Strain gauge, sensor module, bearing mechanism

Abstract

To provide a strain gauge which enables strain in a plurality of directions to be highly accurately detected.SOLUTION: The present strain gauge comprises: a flexible substrate made of resin; a functional layer formed directly on one side of the substrate and formed from metal, alloy, or a metal compound; and a plurality of resistance parts formed in linear shape directly on one side of the functional layer and formed from a film including Cr, CrN, and Cr2 N, and composed mainly of α-Cr. The functional layer has the function of promoting the crystal growth of the α-Cr and the function of depositing a film composed mainly of the α-Cr. The thickness of each of the resistance parts is 0.05 μm to 2 μm inclusive, and the thickness of the functional layer is 1 nm to 100 nm inclusive, with the resistance parts intersecting in the same plane and electrically connected to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a strain gauge, a sensor module, and a bearing mechanism. [Background technology]

[0002] A strain gauge is known that is attached to an object to detect strain in the object. The strain gauge includes a resistor that detects strain, and the resistor is formed on a substrate made of, for example, insulating resin.

[0003] It is also possible to detect strain in multiple directions by stacking multiple strain gauges so that their grid directions intersect with each other (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-31326 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a plurality of strain gauges are stacked so that their grid directions intersect with each other, measurement errors occur due to misalignment during stacking.

[0006] The present invention has been made in view of the above points, and has an object to provide a strain gauge that can detect strain in multiple directions with high accuracy. [Means for solving the problem]

[0007] This strain gauge has a flexible resin substrate, a functional layer formed from a metal, alloy, or metal compound directly on one side of the substrate, and a plurality of resistor portions, primarily composed of α-Cr, formed linearly from a film containing Cr, CrN, and CrN directly on one side of the functional layer, where the functional layer has the function of promoting crystal growth of the α-Cr and forming a film primarily composed of α-Cr, the thickness of each resistor portion being 0.05 μm or more and 2 μm or less, the thickness of the functional layer being 1 nm or more and 100 nm or less, and the resistor portions cross on the same plane to be conductive to each other. [Effects of the Invention]

[0008] According to the disclosed technology, it is possible to provide a strain gauge that can accurately detect strain in multiple directions. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 3] FIG. 10 is a schematic diagram illustrating a sensor module according to a second embodiment. [Figure 4] 10A to 10C are schematic views illustrating a method of using a sensor module according to a second embodiment. [Figure 5] FIG. 10 is a plan view illustrating a strain gauge according to a third embodiment. [Figure 6] FIG. 10 is a schematic diagram illustrating a sensor module according to a fourth embodiment. [Figure 7] FIG. 10 is a perspective view illustrating a bearing mechanism according to a fifth embodiment. [Figure 8] FIG. 10 is a cross-sectional view illustrating a bearing mechanism according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0011] First Embodiment Fig. 1 is a plan view illustrating a strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, taken along line AA in Fig. 1. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30 (resistance portions 31 and 32), and terminal portions 41, 42, 43, and 44.

[0012] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 30 of the substrate 10 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 30 of each portion is provided is referred to as the one side or upper side, and the surface on which the resistor 30 is not provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing an object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

[0013] The substrate 10 is an insulating member that serves as a base layer for forming the resistor 30 and the like, and has flexibility. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of the substrate 10 of 5 μm to 200 μm is preferable in that it can reduce strain sensitivity errors of the resistor 30.

[0014] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0015] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina, for example.

[0016] However, if the substrate 10 does not need to be flexible, the substrate 10 may be made of materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite ceramics (CaTiO3, BaTiO3), etc.

[0017] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strained. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer.

[0018] The resistor 30 includes resistive portions 31 and 32. In other words, the resistor 30 is a general term for the resistive portions 31 and 32, and is referred to as the resistor 30 when there is no need to particularly distinguish between the resistive portions 31 and 32. For convenience, the resistive portions 31 and 32 are shown in a matte finish in FIG. 1 .

