JP2722080B2 - Free filament strain gauge and its manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a free filament strain gauge and a method for manufacturing the same.

[Conventional technology]

Conventionally, free filament strain gauges are, for example,
A thin wire is created by drawing a resistance alloy such as NiCr, NiCrAl, etc.
A method of obtaining a resistance element by appropriately folding the thin wire into a grid or winding to obtain a resistance element, or obtaining a resistance element of a predetermined shape by die-cutting a rolled resistance alloy foil made by rolling a resistance alloy. Manufactured by the method.

[Problems to be solved by the invention]

By the way, the conventional free filament strain gauge has the following problems.

First, a wire made of a resistive alloy and made by praying or winding it (hereinafter, these are collectively referred to as “wire gauge”) has limitations in the processing technology such as winding. There is a problem that it is extremely difficult or impossible to form a complicated shape or a fine shape, and it is difficult to increase the resistance value.

On the other hand, a strain gauge made by stamping a rolled resistance alloy foil has better characteristics by controlling the pattern shape than a wire gauge, but it has the same size as a strain gauge. Therefore, there is a problem that it is difficult to form a complicated shape or a fine shape because the molding is performed by the mold.

Accordingly, both the wire gauge and the stamping type foil gauge have only a simple and relatively large shape uniaxial gauge.

A free filament resistor is generally used for detecting strain at high temperatures, but when a single-axis gauge is used, for example, when a single-axis gauge made of a NiCr resistor is used, 20
A large apparent strain of 000με / 550 ° C was generated, and static strain measurement could not be performed. In particular, in this case, there is a fatal problem that the apparent strain and the thermal hysteresis characteristic are not reproducible, and the apparent strain fluctuates with the aging change during the measurement.

The present invention has been made in view of the above-described problems, and has as its object to be able to form a fine and complicated shape, to have a small apparent strain due to a temperature change, and to cover a wide temperature range from a low temperature to a high temperature. It is an object of the present invention to provide a method for manufacturing a free filament strain gauge which can measure not only dynamic strain but also static strain with high accuracy.

[Means for solving the problem]

In order to achieve the above object, in the method for producing a free filament of the present invention, a resistive foil made of NiCr, NiCrAl, CuNi, FeCrAl, FeNiCr, PtW or the like molded to a thickness of 1 to 30 μm is formed in a subsequent step. A bonding step of bonding to a substrate using an adhesive that has an adhesive strength that can withstand processing such as etching and gauge lead attachment, and that can be separated and removed by dissolution or sublimation in a subsequent separation step; An etching step of etching a resistance foil to form an active gauge grid for strain detection, a dummy gauge grid for temperature compensation, and a gauge tab, a gauge lead connecting step of connecting a gauge lead to the gauge tab by spot welding, and the bonding step. Dissolve the adhesive in the solvent of the adhesive used, or heat to a temperature higher than the decomposition temperature of the polymer material constituting the adhesive and heat-treat for a predetermined time Separating the resistive foil from the substrate by removing the adhesive from a strain gauge in which an active gauge grid, a dummy gauge grid, and a gauge tab are integrated, thereby producing a free filament. It is.

(Operation)

Since the forming to form the resistance foil into a predetermined shape is performed by etching the resistance foil while attaching the resistance foil to the substrate with a predetermined adhesive, the resistance foil is formed into a very fine and complicated shape, that is, an active gauge grid. , The dummy gauge grid and the gauge tab can be formed into a unitary shape.

In addition, after the etching, the adhesive used for bonding is dissolved to peel off the resistive foil from the substrate and completely remove the adhesive, so that a free filament can be completely formed. Therefore, it is possible to obtain a very high-performance free filament strain gauge, which can be used for temperature compensation.
It is possible to provide an element-free filament, that is, a free filament strain gauge in which an active gauge grid and a dummy gauge grid are integrated.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is a perspective view showing an external configuration of an embodiment of a free filament strain gauge according to the present invention.

In the figure, reference numeral 1 denotes an active element as an active gauge grid which extends along the gauge axis and is folded at both ends to form a grid, and 2 denotes an active element corresponding to the active element.
A dummy element as a dummy gauge grid for temperature compensation which is also formed in a grid shape by changing the orientation by 90 °. Both rolled foils of resistance alloy, for example, NiCr (thickness: 1 to 30 μm) are integrally formed by photo-etching. Have been. Gauge tabs 3a, 3b and 3c are integrally connected to one end and the other end of the active element 1 and the dummy element 2, respectively. la, lb, and lc are gauge leads (so-called lead wires) made of, for example, a NiCr alloy, and are spot-welded to the respective ends of the active element 1 and the dummy element 2 and the other ends (common ends) of the elements 1 and 2 respectively. It is connected.

