Strain gauge module

Abstract

To provide a strain gauge module that is excellent in detection sensitivity.SOLUTION: A strain gauge module is mounted to an object to be measured, and is configured to include a film-like strain detection device having a terminal on an upper surface to detect a strain generated in the object to be measured, and a thin substrate having the upper surface and a lower surface. The film-like strain detection device is mounted on the upper surface of the thin substrate through an adhesive, the lower surface is a mounting surface to the object to be measured, and the thin substrate is made of an amorphous material or a nanocrystal material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a strain gauge module. [Background technology]

[0002] As a film-like device, for example, a strain gauge having a resistor formed on a substrate such as a flexible polyimide is known (see, for example, Patent Document 1). In such a film-like device, there is a demand for improving the detection sensitivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-185346 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in view of the above-mentioned points, and has an object to provide a strain gauge module with excellent detection sensitivity. [Means for solving the problem]

[0005] This strain gauge module (1) is composed of a film-shaped strain detection device (30) that is attached to an object to be measured and has terminals (34, 35) on its upper surface for detecting strain occurring in the object to be measured, and a thin plate substrate (10) having an upper surface (10a) and a lower surface (10b), in which the film-shaped strain detection device (30) is mounted on the upper surface (10a) of the thin plate substrate (10) via an adhesive (20) and the lower surface (10b) serves as an attachment surface for the object to be measured, and the thin plate substrate (10) is made of an amorphous material or a nanocrystalline material.

[0006] The reference symbols in parentheses are given for ease of understanding, are merely examples, and are not intended to be limiting of the embodiments shown in the drawings. Effect of the Invention

[0007] According to the disclosed technique, a strain gauge module with excellent detection sensitivity can be provided. [Brief description of the drawings]

[0008] [Figure 1] 1 is a top view illustrating a strain gauge module according to an embodiment of the present invention; [Diagram 2] 1 is a cross-sectional view illustrating a strain gauge module according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a diagram illustrating the relationship between surface roughness Ra and the thickness of an adhesive. [Figure 4] FIG. 4 is a diagram illustrating a resistor region. [Diagram 5] 11A and 11B are diagrams illustrating the coincidence of the centers of gravity of the thin plate substrate and the resistor region. [Figure 6] 1 shows the measurement results of the output of a film-shaped strain detection device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] (Strain gauge module) Fig. 1 is a top view illustrating a strain gauge module according to the present embodiment. Fig. 2 is a cross-sectional view illustrating a strain gauge module according to the present embodiment, showing a cross section along line AA in Fig. 1. Fig. 3 is a diagram for explaining the surface roughness Ra and the thickness of the adhesive. Fig. 4 is a diagram for explaining the resistor region.

[0011] 1 and 2, the strain gauge module 1 includes a thin plate substrate 10, an adhesive 20, and a film-shaped strain detection device 30. The strain gauge module 1 is attached to an object to be measured, and the film-shaped strain detection device 30 can detect strain occurring in the object to be measured.

[0012] The thin plate substrate 10 is a member on which the film-shaped strain detection device 30 is disposed. In detail, the thin plate substrate 10 has an upper surface 10a and a lower surface 10b. The film-shaped strain detection device 30 is mounted on the upper surface 10a of the thin plate substrate 10, and the lower surface 10b is a surface to be attached to an object to be measured.

[0013] Here, the thin plate substrate refers to a substrate having a thickness of 200 μm or less. The thickness of the thin plate substrate 10 is preferably 20 μm or more and 120 μm or less, more preferably 20 μm or more and 80 μm or less, and even more preferably 20 μm or more and 50 μm or less.

[0014] By making the thickness of the thin plate substrate 10 20 μm or more, the distortion can be stably detected. By making the thickness of the thin plate substrate 10 120 μm or less, the distortion can be detected with good sensitivity. Furthermore, by making the thickness of the thin plate substrate 10 thinner, the distortion can be detected with even better sensitivity. Furthermore, if the thickness of the thin plate substrate 10 is 20 μm or more and 80 μm or less, the thin plate substrate 10 can be easily fixed to a curved measurement object. If the thickness of the thin plate substrate 10 is 20 μm or more and 50 μm or less, the thin plate substrate 10 can be even more easily fixed to a curved measurement object.

