JP3072029B2 - Load cell unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell unit in which a strain gauge connected to a lead wire is mounted on a strain generating portion of a strain generating body.

[0002]

2. Description of the Related Art At present, load cell scales for calculating the weight of an article as electrical data are in practical use. In this load cell scale, a strain gauge is provided on a strain generating portion of a strain body to form a load cell, a saucer is connected to a movable end of a load cell having a fixed end connected to a main body housing, and a lead wire is connected to the strain gauge. It has a structure in which a bridge circuit is formed, and the amount of strain generated in the load cell due to the weight of the articles loaded on the pan is electrically measured by a strain gauge to perform weighing.

A first conventional example of such a load cell scale will be described below with reference to FIG. First, in the load cell scale 1, a through-hole 2 is formed in a metal material to form a strain body 6 in which a fixed end 3 and a movable end 4 are connected by a pair of beams 5. Four strain generating parts 7
, Four strain gauges 8 are individually mounted to form a load cell 9.

[0004] The fixed end 3 of the load cell 9 is connected to the main body base 10, and the pan 11 is connected to the movable end 4 of the load cell 9 via a support frame (not shown). The circuit board 1 is fixed to the side surface of the fixed end 3 of the load cell 9 by bolts 13 via spacers 12.
4 is fixed, and the connection terminals 15 of the circuit board 14 are fixed.
To the strain gauge 8 of the load cell 9 with the lead wire 16.
Is connected. Therefore, these strain gauges 8
Forms a bridge circuit (not shown) with the lead wires 16 and the printed wiring of the circuit board 14, and an A / DC (Analog / Digital) connected to the bridge circuit.
A film capacitor 17 which is a circuit component of a convertor is mounted on the circuit board 14. This circuit board 14
In addition to the part of the bridge circuit and the A / DC,
An amplifier and a low pass filter (all not shown) are also included.

In this manner, in the load cell scale 1, the load cell 9 and the circuit board 14 are unitized integrally to form a load cell unit 18.

In such a configuration, when the load cell scale 1 is distorted in the four strain generating portions 7 of the load cell 9 corresponding to the weight of the weighing object (not shown) loaded on the pan 11, these load cells are weighed. The resistance values of the four strain gauges 8 that generate strain together with the strain generating section 7 change. Then, since the analog output of the bridge circuit composed of these strain gauges 8 is converted into a digital value by the A / DC of the circuit board 14, the digital value output from the circuit board 14 is converted into a CPU (Central).
An arithmetic circuit (not shown) such as a processing unit (not shown) receives and performs arithmetic processing to electrically calculate the weight of the weighing object.

In the load cell unit 18 of the load cell balance 1, the circuit board 14 and the load cell 9 are integrated, so that, for example, a processing circuit for correcting the individual difference of the load cell 9 is formed on the circuit board 14. Thus, the load cell unit 18 can be shared by a plurality of devices.

The A / D of such a load cell balance 1 is as follows.
In order to perform A / D conversion by C with good characteristics, a film capacitor 17 is necessary, and this film capacitor 17 protrudes greatly from the surface of the circuit board 14 mounted because it is a large circuit component. Will be.

Here, in such a load cell scale 1,
There is a model (not shown) in which the whole of the load cell unit 18 is shielded by a shield box because a disturbance radio wave may enter the A / DC and generate noise, but this makes it possible to reduce the size and weight of the load cell unit 18. Will be hindered. In particular, as described above, if the load cell unit 18 in which the film capacitor 17 protrudes from the circuit board 14 disposed on the side of the load cell 9 is surrounded by a shield box, the whole becomes extremely large.

Therefore, as a second conventional example which has solved the above-mentioned problems, a load cell unit 19 disclosed in Japanese Patent Application Laid-Open No. 63-52025 proposed by the present applicant will be described below with reference to FIG. explain. The same parts as those in the first conventional example are denoted by the same reference numerals, and description thereof will be omitted. First, in the load cell unit 19, the circuit unit 21 is formed by housing the circuit board 14 on which the film capacitor 17 is mounted in the shield box 20, and the circuit unit 21 is supported by the support plate 22 and the load cell 9 is supported. Is disposed inside the through hole 2. A plurality of through-holes 23 formed in the shield box 20 are provided with through-hole capacitors 24, and lead wires 25 inserted through these through-hole capacitors 24 connect the circuit board 14 to the FPC.
(Flexible Printed Circuit) 26 is connected.
The feedthrough capacitor 24 plays a role in removing high-frequency components that are noises output from the strain gauge 8 and the like.

