WO2024105923A1

WO2024105923A1 - Capacitance measurement circuit and load detection device

Info

Publication number: WO2024105923A1
Application number: PCT/JP2023/024094
Authority: WO
Inventors: 雅規田丸
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2022-11-14
Filing date: 2023-06-28
Publication date: 2024-05-23

Abstract

This capacitance measurement circuit comprises: a reference capacitance (Cr); a switching element (12a) for switching between application and non-application of a voltage to the reference capacitance (Cr); a switching element (12b) for transferring the charge of the reference capacitance (Cr) to a measurement capacitance (Cs); a switching element (13) for connecting a negative electrode of the measurement capacitance (Cs) to ground or a wire having the same potential as a positive electrode of the measurement capacitance (Cs); a measurement unit for measuring the voltage of the measurement capacitance (Cs); and a control unit (11). The control unit (11) executes: a first control for causing the switching element (12b) to perform charge transfer in a state in which the negative electrode of the measurement capacitance (Cs) is connected to ground; a second control for causing the switching element (12b) to perform charge transfer in a state in which the negative electrode of the measurement capacitance (Cs) is connected to the wire having the same potential as the positive electrode of the measurement capacitance (Cs); and a process for calculating the capacitance value of the measurement capacitance (Cs) on the basis of the voltage value measured after the charge transfer is performed by each control.

Description

Capacitance measurement circuit and load detection device

The present invention relates to a capacitance measurement circuit for measuring capacitance, and a load detection device for detecting a load based on the results of capacitance measurement.

　Conventionally, there is known a capacitance-type load sensor in which the capacitance of an element changes depending on the load. In this type of load sensor, for example, the capacitance of the element is detected based on the change in voltage when a voltage is applied to the element. A load detection device using this type of load sensor is described, for example, in Patent Document 1 below.

JP 2021-81209 A

In a capacitance-type load sensor, in addition to the method based on voltage changes as described above, the capacitance of the element unit can also be detected from, for example, the amount of charge accumulated in the element unit when a voltage is applied to the element unit. In this case, for example, the amount of charge accumulated in the element unit can be calculated by measuring the amount of current flowing through the element unit during the period from when a voltage is applied to the element unit until the accumulated charge becomes saturated. Such measurement of the current amount can be performed, for example, by sampling and integrating the current value during this period using an AD converter.

However, when the load applied to the element portion is small, the capacitance of the element portion becomes small, and the period from when a voltage is applied to the element portion until the accumulated charge becomes saturated becomes shorter. For this reason, measuring the amount of current described above requires a high-speed, high-precision AD converter that can sample the current value that changes over a short period of time. However, even when such an AD converter is used, in the range where the load is relatively small, the period until the amount of current becomes saturated is significantly short, making it difficult to stably measure the amount of current during this period.

In addition, the capacitance measurement results are affected by parasitic capacitance due to wiring and other electrical elements. As a result, the calculated capacitance contains an error component due to the parasitic capacitance, and this error component makes it difficult to detect the load accurately.

In view of these problems, the present invention aims to provide a capacitance measurement circuit and load detection device that can stably and accurately measure capacitance even in a small range.

The first aspect of the present invention relates to a capacitance measurement circuit. The capacitance measurement circuit according to this aspect includes a reference capacitance having a predetermined capacitance value, a switching unit that switches between application and non-application of a voltage to the reference capacitance, a transfer unit that transfers the charge stored in the reference capacitance to a measurement capacitance, a connection unit that connects the negative electrode of the measurement capacitance to ground or a wiring having the same potential as the positive electrode of the measurement capacitance, a measurement unit that measures the voltage of the measurement capacitance, and a control unit that controls the switching unit, the transfer unit, and the connection unit. The control unit executes a first control that applies a voltage to the reference capacitance and then causes the transfer unit to transfer the charge while the negative electrode of the measurement capacitance is connected to the ground, a second control that applies a voltage to the reference capacitance and then causes the transfer unit to transfer the charge while the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance, and a process that calculates the capacitance value of the measurement capacitance from the voltage values measured by the measurement unit after the charge is transferred by the first control and the second control, respectively.

The capacitance measurement circuit according to this embodiment calculates the capacitance value of the measurement capacitance based on the voltage value after the charge is transferred from the reference capacitance, so that it is possible to stably measure capacitance values in a small range without using a high-precision AD converter. In addition, in the second control, the negative electrode of the measurement capacitance is connected to a wire having the same potential as the positive electrode of the measurement capacitance, so that the measured voltage value is hardly affected by the measurement capacitance, but is mainly affected by the reference capacitance and parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to ground, so that the measured voltage value is affected by the measurement capacitance as well as the reference capacitance and parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, it is possible to calculate a capacitance value that is not affected by the parasitic capacitance. Therefore, the capacitance value of the measurement capacitance can be measured with high precision.

