JP2000146511A - Strain gauge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the strain gauge which is able to precisely measure local stress. SOLUTION: The strain gauge is equipped with a heat-resisting plastic sheet of <=50 μm in thickness and a metal resistance body which is vapor-deposited on the plastic sheet surface to a thickness of 0.2 to 0.5 μm. A polyimide sheet 1 is used as the heat-resisting plastic sheet and an NiCr film 8 is used as the metal resistance body; and the NiCr film 8 is etched preferably to a size of 1 to 0.5 mm in thickness × 50 to 10 μm in width.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain gauge for measuring a strain, for example, a strain gauge suitable for measuring a strain in a minute portion such as a stress concentration portion of a steam turbine blade, and a strain gauge of the strain gauge. Regarding the manufacturing method.

[0002]

2. Description of the Related Art FIGS. 5 and 6 show the configuration of a conventional adhesive strain gauge. This forms the strain gauge 2 on the polyimide sheet 1. The strain gauge 2 is formed by attaching a metal foil for a gauge to the entire surface of the polyimide sheet 1 and processing it into a comb shape by a photolithography technique and an etching technique. However, in this conventional method of attaching a metal foil, a thickness of at least about 30 μm is required in order to obtain the mechanical strength of the metal foil required for attaching the metal foil. For this reason, the sheet resistance of the square metal foil becomes as low as about 0.5 Ω / □, and when forming a 120 Ω strain gauge 2, the gauge length is 1 to the gauge width.
20 / 0.5 = 240 times, and the line width is 0.
If the gauge is 1 mm, the gauge length is 12 mm.
For this reason, it is necessary to process into a comb-shaped pattern shape in order to suppress the gauge length. Since the thickness of the metal foil is large, the line width which can be processed by etching is limited to about 0.1 mm, and the gauge length needs to be increased because the sheet resistance is small. The minimum dimension of the conventional strain gauge 2 is 1 mm in length.
× The width is about 0.25 mm.

FIG. 2 shows a steam turbine blade 3. In the blade root 4 having such a complicated shape, the static strain generated by the centrifugal force due to the rotation becomes the maximum strain at the stress concentration point 5.

[0004]

In order to measure the concentrated stress on the blade root 4, the strain gauge 2 must be attached to the stress concentration point 5, but the concentrated stress characteristic with respect to the end face position is steep at the contact portion. Since stress is generated and if the gauge area is large, only the averaged strain amount is measured, the value becomes lower than the actual maximum stress, and the measurement error increases. Therefore, an object of the present invention is to provide a strain gauge capable of measuring a local stress with high accuracy.

[0005]

Therefore, the present invention is as follows.

(1) A heat-resistant plastic sheet having a thickness of 50 μm or less and 0.2 μm to
A strain gauge comprising: a 0.5 μm thick metal resistor formed by vapor deposition.

(2) The strain gauge according to (1), wherein a polyimide sheet is used as a heat-resistant plastic sheet and a NiCr film is used as a metal resistor.

(3) The NiCr film is 1 mm to 0.5 mm long × 50 μm to 10 μm wide by etching.
(1) or (2) characterized in that it was processed to the size of
Strain gauge.

(4) A strain gauge according to any one of (1) to (3), wherein a conductive material is deposited on a heat-resistant plastic sheet so that one end thereof is in contact with the metal resistor to form wiring and connection pads.

(5) A method for producing a strain gauge comprising the following steps.
A step of applying an adhesive on a mirror-finished semi-metal or ceramic. A step of bonding a heat-resistant plastic seal serving as a substrate for a strain gauge to the surface to which the adhesive is applied. A step of depositing a metal resistor on the surface of the heat-resistant plastic seal; a step of applying and curing a photosensitive resist agent on the surface of the film of the metal resistor. A step of placing a mask glass having a strain gauge pattern on the surface of the photosensitive resist agent and irradiating reaction light to remove the photosensitive resist agent other than the gauge pattern portion. A step of etching the metal resistor with an etchant to form a gauge pattern; A step of removing the photosensitive resist agent and the adhesive with a solvent;

(6) The method for producing a strain gauge according to (5), wherein a photosensitive resist agent is used as an adhesive, a polyimide sheet is used as a heat-resistant plastic sheet, and NiCr is used as a metal resistor.

(7) The metal resistor is 1 mm to 0.5 mm long × 50 μm to 10 μm wide by etching.
(5) and (6) characterized in that they were processed to the size of
Manufacturing method of strain gauge.

(8) After the step (5), masking is performed on the heat-resistant plastic sheet with a heat-resistant plastic adhesive tape so as to form a connection pad and a wiring connecting one end of the metal resistor. And a method of producing a strain gauge according to any one of (5) to (7), wherein a conductive material is deposited.

