JP7118620B2 - strain gauge - Google Patents

Description

The present invention relates to strain gauges.

A strain gauge is known that is attached to an object to be measured to detect the strain of the object. A strain gauge includes a resistor that detects strain, and a material containing, for example, Cr (chromium) or Ni (nickel) is used as the material of the resistor. Also, the resistor is formed on a base material made of, for example, an insulating resin (see, for example, Patent Document 1).

JP 2016-74934 A

By the way, the strain gauge is used by attaching it to the object to be measured via an adhesive layer, for example. However, when a strain gauge is attached to an object to be measured through an adhesive layer, it takes time for the adhesive layer to harden, and the adhesive layer protrudes to contaminate the object to be measured. Strain gauges cannot be reused either.

SUMMARY OF THE INVENTION It is an object of the present invention to attach a strain gauge to an object to be measured without using an adhesive layer.

The present strain gauge is a strain gauge used for an object to be measured made of a ferromagnetic material, and comprises a flexible substrate and a resistor formed on the substrate from a material containing at least one of chromium and nickel. and a magnetic force layer formed on a surface of the base material opposite to the side on which the resistor is formed and attached to and detached from the object to be measured , wherein the thickness of the magnetic force layer is , 5 μm or more and 200 μm or less .

According to the disclosed technique, the strain gauge can be attached to the object to be measured without using an adhesive layer.

1 is a plan view illustrating a strain gauge according to a first embodiment; FIG. 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment; FIG. FIG. 4 is a diagram illustrating a manufacturing process of the strain gauge according to the first embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First embodiment>
FIG. 1 is a plan view illustrating the strain gauge according to the first embodiment. FIG. FIG. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, showing a cross section along line AA in FIG. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, a terminal portion 41, and a magnetic force layer .

In this embodiment, for the sake of convenience, in the strain gauge 1, the side of the base material 10 on which the resistor 30 is provided is the upper side or one side, and the side on which the resistor 30 is not provided is the lower side or the other side. side. Also, the surface on which the resistor 30 of each part is provided is defined as one surface or upper surface, and the surface on which the resistor 30 is not provided is defined as the other surface or lower surface. However, the strain gauge 1 can be used upside down or arranged at any angle. Planar view refers to the object viewed from the normal direction of the upper surface 10a of the substrate 10, and planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10. and

The base material 10 is a member that serves as a base layer for forming the resistor 30 and the like, and has flexibility. The thickness of the base material 10 is not particularly limited, and can be appropriately selected according to the purpose. In particular, when the thickness of the base material 10 is 5 μm to 200 μm, the transmission of strain from the surface of the strain generating body bonded to the lower surface of the base material 10 via an adhesive layer or the like, and the dimensional stability against the environment. The thickness is preferably 10 μm or more, and more preferable from the viewpoint of insulation.

The substrate 10 is made of, for example, PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, polyolefin resin, or the like. can be formed from an insulating resin film of Note that the film refers to a flexible member having a thickness of about 500 μm or less.

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 substrate 10 may be formed from, for example, an insulating resin film containing a filler such as silica or alumina.

The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that undergoes a change in resistance when subjected to strain. The resistor 30 may be formed directly on the upper surface 10a of the base material 10, or may be formed on the upper surface 10a of the base material 10 via another layer. In addition, in FIG. 1, the resistor 30 is shown with a pear-skin pattern for the sake of convenience.

The resistor 30 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 30 can be made of a material containing at least one of Cr and Ni. Materials containing Cr include, for example, a Cr mixed phase film. Examples of materials containing Ni include Ni—Cu (nickel copper). Materials containing both Cr and Ni include, for example, Ni—Cr (nickel chromium).

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N, or the like is mixed. The Cr mixed phase film may contain unavoidable impurities such as chromium oxide.