[0019] The resistor portion 31 is a thin film formed linearly on the upper surface 10a of the substrate 10 with its longitudinal direction directed in the X direction. The resistor portion 32 is a thin film formed linearly with its longitudinal direction directed in the Y direction. The resistor portions 31 and 32 are orthogonal to each other on the same plane and are electrically connected to each other. The resistor portions 31 and 32 can be patterned, for example, so as to intersect at approximately the center of their respective longitudinal directions.

[0020] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. 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).

[0021] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0022] The thickness of the resistor 30 is not particularly limited and can be selected appropriately depending on the purpose, but can be, for example, approximately 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less is even more preferable because it reduces film cracks and warpage from the substrate 10 caused by internal stress in the film constituting the resistor 30. The width of the resistor 30 is not particularly limited and can be selected appropriately depending on the purpose, but can be, for example, approximately 0.1 μm to 1000 μm (1 mm).

[0023] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50 mass% or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, however, it is preferable that the resistor 30 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0024] The terminal portion 41 extends from one end of the resistor portion 31 and is formed in a generally circular shape, wider than the resistor portion 31, in a plan view. The terminal portion 43 extends from the other end of the resistor portion 31 and is formed in a generally circular shape, wider than the resistor portion 31, in a plan view. The terminal portions 41 and 43 are a pair of electrodes for outputting a change in the resistance value of the resistor portion 31 caused by strain to the outside. For example, a flexible substrate or a lead wire for external connection is joined to the terminal portions 41 and 43. The upper surfaces of the terminal portions 41 and 43 may be coated with a metal having better solderability than the terminal portions 41 and 43. Although the resistor portion 31 and the terminal portions 41 and 43 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. The planar shapes of the terminal portions 41 and 43 are not limited to a circular shape and may be rectangular or the like.

[0025] The terminal portion 42 extends from one end of the resistor portion 32 and is formed in a generally circular shape in a plan view, wider than the resistor portion 32. The terminal portion 44 extends from the other end of the resistor portion 32 and is formed in a generally circular shape in a plan view, wider than the resistor portion 32. The terminal portions 42 and 44 are a pair of electrodes for outputting a change in the resistance value of the resistor portion 32 caused by strain to the outside. For example, a flexible substrate or lead wire for external connection is joined to the terminal portions 42 and 44. The upper surfaces of the terminal portions 42 and 44 may be coated with a metal that has better solderability than the terminal portions 42 and 44. Although the resistor portion 32 and the terminal portions 42 and 44 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. The planar shape of the terminal portions 42 and 44 is not limited to a circular shape and may be rectangular, etc.

[0026] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41 to 44. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the terminal portions 41 to 44.

[0027] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0028] In strain gauge 1, resistor 31 detects strain in the X direction as a change in resistance value and can output the change from a pair of electrodes, terminals 41 and 43. Resistor 32 detects strain in the Y direction as a change in resistance value and can output the change from a pair of electrodes, terminals 42 and 44.

[0029] However, the resistor portion 31 and the resistor portion 32 being perpendicular to each other on the same plane as shown in Figure 1 is merely an example, and the resistor portion 31 and the resistor portion 32 may be formed in a straight line and intersect on the same plane. In this case, the resistor portion 31 and the resistor portion 32 can detect strain in their respective longitudinal directions. For example, the resistor portion 31 can be formed in a straight line with its longitudinal direction aligned in the X direction, and the resistor portion 32 can be formed in a straight line with its longitudinal direction tilted 45 degrees relative to the X direction.

[0030] It should be noted that, based on the strain detected by the resistance portion 31 and the strain detected by the resistance portion 32, the strain in a direction different from the longitudinal direction of the resistance portions 31 and 32 can be calculated.

[0031] To manufacture the strain gauge 1, first, a substrate 10 is prepared, and then the resistor 30 and terminal portions 41 to 44 having a planar shape as shown in Fig. 1 are formed on the upper surface 10a of the substrate 10. The material and thickness of the resistor 30 and terminal portions 41 to 44 are as described above. The resistor 30 and terminal portions 41 to 44 can be integrally formed from the same material.

