JP3268089B2 - Magnetostrictive torque detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive torque detector.

[0002]

2. Description of the Related Art Conventionally, a magnetic core (magnetic head) is disposed close to the surface of a rotating shaft having magnetostriction and oblique to its circumferential direction and axial direction, and an alternating current is applied to a detection coil wound around the magnetic core. 2. Description of the Related Art There is known a magnetostrictive torque detection device that supplies a current and detects a torque of a rotating shaft based on a state quantity related to the impedance.

[0003] JP-A-61-8639 and JP-A-6-8639
Japanese Patent Application Laid-Open No. 1-82126 discloses that in the above device, the detection coil forms a resonance circuit together with the capacitor with respect to the frequency of the alternating current.

[0004]

However, the conventional magnetostrictive torque detecting device described above has a problem that the torque detecting sensitivity is still low. The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetostrictive torque detecting device capable of improving sensitivity.

[0005]

According to the present invention, there is provided a magnetostrictive torque detector according to the present invention, wherein a rotating shaft having magnetostriction is fixed to the surface of the rotating shaft in the axial direction, and both ends are fixed to the surface of the rotating shaft. A magnetic core that is attached and forms a closed magnetic circuit together with the rotating shaft, a detection coil wound around the magnetic core, and an alternating current is supplied to the detection coil,
A circuit for detecting the torque of the rotating shaft based on a state quantity related to the impedance of the detection coil.

[0006] In a preferred aspect, the rotating shaft has a magnetostrictive film in close contact with the both ends of the magnetic core. In a preferred aspect, a capacitor forming a resonance circuit together with the detection coil is fixed to the rotating shaft. In a preferred aspect, a rotating coil disposed on a rotating shaft to supply power to the detection coil, and an AC power disposed in close proximity to the rotating coil and transmitting AC power to the rotating coil in a non-contact state, and in a non-contact manner from the rotating coil A fixed coil that outputs the signal voltage received in the state to the circuit unit.

In a preferred embodiment, the fixed coil is
It consists of a power transmission coil for power transmission and a reception coil for reception.

[0008]

When the circuit supplies an alternating current to the detection coil, an alternating magnetic flux is formed in the magnetic core, and the alternating magnetic flux penetrates the magnetostrictive rotating shaft through the magnetic core. When the magnetic permeability of the rotating shaft having magnetostriction is modulated according to the torque applied to the rotating shaft, the impedance (reactance) of the detection coil is modulated, and the change in the impedance is detected to detect the torque.

Particularly, in the present invention, the magnetic core around which the detection coil is wound is fixed to the rotating shaft, and both ends of the magnetic core are brought into close contact with the surface of the rotating shaft. As a result, for the following reasons:
Signal sensitivity is improved. First, compared to the magnetic circuit of a conventional magnetostrictive torque detector in which the magnetic core is disposed with a gap from the surface of the rotating shaft, the gap is eliminated, and the alternating magnetic flux is greatly increased. I do. Therefore,
The signal voltage increases, and the S / N ratio for various noise voltages improves. Furthermore, the impedance component, which is modulated by the torque, of the total impedance of the detection coil increases relatively and absolutely with respect to the total impedance, and therefore, the signal voltage of the detection coil becomes relative to the noise voltage. And the S / N ratio is improved.

Second, since the surface of the rotating shaft does not rotate with respect to the magnetic core, noise or spurious signals are generated due to impedance fluctuations of the detection coil generated in accordance with variations in the magnetic characteristics of the rotating shaft surface in the circumferential direction. Without that, the SN ratio is improved. Third, unlike the conventional case, the gap length between the pole tip surface of the magnetic core and the surface of the rotating shaft fluctuates periodically with the rotation of the rotating shaft, thereby preventing spurious signals from occurring and improving the SN ratio. Is done.

[0011]

【Example】

(Embodiment 1) Hereinafter, a specific description will be given with reference to FIGS. As shown in FIG. 1, the magnetostrictive torque detecting device supplies a magnetic core 2 fixed to the surface of a rotating shaft 1, a detecting coil 3 wound on the magnetic core 2, and a detecting coil 3 through a capacitor 4. Rotating coil 5, and a feeding coil 6 and a receiving coil 7 which are arranged close to the rotating coil 5 and constitute a rotary transformer together with the rotating coil 5.
And a circuit unit 8 that supplies an alternating current to the feeding coil 6 and receives a signal voltage from the receiving coil 7.