The second aspect of the present invention relates to a capacitance measurement circuit. The capacitance measurement circuit according to this aspect includes a reference capacitance having a predetermined capacitance value, a switching unit for switching between application and non-application of a voltage to the measurement capacitance, a transfer unit for transferring the charge accumulated in the measurement capacitance to the reference capacitance, a connection unit for connecting the negative electrode of the measurement capacitance to the ground or to a wiring having the same potential as the positive electrode of the measurement capacitance, a measurement unit for measuring the voltage of the measurement capacitance, and a control unit for controlling the switching unit, the transfer unit, and the connection unit. The control unit executes a first control for applying a voltage to the measurement capacitance while the negative electrode of the measurement capacitance is connected to the ground, and then causing the transfer unit to transfer the charge, a second control for applying a voltage to the measurement capacitance while the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance, and then causing the transfer unit to transfer the charge, and a process for calculating the capacitance value of the measurement capacitance from the voltage values measured by the measurement unit after the charge has been transferred by the first control and the second control, respectively.

According to the capacitance measurement circuit of this embodiment, the capacitance value of the measurement capacitance is calculated based on the voltage value after the charge is transferred from the measurement capacitance, so that it is possible to stably measure capacitance values in a small range without using a highly accurate AD converter. In addition, in the second control, the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance and a voltage is applied to the measurement capacitance, so that almost no charge is accumulated in the measurement capacitance, and charge is accumulated in the parasitic capacitance. Therefore, the voltage value measured by the second control is hardly influenced by the measurement capacitance, and is mainly influenced by the reference capacitance and the parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to the ground and a voltage is applied to the measurement capacitance, so that charge is applied to the measurement capacitance as well as the parasitic capacitance. Therefore, the voltage value measured by the first control is influenced by the measurement capacitance as well as the reference capacitance and the parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, it is possible to calculate a capacitance value that is not influenced by the parasitic capacitance. Therefore, the capacitance value of the measurement capacitance can be measured with high accuracy.

The third aspect of the present invention relates to a load detection device. The load detection device according to this aspect includes a load sensor having an element unit whose capacitance changes depending on the load, and the capacitance measurement circuit according to the first or second aspect. The control unit performs the first control, the second control, and the capacitance calculation process using the element unit as the measurement capacitance.

The load detection device according to this aspect includes the capacitance measurement circuit according to the first or second aspect, so that the capacitance corresponding to the load can be stably obtained even in a range where the load applied to the element portion is small and the capacitance is small. In addition, since the load detection device includes the capacitance measurement circuit according to the first or second aspect, the capacitance value in which the influence of parasitic capacitance is suppressed can be obtained with high accuracy. Therefore, a small range of load can be detected stably and with high accuracy.

As described above, the present invention provides a capacitance measurement circuit and a load detection device that can stably and accurately measure capacitance even over a small range.

The effects and significance of the present invention will become clearer from the description of the embodiment shown below. However, the embodiment shown below is merely an example of how the present invention may be put into practice, and the present invention is in no way limited to the embodiment described below.

FIG. 1 is a diagram showing a configuration of a capacitance measuring circuit according to the first embodiment. 2A and 2B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the first embodiment. 3A and 3B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the first embodiment. 4A and 4B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the first embodiment. 5A and 5B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the first embodiment. 6A and 6B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the first embodiment. FIG. 7 is a flowchart showing a process for calculating the capacitance value of a measurement capacitance according to the first embodiment. FIG. 8 is a flowchart showing a calculation process of the capacitance value of the measurement capacitance according to the first modification of the first embodiment. FIG. 9 is a diagram showing a configuration of a capacitance measuring circuit according to the second modification of the first embodiment. FIG. 10 is a diagram showing a configuration of a capacitance measuring circuit according to the second embodiment. 11A and 11B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the second embodiment. 12A and 12B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the second embodiment. 13A and 13B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the second embodiment. 14A and 14B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the second embodiment. 15A and 15B are diagrams illustrating the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to the second embodiment. FIG. 16 is a flowchart showing a process for calculating the capacitance value of a measurement capacitance according to the second embodiment. 17A and 17B are graphs showing simulation results of capacitance according to the first and second embodiments, respectively. FIG. 18 is a flowchart showing a process of calculating the capacitance value of the measurement capacitance according to the first modification of the second embodiment. FIG. 19 is a diagram showing a configuration of a capacitance measuring circuit according to a second modification of the second embodiment. Fig. 20(a) is a perspective view showing a base member and a conductive elastic body provided on an upper surface of the base member according to embodiment 3. Fig. 20(b) is a perspective view showing a state in which a conductor wire is provided on the structure of Fig. 20(a) according to embodiment 3. Fig. 21(a) is a perspective view showing a state in which a thread is provided on the structure of Fig. 20(b) according to embodiment 3. Fig. 21(b) is a perspective view showing a state in which a base member is provided on the structure of Fig. 21(a) according to embodiment 3. 22(a) and 22(b) are diagrams each showing a schematic cross section of a load sensor according to the third embodiment. FIG. 23 is a plan view illustrating a schematic internal configuration of the load sensor according to the third embodiment. FIG. 24 is a diagram showing a configuration of a load detection device according to the third embodiment. FIG. 25 is a diagram showing the operation of the load detection device when detecting the capacitance value of the element portion to be measured according to the third embodiment. FIG. 26 is a diagram showing a configuration of a load detection device according to the fourth embodiment. FIG. 27 is a diagram showing the operation of the load detection device when detecting the capacitance value of the element portion to be measured according to the fourth embodiment.