[0032] The resistor 30 and the terminal portions 41 to 44 can be formed, for example, by depositing a film by magnetron sputtering using a target made of a material capable of forming the resistor 30 and the terminal portions 41 to 44, and then patterning the film by photolithography. The resistor 30 and the terminal portions 41 to 44 may be deposited by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like instead of magnetron sputtering.

[0033] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-form a functional layer having a thickness of about 1 nm to 100 nm on the upper surface 10a of the substrate 10 by, for example, conventional sputtering as a base layer before forming the resistor 30 and the terminal portions 41 to 44. After the resistor 30 and the terminal portions 41 to 44 are formed on the entire upper surface of the functional layer, the functional layer is patterned into the planar shape shown in FIG.

[0034] In this application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper layer, the resistor 30. The functional layer preferably also has a function of preventing oxidation of the resistor 30 due to oxygen or moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the resistor 30. The functional layer may also have other functions.

[0035] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the resistor 30, especially when the resistor 30 contains Cr.

[0036] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the resistor 30, and can be appropriately selected depending on the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Examples of suitable metals include one or more metals selected from the group consisting of Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), alloys of any of the metals in this group, and compounds of any of the metals in this group.

[0037] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0038] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0039] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0040] There are no particular restrictions on the combination of the material of the functional layer with the material of the resistor 30 and the terminal portions 41 to 44, and it can be selected appropriately depending on the purpose. For example, it is possible to use Ti for the functional layer and form a Cr mixed phase film containing α-Cr (alpha chromium) as the main component for the resistor 30 and the terminal portions 41 to 44.

[0041] In this case, for example, the resistor 30 and the terminal portions 41 to 44 can be formed by magnetron sputtering using a target made of a material capable of forming a Cr mixed phase film and introducing Ar gas into a chamber. Alternatively, the resistor 30 and the terminal portions 41 to 44 can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas into a chamber together with Ar gas.

[0042] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0043] When the resistor 30 is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the resistor 30, preventing oxidation of the resistor 30 due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the resistor 30. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0044] In this way, by providing a functional layer below the resistor 30, it is possible to promote crystal growth of the resistor 30, and to produce a resistor 30 consisting of a stable crystalline phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material constituting the functional layer into the resistor 30, it is possible to improve the gauge characteristics of the strain gauge 1.

[0045] After forming the resistor 30 and the terminal portions 41 to 44, a cover layer 60 that covers the resistor 30 and exposes the terminal portions 41 to 44 is provided on the upper surface 10a of the substrate 10 as needed, thereby completing the strain gauge 1. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41 to 44, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41 to 44, and then heating and curing the resin.

[0046] Thus, in the strain gauge 1, the resistance portions 31 and 32 are each formed linearly and intersect on the same plane to be electrically connected to each other. As a result, by sequentially connecting the resistance portions 31 and 32 to a bridge circuit, it is possible to detect the strain in the longitudinal direction of each of the resistance portions 31 and 32 based on changes in the resistance values ​​of the resistance portions 31 and 32. In other words, the strain gauge 1 can be used as a multiaxial gauge that can detect strain in two directions.

[0047] In the past, when detecting strain in two directions, for example, two strain gauges were fabricated and stacked so that their grid directions intersected, but this resulted in measurement errors due to misalignment during stacking or differences in the positions of the strain gauges in the stacking direction.In contrast, in strain gauge 1, resistance sections 31 and 32 are patterned simultaneously on the same surface, which simplifies the manufacturing process and makes it less likely that measurement errors will occur due to misalignment, etc.

[0048] Furthermore, since the resistance portions 31 and 32 of the strain gauge 1 are patterned on the same surface, it can be made smaller than a structure in which multiple strain gauges are attached. As a result, it can be easily attached to the desired measurement position.

[0049] Furthermore, in the strain gauge 1, particularly when the resistor 30 is formed from a Cr mixed-phase film, the sensitivity of the resistance value to strain (the amount of change in the resistance value of the resistor 30 for the same strain) is significantly improved compared to when the resistor 30 is formed from Cu—Ni or Ni—Cr. When the resistor 30 is formed from a Cr mixed-phase film, the sensitivity of the resistance value to strain is approximately 5 to 10 times higher compared to when the resistor 30 is formed from Cu—Ni or Ni—Cr. Therefore, by forming the resistor 30 from a Cr mixed-phase film, it becomes possible to detect strain with high accuracy.

