JP2923294B1 - Strain measurement method - Google Patents

Abstract

An object of the present invention is to provide a strain measurement method capable of accurately performing strain measurement of an object even after replacing a strain gauge attached to the object. And strain epsilon ₁ of the last grasp the object based on the output voltage e of the bridge circuit 16 including the A before replacement strain gauge 1a, based on the output voltage e of the bridge circuit 16 including a strain gauge 1b after replacement A value ε ₂ obtained by the following equation from the grasped strain Δε ₂ of the object from the exchange time is measured as the strain ε ₂ of the object from the start of the strain measurement. (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 which generates a resistance value change according to the strain is attached to the object, and an appropriate circuit including the strain gauge (hereinafter referred to as a measuring circuit and a measuring circuit). Conventionally, a method of generating a measurement signal corresponding to the resistance value of the strain gage and grasping the strain of the object (= strain of the strain gage) based on the measurement signal has been known.

In this case, the measuring circuit is usually
A bridge circuit (specifically, a Wheatstone bridge circuit) having the strain gauge on one side and a resistor having a predetermined resistance value on the other three sides is generally used.

[0004] In the present specification, "strain" more precisely means a strain (compression strain or tensile strain) in the compression or tension direction of an object.

When it is desired to measure a strain generated in an object, it is generally important to observe how the strain changes over time from the start of the measurement. Then, in this case, when the strain generated in the object does not become so large from the measurement start time, the strain measurement is continuously or intermittently continued using the strain gauge attached to the object at the measurement start time. be able to.

[0006] However, in the strain measurement (large strain measurement) in which the strain generated in the object becomes large, the strain of the strain gauge itself accompanying the strain of the object is expressed as follows.
There is a possibility that the strain gauge may be broken beyond the durability limit of the strain gauge.

For this reason, in such strain measurement, when the strain to be grasped increases to some extent, the strain gauge to be attached to the object is replaced with a new one to continue the strain measurement.

[0008] Even in the case where the large strain measurement is not performed as described above, if the strain gauge attached to the object is broken by any foreign matter hitting it, a new strain gauge is attached. The strain measurement is continued in exchange for the one.

In this case, when a new strain gauge is attached to an object, the strain gauge is in a strain-free state. Therefore, the strain measured using the replaced strain gauge is the strain from the time of replacement. is there.

Conventionally, the value obtained by adding the strain grasped by using the strain gauge after replacement to the strain finally grasped by using the strain gauge before replacement is calculated from the start of the strain measurement of the object. Considering the strain, after replacing the strain gauge, the above-described addition operation is performed to obtain the strain of the object from the start of the strain measurement.

That is, conventionally, when the strain finally grasped by using the strain gauge before replacement is ε ₁ and the strain grasped at a desired timing by using the strain gauge after replacement is Δε ₂ , After the replacement of the gauge, the value ε obtained by the addition operation of the following equation (2) is grasped as the strain ε from the start of the strain measurement of the object.

[0012]

(Equation 2)

[0013] However, the present inventors have studied that it has been found that such calculation cannot actually accurately grasp the strain ε from the start of the strain measurement of the object.

[0014]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a strain measuring method capable of accurately measuring the strain of an object even after replacing a strain gauge attached to the object. The purpose is to:

[0015]

Means for Solving the Problems The inventors of the present application have studied in detail the case of replacing a gauge in the course of measurement with a strain attached to an object, and have found the following.

For example, assume that a strain gauge in an unstrained state is attached to an object having a length L ₀ in order to measure a strain generated in the object. At this time, assuming that the object receives a compressive or tensile load in its length direction and its length changes by ΔL ₁ , the strain ε ₁ of the object is expressed by the following equation (3). variation for the initial length of the length L ₀ (length of the object at the start of the strain measurement L ₀₎ delta
It is defined as the ratio of L _1.

[0017]

(Equation 3)

Note that the following equation (4) holds between the strain ε ₁ and the resistance value of the strain gauge attached to the object in the state of the length L ₀ .

[0019]

(Equation 4)

Here, in equation (4), K is the gauge factor of the strain gauge, R ₀ is the resistance value of the strain gauge in an unstrained state (nominal resistance value of the strain gauge), and ΔR is the change in the length of the object. The change in the resistance value of the strain gauge according to the minute ΔL ₁ .

In a strain measurement using a strain gauge, a measurement signal corresponding to the above-mentioned resistance change ΔR is generated by a circuit including the strain gauge. Then, the strain ε ₁ is measured from the measurement signal based on the relational expression (4).