The thickness of the resistor 30 is not particularly limited, and can be appropriately selected according to the purpose. In particular, when the thickness of the resistor 30 is 0.1 μm or more, the crystallinity of the crystal (for example, the crystallinity of α-Cr) forming the resistor 30 is preferably improved. It is further preferable in that cracks in the film caused by internal stress of the film constituting the film 30 and warping from the base material 10 can be reduced.

For example, when the resistor 30 is a Cr mixed phase film, the stability of gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component. In addition, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 is 10 or more, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR are within the range of -1000 ppm/°C to +1000 ppm/°C. can be Here, the main component means that the target material accounts for 50% by mass or more of all the materials constituting the resistor. It is preferable to include the above. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

The terminal portions 41 extend from both ends of the resistor 30 and are formed in a substantially rectangular shape wider than the resistor 30 in plan view. The terminal portion 41 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 30 caused by strain, and for example, lead wires for external connection are joined. The resistor 30 extends, for example, from one of the terminal portions 41 while folding back in a zigzag manner, and is connected to the other terminal portion 41 . The upper surface of the terminal portion 41 may be covered with a metal having better solderability than the terminal portion 41 . Although the resistor 30 and the terminal portion 41 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process.

A cover layer 60 (insulating resin layer) may be provided on the substrate 10 so as to cover the resistor 30 and expose the terminal portion 41 . By providing the cover layer 60, the resistor 30 can be prevented from being mechanically damaged. Also, by providing the cover layer 60, the resistor 30 can be protected from moisture and the like.

The cover layer 60 can be made of insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, composite resin (eg, silicone resin, polyolefin resin). The cover layer 60 may contain fillers or pigments. The thickness of the cover layer 60 is not particularly limited, and can be appropriately selected according to the purpose.

The magnetic force layer 70 is formed on the lower surface 10b of the base material 10 and attached to and detached from the object to be measured (strain generating body). Since many objects to be measured for strain measurement are made of a ferromagnetic material such as iron, the provision of the magnetic force layer 70 enables the strain gauge 1 to be detachably attached to the object to be measured. The magnetic force layer 70 can be provided on the entire bottom surface 10b of the base material 10, but may be provided on a partial area of the bottom surface 10b of the base material 10, if necessary.

The magnetic force layer 70 is not particularly limited as long as it is a layer formed of a material that can generate a magnetic force that sticks to a measurement object made of a ferromagnetic material such as iron, and can be appropriately selected according to the purpose. _XNiYFeZ (x+ _y + _z =100), NiFe, FeP, NiFeP, _CoNiFeP , FeB, _NiFeB , _CoNiFeB , Ni-W, _Nd2Fe14B , _SmCo5 , _Sm2Co17 , _SrFe12O19 , _BaFe12 A thin film of an alloy selected from the group consisting of O ₁₉ , a laminated film obtained by laminating thin films of any of the alloys of this group, and a bonded magnet obtained by adding a magnetic powder filler to the material of the substrate 10 can be mentioned. Magnetic powder fillers include, for example, powders of alloys selected from the above group.

The thickness of the magnetic force layer 70 is preferably about 0.5 μm to 500 μm. In particular, by setting the thickness of the magnetic layer 70 to 5 μm or more, the mechanical strength of the magnetic layer 70 can be ensured. Further, by setting the thickness of the magnetic force layer 70 to 200 μm or less, it becomes possible to follow the distortion of the object to be measured, and the displacement of the resistor 30 can be prevented.

The surface magnetic flux density of the magnetic force layer 70 is preferably about 1 mT to 500 mT. In particular, by setting the surface magnetic flux density of the magnetic force layer 70 to 30 mT or more, it is possible to secure a sufficient attractive force for the object to be measured. Further, by setting the surface magnetic flux density of the magnetic force layer 70 to 300 mT or less, the strain gauge 1 can be easily attached to and detached from the object to be measured.