[0050] Second Embodiment In the second embodiment, an example of a sensor module in which a selection circuit is mounted on the strain gauge of the first embodiment is shown. Note that in the second embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0051] 3 is a schematic diagram illustrating a sensor module according to the second embodiment, in which the strain gauge 1 (see FIGS. 1 and 2) is simplified and only terminal portions 41 to 44 are shown.

[0052] Referring to FIG. 3, the sensor module 5 includes a strain gauge 1 and a selection circuit 2.

[0053] The selection circuit 2 is, for example, an IC including switches SW1 and SW2, input terminals I1 to I4, output terminals O1 and O2, a control terminal CNT, and power supply terminals VDD and VSS (positive and negative terminals). A power supply of a predetermined voltage is supplied to the power supply terminals VDD and VSS from outside the sensor module 5. The control terminal CNT and the output terminals O1 and O2 can be electrically connected to the outside of the sensor module 5. The selection circuit 2 can be mounted on, for example, the upper surface 10a or the lower surface 10b of the substrate 10 of the strain gauge 1.

[0054] In the selection circuit 2, the input terminals I1 and I3 are connected to terminals 41 and 43, which are a pair of electrodes of the resistor section 31. In addition, the input terminals I2 and I4 are connected to terminals 42 and 44, which are a pair of electrodes of the resistor section 32.

[0055] The switches SW1 and SW2 are switched in conjunction with each other in response to an H / L signal input from the outside to a control terminal CNT.

[0056] For example, when an H signal is input to the control terminal CNT from the outside, SW1 connects the input terminal I1 to the output terminal O1, and SW2 connects the input terminal I3 to the output terminal O2 (the state shown in FIG. 3). In this case, the output terminals O1 and O2 are connected to the terminals 41 and 43, which are a pair of electrodes of the resistor 31, and the resistance value of the resistor 31 can be measured via the output terminals O1 and O2.

[0057] On the other hand, when an L signal is input to the control terminal CNT from the outside, SW1 connects the input terminal I2 to the output terminal O1, and SW2 connects the input terminal I4 to the output terminal O2. In this case, the output terminals O1 and O2 are connected to the terminals 42 and 44, which are a pair of electrodes of the resistor 32, and the resistance value of the resistor 32 can be measured via the output terminals O1 and O2.

[0058] 4 is a schematic diagram illustrating a method of using the sensor module according to the second embodiment. Referring to FIG. 4, the sensor module 5 can be connected to a measurement unit 7 disposed outside the sensor module 5.

[0059] The measurement unit 7 includes a bridge circuit 71 , an analog front-end unit 72 , and a control unit 73 .

[0060] The bridge circuit 71 has three sides configured with fixed resistors R1, R2, and R3, and the other side connected to output terminals O1 and O2 of the selection circuit 2 of the sensor module 5. A DC voltage V is applied between one pair of diagonal points of the bridge circuit 71. With this configuration, an analog voltage corresponding to the distortion of the resistor section 31 or 32 selected by the selection circuit 2 is output between the other pair of diagonal points of the bridge circuit 71. The voltage output from the bridge circuit 71 is input to the analog front-end section 72.

[0061] Here, the connection between the strain gauge 1 and the bridge circuit 71 is a one-gauge two-wire system, but the present invention is not limited to this.

[0062] The analog front-end unit 72 includes, for example, an amplifier, an analog / digital conversion circuit (A / D conversion circuit), an external communication function (for example, I 2 The analog front-end unit 72 may be provided with a temperature compensation circuit. The analog front-end unit 72 may be implemented as an IC or may be configured using individual components.

[0063] In the analog front-end unit 72, the voltage output from the bridge circuit 71 is amplified by an amplifier, converted into a digital signal by an A / D conversion circuit, and output. If the analog front-end unit 72 is equipped with a temperature compensation circuit, a temperature-compensated digital signal is output.

