JPH05242561A - Tape tension detector - Google Patents

Abstract

PURPOSE:To detect tension stably and accurately in a wide range without a complicated, mechanical and electric adjustment. CONSTITUTION:One end side of a tension arm 1 is held by a rotary shaft 7 freely rotatably and given a specified rotative force around the rotary shaft 7 by a pulling spring 3. A tension post 2 is erected on the other end side of the tension arm 1 and displaced against the rotative force receiving the tension of a magnetic tape 4. A semicircular flat plate 5 is arranged so as to be rotated around the rotary shaft 7 integrally with the tension arm 1 and a semicircular flat plate 6 is fixedly arranged opposed to the flat plate 5 and a variable condensor is formed by the flat plates 5 and 6. In accordance with the displacement of the tension post 2, the tension arm 1 is rotated around the rotary shaft 7 and the capacitance of the variable condensor is changed. The tape tension is detected by detecting the change of this capacitance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tape tension detecting device, and more particularly to a tape tension detecting device used in a magnetic tape recording / reproducing device.

[0002]

2. Description of the Related Art A magnetic tape recording / reproducing apparatus guides a magnetic tape pulled out from a supply reel by a plurality of posts and winds it around a rotating drum to record / reproduce.
The posture is corrected again by multiple posts and wound up on a take-up reel. In this case, the magnetic tape is pressed by the capstan shaft rotating at a predetermined speed and the pinch roller to drive, but in order to keep the tension applied to the magnetic tape constant, the magnetic force is detected by the tape tension detection device. By detecting the tape tension, for example, the rotation torque of the supply reel motor attached to the shaft of the supply reel is controlled.

FIG. 4 is a top view showing an example of a conventional tape tension detecting device. One end side of the tension arm 1 is rotatably mounted around a rotary shaft 7 and the other end side thereof is Tension post 2 is set up,
Further, the tension spring 3 pulls it with a predetermined force Fs.

A magnetic tape 4 is applied to the tension post 2. One of the magnetic tapes 4 is pulled by a force Fc due to the rotation of a capstan shaft (not shown), and the other is supplied to a supply reel (see FIG. It is wound around (not shown) and pulled by a force Fr by a supply reel motor (not shown).

When the three forces Fs, Fc, Fr are balanced and the tension arm 1 around the rotary shaft 7 reaches a predetermined angle, that is, when the tension post 2 reaches a predetermined position, a predetermined force is obtained. The constant of the tension spring 3 is set so that the tape tension can be obtained.

By the way, the tension arm 1 has a magnet 2
No. 1 is attached, and two Hall elements 22 and 23 are provided on the base side to which the tension arm is attached. In the state of a predetermined tape tension, the magnet 21 is arranged so as to come between the two Hall elements 22 and 23. In this way, the tension post 2
The amount of displacement from the predetermined position is detected and, for example, the rotational torque of the supply reel motor is controlled so that the tape tension becomes constant.

Next, the operation will be described. FIG. 5 is a block diagram for explaining the operation of the conventional tape tension detecting device shown in FIG.

When the tape tension decreases and the position of the tension post 2 shifts to the left, the magnet 21 also shifts to the left and moves above the Hall element 22. Therefore, the output voltage of the differential amplifier 24 that amplifies the output of the hall element 22 becomes high, but the output of the hall element 23 on the right side hardly changes, so that the output voltage of the differential amplifier 25 does not change. Therefore, the output voltage Vo of the differential amplifier 26 which receives and amplifies the output voltage of each of the differential amplifiers 24 and 25 increases in the + direction.

On the contrary, when the tape tension increases and the position of the tension post 2 shifts to the right, the magnet 21 also shifts to the right and moves above the Hall element 23, so that the output of the Hall element 23 is amplified. The output voltage of the differential amplifier 25 that operates increases, and at this time, the output voltage of the differential amplifier 24 that amplifies the output of the Hall element 22 does not change. Therefore,
The output voltage Vo of the differential amplifier 26 increases in the-direction.

As described above, when the tension post 2 is displaced leftward and rightward about the predetermined position, the differential amplifier 26
Since the output voltage Vo of No. 1 changes to + and − in proportion to the displacement amount around 0, the tension post 2 is controlled by controlling the rotation torque of the supply reel motor according to the output voltage Vo of the differential amplifier 26. The magnetic tape can be kept at a predetermined position and a constant tension can be applied to the magnetic tape at the same time.

[0011]

In the conventional tape tension detecting device described above, the amount of displacement of the tension post from the predetermined position is detected by the relative position of the magnet and the Hall element. However, since the performance error of the magnet and Hall element itself is large, complicated mechanical and electrical adjustments are required, and the detection range of the Hall element is limited to a relatively narrow range, so the amount of displacement of the tension post is limited. There is a problem that you cannot increase.

An object of the present invention is to provide a tape tension detecting device which can accurately detect a tension post even if the amount of displacement of the tension post is large, without performing complicated mechanical and electrical adjustments.

[0013]

SUMMARY OF THE INVENTION A tape tension detecting device of the present invention comprises a tension arm having one end rotatably held by a rotary shaft and given a predetermined rotational force in a certain direction, and the other end side of the tension arm. A tape tension detecting device having a tension post that is set up on the tape and is displaced by the tension of the tape against the rotational force to rotate the tension arm around the rotation axis. It comprises a capacitance varying means for varying the capacitance, and a means for detecting the displacement of the tension post by detecting the change in the capacitance. The capacity varying means includes at least one first flat plate that rotates about the rotation axis as the tension arm rotates, and at least one second flat plate that is fixedly arranged in parallel with the flat plate. And the opposing areas of the first and second flat plates are
The tension arm may be formed to change in accordance with the rotation of the tension arm, or at least one first flat plate that moves with the rotation of the tension arm and at least one fixedly arranged in parallel to the flat plate. It may be formed of two second flat plates, and the distance between the first and second flat plates may be changed according to the rotation of the tension arm. Further, the capacitance varying means is composed of a plurality of flat plates facing each other and arranged in parallel at a predetermined interval, and at least one high dielectric material that moves with the rotation of the tension arm, and the high dielectric material is the tension arm. It may be formed so as to be inserted between the plurality of flat plates in accordance with the rotation of, or may be formed by providing a high dielectric material between the first and second flat plates.

