JPS60147616A - Load cell - Google Patents

Abstract

PURPOSE:To obtain a high-precision measured value by providing the first strain gauge which generates an output in accordance with a load and the second strain gauge, which is used for detecting the moment of a beam, on the same plane and correcting a deflected load error. CONSTITUTION:A deformable parallelogram 13 is formed with thin deforming parts 9, 10, 11, and 12 of a prismatic beam 5 where two holes 6 and 7 are connected by a groove 8. The first strain gauge 17 (RA, RB, RC, and RD) is provided in accordance with deforming parts 9 and 10, and the second train gauge 18 (RX) is provided between the tensile strain side and the compressive strain side of the gauge 17, and the gauge 17, an input terminal 19, and an output terminal 20 are connected by a lead wire 21. At a measurement time, nonlinearity of variance of the output from the gauge 17 is corrected by detection of RX of the gauge 18. Thus, accurate measurement is possible though strain gauges are provided only on one face of the beam.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a load cell that utilizes a strain gauge that changes its resistance value in accordance with the amount of strain to obtain an electrical output corresponding to a load.

TECHNICAL BACKGROUND AND PROBLEMS There are two types of conventional load cells of this type that utilize a beam: the type shown in FIG. 1 and the type shown in FIG. 3. That is, in the case shown in Fig. 1, four thin-walled deformed parts (
2), and four strain gauges (3) forming a bridge circuit are provided in each of the thin deformed portions (2) on the upper and lower surfaces. A saucer (4) is connected to the free end. This saucer (4) has Wo and W as shown in the figure.
Although the loads L and WR are applied at different positions, the relationship between the load and the output voltage remains constant at each position, as shown in FIG. 2, and the linearity is good. However, arranging the strain gauges (3) on both sides of the beam (1) results in double wiring, and when forming the strain gauges (3) using a thin film formation process, it is necessary to perform similar processing on both sides. This has the disadvantage of increasing costs.

For this reason, as shown in Figure 3, beam (1)
It is common practice to provide a strain gauge (3) only on one side. In this case, since there are four strain gauges (3), two strain gauges (3) are arranged in parallel at each of the thin-walled deformed portions (2) at - locations.

In such a load cell, Fig. 4 (cL) (
The output changes as shown in 41tC+. That is, when WO is applied to the stress center Lσ0, Fig. 4 +a
As shown in FIG. 1, the relationship between the load and the output voltage is linear, and is similar to that shown in FIG. However, when the load is placed on wR, the trap becomes a bulge as shown in Figure 4 (4), and in the case of WL, it becomes a dent in K as shown in Figure 4 (cl). The reason for this deterioration is the moment caused by the unbalanced load, and the effect of the moment is not canceled out as shown in Figure 1. Therefore, in the case where the strain gauge (3) is installed only on one side, High precision cannot be obtained.

OBJECTS OF THE INVENTION An object of the present invention is to provide a load cell that can obtain extremely high precision measurement values even when a strain gauge is provided on only one side of the beam.

Summary of the Invention The present invention provides a first strain gauge that is bridge-coupled and generates an output corresponding to a load on one side of a beam, and a second strain gauge on the same side to detect the moment generated in the beam. In this way, the linearity error caused by the unbalanced load is corrected, and the linearity between the load and the output voltage can be maintained no matter where the load is applied on the saucer. It is.

Embodiments of the Invention A first embodiment of the present invention will be described with reference to FIGS. 5 to 8. First, -r (5) has a prismatic shape and is formed by machining stainless steel or high-strength aluminum. That is, the two holes (6) (7) are connected to the groove (8).
four thin-walled deformed parts (9) αOα
The force is 0. These thin deformed parts (9) <1
A deformable parallelogram portion α] is formed by 0α (b). Two support holes q4 for fixing are formed at one end of the beam (5), and a connecting hole (lee) for connecting the saucer αO is formed at the other end.

Next, on the upper surface of the beam (5), RA, RB,
Four first strain gauges α, denoted Ro and RD, are provided, and a second strain gauge αQ, denoted Rx, is provided between the tensile strain side and compressive strain side of these strain gauges a force. It is provided. The strain gauge aη has input terminals US and Vo"Ve" and Ve-, respectively.
, Vo- is connected to the output terminal (a) by a lead wire eυ. This kind of strain gauge a'h
(18, input terminal (to), output terminal ■, lead wire e)
are integrally formed by a thin film forming process such as vapor deposition or sputtering.

Next, the electrical connection state for functioning as a scale will be explained based on FIG. 7. First, the detection section of the first strain gauge α is connected to a power source vg. The detection part (a) is equipped with a zero point setter (c).
, load cell signal amplifier ■, and converter wires are connected in sequence, a CPU @ is connected to this IV/D converter (c), and a key (c) and a display unit are connected to this CPUv).
is connected. Further, a reference amplifier (G) and a span setter 0 are connected to the power supply in this order, and the span setter 0 is connected to the zero point setter (C) and the A/D.
converter) and connected to the converter. Therefore, the output of the detection section (b) is VL, and the output of the load cell signal amplifier (b) is VIN.

The gain determining feedback network 02 of this load cell signal amplifier (c) is formed by resistors R1e and R4 and the second strain gauge a peak Rx.

Therefore, the relationship between the output VL of the detection section (a) and the output VIN of the load cell signal amplifier (e) is expressed by the following equation.

Here, the gain G of the load cell signal amplifier (c) is simply expressed as the resistance value Rx of the strain gauge α is ΔRx
Subtracting the gain change jG when the gain is changed, the following equation is obtained.

