JPS6337227A - Load cell - Google Patents

Abstract

PURPOSE:To obtain a load cell of which the creep capacity is adjusted in such a state that a strain gauge is adhered, by forming a creep adjusting layer at least to either one of the end parts of the strain gauge except the sensitive part thereof in the main axis direction of said gauge. CONSTITUTION:A creep adjusting end part layer 9, wherein the creep characteristic of the output of a load cell changes in a negative direction as compared with that before adjustment, is formed to the end part of the strain gauge 1, adhered to the thin wall part of a strain generator 11 through the adhesive layer 5 formed thereto, except the sensitive part 7a thereof. Further, A creep characteristic finely adjusting sensitive part layer 10 is formed to the upper surface of the gauge 1 based on the sensitive part 7a. When tensile deformation is generated in the thin wall part, the end part layer 9 extends so as to follow the deformation of the strain generator 11 and the sensitive part 7a further receives tensile force through a laminate 8 in the direction shown by an arrow B. When the end part layer 9 further extends while gradually generating stress-strain creep, the sensitive part 7a is contracting in the direction shown by an arrow C. As a result, since the resistance value of the strain gauge side receiving the tensile force of a Wheatstone bridge advances toward reduction, the output of the load cell becomes negative creep.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application 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 wire strain gauge is attached to a predetermined portion of a load receiver, an extremely important performance thereof is a so-called creep characteristic in which the output value of the load cell changes over time. If this creep characteristic is not good, not only the output value will not be stable, but also other performance problems, especially instrumental error (
characteristics), return to zero, reproducibility, etc. Therefore, in order to improve the accuracy and performance of a load cell, it is necessary to improve the creep characteristics.

A typical method conventionally used to improve creep characteristics is to use a foil strain gauge 1 as shown in Figure 2.
This is a method of improving creep performance by changing the lengths d, , d, of the folded tabs 2 and 3 of the grid. However, this method had the following drawbacks.

(1) Strain gauges with creep characteristics that suit the requirements of load cells with various load ratings are required.

(2) Even in load cells with the same rated load, if the shape of the load receiver is changed based on the design conditions, a strain gauge with creep characteristics suitable for the change is required.

(3) Even for load cells with the same rated load and the same load receptor, if the moisture-proofing treatment is changed, a strain gauge with creep characteristics suitable for the change will be required.

In addition to (1) to (3) above, (4) above (1)
)~(3) As a result of manufacturing a large number of strain gauges,
There is a risk that defective load cells may be manufactured due to misunderstandings such as strain gauge selection.

(5) Considerable losses will occur in the labor required for development, development costs, development schedule, etc.

(6) Also, if the number of load cells manufactured is small, strain gauge manufacturers will be discouraged from developing and manufacturing strain gauges that are compatible with the load cells mentioned above, and even if they are manufactured, the strain gauges will be expensive, making it impossible to manufacture load cells at a low price. .

Furthermore, in Japanese Patent Application Laid-Open No. 55-29756, a strain gauge is bonded in advance so that the overall characteristic with the beam becomes a negative creep characteristic, and the strain gauge is covered with a coating layer having a positive creep characteristic. It describes what was done.

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

Furthermore, the present applicant has previously developed a creep performance improvement method that does not have the above-mentioned drawbacks, and has filed a patent application (Japanese Patent Application No. 59-277800).
No.).

[Problem that the invention seeks to solve]

However, this technique for improving creep characteristics also had the following problems.

(a) In order to shift the creep to the negative side, an adjustment film must be provided under the strain gauge, and the creep must be measured in advance by pasting the same type of strain gauge before the adjustment film is interposed. .

(b) The variation in Nakajima creep of the same type of strain gauge becomes an error of about ±0.03% when taking into account the difference between lots, and it is not possible to deal with the shift of the creep characteristics of individual load cells in the negative direction due to the variation in strain gauges.

The present invention has been made in view of the above-mentioned points, and does not require additional steps such as changing the strain gauge to match the output characteristics of each load cell to which a strain gauge has already been attached.
To provide a load cell whose creep performance is adjusted while a strain gauge is attached.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a load cell having a structure in which a resistance wire strain gauge is attached to a predetermined portion of a load receiver, in which at least one of the longitudinal directions on the strain gauge excluding the sensing part of the strain gauge is provided. A creep adjustment layer is formed at the end of the load cell so that the creep characteristic of the load cell output changes in the negative direction compared to before adjustment, so as to adjust the creep characteristic of the load cell in the positive direction. In addition, if the creep adjustment was excessively adjusted, a creep adjustment layer was formed on the upper surface of the strain gauge, mainly on the sensitive part of the gauge, so that the creep characteristics would be in the positive direction upon readjustment.

