JP4741872B2 - Load cell and weighing device - Google Patents

Description

  The present invention relates to a load cell and a weighing device, and more particularly, to a load cell capable of calculating a load value by detecting, with a strain gauge, that a strain generating portion is deformed by a load, and a weighing device using the load cell.

Conventionally, various types of load cells using strain gauges have been used to measure the weight of an object or measure the force acting on a structure. A general load cell forms a strained body by machining and attaches a strain gauge to the thin part of the strained body, detects the strain generated in the thin part by a load due to load, and converts the load value. It has a structure.
For example, as shown in FIG. 10, a load cell 1 disclosed in Japanese Patent Application Laid-Open No. 2000-346723 or the like includes a cylindrical load receiving portion 2 that receives a load from a load table on which an object to be weighed is mounted, and the load receiving load. A thin frame-shaped strain generating body 3 that is integrally formed on the outer periphery of the portion 2 and deforms by a load acting on the load receiving portion 2, and is joined to the outer periphery of the load receiving portion 2 via the strain generating body 3. A peripheral frame 4 and a plurality of strain gauges 5A and 5B attached to the strain body 3 are provided.

However, according to the load cell 1 of the above publication, the load receiving portion 2 and the peripheral frame 4 are merely connected by a single strain body 3, so that the displacement is caused by a change in the load position with respect to the load receiving portion 2. There is a problem that it is easily affected by errors. In addition, since the strain body 3 is continuous in an annular shape, there is a problem that it is difficult to precisely detect the strain generated in the strain body 3 only by locally attaching the strain gauges 5A and 5B.
JP 2000-346723 A

  This invention is made | formed in view of the said problem, and makes it the subject to provide the load cell and measuring device which can detect a load with high precision.

In order to solve the above-mentioned problem, the present invention provides a load cell in which a plurality of strain gauges are attached to a strain generating portion in which strain occurs due to load loading.
A core portion disposed on the center side, an outer peripheral frame portion disposed at an outer peripheral side of the core portion, and a pair of upper and lower strain generating portions that bridge between the core portion and the outer peripheral frame portion; Including one of the core part or the outer peripheral frame part as a support fixing part and the other as a load-loading part,
The core portion and the outer peripheral frame portion are annularly arranged on concentric circles, and the strain-generating portion has a thickness direction in the vertical direction,
The upper and lower pair of strain generating portions are provided in three sets at equal intervals in the circumferential direction, and the outer peripheral frame portion has a position corresponding to the upper and lower sides of each set of strain generating portions from the outer surface to the inner surface. A through hole is formed, and the circumferential width of the strain-generating portion is 1% to 5% of the outer peripheral length of the core portion.
The pair of upper and lower strain generating portions of each set has a cross-sectional taper shape that gradually increases the thickness toward the both sides in the radial direction with the upper surface of the upper strain portion not contacting the through hole and the lower surface of the lower strain portion. Provide inner and outer taper parts,
When the rated load to be applied is in the range of 200 N to 5 KN, the taper angle θ of the upper and lower radial taper portions is 5 ° to 15 °, and the thickness (t) of the thinnest central portion is 0.8 mm to 1 .7 mm, width b is in the range of 8 mm to 12 mm, and is set to increase according to the increase of the rated load,
The paste strain gauge on the inner and outer tapered portion that is thicker in the vertical pair of the strain generating part, together with the said strain generating portion paste the four strain gauges for each set, by using the strain gauge There is provided a load cell characterized in that a Wheatstone bridge circuit is formed and a circuit for parallelly adding outputs from the respective Wheatstone bridge circuits is provided.

With the above configuration, since the strain generating portions that bridge the core portion and the outer peripheral frame portion are provided in pairs, a robust mechanism that balances even if there is a variation in the position of the load is formed, and the influence of the offset error Can be reduced.
In addition, since the strain generating portions are provided in three groups with a circumferential interval, the strain generated in each strain generating portion can be accurately detected with a locally attached strain gauge. The load detection accuracy can be improved. Here, for example, if the two strain-generating portions are opposed to each other, even if the position variation of the load is shifted on a plane that linearly connects the widths of the two strain-generating portions, the displacement error is minimized. However, if it deviates from the plane, a torsional stress is generated with respect to the strain generating portion, and an offset error tends to occur, resulting in a decrease in accuracy. On the other hand, if there are four sets of strain generating portions, there will be no torsional stress on the strain generating portions due to the variation in the position of the load load, but the four sets of strain generating portions cannot be loaded in a balanced manner. As a result, a load is applied to only three of the sets, and the accuracy decreases. Therefore, if three sets of strain generating portions are provided in the circumferential direction to support three points, the load is evenly applied and the best accuracy is obtained.

