JPS62184323A - Magneto-striction type torque sensor - Google Patents

Abstract

PURPOSE:To obtain a small-sized, high-performance noncontact torque sensor which is easily mounted by providing a magneto-strictive layer directly on a shaft in a cylindrical shape which has the center line of the shaft on the shaft surface as an axis of rotational symmetry. CONSTITUTION:The magneto-strictive layer 6 which has uniform magnetic characteristics is formed by a plasma spraying method, etc., on the outer periphery of the torque transmission shaft 1 without any seam, a couple of coils 7 and 8 containing U-shaped iron cores are arranged having their magnetic pole surface directions made coincident with the direction of the magneto- strictive layer 6 without contacting, and the directions of the magnetic electrode couple of the coils is + or -alpha deg. (alphanot equal to 0, alphanot equal to 90) to the axial direction of the torque transmission shaft. The magneto-strictive layer is properly 50-300mum in consideration of sensitivity and the joining strength between the magneto-strictive layer and torque transmission shaft. Further, ferrite, 'Permalloy(R)' which has high magnetic permeability and superior frequency characteristics, or an amorphous magnetic body with a small saturation magneto-striction constant lambdas is suitable to the U-shaped iron core material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a non-contact torque sensor based on magnetostrictive phenomena.

[Conventional technology]

Information about torque is required for advanced control of various machines or electromechanical systems. In particular, non-contact torque sensors with a simple structure and high performance are needed for robot operation control, advanced control of engines and motors, etc. In this technical field, the characteristics required of a torque sensor are that the torque detection sensitivity is constant regardless of the rotational speed of the torque transmission shaft, that it has instantaneous response characteristics, and that it is reliable. In addition, the parts of mechanical devices that require torque detection are usually located within a limited narrow space, so the torque sensor must have a small size and a structure that is easy to install.

Conventionally, as a non-contact torque sensor using an excitation and detection coil system that is easy to install, one that has a coil system with an iron core placed outside the torque transmission shaft has already been used in R6, Beth and W, W, M.
Review of 5cien ific Instrument + Vol. 25
+ ASEA in 1954 and by 00 Dahle
Journal, Vol. 33. Papers were published in 1960. Both of these sensors utilize the fact that the magnetization characteristics of the torque transmission shaft itself, which has an inverse magnetostrictive effect, changes depending on the applied torque, and they have almost the same advantages and disadvantages. Therefore, here 0. The basic configuration of the Dahle torque sensor will be shown, and its simple operating principle and problems will be explained. FIG. 10(a) shows its basic configuration. A torque transmission shaft 1 having an inverse magnetostrictive effect and two U-shaped cored excitation coils 2 and a detection coil 3 are arranged with a slight gap therebetween. Now, when the torque T is applied as shown in the figure, a tensile stress σ4 and a compressive stress −σ5 are generated on the surface of the torque transmission shaft in directions perpendicular to each other. The direction of each stress is ±45° with respect to the axial direction of the torque transmission shaft. Therefore, the magnetic permeability near the surface of the torque transmission shaft changes due to the inverse magnetostriction effect, and assuming the saturation magnetostriction constant λsho of the torque transmission shaft, it increases in the σ direction, and −σ
It will decrease in the direction. In this case, the difference in magnetic permeability in the two directions is proportional to the applied torque T. The two U-shaped core-containing excitation coils 2 and detection coils 3 are capable of detecting the difference in magnetic permeability in the two directions, including the sign, in a non-contact manner based on the principle of a magnetic circuit bridge. As a result, the applied torque can be detected including its sign. As described above, having the hour wheel principle and ease of installation are major features of the torque sensor, but this method has the following serious drawbacks. In other words, in the manufacturing process of torque transmission shafts made of ordinary steel, attention is paid only to strength and little consideration is given to magnetic properties, and as a result, magnetic properties near the surface of the torque transmission shaft are extremely non-uniform. As shown in FIG. 10(b), a large output drift occurs as the torque transmission shaft 1 rotates. Therefore, depending on this method, it has been difficult to realize a torque sensor having instantaneous response characteristics.

