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 metal substrate having the upper surface and a lower surface. The film-like strain detection device is mounted on the upper surface of the thin metal substrate through an adhesive, the lower surface is a mounting surface to the object to be measured, and a thin portion obtained by partially reducing plate thickness is formed on the lower surface of the thin metal substrate.SELECTED DRAWING: Figure 6

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 metal 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 metal substrate (10) via an adhesive (20), the lower surface (10b) serves as an attachment surface for the object to be measured, and a thin portion (11) that is partially thinned on the lower surface (10b) of the thin metal substrate (10).

[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 (part 1) 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] 10A and 10B are diagrams illustrating the coincidence of the center of gravity of the thin metal substrate and the resistor region. [Figure 6] 4 is a cross-sectional view (part 2) illustrating the strain gauge module according to the embodiment. FIG. [Figure 7] 2 is a bottom view illustrating the strain gauge module according to the embodiment. FIG. [Figure 8] 1 is a bottom view (part 1) illustrating variations in the shape of the thin portion. FIG. [Figure 9] 13 is a bottom view (part 2) illustrating variations in the shape of the thin portion. FIG. [Figure 10] FIG. 11 is a bottom view (part 3) illustrating variations in the shape of the thin portion. [Figure 11] This is the measurement result of the output of a film-type strain detection device (1). [Figure 12] This is the measurement result of the output of the film-type strain detection device (2). [Figure 13] This is the measurement result of the output of the film-type strain detection device (3). [Figure 14] This is the measurement result of the output of the film-type strain detection device (4). [Figure 15] This is the measurement result of the output of a film-type strain detection device (5). 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 (part 1) illustrating the 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 metal 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 metal substrate 10 is a member on which the film-shaped strain detection device 30 is disposed. In detail, the thin plate metal 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 metal substrate 10, and the lower surface 10b is a surface to be attached to an object to be measured.

[0013] Here, the thin metal substrate refers to a metal substrate having a thickness of 200 μm or less. The thickness of the thin metal 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. The thickness of the thin metal substrate 10 here refers to the thickness of the region other than the thin portion 11 described below.

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

[0015] The surface roughness Ra of the upper surface 10a of the thin plate metal substrate 10 is preferably 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 metal 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 metal substrate 10 on the film-shaped strain detection device 30, and the 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 material of the thin metal substrate 10 is preferably SUS (stainless steel / iron-based alloy) which has high hardness (easy propagation of strain) for transmitting strain, but is not limited thereto, and aluminum alloy, copper alloy, etc. may also be used. SUS is also preferable because it is easily available. The size of the thin metal substrate 10 is not particularly limited, but is larger than the size of the film-shaped strain detection device 30 in a plan view.

[0018] The film-shaped strain detection device 30 is mounted on the upper surface 10a of the thin metal 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.

[0019] 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 metal 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 the abnormal protrusion (spike), on the upper surface 10a of the thin plate metal 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 gap between the unevenness of the upper surface 10a of the thin plate metal substrate 10, is filled with the adhesive 20.

[0020] 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 metal 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 metal substrate 10, so that the strain of the thin plate metal substrate 10 can be transmitted to the film-shaped strain detection device 30 more efficiently.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] 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).

[0026] The resistor 32 may be made of a Cr mixed-phase film. Here, the Cr mixed-phase film is made of Cr, CrN, Cr 2 The Cr mixed-phase film may contain unavoidable 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.

[0027] 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.

[0028] 2, the strain gauge module 1 may have a resin part 36 covering the film-shaped strain detection device 30 on the thin plate metal 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 metal 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.

[0029] 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.

[0030] [Positional relationship between the thin metal substrate and the resistor area] The thin metal substrate 10 is preferably rectangular in plan view. By making the thin metal substrate 10 rectangular in plan view, the longitudinal strain can be detected with good sensitivity. In FIG. 1, the thin metal 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 metal substrate 10. That is, the straight line L1 is a line that divides the thin metal 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 metal substrate 10. That is, the straight line L2 is a line that divides the thin metal substrate 10 in half in the lateral direction. The intersection of the straight lines L1 and L2 passes through the center of gravity Gp of the thin metal 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 metal substrate 10 is the center of gravity of a rectangle shown in FIG. 1 without considering the thickness of the thin metal substrate 10.

[0031] 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 Gr of the resistor region R.

[0032] 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 metal substrate 10. Furthermore, in the strain gauge module 1, it is preferable that the center of gravity Gp of the thin plate metal substrate 10 and the center of gravity Gr of the resistor region R coincide with each other. In the present application, "the center of gravity of A and the center of gravity of B coincide with each other" includes not only the case where the center of gravity of A and the center of gravity of B coincide completely 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. In addition, 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.

