JP7342982B2 - strain sensor - Google Patents

Description

The technology disclosed herein relates to a strain sensor.

Patent Document 1 discloses a strain sensor that is manufactured by mixing and molding an epoxy resin with carbon nanofiller that has been subjected to metal surface treatment. The strain sensor expands in response to an external force applied to the strain sensor. Strain is detected by the change in resistance value caused by stretching of the strain sensor.

JP2012-52864A

In a strain sensor, it is desirable that the gauge factor is high and that the resistance value gradually changes depending on the strain. In this specification, a technology is provided in which the gauge factor is high and the resistance value can gradually change in accordance with strain.

The strain sensor disclosed herein includes a first slit, an insulating substrate that is elastically deformable in a direction in which the first slit opens, and a first slit disposed on one side of the first slit. and a conductive member, which is disposed on the other side of the first slit, contacts the first conductive member when the first slit is closed, and contacts the first conductive member when the first slit is open. a second conductive member spaced apart from the first conductive member; and a first conductive particle layer disposed on each of a pair of mutually opposing inner surfaces of the first slit, the first conductive member , the first slit may be electrically connected to the second conductive member via the first conductive particle layer in an open state.

In this configuration, when an external force is applied to the strain sensor in the direction in which the first slit opens, the insulating substrate elastically deforms depending on the magnitude of the external force. When the insulating substrate is deformed and the first slit is opened, the first conductive member and the second conductive member are separated. As a result, the first conductive member and the second conductive member are electrically connected via the first conductive particle layer arranged on the inner surface of the first slit. This changes the current path between the first conductive member and the second conductive member. As the first slit opens, the distance between the pair of inner surfaces of the first slit gradually increases. As a result, the position where the first conductive particle layer disposed on one of the pair of inner surfaces of the first slit and the first conductive particle layer disposed on the other inner surface are in contact with each other is the first conductive particle layer. It gradually moves from the center of the slit to the ends. As a result, the current path between the first conductive member and the second conductive member gradually changes depending on how the first slit opens, that is, the deformation of the insulating substrate. As a result, the resistance value between the first conductive member and the second conductive member can be gradually changed as the strain gradually increases. Further, the current path, that is, the resistance value, between the first conductive member and the second conductive member can be greatly changed between a state in which the first slit is closed and a state in which the first slit is open. I can do it. Thereby, the gauge factor can be increased.

The first conductive particle layer may include fibrous particles.

In this configuration, when the first slit is closed, the fibrous particles arranged on one of the pair of inner surfaces of the first slit are located between the fibrous particles arranged on the other inner surface. By entering, they are in contact with each other. According to this configuration, when the first slit is open, the fibrous particles arranged on one of the pair of inner surfaces of the first slit form a gap between the fibrous particles arranged on the other inner surface. By entering, the first conductive particles arranged on one inner surface and the first conductive particles arranged on the other inner surface can be brought into contact. As a result, it is possible to prevent the first conductive particle layers on the pair of inner surfaces of the first slit from immediately separating when the first slit opens. Thereby, the resistance value between the first conductive member and the second conductive member can be gradually changed.

In a state where the first slit is closed, the pair of inner surfaces may be arranged without any gap with the first conductive particle layer interposed therebetween.

In this configuration, when the first slit is closed, that is, when no external force is applied to the strain sensor, the conductive particle layer disposed on one of the pair of inner surfaces of the first slit and the conductive particle layer disposed on the other inner surface of the pair of inner surfaces of the first slit are It is possible to bring the entire surface into contact with the conductive particle layer arranged on the inner surface. According to this configuration, the range of change in resistance value between the first conductive member and the second conductive member with respect to strain can be increased.