Next, it is assumed that the strain gauge to be attached to the object is replaced with a new one while the length of the object has changed from L ₀ by ΔL ₁ as described above. In other words, it is assumed that the strain gauge previously attached to the object is peeled off in a state where the length of the object is (L ₀ + ΔL ₁ ), and a new strain gauge in a non-strain state is attached to the same place. If the length of the object further changes by ΔL ₂ after the replacement of the strain gauge, the change in the length of the object from the initial length L ₀ is (ΔL ₁ + ΔL ₂ ). The strain from the start of the strain measurement of the object at is represented by the following equation (5), where ε ₂ is set.

[0023]

(Equation 5)

The new strain gauge after replacement is
If the body length is (L₀+ ΔL₁) State without strain
The new strain gauge
With the same gauge as before the replacement
The strain that is _TwoThen, the following equation (6)
Is represented by

[0025]

(Equation 6)

That is, the strain Δε ₂ measured using the new strain gauge after the replacement of the strain gauge is equal to the length (L ₀ + ΔL ₁ ) of the object at the time of the replacement (at the time of attaching the new strain gauge). , The ratio of the change ΔL ₂ in the length of the object from the time of the replacement.

From this, it is apparent that strain gauge
When replacing the strain, the strain before replacement
The strain of the object that was last grasped using the gauge (this
Is the strain ε expressed by equation (3)₁Is equivalent to
Of the object grasped using the replaced strain gauge
Strain (this is the strain Δε expressed by equation (6)_TwoPhase
(2), the measurement is started.
Body strain ε from time _TwoIt is not possible to grasp
It turns out that you can't. In fact, the strain represented by equation (3)
Only ε₁And the strain Δε expressed by equation (6)_TwoAdd
However, the original strain to be measured represented by equation (5)
Only ε_TwoCan not get.

On the other hand, according to the above equation (6), ΔL ₂ = Δ
Since ε ₂ · (L ₀ + ΔL ₁ ), the following equation (7) is obtained by substituting this into equation (5) and rearranging it.

[0029]

(Equation 7)

Then, in this equation (7), (ΔL₁
/ L₀) Is, as shown in equation (3),
(L₀+ ΔL₁Strain ε in the state of)₁And this
Ε ₁Using the strain gauge before replacement
Immediately before).

Therefore, after the replacement of the strain gauge, the strain ε ₂ from the start of the strain measurement of the object can be correctly obtained by the following equation (8).

[0032]

(Equation 8)

This is the principle of strain measurement according to the present invention.

Therefore, in order to achieve the above object, the strain measuring method of the present invention uses a circuit including a strain gauge attached to an object so as to generate a resistance value change according to the strain of the object. In the strain measurement method of generating a measurement signal according to the resistance value of, and measuring the strain of the object based on the measurement signal, when replacing the strain gauge with a new strain gauge during the measurement, the strain gauge A method for measuring the strain of the object from the start of the strain measurement after the replacement of, the strain ε _{1 of the} object finally grasped based on the measurement signal of the circuit including the strain gauge before the replacement, From the strain Δε _{2 of the} object from the time of the replacement, which is grasped based on the measurement signal of the circuit including the strain gauge after the replacement, the above equation (8)
Characterized by measuring the strain epsilon ₂ of the object from the beginning of the calculated value epsilon ₂ strain measurement by calculation.

According to this invention, the value ε ₂ obtained by the calculation of the equation (8) is measured as the strain ε ₂ of the object from the start of the strain measurement, so that the strain gauge can be replaced during the measurement. after the replacement may also be measured accurately strain epsilon ₂ of the object from the beginning of the strain measurement.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. 1 is a circuit configuration diagram of a strain measuring apparatus to which an embodiment of the present invention is applied, FIG. 2 is a circuit configuration diagram of a main part of the apparatus of FIG. 1, and FIG. 3 is a flowchart for explaining the operation of the apparatus of FIG. is there.

Referring to FIG. 1, a strain measuring apparatus 10 according to the present embodiment performs a strain measurement by a so-called one-gauge three-wire method (more specifically, a measurement of compression / tensile strain), and is attached to an object. Connection terminals 11 and 12 for connecting a pair of lead wires 2a and 3a respectively connected to both ends of the strain gauge 1a to be connected in advance, and a sub-lead wire connected to one end of the strain gauge 1a on the lead wire 3a side together with the lead wire 3a. 4a are provided.

