JPH0652204B2 - Load cell - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion preventive structure for a load cell.

2. Description of the Related Art A load cell is configured such that a strain gauge is attached to a strain-generating body and the extent to which the strain-generating body is elastically deformed by a load is detected from a change in the output voltage of the strain gauge.
Since the strain gauge is a thin film resistor formed on the film, it is vulnerable to corrosion. Conventionally, as shown in FIGS. 5 and 6, the strain gauges 2A to 2D are firmly fixed to the strain-generating body 1. Is coated with synthetic resins 3A and 3D to form a moisture-proof structure. 4A and 4B are bolts for attaching to the fixed side 5, 1A is a fixed end of the flexure element 1, and 1B is a force application point of the flexure element 1.

As the material of the flexure element 1, a material having a high tensile strength and a small hysteresis is required. Conventionally, an aluminum alloy (Al-Cu alloy JIS material code H4040,
Type 2000 series) and carbon steel alloy for machine structure (Ni-Cr-
Heat-treated Mo steel JIS material code G4103) is used.

However, although to a different extent, all of the above materials have poor corrosion resistance. Aluminum alloys, which are often used for strain cells of low capacity load cells, are inferior in corrosion resistance to carbon steel alloys for machine structural use because they contain Cu, and are extremely weak particularly in alkaline aqueous solutions. For carbon steel alloys for machine structure,
Corrosion resistance is inferior to weakly acidic aqueous solution, though not as good as aluminum alloy.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Under the current circumstances in which the flexure element 1 is poor in corrosion resistance,
Even if only the attachment positions of the strain gauges 2A to 2D are coated, the strain-flexing body 1 is corroded, and moisture penetrates into the inside from the boundary surface 6 between the strain-flexing body 1 and the synthetic resins 3A and 3B. 2A to 2D corrode, and the reliability of the weight value decreases. Therefore, it is conceivable to apply the coating to the exposed portion of the flexure element 1, but the coating film is easily peeled off, and when the coating film is peeled off, corrosion of the flexure element 1 starts from that portion, and the flexure element 1 and the synthetic resin Moisture penetrates into the inside from the boundary surface 6 between 3A and 3B, and the strain gauges 2A to 2D corrode. When the film thickness is increased so that the coating film does not come off easily, the hardness of the coating material acts to reduce the weighing accuracy. Therefore, the moisture-proof measure by coating cannot be applied to the low capacity load cell.

It is an object of the present invention to provide a load cell capable of protecting a strain element from corrosion without lowering weighing accuracy and more reliably preventing moisture from entering a strain gauge.

Means for Solving the Problem The load cell of the present invention has a connecting point made of a material having a higher corrosion resistance than the material forming the strain generating element at the force application point and the fixed end of the strain generating element attached with the strain gauge, It is characterized in that it is mounted with an insulator interposed, and is molded from the strain-generating body and the strain-generating body to the connecting member with a synthetic resin having elasticity in a cured state.

Operation According to this configuration, the load cell is attached to the fixed side via the connecting member attached to the fixed end of the strain generating element.
The load acting on the connecting member attached to the force applying point of the strain generating body is supported via the insulator, the strain generating body, and the connecting member attached to the fixed end. An insulator is interposed on the contact surface between the connecting member and the strain generating body, and the two metal materials are electrically separated on this contact surface.

The surface of the load cell is molded with an elastic synthetic resin except for a part of the connecting member attached to the fixed end of the flexure element and a part of the connecting member attached to the force applying point of the flexure element. Therefore, the strain body is not exposed.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. It should be noted that components having the same functions as those in FIGS.

FIG. 1 shows a load cell of the present invention. At the fixed end 1A and the force applied point 1B of the flexure element 1 formed of an aluminum alloy, connecting members 7A and 7B formed of stainless steel SUS-304, which is superior in corrosion resistance to the aluminum alloy, are provided between them. As shown in FIG. 2, it is attached with bolts 8A and 8B with insulating sheets 14A and 14B interposed.
Further, the exposed surface of the flexure element 1 is molded with a polyurethane resin 9 having elasticity in a cured state. The abutting portion between the strain generating body 1 and the connecting members 7A and 7B is covered with the polyurethane resin 9 from the strain generating body 1 to the connecting members 7A and 7B as shown in FIGS. 10 is a synthetic resin for filling holes.