[0064] The control unit 73 can switch the switches SW1 and SW2 by inputting an H signal or an L signal to the control terminal CNT of the selection circuit 2 of the sensor module 5. The control unit 73 can be configured to include, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), main memory, etc.

[0065] In this case, the various functions of the control unit 73 can be realized by reading a program recorded in a ROM or the like into a main memory and executing it by a CPU. However, part or all of the control unit 73 may be realized only by hardware. Furthermore, the control unit 73 may be physically configured by multiple devices or the like.

[0066] In this way, the switches SW1 and SW2 of the selection circuit 2 can be switched by an H signal or L signal input from outside to the control terminal CNT of the selection circuit 2 of the sensor module 5. This makes it possible to selectively measure the resistance value of the resistance section 31 and the resistance value of the resistance section 32 of the strain gauge 1. In other words, it is possible to selectively measure strain in the X direction and strain in the Y direction.

[0067] Third Embodiment The third embodiment shows an example of a strain gauge that detects strain in more directions than the first embodiment. Note that in the third embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0068] Fig. 5 is a plan view illustrating a strain gauge according to the third embodiment. The cross-sectional shape of the strain gauge according to the third embodiment is the same as that of Fig. 2, and is therefore not shown. Referring to Fig. 5, strain gauge 1A differs from strain gauge 1 (see Figs. 1 and 2) in that the number of pairs of resistors and pairs of terminals is increased from two to four. In other words, strain gauge 1A is a multi-axial gauge capable of detecting strain in four directions.

[0069] In the strain gauge 1A, the resistor 30A is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when subjected to strain. The resistor 30A may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. The material, thickness, manufacturing method, etc. of the resistor 30A may be the same as those of the resistor 30.

[0070] Resistor 30A includes resistance portions 31, 32, 33, and 34. In other words, resistor 30A is a general term for resistance portions 31, 32, 33, and 34, and will be referred to as resistor 30A when there is no need to particularly distinguish between resistance portions 31, 32, 33, and 34. For convenience, resistors 31, 32, 33, and 34 are shown with a matte finish in FIG. 5.

[0071] Resistance portion 31 is a thin film formed linearly on the upper surface 10a of substrate 10 with its longitudinal direction aligned in the X direction. Resistance portion 32 is a thin film formed linearly on the upper surface 10a of substrate 10 with its longitudinal direction aligned in the Y direction. Resistance portion 33 is a thin film formed linearly on the upper surface 10a of substrate 10 with its longitudinal direction aligned in a direction such that the angle θ1 between its longitudinal direction and the X direction is −45 degrees. Resistance portion 34 is a thin film formed linearly on the upper surface 10a of substrate 10 with its longitudinal direction aligned in a direction such that the angle θ2 between its longitudinal direction and the X direction is +45 degrees. Note that the counterclockwise direction is considered a positive angle here.

[0072] The resistor portions 31, 32, 33, and 34 are electrically connected to one another by intersecting on the same plane. The resistor portions 31, 32, 33, and 34 can be patterned, for example, to intersect at approximately the center of their respective longitudinal directions. That is, the resistor portions 31, 32, 33, and 34 are each formed linearly, are electrically connected to one another by intersecting on the same plane, and adjacent resistor portions form an angle of 45 degrees.

[0073] The terminal portion 45 extends from one end of the resistor portion 33 and is formed in a generally circular shape in a plan view, wider than the resistor portion 33. The terminal portion 47 extends from the other end of the resistor portion 33 and is formed in a generally circular shape in a plan view, wider than the resistor portion 33. The terminal portions 45 and 47 are a pair of electrodes for outputting a change in the resistance value of the resistor portion 33 caused by strain to the outside. For example, a flexible substrate or a lead wire for external connection is joined to the terminal portions 45 and 47. The upper surfaces of the terminal portions 45 and 47 may be coated with a metal that has better solderability than the terminal portions 45 and 47. Although the resistor portion 33 and the terminal portions 45 and 47 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. The planar shape of the terminal portions 45 and 47 is not limited to a circular shape and may be rectangular, etc.

