JP2000009557A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cause of the nonreciprocal phenomenon to reduce the hysteresis by providing a d-c magnetic field applying means (permanent magnet etc.), for normally applying a d-c magnetic field to a magnetic anisotropic peripheral part of the outside face of a torque transmitting shaft. SOLUTION: A first and a second magnetic anisotropic part 2, 3 composed of many rectangular magnetic belts inclined mutually in opposite directions at specified angles to the axial line are formed on the outside face of a toque transmitting shaft 1. When a torque is located on the torque transmitting shaft 1, compression strains occur in the belts of either magnetic anisotropic parts 2, 3 and tensile strains occur in the belts of the other. At both axial ends of a yoke 6, permanent magnets 12, 13 magnetized at both radial ends are disposed to apply d-c magnetic fields to thereby the magnetic anisotropic parts 2, 3. Thus the normally applied d-c magnetic fields to the magnetic anisotropic parts 2, 3 restrain the magnetic domains in the magnetic anisotropic parts 2, 3 from reducing and moving.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a torque sensor, and more particularly to a magnetostrictive torque sensor.

[0002]

2. Description of the Related Art As one of known torque sensors, first and second magnetic anisotropic portions are provided on an outer peripheral surface of a torque transmission shaft, and one of them is compressed when a torque is applied to the torque transmission shaft. The first and second magnetically anisotropic portions are formed on the outer peripheral sides of the first and second magnetically anisotropic portions at a predetermined frequency (10 to 50 k).
And a first and second excitation coil connected in series to excite the detection coil when a sine wave AC voltage (approximately 1 Hz) is applied thereto. There is a magnetostrictive torque sensor that is arranged so as to convert the change into a change and generates a signal voltage indicating the direction and magnitude of the torque from the difference between the voltages at one end of both detection coils.

Japanese Patent Application Laid-Open No. Hei 2-221830 discloses that the above torque sensor is irreversible by subjecting the surface of a magnetically anisotropic portion of a torque transmission shaft to shot peening or the like to limit the reduction of domain walls and the movement of domain walls. It is disclosed that the cause of a severe magnetostriction phenomenon is reduced and the hysteresis is reduced.

[0004]

However, since the surface of the magnetically anisotropic portion of the torque transmitting shaft is subjected to shot peening or the like, the number of manufacturing steps for the torque transmitting shaft increases, and the manufacturing cost increases. In addition, there is a disadvantage that the dimensional error on the surface of the magnetically anisotropic portion is increased by performing shot peening, and the range of variation in detection sensitivity is increased.

The invention of this application reduces the cause of irreversible magnetic phenomena by reducing the domain wall of the magnetically anisotropic portion and restricting the movement of the domain wall without causing the above-mentioned problems, thereby reducing the hysteresis. Its main purpose is to reduce it.

[0006]

According to the first aspect of the present invention, the first and second magnetically anisotropic portions are provided on the outer peripheral surface of the torque transmitting shaft, and when torque is applied to the torque transmitting shaft. The first and second detection coils and a sine-wave AC voltage are applied to outer peripheral sides of the first and second magnetically anisotropic portions so that one is compressed and the other is stretched. A first and a second excitation coil connected in series to excite the detection coil are disposed so as to convert a change in the magnetic permeability of the magnetically anisotropic part into a change in the voltage at one end of the detection coil. In a torque sensor configured to generate a signal voltage representing a direction and a magnitude of a torque from a difference between voltages at one end of a coil, a direct current magnetic field application for constantly applying a direct current magnetic field to the first and second magnetic anisotropic parts. A torque sensor comprising means.

The invention according to claim 2 of the present application is the torque sensor according to claim 1, wherein the DC magnetic field applying means is a permanent magnet.

According to a third aspect of the present invention, there is provided the torque sensor according to the first aspect, wherein the DC magnetic field applying means is a DC offset power supply for supplying a DC current to the exciting coil. Is a torque sensor.

