JPS62206421A - Torque sensor - Google Patents

Abstract

PURPOSE:To detect a torque applied to a nonmagnetic rotating shaft by providing the circumferential surface of the nonmagnetic rotating shaft with a magnetic film having a uniaxial anisotropy wherein an axis of easy magnetization is in a circumferential direction and an axis of difficult magnetization is in an axial direction and measuring the magnetic characteristics of the magnetic film by a detecting circuit having solenoid coils. CONSTITUTION:A nonmagnetic rotating shaft 20 is provided on its circumferential surface with a magnetic film 21 having a uniaxial anisotropy wherein an axis of easy magnetization is in a circumferential direction and an axis of difficult magnetization is in an axial direction. A torque applied to the rotating shaft 20 is detected by conducting the noncontact detection of the change in the magnetic characteristics of the magnetic film 21 by a detecting circuit having solenoid coils C1-C4. The solenoid coils C1 and C2 are located in a portion wherein the magnetic film 21 is present and the solenoid coils C3 and C4 are located in a portion wherein not magnetic film 21 is present. Those four solenoid coils are incorporated into a bridge circuit. The output voltage of the bridge circuit produced when a torsional stress is applied to a specimen takes the maximum value when the torque is equal to zero and is decreased inversely proportionally to the increase in the torque.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a torque sensor that non-contact detects torque by utilizing the change in the magnetic properties of a magnetic film due to the torque applied to a rotating shaft. In particular, the present invention relates to a torque sensor suitable for detecting torque of rotating shafts of automobiles, machine tools, robots, etc.

[Conventional technology]

Accurate detection of torque applied to rotating shafts is required in technologies for automobiles, machine tools, robots, etc. In this case, a non-contact method in which the detection body does not come into contact with the shaft of one rotation is suitable.

Recently, non-contact torque sensors have been developed to measure torque by measuring the magnetostrictive phenomenon caused by the rotational twisting of the magnetic material by using a magnetic material as the rotating shaft or by attaching a magnetic material to a non-magnetic rotating shaft. Detection is becoming mainstream.

A weight of several tens of kilograms, such as the drive shaft and steering wheel of a car,
In a member to which a torque of 1 meter or more is applied, a magnetic material for a torque sensor is attached to a portion of the rotating shaft for mechanical strength and material cost reasons. When torque is applied to the rotating shaft, strain occurs in the direction of 45° to the longitudinal direction, but strain occurs in the magnetostrictive material attached to the rotating shaft in the direction of 45°, which causes magnetic Anisotropy, that is, a difference in magnetic permeability depending on the magnetic flux detection direction, occurs, and by detecting this with a magnetic flux detector such as a magnetic head, it is possible to determine the torque applied to the rotating shaft.

As a method for non-contact detection of magnetostriction, a method has recently been devised that employs a solenoid coil-shaped excitation winding and a detection winding around a rotating shaft. This is done by changing the inductance of the solenoid coil that covers the patented area. An alternating current is passed through the solenoid coil, and an electrical signal output that depends on the torque applied to the rotating shaft is obtained depending on the current value, the number of turns of the coil (9 frequencies), etc.

A feature of this method is that it does not use a magnetic path that locally forms a magnetic circuit with the rotating shaft for excitation and detection, but in this case, the selection of the magnetic material to be attached to the rotating shaft is important. .

JP-A-59-61731 proposes the use of an amorphous magnetic alloy thin film as the magnetic material in such a case.

[Problem that the invention seeks to solve]

According to the research conducted by the present inventors, there is room for improvement in the hysteresis and thermal stability of amorphous magnetic alloy ribbons. Magnetic materials other than amorphous alloys that have been widely used in the past, such as iron-based alloy materials, have small magnetostriction coefficients and cannot provide sufficient output characteristics.

Ordinary nickel-based alloys with uncontrolled magnetic domain structures have large magnetostriction coefficients, but do not provide output reproducibility or thermal stability.

Torque sensors that detect magnetostriction using a detection circuit having a solenoid coil lack sensitivity and reliability because no suitable magnetic material has been found.

An object of the present invention is to provide a torque sensor that detects magnetostriction using a detection circuit having a solenoid coil and has high sensitivity and high reliability.