The insulating substrate may further have a second slit, and may be elastically deformable in a direction in which the second slit opens. The strain sensor further includes a third conductive member disposed on one side of the second slit, and a third conductive member disposed on the other side of the second slit, and the third conductive member is disposed on the other side of the second slit. 3. A fourth conductive member that is in direct contact with the third conductive member and is separated from the third conductive member while the second slit is open, and a pair of mutually opposing inner surfaces of the second slit, respectively. and a second conductive particle layer disposed in the conductive particle layer. The first conductive member and the second conductive member may be connected in parallel with the third conductive member and the fourth conductive member.

A combination of a first slit, a first conductive member, a second conductive member, and a first conductive particle layer, and a combination of a second slit, a third conductive member, a fourth conductive member, and a second conductive particle layer In a situation where either combination of and does not function properly, distortion can be detected by a combination that functions properly.

The insulating substrate may further have a third slit, and may be elastically deformable in a direction in which the third slit opens. The strain sensor further includes a fifth conductive member disposed on one side of the third slit, and a fifth conductive member disposed on the other side of the third slit. a sixth conductive member that is in direct contact with the fifth conductive member and is separated from the fifth conductive member while the third slit is open; and a pair of mutually opposing inner surfaces of the third slit, respectively. and a third conductive particle layer disposed in the conductive particle layer. The first conductive member and the second conductive member may be connected in series with the fifth conductive member and the sixth conductive member.

For example, if many conductive particles are arranged in the conductive particle layer within the slit, even if the slit is opened, the conductive particle layers arranged on each of the pair of inner surfaces are difficult to separate from each other. As a result, the change in resistance value with respect to strain changes becomes smaller. A combination of a first slit, a first conductive member, a second conductive member, and a first conductive particle layer, and a combination of a third slit, a fifth conductive member, a sixth conductive member, and a third conductive particle layer By arranging and in series, it is possible to detect strain in the other combination even if the change in resistance to strain is small in one of the above two combinations. can do.

The strain sensor may further include a cover that is disposed on the insulating substrate and covers the first slit, the first conductive member, and the second conductive member.

According to this configuration, it is possible to suppress a change in resistance value due to soiling of at least one of the first slit, the first conductive member, and the second conductive member.

FIG. 2 is a plan view of the strain sensor of the first embodiment. FIG. 3 is an enlarged plan view of the slit and its surroundings for explaining the deformation of the strain sensor. FIG. 3 is an enlarged plan view of the periphery of the slit for explaining the deformation of the strain sensor following FIG. 2; FIG. 4 is an enlarged plan view around the slit for explaining the deformation of the strain sensor following FIG. 3 . FIG. 3 is a diagram for explaining a method for manufacturing a strain sensor. FIG. 6 is a diagram for explaining the method of manufacturing a strain sensor following FIG. 5. FIG. FIG. 7 is a diagram for explaining the method of manufacturing a strain sensor following FIG. 6 . FIG. 8 is a diagram for explaining the method of manufacturing a strain sensor following FIG. 7; FIG. 9 is a diagram for explaining the method of manufacturing a strain sensor following FIG. 8 . A vertical cross-sectional view of a strain sensor. An example of experimental results showing the relationship between strain and resistance value. FIG. 3 is a plan view of a strain sensor according to a second embodiment.

(First example)
The strain sensor 10 of this embodiment will be explained with reference to FIGS. 1 to 11. The strain sensor 10 is attached to a flexible object, such as a fiber, and is used to detect the strain of the object. Note that the object to which the strain sensor 10 is attached may be an object other than a flexible object such as a fiber. As shown in FIG. 1, the strain sensor 10 includes a substrate 12, a pair of conductive members 16 and 18, a slit 14, and conductive particle layers 20 and 22 (see FIGS. 3 and 4). Note that, as shown in FIG. 10, the strain sensor 10 includes covers 30 and 32, but they are not shown in FIG. 1.

The substrate 12 is made of polyurethane and has a flat plate shape. The substrate 12 has a rectangular flat plate shape. Note that the shape of the substrate 12 may be any suitable shape depending on the position and condition of use. For example, the substrate 12 is not limited to a rectangular shape, and may be polygonal, circular, etc., and may not have a flat plate shape. Further, the material of the substrate 12 is not limited to polyurethane, and a material having elasticity and insulating properties that corresponds to the strain assumed in the object to which the strain sensor 10 is applied may be used.

