JP4165358B2 - Load cell and method of manufacturing load cell - Google Patents

Description

  The present invention relates to a load cell used for a load detection mechanism such as an electronic balance and a method for manufacturing the load cell.

  Conventionally, the load detection mechanism of an electronic balance mainly comprises a Robert valve mechanism, and has a beam member (hereinafter referred to as a load cell mother body) having a strain generating portion that generates strain at its fulcrum, and is attached to the strain generating portion. A load cell composed of a strain gauge for detecting a strain amount is used. This load cell generally has a rectangular parallelepiped duralumin or other metal block as shown in FIG. 3 as a load cell base 1, and the inside of the load cell is cut into a spectacle shape so that one end has a fixed column portion 11 and the other end has a movable column. The upper side beam 13 having the strain generating portions S1 and S2 on the upper side and the lower side beam 14 having the strain generating portions S3 and S4 on the lower side are formed, and arranged at each vertex of the parallelogram. Corresponding strain gauges G1, G2, G3, and G4 are attached on the outer surfaces of the strain generating portions S1, S2, S3, and S4.

The sample pan D of the electronic balance is mounted on the movable column portion 12 as shown in FIG. 3, and the distortion of each strain generating portion S1 to S4 generated by the load from the sample tray D carrying the sample to be measured is The load is detected by the strain gauges G1 to G4 attached to each, and each load detection signal is input to an arithmetic processing unit (not shown). This load detection signal is arithmetically processed based on a load detection arithmetic expression stored in advance in the arithmetic processing unit, and converted into a load signal corresponding to the sample to be measured. This load signal is input to a display (not shown), and a measured value (weighing value) is displayed.
JP-A-2-66413 Japanese Patent Laid-Open No. 4-290927

  The conventional load cell is configured as described above. However, when the weight of the sample pan D is larger than the measurement range (weighing range) of the electronic balance, for example, the sample pan D is an electronic scale having a measurement range of 100 g. When the weight of the sample is 50 g, considerable strain has already occurred in the state where only the sample dish D is mounted, as illustrated in FIG. The applied strain range B of the strain gauge cannot be effectively used in the measurement range of the electronic balance.

  That is, since a considerable portion of the applied strain range B has already acted on the strain gauges G1 to G4 with no sample placed, it is necessary to cover the measurement range of the electronic scale with the remaining strain range C. As a result, there is a need to widen the span to cover the measurement range, and thus there is a problem that the measurement accuracy decreases with the resolution.

  The present invention has been made in view of the above points, and can make the most effective use of the applied strain range of the attached strain gauge. When incorporated in an electronic balance, the load detection is higher than in the past. An object of the present invention is to provide a load cell having a resolution and a method for manufacturing the load cell.

The load cell of the present invention is provided with a plurality of strain generating portions that generate distortion due to a load applied from the sample pan on the upper side and lower side of the beam member, and the output signal of the load cell is undistorted in a state where only the load of the sample pan is loaded. A strain generating portion in a state where a load similar to that of the sample dish is applied to the beam member is formed so as to be a state signal, and the strain gauge is attached to a processed surface where the strain generating portion is processed.
In addition, the load cell manufacturing method includes a step of providing a plurality of strain generating portions that generate distortion due to a load applied from the sample pan on the upper side and lower side of the beam member, and an output signal of the load cell in a state in which only the load of the sample pan is applied. Generating a strain generating portion in a state in which a load similar to that of the sample pan is applied to the beam member in advance so that the signal becomes an unstrained state signal, a step of processing the strain generating portion to form a processed surface, And a step of attaching a strain gauge to the processed surface.

  In the present invention, the load cell base is fixed with a fixture that generates a deflection that gives the same strain as the strain generated in the load cell base due to the load (dead load) applied from the sample pan, so that no stress is applied to the strain gauge. Since the strain gauge is attached after processing the strained part, no stress is applied to the strain gauge when the sample is not placed, so the sample can be measured using the effective measurement range of the strain gauge, A load cell with high measurement resolution and high accuracy and a method for manufacturing the same can be obtained.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a processing method for removing strain generated by a load applied by a sample pan of an electronic balance from the load cell base, and FIG. 2 is a strain gauge attached to the load cell base processed as shown in FIG. It is a figure which shows the method of manufacturing the load cell which detects distortion amount by doing.

  The original shape of the load cell base 1a used in the present invention shown in FIG. 1 is a horizontally long rectangular parallelepiped like the conventional load cell base 1 shown in FIG. By hollowing out the shape, an upper side beam 13 in which the strain generating portions S1 and S2 are arranged at regular intervals is formed on the upper side, and a lower side beam 14 in which the strain generating portions S3 and S4 are arranged at the same interval is formed on the lower side. In addition, the strain generating portions S1 to S4 are disposed at each corner of the quadrilateral. The upper side beam 13 and the lower side beam 14 are parallel to each other, and one end side thereof is coupled to the movable column portion 12 and the other end side is coupled to the fixed column portion 11.

  Moreover, the fixing tool 2 and the fixing tool 3 of FIG. 1 are fixing jigs used for generating strain corresponding to the purpose of use (for example, an electronic scale) in the strain generating portions S1 to S4 of the load cell base 1a. When the load cell of the present invention is used as a load detection mechanism of an electronic balance, the load cell base 1a is incorporated in advance in the load detection mechanism of the applied electronic balance as shown in FIG. A load (dead load) of only D is applied, and the displacement (deflection) of the movable column part 12 with respect to the fixed column part 11 is measured, and this displacement and the amount of deflection δ applied to the load cell 1a by the fixtures 2 and 3 are obtained. The shapes of the fixtures 2 and 3 are determined so as to match. That is, the fixtures 2 and 3 can insert the load cell base 1a and couple them so that the movable column portion 12 of the load cell base 1a can be bent by the deflection amount δ with respect to the fixed column portion 11.