Further, since the outer peripheral frame portion has a through-hole penetrating from the outer surface to the inner surface at a position corresponding to the upper and lower portions of the pair of upper and lower strain generating portions, the core portion, the strain generating portion, and the outer peripheral frame are formed. There is an advantage that it is very easy to perform a processing operation to form the part as a single body. That is, in order to accurately reflect the load amount in the strain amount, it is desirable that the load load portion and the strain-generating portion are not separate objects but an integrated object, but cutting is performed from the through hole toward the center side. It is possible to easily form a strain generating portion that is divided into upper and lower portions by simply performing the above, and the manufacturing efficiency is very good.
Further, since the outputs from the respective Wheatstone bridge circuits formed by the strain gauges of the respective strain generating portions are summed in parallel to obtain the output of the load cell, the output error due to the load position can be reduced.

As described above, the width in the circumferential direction of the strain generating part it is 1% to 5% of the circumferential length of the core.

  With the above-described configuration, since sufficient spacing is provided in the circumferential direction between the three sets of strain generating portions, the load generated in the load application portion appears locally as a strain in each strain generating portion, and locally It is possible to accurately detect with the attached strain gauge, and it is possible to improve the load detection accuracy. When the load cell is reduced to 1% to 5%, the strain gauge cannot be attached to the strain-generating portion when the load cell is downsized. On the other hand, when the load cell exceeds 5%, the strain-generating portion becomes larger than the strain gauge. This is because the detection accuracy decreases when the strain on the strain generating portion is not uniform.

Strain-generating-portions of each pair of upper and lower, as above, the inner tapered portion and the outer tapered portion is provided as a cross-sectional tapered shape gradually the thickness to a large toward the both sides in the radial direction, the radial direction of the strain gauge that are affixed to the inner tapered portion and the outer tapered portion of both sides.

  That is, it is known that the stress generated in the strain-generating portion tends to increase toward both sides in the radial direction, but with the above configuration, the thickness of the strain-generating portion increases toward both sides in the radial direction. Therefore, the radial distribution of stress values can be made uniform, and strain detection errors due to variations in the strain gauge mounting position can be reduced.

As described above, the core portion and the outer peripheral frame portion with an annular shape which is arranged concentrically, wherein the strain generating part has a thickness direction and the vertical direction.

  With the above configuration, since the core portion and the outer peripheral frame portion are arranged concentrically as an annular shape, stress generation due to load is likely to be isotropic, which contributes to improvement in measurement accuracy. In addition, by forming the strain generating portion in a plate shape whose thickness direction is the vertical direction, strain due to a load in the vertical direction can be suitably generated in the strain generating portion.

  Moreover, this invention uses the said load cell, and while fixing one of the said core part or the said outer periphery frame part of the said load cell to a support fixing material, the other is being fixed to the container side which accommodates a to-be-measured object. A weighing device is provided.

  With the above configuration, when an object to be weighed is accommodated in the container, a load is applied to the side where the container of the core part or the outer peripheral frame is fixed, and the weight of the object to be weighed can be measured.

  As is clear from the above description, according to the present invention, the pair of strain generating portions for bridging the core portion and the outer peripheral frame portion is provided in a pair of upper and lower portions, so that the Roverval mechanism is balanced even if there is a change in load position. Is formed, and the deviation error can be reduced. In addition, since the strain generating part is divided into three groups with a gap in the circumferential direction, the strain generated in each strain generating part can be accurately detected with a locally attached strain gauge, and the load detection accuracy Will improve. Furthermore, since the outer peripheral frame portion has a through-hole penetrating from the outer surface to the inner surface at a position corresponding to the upper and lower portions of the pair of upper and lower strain generating portions, the pair of upper and lower strain generating portions are connected to the core portion. In addition, it is easy to perform an operation of forming an integral part with the outer peripheral frame portion, and the workability is improved.