[0014]

The present invention will be described below with reference to the drawings.

FIG. 1 is a top view showing an embodiment of the present invention. The difference from the conventional tape tension detecting device shown in FIG. 4 is that it rotates with a tension arm 1 instead of a magnet and a Hall element. That is, the semicircular flat plate 5 and the semicircular flat plate 6 fixed to the base side to which the tension arm 1 is attached are provided. The same parts as those in FIG. 4 are designated by the same reference numerals.

By the way, the semicircular flat plates 5 and 6 are made of conductive metal plates and are arranged in parallel and opposite to each other to form a variable capacitor. Here, when the tension post 2 comes to a predetermined position, the flat plate 5,
6 are attached so as to be offset from each other by 90 ° in the rotational direction. That is, as shown in FIG. 1, the shaded portions face each other.

If the electrostatic capacity of the variable capacitor is Ct, Ct is the area of the portion where the flat plates 5 and 6 face each other,
That is, it is proportional to the angle θ formed by the flat plates 5 and 6. When the amount of displacement of the tension post 2 is very small,
Since the displacement amount is proportional to the angle θ, the displacement amount of the tension post can be known by detecting the electrostatic capacitance Ct. Now, as a method of detecting the electrostatic capacitance Ct, a method of using a bridge circuit as shown in FIG. 2 or a method of changing an oscillation frequency by an oscillation circuit and comparing with a reference signal as shown in FIG. is there.

In the case of the bridge circuit shown in FIG. 2,
A resistor R and a capacitor C are connected in order to establish an electrical balance with the electrostatic capacitance Ct. In this case, the capacitance C has the same structure as the electrostatic capacitance Ct, and the both are arranged in the vicinity to balance the capacitance. Can be easily obtained, the temperature can be stabilized against temperature changes, and the sensitivity can be increased.

In the case of the oscillation circuit shown in FIG. 3, since the change of the electrostatic capacitance Ct is proportional to the displacement amount of the tension post, the oscillation frequency is proportional to the displacement amount, and the circuit configuration for detecting the displacement amount. Can be simplified.

By doing so, the tension arm 1 can rotate 180 ° about the rotary shaft 7, so that stable detection can be performed even if the displacement amount of the tension post 2 becomes large.

In this embodiment, the electrostatic capacitance is changed by changing the facing area of the flat plates facing each other in parallel according to the rotation of the tension arm, but the facing area is changed according to the rotation of the tension arm. The capacitance can be changed by changing the distance between the flat plates. Further, the electrostatic capacitance can be changed by inserting a dielectric having a high dielectric constant between the flat plates according to the rotation of the tension arm. Further, the number of flat plates may be three or more.

[0022]

As described above, according to the present invention, the capacitance of the flat plates facing each other is changed according to the rotation of the tension arm, and the displacement of the tension post is detected by detecting this capacitance. Detects complex mechanical,
The tape tension can be accurately detected without making electrical adjustment and even when the displacement amount of the tension post is large.

[Brief description of drawings]

FIG. 1 is a top view showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of detecting electrostatic capacitance by a bridge circuit.

FIG. 3 is a circuit diagram showing an example of detecting capacitance by an oscillation circuit.

FIG. 4 is a top view showing an example of a conventional tape tension detecting device.

5 is a block diagram of the conventional tape tension detecting device shown in FIG.

[Explanation of symbols]

 1 Tension arm 2 Tension post 3 Tension spring 4 Magnetic tape 5,6 Flat plate 7 Rotation axis

Claims (5)

[Claims] 1. A tension arm whose one end side is rotatably held by a rotating shaft and is given a predetermined rotational force in a certain direction, and a tension arm which is erected on the other end side of the tension arm and opposes the rotational force by the tension of a tape. In the tape tension detecting device having a tension post that is displaced while rotating the tension arm about the rotation axis, a capacitance varying unit that changes capacitance according to rotation of the tension arm; And a means for detecting the displacement of the tension post by detecting a change in the tape tension. 2. The capacity varying means includes at least one first flat plate that rotates about the rotation axis as the tension arm rotates, and at least one first flat plate that is fixedly disposed so as to face the flat plate in parallel. 2. The tape tension detecting device according to claim 1, wherein the tape tension detecting device comprises two flat plates, and the opposing areas of the first and second flat plates are formed so as to change in accordance with the rotation of the tension arm. .. 3. The capacity varying means comprises at least one first flat plate that moves with the rotation of the tension arm, and at least one second flat plate that is fixedly arranged in parallel with the flat plate. The tape tension detecting device according to claim 1, wherein the distance between the first and second flat plates is formed so as to change in accordance with the rotation of the tension arm. 4. The capacitance varying means comprises a plurality of flat plates facing each other and arranged in parallel at a predetermined interval, and at least one high dielectric material that moves with the rotation of the tension arm. The tape tension detecting device according to claim 1, wherein the tape tension detecting device is formed so as to be inserted between the plurality of flat plates according to rotation of the tension arm. 5. A high dielectric material is provided between the first and second flat plates.
The tape tension detection device described.