[0015] The thin plate substrate 10 preferably has flatness with no waviness or warpage over the entire surface. The thin plate substrate 10 also preferably has a surface roughness Ra of 3 μm to 20 μm, more preferably 3 μm to 10 μm, and even more preferably 3 μm to 5 μm. By setting the surface roughness Ra of the upper surface 10a of the thin plate substrate 10 to 3 μm to 20 μm, it is possible to reduce the effect of the surface roughness Ra of the upper surface 10a of the thin plate substrate 10 on the film-like strain detection device 30, and strain can be easily and accurately measured.

[0016] Here, the surface roughness Ra is a type of numerical value that indicates surface roughness, and is called the arithmetic mean roughness. Specifically, as shown in FIG. 3, it is the arithmetic mean of the absolute value of the height change within a reference length L measured from the surface, which is the average line.

[0017] The thin plate substrate 10 is made of an amorphous material or a nanocrystalline material. Specifically, the material of the thin plate substrate 10 is glass, which is an example of an amorphous material. Alternatively, the material of the thin plate substrate 10 is an amorphous alloy, which is an example of a nanocrystalline material. In particular, the amorphous alloy is mainly made of Fe-based, Ni-based, or cobalt-based materials currently used, which contain 15 to 30 atomic % of boron, carbon, silicon, phosphorus, etc., and has excellent characteristics in terms of strength, corrosion resistance, and soft magnetic properties, and is used in a wide range of environments. Amorphous materials such as these glasses and amorphous alloys are known to have properties that avoid strain attenuation caused by crystal structures and recover or amplify attenuated strain. The thin plate substrate 10 using such materials is formed by an appropriate method such as a corrosion method, an electrolytic polishing method, or a mechanical cutting method. The size of the thin plate substrate 10 is not particularly limited, but is larger than the size of the film-shaped strain detection device 30 in a planar view.

[0018] In a structure in which the film-shaped strain detection device 30 is bonded to the thin plate substrate 10, the sensitivity characteristics of the film-shaped strain detection device 30 may be attenuated due to the crystal structure (grain boundaries). In the strain gauge module 1, by using an amorphous material or a nanocrystalline material as the material for the thin plate substrate 10, the properties of the material can be utilized to avoid strain attenuation caused by the crystal structure, or to recover or amplify attenuated strain. This makes it possible to suppress the characteristic fluctuation of the film-shaped strain detection device 30 and realize a highly sensitive strain gauge module 1 with excellent stability.

[0019] The film-shaped strain detection device 30 is mounted on the upper surface 10a of the thin plate substrate 10 via an adhesive 20. For example, an epoxy resin or the like can be used as the adhesive 20. The flexural modulus of the adhesive 20 can be, for example, 3 GPa or more and 20 GPa or less. The adhesive 20 may contain a filler as necessary. When the adhesive 20 contains a filler, the filler contained may be an inorganic filler or an organic filler. When the adhesive 20 contains an inorganic filler, the filler diameter is preferably 5 μm or less, and when the adhesive 20 contains an organic filler, the filler diameter is preferably 10 μm or less.

[0020] The thickness T of the adhesive 20 is preferably 30 μm or less. If the thickness T of the adhesive 20 is 30 μm or less, the distortion of the thin plate substrate 10 can be efficiently transmitted to the film-like distortion detection device 30. As shown in FIG. 3, the thickness T of the adhesive 20 is the distance from the tip of the convex portion shown by the solid line, excluding abnormal protrusions (spikes), on the upper surface 10a of the thin plate substrate 10 to the lower surface of the base material 31. The unevenness shown by the dashed line in FIG. 3 is a virtual image. The portion U in FIG. 3, i.e., the gaps between the unevenness on the upper surface 10a of the thin plate substrate 10, is filled with the adhesive 20.

[0021] It is preferable that the entire lower surface of the film-shaped strain detection device 30 is adhered to the upper surface 10a of the thin plate substrate 10 by the adhesive 20. In this case, it is preferable that the variation in thickness of the adhesive 20 is ±5 μm or less. This allows the entire film-shaped strain detection device 30 to be held flat on the upper surface 10a of the thin plate substrate 10, so that the strain of the thin plate substrate 10 can be transmitted to the film-shaped strain detection device 30 more efficiently.

