JPH10339677A - Load cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost of a load cell evading its increase in size. SOLUTION: In a stationary part 14 a terminal board housing part 22 is provided, and by a communicating hole 26 the housing part 22 is connected to a through hole 18, with an opening filled in by a sealing plug 24. In the housing part 22, cable inserting holes 28 are formed in three sides of the stationary part 14. Inside the housing part 22, a terminal board 29 is arranged. The leads 20a of a strain gauge 20 are led out to the terminal board housing part 22 through the communicating hole 26, and a bridge circuit is formed by performing connection with solder on the terminal board 29. The lead of an electric cable 30 is electrically connected to two counter junctions of the bridge circuit respectively. Power is fed from two junctions on one side of the bridge circuit. And a detection signal is taken out from the other side. When connection work of the leads 20a of the strain gauge 20 and the electric cable 30 on the terminal board 29 is finished, the housing part 22 is filled up with a setting resin 31 to perform sealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell, and more particularly to a technique for improving the electrical connection of a load cell of this type.

[0002]

2. Description of the Related Art As a load measuring means, a load cell using a strain gauge is known. This type of load cell detects the applied gravitational load with a strain gauge, and calculates and processes the electric signal detected by the strain gauge.
An applied load value is determined.

A load cell having such a function is generally provided with a cylindrical strain body, and the strain body has a fixed portion formed on one end side and a fixed portion formed on the other end side. It has a movable part to which a load is applied, a strain generating part that is deformed by the load applied to the movable part, and a strain gauge attached to the strain generating part.

Usually, four strain gauges are used, these are connected to a bridge circuit, a voltage is applied between two opposite connection points of the bridge circuit, and the other two connection points of the bridge circuit are connected. The voltage between the points is used as a detection signal.

In such a bridge circuit, when deformation occurs in the strain generating portion due to an applied load, the resistance value of the strain gauge changes in response to the deformation, and the resistance value changes in response to the change in the resistance value. Since the detection signal of the bridge circuit changes, the applied load value can be calculated from the detection signal.

In a load cell having such a function, it is necessary to form a bridge circuit with a plurality of strain gauges, supply power to the bridge circuit, and take out a detection signal from the bridge circuit.

Therefore, conventionally, in order to make such a circuit connection, a terminal box is attached to a strain body, a terminal plate is installed in the terminal box, and a bridge circuit is formed on the terminal plate. Such electrical connections were made.

[0008] However, such means for processing the electrical connection portion has the following problems.

[0009]

That is, the structure in which the terminal box is attached to the flexure element has a problem that the entire load cell becomes large, the number of parts increases, and the cost increases.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a load cell capable of reducing costs by reducing the number of components and achieving downsizing. It is in.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a fixed part formed at one end, a movable part formed at the other end, and a movable part applied to the movable part. In a load cell having a strain generating body composed of a strain generating portion deformed by a load and a plurality of strain gauges attached to the strain generating portion, the load cell is formed integrally with the fixing portion, and the opening is a plug. A terminal board storage portion sealed by the above, a bridge circuit forming terminal plate of the strain gauge disposed in the storage portion, and one end communicating with the storage portion, and the other end opening to the surface side of the fixing portion. A cable insertion hole; and an electric cable having one end connected to the terminal plate via the cable insertion hole, for supplying power to the bridge circuit and extracting a detection signal. According to the load cell configured as described above, a bridge circuit is formed by a plurality of strain gauges, and an accommodating portion of a terminal plate to which an electric cable for supplying power to the bridge circuit and extracting a detection signal is connected, Since it is provided integrally with the fixing portion of the strain body, a separate terminal box is not required. After connecting the strain gauge and the electric cable to the terminal plate, the terminal plate housing portion can be sealed by filling with a curable resin. According to this configuration,
The connection state on the terminal board can be stably maintained for a long time. The cable insertion hole is constituted by a plurality of openings on the side surface and the end surface of the fixing portion, and the electric cable is attached to one arbitrarily selected cable insertion hole, and the unselected cable insertion hole is blind-plugged. Can be used to seal. According to this configuration, the extension direction of the electric cable can be selected from a plurality of directions.