In addition, with the aim of alleviating these problems, increasing the degree of anger, and enabling torque detection even if the torque transmission shaft is non-magnetic, Japanese Patent Laid-Open No. 58-9034 discloses that There is a torque sensor that does not utilize the inverse magnetostriction effect, but rather utilizes the excellent inverse magnetostriction effect by wrapping and fixing a high magnetostrictive amorphous ribbon around the outer periphery of a torque transmission shaft.

On the other hand, as a torque sensor whose torque detection sensitivity is constant regardless of the rotational speed of the torque transmission shaft and has instantaneous response characteristics, a high magnetostrictive amorphous ribbon is fixed around the torque transmission shaft and changes in response to the applied torque. A method for non-contact detection of the magnetic permeability of a high magnetostrictive amorphous ribbon using a solenoid coil system was published in the Institute of Electrical Engineers of Japan Magnetics Study Group Material MAG-82-162 (1982).

[Problem that the invention seeks to solve]

However, the former sensor still suffers from non-uniformity in magnetic properties due to the beginning and end of winding of the high magnetostrictive amorphous ribbon, and the problem of large output drift due to rotation of the torque transmission shaft remains unsolved.

In addition, IHFT torque sensors have the problem of not being easy to install because they require a conductive wire to be wrapped around the torque transmission shaft. In order to realize a torque sensor, the length of the solenoid coil must be equal to or longer than the diameter of the solenoid, and there is a limit to miniaturization.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact, high-performance, non-contact torque sensor that is easy to install and solves all of the above problems.

[Means for solving problems]

The present invention provides a magnetostrictive torque sensor that detects torque applied to a shaft by utilizing an inverse magnetostrictive effect in a magnetostrictive layer provided on the surface of the shaft. It is characterized by having a cylindrical shape with a line as the axis of rotation, and a magnetostrictive layer is provided directly on the axis.

The magnetostrictive layer is preferably formed by a plasma spraying method. Formation of a magnetostrictive layer by thermal spraying is possible under normal conditions, and the formation speed is faster than other techniques available for forming magnetostrictive layers, such as sputtering, single deposition, electrodeposition, etc. Moreover, since the torque transmission shaft is not rotated, by forming the magnetostrictive layer, its magnetic properties become rotationally symmetrical, which is advantageous for the purpose of the present invention.

[For production]

The present invention fundamentally solves the problem of output drift due to the rotation of the torque transmission shaft due to non-uniformity of magnetic properties, enables instantaneous response, and also enables the fixation of the magnetostrictive layer using any adhesive. Since the torque sensor does not use any heat, a highly reliable torque sensor can be obtained over a wide operating temperature range.

〔Example〕

Embodiments will be described in detail below with reference to the drawings. Figure 1(a)
1 shows the basic configuration of the first embodiment of the present invention. A magnetostrictive layer 6 with uniform magnetic properties is seamlessly formed on the outer periphery of the torque transmission shaft 1 by a thermal spraying method such as a plasma spraying method, and a pair of U-shaped cored coils 7.8 are attached to the magnetostrictive layer 6 in the direction of the magnetic pole surface. are arranged in a non-contact manner in the direction of the magnetostrictive layer 6, and the direction of the magnetic pole pair of each coil is at ±α° (α≠01α≠90) with respect to the axial direction of the torque transmission shaft. In this case, the magnetostrictive layer composition is the saturation magnetostriction constant λS and the saturation magnetization Is
From the viewpoint of sensitivity, it is ideal to have both large values and small magnetocrystalline anisotropy, but sufficient output can be obtained by using the magnetic flux convergence effect of the high magnetic permeability U-shaped core and by increasing the excitation frequency to about 100 kHz. Therefore, the saturation magnetostriction constant λS does not need to be particularly large. For this reason, Ni-Fe alloy (45 permalloy) or Fe-C, which has been known as a magnetostrictive vibrator material.

