JPS6225977B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a load cell in which a strain gauge resistor or the like is directly formed on a strain-generating portion of a beam body by means such as vapor deposition or sputtering.

A load cell measures a load by applying a load to a beam body to cause strain, and by utilizing this change in the resistance value of a resistor installed in the strain-generating part of the beam body. A conventional load cell of this type was constructed by adhering an insulating film provided with a resistor pattern to a strain-generating portion of a beam body.

However, manufacturing such a load cell requires a large number of man-hours, and requires strict process control, especially in the process of bonding the insulating film to the beam body. Moreover, automation is difficult, making mass production difficult and high costs. There were flaws. Furthermore, since there is a limit to how thin the insulating film can be, the strain in the beam cannot be accurately transmitted to the resistor, resulting in large measurement errors. Furthermore, since the resistor pattern is formed from metal foil, there is a limit to how thin it can be (approximately 5μ), making it difficult to obtain a large resistance (approximately 350 to 500Ω), resulting in low power consumption. There were also major problems.

The present invention was made based on these circumstances, and its purpose is to reduce the number of man-hours, to easily manufacture without requiring strict process control, and to increase mass productivity through automation. In addition to reducing costs, the resistor and insulating layer can be formed extremely thin, reducing power consumption during measurement and obtaining highly accurate measurement values, especially for bridge balance compensation. It is also an object of the present invention to provide a method for manufacturing a load cell that also facilitates bridge balance temperature compensation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described below based on embodiments shown in the drawings.

1 and 2 show the structure of the load cell, and the beam body 1 is made of, for example, stainless steel (SUS630), duralumin (A2014, A2024,
It is formed by cutting metal materials such as A2218). This beam body 1 is used by being fixed to an arbitrary fixing part 3 by passing mounting bolts 2A, 2A through mounting holes 2, 2 provided at one end. In addition, a pair of circular holes 4, 4 are provided in the middle part of the beam body 1, passing through them in the width direction.
The upper and lower parts of each circular hole 4, 4 are thinned, and especially the upper part of each circular hole 4, 4 is formed with strain-generating parts 6A, 6.
It is set as B. Further, a locking hole 7 is provided at the other end of the beam body 1, and a hanging metal fitting 8, for example, is attached to this locking hole 7, so that the load W to be measured is applied as shown by the arrow. When the load W is applied, the beam body 1 deforms the portion between the two circular holes 4 into a parallelogram shape as shown in FIG. As a result, maximum compressive strain is produced on the upper surface of the other strain-generating portion 6B. Then, strain gauge resistor patterns R ₁ and R ₂ are placed on the top surface of one strain-generating portion 6A where the maximum tensile strain occurs, and strain gauge resistor patterns R are placed on the top surface of the other strain-generating portion 6B where the maximum compressive strain occurs. ₃ and _R4 are provided, respectively.
Further, on the upper surface of the beam body 1, the strain generating parts 6A, 6
Bridge balance compensation resistor patterns R ₀₁ , R ₀₃ , bridge balance temperature compensation resistor patterns R _T1 , R _T3 , span resistor pattern for temperature compensation R _S , span temperature characteristic nonlinearity by avoiding B as much as possible Compensating resistor patterns R _C , input terminals VE _{and VE} , and output terminals VO _{and VO are} provided, respectively, and ends of lead patterns L are connected to each terminal.

The strain gauge resistor patterns R ₁ , R ₂ ,
R ₃ and R ₄ are lead pattern L as shown in Figure 3.
... are connected in the order of R ₁ - R ₄ - _{R 2} - R ₃ - _{R 1} , and the contact a between R ₁ and R ₃ is connected to one input terminal V _E
In addition, the contact point c between R ₂ and R ₄ is connected to the other input terminal V _E through a parallel circuit in series with the span resistor pattern R _S and the span temperature characteristic nonlinearity compensation resistor R _C. . Also, contact point b between R ₂ and R ₃
is connected to one output terminal _VO , and the contact d between R ₄ and R ₁ is connected to the other output terminal _VO . In addition, the bridge balance compensation resistor pattern R ₀₁
and bridge balance temperature compensation resistor pattern R
_T1 is connected in series, and the series circuit is connected in series with _R1 between contacts a and d. Further, the bridge balance compensation resistor pattern R ₀₃ and the bridge balance temperature compensation resistor pattern R _T3 are connected in series, and the series circuit has R ₃ between contacts a and b.
connected in series with.

The strain gauge resistor patterns R ₁ , R ₂ ,
In order to easily obtain a large resistance value, R ₃ and R ₄ both have a zigzag shape as shown in FIG. 4, and lead patterns L are connected to both ends.

