JPH0715416B2 - Load cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a load cell having a structure in which a resistance wire strain gauge is attached to a predetermined portion of a load receiver and creep adjustment is performed.

[Prior art]

In a load cell having a structure in which a resistance line strain gauge is attached to a predetermined portion of a load receiver, a so-called creep characteristic in which the output value of the load cell changes with time is an extremely important performance. If this creep characteristic is not good, not only the output value will not be stable, but other performances, especially instrumental error (characteristics), zero return, and reproducibility will be greatly affected. Therefore, it is necessary to improve the creep characteristics in order to improve the accuracy and performance of the load cell.

A typical method conventionally used for improving this creep characteristic is a foil strain gauge 1 as shown in FIG.
This is a method of improving creep performance by changing the lengths d ₁ and d ₂ of the folding tabs 2 and 3 of the grit. However, this method has the following drawbacks.

(1) Strain gauges having creep characteristics adapted to the requirements of load cells of various rated loads are required.

(2) Even in a load cell having the same rated load, if the shape of the load receiver is changed from the design condition, a strain gauge having a creep characteristic suitable for it is required.

(3) Even in a load cell having the same rated load and the same load receiver, if the moisture-proof treatment is changed, a strain gauge having a creep characteristic suitable for it is required.

Further, in addition to the above (1) to (3), (4) As a result of manufacturing a large number of strain gauges as in the above (1) to (3), a defective load cell is manufactured due to misidentification of strain gauge selection or the like. There is a risk that

(5) A considerable loss occurs in labor required for development, development cost, development schedule, and the like.

(6) Further, when the number of load cell filters manufactured is small, the strain gauge manufacturer loses the motivation to develop and manufacture strain gauges suitable for the above load cells, and even if it is produced, it becomes an expensive strain gauge and the load cells can be manufactured at low cost. Disappear.

Also, in Japanese Patent Laid-Open No. 55-29756, a strain gauge is bonded in advance to set the total characteristic with the beam to be a negative creep characteristic, and the strain gauge is covered with a coating layer having a positive creep characteristic. The above is described.

However, this method has a drawback that creep cannot be transferred to the negative side.

Further, the present applicant has previously developed a creep performance improving method which does not have the above-mentioned defects and has applied for a patent (Japanese Patent Application No. 59-277800).

[Problems to be solved by the invention]

However, the creep characteristic improving method also has the following problems.

(A) In order to shift creep to the minus side, an adjusting film must be provided under the strain gauge, and the creep before interposing the adjusting film must be measured by attaching the same strain gauge. .

(B) Variation in creep in strain gauges of the same type has an error of about ± 0.03% in consideration of the difference in lots, and it is not possible to cope with the shift of creep characteristics in the negative direction of each load cell due to variation in strain gauge.

The present invention has been made in view of the above points, without adding a step such as re-straining the strain gauge again in accordance with the output characteristics of the individual load cells to which the strain gauge is already pasted,
It is to provide a load cell whose creep performance is adjusted with the strain gauge attached.

[Means for solving problems]

In order to solve the above problems, the present invention is a load cell having a structure in which a resistance wire strain gauge is attached to a predetermined portion of a load receiver, and at least on the resistance wire strain gauge except on the sensing portion of the resistance wire strain gauge. A creep adjustment layer whose load characteristics of the load cell output change continuously in the negative direction compared to before the adjustment was formed by applying paint on the load receiver at either end in the main axis direction or around it. Characterize.

Further, for fine adjustment, a creep adjusting layer is applied to the resistance wire strain gauge mainly on the sensitive portion of the resistance wire strain gauge so that the creep characteristics of the output of the load cell are in the positive direction. It is characterized by being formed.

Further, a creep adjusting layer is provided so that the creep characteristic of the output of the load cell becomes a predetermined creep characteristic value in the negative direction, and the load cell is provided with a coating for canceling the predetermined creep characteristic value.