However, the drawings are for illustrative purposes only and do not limit the scope of the invention.

Below, embodiments of the present invention will be described with reference to the drawings. In embodiments 1 and 2, the configuration of a capacitance measurement circuit is shown, and in embodiments 3 and 4, the configuration of a load detection device is shown.

In the first and second embodiments, switch element 12a, switch element 12b, and switch element 13 correspond to the "switching unit," "transfer unit," and "connection unit" described in the claims, respectively. However, this description is merely intended to associate the configurations of the claims with the configurations of the embodiments, and the above association does not in any way limit the inventions described in the claims to the configurations of the embodiments. Furthermore, the configurations that realize the inventions described in the claims are not limited to the following embodiments 1 to 4.

<Embodiment 1>
FIG. 1 is a diagram showing a configuration of a capacitance measuring circuit 10 according to the first embodiment.

As shown in FIG. 1, the capacitance measurement circuit 10 includes a control unit 11, switch elements 12a to 12c, switch element 13, a measurement unit 14, and a reference capacitance Cr. The reference capacitance Cr is connected in parallel to the measurement capacitance Cs via switch element 12b. The measurement capacitance Cs is the capacitance to be measured. The capacitance value of the reference capacitance Cr is greater than the capacitance value of the measurement capacitance Cs.

The control unit 11 is configured with a microcomputer, FPGA, etc., and controls the switch elements 12a to 12c and 13. The control unit 11 also calculates the capacitance value of the measurement capacitance Cs based on the voltage value measured by the measurement unit 14.

The switch element 12a switches between applying and not applying the power supply voltage Vdd to the reference capacitance Cr. When the switch element 12a changes from a non-conductive state to a conductive state, the power supply voltage Vdd is applied to the reference capacitance Cr, and charge is accumulated in the reference capacitance Cr.

The switch element 12b switches the positive electrode of the reference capacitance Cr and the positive electrode of the measurement capacitance Cs between a connected state and a disconnected state. When the switch element 12b changes from a non-conductive state to a conductive state, the positive electrode of the reference capacitance Cr and the positive electrode of the measurement capacitance Cs are connected, and the charge accumulated in the reference capacitance Cr is transferred to the measurement capacitance Cs. In this way, the switch element 12b transfers the charge accumulated in the reference capacitance Cr to the measurement capacitance Cs.

The switch element 12c switches between a connected state and a disconnected state between the positive electrode of the measurement capacitance Cs and the ground. When the switch element 12c changes from a non-conductive state to a conductive state, the positive electrode of the measurement capacitance Cs is connected to the ground, and the charge accumulated in the measurement capacitance Cs is discharged to the ground.

Switch elements

12a and 12b are configured with P-type FETs and become conductive when a low-level gate signal is applied to their gates. Switch element 12c is configured with N-type FETs and becomes conductive when a high-level gate signal is applied to their gates. Switch elements 12a to 12c may be other switch elements of a type other than FETs.

The switch element 13 connects the negative electrode of the measurement capacitance Cs to ground or to the positive electrode of the measurement capacitance Cs. When the positive and negative electrodes of the measurement capacitance Cs are connected by the switch element 13, these positive and negative electrodes have the same potential, so that the measurement capacitance Cs is in a state where it disappears from the circuit (disabled state).

The measurement unit 14 measures the voltage of the measurement capacitance Cs. When the switch element 12b is conductive while the switch element 13 is connected to ground, the charge of the reference capacitance Cr is transferred to the measurement capacitance Cs and distributed. As a result, a voltage corresponding to the capacitance ratio between the electrostatic capacitance value of the reference capacitance Cr and the electrostatic capacitance value of the measurement capacitance Cs is generated in the measurement capacitance Cs. The measurement unit 14 measures this voltage.

