JP4013633B2 - Load cell - Google Patents

Description

とすれば、荷重をＰ１に負荷したときの出力Ｗｏｕｔは、
Ｗｏｕｔ＝Ｗ＋Ａ₁ ＋α・Ａ₂ ＋Ａ₃ ＋β・Ａ₄ ・・・・（３）
となる。
【００２５】
また、荷重をＰ２に負荷したときの出力Ｗｏｕｔは、
Ｗｏｕｔ＝Ｗ＋Ｂ₁ ＋α・Ｂ₂ ＋Ｂ₃ ＋β・Ｂ₄ ・・・・（４）
となり、同じくＰ３に負荷したときの出力Ｗｏｕｔは、
Ｗｏｕｔ＝Ｗ−Ｂ₁ −α・Ｂ₂ −Ｂ₃ −β・Ｂ₄ ・・・・（５）
で、Ｐ４に負荷したときには、
Ｗｏｕｔ＝Ｗ−Ａ₁ −α・Ａ₂ −Ａ₃ −β・Ａ₄ ・・・・（６）
となる。
【００２６】
ここで、
Ａ₁ ＋α・Ａ₂ ＋Ａ₃ ＋β・Ａ₄ ＝０ ・・・・（７）
Ｂ₁ ＋α・Ｂ₂ ＋Ｂ₃ ＋β・Ｂ₄ ＝０ ・・・・（８）
となるようなαおよびβを算出すると、（１）式で表されるＷｏｕｔは、測定皿５３上のＰ１〜Ｐ４のいずれに荷重を負荷しても、Ｐ０に荷重を負荷したときの値と同じＷとなり、偏置誤差を解消した荷重検出出力を得ることができる。
【００２７】
なお、（７），（８）式を用いた連立方程式から求めたαおよびβは、
α＝｛（Ｂ₁ ＋Ｂ₃ ）／Ｂ₄ −Ａ₁ −Ａ₃ ｝／（Ａ₂ −Ｂ₂ ／Ｂ₄ ）
β＝｛（Ａ₁ ＋Ａ₃ ）／Ａ₂ −Ｂ₁ −Ｂ₃ ｝／（Ｂ₄ −Ａ ₄／Ａ ₂）
となる。
【００２８】
以上の本発明の実施の形態において特に注目すべき点は、ロードセルの偏置誤差の調整に際して、起歪体を削る必要がなく、複数のホイトストーンブリッジ２１〜２４の偏置誤差を測定して、線形和の演算式における係数を算出して設定するだけでよい点であり、これにより、熟練をようすることなく、随時に正確な偏置誤差調整が可能となる。
【００２９】
なお、本発明においては、起歪体の構造・形状については、上記した実施の形態において用いたもののほか、他の公知の構造・形状のものを用い得ることは勿論である。
【００３０】
【発明の効果】
以上のように、本発明によれば、両端部に可撓部を有する上下２本の梁を有する起歪体と、上記各可撓部にそれぞれ歪みゲージを貼着してなるロードセルにおいて、上記各可撓部のそれぞれに前記梁の短手方向にオフセットして貼着された複数の歪みゲージと、梁の一方の可撓部に貼着された歪みゲージと、他方の可撓部に貼着された歪みゲージと、を含むホイトストーンブリッジの複数と、その各ホイトストーンブリッジの出力の線形和を算出して当該ロードセルに作用する荷重の検出値として出力する演算手段とを備えるとともに、その線形和の算出時に各ホイトストーンブリッジの出力に乗じる係数が、当該各ホイトストーンブリッジの出力に現れる偏置誤差を相殺する値に設定されているので、偏置誤差の調整に当たって、従来のように起歪体を削る必要がなく、熟練を要することなく、常に正確な調整を行うことが可能となった。また、起歪体を削ることなく偏置誤差の調整が可能であることから、電子はかりなどの装置に組み込んだ状態で偏置誤差を簡単に調整することができ、偏置誤差の調整作業を大幅に簡素化することが可能となった。
【図面の簡単な説明】
【図１】本発明の実施の形態の斜視図である。
【図２】図１における各歪みゲージＳ１〜Ｓ８の結線図である。
【図３】従来のロードセルの例を示す斜視図である。
【図４】図３の従来のロードセルの各歪みゲージの結線図である。
【図５】ロードセルを荷重センサとした電子はかりの構成例の説明図である。
【図６】電子はかりの測定皿の平面図で示す、偏置誤差の調整時における荷重の負荷位置の説明図である。
【符号の説明】
１０ 起歪体
１１ａ，１１ｂ 柱部
１２ａ，１２ｂ 梁
ｅ 可撓部
Ｓ１〜Ｓ８ 歪みゲージ
２１〜２４ ホイトストーンブリッジ
３ 演算部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a load cell using a strain gauge, and more particularly to a load cell that can be used for a load sensor or the like of an electronic balance and that can adjust the displacement error very easily.
