JP2923293B1 - Strain measurement method - Google Patents

Abstract

An object of the present invention is to provide a strain measurement method capable of performing accurate strain measurement by appropriately eliminating the influence of apparent strain caused by a change in resistance value of a strain gauge according to temperature. In a strain-free state of an object to which the strain gauge 1 is attached at the same temperature as the temperature of the strain gauge 1 at the time of strain measurement, it is grasped due to a change in the resistance value of the strain gauge 1 according to the temperature. The apparent strain ε _T
The value ε obtained by the calculation of the following equation (1) from the strain ε _D grasped from the output voltage e of the bridge circuit 7 at the time of strain measurement is used as the strain that excludes the influence of the change in the resistance value of the strain gauge 1 according to the temperature. Obtained as measurements. (Equation 1)

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a strain measuring method using a strain gauge.

[0002]

2. Description of the Related Art As a method of measuring a strain generated in an object, a strain gauge that changes the resistance value according to the strain is attached to the object, and the strain gauge and a plurality of resistors having a predetermined resistance are used to measure the strain. Have a gauge on one side,
It is generally known to form a bridge circuit (specifically, a Wheatstone bridge circuit) having resistors on the remaining three sides, and to perform strain measurement using this bridge circuit.

As a strain measuring method using a bridge circuit in which a strain gauge attached to an object is incorporated on one side as described above, a so-called one-gauge method has been generally known. One gauge two wire method and one gauge three wire method are known.

FIG. 1 is a circuit diagram for explaining a technique for measuring strain by, for example, a one-gauge three-wire method. In this measurement method, a pair of lead wires 2 and 3 are connected in advance to both ends of a strain gauge 1 attached to an object, and another sub-lead is connected to one end of the strain gauge 1 (the lead wire 3 side in the figure). Line 8 is connected (for this reason, 3
Called the line method).

[0005] As shown in the figure, the strain gauge 1 is connected to a resistance circuit formed by interconnecting resistors 4, 5 and 6 via the lead wires 2 and 3, whereby the strain gauge 1 is connected to one side. And a bridge circuit 7 having resistors 4, 5, and 6 on the remaining three sides, respectively.

The resistors 4, 5, and 6 are basically formed by
Each resistance value R_Two, R_Three, R_FourIs generated on the object to be measured.
Resistance element that is constant regardless of the strain
For example, a resistance element having a fixed resistance value). Also,
Resistance value R of resistors 4, 5, and 6 _Two, R_Three, R_FourIs the strain
Gauge 1 in the unstrained state (state in which no strain occurs)
The reference resistance (nominal resistance of strain gauge 1) at
R₀And R₀= R_Two= R_Three= R_FourTo be
It is an example.

At the time of strain measurement using the bridge circuit 7, the connection portion between the lead wire 2 and the resistor 5 or a portion having the same potential as this, and the connection portion between the resistor 4 and the resistor 6 or And a portion having the same potential as a pair of power input portions I ₁ and I ₂ , and these power input portions I ₁ and I 2
The power supply voltage V of the bridge circuit 7 is applied between the _two .

Then, one end of the strain gauge 1 to which the lead wire 3 and the sub-lead wire 8 are connected, and the connection portion between the resistor 5 and the resistor 6 or a portion having the same potential as this are connected to the power supply voltage V as described above. Are provided as a pair of output portions O ₁ and O ₂ of the bridge circuit 7, and an output voltage e which is a measurement signal generated by the bridge circuit 7 between these output portions O ₁ and O _2.
Is detected via the sub lead wire 8.

At this time, the output voltage e of the bridge circuit 7 is
Is based on the resistance value of the strain gauge 1 that causes a change in the resistance value according to the strain of the object. Therefore, the strain of the object can be grasped from the detected value of the output voltage e.

More specifically, for example, it is assumed that the resistance values r ₁ and r ₂ of the lead wires 2 and 3 of the strain gauge 1 are sufficiently small so that they can be ignored (r ₁ ≒ 0, r ₂ ≒ 0). Further, when the power supply voltage V of the bridge circuit 7 is V = 2 [V] and the gauge factor K of the strain gauge 1 is K = 2, as is well known, the strain ε of the object to which the strain gauge 1 is attached,
The following relational expression (2) holds between the output voltage e of the bridge circuit 7 and the output voltage e.

[0011]

(Equation 2)

Accordingly, the strain ε of the object can be determined from the output voltage e of the bridge circuit 7 based on the above equation (2). This is a basic method of strain measurement by the one-gauge three-wire method.

The 1-gauge 2-wire method is a method in which the sub-lead wire 8 is removed from the strain gauge 1 in the above-described 3-wire method (only two lead wires 2 and 3 are connected to the strain gauge 1). In this case, as shown in FIG.
A connection portion between the lead wire 3 and the resistor 4 of the strain gauge 1 or a portion having the same potential as the connection portion, and the resistor 5 and the resistor 6
And a part having the same electric potential as the connection part between the output part and the output part of the bridge circuit 7 is detected as an output voltage e generated by the bridge circuit 7 between these output parts. Then, as in the case of the three-wire method, the distortion of the object is grasped from the detected value of the output voltage e, for example, based on the equation (2). In other words, 1 gauge 2 wire method and 1 gauge 3
The difference from the wire method is only in which part of the bridge circuit 7 in which the strain gauge 1 is incorporated via the lead wires 2 and 3 from which the output voltage as the measurement signal is obtained. However, 1
The three-wire gauge method eliminates the influence that the resistance values of the lead wires 2 and 3 of the strain gauge 1 incorporated in the bridge circuit 7 have on the accuracy of the strain measurement when the resistance value changes due to the influence of the environmental temperature. It is widely used as a more effective measurement method than the one-gauge two-wire method.

In the above-described measurement method using the 1-gauge method, the case where the strain of the object is grasped from the output voltage e of the bridge circuit 7 based on the equation (2) has been described. If it is considered small, the denominator term on the right side of equation (2) may be ignored and the strain ε may be grasped as ε = e.

Further, a method for obtaining the strain ε by the equation (2)
The method is the bridge in the strain-free state of the strain gauge 1.
The output voltage e of the circuit 7 is e = 0 or sufficiently small.
(That the bridge circuit 7 is in an equilibrium state)
It is the most basic method assumed, but strain gauge 1
Reference resistance value R₀And the resistance value R of the resistors 4, 5, 6_Two, R
_Three, R_FourOf resistance and the resistance of lead wires 2 and 3
The strain gauge 1 is in the non-strain state (start of strain measurement)
Output voltage e of the bridge circuit 7 in the previous state)
Below, this is the initial unbalanced output voltage e₀Is relatively large
In some cases. In such a case,
According to the findings of the inventors, any of the following equations (3) to (6)
By grasping strain ε by calculation of
Output voltage e ₀Performs strain measurement while properly eliminating the effects of
(This technology was first disclosed by the applicant of the present application in Japanese Patent Application
No. 341715).

[0016]

(Equation 3)

[0017]

(Equation 4)

[0018]

(Equation 5)

[0019]

(Equation 6)

[0020] Here, V ₃ is as shown in FIG. 1 in the formula (4) to (6), the voltage generated to the side having the resistor 5 of the bridge circuit 7, the resistor 6 in the V ₄ bridge circuit 7 This is the voltage generated on the side having the parameter, and the other parameters are as described above.

Further, when the resistance values r ₁ and r _{2 of} the lead wires 2 and 3 connected to the strain gauge 1 are relatively larger than the reference resistance value R ₀ of the strain gauge 1, The output voltage e corresponds to the resistance values r ₁ , r
Also affected by ₂ . In such a case, the value of the calculation result of the above equations (3) to (6) is further corrected by the calculation of the following equation (7), thereby adding to the influence of the initial unbalanced output voltage e _0. Thus, the strain ε can be grasped without affecting the resistance of the lead wires 2 and 3.

[0022]

(Equation 7)

Here, in equation (7), ε 'is the value of the operation result of any of equations (3) to (6).
Also, r is the resistance value of the lead wire incorporated in the bridge circuit 7 on the same side as the strain gauge 1, which is 1
In the three-wire gauge method, the resistance value of the lead wire 2 in FIG. 1 is r ₁ (r = r ₁ ), and in the one-gauge two-wire method, it is the sum of the resistance values r ₁ and r ₂ of the lead wires 2 and 3 (r = R ₁ + r ₂ ).