The capacitance value of the reference capacitance Cr is set to a value that allows the measurement unit 14 to accurately measure the voltage that occurs in the measurement capacitance Cs after the charge is distributed in this manner. In other words, the capacitance value of the reference capacitance Cr is set at least so that the voltage that occurs in the measurement capacitance Cs after the charge is distributed as described above is equal to or greater than the lower limit of the measurable range of the measurement unit 14.

Next, the operation of the capacitance measurement circuit 10 when measuring the capacitance value of the measurement capacitance Cs will be described with reference to Figures 2(a) to 6(b).

For convenience, in Fig. 2(a) to Fig. 6(b), the switch elements 12a to 12c that are in an operating state and the paths through which the switch elements charge, discharge, or transfer electric charge are indicated by thick lines. In addition, when the reference capacitance Cr and the measurement capacitance Cs are in a charged state, these capacitances are indicated by diagonal hatching.

First, as shown in FIG. 2(a), with switch element 13 connected to ground,

switch elements

12a and 12c are each switched to a conductive state. This applies power supply voltage Vdd to reference capacitance Cr, and charge is accumulated in reference capacitance Cr. In addition, the positive electrode of measurement capacitance Cs is connected to ground, and discharging to measurement capacitance Cs is performed. Switch element 12a is set to a conductive state at least until reference capacitance Cr is fully charged. Whether reference capacitance Cr is fully charged can be determined, for example, by measuring the voltage of reference capacitance Cr with a measurement unit other than measurement unit 14 and checking whether the measurement result reaches power supply voltage Vdd and becomes stable.

Next, as shown in FIG. 2(b), switch element 12a is switched to a non-conductive state, and reference capacitance Cr is disconnected from power supply voltage Vdd. Also, as shown in FIG. 3(a), switch element 12c is switched to a non-conductive state, and the positive electrode of measurement capacitance Cs is disconnected from ground. Then, as shown in FIG. 3(b), switch element 12b is switched to a conductive state, and the positive electrode of reference capacitance Cr and the positive electrode of measurement capacitance Cs are connected. This causes the charge stored in reference capacitance Cr to be transferred to measurement capacitance Cs.

The measurement value of the measurement unit 14 immediately after the switch element 12b is switched to the conductive state is a voltage value according to the accumulated charge in the reference capacitance Cr, i.e., a voltage value approximately equal to the power supply voltage Vdd. Thereafter, as the transfer of charge to the measurement capacitance Cs progresses, the measurement value of the measurement unit 14 gradually decreases, and when the transfer of charge is completed, the measurement value of the measurement unit 14 stabilizes (saturates) at a constant value according to the capacitance ratio between the reference capacitance Cr and the measurement capacitance Cs.

After the voltage value has stabilized in this way, as shown in FIG. 4(a), the voltage value measured by the measurement unit 14 is obtained as the first voltage value Vx1. As described above, this first voltage value Vx1 is determined mainly according to the capacitance ratio between the reference capacitance Cr and the measurement capacitance Cs, but is also affected by the parasitic capacitances of the wiring between the reference capacitance Cr and the measurement capacitance Cs and the

switch elements

12b and 13, etc. For this reason, if the capacitance value of the measurement capacitance Cs is calculated from only the first voltage value Vx1, errors due to these parasitic capacitances will be included in the calculation result.

To avoid this, in this embodiment, further operations are performed to suppress errors due to parasitic capacitance.

That is, as shown in FIG. 4(b), the switch element 13 is switched to the positive electrode side of the measurement capacitance Cs. Next, as shown in FIG. 5(a), the

switch elements

12a and 12c are each switched to a conductive state. As a result, the power supply voltage Vdd is applied to the reference capacitance Cr, and charge is accumulated in the reference capacitance Cr. In addition, the positive electrode of the measurement capacitance Cs is connected to ground, and discharging to the measurement capacitance Cs is performed. The switch element 12a is set to a conductive state at least until the reference capacitance Cr is fully charged.

As shown in FIG. 4(b), since the reference capacitance Cr still has charge after distribution, charging of the reference capacitance Cr in FIG. 5(a) is performed more quickly than in the case of FIG. 2(a). In other words, rather than first discharging the charge of the reference capacitance Cr from the state of FIG. 4(b) and then proceeding to the operation of FIG. 5(a), proceeding directly from the state of FIG. 4(b) to the operation of FIG. 5(a) as described above can speed up the operational sequence.