[0074] The terminal portion 46 extends from one end of the resistor portion 34 and is formed in a generally circular shape in a plan view, wider than the resistor portion 34. The terminal portion 48 extends from the other end of the resistor portion 34 and is formed in a generally circular shape in a plan view, wider than the resistor portion 34. The terminal portions 46 and 48 are a pair of electrodes for outputting a change in the resistance value of the resistor portion 34 caused by strain to the outside. For example, a flexible substrate or lead wire for external connection is joined to the terminal portions 46 and 48. The upper surfaces of the terminal portions 46 and 48 may be coated with a metal that has better solderability than the terminal portions 46 and 48. Although the resistor portion 34 and the terminal portions 46 and 48 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. The planar shape of the terminal portions 46 and 48 is not limited to a circular shape and may be rectangular, etc.

[0075] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30A and expose the terminal portions 41 to 48. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30A. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30A from moisture and the like. The cover layer 60 may be provided so as to cover the entire portion except for the terminal portions 41 to 48.

[0076] In strain gauge 1A, resistor unit 31 detects strain in the X direction as a change in resistance value and can output it from a pair of electrodes, terminal units 41 and 43. Resistor unit 32 detects strain in the Y direction as a change in resistance value and can output it from a pair of electrodes, terminal units 42 and 44. Resistor unit 33 detects strain in a direction where the angle θ1 it forms with the X direction is −45 degrees as a change in resistance value and can output it from a pair of electrodes, terminal units 45 and 47. Resistor unit 34 detects strain in a direction where the angle θ2 it forms with the X direction is +45 degrees as a change in resistance value and can output it from a pair of electrodes, terminal units 46 and 48.

[0077] As described above, in the strain gauge 1A, the resistor portions 31, 32, 33, and 34 are each formed linearly and intersect on the same plane to be electrically connected to each other, with adjacent resistor portions forming a 45-degree angle. By sequentially connecting the resistor portions 31, 32, 33, and 34 to a bridge circuit, the longitudinal strain of each of the resistor portions 31, 32, 33, and 34 can be detected based on changes in the resistance values ​​of the resistor portions 31, 32, 33, and 34. Furthermore, the magnitude and direction of the principal strain can be calculated based on the strain detection results of the resistor portions 31, 32, 33, and 34. Other advantages are the same as those of the first embodiment.

[0078] Fourth Embodiment In the fourth embodiment, an example of a sensor module in which a selection circuit is mounted on the strain gauge of the third embodiment is shown. Note that in the fourth embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0079] Fig. 6 is a schematic diagram illustrating a sensor module according to the fourth embodiment. In Fig. 6, the strain gauge 1A (see Fig. 5) is simplified, and only the terminal portions 41 to 48 are shown.

[0080] Referring to FIG. 6, a sensor module 5A includes a strain gauge 1A and a selection circuit 2A.

[0081] The selection circuit 2A is, for example, an IC including switches SW1 and SW2, input terminals I1 to I8, output terminals O1 and O2, control terminals CNT1 and CNT2, and power supply terminals VDD and VSS (positive and negative terminals). A power supply of a predetermined voltage is supplied to the power supply terminals VDD and VSS from outside the sensor module 5A. The control terminals CNT1 and CNT2 and the output terminals O1 and O2 can be electrically connected to the outside of the sensor module 5A. The selection circuit 2A can be mounted, for example, on the upper surface 10a or lower surface 10b of the substrate 10 of the strain gauge 1A.

[0082] In the selection circuit 2A, the input terminals I1 and I5 are connected to terminals 41 and 43, which are a pair of electrodes of the resistor section 31. The input terminals I2 and I6 are connected to terminals 42 and 44, which are a pair of electrodes of the resistor section 32. The input terminals I3 and I7 are connected to terminals 45 and 47, which are a pair of electrodes of the resistor section 33. The input terminals I4 and I8 are connected to terminals 46 and 48, which are a pair of electrodes of the resistor section 34.

[0083] The switches SW3 and SW4 are switches that are switched in conjunction with each other in accordance with the combination of H / L signals input from the outside to the control terminals CNT1 and CNT2.