[0022] The film-shaped strain detection device 30 has a substrate 31, a resistor 32, wiring 33, and terminals 34 and 35. There are no particular limitations on the size of the film-shaped strain detection device 30, but from the viewpoint of miniaturizing the strain gauge module 1, it is preferable that the film-shaped strain detection device 30 is also small, and for example, the substrate 31 can be in a square or rectangular shape with one side measuring approximately 1.5 mm to 2 mm.

[0023] The substrate 31 is a flexible member that serves as a base layer for forming the resistor 32. There is no particular limit to the thickness of the substrate 31, and it can be appropriately selected depending on the purpose. The substrate 31 can be formed from an insulating resin film such as a PI (polyimide) resin.

[0024] The resistor 32 is a thin film formed on the upper surface of the substrate 31, and is a sensing part that generates a resistance change when strained. The resistor 32 may be formed directly on the upper surface of the substrate 31, or may be formed on the upper surface of the substrate 31 via another layer. There is no particular limit to the thickness of the resistor 32, and it can be appropriately selected depending on the purpose, but it is, for example, 0.05 μm or more and 50 μm or less.

[0025] The resistor 32 has a structure in which multiple elongated parts are arranged at regular intervals with their longitudinal direction in the same direction (the direction perpendicular to the line AA in the example of FIG. 1), and the ends of adjacent elongated parts are alternately connected, folding back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated parts is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction of the line AA in the example of FIG. 1).

[0026] The resistor 32 can be made of, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 32 can be made of a material containing at least one of Cr and Ni. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0027] A Cr mixed-phase film may be used as the resistor 32. Here, the Cr mixed-phase film is a film in which Cr, CrN, Cr2N, etc. are mixed. The Cr mixed-phase film may contain inevitable impurities such as chromium oxide. When the Cr mixed-phase film is used as the resistor 32, the film-shaped strain detection device 30 can be made highly sensitive and compact.

[0028] The terminals 34 and 35 are formed on the upper surface near the end of the wiring 33. The terminals 34 and 35 are connected to both ends of the resistor 32 via the wiring 33 made of copper or the like, and are formed, for example, in a rectangular shape in a plan view. The terminals 34 and 35 are a pair of electrodes for outputting a change in the resistance value of the resistor 32 caused by distortion. The terminals 34 and 35 are made of, for example, copper or the like. A gold film or the like may be laminated on the surface of the copper or the like.

[0029] 2, the strain gauge module 1 may have a resin part 36 covering the film-shaped strain detection device 30 on the thin plate substrate 10. The resin part 36 can be formed, for example, so as to expose a part or all of the terminals 34 and 35 of the film-shaped strain detection device 30. By providing the resin part 36 covering the film-shaped strain detection device 30 on the thin plate substrate 10, the mechanical strength of the terminals 34 and 35 of the film-shaped strain detection device 30 can be improved, and the environmental resistance (humidity, gas) of the film-shaped strain detection device 30 can be improved.

[0030] In order to suppress the output (offset) of the film-shaped strain detection device 30 when no strain is applied, the resin part 36 is preferably made of a material that does not contain filler or that contains inorganic or organic filler of 3 μm or less. The resin part 36 is preferably made of a material that has a hardness suitable for strain propagation of D90 to A15 and a tensile strength of 0.3 MPa to 10 MPa. Examples of such materials include thermosetting or photosetting silicone resins and epoxy resins. By using such a low-stress resin as the material for the resin part 36, the effect of covering the film-shaped strain detection device 30 with the resin part 36 on its characteristics (sensitivity) can be reduced.

[0031] [Positional relationship between thin plate substrate and resistor area] The thin plate substrate 10 is preferably rectangular in plan view. By making the thin plate substrate 10 rectangular in plan view, the longitudinal distortion can be detected with good sensitivity. In FIG. 1, the thin plate substrate 10 is rectangular in plan view, and a straight line L1 indicates a line passing through the midpoints of the opposing short sides of the thin plate substrate 10. That is, the straight line L1 is a line that divides the thin plate substrate 10 in half in the longitudinal direction. Also, a straight line L2 indicates a line that passes through the midpoints of the opposing long sides of the thin plate substrate 10. That is, the straight line L2 is a line that divides the thin plate substrate 10 in half in the short direction. The intersection of the straight lines L1 and L2 passes through the center of gravity Gp of the thin plate substrate 10 in plan view. The center of gravity here is the center of gravity in plan view, that is, the center of gravity of a plane figure. For example, the center of gravity Gp of the thin plate substrate 10 is the center of gravity of a rectangle shown in FIG. 1 without considering the thickness of the thin plate substrate 10.

