STRAIN MEASURING SYSTEM

A strain measuring system includes a piezoelectric element and a resistor provided on an object. The system also includes a resistance detection circuit to detect a change in resistance of the resistor, and a piezoelectric effect detection circuit to detect a piezoelectric effect of the piezoelectric element. A strain calculation circuit detects a strain changing time while the strain of the object is changing using a detection result from the piezoelectric effect detection circuit, calculates a change in resistance of the resistor during the strain changing time, and calculates a degree of strain of the object using a calculation result of the change in resistance.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese patent application No. 2023-036380, filed on Mar. 9, 2023, which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a strain measuring system for measuring strain of an object.

As for a strain gauge to measure strain of the object to be measured, those using an electrical resistance method is widely used which detects strain from a change in resistance accompanying a deformation of resistor. However, a resistance of resistor changes not only due to strain but also due to temperature. Thus, in order to accurately detect strain using such strain gauge, it is necessary to remove a resistance change component caused specifically by strain from an overall change in resistance.

For example, regarding a strain detection sensor of a conventional electrical resistance type, there is a method of detecting strain of the object by adding a resistor for temperature change detection in addition to a resistor for strain detection which is not affected by strain of the object in order to remove the effect of the temperature change calculated from an output of the temperature detection resistor.[Patent Document 1] JP Patent Application Laid Open No. 2000-111368

SUMMARY

Regarding a conventional strain detection system, there is a possibility of a detection error, since resistance may change due to factors other than strain of the object and an atmosphere temperature change, such as self-heating of the resistor, a change in resistance over time, and so on. Also, regarding the conventional strain detection sensor, power consumption becomes larger in order to detect both resistance of a strain detection resistor and resistance of a temperature detection resistor.

Thus, it is desirable to provide a strain detection system capable of effectively detecting a resistance change caused by strain and also capable of suppressing a power consumption.

Accordingly, in an exemplary aspect, the strain measuring system according to the present disclosure, includes a piezoelectric element and a resistor provided on an object. The system also includes a resistance detection circuit to detect a change in resistance of the resistor, and a piezoelectric effect detection circuit to detect a piezoelectric effect of the piezoelectric element. A strain calculation circuit detects a strain changing time while the strain of the object is changing using a detection result from the piezoelectric effect detection circuit, calculates a change in resistance of the resistor during the strain changing time, and calculates a degree of strain of the object using a calculation result of the change in resistance.

DETAILED DESCRIPTION

Hereinbelow, the present disclosure is described based on the exemplary embodiments shown in the figures.

First Embodiment

FIG.1is a conceptual diagram showing a schematic configuration of a strain measuring system10according to the first embodiment. As shown inFIG.1, the strain measuring system10includes a resistor22and a piezoelectric element32which are provided on an object for strain measurement90, and a detection operation unit40that includes circuitry to perform the functions described herein. The object90is an object for strain measurement using the strain measuring system10. For example, as the object90, a plate may be mentioned which may be strained depending on an angle of a robot arm, or a pressure receiving plate which may be strained depending on applied pressure. Note that, as for the object90, as long as it can be strained, shapes and materials are not particularly limited. The same applies to other embodiments as well.

The resistor22is directly or indirectly fixed on a surface of the object90using, for example, an adhesive, and the resistor22itself also deforms along with deformation of the object90. The resistor22is made of, for example, an alloy material of which the resistance (electrical resistance) changes according to the degree of strain, and functions as a so-called strain gauge. As a material of the resistor22, a Ni—Cr based alloy, a Cr—Al based alloy, a Cu—Ni based alloy, and so on may be mentioned.

The resistor22is produced, for example, by patterning a conductive thin film made by above-mentioned metals into a predetermined form. The resistor22may include elements other than Ni, Cr, Cu, and Al; and for example, the resistor22may include O and N. Also, besides Ni, Cr, Cu, and Al, the resistor22may include other metal elements and base elements.

The resistor22is electrically connected to the detection operation unit40via electrodes not shown in the figure and a wiring76. Also, the resistor22only needs to be fixed in a way that it can deform along with the deformation of the object90, and other members, for example, such as a substrate, or an adhesive layer may be placed between the resistor22and the object90. The same applies to the other embodiments as well.

Similar to the resistor22, the piezoelectric element32is fixed directly or indirectly to the surface of the object90using, for example, an adhesive, and the piezoelectric element32itself also deforms along with the deformation of the object90. The piezoelectric element32includes a piezoelectric body and electrodes holding the piezoelectric body. An electric change (a change in voltage due to surface electric charge) due to a piezoelectric effect caused together with the deformation of the piezoelectric element32(piezoelectric body) is transferred to the detection operation unit40via the circuit76connected to the electrodes of the piezoelectric element32.

A material constituting the piezoelectric body of the piezoelectric element32is not particularly limited as long as it exhibits a piezoelectric effect. For example, barium titanate (BaTiO3) and lead zirconate titanate (Pb[Zrx-1Ti1-x]O3) having a perovskite structure, quartz (SiO2), zinc oxide (ZnO), and so on may be used.

Similar to the resistor22, the piezoelectric element32only needs to be fixed in a way that it can deform along with the deformation of the object90, and other members such as a substrate, an adhesive layer, etc., may be placed between the piezoelectric element32and the object90. The same applies to the other embodiments as well.

As shown inFIG.1, the detection operation unit40includes a resistance detection unit42, a piezoelectric detection unit44, and strain calculation unit52, which may each include circuitry to perform their corresponding functions as explained in detail below. The detection operation unit40may also be configured, for example, by circuitry such as a microprocessor that carries out operations using output from the resistor22and the piezoelectric element32. The detection operation unit40is separate from the resistor22and the piezoelectric element32, and it is not directly fixed to the object90. Note that detection operation unit40may be formed integrally with the resistance detection unit42and the piezoelectric detection unit44, and it may be provided on the object90. Also, the detection operation unit40may also be configured using an analog circuit as one of ordinary skill would recognize. The same applies to the other embodiments as well.

The resistance detection unit42detects a change in resistance43of the resistor22(seeFIG.3). As described in below, the resistance43of the resistor22changes depending on the degree of strain of the resistor22, and also changes depending on the temperature of the resistor22. The detection result of resistance of the resistor22detected using the resistance detection unit42is passed to the strain calculation unit52. The resistance detection unit42is not limited to those directly detecting the resistance of the resistor22, and it may also be those detecting the change in resistance of the resistor22using voltage and current of the circuit.