[0084] For example, when an H signal is externally input to control terminal CNT1 and an H signal is externally input to control terminal CNT2, SW3 connects input terminal I1 and output terminal O1, and SW4 connects input terminal I5 and output terminal O2 (the state shown in FIG. 6). In this case, output terminals O1 and O2 are connected to terminals 41 and 43, which are a pair of electrodes of resistor 31, and the resistance value of resistor 31 can be measured via output terminals O1 and O2.

[0085] Furthermore, when an H signal is externally input to control terminal CNT1 and an L signal is externally input to control terminal CNT2, SW3 connects input terminal I2 to output terminal O1, and SW4 connects input terminal I6 to output terminal O2. In this case, output terminals O1 and O2 are connected to terminals 42 and 44, which are a pair of electrodes of resistor 32, and the resistance value of resistor 32 can be measured via output terminals O1 and O2.

[0086] Furthermore, when an L signal is externally input to control terminal CNT1 and an H signal is externally input to control terminal CNT2, SW3 connects input terminal I3 to output terminal O1, and SW4 connects input terminal I7 to output terminal O2. In this case, output terminals O1 and O2 are connected to terminals 45 and 47, which are a pair of electrodes of resistor 33, and the resistance value of resistor 33 can be measured via output terminals O1 and O2.

[0087] Furthermore, when an L signal is externally input to control terminal CNT1 and an L signal is externally input to control terminal CNT2, SW3 connects input terminal I4 to output terminal O1, and SW4 connects input terminal I8 to output terminal O2. In this case, output terminals O1 and O2 are connected to terminals 46 and 48, which are a pair of electrodes of resistor 34, and the resistance value of resistor 34 can be measured via output terminals O1 and O2.

[0088] The method of using the sensor module 5A is the same as that described with reference to FIG. 4, except that the control unit 73 controls the control terminals CNT1 and CNT2 of the selection circuit 2A.

[0089] In this way, the switches SW3 and SW4 of the selection circuit 2A can be switched by combining H / L signals input from the outside to the control terminals CNT1 and CNT2 of the selection circuit 2A of the sensor module 5A. This makes it possible to selectively measure the resistance values ​​of the resistance units 31, 32, 33, and 34 of the strain gauge 1A. In other words, it is possible to selectively measure strain in the X direction, strain in the Y direction, and strain in directions that form an angle of ±45 degrees with the X direction.

[0090] Fifth Embodiment In the fifth embodiment, an example of a bearing mechanism having a strain gauge will be described. Note that in the fifth embodiment, the description of the same components as those in the embodiments already described may be omitted.

[0091] Fig. 7 is a perspective view illustrating a bearing mechanism according to a fifth embodiment, and Fig. 8 is a cross-sectional view illustrating the bearing mechanism according to the fifth embodiment.

[0092] 7 and 8, the bearing mechanism 100 has a rotating shaft 110, a bearing 120, and a strain gauge 1. The rotating shaft 110 is rotatably supported by the bearing 120. The strain gauge 1 is attached to the side wall of the bearing 120.

[0093] By attaching a strain gauge 1 to the side wall of the bearing 120, it is possible to detect vibrations of the bearing 120. The life of the bearing 120 is significantly affected by vibrations in addition to the original rolling fatigue life. By attaching a strain gauge 1 to the bearing 120 and detecting vibrations, it is possible to predict the life of the bearing 120 based on the results of vibration detection by the strain gauge 1.

[0094] Furthermore, by feeding back the vibration information obtained from the strain gauge 1, it becomes possible to avoid adverse effects on various products that use the bearing 120. In particular, because the strain gauge 1 is a two-axis gauge, it is possible to simultaneously detect vibration components in a direction perpendicular to the rotation axis 110 and vibration components in the direction of the rotation axis 110. As a result, it becomes possible to predict the lifespan of the bearing 120 with higher accuracy.

[0095] Also, strain gauge 1A can be used in place of strain gauge 1. If bearing mechanism 100 is unbalanced, it is likely to vibrate in a direction perpendicular to rotating shaft 110, and if it is misaligned, vibration occurs in the direction of rotating shaft 110.