As is well known, a relationship σ = E · ε (E: Young's modulus of the object) is established between the stress σ and the strain ε of the object. Therefore, if the strain ε is measured as described above, the stress of the object can be measured by multiplying the strain ε by the Young's modulus E of the object.

In general, the resistance value of the strain gauge 1 not only changes according to the strain of the object to which the strain gauge 1 is attached, but also the temperature of the strain gauge 1 (this is the strain gauge 1 of the object). (Which is also the temperature of the part to which is adhered).

That is, even when the strain gauge 1 alone is in a non-strain state, the resistance value of the strain gauge 1 changes with the temperature change of the strain gauge 1 in accordance with the so-called resistance temperature coefficient of the strain gauge 1. I do. Further, since the strain gauge 1 and the object to which the strain gauge 1 is attached generally have a difference in their linear expansion coefficients, when the strain gauge 1 is attached to the object and a temperature change occurs, the strain gauge 1 and the object are attached. A difference in expansion rate or contraction rate occurs due to the temperature change, and therefore, even if the object is not distorted, the strain gauge 1
Is generated, and the resistance value of the strain gauge 1 changes.

Incidentally, such a change in the resistance value of the strain gauge 1 due to the temperature change is caused in a complex manner, and depending on the above-mentioned resistance temperature coefficient and linear expansion coefficient, the resistance value changes corresponding thereto are opposite to each other. (Canceling direction). Then, by appropriately adjusting the temperature coefficient of resistance or the like of the strain gauge 1 by utilizing this, the self-temperature compensation type in which the resistance value change of the strain gauge 1 combined with these resistance value changes is made as small as possible. Strain gauges are also known, but even with such strain gauges, a change in resistance due to a change in temperature cannot be completely excluded.

In the present specification, these resistance changes of the strain gauge 1, that is, the resistance change occurring in the strain gauge 1 with the temperature change according to the temperature coefficient of resistance of the strain gauge 1, The change in the resistance value of the strain gauge 1 that accompanies the temperature change according to the difference in the coefficient of linear expansion of the object to which it is adhered is also referred to as the change in the resistance value of the strain gauge according to the temperature.

In the case where the above-described strain measurement is performed to some extent continuously, if the resistance value of the strain gauge 1 changes as described above due to a change in environmental temperature, the strain gauge 1 is attached. The output voltage e of the bridge circuit 7 changes even if the actual distortion of the worn object does not change. Accordingly, the strain grasped from the output voltage e as described above includes an apparent strain caused by a change in the resistance value of the strain gauge 1 according to the temperature (the change in the resistance value of the strain gauge 1 according to the temperature becomes a strain of the object. (Appearing distortion that would be recognized if it was assumed to be a response). That is, in a measurement environment in which the resistance value of the strain gauge 1 changes according to the temperature, the strain grasped from the output voltage e of the bridge circuit 7 is the same as the strain component of the original object to be measured and the apparent component. This is the sum of the strain components (sum of both components).

As described above, when the distortion grasped from the output voltage e of the bridge circuit 7 includes the above-mentioned component of the apparent distortion, the distortion grasped from the output voltage e is the original distortion to be measured. Therefore, in order to properly measure the original distortion, it is necessary to eliminate the influence of the apparent distortion (remove the apparent distortion component from the distortion grasped from the output voltage e).

In this case, in the conventional measuring method using the 1-gauge method, the influence of the apparent distortion is eliminated by the following method.

In one method, a specimen having the same material or substantially the same coefficient of linear expansion as the object whose strain is to be measured is subjected to strain while maintaining the specimen in an unstrained state. The data of the temperature characteristics of the apparent strain when the gauge 1 is attached is created in advance based on experiments and the like.

Then, when measuring the strain of the object, the temperature of the strain gauge 1 is measured using a temperature sensor or the like, and based on the measured temperature value,
Obtain the apparent strain at the temperature during strain measurement. Furthermore, by subtracting the obtained apparent strain from the strain grasped from the output voltage of the bridge circuit 7 at the time of strain measurement, the influence of the apparent strain caused by the change in the resistance value of the strain gauge 1 according to the temperature is eliminated. I do.
That is, when the strain grasped from the output voltage e of the bridge circuit 7 at the time of strain measurement is ε _D , and the apparent strain obtained from the measured value of the temperature as described above is ε _T , ε =
The value ε obtained by ε _D −ε _{T is} obtained as a strain measurement value excluding the influence of the apparent strain.

In another method, a strain gage having the same characteristics (strain gage having the same gage factor K, reference resistance value R ₀ , material, etc.) as the strain gage 1 attached to the object is used for strain measurement. A dummy gauge is prepared, and the dummy gauge is maintained at a location where the temperature is substantially the same as that of the strain gauge 1 so as not to cause distortion of the object, or is maintained in an unstrained state by using the same material as the object. To the dummy body. And strain gauge 1
A dummy gauge is incorporated in a bridge circuit (hereinafter, referred to as a dummy bridge circuit) having the same circuit configuration as the bridge circuit 7 in which the strain gauge 1 is incorporated, and the strain measurement by the bridge circuit 7 in which the strain gauge 1 is incorporated is almost simultaneously (with a slight time lag). Then, the output voltage of the dummy bridge circuit is detected.

At this time, the output voltage of the dummy bridge circuit corresponds to the output voltage of the bridge circuit 7 in an unstrained state of the object on which the strain gauge 1 is adhered under the condition of the environmental temperature at the time of strain measurement. . Therefore, the distortion grasped from the output voltage of the dummy bridge circuit in the same manner as in the case of normal distortion measurement corresponds to the apparent distortion. Therefore, in this method, the distortion grasped from the output voltage of the dummy bridge circuit at the time of strain measurement by the bridge circuit 7, that is, the apparent strain is subtracted from the strain grasped from the output voltage of the bridge circuit 7 at the time of strain measurement. Thus, a strain measurement value excluding the influence of the apparent strain is obtained.

However, according to various studies conducted by the inventors of the present invention, even if the influence of the apparent strain caused by the change in the resistance value of the strain gauge according to the temperature is eliminated by the above-described method, the original strain can be reduced. It has been found that (true strain) cannot be measured accurately.

That is, in the conventional method as described above, the temperature of the strain gauge 1 (the temperature of the part of the object where the strain gauge 1 is adhered) is at a certain temperature in the non-strain state of the object to which the strain gauge 1 is adhered. And the change in the resistance value of the strain gauge 1 when the temperature of the strain gauge 1 changes by the predetermined temperature in a state where the object to be measured is distorted. It is assumed that the minutes will be the same. However, in practice, those resistance changes are measured by strain gauge 1
There is a difference between the unstrained state of the object to which is attached and the state in which the strain is generated. For this reason, especially in the strain measurement under the environment where the temperature change is relatively large, the conventional method as described above appropriately eliminates the influence of the apparent strain caused by the change in the resistance value of the strain gauge according to the temperature. Thus, accurate strain measurement cannot be performed.

A so-called two-gauge common dummy method is known as a method for performing strain measurement while compensating for the influence of apparent strain caused by a change in resistance value of a strain gauge according to temperature. Measurements generally tend to be expensive.

In some cases, a strain gauge that does not easily cause a change in resistance according to the temperature is used. In this case, however, the strain gauge is expensive.

[0040]

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to perform accurate strain measurement by appropriately eliminating the influence of apparent strain caused by a change in resistance value of a strain gauge according to temperature. It is an object of the present invention to provide a method for measuring strain that can be performed.

[0041]

Means for Solving the Problems The inventors of the present invention have made various studies in view of the above background, and have obtained the following findings.

First, the strain ε of the object to which the strain gauge is attached is determined by using the change ΔR of the resistance value of the strain gauge according to the strain ε, the reference resistance value R _{0 of the} strain gauge and the gauge factor K. And is generally expressed by the following equation (8).

[0043]

(Equation 8)

Since ΔR = R ₀ · K · ε according to the equation (8), when the strain ε is generated (including the case where ε = 0), the resistance value of the strain gauge is expressed by R _e (= R ₀ + Δ
R), the resistance value _Re is expressed by the following equation (9).

