JPH0495738A - Load cell - Google Patents

Abstract

PURPOSE:To obtain a load cell having the high gauge rate by using cobalt, tungsten, molybdenum, niobium or tantalum and iron containing the small amount of impurities for a strain yielding part comprising ceramics. CONSTITUTION:This load cell has the structure wherein one end of a strain yielding body 1 is fixed to a supporting member 11, and the other end is made to be the free end. The strain yielding body 10 comprises ceramic material. Both ends of an upper beam 10a and a lower beam 10b which are in parallel to each other are connected with linking parts 10c and 10d in this structure. Strain yielding parts 10e, 10f, 10g and 10h which are arc-shaped recess pats are provided at the upper and lower beams 10a and 10b at the four corners of a rectangular hole 12 formed of the upper beam 10a, the lower beam 10b and the linking parts 10c and 10c. The strain gauge material comprises one kind, two kinds or more of chromium, cobalt, tungsten molybdenum, niobium and tantalum, a small amount of impurities and iron for a remaining part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a load cell in which at least a strain-generating portion (flexible portion) of a strain-generating body is made of a ceramic material.

[Prior art]

BACKGROUND ART Conventionally, there is a load cell using a ceramic material at least in the strain-generating portion of a strain-generating body, as disclosed in, for example, Japanese Patent Application Laid-Open No. 63-273029. Since the strain-generating part of this load cell is made of ceramic, it does not undergo layer deformation, is hardly affected by temperature, and has the highest environmental resistance. Furthermore, by forming a resistor pattern that serves as a strain gauge directly on the surface of the ceramic body, it is easier to transmit deflection to the strain gauge, which improves linearity, creep resistance, hysteresis, and repetition resistance, which are important characteristics for a load cell. A load cell capable of highly accurate measurement can be provided.

[Problem to be solved by the invention]

However, although load cells using ceramic for the flexure element have the above-mentioned advantages, they have the following advantages compared to, for example, the case where A2024 material (duralumin), which is generally used up, is used as the flexure element material. There was a problem like this.

In the case of alumina ceramic, Young's modulus and bending strength are respectively Young's modulus E r -37,000) cg/wn"
In the case of A2024 material, the Young's modulus and bending strength are Young's modulus E, -7.350 kg/■8 and bending strength -33 kg/MID, respectively.

Output V when compressive and tensile strain gauges are combined as shown in Figure 5. tJT is voIj, = V IN' K f/E
(1) σ-34! w/2bh” (approximate formula) (2
) Here, v, H are applied voltages, K is cage modulus, E is Young's modulus, ! is the pitch of the strain-generating portions 102 of the strain-generating body 101 shown in FIG. 6 (horizontal interval between strain-generating portions 102)
, b is the width of the strain-generating portion 102, and h is the thickness of the strain-generating portion 102.

Now, assume that the input condition v4 is the same, the gauge factor is usually equal to a value around 2.0, and the bending strength of alumina ceramic and the yield strength of A2024 material are also approximately equal, so the width, thickness, and pitch of the strain-generating part are ! If both are made equal and the stress is made the same, then the output V of a load cell using an alumina ceramic material as a strain body. Load cell output ■ using tlYl and A2024 material for the strain body. , J□ is V ouy I/V oars −E −/E.

7350/37000 F115, alumina ceramic load cell output V. 0ts
HA 20240-Docell output V oats (7) 1
/ 5 It becomes. Therefore, the reading accuracy after A/D conversion is significantly reduced. In addition, the specifications of A2024 material can usually be used at an output of 1 to 2 mV/V,
Assuming an output of 1 mV/V, V out/ V IN-K (1/ E-10-"σ-E/Kxto-' If you try to use an alumina ceramic load cell with an output of 1 mV/V, σ-37000/2 The stress value becomes .OX 10-''-18.5kg/■1, and the safety factor becomes less than twice as high.

Therefore, there is a risk that it will break even if a slight impact is applied to it. Of course, in this case, it is not possible to add a vertically downward bending moment or twisting moment outside the blade.