Embodiments of the present invention will be described with reference to the drawings.
The load cell 10 of the present embodiment is a load meter for measuring a hopper. As shown in FIGS. 1 to 3, the load cell 10 has a substantially cylindrical shape with a gap 15 formed on the outer peripheral side of a cylindrical core portion 11 having a center hole 11a. The outer peripheral frame portion 12 is arranged on a concentric circle, and three pairs of upper and lower strain generating portions 13 and 14 that bridge the core portion 11 and the outer peripheral frame portion 12 at equal intervals in the circumferential direction are formed. Moreover, the core part 11, the outer peripheral frame part 12, and the strain generating parts 13 and 14 are made of metal, specifically, integrally formed of aluminum, stainless steel, iron, alloys thereof, or the like. It is preferable to use an alloy.

The core portion 11 has a cylindrical shape having a center hole 11a for receiving a hopper, and has a bolt hole 11b for attachment at a required location.
The outer peripheral frame portion 12 is provided with a thin protruding portion 12b that protrudes inward from the inner surface of the cylindrical portion 12a. A through hole 12c having an oval cross section is formed on the side surface. In addition, a bolt hole 12d for mounting is drilled at a required location, and a notch 12e is provided at a position where the strain-generating portions 13 and 14 of the projecting portion 12b are present so that the diameter of the strain-generating portions 13 and 14 is increased. The direction length is secured.

  As shown in FIGS. 2 to 4, the strain generating portions 13 and 14 are plate-like plates arranged at the same vertical interval as the height of the through hole 12 c, and the circumferential width b is the outer peripheral length of the core portion 11. 1% to 5%. The radial length p of the strain generating portions 13 and 14 is 10 mm to 25 mm, preferably 15 mm to 20 mm. As shown in FIG. 4, the strain generating portions 13 and 14 are formed with inner tapered portions 13a and 14a and outer tapered portions 13b and 14b so that the thickness gradually increases toward both radial sides. The thickness t of the thinnest part at the center of the strain-generating parts 13 and 14 is 0.5 mm to 2.0 mm, preferably 0.8 mm to 1.7 mm. The taper angle θ of the inner taper portions 13a and 14a and the outer taper portions 13b and 14b is set to 5 ° to 30 °, preferably 15 ° to 25 °.

  A total of four strain gauges SG1 to SG4 are bonded to the inner tapered portions 13a and 14a and the outer tapered portions 13b and 14b of the upper and lower strain generating portions 13 and 14, respectively. As shown in FIG. 5, the strain gauges SG <b> 1 to SG <b> 4 form one Wheatstone bridge circuit WH <b> 1, WH <b> 2, WH <b> 3 for each pair of strain generating portions 13, 14 in a pair of upper and lower, and each Wheatstone bridge circuit WH <b> 1. The circuit configuration is such that outputs from WH2 and WH3 are summed in parallel. When the distance between adjacent strain gauges SG1 and SG2 and SG3 and SG4 is l, l = 6 mm to 20 mm, and preferably 8 mm to 12 mm.

  According to the load cell 10 having the above configuration, the outer peripheral frame portion 12 is supported and fixed to the fixing member, a hopper (not shown) to be measured is fixed to the core portion 11, and the supply path of the hopper is set to the center hole 11a. If installed through, the stress generated in the strain generating portions 13 and 14 when the load of the hopper is applied to the core portion 11 is detected by each of the strain gauges SG1 to SG4, and the load value is calculated from the parallel summed output value. It can be converted. On the contrary, the same result can be obtained by supporting and fixing the central hole 11a of the core portion 11 in the supply path and fixing the hopper to the outer peripheral frame portion 12. Further, the same result can be obtained even when a load is applied by closing the center hole 11a with a metal plate or the like and placing a heavy object thereon.

  Further, since the load cell 10 is provided with a pair of upper and lower strain generating portions 13 and 14 that bridge the core portion 11 and the outer peripheral frame portion 12, even if there is a variation in the position of the load applied to the core portion 11, the load cell 10 is balanced. A Roverval mechanism is formed to reduce the deviation error. In addition, since the strain generating portions 13 and 14 are divided into three groups at intervals in the circumferential direction, the strain gauges SG1 to SG4 to which the stress generated in each of the strain generating portions 13 and 14 is locally attached. Can be detected accurately and the load detection accuracy is improved.