In this manner, since the circuit board 14 is shielded by the shield box 20, it is possible to prevent disturbance radio waves from entering the A / DC, and the circuit board 14 from which the film capacitor 17 protrudes greatly is connected to the load cell. Since the film capacitor 17 is located inside the through-hole 9, the overall size of the film capacitor 17 does not increase.

[0012]

In the load cell unit 19 described above, the circuit board 14 is housed in the shield box 20 to prevent the occurrence of noise due to disturbance radio waves and the like, and the circuit board 14 is housed in the shield box 20. By arranging the circuit unit 21 thus formed inside the through hole 2 of the load cell 9, the overall size is reduced.

However, in this case, the shield box 20 is necessarily larger than the circuit board 14, and the load cell 9 is larger than the shield box 20, so that it is difficult to reduce the size of the whole.

[0014]

According to the first aspect of the present invention,
A fixed end and a movable end are connected by a pair of beams to provide a strain body having a through hole formed therein. A strain gauge is attached to a strain section of the strain body to form a load cell, and the strain of the load cell is formed. The circuit components of the processing circuit connected to the gauge are mounted on the first surface of the circuit board, the first shield cover is mounted on the first surface of the circuit board, and the second shield cover is mounted on the second surface. A unit was formed, the first shield cover of the circuit unit was placed inside the through hole of the load cell, and the circuit board was placed on the side of the load cell.

According to a second aspect of the present invention, in the first aspect, a through-hole is formed in the circuit board, and the first shield cover and the second shield cover are grounded through the through-hole. Connected with.

According to a third aspect of the present invention, there is provided a flexure element in which a fixed end and a movable end are connected by a pair of beams and a through hole is formed, and a strain gauge is attached to a flexure portion of the flexure element. To form a load cell, mount the circuit components of the processing circuit connected to the strain gauge of the load cell on the first surface of the circuit board, and attach a shield cover to the first surface of the circuit board to form a circuit unit Then, the shield cover of this circuit unit was arranged inside the through hole of the load cell, and the circuit board was arranged on the side of the load cell.

[0017]

According to the first aspect of the present invention, the second shield cover has a flat shape because it is mounted on the second surface of the circuit board having no large protrusion, and the flat surface faces outward. Since the circuit board and the second shield cover are arranged on the side of the load cell, the circuit board and the second shield cover do not protrude greatly from the load cell, and the entire circuit board is arranged inside the through hole of the load cell. The load cell itself does not increase in size as compared with the case in which the load cell is used. Since the circuit components of the processing circuit projecting from the circuit board and the first shield cover covering the circuit components are arranged in the through holes of the load cell, the circuit components of the processing circuit and the first shield cover make the entire apparatus large. Do not make it. Therefore, the entire device becomes extremely small.

According to the second aspect of the present invention, the first shield cover and the second shield cover separately mounted on the first surface and the second surface of the circuit board are electrically integrated by the conductive member and ground. Is done.

According to the third aspect of the present invention, the second surface of the circuit board has a substantially planar shape because there are no large protrusions, and the circuit substrate is mounted on the load cell with the second surface having such a planar shape facing outward. , The circuit board does not protrude significantly from the load cell, and the load cell itself does not become larger than when the entire circuit board is arranged inside the through hole of the load cell. Since the circuit components of the processing circuit projecting from the circuit board and the shield cover covering the circuit components are arranged in the through holes of the load cell, the circuit components of the processing circuit and the shield cover do not increase the size of the entire apparatus. Therefore, the entire device becomes extremely small.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. Regarding the load cell unit 27 illustrated in this embodiment, the same parts as those of the load cell units 18 and 19 described above as the first and second conventional examples use the same names and reference numerals, and detailed description thereof will be omitted. I do.

First, in the load cell unit 27,
A film capacitor 17 which is a circuit component of the A / DC which is a processing circuit is mounted on the first surface of the circuit board 14,
The circuit unit 30 is formed by attaching the first shield cover 28 to the first surface of the circuit board 14 and attaching the second shield cover 29 to the second surface.
As shown in FIGS. 1 and 2, the first shield cover 28 of the circuit unit 30 is connected to the load cell 9 by the support plate 22, so that the first shield cover 28 is inserted into the through hole 2 of the load cell 9. The cover 28 is arranged, and the circuit board 14 is arranged on the side of the load cell 2.

