JPH0285702A - Free filament strain gage and production thereof - Google Patents

Abstract

PURPOSE:To decrease the apparent strains arising from a temp. change and to measure dynamic and static strains over a wide temp. range at high accuracy by molding rolled foil to a prescribed shape by photoetching. CONSTITUTION:The rolled foil 4 is prepd. and NiCr, etc., are used as the material thereof. The thickness thereof is confined to 1 to 30mum. The rolled foil 4 is adhered under pressurization via a polyimide film 7 to a glass substrate 5 by using an epoxy adhesive agent 6. A photoresist film 10 is coated on the surface of the rolled foil 4. The resist film 10 is subjected to an exposing treatment to irradiate the film with light and further to a development processing so that the resist film 10 is made to remain selectively. The unnecessary rolled foil 11 of the rolled foil 4 is removed by etching with the resist film 10 as a mask. The resistance value is thereafter measured and is adjusted in such a manner that the resistance value attains a prescribed value. Lead wires are then spot-welded. A stain gage element 12 is removed from the substrate 5 and further the adhesive agent 6 is completely removed from the element 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a free filament strain gauge and a method for manufacturing the same.

[Conventional technology]

Free filament strain gauges are conventionally used, e.g.
A method of drawing a resistance alloy such as iCr or N1CrAQ to make a thin wire, and folding the thin wire appropriately to form a lattice shape or winding it to obtain a resistance element, or a rolled resistance alloy foil made by rolling a resistance alloy. The resistor element was manufactured by die-cutting the resistor element to obtain a resistor element in a predetermined shape.

[Problems that the invention attempts to solve]

By the way, conventional free filament strain gauges have the following problems.

First, there are limitations in processing technology such as winding for products made by making thin wires from resistance alloys and winding them (hereinafter collectively referred to as "wire gauges"). There are problems in that it is extremely difficult or impossible to form a complex shape or a fine one, and it is also difficult to increase the resistance value.

On the other hand, strain gauges made by punching rolled resistance alloy foil can control the pattern shape and provide better characteristics compared to wire gauges, but the A mold is required, and since the mold is used for molding, there is a problem that it is difficult to produce products with complex shapes or minute shapes.

Therefore, only simple and relatively large axle gauges existed, both wire gauges and punched foil gauges.

Free filament resistors are generally used for strain detection under high temperatures, but when an axle gauge is used, for example, an axle gauge made of a NiCr resistor produces a large apparent strain of 20,000 με 1,550°C. Therefore, static strain measurement was not possible.

In particular, there was a fatal problem in that the apparent strain and thermal hysteresis characteristics in this case were not reproducible, and the apparent strain also varied due to changes over time during measurement.

The present invention has been made in view of the above-mentioned problems, and aims to be able to form fine and complex shapes, have small apparent distortion due to temperature changes, and have a wide temperature range from low to high temperatures. The object of the present invention is to provide a free filament strain gauge that can measure not only dynamic strain but also static strain with high precision, and a method for manufacturing the same.

[Means to solve the problem]

In order to achieve the above object, the free filament strain gauge of the present invention includes an active gauge grid for strain detection, a dummy grid for temperature compensation that substantially cancels out the temperature coefficient of resistance of the active gauge grid, The gauge tab for connecting the gauge lead is
NiCr with a thickness of 1 to 30 μm by etching
, NiCrAl, CuNi, FeCrAQ, FeNiC
It is integrally formed with resistive foil such as R, PtW, etc.

Moreover, in order to achieve the above object, in the method for manufacturing a free filament of the present invention, NiCr or N1CrAQ is molded to a thickness of 1 to 30 μra.

An adhesive that has adhesive strength that can withstand processing such as etching and gauge lead attachment in later processes, and can be separated and removed by melting or sublimation in the later separation process, for resistive foils made of CuNi, FeCrAQ, FeNiCr, PtW, etc. an adhesion process in which the resistive foil on the substrate is etched 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 in which the gauge leads are connected by spot welding, and a step in which the adhesive is dissolved in the solvent of the adhesive used in the bonding step or heated to a temperature higher than the decomposition temperature of the polymeric material constituting the adhesive for a predetermined period of time. A free filament is manufactured through a separation step of separating the resistance foil from the substrate by heat treatment and removing the adhesive from the strain gauge in which the active gauge grid, the dummy gauge grid, and the gauge tab are integrated. This is what I did.

[For production]

The resistor foil is formed into a predetermined shape by etching the resistor foil after it has been bonded to the substrate with a predetermined adhesive, so the resistor foil can be shaped into a very fine and complex shape, i.e., an active gauge grid. , a dummy gauge grid and a gauge tab can be molded into an integrated shape.