[0038] In the figure, those given the reference numeral 1b are:
This is a strain gauge connected to the strain measuring device 10 in place of the strain gauge 1a during the later-described measurement. This strain gauge 1b has the same connection terminal 1 as the strain gauge 1a.
Three lead wires 2b, 3b,
4b is connected. In the following description, when it is not necessary to particularly distinguish the strain gauges 1a and 1b, they are collectively referred to as a strain gauge 1, and similarly,
Lead wires 2a and 2b are replaced with lead wire 2, lead wires 3a and 3b
Are referred to as a lead wire 2 and the sub lead wires 4a and 4b are referred to as a sub lead wire 4.

The structure of the strain measuring device 10 is roughly divided into a measuring unit 14 and a control unit 1.
And 5.

The measuring unit 14 incorporates resistors 17, 18, and 19 for constituting a bridge circuit (Wheatstone bridge circuit) 16 shown in FIG.

These resistors 17, 18 and 19 are, for example, 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, a circuit pattern formed on a circuit board (not shown) such that a bridge circuit 16 having the strain gauge 1 on one side and resistors 17, 18, and 19 on the remaining three sides is configured. And are connected to the connection terminals 11 and 12.

The bridge circuit 16 includes the strain gauge 1
When a power supply voltage V (constant voltage) is applied between the pair of power supply input portions I ₁ and I _{2 of the} bridge circuit 16, the bridge circuit ₁ generates a measurement signal corresponding to the resistance value of the bridge circuit 1.
6, an output voltage e (measurement signal) corresponding to the resistance value of the strain gauge 1 is generated between the pair of output portions O ₁ and O ₂ .

Here, as shown in FIG. 2, a pair of power input portions I ₁ and I ₂ of the bridge circuit 16 are connected to the lead wire 2 of the strain gauge 1 and the resistor 18 or to a portion having the same potential as this. In addition, it is a connection portion between the resistor 17 and the resistor 19 or a portion having the same potential as this. The pair of output portions O ₁ and O ₂ of the bridge circuit 16 are connected to the lead wire 3.
And one end of the strain gauge 1 to which the sub-lead wire 4 is connected,
And a connection portion between the resistor 17 and the resistor 18 or a portion having the same potential as the connection portion.

The resistance values R _{2 to} R ₄ of the resistors 17, 18, 19 are usually balanced by the bridge circuit 16 when the strain gauge 1 incorporated in the bridge circuit 16 has no strain (output voltage). The reference resistance value (nominal resistance value) of the strain gauge to be connected to the measuring instrument in the unstrained state so that e becomes "0" or a minute value.
Is assumed to be equal to However, in the present embodiment, the output voltage e detectable at the time of strain measurement is set to the bridge circuit 16.
Is not necessarily required to be set as described above if the resistance values R _{2 to} R ₄ of the resistors 17, 18 and 19 can be generated.

The measuring unit 14 has a pair of power input terminals 20 and 21 for externally inputting a power supply voltage V of the bridge circuit 16 and a pair of output portions O ₁ and O ₂ of the bridge circuit 16. A pair of output terminals 22 and 2 for outputting any one of the output voltage e and the voltage V ₄ generated on the side having the resistor 19 of the bridge circuit 16 to the outside.
3 are provided.

The power input terminals 20 and 21 are connected to the power input portions I ₁ and I ₂ of the bridge circuit 16, respectively, and the output terminals 22 and 23 are connected to the output terminals O ₁ and O ₂ of the bridge circuit 16, respectively. Have been.

The control unit 15 is connected to a pair of power input terminals 20 and 21 of the measuring unit 14 and is connected to the bridge circuit 1 via the power input terminals 20 and 21.
6, a bridge power supply circuit 24 for generating a power supply voltage V (constant voltage) applied between the power supply input units I ₁ and I ₂ , and a pair of output terminals 22 and 23 of the measurement unit 14. , 23, an amplifier circuit 25 for amplifying the output voltage e of the bridge circuit 16, an A / D converter circuit 26 for A / D converting the output of the amplifier circuit 25, and various data processing and control processing described later. A control circuit 27 for performing the operation, a storage circuit 28 for storing various data to be described later, programs necessary for the processing performed by the control circuit 27, and the like, are driven by the control circuit 27 via a display circuit 29, and display strain measurement values and the like. And an interface circuit 3 for the control circuit 27 to transmit and receive various data between an operating device (not shown) and a personal computer outside the control unit 15. When, and a main power supply circuit 32 for generating the power supply voltage of the entire control unit 15 from a commercial power supply or the like. The control circuit 27 is composed of a microprocessor or the like, and the storage circuit 28 is a ROM, an R,
It is composed of an AM, an EEPROM and the like. Further, a battery may be used as the power supply of the control unit 15.