As shown in FIG. 4, the second shield cover 29 has openings 31 formed on three sides, and a feedthrough capacitor 32 is formed on the second surface of the circuit board 14 at the positions of these openings 31. Has been implemented. Further, the circuit board 1
A connector 33 is mounted on an end of the second surface of the lead 4, and the connector 33 and the strain gauge 8 of the load cell 9 are connected to the A / DC of the circuit board 14 through the lead wire 16 penetrating the through capacitor 32. Are connected by

Further, as shown in FIG.
Are formed on the first surface and the second surface of the circuit board 14 through the through hole 34 and are ground wires 35 which are conductive members and are electrically connected to the load cell 9. Is conducting. Then, the through hole 36 of the first shield cover 28 and the circuit board 14
A screw 38 that sequentially passes through the through hole 34 of the second shield cover 29 and the through hole 37 of the second shield cover 29 is fastened to the nut 39, so that the first and second shield covers 28, 2
Reference numeral 9 is connected to the ground wiring 35 and is grounded.

Although the ground wiring 35 is shown in the same thickness as the circuit board 14 and the like for the sake of simplicity in the drawing, this is actually formed by a thin film which is difficult to show. ing. Also, in the drawings, for simplicity of illustration, the number of the feedthrough capacitors 32 connected to the connector 33 is three, but this feedthrough capacitor 32
Are mounted on the circuit board 14 in a number necessary for input and output, similarly to the terminals of the connection connector 33.

In such a configuration, a load cell scale (not shown) using the load cell unit 27
When strain occurs in the four strain generating portions 7 of the load cell 9 corresponding to the weight of the weighing object (not shown) and the resistance values of the four strain gauges 8 change, the bridge circuit composed of these strain gauges 8 Analog output is A / DC of circuit board 14
Is converted to a digital value, and the weight of the weighing object is electrically calculated by performing arithmetic processing on the digital value.

Here, the load cell unit 27
The A / DC film capacitor 17 mounted on the circuit board 14 is shielded by the first shield cover 28,
Is shielded by the second shield cover 29, thereby preventing the generation of noise due to disturbance radio waves and the like. Moreover, the first shield cover 2 of the circuit unit 30
8 is arranged inside the through hole 2 of the load cell 9, and the circuit board 14 is arranged on the side of the load cell 2, so that the whole is favorably miniaturized.

That is, in this load cell unit 27, in order to form an A / DC having good characteristics, the circuit board 1
4, the first shield cover 28 that shields the film capacitor 17 is disposed inside the through hole 2 of the load cell 9, so that the film capacitor 17 is The load cell unit 27 is prevented from increasing in size.

Since the large-area flat circuit board 14 on which the film capacitor 17 is mounted as described above is not disposed inside the through hole 2 of the load cell 9 but is arranged in parallel to the side, It is not necessary to increase the size of the load cell 9 so that the circuit board 14 can be disposed inside the through hole 2, and the entire load cell unit 27 is favorably reduced in size.

Further, in order to realize the above-described operation, the first shield cover 28 and the second shield cover 29 are separately mounted on the first surface and the second surface of the circuit board 14, respectively. Of the circuit board 1
4 is connected to a ground wiring 35 passing through the through hole 34. Therefore, these shield covers 28,
Numeral 29 is electrically integrated and well grounded, so that the A / DC of the circuit board 14 can be shielded well.

A second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description is omitted. In the load cell unit 27 of this embodiment, the second shield cover 29 is not provided on the second surface of the circuit board 14 in the circuit unit 30. The circuit board 14 includes various circuit components including a part of the bridge circuit, an A / DC connected to the bridge circuit, and an IC and a resistor constituting the amplifier circuit connected to the A / DC. Are mounted, and a part 41 of this circuit component is also arranged on the second surface of the circuit board 14.
FIG. 5 omits a wiring pattern relating to a part 41 of the circuit component. The circuit including the wiring pattern is configured in a pattern so as to have a deterrent effect on noise generation due to weak disturbance radio waves entering the A / DC. More specifically, even if a weak external radio wave enters the second surface of the circuit board 14, the pattern configuration is such that the external radio wave does not easily enter the A / DC.

In such a configuration, the first shield cover 28 that covers the film capacitor 17, which is a main component of the A / DC, prevents generation of noise due to invasion of an external radio wave into the A / DC. Although the shield cover is not provided on the second surface of the circuit board 14, even if the disturbing radio wave enters the part 41 of the circuit components mounted on the second surface of the circuit board 14, A / DC hardly penetrates, so that noise is hardly generated from the A / DC.