The piezoelectric effect detection unit44detects a piezoelectric effect of the piezoelectric element32. For example, as shown inFIG.3, the piezoelectric effect detection unit44detects the piezoelectric effect of the piezoelectric element32using an electrical potential difference change45generated between the piezoelectric element32and the electrodes. The detection result of the piezoelectric effect detected by the piezoelectric effect detection unit44is passed to the strain calculation unit52as similar to the change in resistance43of the resistor22detected by the resistance detection unit42.

FIG.2is a conceptual diagram showing a gist of a circuit and signal processing of the strain measuring system10shown inFIG.1. As shown inFIG.2, between the piezoelectric effect detection unit44and the piezoelectric element32, a load resistor62is connected in parallel to the piezoelectric element32.

The power consumption of the detection unit for the piezoelectric effect is not particularly limited, and for example, the power consumption of the detection unit for the piezoelectric effect is preferably lower than the power consumption of the detection circuit of the resistance43including the resistance detection unit42and the resistor22; and further preferably it is lower than the power consumption of the detection circuit of the resistance43by 1/10 or lower.

The strain calculation unit52shown inFIG.1andFIG.2detects the strain changing time46which is a time when the change in strain is happening to the object90using the detection result of the piezoelectric effect detection unit44. Further, the strain calculation unit52calculates the change in resistance43of the resistor22occurring during the strain changing time46(see R2−R1 ofFIG.3). Further, the strain calculation unit52calculates the degree of strain of the object90using the calculation results of and the change in resistance43(R2−R1). Also, the strain measuring system10can export the information regarding the degree of strain of the object90which is the operation result of the strain calculation unit52.

FIG.3is a conceptual diagram explaining a first example of signal processing by the strain measuring system10shown inFIG.1andFIG.2. A graph shown inFIG.3shows, from top to bottom, a strain change of the object90, the resistance43which is the detection result from the resistance detection unit42, a temperature change of the object90, a change in electric potential45of the piezoelectric element32detected by the piezoelectric effect detection unit44, and a strain resistance change53calculated by the strain calculation unit52. Note that, inFIG.3, the strain change of object90and the temperature change of the object90are controlled values or theoretical values; however, on the other hand, the resistance43, the change in electric potential difference45of the piezoelectric element32, and the strain resistance change53are detected values or calculated values obtained using the strain measuring system10. The same applies to the other embodiments.

As can be understood by comparing strain change, a change in resistance detected by the resistance detection unit42, and the temperature change shown inFIG.3, the change in resistance43occurs not only by the strain change of the object90(the change in resistance can be observed between the time t3 and the time t4) but also by the temperature change of the object90(the change in resistance can be observed between the time t1 and the time t2). Also, the resistance43detected by the resistance detection unit42changes depending on factors other than physical quantities of the object90such as self-heating, deterioration over time, and so on (such change can be observed around the time t5.

For the strain measuring system10, in order to accurately calculate the degree of strain of the object90, among the change in resistance43detected by the resistance detection unit42, it is necessary to remove the change in resistance43which is not caused by strain of the object90. Thus, using the detection result of the piezoelectric effect detection unit44, the strain calculation unit52of the strain measuring system10detects from the detection results of the strain changing time46which is a period of time when strain of the object90is changing. In the example shown inFIG.3, a time range between the time t3 which is the starting point that the electric potential of the piezoelectric element32starts to change and the time t4 which is the end point of the change in the electrical potential of the piezoelectric element32is detected by the strain calculation unit52as the strain changing time46.

Next, the strain calculation unit52calculates the change in resistance43of the resistor22during the strain changing time46using the output of the resistance detection unit42. In the example shown inFIG.3, the difference between R2 and R1 (R2−R1) is calculated by the strain calculation unit52as the change in resistance43of the resistor22during the strain changing time46, in which R2 is the resistance43at the time t4 that is the end point of the strain changing time46and R1 is the resistance43at the time t3 that is the starting point of the straining changing time46.

As such, the strain calculation unit52of the strain measuring system10can accurately calculate the degree of strain of the object90by removing the change in resistance43which is not derived from strain of the object90from the change in the resistances43detected by the resistance detection unit42. That is, as shown inFIG.3, in the strain calculation unit10, the change in resistance detected by the detection of the piezoelectric effect during other than strain changing time46(such as the change in the resistance observed between the time t1 and the time t2, and at time t5) is not included in the calculation for the degree of strain of the object90.

InFIG.3, the detection of strain using the strain measuring system10is explained using a simple example. However, the strain measuring system10can carry out complicated and long period of strain detection.FIG.5is a conceptual diagram showing a second example of signal processing using the strain measuring system10shown inFIG.1andFIG.2.

Similar toFIG.3,FIG.5shows, from top to bottom, a strain change of the object90, the resistance43which is the detection result by the resistance detection unit42, a temperature change of the object90, a change in electric potential45of the piezoelectric element32detected by the piezoelectric effect detection unit44, and a strain resistance change53calculated by the strain calculation unit52.

The example shown inFIG.5is an example assuming that two step deformations shown inFIG.4have occurred to the object90. That is, the first deformation (shown in the second figure from the top ofFIG.4) occurs between the time t6 and the time t7 (a strain changing time46a) shown inFIG.5, and the second deformation (the third figure from the top ofFIG.4) occurs between the time t8 and the time t9 (a strain changing time46b). Also, as it is shown in a graph of temperature change ofFIG.5, the example shown inFIG.5assumes that the temperature of the object90gradually decreases.

Even in the case that the temperature change occurs to the object90between the strain changing time46aand the strain changing time46b(between the time t7 and the time t8) as shown inFIG.5, the strain measuring system10shown inFIG.1andFIG.2can accurately calculate the degree of strain of the object90. That is, as shown inFIG.5, using the detection results of the piezoelectric effect detection unit44, the strain calculation unit52of the strain measuring system10detects the strain changing times46aand46b, which are times that the change in strains of the object90occur.

Next, the strain calculation unit52uses output of the resistance detection unit42to calculate the change in resistance43of the resistor22during the strain changing times46aand46b. In the example shown inFIG.5, the strain calculation unit52calculates R2−R1, as a change in resistance43of the resistor22during the strain changing time46a, which is a difference between the resistance43(R2) at the time t7 that is the end point of the strain changing time46aand the resistance43(R1) at the time t6 that is the starting point of the strain changing time46a. Also, at the same time, the strain calculation unit52calculates R4−R3, as a change in resistance43of the resistor22during the strain changing times46b, which is a difference between the resistance43(R3 and R4) of before and after the strain changing time46b.