Further, a resonance circuit B having the same configuration as the resonance circuit A including the magnetic core 2, the detection coil 3, the capacitor 4, the rotating coil 5, the power supply coil 6, and the reception coil 7 described above.
The resonance circuit B includes a magnetic core 20 (see FIG. 4) fixed to the magnetic core 2 on the same circumference of the surface of the rotating shaft 1 at a distance of 180 degrees from the magnetic core 2 (see FIG. 4). , A rotary coil 50 for supplying power to the detection coil 30 through a capacitor (not shown), and a rotary transformer disposed close to the rotary coil 50 together with the rotary coil 50. The circuit unit 8 includes a power supply coil 60 and a reception coil 70,
An AC current is supplied to the power supply coil 60 and a signal voltage is received from the reception coil 70.

The rotating shaft 1 is made of S45C and has a diameter of 20 mm.
mm, a pair of grooves 11 is formed in the surface of the rotating shaft 1 with a torsion angle of +45 degrees with respect to the axial direction, with a width of 0.6 mm, a length of 25 mm, and a depth of 0.5 μm. In addition, a pair of not-shown grooves are formed in the same shape at a twist angle of -45 degrees, which are located on the opposite side of the grooves 11 in the circumferential direction.

It is to be noted that the magnetic core 2
, Nickel, boron (Fe-Ni-
An amorphous magnetostrictive film having a thickness of about 20 to 40 μm made of B) may be formed. It is to be noted that deposition on unnecessary portions of the rotating shaft 1 is prevented by performing a masking process. The magnetic cores 2 and 2a are formed in a gate shape using permalloy or soft magnetic ferrite as a material. The magnetic cores 2 and 2a are embedded in core receiving grooves formed in the inner periphery of an annular holder 10 (see FIG. 4 and omitted in FIG. 1) made of resin. After that, it is adhered to the rotating shaft 1 with an adhesive. The magnetic pole ends at both ends of the magnetic cores 2 and 2a are in close contact with the surface of the rotating shaft 1 between the pair of grooves 11.

It should be noted that in preparation for a case where the diameter of the rotating shaft 1 changes variously, the holders 10 having various inner diameters may be manufactured, and the magnetic cores 2 and 2a may be appropriately embedded. Of course, the holder 10 may be made of metal (for example, an aluminum die-cast product), or a metal wire may be embedded in the holder 10. The rotating coils 5 and 50 each include a pair of coils 5.
a and 5b, and both coils 5a and 5b are wound in opposite directions and are arranged in the axial direction with a gap d therebetween.

The power supply coils 6 and 60 are arranged close to the surface of the rotary shaft 1 at positions facing the gap d, and their axes extend in the radial direction of the rotary shaft 1. The receiving coils 7 and 70 are also disposed close to the surface of the rotating shaft 1 at positions facing the gap d, and their axes extend in the radial direction of the rotating shaft 1. Hereinafter, the operation of the magnetostrictive torque detecting device of this embodiment shown in FIG. 1 will be described with reference to the equivalent circuit diagram of FIG.

However, the operation of the resonance circuit B is the same as that of the resonance circuit A.
Therefore, only the operation of the resonance circuit A will be described as a representative. The circuit section 8 includes an oscillation circuit 81, a reception circuit 8
2. Oscillation circuit 8 comprising torque signal voltage output circuit 83
1 supplies an AC current to the feeding coil 6, an AC voltage is induced in the rotating coil 5, an AC current flows through a resonance circuit A including the rotating coil 5, the capacitor 4, and the detection coil 3, and the AC current flows through the receiving coil 7. The AC signal voltage is induced according to the AC current flowing through the rotating coil 5. The AC signal voltage induced in the receiving coil 7 is processed by a receiving circuit 82, and the receiving circuit 82 generates an oscillation circuit 81 based on the AC signal voltage.
A control signal for controlling the oscillation frequency of the resonance circuit A to the resonance frequency of the resonance circuit A is output, and the received AC signal voltage is output to the torque signal voltage output circuit 83. The torque signal voltage output circuit 83 detects the torque of the rotating shaft 1 based on the frequency of the input AC signal voltage. Note that the circuit 83 may have a microcomputer configuration or an analog or digital circuit configuration, but the detailed circuit configuration is not the gist of the present invention, and a description thereof will be omitted.