[0002]
[Prior art]
In a strain gauge type load cell, generally, a plurality of strain gauges are attached to a strain generating body that is elastically deformed by the action of a load, and a Wheatstone bridge is formed by each strain gauge, and the output of the Wheatstone bridge is output. This is used as a detection output of the load acting on the strain generating body.
[0003]
FIG. 3 is a perspective view showing an example of a conventional load cell of this type. The strain body 40 in this example includes a pair of column portions 41a and 41b, and connects the column portions 41a and 41b with upper and lower two beams 42a and 42b having flexible portions e at both ends. In total, four strain gauges S1 to S4 are attached to each of the four flexible portions e. Then, a Wheatstone bridge as shown in FIG. 4 is assembled by these strain gauges S1 to S4.
[0004]
In the above configuration, when one of the column portions 41a and 41b, for example, the column portion 41a is fixed and a load is applied to the other column portion 41b, each strain is caused by elastic deformation of each flexible portion e. The resistance values of the gauges S1 to S4 change, whereby the output Vout of the Wheatstone bridge becomes a magnitude corresponding to the load.
[0005]
When such a load cell is used as a load sensor for an electronic scale, as shown in FIG. 5, the bottom of one column 41a is fixed to the base 51, and a tray receiver 52 is mounted on the upper surface of the other column 41b. A configuration in which the measurement tray 53 is placed on the tray receiver 52 is often used.
[0006]
In such an electronic balance, it is necessary to adjust so that the difference in the weight measurement result depending on the mounting position of the object to be measured on the measurement pan 53, that is, the deviation error becomes as small as possible.
[0007]
Adjustment of the deviation error in this type of conventional electronic scale is performed when the object to be measured is placed on the central portion P0 and the four corners P1 to P4 of the measuring plate 53 as shown in the plan view of the measuring plate 53 in FIG. This is done by cutting the four flexible portions e of the strain-generating body 10 of the load cell so that the weight measurement results match each other or fall within a set range.
[0008]
[Problems to be solved by the invention]
By the way, the above-described conventional adjustment operation of the deviation error requires considerable skill, and depending on the level of proficiency thereof, not only a considerable time is required but also the risk of damaging the load cell when the flexible portion e is cut. There is sex.
[0009]
In addition, there is a problem that a high-resolution load cell needs to be readjusted each time it is attached to a device, such as being incorporated into an electronic scale.
[0010]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a load cell that can easily adjust an offset error at any time without cutting a strain generating body and without requiring skill. Yes.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a load cell according to the present invention includes a strain generating body having two upper and lower beams each having a flexible portion at both ends , and a load cell in which a strain gauge is attached to each flexible portion. in a plurality of strain gauges which are attached to offset in the lateral direction of the beam, each of said respective flexible portions, and the strain gauge is adhered to one of the flexible portion of the beam, the other flexible A plurality of Wheatstone bridges including a strain gauge affixed to the section, and a calculation means for calculating a linear sum of outputs of the respective Wheatstone bridges and outputting as a detection value of a load acting on the load cell. In addition, the coefficient by which the output of each Wheatstone bridge is multiplied when calculating the linear sum is set to a value that cancels out the offset error that appears in the output of each Wheatstone bridge. That.
[0012]
In the present invention, when the load application position is at a diagonal position across the center of the load receiver of the load cell (P1 and P4 in FIG. 6 or P2 and P3), the displacement error is approximately inverted to positive and negative values. By using this, a plurality of strain gauges are attached to each flexible part of the strain generating body, a plurality of Wheatstone bridges are assembled by these, and a load detection output is obtained by a linear sum thereof. By using a coefficient that cancels out the offset error component included in the output of each Wheatstone bridge when calculating the linear sum, the intended purpose is achieved.
[0013]
That is, a plurality of strain gauges are attached to each flexible part of one strain generating body to form a plurality of Wheatstone bridges, and the load detection output is represented by a linear sum of the outputs. Then, by measuring the offset error appearing at the output of each Wheatstone bridge, the coefficient for canceling the offset error and canceling the offset error from the linear sum can be obtained from a simple simultaneous equation. It is possible (see equations (7) and (8) described later).