In addition, in FIG. 5(a), since the switch element 13 is connected to the positive electrode of the measurement capacitance Cs, in addition to the charge stored in the measurement capacitance Cs, the charge stored in the parasitic capacitance of the switch element 13 and the wiring between the switch element 13 and the positive electrode of the measurement capacitance Cs is also discharged to ground. This makes it possible to more reliably eliminate the effects of parasitic capacitance.

After that, as shown in FIG. 5(b), the switch element 12a is switched to a non-conductive state, and the reference capacitance Cr is disconnected from the power supply voltage Vdd. Also, the switch element 12c is switched to a non-conductive state, and the positive electrode of the measurement capacitance Cs is disconnected from ground. Then, as shown in FIG. 6(a), the switch element 12b is switched to a conductive state, and the positive electrode of the reference capacitance Cr and the positive electrode of the measurement capacitance Cs are connected. This causes the charge stored in the reference capacitance Cr to be transferred.

In this case, as shown in FIG. 6(a), the switch element 13 is switched to the positive electrode side of the measurement capacitance Cs, so the positive and negative electrodes of the measurement capacitance Cs are at the same potential. Therefore, during this charge transfer, no charge is distributed to the measurement capacitance Cs, but the charge is distributed to parasitic capacitances other than the measurement capacitance Cs. Therefore, in this case, the measurement value of the measurement unit 14 stabilizes to a voltage value according to the charge distribution to the parasitic capacitances.

After the voltage value has stabilized in this way, as shown in FIG. 6(b), the voltage value measured by the measurement unit 14 is acquired as the second voltage value Vx2. Then, the capacitance value of the measured capacitance Cs is calculated from the acquired second voltage value Vx2 and the first voltage value Vx1 acquired during the operation of FIG. 4(a).

The capacitance value of the measured capacitance Cs is calculated as follows:

First, as shown in Figure 2(a), the charge amount Qr of the reference capacitance Cr when the reference capacitance Cr is fully charged is expressed by the following formula, assuming that the capacitance value (known) of the reference capacitance Cr is Cr.

　　Qr＝Cr×Vdd…（１）

Furthermore, when the charge transfer is complete as shown in FIG. 4(a), if the capacitance value of the measured capacitance Cs is Cs1, the following relationship holds:

　　Qr＝（Cr＋Cs1）×Vx1　…（2）

Therefore, the following relationship can be derived from equations (1) and (2):

However, as described above, this capacitance value Cs1 includes an error component due to parasitic capacitance. This error component Ce can be expressed by the following equation using the second voltage value Vx2 obtained by the operation of FIG. 6(b).

In other words, during the operation shown in Figures 5(a) to 6(b), the positive and negative electrodes of the measurement capacitance Cs are at the same potential, so the measurement capacitance Cs is invalidated, and only the reference capacitance Cr and the parasitic capacitance become the capacitance components. Therefore, the electrostatic capacitance value of the parasitic capacitance, i.e., the error component Ce, can be expressed by the above formula (4).

The capacitance value Cs of the measured capacitance Cs is the capacitance value Cs1 in equation (3) minus the error component Ce, and is calculated from equations (3) and (4) above using the following equation:

In equation (5), the capacitance value Cr and the power supply voltage Vdd are known, and the first voltage value Vx1 and the second voltage value Vx2 are obtained by the operations shown in Figures 4(a) and 6(b), so the capacitance value of the measured capacitance Cs can be calculated from equation (5) above.

FIG. 7 is a flowchart showing the process of calculating the capacitance value of the measurement capacitance Cs by the operations shown in FIGS. 2(a) to 6(b).

In FIG. 7, steps S101 to S105 correspond to the first control C1 for obtaining the first voltage value Vx1, and steps S106 to S110 correspond to the second control C2 for obtaining the second voltage value Vx2.

First, as shown in FIG. 2(a), the control unit 11 connects the negative electrode of the measurement capacitance Cs to ground (S101), and executes charging of the reference capacitance Cr and discharging of the measurement capacitance Cs (S102). When charging of the reference capacitance Cr is completed, the control unit 11 disconnects the positive electrode of the reference capacitance Cr from the power supply voltage Vdd and the positive electrode of the measurement capacitance Cs from ground (S103), as shown in FIG. 2(b) and FIG. 3(a). Then, as shown in FIG. 3(b), the control unit 11 connects the positive electrode of the reference capacitance Cr and the positive electrode of the measurement capacitance Cs, and transfers the charge of the reference capacitance Cr to the measurement capacitance Cs (S104). After a period of time has elapsed until the measurement value of the measurement unit 14 becomes stable (saturated), the control unit 11 acquires the measurement value of the measurement unit 14 as the first voltage value Vx1 (S105), as shown in FIG. 4(a). In this way, the first control C1 ends.