According to the invention of claim 4 of the present application, the first and second magnetically anisotropic portions are provided on the outer peripheral surface of the torque transmission shaft, and when the torque is applied to the torque transmission shaft, one of them is compressed and The other is formed to be pulled, and the first and second
The first and second detection coils, and the first and second excitation coils connected in series with each other and applied with a sine wave AC voltage to excite the detection coils, A change in the magnetic permeability of the anisotropic portion is arranged to be converted into a change in the voltage at one end of the detection coil, and a signal voltage representing the direction and magnitude of the torque is generated from the difference between the voltages at the one end of both detection coils. In the torque sensor having the above structure, the torque transmission shaft is magnetized.

[0010]

FIG. 1 shows a detecting section of a torque sensor according to the present invention, and FIG. 2 shows a detecting circuit thereof.
In FIG. 1, on the outer peripheral surface of the torque transmitting shaft 1 made of a magnetic material, there are formed a plurality of short magnetic material bands that are inclined at opposite angles to each other at a predetermined angle (for example, 45 degrees) from the direction of the axis. The first magnetic anisotropic part 2 and the second magnetic anisotropic part 3 are formed by machining such as rolling. Since the band of the first magnetic anisotropic part 2 and the band of the second magnetic anisotropic part 3 are inclined in opposite directions, when the torque is applied to the torque transmission shaft 1, the first magnetic anisotropy is formed. A compressive strain is generated in one of the bands of the portions 2 and 3, and a tensile strain is generated in the other band.

On the outer peripheral side of the magnetic anisotropic part 2, an exciting coil 4a and a detection coil 4b on the outer peripheral side of the exciting coil 4a are arranged. Similarly, an exciting coil 5a and a detection coil 5b on the outer circumferential side of the exciting coil 5a are also provided on the outer circumferential side of the magnetic anisotropic part 3. A yoke 6 made of a soft magnetic material is provided on the outer peripheral side of these coils.

As shown in FIG. 2, the exciting coils 4a, 5a
Are connected in series to the high-frequency power supply 8, and the high-frequency power supply 8 applies a sine-wave AC voltage of a predetermined frequency to the excitation coils 4a, 5a. When torque is applied to the torque transmission shaft 1, the magnetic permeability of the magnetic anisotropic part 2 and the magnetic anisotropy
Of the coils 4a, 4b in the magnetic coupling relationship and the inductance of the coils 5a, 5b in the magnetic coupling relationship change (increase or decrease) to each other. Decreased,
The voltage V1 at one end of the detection coil 4b and the voltage V2 at one end of the detection coil 5b change. These voltages V1 and V2 are input to the differential amplifier circuit 8, and a voltage proportional to a voltage obtained by subtracting the voltage V1 from the voltage V2 is output from the differential amplifier circuit 8. This voltage is supplied to the synchronous detection circuit 9, the filter circuit 1
0, which is output as a signal voltage Vr that is proportional to the torque applied to the torque transmission shaft 1 via the DC amplifier circuit 11.

Here, according to the invention of this application, the yoke 6
A permanent magnet 1 magnetized at both ends in the radial direction
DC magnetic fields are applied to the magnetically anisotropic parts 2 and 3 by the permanent magnets 12 and 13. When a DC magnetic field is constantly applied to the magnetic anisotropic parts 2 and 3, the reduction of the domain wall and the movement of the domain wall in the magnetic anisotropic parts 2 and 3 are restrained, and the irreversible magnetostriction phenomenon is reduced. Is reduced.

The effect of applying a DC magnetic field to the magnetically anisotropic parts 2 and 3 will be described with reference to a graph of B (residual magnetic flux density) -H (coercive force) in FIG. In FIG. 3, when a DC magnetic field is not applied, the region a where the hysteresis of the BH curve is large is used. Therefore, the application of the torque causes the magnetostriction phenomenon due to the domain wall movement in the irreversible region of the magnetically anisotropic portion of the torque transmission shaft. And a magnetostriction phenomenon due to a rotating magnetic field in a reversible region exists. Therefore, even if the torque is returned to zero, the movement of the domain wall in the irreversible region does not return to the original state, but appears as hysteresis of the sensor output.
When a DC magnetic field is applied, the region b having a small hysteresis is used. Therefore, when a torque is applied, a magnetostriction phenomenon caused by domain wall movement in an irreversible region in a magnetic anisotropic portion of a torque transmission axis and a rotating magnetic field in a reversible region are performed. The ratio of the magnetostriction caused by the domain wall movement in the irreversible area where the hysteresis occurs in the sensor output due to the change of the magnetostriction due to the change in the sensor output decreases, and the hysteresis also decreases. According to the experiment, the hysteresis when the DC magnetic field was not applied was 3.85% FS, but was reduced to 1% FS when the DC magnetic field was applied.