All metal magnetic materials including alloy (2V-permendur) etc. are suitable, and iron and martensitic stainless steel may also be used. Alternatively, it may be an Fe-based amorphous (non-crystalline) magnetic material. The thickness of the magnetostrictive layer is 50 μm to 30 μm.
Approximately 0 μm is appropriate from the viewpoint of sensitivity and bonding strength between the magnetostrictive layer and the torque transmission shaft. Further, as the U-shaped core material, ferrite, permalloy, which has high magnetic permeability and excellent frequency characteristics, or an amorphous magnetic material with a small saturation magnetostriction constant λS is suitable.

By the way, the magnetic flux that intersects with the detection coil is roughly proportional to the thickness of the magnetostrictive layer, so in order to increase the torque detection sensitivity, the magnetostrictive layer should be It is necessary to increase the thickness as much as possible.

The most suitable method for this purpose is the thermal spraying method, which has both a high magnetostrictive layer formation rate and strong adhesion strength.

The thermal spraying method allows the formation of a magnetostrictive layer under normal conditions, can be easily incorporated as a step in the production line of various mechanical devices, and is suitable for mass production.

Other methods such as sputtering and vapor deposition are possible, but these require a low-pressure gas discharge container or vacuum container when forming a thin layer, and electrodeposition requires a plating bath, so they can be easily incorporated as one step in the production line. I can't say that. Secondly, the rate of formation of the magnetostrictive layer is extremely slow in any of these methods. for example,
The standard film formation speed of RF sputtering is approximately 100%.
Approximately 1 person/S.

Plasma spraying is also a suitable method for forming magnetostrictive layers, but
The concern that may be raised is the magnitude of the coercive force He, but in an example measured for a Ni layer as a magnetostrictive layer, it was about I(, = 30 to 50 (Oe)) in the polished state after thermal spraying, and this If further annealing is applied to the steel, the coercive force can be expected to be reduced, so there is no risk of this happening.

Furthermore, if an iron-core coil is used as the excitation coil and the excitation magnetic field is several hundred Gauss (G) or more, sufficient sensitivity can be obtained and hysteresis errors do not pose a practical problem. Therefore, thermal spraying or plasma spraying is most suitable for forming the magnetostrictive layer.

Now, when torque T is applied as shown in the figure, tensile stress 4 and compressive stress 5 are generated on the surface of the torque transmission shaft, and similar stress is induced in the magnetostrictive layer that is firmly bonded to the surface of the torque transmission shaft. be done. Therefore, the saturation magnetostriction constant λs of the magnetostrictive layer
If ho, the magnetic permeability of the magnetostrictive layer increases in the σ direction and decreases in the −σ force direction, as in the case of FIG. 10(a). Therefore, the self-inductance increases in the U-shaped cored coil 8, and conversely decreases in the coil 7.

FIG. 1(b) shows the relationship between applied torque and each self-inductance. The direction of torque application shown in FIG. 1(a) is defined as positive. From this, it can be seen that if the difference between the two self-inductances is detected including the sign, non-contact detection including the direction of the torque is possible. As a circuit for detecting the difference between two self-inductances, for example, BRIDGE and GE are well known. FIG. 2 shows an example of the configuration of a torque sensor based on this circuit. A sine wave power source 9 is used as an excitation power source, and a phase detection circuit 10 outputs a bridge unbalanced voltage 1) proportional to torque as a direct current.

In this case, since the sign of the difference between the two self-inductances has a one-to-one relationship with the phase of the bridge unbalanced voltage II, the direction of the torque can be identified by the phase detection circuit.

The phase control signal of the phase detection circuit is configured with the phase of the sine wave power supply voltage or excitation current 12 as a reference. Variable resistance
The resistor 13 performs zero adjustment.