[Means for solving problems]

The present invention provides a magnetic film having an axle anisotropy in which the circumferential direction of the rotating shaft is an axis of easy magnetization and the axial direction is an axis of difficult magnetization, on the outer periphery of a non-magnetic rotating shaft, and a solenoid is detected. It is something.

The material of the magnetic film in the torque sensor of the present invention includes magnetic materials generally known as strain-sensitive materials, such as nickel, an alloy of nickel and iron, an alloy of nickel and cobalt, an alloy of cobalt and iron, and iron and aluminum. Crystalline materials such as alloys of iron, nickel, and cobalt, and amorphous alloys containing iron, nickel, boron, and silicon can all be used.

A magnetic film made by plating has very good magnetic sensitivity characteristics against strain, and is most suitable as a magnetic film. Among the plated magnetic films, it is most preferable to use an alloy of iron and nickel, particularly permalloy, as the magnetic material. A permalloy uniaxially anisotropic film produced by plating in a magnetic field can easily obtain anisotropy in the range of 102 to 10'' J/r+ (and is optimal as a magnetic film.

The conventional and common method for detecting magnetostriction is to use a magnetic circuit bridge formed by U-shaped excitation and detection magnetic cores and torque sensor magnetic materials arranged in a non-contact manner. be.

This method is excellent if the torque sensor magnetic material is uniform, but in reality, the coupling between the excitation magnetic core and the detection magnetic core, which are arranged in a non-contact manner, and the torque sensor magnetic material on the rotating shaft requires complete rotation. Fluctuations in the output due to the rotation angle are unavoidable due to the difficulty in achieving symmetry and local unevenness in the torque sensor magnetic material on the rotation shaft. In order to compensate for such drawbacks, there are measures such as making the detection sensor have a multipolar structure, but such a matter leads to an increase in cost and is not practical.

According to the method described above in which the solenoid coil is used in the detection circuit, these drawbacks can be eliminated.

In a magnetostrictive ring type torque sensor that detects the magnetostrictive phenomenon of the rotating shaft using a solenoid-like excitation winding and a detection winding, the main requirements for the rotating shaft are as follows.

(1) High sensitivity. The sensitivity is related to the magnetostrictive coefficient and magnetic domain structure of the magnetostrictive material. Also relevant is the level of operating flux of the magnetostrictive material.

Furthermore, magnetostriction sensitivity can be increased by optimizing the excitation frequency, so it is important to select these.

(2) Hysteresis is small. For this reason, it is required that the magnetization changes reversibly in response to external stress. It is known that hysteresis is small when, for example, a magnetic material having -axis anisotropy is excited in the hard axis direction by excitation by a coil.

(3) Small temperature changes. Because of the temperature dependence of the magnetic properties of magnetostrictive materials, thermally stable magnetic materials are required.

It has been found that a magnetic film having uniaxial anisotropy, particularly a magnetic film produced by plating, has the above three properties.

[Effect]

By providing a magnetic film on the outer periphery of the non-magnetic rotating shaft with uniaxial anisotropy in which the circumferential direction of the rotating shaft is the axis of easy magnetization and the axial direction is the axis of difficult magnetization, sensitivity to magnetostriction is increased and the magnetization is reversible. This results in an axle anisotropic film suitable for rotational magnetization.

As a result, the relationship between torque and electrical signal output, especially the output change when torque is repeatedly applied, can be reduced, and many benefits are obtained, such as improved torque detection sensitivity and improved reliability in use environments including temperature. It will be done. Furthermore, by using a magnetically superior uniaxial anisotropic film, a Wheatstone bridge type circuit can be adopted as the input/output circuit as a torque sensor, and a large output can be obtained at low cost. In other words, by using a uniaxial anisotropic magnetic film, a Wheatstone bridge type circuit is adopted as a convenient circuit system, and as a non-contact torque sensor, the configuration is significantly simpler and the sensitivity is higher than that of conventional ones. can be realized.