Additionally, since the temperature guarantee resistor of the load cell is currently placed on the input side of the Wheatstone bridge, when trying to maintain an output of 1 mV/V, the stress value will actually be higher (about 20%), so if the gauge factor If the value is close to 10, it is possible to obtain the same output value as the conventional safety factor. Furthermore, experience has shown that the limit for the thickness of the strain-generating part of A20240-Docelle is about 0.5-, and even if it were possible to process a material with a thickness less than this, it would be extremely susceptible to deformation during handling, making it actually difficult. However, in the case of ceramic, the processing limit is approximately 1 µl. Therefore, the output is 11
Even if 5 were acceptable, there was a problem that the load cell could only have a rated load at least 4 times that of A20240-Docell, and could not handle lower weights. In other words, despite the advantages mentioned above when using ceramic for the strain body of a load cell, load cells using ceramic for the strain body still cannot be put into practical use due to the problems mentioned above. is the current situation.

The present invention has been made in view of the above-mentioned points, and provides an extremely highly practical load cell in which a ceramic material having extremely excellent properties is used as a material for the strain-generating body or at least in the strain-generating part. The purpose is to

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides a load cell equipped with a strain-generating body in which at least a strain-generating part is made of ceramic, by polishing the surface of at least a portion of the strain-generating body that forms a strain gauge, or by applying amorphous glass to the surface. Coating is applied,
A strain gauge made of an alloy consisting of one or more of chromium, cobalt, tungsten, molybdenum, niobium, and tantalum, a small amount of impurities, and the remainder iron is directly placed on the polished surface or glass-coated surface with a lid, a lid, or a lid. It is characterized by being formed by a sputtering method.

Further, it is characterized in that a strain gauge for detecting a torsional moment and a strain gauge for detecting a bending moment are formed in addition to a strain gauge for detecting a load on the upper surface or the lower surface forming the strain gauge of the strain generating part.

[Effect]

As mentioned above, one of cobalt, tungsten, molybdenum, niobium, and tantalum is added to the strain-generating part made of ceramic.
By forming a strain gauge using an alloy made of iron containing one or more species and a small amount of impurity, it is possible to strain ceramics, which have a low allowable stress compared to Young's modulus and are extremely brittle. When used in a body, the thickness cannot be made as thin as an aluminum alloy, and the stress will be small. However, this strain gauge has a high gauge factor and can produce high output, making it an extremely practical load cell.

In addition, by polishing the surface of the strain gauge forming part of the strain-generating body made of ceramic material or applying an amorphous glass coating to the surface, the strain gauge forming surface becomes extremely smooth, and it can be formed by vapor deposition or sputtering. The resulting strain gauge pattern has no disconnections or similar conditions, and the resistance value is extremely uniform.

Further, since the strain gauge has a large specific resistance, the area of the strain gauge to obtain the necessary output becomes small.

〔Example〕

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

Figure 1 is a diagram showing the structure of the load cell of the present invention.
Figure a) is a plan view of the load cell, Figure (b) is a front view, and Figure (c) is a right side view.

This load cell has a structure in which one end of the strain body 10 is fixed to a support member 11 and the other end is a free end. The strain body 10 is made of a ceramic material, and has an upper beam 10m and a lower beam 10b that are parallel to each other, and their ends are connected to connecting parts 10c and 1.
These upper beams 10a are integrally formed at 0d.
, the upper and lower beams 10@, 10 at the four corners of the rectangular hole 12 formed by the lower beam 10b and the connecting parts 10e, 10d.
Strain generating parts 10e, 10f, 1 with arc-shaped recesses formed in b
This is a structure in which 0g and 10h are provided. Here, the distance between the strain-generating portions 10e and 1Of and the distance between the strain-generating portions 10g and 10h are! , the thickness of the strain-generating parts 10e, 10f', 10g, and 10h, and the width of the strain-generating body 10. Strain-generating portion 10 of strain-generating body 10
e, strain gauges A, B, C, D, E, F are on the top surface of 10f.
,G.

H, P, Q, R, and S are formed. This strain gauge A
, B, C, D, E, F, G, H, P.

Therefore, form. Prior to this formation, the upper surface of the strain-generating body is sufficiently polished or coated with amorphous glass to prevent pinholes from forming in the strain gauge or uneven thickness when the strain gauge is formed. do. strain gauge P,
Q, R, and S are load detection strain gauges, which are arranged parallel to the axis of the strain body 10. Strain gauges A, B, G, and H are strain gauges for detecting torsional moments, and are arranged at a predetermined angle with respect to the axis of the strain body 10.