[0033] Furthermore, the fact that the center of gravity Gp of the thin plate metal substrate 10 and the center of gravity Gr of the resistor region R coincide with each other means that, if the thin plate metal substrate 10 and the resistor region R are rectangular in plan view, the intersection of the diagonals of the thin plate metal 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 metal 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.

[0034] The center of gravity Gp of the thin plate metal substrate 10 is the point at which strain is most concentrated when the thin plate metal 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 metal 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 metal substrate 10 is not rectangular in plan view.

[0035] 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 metal 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 metal substrate 10 and the center of gravity Gr of the resistor region R completely coincide with each other.

[0036] An arrow D in FIG. 1 indicates the vibration propagation direction. When the thin plate metal substrate 10 is rectangular in plan view, it is preferable that the vibration propagation direction D and the longitudinal direction of the thin plate metal substrate 10 coincide. It is also preferable that the vibration propagation direction D and the grid direction of the resistors 32 formed in the resistor region R coincide. In other words, it is preferable that the longitudinal direction of the thin plate metal substrate 10 and the grid direction of the resistors 32 formed in the resistor region R coincide. This relationship can improve the detection sensitivity of distortion in the vibration propagation direction D.

[0037] [Positional relationship between thin metal substrate and thin part] Fig. 6 is a cross-sectional view (part 2) illustrating the strain gauge module according to this embodiment, showing a cross section along line BB in Fig. 1. Fig. 7 is a bottom view illustrating the strain gauge module according to this embodiment.

[0038] 6 and 7, a thin portion 11 recessed from the lower surface 10b toward the upper surface 10a is formed on the lower surface 10b of the thin metal substrate 10. In the example of Fig. 6 and Fig. 7, the thin portion 11 includes a first portion 11a, a second portion 11b, and a third portion 11c.

[0039] In a plan view, the first portion 11a is an elongated portion inclined with respect to the straight line L1. The second portion 11b is an elongated portion inclined with respect to the straight line L1 at an angle different from that of the first portion 11a. The first portion 11a and the second portion 11b intersect so as to pass through the center of gravity Gp of the thin plate metal substrate 10, forming, for example, an X-shape. The third portion 11c is formed at a position including the center of gravity Gp of the thin plate metal substrate 10. The third portion 11c is, for example, rectangular, but may be circular or elliptical.

[0040] The maximum depth of the thin portion 11 based on the lower surface 10b of the thin metal substrate 10 can be 10 percent or more of the thickness of the thin metal substrate 10. The maximum depth of the thin portion 11 based on the lower surface 10b of the thin metal substrate 10 can be 50 percent or less of the thickness of the thin metal substrate 10. The thin portion 11 can be formed by an appropriate method such as, for example, a corrosion method, an electrolytic polishing method, or a blasting method.

[0041] In the first portion 11a and the second portion 11b, the shape of a vertical cross section cut in a direction perpendicular to the longitudinal direction is, for example, rectangular, but may also be semicircular (U-shaped), triangular (V-shaped), trapezoidal, etc. In the third portion 11c, the shape of a vertical cross section cut along the straight line L1 or L2 is, for example, rectangular, but may also be semicircular (U-shaped), triangular (V-shaped), trapezoidal, etc.

[0042] It is preferable that the depth of the deepest part is approximately constant regardless of location in thin portion 11. For example, it is preferable that the depth of the deepest part of first portion 11a, the depth of the deepest part of second portion 11b, and the depth of the deepest part of third portion 11c in thin portion 11 are the same.

[0043] In a structure in which the film-shaped strain detection device 30 is bonded to the thin metal substrate 10, the sensitivity characteristics of the film-shaped strain detection device 30 may be attenuated. In the strain gauge module 1, by forming the thin portion 11 on the lower surface 10b of the thin metal substrate 10, the attenuated strain can be concentrated and thereby restored or amplified. 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.

[0044] The effect of recovering or amplifying the attenuated strain is obtained by forming a thin portion on the lower surface 10b of the thin plate metal substrate 10. Therefore, the shape of the thin portion for obtaining the above effect is not limited to the shape of the thin portion 11. However, from the viewpoint of further enhancing the above effect, it is preferable that the thin portion has an axisymmetric shape with respect to a straight line passing through the center of gravity Gp of the thin plate metal substrate 10 in a plan view.

[0045] Examples of the straight line passing through the center of gravity Gp of the thin plate metal substrate 10 include the straight line L1 and the straight line L2. The straight line passing through the center of gravity Gp of the thin plate metal substrate 10 is not limited to the straight line L1 and the straight line L2, but the above-mentioned effect can be particularly enhanced when the thin portion has a line-symmetric shape with respect to the straight line L1 parallel to the longitudinal direction of the thin plate metal substrate 10. The thin portion 11 has a line-symmetric shape with respect to the straight line L1 and the straight line L2.