Next, the control unit 11 connects the negative electrode of the measurement capacitance Cs to the positive electrode of the measurement capacitance Cs as shown in FIG. 4(b) (S106), and executes charging of the reference capacitance Cr and discharging of the measurement capacitance Cs as shown in FIG. 5(a) (S107). When charging of the reference capacitance Cr is completed, the control unit 11 disconnects the positive electrode of the reference capacitance Cr from the power supply voltage Vdd as shown in FIG. 5(b) and disconnects the positive electrode of the measurement capacitance Cs from the ground as shown in FIG. 5(b) (S108). Then, the control unit 11 connects the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs as shown in FIG. 6(a) and transfers the charge of the reference capacitance Cr (S109). After a period of time has elapsed until the measurement value of the measurement unit 14 becomes stable (saturated), the control unit 11 acquires the measurement value of the measurement unit 14 as the second voltage value Vx2 as shown in FIG. 6(b) (S110). In this way, the second control C2 ends.

Then, the control unit 11 applies the acquired first voltage value Vx1 and second voltage value Vx2 to the above formula (5) to calculate the capacitance value of the measured capacitance Cs (S111). In this way, the control unit 11 ends the process of FIG. 7.

Effects of First Embodiment
As shown in FIG. 4(a) and FIG. 6(b), the stable (saturated) voltage values (first voltage value Vx1, second voltage value Vx2) after the charge is transferred from the reference capacitance Cr are measured by the measurement unit 14, so that the capacitance value in a small range can be stably measured without using a high-precision AD converter. In addition, in the second control C2 shown in FIG. 7, the negative electrode and the positive electrode (the wiring having the same potential as the positive electrode) of the measurement capacitance Cs are connected in step S106, so that the measured second voltage value Vx2 is hardly influenced by the measurement capacitance Cs, but is mainly influenced by the reference capacitance Cr and the parasitic capacitance. In contrast, in the first control C1, the negative electrode of the measurement capacitance Cs is connected to the ground in step S101, so that the measured first voltage value Vx1 is influenced by the measurement capacitance Cs as well as the reference capacitance Cr and the parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance Cs from these two voltage values, the capacitance value without the influence of the parasitic capacitance can be calculated. Therefore, the capacitance value of the measurement capacitance Cs can be measured with high accuracy.

Here, the control unit 11 calculates the capacitance value of the measured capacitance Cs using the above formula (5) from the first voltage value Vx1 obtained by the first control C1, the second voltage value Vx2 obtained by the second control C2, the power supply voltage Vdd applied to the reference capacitance Cr, and the capacitance value of the reference capacitance Cr. This makes it possible to suppress the effect of error components due to parasitic capacitance on the capacitance value of the measured capacitance Cs, as described above, and to accurately obtain the capacitance value of the measured capacitance Cs.

<Modification 1>
In the first embodiment, in the first control C1 of Fig. 7, after the charge of the reference capacitance Cr is transferred to the measurement capacitance Cs (S104), a fixed period from the completion of the transfer until the measurement value of the measurement unit 14 becomes stable (saturated) has elapsed, and the first voltage value Vx1 is acquired (S105). Here, this fixed period is defined in relation to the upper limit of the range (measurement range) that can be assumed as the capacitance value of the measurement capacitance Cs. In other words, when the capacitance value of the measurement capacitance Cs is this upper limit, a period slightly longer than the period from the start of the transfer of the charge of the reference capacitance Cr until the measurement value of the measurement unit 14 becomes stable (saturated) is set as this fixed period.

However, if the actual capacitance value of the measurement capacitance Cs is significantly smaller than this upper limit, even though the measurement value of the measurement unit 14 quickly stabilizes (saturates) after the charge is transferred, it is necessary to wait until a fixed period of time has elapsed before obtaining the first voltage value Vx1. This causes a corresponding delay in the processing sequence, and the measurement results of the measurement capacitance Cs cannot be obtained quickly. This problem becomes more pronounced the wider the measurement range of the measurement capacitance Cs.

In modification example 1, the process in Figure 7 is partially modified to solve this problem.

FIG. 8 is a flowchart showing the process for calculating the capacitance value of the measurement capacitance Cs in the first modification example.

Compared to FIG. 7, steps S121 to S124 have been added to the process in FIG. 8. The processes in steps S101 to S111 are the same as the corresponding steps in FIG. 7.

In step S121, the control unit 11 sets a waiting period Tw. Here, the waiting period Tw that is initially set is set to a period slightly longer than the period from the start of charge transfer until the measurement value of the measurement unit 14 stabilizes (saturates) when the capacitance value of the measurement capacitance Cs is at the lower limit of the measurement range, for example. Next, the control unit 11 executes the processes of steps S102 to S104 as in the case of FIG. 7. Then, after starting the charge transfer in step S104, the control unit 11 waits for the waiting period Tw to elapse (S122). When the waiting period Tw has elapsed (S122: YES), the control unit 11 acquires the measurement result of the measurement unit 14 at that time as the first voltage value Vx1 (S105).