Further, the strain calculation unit52uses R2−R1 and R4−R3 which are the calculated values of the changes in resistance43of the resistor22during the strain changing times46aand46bto calculate the degree of strain of the object90. For example, an initial value R0 of the resistance43is added to R2−R1 which is the calculated value of the change in resistance43during the strain changing time46a; and the added value is considered as the strain resistance change53(R′) which is a change in resistance corresponding to the degree of strain of the object90shown in the second figure from the top ofFIG.4. The strain resistance change53is multiplied by a constant of proportionality and the obtained value can be considered as a degree of strain of the object90shown in the second figure from the top shown inFIG.4. Similarly, the strain calculation unit52calculates a strain resistance change53(R″) corresponding to the degree of strain of the object90shown in the third figure from the top shown inFIG.4, and the degree of strain of the object90shown in the third figure from the top shown inFIG.4can be calculated.

Note that the example shown inFIG.5shows that in order to increase the accuracy of the strain measurement, the strain changing times46aand46bpreferably occur within a short period of time. In other words, a strain rate of the object90is preferably 1×10−2(s−1) or faster. As such, the strain measuring system10according to the first embodiment effectively detects the resistance change caused by the strain of resistor22; and even in the case that temperature change, a self-heating of the resistor22, or so is expected to occur, the strain of the object90can be measured accurately.

Also, the power consumption at the circuit for detecting the piezoelectric effect of the piezoelectric element32used in the strain measuring system10can be smaller compared to the power consumption at the resistance detection circuit for temperature correction which is used in a conventional technology. Further, the temperature difference detected by a conventional resistor for temperature detection and the temperature detected by the resistor22for strain detection becomes a problem; however, the strain measuring system10can avoid such problem.

Second Embodiment

FIG.6is a conceptual diagram showing a schematic configuration of a strain measuring system110according to the second embodiment. The strain measuring system110is basically the same as the strain measuring system10shown inFIG.1andFIG.2, except that for the strain measuring system110, a rectifier164is added between the piezoelectric element32and the piezoelectric effect detection unit44. Regarding the strain measuring system110, differences between the strain measuring system10shown inFIG.1andFIG.2are mainly discussed, and for the common configurations with the strain measuring system10, the same numerical references are given and explanations of such configurations are omitted.

The rectifier164converts electrical signals from the piezoelectric element32which include both positive and negative signals into a positive signal only (or a negative signal only) and output to the piezoelectric effect detection unit44. The rectifier164is, for example, configured by a circuit including diode, and a specific configuration of the rectifier164is not particularly limited.

FIG.7is a conceptual diagram explaining one example (the third example) of signal processing carried out in the strain measuring system110shown inFIG.6.FIG.7shows, from top to bottom, a strain change of the object90, a resistance143which is the detection result detected by the resistance detection unit42, a temperature change of the object90, a change in electrical potential difference145aoccurring in the electrodes of the piezoelectric element32, a change in electrical potential difference145bdetected by the piezoelectric effect detection unit44, and a strain resistance change53detected by the strain calculation unit52.

Similar to the example 2 shown inFIG.5, the third example shown inFIG.7shows the case assuming that the two step deformations have occurred to the object90. However, unlike the second example shown inFIG.5, signs which indicate whether the strain is tensile strain or compression strain is reversed between the first deformation and the second deformation. That is, the first deformation (a strain changing time146a, tensile strain) occurs between the time t11 and the time t12 shown inFIG.7, and the second deformation occurs between the time t13 and the time t14 (a strain changing time146b, compression strain) shown inFIG.7. Note that, for the temperature change, it is the same as the example shown inFIG.5.

As can be understood from the fourth graph from the top in theFIG.7, the change in electrical potential difference145adetected by the electrodes of the piezoelectric element32has opposite signs depending on whether it is a tensile strain or a compression strain. However, in the piezoelectric effect detection unit44, it is only necessary to have information regarding the starting point and the end point of the strain changing times146aand146bduring which the object undergoes deformation. Here, in the strain measuring system110shown inFIG.6, the signals from the piezoelectric element32are rectified by the rectifier164, and the signals are transferred to the piezoelectric effect detection unit44(the change in electric potential145bdetected by the piezoelectric effect detection unit44). Thereby, the piezoelectric effect detection unit44can receive a simplified form of signal information necessary for calculating the strain changing times146aand146bduring which the strain of the object90changes.

The method for calculating the degree of strain which is carried out by the strain calculation unit52of the strain measuring system110is similar to the strain calculation unit52of the strain measuring system10. For example, in the example shown inFIG.7, the calculation result of R2−R1 which is the change in resistance143during the strain changing time146ais added to the initial resistance R0 of the resistance143, and the added value is considered as the strain resistance change53(R′) which is the change in resistance corresponding to the degree of strain of the object90after the first deformation. As such, the degree of strain of the object90after the first deformation can be calculated. Similarly, the calculation result R2−R1 which is the change in resistance143during the strain changing time146aand the calculation result R4−R3 which is the change in resistance143during the strain changing time146bare added to the initial value R0 of the resistance143in the strain calculation unit52, and the added value is considered as the strain resistance change53(R″) which is the change in resistance corresponding to the degree of strain of the object90after the second deformation. As such, the degree of strain of the object90after the second deformation can be calculated.

In such strain measuring system110, the signals rectified by the rectifier164are input to the piezoelectric effect detection unit44, hence, the circuit configuration, signal processing, and so on of the piezoelectric effect detection unit44and the strain calculation unit52in the detection operation unit40can be further simplified. Also, regarding the configurations which are the same as the strain measuring system10, the strain measuring system110exhibits the same effects as the strain measuring system10.

Third Embodiment

FIG.8is a conceptual diagram showing a schematic configuration of a strain measuring system210according to the third embodiment. The strain measuring system210is basically the same as the strain measuring system10shown inFIG.1andFIG.2, except that an amplifier266is added between the piezoelectric element32and the piezoelectric effect detection unit44. Regarding the strain measuring system210, differences between the strain measuring system10shown inFIG.1andFIG.2are mainly discussed, and for the common configurations with the strain measuring system10, the same numerical references are given, and explanations of such configurations are omitted.

The amplifier266amplifies the electrical signals output from the piezoelectric element32, and the amplified electrical signals are output to the piezoelectric effect detection unit44. The amplifier266is, for example, configured by a voltage amplifier including an operational amplifier and so on, and a specific configuration of the amplifier266is not particularly limited.