[0045]

(Equation 9)

Next, in a state where the strain ε is occurring (strain state of the resistance value = R _e gauge), the strain gauge temperature (temperature of object) has changed by Δt [deg].
At this time, the resistance value of the strain gauge after the temperature change is represented by R
putting the _et, the resistance R _et, using the resistance value R _e strain gauge before a temperature change is generally expressed by the following equation (10). Here, α in the equation (10) is a value determined by the difference between the temperature coefficient of resistance of the strain gauge, the gauge factor K, and the coefficient of linear expansion between the strain gauge and an object to which the strain gauge is attached. If the resistance temperature coefficient is γ, the linear expansion coefficient is β _g , and the linear expansion coefficient of the object is β _s , α = γ + K ·
Is a (β _s -β _g). When the linear expansion coefficients β _s and β _{g of} the strain gauge and the object to which the strain gauge is attached are equal or substantially equal, α = γ.

[0047]

(Equation 10)

Therefore, the strain gauge due to the temperature change of Δt
ΔR_t(= R _et-R_e)far
And the resistance change ΔR_tTransforms the above equation (10)
By doing so, it is represented by the following equation (11).

[0049]

[Equation 11]

[0050] Also, by placing a the epsilon _t (apparent strain in a state in which strain epsilon is occurring) strain apparent that corresponds to the resistance value variation [Delta] R _t of strain gauge by the temperature change,該見subjected strain ε _t is the above-mentioned equation (8), which is a basic equation representing the relationship between the change in the resistance value of the strain gauge and the strain.
Can be expressed by the following equation (12).

[0051]

(Equation 12)

The following equation (13) is obtained by applying the equations (9) and (11) to the equation (12).

[0053]

(Equation 13)

This equation (13) indicates that the apparent strain corresponding to the change ΔR _t in the resistance value of the strain gauge when a temperature change Δt occurs in a state where a strain ε of an arbitrary magnitude is generated in the object. It represents ε _t . As apparent from the equation (13), the apparent strain ε _t corresponding to the resistance change ΔR _t of the strain gauge when a temperature change of Δt occurs is affected by the strain ε generated at that time.

On the other hand, in the no-strain state of the object adhered a strain gauge, the strain apparent by strain gauge resistance change amount [Delta] R _t when the temperature change Δt has occurred (this, here strain apparently no strain state Is)
Is the apparent strain epsilon _t when the epsilon of the right side of equation (13) as the epsilon = 0. Thus, the apparent strain unstrained state, when put to as epsilon _T, represented by the formula (14).

[0056]

[Equation 14]

By substituting equation (14) into equation (13), the following equation (15) is obtained.

[0058]

(Equation 15)

When the strain grasped from the output voltage of the bridge circuit by the one-gauge method is ε _D , the strain ε to be measured is expressed by the output of the bridge circuit as expressed by the following equation (16). The strain grasped from the voltage is obtained by removing the apparent strain ε _{t in the} state where the strain ε is generated from ε _D.

[0060]

(Equation 16)

The following equation (17) is obtained by substituting the equation (15) into the equation (16) and rearranging the equation.

[0062]

[Equation 17]

Therefore, in order to properly eliminate the influence of the change in the resistance value of the strain gauge in accordance with the temperature when measuring the strain by the one-gauge method, the strain ε _D grasped from the output voltage of the bridge circuit 7 must be used. It can be seen that not only is the apparent state of strain ε _T subtracted, but the result of the subtraction must be further divided by the denominator (1 + K · ε _T ) of equation (17).

The strain measuring method of the present invention is based on the above description.

That is, in order to achieve the above object, the strain measuring method of the present invention has a strain gauge attached to one side of an object so as to cause a change in resistance according to the strain of the object, and A strain measurement method according to a 1-gauge method of generating a measurement signal corresponding to the resistance value of the strain gauge by a bridge circuit having a resistor having a predetermined resistance value on the other three sides, and measuring the strain of the object based on the measurement signal. In the case where the bridge circuit is operated at the same temperature as the temperature of the strain gauge at the time of measuring the strain of the object and in an unstrained state of the object to which the strain gauge is attached, a strain corresponding to the temperature is obtained. due to the change in resistance of strain gauge apparent grasped on the basis of the measurement signal the bridge circuit generates epsilon _T (which is strain apparent the no strain state) A step of Tokusuru, the obtained value epsilon by the following calculation (1) and a strain epsilon _D wherein the apparent strain epsilon _T where the bridge circuit during strain measurement of the object is grasped on the basis of the measurement signal generated, according to the temperature Obtaining a strain measurement value from which the influence of the change in the resistance value of the strain gauge has been eliminated. Here, K in the equation (17) is the gauge factor of the strain gauge as described above.

According to the present invention, the value ε obtained by the calculation of the equation (17) is obtained as a strain measurement value excluding the influence of the change in the resistance value of the strain gauge according to the temperature. Accurate strain measurement can be performed by properly eliminating the influence of apparent strain caused by a change in the resistance value of the strain gauge.

In the present invention, the distortion ascertained based on the measurement signal generated by the bridge circuit can be calculated, for example, by the above-described equation (2) or the arithmetic processing of equations (3) to (6) and (7). Strain is determined, more precisely, without considering the change in resistance value of the strain gauge according to the temperature, assuming that the change in resistance value is caused only by the strain of the object to which the strain gauge is attached, This is distortion that is grasped from a measurement signal generated by the bridge circuit according to the change in the resistance value.

In the present invention, the stress of the object is obtained by multiplying the strain ε obtained by the above equation (17) by the Young's modulus of the object. The strain measurement method of the present invention includes such stress measurement and is referred to as strain measurement.

In the present invention, the apparent strain ε _T (apparent strain in a no-strain state) required for the calculation of the equation (17) can be obtained by a method similar to the conventional method.

In one of the methods, the apparent strain ε
Obtaining a _T includes the steps of measuring the temperature of the strain gauge during strain measurement of the object, from the measured value of the temperature, the type based on the data of the pre-made temperature characteristics of the apparent strain epsilon _T Obtaining the apparent strain ε _T used in the calculation of (1).

According to this, only by measuring the temperature of the strain gauge at the time of strain measurement, the apparent strain ε _T used for the calculation of the equation (17) is calculated from the measured temperature value based on the data of the temperature characteristic. It can be easily obtained. In this case, operation as the data of the temperature characteristic, expressed and table data of the apparent strain epsilon _T (strain apparently no strain state) for different temperatures, by a function such as a polynomial of the temperature as a variable該見over strain epsilon _T Expression data and the like. These data may be determined based on experiments and the like.

In another method, the step of obtaining the apparent strain ε _T includes preparing in advance a strain gauge having the same characteristics as the strain gauge as a dummy gauge, and using the dummy gauge substantially as the strain gauge. Affixing to a part where the object is maintained in a non-strain state at a location where the temperature is the same or a dummy object which is made of the same material as the object and is maintained in a non-strain state, and when measuring the strain of the object Generating a measurement signal according to the resistance value of the dummy gauge by a bridge circuit having the dummy gauge on one side in the same circuit configuration as the bridge circuit, and based on the measurement signal according to the resistance value of the dummy gauge. Obtaining the strain to be grasped as the apparent strain ε _T used in the calculation of the equation (1).

That is, at the time of strain measurement of the object, a measurement signal corresponding to the resistance value of the dummy gauge is generated by the bridge circuit having the dummy gauge on one side with the same circuit configuration as the bridge circuit using the dummy gauge. When the bridge circuit including the strain gauge is operated at the same temperature as the temperature at the time of the strain measurement in a state where the object to which the strain gauge is attached is in the unstrained state, It corresponds to the measurement signal expected to be generated. Therefore, the strain grasped based on the measurement signal generated by the bridge circuit including the dummy gauge can be used as the apparent strain ε _T used in the calculation of the equation (17).