The control unit 11 determines whether the acquired first voltage value Vx1 is a voltage value after saturation (after stabilization) (S123). If the acquired first voltage value Vx1 is not a voltage value after saturation (after stabilization) (S123: NO), the control unit 11 returns the process to step S121 and resets the waiting period Tw.

For example, the control unit 11 sets the current waiting period Tw to be longer than the previous waiting period Tw by a predetermined time. Then, the control unit 11 executes the processes from step S102 onwards in the same manner. As a result, the waiting period Tw from when the charge transfer is started in step S104 until the first voltage value Vx1 is obtained is lengthened by a predetermined time. Therefore, in step S105, the voltage value after saturation (after stabilization) is more likely to be obtained as the first voltage value Vx1.

In this way, the control unit 11 repeatedly executes the processes from step S102 onwards while resetting the waiting period Tw (S121) until the first voltage value Vx1 acquired in step S105 becomes the saturated (stable) voltage value (S123: NO). Then, when the determination in step S123 becomes YES, the control unit 11 holds the first voltage value Vx1 acquired at that time as the first voltage value Vx1 to be used in the capacitance value calculation process (S111).

The determination in step S123 is performed, for example, as follows:

For example, the control unit 11 determines whether the first voltage value Vx1 acquired by the previous processing of step S105 and the first voltage value Vx1 acquired this time are substantially the same (the difference between the two is within an allowable fluctuation range). Alternatively, the control unit 11 determines whether the first voltage values Vx1 acquired by the processing of step S105 several times in the past (for example, five times), including the current time, were substantially the same. Then, if these determinations are YES, the control unit 11 determines YES in step S123.

However, the method of determining whether the first voltage value Vx1 obtained in step S105 is a saturated (stable) voltage value is not limited to these, and this determination may be made by other methods.

Then, the control unit 11 executes the processes of steps S106 to S109 as in the case of FIG. 7. The control unit 11 then waits for a waiting period Tw to elapse from the start of charge transfer in step S109 (S124). This waiting period Tw is set to the last waiting period Tw repeatedly reset in step S121. Normally, the parasitic capacitance is smaller than the measurement capacitance Cs. For this reason, when the waiting period Tw in step S124 is set in this way, the measurement result (second voltage value Vx2) of the measurement unit 14 after the waiting period Tw has elapsed is in a stable state.

The waiting period Tw in step S124 may be set as a fixed period in relation to the capacitance value of the parasitic capacitance that can be normally assumed. In other words, the waiting period Tw in step S124 may be set to a period slightly longer than the period until the charge distribution of the reference capacitance Cr is completed for the parasitic capacitance of the capacitance value that can be normally assumed.

When the waiting period Tw has elapsed (S124: YES), the control unit 11 acquires the measurement result of the measurement unit 14 at that time as the second voltage value Vx2 (S110). Then, the control unit 11 applies the acquired second voltage value Vx2 and the first voltage value Vx1 when the determination in step S123 is YES to the above formula (5) to calculate the capacitance value of the measured capacitance Cs (S111).

<Effects of Modification Example 1>
8, the control unit 11 repeatedly executes the first control C1 (steps S101 to S105) while changing the waiting period Tw from the transfer of the charge in step S104 to the acquisition of the first voltage value Vx1 in step S105 (S121) until the first voltage value Vx1 is saturated (S123: NO), and calculates the capacitance value using the saturated first voltage value Vx1 (S111). Therefore, when the capacitance value of the measurement capacitance Cs is small and the measurement value of the measurement unit 14 is saturated and stabilized early, the first voltage value Vx1 can be quickly obtained by the short waiting period Tw. Therefore, the calculation process of the capacitance value of the measurement capacitance Cs can be performed quickly.

In addition, the control unit 11 lengthens the waiting period Tw each time the first control C1 is repeated. This allows the waiting period Tw to gradually approach the length at which the first voltage value Vx1 saturates. This makes it possible to smoothly set the waiting period Tw appropriate for the measured capacitance Cs.

The method of changing the waiting period Tw in step S121 is not limited to the method of gradually lengthening it from the minimum value as described above. For example, the waiting period Tw may be decreased and increased by a predetermined length from near the middle of the possible range (set range) of the waiting period Tw, and if at least two of the first voltage values Vx1 obtained from these three waiting periods Tw are substantially the same, one of these two first voltage values Vx1 may be used in the capacitance calculation process. If at least two of the first voltage values Vx1 obtained from the three waiting periods Tw are not substantially the same, the waiting period may be increased from the maximum value of these three waiting periods until the first voltage value Vx1 is saturated, and the first voltage value Vx1 used in the capacitance calculation may be obtained.