FIG.9is a conceptual diagram explaining an example (the fourth example) of signal processing carried out by the strain measuring system210shown inFIG.8.FIG.9shows from top to bottom, a strain change of the object90, the resistance43which is the detection result detected by the resistance detection unit42, a temperature change of the object90, a change in electrical potential difference245aoccurring in the electrodes of the piezoelectric element32, a change in electrical potential difference245bdetected by the piezoelectric effect detection unit44, and a strain resistance change53detected by the strain calculation unit52.

Similar to the example shown inFIG.5, the example shown inFIG.9also shows the case assuming that the two step deformations have occurred to the object90while the object90undergoes temperature changes.

As can be understood from the fourth graph from the top shown inFIG.9, the change in electrical potential difference245aoccurring in the electrodes of the piezoelectric element32is influenced by the degree of strain of the object90, the size of the piezoelectric element32, and so on. For example, when the degree of strain of the object90is small, the change in electrical potential difference245aoccurring in the electrodes of the piezoelectric element32is small, hence, the detection accuracy of the strain changing time detected by the piezoelectric effect detection unit44may decline.

Thus, in the strain measuring system210shown inFIG.8, the amplifier266amplifies the change in electrical potential difference245aoccurring in the electrodes of the piezoelectric element32, and the amplified signal is output to the piezoelectric effect detection unit44. Thereby, as shown in the fifth graph from the top shown inFIG.9, the change in electrical potential difference245bdetected by the piezoelectric effect detection unit44shows sharp rise and sharp drop, and the detection accuracy of the strain changing times46aand46bdetected by the piezoelectric effect detection unit44can be enhanced.

As shown inFIG.9, the shapes of sharp signal and sharp drop of signals showing the strain changing times46aand46bwhich are input to the piezoelectric effect detection unit44are preferably closer to a square shape compared to the shapes of signals of the change in electrical potential difference245aoccurring in the electrodes of the piezoelectric element32. Such strain measuring system210can enhance the detection accuracy of the strain changing times46aand46b, and the strain of the object90can be measured accurately.

Fourth Embodiment

FIG.10is a conceptual diagram showing a schematic configuration of a circuit and signal processing of a strain measuring system310according to the fourth embodiment. The strain measuring system310is basically the same as the strain measuring system10shown inFIG.1andFIG.2, except that a detection operation unit340of the strain measuring system310includes circuitry, such as a temperature change calculation unit372and a strain calculation unit352of the strain measuring system310includes circuitry, such as a sensitivity correction unit355. Of course, one of ordinary skill will recognize that the temperature change calculation unit372, the strain calculation unit352, and the sensitivity correction unit355all include circuitry to perform their respective functions as described herein. Regarding the strain measuring system310, differences between the strain measuring system10shown inFIG.1andFIG.2are mainly discussed, and for the common configurations with the strain measuring system10, the same numerical references are given, and explanations of such configurations are omitted.

The temperature change calculation unit372shown inFIG.10detects, using the detection result from the piezoelectric effect detection unit, a strain non-changing time which is a period of time when there is no change in strain of the object90, calculates the change in resistance of the resistor22of the strain non-changing time, and calculates a temperature change of the resistor22.

FIG.11is a conceptual diagram explaining the fifth example of signal processing carried out by the strain measuring system310shown inFIG.10. Similar toFIG.3,FIG.10shows from top to bottom, a strain change of the object90, resistance343which is the detection result detected by the resistance detection unit42, a temperature change of the object90, a change in electrical potential difference45of the piezoelectric element32detected by the piezoelectric effect detection unit44, a strain resistance change353calculated by the strain calculation unit352, and a non-strain resistance change356calculated by the temperature change calculation unit372.

Similar to the strain calculation unit52shown inFIG.2, the strain calculation unit352of the strain measuring system310detects, using the detection results of the piezoelectric effect detection unit44, the strain changing time46which is a period of time when strain of the object90changes. Further, similar to the strain calculation unit52shown inFIG.2, the strain calculation unit352calculates, using the output value (the resistance343) of the resistance detection unit42, the strain resistance change353(the fifth graph from the top inFIG.11) which is a cumulative value of a change in resistance343of the resistor22during the strain changing time46. In the example shown inFIG.11, the strain calculation unit352calculates R2−R1 which is the difference between the resistance343(R2) at the end point of the strain changing time46and the resistance343(R1) at the starting point of the strain changing time46as the change in resistance343of the resistor22during the strain changing time46. Then, the calculated value is added to R0 which is the initial resistance343detected by the resistance detection unit42. As such, the strain calculation unit352calculates the strain resistance change353which is the change in resistance343of the resistor22during the strain changing time46.

The temperature change calculation unit372of the strain measuring system310detects, using the detection results from the piezoelectric effect detection unit44, strain non-changing times347aand347bwhich are when there is no change in strain of the object90. For example, as shown in the fourth graph from the top inFIG.11, the temperature change calculation unit372detects the state where there is no change in electrical potential difference of the electrodes of the piezoelectric element32detected by the piezoelectric effect detection unit44as the strain non-changing times347aand347b. Also, the temperature change calculation unit372may detect a period of time other than the strain changing time46as the strain non-changing times347aand347b.

Further, the temperature change calculation unit372calculates the change in resistance343of the resistor22during the strain non-changing times347aand347busing the output from the resistance detection unit42. In the example shown inFIG.11, the temperature changing calculation unit372calculates R1−R0, which is the difference between the resistance343(R1) at the end point of the strain non-changing time347aand the resistance343(R0) at the starting point of the strain non-changing time347a, as the change in resistance343of the resistor22during the strain non-changing time347a. Similarly, the temperature change calculation unit372calculates R3−R2 which is the difference between the resistance343(R3) at the end point of the strain non-changing time347band the resistance343(R2) at the start point of the strain non-changing time347b, and the calculated value is considered as the change in resistance343of the resistor22during the strain non-changing time347b. Further, the temperature change calculation unit372calculates the non-strain resistance change356which is a cumulative value of the change in resistance343of the resistor22during the strain non-changing times347aand347b.

Also, the temperature change calculation unit372detects the temperature of the resistor22and the temperature of the object90to which and the resistor22are fixed, using the non-strain resistance change356which is the calculation result of the cumulative value of the change in resistance343of the resistor22during the strain non-changing times347aand347b. For example, in the temperature calculation unit372, the non-strain resistance change356is multiplied by the predetermined constant of proportionality and the obtained value is calculated as the temperature of the resistor22, and then the calculation result can be output to outside.