[0032] The film-shaped strain detection device 30 has a resistor region R on its upper surface. As shown in Fig. 4, the resistor region R is a rectangular region in a plan view on the upper surface of the substrate 31 where the resistor 32 is formed. The resistor region R is the smallest rectangular region that can be drawn so as to include all of the resistor 32. Gr shown in Fig. 4 indicates the center of gravity of the resistor region R.

[0033] As shown in Fig. 5, in the strain gauge module 1, it is preferable that the resistor 32 includes a portion overlapping with the center of gravity Gp of the thin plate substrate 10. Furthermore, in the strain gauge module 1, it is preferable that the center of gravity Gp of the thin plate substrate 10 and the center of gravity Gr of the resistor region R coincide with each other. In this application, "the center of gravity of A and the center of gravity of B coincide" includes not only the case where the center of gravity of A and the center of gravity of B completely coincide with each other in a plan view, but also the case where the deviation between the center of gravity of A and the center of gravity of B is within a range of 50 µm. Furthermore, the direction of deviation may be arbitrary, and it is sufficient that the center of gravity of B is located within a radius of 50 µm from the center of gravity of A.

[0034] Furthermore, the fact that the center of gravity Gp of the thin plate substrate 10 and the center of gravity Gr of the resistor region R coincide with each other means that, if the thin plate substrate 10 and the resistor region R are rectangular in plan view, the intersection of the diagonals of the thin plate substrate 10 coincides with the intersection of the diagonals of the resistor region R. The allowable amount of deviation between the intersection of the diagonals of the thin plate substrate 10 and the intersection of the diagonals of the resistor region R is the same as in the above case. In other words, if the amount of deviation between the intersections of the two diagonals is within a range of 50 μm, the intersections of the two diagonals are considered to coincide with each other.

[0035] The center of gravity Gp of the thin plate substrate 10 is the point at which strain is most concentrated when the thin plate substrate 10 is attached to an object to be measured and receives strain from the object to be measured. Therefore, by making the center of gravity Gp of the thin plate substrate 10 coincident with the center of gravity Gr of the resistor region R, the strain detection sensitivity of the film-shaped strain detection device 30 can be improved. In other words, a strain gauge module 1 with excellent detection sensitivity can be realized. This effect can also be obtained when the thin plate substrate 10 is not rectangular in plan view.

[0036] From the viewpoint of further improving the strain detection sensitivity in the film-shaped strain detection device 30, it is preferable that the center of gravity Gr of the resistor region R be located within a radius of 20 μm of the center of gravity Gp of the thin plate substrate 10, it is more preferable that the center of gravity Gr of the resistor region R be located within a radius of 10 μm, it is even more preferable that the center of gravity Gr of the resistor region R be located within a radius of 5 μm, and it is particularly preferable that the center of gravity Gp of the thin plate substrate 10 and the center of gravity Gr of the resistor region R completely coincide with each other.

[0037] An arrow D in Fig. 1 indicates the vibration propagation direction. When the thin plate substrate 10 is rectangular in plan view, it is preferable that the vibration propagation direction D coincides with the longitudinal direction of the thin plate substrate 10. It is also preferable that the vibration propagation direction D coincides with the grid direction of the resistors 32 formed in the resistor region R. In other words, it is preferable that the longitudinal direction of the thin plate substrate 10 coincides with the grid direction of the resistors 32 formed in the resistor region R. This relationship can improve the detection sensitivity of distortion in the vibration propagation direction D.

[0038] Since the bottom layer of the strain gauge module 1 is the thin plate substrate 10, the bottom surface 10b of the thin plate substrate 10 can be easily fixed to the object to be measured using a liquid or film (tape) adhesive or pressure-sensitive adhesive. The thickness of the adhesive or pressure-sensitive adhesive can be, for example, about 25 μm.

[0039] That is, the strain gauge module 1 is easy to attach to the measurement object because the bottom layer is not made of flexible resin (polyimide, etc.) as in conventional strain gauges. Also, since polyimide is a poorly adhesive material, a special adhesion method (heating and pressure) is required to attach it to the measurement object, but no special adhesion method is required to attach the thin plate substrate 10 to the measurement object.

