JPH0875572A - Load cell unit - Google Patents

Abstract

PURPOSE: To integrate a circuit substrate in a load cell and miniaturize the whole better in a load cell unit shielding the circuit board. CONSTITUTION: Circuit parts of a processing circuit connected to a load cell 9 are mounted on the first face of a circuit board 14, and a first shield cover 28 is installed on the first face of the circuit board. The first shield cover 28 is arranged in the inside of a through hole 2 of the load unit 9, and the circuit board 14 is disposed in the side of the load cell 9.

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 to which a lead wire is connected is attached to a strain generating portion of a strain generating body.

[0002]

2. Description of the Related Art At present, a load cell balance for calculating the weight of an article as electric data is put into practical use. In this load cell scale, a strain gauge is provided in the strain generating part of the strain generating body to form a load cell, a fixed end is connected to the main body housing, a saucer is connected to the movable end of the load cell, and a lead wire is connected to the strain gauge. The structure is such that a bridge circuit is formed, and the strain amount generated in the load cell due to the weight of the articles loaded on the tray is electrically measured by a strain gauge to perform weighing.

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

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). Further, the circuit board 1 is fixed to the side surface of the fixed end 3 of the load cell 9 with a bolt 13 through a spacer 12.
4 is fixed, and the connection terminal 15 of the circuit board 14 is fixed.
The lead wire 16 is attached to the strain gauge 8 of the load cell 9.
Is connected. Therefore, these strain gauges 8
Forms a bridge circuit (not shown) with the lead wire 16 and the printed wiring of the circuit board 14, and an A / DC (Analog / Digital) connected to the bridge circuit is formed.
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 a part of the bridge circuit and the A / DC,
An amplifier and low pass filter (all not shown) are also included.

By doing so, in the load cell balance 1, the load cell 9 and the circuit board 14 are integrated into a unit to form a load cell unit 18.

In the load cell balance 1 having such a structure, when strain occurs in the four strain generating portions 7 of the load cell 9 in correspondence with the weight of the weighing object (not shown) loaded on the pan 11, these load cell scales 1 The resistance values of the four strain gauges 8 that generate strain together with the strain generating unit 7 change. Therefore, 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 by this circuit board 14 is converted to a CPU (Central
An arithmetic circuit (not shown) such as a Processing Unit) 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, since the circuit board 14 and the load cell 9 are integrated, for example, a processing circuit for correcting the individual difference of the load cell 9 is formed on the circuit board 14. The load cell unit 18 can be shared by a plurality of devices.

A / D of such a load cell balance 1
The film capacitor 17 is necessary to perform the A / D conversion by C with good characteristics. Since the film capacitor 17 is a large-sized circuit component, it greatly projects from the surface of the mounted circuit board 14. It will be.

Here, in such a load cell balance 1,
Since disturbance radio waves may enter the A / DC and generate noise, there is a model (not shown) in which the entire load cell unit 18 is shielded by a shield box, but this reduces the size and weight of the load cell unit 18. Will be hindered. In particular, in the load cell unit 18 in which the film capacitor 17 projects from the circuit board 14 arranged on the side of the load cell 9 as described above, if the load cell unit 18 is surrounded by the shield box, the entire size becomes extremely large.

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

By doing so, 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 in which the film capacitor 17 is largely projected is the load cell. Since it is located inside the through hole 2 of 9, the film capacitor 17 does not increase in size as a whole.

[0012]

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

However, this inevitably causes the shield box 20 to be larger than the circuit board 14 and the load cell 9 to be larger than the shield box 20, so that it is difficult to downsize the whole.

[0014]

According to the first aspect of the present invention,
A strain gauge is provided in which the fixed end and the movable end are connected by a pair of beams to form a through hole, and a strain gauge is attached to the strain gauge of the strain gauge to form a load cell. 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 this circuit board, and the second shield cover is mounted on the second surface. A unit was formed, the first shield cover of this circuit unit was arranged inside the through hole of the load cell, and the circuit board was arranged laterally of the load cell.

According to a second aspect of the present invention, in the first aspect of the invention, 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. I was connected with.

According to a third aspect of the present invention, a strain-generating body having a through-hole formed by connecting a fixed end and a movable end with a pair of beams is provided, and a strain gauge is attached to the 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 shield cover to the first surface of the circuit board to form the 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 invention, the second shield cover has a flat shape because it is attached to the second surface of the circuit board without large protrusions, 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 significantly protrude 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 become larger than in the case of doing so. Since the circuit component of the processing circuit that projects from the circuit board and the first shield cover that covers this circuit component are arranged in the through hole of the load cell, the circuit component of the processing circuit and the first shield cover increase the size of the entire device. Do not turn Therefore, the entire device becomes extremely small.

According to the second aspect of the invention, the first shield cover and the second shield cover, which are separately mounted on the first surface and the second surface of the circuit board, are electrically integrated by the conductive member and grounded. To be done.

