WO2024084956A1

WO2024084956A1 - Sensor module and computation circuit

Info

Publication number: WO2024084956A1
Application number: PCT/JP2023/036041
Authority: WO
Inventors: 芽衣渡邊; 勇希橘; 尚志木原; 宏明北田
Original assignee: 株式会社村田製作所
Priority date: 2022-10-18
Filing date: 2023-10-03
Publication date: 2024-04-25

Abstract

This sensor module comprises a sensor that outputs a signal corresponding to deformation of an elastic member, and a computation circuit that receives the signal from the sensor. The computation circuit measures the length of time of a target period in which the signal strength is outside a range defined by threshold values, calculates a signal gradient on the basis of the length of at least one portion of the target period and the amount of variation in the signal in the at least one portion of the target period, and computes a stress value representing the stress applied to the elastic member on the basis of the gradient and the length of time of the target period.

Description

Sensor module and arithmetic circuit

The present invention relates to a calculation circuit that calculates a stress value that indicates the stress applied to a member, and a sensor module that includes the calculation circuit.

Patent document 1 describes a pressure distribution detection device that calculates the pressure applied to a member. The pressure distribution detection device includes a piezoelectric element and a data processing device. The data processing device calculates the pressure applied to the member based on the discharge time of the piezoelectric element.

Japanese Patent Application Laid-Open No. 1-260333

In the field of the pressure distribution detection device described in Patent Document 1, there is a demand to accurately identify the stress value that indicates the stress applied to a component.

The object of the present invention is to provide a sensor module and an arithmetic circuit that can easily and accurately identify a stress value that indicates the stress applied to a component.

The sensor module according to an embodiment of the present invention includes:
a sensor that outputs a signal corresponding to the deformation of the elastic member;
a computing circuit for receiving the signal from the sensor;
Equipped with
The arithmetic circuit includes:
measuring the length of time during a period of interest during which the strength of the signal falls outside a range defined by a threshold;
Calculating a slope of the signal based on a length of at least a portion of the time period of interest and an amount of fluctuation of the signal during at least a portion of the time period of interest;
A stress value indicating the stress applied to the elastic member is calculated based on the length of time of the target period and the inclination.

An arithmetic circuit according to an embodiment of the present invention comprises:
receiving a signal having a value that increases and then decreases over time from a sensor that outputs a signal in response to deformation of the elastic member;
A stress value is calculated that changes when the slope of the signal changes during at least a portion of the period during which the signal strength is increasing, and that changes when the length of the period from when the signal strength increases to when it decreases changes.

In the following, X and Y are parts or members of the sensor module. In this specification, "X is located above Y" means that X is located directly above Y. Therefore, when viewed in the vertical direction, X overlaps with Y. "X is located above Y" means that X is located directly above Y and that X is located diagonally above Y. Therefore, when viewed in the vertical direction, X may or may not overlap with Y. This definition also applies to directions other than the upward direction.

The sensor module or arithmetic circuit according to one embodiment of the present invention makes it easier to accurately identify the stress value that indicates the stress applied to a component.

FIG. 1 is a right-hand view of an electronic device EE equipped with a sensor module 1 according to the first embodiment. FIG. 2 is a diagram showing the elastic member 10 and the sensor 11 viewed from above. FIG. 3 is a cross-sectional view taken along line AA in FIG. FIG. 4 is a diagram showing an example of the signal Sig output from the sensor 11 when the elastic member 10 is deformed. FIG. 5 is a graph showing the relationship between the stress value applied to the elastic member 10 and the slope of the signal Sig. FIG. 6 is a flowchart showing an example of a process P executed by the arithmetic circuit 12. FIG. 7 is a diagram showing values of the signal Sig in the vicinity of time t10 shown in FIG. FIG. 8 is a graph showing the relationship between the length of the second period and the stress value. FIG. 9 is a graph showing the relationship between the length of the second period and the stress value, and is obtained by performing an experiment three times in which the elastic member 10 is pressed at different speeds. FIG. 10 is a diagram showing a case where the sensor 11 outputs a signal Sig having a value that exceeds the measurement range of the sensor 11. In FIG. FIG. 11 is a flowchart showing an example of a process Q executed by the arithmetic circuit 12a included in the sensor module 1a according to the first modification. FIG. 12 is a diagram showing a case where noise occurs in the signal Sig between time t14 and time t15. FIG. 13 is a diagram showing a sensor module 1b according to the second modification. FIG. 14 is a table Tb showing an example of the load values calculated by the arithmetic circuit 12 in the sensor module 1b.

[First embodiment]
A sensor module 1 according to a first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a right-hand view of an electronic device EE including a sensor module 1 according to the first embodiment. Fig. 2 is an upward view of an elastic member 10 and a sensor 11. Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2.

In this embodiment, the directions are defined as follows. As shown in FIG. 1, the direction in which the elastic member 10 and the sensor 11 are lined up is defined as the up-down direction. The direction in which the elastic member 10 and the sensor 11 are lined up in this order is defined as the down direction. The direction in which the sensor 11 and the elastic member 10 are lined up in this order is defined as the up-down direction. As shown in FIG. 2, the direction parallel to the direction in which the long side of the elastic member 10 extends is defined as the front-rear direction. The direction perpendicular to the up-down direction and the front-rear direction is defined as the left-right direction. However, the up-down direction, the front-rear direction, and the left-right direction are directions defined for the purpose of explanation. Therefore, the up-down direction, the front-rear direction, and the left-right direction during actual use of the sensor module 1 do not necessarily have to match the up-down direction, the front-rear direction, and the left-right direction in this embodiment. For example, the direction parallel to the direction in which the long side of the elastic member 10 extends may be defined as the left-right direction.