In addition, the bridge balance compensation resistor pattern
R ₀₁ , R ₀₃ , bridge balance temperature compensation resistor patterns R _T1 , R _T3 , temperature compensation span resistor pattern R _S , and span temperature characteristic nonlinear compensation resistor pattern R _C all have rough resistance values. In order to facilitate adjustment and fine adjustment, a large number of bypass lines 9 are provided in a part of the zigzag pattern as shown in FIG. 5, and mutually opposing lead patterns L,
A large number of resistance patterns 10 are also provided in parallel between L. Therefore, by removing any of the bypass lines 9, the resistance value can be roughly adjusted, and by removing an appropriate number of resistance patterns 10 provided in parallel, the resistance value can be finely adjusted. I can do it.

The strain gauge resistor patterns R ₁ , R ₂ ,
R ₃ and R ₄ are formed of metal thin films, such as nichrome, which have a relatively high specific resistance and a small temperature coefficient of resistance. Furthermore, the bridge balance compensation resistor patterns R ₀₁ and R ₀₃ are also formed of the same metal thin film as the strain gauge resistor patterns. The bridge balance temperature compensation resistor patterns R _T1 and R _T3 compensate for the temperature drift of the bridge balance in the bridge circuit, and are made of a resistor metal having a positive temperature coefficient, such as titanium or nickel. The temperature compensation span resistor pattern R _S compensates for the temperature dependence of the output voltage (span), and is made of the same metal material (titanium, nickel, etc.) as the bridge balance temperature compensation resistor patterns R _T1 and R _T3 . ) is formed by. The temperature compensation of the span is generally performed by this temperature compensation span resistor pattern R _S . FIG. 6A shows the temperature-output voltage characteristic when the resistor pattern R _S is not provided, and FIG. 6B shows the temperature-output voltage characteristic when the resistor pattern R _S is provided for temperature compensation. However, as shown in FIG. 6B, simply providing the resistor pattern R _S does not ensure temperature compensation. This is resistor pattern R
This is because the temperature-output voltage characteristic compensated by _S becomes nonlinear. This nonlinearity of the span temperature characteristic is compensated by the span temperature characteristic nonlinearity compensating resistor pattern R _C . Note that the span temperature characteristic nonlinearity compensation resistor pattern R _C is preferably formed of the same metal thin film as the strain gauge resistor patterns R ₁ , R ₂ , R ₃ , and R ₄ because it is desirable that the temperature coefficient of resistance is small. ing.

Further, the relationship between the input voltage V _E and the output voltage V _O in the bridge circuit of FIG. 3 is as follows.

However, R is the resistance of the bridge circuit viewed from the input side.

Next, when a load W is applied to the load cell as shown in FIG. 2, the strain gauge resistor pattern R ₁ ,
R ₂ causes tensile strain and its resistance value increases (the amount of change in each resistance value is △R ₁ and △R ₂ ), and the other two strain gauge resistor patterns R ₃ and R ₄ cause compressive strain. (The amount of change in each resistance value is △
R ₃ and △R ₄ ). At this time, the output voltage V _O is Here, the beam body 1 and each resistor pattern are designed so that R ₁ = R ₂ = R ₃ = R ₄ = R, and R ₁ ≫R ₀₁ +R _T1 , R ₃ ≫R ₀₃ +R From the relationship of _T3 , The following relational expression holds true. This formula is based on the relationship △R/R=KE (where K is the gauge factor of the strain gauge resistor pattern and E is the amount of strain generated in the beam body 1). The amount of distortion E can be obtained from this formula. Also, since the amount of strain E is proportional to the load W, the load W can be determined. Also, from the above formula, the output voltage is the input voltage V
It is obvious that it is proportional to _E and the amount of strain E, but
Since the strain amount E and the gauge factor K vary due to temperature changes, the output voltage V _O also changes due to temperature changes. Therefore, span resistor pattern R _S and span temperature characteristic nonlinear compensation resistor pattern R _C
By appropriately adjusting each resistance value of
Temperature compensation for _O is performed.

By the way, according to experiments, when the beam body 1 is formed of duralumin A2218 and the strain gauge resistor patterns R ₁ , R ₂ , R ₃ , R ₄ are 1KΩ (resistance temperature coefficient ±10ppm/℃ or less), the span The resistor pattern R _S is 240Ω (resistance temperature coefficient +
By setting the span temperature characteristic nonlinearity compensation resistance R _C to 1150Ω, temperature compensation of the output voltage V _O could be performed.

