guide member using a leaf spring member near the exit of the cassette. Furthermore, in some types of cassettes, when the winding diameter of the T-reel 3 exceeds a certain size, the tape may come into contact with the flange of the S-reel 2, causing friction. In this example, the frictional torque inside the cassette 1 includes the various types of friction described above, and is hereinafter referred to as cassette loss.

Under each of the above conditions, the tension ratio at the inlet/outlet of the cassette 1 is T ₂ /T ₁ =1.5-12. Under the above conditions, the allowable values of T ₁ to _{T 3} and their reasons are as follows: For Γ T ₁ , the minimum allowable value = 20 g...In order to operate the tension servo stably.

Regarding Γ T ₂ , the minimum allowable value = 45g... If it is lower than this, irregular winding or step winding will occur.

Maximum allowable value = 240g...If this is exceeded, tape curl will occur.

Regarding Γ T ₃ : Minimum allowable value = 30g...For normal image reproduction.

Therefore, in the tension servo, it is necessary to maintain the above-mentioned allowable values of T ₁ to _{T 3} regardless of changes in the reel diameter, cassette loss, and other friction.

For example, a servo loop schematically shown in FIG. 3 can be considered as a method for performing tension servo.

In the figure, a tension detector 8 is provided near the tape entrance, the detected tension is compared with a target tension Tref by a comparator 9, and the T-reel drive motor 10 is controlled by the output of the difference. On the other hand, the S reel drive motor 11
The output of an FG (frequency generator) 12 that detects the speed of the motor 12 and the target speed Sref are compared by a comparator 13, and the motor 11 is controlled to a constant speed based on the output of the difference.

In this method, the tension ratio T ₂ /T ₁ enters the servo loop as a gain, so the loop gain is set at the maximum value of 12 of T ₂ /T ₁ . Therefore,
It is not possible to obtain a large loop gain for the intermediate or minimum value (=1.5) of T ₂ /T ₁ , and for this reason, the reel diameter,
Tension fluctuations due to changes in cassette loss cannot be controlled. In addition, in this servo loop, the transmission frequency characteristic of the mechanical part that inputs the torque τ of the motor 10 and outputs the tape tension T ₂ has a resonance frequency _R around 2 to 3 Hz, as shown in Figure 4. . Therefore, in an actual servo loop, it is necessary to provide a delay compensation circuit between the comparator 9 and the motor 10, which has a time constant such that the gain is lower than 0 dB at _R. The time constant required for this delay compensation is a relatively large value of about 4 to 5 seconds. If you increase the time constant, you can also increase the DC gain, but the response at the time of starting high-speed driving will be slower.
Problems such as the tape becoming slack may occur. The actually required loop gain may be about 10 to 20 dB, but since the tension ratio T ₂ / T ₁ has a width of 1.5 to 12 times, if you try to satisfy the above loop gain, the maximum gain will be 20 dB or more higher. Therefore, if delay compensation is included to obtain stability, the response speed will not be satisfied.

As another method of tension servo, a method can be considered in which a speed servo similar to that shown in FIG. 3 is applied to the S reel 2, and a tension detector is provided near the tape exit to detect _T1 and control the motor 10. According to this method, since the loop gain is changed only by the tape winding diameter, a minimum loop gain of about 10 dB can be achieved, and the tape tension can be stabilized.
However, this time, the tape running system such as guide pins 7, 5 and drum 6 are outside the loop, so the inlet tension T ₂
changes by the amount of change in tension in the running system, so the range of change becomes too wide. That is, T ₂ is maximum
Since it needs to be 240g, T ₁ is set to 20g, but then when the tension ratio is the lowest (= 1.5), T ₂
is 30g, which is too low than the minimum allowable value = 45g.

The present invention is intended to solve the various problems mentioned above, and an embodiment of the present invention will be described below with reference to FIG. 5. Furthermore, Figure 5 shows the REW search mode.
Components common to those in FIG. 3 are given the same reference numerals.