As shown in FIG. 1, the sensor module 1 is a module provided in an electronic device EE such as a smartphone. The sensor module 1 includes an elastic member 10, a sensor 11, and an arithmetic circuit 12.

As shown in Figs. 1 and 2, the elastic member 10 has a plate shape with long sides extending in the front-rear direction and short sides extending in the left-right direction. The elastic member 10 has elasticity. The elastic member 10 is deformed by a force applied to the elastic member 10. For example, as shown in Fig. 1, the user 200 presses the elastic member 10 downward. The elastic member 10 is deformed by the downward force applied to the elastic member 10. The elastic member 10 is a member that has components such as a touch panel, for example.

As shown in FIG. 2, the sensor 11 has a rectangular shape with long sides extending in the front-rear direction and short sides extending in the left-right direction. The length of the sensor 11 in the left-right direction is shorter than the length of the elastic member 10 in the left-right direction. The length of the sensor 11 in the front-rear direction is shorter than the length of the elastic member 10 in the front-rear direction. As shown in FIG. 3, the sensor 11 includes a piezoelectric film 111, an upper electrode 110, a lower electrode 112, and a detection circuit (not shown).

As shown in Figures 2 and 3, the piezoelectric film 111 has a sheet shape with long sides extending in the front-rear direction and short sides extending in the left-right direction. The piezoelectric film 111 has an upper principal surface SF1 and a lower principal surface SF2 aligned in the vertical direction. The upper principal surface SF1 and the lower principal surface SF2 are aligned in this order in the downward direction.

The piezoelectric film 111 generates an electric charge according to the deformation amount of the piezoelectric film 111. The polarity of the electric charge generated when the piezoelectric film 111 is stretched in the left-right direction is opposite to the polarity of the electric charge generated when the piezoelectric film 111 is stretched in the front-back direction. Specifically, the piezoelectric film 111 is a film formed from a chiral polymer. An example of a chiral polymer is polylactic acid (PLA), particularly L-type polylactic acid (PLLA). PLLA has a helical structure in the main chain. PLLA has a piezoelectricity in which the molecules are oriented by uniaxial stretching. The piezoelectric film 111 has a piezoelectric constant of d14. As shown in FIG. 2, the uniaxial stretching direction OD of the piezoelectric film 111 forms an angle of 45 with respect to the front-back direction and the left-right direction. This 45 degrees includes, for example, an angle of about 45 degrees ± 10 degrees. As a result, the piezoelectric film 111 generates an electric charge when the piezoelectric film 111 is stretched in the front-back direction or compressed in the left-right direction. For example, when the piezoelectric film 111 is stretched in the forward or backward direction, it generates a positive charge. The magnitude of the charge depends on the differential value of the deformation of the piezoelectric film 111 due to the stretching or compression.

The upper electrode 110 is a reference electrode connected to a reference potential. The upper electrode 110 is fixed to the upper principal surface SF1 by an adhesive (not shown) such as OCA (Opticaly Clear Adhesive). The upper electrode 110 covers the upper principal surface SF1.

The lower electrode 112 is a signal electrode. The lower electrode 112 is fixed to the lower principal surface SF2 with an adhesive (not shown) such as OCA. The lower electrode 112 covers the lower principal surface SF2.

The detection circuit includes a charge amplifier (not shown), an AD converter (not shown), and the like. The charge amplifier converts the charge generated by the piezoelectric film 111 into a voltage signal. The AD converter generates a digital signal by AD converting the voltage signal.

The sensor 11 outputs a signal Sig corresponding to the deformation of the elastic member 10. Specifically, the sensor 11 is provided near the center of the elastic member 10 in the front-rear and left-right directions. The sensor 11 is fixed to the lower main surface of the elastic member 10 by an adhesive (not shown). This causes the sensor 11 to deform in accordance with the deformation of the elastic member 10. The sensor 11 outputs a signal Sig corresponding to the deformation of the sensor 11.

In this embodiment, the value of the signal Sig depends on the differential value of the displacement of the sensor 11. Specifically, the piezoelectric film 111 of the sensor 11 deforms in accordance with the deformation of the elastic member 10. The magnitude of the charge generated by the piezoelectric film 111 depends on the differential value of the deformation of the piezoelectric film 111. The sensor 11 obtains the signal Sig by converting the charge generated by the piezoelectric film 111 into a digital signal. The signal Sig includes an electrical parameter that changes in response to the deformation of the elastic member 10. In this embodiment, the electrical parameter is a voltage value.

Below, an example of the signal Sig output from the sensor 11 in response to the deformation of the elastic member 10 will be described with reference to the drawings. FIG. 4 is a diagram showing an example of the signal Sig output from the sensor 11 when the elastic member 10 is deformed. The horizontal axis in FIG. 4 is time. The vertical axis in FIG. 4 is the value (intensity) of the signal Sig. In FIG. 4, the value of the signal Sig is a voltage value. In FIG. 4, time t13 is a time after time t10. Time s10 is a time after time t13. Time s11 is a time after time s10.