[0096] Since vibrations have characteristics in the direction in which they occur depending on the type of abnormality, it is preferable to measure them in three directions: vertical, horizontal, and axial. By using strain gauge 1A, it is possible to simultaneously detect vibrations in three directions, greatly improving the ability to isolate the source of vibration.

[0097] In this way, in the bearing mechanism 100, by attaching the strain gauge 1 or 1A to the side wall of the bearing 120 and detecting vibration of the bearing 120, abnormal modes of vibration occurring in the bearing 120 can be detected with high accuracy.

[0098] It should be noted that the strain gauge 1 or 1A may be replaced by a sensor module 5 or 5A.

[0099] The above describes in detail preferred embodiments, but 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.

[0100] For example, the bridge circuit 71 may be incorporated into the sensor module 5 or 5A. Alternatively, the bridge circuit 71 and the analog front-end unit 72 may be incorporated into the sensor module 5 or 5A. In this case, for example, the bridge circuit 71 and the analog front-end unit 72 can be integrated into an IC and mounted on the upper surface 10a or the lower surface 10b of the substrate 10.

[0101] Furthermore, in a multi-axis gauge, the number of resistance portions is not limited to two or four, but may be three or five or more. [Explanation of symbols]

[0102] 1, 1A strain gauge, 2, 2A selection circuit, 5, 5A sensor module, 7 measurement unit, 10 substrate, 10a upper surface of substrate, 10b lower surface of substrate, 30, 30A resistor, 31 to 34 resistor unit, 41 to 48 terminal unit, 60 cover layer, 71 bridge circuit, 72 analog front end unit, 73 control unit, 100 bearing mechanism, 110 rotating shaft, 120 bearing

Claims

1. a flexible resin substrate; a functional layer formed of a metal, an alloy, or a metal compound directly on one surface of the substrate; Cr, CrN, and Cr are directly applied to one surface of the functional layer. ２ a plurality of resistor portions formed linearly from a film containing N and containing α-Cr as a main component; the functional layer has a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component; the thickness of each of the resistor portions is 0.05 μm or more and 2 μm or less; The thickness of the functional layer is 1 nm or more and 100 nm or less, A strain gauge in which the resistance portions cross each other on the same plane and are electrically connected to each other.

2. The strain gauge according to claim 1 , wherein the plurality of resistor portions include resistor portions that are orthogonal to each other.

3. 3. The strain gauge according to claim 1, wherein the plurality of resistance portions include resistance portions that form an angle of 45 degrees with each other.

4. 4. The strain gauge according to claim 1, wherein the number of the resistance portions is four or more.

5. 5. The strain gauge according to claim 1, wherein a pair of electrodes is formed on both ends of each of the resistor portions.

6. The strain gauge according to claim 5 , wherein each of the electrodes has a circular shape in a plan view.

7. 7. The strain gauge according to claim 5, wherein each of the electrodes is arranged along the circumference of a circle having a center at a point where each of the resistor portions intersects.

8. A strain gauge according to any one of claims 5 to 7 and a selection circuit, The selection circuit input terminals connected to the pair of electrodes of each of the resistor units; a switch that selects one of the pair of electrodes of the resistor units from the pair of electrodes of each of the resistor units connected to the input terminal and connects it to a pair of output terminals.

9. The sensor module according to claim 8 , wherein the selection circuit is mounted on one side or the other side of the substrate.

10. 10. The sensor module according to claim 8, further comprising a bridge circuit in which the pair of output terminals are connected to one side and the other three sides are configured with fixed resistors.

11. 11. The sensor module according to claim 10, further comprising an analog front-end section that amplifies the analog voltage output from the bridge circuit, converts it into a digital signal, and outputs it.

12. A strain gauge according to any one of claims 1 to 7 or a sensor module according to any one of claims 8 to 11; A rotation axis; a bearing that rotatably supports the rotating shaft, A bearing mechanism that detects vibrations of the bearing using the strain gauge or the sensor module.

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