In this embodiment, a tension detector 8 is provided near the tape entrance of the cassette 1, and a tension detector 15 is provided near the exit. The tension detected by the detector 8 and the target tension Tre are compared by a comparator 9, and this comparison output is used as a target value, and this target value and the tension detected by the detector 15 are compared by a comparator 16. The comparison output of this comparator 16 is the delay compensation circuit 1
7 to control the motor 10. Furthermore, motor 1
Speed servo is applied to 1 in the same way as in FIG.

As described above, the present invention includes the detector 15 and the comparator 1.
6 and motor 10 to form an inner loop,
By forming an outer loop with the detector 8 and the comparator 9, a tension servo loop is formed twice, and the target value of the inner loop is created by the difference between the detected value of the outer loop and the target value Tre. By this, the winding diameter,
Tension fluctuations due to cassette loss can be suppressed in the inner loop, and tension fluctuations due to the tension ratio T ₂ /T ₁ can be suppressed in the outer loop. Therefore, the drawbacks of the method shown in FIG. 3 and the other methods described above can be eliminated, and the range of change in tape tension can be reduced. Note that the loop gain of the outer loop is set to be "1" when the tension ratio is maximum, that is, when T ₂ /T ₁ =12.

The cassette loss is added to the outlet side _tension T ₁
substantially increases. In order to counteract this, the inner loop is designed to generate torque in the feeding direction. Therefore, in the double loop method, when the tension ratio becomes abnormally large and T ₂ /T ₁ >12, the target value of the inner loop, that is, the output value of the comparator 9 decreases. For this reason, when _T1 falls below 20 g, the tension of the tension servo may drop too much, and the tape 4 may become slack within the cassette 1. In order to prevent this, a limiter may be provided to limit the lower limit of the target value of the inner loop.

FIG. 6 shows a specific circuit embodiment of a portion of the double loop of FIG. 5, including the limiter described above.

In the figure, the comparator 9 is an operational amplifier 18, a resistor
It is composed of R ₁ , R ₂ , and R ₃ and includes a target value voltage V _Tre (corresponding to the target value _Tre in FIG. 5) applied to the terminal 19 and a tension detection voltage V _T2 applied to the terminal 20.
are compared. Incidentally, the detection voltage V _T2 is obtained from the tension detector 8 shown in FIG. In addition, by connecting a diode D to the connection point between _R1 and _R2 and applying a lower limit reference voltage V _S to the terminal 21, the limiter 2
2 are configured. The comparator 16 is composed of an operational amplifier 23, R ₄ , R ₅ , R ₆ , R ₇ , and the tension detection voltage applied to the output of the comparator 16 and the terminal 24 is
V _T1 is compared. The detected voltage V _T1 is obtained from the tension detector 15 in FIG. Delay compensation circuit 17
is composed of capacitors C, R ₈ and R ₉ , and its output voltage Vo is taken out from the output terminal 25 . This voltage Vo controls the motor 10 via a motor drive circuit. In addition, the terminal 26 is connected to the T shown in FIG.
A voltage corresponding to the speed of the motor 10 based on the output of an FG (not shown) provided in the reel motor 10 (for example, a voltage obtained by frequency-discriminating the FG output)
V _sp is added. This voltage V _sp is determined by the inverting amplifier 2 which is composed of operational amplifier 27, R ₁₀ , R ₁₁ and R ₁₂ .
8, and this inverted voltage is divided by R ₁₃ and R ₉ and applied to the connection point of C and R ₉ .

According to the above configuration, the lower limit of the input voltage V _T2 of the comparator 16 is limited by the limiter 22 to V _S +V _H (V _H : threshold voltage of D). This prevents the tape from sagging within the cassette when the input tension _T2 becomes excessive. Note that the tape may be stopped when the limiter 22 detects that the input tension has become excessive.