A pair of conductive members 16 and 18 are placed on the surface of the substrate 12. The pair of conductive members 16 and 18 are arranged on the same straight line. The pair of conductive members 16 and 18 are arranged at the center of the substrate 12 in the lateral direction (that is, the vertical direction in FIG. 1). The pair of conductive members 16 and 18 are arranged parallel to the longitudinal direction of the substrate 12 (ie, the left-right direction in FIG. 1). The pair of conductive members 16 and 18 have the same shape. The pair of conductive members 16 and 18 are arranged continuously and are in contact with each other at their boundaries. The pair of conductive members 16 and 18 are made using carbon nanotubes.

A slit 14 is arranged in the substrate 12 at the boundary between the pair of conductive members 16 and 18. The slit 14 penetrates the substrate 12 from the front surface to the back surface. The slit 14 is arranged at the center of the substrate 12 in the lateral direction. In the lateral direction of the substrate 12, the length of the slit 14 is longer than the length of the pair of conductive members 16 and 18. A pair of conductive members 16 and 18 are arranged at the center of the slit 14 in the lateral direction of the substrate 12 . As shown in FIG. 3, conductive particle layers 20 and 22 are disposed on each of the pair of opposing inner surfaces 14a and 14b of the slit 14, respectively. The conductive particle layers 20, 22 are thin layers made of carbon nanotubes. In FIGS. 3 and 4, carbon nanotubes constituting the conductive particle layers 20 and 22 are schematically shown in an enlarged manner. In the conductive particle layers 20 and 22, a large number of fibrous carbon nanotubes are arranged on the pair of inner surfaces 14a and 14b.

In the slit 14, when the substrate 12 is not deformed, the pair of inner surfaces 14a and 14b facing each other are arranged with the conductive particle layers 20 and 22 in between, and the conductive particle layers 20 and 22 are Fully in contact. Therefore, when the substrate 12 is not deformed, the pair of inner surfaces 14a and 14b are not in complete contact with each other, but the slit 14 is similar to the state of the slit 14 when the substrate 12 is not deformed. This is called the closed state.

A conductive wire 52 is electrically connected to the conductive member 16 . A conductive wire 54 is electrically connected to the conductive member 18 . A resistance value measuring device 50 is connected to the conductive wires 52 and 54. The resistance value measuring device 50 applies a voltage to the conductive wire 52 and measures the resistance value of the current path composed of the conductive members 16 and 18 and the slit 14 of the strain sensor 10. The resistance value measuring device 50 supplies the measured resistance value to a control device (not shown). The control device performs calculations to convert the resistance value into strain. The control device stores in advance a program, a table, etc. for executing calculations for converting resistance values into strain.

(Deformation of strain sensor)
Modifications of the strain sensor 10 will be described with reference to FIGS. 2 to 4. The strain sensor 10 is used to detect strain when an object is deformed by a force applied to the object in the direction indicated by arrow F in FIG. 1 (hereinafter referred to as "direction F"). As shown in FIG. 2, when the substrate 12 is not deformed, the slit 14 is closed. In this state, current flows linearly through the conductive members 16, 18, as shown by arrow 100. Note that the arrow 100 simply represents the direction of current.

As shown in FIG. 3, when the strain of the object increases, the substrate 12 is elastically deformed in the direction in which the slit 14 opens. The slit 14 is widest at the center of the substrate 12 in the lateral direction. The degree of opening of the slit 14 gradually becomes smaller toward both ends of the substrate 12 in the lateral direction. By opening the slit 14, the conductive member 16 and the conductive member 18 are separated. When the amount of deformation of the substrate 12 is small, that is, when the strain of the object is small, the distance between the pair of inner surfaces 14a and 14b is small. In this state, the conductive particle layer 20 on the inner surface 14a and the conductive particle layer 22 on the inner surface 14b are in contact with each other at both ends of the substrate 12 in the transverse direction. Specifically, the fibrous carbon nanotubes of the conductive particle layer 20 and the fibrous carbon nanotubes of the conductive particle layer 22 are in contact with each other. As a result, in the state of FIG. 3, as shown by an arrow 102, the current passes from the conductive member 16 through the conductive particle layer 20, and reaches a position midway in the lateral direction of the substrate 12 of the slit 14, that is, the conductive It flows toward the conductive particle layer 22 at the position where the conductive particle layer 20 and the conductive particle layer 22 are in contact with each other.