[0014]
Therefore, according to the present invention, the offset error that appears in the output of each Wheatstone bridge is measured without cutting the flexible portion of the strain generating body, and the measurement result is used to calculate the output of each Wheatstone bridge in the linear sum. By calculating the coefficient to be multiplied and setting it in the calculation unit, it is possible to eliminate the load cell's offset error, and it is possible to adjust the offset error without requiring skill. Adjustment is possible.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a diagram showing a connection state of the strain gauges S1 to S8.
[0016]
The strain body 10 has a structure equivalent to that of the conventional one shown in FIG. 3 and includes a pair of column portions 11a and 11b, and the column portions 11a and 11b are provided at both ends. It has a structure in which two upper and lower beams 12a and 12b having a flexible portion e are connected.
[0017]
Two each of the strain gauges S1 and S3, S2 and S4, S5 and S7, and S6 and S8 are attached to each flexible part e of the strain generating body 10, and each of these strain gauges S1 to S4 is attached. As shown in FIG. 2, S8 is connected to each other so as to form four Wheatstone bridges 21, 22, 23 and 24 together with two fixed resistors R0. One end of each of the Wheatstone bridges 21, 22, 23, and 24 is grounded, and a constant DC voltage V _B is applied to the other end.
[0018]
In the above circuit configuration, the output Vout1~Vout4 each Hoyt Stonebridge 21, 22, 23 and 24, as shown in FIG. 2, the voltage between the strain gauges S1 and S2 V _1, the strain gauge S3 and S4 the voltage between V _2, V ₃ and the voltage between the strain gauges S5 and S6, voltage V ₄ between the strain gauge S7 and S8, the further the voltage between the two fixed resistors R0, R0 and V _0,
Vout1 = V ₁ -V ₀
Vout2 = V ₂ -V ₀
Vout3 = V ₃ -V ₀
Vout4 = V ₄ -V ₀
It becomes.
[0019]
Then, the outputs Vout1 to Vout4 of each of the above Wheatstone bridges 21 to 24 are introduced into the calculation unit 3, and these linear sums are calculated by the calculation shown in the following equation (1), and the linear sum is determined by the load cell. It is taken out as a load detection output Wout.
Wout = Vout1 + α · Vout2 + Vout3 + β · Vout4 (1)
[0020]
In the equation (1), the coefficients α and β are calculated and set as shown below, so that the offset error components included in the outputs of the Wheatstone bridges 21 to 24 are canceled out, and the load detection output Wout is a signal that does not include an offset error component.
[0021]
As shown in FIG. 5 described above, with the embodiment of the present invention incorporated in an electronic balance, predetermined weights and the like are sequentially placed on P0 to P4 on the measurement pan 53 as shown in FIG. The outputs Vout1 to Vout4 of the bridges 21 to 24 are measured.
[0022]
The outputs Vout1 to Vout4 of the Wheatstone bridges 21 to 24 when a load is applied to the central portion P0 of the measurement dish 53 are Vout1 = W _1.
Vout2 = W ₂
Vout3 = W ₃
Vout4 = W ₄
And the output when a load is applied to P1, respectively, Vout1 = W ₁ + A ₁
Vout2 = W ₂ + A ₂
Vout3 = W ₃ + A ₃
Vout4 = W ₄ + A ₄
And Further, the outputs when a load is applied to P2 are Vout1 = W ₁ + B ₁ , respectively.
Vout2 = W ₂ + B ₂
Vout3 = W ₃ + B ₃
Vout4 = W ₄ + B ₄
And
[0023]
In this case, when a load is applied to the equidistant position on the diagonal line across the center of the measurement pan 53, the displacement error is a value with the polarity reversed, so the output when the load is applied to P3 is
Vout1 = W ₁ −B ₁
Vout2 = W ₂ -B ₂
Vout3 = W ₃ -B ₃
Vout4 = W ₄ -B ₄
It becomes. Similarly, the output that P4 is loaded is
Vout1 = W ₁ -A ₁
Vout2 = W ₂ -A ₂
Vout3 = W ₃ -A ₃
Vout4 = W ₄ -A ₄
It becomes.
[0024]
Now, when considering the above-described equation (1), when a load is applied to the central portion P0 of the measurement dish 5,

Then, the output Wout when the load is applied to P1 is
Wout = W + A ₁ + α · A ₂ + A ₃ + β · A ₄ ... (3)
It becomes.