Furthermore, after etching, the adhesive used for bonding is dissolved, the resistive foil is peeled off from the substrate, and the adhesive is completely removed, so that a completely free filament can be obtained.

Therefore, a very high-performance free filament strain gauge can be obtained, thereby providing a temperature-compensable two-element free filament, that is, a free filament strain gauge that integrates an active gauge grid and a dummy gauge grid. This has become possible.

〔Example〕

Hereinafter, the present invention will be explained in detail according to illustrated embodiments.

FIG. 1 is a perspective view showing the 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 that extends along the gauge axis and is folded back at both ends to form a lattice-like structure, and 2 corresponds to the active element 9
Dummy elements as dummy gauge grids for temperature compensation are similarly formed in a lattice shape with the orientation changed by 0 degrees, and both are formed integrally with rolled foil (thickness 1 to 30 μm) of a resistance alloy such as NiCr by photoetching. has been done.

Gauge tabs 3a, 3b and 3C are provided at each end and the other end of the active element 1 and dummy element 2, respectively.
are connected together. Qa, Qb and Qc
is a gauge lead (so-called lead, m) made of, for example, a NiCr alloy, and the active element 1. Dummy element 2
and the other end (common end) of the pixel elements 1 and 2 by spot welding.

This two-element strain gauge is a free filament, and naturally the resistance elements 1 and 2 are peeled off from the substrate.
(However, gauge tab 3, gauge lead Qa, Ωb
, Qc), and is attached to an object to be measured such as a machine or a structure after being electrically insulated by adhesion with an electrically insulating adhesive, thermal spraying, or ceramic pressure welding.

For strain measurement, a free filament strain gauge is inserted into a circuit to form a strain measurement circuit as shown in FIG.

That is, the strain measurement circuit has one end connected to the input terminals Tl and T2 of the input voltage ein, and the other end connected to the output voltage ein.
Two fixed resistors R1 and R2 are commonly connected to one output terminal T3 of out, one end (gauge tab 3a) is connected to one input terminal T2 via a gauge lead Qa, and the other end (common gauge tab 3c). ) is connected to the other output terminal T4 via the gauge lead Re,
One end (gauge tab 3b) is connected to one input end T1 via a gauge lead Qb, and the other end is connected to the other end of the active element 1 and the other output end T4 via a gauge lead Qc.
The dummy element 2 is connected to the dummy element 2. According to such a strain measurement circuit, when the strain generated in the object to be measured is measured as a change in the resistance of the active element 1, the resistance change due to the temperature change that occurs, that is, the resistance temperature coefficient of the active element 1 and the measured object Apparent strain caused by changes in thermal expansion of the body can be canceled by the dummy element 2, thereby performing temperature compensation. Therefore, strain can be measured over a wide temperature range from low to high temperatures while reducing the influence of temperature changes.

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

(A) First, a rolled foil 4 as a resistance foil as shown in FIG. 3(A) is prepared. In this example, the material is NiC
r, but other materials such as NiCrAl, CuNi,
FaCrAQ, FeNiCr, PtW, etc. may also be used. From the viewpoint of shape retention, the appropriate thickness is 1 to 30 μm, which is thicker than conventional strain gauge materials with gauge bases.
The most appropriate value is approximately μm.

(B) Next, as shown in FIG. 3(B), the rolled foil 4 is pressure-bonded to the glass substrate 5 using an epoxy adhesive 6 via a polyimide film 7. To adhere the rolled foil 4 to the glass substrate 5, place the glass substrate 5 on a flat base 8, and overlay the epoxy adhesive 6 (or coating),
After stacking the rolled foil 4 on top of the rolled foil 4, it is pressed with a pressure plate 9 in the direction of the arrow at a predetermined pressure. This is pressure backing adhesive. The rolled foil 4 is bonded via the epoxy adhesives 6, 6 formed on both sides of the polyimide film 7, and using the polyimide film 7 in this way is effective in eliminating uneven adhesion. That's why. These materials need to be able to withstand subsequent steps such as etching. That is, coating the rolled foil 4 with a photoresist film, exposing it to light, developing it,
Etching treatment, resistance value adjustment (trimming), and lead wire (gauge lead) attachment are performed, but the epoxy adhesives 6, 6 and polyimide film 7 can withstand these treatments sufficiently and function as adhesives. Moreover, it has the advantage that bubbles and uneven adhesion are less likely to occur. but,
Other adhesives may be used as long as they meet these conditions.