Also, as shown inFIG.10, the temperature change calculation unit372may output the temperature information of the resistor22, which is the calculation result, to the strain calculation unit352. For example, the strain calculation unit352includes the sensitivity correction unit355, and the sensitivity correction unit355can correct the constant of proportionality used for calculating the strain based on the temperature information of the resistor22input to the strain calculation unit352. For example, in the strain calculation unit352of the strain measuring system310, the strain resistance change353calculated as shown in the fifth graph from the top inFIG.11is multiplied by the constant of proportionality which has been temperature corrected in the sensitivity correction unit355based on the temperature information of the resistor22calculated by the temperature change calculation unit372. The obtained value is the degree of strain of the object90.

The strain measuring system310shown inFIG.10andFIG.11includes the temperature change calculation unit372detecting the temperatures of the resistors22and the object90using the detection results of the piezoelectric element32and the resistor22. Such strain measuring system310can detect both strain and temperature with smaller power consumption compared to a conventional method of measuring the temperature using a resistor provided separately from the resistor22for strain detection. Also, such strain measuring system310detects both strain and temperature based on the change in resistance343detected by the resistor22and the resistance detection unit42. Hence, for the strain measuring system310, the measured temperatures do not vary depending on the place of the resistor, which is the case for the conventional technology detecting strain and temperature using separate resistors. Therefore, the strain calculation unit352of the strain measuring system310can accurately carry out temperature correction while calculating the strain of the object90.

The strain measuring system310exhibits the same effects as the strain measuring system10regarding the common configurations with the strain measuring system10.

Fifth Embodiment

FIG.12AandFIG.12Bare conceptual diagrams showing schematic configurations of a strain measuring system according to the fifth embodiment. The strain measuring system410is basically the same as the strain measuring system10shown inFIG.1andFIG.2, except that the arrangements of a resistor422and a piezoelectric element432with respect to an object to be measured490are different. Regarding the strain measuring system410, differences between the strain measuring system10shown inFIG.1andFIG.2are mainly discussed, and for the common configurations with the strain measuring system10, the same numerical references are given, and explanations of such configurations are omitted.

FIG.12Ais a plan view of the strain measuring system410, andFIG.12Bis a cross sectional diagram of the strain measuring system410. As shown inFIG.1, in the strain measuring system10, the resistor22and the piezoelectric element32are aligned on one plane of the object90for strain measurement. This arrangement of the resistor22and the piezoelectric element32as shown inFIG.1is not a problem when the object90is strained roughly uniformly. However, when strain of the object90differs between the position where the resistor22is arranged and the position where the piezoelectric element32is arranged, then the error included in the calculated value of strain may increase.

Therefore, in the strain measuring system410shown inFIG.12AandFIG.12B, the resistor422, the piezoelectric element432, and the object490are at least partially overlapped with each other along a first direction D1 which is the predetermined direction. That is, as shown inFIG.12B, in the strain measuring system410, the piezoelectric element432is fixed on one plane490aof the object490, and the resistor422is fixed on the piezoelectric element432; thus, the resistor422, the piezoelectric element432, and the object490are overlapped with each other along the first direction D1.

As shown inFIG.12B, the piezoelectric element432includes a lower electrode436fixed on one plane490aof the object490, a piezoelectric body434stacked on the lower electrode436, and an upper electrode438stacked on the piezoelectric body434. The piezoelectric body434is placed between the lower electrode436and the upper electrode438.

The resistor422is fixed on the piezoelectric element432via a resistor base part424. The resistor base part424is configured using, for example, a thin insulation layer. A method for fixing the resistor422, the resistor base part424, and the piezoelectric element432is not particularly limited; and for example, methods such as adhesion, physical suction, chemical suction, welding, and so on may be mentioned.

As shown inFIG.12AandFIG.12B, the strain measuring system410has a structure that the resistor422, the piezoelectric element432, and the object490are stacked along the direction D1 which is a stacking direction; thus, the resistor422and the piezoelectric element432are arranged roughly at the same position of the object490in the plan view direction.

Therefore, in the strain measuring system410, the period of time while the change in resistance43of the resistor422occurs due to the strain change shown inFIG.3can be detected using the piezoelectric element432with high accuracy as the strain changing time46. Thereby, a highly accurate strain measurement can be achieved. Also, even in the case that strain of the object490is not uniform, the resistor422and the piezoelectric element432detect the temperature change and the change in resistance43of the same place of the object490; thus, at such place of the object490, a highly accurate strain measurement can be achieved.

Also, in the strain measuring system410, the resistor422and the piezoelectric element432can be arranged on a small area of the object490; thus, this is advantageous from the point of achieving compact strain measuring system, and suited for the strain measurement of a small object490. Further, regarding the same configurations as the strain measuring system10, the strain measuring system410exhibits the same effects.

Sixth Embodiment

FIG.13AandFIG.13Bare conceptual diagrams showing the schematic configurations of a strain measuring system510according to the sixth embodiment. The strain measuring system510is basically the same as the strain measuring system410shown inFIG.12AandFIG.12B, except that the arrangement of the resistor422and the piezoelectric element432against the object490is different. Regarding the strain measuring system510, differences between the strain measuring system410shown inFIG.12AandFIG.12Bare mainly discussed, and for the common configurations with the strain measuring system410, the same numerical references are given, and explanations of such configurations will be omitted.

FIG.13Ais a plan view of the strain measuring system510, andFIG.13Bis a cross sectional diagram of the strain measuring system510. As shown inFIG.13B, in the strain measuring system510, the resistor422is fixed via the resistor base part424on one plane490aof the object490, and the piezoelectric element432is fixed on the other plane490bwhich is the opposite plane of the plane490aof the object490. Thereby, similar to the strain measuring system410, in the strain measuring system510, the resistor422, the piezoelectric element432, and the object490are stacked along the direction D1 which is a thickness direction. Hence, the resistor422and the piezoelectric element432are arranged on roughly the same position of the object490in the plan direction.

Therefore, similar to the strain measuring system410, in the strain measuring system510, the period of time when resistance of the resistor422is changing due to a predetermined strain change is accurately detected as the strain changing time46using the piezoelectric element432; thus, a highly accurate strain detection is achieved. Also, in the strain detection system510, a piezoelectric element432is not arranged between the resistor422and the object490, and the resistor422is not arranged between the piezoelectric element432and the object490. Thus, deformation stress due to strain of the object490and heat of the object490are transferred even more directly to the piezoelectric element490and the resistor422. Therefore, in the strain measuring system510, strain of the object490can be detected even more accurately. Also, even in the case of the strain measuring system510, the resistor422and the piezoelectric element432detect the change in resistance43and the temperature change of the same place of the object490; thus, at such place of the object490, a highly accurate strain measurement can be achieved.