In this case, the bridge circuit including the strain gauge to be attached to the object and the bridge circuit including the dummy gauge are different if the resistance values of the resistors on the sides other than those gauges are the same. A separate circuit may be configured using the above-described resistor. For example, a resistor circuit for configuring a bridge circuit including a strain gauge attached to an object together with the strain gauge (the resistors 4 and 5 in FIG. 1) may be used. , 6) so that the strain gauge and the dummy gauge can be switched and connected via a switch circuit or the like. In this case, the bridge circuit including the dummy gauge is constituted by switching the dummy gauge to the resistance circuit immediately before or immediately after the measurement by the bridge circuit including the strain gauge attached to the object. be able to.

[0075]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. 1 and FIGS. FIG. 2 is a circuit configuration diagram of a strain measuring device to which the first embodiment of the present invention is applied, FIG. 3 is a diagram showing data of temperature characteristics of apparent strain used in the strain measuring device, and FIG. 6 is a flowchart showing the calculation processing according to FIG. It is to be noted that the present embodiment is based on the one-gauge three-wire method, and the same components as those in FIG. 1 will be described using the same reference numerals as in FIG. Referring to FIG. 2, reference numeral 10 denotes a strain measuring device, to which a pair of lead wires 2 and 3 connected in advance to both ends of a strain gauge 1 to be attached to an object (not shown) are connected. Connection terminal 1
1 and 12, and a connection terminal 13 for connecting a sub-lead 8 connected to the lead 3 at one end of the strain gauge 1 on the lead 3 side. Further, when the strain gauge 1 is attached to an object, a temperature sensor 14 which is disposed near the strain gauge 1 and has a temperature substantially equal to that of the strain gauge 1 is attached to the strain measuring device 10 with a lead wire 15. , 16 connected via connection terminals 17, 1
8 are provided.

As the temperature sensor 14, various sensors such as a thermistor and a thermocouple can be employed as long as they can detect the temperature of the strain gauge 1 or its surroundings. Furthermore, by using one of the two wires of the strain gauge 1 of different materials for any two of the lead wires 2, 3, and 8, a thermocouple is formed by the two lead wires, and the thermocouple is formed by the thermocouple. It is also possible to detect the temperature of the strain gauge 1.

The structure of the strain measuring apparatus 10 is roughly divided into a measuring unit 19 and a control unit 2.
0. Note that the measurement unit 19 and the control unit 20 do not necessarily have to be integrally formed, but may be formed separately.

The measuring unit 19 includes the strain gauge 1
Resistors 4 to form the bridge circuit 7 in conjunction with
5 and 6 are provided. These resistors 4, 5, and 6 are constituted by resistance elements having a fixed resistance value, and lead wires 2 and 3 of the strain gauge 1 are connected to connection terminals 11 and 1, respectively.
2 are connected to each other via a circuit pattern formed on a circuit board (not shown) so that the bridge circuit 7 shown in FIG. It is connected.

The measuring unit 19 has a pair of power input terminals 21 and 21 for externally inputting a power voltage V applied to the pair of power input portions I ₁ and I ₂ of the bridge circuit 7.
22 for outputting any one of the output voltage e generated at the pair of output portions O ₁ and O ₂ of the bridge circuit 7 and the voltage V ₄ generated at the side having the resistor 6 of the bridge circuit 7 to the outside. A pair of output terminals 23 and 24 are provided.

In this case, the power input terminals 21 and 22 are connected to the power input sections I ₁ and I ₂ of the bridge circuit 7, respectively. Further, the pair of output terminals 23 and 24, output terminal 24 is connected to one output section O ₂ of the bridge circuit 7, the output terminal 23, the other output section O ₁ and the power input of the bridge circuit 7 It is connected to I ₂ via switch elements 25 and 26 which are respectively connected and disconnected by an external control signal.

Therefore, the switch elements 25 and 26 are turned ON while the power supply voltage V is applied to the bridge circuit 7.
In the OFF state, an output voltage e generated by the bridge circuit 7 is generated between the output terminals 23 and 24, and the switch elements 25 and 26 are turned OFF and O, respectively.
When the N state, between the output terminals 23 and 24, voltage V ₄ is produced which occurs sides with resistor 6 in the bridge circuit 7.

Reference numeral 27 denotes a control signal for performing the disconnection operation of the switch elements 25 and 26 from a control circuit 32 of the control unit 20 which will be described later.
Is a control terminal for giving

The control unit 20 is connected to a pair of power input terminals 21 and 22 of the measurement unit 19, and is connected to the bridge circuit 7 via the power input terminals 21 and 22.
And a pair of output terminals 23 and 24 of the measurement unit 19, which are connected to a bridge power supply circuit 28 for generating a power supply voltage V (constant voltage) applied between the power supply input units I ₁ and I ₂ . Amplifying circuit 29 for amplifying a voltage (e or V ₄ ) generated between 24; an amplifying circuit 30 connected to the connection terminals 17 and 18 for amplifying a signal corresponding to the temperature generated by the temperature sensor 14; , These amplifier circuits 29, 3
An A / D conversion circuit 31 for A / D converting the output of 0.

Further, the control unit 20 includes a control circuit 32 for performing various data processing and control processing described later,
A storage circuit 33 for storing and holding various data described later and programs necessary for processing performed by the control circuit 32;
The control circuit 32 transmits and receives various data between a display 35, which is driven by a display circuit 34 via the display circuit 34 and displays strain measurement values and the like, and an operation unit (not shown), a personal computer, and the like outside the control unit 20. Interface circuit 36 for performing the control unit 2
And a main power supply circuit 37 for generating the entire power supply voltage from a commercial power supply or the like.

The control circuit 32 comprises a microprocessor or the like, and the storage circuit 33 comprises a ROM, RA
M, EEPROM and the like. Further, a battery may be used as the power supply of the control unit 20.

In this case, although the details will be described later, when the strain is measured by the strain measuring device 10, the following equation (18) obtained by using the calculation result of the equation (5) as ε ′ in the equation (7) is used. , Which is the value obtained by performing the correction of the equation (7) on the value of the calculation result of the equation (5), and the value ε _{D obtained} from the output voltage of the bridge circuit 7 (temperature strain grasped from the output voltage of the bridge circuit 7 without considering the change in resistance of the strain gage 1 in accordance with the epsilon _D. hereinafter referred to as the temporary strain measurement epsilon _D it)
As you get.

[0087]

(Equation 18)

The final strain measurement value is obtained by performing the calculation of the above equation (17) using the provisional strain measurement value ε _D.

In order for the control circuit 32 to perform such processing, the storage circuit 33 stores in advance the reference resistance value R ₀ and the gauge factor K of the strain gauge 1 used in the strain measuring device 10, the bridge power supply circuit 28. , The value of the power supply voltage V of the bridge circuit 7, the resistance value r ₁ of the lead wire 2 incorporated on the same side as the strain gauge 1 in the bridge circuit 6 (in the one-gauge three-wire method, this resistance value r ₁ is represented by the equation ( 1
8) is “r”), and the program of the processing procedure is stored and held in advance.

Here, the resistance value r ₁ of the lead wire 2 stored and held in the storage circuit 33 is a resistance value actually measured in advance for the lead wire 2 at the time of measurement, or the resistance value r ₁ of the lead wire 2.
Is a value obtained from the material, length, thickness, etc.

The storage circuit 33 further includes a strain gauge 1
Of the apparent strain (the apparent strain corresponding to the change in the resistance value of the strain gauge 1 according to the temperature) caused by the change in the resistance value of the strain gage 1 according to the temperature in an unstrained state of the object to which is attached. Temperature characteristic data (shown in FIG. 3) is stored and held in advance. The data of this temperature characteristic is
The relationship between the temperature of the object to which the strain gauge 1 is adhered and the apparent strain value in an unstrained state is determined based on an experiment, and is created by, for example, performing the following experiment in advance.

That is, for example, a strain gauge having the same characteristics as the strain gauge 1 is adhered to a test specimen having the same material or substantially the same linear expansion coefficient as the object to be measured and maintained in a non-strain state. Is changed to various values. In this case, when the linear expansion coefficients of the strain gauge 1 and the object to be measured are substantially the same, the strain gauge may be maintained in an unstrained state without being attached to the specimen. Then, under these various temperature conditions, a strain measurement using the strain gauge is performed (a strain measurement is performed based on an output voltage of a bridge circuit incorporating the strain gauge), thereby obtaining the data of the temperature characteristics. Is obtained.