[Action]

According to the present invention, by adopting the above configuration, the creep characteristic of the load cell output is continuously provided on the end portion on the strain gauge of the load cell in which the resistance wire strain gauge is attached to the load receiver and on the load receiver around the end portion. However, the creep characteristics can be adjusted extremely easily without the above-mentioned problems by only forming the creep adjusting layer that changes in the negative direction as compared with before adjustment.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing a portion of a strain-generating body of a load cell according to the present invention, to which a strain gauge is attached. FIG. 1 (a) is a plan view and FIG. 1 (b) is a side view. As shown in the figure, the strain gauge 1 includes a base 6, a sensing section 7a and a terminal section 7b on the base 6.
And a lead wire 4 connected to a terminal portion 7b of the pattern portion 7, and a laminate 8 formed on the pattern portion 7 and the lead wire 4. In the load cell, the strain gauge 1 configured as described above is attached by forming the adhesive layer 5 on the thin-walled portion 11a of the strain-generating body 11. An end layer 9 for creep adjustment is formed at the end of the strain gauge 1 excluding the sensitive portion 7a so that the creep characteristic of the output of the load cell changes in the negative direction as compared with that before adjustment. Further, for fine adjustment of the creep characteristics, a sensitizing portion layer 10 for creep adjustment is formed on the upper surface of the strain gauge 1 mainly on the sensitizing portion 7a of the strain gauge 1. Edge layer 9 and sensing layer 10
Is formed, for example, by applying an epoxy-based paint.

Next, the operation of the load cell configured as described above will be described. The strain gauge 1 is a thin portion of the strain-generating body 11 to which it is attached.
Depending on the position of 11a, there are those that receive tensile force and those that receive compressive force.

First, a case where a tensile force acts on the strain gauge 1 will be described. FIG. 3 is a conceptual diagram showing the deformation process when tensile force is applied to the thin portion of the flexure element 11, where FIG. 3 (a) shows the state before the tensile force is applied, and FIG. 3 (b) shows the tensile force applied. Immediately after being deformed, the figure (c) shows that after being deformed by applying a tensile force,
The state in which the edge layer 9 creeps and the sensing section 7a returns is shown. Now, when tensile deformation occurs in the thin portion of the strain generating body 11, the end layer 9 extends following the deformation of the strain generating body, but the end layer 9 indirectly connects the end of the sensitive portion 7a via the laminate 8. (The strain gauge 1 without the laminate 8 holds the end of the sensitive portion 7a through the base 6), and the sensitive portion 7a is further stretched as compared with the case where the end layer 9 is not provided. Will be received from the vertical direction {see arrow B in FIG. 3 (b)}. Furthermore, as the end layer 9 gradually expands due to stress-strain creep, the effect of the end layer 9 that the above-mentioned sensitive portion 7a is pulled in the vertical direction is reduced, and the sensitive portion 7a shrinks. 3 See arrow C in FIG. 3 (c)}. Therefore, the resistance value of the strain gauge side that receives the tensile force of the Wheatstone bridge is in the direction of returning to the resistance value before receiving the tensile force (direction of decreasing the resistance value), and the load cell output becomes negative creep.

Next, a case where a compressive force acts on the strain gauge 1 will be described. FIG. 4 is a conceptual diagram showing a case where a compressive force is applied to the thin portion of the flexure element 11, where FIG. 4 (a) is an initial state before the compressive force is applied, and FIG. 4 (b) is deformed by the compressive force. Immediately after
FIG. 7C shows a state in which the end layer 9 creeps and the sensing portion 7a returns after being deformed by applying a compressive force.