FIG. 3 is a diagram illustrating the manufacturing process of the strain gauge according to the first embodiment, showing a cross section corresponding to FIG. In order to manufacture the strain gauge 1, first, in the step shown in FIG. to form The materials and thicknesses of the resistor 30 and the terminal portion 41 are as described above. The resistor 30 and the terminal portion 41 can be integrally formed from the same material.

The resistor 30 and the terminal portion 41 can be formed, for example, by forming a film by magnetron sputtering using a raw material capable of forming the resistor 30 and the terminal portion 41 as a target, and patterning the film by photolithography. The resistor 30 and the terminal portion 41 may be formed by using a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulse laser deposition method, a printing method, or the like instead of the magnetron sputtering method.

From the viewpoint of stabilizing the gauge characteristics, before forming the resistor 30 and the terminal part 41, a film thickness of about 1 nm to 100 nm is formed on the upper surface 10a of the base material 10 as a base layer by, for example, conventional sputtering. Vacuum deposition of the layer is preferred.

In the present application, a functional layer refers to a layer having a function of promoting crystal growth of at least the resistor 30 as an upper layer. The functional layer preferably further has a function of preventing oxidation of the resistor 30 due to oxygen and 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.

Since the insulating resin film that constitutes the base material 10 contains oxygen and moisture, especially when the resistor 30 contains Cr, Cr forms a self-oxidizing film. Being prepared helps.

The material of the functional layer is not particularly limited as long as it has a function of promoting the crystal growth of the resistor 30, which is the upper layer, and can be appropriately selected according to the purpose. 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), 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), Al (aluminum) metals, alloys of any metal of this group, or compounds of any metal of this group.

Examples of the above alloy include FeCr, TiAl, FeNi, NiCr, CrCu, and the like. Examples of the above compounds include TiN, _TaN , _Si3N4 , _TiO2 , _Ta2O5 , _{SiO2 and} the like.

The functional layer can be formed, for example, by a conventional sputtering method in which a raw material capable of forming the functional layer is used as a target and Ar (argon) gas is introduced into the chamber. By using the conventional sputtering method, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, so that the amount of film formation of the functional layer can be minimized and the effect of improving adhesion can be obtained.

However, this is an example of the method of forming the functional layer, and the functional layer may be formed by another method. For example, before forming the functional layer, the upper surface 10a of the substrate 10 is activated by a plasma treatment using Ar or the like to obtain an effect of improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering. You may use the method to do.

The combination of the material of the functional layer and the material of the resistor 30 and the terminal portion 41 is not particularly limited and can be appropriately selected according to the purpose. It is possible to deposit a Cr mixed phase film containing α-Cr (alpha chromium) as a main component.

In this case, for example, the resistive element 30 and the terminal portion 41 can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed-phase film as a target and introducing Ar gas into the chamber. Alternatively, the resistive element 30 and the terminal portion 41 may be formed by reactive sputtering using pure Cr as a target, introducing an appropriate amount of nitrogen gas together with Ar gas into the chamber.

In these methods, the growth surface of the Cr mixed phase film is defined by the functional layer made of Ti, and a Cr mixed phase film containing α-Cr, which has a stable crystal structure, as a main component can be formed. In addition, diffusion of Ti constituting the functional layer into the Cr mixed phase film improves gauge characteristics. For example, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range 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).

When the resistor 30 is a Cr mixed phase film, the functional layer made of Ti has a function of promoting crystal growth of the resistor 30 and a function of preventing oxidation of the resistor 30 due to oxygen and moisture contained in the base material 10. , and the function of improving the adhesion between the substrate 10 and the resistor 30 . The same is true when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

In this way, by providing the functional layer under the resistor 30, it becomes possible to promote the crystal growth of the resistor 30, and the resistor 30 having a stable crystal phase can be manufactured. As a result, in the strain gauge 1, the stability of gauge characteristics can be improved. In addition, by diffusing the material forming the functional layer into the resistor 30, the gauge characteristics of the strain gauge 1 can be improved.

