Strain gauge

Abstract

To provide strain gauges that enhance user convenience and minimize the impact on their properties. [Solution] Gauge base 11 and, A grid 13 located on a gauge base 11 and having multiple parallel straight sections, A surface protection part 15 that covers the grid 13, A strain gauge 1 having a gauge tab 3 which is a part for attaching lead wires, The gauge tab 3 has a first gauge tab 3a and a second gauge tab 3b connected to each of the two straight sections located at both ends of the grid 13. The gauge tab 3 has a gold-plated portion 5. The gold-plated portion 5 is located on the portion of the first gauge tab 3a and the second gauge tab 3b that is not covered by the surface protection portion 15, and is part of the strain gauge 1.

Description

Technical Field

[0001] This invention relates to a strain gauge. More specifically, it relates to a strain gauge having a gold-plated portion on a gauge tab.

Background Art

[0002] For example, strain gauges are described in Japanese Patent No. 6162670, Japanese Patent No. 4250064, and Japanese Patent No. 3546203. Thus, strain gauges are well-known.

[0003] A strain gauge is formed, for example, by forming a grid-like resistance wire or a photo-etched resistance foil on a base of a thin electrical insulator. And the strain gauge is attached to a measurement object during use. After that, the user solders a lead wire to the gauge tab of the strain gauge. The gauge tab is usually made of the same material as the sensing portion, has a length of 0.4 mm or more and 4 mm or less, a width of 0.3 mm or more and 4 mm or less, and a thickness of several microns. Therefore, soldering by the user is not easy. Also, when the user performs soldering, an oxide film may occur on the sensing portion, and the characteristics of the strain gauge may deteriorate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0006] This invention is fundamentally based on the realization that by providing a gold-plated portion 5 on the gauge tab 3, users can easily solder lead wires to the strain gauge. Furthermore, this invention is based on the realization that by providing the gold-plated portion 5 in an appropriate location, it is possible to provide a strain gauge 1 in which an oxide film is less likely to form on the sensing portion even after soldering.

[0007] The first invention relates to a strain gauge. This strain gauge 1 has a gauge tab 3 which is a part for attaching lead wires. The gauge tab 3 has a gold-plated portion 5. [Effects of the Invention]

[0008] This invention allows users to easily solder lead wires to the strain gauge 1 by providing a gold-plated portion 5 on the gauge tab 3. Furthermore, by providing the gold-plated portion 5 in an appropriate location, this invention can provide a strain gauge 1 in which an oxide film is less likely to form on the sensing portion even after soldering. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a conceptual diagram illustrating an example of the strain gauge of the present invention. [Figure 2] Figure 2 is a conceptual diagram showing an example where the gold plating is formed on a part of the gauge tab. [Figure 3] Figure 3 is a conceptual diagram showing a strain gauge with lead wires connected. [Modes for carrying out the invention]

[0010] The following describes embodiments for carrying out the present invention with reference to the drawings. The present invention is not limited to the embodiments described below, but also includes modifications made to the embodiments described below to the extent that is obvious to those skilled in the art.

[0011] The first invention relates to a strain gauge. A strain gauge, also called a strain gauge or strain sensor, is a known device. Strain gauge 1 is known as described in Japanese Patent Publication No. 6162670, Japanese Patent Publication No. 4250064, and Japanese Patent Publication No. 3546203. The strain gauge of this specification can appropriately adopt the configurations described in these publications or known configurations. The strain gauge is attached to an object whose strain is to be measured. In this case, for example, the strain gauge may be attached to the object using an adhesive. When strain occurs in the object, the length and cross-sectional area of ​​the circuit constituting the grid change in response to that strain. When the length and cross-sectional area of ​​the circuit change, the resistance value changes. By converting this change in resistance value into a change in voltage using a measuring circuit such as a Wheatstone bridge circuit, the strain of the object can be measured. The change in resistance value can be measured using a circuit connected to lead wires connected to the gauge tab. The lead wires may be attached to the strain gauge beforehand, and then the strain gauge may be attached to the object. Alternatively, the lead wires may be attached to the strain gauge after it has been attached to the object.

[0012] Figure 1 is a conceptual diagram illustrating an example of the strain gauge of the present invention. Figure 1(a) is a front view, and Figure 1(b) is a side view. As shown in Figure 1, the strain gauge 1 includes a gauge base 11, a grid 13 located on the gauge base 11 and having a plurality of parallel straight sections, and a surface protection section 15 covering the grid 13. The gauge base 11 is a substrate made of, for example, an insulating resin (e.g., a plastic such as epoxy resin, imidoamide resin, or polyimide resin).

[0013] The grid 13 has a circuit formed by the material that forms the sensing element. Multiple linear sensing elements are arranged in parallel on the gauge base 11, and each sensing element is connected alternately to an adjacent sensing element at its end to form the grid 14. The strain gauge 1 also has gauge tabs 3, which are parts for attaching lead wires. The gauge tabs 3 have, for example, a first gauge tab 3a and a second gauge tab 3b connected to each of the two linear sections located at both ends of the grid 13. The gauge tabs 3a and 3b may be made of the same material as the sensing element. An example of material is metal foil (for example, copper-nickel alloy, nickel-chromium alloy, or stainless steel alloy). The gauge tabs 3a and 3b may be formed at the same time as the sensing element. The shape of each gauge tab 3a and 3b may be adjusted as appropriate depending on the application. The shape of each gauge tab 3a and 3b may be rectangular, or have a tapered section and a rectangular section connected to the tapered section, as shown in Figure 1. The tapered section means a section in which the width gradually changes. The rectangular portion may have a chamfered or rounded (rounded) shape. The shape of each gauge tab 3a, 3b may include a circular portion or an elliptical portion. The length of each gauge tab 3a, 3b (the length from the portion wider than the straight portion of the sensing element to the end of the gauge tab) may be 0.1 mm or more and 1 cm or less, 0.4 mm or more and 4 mm or less, or 1 mm or more and 3 mm or less. The width of each gauge tab 3a, 3b (the maximum width in the length direction and perpendicular direction) may be 0.1 mm or more and 1 cm or less, or 0.3 mm or more and 4 mm or less.