[Effect]

By configuring the load cell as described above, the above-mentioned problems can be avoided by simply forming a creep adjustment layer at the end of the load cell on which the strain gauge is attached to the load receiver, and it is extremely easy to use. It becomes possible to adjust the creep characteristics.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing a portion of a strain body of a load cell according to the present invention to which a strain gauge is attached, and FIG. 1(a) is a plan view, and FIG.
b') is a side view. As shown in the figure, the strain gauge 1 includes a base 6, a pattern section 7 on the base 6 consisting of a sensing section 7a and a terminal section 7b, and a lead wire 4 connected to the terminal section 7b of the pattern section 7. It is composed of the pattern section 7 and a laminate 8 formed on top of the lead wire 4. In the load cell, the strain gauge 1 constructed as described above is attached to the - of the thin part 11a of the strain generating body 11 with an adhesive layer 5 formed thereon. An end layer 9 for creep adjustment is formed at the end of the strain gauge 1 excluding the sensing portion 7a, which changes the creep characteristic of the output of the load cell in a negative direction compared to before adjustment. Further, in order to finely adjust the creep characteristics, a sensing layer 10 for creep adjustment is formed on the upper surface of the strain gauge 1 mainly on the sensing portion 7a of the strain gauge 1. The end layer 9 and the sensing layer 10 are formed by applying, for example, an epoxy paint.

Next, the operation of the load cell configured as described above will be explained. The strain gauge 1 may be subjected to tensile force or compressive force depending on the position of the thin wall portion 11a of the strain body 11 to which it is attached.

First, a case where a tensile force acts on the strain gauge 1 will be explained. FIG. 3 is a conceptual diagram showing the deformation process when a tensile force is applied to the thin wall portion of the flexure element 11. FIG. 3(a) shows the state before the tensile force is applied, and FIG. FIG. 2C shows a state immediately after the end layer 9 is deformed by applying a tensile force, and then the end layer 9 creeps and the sensing part 7a returns to its original state. Now, when tensile deformation occurs in the thin wall portion of the flexure element 11, the end layer 9 extends following the deformation of the flexure element 11, but the end layer 9 connects the end of the sensing part 7a with the laminate 8. (For strain gauge 1 without laminate 8, base 6
(holding the end of the sensing part 7a through the edge layer 9), the sensing part 7a receives more tension from the vertical direction than when there is no end layer 9 (as shown by the arrow B in FIG. 3(b)). reference). Furthermore,
As the end layer 9 gradually causes stress creep and stretches, the influence of the end layer 9, which pulls the sensing section 7a in the vertical direction, weakens, and the sensing section 7a shrinks (Fig. 3). (c
)). Therefore, the resistance value of the strain gauge side of the Wheatstone bridge that receives the tensile force tends to return to the resistance value before receiving the tensile force (in the direction that the resistance value decreases), so the load cell output becomes negative creep.

Next, a case where a compressive force acts on the strain gauge 1 will be explained. FIG. 4 is a conceptual diagram showing a case in which a compressive force is applied to the thin wall portion of the strain body 11. FIG. Immediately after the end layer 9 is deformed by compressive force, the end layer 9
shows a state in which the sensing portion 7a returns to its normal state due to creep.

Now, when compressive deformation occurs in the thin part of the flexure element 11, the end layer 9
shrinks following the deformation of the strain body, but the end layer 9
The end of a is pushed indirectly through the laminate 8 (in the strain gauge 1 without the laminate 8, the end of the sensing part 7a is pushed through the base 6), and the sensing part 7a has no end layer 9. Compared to the case, the compressive force is further applied in the vertical direction (see the arrow in FIG. 4(b)). Furthermore, as the end layer 9 gradually causes stress creep and shrinks, the influence of the end layer 9, which compresses the sensing section 7a in the longitudinal direction, weakens, and the sensing section 7a stretches (first (See arrow E in Figure 4 (C)).

Therefore, the resistance value of the strain gauge side subjected to the compressive force of the Wheatstone bridge tends to return to the resistance value before being compressed (in the direction in which the resistance value increases), so that the load cell output exhibits negative creep.