For example, in FIG. 4, the user 200 starts to press the front of the elastic member 10 downward at time t10. At this time, the piezoelectric film 111 is stretched in the front-rear direction. In this case, the piezoelectric film 111 outputs a positive charge. Therefore, as shown in FIG. 4, the sensor 11 outputs a signal Sig having a positive polarity with respect to the reference potential VE between time t10 and time t13. In this case, the signal Sig has an intensity (value) that increases and then decreases over time. The user 200 stops pressing the elastic member 10 downward. At this time, the extension of the piezoelectric film 111 stops. Therefore, as shown in FIG. 4, the intensity (value) of the signal Sig does not change between time t13 and time s10. Next, the user 200 removes the finger of the user 200 from the elastic member 10 at time s10. At this time, the sensor 11 tries to return to its pre-deformation shape due to the stress generated in the sensor 11. This stress causes the piezoelectric film 111 to be compressed in the front-rear direction. In this case, the piezoelectric film 111 outputs a negative charge. Therefore, as shown in FIG. 4, the sensor 11 outputs a signal Sig having a negative polarity with respect to the reference potential VE during the period from time s10 to time s11 (period PEs).

The arithmetic circuit 12 is, for example, a microcontroller including a CPU, ROM, and RAM. As shown in FIG. 1, the arithmetic circuit 12 is provided, for example, in the electronic device EE. The arithmetic circuit 12 is electrically connected to the sensor 11, for example, via a signal line (not shown). The arithmetic circuit 12 receives the signal Sig from the sensor 11. The arithmetic circuit 12 removes noise contained in the signal Sig. For example, the arithmetic circuit 12 includes a low-pass filter. The low-pass filter removes noise contained in the signal Sig. The low-pass filter is, for example, an RC circuit including a resistor and a capacitor.

The calculation circuit 12 calculates a stress value indicating the stress applied to the elastic member 10 based on the signal Sig. In this embodiment, the calculation circuit 12 calculates the stress value based on the slope of the signal Sig and the length of time during which the intensity (value) of the signal Sig is outside the range determined by the threshold (hereinafter referred to as the target period). Specifically, the calculation circuit 12 calculates the stress value based on the slope of the signal Sig and the length of time during which the intensity (value) of the signal Sig increases and decreases (hereinafter referred to as the increase/decrease period). For example, when the user 200 presses the elastic member 10, the intensity (value) of the signal Sig increases. In this case, the intensity (value) of the signal Sig exceeds an arbitrary threshold and then falls below the threshold. At this time, the increase/decrease period is the period from when the intensity (value) of the signal Sig exceeds the threshold to when it falls below the threshold. In this embodiment, the slope of the signal Sig is the value obtained by dividing the amount of signal fluctuation during at least a portion of the period during which the intensity (value) of the signal Sig is increasing (hereinafter referred to as the first period) by the length of the first period. The period of increase/decrease is, for example, from time t10 to time t13, as shown in FIG. 4.

Below, the process (hereinafter referred to as process P) in which the calculation circuit 12 calculates the stress value will be described with reference to the drawings. FIG. 5 is a graph showing the relationship between the stress value applied to the elastic member 10 and the slope of the signal Sig. FIG. 5 is a graph obtained by performing multiple experiments in which the elastic member 10 is pressed at a predetermined speed. The speed at which the elastic member 10 is pressed differs in each of the multiple experiments. The horizontal axis in FIG. 5 shows the slope of the signal Sig. The vertical axis in FIG. 5 shows the value obtained by dividing the stress value by the length of time of the increase/decrease period (hereinafter referred to as the divided value). The straight line ST1 in FIG. 5 is a regression line showing the relationship between the divided value and the slope of the signal Sig.

As shown in Figure 5, there is a correlation between the slope of the signal Sig and the division value. Specifically, as the slope of the signal Sig increases, the division value tends to increase. In other words, the division value tends to be directly proportional to the slope of the signal Sig. Therefore, the following formula 1 holds. Furthermore, from formula 1, formula 2 holds.

The coefficient is obtained by performing an experiment in which the elastic member 10 is pressed at a predetermined speed multiple times. The coefficient is the slope of the straight line ST1. As an example, the coefficient is approximately 4.7. For example, if the slope of the signal Sig is "0.002", the length of the increase/decrease period is 200 msec, and the coefficient is 4.7, the stress value is "4.7 x 0.002 x 200 ≒ 1.88 (N)" based on formula 2.

From Equation 2, the stress value is directly proportional to the slope of the signal Sig. Therefore, the stress value changes when the slope of the signal Sig changes in the first period (at least a portion of the period during which the intensity (value) of the signal Sig is increasing). Specifically, if the slope of the signal Sig increases, the stress value increases. If the slope of the signal Sig decreases, the stress value decreases.

From Equation 2, the stress value is directly proportional to the length of the increase/decrease period. Therefore, the stress value changes when the length of the increase/decrease period (the period from when the intensity (value) of the signal Sig increases to when it decreases) changes. Specifically, if the length of the increase/decrease period increases, the stress value increases. If the length of the increase/decrease period decreases, the stress value decreases.

As described above, the calculation circuit 12 can find the stress value by executing process P, which includes a process for calculating the slope of the signal Sig and a process for calculating the period of increase or decrease. The flow of process P will be described below with reference to the drawings. FIG. 6 is a flowchart showing an example of process P executed by the calculation circuit 12. FIG. 7 is a diagram showing the value of the signal Sig near time t10 shown in FIG. 4. The following describes an example in which the calculation circuit 12 executes process P based on a voltage value.

The calculation circuit 12 starts process P, for example, when the power supply of the calculation circuit 12 is turned on (FIG. 6: START).

After starting, the calculation circuit 12 calculates the reference potential VE (FIG. 6: step S10). Specifically, the calculation circuit 12 calculates a moving average of the voltage values. For example, the calculation circuit 12 calculates a moving average of the voltage values received in one second. In the example shown in FIG. 4 and FIG. 7, the calculation circuit 12 calculates the reference potential VE=1.6V.