As mentioned above, the time constant of the delay compensation circuit 17 is 4.
Since the time is as long as ~5 seconds, the tape tension increases while the tape is accelerated after the start of rewinding. In order to prevent this, it is necessary to increase the torque of the T-reel motor 10 by the amount of acceleration. In FIG. 6, as the speed increases during acceleration, the voltage across _R9 decreases, lowering the terminal voltage of C, that is, the output voltage Vo. As a result, the torque of the motor 10 decreases or increases in the feeding direction, thereby suppressing an increase in tension. Therefore, it is possible to eliminate an increase in tension from the start of unwinding until the predetermined speed is reached.
Further, the rise can be made faster while maintaining the tension at a predetermined value.

Figure 7 shows the frequency characteristics of the inner loop, where a is T
Indicates when the winding diameter of reel 3 is maximum (6 cm),
b indicates the minimum (2 cm).

Figure 8 shows T ₁ for T ₂ of the double loop in Figure 5.
Indicates a characteristic that shows a change in. Note that the dotted line indicates the characteristics of only the inner loop when there is no outer loop. According to this diagram, the limiter works around T ₂ = 200g, so
It can be seen that T ₁ does not rise or fall by 20g.

The above explanation has been given using the REW search mode as an example, but in the case of the FF search mode, the T reel 3 side is the inlet tension T ₂ and the S reel 2 side is the outlet tension.
As _T1 , tension servo is applied to the S reel 2 by a double loop, and speed servo is applied to the T reel 3, thereby performing the operation exactly the same as described above.

The present invention is a reel tension servo of this type, by providing a double loop, so that the range of tension fluctuation is sufficiently small in response to changes in the running system tension, winding diameter, cassette loss, etc., and it can be used under any conditions. It is possible to run the tape stably at high speed while it is still wound around the drum.

Further, by limiting the lower limit value to the input tension at the entrance of the outer loop, it is possible to prevent the tape inside the cassette from sagging when the tension ratio becomes excessive. Furthermore, by changing the voltage of the capacitor of the delay compensation circuit in accordance with the acceleration, it is possible to obtain acceleration with a quick rise while suppressing an increase in tension during acceleration.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a running system of a VTR to which the present invention can be applied, FIG. 2 is a schematic plan view of the running system in rewind search mode, and FIG. 3 is a process leading to the present invention. A plan view and a circuit system diagram in which a servo loop is added to the above traveling system to explain the
Figure 4 is a frequency characteristic diagram of the above servo loop, Figure 5
The figure is a plan view and circuit system diagram showing an embodiment of the present invention, FIG. 6 is a circuit diagram showing an example of a specific circuit configuration of the main part of FIG. 5, and FIG. 7 is an inner loop of FIG. 5. FIG. 8 is an inlet tension-outlet tension characteristic diagram of the servo loop of FIG. 5. In addition, in the symbols used in the drawings, 2...S
Reel, 3...T reel, 4...tape, 6...
Drum, 8, 15...Tension detector, 13, 16...
. . comparator, 17 . . . delay compensation circuit, 22 . . . limiter.

Claims (1)

[Scope of Claims] 1. A tape unwound from a supply reel is wound up by a take-up reel through a predetermined running path, and the outlet tension of the tape at the outlet of the supply reel and the take-up reel are A tension servo device that controls the entrance tension of the tape at the entrance of the tape to maintain a predetermined value, a first servo loop that compares the entrance tension with a predetermined target value, and A tension servo device comprising a second servo loop that compares the output tension with the outlet tension and controls the supply reel according to the comparison output value. 2. The tension servo device according to claim 1, wherein the lower limit value of the inlet tension applied to the first servo loop is controlled. 3. The supply reel is controlled via a time constant circuit by a voltage corresponding to the comparative output value in the second servo loop, and the voltage of the capacitor of the time constant circuit is controlled by the acceleration of the supply reel. 2. The tension servo device according to claim 1, wherein the tension servo device is configured to change the tension according to.