[0046] In order to further enhance the above-mentioned effects, it is preferable that the thin portion 11 is formed at a position including the center of gravity Gp of the thin plate metal substrate 10 in a plan view, and that the resistor 32 includes a portion overlapping with the center of gravity Gp of the thin plate metal substrate 10. It is preferable that the center of gravity Gt1 of the thin portion 11 and the center of gravity Gp of the thin plate metal substrate 10 coincide with each other. It is particularly preferable that the center of gravity Gt1 of the thin portion 11, the center of gravity Gp of the thin plate metal substrate 10, and the center of gravity Gr of the resistor region R coincide with each other.

[0047] In order to further enhance the above-mentioned effects, the thin portion is preferably a combination of two or more patterns. For example, the thin portion 11 is a combination of three patterns: a first portion 11a which is a first pattern, a second portion 11b which is a second pattern, and a third portion 11c which is a third pattern.

[0048] Since the bottom layer of the strain gauge module 1 is the thin metal substrate 10, the bottom surface 10b of the thin metal 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.

[0049] 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 metal substrate 10 to the measurement object.

[0050] When adhering the strain gauge module 1 to the object to be measured, it is preferable to apply an adhesive to the entire lower surface 10b of the thin metal substrate 10 and fill the entire inside of the thin portion 11 with the adhesive. This prevents voids from being formed inside the thin portion 11, so that strain from the object to be measured can be efficiently transmitted to the thin metal substrate 10. Examples of adhesives used to adhere the strain gauge module 1 to the object to be measured include epoxy resins.

[0051] In addition, the thin metal 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 strain from the object to be measured to be efficiently transmitted to the thin metal substrate 10.

[0052] [Variations in thin and thick part shapes] 8 to 10 are bottom views illustrating variations in the shape of the thin portion. The shape of the thin portion may be the shape of thin portion 11 shown in Fig. 7 etc., the shapes of thin portions 12 to 14 shown in Fig. 8 to 10, or other shapes.

[0053] The strain gauge module 1A shown in FIG. 8 has the same structure as the strain gauge module 1, except that a thin portion 12 is formed instead of the thin portion 11. The thin portion 12 is a combination of two patterns including a first portion 12a and a second portion 12b. The first portion 12a has a substantially semicircular shape that draws an arc toward the straight line L1 side. The second portion 12b has a shape that is line-symmetrical to the first portion 12a with respect to the straight line L1. The first portion 12a and the second portion 12b each have a shape that is line-symmetrical with respect to the straight line L2. It is preferable that the center of gravity Gt2 of the thin portion 12 and the center of gravity Gp of the thin metal substrate 10 coincide with each other.

[0054] The strain gauge module 1B shown in FIG. 9 has the same structure as the strain gauge module 1, except that a thin portion 13 is formed instead of the thin portion 11. The thin portion 13 is a combination of three patterns including a first portion 13a, a second portion 13b, and a third portion 13c. The first portion 13a has a substantially semi-elliptical shape that draws an arc toward the straight line L1 side. The second portion 13b has a shape that is line-symmetrical with the first portion 13a with respect to the straight line L1. The third portion 13c has a substantially rectangular shape and is provided at a position that bridges the first portion 13a and the second portion 13b. The third portion 13c is formed at a position that includes the center of gravity Gp of the thin plate metal substrate 10. The thin portion 13 has a shape that is line-symmetrical with respect to the straight lines L1 and L2. It is preferable that the center of gravity Gt3 of the thin portion 13 and the center of gravity Gp of the thin plate metal substrate 10 coincide with each other.

[0055] The strain gauge module 1C shown in FIG. 10 has the same structure as the strain gauge module 1, except that a thin portion 14 is formed instead of the thin portion 11. The thin portion 14 is a combination of three patterns including a first portion 14a, a second portion 14b, and a third portion 14c. The first portion 14a has a substantially semicircular shape that draws an arc toward the periphery of the thin plate metal substrate 10. The second portion 14b has a shape that is line-symmetrical with the first portion 14a with respect to the straight line L1. The third portion 14c has a rectangular shape and a shape that is line-symmetrical with respect to the straight lines L1 and L2. The third portion 14c is formed at a position that includes the center of gravity Gp of the thin plate metal substrate 10. The thin portion 14 has a shape that is line-symmetrical with respect to the straight lines L1 and L2. It is preferable that the center of gravity Gt4 of the thin portion 14 and the center of gravity Gp of the thin plate metal substrate 10 coincide with each other.

[0056] [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.

[0057] 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 having the same structure as the strain gauge module 1 except that no thin portion was formed was fabricated (for convenience, referred to as strain gauge module 100), and the output of the film-shaped strain detection device 30 was measured when it was attached to the object to be measured.