Further, since the outer peripheral frame portion 12 is provided with a through hole 12c penetrating from the outer surface to the inner surface, a pair of upper and lower strain generating portions 13 and 14 between the core portion 11 and the outer peripheral frame portion 12 are formed. Can be easily formed by cutting through the through-hole 12c, and the workability is good.
Further, as shown in FIG. 4B, the stress generated in the strain generating portions 13 and 14 usually tends to increase toward both sides in the radial direction, but the strain generating portions 13 and 14 are directed toward both sides in the radial direction. Since the inner tapered portions 13a, 14a and the outer tapered portions 13b, 14b are provided so that the thickness gradually increases,
Both side regions R of the radial distribution of stress values are flattened to make the stress distribution uniform. Therefore, even if the attachment positions of the strain gauges SG <b> 1 to SG <b> 4 are slightly misaligned in the both side areas R, the detection error is devised so as not to occur as much as possible.

Next, a preferable shape example of the strain generating portions 13 and 14 will be shown.

It is preferable to have a shape as shown in Table 1 depending on the magnitude of the rated load. That is, the plate thickness t, the taper angle θ, and the width of the strain generating portions 13 and 14 so that the amount of strain generated when the rated load is applied to the strain generating portions 13 and 14 falls within the strain detection range of the strain gauges SG1 to SG4. A value such as b is determined. In particular,
σ = [3wl / {2b (t + 1/2 · tan θ) ² }] / 3
To calculate the stress σ generated in the strain-generating portions 13, 14,
ε = (σ / E) · 4
Then, the strain ε generated in the strain generating portions 13 and 14 is calculated and confirmed.
Here, w is the load value [kg · f], l is the distance l between adjacent strain gauges SG1 and SG2, b is the width of the strain-generating portions 13 and 14, and t is the thinnest portion of the strain-generating portions 13 and 14. Thickness.

Next, examples and comparative examples will be described with reference to FIG.
An example is the same as that of the embodiment, and three pairs of upper and lower strain generating portions 13 and 14 are arranged at three equal intervals in the circumferential direction. In Comparative Example 1, a pair of left and right strain generating portions are arranged in parallel in one place in the circumferential direction. In Comparative Example 2, two pairs of upper and lower strain generating portions are arranged at two equal intervals in the circumferential direction. Examples and Comparative Examples 1 and 2 have the same other conditions.

FIG. 6 shows experimental results for nonlinearity and hysteresis, and both target specifications are 0.03% RO. In the example, it can be seen that both the non-linearity and the hysteresis are very close to the target specification of 0.03% RO as compared with Comparative Examples 1 and 2.
As shown in FIG. 7, the non-linearity refers to the output when the load increases with respect to the reference straight line connecting the output at no load and the output at the rated load and the maximum deviation expressed as a percentage of the rated output. . Hysteresis is the maximum value of the difference in output with respect to the same test when the load is reciprocated between when the load is increased up to the rated load and when the load is decreased, and is expressed as a percentage of the rated output. RO means rated output.

Next, FIG. 8 shows a weighing device 100 using the load cell 10.
The outer peripheral frame portion 12 of the load cell 10 is fastened and fixed to the support fixing material 21 with bolts B2. On the other hand, the center hole 11a of the core part 11 penetrates the cylindrical part 20a of the cylindrical member 20, and the flange part 20b protruding laterally from the upper outer periphery of the cylindrical part 20a is connected to the bolt hole 11b of the core part 11 by the bolt B1. It is fastened and fixed with. An annular member 23 is fitted and fixed to the lower outer periphery of the cylindrical portion 20 a of the cylindrical member 20, and the outer peripheral surface of the container 26 is press-contacted by an elastic material 25 provided on the lower end inner surface of the vertical piece 24 suspended from the annular member 23. keeping. Further, a charging pipe 22 for supplying the object to be weighed W is loosely inserted into the upper surface opening of the cylindrical member 20.
According to the above configuration, the object to be weighed W dropped from the input pipe 22 is accumulated in the container 26, and the weight of the object W to be weighed loaded on the container 26 is the core of the load cell 10 via the cylindrical member 20. 11, the weight of the object to be weighed W can be measured.