Here, as is well known, spot welding is performed by laminating a metal plate to be welded (material to be welded), applying pressure by an electrode, applying a current by applying a voltage, and heating the weld by Joule heating (resistance heating). This is a welding method in which the material to be welded is metallurgically joined by local melting.

That is, if this is specifically explained, the gauge tab 3a (3
The gauge leads la (same for lb and lc) are placed on top of the b and 3c), and the top and bottom are pressed with a pair of positive and negative electrodes (tips). For example, 160
(Approximately 250 A), and the portion sandwiched between the pair of electrodes is heated by Joule heat to locally separate (spot) and join the gauge lead la to the gauge tab 3a.

The two-element strain gauge is a free filament, and naturally, the resistance elements 1, 2 separated from the substrate.
(Including the gauge tab 3 and the gauge leads la, lb, lc), and to the object to be measured, such as a machine or a structure, by bonding or spraying with an electrically insulating adhesive, or by pressing with ceramic. It is attached after being electrically insulated.

In measuring strain, a free filament strain gauge is inserted into a circuit so as to form a strain measuring circuit as shown in FIG.

That is, the strain measurement circuit has two fixed resistors R1, R2 each having one end connected to the input terminals T1, T2 of the input voltage ein and the other end commonly connected to one output terminal T3 of the output voltage eout.
2, one end (gauge tab 3a) is connected to one input end T2 via a gauge lead la, and the other end (common gauge tab
3c) is connected to the other output terminal T4 via the gauge lead lc, and one end (gauge tab 3b) is connected to one input terminal T1 via the gauge lead lb, and the other end is connected to the gauge lead lc. And a dummy element 2 connected to the other output terminal T4 together with the other end of the active element 1 through the dummy element 2. According to such a strain measurement circuit, a resistance change due to a temperature change occurring when measuring a strain generated in the measured object as a change in resistance of the active element 1, that is, a resistance temperature coefficient of the active element 1 and a measured temperature coefficient. Apparent strain caused by a change in thermal expansion of the body can be canceled by the dummy element 2, thereby performing temperature compensation. Therefore, the strain can be measured over a wide temperature range from a low temperature to a high temperature with less influence of a temperature change.

3 (A) to 3 (F) are cross-sectional views showing a method of manufacturing the free filament strain gauge shown in FIG. 1 in the order of steps.

(A) First, a rolled foil 4 as a resistance foil as shown in FIG. 3 (A) is prepared. The material is NiCr in this case, but other materials such as NiCrAl, CuNi, FeCrAl, FeNiCr,
PtW or the like may be used. The thickness is suitably from 1 to 30 μm, which is thicker than the conventional strain gauge material with a gauge base, from the viewpoint of shape retention, and most preferably about 15 μm.

(B) Next, as shown in FIG. 3 (B), the rolled foil 4 is pressure-bonded to the glass substrate 5 using the epoxy adhesive 6 via the polyimide film 7. In order to bond the rolled foil 4 to the glass substrate 5, the glass substrate 5 is placed on a flat base 8, and an epoxy-based adhesive 6 is laminated on the glass substrate 5 with a polyimide film 7 interposed therebetween (or After the rolling foil 4 is overlaid thereon, a pressure plate 9 is pressed in a direction indicated by an arrow with a predetermined pressure. This is pressure backing bonding. The rolled foil 4 is bonded via the epoxy adhesives 6, 6 formed on both sides of the polyimide film 7, but the use of the polyimide film 7 in this manner is effective for eliminating uneven bonding. That's why. And
These must be able to withstand various processes such as etching later. That is, application of a photoresist film, exposure processing, development processing, etching processing, resistance value adjustment (trimming), and lead wire (gauge lead) attachment are performed on the rolled foil 4. 6, 6 and the polyimide film 7 have the advantage that they can withstand sufficiently and sufficiently fulfill the function as an adhesive, and that air bubbles and uneven adhesion are hardly generated. However, other adhesives that satisfy the conditions may be used.

(C) Next, as shown in FIG. 3 (C), a photoresist film 10 is applied to the surface of the rolled foil 4.

(D) Next, an exposure process of irradiating the photoresist film 10 with light (for example, ultraviolet rays) through a photomask (not shown) on which a predetermined pattern is drawn, and a development process are performed. As shown in FIG.
Is selectively left.