Next, the arithmetic circuit 12 determines whether or not the intensity (value) of the signal Sig is outside the range defined by the threshold Th1. In this embodiment, the range defined by the threshold Th1 is between the reference potential VE and the threshold Th1 (see FIG. 4). The threshold Th1 is a value greater than the reference potential VE. The arithmetic circuit 12 determines whether or not the voltage value exceeds the threshold Th1 (FIG. 6: step S11). In the example shown in FIG. 4, the threshold Th1 is 1.7 V. In this case, the arithmetic circuit 12 determines whether or not the voltage value exceeds 1.7 V. For example, the ROM of the arithmetic circuit 12 stores the threshold Th1.

When the calculation circuit 12 determines that the voltage value has exceeded the threshold value Th1 (FIG. 6: step S11: Yes), it identifies the time when the voltage value exceeded the threshold value Th1 (hereinafter referred to as the second time) (FIG. 6: step S12). The second time is a time after the time when the voltage value exceeded the reference potential VE (hereinafter referred to as the first time). In the examples shown in FIGS. 4 and 7, the voltage value exceeds the threshold value Th1 at time t11. Therefore, the calculation circuit 12 identifies time t11 as the second time.

After step S12, the calculation circuit 12 calculates the slope of the signal Sig (FIG. 6: step S13). Specifically, the calculation circuit 12 calculates the slope of the signal Sig based on the length of at least a portion of the target period and the amount of fluctuation of the signal Sig during at least a portion of the target period. In this embodiment, the calculation circuit 12 calculates the slope of the signal Sig based on the length of the first period (at least a portion of the period during which the intensity (value) of the signal Sig is increasing) and the amount of fluctuation of the signal Sig during the first period. Specifically, the calculation circuit 12 calculates the slope by dividing the amount of increase in the voltage value during the first period by the length of the first period.

For example, the calculation circuit 12 records the intensity (value) of the signal Sig at times t8, t9, and t10, which are times before time t11 (second time). Time t9 is a time before time t10. Time t8 is a time before time t9. At this time, the calculation circuit 12 calculates a slope p8 of the signal Sig by dividing the increase in the signal Sig from time t8 to time t11 by the length of time between time t8 and time t11. Similarly, the calculation circuit 12 calculates a slope p9 by dividing the increase in the signal Sig from time t9 to time t11 by the length of time between time t9 and time t11. The calculation circuit 12 calculates a slope p10 by dividing the increase in the signal Sig from time t10 to time t11 by the length of time between time t10 and time t11.

The calculation circuit 12 selects the slope having the largest value among the slopes p8, p9, and p10 as the slope of the signal Sig. In the example shown in FIG. 7, the calculation circuit 12 selects the slope p10 as the slope of the signal Sig. In this case, as shown in FIG. 7, the first period is the period PE1 between time t10 (first time) and time t11 (second time). For example, in the example shown in FIG. 7, the increase in the voltage value in the period PE1 is 0.1 V. For example, the length of the period PE1 is 100 msec. In this case, the calculation circuit 12 calculates the slope to be "0.001".

After step S13, the calculation circuit 12 measures the length of the target period. In this embodiment, the calculation circuit 12 measures the length of the increase/decrease period (the length of time from when the intensity (value) of the signal Sig increases to when it decreases). In this embodiment, the calculation circuit 12 measures the length of the period from when the voltage value exceeds the threshold value Th1 to when it falls below the threshold value Th1 (hereinafter referred to as the second period) (FIG. 6: step S14). In the example shown in FIG. 4, the voltage value falls below the threshold value Th1 at time t12 (third time). Time t12 (third time) is a time after time t11 (second time). In this case, the second period is the period PEt between time t11 and time t12 (see FIG. 4). The calculation circuit 12 obtains the length of the period PEt as the length of the second period.

After step S14, the calculation circuit 12 calculates the stress value based on the formula 2 (FIG. 6: step S15). Specifically, the calculation circuit 12 calculates the stress value based on the length of the target period and the slope of the signal Sig. In this embodiment, the calculation circuit 12 calculates an integrated value by multiplying the slope of the signal Sig by the length of the period PEt (the length of the second period). The calculation circuit 12 calculates the stress value based on the integrated value. More specifically, the calculation circuit 12 calculates the stress value by multiplying the integrated value by a coefficient based on the formula 2. For example, if the slope is "0.001", the length of the period PEt is "100 msec", and the coefficient is 4.7, the stress value is "0.001 x 100 x 4.7 ≒ 0.47 (N)" based on the formula 2.

In step S11, the calculation circuit 12 may determine that the voltage value does not exceed the threshold value Th1 (FIG. 6: step S11 No). For example, if the voltage value has negative polarity with respect to the reference potential VE, the voltage value does not exceed the threshold value Th1. At this time, the calculation circuit 12 determines whether the voltage value is below the threshold value Th2 (FIG. 6: step S16). The threshold value Th2 is a value smaller than the reference potential VE. In the example shown in FIG. 4, the calculation circuit 12 calculates the threshold value Th2=1.5V. If the calculation circuit 12 determines that the voltage value is below the threshold value Th2 (FIG. 6: step S16 Yes), it identifies the time when the voltage value fell below the threshold value Th2 (FIG. 6: step S17).

After step S17, the calculation circuit 12 calculates the slope of the signal Sig in the same manner as in step S13 (FIG. 6: step S18). Specifically, the calculation circuit 12 calculates the slope of the signal Sig based on the length of at least a portion of the period during which the intensity (value) of the signal Sig is decreasing, and the amount of fluctuation of the signal Sig during at least a portion of the period during which the intensity (value) of the signal Sig is decreasing. In this case, the slope of the signal Sig is negative.