[0025]
The output Wout when the load is applied to P2 is
Wout = W + B ₁ + α · B ₂ + B ₃ + β · B ₄ ... (4)
Similarly, the output Wout when P3 is loaded is
Wout = W−B ₁ −α · B ₂ −B ₃ −β · B ₄ ... (5)
And when P4 is loaded,
Wout = W−A ₁ −α · A ₂ −A ₃ −β · A ₄ ... (6)
It becomes.
[0026]
here,
A ₁ + α · A ₂ + A ₃ + β · A ₄ = 0 (7)
B ₁ + α · B ₂ + B ₃ + β · B ₄ = 0 (8)
Wout represented by the equation (1) is a value obtained when a load is applied to P0, regardless of which of P1 to P4 on the measurement pan 53 is applied. It becomes the same W and the load detection output which eliminated the deviation error can be obtained.
[0027]
Note that α and β obtained from the simultaneous equations using the equations (7) and (8) are:
α = {(B ₁ + B ₃ ) / B ₄ −A ₁ −A ₃ } / (A ₂ −B ₂ / B ₄ )
β = {(A ₁ + A ₃ ) / A ₂ −B ₁ −B ₃ } / (B ₄ −A ₄ / A ₂ )
It becomes.
[0028]
Of particular note in the embodiments of the present invention described above is that when adjusting the displacement error of the load cell, it is not necessary to cut the strain-generating body, and the displacement errors of the plurality of Wheatstone bridges 21 to 24 are measured. Therefore, it is only necessary to calculate and set the coefficient in the arithmetic expression of the linear sum. This makes it possible to accurately adjust the offset error at any time without skill.
[0029]
In the present invention, as to the structure and shape of the strain generating body, it is needless to say that other known structures and shapes can be used in addition to those used in the above embodiment.
[0030]
【The invention's effect】
As described above, according to the present invention, in the strain cell having two upper and lower beams having flexible portions at both ends , and in the load cell in which a strain gauge is attached to each of the flexible portions, a plurality of strain gauges which are attached to offset in the lateral direction of the beam to each of the flexible portions, and the strain gauge is adhered to one of the flexible portion of the beam, bonded to the other of the flexible portion A plurality of Wheatstone bridges including a strain gauge, and a calculation means for calculating a linear sum of outputs of the respective Wheatstone bridges and outputting them as a detection value of a load acting on the load cell. The coefficient that is multiplied by the output of each Wheatstone bridge when calculating the linear sum is set to a value that cancels out the deviation error that appears in the output of each Wheatstone bridge. It is not necessary to cut the strain body to, without requiring skill, always it is possible to perform accurate adjustment. In addition, since it is possible to adjust the displacement error without cutting the strain body, it is possible to easily adjust the displacement error when it is incorporated in a device such as an electronic scale. It became possible to greatly simplify.
[Brief description of the drawings]
FIG. 1 is a perspective view of an embodiment of the present invention.
FIG. 2 is a connection diagram of strain gauges S1 to S8 in FIG.
FIG. 3 is a perspective view showing an example of a conventional load cell.
4 is a connection diagram of each strain gauge of the conventional load cell of FIG. 3. FIG.
FIG. 5 is an explanatory diagram of a configuration example of an electronic balance using a load cell as a load sensor.
FIG. 6 is an explanatory diagram of a load position of a load when adjusting an offset error, which is shown in a plan view of a measuring pan of an electronic balance.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Strain body 11a, 11b Column part 12a, 12b Beam e Flexible part S1-S8 Strain gauge 21-24 Whitestone bridge 3 Calculation part

Claims (1)

In a strain cell having two upper and lower beams each having a flexible portion at both ends, and a load cell in which a strain gauge is attached to each flexible portion, a short of the beam is attached to each flexible portion. Hoyt stone comprising a plurality of strain gauges which are attached to offset the longitudinal direction, and strain gauges affixed to one of the flexible portion of the beam, the strain gauge is adhered to the other of the flexible portion, the A plurality of bridges , and calculating means for calculating a linear sum of outputs of the respective Wheatstone bridges and outputting them as detection values of a load acting on the load cell, and at the time of calculating the linear sum, outputs of the respective Wheatstone bridges A load cell characterized in that a coefficient to be multiplied by is set to a value that cancels out an offset error appearing in the output of each Wheatstone bridge.

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