JPH05281059A - Strain detecting device - Google Patents

Abstract

PURPOSE:To reduce dispersion being due to the temperature of a product in output by using a raw material approximate to a shaft material in the coefficient of thermal expansion for a bobbin material in which a detecting coil is set. CONSTITUTION:A bobbin 5A is formed of liquid crystal polymer having the coefficient of thermal expansion approximate to that of material for a driven shaft 1A. When their temperature changes, magnetic layers 3,4 adhering onto the driven shaft 1 are displaced in their absolute positions in the same direction by the thermal expansion of the driven shaft 1A mainly in the direction of a central shaft 2. Since the bobbin 5A expands thermally mainly in the same direction as that of the driven shaft 1A, detecting coils 10, 11 wound on the bobbin 5A are displaced in their absolute positions in the same direction as that of the bobbin 5A. Since the driven shaft 1A and the bobbin 5A are mutually approximate in the coefficient of thermal expansion, the magnetic layers 3,4 and the detecting coils 10, 11 are almost the same in the quantity and direction of displacement, and a relative position between the magnetic layer 3 and the detecting coil 10 and that between the magnetic layer 4 and the detecting coil 11 scarcely change even when their temperatures increase. Thus dispersion caused by the temperature of a product in output is little.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain detecting device,
More specifically, the present invention relates to a strain detection device for detecting strain when an external force is applied to a passive shaft such as a rotating shaft.

[0002]

2. Description of the Related Art For example, FIG. 4 is a diagram showing the structure of a magnetostrictive torque sensor previously proposed by the applicant. In FIG. 4, reference numeral 1 is a passive shaft composed of a rotary shaft, and 31, 32 are passive shafts 1.
Is a bearing that rotatably supports. The first and second magnetic layers 3 and 4 made of a high magnetic material are fixed on the outer peripheral surface of the passive shaft 1 at intervals.

A plurality of elongated first magnetic layers 3 are formed in the +45 degree direction with respect to the central axis 2 of the passive axis 1, and a second magnetic layer 4 is formed with a plurality of elongated lines in the −45 degree direction with respect to the central axis 2. There is. In addition, shields 40, 4 are provided on the outer circumferences of the magnetic layers 3, 4.
There is a cylindrical bobbin 5 made of engineering plastic in which 1 is insert-molded, and detection coils 11 and 10 are wound around this bobbin 5.

As shown in FIG. 5, the shields 40 and 41 are provided with notches so that the resin can flow during insert molding. The cutouts that cut off the ring in FIG. 5 are for coil wiring. The coil ends of the detection coils 10 and 11 are connected to lead wires 34 and led to a detection circuit (not shown) as shown in FIG. 6 as a cross section taken along the line AA of FIG.

A magnetic focusing layer 33 as a yoke is arranged around the bobbin 5 around which the detection coils 10 and 11 are wound.
A shield 35 is arranged on the outer side thereof, and these are integrally housed in a case 37. The bearing 31 is the passive shaft 1
It is press-fitted in close contact with the step provided on the
Is press-fitted into the case 38a.

A case 37 containing the detection coils 10 and 11
In order to reduce the relative position error with the magnetic layers 3 and 4, the cases 38a and 3 are preloaded by the wave washer 42 so that the end surface of the bobbin 5 is in close contact with the bearing 31.
8b, the cases 38a and 38b are fixed with screws. Reference numeral 50 is a rubber-like grommet for supporting the lead wire 34 and shielding it from the external environment.

Next, the operation will be described. When a torque is applied to the passive shaft 1 from the outside, a tensile force is generated in one of the magnetic layers 3 and 4, and a compressive force is generated in the other, which causes strain. When this strain occurs, the magnetic permeability changes, and the magnetic permeability changes in the opposite direction depending on the tensile force and the compressive force. The detection coils 10 and 11 detect a change in magnetic permeability of the magnetic layers 3 and 4 as a change in magnetic impedance, and a detection circuit (not shown) receives the outputs of the detection coils 10 and 11 and receives a distortion of the passive shaft 1. The detection voltage corresponding to the quantity is output.

[0008]

Since the conventional strain detecting device is constructed as described above, the thermal expansion coefficient of the passive shaft 1 and that of the bobbin 5 made of engineering plastic are greatly different from each other, so that the temperature rises. Then, the relative positions of the magnetic layers 3 and 4 on the passive shaft 1 and the bobbin 5, that is, the detection coils 10 and 11 are deviated, the inductance in the detection coils 10 and 11 changes, and the output is output even if torque is not applied to the passive shaft 1. There was a problem that it would occur.

The present invention has been made to solve the above problems, and provides a strain detecting device capable of preventing the output from fluctuating because the relative position of the bobbin and the magnetic layer changes due to the temperature. With the goal.