After step S18, the calculation circuit 12 determines the length of the period from when the voltage value falls below the threshold value Th2 to when it exceeds the threshold value Th2 (FIG. 6: step S19). After step S19, the calculation circuit 12 calculates the stress value based on Equation 2. Specifically, the calculation circuit 12 calculates the stress value based on the length of time from when the intensity (value) of the signal Sig decreases to when it increases, and on the slope of the signal Sig.

If, in step S16, the calculation circuit 12 determines that the voltage value is not below the threshold value Th2 (FIG. 6: step S16 No), it does not execute the process of calculating the stress value.

The arithmetic circuit 12 repeats the process from step S10 to step S19. For example, the arithmetic circuit 12 executes the process from step S10 to step S19 as one cycle each time the arithmetic circuit 12 receives the signal Sig from the sensor 11 at a predetermined sampling interval.

The calculation circuit 12 ends process P, for example, when the power supply to the calculation circuit 12 is turned off (FIG. 6: END).

(effect)
The sensor module 1 makes it easier to accurately identify the stress value applied to the elastic member 10. Below, the arithmetic circuit 12 will be compared with the arithmetic circuit according to Comparative Example 1 with reference to the drawings. FIG. 8 is a diagram showing the relationship between the length of the second period and the stress value. FIG. 8 is a graph obtained by performing an experiment nine times in which the elastic member 10 is pressed at a predetermined speed. In FIG. 8, the horizontal axis represents the length of the second period, and the vertical axis represents the stress value.

Figure 9 is a graph showing the relationship between the length of the second period and the stress value, obtained by performing an experiment three times in which the elastic member 10 is pressed at different speeds. In Figure 9, the horizontal axis is the length of the second period, and the vertical axis is the stress value. In Figure 9, line L1 is a regression line showing the relationship between the length of the second period and the stress value when the elastic member 10 is pressed at a speed of 1 mm/sec. Line L2 is a regression line showing the relationship between the length of the second period and the stress value when the elastic member 10 is pressed at a speed of 3 mm/sec. Line L3 is a regression line showing the relationship between the length of the second period and the stress value when the elastic member 10 is pressed at a speed of 6 mm/sec.

The calculation circuit of Comparative Example 1 differs from the first embodiment only in the method of calculating the stress value. Specifically, the calculation circuit of Comparative Example 1 calculates the stress value by multiplying the length of the second period by the first coefficient. Specifically, as shown in FIG. 8, the stress value is directly proportional to the length of the second period. Therefore, the calculation circuit of Comparative Example 1 calculates the stress value based on the formula "stress value ≒ first coefficient × length of the second period".

However, as shown in FIG. 9, the slopes of the lines L1, L2, and L3 are different. Therefore, the value of the first coefficient differs depending on the speed at which the elastic member 10 is pressed. For this reason, the arithmetic circuit of Comparative Example 1 needs to calculate the stress value based on the value of the first coefficient that corresponds to the speed at which the elastic member 10 is pressed. If the arithmetic circuit of Comparative Example 1 calculates the stress value based on the value of the first coefficient that does not correspond to the speed at which the elastic member 10 is pressed, the stress value calculated by the arithmetic circuit of Comparative Example 1 will be an incorrect value. Therefore, a sensor module equipped with the arithmetic circuit of Comparative Example 1 may not be able to accurately identify the stress value applied to the elastic member.

On the other hand, in the sensor module 1, the arithmetic circuit 12 calculates the stress value taking into account the speed at which the elastic member 10 is pressed. Specifically, when the elastic member 10 is pressed by the user 200, the arithmetic circuit 12 calculates the slope of the signal Sig. The slope of the signal Sig changes based on the speed at which the elastic member 10 is pressed. Therefore, the arithmetic circuit 12 can calculate the stress value applied to the elastic member 10 based on the slope of the signal Sig that corresponds to the speed at which the elastic member 10 is pressed. Therefore, in the sensor module 1, an event does not occur in which the arithmetic circuit 12 calculates an incorrect stress value by using a value (first coefficient) that does not correspond to the speed at which the elastic member 10 is pressed. As a result, the sensor module 1 can easily accurately identify the stress value applied to the elastic member 10.

The sensor module 1 allows the arithmetic circuit 12 to more easily and accurately determine the stress value applied to the elastic member 10. Below, the arithmetic circuit 12 will be compared with the arithmetic circuit of Comparative Example 2 with reference to the drawings.

FIG. 10 is a diagram showing a time when the sensor 11 outputs a signal Sig having a value that exceeds the measurement range of the sensor 11. In FIG. 10, the horizontal axis represents time, and the vertical axis represents the value of the signal Sig. Time u1 in FIG. 10 is the time when the value of the signal Sig exceeds the measurement range of the sensor 11. Time u2 is the time when the value of the signal Sig falls below the measurement range of the sensor 11. In the example shown in FIG. 10, the upper limit UL of the measurement range of the sensor 11 is 3.0 V.

Similarly, the calculation circuit according to the comparative example 2 differs from the first embodiment only in the calculation method of the stress value. Specifically, the calculation circuit according to the comparative example 2 calculates the stress value by integrating the value of the signal Sig received from the sensor 11. Here, the elastic member 10 may be deformed beyond the deformation amount that the sensor 11 can measure. In the example shown in FIG. 10, the elastic member 10 is deformed beyond the deformation amount that the sensor 11 can measure between time u1 and time u2. In this case, the sensor 11 does not output a signal Sig having a value exceeding the upper limit UL between time u1 and time u2. For example, the sensor 11 outputs the value of the signal Sig between time u1 and time u2 as 3.0 V, which is the upper limit UL. At this time, the calculation circuit according to the comparative example 2 performs an integration process to calculate the stress value with the value of the signal Sig from time u1 to time u2 set to 3.0 V. In this case, the stress value obtained by the calculation of the calculation circuit according to the comparative example 2 is lower than the stress value indicating the stress applied to the elastic member 10. Therefore, the calculation circuit of Comparative Example 2 may not be able to accurately determine the stress value applied to the elastic member 10.