According to the third aspect of the present invention, the second surface of the circuit board has a substantially flat shape because there are no large protrusions, and the circuit board is loaded with the second surface having such a flat shape facing outward. This circuit board does not significantly project from the load cell because it is arranged laterally, 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 component of the processing circuit and the shield cover that covers the circuit component protruding from the circuit board are arranged in the through hole of the load cell, the circuit component 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 as the first and second conventional examples are denoted by the same names and reference numerals, and detailed description thereof will be omitted. To do.

First, in the load cell unit 27,
A film capacitor 17 which is a circuit component of A / DC which is a processing circuit is mounted on the first surface of the circuit board 14,
A circuit unit 30 is formed by mounting the first shield cover 28 on the first surface of the circuit board 14 and the second shield cover 29 on the second surface.
Then, 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 is provided inside the through hole 2 of the load cell 9. The cover 28 is arranged, and the circuit board 14 is arranged beside 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. It is implemented. Furthermore, the circuit board 1
A connection connector 33 is mounted on an end portion of the second surface of No. 4, and the connection connector 33 and the strain gauge 8 of the load cell 9 have a lead wire 16 penetrating the feedthrough capacitor 32 to A / DC of the circuit board 14. It is connected with.

Further, as shown in FIG. 3, the circuit board 14
A through hole 34 is formed in the through hole 34, and a ground wire 35, which is a conductive member, is formed on the first surface and the second surface of the circuit board 14 through the through hole 34 and is 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
The screw 39, which successively penetrates the through hole 34 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
9 is connected to the ground wiring 35 and is grounded.

In the figure, the ground wiring 35 is shown to have a thickness equivalent to that of the circuit board 14 or the like for the sake of simplification of the structure. However, this is actually formed of a thin film which is difficult to illustrate. ing. Further, in the drawing, in order to simplify the illustration, the number of the feedthrough capacitors 32 connected to the connection connector 33 is three, but this feedthrough capacitor 32 is shown.
Are mounted on the circuit board 14 in the same number as the terminals of the connector 33, which are necessary for input and output.

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

Here, the load cell unit 27 is
The A / DC film capacitor 17 mounted on the circuit board 14 is shielded by the first shield cover 28,
By shielding the printed wiring of No. 2 with the second shield cover 29, the generation of noise due to disturbance radio waves or the like is prevented. 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 entire size is favorably reduced.

That is, in the load cell unit 27, in order to form an A / DC having good characteristics, the circuit board 1
Although the film capacitor 17 mounted in FIG. 4 largely projects, 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 projected. The load cell unit 27 is prevented from increasing in size.

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

In addition, in order to realize the above, 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. The shield covers 28, 29 of the circuit board 1
4 is connected to the ground wiring 35 passing through the through hole 34. Therefore, these shield covers 28,
Reference numeral 29 is electrically integrated and both are well grounded so that A / DC of the circuit board 14 can be well shielded.

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

In such a structure, the first shield cover 28 that covers the film capacitor 17, which is a main component of the A / DC, prevents the generation of noise due to the entry of external radio waves into the A / DC. Although the shield cover is not provided on the second surface of the circuit board 14, even if the disturbance radio wave enters the part 41 of the circuit component mounted on the second surface of the circuit board 14, the disturbance radio wave will be A / DC is unlikely to invade, and thus noise is unlikely to be generated from A / DC.

[0032]

According to the invention described in claim 1, 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 at 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 the first shield cover is mounted on the first surface of the circuit board. By forming a circuit unit by mounting the second shield cover on the second surface, by arranging the first shield cover of this circuit unit inside the through hole of the load cell and arranging the circuit board laterally of the load cell. , Only the first shield cover that 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, in the first aspect of the invention, 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
Since the first shield cover and the second shield cover, which are separately connected to the first surface and the second surface of the circuit board, can be electrically integrated and grounded, these shield covers can be used to process the circuit of the circuit board. Can be well shielded.

According to a third aspect of the present invention, a strain-generating body having a through hole formed by connecting the fixed end and the movable end with a pair of beams is provided, and a strain gauge is provided at the strain-generating portion of the strain generating body. The load cell is mounted to form the 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 the shield cover is mounted on the first surface of the circuit board to mount 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 Can be placed inside the through-hole of the load cell, and the circuit board is not placed inside the through-hole of the load cell, so there is no need to upsize the load cell, which contributes to the overall downsizing. It is possible.

[Brief description of 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]

 2 Through hole 3 Fixed end 4 Movable end 5 Beam 6 Strain element 7 Strain element 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

Claims (3)

[Claims] 1. A strain-flexing body having a through-hole formed by connecting a fixed end and a movable end with a pair of beams, and a strain gauge is attached to the strain-flexing portion of the strain-flexing 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, 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, the first shield cover of the circuit unit is arranged inside the through hole of the load cell, and the circuit board is arranged laterally 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 through the through hole. unit. 3. A strain-generating body having a through-hole formed by connecting a fixed end and a movable end with a pair of beams, and a strain gauge is attached to the 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 the shield cover is attached to the first surface of the circuit board to form the circuit unit. A load cell unit, wherein the shield cover is arranged inside a through hole of the load cell, and the circuit board is arranged laterally of the load cell.