FIG. 3 shows a circuit for compensating for sensitivity changes due to changes in the air gap between the pair of U-shaped cored coils 7.8 and the magnetostrictive layer 6 in FIG. 1(a). This is because the variable gain amplifier 14 compensates for the decrease in sensitivity due to the increase in air gap. As the air gap increases, the self-inductance of the coil 7.8 decreases monotonically due to the demagnetizing field effect of the U-shaped core, and as a result, the excitation current 12 increases monotonically, so that the change in the air gap is caused by the change in the amplitude of the excitation current 12. Detected from. Therefore, the gain of the variable gain amplifier 14 may be increased in proportion to the amplitude of the excitation current 12. In this embodiment, in order to achieve this, the excitation current amplitude is detected by the current detector 16 and changed to a DC voltage by the rectifier circuit 17, which is used as the gain control signal 18 of the variable gain amplifier.

However, in this case, the compensable air gap change mode is limited to the case where the air gap between the pair of U-shaped cored coils 7.8 and the magnetostrictive layer 6 changes equally in FIG. 1(a).

FIG. 4 shows a second embodiment of the invention. In FIG. 1(a), a pair of U-shaped cored coils 7
．． 8 were arranged parallel to the axial direction of the torque transmission shaft 1, but in this example, a pair of U-shaped iron cored coils were rotated 90 degrees while maintaining their relative positional relationship, and 1
The pair of U-shaped cored coils 19 and 20 are arranged perpendicularly to the axial direction of the torque transmission shaft 1. Even if a temperature gradient occurs in the axial direction of the torque transmission shaft 1 due to an external factor, the temperatures immediately below the pair of U-shaped cored coils 19 and 20 are always equal, and the influence of temperature becomes an in-phase disturbance. Therefore, the common mode disturbance is completely removed by the differential structure detection circuit shown in FIG. 2, for example, so that it has the characteristic that no output drift occurs.

FIG. 5 shows a third embodiment of the present invention. This coil 21.22.23.24 with a U-shaped iron core is arranged in a non-contact manner with respect to the torque transmission shaft l.
2 and 23 and 24 are connected in series, forming a pair of coil systems as a whole. In this case, coil 2
1.22 is on the straight line 25, and 23.24 is on the straight line 26. Furthermore, the directions of these two straight lines 25 and 26 are ±α° with respect to the axial direction of the torque transmission axis l.
(α≠0, α≠90). When detecting torque by opening the U-shaped cored coil structure of this embodiment, for example, the differential structure detection circuit shown in FIG. 2 can be used. The effect of this embodiment is that the compensation method for air gap changes of the first embodiment can eliminate non-uniform air gap changes that could not be compensated for, that is, the entire coil system can compensate for the relative positional relationship between the four U-shaped cored coils. It is possible to automatically compensate for a mode in which the air gap changes obliquely with respect to the magnetostrictive layer 6 while keeping it unchanged. - As an example, consider the case where the air gap between the coil 22, 23 with a U-shaped iron core and the magnetostrictive layer 6 decreases, and conversely, the air gap between the coil 21, 24 and the magnetostrictive layer 6 increases. This is because the sum of the self-inductances of 21 and 22 and the sum of the self-inductances of 23.24 are always equal, and do not affect the differential output.

FIG. 6 shows a power supply circuit used in the present invention.

This is a detection circuit system in which an alternating excitation current is obtained directly from a DC power source using a transistor switch, without using a sinusoidal excitation power source, which has a complicated circuit and poor power utilization. The transistor 27 operates as an emitter follower with a small output resistance, and the transistor 28 is a transistor switch that performs normal on/off operation, and these are alternately turned on and off by a switching control pulse 29 with a duty ratio of 1:1. The capacitor 30 is inserted for the purpose of causing LC series resonance with the inductance of the pair of U-shaped cored coils 7.8 to reduce impedance. Further, the diode 31 has the effect of short-circuiting one end of the capacitor 30 to the ground voltage through the transistor 28 which is in an on state when the transistor 27 is off. Therefore, the LCR series-parallel circuit consisting of the capacitor 30, a pair of U-shaped cored coils 7.8, and a resistor is as follows:
This is equivalent to being driven by a rectangular voltage source with small output resistance. In this case, the excitation current becomes only the fundamental wave component of the switching control pulse 29 due to LC series resonance, and is equivalent to excitation by a sinusoidal excitation power source.