[0012]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIGS. 1 to 4 show an embodiment of a load cell according to the present invention. This embodiment shows a case where the present invention is applied to a pressure-resistant explosion-proof load cell.

The load cell shown in FIG. 1 is formed in the shape of a rectangular tube having a substantially square cross section, and has a strain generating body 10 made of a light metal such as aluminum or ceramics. The flexure element 10 includes a flexure section 12 located at a central portion, a fixed section 14 located on the left side of the flexure section 12, and a movable section 16 located on the right side of the flexure section 12. .

[0014] Between the opposing side surfaces of the strain generating portion 12,
A through-hole 18 having a circular cross section whose center is located on the central axis in the longitudinal direction of the prismatic strain-generating body 10 is formed. Four strain gauges 20 are attached to the inner peripheral surface of the through hole 18.

The attachment position of the strain gauge 20 is
Are located on the same circumference, and are arranged so that each pair faces the center of the circle.

On the back side of the attachment position of each strain gauge 20, a concave cutting portion 21 having an arc-shaped cross section is provided. The concave cutting portion 21 is formed by cutting the outer surface of the strain generating portion 12, and the deformation of the strain generating portion 12 is facilitated by reducing the thickness of the portion where each strain gauge 20 is attached. .

The concave cutting portion 21 having such an operation
By adjusting the amount of cutting, the amount of deformation detected by the strain gauge 20 can be changed, so that bending and torsional moments can be corrected.

The fixing portion 14 is provided with a terminal plate storage portion 22. One end of the terminal plate storage portion 22 has the through hole 1.
8 is a concave circular shape opened on the side face not provided, and the opening is sealed by a hermetic plug 24 and communicates with the through hole 18 by a communication hole 26.

The terminal plate housing 22 has three sides of the rectangular fixed portion 14 (in this embodiment, the fixed portion 14
And a cable insertion hole 28 that is open at the end face of the cable and two side surfaces provided with the through holes 26).

One of the cable insertion holes 28 is used according to the request of the user. In the case of the present embodiment, the insertion hole 28 is opened at the end face of the fixing portion 14.
An electric cable 30 is mounted on the first and second insertion holes 28, and the other two insertion holes 28 are sealed by filling with a curable synthetic resin.

A terminal plate 29 is disposed in the terminal plate storage section 22. Each lead wire 20a of each of the four strain gauges 20 is led out to the terminal plate housing portion 22 through the communication hole 26, and is connected by soldering on the terminal plate 29 to form a bridge circuit.

The lead wires of the electric cable 30 are electrically connected by solder to two opposing connection points of the bridge circuit, respectively, to supply power from one of the two connection points of the bridge circuit and to supply a detection signal from the other. Take out.

When the connection between the lead wire 20a of the strain gauge 20 and the electric cable 30 is completed on the terminal plate 29, the terminal plate housing portion 22 is sealed by using a blind plug.

The curable resin 31 used here is a room-temperature or heat-curable adhesive such as an epoxy resin.

The load cell thus configured fixedly supports the fixed portion 14 side, and when a load is applied to the movable portion 16 side, the strain generating portion 12 is deformed, and the strain corresponding to this deformation is applied to the strain gauge 20. , And the magnitude of the load can be calculated based on the detected value.

Further, in the load cell of this embodiment, an explosion-proof structure is obtained by effectively utilizing the explosion-proof gap allowed in the standard. This specific configuration is shown in FIG.
As shown in detail in FIG. 3, a pair of male and female plugs 32 and 34 are inserted into the through holes 18 from both ends thereof, and both are tightened with bolts 36 to penetrate the outer surfaces of the plugs 32 and 34. Hole 18
The gap d for explosion proof is formed between the inner surface and the inner surface (part indicated by O in FIG. 2).