Here, the heat-resistant plastic sheet may be any sheet that can withstand etching or heat treatment.
A typical example is a polyimide sheet. The thickness should be 50 μm or less so that the strain at the stress concentration portion can be appropriately transmitted to the metal resistor.

The metal resistor may be any metal resistor that can be deposited and can be used as a strain gauge resistor. A typical example is a NiCr alloy. The thickness of the metal resistor is
It is preferable that the thickness is as thin as possible because the sensitivity to strain is improved. 0.5 μm because the sensitivity to strain decreases and the length of the required metal resistor increases.
Should be:

The conductive material is obtained by forming wiring portions and connection pads on a heat-resistant plastic by vapor deposition using a material having good conductivity in order to extract an electric resistance value from a metal resistor. The connection pad is a place where soldering or the like can be performed in order to conduct a cable from a measuring device that measures strain from electric resistance to a strain gauge, and the wiring portion connects the connection pad and a metal resistor. To conduct. Therefore, typically, copper or a copper alloy having good conductivity is frequently used. In addition, the wiring portion / metal resistor has a cross-sectional area ratio perpendicular to the current direction so that the wiring portion does not affect the electric resistance value. 1
Should be greater than or equal to 00.

The mirror-polished semi-metal or ceramic keeps the strain gauge smooth during the production of the strain gauge, and has heat resistance and oxidation resistance such as Si wafer, silica, alumina, quartz and glass. Is preferred.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart showing a procedure for manufacturing a strain gauge according to a first embodiment of the present invention, and FIG. 2 schematically shows a stress concentration portion of a steam turbine blade as an example of a minute portion. , FIG. 3 is a schematic view showing the strain gauge according to the embodiment of the present invention attached to a steam turbine blade, and FIG. 4 is a perspective view schematically showing a situation where the steam turbine blade of FIG. The figure is shown.

With reference to FIG. 1, a procedure for manufacturing a strain gauge according to the first embodiment of the present invention will be described. First, a photosensitive resist 7 for photolithography is applied on a mirror-polished Si wafer 6 to a thickness of about 1 μm. Here, as the photosensitive resist 7, for example, there is an OMR-based resist agent manufactured by Tokyo Ohka Co., Ltd., and various types are commercially available for each company. A 50 μm polyimide sheet 1 serving as a substrate for a strain gauge is adhered to the photosensitive resist 7 and sintered at a temperature of 150 ° C. Thereby, an appropriate tension can be applied to the polyimide sheet 1, the flatness of the surface can be optimized, and a thin film can be formed. Furthermore, the photosensitive resist material 7 sintered at 150 ° C. is not melted by the developing process at the time of photolithography, but is melted at the time of the resist removing process after the metal film etching process. The sheet 1 can be easily removed from the Si plate 2, and does not increase wet etching processing. Thus, the increase in the process can be suppressed, and the yield of the gauge is improved. Next, 0.2 μm NiC was formed on the surface of the polyimide sheet 1 by sputtering.
An r film 8 is formed by vapor deposition. Thereafter, a 0.5 μm resist material is applied to the surface of the NiCr film 8 and sintered at 80 ° C. Put the mask glass of the strain gauge pattern on top,
UV irradiation is performed. Thereafter, a developing process is performed with a dedicated developing solution for the photosensitive resist 7 material, and the portions other than the gauge pattern-shaped photosensitive resist 7 material are removed. For example, when an OMR resist is used as a photosensitive resist material, it is preferable to use a commercially available OMR developer (trade name: manufactured by Tokyo Ohka Co., Ltd.) as a dedicated developer. Thereafter, N 2 is added with a mixed solution of phosphoric acid and nitric acid.
The iCr film 8 is etched, and the gauge pattern processing is performed. After that, the photosensitive resist 7 material remaining on the surface of the NiCr film 8 and the photosensitive resist 7 material between the polyimide sheet 1 and the Si plate 6 are removed by using a dedicated removing material for the photosensitive resist 7, thereby completing the strain gauge body. Let it. For example, when an OMR resist is used as the photosensitive resist material, it is preferable to use a commercially available OMR stripper (trade name: manufactured by Tokyo Ohkasha Co., Ltd.) as the exclusive remover. Finally, the NiCr
Masking is performed on a polyimide sheet with a Kapton tape as a heat-resistant plastic adhesive tape so that one end is connected to the film 8 to form a wiring and a connection pad, and a copper material is vapor-deposited to complete.