In this case, the strain measuring device 1 of the present embodiment
At 0, the control circuit 27 of the control unit 24
By calculating, for example, the following equation (9) from the data of the output voltage e of the bridge circuit 16 detected as described later, the strain ε (more precisely, the strain gauge 1 (Distortion from the time of sticking to the object).

[0049]

(Equation 9)

Here, in the equation (9), V is the power supply voltage of the bridge circuit 16 as described above, K is the gauge factor of the strain gauge 1, and R ₀ is the reference resistance value of the strain gauge 1 in the non-strain state. (Nominal resistance value of the strain gauge 1). R ₃ and R ₄ are resistors 18,
19 is the resistance value. Further, r is the resistance of the lead to be incorporated into the same side as the strain gauge 1 in the bridge circuit 16, which is the resistance value r ₁ of the lead wire 2 as measured by 1 gage three-wire method of the present embodiment .

Also, e₀Is built into the bridge circuit 16
When the strain gauge 1 is in a strain-free state, the bridge
When the power supply voltage V is applied to the circuit 16, the bridge circuit
16 is the output unit O₁, O_TwoThe output voltage generated during (below,
This is the initial unbalanced output voltage e ₀It is). Further
And e is the state where the strain gauge 1 is attached to the object to be measured.
When the power supply voltage V is applied to the bridge circuit 16 in the
The bridge circuit 16 outputs the output O₁, O_Twowhile
Is the output voltage generated.

The method for measuring strain based on the above equation (9) is a technique proposed by the present applicant in Japanese Patent Application No. 9-341715, and the details thereof will not be described here. , The operation term in square brackets on the right side of equation (9) is
When the initial unbalanced output voltage e _{0 of the} bridge circuit 16 is relatively large, this is an operation term for eliminating the influence and grasping the distortion from the output voltage e of the bridge circuit 16 at the time of strain measurement. The term (R ₀ + r) / R ₀ by which the calculation result in the brackets is multiplied is large in order to eliminate the influence of the relatively high resistance value of the lead wires 2 and 3 of the strain gauge 1. This is a term for correcting the calculation result in parentheses.

Further, the strain measuring apparatus 10 of the present embodiment
In the case where the strain gage 1 is replaced with a new one during the measurement as described later, the control circuit 27 of the control unit 24 sets the bridge circuit 16 using the strain gage 1 before replacement after the replacement. from the output voltage e and the end on the basis of the equation (9) (denoted by the reference numeral epsilon ₁ to) the strain epsilon is grasped (immediately before the exchange), the bridge circuit 16 using a strain gauge 1 after replacement of by performing the calculation of the output voltage (denoted by the reference thereto numeral [Delta] [epsilon] ₂₎ strain ε is grasped on the basis of the equation (9) from e because the equation (8), at the beginning of the object strain measurement (exchange It has a previous strain gauge 1 to obtain the strain epsilon ₂ of the object from the time) that initiated the stuck to strain measurement on the object.

The processing procedure shown in the flowchart of FIG. 3 is programmed in advance in the storage circuit 28 of the control unit 15 to cause the control circuit 27 to execute the above-described arithmetic processing. Further, the storage circuit 28 previously stores data such as the power supply voltage V of the bridge circuit 16 and the resistance values R ₃ and R ₄ of the resistors 18 and 19.

Next, the operation of strain measurement by the strain measuring apparatus 10 of the present embodiment will be described in detail.

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

In the strain measuring apparatus 10 according to the present embodiment, for example, when the strain measurement is started using the strain gauge 1a, the gauge factor K of the strain gauge 1a (hereinafter referred to as “the strain gauge 1a”) is set prior to the strain measurement. Sign K
a) and a reference resistance value R ₀ (hereinafter referred to as a reference symbol R _0a ), and a resistance value r ₁ of a lead wire 2a of the strain gauge 1a (hereinafter referred to as a reference symbol r _1a) . Is input to the storage circuit 28 from an appropriate operating device or the like outside the strain measuring apparatus 10 via the interface circuit 31 and the control circuit 27, and is stored and held in the storage circuit 28.

In this case, as the value of the gauge factor Ka of the strain gauge 1a stored and held in the storage circuit 28, its nominal value is used, for example. As the reference resistance value R _0a of the strain gauge 1a, its nominal value or a reference resistance value actually measured in advance for the strain gauge 1a is used. further,
Resistance r ₂ of the leads 2a are actually measured resistance value, or the material and length of the lead 2a, using the values obtained from the thickness and the like.

When the gauge factor K and the reference resistance value R _{0 of the} strain gauge 1 to be used in the strain measuring device 10 are predetermined, the values of the gauge factor K and the reference resistance value R ₀ are Alternatively, the power supply voltage V and the resistance values R ₃ and R ₄ of the resistors 18 and 19 may be stored and stored in the ROM of the storage circuit 28 at the stage of manufacturing the strain measuring device 10.