The male plug 32 includes a large-diameter cylindrical portion 32a and a small-diameter cylindrical portion 32 provided on the distal end side of the large-diameter cylindrical portion 32a.
b and a flange portion 32c provided at the upper end of the large-diameter cylindrical portion 32a.

The large-diameter cylindrical portion 32a is formed to have a smaller diameter than the inner diameter of the through hole 18, and its outer surface forms a joint surface facing the inner surface of the through hole 18, and this joint surface forms an explosion-proof gap d. (See FIG. 3).

The small-diameter cylindrical portion 32b has a smaller diameter than the large-diameter cylindrical portion 32a, and forms an annular space 38 for attaching the strain gauge 20 to the inner surface of the through hole 18. ing.

The flange portion 32c has an outer diameter larger than the inner diameter of the through hole 18, and is engaged with the peripheral edge on one side of the through hole 18. The female plug 34 includes a cylindrical portion 34a and a cylindrical portion 34.
It comprises a concave portion 34b provided at the center of a and a flange portion 34c provided at a lower end of the cylindrical portion 34a.

The cylindrical portion 34a is formed to have a smaller diameter than the inner diameter of the through hole 18, and its outer surface forms a joint surface facing the inner surface of the through hole 18, and this joint surface forms an explosion-proof gap d.
(See FIG. 3). The male plug 3 is provided in the recess 34b.
The distal end side of the second small-diameter cylindrical portion 32b is fitted.

The flange portion 34c has an outer diameter larger than the inner diameter of the through hole 18, and is engaged with the other peripheral edge of the through hole 18. The fastening structure between the plugs 32, 34 is not limited to the means by the bolt 36 shown in this embodiment, but may be, for example, between the concave portion 34b of the female plug 34 and the small-diameter cylindrical portion 32b of the male plug 32. It is also possible to provide screws that are screwed to each other and tighten the plugs 32 and 34 by screw connection.

The explosion-proof gap d is such that the sum of the inner volume from the outer end of each of the joint surfaces of the plugs 32 and 34 and the inner volumes of the terminal plate housing 22 and the communication hole 26 is 100 cm ³ or less,
When the depth L of the joint surface is 6 mm or more and 25 mm or less, in order to satisfy the provisions of the Industrial Safety Research Institute technical guidelines,
It is set to 0.2 mm or less.

The explosion-proof gap d not only conforms to the provisions of the Technical Guidelines of the Industrial Safety Research Institute, but also has the same provisions in, for example, the standard for explosion-proof construction of electric machines and equipment, the technical standard, and the IEC standard. Therefore, it can be set to conform to these regulations.

In the case of this embodiment, each plug 32,
The joint surface between the flange portions 32c, 34c of the 34 and the peripheral edge of the through hole 18 is set so as to be larger than the explosion-proof gap d.

According to the load cell configured as described above, a bridge circuit is formed by the plurality of strain gauges 20, and the electric cable 30 for supplying power to the bridge circuit and extracting a detection signal is connected. The storage portion 22 of the terminal plate 29 is provided integrally with the fixing portion 14 of the strain body 10, so that a separate terminal box is not required, so that the load cell can be prevented from becoming large and components can be avoided. Points can be reduced.

In the case of the present embodiment, the terminal plate housing portion 22 is sealed by filling with the curable resin 31 after connecting the strain gauge 20 and the electric cable 30 to the terminal plate 29.

Therefore, the electrical connection state of the terminal plate 29 can be stably maintained for a long time.

Furthermore, in this embodiment, the cable insertion hole 2
Numeral 8 denotes a plurality of cable insertion holes 2 arbitrarily selected from a plurality of openings formed on the side and end surfaces of the fixing portion 14.
An electric cable 30 is mounted on the cable 8 and a non-selected cable insertion hole is sealed with a curable resin.