Next, FIG. 9 shows an example of another weighing device 200 using the load cell 10.
It passes through the cylindrical portion 30a of the input pipe 30 (supporting and fixing material) supported and fixed to supply the object W to the center hole 11a of the core portion 11 of the load cell 10, and from the outer periphery of the cylindrical portion 30a. The flange portion 30b protruding in the direction is fastened and fixed to the bolt hole 11b of the core portion 11 by the bolt B1. On the other hand, on the outer peripheral frame 12, a flange 31b protruding laterally from the upper end edge of the cylindrical portion 31a of the large-diameter cylindrical member 31 is fastened and fixed to the bolt hole 12d with a bolt B2. An annular member 32 is fitted and fixed to the outer periphery of the cylindrical portion 31 a of the cylindrical member 31, and the outer peripheral surface of the container 35 is pressed and held by an elastic material 34 provided on the lower end inner surface of the vertical piece 33 suspended from the annular member 32. ing.
According to the above configuration, the object to be weighed W dropped from the input pipe 30 is accumulated in the container 35, and the weight of the object W to be weighed loaded on the container 35 is connected to the outer peripheral frame of the load cell 10 via the cylindrical member 31. Since the load is applied to the part 12, the weight of the object to be weighed W can be measured.

It is a perspective view which shows the load cell of embodiment of this invention. It is a top view of a load cell. It is the sectional view on the AA line of FIG. (A) is principal part sectional drawing, (B) is a graph which shows a stress curve. It is a circuit block diagram of the strain gauge adhere | attached on the strain body. It is drawing which shows an Example and a comparative example. It is a graph explaining a nonlinearity and a hysteresis. It is drawing which shows the measuring device which uses a load cell. It is drawing which shows another weighing | measuring apparatus using a load cell. (A) is a top view which shows a prior art example, (B) is sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Load cell 11 Core part 12 Outer periphery frame part 12c Through-hole 13, 14 Strain-generating part 13a, 14a Inner taper part 13b, 14b Outer taper part 15 Cavity 26, 35 Container 100, 200 Weighing device SG1-SG4 Strain gauge W WH1-WH3 Wheatstone bridge circuit

Claims (2)

In a load cell in which a plurality of strain gauges are attached to a strain generating portion where distortion occurs due to a load,
A core portion disposed on the center side, an outer peripheral frame portion disposed at an outer peripheral side of the core portion, and a pair of upper and lower strain generating portions that bridge between the core portion and the outer peripheral frame portion; Including one of the core part or the outer peripheral frame part as a support fixing part and the other as a load-loading part,
The core portion and the outer peripheral frame portion are annularly arranged on concentric circles, and the strain-generating portion has a thickness direction in the vertical direction,
The upper and lower pair of strain generating portions are provided in three sets at equal intervals in the circumferential direction, and the outer peripheral frame portion has a position corresponding to the upper and lower sides of each set of strain generating portions from the outer surface to the inner surface. A through hole is formed, and the circumferential width of the strain-generating portion is 1% to 5% of the outer peripheral length of the core portion.
The pair of upper and lower strain generating portions of each set has a cross-sectional taper shape that gradually increases the thickness toward the both sides in the radial direction with the upper surface of the upper strain portion not contacting the through hole and the lower surface of the lower strain portion. Provide inner and outer taper parts,
When the rated load to be applied is in the range of 200 N to 5 KN, the taper angle θ of the upper and lower radial taper portions is 5 ° to 15 °, and the thickness (t) of the thinnest central portion is 0.8 mm to 1 .7 mm, width b is in the range of 8 mm to 12 mm, and is set to increase according to the increase of the rated load,
The paste strain gauge on the inner and outer tapered portion that is thicker in the vertical pair of the strain generating part, together with the said strain generating portion paste the four strain gauges for each set, by using the strain gauge A load cell comprising a Wheatstone bridge circuit, and a circuit for parallelly adding outputs from the Wheatstone bridge circuits. The load cell according to claim 1, wherein one of the core portion or the outer peripheral frame portion of the load cell is fixed to a support fixing material, and the other is fixed to a container side that accommodates an object to be measured. A weighing device characterized by

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