Next, the lead wires 2a to 4a are connected to the connection terminals 11 to 13 of the strain measuring device 10 without attaching the strain gauge 1a to the object (in a state where the strain gauge 1a is not strained).
Then, the control unit 15 is operated by a predetermined operation or the like of the strain measuring device 10 after the bridge circuit 16 is configured by being connected via the.

At this time, the control circuit 27 of the control unit 15 first activates the bridge power supply circuit 24, and from the bridge power supply circuit 24 to the power supply input terminals I ₁ and I ₂ of the bridge circuit 16, the power supply input terminal 20, The power supply voltage V is applied via the power supply 21.

In this state, the control circuit 27 inputs the output voltage e generated between the output portions O ₁ and O ₂ of the bridge circuit 16 to the amplifier circuit 25 via the output terminals 22 and 23. The control circuit 27 then outputs the output voltage e generated by the bridge circuit 16 to the amplifier circuit 25 and A
/ D conversion circuit 26, and recognizes the value of the output voltage e as the bridge circuit 16
_Is stored in the storage circuit 28 as the initial unbalanced output voltage e ₀ (hereinafter referred to as a reference symbol e _0a ).

Next, after attaching the strain gauge 1a to the object to be measured (not shown) to start the strain measurement, the control circuit 27 sets the timing designated by a predetermined operation of the measurer or the like. Also, according to a preset time schedule, a strain measurement is performed as follows.

At the timing of strain measurement (at the time of strain measurement), the control circuit 27 _changes the power supply input section I of the bridge circuit 16 from the bridge power supply circuit 24 in the same manner as when the initial unbalanced output voltage e _0a is detected. _1, I ₂ to allowed impart supply voltage V, this time the bridge circuit 16 is output section O _1, O ₂ between the output voltage e to be generated (hereinafter, this assigned the reference numerals e _a) to the amplifier circuit 25 Input.
Then, the control circuit 27, the value of the output voltage e _a inputted to the amplifier circuit 25, it recognizes the data supplied through the amplifying circuit 25 and the A / D conversion circuit 26, the output voltage e which is the recognition The value of _a is stored and held in the storage circuit 28.

Then, the control circuit 27 obtains the strain ε (strain from the start of the measurement) of the object by performing the processing of the flowchart of FIG.

That is, the control circuit 27 first determines whether or not the later-described gauge replacement data indicating that the strain gauge 1 has been replaced is stored in the storage circuit 28 (STEP 1).

At this time, since the replacement of the strain gauge 1 has not been performed yet, the gauge replacement data is not stored and held in the storage circuit 28. In this case, the STE
Proceed to P2.

In STEP 2, the control circuit 27 controls the bridge circuit 16 stored in the storage circuit 28 as described above.
Power supply voltage V, the resistances R ₃ , R ₄ of the resistors 18 and 19,
Gauge factor Ka of strain gauge 1a and reference resistance value R _0a ,
Resistance r _1a of the lead 2a, reads the data of the output voltage e _a of the bridge circuit 7 in the initial unbalanced output voltage e at _0a and strain measurement of the bridge circuit 16 from the memory circuit 28.

Then, the equation (9) is used to calculate the strain ε using the read values of the respective data (STEP 3). In this case, K, e ₀ , e, R ₀ , and r in Equation (9) are replaced with Ka, e _0a , e _a , R _0a , and r _1a , respectively, as shown in the figure.

The control circuit 27 that has obtained the strain ε in this way displays the value of the strain ε on the display 30 via the display circuit 29 and stores and holds the value in the storage circuit 28 (STEP 4).

Such processing is repeated at an appropriate timing for performing the strain measurement, and the data of the value of the strain ε at each time is stored and held in the storage circuit 28 in a time-series manner.
The data of the value of the strain ε may be recorded on a hard disk or a floppy disk.

During the strain measurement using the strain gauge 1a, for example, when the strain ε obtained as described above becomes a large value close to the durability limit of the strain gauge 1a, or when the strain gauge When 1a is damaged, the measurement is continued by replacing the strain gauge 1a with a new strain gauge 1b.

In this case, prior to the replacement of the strain gauge 1a, first, the following processing is performed.

That is, first, a new strain gauge 1b
Of the gauge factor K (hereinafter referred to by the reference symbol Kb)
Value and reference resistance R₀(Hereinafter, this is referred to as R_0bWith
And the resistance value r of the lead wire 2b of the strain gauge 1b.
_Two(Hereinafter referred to by the reference _2b) And strain
The interface is provided from an appropriate operating device or the like external to the measuring device 10.
The storage circuit 2 via the face circuit 31 and the control circuit 27
8 and stored in the storage circuit 28.