In the present embodiment, the data of the temperature characteristics is based on, for example, a temperature of 20 ° C. (normal temperature).
The apparent strain at ° C is “0”.

In the present embodiment, the data of the temperature characteristics of the apparent strain is represented by a predetermined function formula (for example, a fourth-order polynomial) using the temperature as a variable, and the function formula is stored. The information is stored in the circuit 33.
However, such temperature characteristic data may be stored and held in the storage circuit 33 as, for example, table data.

Next, the operation of the strain measuring apparatus 10 according to the present embodiment will be specifically described.

In the strain measuring apparatus 10 of the present embodiment, the following processing is performed before measuring the strain of the object.

That is, first, without attaching the strain gauge 1 to an object (the strain gauge 1 is in a non-strained state), the connection terminals 11 to 13 of the strain measuring device 10 are connected to the connection terminals 11 to 13 via the lead wires 2 and 3 and the sub-lead wire 8 respectively. In the connected state, the control unit 20 is operated by a predetermined operation of the strain measuring device 10 or the like.

[0098] At this time, the control circuit 32 of the control unit 20 first activates the bridge power supply circuit 28, the bridge power supply input I ₁ from the circuit 28 the bridge circuit 7, I ₂ to the power input terminal 21, The power supply voltage V is applied through the power supply 22.

In this state, the control circuit 32 turns on the switch elements 25 and 26 of the measurement unit 23, respectively.
The output voltage e generated between the output portions O ₁ and O ₂ of the bridge circuit 7 is input to the amplifier circuit 29 through the output terminals 23 and 24 by controlling the state to the OFF state. Then, the control circuit 32 recognizes the output voltage e generated by the bridge circuit 7 at this time by the data supplied through the amplifier circuit 29 and the A / D conversion circuit 31, and bridges the recognized value of the output voltage e to the bridge circuit 7. The storage circuit 33 stores and holds the initial unbalanced output voltage e ₀ of the circuit 7. Further, the control circuit 32 stores the initial unbalanced output voltage e ₀ in the storage circuit 33 as described above, and then switches the switch elements 25 and 26.
Are controlled to an OFF state and an ON state, respectively, so that the voltage V ₄ generated on the side of the bridge circuit 7 including the resistor 6 is input to the amplifier circuit 29. Then, the control circuit 32
At this time, the voltage V ₄ input to the amplifier circuit 29 is recognized by the data supplied through the amplifier circuit 29 and the A / D conversion circuit 31, and the value of the recognized voltage V ₄ is stored and held in the storage circuit 33. . The detection and storage of the voltage V ₄ may be performed after attaching the strain gauge 1 to an object, or may be performed before connecting the strain gauge 1 to the strain measuring device 10. Good. Further, since the value of the voltage V ₄ should be V · R ₄ / (R ₃ + R ₄ ), when the variation of the voltage V ₄ is small, the power supply voltage V of the bridge circuit 7 and the resistor 5 , stores holds a value obtained by calculation of V · R ₄ / a resistance value of 6 R _3, R ₄ Metropolitan (R ₃ + R ₄₎ in the memory circuit 33 as the value of the voltage V _4, the voltage V ₄ The measurement may not be performed.

Next, in order to start the strain measurement, the strain gauge 1 is attached to an object (not shown), and a location where the temperature is substantially the same as that of the strain gauge 1 (basically a location near the strain gauge 1). The temperature sensor 14 is installed at the second position. Then, when the control unit 20 is operated by a predetermined operation in this state, the control circuit 32 firstly detects the detection signal input from the temperature sensor 14 to the amplifier circuit 30, that is, the temperature of the strain gauge 1 at the start of the measurement. Data representing the initial gauge temperature T ₀ (hereinafter, referred to as an initial gauge temperature T ₀ ) is acquired via the amplifier circuit 29 and the A / D conversion circuit 31, and the initial gauge temperature T ₀ represented by the acquired data is stored in the storage circuit 33. Hold.

Thereafter, the control circuit 35 measures the strain in the following manner in accordance with the timing designated by a predetermined operation of the measurer or the time schedule set in advance.

The control circuit 32 sends the signals from the bridge power supply circuit 28 to the power supply input sections I ₁ and I ₂ of the bridge circuit 7 at the timing of performing the strain measurement in the same manner as when the initial unbalanced output voltage e ₀ is detected. In a state where the power supply voltage V is applied, the switch elements 25 and 2 of the measurement unit 19 are
By controlling the ON state and the OFF state of 6 respectively,
The output voltage e of the bridge circuit 7 is input to the amplifier circuit 29. Then, the control circuit 32 recognizes the value of the output voltage e input to the amplifier circuit 29 by the data supplied through the amplifier circuit 29 and the A / D conversion circuit 31,
The storage circuit 33 stores the recognized value of the output voltage e.

Subsequently, the control circuit 32 transmits the current value of the strain gauge 1 from the temperature sensor 14 via the amplification circuit 30 and the A / D conversion circuit 31 in the same manner as when the data of the initial gauge temperature T ₀ is obtained. The data of the temperature T (temperature at the time of strain measurement) is obtained, and the data is stored and held in the storage circuit 33.

The detection of the temperature T may be performed immediately before the measurement of the strain (detection of the output voltage e).

Next, the control circuit 32 obtains the distortion ε of the object by performing the processing of the flowchart of FIG.

That is, the control circuit 32 determines the reference resistance value R ₀ and the gauge factor K of the strain gauge 1 stored in the storage circuit 33 as described above, the power supply voltage V of the bridge circuit 7,
The initial unbalanced output voltage e _{0 of} the bridge circuit 7, the voltage V _{4 of} the bridge circuit 7 having the resistor 6, the resistance r ₁ (= r) of the lead wire 2, and the output of the bridge circuit 7 when measuring strain. The data of the voltage e is read from the storage circuit 33 (ST
EP4-1).

Then, the above-mentioned read data values are used to perform the operation of the above equation (18), thereby obtaining the provisional strain measurement value ε _D (STEP 4-2).

Further, the control circuit 32 stores the data of the initial gauge temperature T ₀ of the strain gauge 1 and the temperature T at the time of strain measurement stored in the storage circuit 33 as described above.
3 (STEP 4-3).

The storage circuit 33 stores the values of the apparent strains (apparent strains in the unstrained state) corresponding to the read initial gauge temperature T ₀ and the temperature T at the time of strain measurement.
Is obtained based on the temperature characteristic data (see FIG. 3) stored and stored in the storage unit, and the difference between the values of the apparent strains corresponding to the respective temperatures T ₀ and T is used in the calculation of the equation (17). Strain (apparent strain without strain) ε
Obtained as _T (STEP 4-4). Thus, the strain-free apparent strain ε _T used in the calculation of equation (17)
Is determined in such a manner that the apparent strain ε _{T in the non-} strain state corresponds to a change in the resistance value of the strain gauge 1 due to a temperature change, and the temperature characteristic data in FIG.
° is because are based on the temperature of the C (initial gauge temperature T ₀ is not always 20 ° C).

Next, the control circuit 32 operates in this manner.
Obtained strain-free apparent strain ε _TAnd before asking before
Temporary strain measurement ε_DAnd stored in the storage circuit 33.
Of the above equation (17) from the data of the gauge factor K
By performing the above, the value ε of the calculation result is
Constant value (more precisely, the initial unbalanced output voltage e₀Impact of
And the resistance value r of the lead wire 2 of the strain gauge 1₁Impact of
And the effect of the resistance value change according to the temperature of the strain gauge 1
(STEP 4-)
5).

The control circuit 32 causes the display 35 to display the finally obtained strain measurement value ε via the display circuit 34.