[0032]

According to the first aspect of the present invention, there is provided a strain-generating body in which a fixed end and a movable end are connected by a pair of beams to form a through-hole, and a strain gauge is provided in a strain-generating portion of the strain-generating body. To form a load cell, mount the circuit components of the processing circuit connected to the strain gauge of the load cell on the first surface of the circuit board, and attach the first shield cover to the first surface of the circuit board. By mounting a second shield cover on the second surface to form a circuit unit, by arranging the first shield cover of this circuit unit inside the through hole of the load cell and arranging the circuit board on the side of the load cell Only the first shield cover which shields the circuit components protruding from the surface of the circuit board can be arranged inside the through hole of the load cell, and the circuit board is not arranged inside the through hole of the load cell. In it is not necessary to increase the size of the load cell, it can contribute to the overall downsizing.

According to a second aspect of the present invention, there is provided the conductive member according to the first aspect, wherein a through hole is formed in the circuit board, and the first shield cover and the second shield cover are grounded through the through hole. By connecting with
The first shield cover and the second shield cover separately connected to the first surface and the second surface of the circuit board can be electrically integrated and grounded. Can be shielded well.

According to a third aspect of the present invention, there is provided a flexure element in which a fixed end and a movable end are connected by a pair of beams and a through hole is formed, and a strain gauge is provided on a flexure portion of the flexure element. Mounting to form a load cell, mounting the circuit components of the processing circuit connected to the strain gauge of this load cell on the first surface of the circuit board, mounting a shield cover on the first surface of the circuit board, and mounting the circuit unit By forming the shield cover of this circuit unit inside the through hole of the load cell and arranging the circuit board on the side of the load cell, only the shield cover that shields the circuit components protruding from the surface of the circuit board is loaded. Since the circuit board is not disposed inside the through hole of the load cell, there is no need to increase the size of the load cell, which contributes to the overall downsizing. It is possible.

[Brief description of the drawings]

FIG. 1 is a perspective view of a load cell unit showing a first embodiment of the present invention.

FIG. 2 is a perspective view of a load cell unit.

FIG. 3 is a vertical sectional front view of a circuit unit.

FIG. 4 is a perspective view of a circuit unit.

FIG. 5 is a perspective view of a circuit unit showing a second embodiment of the present invention.

FIG. 6 is an exploded perspective view showing a load cell scale including a load cell unit as a first conventional example.

FIG. 7 is an exploded perspective view showing a load cell unit as a second conventional example.

[Explanation of symbols]

 Reference Signs List 2 through hole 3 fixed end 4 movable end 5 beam 6 strain generator 7 strain generator 8 strain gauge 9 load cell 14 circuit board 17 circuit component 27 load cell unit 28 first shield cover, shield cover 29 second shield cover 30 circuit unit 34 Through hole 35 Conductive member

────────────────────────────────────────────────── (5) References JP-A-63-52025 (JP, A) JP-A-63-52026 (JP, A) JP-A-1-91030 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01L 1/22 G01G 3/14

Claims (3)

(57) [Claims] 1. A strain cell having a fixed end and a movable end connected by a pair of beams and having a through-hole formed therein, and a strain gauge attached to a strain-generating portion of the strain element to form a load cell. The circuit components of the processing circuit connected to the strain gauge of the load cell are mounted on the first surface of the circuit board, the first shield cover is mounted on the first surface of the circuit board, and the second shield cover is mounted on the second surface. To form a circuit unit, wherein the first shield cover of the circuit unit is disposed inside the through hole of the load cell, and the circuit board is disposed on a side of the load cell. . 2. The load cell according to claim 1, wherein a through hole is formed in the circuit board, and the first shield cover and the second shield cover are connected by a grounded conductive member via the through hole. unit. 3. A strain generating body having a fixed end and a movable end connected by a pair of beams to form a through hole, and a strain gauge is attached to a strain generating portion of the strain generating body to form a load cell. The circuit components of the processing circuit connected to the strain gauge of the load cell are mounted on the first surface of the circuit board, and a shield cover is attached to the first surface of the circuit board to form a circuit unit. The load cell unit, wherein the shield cover is disposed inside the through hole of the load cell, and the circuit board is disposed on a side of the load cell.