Strain gauges C and D are strain gauges for detecting bending moments, and are arranged to be inclined at a predetermined angle with respect to the axis of the strain body 10. Strain gauges E and F are dummy resistors, and strain body 1
It is placed in the center of 0 at right angles to the axis.

The strain gauge material is chromium (Cr), one or more strain gauge materials made of iron containing a small amount of cobalt impurity are deposited directly on the upper surface of the strain body 10 by vapor deposition or sputtering,
The ingredients and manufacturing method of an alloy strain gauge material consisting of a small amount of impurities and the remainder iron (Fe) are disclosed in Japanese Patent Application Laid-Open No. 1983-1982.
15914, the details thereof will be omitted.

In the load cell configured as described above, when a load is applied to the free end of the strain-generating body 10, the strain-generating body 10 is displaced as shown by the dashed line in FIG. Compressive stress acts on the surface, and tensile stress acts on the gauge surface corresponding to the strain-generating portion 10f. Therefore, forces corresponding to the compressive stress and tensile stress act on the strain gauges P, Q, R, and S, and their resistance values change, so that the strain gauges P, Q, and By incorporating R and S into the Wheatstone bridge, only the load can be detected.

Also, depending on the point at which the load acts, the strain body 10 may be affected as shown in FIG.
A torsional moment as shown by the arrows @) and (C) acts, and this torsional moment causes stress to act on the gauge surface corresponding to the strain-generating parts 10e and 10f of the strain-generating body 10, and a force corresponding to this stress is generated. acts on strain gauges A, B, H, and G,
Its resistance value changes. Therefore, by combining these with the Wheatstone bridge shown in FIG. 2(b), only the torsional moment can be detected. In addition, the strain body 1
By the bending moment M acting on the strain body 1
0 is displaced as shown by the broken line in FIG. 1(b), a force corresponding to this stress acts on the strain gauges C and D, and their resistance values change. Therefore, the bending moment can be detected by incorporating it into the Wheatstone bridge as shown in FIG. 2 (C).

A strain gauge using an alloy strain gauge material consisting of impurities and the rest iron has a high specific resistance, so the area of the strain gauge is small to obtain the required output. ), it is quite possible to form a large number of strain gauges only on the upper surface of the strain-generating body 10. By forming the strain gauge only on the top surface in this way, it is easy to form the strain gauge pattern, and the wiring is also easy.
Productivity will also improve.

FIG. 3 is a diagram showing the structure of another load cell according to the present invention, where (1 &) is a plan view of the load cell, (b) is a front view, (c) is a right side view, and ( d) is the bottom view 0
This load cell has strain gauges A, B, C, D, E, F, G made of the same material as the strain gauge material shown in FIG. H,P.

It is formed by Q, R, and S. In the figure, strain gauges P, Q, R, and S are strain gauges for detecting loads, strain gauges A, B, G, and H are strain gauges for detecting torsional moments, and strain gauges C, D, E, and F are strain gauges for bending. This is a strain gauge for moment detection.

FIGS. 4(a), 4(b), and 4(c) are diagrams showing bridge configurations for load detection, torsional moment detection, and bending moment detection, respectively. By assembling strain gauges P, Q, R, and S into the bridge shown in Fig. 3(m), the output V can be adjusted according to the load. UTm is output, strain gauges A, B, H, G
By assembling as shown in the same figure (b), the output V out according to the torsional moment is 8 ft, H'l
-DiC#D#E.

By assembling F as shown in the same figure (c), output V can be obtained according to the bending moment. . 1 can be output.

In addition, Cu-Ni system and NI-CT, which have not been put into practical use so far,
system alloy or special purpose Fe-Cr-Al system alloy or PT
Even with strain gauge materials such as base alloys, by making the film thickness of the strain gauge considerably thinner, the gauge factor can be improved without heat treatment. Although it is possible to use strain gauges made of ceramic materials, even better effects can be expected in the case of strain gauges made of alloys with a high gauge factor of 10 or more used in the load cell of the present invention.

In addition, the shape of the load cell is not limited to the shape shown in the above embodiments, and may be a so-called single beam type, shear type,
The column-shaped portion may have any shape.