In the apparatus shown in FIG. 1, a pair of grooves 1
When the torque is applied in either direction due to the recess of 1,
A tensile force or a compressive force is applied to the gap between the pair of grooves 11, and a compressive force or a tensile force is applied to the gap between the pair of not-shown grooves, whereby the reactance of the detection coil 3 and the detection (not shown) are detected. The reactance of the coil changes in the opposite direction.

Therefore, if the reactance of the detection coil 3 fluctuates due to the torque change, the AC signal voltage input to the receiving circuit 82 changes based on the change, and the oscillation frequency of the oscillation circuit 81 changes based on the change. The resonance frequency may be adjusted, and a torque value corresponding to the resonance frequency may be output from the torque signal voltage output circuit 83 based on the resonance frequency.

Hereinafter, an example of the oscillation circuit 81 and the reception circuit 82 will be described with reference to FIG. Although the above-described capacitor 4 is connected in series with the detection coil 3 to form a series resonance circuit, the capacitor 4 may be connected in parallel with the detection coil 3 to form a parallel resonance circuit. In this circuit, the voltage controlled oscillator 815 excites the resonance circuit A via the feeding coil 6, and a current flowing through the rotating coil 5 induces a reception voltage V <b> 2 in the reception coil 7.

Here, the excitation frequency, that is, the frequency of the excitation voltage V1 applied to the feeding coil
Excitation voltage V1 and reception voltage V
The phase difference from 2 is π / 2. Therefore, by controlling the voltage-controlled oscillator 815, the phase difference between the reception voltage V2 and the excitation voltage V1 can be adjusted to π / 2, and the frequency value of the reception voltage V2 at that time can be detected as the resonance frequency fr.

More specifically, a voltage controlled oscillator (hereinafter abbreviated as VCO) 815 is designed to operate near the resonance frequency of the resonance circuit A. The waveform of the reception voltage V2 is converted into a rectangular wave voltage having the same phase as the reception voltage V2 by the Schmitt trigger (reception circuit) 82, and the exclusive OR circuit 811 outputs the output voltage V1 of the VCO 815.
Is compared to The output voltage of the exclusive OR gate 811 goes low if V1 is equal to the rectangular wave voltage, and goes high if V1 is different. Exclusive OR gate 811
Is converted by a low-pass filter 812 into a DC voltage having a different level depending on the duty ratio, and this DC voltage is compared with a reference voltage of a reference voltage generator 813 in a control voltage generator 814.

The control voltage generator 814 outputs an output voltage so that the difference voltage between the DC voltage and the reference voltage becomes 0, and the VCO 815 outputs a signal having a frequency determined by the output voltage value of the control voltage generator 814. Output a square wave. Here, if the phase difference between the rectangular wave voltage output from the Schmitt trigger (receiving circuit) 82 and the output signal V1 of the VCO 815 is π / 2, the duty of the output voltage of the exclusive OR gate 811 is used. The ratio is set to 0.5, and the output voltage of the low-pass filter 812 at this time is half the peak value of the output voltage of the exclusive OR gate 811. Therefore, by setting the value of the reference voltage output from the reference voltage generator 813 to half of the output voltage of the exclusive OR gate 811, the oscillation frequency of the VCO 815 always becomes the resonance frequency of the resonance circuit.

In the above description, the method of obtaining the frequency f1 by the signal processing of the resonance circuit A has been described. However, the frequency f2 can be similarly obtained by the signal processing of the resonance circuit B. And
The torque signal voltage output circuit 83 of the circuit section 8 outputs the frequency f1
, A corresponding torque T1 is output, a corresponding torque T2 is output from the frequency f2, and the torque T is obtained as the sum of the absolute values of the torques T1 and T2. (Embodiment 2) Another embodiment will be described with reference to FIG.

In this embodiment, the feeding coil 6 is wound around the magnetic head 6a, the receiving coil 7 is wound around the magnetic head 7a, and the rotating coil 5 is arranged between the magnetic pole faces of the magnetic heads 6a, 7a. ing. This improves the electromagnetic conversion efficiency of the rotary transformer. (Embodiment 3) Another embodiment will be described with reference to FIG.

In this embodiment, the rotating shaft 1 having magnetostriction is used.
A ceramic film, an amorphous magnetic film, or a resin film is applied as an insulating film 101 having an electrical insulation property to the outer peripheral surface of the coil 00, and a spiral coil 102 is formed thereon by a method such as electroless plating. A magnetic film 103 having an insulating property (for example, a ferrite film or an amorphous magnetic film) is formed by a method such as coating or electroless plating.
However, the magnetic film 103 constituting the magnetic core referred to in the present invention
Directly contact the surface of the rotating shaft 1 to form a so-called gapless closed magnetic circuit.