Further, for the common configurations with the strain measuring system410, the strain measuring system510exhibits the same effects as the strain measuring system410.

Seventh Embodiment

FIG.14is a conceptual diagram showing a schematic configuration of a strain measuring system610according to the seventh embodiment. As shown inFIG.14, the strain measuring system610differs from the strain measuring system10shown inFIG.1that the strain measuring system610includes a bridge circuit620including a resistor622, and a resistance detection unit642, which includes circuitry, detects the change in resistance of the resistor622by measuring the output of the bridge circuit620(see voltage643ofFIG.16). However, the strain measuring system610shown inFIG.14is basically the same as the strain measuring system10shown inFIG.1, except that the configurations of the bridge circuit620and the resistance detection unit642of the strain measuring system610differ from those of strain measuring system10. Regarding the strain measuring system610, differences between the strain measuring system10shown inFIG.1are mainly discussed, and for the common configurations with the strain measuring system10, the same numerical references are given, and explanations of such configurations are omitted.

FIG.15is a conceptual diagram showing a schematic configuration of a circuit and signal processing of the strain measuring system610shown inFIG.14. As shown inFIG.15, in addition to the resistor622provided on the object90, the bridge circuit620includes bridge resistors621a,621b, and621cwhich are other resistors configuring the bridge circuit620; and the resistor622and the bridge resistors621a,621b, and621cconfigure a Wheatstone bridge. Similar to the resistor22shown inFIG.2, the resistor622also deforms along with the deformation of the object90, and the resistance changes in accordance with the deformation. Materials, methods, and so on for producing the resistor622are the same as the resistor22shown inFIG.2.

The bridge resistances621a,621b, and621cshown inFIG.15are different from the resistor622, and these do not generate the change in resistance depending on the shape of the object90. Power voltage Vdd is applied from a power supplying unit, or power supply circuit, not shown in the figure, to the bridge circuit620. The output of the bridge circuit620is passed to the resistance detection unit642of the detection operation unit640. The resistance detection unit642detects the change in resistance of the resistor622by measuring the voltage643(seeFIG.16) which is the output of the bridge circuit620. Note that, regarding the bridge circuit620shown inFIG.15, only the resistor622which is one of the resistors configuring the bridge circuit620generates the change in resistance along with the deformation of the object90. However, the bridge circuit620is not limited to this, and it may have a plurality of resistors which generates the change in resistance along with the deformation of the object90.

FIG.16is a conceptual diagram explaining the sixth example of signal processing of the strain measuring system610shown inFIG.14andFIG.15.FIG.16shows from top to bottom, a strain change of the object90, the voltage643which is the output of the bridge circuit620detected by the resistance detection unit642, a temperature change of the object90, a change in electrical potential difference45of the electrodes of the piezoelectric element32detected by the piezoelectric effect detection unit44, and a strain resistance change653which is calculated by the strain calculation unit52. Note that, inFIG.16, the strain change of the object90and the temperature change of the object90are controlled values or theoretical values, and the voltage643of the bridge circuit, the change in electrical potential difference45of the piezoelectric element32, and the strain resistance change653are the detected values or the calculated values obtained in the strain measuring system610.

As shown inFIG.16, in the strain calculation unit52of the strain measuring system610, the strain changing time46, which is a period of time when strain of the object90changes, is detected using the detection result of the piezoelectric effect detection unit44. Next, using the detection result of the resistance detection unit642, the strain calculation unit52calculates the change in resistance of the resistor622which appears as the output of the bridge circuit620during the strain changing time46. In the example shown inFIG.16, the strain calculation unit52calculates V2−V1, which is the difference between the detected value of the resistance detection unit642at the time t4 that is the end point of the strain changing time46and the detected value of the resistance detection unit642at the time t3 that is the starting point of the strain changing time46, as the information corresponding to the change in resistance (strain resistance change653) of the resistor22during the strain changing time46.

Further, the strain calculation unit52calculates the degree of strain of the object90using V2−V1 which is the change in output of the bridge circuit620corresponding to the change in resistance of the resistor22. For example, in the strain calculation unit52, the initial output V0 of the bridge circuit620is added to V2−V1 which is the calculated value of the change in output643during the strain changing time46, and the added value is considered as the information corresponding to the degree of strain of the object90at the time t4. The strain resistance change653is multiplied by the predetermined constant of proportionality, thereby the degree of strain of the object90at the time t4 can be obtained.

Such strain measuring system610detects the change in resistance of the resistor622using the bridge circuit620, and together with the detection result of the strain changing time46using the piezoelectric element32, a highly sensitive and a highly accurate strain detection can be achieved. Furthermore, for the common configurations with the strain measuring system10, the strain measuring system610exhibits the same effects as those of the strain measuring system10.

Eighth Embodiment

FIG.17is a conceptual diagram showing schematic configurations of the strain measuring system710according to the eighth embodiment. As shown inFIG.17, the strain measuring system710is basically the same as the strain measuring system610shown inFIG.14, except that the strain measuring system710has a differential amplifier774arranged between the resistance detection unit642and the bridge circuit620including the resistor622. Regarding the strain measuring system710, differences between the strain measuring system610shown inFIG.14andFIG.15are mainly discussed, and for the common configurations with the strain measuring system610, the same numerical references are given, and explanations of such configurations are omitted.

FIG.18is a conceptual diagram showing a schematic configuration of a circuit and signal processing of strain measuring system710shown inFIG.17. As shown inFIG.18, the strain measuring system710includes the differential amplifier774which amplifies the output of the bridge circuit620. The resistance detection unit642detects the change in resistance of the resistor622by measuring the output of the bridge circuit which has been amplified by the differential amplifier774. Regarding the bridge circuit620, the resistance detection unit642, the strain calculation unit52, and so on included in the strain measuring system710, these are the same as the bridge circuit620, the resistance detection unit642, the strain calculation unit52, and so on included in the strain measuring system610shown inFIG.14andFIG.15.

The differential amplifier774amplifies the output of the bridge circuit620which detects the change in resistance of the resistor622and passes the amplified output to the resistance detection unit642; thus, a highly sensitive and a highly accurate strain detection can be achieved. Regarding the conventional circuit which amplifies the output of the bridge circuit620by the differential amplifier774, there is a risk that error may occur due to drift of the differential amplifier774during the calculation of strain using the strain calculation unit52. However, the strain measuring system710uses the bridge circuit620and the differential amplifier774together with the detection result of the strain changing time46using the piezoelectric element32; thereby, it is possible to exclude the influence of drift of the differential amplifier774occurring at the period of time other than the strain changing time46.