Now, when compressive deformation occurs in the thin portion of the flexure element 11, the end layer 9 shrinks following the deformation of the flexure element, but the end layer 9 indirectly connects the end of the sensitive portion 7a via the laminate 8. (The strain gauge 1 without the laminate 8 has a base 6 and a sensing unit.
7a), the sensing portion 7a receives a compressive force further in the longitudinal direction as compared with the case where the end layer 9 is not provided (see arrow D in FIG. 4 (b)). Further, as the end layer 9 gradually contracts due to stress-strain creep, the effect of the end layer 9 in which the above-mentioned sensing portion 7a is compressed in the vertical direction is reduced, and the sensing portion 7a expands. 4 See arrow E in FIG. 4 (c)}. Therefore, the resistance value of the strain gauge side that receives the compressive force of the Wheatstone bridge goes in the direction of returning to the resistance value before being compressed (the direction in which the resistance value increases), and the load cell output becomes negative creep.

As described above, the load cell output becomes negative creep regardless of whether the strain gauge 1 that receives the tensile force of the Wheatstone bridge or the strain gauge 1 that receives the compressive force is taken. Even if one, two, or three Wheatstone bridges are active gauges and the other are dummy resistors, the action and effect are not changed at all, and the creep characteristic can be shifted in a predetermined negative direction. Therefore, in the initial stage, the creep can be totally reduced to zero by applying the above treatment to the load cell of plus creep.

If the positive creep characteristics are not yet offset by the above treatment, increase the thickness of the end layer 9 or form a layer of another kind of material more susceptible to stress-strain creep. You may. In addition, when the strain gauge 1 is dispersed on the tip end side, there is little swelling and it is effective in mounting {see the portion B surrounded by the one-dot chain line in FIG. 1 (b)}.

Further, when the above-mentioned treatment causes an excessive amount of minus creep, a thin layer for stress-strain creep may be formed on the sensitive portion 7a for fine adjustment. The sensing portion layer 10 in FIG. 1 is a layer for fine adjustment. By forming the sensing portion layer 10, it is possible to bring the over-passing negative creep close to zero.

In addition, the load cell is often used by applying a coating for moisture proof and waterproof or by performing a sealing treatment. When moisture-proof and waterproof treatment is performed in this way,
Even if the load cell is an ideal load cell in which almost no creep occurs before the moisture-proof and waterproof treatment, plus creep occurs in most cases when the moisture-proof and waterproof treatment is performed. In such a case, after determining in advance how much creep will move by performing moisture-proofing and waterproofing treatment, the above-mentioned treatment is applied to that extent and the creep characteristic is set to the negative side by a predetermined amount, and the moisture-proofing and waterproofing treatment is performed. As a result, the creep characteristic on the minus side can be canceled and the creep characteristic can be shifted to substantially zero.

Further, individual physical properties (for example, elastic modulus, hardness, and stress-strain creep amount) of the material forming each load cell change at low temperature, normal temperature, and high temperature. Therefore, the creep characteristic at each temperature changes as a characteristic of the load cell. Then, as the temperature of the laminate decreases, the effect of the stress-strain creep of the laminate on the strain gauge 1 (+ creep) becomes relatively stronger due to the curing of the laminate, and the curing of the base material and the adhesive layer material causes The recovery phenomenon (minus creep) is reduced, and as a result, the positive creep tends to increase. When moisture-proofing and waterproofing treatment is further applied, the moisture-proofing waterproof layer hardens at low temperature, and the strain gauge 1 causes strain.
Since the effect on 11 becomes stronger, the tendency of positive creep at low temperatures becomes remarkable. At this time, how the end layer 9 works is that it hardens as the temperature becomes lower, so that the influence of pressing the strain gauge 1 becomes stronger, and as the influence on the load cell, the negative creep becomes negative. Increase. Therefore, if the end layer 9 made of a material whose physical properties change appropriately with respect to temperature is formed, the change in creep characteristics due to temperature is affected by the load cell whose positive creep increases as the temperature becomes lower, particularly the load cell subjected to moisture-proof and waterproof treatment. It is possible to provide a superior load cell that can well offset the above and does not cause creep at low or high temperatures. FIG. 5 and FIG. 6 are diagrams showing the experimental results when the above treatment is applied.