When the new strain gauge 1b has the same characteristics as the strain gauge 1a, the gauge factor Kb and the reference resistance value R _0b of the strain gauge 1b are stored in the storage circuit 28. Gauge factor Ka of gauge 1a
And the reference resistance value R _0a , the input process of the gauge factor Kb and the reference resistance value R _0b may be omitted. Further, when the length or the wire type of the lead wire 2b of the new strain gauge 1b is equal to the length or the wire type of the lead wire 2a of the strain gauge 1a, the resistance value r of the lead wire 2b of the strain gauge 1b is changed.
_1b, since already equal to the resistance value r _1a leads 2a of the strain gauge 1a stored in the storage circuit 28, may be omitted even if the input process of the resistance value r _1b.

Next, the lead wire 2a of the strain gauge 1a
4a are removed from the strain measuring device 10, and the lead wires 2b to 4b are connected to the connection terminals 11 to 13 of the strain measuring device 10 without attaching a new strain gauge 1b to the object (with the strain gauge 1b in a non-strain state). Then, the control unit 15 is operated by a predetermined operation or the like of the strain measuring device 10 after the bridge circuit 16 is configured by being connected via the.

At this time, the control circuit 27 of the control unit 15 _changes the power supply input I ₁ of the bridge circuit 16 from the bridge power supply circuit 24 in the same manner as the detection of the initial unbalanced output voltage e _0a relating to the strain gauge 1a. , imparting a power supply voltage V to I _2. Further, in this state, the control circuit 27 recognizes the output voltage e of the bridge circuit 16 via the amplifier circuit 25 and the A / D conversion circuit 26, and recognizes the recognized value of the output voltage e as the initial value of the bridge circuit 16. The storage circuit 28 stores and holds the output voltage as an unbalanced output voltage e ₀ (hereinafter, a reference numeral e _0b will be given).

When the reference resistance values R _0a and R _{0b of} the strain gauges 1a and 1b are equal to each other, and the resistance values of the lead wires 2a and 3a are equal to the respective resistance values of the lead wires 2b and 3b. , The initial unbalanced output voltage e _0b of the bridge circuit 16 relating to the new strain gauge 1b is
Basically, it is considered to be equal to the initial unbalanced output voltage e _0a relating to the strain gauge 1a already stored and held in the storage circuit 28. Therefore, in this case, the detection and storage of the initial unbalanced output voltage e _0b of the bridge circuit 16 relating to the new strain gauge 1b may be omitted.

Next, in order to start the strain measurement using the new strain gauge 1b, the strain gauge 1a attached to the object is peeled off, and the strain gauge 1b is
Is attached to the object to replace the strain gauge 1.
Further, gauge replacement data indicating that the strain gauge 1 has been replaced is input to the storage circuit 28 via the interface circuit 31 and the control circuit 27 from an appropriate operating device or the like external to the strain measurement device 10. 28. Further, at this time, the control circuit 27 uses the strain gauge 1a before the exchange for the latest one of the time series data of the strain ε measured using the strain gauge 1a and stored in the storage circuit 28. the last strain epsilon ₁ of the data grasped, namely, aware as strain measured strain epsilon ₁ of data exchange immediately before the gauge 1.

Thereafter, the control circuit 27 of the control unit 15 performs the following strain measurement in accordance with the timing specified by a predetermined operation of the measurer or the time schedule set in advance.

The control circuit 27 includes the above-described strain gauge 1
as in the case of measurement using a, at the timing (time of strain measurement) performing strain measurement, the power supply voltage V allowed imparted to the bridge circuit 16 from the bridge power supply circuit 24, a bridge circuit 16 at this time is output section O ₁ , the output voltage e to be generated between O ₂ (hereinafter, this assigned the reference numerals e _b) a through the amplifier circuit 25 and a / D conversion circuit 26 recognizes. And then stores the value of the output voltage e _b that the recognition in the memory circuit 28.

Then, the control circuit 27 obtains the strain of the object (the strain from the start of the measurement using the strain gauge 1a) by performing the processing of the flowchart of FIG.

That is, the control circuit 27 first determines whether or not the gauge exchange data is stored in the storage circuit 28 (STEP 1). In this case, since the gauge exchange data is stored and held in the storage circuit 28 as described above, the process proceeds to STEP5.