〔Example〕

This will serve as a plating base for the strain-sensitive magnetic film. After cutting, polishing, cleaning, and pre-plating treatment, the steel is coated with a magnetic alloy approximately 10 micrometers thick using a plating solution using sulfamate. Plate on top of that. in this case,
Depending on conditions such as plating solution composition, plating current, plating temperature, placement of the object to be plated in the plating bath, and applied magnetic field during plating, the crystal grain size, dislocation density, internal stress, electrodeposited fiber structure, and -axial magnetic anisotropy may vary. Match the orientation to the purpose.

Next, heat treatment is performed to align and alloy the interface between the nonmagnetic stainless steel and the plated magnetic film, and to alleviate residual stress in the plated film. As a result, the adhesion between the stainless steel base and the plated magnetic film is perfect, and it will not peel off due to repeated rotational stress, and the internal stress remaining in the plated film is reduced, resulting in good magnetic sensitivity characteristics against strain. becomes.

Next, a protective film is applied on the magnetic plating film, taking into consideration environmental conditions such as moisture resistance. On the other hand, for example, a resin coating such as polyimide is effective.

) Hereinafter, one embodiment of the present invention will be described.

Example 1 FIG. 1 is a schematic diagram of an apparatus for producing a magnetic alloy plating film used in the experiment. 1 is a plating tank, 2 is a plating liquid circulation direction, 3 is a plating liquid storage tank, 4 is a temperature controller, 5 is a pump, 6 is a filter, and 7 is a flow meter. 8 is the cathode to be plated, which is the stainless steel tube that will be the sample. 9 is 8
The anode is a nickel plate that surrounds the

10 is a gear that rotates the stainless steel tube 8 which is the object to be plated, and 11 is a motor. Reference numeral 12 denotes a current-carrying conductor, which is a copper rod, for generating a circumferential magnetic field in the stainless steel tube. Magnetic alloy plating is produced by electroplating while applying a magnetic field in the circumferential direction of the stainless steel tube and while applying rotation in that direction.

Outer diameter 20mm, inner diameter 12mm, length 100+++n
The outer surface of the + stainless steel pipe (material JIS standard 5US32).

The stainless steel tube was finished smooth by machining, and then immersed in an alkaline degreasing solution, and then electroplated with a magnetic alloy while rotating the stainless steel tube in a horizontal plating bath shown in FIG. The tamping liquid used is shown in Table 1.

Table 1 Plating solution composition Plating conditions include current density 5 A/drrl'
, the liquid temperature was 50° C., and a magnetic field strength of 800 AT was applied in the circumferential direction of the stainless steel tube. When plating, the stainless steel tube is
Rotates at 0 rpm and has a thickness of 0.0111111? The average composition of the film is Ni − 70% by weight of nickel and 30% by weight of iron.
A Fe alloy film was obtained. The crystal grain size as plated is approximately 20
0 people, dislocation density approximately 10"/d, internal stress approximately 200
It was MPa.

Next, this was heat-treated at 400° C. for 30 minutes in a hydrogen atmosphere. After heat treatment, the Ni-Fe alloy film has a fibrous structure with the (111) crystal plane as the surface, and the degree of integration is about 80%. Ta.

The magnetic properties and adhesion of the Ni-Fs alloy film plated on the surface of the stainless steel tube produced as described above were investigated. FIG. 2 shows the DC magnetization curves when the tube is magnetized with O in the circumferential direction and when it is magnetized along the longitudinal direction of the tube. Circumferential B go.

(Magnetic flux density at H = 800 A/m) is 1.0 Tesla, coercive force Hc is 400 A/m, squareness ratio Br/
Bm is 0.96. B go in the longitudinal direction of the tube.

is 0.9 Tesla, Hc is 15A/m, and Br/Bm is 0.
It is 06. In this way, the magnetic film has uniaxial anisotropy with the easy axis in the circumferential direction.

Next, in order to evaluate the adhesion between the stainless steel tube and the magnetic film plated, one end of the stainless steel tube was fixed, a rotational force was applied to the other end, and a maximum torque of 2ON-m was applied 106 times. No peeling or cracking of the film was observed.