As mentioned above, the load cell output will be negative creep regardless of whether the strain gauge 1 receives the tensile force of the Wheatstone bridge or the strain gauge 1 receives the compressive force. Incidentally, even if one, two, or three of the Wheatstone bridges are active gauges and the others are dummy resistors, the effect remains unchanged and the creep characteristic can be shifted in a predetermined negative direction. Therefore, if the above treatment is applied to the positive creep load cell in the initial stage, it is possible to reduce the creep to zero overall.

If the positive creep characteristics are still not completely offset even after the above measures are taken, the thickness of the end layer 9 may be increased, or a layer made of another type of material that is more likely to cause stress creep may be formed. You may do so.

In addition, if they are distributed on the tip end side of the strain gauge 1, there will be less swelling and it will be more effective for mounting (see part B surrounded by the dashed-dotted line in FIG. 1(b)).

Furthermore, if the above-mentioned measures result in excessive negative creep, it is sufficient to form a thin layer on -1 of the sensing portion 7a that causes stress creep for fine adjustment. The sensitive layer 10 in FIG. 1 is a layer for fine adjustment. By forming the sensing layer 10, excessive negative creep can be brought close to zero.

In addition, load cells are often coated with moisture-proof and waterproof coatings, or sealed. When moisture-proofing and waterproofing are performed in this way,
Even if an ideal load cell has almost no creep before being subjected to moisture-proofing and waterproofing, positive creep occurs in most cases when the moisture-proofing and waterproofing treatments are applied. In such a case, determine in advance how much the creep will move by applying moisture-proofing and waterproofing treatment, and then apply the above measures accordingly to bring the creep characteristics to the negative side by a predetermined amount, and then apply the moisture-proofing and waterproofing treatment. By doing so, it is possible to cancel out the creep characteristic on the negative side and shift the creep characteristic to approximately zero.

In addition, the individual physical properties (eg, elastic modulus, hardness, and stress creep amount) of the materials constituting each load cell change at low temperature, room temperature, and high temperature. Therefore, it is common for the creep characteristics of a load cell to change at each temperature. As the temperature decreases, the effect of stress creep of the laminate on strain gauge 1 (+creep) becomes relatively stronger due to the hardening of the laminate.
As the adhesive layer material hardens, the return phenomenon (minus creep) of the sensitive part 7a decreases, and as a result, positive creep tends to increase.Furthermore, when moisture-proofing and waterproofing treatment is performed, the moisture-proof waterproof layer hardens at low temperatures, causing distortion. Gauge 1, strain body 1
1, the positive creep tendency becomes more pronounced at low temperatures. At this time, how the end layer 9 acts is as it hardens as the temperature decreases, its influence on the strain gauge 1 becomes stronger, and its effect on the load cell is that as the temperature decreases, negative creep occurs. increase Therefore, if the end layer 9 is formed of a material whose physical properties change appropriately with respect to temperature, the creep characteristics will change with temperature for a load cell in which positive creep increases as the temperature decreases, especially for a load cell subjected to moisture-proofing and waterproofing treatment. It is possible to provide an excellent load cell that does not cause creep even at low or high temperatures. FIG. 5 and FIG. 6 are diagrams showing the experimental results when the above treatment was performed.

5(a) and 5(b), as shown in FIG. 5(c), an end layer 9 (hardened) of approximately 100 μm in thickness is coated with epoxy paint on the end of the strain gauge 1, excluding the sensing part 7a. The hardness of the rear end layer 9 is a graph showing creep characteristics and zero return characteristics when forming a pencil hardness H). (a) shows before correction, (
b) shows after correction. It can be confirmed that by forming the end layer 9 as shown in the figure, the creep characteristics and zero return characteristics are significantly improved.

6(a) and 6(b), as shown in FIG. 6(c), an end layer 9 (hardened) of approximately 100 μm in thickness is coated with epoxy paint on the end of the strain gauge 1, excluding the sensing part 7a. The hardness of the rear end layer 9 is 4H on the pencil hardness scale. (a) shows before correction, and (b) shows after correction. It can be confirmed that by forming the end layer 9 as shown in the figure, the creep characteristics and zero return characteristics are significantly improved.

It can also be confirmed from FIGS. 5 and 6 that the higher the hardness of the end layer 9, the greater the effect of shifting the positive creep in the negative direction.