[0040] In addition, the thin plate substrate 10 is preferably attached to the object to be measured in a substantially flat state with an adhesive having a thickness within a range of about 3 to 100 μm and a thickness variation of about ±5 μm, for example. This allows the distortion from the object to be measured to be efficiently transmitted to the thin plate substrate 10.

[0041] [Changes in detection sensitivity] In the strain gauge module 1, the change in detection sensitivity of the film-shaped strain detection device 30 was examined.

[0042] First, the output of the film-shaped strain detection device 30 was measured when the film-shaped strain detection device 30 was directly attached to the object to be measured. Next, as a comparative example, a strain gauge module was fabricated (for convenience, referred to as strain gauge module 100) having the same structure as the strain gauge module 1 except that a metal substrate was used for the thin plate substrate 10, and the output of the film-shaped strain detection device 30 was measured when attached to the object to be measured. Next, a strain gauge module 1 was fabricated using a glass substrate for the thin plate substrate 10, and the output of the film-shaped strain detection device 30 was measured when attached to the object to be measured.

[0043] Fig. 6 shows the measurement results. In Fig. 6, the measurement results of the film-shaped strain detection device 30 alone are shown by the dashed line 30 alone, the measurement results of the strain gauge module 100 according to the comparative example are shown by the solid line 100, and the measurement results of the strain gauge module 1 are shown by the dashed line 1. In Fig. 6, the vertical axis shows the amount of change in the value (for convenience, referred to as output) obtained by analog / digital conversion of the resistance value of the film-shaped strain detection device 30, with the output increasing toward the top of the vertical axis. In Fig. 6, the horizontal axis shows the elapsed time.

[0044] In FIG. 6, when the measurement result of the film-shaped strain detection device 30 alone (dashed line 30 alone) is compared with the measurement result of the strain gauge module 100 (solid line 100), it is found that the output of the strain gauge module 100 is attenuated by about 2% compared to the film-shaped strain detection device 30 alone. In contrast, it is found that the output of the film-shaped strain detection device 30 is increased in the strain gauge module 1 compared to the strain gauge module 100. In other words, it was confirmed that by using a glass substrate as the thin plate substrate 10, the attenuated strain (solid line 100) when a metal substrate is used can be recovered or amplified compared to the strain when a metal substrate is not used (dashed line 30 alone), thereby improving the detection sensitivity. When an Fe-based amorphous alloy substrate was used as the thin plate substrate 10, the results were almost the same as when a glass substrate was used as the thin plate substrate 10.

[0045] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0046] 1 strain gauge module, 10 thin plate substrate, 10a upper surface, 10b lower surface, 20 adhesive, 30 film-shaped strain detection device, 31 substrate, 32 resistor, 33 wiring, 34, 35 terminal, 36 resin part

Claims

1. The film-shaped strain detection device is attached to a measurement object and has a terminal on an upper surface thereof for detecting a strain occurring in the measurement object, and is configured to include a thin plate substrate having an upper surface and a lower surface, the film-shaped strain detection device is mounted on the upper surface of the thin plate substrate via an adhesive, and the lower surface is used as an attachment surface for the measurement object; The thin plate substrate is a strain gauge module made of an amorphous material or a nanocrystalline material.

2. 2. The strain gauge module according to claim 1, wherein the thin plate substrate has a thickness of 20 μm or more and 120 μm or less.

3. 3. The strain gauge module according to claim 1, wherein the surface roughness Ra of the upper surface of the thin plate substrate is 3 μm or more and 20 μm or less.

4. 4. The strain gauge module according to claim 1, wherein the thin plate substrate is made of glass.

5. 4. The strain gauge module according to claim 1, wherein the material of the thin plate substrate is an amorphous alloy.

6. 6. The strain gauge module according to claim 5, wherein the material of the thin plate substrate is an Fe-based amorphous alloy.

7. The strain gauge module according to claim 1 , wherein the thin plate substrate has a rectangular shape in a plan view.

8. The film-like strain detection device includes a resistor region in which a resistor is formed, The strain gauge module according to claim 1 , wherein the resistor includes a portion overlapping the center of gravity of the thin plate substrate.

9. 9. The strain gauge module according to claim 8, wherein the center of gravity of the thin plate substrate coincides with the center of gravity of the resistor region.

10. 10. The strain gauge module according to claim 8, wherein the film-shaped strain detection device includes a base material made of polyimide, and the resistor is formed on the base material.

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