[0014] Examples of the thickness of the sensing elements constituting the grid 13 and the gauge tab 3 are between 3 μm and 100 μm. An example of the grid 13 is that it has a metal resistive foil as the resistive part, with a thickness of between 3 μm and 6 μm. In other words, the thickness of the resistor is about 0.003 to 0.006 mm (3 to 6 μm, for example, 3 to 5 μm, or 4 to 6 μm). Therefore, the thickness of the grid 13 may be between 3 μm and 100 μm, between 3 μm and 20 μm, between 3 μm and 10 μm, or between 5 μm and 8 μm.

[0015] Furthermore, the gauge tab 3 has a gold-plated portion 5. The gold-plated portion 5 is located, for example, on the portion of the first gauge tab 3a and the second gauge tab 3b that is not covered by the surface protection portion 15. In the example shown in Figure 1, the gold-plated portion 5 is formed over the entire portion of the first gauge tab 3a and the second gauge tab 3b that is not covered by the surface protection portion 15. In this way, the gauge tab 3 is completely covered by the surface protection portion 15 or the gold-plated portion 5, effectively preventing the gauge tab 3 from deteriorating due to exposure to air. In addition, when a lead wire is soldered to the gauge tab 3 via the gold-plated portion 5, the formation of an oxide film by the gold-plated portion 5 is effectively prevented.

[0016] The thickness of the gold-plated portion is, for example, 0.1 μm to 10 μm. An example of the gold-plated portion 5 is electrolytic nickel-gold plating or electroless nickel-gold plating. The gold-plated portion can be formed by electrolytic nickel-gold plating or electroless nickel-gold plating. An example of the Ni thickness in nickel-gold plating is 3 to 5 μm, and an example of the Au thickness is 0.05 to 0.3 μm.

[0017] The surface protection portion 15, also known as a surface protection film, is well known in strain gauges. The surface protection portion 15 can be formed from, for example, a known plastic. Examples of surface protection films include epoxy resin films, polyester films, or polyimide films.

[0018] Figure 2 is a conceptual diagram showing an example where the gold-plated portion is formed on a part of the gauge tab. As shown, the gold-plated portion 5 may be formed on a part of the gauge tab 3 that is not covered by the surface protection portion 15. In the case of Figure 2 as well, it is preferable to form a second surface protection portion 15 on the part of the gauge tab 3 that is not covered by the surface protection portion 15 and on which the gold-plated portion 5 is not formed, so that the gauge tab is covered by the gold-plated portion 5 or the (second) surface protection portion.

[0019] Figure 3 is a conceptual diagram showing a strain gauge to which a lead wire is connected. The strain gauge of the present invention may be in a state where the lead wire 23 is not soldered via the gold plating portion 5, or may be in a state after the lead wire 23 is soldered via the gold plating portion 5. In the latter case, the strain gauge will further include a solder portion 21 on the gold plating portion 5 and a lead wire 23 connected to the solder portion. The lead wire is also called a gate lead or a lead-out wire.

Example

[0020] A metal foil material (copper nickel alloy or nickel chromium alloy) with a gauge factor K of 1.8 - 2.1 and a thickness of 2 - 15 μm or a metal foil material (stainless alloy) with a gauge factor K of 3 - 5 and a thickness of 2 - 6 μm was used. A plastic resin base (epoxy resin, imide amide resin or polyimide resin) having a thickness of 15 - 30 μm was laminated. The strain gauge shape capable of gold plating was etched with a ferric chloride solution and finished into a shape where the foil material has a gauge resistance value of 60 - 1000 Ω or more. Among the gauge tabs, the surface of the metal foil material outside the range to be gold plated was surface protected using a polyester film or a polyimide film with a thickness of 12 - 25 μm. Electrolytic nickel gold plating or electroless nickel gold plating having a Ni thickness of 3 - 5 μm and an Au thickness of 0.05 - 0.3 μm was applied on the gauge tab.

[0021] The strain gauge obtained by the example had a gold plating portion formed on the gauge tab, and soldering could be easily performed through the gold plating portion. Therefore, the characteristics of the strain gauge were stabilized and extremely good characteristics could be maintained.

Industrial Applicability

[0022] This invention can be used in the field related to strain gauges.

Explanation of Reference Numerals

[0023] 1. Strain gauge 3 Gauge Tabs 3a First gauge tab 3b Second gauge tab 5 Gold-plated part 11 gauge base 13 grid 15 Surface protection part 21 Soldering section 23 Lead wires

Claims

1. A strain gauge (1) having a gauge tab (3) which is a part for attaching lead wires, The gauge tab (3) is a strain gauge (1) having a gold-plated portion (5).

2. A strain gauge (1) according to claim 1, wherein the strain gauge (1) is Gauge base (11), A grid (13) is located on the gauge base (11) and has a plurality of parallel straight sections, The grid (13) has a surface protection portion (15) that covers it, The gauge tab (3) has a first gauge tab (3a) and a second gauge tab (3b) connected to each of the two straight sections located at both ends of the grid (13), The gold-plated portion (5) is located on the portion of the first gauge tab (3a) and the second gauge tab (3b) that is not covered by the surface protection portion (15), and is part of the strain gauge (1).

3. A strain gauge (1) according to claim 1, wherein the gold-plated portion (5) is electrolytic nickel-gold plating or electroless nickel-gold plating.

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