In this manner, the effects of the present invention can be achieved while avoiding problems such as centrifugal resistance associated with fixing the magnetic core to the rotating shaft 1. (Modification) As a matter of course, torque can be detected using only one of the resonance circuits A and B instead of using two circuits.

The feeding coil 6 can also serve as the receiving coil 7. Instead of detecting the torque based on a change in the oscillation frequency due to a change in the reactance of the detection coil 3, the torque can be detected based on a change in the current, phase, or voltage of the detection coil 3 due to a change in the reactance of the detection coil 3. The amorphous magnetostrictive film 9 applied to the rotating shaft 1 may be applied only to a region in contact with the magnetic pole end surface of the magnetic core 2,
Further, another magnetostrictive film may be formed instead of the amorphous magnetostrictive film 9, or the magnetostrictive property of the rotating shaft 1 itself may be used without forming the magnetostrictive film.

Instead of arranging the pair of magnetic cores 2 and 2a 180 degrees apart on the same circumference of the rotating shaft 1, a pair of magnetic cores are arranged at the same position on the same circumference of the rotating shaft 1, A so-called crosshead structure in which the lead angle of the magnetic core is +45 degrees or -45 degrees may be adopted, but in this case, the groove 11 is omitted. The operation and effect of the magnetostrictive torque detection device of the present embodiment described above will be described.

First, since the magnetic core 2 is fixed to the surface of the rotating shaft 1, the gap between the magnetic core 2 and the rotating shaft 1 (more precisely, the amorphous magnetostrictive film 9) is eliminated, so that the signal voltage is reduced. Is increased, and the SN ratio is improved. Further, since the magnetic core 2 is fixed to the surface of the rotating shaft 1, even if the magnetic characteristics of the rotating shaft 1 (or the amorphous magnetostrictive film 9 attached to the rotating shaft 1) vary in the circumferential direction, the influence does not occur.

Further, since the rotating shaft 1 has the groove 11 obliquely and the amorphous magnetostrictive film 9 is attached, the sensitivity can be increased. Further, since a pair of magnetic cores (one not shown) 2 is attached on the same circumference of the rotating shaft 1, even if there is a temperature gradient in the axial direction of the rotating shaft 1, the influence can be offset. it can.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing the entire configuration of a first embodiment of the present invention,

2 is an equivalent circuit diagram of the device of FIG. 1,

FIG. 3 is a specific circuit diagram of the device of FIG. 2,

FIG. 4 is an enlarged sectional view of a main part showing a fixing method of a magnetic core;

FIG. 5 is a cross-sectional view showing a modification of the power supply coil.

FIG. 6 is a cross-sectional view showing a modification of the magnetic core and the detection coil.

[Explanation of symbols]

1 is a rotating shaft, 2 is a magnetic core, 3 is a detection coil, 4 is a capacitor, 5 is a rotating coil, 6 is a feeding coil, 7 is a receiving coil, and 8 is a circuit unit.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-26949 (JP, A) JP-A-7-63627 (JP, A) JP-A-63-317732 (JP, A) JP-A 64-64 9339 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01L 3/10

Claims (5)

(57) [Claims] 1. A rotating shaft having magnetostriction, fixed to the surface of the rotating shaft in the axial direction, and both ends are fixed to the surface of the rotating shaft and constitute a closed magnetic circuit together with the rotating shaft. A magnetic core, a detection coil wound around the magnetic core, and a circuit unit for supplying an alternating current to the detection coil and detecting a torque of the rotary shaft based on a state quantity related to an impedance of the detection coil. And a magnetostrictive torque detector. 2. The magnetostrictive torque detecting device according to claim 1, wherein said rotating shaft has a magnetostrictive film in close contact with said both ends of said magnetic core. 3. The magnetostrictive torque detecting device according to claim 1, wherein a capacitor forming a resonance circuit together with the detecting coil is fixed to the rotating shaft. 4. A rotating coil disposed on the rotating shaft to supply power to the detecting coil, and an AC power source disposed in close proximity to the rotating coil for transmitting AC power to the rotating coil in a non-contact state, and further comprising: The magnetostrictive torque detecting device according to claim 1, further comprising: a fixed coil that outputs a signal voltage received in a contact state to the circuit unit. 5. The magnetostrictive torque detector according to claim 4, wherein said fixed coil comprises a power transmission coil for power transmission and a reception coil for reception.