(E) Next, as shown in FIG. 3 (E), the unnecessary rolled foil 11 of the rolled foil 4 is removed by etching using the photoresist film 10 as a mask. After that, measure the resistance value,
The resistance value is adjusted by etching or polishing so that it becomes a predetermined value. Thereafter, a lead wire (or band) as a gauge lead made of NiCr or CuNi is spot-welded. As a result, the strain gauge element is formed on the glass substrate 5 in a bonded state.

(F) Thereafter, the polyimide film 7 is subjected to a heat treatment at a high temperature of 300 to 500 ° C. for about 2 to 5 hours, or an epoxy adhesive 6, 6 with dichloromethane as a solvent, or a mixed solution of potassium hydroxide and ethyl alcohol. After dissolving and removing, the strain gauge element 12 is peeled off from the glass substrate 5 as shown in FIG. 3 (F), and the epoxy adhesive 6 is completely removed from the gauge element 12.

As described above, in the present invention, since the alloy resistance rolling foil 4 is formed into a predetermined shape by photoetching, a very fine and complicated shape can be formed with high precision. Then, the strain gauge element 11 formed in a predetermined shape decomposes the adhesives 6, 6, 7 for bonding the same to the glass substrate 5 by, for example, heat treatment or the like, and peels off the glass substrate 5.
Further, by completely removing the adhesives 6, 6, and 7, a free filament can be formed.

Thus, it has become possible to obtain a very high-precision free filament strain gauge. In particular, by using two free filament strain gauges to enable temperature compensation, a strain measurement value independent of a temperature change can be obtained.

FIG. 4 shows an example of a change in apparent strain with temperature for a two-element free filament strain gauge according to the present invention when a NiCr resistance alloy is used and a conventional uniaxial free filament strain gauge, The solid line indicates the case according to the present invention, and the broken line indicates the case of the conventional single axis.

As is clear from this figure, in the case of the conventional uniaxial gauge without temperature compensation, the magnitude of the apparent strain greatly changes to 20,000 με / 550 ° C. due to the temperature change. According to the figure, it can be seen that the change in the apparent strain due to the temperature change is very small at 1000 με / 550 ° C.

〔The invention's effect〕

As is apparent from the above detailed description, according to the present invention, the resistive foil formed into a predetermined shape by photoetching on the substrate is separated from the substrate by dissolving the adhesive and bonded. Since a special method of removing the agent was used, which could not be found by the person skilled in the art, very fine, complicated shapes and high resistance can be easily obtained, and the apparent temperature It is possible to provide a method for producing a highly reliable free filament strain gauge with little change in strain and change with time.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an external configuration of a free filament strain gauge formed by a manufacturing method according to the present invention,
FIG. 2 is a circuit diagram showing a strain measurement bridge circuit using the free filament strain gauge according to the embodiment, and FIGS. 3 (A) to 3 (F) are diagrams for manufacturing the free filament strain gauge shown in FIG. FIG. 4 is a cross-sectional view showing the method in the order of steps, and FIG. 4 compares the temperature dependence of apparent strain with temperature in the case of the present invention and in the case of the conventional example using nickel-chromium as a resistive foil as an example. It is a characteristic diagram. 1 Active element, 2 Dummy element, 3a, 3b, 3c Gauge tab, 4 Rolled foil, 5 Glass substrate, 6 Epoxy adhesive, 7 Polyimide film, 8 Base, 9 ... Pressure plate, 10 ... Photoresist film, 11 ... Unnecessary rolled foil, 12 ... Strain gauge element, la, lb, lc ... Gauge lead.

Claims (1)

(57) [Claims] 1. NiCr and NiCrA formed to a thickness of 1 to 30 .mu.m.
l, CuNi, FeCrAl, FeNiCr, PtW, etc., have resistance to withstand processing in subsequent processes such as etching and mounting of gauge leads, and are separated and removed by dissolution or sublimation in subsequent separation processes. A bonding step of bonding to the substrate using a possible adhesive, an etching step of etching the resistance foil on the substrate to form an active gauge grid for strain detection, a dummy gauge grid for temperature compensation, and a gauge tab, A gauge lead connecting step of connecting a gauge lead to a gauge tab by spot welding, and dissolving the adhesive with a solvent of the adhesive used in the bonding step or heating the polymer to a decomposition temperature or higher of a polymer material constituting the adhesive. Separate the resistive foil from the substrate by performing heat treatment for a predetermined time, and measure the active gauge grid, the dummy gauge grid, and the gauge. Free filament strain producing method of gauge and having a separation step in which the blanking of removing the adhesive from the integrated strain gauge, a.