The permanent magnet may be arranged on the torque transmission shaft 1 as shown in FIG. In FIG. 4, a torque transmission shaft 1 has a central portion 1 having magnetically anisotropic portions 2 and 3.
a and permanent magnets 15 and 16 which are composed of nonmagnetic material ends 1b and 1c and are magnetized in the axial direction are installed at the joint between the central portion 1a and the ends 1b and 1c. I have.

As a means for constantly applying a DC magnetic field to the magnetically anisotropic portion of the torque transmission shaft, a DC current may be supplied to the exciting coil, an example of which is shown in FIG. 5, a DC offset power supply 17 in series with the high frequency power supply 8 is added to the configuration of FIG.

Further, instead of constantly applying a DC magnetic field to the magnetically anisotropic portion of the torque transmitting shaft, by applying saturation magnetism to the torque transmitting shaft, the torque transmitting shaft including the magnetically anisotropic portion is magnetized. Is also good.

[0018]

As described above, the torque sensor according to the invention of the present application provides a magnetic anisotropic structure without increasing the number of manufacturing steps of the torque transmitting shaft and increasing the dimensional error of the surface of the magnetic anisotropic portion. By reducing the domain wall of the active part and restricting the movement of the domain wall, the cause of the irreversible magnetic phenomenon can be reduced, and the hysteresis can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a detection unit of a torque sensor according to the invention of this application.

FIG. 2 is a diagram illustrating a configuration of a detection circuit applied to the detection unit in FIG. 1;

FIG. 3 is a diagram showing a BH curve.

FIG. 4 is a diagram showing a configuration of a second embodiment of the detection unit of the torque sensor according to the invention of this application.

FIG. 5 is a diagram illustrating a configuration of a detection circuit different from the detection circuit of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Torque transmission shaft 2, 3 ... Magnetic anisotropic part 4a, 5a ... Excitation coil 4b, 5b ... Detection coil 8 ... High frequency power supply 12, 13, 15, 16 ... Permanent magnet 17 DC offset power supply

Claims (4)

[Claims] 1. A first and a second magnetic anisotropic portion are formed on an outer peripheral surface of a torque transmission shaft such that one is compressed and the other is tensioned when a torque is applied to the torque transmission shaft. , On the outer peripheral side of the first and second magnetic anisotropic parts,
A change in the magnetic permeability of the magnetically anisotropic portion is detected by the first and second detection coils and the first and second excitation coils connected in series to excite the detection coil when a sine wave AC voltage is applied. A torque sensor arranged to convert the change in voltage at one end of the coil and generating a signal voltage indicating the direction and magnitude of torque from the difference between the voltages at one end of both detection coils; A torque sensor comprising a DC magnetic field applying means for constantly applying a DC magnetic field to the second magnetic anisotropic part. 2. The torque sensor according to claim 1, wherein said DC magnetic field applying means is a permanent magnet. 3. The torque sensor according to claim 1, wherein said DC magnetic field applying unit is a DC offset power supply for supplying a DC current to said exciting coil. 4. A first and a second magnetic anisotropic portion are formed on an outer peripheral surface of a torque transmission shaft such that one is compressed and the other is tensioned when a torque is applied to the torque transmission shaft. , On the outer peripheral side of the first and second magnetic anisotropic parts,
A change in the magnetic permeability of the magnetically anisotropic portion is detected by the first and second detection coils and the first and second excitation coils connected in series to excite the detection coil when a sine wave AC voltage is applied. A torque sensor arranged to convert the change in voltage at one end of the coil and generating a signal voltage indicating the direction and magnitude of torque from the difference between the voltages at one end of the two detection coils; A torque sensor characterized by magnetizing.