Next, the method for manufacturing the load cell described above is shown in Figure 7A.
Examples are shown in ~D. That is, (A) First, the upper surface of the beam body 1 obtained by cutting is polished to a mirror finish, then degreased and cleaned, and a varnish-like heat-resistant insulating material (for example, polyimide, epoxy, amide-imide, Drop an insulating resin liquid such as epoxy modified polyimide). Then, by rotating the beam body 1 at a speed of about 1600 rpm with a spinner, an insulating material is uniformly applied to the upper surface of the beam body 1, and then dried for about 1 hour in an N ₂ gas atmosphere at about 100°C. Subsequently, heating is performed at about 250° C. for about 5 hours, and a heat-resistant insulating coating 11 having a thickness of 4 to 5 μm is formed on the upper surface of the beam body 1.

Next, on the insulating film 11, a metal material such as nichrome (80% Ni, 20% Cr), whose resistance value does not change much with temperature changes, is deposited by vapor deposition or sputtering to a thickness of approximately
A metal layer 12 for strain gauge resistance of 400 Å is formed.

Next, a metal material such as titanium or nickel (especially preferably titanium, which is resistant to gold etching liquid) is deposited on the strain gauge resistance metal layer 12 in the region of the strain-generating portion 5 on the surface of the beam body 1 by vapor deposition or sputtering. A temperature compensating metal layer 13 having a thickness of about 1000 Å is formed by depositing the same.

Next, a metal material such as gold having excellent conductivity is deposited on the temperature compensation metal layer 13 by vapor deposition or sputtering to form a lead pattern metal layer 14 having a thickness of approximately 2 μm.

(B) Next, the lead pattern metal layer 14 is
Using an etchant appropriate for the material (for example, gold), the lead pattern L..., the input terminals _VE , _VE , and the output terminals _VO , _{VO are} formed by photo-etching.
Remove all but leave.

(C) Next, the temperature compensation metal layer 13 is photo-etched using an etchant appropriate for the material (for example, titanium) of the bridge balance temperature compensation resistor patterns R _T1 , R _T3 and the temperature compensation span resistor. body pattern R _S is removed.

(D) Finally, the strain gauge resistance metal layer 1
1 into strain gauge resistor patterns R ₁ , R ₂ , R ₃ , R ₄ by photo-etching using an etchant appropriate for the material (for example, nichrome).
Bridge balance compensation resistor pattern R ₀₁ , R ₀₃
After removing the resistor pattern RC and the span-temperature characteristic nonlinearity compensating resistor pattern R _C , heat treatment is performed to stabilize each metal layer to complete the process.

Although FIGS. 7B to 7D show all the resistor patterns in a simplified manner, it is as described above that these are formed as shown in FIGS. 4 or 5.

According to the above-described manufacturing method, for example, the -section and -section of FIG. 7D become as shown in FIGS. 8 and 9, respectively. In other words, the strain gauge resistor patterns R ₁ and R ₃ (same as R ₂ and R ₄ ), the bridge balance compensation resistor pattern R ₀₁ (same as R ₀₃ ), and the span temperature characteristic nonlinearity compensation resistor pattern R _C are It is formed of only a strain gauge resistance metal layer 12 such as nichrome. Furthermore, the bridge balance temperature compensation resistor pattern R _T1 (the same applies to R _T3 ) and the temperature compensation span resistor pattern _R It is formed of a metal layer. Furthermore, lead pattern L and terminals V _E , V _E , V _O , V _O
is formed of three metal layers: the strain gauge resistance metal layer 12, the temperature compensation metal layer 13, and the lead pattern metal layer 14 made of gold or the like.

In the above manufacturing process, the resistor patterns R ₁ , R ₂ , R ₃ , R ₄ , R ₀₁ , R ₀₃ and R _C are formed by the common metal layer 12, and the resistor patterns R _T1 , R
Since _T3 and R _S are each formed of the common metal layer 13, the structure is simple and manufacturing can be performed easily. Furthermore, titanium, nickel, etc., which are the material of the temperature compensation metal layer 13, are resistant to etchants such as gold, which are the material of the lead pattern metal layer 14, so that the lead pattern L and the terminals V _E , V _E , V _O , There is no risk that the temperature compensating metal layer 13 will be destroyed when forming _VO , and
In the final heat treatment, the lead pattern metal layer 14
It can prevent the spread to. Also, the temperature compensation metal layer 1
The temperature coefficient of resistance of titanium, nickel, etc., which is the material No. 3, is significantly larger than that of nichrome, etc., which is the material of the strain gauge resistance metal layer 12 (titanium is
2000-3000ppm/℃, Nickel +4000ppm/
℃, nichrome is about ±10ppm/℃), and the sheet resistance is 30Ω/cm ² for nichrome compared to 0.5Ω/cm ² for nickel.
Therefore, the bridge balance temperature compensation resistance R _T
1 , R _T3 and temperature compensation span resistor pattern R
The electrical resistance characteristics of _S are generally determined by the material of the strain gauge resistance metal layer 12. Furthermore, since the material of the strain gauge resistance metal layer 12, such as nichrome, has excellent adhesive properties, the strain gauge resistance metal layer 12 and the temperature compensation metal layer 13 can be stabilized.