On the other hand, the calculation circuit 12 calculates the stress value based on the slope of the signal Sig and the length of the second period (the length of the period from when the voltage value exceeds the threshold value Th1 to when it falls below the threshold value Th1). In this case, the calculation circuit 12 does not calculate the stress value based on the value of the signal Sig acquired between time u1 and time u2 shown in FIG. 10. Therefore, even if the sensor 11 outputs a signal Sig having a value that exceeds the upper limit UL, the calculation circuit 12 can accurately determine the stress value. In other words, the sensor module 1 equipped with the calculation circuit 12 makes it easier to accurately determine the stress value that indicates the stress applied to the elastic member 10.

[Modification 1]
The sensor module 1a according to the first modification will be described below with reference to the drawings. Fig. 11 is a flow chart showing an example of a process Q executed by the arithmetic circuit 12a included in the sensor module 1a according to the first modification. Fig. 12 is a diagram showing a case where noise occurs in the signal Sig between time t14 and time t15. Time t15 is a time after time t14.

Sensor module 1a differs from sensor module 1 in that it includes an arithmetic circuit 12a instead of arithmetic circuit 12. As shown in FIG. 11, arithmetic circuit 12a executes process Q, which is different from process P. Steps S10 to S19 in process Q are the same as steps S10 to S19 in process P, and therefore will not be described.

In process Q, after step S14, the calculation circuit 12a determines whether the length of the second period (the period from when the voltage value exceeds the threshold value Th1 until when it falls below the threshold value Th1) is equal to or greater than the threshold value Th3 (FIG. 11: step S20). The threshold value Th3 is, for example, 30 msec. In the example shown in FIG. 12, the calculation circuit 12a determines whether the length of the period PEt (second period) is equal to or greater than the threshold value Th3.

If the calculation circuit 12a determines that the length of the second period is equal to or greater than the threshold value Th3 (FIG. 11: step S20 Yes), it executes step S15. In the example shown in FIG. 12, the length of the period PEt is equal to or greater than the threshold value Th3. In this case, the calculation circuit 12a calculates the stress value during the period PEt.

On the other hand, if the calculation circuit 12 determines that the length of the second period is less than the threshold value Th3 (FIG. 11: step S20 No), it does not execute step S15. In the example shown in FIG. 12, between time t14 and time t15, the voltage value exceeds threshold value Th1 and then falls below threshold value Th1. Therefore, the calculation circuit 12a determines whether the length of time between time t14 and time t15 is greater than or equal to threshold value Th3. The length of time between time t14 and time t15 is less than threshold value Th3. For this reason, the calculation circuit 12a does not calculate the stress value between time t14 and time t15.

Similarly, in process Q, after step S19, the calculation circuit 12a determines whether the length of time from when the voltage value falls below threshold Th2 to when it exceeds threshold Th2 is equal to or greater than threshold Th3 (FIG. 11: step S20).

(effect)
According to the sensor module 1a, the possibility that the arithmetic circuit 12a makes an erroneous determination can be reduced. For example, between time t14 and time t15, the user 200 erroneously operates the sensor module 1a. The erroneous operation is, for example, an operation in which the user 200 places the hand of the user 200 on the elastic member 10. In this case, as shown in FIG. 12, the voltage value may exceed the threshold value Th1 between time t14 and time t15. Therefore, the arithmetic circuit that does not execute the process of step S20 (hereinafter, referred to as the arithmetic circuit according to the comparative example 2) may erroneously determine that the user 200 has performed a pressing operation between time t14 and time t15.

On the other hand, the arithmetic circuit 12a executes step S20 to determine whether or not a pressing operation has been performed by the user 200. The threshold value Th3 is, for example, a time shorter than the time required for the user 200 to perform a pressing operation. As a result, the arithmetic circuit 12a can determine that the signal Sig has been generated due to an erroneous operation by the user 200, for example, when the length of the second period is less than the threshold value Th3. As a result, the arithmetic circuit 12a is less likely to erroneously determine that an erroneous operation by the user 200 is a pressing operation by the user 200.

The sensor module 1a makes it easier for the calculation circuit 12a to calculate the stress value. For example, when the difference between the threshold value Th1 and the reference potential VE is small, the voltage value generated by noise is likely to exceed the threshold value Th1. For this reason, the calculation circuit in Comparative Example 2 may erroneously determine that the user 200 has performed a pressing operation when the user 200 has not performed a pressing operation.

On the other hand, even if the voltage value exceeds threshold Th1, if the length of the second period is less than threshold Th3, the arithmetic circuit 12a determines that no pressing operation has been performed by the user 200. Therefore, even if threshold Th1 is a small value, the arithmetic circuit 12a is less likely to make an erroneous determination. In other words, the value of threshold Th1 can be made small. Therefore, the arithmetic circuit 12a can calculate the stress value even if the force applied to the elastic member 10 by the user 200 is small.

[Modification 2]
The sensor module 1b according to the second modification will be described below with reference to the drawings. Fig. 13 is a diagram showing the sensor module 1b according to the second modification.

Sensor module 1b differs from sensor module 1 in that it has two or more sensors. In the example shown in FIG. 13, sensor module 1b has

sensors

11a, 11b, and 11c in addition to sensor 11.