As shown in FIG. 1, in this embodiment,
Instead of the conventional bonding type, a strain gauge is formed by a vapor deposition technique. Thereby, an extremely thin metal film 8 of 0.2 μm can be formed on the polyimide sheet 1. For this reason, the resistance value per area can be increased, a predetermined gauge resistance can be obtained with a small gauge pattern, and a small strain gauge 2 can be formed. However, when a vapor deposition process is performed on the polyimide sheet 1, the surface roughness of the sheet is several μm.
Usually, good yield cannot be obtained unless the film is formed with a film thickness larger than this. In this embodiment, in order to suppress deformation of the polyimide sheet 1 at the time of film formation and etching processing, the polyimide sheet 1 is coated with a photosensitive resist 7 agent using Si.
It is adhered to the surface of the plate 6. As a result, a thin gauge metal film 8 of about 0.2 μm can be formed on the surface of the polyimide sheet 1. FIG. 3 shows a configuration diagram when the strain gauge 2 is applied to measurement of blade stress during rotation. The polyimide sheet 1 on which the strain gauge 2 is formed conforms to the shape of the blade root 4. From the connection pad 9 to the telemeter capsule 10
Wiring between them, measuring the concentrated stress of the rotating blade root 4,
Since the size of the strain gauge 2 is only 0.05 mm × 1 mm, it is possible to measure the strain at the wing tip substantially.

As described above, since the strain gauge of the present embodiment can be reduced in size to 1/5 or less in width as compared with the size of the conventional gauge, it is generated at a minute portion such as a local stress. The amount of distortion can be measured with high spatial resolution. Further, since a photolithography technique is used for forming the gauge, it is possible to form a dedicated gauge in a custom-made form at a measurement site, such as a gauge pattern for multipoint measurement.

[0022]

Since the strain gauge of the present invention can be miniaturized, it is possible to measure the amount of strain generated in a minute portion such as local stress with high spatial resolution. Further, since the photolithography technique is used for forming the gauge, it is possible to form a dedicated gauge in a custom-made form at the measurement site, such as a gauge pattern for multipoint measurement.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure for manufacturing a strain gauge according to a first embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a stress concentration portion of the steam turbine blade.

FIG. 3 is a schematic diagram illustrating a strain gauge according to the first embodiment of the present invention attached to a steam turbine blade.

FIG. 4 is a perspective view schematically showing a state in which the steam turbine blade of FIG. 3 is attached to a steam turbine.

FIG. 5 is a plan view of a conventional strain gauge.

FIG. 6 is a side view of a conventional strain gauge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Polyimide sheet 2 Strain gauge 3 Steam turbine blade 4 Blade root part 5 Stress concentration place 6 Si plate 7 Photoresist 8 NiCr 9 Connection pad

Claims (8)

[Claims] 1. A heat-resistant plastic sheet having a thickness of 50 μm or less, and 0.2 μm to 0.5 μm
A strain gauge comprising a metal resistor deposited and formed to a thickness of μm. 2. The strain gauge according to claim 1, wherein a polyimide sheet is used as the heat-resistant plastic sheet and a NiCr film is used as the metal resistor. 3. The strain gauge according to claim 1, wherein said NiCr film is processed into a size of 1 mm to 0.5 mm in length × 50 μm to 10 μm in width by etching. 4. The strain gauge according to claim 1, wherein a conductive material is deposited on the heat-resistant plastic sheet so that one end thereof is in contact with the metal resistor to form wiring and connection pads. 5. A method for producing a strain gauge comprising the following steps. A step of applying an adhesive on a mirror-finished semi-metal or ceramic. A step of bonding a heat-resistant plastic seal serving as a substrate for a strain gauge to the surface to which the adhesive is applied. A step of depositing a metal resistor on the surface of the heat-resistant plastic seal; a step of applying and curing a photosensitive resist agent on the surface of the film of the metal resistor.
A step of placing a mask glass having a strain gauge pattern on the surface of the photosensitive resist agent and irradiating reaction light to remove the photosensitive resist agent other than the gauge pattern portion. A step of etching the metal resistor with an etchant to form a gauge pattern;
A step of removing the photosensitive resist agent and the adhesive with a solvent; 6. The method of claim 5, wherein a photosensitive resist agent is used as an adhesive, a polyimide sheet is used as a heat-resistant plastic sheet, and NiCr is used as a metal resistor. 7. The strain gauge manufacturing method according to claim 5, wherein said metal resistor is processed into a size of 1 mm to 0.5 mm × 50 μm to 10 μm in width by etching. . 8. The method according to claim 5, wherein the conductive material is masked on a heat-resistant plastic sheet with a heat-resistant plastic adhesive tape so as to form a wiring and a connection pad connecting one end of the metal resistor. The method for producing a strain gauge according to claim 5, wherein the strain gauge is deposited.