FIG. 7 is a diagram showing experimental results of re-correction when creep correction has gone too far. FIG. 4(a) shows the creep characteristics and zero return characteristics before correction. The figure (b) shows an end layer of about 100μ thick coated with epoxy paint on the terminal part 7b at a distance of 0.5 mm from the sensitive part 7a of the strain gauge 1, as shown in figure (e). 9 (the hardness of the end layer 9 after hardening is 4H on a pencil hardness) is a diagram showing creep characteristics and zero return characteristics when formed. As shown in the figure, it can be confirmed that by forming the end layer 9, the creep characteristics and zero return characteristics have gone too far in the negative direction. Therefore, as shown in FIG. 5(f), the end layer 9 is applied with a thickness of about 100 μm by digging into the sensitive part 7a of the strain gauge 1 by 1.5 mm and applying an epoxy paint (the hardness of the end layer 9 after hardening is a pencil). The creep characteristics and zero return characteristics when a hardness of 4H) is formed and re-corrected are not shown in the same figure (c). By forming the end layer 9 by biting into the sensing portion 7a as shown in the figure, the creep characteristics and zero return characteristics that have shifted too much in the negative direction can be returned to near zero.

FIG. 8 is a diagram showing experimental results when the above treatment according to the present invention was performed using the load cell shown in FIG. 9. The load cell shown in FIG. 9 has a structure in which strain gauges 1 are affixed to thin parts 11a to lid of a strain body 11 whose one end is supported by a support member 12, and furthermore, the upper surface of the strain body 11 is attached to a jill plate 13a. .

The strain gauge 1 has a moisture-proof and waterproof structure by being sealed with an aluminum foil 13 on which 13b is formed. FIG. 8(a) is a diagram showing the creep characteristics when the strain gauge 1 is simply sealed with aluminum foil 13, and FIG. 8(b) is a diagram showing the creep characteristics when an end layer 9 is further formed at the end of the strain gauge 1. It 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.

The following methods can be used to form the end layer 9 and the sensitive layer 10.

(1) Apply paint.

(2) Mask only the sensing part and put it in the paint.

(3) Glue or paste a thin film.

(4) Sputtering, vapor deposition, or ion blating, in which metal is ionized and projected.

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

(1) Epoxy, polymide, silicone, other polymer compounds or paints.

(2) Metal foil.

(3) Combination or multilayering of (1) and (2) above.

In addition, in the above embodiment, the case where the end layer is used only for creep adjustment is shown, but the end layer is used for moisture proofing, waterproofing, insulation, protection layer for scratches, etc. of the terminal and wiring part, and for protecting the strain body. It can also serve as an anti-corrosion coat.

〔Effect of the invention〕

As explained above, according to the present invention, the creep adjustment layer is formed on at least one end of the strain gauge in the main axis direction, excluding the sensing part of the strain gauge, so that the creep adjustment layer is formed as shown below. Excellent effects can be obtained.

(1) To meet the demand for a wide variety of load cells in small quantities, labor, development costs,
Highly accurate load cells can be supplied at low cost without requiring a long development schedule.

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

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

(4) Adjustments can be made by offsetting changes in creep characteristics due to moisture-proofing and waterproofing treatments.

(5) Creep characteristics that vary depending on temperature can be made to not change much depending on temperature.

(6) Since a creep adjustment layer that changes in the negative direction is provided at the end of the strain gauge or a creep adjustment layer that changes in the positive direction is provided on the sensitive part, for example, by anticipating creep in one direction in advance, There is no need to set strain gauges.

[Brief explanation of drawings]

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

Claims (3)

[Claims] (1) In a load cell having a structure in which a resistance wire strain gauge is attached to a predetermined part of a load receiver, the load cell output is applied to at least one end of the strain gauge in the main axis direction, excluding the sensing part of the strain gauge. A load cell characterized by forming a creep adjustment layer whose creep characteristics change in a negative direction compared to before adjustment. (2) In Claim No. (1), a creep adjustment layer is provided on the upper surface of the strain gauge, mainly on the sensitive part of the strain gauge, so that the creep characteristic of the output of the load cell is in the positive direction for further fine adjustment. A load cell characterized by the following: (3) The load cell according to claim (1) or (2), characterized in that a moisture-proof coating is further applied on the strain gauge in advance so as to offset the creep property of the coating material.