In the strain measurement of the present embodiment, since the strain ε is obtained by the operation of the above equation (17), the effect of the resistance value change of the strain gauge 1 in accordance with the temperature is properly eliminated to achieve accurate strain measurement. It can be performed. In particular, in the present embodiment, the provisional strain measurement value ε _D , that is, the strain grasped from the output voltage e of the bridge circuit 7 without considering the change in the resistance value of the strain gauge 1 according to the temperature is calculated by the above equation ( 18), the effect of the initial unbalanced output voltage e ₀ of the bridge circuit 7 and the effect of the resistance value r ₁ of the lead wire 2 of the strain gauge 1 can be properly eliminated, and higher accuracy can be achieved. Can be measured.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a circuit configuration diagram of a strain measuring device to which the second embodiment of the present invention is applied, and FIG. 6 is a flowchart showing a calculation process by the strain measuring device. In the description of the strain measuring device of the present embodiment, the same components as those of the strain measuring device of FIG. 2 described above are denoted by the same reference numerals as in FIG.

Referring to FIG. 5, the strain measuring device 40 of the present embodiment is roughly composed of a measuring unit 41 and a control unit 42, similarly to the above-described strain measuring device 10.

The measuring unit 41 has connection terminals 11 to 13 for connecting the lead wires 2 and 3 and the sub-lead wire 8 of the strain gauge 1 to be attached to an object (not shown) similarly to the above-described strain measuring device 10. In addition to the above, there are further provided connection terminals 44 to 46 for connecting a strain gauge (dummy gauge) 43 having the same characteristics (same reference resistance value, gauge ratio, material, etc.) as the strain gauge 1 by a three-wire method.

In this case, similar to the strain gauge 1, the dummy gauge 43 has lead wires 47 connected to both ends thereof.
48 to the connection terminals 44 and 45, respectively.
The sub lead wire 52 connected to one end of the dummy gauge 43 on the lead wire 48 side is connected to the connection terminal 46. The dummy gauge 43 is provided at a location where the temperature becomes substantially the same as that of the strain gauge 1 to be attached to an object during strain measurement.
It is attached to a portion where the object is not distorted, or to a dummy body made of the same material as the object and maintained in an unstrained state.

Further, the measuring unit 41 is connected to the switch elements 49a, 49b, 49c connected to the connection terminals 11 to 13 corresponding to the strain gauge 1 and the connection terminals 44 to 46 corresponding to the dummy gauge 43, respectively. Provided switching elements 50a, 50b, 50c. Further, the measuring unit 41 includes resistors 4, 5, 5 as in the measuring unit 19 of the strain measuring device 10 in FIG.
6, switch elements 25 and 26, a pair of power input terminals 2
1 and 22; a pair of output terminals 23 and 24;
7 are provided.

When the switch elements 49a, 49b and 49c corresponding to the strain gauge 1 are turned on, the connection terminals 21 and 22 to which the lead wires 2 and 3 of the strain gauge 1 are connected are connected to the resistor 4 , 5 and 6 to form the bridge circuit 7 shown in FIG. 1, and connect the connection terminal 23 to which the sub-lead wire 8 of the strain gauge 1 is connected to the output terminal 23 via the switch element 25. It is provided to be.

Similarly, when the switch elements 50a, 50b, 50c corresponding to the dummy gauge 43 are turned on, the lead wires 47, 48 of the dummy gauge 43 are turned on.
Are connected to the resistor circuits of the resistors 4, 5, and 6 to form the bridge circuit 7, and
The connection terminal 46 to which the sub lead wire 52 of the dummy gauge 43 is connected is provided to be connected to the output terminal 23 via the switch element 25.

That is, the switching elements 49a, 49b, 4
9c (hereinafter referred to as a switch group 49)
And a set of switch elements 50a, 50b, 50c (hereinafter, referred to as
By performing ON / OFF switching with a switch group 50), a bridge circuit 7 having a strain gauge 1 on one side (hereinafter, this bridge circuit is referred to as a measurement-side bridge circuit 7) and a dummy gauge 43 (Hereinafter, this bridge circuit is referred to as a dummy bridge circuit 7) is configured to be switchable with the same circuit configuration.

Each of the switch groups 49 and 50 has its ON
The control terminal 51 provided in the measurement unit 41 for the / OFF state
Is controlled by a control signal applied to the The configuration of the measurement unit 41 other than that described above is the same as that of the measurement unit 19 of the strain measurement device 10 in FIG.

The control unit 42 has the same basic circuit configuration as the control unit 20 of the strain measuring apparatus 10 shown in FIG.
9, A / D conversion circuit 31, control circuit 32, storage circuit 3
3, a display circuit 34 and a display 35, an interface circuit 36, and a main power supply circuit 37. Similar to the strain measuring apparatus 10, the bridge power supply circuit 28 and the amplification circuit 29
Are connected to the measurement unit 41. However, in this case, since the temperature measurement is not performed in the strain measuring device 40 of the present embodiment, the amplifier circuit 30 for the temperature sensor 14 shown in FIG. 2 is not provided. The control circuit 32 controls the ON / OFF state of each of the switch groups 49 and 50 by applying a control signal to the control terminal 51 of the measurement unit 41.

The details of the control circuit 32 will be described later.
The distortion ε of the object is calculated using the arithmetic processing of the equation (18) and the arithmetic processing of the equation (17). In order to cause the control circuit 32 to execute this arithmetic processing, the storage circuit 33 Is pre-programmed with the arithmetic processing procedure shown in the flowchart of FIG.

The storage circuit 33 has a strain gauge 1
And the reference resistance value R of the dummy gauge 43 having the same characteristics.
₀And gauge factor K, power supply voltage V of bridge circuit 7, strain
Resistance value r of lead wire 2 of gauge 1₁Is the strain measurement
As in the case of the setting device 10
And the resistance of the lead wire 47 of the dummy gauge 43
Resistance r₁'Data is the same as that of the strain measurement device 10 described above.
Similarly, it is stored and held in advance. Where the memory circuit
33, the resistance value r of the lead wire 47 stored and held ₁'
Resistance value r of lead wire 2₁In the same way as in
7 or the measured resistance value
This is a value obtained from the material, length, thickness, and the like of the lead wire 47.

The strain measurement by the strain measuring device 40 according to the present embodiment is performed as follows.

That is, first, prior to the strain measurement,
When the strain gauge 1 and the dummy gauge 43 are not attached to the object and are connected to the measuring unit 41 (at this time, the strain gauge 1 and the dummy gauge 43 are in a non-strain state), a predetermined operation of the strain measuring device 40 and the like are performed. Thereby, the control unit 42 is operated.

At this time, the control circuit 32 of the control unit 42 first activates the bridge power supply circuit 28, and the power supply input sections I ₁ , I ₂
Is supplied with power supply voltage V via power supply input terminals 21 and 22.
6 are turned on and off, respectively. Then, in this state, the control circuit 32 controls the switch group 49 corresponding to the strain gauge 1 and the switch group 50 corresponding to the dummy gauge 43 to be in the ON state in order, thereby turning the strain gauge 1 and the dummy gauge 43 on. The measurement-side bridge circuit 7 and the dummy-side bridge circuit 7 are sequentially connected to the resistance circuits of the resistors 4, 5, and 6, respectively. At this time, in the configuration of each of the measurement-side bridge circuit 7 and the dummy-side bridge circuit 7, the output voltage e generated between the output portions O ₁ and O _{2 of} each bridge circuit 7 becomes the initial unbalanced output of the bridge circuit 7. The voltage e ₀ is input to the amplifier circuit 29 via the output terminals 23 and 24. Then, the control circuit 32 is thus determined side bridge circuit 7 and the dummy-side bridge circuit 7 the initial unbalanced output voltage e ₀ generated respectively (hereinafter, referred to the initial unbalanced output voltage e ₀ of the measuring-side bridge circuit 7 The reference symbol e _0X is _assigned to the initial unbalanced output voltage e ₀ of the dummy-side bridge circuit 7.
_0D ) to the amplification circuit 29 and the A / D conversion circuit 31.
, And sequentially detects the values of the detected initial unbalanced output voltages e _0X and e _0D.
3 is stored.