) Finally, the stainless steel tube is magnetized in the longitudinal direction using a solenoid coil, and a torque is applied to the stainless steel tube that is the sample.
The magnetic permeability was measured when torsional strain was applied to the magnetic film plated thereon. As a typical characteristic, excitation frequency 1
FIG. 3 shows the relationship between applied torque and relative permeability at 00 kHz and excitation amplitude of 80 A/m. The relative magnetic permeability was 900 without torque, but the relative magnetic permeability decreased almost in proportion to the applied torque, and the relative magnetic permeability was 300 when a torque of 3 ON-m was applied. In this way, the relative magnetic permeability changes significantly in response to torque, and the rate of change is much larger than that of conventional magnetic materials, so the Ni-F e used in this experiment was used as an excellent magnetostrictive torque sensor material. The alloy plated film can be said to be a good choice.

Example-2 Thickness 0.01n on the surface of a stainless steel pipe with an outer diameter of 201m1
A Ni-Fe alloy magnetic film of yn was partially plated in a ring shape with a width of 70 mm. The plating bath, plating solution, plating conditions, magnetic field application during plating, etc. are the same as those described in Example-1. A heat treatment and a protective surface coating were then applied. The magnetic domain structure of the magnetic film produced in this way has uniaxial anisotropy such that the circumferential direction of the stainless steel tube and the direction of the 180° magnetic domain coincide, and the longitudinal direction of the stainless steel tube is the axis of difficulty in magnetization. Met. Such a sample was subjected to the following experiment.

Figure 4 shows the positional relationship between the sample stainless steel tube and the coil. The solenoid coils C1 and C2 were placed on the plated parts, and the solenoid coils C8 and C4 were placed on the unplated parts. Each solenoid coil had the same dimensions and the same number of turns. The specifications of the solenoid coil are shown in the table.

These four solenoid coils were assembled into a bridge circuit as shown in FIG. 5, and the output voltage was measured when torsional stress was applied to the sample. A 100 kHz, sine wave constant current power supply was used for the input circuit, and the output voltage was measured as an effective value voltage. Figure 6 shows the relationship between torque and output voltage. The output voltage is maximum when the torque is zero, and as the torque increases, the output voltage decreases approximately in proportion to the torque. The output voltage has a change of about 80mV/Nm without an amplifier, and is comparable to other methods as a torque sensor output. The reproducibility of the torque-voltage characteristics is sufficiently good, and as a non-contact torque sensor, it has a significantly simpler configuration than conventional ones, and has achieved high sensitivity and high output, so its practical effects are is big.

In the present invention, it is very preferable that the axis of easy magnetization of the magnetic film is slightly tilted from the circumferential direction to the axial direction. The tilting range is preferably 10''±5'', particularly around 10°.

The reason for this will be explained below.

The angle at which the direction of easy magnetization is tilted is determined by the magnitude of the magnetic anisotropy Ki inherent to the plated magnetic film and the magnitude of σ in the magnetic anisotropy induced by rotational torque. Below, these relationships will be explained using mathematical formulas.

As shown by the theory of reversible rotational magnetization, when a magnetic body with uniaxial anisotropy Ku is placed at an angle θO with the magnetic field H, the spontaneous magnetization Bs rotates and settles at the angle θ.

If the excitation field H is small enough, the deflection angle 〇=00-〇 is Ku, so from the relationship B=Bscosθ, the following (2) is obtained.
The formula is obtained.

(stress 1 induced), and as shown in equation (3) in FIG. Assuming that the diameter is sufficiently small compared to the pipe wall thickness, the stress-induced anisotropy due to torque T is σ
is given when the magnetostrictive coefficient of the magnetostrictive ring material is λ. Here, dl and dl are the inner diameter and outer diameter of the pipe,
GR and GP are the stiffness and modulus of the magnetic ring material and pipe material. In a magnetic torque sensor, Kσ is I x 102
~lX10'J/i is suitable. This is because Kσ is Ku
This is because it is related to μm as shown in equation (2).

As shown in equation (3), Ku is the stress-induced anisotropy σ and the uniaxial anisotropy Kt that the magnetic film inherently has when it is made.
is the sum of The direction of Kσ is 4 with respect to the circumferential direction of the pipe.
5", now if Kl is tilted by α0 from the circumferential direction. Therefore, the methods of inherently imparting anisotropy to an iron/nickel plated magnetic film are plating in a magnetic field, plating base, or plating. Methods such as cutting grooves in the membrane are effective.