5 (a) and 5 (b), as shown in FIG. 5 (c), the end portion 9 of the strain gauge 1 having a thickness of about 100 μ (cured) is formed by epoxy coating on the end portion excluding the sensitive portion 7a. The hardness of the rear end layer 9 is a diagram showing the creep characteristic and the zero return characteristic when a pencil hardness H) is formed. (A) shows before correction, (b)
Indicates the value after correction. It can be confirmed that by forming the end layer 9 as shown in the figure, the creep characteristic and the zero return characteristic are significantly improved.

6 (a) and 6 (b), as shown in FIG. 6 (c), the end portion 9 of the strain gauge 1 having a thickness of about 100 μ (cured) is formed by epoxy coating on the end portion excluding the sensitive portion 7a. The hardness of the rear end layer 9 is a diagram showing the creep characteristic and the zero return characteristic when a pencil hardness of 4H) is formed. (A) shows before correction,
(B) shows after correction. It can be confirmed that the formation of the end layer 9 as shown in the figure significantly improves the creep characteristic and the zero return characteristic.

From FIGS. 5 and 6, it can be also confirmed that the higher the hardness of the end layer 9 is, the greater the effect of shifting the pre-screep in the negative direction is.

FIG. 7 is a diagram showing an experimental result of re-correction when creep correction is excessive. FIG. 11A shows the creep characteristic and the zero return characteristic before correction. As shown in FIG. 2B, the terminal portion 7b has a thickness of 100 mm and is made of epoxy-based paint at a distance of 0.5 mm from the sensitive portion 7a of the strain gauge 1 as shown in FIG.
It is a figure which shows the creep characteristic and zero return characteristic at the time of forming the edge part layer 9 (The hardness of the edge part layer 9 after hardening is 4H in pencil hardness). As shown in the figure, by forming the end layer 9, it can be confirmed that the creep characteristic and the zero return characteristic have gone too far in the negative direction. Therefore, as shown in FIG. 2F, the end layer 9 having a thickness of about 100 μ is digged into the sensitive portion 7a of the strain gauge 1 by 1.5 mm, and the end layer 9 after curing (the hardness of the end layer 9 after curing is pencil hardness). 4H) is formed and re-corrected, the creep characteristics and the zero return characteristics are shown in FIG. By forming the end layer 9 by biting into the sensitive portion 7a as shown in the figure, the creep characteristic and the zero return characteristic that have moved too much in the negative direction can be returned to near zero.

FIG. 8 is a diagram showing an experimental result when the above-described treatment according to the present invention is performed using the load cell shown in FIG. The load cell shown in FIG. 9 has a structure in which a strain gauge 1 is attached to the thin portions 11a to 11d of a strain-generating body 11 whose one end is supported by a supporting member 12, and the upper surface of the strain-generating body 11 is further provided with a bellows 13a. , 13b
The strain gauge 1 has a structure that is moisture-proofed and waterproofed by being sealed with an aluminum foil 13 on which is formed. FIG. 8 (a) is a diagram showing the creep characteristic just sealed with the aluminum foil 13, and FIG. 8 (b) is a diagram showing the creep characteristic when the end layer 9 is further formed at the end of the strain gauge 1. Is. As shown in the figure, it can be confirmed that by applying the end layer 9, the creep characteristics are improved and the variation in creep due to temperature is reduced.

As a method of forming the end layer 9 and the sensing portion layer 10, the following method can be used.

(1) Apply paint.

(2) Mask only the sensitive area and put in the paint.

(3) Adhere or stick a thin film.

(4) Sputtering for ionizing and projecting metal, vapor deposition, or ion plating.

Further, the following materials are suitable as materials for the end layer 9 and the sensing layer 10.

(1) Epoxy, polyimide, silicone, other polymer compound or paint.