In this modified example, the sensor 11 is provided, for example, at the right end of the elastic member 10 (see FIG. 13). The sensor 11a is provided at the left end of the elastic member 10. The sensor 11b is provided at the rear end of the elastic member 10. The sensor 11c is provided at the front end of the elastic member 10. The other configurations of the

sensors

11a, 11b, and 11c are the same as the configuration of the sensor 11, so the description will be omitted.

In this modified example, the calculation circuit 12 calculates the load applied to the elastic member 10 based on the signals Sig output by each of the

sensors

11, 11a, 11b, and 11c. In this modified example, the calculation circuit 12 can calculate the load applied to the elastic member 10 with high accuracy. The following description will be given with reference to the drawings. FIG. 14 is a table Tb showing an example of load values calculated by the calculation circuit 12 in the sensor module 1b. For example, nine areas Ar1 to Sr9 are defined on the elastic member 10. Each of the areas Ar1 to Ar9 has the same size. FIG. 14 is obtained by performing an experiment (hereinafter referred to as experiment Z) in which each of the areas Ar1 to Ar9 on the elastic member 10 is pressed with a load of 150 g.

In the example shown in FIG. 14, when area Ar2 is pressed with a load of 150 g, the calculation circuit 12 estimates the load applied to the elastic member 10 to be 161 g. Load: 161 g is the largest estimated load (hereinafter referred to as the maximum estimated load) among the estimated loads obtained in experiment Z. In the example shown in FIG. 14, when area Ar6 is pressed, the calculation circuit 12 calculates the load applied to the elastic member 10 to be 143 g. Load: 143 g is the smallest estimated load (hereinafter referred to as the minimum estimated load) among the estimated loads obtained in experiment Z. Here, the value obtained by dividing the minimum estimated load by the maximum estimated load and multiplying this value by 100 is defined as the in-plane distribution. In this case, the in-plane distribution in the example shown in FIG. 14 is "143/161×100≒89%". The calculation circuit 12 can calculate the load applied to the elastic member 10 while maintaining a high degree of accuracy of 89% in-plane distribution.

[Other embodiments]
The sensor module according to the present invention is not limited to the sensor module 1, and can be modified within the scope of the gist thereof.

The elastic member 10 does not necessarily have to have a plate shape. The elastic member 10 may be, for example, rod-shaped.

The electronic device EE does not necessarily have to be a smartphone. The electronic device EE may be any device that allows the user 200 to perform a pressing operation. The electronic device EE may be a pen tablet, TWS (True Wireless Stereo), etc. In other words, the sensor 11 can be attached to the elastic member 10 regardless of the housing structure of the electronic device EE. This allows the arithmetic circuits 12, 12a to calculate the stress value regardless of the housing structure of the electronic device EE.

The sensor module 1 may include two or three sensors. The sensor module 1 may include five or more sensors.

The elastic member 10 may also be square-shaped.

Note that the electrical parameter contained in the signal Sig does not necessarily have to be a voltage value. For example, the electrical parameter contained in the signal Sig may be a current value.

Note that the uniaxial stretching direction OD does not necessarily have to form an angle of 45 degrees with respect to the front-to-rear and left-to-right directions. For example, the uniaxial stretching direction OD may form an angle of 0 degrees with respect to the front-to-rear direction.

When the calculation circuit 12 acquires the signal Sig having a negative polarity with respect to the reference potential VE, the calculation circuit 12 may invert the waveform of the signal Sig with respect to the reference potential VE. In this case, the intensity (value) of the signal Sig has a positive polarity with respect to the reference potential VE. Therefore, the calculation circuit 12 can calculate the stress value by executing the processes from step S10 to step S15.

The calculation circuit 12 repeatedly executes one cycle of processing from step S10 to step S19. At this time, the calculation circuit 12 adds up the stress values acquired in each cycle. In this way, the calculation circuit 12 calculates the stress value at the time when the processing P is executed. For example, as shown in FIG. 4, the calculation circuit 12 calculates a stress value of 1.4 N in one cycle from time t10 to time t12 (hereinafter referred to as the first stress value). Next, the calculation circuit 12 calculates a stress value of -1.4 N in one cycle from time s10 to time s11 (hereinafter referred to as the second stress value). In this case, the value obtained by adding the second stress value to the first stress value is 0. Therefore, the calculation circuit 12 can determine that no force is applied to the elastic member 10 at time s11.

The calculation circuit 12 may transmit a signal (hereinafter referred to as the first signal) corresponding to the calculated stress value to a device other than the calculation circuit 12. In this case, the value of the first signal depends on the slope of the signal Sig or the length of the second period. Therefore, if the slope of the signal Sig changes, the intensity (value) of the first signal changes. If the length of the second period changes, the intensity (value) of the first signal changes. Therefore, a processing device that outputs a first signal having an intensity (value) that changes with changes in the signal Sig and an intensity (value) that changes with changes in the length of the second period is considered to be performing processing related to the calculation circuit 12.

The sensor module 1 may also be equipped with a display that displays the stress value. The display is, for example, an organic EL display. In this case, if the slope of the signal Sig or the length of the second period changes, the stress value displayed on the display changes. Therefore, a processing device (such as a smartphone) that has a display that displays a stress value that changes with a change in the slope of the signal Sig and that displays a stress value that changes with a change in the length of the second period is considered to be executing processing related to the arithmetic circuit 12.

The value of the signal Sig does not have to depend on the differential value of the displacement of the sensor 11. For example, depending on the frequency of the input signal, it may contain components that are not dependent on the differential value.