In STEP 5, the control circuit 27 determines the power supply voltage V of the bridge circuit 16, the resistance values R ₃ and R ₄ of the resistors 18 and 19, the gauge factor Kb of the strain gauge 1b, and the reference value, as in STEP 2. resistance R _0b, reads the resistance value r _1b leads 2b, and the data of the output voltage e _b of the bridge circuit 7 in the initial unbalanced when the output voltage e _0b and strain measurement of the bridge circuit 16 from the memory circuit 28.

Then, the read values of the above data are
By using the above equation (9), the strain Δε
_Two(STEP 6). In this case, the expression
K, e in (9)₀, E, R₀, R are figures
Kb, e as shown in_0b, E_b, R _0b, R_1bReplace with
You.

The strain Δε ₂ obtained in STEP 6 in this manner is based on the time when the strain gauge 1 is replaced with the strain gauge 1b from the strain gauge 1a (more precisely, when the strain gauge 1b is attached to an object). , The strain of the object ascertained from the output voltage e of the bridge circuit 16 incorporating the strain gauge 1b.

Next, the control circuit 27 reads from the storage circuit 28 the data of the last strain ε ₁ (strain data of the object immediately before replacement) grasped using the strain gauge 1a before replacement from the storage circuit 28 (STEP 7). its strain epsilon ₁ of data, performing the calculation of the equation (8) using the strain [Delta] [epsilon] ₂ data obtained in STEP6 (STEP 8).

At this time, the control circuit 27 uses the value ε ₂ obtained by the equation (8) at the start of the strain measurement of the object (the strain gauge 1 before replacement is attached to the object to start the strain measurement). Is displayed on the display 30 and stored in the storage circuit 28 (STEP 9).

[0089] After replacement of the gauge 1 such processing strain be repeated at an appropriate timing for strain measurement, data of the occasional strain epsilon ₂ values will be stored circuit 28 in time series manner memory retention . The data of the strain ε ₂ is recorded in the same manner as the data before the strain gauge 1 is replaced.
The processing may be performed on a hard disk or a floppy disk.

As described above, after the replacement of the strain gauge 1, after the replacement of the strain ε _{1 obtained} based on the output voltage e of the bridge circuit 16 using the strain gauge 1a before the replacement, Δ which was finally grasped based on the output voltage e of the bridge circuit 16 using the strain gauge 1b
By calculating the equation (8) from the strain ε ₁ (strain of the object from the time of replacement), even after the strain gauge 1 is replaced, the strain of the object from the start of the measurement before the replacement can be accurately determined. Well can be measured continuously.

Particularly, in this embodiment, the strain ε based on the output voltage e of the bridge circuit 16 using the strain gauge 1a
₁ and bridge circuit 1 using strain gauge 1b
Since the grasp of the strain Δε ₂ based on the output voltage e of 6 is performed by using the calculation of the equation (9), the reference resistance value of each strain gauge 1 and the resistance values of the resistors 16 to 18 are calculated. The influence of the initial unbalanced output voltage e ₀ generated by the bridge circuit 16 and the resistance values of the lead wires 2 and 3 in the strain-free state of the strain gauge 1 due to variations, the resistance values of the lead wires 2 and 3, etc. is eliminated. And can be performed with high accuracy. As a result,
Before and after replacing the strain gauge 1,
A highly accurate measurement of the strain of the object can be performed.

In the above-described embodiment, the case where the replacement of the strain gauge 1 is performed only once has been described as an example. However, every time the strain gauge is replaced with a new one, the above processing is repeated. Even when the strain gauge is replaced a plurality of times, accurate strain measurement can be continuously performed.

[0093] In the above embodiment, based on the calculation of Expression (9), but so as to grasp the strain [Delta] [epsilon] ₂ of strain epsilon ₁ and after replacement of the previous exchange of strain gauges 1, any strain epsilon ₁ , Δε ₂ , if the initial unbalanced output voltage e ₀ is sufficiently small, the calculation in the square brackets of the equation (9) is performed as e ₀ = 0 (fixed value). You may do so. In this case, the power supply voltage V of the bridge circuit 16 is V = 2 [v], the gauge factor K of the strain gauge 1 is K = 2, and the resistance values R ₃ and R ₄ of the resistors 18 and 19 are R _3. = when set to R _4, the operation result in the brackets of equation (9) is a value epsilon 'which is obtained by the following equation (10). This equation (10) is an equation generally used as a basic equation for grasping the strain from the output voltage of the bridge circuit including the strain gauge in the strain measurement using the strain gauge.

[0094]

(Equation 10)

Further, the leads 2 and 3 of the strain gauge 1
Is the reference resistance value R of the strain gauge 1.₀Against
If it is sufficiently small, (R₀+ R)
/ R ₀The distortion ε₁, Δε_Two
May be grasped.