[0058] Fig. 11 shows the measurement results. In Fig. 11, the measurement results of the film-shaped strain detection device 30 alone (device alone) are shown by a dashed line, and the measurement results of the strain gauge module 100 according to the comparative example are shown by a dashed line (no thin portion). In Fig. 11, 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. 11, the horizontal axis shows the elapsed time.

[0059] In Figure 11, when the dashed line showing the measurement result of the film-shaped strain detection device 30 alone (device alone) is compared with the dashed line showing the measurement result of the strain gauge module 100 of the comparative example (no thin section), it was found that the output of the strain gauge module 100 of the comparative example was attenuated by about 2% compared to the output of the film-shaped strain detection device 30 alone.

[0060] Next, a strain gauge module 1 having a thin portion 11 as shown in Fig. 6 and Fig. 7 was produced, and the output of the film-like strain detection device 30 was measured when it was attached to an object to be measured. The measurement results are shown in Fig. 12 by a solid line (thin portion 11). Note that Fig. 12 also shows the dashed line (device alone) and dashed line (without thin portion) shown in Fig. 11 for comparison. The same applies to the following Figs. 13 to 15.

[0061] Next, a strain gauge module 1A having a thin portion 12 as shown in FIG. 8 was fabricated, and the output of the film-shaped strain detection device 30 was measured when it was attached to an object to be measured. The measurement result is shown in FIG. 13 by a solid line (thin portion 12). A strain gauge module 1B having a thin portion 13 as shown in FIG. 9 was fabricated, and the output of the film-shaped strain detection device 30 was measured when it was attached to an object to be measured. The measurement result is shown in FIG. 14 by a solid line (thin portion 13). A strain gauge module 1C having a thin portion 14 as shown in FIG. 10 was fabricated, and the output of the film-shaped strain detection device 30 was measured when it was attached to an object to be measured. The measurement result is shown in FIG. 15 by a solid line (thin portion 14).

[0062] In Figs. 12 to 15, when the dashed lines (without thin portions) are compared with the solid lines (each thin portion), the solid lines (each thin portion) exceed the dashed lines (without thin portions). In other words, Figs. 12 to 15 show that when the thin portions 11 to 14 are formed, the output of the film-shaped strain detection device 30 is increased compared to when there are no thin portions. That is, it was confirmed that by forming a thin portion recessed from the lower surface 10b to the upper surface 10a on the lower surface 10b of the thin plate metal substrate 10, the strain (dashed line (without thin portions)) attenuated by the structure in which the film-shaped strain detection device 30 is bonded to the thin plate metal substrate 10 can be recovered or amplified, thereby improving the detection sensitivity.

[0063] 6 and 7, it is mainly the first portion 11a and the second portion 11b that contribute to improving the detection sensitivity. However, by forming the third portion 11c, the flow of the adhesive filled inside the thin portion 11 is improved, so that the adhesive can be filled evenly throughout the thin portion 11.

[0064] 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]

[0065] 1, 1A, 1B, 1C strain gauge module, 10 thin metal substrate, 10a upper surface, 10b lower surface, 11, 12, 13, 14 thin portion, 11a, 12a, 13a, 14a first portion, 11b, 12b, 13b, 14b second portion, 11c, 13c, 14c third portion, 20 adhesive, 30 film-shaped strain detection device, 31 substrate, 32 resistor, 33 wiring, 34, 35 terminal, 36 resin portion

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 metal substrate having an upper surface and a lower surface, the film-shaped strain detection device is mounted on the upper surface of the thin metal substrate via an adhesive, and the lower surface is used as an attachment surface for the measurement object; The thin metal substrate has a thin portion formed on the lower surface thereof, the thin metal substrate having a thickness partially reduced.

2. The strain gauge module according to claim 1 , wherein, in a plan view, the thin portion has an axisymmetric shape with respect to a straight line passing through a center of gravity of the thin metal substrate.

3. The film-like strain detection device includes a resistor region in which a resistor is formed, 3. The strain gauge module according to claim 1, wherein the thin portion is formed at a position including a center of gravity of the thin metal substrate in a plan view, and the resistor includes a portion overlapping with the center of gravity of the thin metal substrate.

4. 4. The strain gauge module according to claim 3, wherein the center of gravity of said thin portion, the center of gravity of said thin metal substrate, and the center of gravity of said resistor region are aligned.

5. 5. The strain gauge module according to claim 3, wherein the film-shaped strain detection device includes a base material made of polyimide, and the resistor is formed on the base material.

6. 6. The strain gauge module according to claim 1, wherein the maximum depth of the thin portion is 10 percent or more of the thickness of the thin metal substrate.

7. 7. The strain gauge module according to claim 1, wherein the thickness of the thin metal substrate in the region other than the thin portion is not less than 20 [mu]m and not more than 120 [mu]m.

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

9. 9. The strain gauge module according to claim 1, wherein the material of the thin metal substrate is stainless steel.

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

Images