JPS6326723Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a rotation angle detection device that is particularly useful for detecting tape tension in a magnetic recording/reproducing device.

Magnetic tape in magnetic recording and reproducing devices is used for recording and reproducing.
In order to apply an appropriate tension during playback, it is necessary to detect the running tape tension and control the rotational force of the supply reel or take-up reel based on the detected value.

For this reason, tension detection mechanisms that use mechanical tension regulators or photoconductive CdS elements have been used in the past, but their detection functions are inadequate in terms of sensitivity, temperature characteristics, and linearity. However, I could not say that.

That is, normally, tape tension detection is performed as shown in Fig. 1. When the tension of the running tape T increases, the rotating arm A around the pivot point P resists the tension of the spring F and moves as shown by the dotted line. Therefore, it is sufficient to detect the rotation angle θ at that time.
To detect the rotation angle θ, for example, if a magnet M is attached to the other end of the rotating arm A and a magnetoresistive element DME is fixed within the magnetic field of the magnet M, the resistance of the magnetoresistive element DME will be increased by the magnetic field of the magnet M. Since the value changes, tape tension can be detected. Therefore, if the tape feeding or winding is controlled using this detection signal, the tape tension can be kept constant, but in such a detection device, the rotation angle θ is not proportional to the detection signal, and the detection signal is not proportional to the rotation angle θ. Depending on the temperature characteristics of the element, a constant detection signal may not always be obtained.

This invention has been made in view of these points, and is intended to provide a rotation angle detection device that utilizes a magnetoresistive element and eliminates the drawbacks of conventional tension detection devices.

FIG. 2 shows an embodiment in which this invention is applied to a tape tension detection device, in which 1 is a running tape, 2 is a tension arm, 3 is a rotating shaft, 4 is a support plate, 5a, 5b represents a pair of magnets, and 6 represents a magnetoresistive element (DME). In addition,
7 is a spring, and 8 is an arm post.

Next, the detection action will be explained.

When the tension of tape 1 increases during running,
The arm post 8 moves in the direction of arrow T against the tensile force of the spring 7, and the rotating shaft 3 receives a rotational moment.
It rotates in response to M _T (on the contrary, when the tape tension decreases, a rotational moment M _F in the direction of the arrow acts due to the tensile force of spring 7). Therefore, a pair of magnets 5 fixed to the support plate 4
Since a and 5b also rotate, the pair of magnets 5a,
The direction of the parallel magnetic field formed between 5b changes. Since this change in the direction of the magnetic field appears as a change in resistance of the magnetoresistive element 6, the current flowing through the magnetoresistive element 6 changes, and the rotation angle can be detected as an output voltage.

Figures 3a and 3b show the relationship between the magnetoresistive element 6, which is an embodiment of this invention _, the direction of the magnetic field, and the output voltage at that time _.
R _c and R _d are Wheatstone bridge connections, and each symmetrical connection point of the bridge is used as an applied voltage terminal and output terminals T ₁ and T ₂ . FIG. 3b shows the output voltage when such a magnetoresistive element 6 is installed in a parallel magnetic field B and the direction of the parallel magnetic field B is changed to B ₀ , B ₁ , and B ₂ . From these figures, it can be seen that when the rotation angle of the parallel magnetic field B is in the range of 90° (180°) to ±15°, the output voltage is approximately proportional to the rotation angle.

FIG. 4 shows a block diagram when the tension detection device shown in FIG. 2 is applied to a tape tension servo, and 10 is a magnetoresistive element 6.
output terminal, 11 is an amplifier, 12 is a comparator, 13
14 is a reference voltage source, and 14 is a drive circuit for a motor 15 that drives the supply reel. If the voltage e _c of the reference voltage source 13 connected to the comparator 12 is set as the tape tension detection voltage e _d during normal tape running, if the tape tension changes from the normal value, the comparator 12 will detect a ± error. Output occurs.
Therefore, if the motor 15 that drives the supply reel is controlled using this ± error output, the tape tension can be kept constant.

FIG. 5 shows experimental data showing the relationship between the tape tension g and the output voltage of the magnetoresistive element 6 in the configuration shown in FIG. is -5℃~+
It can be seen that the properties at 45°C are almost the same as at room temperature.

Moreover, FIG. 6 shows experimental data showing the relationship between the output voltage of the magnetoresistive element 6 and the rotation angle of the pair of magnets 5a and 5b.The characteristics of both the cases where the opposing surfaces of the magnets are 4 mm and 2 mm are as follows. It will be appreciated that the output voltage of the magnetoresistive element 6 is linear within a rotation angle of 30 degrees.

In addition, in the configuration shown in FIG. 2, the deflection of the tension arm 2 differs depending on the running direction of the tape 1, but by using the arm post 8 as a rotating roller, the deflection in the forward direction (FWD) and reverse direction (REV) is changed. The same degree of tension can be detected even when the tape is running.

Although the above-mentioned embodiment describes the case where the rotation angle detection device of this invention is applied to a tension servo, the present invention is not limited to this embodiment.
It goes without saying that this method can generally be used to detect angular deviation of the rotating shaft. Furthermore, a magnetoresistive element may be provided on the rotating shaft.

As explained above, the rotation angle detection device of this invention uses a parallel magnetic field that rotates according to the rotation angle, and a magnetoresistive element that is placed within this parallel magnetic field and is rotatable relative to the parallel magnetic field. Since it is equipped with a magnetic field detection section connected to a Wheatstone bridge, the rotation angle detection signal can be output directly from the symmetrical connection point of the bridge, and this output signal is linear with respect to the rotation angle, and at the same time its temperature characteristics It also has the effect of improving detection sensitivity.

Furthermore, when the rotation angle detection device of the present invention is used as an angle detector for a mechanical servo device, no special compensation circuit is required, which has the advantage that the mechanical servo circuit can be simplified and can operate accurately.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of conventional tape tension detection, Figure 2 is a block diagram of this invention adopted for tape tension detection, and Figures 3 a and b show the relationship between the magnetoresistive element and its output voltage. An explanatory diagram, Fig. 4 is a servo circuit diagram of the tape tension, Fig. 5 is a data diagram showing the relationship between the tape tension and the output voltage of the magnetoresistive element, and Fig. 6 is a diagram showing the relationship between the rotation angle and the output voltage of the magnetoresistive element. FIG. In the figure, 2 is a tension arm, 3 is a rotation axis, and 4 is a tension arm.
5 shows a support plate, 5a and 5b are magnets, and 6 is a magnetoresistive element.

Claims (1)

[Scope of utility model registration request] A Wheatstone bridge circuit comprising a plurality of magnetoresistive elements and a pair of magnets forming a parallel magnetic field in a direction perpendicular to a rotation axis, the Wheatstone bridge circuit being located within the parallel magnetic field, and Either the Wheatstone bridge circuit or the pair of magnets is attached to the rotating shaft so that the Wheatstone bridge circuit and the pair of magnets can rotate relative to each other, and a first symmetrical connection of the Wheatstone bridge circuit is provided. The Wheatstone bridge circuit is characterized in that by applying a predetermined voltage between the points, a voltage corresponding to the rotation angle of the rotating shaft is generated between the second symmetrical connection points of the Wheatstone bridge circuit. Rotation angle detection device.