JPH06265422A - Magneto-strictive torque sensor - Google Patents

Abstract

PURPOSE:To control the flutuation, resulting from the magnetic directional property of each crystal grain, of torque detecting output to the minimum by applying the minuter crystal grain to that in a part between both the poles of the exciting coil or detecting coil of a torque trabsmitting shaft being a measuring object. CONSTITUTION:An exciting coil 12 and a detecting coil 13 whose distances between both poles are equally 5mm are arranged on the outer periphery of a torque transmitting shaft 11. The fluctuation of the output of the coil 13 while the torque transmitting shaft 11 rotated under the torque of 15kgf m given by three torque transmitting shafts makes one rotation is measured. The result of the output fluctuation plotted to the size of a crystal grain shows that when the diameter of the crystal grain exceeds 1/50 of the distance between poles, the fluctuation rate of output exceeds 10%FS (full scale), and the stable output is not obtained. Thus in order to carry out precise torque measurement, in the case where the distance between the poles is 5mm, the diameter of the crystal grain is required to be less than about 10mum. Namely, in order to keep the fluctuation of the output of torque sensor less than 1O%FS, the diameter of crystal grain shall be 1/50 of the doistance between poles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting a transmission torque of a rotary shaft, and more particularly to a non-contact type magnetostrictive torque sensor.

[0002]

2. Description of the Related Art A magnetostrictive torque sensor is used as a sensor for non-contactly detecting a torque applied to a torque transmission shaft of a rotary drive system in an industrial machine such as an electric motor or a machine tool or an automobile. In this method, an alternating magnetic field is applied to the shaft surface, and a change in magnetic permeability caused by the torque on the shaft surface is detected as an electric quantity. There are various types of magnetostrictive torque sensors, which use coils each having a U-shaped iron core for excitation and detection, and arrange these coils in the vicinity of the torque transmission shaft to be measured. A magnetic head type that detects changes in the permeability of the principal stress (± 45 ° with respect to the longitudinal direction of the shaft) that occurs on the surface, or a torque transmission shaft that is to be measured is easy to magnetize in a direction that is pre-tilted with respect to the longitudinal direction. It is known that magnetic anisotropy as an axis is given and an exciting solenoid coil and a permeability change solenoid coil are arranged in the vicinity thereof.

On the other hand, in terms of form, rotational power (engine,
Recently, a unit type (single type) torque sensor has been widely used by detecting the torque transmitted between the power and the load by detachably connecting the motor and the load to each other. .

[0004]

In the magnetic head type magnetostrictive torque sensor, the distance between the torque transmission shaft to be measured and the exciting coil, the detecting coil and the like has a great influence on the strength of the detection signal. If this interval changes during one rotation of the torque transmission shaft, the detection output fluctuates, and highly accurate torque detection becomes impossible. Therefore, in the conventional torque sensor, the positions of the torque transmission shaft and both coils are assembled very carefully and with high precision.

However, conventionally, even if the mechanical precision of the assembly is improved in this way, the phenomenon that the detection output slightly fluctuates cannot be avoided. The present invention has been made to solve such a problem, and an object thereof is to provide a torque sensor that stabilizes a detection output and enables highly accurate torque measurement.

[0006]

According to the present invention, which has been made to solve the above problems, an excitation coil and a detection coil having a U-shaped iron core are arranged around a rotary shaft, and a torque applied to the rotary shaft is set. In a magnetic head type magnetostrictive torque sensor that measures the transfer torque by detecting the change in the magnetic characteristics of the shaft material due to the distortion of the rotating shaft due to, the magnetic grains of at least the surface part of the metal material that constitutes the rotating shaft It is characterized in that the size is one-fifth or less of the distance between the poles of the exciting coil or the detecting coil.

[0007]

[Function] In the magnetostrictive torque sensor, the rotating shaft (torque transmission shaft) is magnetized by the magnetic flux between the two poles of the exciting coil, and the detection coil detects an asymmetric change in the magnetic characteristics of the ferrite phase of the shaft material between the two poles. . The metal material that is the material of the rotating shaft is generally polycrystalline, and the orientation of each crystal grain is usually random. Since the magnetic characteristics of each ferrite crystal grain (single crystal) depend on its orientation, when the number of crystal grains between the two poles of the exciting coil decreases, the magnetic characteristics of each crystal grain appear relatively large. Therefore, the torque transmission shaft as a whole exhibits magnetic directionality. Since this magnetic directivity varies from place to place, it appears as a fluctuation in the detected output when the torque transmission shaft rotates. Therefore, by setting the number of crystal grains between the two poles of the exciting coil to about 50 or more, the variation in the orientation of each crystal grain is averaged, and the difference between the locations can be almost ignored. Fluctuation can be suppressed. The same argument holds for the gap between the detection coils.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. In this embodiment, the magnetic head type magnetostrictive torque sensor is targeted, and the surface layer of the torque transmission shaft (500 from the surface)
An experiment was conducted to measure the relationship between the size of the ferrite crystal grains (within μm) and the fluctuation (during shaft rotation) of the torque detection output. The magnetic head type torque sensor is, as shown in FIG. 3A, a single yoke type excitation coil 12 and a detection coil 13 arranged on the outer periphery of a torque transmission shaft. Both poles 121 and 122
As shown in FIG. 3 (b), / 131 and 132 are arranged on the surface of the torque transmission shaft 11 so as to intersect with each other at 90 °, and one of them is arranged in the axial direction and the other is arranged in the rotational direction. Will be placed.