Further, the control circuit 32 stores and holds the initial unbalanced output voltage e _0X of the measurement-side bridge circuit 7 and the initial unbalanced output voltage e _0D of the dummy-side bridge circuit 7 as described above. Thereafter, by controlling the switch elements 25 and 26 to the OFF state and the ON state, respectively, the voltage V ₄ generated on the side of the bridge circuit 7 including the resistor 6 is input to the amplifier circuit 33. Then, the control circuit 32 outputs the voltage V ₄ input to the amplifier circuit 29 at this time to the amplifier circuit 29.
And recognized by a data provided via the A / D conversion circuit 31, the recognized value of the voltage V ₄ (this value is the same for both measurement side bridge circuit 7 and the dummy-side bridge circuit 7) a storage circuit 33.
The detection of the voltage V ₄ and the storage of the voltage V ₄ are performed even when all the sets of the switch groups 49 and 50 are set to the OFF state.
Or turn on either one of the switch groups 49 or 50
The state may be performed, or either may be performed. The voltage V
The detection of ₄ and the storage thereof may be performed before the detection of the initial unbalanced output voltages e _0X and e _0D and the storage thereof.

Next, the strain gauge 1 is attached to an object (not shown) to start the strain measurement. Further, the dummy gauge 43 is attached to a portion where the temperature becomes substantially the same as that of the strain gauge 1 (basically, a portion near the strain gauge 1) so as not to cause distortion of the object. Alternatively, at a location where the temperature is substantially the same as that of the strain gauge 1 (basically, a location near the strain gauge 1)
A dummy body prepared in advance and made of the same material as the object is placed in a strain-free state, and a dummy gauge 43 is attached to the dummy body.
In the case where the coefficient of linear expansion between the object and the strain gauge 1 is substantially the same, the dummy gauge 1 is simply arranged so as not to generate strain at a location where the temperature becomes substantially the same as the strain gauge 1. You may.

After such setting, the control unit 42 is operated at a required timing (during strain measurement).

At this time, the control unit 42
The control circuit 32 includes a bridge circuit from the bridge power supply circuit 28.
7 power input section I₁, I_TwoApply power supply voltage V during
At the same time, the switch elements 25 and 26 are turned on, respectively.
Control to OFF state. And in this state,
Unbalanced output voltage e_0X, E_0DAs with the detection of
Controlling the switch groups 49 and 50 in the ON state in order
The measurement side bridge circuit 7 and the dummy side bridge circuit
The paths 7 are constructed in order and their respective bridge circuits
7 output voltage e (hereinafter, corresponding to the measurement side bridge circuit 7).
The output voltage e_XWith a dummy bridge
The output voltage e corresponding to the circuit 7 _DAttached)
Through an amplifier circuit 33 and an A / D conversion circuit 34, respectively.
Output voltage e_X, E_DIs stored in the storage circuit 33.
Will be retained.

Next, the control circuit 32 obtains the strain ε at the place where the strain gauge 1 is attached to the object by performing the processing of the flowchart of FIG.

That is, the control circuit 32 transmits the data of the reference resistance value R ₀ , the gauge factor K, the power supply voltage V, and the voltage V ₄ stored in the storage circuit 33 as described above (these data are stored in the measurement-side bridge circuit 7. And the dummy side bridge circuit 7), the resistance value r ₁ of the lead wire 2 corresponding to the measurement side bridge circuit 7, and the initial unbalanced output voltage e.
Read and _0X and strain output voltage e _X of the data at the time of measurement (STEP6-1).

Then, the above equation (18) is used to calculate the value of each of the above data (in this case, “e ₀ ” in the equation (18) becomes “e _0X ” and “e _0X ” e "in the" e _X 'is replaced with "r""r_1"), the strain is grasped from the output voltage of the measuring-side bridge circuit 7 without considering the change in resistance of the strain gage 1 in accordance with the temperature obtaining a temporary strain measurements epsilon _D is (STEP6-2). This arithmetic processing is the same as the processing of STEP 4-2 of FIG.

Next, the control circuit 32 determines the resistance value r ₁ ′ of the lead wire 47 stored in the storage circuit 33 and the initial unbalanced output voltage e with respect to the dummy bridge circuit 7 as described above.
_0D and strain read data of the output voltage e _D at the time of measurement (STEP6-3).

The resistance of the read lead wire 47 is
Resistance r₁', Initial unbalanced output voltage e_0DAnd strain measurement
Output voltage e_DRead in STEP6-1
Gauge factor K, power supply voltage V, voltage V_FourFrom the data
By performing the operation of Expression (18) (in this case, Expression (1)
8) "e"₀Is "e_0D, And "e" is replaced with "e_D"
"R" becomes "r₁')), The calculation of equation (17)
Apparent strain used ε _TAsk for. (STEP6-
4).

In this case, the apparent strain ε _T determined in STEP 6-4 is the value obtained by attaching the dummy gauge 43 (a portion where the object does not cause distortion or the dummy body).
In the non-strain state, the strain grasped by the output voltage of the dummy-side bridge circuit 7 due to the change in the resistance value of the dummy gauge 4 according to the temperature at the time of strain measurement (more precisely, the output of the dummy-side bridge circuit 7) The distortion is grasped from the voltage excluding the influence of the initial unbalanced output voltage e _0D of the bridge circuit 7 and the influence of the resistance value r ₁ ′ of the lead wire 47). The bridge circuits 7 have the same circuit configuration, and the strain gauges 1 and the dummy gauges 43 incorporated in these bridge circuits 7 have the same characteristics (the resistance change according to temperature is also equal). Further, the object to which the dummy gauge 43 is attached is an object to be measured or a dummy body of the same material as the object. For this reason, the apparent strain ε _T determined in STEP 6-4 is obtained by operating the measurement-side bridge circuit 7 in the unstrained state of the portion of the object to which the strain gauge 1 is adhered and at the same temperature as the strain measurement. In this case, the distortion corresponds to the apparent distortion in the distortion-free state grasped from the output voltage of the bridge circuit 7 on the measurement side.

Then, the control circuit 32 next proceeds to STEP
And provisional strain measurements epsilon _D obtained in 6-2, STEP6-4
By calculating the above equation (17) from the apparent strain ε _T (apparent strain in a no-strain state) determined by the above and the data of the gauge factor K stored and held in the storage circuit 33,
The value ε of the calculation result is determined according to the final strain measurement value (more precisely, the influence of the initial unbalanced output voltage e ₀ , the resistance value r ₁ of the lead wire 2, and the temperature of the strain gauge 1. (Strain measurement value excluding the influence of the change in resistance value) (STEP 6-5).

The control circuit 32 causes the display 35 to display the finally obtained strain measurement value ε via the display circuit 34.

In the strain measurement of this embodiment,
Can be calculated by the equation (17).
The effect of the change in the resistance value of the strain gauge 1 according to the temperature
It is possible to perform accurate strain measurement with proper exclusion.
You. Further, the resistance value of the strain gauge 1 changes according to the temperature.
From the output voltage of the bridge circuit 7 on the measurement side without considering
The measured temporary strain ε_DAnd a dummy gauge 1
From the output voltage of the bridge circuit 7 on the dummy side
Apparent strain ε_TIs calculated by the equation (18).
Therefore, the measurement side bridge circuit 7 and the dummy side
Initial unbalanced output voltage e of the ridge circuit 7_0X, E_0DImpact of,
And the resistance value r of the lead wires 2 and 47₁, R ₁'
It can be eliminated properly and more accurate strain measurement
It can be carried out.

In the first and second embodiments described above, the one-gauge three-wire method has been described as an example. However, the present invention can be applied to the one-gauge two-wire method. In the embodiment in this case, for example, the connection terminal 12 of the strain measuring instrument 10 in FIG. 2 is connected to the output terminal 23 via the switch element 25 inside the measurement unit 19. If the strain gages to which only the two lead wires 2 and 3 are connected are connected to the connection terminals 11 and 12, the strain (gage) by the 1-gauge two-wire method can be obtained in exactly the same procedure (processing) as in the first embodiment. The measurement can be performed in exactly the same way as in the first embodiment.

Alternatively, for example, the connection terminal 12 of the strain measuring device 40 in FIG. 5 is connected to the output terminal 23 via the switch element 49b and the switch element 25 inside the measurement unit 41, and the connection terminal 45 is connected to the measurement unit. 4
1 is connected to the output terminal 23 via the switch element 50b and the switch element 25 (switch element 49).
b and 50b and the resistor 4 are connected to the switch element 2
5 is connected to the output terminal 23). And 2
The strain gages to which only the two lead wires 2 and 3 are connected are connected to the connection terminals 11 and 12 and the two lead wires 4 and
Connect dummy gauges with only 7 and 48 connected to connection terminals 4
If the connection is made to 4, 45, the strain measurement by the 1-gauge two-wire method can be performed in exactly the same manner as in the second embodiment by the same procedure (processing) as in the second embodiment.