Therefore, the extending direction of the electric cable 30 can be selected from a plurality of directions.

Further, according to the load cell of this embodiment, it is possible to prevent the performance of the load cell from deteriorating due to the explosion-proof structure.

That is, in the case of the present embodiment, the joint surface forming the explosion-proof gap d is the large-diameter cylindrical portion 32 of the male plug 32.
a, the outer surface of the cylindrical portion 34a of the female plug 34, and the inner surface of the through-hole 18, both of which have a circular cross section.

For this reason, when the flexure element 10 is installed, for example, as shown in FIG. 4, the inner weight of the through hole 18 and the outer diameter of the large-diameter cylindrical section 32a are reduced by the weight acting on the plugs 32 and 34. The surface or the outer surface of the cylindrical portion 34a of the female plug 34,
It comes into a state of point contact.

When the plugs 32 and 34 are in contact with each other in such a state, the plugs 32 and 34 prevent the deformation of the strain generating portion 12 when a load is applied to the movable portion 16 of the load cell. Is prevented.

At this time, the explosion-proof gap d is not uniformly formed on the outer surface of the large-diameter cylindrical portion 32a or the outer surface of the cylindrical portion 34a of the female plug 34 as shown in FIG. The use gap d does not necessarily need to be formed uniformly outside the plugs 34 and 32. If at least a part satisfies the standard, there is no problem because an explosion-proof function can be obtained.

That is, according to the explosion-proof structure of the present embodiment, the requirements specified in the explosion-proof standard can be satisfied without affecting the load detection performance.

In the above embodiment, the shape of the flexure element 10 is a rectangular tube, but the present invention is not limited to this.
The present invention is not limited to this, and may be, for example, a cylindrical elastic body.

Further, in the above embodiment, the case where the present invention is applied to a pressure-resistant explosion-proof type structure is exemplified. However, it is needless to say that the present invention can be applied to a load cell having a normal structure.

[0049]

As described above in detail with the embodiments, according to the load cell according to the present invention, the number of parts can be reduced because the receiving portion of the terminal plate is provided integrally with the fixing portion of the strain body. In addition, the cost can be reduced, and the size can be avoided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a flexure element showing one embodiment of a load cell according to the present invention.

FIG. 2 is a partially cutaway side view showing a state in which a plug for obtaining an explosion-proof structure is attached to a through hole of the strain generating element.

FIG. 3 is an enlarged view of a portion A in FIG. 2;

FIG. 4 is a sectional view of a main part of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Strain generating body 12 Strain generating part 14 Fixed part 16 Movable part 18 Through hole 20 Strain gauge 20a Lead wire 21 Concave cut part 22 Terminal board storage part 24 Seal plug 26 Communication hole 28 Cable insertion hole 29 Terminal board 30 Electric cable 31 Curability Resin 32 Male plug 34 Female plug

Claims (3)

[Claims] A flexure element comprising a fixed portion formed at one end, a movable portion formed at the other end, and a flexure portion deformed by a load applied to the movable portion; In a load cell including a plurality of strain gauges attached to a strain portion, a terminal plate storage portion integrally formed with the fixing portion, and an opening portion is sealed by a plug, and is disposed in the storage portion, A terminal plate for forming a bridge circuit of the strain gauge, a cable insertion hole having one end communicating with the housing portion, and the other end opening to the surface side of the fixing portion; and the terminal plate having one end through the cable insertion hole. And an electric cable connected to the bridge circuit for supplying power to the bridge circuit and extracting a detection signal. 2. The load cell according to claim 1, wherein the terminal plate housing is sealed by filling with a curable resin after connecting the strain gauge and an electric cable to the terminal plate. 3. The cable insertion hole is constituted by a plurality of openings on the side and end surfaces of the fixing portion, and the electric cable is mounted in one arbitrarily selected cable insertion hole and a non-selected cable is provided. 3. The insertion hole is sealed by blind plugging.
The load cell as described.