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

(D) Next, light (
For example, exposure treatment to irradiate ultraviolet light a) is performed, and further development treatment is performed to selectively leave the photoresist film 10 as shown in FIG. 3(D).

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

(F) After that, the epoxy adhesive 6.6. Further, the polyimide film 7 is dissolved and removed using a mixture of potassium hydroxide and ethyl alcohol, 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 applied to the gauge. completely removed from element 12.

As described above, in the present invention, since the alloy resistance rolled foil 4 is formed into a predetermined shape by photoetching, it is possible to form a very fine and complicated shape with high precision. The strain gauge element 11 formed into a predetermined shape is bonded to the glass substrate 5 using adhesives 6, 6 .
7 can be decomposed by heat treatment or the like, peeled off from the glass substrate 5, and the adhesives 6, 6.7 can be completely removed to form free filaments.

It has thus become possible to obtain a free filament strain gauge with very high precision. In particular, by using a two-element free filament strain gauge to enable temperature compensation, it has become possible to obtain strain measurements that are independent of temperature changes.

FIG. 4 shows an example of changes in apparent strain due to temperature for a two-element free filament strain gauge according to the present invention and a conventional axle free filament strain gauge when NiCr resistance alloy is used. is according to the present invention, and the dashed line shows the case of a conventional axle.

As is clear from this figure, in the case of a conventional axle gauge without temperature compensation, the apparent strain increases by 20% due to temperature changes. Although it changes greatly from OOOμE1550'C,
According to the two-element free filament strain gauge according to the present invention, the change in apparent strain due to temperature change is 1000
It can be seen that με is very small, 1550'C.

〔Effect of the invention〕

As is clear from the detailed description above, according to the present invention, a very fine active gauge grid, a dummy gauge grid, and gauge leads at each end thereof are integrally formed with a resistance foil of 5 to 30 μm. Therefore, the active gauge grid and the dummy gauge grid can be attached to a part of the object to be measured that can be considered to be almost the same part, and since both grids exhibit the same change in physical properties, apparent distortion due to temperature changes is extremely small. It is possible to provide a free filament strain gauge that is small and can therefore measure not only dynamic strain but also static strain with high precision over a wide temperature range from low to high temperatures, and a method for manufacturing the same.

Furthermore, according to the present invention, a resistive foil formed into a predetermined shape on a substrate by photo-etching is peeled off from the substrate by dissolving the adhesive, and the attached adhesive is removed cleanly. Because we have adopted a special method that no other manufacturer could have invented, we can easily obtain products with extremely fine, complex shapes and high resistance, and with little apparent distortion due to temperature and little change over time, we are extremely reliable. A method for manufacturing a free filament strain gauge with high properties can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the external configuration of a free filament strain gauge 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 same embodiment, and FIG. (A) to (F) are
FIG. 4 is a cross-sectional view showing the manufacturing method of the free filament strain gauge shown in FIG. 1 in the order of steps.
FIG. 4 is a characteristic diagram comparing the temperature dependence of apparent strain due to temperature in a case according to the present invention and a case according to a conventional example using nickel chromium as a resistance foil as an example. 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, Qa, Qb, Qc...Gauge lead. 1 Figure 1 Figure 2 Figure 3 Temperature

Claims (2)

[Claims] (1) an active gauge grid for strain detection; a dummy gauge grid for temperature compensation that substantially cancels out the temperature coefficient of resistance of the active gauge grid;
The gauge tab for connecting the gauge lead is made of NiCr or NiCrAl having a thickness of 1 to 30 μm by etching.
, CuNi, FeCrAl, FeNiCr, PtW, or the like is integrally formed with a resistance foil. (2) NiCr, Ni molded to a thickness of 1 to 30 μm
CrAl, CuNi, FeCrAl, FeNiCr, P
A resistive foil made of tW or the like is bonded to a substrate using an adhesive that has adhesive strength that can withstand processing such as etching and gauge lead attachment in later steps, and can be separated and removed by melting or sublimation in a later separation step. an etching process of etching the resistance foil on the substrate to form an active gauge grid for strain detection, a dummy gauge grid and a gauge tab for temperature compensation, and attaching gauge leads to the gauge tabs by spot welding. In the step of connecting the gauge leads, the adhesive is dissolved in the solvent of the adhesive used in the bonding step, or the adhesive is heated to a temperature higher than the decomposition temperature of the polymeric material constituting the adhesive and heat-treated for a predetermined period of time. Manufacturing a free filament strain gauge, comprising: separating a resistance foil from the substrate and removing the adhesive from a strain gauge in which an active gauge grid, a dummy gauge grid, and a gauge tab are integrated. Method.