The wider the slit 14 opens, the more the position where the conductive particle layer 20 and the conductive particle layer 22 are in contact moves toward the end of the substrate 12 in the lateral direction. Therefore, the wider the slit 14 opens, the longer the current path extends and the resistance value of the strain sensor 10 increases.

As shown in FIG. 4, when the strain of the object becomes even greater than in the state shown in FIG. The slit 14 is wide open until the state is reached. In this state, as shown by an arrow 104, current passes from the conductive member 16 through the conductive particle layer 20, and flows from the end of the slit 14 in the transverse direction of the substrate 12 toward the conductive particle layer 22.

As mentioned above, as the strain of the object increases, the slit 14 gradually opens. In this configuration, the current path gradually moves toward the end of the slit 14 as the slit 14 opens. As a result, the current path gradually becomes longer as the slit 14 opens. FIG. 11 shows experimental results using the strain sensor 10. In this experiment, the strain and resistance in a state where the strain sensor 10 is deformed by applying a force in the direction F are specified. The horizontal axis in FIG. 11 represents strain, and the vertical axis represents resistance value R.

In the strain sensor 10, when the strain exceeds a predetermined value, the resistance value R can be gradually increased as the strain increases. The state before the strain exceeds a predetermined value is a state in which the slit 14 is closed, and the state after the strain exceeds a predetermined value is a state in which the slit 14 is open. According to the strain sensor 10, it is possible to realize a continuous change in resistance value in response to an increase in strain. Furthermore, the current path is significantly different between the state in which the slit 14 is closed and the state in which it is open. As a result, the resistance value changes greatly between the closed state and the open state of the slit 14. According to this configuration, the sensitivity to strain can be increased and the gauge factor can be increased, compared to a configuration in which the current path changes by extending the conductive member according to the strain.

(Manufacturing method of strain sensor)
A method for manufacturing the strain sensor 10 will be described with reference to FIGS. 5 to 8. First, as shown in FIG. 5, a substrate 12 is prepared. Next, as shown in FIG. 6, a mask 200 with openings for the conductive members 16 and 18 is placed on the surface of the substrate 12, and a carbon nanotube dispersion is applied in the direction of the arrow 202. The mask 200 is, for example, a film made of heat-resistant polyimide. Next, the dispersion is dried by heat treatment, and the mask 200 is removed. As a result, a pair of conductive members 16 and 18 are formed simultaneously.

Next, as shown in FIG. 7, a slit 14 is formed by inserting a cutting blade 204 into the boundary between the pair of conductive members 16 and 18. Next, as shown in FIG. 8, the carbon nanotube dispersion liquid is dropped toward the slit 14 in the direction of the arrow 206. As a result, the carbon nanotubes enter the slit 14 and adhere to the pair of inner surfaces 14a and 14b. As a result, conductive particle layers 20 and 22 are formed. The strain sensor 10 is produced by wiping off the dispersion and drying it. The concentration of carbon nanotubes in the dispersion for forming the conductive particle layers 20 and 22 may be lower than the concentration of carbon nanotubes in the dispersion for forming the pair of conductive members 16 and 18.

As shown in FIG. 9, in the strain sensor 10, covers 30 and 32 may be placed on each of the front and back surfaces of the substrate 12. The covers 30 and 32 are polyurethane films. The covers 30, 32 are bonded to the substrate 12 at their peripheral edges by thermocompression bonding.