The present invention has the following structure:

(1)
a sensor that outputs a signal corresponding to the deformation of the elastic member;
a computing circuit for receiving the signal from the sensor;
Equipped with
The arithmetic circuit includes:
measuring the length of time during a period of interest during which the strength of the signal falls outside a range defined by a threshold;
Calculating a slope of the signal based on a length of at least a portion of the time period of interest and an amount of fluctuation of the signal during at least a portion of the time period of interest;
calculating a stress value indicating a stress applied to the elastic member based on the length of the target period and the slope;
Sensor module.

(2)
The arithmetic circuit includes:
measuring the length of time between an increase and a decrease in the strength of the signal;
Calculating the slope based on a length of at least a portion of a period during which the intensity of the signal is increasing and an amount of fluctuation of the signal during at least a portion of the period during which the intensity of the signal is increasing;
calculating a stress value indicating a stress applied to the elastic member based on the length of time from when the intensity of the signal increases to when it decreases and on the slope of the signal;
The sensor module described in (1).

(3)
The arithmetic circuit includes:
measuring the length of time between a decrease and an increase in the strength of the signal;
Calculating the slope based on a length of at least a portion of a period during which the intensity of the signal is decreasing and an amount of fluctuation of the signal during at least a portion of the period during which the intensity of the signal is decreasing;
calculating a stress value indicating a stress applied to the elastic member based on the length of time from when the intensity of the signal decreases to when it increases and on the slope of the signal;
A sensor module according to (1) or (2).

(4)
If the slope increases, the stress value increases;
If the slope decreases, the stress value decreases.
A sensor module according to any one of (1) to (3).

(5)
the signal includes an electrical parameter that varies in response to deformation of the elastic member;
A sensor module according to any one of (1) to (3).

(6)
The electrical parameter is a voltage value.
The sensor module according to (5).

(7)
the first time is the time when the voltage value exceeds a reference potential;
the threshold value is a value greater than the reference potential,
the second time is a time after the first time and is a time at which the voltage value exceeds the threshold value;
a third time point is a time point after the second time point and is a time point at which the voltage value falls below the threshold value;
the first period is a period between the first time and the second time,
the second period is a period between the second time and the third time,
The arithmetic circuit includes:
calculating the slope by dividing an increase in the voltage value during the first period by a length of the first period;
calculating the stress value based on an integrated value obtained by integrating the slope by the length of the second period;
The sensor module according to (6).

(8)
the calculation circuit calculates the stress value by multiplying the integrated value by a coefficient;
The sensor module according to (7).

(9)
receiving a signal having a value that increases and then decreases over time from a sensor that outputs a signal in response to deformation of the elastic member;
A stress value that changes when a slope of the signal changes in at least a part of a period during which the intensity of the signal is increasing, and that changes when a length of a period from when the intensity of the signal increases to when it decreases changes.
Arithmetic circuit.

1, 1a, 1b: sensor module 10:

elastic member

11, 11a, 11b, 11c: sensor 12, 12a: arithmetic circuit PE1, PEs, PEt: period Sig: signal Th1, Th2, Th3: threshold value VE: reference potential

Claims

a sensor that outputs a signal corresponding to the deformation of the elastic member;
a computing circuit for receiving the signal from the sensor;
Equipped with
The arithmetic circuit includes:
measuring the length of time during a period of interest during which the strength of the signal falls outside a range defined by a threshold;
Calculating a slope of the signal based on a length of at least a portion of the time period of interest and an amount of fluctuation of the signal during at least a portion of the time period of interest;
calculating a stress value indicating a stress applied to the elastic member based on the length of the target period and the slope;
Sensor module.
The arithmetic circuit includes:
measuring the length of time between an increase and a decrease in the strength of the signal;
Calculating the slope based on a length of at least a portion of a period during which the intensity of the signal is increasing and an amount of fluctuation of the signal during at least a portion of the period during which the intensity of the signal is increasing;
calculating a stress value indicating a stress applied to the elastic member based on the length of time from when the intensity of the signal increases to when it decreases and on the slope of the signal;
The sensor module according to claim 1 .
The arithmetic circuit includes:
measuring the length of time between a decrease and an increase in the strength of the signal;
Calculating the slope based on a length of at least a portion of a period during which the intensity of the signal is decreasing and an amount of fluctuation of the signal during at least a portion of the period during which the intensity of the signal is decreasing;
calculating a stress value indicating a stress applied to the elastic member based on the length of time from when the intensity of the signal decreases to when it increases and on the slope of the signal;
The sensor module according to claim 1 or 2.
If the slope increases, the stress value increases;
If the slope decreases, the stress value decreases.
The sensor module according to claim 1 .
the signal includes an electrical parameter that varies in response to deformation of the elastic member;
The sensor module according to claim 1 .
The electrical parameter is a voltage value.
The sensor module according to claim 5 .
the first time is the time when the voltage value exceeds a reference potential;
the threshold value is a value greater than the reference potential,
the second time is a time after the first time and is a time at which the voltage value exceeds the threshold value;
a third time point is a time point after the second time point and is a time point at which the voltage value falls below the threshold value;
the first period is a period between the first time and the second time,
the second period is a period between the second time and the third time,
The arithmetic circuit includes:
calculating the slope by dividing an increase in the voltage value during the first period by a length of the first period;
calculating the stress value based on an integrated value obtained by integrating the slope by the length of the second period;
The sensor module according to claim 6 .
the calculation circuit calculates the stress value by multiplying the integrated value by a coefficient;
The sensor module according to claim 7.
receiving a signal having a value that increases and then decreases over time from a sensor that outputs a signal in response to deformation of the elastic member;
A stress value that changes when a slope of the signal changes in at least a part of a period during which the intensity of the signal is increasing, and that changes when a length of a period from when the intensity of the signal increases to when it decreases changes.
Arithmetic circuit.