With this configuration, the fixed side 1A of the load cell is fixed to the fixed side 5 through the bolts 11A to 11D through the holes formed in the connecting member 7A, and the force application point 1B is provided with the screw hole 12A formed in the connecting member 7B. A load pedestal is attached to ~ 12D with a bolt (not shown).

The load cell is covered with a polyurethane resin 9 having elasticity except for a part of the connecting members 7A and 7B, and the strain element 1 made of an aluminum alloy, which is easily corroded, is molded so as not to be exposed. It is possible to prevent corrosion of the flexure element 1 without degrading the accuracy, and even if the flexure element 1 and the synthetic resins 3A to 3B are used for a long period of time, moisture invades from the boundary surface 6 between the flexure element 1 and the synthetic resins 3A to 3B. And the strain gauges 2A to 2D can be protected from corrosion.

The aluminum alloy forming the flexure element 1 has a reaction tendency −
Since 0.7-potential bolt and stainless steel forming the connecting members 7A and 7B have a reaction tendency different from -0.09-potential bolt, dissimilar metal contact corrosion occurs when both are directly contacted with each other. Since 14A and 14B are interposed, it is possible to maintain the opposing surfaces of the strain generating element 1 and the connecting members 7A and 7B in a flat state without the above-described corrosive contact with dissimilar metals. Here, the bolts 8A, 8B and the flexure element 1
The space between them is also electrically insulated as follows. Bolt 8
An insulating plate 15 is interposed between the heads of the A and 8B and the strain-generating body 1, and the portion under the neck of the bolts 8A and 8B is coated with the synthetic resin 16 and is drilled in the strain-generating body 1. Inserted hole 17
Achieves electrical insulation with the inner surface of the.

Thus, although the connecting members 7A, 7B and the strain element 1 are made of different metals, they are completely electrically insulated from each other, so that there is no contact corrosion of the different metals, and the connecting member 7A can be used for a long period of time. , 7B and the flexure element 1 do not rattle, and it is possible to prevent a situation in which a gap is generated between the synthetic resin 9 and the connecting members 7A, 7B and water enters.

In the above embodiment, the case of the cantilever beam type load cell has been described as an example, but this is the same in the case of the both ends fixed type beam type load cell shown in FIG. Here, the steel ball receiving seat 13 is placed on the connecting member 7B.

In each of the above-mentioned embodiments, the polyurethane resin 9 is coated up to half the thickness of the connecting members 7A and 7B. However, this causes strain on the connecting members 7A and 7B, leaving only the load receiving surface and the mounting surface to the fixed side 5. As described above, according to the present invention, according to the present invention, a material forming the strain-generating body at the force application point and the fixed end of the strain-generating body to which the strain gauge is attached. Since a connecting member made of a material having higher corrosion resistance than that is attached and molded by the synthetic resin having elasticity in a cured state from the strain generating body and the connecting member to the connecting member, even a low capacity load cell is weighed. The strain element can be protected from corrosion without sacrificing accuracy, and the strain gauge can be protected from corrosion, even in an environment where corrosive gas, acid or alkaline solution is handled. It can be expected a stable load conversion operation over the period. Furthermore, since an insulator is interposed between the strain body and the connecting member for electrical insulation, dissimilar metal contact corrosion does not occur, and rattling does not occur between the connecting member and the strain body even after long-term use. In addition, it is possible to prevent a situation in which a gap is generated between the synthetic resin and the connecting member and moisture enters, and the reliability of the anticorrosion structure is further ensured.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the load cell of the present invention, FIG.
FIG. 3 is a vertical sectional view of the same apparatus, FIG. 3 is a vertical sectional view of FIG. 2 taken along line XX ′, FIG. 4 is a vertical sectional view of another embodiment, and FIG. 5 is a plan view of a conventional load cell. The figure is a partially cutaway front view of FIG. 1 ... Aluminum alloy flexure element, 1A ... Fixed end of flexure element 1, 1B ... Force point of flexure element 1, 2A-2D ...
... Strain gauge, 4A-4D ... Mounting bolts, 7A, 7B ... Stainless steel connecting member, 9 ...
Polyurethane resin, 14A, 14B, 15 ... Insulation sheet [insulator].

Claims (1)

[Claims] 1. A connecting member made of a metal material having a corrosion resistance higher than that of a metal material forming the strain-generating body, with an insulator interposed, at an attachment point and a fixed end of the strain-generating body to which the strain gauge is attached. A load cell formed by molding the strain-generating body and the connecting member from the strain-generating body with a synthetic resin having elasticity when attached and cured.