Besides this, regarding the common configurations between the strain measuring system710and the strain measuring system610, the strain measuring system710exhibits the same effects as the strain measuring system610.

Hereinabove, the strain measuring system according to the present disclosure was described using the embodiments. However, the technical scope of the strain measuring system according to the present disclosure is not limited to the above-mentioned embodiments, and many other embodiments and modification examples are included. For example, the arrangement of the resistor22and the piezoelectric element32with respect to the object90is not limited to the arrangement described in the above-mentioned embodiments; and as in the case of a strain measuring system810according to the modification examples shown inFIG.19, the direction of arrangement of the resistor22and the piezoelectric element32may match a longitudinal direction of the resistor22and the piezoelectric element32. A longitudinal direction of the resistor22and a longitudinal direction of the piezoelectric element32may align with a longitudinal direction of the object90, or may not align therewith. A central axis of the resistor22along the longitudinal direction of the resistor22, a central axis of the piezoelectric element32along the longitudinal direction of the piezoelectric element32, and a central axis of the object90along the longitudinal direction of the object90may overlap, or may not overlap.

Also, regarding the configurations of the circuit and the control block for achieving the strain measuring system, those shown inFIG.2,FIG.10,FIG.15,FIG.18, and so on are simply examples, and various modifications, additions, removals, and so on may be carried out to the circuit configurations shown in the examples without departing from the scope of the present disclosure. The strain measuring system achieved using such circuits is also included in the technical scope of the strain measuring system according to the present disclosure.

As can be understood from the above, the present specification discloses the below.

Supplementary note 1

A strain measuring system, comprising:a piezoelectric element and a resistor provided on an object;a resistance detection circuit configured to detect a change in resistance of the resistor;a piezoelectric effect detection circuit configured to detect a piezoelectric effect of the piezoelectric element; anda strain calculation circuit configured to detect a strain changing time while the strain of the object is changing using a detection result from the piezoelectric effect detection circuit, calculate a change in resistance of the resistor during the strain changing time, and calculate a degree of strain of the object using a calculation result of the change in resistance.

Such strain measuring system detects the strain changing time by detecting the piezoelectric effect of the piezoelectric element, and calculates the change in resistance of the resistor during the strain changing time; thus, unless the strain rate is extremely slow than expected, the resistance change of the resistor can be effectively detected. Also, the power consumption for detecting the piezoelectric effect of the piezoelectric element is smaller than the power consumption for detecting the resistance of the resistor, thus such strain measuring system can reduce the power consumption.

Supplementary note 2

The strain measuring system according to the present disclosure further comprises a temperature change calculation circuit configured to calculate a strain non-changing time which is a period of time when no change occurs in the strain of the object using the detection result from the piezoelectric effect detection circuit, calculate a change in the resistance of the resistor during the strain non-changing time, and calculate a temperature change of the resistor.

Such strain measuring system can detect a change in the environmental temperature. Also, using the detected value of the calculated temperature change, it is possible to accurately carry out sensitivity correction between the change in resistance and strain. Hence, strain can be accurately measured in a wide temperature range. Also, since the strain non-changing time is detected using the detection result of the piezoelectric effect detection circuit, such strain measuring system can reduce the power consumption compared to those detecting the temperature using the change in resistance.

Supplementary Note 3

The resistor, the piezoelectric element, and the object are at least partially overlapped with each other along a predetermined direction.

In such strain detection system, the resistor and the piezoelectric element can be arranged close to each other; thus, this can effectively prevent the problem that the detection result of the strain changing time from the piezoelectric element not accurately matching the time when strain is actually changing in the resistor. Also, such strain measuring system is advantageous from the point of achieving compact device.

Supplementary Note 4

The strain measuring system according to the present disclosure further comprises a bridge circuit including the resistor; and the resistance detection circuit detects the change in resistance of the resistor by measuring output of the bridge circuit.

Such strain measuring system achieves a highly sensitive and a highly accurate strain detection.

Supplementary Note 5

The strain measuring system according to the present disclosure further comprises a bridge circuit including the resistor and an amplifier amplifying an output of the bridge circuit; and the resistance detection unit detects the change in resistance of the resistor by measuring the output of the bridge circuit amplified by the amplifier.

Such strain measuring system achieves a highly sensitive and a highly accurate strain detection. Also, the strain calculation unit calculates the degree of strain of the object by using the change in resistance of the resistor during the strain changing time; thus, it is unlikely to be influenced by drift of an amplifier. Therefore, a highly accurate strain measurement is possible.

Circuit Example

The strain measuring system according to the present disclosure can be realized by using circuits shown inFIG.20andFIG.22, or by using computer processing based on flowcharts shown inFIG.21andFIG.23.

FIG.20shows an example of a circuit realizing the resistance detection unit, the piezoelectric effect detection unit, and the strain calculation unit according to the present disclosure.

Regarding the circuit shown inFIG.20, in a resistance detection unit740includes circuitry in which a voltage decline in a shunt resistor741connected in series with the resistor22is detected and amplified, the amplified signal by an operational amplifier742is converted into a digital signal by an Analog-to-Digital (AD) convertor743, and the converted digital signal is used for a predetermined operation in a current calculation unit744that includes circuitry to calculate a signal representing a current. Then, the signal representing the current is output to a resistance calculation unit748. Also, voltage at both sides of the resistor22is detected and amplified using an operational amplifier746, and the amplified signal is converted into a digital signal using an AD convertor747. Then, the converted digital signal is output to the resistance calculation unit748. Further, the resistance calculation unit includes circuitry with which the resistance43of the resistor22is calculated based on the signal from the current calculation unit744representing the current in the resistor22, and based on the signal from the AD convertor747representing voltage at both ends of the resistor22.

Note that, the current calculation unit744may be realized by using a microcomputer, by using a logic circuit which uses memory in ROM corresponding to an output signal from the AD convertor743and the signal representing current, or by using an operation resource of other computers and logic circuits included in the strain measuring system of the present disclosure.

Also, the resistance calculation unit748may be realized by using a microcomputer, or by using an operation resource of other computers and logic circuits included in the strain measuring system of the present disclosure may be used.

In the circuit shown inFIG.20, the piezoelectric effect detection unit44includes a comparator441. The piezoelectric effect detection unit44is connected to the piezoelectric element32via the load resistor62connected in parallel. The signal showing electrical potential difference between the electrodes of the piezoelectric element32is input to the comparator441and compared to a standard voltage, and the signal is converted into a square wave. In the signal converted into a square wave, a rising edge part shows that the object is strained, and a falling edge part shows that strain of object is released. The piezoelectric effect detection unit44outputs this square signal to the strain calculation unit52.