In the measurement by the one-gauge two-wire method as described above, when calculating the provisional strain measurement value ε _D by the calculation of the equation (18), the value of “r” in the equation (18) is used. The resistance values r ₁ and r ₂ of the lead wires 2 and 3
(= R ₁ + r ₂ ). Similarly, 1 gauge 2
In the measurement by the line method, when calculating the apparent strain ε _T by the calculation of the equation (18) corresponding to the second embodiment, as the value of “r” in the equation (18),
The sum of the resistance values of the lead wires 47 and 48 is used.

In each of the above-described embodiments, the provisional strain measurement value ε _D is obtained by the calculation of the equation (18). In the second embodiment, the apparent strain ε _T (the apparent strain in a no-strain state) is also calculated. The temporary strain measurement values ε _D (first and second values) were obtained by the calculation of equation (18).
Embodiment) and apparent strain ε _T (second embodiment)
Is defined as “ε ′” in the equation (7),
(4) It may be determined by an equation using the calculation results of (6).

Specifically, for example, when the provisional strain measurement value ε _D and the apparent strain ε _T are obtained by the equation using the calculation result of the above equation (3) as “ε ′” of the above equation (7), In the first and second embodiments, the storage circuit 33 stores the reference resistance value R ₀ , the gauge factor K, the power supply voltage V, and the resistance values r ₁ and r ₁ ′ of the lead wires 2 and 47 (resistance value r ₁ '
(Only in the case of the second embodiment), the resistance values R ₃ and R ₄ of the resistors 5 and 6 are stored and held in advance together with the data of FIG. Then, in the processing of STEP 4-2 in FIG. 4 and STEPs 6-2 and 6-4 in FIG. 6, the operation of the equation (3) is performed using the data, and the value ε ′ of the operation result is used. it suffices to determine the temporary strain measurements epsilon _D or the apparent strain epsilon _T by performing the calculation of expression (7). In this case, there is no need to detect the voltage V ₄ on the side having the resistor 6.

Further, for example, when the provisional strain measurement value ε _D and the apparent strain ε _T are obtained by an equation using the calculation result of the above equation (4) as “ε ′” of the above equation (7), the first In the second embodiment, the voltage V ₃ (see FIG. 1) of the side having the resistor 5 is detected in the same manner as in the case of detecting the voltage V ₄ of the side having the resistor 6. deep. Then, STEP4-2 in FIG. 4 and STE in FIG.
In the processing of P6-2 and P6-2, the detected voltage V
_{As shown in FIG. 3} , the provisional strain measurement value ε _D and the apparent strain ε _T are obtained by performing the calculation of the equation (4) using the equation (3) and further performing the calculation of the equation (7) using the value ε ′ of the calculation result. do it.

Further, the voltage V on the side having the resistor 6
₄ and the voltage V _{3 on the} side having the resistor 5 are detected in the processing of STEP 4-2 of FIG. 4 and STEPs 6-2 and 6-4 of FIG. Using the voltages V ₃ and V ₄ , the calculation of the equation (6) is performed, and the calculation of the equation (7) is performed using the value ε ′ of the calculation result, thereby obtaining the provisional strain measurement value ε _D and the apparent strain ε. _T may be obtained.

In each of the first and second embodiments, the influence of the resistance values r ₁ , r ₁ ′ of the lead wires 2, 47 when obtaining the temporary strain measurement value ε _D and the apparent strain ε _T is determined. To eliminate this, the calculation of equation (7) was used, but the resistance values r ₁ and r ₁ ′ of the strain gage 1 and the dummy gage 43
If the reference resistance value R ₀ is sufficiently smaller than the reference resistance value R ₀ , the provisional strain measurement value ε _D and the apparent strain ε _T may be obtained by any one of the equations (3) to (6).

Furthermore, the initial unbalance of the bridge circuit 7
Force voltage e₀Is sufficiently small (e ₀≒ 0), the initial
Unbalanced output voltage e₀Do not need to consider the effects of
In this case, the provisional strain measurement ε_DAnd apparent strain ε_TThrough
It is obtained by the calculation of the above formula (2) which is usually used.
You may do so.

In the first and second embodiments,
Although the case where the strain itself is measured has been described, the stress of the object can be measured by multiplying the finally obtained strain ε by the Young's modulus of the object as described above.

In the first and second embodiments,
Although the single point measurement of strain has been described as an example, it goes without saying that the present invention can also be applied to a case where multipoint strain measurement is performed on a plurality of points or a plurality of objects.

Further, in the first and second embodiments,
In the strain measuring devices 10 and 40, the process for obtaining the final strain ε has been described.
If the data of the initial unbalanced output voltage e ₀ and the output voltage e at the time of strain measurement stored in the storage circuit 33 as described above can be transferred to a personal computer by communication or the like, The personal computer may be made to perform a process of obtaining the strain ε by using the data and calculating the equations (18) and (17). Then, in this case, the above equation (1) for causing the personal computer to perform such processing.
A program including the arithmetic expression 7) may be recorded on a recording medium such as a floppy disk or a CD-ROM used by the personal computer.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram for explaining a method of measuring strain by a 1-gauge method.

FIG. 2 is a circuit configuration diagram of a strain measuring device to which the first embodiment of the strain measuring method of the present invention is applied.

FIG. 3 is a diagram showing data of temperature characteristics of apparent strain used in the apparatus of FIG. 2;

FIG. 4 is a flowchart showing a calculation process by the device of FIG. 2;

FIG. 5 is a circuit configuration diagram of a strain measuring apparatus to which a second embodiment of the strain measuring method according to the present invention is applied.

FIG. 6 is a flowchart showing a calculation process by the device of FIG. 5;

[Explanation of symbols]

1 ... strain gauge, 7 ... bridge circuit, 43 ... dummy gauge.

Claims (3)

(57) [Claims] 1. A bridge circuit having a strain gauge attached to one side of an object so as to generate a resistance change according to the strain of the object on one side and a resistor having a predetermined resistance value on the other three sides. In a strain measurement method according to a 1-gauge method of generating a measurement signal according to a resistance value of a strain gauge and measuring the strain of the object based on the measurement signal, the same as the temperature of the strain gauge at the time of measuring the strain of the object. When the bridge circuit is operated at a temperature of and without distortion of the object to which the strain gauge is attached, a measurement signal generated by the bridge circuit due to a change in the resistance value of the strain gauge according to the temperature see the the step of obtaining an apparent strain epsilon _T is grasped based, and strain epsilon _D the bridge circuit is grasped on the basis of the measurement signal generated upon strain measurement of the object The value ε obtained by the calculation of the following equation (1) from the applied strain ε _T is
Obtaining a strain measurement value excluding the effect of a change in resistance value of the strain gauge according to temperature. (Equation 1) However, in the equation (1), K is a gauge factor of the strain gauge. 2. The step of obtaining the apparent strain ε _T comprises:
It used a step of measuring the temperature of the strain gauge during strain measurement of the object, from the measured value of the temperature, the calculation of the equation based on the data of the pre-made temperature characteristics of the apparent strain ε _T (1) 2. The method according to claim 1, further comprising the step of obtaining an apparent strain ε _T. 3. The step of obtaining the apparent strain ε _T comprises:
A strain gauge having the same characteristics as the strain gauge is prepared in advance as a dummy gauge, and the dummy gauge is the same as a portion or a portion where the object is maintained in an unstrained state at a location having substantially the same temperature as the strain gauge. A step of attaching the dummy gauge to a dummy object which is made of a material and maintained in a strain-free state, and a bridge circuit having the same dummy gauge as one side in the same circuit configuration as the bridge circuit when measuring the strain of the object. Generating a measurement signal corresponding to the resistance value of the dummy gauge, and obtaining a strain grasped based on the measurement signal corresponding to the resistance value of the dummy gauge as an apparent strain ε _T used in the calculation of the equation (1). The strain measurement method according to claim 1, wherein the strain measurement is performed.