Therefore, Δ becomes as shown in the following equation.

Here, in the RxO value and the value of vL, the load applied to the detection unit (2) is not entirely an effective component, but an inactive component is generated. As a result, the value of VL changes by one ΔvL. Let this rate of change be -aVL/VL.

This invalid component is detected by Rx, and VL due to the invalid component is
A feature of the present invention is to correct for changes in .

Therefore, if we look at the change in vIN, we can see that WR in Figure 6
If there is a load on , the result will be as shown in Figure 8 (K as in at), and if there is a load on WL in Figure 6, the result will be as shown in Figure 8.

Therefore, if we calculate the rate of change in vIN, we get: Here, since lVj changes in the opposite direction to ΔRx, the following equation is obtained.

Therefore, since ΔVIN/VIN=o is a state in which the load is not affected by the load application position, the following relationship is established. This equation shows that changes in VL can be corrected by changes in Rx.

Next, examples will be shown. First, the beam (5) is made of high-strength aluminum, and its Young's modulus E is 7 x 10' Kt.
/d, the width of the beam (5) is 20 mm, and the thickness h is 8
Let it be m. It is assumed that a load W of 8 to 4 is acting at a position of 150IIIli (υ) from the stress center LσO as WR.

The moment applied to Rx in this state is M=WXLK. On the other hand, the stress σ applied to the beam (5) is σ=WXL
/Z (Z is the second moment of area knee bh3/12teal). When ε is the amount of strain, σ = εE, so ε = 1.9 x 1g-', and IR/R = K
From the relational expression ε (K is a gauge factor and 2 is adopted where reliable), ΔR = 2 x 1.9 x 10-' = 3.8 x 10-' ...・・・・・・
・・・・・・・・・・・・・・・・・・・・・■.

Furthermore, when ΔVIN/VIN was actually measured under the above conditions, it was found to be negative.

Here, R2+ R1+ Rx lΔRx/ shown by the formula ■
From selecting Rx appropriately, the above OJVIN/'VI
N = 1/3000 O nonlinearity can be corrected. Therefore, R, = 1.8 kΩ, R, = 1
By choosing 00Ω, Rx = 13.9 kΩ,
■The value of the first term in the equation is +1/3000 K, as shown in Figure 8 (
A state of good linearity as shown in Gl can be obtained.

Next, a second embodiment of the present invention will be described based on FIG. In this embodiment, the load cell signal amplifier (c) is R2=
A feedback circuit network 02 for determining the gain on the inverting side and the non-inverting side having the relationship R2', Rx=Rx', at=B1/ is provided. Here, when the output of the zero point setter (c) is set to VB, the relationship between VIN and VL is as shown in the following equation.

Here, by subtracting the change ΔVIN in VIN when Rx changes ΔRx%VL by ΔvL, the following equation is obtained.

Therefore, if we calculate the rate of change when VIN changes by ΔVIN, we get the following equation.

Here, VL changes in the opposite direction to ΔRx, so if -lVj is set, the condition that IVIH/VH4=g is set. R, and Rx so as to satisfy this relationship of equation 0.
By selecting .DELTA.vL/'VL, it is possible to correct .DELTA.vL/'VL.

In addition, in practice, not only the first and second strain gauges α't)α→ but also the resistors R1+R2 of the gain determining feedback network 0→ may be formed simultaneously in the thin film forming process. . As a result, it can be manufactured using the same process and the same number of man-hours, and can be manufactured at low cost. In addition, there is little variation in material, for example, variation in TCR (temperature coefficient of resistance) is ±
A value of ippm/°C or less can be obtained. Therefore, the gain G is also stable without being affected by temperature, and a highly accurate circuit can be formed.

Effects of the Invention The present invention provides a first strain gauge that forms a bridge circuit on one side of the beam as described above, and a second strain gauge that prevents the output from becoming non-linear due to the influence of the moment acting on the beam. Since the K is designed to compensate for the strain, high accuracy can be maintained even if the strain gauge is formed only on one side of the beam.This allows accurate measurement values to be obtained no matter where the load is applied on the saucer. This is something that can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a side view of a conventional example, Fig. 2 is a graph showing the relationship between load and output voltage, Fig. 3 is a side view of another conventional example, and Fig. 4 (alt$1 ( Q) is a graph showing the relationship between the load and the output voltage, FIG. 5 is a perspective view of the beam showing the first embodiment of the present invention, FIG. 6 is a side view, and FIG.
The figure is a circuit diagram, FIG. , 9-12... Thin-walled deformed portion, 13...
・Parallelogram part, 17...first strain gauge, 1
8... Second strain gauge, z5... Load cell signal amplifier, 32... Feedback circuit network for determining gain

Claims (1)

[Scope of Claims] 1. Forming four thin-walled deformed parts in the beam to form a parallelogram part that deforms according to the load, and forming a bridge circuit only in the thin-walled deformed parts on one side of the beam. A load cell equipped with a first strain gauge, characterized in that a second strain gauge for compensating and correcting the nonlinearity of the output of the bridge circuit is provided on the same surface as the first strain gauge. . 2. The load cell according to claim 1, wherein a second strain gauge is inserted into a gain determining feedback circuit of the load cell signal amplifier. 3. The second strain gauge is provided between the first strain gauge on the positive tensile side and the first strain gauge on the compressive strain side. load cell. 4. The load cell according to claim 1, wherein the first strain gauge and the second strain gauge are integrally formed by a thin film forming process such as vapor deposition or sputtering.