By these methods, 1 becomes 2 x 10” ~ 2 x 108
J/rrr.

In the relationship between μm and σ in equation (7), K1 and sinα
By optimizing σ, it becomes unique from the positive region to the negative region. As a specific numerical example, l Ki I
= 10 x 10”J/rrr, a= 10°(si
n+ α=0.174), σ=-5×10” to 45×10”
In J/rrr, the relationship between σ and Ku is unique.

As can be seen from the above discussion, by setting Kl at an appropriate angle, the magnetic permeability of the magnetic film becomes unique with respect to forward and reverse torques. That is, by detecting changes in magnetic permeability, torque including forward and reverse torques can be detected. A suitable angle is 10'±5°.

Torque is detected by changes in the inductance of the solenoid coil that covers the plated magnetic film on the rotating shaft. The input/output circuit can adopt a Wheatstone bridge type circuit, and an alternating current is passed through the solenoid coil, and an electric signal output that depends on the torque applied to the rotating shaft is generated depending on the current value, number of coil turns, frequency, etc. can get.

A magnetic film made of an iron-nickel alloy with an appropriate size of inherent uniaxial anisotropy and stress-induced anisotropy is placed on a rotating shaft made of non-magnetic stainless steel, and changes in magnetic permeability due to torque are controlled by a solenoid-like magnetic film. By detecting in the reversible magnetization range with a coil,
A magnetic torque sensor that is superior in many respects such as a unique relationship between torque and electrical signal output, particularly small output changes when torque is repeatedly applied, and improved torque detection sensitivity, is made possible. As a non-contact type torque sensor, the torque sensor of the present invention has a significantly simpler structure than conventional ones.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a highly reliable torque sensor with improved magnetostriction detection sensitivity and excellent thermal stability. Furthermore, since a Wheatstone bridge type detection circuit can be used, the detection method is also simplified.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an apparatus for producing a fitted magnetic film, Fig. 2 is a DC magnetization curve diagram of a torque sensor according to an embodiment of the present invention, and Fig. 3 is a diagram showing the magnetic permeability and magnetic permeability of a torque sensor according to an embodiment of the present invention. A characteristic diagram showing the relationship between torques, FIG. 4 is a layout configuration diagram of a torque sensor according to an embodiment of the present invention, FIG. 5 is a circuit diagram showing an embodiment of a detection circuit of a torque sensor according to the present invention, and FIG. 6 7 is a characteristic diagram showing the relationship between torque and output voltage, and FIG. 7 is a perspective view showing another example of the torque sensor. 20... Stainless steel tube (rotating shaft), 21... Magnetic film.

Claims (7)

[Claims] 1. A torque sensor that detects torque applied to the rotating shaft by providing a magnetic film on the outer periphery of a non-magnetic rotating shaft and detecting changes in the magnetic properties of the magnetic film in a non-contact manner using a detection circuit having a solenoid coil. has uniaxial anisotropy in which the circumferential direction of the rotating shaft is an axis of easy magnetization and the axial direction is an axis of difficult magnetization. 2. The torque sensor according to claim 1, wherein the magnetic film is a plated film. 3. 3. The torque sensor according to claim 2, wherein the magnetic film is made of an alloy of iron and nickel. 4. 4. The torque sensor according to claim 3, wherein the magnetic film is a tamped film that has been heat-treated to remove residual stress. 5. The torque sensor according to claim 1, wherein the axis of easy magnetization of the magnetic film is in a direction inclined by 10 degrees ± 5 degrees from the circumferential direction of the rotating shaft toward the axial direction. 6. A torque sensor that detects torque applied to the rotating shaft by providing a magnetic film on the outer periphery of a non-magnetic rotating shaft and detecting changes in the magnetic properties of the magnetic film in a non-contact manner using a detection circuit having a solenoid coil. has uniaxial anisotropy in which the circumferential direction of the rotating shaft is an axis of easy magnetization and the axial direction is an axis of difficult magnetization, and the detection circuit is comprised of a Wheatstone bridge type detection circuit. . 7. The torque sensor according to claim 6, wherein the Wheatstone bridge type detection circuit includes two solenoid coils covering the magnetic film and two solenoid coils located away from the magnetic film. .