[0010]

In the strain detecting apparatus of the present invention, the material of the bobbin around which the detection coil is wound is a material such as a liquid crystal polymer having a thermal expansion coefficient close to that of the passive shaft material or the same material as the passive shaft material. ..

[0011]

In the strain detecting device according to the present invention, the relative positions of the magnetic layer fixed on the passive shaft and the detecting coil wound around the bobbin are not easily influenced by temperature, and the output variation due to the temperature of the product is small.

[0012]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the same reference numerals 2-4, 1 as those in FIG.
0, 11, 31-35, 37, 38, 41, 42, 50
The part is the same as the conventional example, and the description thereof is omitted. Further, the passive shaft 1A is the same as the passive shaft 1 of FIG.
4 correspond to the bobbins 5 in FIG. 4, respectively, and the passive shaft 1A and the bobbin 5A have the same structure as that of the conventional example, except that their mutual thermal expansion coefficients differ from those of the conventional example.

The cylindrical bobbin 5A is made of a liquid crystal polymer in which the shield 41 is insert-molded and which has a thermal expansion coefficient close to that of the material of the passive shaft 1A. In FIG. 4, the shield 40 that partitions the detection coils 10 and 11 is provided, but when the relative position displacement is small, the magnetic flow is stable even if the temperature rises, so the shield 40 is used in the first embodiment. It becomes unnecessary.

When the temperature changes, the thermal expansion of the passive shaft 1A mainly in the direction of the central axis 2 causes the magnetic layers 3 and 4 fixed on the passive shaft 1A to be displaced in absolute positions in the same direction. On the other hand, since the bobbin 5A also thermally expands mainly in the same direction, the bobbin 5A
The detection coils 10 and 11 wound around the coil displace the absolute position in the same direction. Since the passive shaft 1A and the bobbin 5A have similar thermal expansion coefficients, the magnetic layers 3, 4 and the detection coils 10, 1
The amount of displacement and the direction of displacement are substantially the same as those of No. 1 and the relative positions of the magnetic layer 3 and the detection coil 10 and between the magnetic layer 4 and the detection coil 11 hardly change even when the temperature rises. Therefore, passive axis 1
Unless the torque is applied to A, the detection coils 10 and 11 produce no output.

Example 2. FIG. 2 is a cross-sectional view showing the configuration of the strain detecting apparatus of another embodiment, and the same or corresponding portions as those in the first embodiment are designated by the same reference numerals as those in FIG. Next, parts different from the first embodiment will be described. The material of the bobbin 5A is the passive shaft 1
It has the same coefficient of thermal expansion as that of the material A. When a non-magnetic material is used as the material of the passive shaft 1A, the bobbin may be made of the same material as the passive shaft.

However, since it is difficult to insert-mold the shield 41 when the shaft member is made of metal, the shield 41 is divided into two pieces and mounted on the shield pieces 41a and 41b as shown in FIG. As shown in FIG. 2, when the same material is used, the bobbin 5A has a slightly different shape, and the bobbin 5A has a wide contact surface with the shield 41 so that the shield 41 can be easily supported. Since other operations are the same as those in the first embodiment, the description thereof will be omitted.

[0017]

As described above, according to the present invention, since the bobbin containing the detection coil is made of a material having a thermal expansion coefficient close to that of the shaft material, the relative position of the magnetic layer and the detection coil depends on the temperature. It is not easily affected and has the effect of less variation in output due to product temperature.

[Brief description of drawings]

FIG. 1 is a sectional view showing a strain detector according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a strain detecting device according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of a shield of another embodiment.

FIG. 4 is a sectional view of a conventional strain detection device.

FIG. 5 is a plan view of a shield.

6 is a cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

 1A Passive shaft 3,4 Magnetic layer 5A Bobbin 10,11 Detection coil 31,32 Bearing 33 Magnetic focusing layer (yoke) 34 Lead wire 35 Shield 37 Case 38a, 38b Case 41 Shield 42 Wave washer

Claims (1)

[Claims] 1. A passive shaft which receives an external force, a magnetic layer which is fixed on the outer peripheral surface of the passive shaft, and which is made of a soft magnetic material having a high magnetic permeability and a predetermined magnetic constant, and a magnetic layer wound around a bobbin. A detection coil arranged on the outer periphery of the layer for detecting a change in magnetic permeability of the magnetic layer caused by an external force applied to the passive shaft, and a shield and a yoke arranged around the detection coil. With a case stored,
A strain detecting device in which this case is preloaded in the axial direction with respect to the passive shaft so that the relative position of the detection coil and the magnetic layer on the passive shaft does not shift, and the passive coil is used as a material of the bobbin. A strain detecting device characterized by using a material having a coefficient of thermal expansion close to that of the material of the shaft.