JPS5920088B2 - load cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load cell for a load cell scale that measures load by electrically detecting deformation of a strain gauge.

Conventionally, a load cell is basically configured as shown in FIG.

That is, a beam 3a is formed with one end fixed to the fixed part 1a and the other free end serving as the load receiving part 2a, and two elliptical holes 4a are formed in series in the center of the beam 3a. Four thin deformed portions 5a are formed, and strain gauges a are adhered to these deformed portions 5a with an adhesive 7a.

The structure of these strain gels is 5μ thick on a base of about 20μ thick such as phenol resin or epoxy resin.
A resistor of a certain thickness is formed by vapor deposition, and the resistor is etched to form a pattern of a predetermined shape.

A three-layer structure is also used in which the same material as the base layer is laminated on the surface of the resistor.

After adhering such a strain a to the deformed part 5a,
It is covered with a coating layer 8a made of silicone rubber, silicone resin, etc. for moisture resistance and gas resistance.

In such a conventional load cell, an electronic circuit is connected to the strain gauge a and the deformation of the deformable portion 5a that occurs when a load is applied to the load receiving portion 2a is extracted as an electrical output.

However, as shown in Figure 3, the output generated when a constant load is applied decreases over time, and when the load is removed, the output drops below zero and gradually returns to zero, resulting in a leap phenomenon. arise.

Here, when the output gradually decreases after the load is applied, it is called a negative creep characteristic, and when it increases, it is called a positive creep characteristic.

To explain such negative creep characteristics and positive creep characteristics in another way, the shrinkage of the strain gauge a over time from when a load is applied is called negative creep property, and the expansion is called positive creep property. This is called creep property.

In other words, when the strain gauge a shrinks, the output decreases,
As it stretches, the output increases.

Therefore, the leap characteristic described above is
It exists not only in the single Shiro A, but also in the beam 3a, the adhesive 7a, and the coating layer 8a, and as a comprehensive characteristic, whether these act as a whole causes the straining Shiro A to shrink or expand. It shows negative and positive creep characteristics.

Note that the beam 3a is made of metal and is estimated to have positive creep characteristics.

However, metal creep is so minute that it is currently impossible to measure and has not been proven.

The present invention has been made in view of these points, and an object of the present invention is to provide a load cell that can improve creep characteristics and obtain a highly accurate load cell weighing device.

The present invention forms thin deformed parts in a beam having one end fixed and the other end used as a load receiving part, and adheres strain gauges having negative creep characteristics to these deformed parts to improve the overall characteristics of the beam. is set so that it has a negative creep characteristic,
The strain gauge is characterized in that the strain gauge is covered with a coating layer having positive creep characteristics.

Therefore, the coating layer having positive creep characteristics can prevent creep from occurring in the overall characteristics, thereby making it possible to obtain a highly accurate load cell weigher.

An embodiment of this invention will be explained based on FIGS. 4 to 9.

First, reference numeral 1 denotes a base, and on one side of this base 10, a column 2 is vertically and integrally erected.

A parallelogram-shaped arm portion 3 is fixed to this support 2.

That is, this arm portion 3 is made up of a thick base portion 4, a force-receiving portion 5, and a thin upper side 6 and lower side 7.

The base portion 4 is formed with a cutout portion 8 into which the support column 2 is fitted and unscrewed, and is fixed with two fixing bolts 9, and the force receiving portion 5 is also provided with a cutout portion 10 to support the support shaft of the saucer plate 11. 12
is inserted and fixed.

Furthermore, a thick protruding side 13 is formed at the upper part of the force receiving portion 5 and horizontally protrudes inward.

Further, a beam 14 extending from the inner surface of the base portion 4 to below the protruding side 13 is integrally formed.

That is, this beam 14 is located in the same plane as the arm 3, has a load receiving part 15 at its tip, and two elliptical holes 16 that communicate with each other are formed in the middle part. The hole 16 forms a parallelogram,
A thin circular deformed portion 17 is formed.

Strain gauges 18 are attached to the outer peripheries of these deformable portions 17, as will be described later, and a bridge circuit (not shown) is formed so that the deformation of the deformable portions 17 is extracted as an electrical signal. ing.

Further, a circular collar 1 is provided at the base and tip side of the beam 140.
9 are integrally formed, and both ends of a bellows-shaped cover 20 are hermetically fixed to these collars 19 without mechanical influence.