Although the ceramic used for the strain body is alumina ceramic in the embodiment, other ceramics such as silicon chamber, zirconia, etc. may be used.

〔Effect of the invention〕

As explained above, according to the present invention, the surface of at least the portion forming the strain gauge of the strain-generating body whose strain-generating portion is made of a ceramic material is polished or the surface is coated with amorphous glass, and the polished surface or Chrome and cobalt on the glass coating surface.

An alloy made of one or more of tungsten, molybdenum, niobium, and tantalum, a small amount of impurities, and the balance iron is formed as a strain gauge by direct vapor deposition or sputtering, and the following excellent effects can be obtained. It will be done.

(1) Characteristics of a load cell using ceramic material for the strain body: ■High linearity with no hysteresis; ■Small output fluctuations due to temperature changes; ■High natural frequency; ■Corrosion resistance. In addition, this strain gauge has a high gauge factor, so even if the stress in the strain-generating part is small, it can output more than normal.
Furthermore, since the thickness of the strain-generating part can be increased to within the allowable stress range, it has sufficient strength and is easy to process. It is possible to put into practical use a load cell with much superior characteristics compared to a load cell made using the same method. Furthermore, since the thickness of the strain-generating portion can be increased, it becomes possible to create a load cell with a low basis weight, which was not possible with a load cell using ceramic for the strain-generating body.

(2) By polishing and smoothing the surface of the strain-generating body on which the strain gauge will be formed, or by applying an amorphous glass coating, the formed strain gauge becomes a thin-film resistor without pinholes, which concentrates stress. The performance of the load cell is improved by reducing wire breakage and variations in the resistance value of the strain gauge pattern.

(3) The internal resistance value of the strain gauge pattern becomes uniform, and the linearity, reproducibility, and hysteresis performance against instrumental errors are also improved.

(4) Since strain gauges made of materials with high specific resistance are used, the area of the strain gauge part is reduced, so each strain gauge can be formed on one side, making it easier to arrange the strain gauge pattern, increasing productivity. can be improved, and the width of the strain-generating body can also be made thinner or the same as before.
High performance load cells can be provided at low cost.

[Brief explanation of drawings]

Fig. 1 shows the structure of the load cell of the present invention, in which Fig. 1(a) is a plan view of the load cell, Fig. 1(b) is a front view, Fig. 1(c) is a right side view, and Fig. 2(a) is a plan view of the load cell. a), (b), and (c) are diagrams showing the bridge configuration for detecting the bridge weight and torsion moment detection 9 and bending moment of the load cell in Figure 1, respectively, and Figure 3 is a diagram showing the bridge configuration for detecting the bending moment of the load cell of the other load cell of the present invention. The diagrams show the structure. Figure (a) is a plan view of the load cell, Figure (b) is a plan view of the load cell.
is a front view, (c) is a right side view, (d) is a bottom view, and Figures 4 (a), (b), and (c) are load detection and torsion of the load cell in Figure 3, respectively. Moment Detection 2 A diagram showing a bridge configuration for detecting a bending moment, Figure 5 is a diagram showing an example of a combination of compressive and tensile strain gauges, and Figure 6 is a watercolor drawing of the schematic structure of a load cell. j"'Jt-men F feathers t#Iην・/n (b) 1+j"i-mentoneli'tjl17 rinon. (C) Figure 2 Honkuro's low F (Le Nechiro 1st Figure tb) (a) bLIJt-Mel) 4 prizes -1 So/CC) Figure 4

Claims (2)

[Claims] (1) In a load cell including a strain-generating body in which at least the strain-generating portion is made of a ceramic material, the surface of at least the portion forming the strain gauge of the strain-generating body is polished or coated with amorphous glass, and An alloy consisting of one or more of chromium, cobalt, tungsten, molybdenum, niobium, and tantalum, a small amount of impurities, and the balance iron is applied to the polished surface or glass coating surface by direct vapor deposition or sputtering as a strain gauge. A load cell characterized by the following: (2) Claim (1) characterized in that a strain gauge for detecting a torsional moment and a strain gauge for detecting a bending moment are formed on at least the upper surface or the lower surface of the strain-generating portion forming a strain gauge, together with a strain gauge for detecting a load. ) Load cell listed.