In the present embodiment, the operation of equation (9) is
In order to perform this operation, the resistance values R of the resistors 18 and 19 are determined._Three, R_FourTo
R, which appears in the denominator on the right side of equation (9)_Three/
(R _Three+ R_Four), R_Four/ (R_Three+ R_Four)
Then, the value of those terms obtained in advance (for example,
R_Three= R_FourIn the case of_Three/ (R_Three+ R_Four) = R_Four/
(R_Three+ R_Four) = １ ／) may be used.

[0097] Furthermore, V · R ₃ / appears in the denominator of the right side of equation _{(9) (R 3 + R} 4) _{sections, V · R 4 / (R} 3 + R
₄ ) are the voltage V _{3 on} the side of the resistor 18 (see FIG. 2) and the voltage V _{4 on} the side of the resistor 19 (see FIG. 2) in the bridge circuit 16, respectively. it may be used a value of the voltage V _3, V _4. In this case, as the values of the voltages V ₃ and V ₄ , values obtained in advance by calculation from the resistance values R ₃ and R ₄ of the resistors 18 and 19 and the value of the power supply voltage V of the bridge circuit 15 may be used. Alternatively, a value actually measured at the time of strain measurement may be used. Alternatively, one of the values of the voltages V ₃ and V ₄ may be actually measured, and the other may be obtained by subtracting one of the actually measured values from the value of the power supply voltage V.

In the above-described embodiment, the strain measurement by the one-gauge three-wire method has been described as an example.
The present invention can be applied to strain measurement by the two-wire gauge method. In this case, in the bridge circuit 16 of FIG. 2, the voltage generated between the connection between the lead 3 of the strain gauge 1 and the resistor 17 and the connection between the resistors 18 and 19 is applied to the bridge circuit 16. , The strain can be measured as in the case of the 1-gauge three-wire method. However, in this case, (R
_{When the} strain ε is grasped by an operation including the term of ₀ + r) / R ₀ , the sum of the resistance values of both the lead wires 2 and 3 of the strain gauge 1 is used as the value of r. Further, in the above embodiment, the case where the strain itself of the object is measured has been described as an example. However, as is well known, σ = E · ε (E: Young Since there is a proportional relationship, the stress of the object can be measured by multiplying the strain ε (ε ₂ after the strain gauge is replaced) measured as described above by the Young's modulus E of the object.

In the above-described embodiment, the case where a single point strain measurement is performed on one part of the object has been described. However, the present invention can be applied to a case where multi-point strain measurement is performed on a plurality of parts of the object or a plurality of objects. Can be applied. In this case, the above-described processing may be performed for each measurement point.

In the above embodiment, the strain measuring device 1
0, the process of obtaining the strain ε is performed. However, if the data of the output voltage e of the bridge circuit 16 and the gauge exchange data and the like are transferred from the strain measuring device 10 to an external personal computer, those processes are performed. The processing for obtaining the strain ε from the data and the processing for analyzing it can be performed by a personal computer.

In the above embodiment, the strain gauge 1
Although the bridge circuit 16 is used as a circuit for generating a measurement signal corresponding to the resistance value of the strain gauge 1, any other type of circuit may be used as long as the circuit can generate a signal corresponding to the resistance value of the strain gauge 1. You may. That is, by grasping the resistance value of the strain gauge from the signal generated by the circuit, the strain can be grasped by the relational expression of the above equation (4).

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a strain measuring apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a circuit configuration diagram of a main part of the apparatus of FIG. 1;

FIG. 3 is a flowchart for explaining the operation of the apparatus of FIG. 1;

[Explanation of symbols]

 1a, 1b: strain gauge; 16: bridge circuit.

Claims (1)

(57) [Claims] 1. A measurement signal corresponding to the resistance value of a strain gauge is generated by a circuit including a strain gauge attached to the object so as to generate a resistance value change according to the strain of the object, and based on the measurement signal. In the strain measurement method of measuring the strain of the object, when replacing the strain gauge with a new strain gauge during the measurement, to measure the strain of the object from the start of the strain measurement after the replacement of the strain gauge a method, and strain epsilon ₁ of the object was last grasped based on the measurement signal of the circuit including the strain gauges before the exchange, it is grasped based on the measurement signal of the circuit including a strain gauge after the replacement A value ε ₂ obtained by the calculation of the following equation (1) from the strain Δε _{2 of the} object from the time of the exchange is measured as the strain ε ₂ of the object from the start of strain measurement. A strain measurement method characterized by the above-mentioned. (Equation 1)