Note that, if sample hold circuits521and522allow, the piezoelectric effect detection unit44does not have to convert the signal representing the electrical potential difference between the electrodes of the piezoelectric element32into a square wave, and the signal representing the electrical potential difference may be simply shaped into a waveform, and the waveform-shaped signal may be output to the strain calculation unit52as a sampling trigger signal.

Regarding the circuit shown inFIG.20, the strain calculation unit52includes circuitry in which a first sample hold circuit521holds a signal which has been input from the resistance calculation unit748of the resistance detection unit740at the rising edge part of the signal input from the comparator441of the piezoelectric effect detection unit44. That is, the first sample hold circuit521holds the resistance43of the resistor22at the point when the electrical potential difference signal between the electrodes of the piezoelectric element32stands up. Also, a second sample hold circuit522holds a signal which has been input from the resistance calculation unit748of the resistance detection unit740at the time of the falling edge part of the signal input from the comparator441of the piezoelectric effect detection unit44. That is, the second sample hold circuit522holds the resistance43of the resistor22at the point when the electrical potential difference signal between the electrodes of the piezoelectric element32falls. Then, a difference between the signal held by the second sample hold circuit522and the signal held by the first sample hold circuit521is detected by an adder circuit (accumulator)523, thereby an amount of change in resistance of the resistor22is calculated.

The amount of change in resistance of the resistor22calculated by the accumulator523is added by an adder circuit (accumulator)524to a resistance change amount (a cumulative resistance change amount) up until it is read from a memory525; thereby, the cumulative resistance change amount within a measuring period is obtained as a cumulative result. The obtained cumulative resistance change is stored in the memory525as an updated cumulative resistance change amount. Then, based on this cumulative resistance change amount, the amount of strain showing the degree of strain of the object is calculated in a strain calculator526, and the calculated amount of strain is output to outside.

Note that, the strain calculator526may be realized by using a microcomputer, or by using an operation resource of other computers and logic circuits included in the strain measuring system of the present disclosure.

Also, the overall processing in the strain calculation unit52may be realized using circuits such as a microcomputer or a processing unit (PU). In such case, the processing may be carried out as shown in the flowchart ofFIG.21.

That is, first, the strain calculation unit52obtains (temporarily memorize) the resistance measurement data43of the resistor22which has been input from the resistance detection unit740(a step S11). Next, based on the signals representing the electrical potential difference between the electrodes of the piezoelectric element32which has been input from the comparator441of the piezoelectric effect detection unit44, the strain calculation unit52takes the resistance measurement data43(R1 and R2) for sampling (i.e., memorize in a readable manner) at the time when the signals stand up and falls (a step S12). Next, the strain calculation unit52calculates a difference (the resistance change amount due to strain of the resistor22) between the sampled resistance measurement data (R1) at the time when the signal stands up and the sampled resistance measurement data (R2) at the time when the signal falls (a step S13). Next, the previously memorized resistance change amount (the cumulative resistance change amount) is read from the memory, and the newly calculated resistance change amount of the difference (the resistance change amount due to strain of the resistor22) is added to the resistance change amount which has been read out, and the added resistance change amount is memorized in the memory as an updated cumulative resistance change amount (a step S14). Then, once a predetermined measuring period is completed and when requested from outside, or per predetermined period of time, the strain amount is calculated and output (a step S16) based on the new resistance change amount calculated at the step S13, the cumulative resistance change amount calculated and updated at the step S14, or the desired resistance change amount (cumulative resistance change amount) memorized in the memory.

FIG.22shows another example of circuit used in the strain measuring system according to the present disclosure; and it is a figure showing an example of circuit realizing the resistance detection unit, the piezoelectric effect detection unit, the strain calculation unit, and the temperature change calculation unit.

The circuit shown inFIG.22is basically the same as the circuit20, except that a temperature change calculation unit372and a sensitivity correction unit527are added to the circuit shown inFIG.22.

That is, the temperature change calculation unit372shown inFIG.22includes circuitry in which when the signal which has been input from the comparator441of the piezoelectric effect detection unit44is at low level, the sample holding circuit375holds the input signal from the resistance calculation unit748of the resistance detection unit740. That is, the sample hold circuit375holds the resistance of the resistor22when the object is not strained (during the strain non-changing time). Next, based on the resistance of the resistor22when the object is not strained (during the strain non-changing time), the temperature calculation unit376calculates the temperature of the resistor22(or the temperature of the object where the resistor22is fixed), and the calculated temperature is output to the sensitivity correction unit527of the strain calculation unit52. For example, in the temperature calculation unit376, the resistance of the resistor22or the change in resistance may be multiplied by the predetermined constant of proportionality, and the calculated value may be considered as the temperature of the resistor22and so on. In the sensitivity correction unit527of the strain calculation unit52, the constant of proportionality used for calculating the strain is corrected based on the input temperature information of resistor22, and the corrected constant of proportionality is output to the strain calculator526. In the strain calculator526, using the corrected constant of proportionality, the strain amount is calculated based on the input accumulated resistance change amount.

Processing carried out in the temperature change calculation unit372of the circuit shown inFIG.22and processing carried out in the strain calculation unit52may be realized by circuitry such as a microcomputer or a processing unit (PU). In such case, processing may be carried out as shown in the flowchart ofFIG.23.

The flowchart shown inFIG.23is basically the same as the flowchart shown inFIG.21, except that the flowchart ofFIG.23has additional steps S21, S22, and S15for a detection of temperature change and for a sensitivity correction based on the detected temperature change.

Regarding the processing shown in the flowchart ofFIG.22, as the processing carried out in the circuitry of the temperature change calculation unit372, first, when the signal representing the electrical potential difference between the electrodes of the piezoelectric element32which has been input from the comparator441of the piezoelectric effect detection unit44is at low level, the temperature change calculation unit372holds the signal which has been input from the resistance calculation unit748of the resistance detection unit740(a step S21). Next, based on the held resistance, that is, based on the resistance of the resistor22when the object is not strained (during the strain non-changing time), the temperature of the resistor22(or the temperature of the object where the resistor22is fixed) is calculated, and the calculated temperature signal is output to the strain calculation unit52. Then, in the strain calculation unit52, based on the input temperature information of the resistor22, the constant of proportionality used for calculating the strain is corrected (a step S15), and using the corrected constant of proportionality, the strain amount is calculated based on the input accumulated resistance change amount (a step S16).

REFERENCE SIGNS LISTS