FIG. 7 shows an example in which torque was actually detected by the detection circuit of this embodiment. Around a ferromagnetic round bar with a diameter of 12 mm, a Ni layer of about 300 ml was uniformly coated using a plasma spraying method.
ttm thick, and a pair of U-shaped cored coils were arranged as shown in FIG. 1(a).

In addition, a U-shaped ferrite magnetic core is used as the U-shaped iron core,
The size of the void was 0.3 fin. This figure shows that characteristics with good linearity can be obtained. FIG. 8 shows an investigation of the dependence of the output on the rotational speed of the torque transmission shaft using an experimental device that combines an electric motor and a generator. This shows that the sensitivity is constant over 180 rpm from the rest state. FIG. 9 shows an investigation of instantaneous response, which is the most important aspect of the present invention. The detected symmetrical torque is the natural frequency of about 5 that occurs in the torque transmission shaft when the experimental equipment that combines an electric motor and a generator is in a steady rotation state of about 180 Orpm! This is a torque vibration of H1z. The amplitude of the torque vibration is approximately 3 Nm, and its period is approximately two periods per one rotation of the torque transmission shaft. The upper waveform is a reference output from a contact type strain gauge torque meter having a commutator, and the lower waveform is a torque output waveform according to this embodiment.

There is a basic agreement between both waveforms.

〔Effect of the invention〕

As described above, in the torque sensor according to the present invention, the torque detection sensitivity is constant regardless of the rotation speed of the torque transmission shaft,
It was shown that it has instantaneous response characteristics. Since the torque sensor according to the present invention has a structure that is inherently simple and easy to install,
It has great effects in various fields including motion control of robots, advanced control of engines and motors, etc.

[Brief explanation of drawings]

FIG. 1(a) is a perspective view showing one embodiment of the present invention.
Figure (b) is a graph showing the relationship between torque and self-inductance generated in the coil, Figure 2 is a detection circuit diagram, and Figure 3 is a graph showing the relationship between torque and self-inductance generated in the coil.
The figure is a detection circuit diagram with air gap compensation, Figures 4 and 5 are perspective views showing the positional relationship between the magnetostrictive layer and the detection coil, Figure 6 is a power supply circuit diagram used in the present invention, and Figure 7 is an application circuit diagram. Figure 8 is a diagram of the relationship between torque and the output of the detection circuit, Figure 8 is a rotation speed-output diagram under constant torque conditions, Figure 9 is an oscillograph diagram examining instantaneous response, and Figure 10 (a) is a diagram of the conventional sensor. The perspective view shown in FIG. 10(b) is a characteristic diagram of a conventional sensor. 1... Torque transmission shaft (shaft) 3... Magnetostrictive layer 7.8.21-24... Coil 14... Variable gain amplifier 16... Current detector 17... Rectifier circuit Fig. 1 (α) (b) Figure 2 Figure 4 Figure 6 Random rotation number (rpml Figure 9 #axis 1.5 N-m/dlv 5ms/dlv Inbuzi Torque Meter Tsudega ((To and Demonic Dzuri) 1 Fake 1000, Ousen ξde (1 Ritoru To J Rex 4 Sensor Type 2 Figure 10 (b) Solid Mighty Bird (Agitation)

Claims (3)

[Claims] (1) In a magnetostrictive torque sensor that detects torque applied to a shaft by utilizing an inverse magnetostrictive effect in a magnetostrictive layer provided on the surface of the shaft, the center line of the shaft is displayed on the surface of the shaft. A magnetostrictive torque sensor characterized in that it has a cylindrical shape with a rotational axis of , and a magnetostrictive layer is provided directly on the axis. (2) The magnetostrictive torque sensor according to claim (1), wherein the cylindrical magnetostrictive layer is formed by a thermal spraying method. (3) The magnetostrictive torque sensor according to claim (1), wherein the cylindrical magnetostrictive layer is formed by a plasma spraying method.