(2) Metal foil.

(3) A combination of the above (1) and (2) or multiple layers.

In the above examples, the case where the end layer is used only for creep adjustment is shown, but the end layer is a protective layer for terminals such as moisture-proof, waterproof, insulating, and scratching of the wiring part and a strain body. It can also serve as an anticorrosion coat.

〔The invention's effect〕

As described above, according to the present invention, the load cell is continuously provided on at least one of the ends of the resistance wire strain gauge in the main axis direction and the load receiver around the resistance wire strain gauge except on the sensing portion. Since the creep adjusting layer in which the creep characteristic of the output changes in the negative direction as compared with that before the adjustment is formed by applying the coating material, the following excellent effects can be obtained.

(1) Efforts, development costs, and demands for various types of small load cells
It is possible to supply accurate load cells at low cost without spending the development schedule.

(2) Since the creep adjustment can be performed after the strain gauge is attached, the creep adjustment work becomes extremely easy.

(3) It is also possible to deal with variations in individual creep characteristics of load cells to which the same type of strain gauge is attached.

(4) Adjustment can be made by offsetting the movement of creep characteristics due to moisture proofing and waterproofing.

(5) The creep characteristic that varies depending on temperature can be set so as not to change much depending on temperature.

(6) Since the creep adjusting layer that changes in the negative direction or the creep adjusting layer that changes in the positive direction is provided on the end of the strain gauge or on the sensitive portion, for example, a strain element that predicts creep in one direction in advance, There is no need to set strain gauges.

[Brief description of drawings]

FIG. 1 is a diagram showing a portion in which a strain gauge is attached to a strain-generating body of a load cell according to the present invention. FIG. 1 (a) is a plan view, FIG. 1 (b) is a side view, and FIG. 2 is a strain gauge. 3 is a plan view showing the structure of FIG. 3, FIGS. 3 (a), (b), and (c) are conceptual diagrams showing the deformation process when a tensile force is applied to the thin-walled portion of the flexure element, and FIG. 5 and 6 are conceptual diagrams showing a deformation process when a compressive force is applied to a thin portion, and FIGS. 5 and 6 are diagrams showing results of actually measuring creep characteristics and zero return characteristics by forming an end layer on an end portion of a strain gauge. Fig. 7 shows the measured results of creep characteristics and zero return characteristics when creep adjustment and readjustment were performed by changing the formation range of the end layer, and Fig. 8 shows a load cell in which the strain gauge was sealed with aluminum foil. FIG. 9 is a diagram showing the result of actual measurement of creep adjustment, and FIG. 9 is a diagram showing the structure of the load cell used in the actual measurement of FIG. In the figure, 1 ... Strain gauge, 4 ... Terminal, 5 ... Adhesive layer, 6
…… Base, 8 …… Laminate, 9 …… Edge layer, 10 ……
Sensing part layer, 11 ... Strain element.

Claims (3)

[Claims] 1. A load cell having a structure in which a resistance wire strain gauge is attached to a predetermined portion of a load receiver, wherein at least one of the resistance wire strain gauges in the main axis direction is on the resistance wire strain gauge except on the sensing portion. A load cell characterized by being formed by applying a coating material to a creep adjusting layer in which the creep characteristics of the output of the load cell continuously change in the negative direction as compared with those before the adjustment on the load receivers at the ends and the periphery thereof. 2. The load cell according to claim 1, further comprising a main part on the sensitive portion of the resistance wire strain gauge so that the creep characteristic of the output of the load cell is in a positive direction for further fine adjustment. A load cell in which a creep adjusting layer is formed by applying a paint on the resistance line strain gauge. 3. The load cell according to claim 1 or 2, wherein a creep adjusting layer is provided so that the creep characteristic of the output of the load cell has a predetermined negative creep characteristic value. A load cell, wherein a coating for canceling the predetermined creep characteristic value is applied to the load cell.