In the above embodiments, the insulating film 11 is formed of a resin such as polyimide, but it is also possible to form a film of silicon dioxide (SiO ₂ ), which has excellent heat resistance, by sputtering. This makes it particularly suitable for use at high temperatures.

Furthermore, after completing the steps A to D in FIG. 7, it may be possible to further overcoat with a resin film such as polyimide. In this way, the pattern on the surface of the beam body 1 is protected and weather resistance is improved. Therefore, even higher reliability can be obtained.

As described above based on the embodiments, the load cell according to the present invention has an insulating coating formed directly on the surface of a beam body, a metal layer for strain gauge resistance being directly formed on the insulating coating, and a metal layer for strain gauge resistance being directly formed on it. , a plurality of strain gauge resistor patterns made of metal layers for strain gauge resistance, bridge balance compensation resistor patterns R ₀₁ and R ₀₃ , and span temperature characteristic nonlinear compensation resistor patterns, and other parts are made of temperature compensation metal. This temperature compensation metal layer is covered with a lead pattern metal layer, leaving the bridge balance temperature compensation resistor pattern and the temperature compensation span resistor pattern.

Therefore, since the insulating layer and metal layer are laminated directly on the surface of the beam body, there is no need to bond separately provided elements to the surface of the beam body or connect lead wires, reducing manufacturing man-hours. It is easy to manufacture, mass production is improved through automation, and costs are reduced. Furthermore, since the resistor pattern and insulating layer can be formed extremely thin, power consumption during measurement can be reduced, highly accurate measured values can be obtained, and bridge balance compensation and temperature compensation can be easily performed. can.

[Brief explanation of the drawing]

Figure 1 is an external perspective view of the load cell, Figure 2 is a sectional view of the same, Figure 3 is a circuit configuration diagram of the same, Figures 4 and 5.
The figures are partially enlarged views of the same embodiment,
Figures 6A and B are temperature-output voltage characteristic diagrams, Figure 7A
-D show the manufacturing method of the load cell in the above embodiment, A is an enlarged cross-sectional view, B-D are pattern plan views, FIG. 8 is a cross-sectional view of FIG. 7D, and FIG. 9 is a cross-sectional view of FIG. 7D. -This is a cross-sectional view. R ₁ , R ₂ , R ₃ , R ₄ ... Strain gauge resistor pattern, R ₀₁ , R ₀₃ ... Bridge balance compensation resistor pattern, R _T1 , R _T3 ... Bridge balance temperature compensation resistor pattern, R _S ... Span resistor pattern for temperature compensation, R _C ...Span temperature characteristic nonlinearity compensation resistor pattern, L...Lead pattern, W...Load,
DESCRIPTION OF SYMBOLS 1... Beam body, 6A, 6B... Strain-generating part, 9... Bypass line, 10... Resistance pattern, 11... Insulating coating, 1
2... Metal layer for strain gauge resistance, 13... Metal layer for temperature compensation, 14... Metal layer for lead pattern.

Claims (1)

[Claims] 1. To form a bridge circuit with four strain gauge resistors whose resistance value changes according to the deformation of a beam body to which a load to be measured is applied, and to adjust the bridge balance in the bridge circuit. A bridge balance compensation resistor and a bridge balance temperature compensation resistor for compensating for the temperature drift of the bridge balance are inserted, and a temperature compensation span for compensating for the temperature dependence of the output voltage is inserted into the bridge circuit. In a load cell in which a parallel circuit of a resistor and a span temperature characteristic nonlinearity compensating resistor for compensating for the nonlinearity of the span resistor is externally connected to the input terminal side, an insulating coating is provided on the surface of the beam body. A strain gauge resistance metal layer made of a material with a relatively high specific resistance and a small resistance temperature coefficient is directly formed on the insulating film, and a strain gauge resistance metal layer made of a material with a large resistance temperature coefficient is directly formed on the resistance metal layer. At the same time, a metal layer for lead pattern is formed on the temperature compensation metal layer, and in this state, first, the metal layer for lead pattern is removed leaving the lead pattern and input/output terminals. death,
Subsequently, the temperature compensation metal layer is removed leaving behind the bridge balance temperature compensation resistor pattern and the temperature compensation span resistor pattern, and finally the strain gauge resistance metal layer is removed from each of the strain gauge resistors. , the pattern of the bridge balance compensating resistor, and the pattern of the span temperature characteristic nonlinearity compensating resistor are removed while leaving behind, and a lead pattern, an input/output terminal, and each resistor are formed. Method.