The arm portion 3 and the beam 14 are integrally formed by forging, but an arc-shaped concave portion is formed by machining at the base of the upper side 6 and the lower side 7, so that a thin bent portion is formed. Sections 21 are formed at four locations.

Further, the upper side 6, the lower side 7, the projecting side 13, and the force receiving part 15 have holes 22, 23 located on the same vertical line.
, 24°25 are formed.

A pivot 26 is fitted in the shaft portion of the hole 24 and fixed downward, and a pivot 27 is also placed in the hole 25.
is fixed upward by fitting its shaft.

A connecting shaft 28 is attached between these pivots 26 and 27, making point contact with each other.

The coupling shaft 28 is attached by deforming the arm portion 3.

The strain gauge 18 is bonded to the deformed portion 17 of the beam 14 using an adhesive 29 with an adhesive layer 30 of a predetermined thickness, and is covered with a coating layer 31 after this bonding.

That is, since the beam 14 is made of a metal material, it exhibits positive creep characteristics, but the strain gauge 18 is selected to have a negative creep characteristic larger than that of the beam 14 and is bonded thereto.

The material for the coating layer 31 is selected to have positive creep characteristics, and preferably is the same material as the adhesive 29.

To form such a covering layer 31, the strain gauge 18 is bonded to the deformed portion 17, and then a predetermined amount of adhesive 29 is poured onto the strain gauge 18 to bond the Teflon sheet 32. 7 kg by a metal plate 34 with a cushioning material 33 made of silicone rubber etc. interposed from above.
Press with a pressure of about /cm2.

Since the thickness of the coating layer 31 formed by such operations is limited and extremely thin, the coating layer 31
After determining the creep characteristics in a free state, multiple layers of overcoating are applied as necessary.

As a result, the negative creep characteristics are gradually corrected in the positive direction, and eventually approach zero.

In such a configuration, when the weighing section is placed on the saucer 11, the weight is transferred to the force receiving section 5 of the arm section 3 via the support shaft 12.
However, since the mechanical strength of the bending part 21 in the plane direction including the arm part 3 is extremely weak, a vertical load is applied from the protrusion 13 to the tip of the beam 14 via the pivots 26, 27 and the connecting shaft 28, This deforms the beam 14 and is extracted as an electrical signal by the strain gauge 18.

At this time, if a weighed object is placed in one corner of the saucer 11, a moment will act on the force receiving part 5, but the bent part 21 of the arm part 3 is strong against stretching and twisting, and the arm part 3 itself can handle loads other than the vertical direction. Moreover, even if some tilting or twisting occurs, the coupling shaft 28 tilts only slightly, and a nearly perpendicular load acts on the force-receiving portion 15 of the beam 14.

Therefore, no matter where the weighed object is placed on the tray 11, the measurement error is extremely small and does not cause any practical problems.

Since creep does not occur during such operations, accuracy is greatly improved.

In the present invention, in which a strain gauge is bonded to a deformed part of a beam and its outer surface is covered with a coating layer, the strain gauge is selected to exhibit negative creep characteristics, and the coating layer is positive. By selecting a material that exhibits creep characteristics, it is possible to obtain a state in which creep does not occur as an overall characteristic, thereby making it possible to significantly improve accuracy.

[Brief explanation of the drawing]

Figure 1 is a side view showing the principle of the load cell, Figure 2 is an enlarged side view of the strain gauge attachment part, Figure 3 is a graph showing an example of creep characteristics, Figure 4 is a perspective view of the load cell scale, Figure 5 6 is a sectional view taken along line A-A in FIG. 5, FIG. 7 is a partially enlarged vertical sectional side view, and FIG. 8 is a vertical sectional side view during formation of the coating layer. DESCRIPTION OF SYMBOLS 14...Beam, 15...Load receiving part, 17...Deformation part, 18...S[lenghage], 31...Coating layer.

Claims (1)

[Claims] 1. Thin deformed parts are formed in a beam with one end fixed and the other end used as a load receiving part, and strain gauges having negative creep characteristics are bonded to these deformed parts to connect the beam. A load cell characterized in that the overall characteristic of the strain gauge is set to be a negative creep characteristic, and the strain gauge is covered with a coating layer having a positive creep characteristic. 2. Claim 1, characterized in that the coating layer is made of the same material as the adhesive used to adhere the strain gauge to the beam.
Load cell as described in section.