As shown in FIG. 3B, the adjacent poles 12
Torque transmission shaft 1 sandwiched between 1, 131, 122 and 132
Assuming that the areas of the surface of 1 are A, B, C, and D, these areas A, B, C, and D are magnetically coupled as shown in FIG. That is, the exciting coil 12
A magnetic path is formed by the two poles 121, 122 of the region A-region B and the route of the region C-region D, and the change of the magnetic potential at the intermediate point of both routes is detected by the two poles 131, 132 of the detection coil 13. To be done. As torque is applied to the torque transmission shaft 11, as shown in FIG. 3A, + is applied in the principal stress direction of the shaft surface (direction inclined by ± 45 ° with respect to the axial direction).
When the σ and −σ tensile (compressive) stresses are generated, the balance between both routes is lost, and the amount is detected by the detection coil 13 and converted into torque.

In the magnetic head type magnetostrictive torque sensor having such a structure, the exciting coil 12 and the detecting coil 1
In the regions A, B, C, D between the poles of No. 3, if the magnetic characteristics of the material (particularly the surface layer) of the torque transmission shaft 11 are not uniform, the detection coil is rotated during one rotation of the torque transmission shaft 11. The output from 13 varies. From the viewpoint of strength, the torque transmission shaft 11 is usually made of a quenching / tempering material of carbon steel or low alloy steel, but these materials are polycrystalline and the magnetic characteristics as a whole are individual. The magnetic properties of the crystal are added (in vector terms). Therefore, each coil 1
When the number of crystal grains in the portion sandwiched between the poles 121, 131, 122 and 132 of 2 and 13 decreases, the directionality of each crystal grain has a great influence on the characteristics as a whole.
Therefore, the relationship between the size of the crystal grains of the torque transmission shaft 11 and the fluctuation of the output was investigated as follows.

Carbon steel S25C and manganese steel SMn40 having a diameter of 36 mm were used as materials, and various heat treatments were applied to the grains to change the crystal grain size. These materials were machined into a precision round bar having a diameter of 35 mm to prepare the torque transmission shaft 11 of the magnetic head type torque sensor shown in FIG. Then, on the outer circumference of the torque transmission shaft 11, a gap between both poles 121,
The excitation coil 12 and the detection coil 13 in which the distances 122/131 and 132 are both 5 mm are arranged. The fluctuation of the output of the detection coil 13 during one rotation of the torque transmission shaft 11 was measured when the torque transmission shaft 11 was rotated by applying a torque of 15 kgf · m. FIG. 2 shows an example of how the detection output fluctuates during one rotation of the torque transmission shaft 11. The result of plotting the fluctuation of the output against the size of the crystal grain is as shown in FIG. In addition,
The ferrite crystal grain size is obtained by cutting a part of the surface after machining and measuring the surface layer portion of 500 μm or less from the surface. It can be seen from FIG. 1 that when the crystal grain size exceeds 1/50 of the inter-electrode distance, the output fluctuation rate exceeds 10% FS (full scale), and a stable output cannot be obtained. Therefore, in order to perform accurate torque measurement,
In the case of the distance between the electrodes (5 mm), the crystal grain size is about 10
It should be 0 μm or less.

As described above, since the output stability depends on the relative relationship between the size of the crystal grains in the surface layer of the shaft material and the distance between the poles, the size of the entire torque sensor changes and the exciting coil ( And / or if the interelectrode distance of the detection coil) changes, the allowed grain size also changes accordingly. From the above experimental results, it is understood that the crystal grain size should be 1/50 of the inter-electrode distance in order to suppress the fluctuation of the output of the torque sensor to 10% FS or less.

[0013]

In the magnetostrictive sensor according to the present invention, by making the crystal grains in the portion between the two poles of the excitation coil or the detection coil of the torque transmission shaft to be measured finer, the magnetic directionality of each crystal grain can be improved. Minimize the fluctuation of torque detection output caused by it. Therefore, a stable output can be obtained, and precise shaft transmission torque can be detected and measured.

[Brief description of drawings]

FIG. 1 shows a magnetic head type magnetostrictive torque sensor.
The graph which shows the fluctuation | variation of a torque output when changing the size of the crystal grain of the material of a torque transmission shaft.

FIG. 2 is a graph showing variations in the output of the detection coil during one rotation of the torque transmission shaft.

FIG. 3 is a perspective view showing a configuration of a magnetic head type magnetostrictive torque sensor which is an embodiment of the present invention (a), an explanatory view showing an arrangement of poles of an exciting coil and a detecting coil (b), and a magnetic path. 3C is a circuit diagram showing the configuration of FIG.

[Explanation of symbols]

11 ... Torque transmission shaft 12 ... Excitation coil 121, 122 ... Excitation coil pole 13 ... Detection coil 131, 132 ... Detection coil pole

Claims (1)

[Claims] 1. An excitation coil and a detection coil having a U-shaped iron core are arranged around the rotary shaft to detect a change in magnetic characteristics of the shaft material due to distortion of the rotary shaft due to torque applied to the rotary shaft. In a magnetic head type magnetostrictive torque sensor that measures the transmitted torque by doing so, the size of the crystal grains of at least the surface portion of the metal material forming the rotating shaft is set to 50 minutes of the distance between the poles of the exciting coil or the detecting coil. A magnetostrictive torque sensor characterized in that it is 1 or less.