  A procedure for manufacturing the load cell of the present invention using the load cell 1a and the fixtures 2 and 3 will be described below. First, as shown in FIG. 1, the load cell base 1 a is sandwiched between the fixture 2 and the fixture 3, and the fixtures 2 and 3 are coupled to each other by coupling screws 4 a and 4 b. As a result, a load is applied to the upper portion of the movable column portion 12 with respect to the fixed column portion 11, and a deflection amount δ is generated between the fixed column portion 11 and the movable column portion 12. Occurs in the parts S1 to S4.

  Next, in a state in which the load cell base 1a is fixed with the fixtures 2 and 3, an additional process is performed in which a part of the inclined portions on the outer surface of the strain generating portions S1 to S4 in FIG. Thus, the load cell matrix 1b (FIG. 2) is formed, in which the adhering portions 6a, 6b, 6c, and 6d that can be bonded without giving strain to the strain gauge.

  Next, an adhesive is applied on the flat surfaces of the adhering portions 6a, 6b, 6c, and 6d, and the corresponding strain gauges G1, G2, G3, and G4 are adhered. Then, as shown in FIG. 2, the pressing plate 5 is pressed against the upper surface of each of the strain gauges G1 to G4, the upper surface is pressed with the pressing screws 6, 7, 8, and 9, and is heated and cured for a certain time. To wear.

  When the load cell 10 to which the strain gauges G1, G2, G3, and G4 are attached as described above is detached from the fixtures 2 and 3, the movable column portion 12 of the load cell base body 1b returns to the original height. Therefore, the flat surfaces of the sticking portions 6b and 6c formed in the strain generating portions S1, S2, S3, and S4 shown in FIG. 1 are deformed into concave surfaces, and the flat surfaces of the sticking portions 6a and 6d are deformed into convex shapes. As a result, the strain gauges G2 and G3 are subjected to a compressive strain (stress), and the strain gauges G1 and G4 are subjected to a tensile strain.

  When the load cell 10 manufactured according to the above embodiment is incorporated into an electronic balance, the deflection caused by the load from the sample pan and the sample to be measured placed thereon is in the same direction as the deflection amount δ given by the fixtures 2 and 3. Incorporate to occur.

When the sample dish is mounted on the movable column portion 12 of the load cell 10 incorporated in this way, the load cell base body 1b bends in the same direction as the deflection amount δ due to its weight, and therefore each strain gauge G1, G2, G3, G4 is not present. Head for distortion. That is, the strain gauges G1, G2, G3, and G4 are distorted in such a direction that the distortion in the state before mounting the sample pan is canceled by the strain due to the initial load caused by mounting the sample pan. As a result, the strain amount of each strain gauge G1, G2, G3, G4 is smaller than the conventional amount indicated by A in FIG. It becomes possible to correspond to the range. As the deflection amount δ at the time of attaching the strain gauge and the deflection due to the dead load at the time of mounting the sample dish are closer, the entire applied strain range B can be made to correspond to the measurement range of the electronic balance.
Note that the output variation from the strain gauge in dead load is easily affected by the material and bonding conditions of the load cell base 1a, so when mass-producing the load cell, use the same lot of material and adhesive in the same process. It is desirable to manufacture with.

  By manufacturing the same shape as that of the unstrained state of the load cell base body 1b obtained by the embodiment by die molding, the processing for making a flat surface can be omitted.

It is a processing drawing of the load cell mother body using the fixture concerning the present invention. It is a strain gauge affixing figure of a load cell base material using a fixture concerning the present invention. It is a schematic block diagram of the conventional load detection mechanism. It is a figure which shows the relationship between an action load and distortion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a, 1b Load cell base body 2, 3 Fixing tool 4a, 4b Coupling screw 5 Push plate 6, 7, 8, 9 Push screw 10 Load cell 11 Fixed column part 12 Movable column part 13 Upper side beam 14 Lower side beam D Sample plate G1 , G2, G3, G4 Strain gauge S1, S2, S3, S4 Strain generation part

Claims (2)

A sample pan for placing the sample to be measured is placed on one end of the beam member, the other end is fixed, and the amount of strain generated in the beam member is detected to detect the load of the sample to be measured, In the load cell in which a plurality of strain generating portions that generate strain due to the load applied from the sample plate are provided on the upper and lower sides of the beam member, and a strain gauge that detects strain is attached to the strain generating portion, only the sample plate is provided. In order to make the output signal of the load cell become an unstrained state signal when a load of a load is applied, a strain generating part in a state where a load similar to that of the sample pan is applied is formed on the beam member, and the strain generating part is processed. A load cell, wherein the strain gauge is attached to a processed surface. A sample pan for placing the sample to be measured is placed on one end of the beam member, the other end is fixed, and the amount of strain generated in the beam member is detected to detect the load of the sample to be measured, A step of providing a plurality of strain generating portions that generate strain due to a load applied from the sample plate on the upper side and lower side of the beam member, so that the output signal of the load cell becomes an unstrained state signal with a load of only the sample plate loaded A step of generating a strained portion in a state in which the same load as the sample pan is applied to the beam member in advance, a step of processing the strained portion to form a processed surface, and attaching a strain gauge to the processed surface A process for producing a load cell.

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