Next, in the step shown in FIG. 3B, the magnetic force layer 70 is formed on the lower surface 10b of the base material 10. Next, in the step shown in FIG. The magnetic force layer 70 can be formed by, for example, a sputtering method, a plating method (electrolytic plating or electroless plating), a printing method, or the like. The material and thickness of the magnetic force layer 70 are as described above. After forming the magnetic layer 70, the magnetic layer 70 is magnetized. The surface magnetic flux density of the magnetic force layer 70 is as described above.

Any of the resistor 30 and the terminal portion 41 and the magnetic force layer 70 may be formed first. In other words, either the step shown in FIG. 3A or the step shown in FIG. 3B may be performed first.

After forming the resistor 30 and the terminal portion 41, the strain gauge 1 is completed by providing a cover layer 60 covering the resistor 30 and exposing the terminal portion 41 on the substrate 10, if necessary. The cover layer 60 is produced, for example, by laminating a semi-cured thermosetting insulating resin film on the substrate 10 so as to cover the resistor 30 and expose the terminal portions 41, and heat and cure the film. be able to. The cover layer 60 may be produced by applying a liquid or paste thermosetting insulating resin on the substrate 10 so as to cover the resistors 30 and expose the terminal portions 41, and heat and harden the resin. good.

By forming the magnetic force layer 70 on the lower surface 10b of the base material 10 in this way, an adhesive layer is not required when attaching to the object to be measured. , the strain measurement can be simplified. In addition, it is possible to prevent contamination of the object to be measured due to protrusion of the adhesive layer. In addition, since the strain gauge 1 can be attached to and detached from the object to be measured through the magnetic force layer 70, the strain gauge 1 can be reused.

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

Reference Signs List 1 strain gauge 10 substrate 10a upper surface 10b lower surface 30 resistor 41 terminal portion 60 cover layer 70 magnetic force layer

Claims (9)

A strain gauge used for a measurement object made of a ferromagnetic material,
a flexible substrate;
a resistor formed of a material containing at least one of chromium and nickel on the base;
a magnetic force layer formed on a surface of the base material opposite to the side on which the resistor is formed and attached to and detached from the object to be measured ;
The strain gauge , wherein the magnetic force layer has a thickness of 5 μm or more and 200 μm or less . A strain gauge used for a measurement object made of a ferromagnetic material,
a flexible substrate;
a resistor formed of a material containing at least one of chromium and nickel on the base;
a magnetic force layer formed on a surface of the base material opposite to the side on which the resistor is formed and attached to and detached from the object to be measured ;
The magnetic layer is Co _X Ni _Y Fe _Z (x+y+z=100), NiFe, FeP, NiFeP, CoNiFeP, FeB, NiFeB, CoNiFeB, Ni-W, Nd ₂ Fe ₁₄ B, SmCo ₅ , Sm ₂ Co ₁₇ , SrFe A strain gauge comprising a thin film of an alloy selected from the group consisting of 12 O 19 and BaFe 12 O 19 , a laminated film in which thin films of the alloy are laminated, or a bonded _magnet containing _powder of _the alloy _. 3. The strain gauge according to claim 1, wherein the magnetic force layer has a surface magnetic flux density of 30 mT or more and 300 mT or less. The strain gauge according to any one of claims 1 to 3 , wherein the resistor contains alpha chrome as a main component. 5. The strain gauge according to claim 4 , wherein the resistor contains 80% by weight or more of alpha chrome. 6. A strain gauge according to claim 4 or 5 , wherein said resistor contains chromium nitride. Having a functional layer formed of a metal, an alloy, or a metal compound on one surface of the base material,
The strain gauge according to any one of claims 1 to 6 , wherein the resistor is formed on one surface of the functional layer. 8. The strain gauge according to claim 7 , wherein said functional layer has a function of promoting crystal growth of said resistor. 9. The strain gauge according to claim 1 , further comprising an insulating resin layer covering said resistor.

Images