FIG. 10 shows a cross section of the center in the lateral direction of the substrate 12 of the strain sensor 10 with the covers 30 and 32 attached. As shown in FIG. 10, the covers 30 and 32 cover the entire pair of conductive members 16 and 18 and the slit 14. As shown in FIG. Thereby, it is possible to prevent dirt from adhering to the pair of conductive members 16 and 18 and the slit 14. This can prevent the resistance value of the strain sensor 10 from varying due to dirt.

(Second example)
With reference to FIG. 12, a strain sensor 510 according to a second embodiment will be described. Strain sensor 510 includes a substrate 512, conductive members 516, 518, 520, 522, 524, multiple slits 514a, multiple slits 514b, and multiple slits 514c. The substrate 512 has a similar configuration to the substrate 12.

Conductive members 516, 518, 520, 522, and 524 are placed on the surface of the substrate 512. The conductive member 516 branches into three conductive members 520, 522, and 524. Conductive members 520, 522, 524 are connected in parallel. Conductive members 520, 522, and 524 each extend parallel to the longitudinal direction of substrate 512. Conductive members 520, 522, 524 are each connected to conductive member 518. Each of conductive members 516, 518, 520, 522, 524 is made similarly to conductive members 16, 18.

At an intermediate position of the conductive member 520, a plurality of slits 514a are lined up at intervals in the longitudinal direction of the substrate 512. Similarly, at an intermediate position of the conductive member 522, a plurality of slits 514b are arranged at intervals in the longitudinal direction of the substrate 512, and at an intermediate position of the conductive member 524, a plurality of slits 514c are arranged on the substrate. 512 are lined up at intervals from each other in the longitudinal direction. Each slit 514a, 514b, 514c has a similar configuration to the slit 14. A conductive particle layer similar to the conductive particle layers 20 and 22 is arranged on the inner surface of each pair of slits 514a, 514b, and 514c.

When the substrate 512 is not deformed, the conductive member 520 is connected across the plurality of slits 514a. Similarly, the conductive member 522 is connected across the plurality of slits 514b, and the conductive member 524 is connected across the plurality of slits 514c.

Conductive member 516 is connected to conductive wire 52 and conductive member 518 is connected to conductive wire 54.

Below, among the plurality of slits 514a, the slit 514a arranged at the end on the conductive member 516 side will be referred to as slit 514a1, the slit 514 arranged next to slit 514a1 will be referred to as slit 514a2, and among the plurality of slits 514b, The following description focuses on the slit 514b arranged at the end on the conductive member 516 side as a slit 514b1.

Conductive members 520a and 520b, which are part of the conductive member 520, are arranged on each side of the slit 514a1. Conductive members 520b and 520c, which are part of the conductive member 520, are arranged on each side of the slit 514a2. Conductive members 522a and 522b, which are part of the conductive member 522, are arranged on each side of the slit 516a1.

Conductive members 520a, 520b are connected in parallel with conductive members 522a, 522b. Conductive members 520a, 520b, and 520c are connected to each other in series.

When strain occurs in the object and the strain sensor 510 is deformed, each of the slits 514a, 514b, and 514c opens. For example, if the conductive particle layer disposed on the inner surface of the slit 514a1 is insufficient and the slit 514a1 opens, the conductive members 520a and 520b may not be electrically conductive. According to the strain sensor 510, even in a situation where the combination of the conductive particles 520a, 520b and the conductive particle layer arranged on the inner surface of the slit 514a1 does not function properly, the strain sensor 510 is arranged in parallel with the conductive members 520a, 520b. Strain can be detected using conductive members 522a, 522b.

Further, for example, if there are many conductive particle layers arranged on the inner surface of the slit 514a1, even if the slit 514a1 is opened, the current path from the conductive member 520a to the conductive member 520b does not change significantly. According to the strain sensor 510, even in a situation where the resistance value in the combination of the conductive members 520a, 520b and the conductive particle layer arranged on the inner surface of the slit 514a1 does not change significantly, the conductive particles layer arranged in series with the conductive members 520a, 520b. Strain can be detected using changes in resistance values in the conductive members 520b, 522c and the slit 514a1.

