JPH03251704A - Manufacture of strain gauge - Google Patents

Abstract

PURPOSE:To prevent infiltration of water into a cover film by a method wherein a strain gauge element is formed on a synthetic resin base and a synthetic resin cover film laminated with a metal foil on the upper layer thereof beforehand is bonded thereon. CONSTITUTION:A gauge element 12 is formed on a base 11 made of a synthetic resin or the like as current path using a conducting foil or the like. Then, a cover film 13 which is laminated with a metal foil 13b on the top surface of a film 13a comprising a non-conducting material such as synthetic resin is prepared and the cover film 13 is bonded from the top surfaces of the base 11 and the gauge element 12 leaving an end 12a of the gauge element 12 serving as connection of a lead 14. Finally, the lead 14 is connected to the end 12a of the gauge element 12 by a spot welding, soldering or the like. This can prevent infiltration of water into the cover film thereby achieving a higher measuring accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a strain gauge used in a strain gauge or the like.

[Prior Art] It is known that when stress is applied to an electrical resistor, its resistance value changes. Utilizing this phenomenon, the amount of distortion can be determined by measuring the change in resistance using a bridge circuit.

A so-called strain gauge, which is normally used as an electric resistor for strain measurement, is shown in Fig. 3fal.
As shown in fb), a gauge pattern serving as a current path is formed on a flexible base l by a method such as pasting a strain gauge element 2 made of conductive foil.
There are leads on both ends of the gauge element 2 to connect it to a measuring instrument! ! 3 are connected by spot welding, soldering, etc. Further, as shown in FIG. 4, a flexible cover film 4 is often attached to the upper surface of the gauge element 2 in order to physically and electrically protect the gauge element 2.

Such a strain gauge is used by attaching the lower surface of the base 1 to an object to be measured. The attached base 1 bends following the distortion of the object to be measured, and the same distortion is transferred to the gauge element 2. At this time, by measuring the electrical resistance values at both ends of the gauge element 2, the distortion of the object to be measured can be determined. It is also known that by appropriately selecting the shape of the gauge element 2, a strain gauge with good sensitivity to strain in a specific direction can be obtained, and is useful for various stress analyses.

By the way, it is desirable that these strain gauges have sufficient flexibility and flexibly follow the strain of the object to be measured, so that the same strain is reliably transferred to the gauge element 2. In order to satisfy this requirement, In addition, organic materials such as synthetic resins are usually used for the base 1 and the cover film 4.

[Problems to be Solved by the Invention] However, organic materials such as synthetic resins generally have high gas permeability, and even synthetic resins such as Mylar, which is most often used for the base l and cover film 4, can easily pass water vapor. Are known. In this way, however, base 1
After the base 1 and the cover film 4 are attached to the object to be measured, there is little risk of moisture intruding from the object to be measured, but moisture from the air is likely to enter the cover film 4. When it absorbs moisture, a swelling phenomenon occurs in the base l,
Slight changes occur due to changes in the shape and volume of the base 1. A resistance change follows this change, making the bridge circuit unstable and preventing correct measurement values.
Once the base 1 and cover film 4 have absorbed moisture, they may swell and the adhesive portion may peel off, lose their ability to follow strain, or become warped and deformed when dried, leaving undesirable internal stress in the strain gauge itself. There is also a risk of it being lost.

In order to prevent such moisture from entering, after the strain gauge is attached to the object to be measured, a thin metal sheet that does not impair flexibility may be attached to the top surface of the cover film 4. Attaching such a metal sheet on-site during installation is extremely difficult and is not reliable as it may cause the metal sheet to tear. However, it cannot be avoided that the measurement accuracy will be affected to some extent.
Furthermore, since the adhesion work is performed twice and the work process becomes longer, there is a risk that it will not be possible to respond to urgent measurements, and that the moisture that permeated and penetrated before pasting the metal foil will not be released to the outside. .

An object of the present invention is to provide a method for manufacturing a strain gauge that can solve the above-mentioned problems, reliably prevent moisture from entering the strain gauge, and enable accurate strain measurement.

[Means for Solving the Problems 1] In order to achieve the above-mentioned object, in the method for manufacturing a strain gauge according to the present invention, thin flaky strain gauge elements are formed on a base of a synthetic resin material, and on these It is characterized in that a synthetic resin cover film on which metal foil is laminated in advance is adhered to the top layer.

[Function] The method for manufacturing a strain gauge having the above-mentioned configuration has good workability because a cover film, which is a film in which metal foil is laminated in advance, is adhered to the upper layer of the strain gauge element during manufacturing. Since it is designed and manufactured with the gauge performance in mind, it does not affect measurement accuracy.

[Example] The method according to the present invention will be explained in detail based on the example illustrated in FIGS. 1 and 2.

The manufacturing process will be explained based on FIG.
Form a gauge element 12 to serve as a current path using a conductor foil or the like having a thickness of 3 to 5 μm on the top of the conductive foil.
A cover film 13 having a structure in which a metal foil 13b with a thickness of about 5 μm is laminated on the upper surface of a film 13a made of an electrically nonconductive material with good flexibility such as synthetic resin with a thickness of about 5 μm is prepared in advance. Base 11 on film 13
, the gage element 12 is bonded from the upper surface leaving the end 12a of the gage element 12 where the lead wire 14 will be connected. Finally, the strain gauge is completed by connecting the lead wire 14 to the end 12a of the gauge element 12 by spot welding, soldering, or the like.

According to this manufacturing method, since the metal foil 13b is laminated on the film 13a in advance during manufacture of the cover film 13, there is no damage to the metal foil 13b, moisture is blocked by the metal foil 13b, and the film 13a is Moreover, since the strain gauge of the product is sealed immediately after manufacture, the base 11 etc. are not exposed to air until immediately before use.

Note that as shown in Figure 1, it is preferable that the metal foil 13b is not provided on the film 13a near the connection portion of the lead wire 14.
In other words, by separating the metal foil 13b from the lead wire 14, the lead wire 14 may come into contact with the metal foil 13b and the measured value may become inaccurate, or the leads 114 and 114 may come into contact with the metal foil 13b.
This prevents the risk of short-circuiting through.

Further, in the above method, the lead wires 14 are connected after the cover film 13 is bonded, but it goes without saying that this order may be reversed.

Furthermore, as shown in FIG. 2 (al lb), the cover film 13 can extend over the side of the base 11. In this way, base 11, cover film 1
It is possible to further reduce the infiltration of moisture from the side into the area 3.

On the other hand, when bonding the cover film 13 after connecting the lead wire 14 to the end 12a of the gauge element 12,
The connecting portion may also be covered.

[Effects of the Invention] As explained above, in the strain gauge manufacturing method according to the present invention, since the metal foil is attached at the time of manufacturing, there is no need to worry about damage, and it is possible to reliably prevent moisture from entering the cover film. Since the measurement accuracy is hardly affected by the intrusion of the strain, accurate strain measurement is possible.

[Brief explanation of drawings]

The drawings show an embodiment of the strain gauge manufacturing method according to the present invention, and FIG. 1 (al is a plan view of the strain gauge, FIG. 2(b) is a sectional view, and FIG. The plan view, Tb) is a sectional view, and FIG.
a) is a plan view of a conventional strain gauge; [bl is a sectional view; FIG. 13 is a gauge element, 13 is a cover film, 13a is a film, 13b is a metal foil, and 14 is a lead wire.

Claims (1)

[Claims] 1. A method for manufacturing a strain gauge, which comprises forming a thin flaky strain gauge element on a synthetic resin base, and adhering a synthetic resin cover film on which a metal foil is laminated as an upper layer in advance. .