(correspondence)
The slit 514a1 is an example of a "first slit," the slit 514b1 is an example of a "second slit," and the slit 514a2 is an example of a "third slit." The conductive member 520a is an example of a "first conductive member," the conductive member 520b is an example of a "second conductive member," and the conductive member 522a is an example of a "third conductive member." , the conductive member 522b is an example of a "fourth conductive member", the conductive member 520b is an example of a "fifth conductive member", and the conductive member 520c is an example of a "fifth conductive member". be.

Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims as filed. Furthermore, the techniques illustrated in this specification or the drawings can achieve multiple objectives simultaneously, and achieving one of the objectives has technical utility in itself.

<Modified example>
At least a portion of the conductive members 16, 18, 516, 518, 520, 522, 524 may be made of a conductive material other than carbon nanotubes.

There is no limit to the number of slits 514a, 514b, and 514c in the second embodiment. For example, any one of slits 514a, 514b, and 514c may include only one slit. Alternatively, any one of the plurality of slits 514a, the plurality of slits 514b, and the plurality of slits 514c may not be arranged. For example, while the strain sensor 510 includes a plurality of slits 514a, it may not include a plurality of slits 514b and a plurality of slits 514c. In this configuration, the conductive member connected in parallel to the conductive member 520 may not be arranged.

At least one of the covers 30, 32 may not be provided.

10: strain sensor, 12: substrate, 14: slit, 14a, 14b: inner surface, 16, 18: conductive member, 20, 22: conductive particle layer, 30, 32: cover

Claims (6)

an insulating substrate having a first slit and elastically deformable in a direction in which the first slit opens;
a first conductive member disposed on one side of the first slit;
is disposed on the other side of the first slit, contacts the first conductive member when the first slit is closed, and contacts the first conductive member when the first slit is open. a second conductive member spaced apart;
a first conductive particle layer disposed on each of a pair of mutually opposing inner surfaces of the first slit,
The first conductive member is a strain sensor that is electrically connected to the second conductive member via the first conductive particle layer while the first slit is open. The strain sensor according to claim 1, wherein the first conductive particle layer includes fibrous particles. 3. The strain sensor according to claim 1, wherein when the first slit is closed, the pair of inner surfaces are arranged with no gap between them with the first conductive particle layer in between. The insulating substrate is
Furthermore, it has a second slit,
the second slit is elastically deformable in an opening direction;
The strain sensor further includes:
a third conductive member disposed on one side of the second slit;
The third conductive member is disposed on the other side of the second slit, is in direct contact with the third conductive member when the second slit is closed, and is in direct contact with the third conductive member when the second slit is open. a fourth conductive member spaced apart from the sexual member;
a second conductive particle layer disposed on each of a pair of mutually opposing inner surfaces of the second slit,
The first conductive member and the second conductive member are connected in parallel to the third conductive member and the fourth conductive member, according to any one of claims 1 to 3. Strain sensor. The insulating substrate is
Furthermore, it has a third slit,
The third slit is elastically deformable in an opening direction,
The strain sensor further includes:
a fifth conductive member disposed on one side of the third slit;
The fifth conductive member is disposed on the other side of the third slit, is in direct contact with the fifth conductive member when the third slit is closed, and is in direct contact with the fifth conductive member when the third slit is open. a sixth conductive member spaced apart from the sexual member;
a third conductive particle layer disposed on each of a pair of mutually opposing inner surfaces of the third slit,
The first conductive member and the second conductive member are connected in series with the fifth conductive member and the sixth conductive member, according to any one of claims 1 to 4. Strain sensor. Any one of claims 1 to 5, further comprising a cover disposed on the insulating substrate and covering the first slit, the first conductive member, and the second conductive member. Strain sensor described in.

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