<Modification 2>
In the first embodiment, the capacitance value of the reference capacitance Cr is fixed. However, in the second modification, the capacitance value of the reference capacitance Cr is changeable.

FIG. 9 shows the configuration of the capacitance measurement circuit 10 according to the second modification.

As shown in FIG. 9, the capacitance measurement circuit 10 according to the second modification includes four capacitors Cra to Crd, four switch elements 16a to 16d, and a capacitance selection unit 15 as a capacitance value change unit for changing the capacitance value of the reference capacitance Cr. The switch elements 16a to 16d are switched between conductive and non-conductive by the capacitance selection unit 15. When the switch elements 16a to 16d are conductive, the capacitors Cra to Crd are each connected between the wiring between the

switch elements

12a, 12b and ground.

In this configuration, the reference capacitance Cr in FIG. 1 is formed by the combined capacitance of the four capacitors Cra to Crd that are connected between this wiring and ground. Therefore, the capacitance value of the reference capacitance Cr changes depending on which of the switch elements 16a to 16d is made conductive by the capacitance selection unit 15.

The control unit 11 changes the switch element that is turned on by the capacitance selection unit 15 according to the measurement range (dynamic range) of the measurement capacitance Cs, and sets the capacitance value of the reference capacitance Cr to a value suitable for that dynamic range. That is, as described above, the capacitance value of the reference capacitance Cr is set so that the measurement unit 14 can properly measure the voltage value of the measurement capacitance Cs after charge is transferred from the reference capacitance Cr to the measurement capacitance Cs. The dynamic range of the measurement capacitance Cs is set in the control unit 11 by the user, for example, via a higher-level terminal (not shown).

<Effects of Modification Example 2>
According to the second modification, as described above, the capacitance value of the reference capacitance Cr can be adjusted to a value suitable for the dynamic range of the measurement capacitance Cs. Therefore, even if the dynamic range of the measurement capacitance Cs is changed, the capacitance value of the measurement capacitance Cs can be properly measured within the dynamic range.

In the configuration of FIG. 9, four capacitors Cra to Crd and four switch elements 16a to 16d are arranged to change the capacitance value of the reference capacitance Cr, but the number of pairs of capacitors and switch elements is not limited to this. The number of pairs may be set to a predetermined number of two or more in relation to the range of the dynamic range that can be supported.

Note that the configuration for changing the capacitance value of the reference capacitance Cr is not limited to the configuration shown in FIG. 19. For example, a variable capacitance may be arranged instead of the four capacitors Cra to Crd and the four switch elements 16a to 16d. In this case, the control unit 11 may control the capacitance value of the variable capacitance to a capacitance value that corresponds to the measurement range (dynamic range) of the measurement capacitance Cs.

<Embodiment 2>
In the above-described embodiment 1, the charge stored in the reference capacitance Cr is distributed to the measurement capacitance Cs to calculate the capacitance value, whereas in the embodiment 2, the charge stored in the measurement capacitance Cs is distributed to the reference capacitance Cr to calculate the capacitance value.

FIG. 10 is a diagram showing the configuration of a capacitance measurement circuit 10 according to embodiment 2.

In FIG. 10, the positions of the reference capacitance Cr, the measurement capacitance Cs, the switch element 13, and the measurement unit 14 are changed compared to FIG. 1. That is, the measurement capacitance Cs is placed upstream of the reference capacitance Cr (on the power supply voltage Vdd side), and the positions of the switch element 13 and the measurement unit 14 are changed accordingly. The functions of the switch element 13 and the measurement unit 14 are the same as in the above-mentioned embodiment 1. Of the switch elements 12a to 12c, the switch element 12b can be changed to an N-type FET. The configuration and function of the

switch elements

12a and 12c are the same as in the above-mentioned embodiment 1.

FIGS. 11(a) to 15(b) are diagrams showing the operation of the capacitance measurement circuit 10 when measuring the capacitance value of the measurement capacitance Cs. FIG. 16 is a flowchart showing the processing of the control unit 11 when measuring the capacitance value of the measurement capacitance Cs.

First, as shown in FIG. 11(a), the control unit 11 connects the negative electrode of the measurement capacitance Cs to ground (S201), switches the

switch elements

12a and 12c to a conductive state, and charges the measurement capacitance Cs and discharges the reference capacitance Cr (S202). Thereafter, as shown in FIG. 11(b), the control unit 11 disconnects the positive electrode of the reference capacitance Cr from ground, and after the measurement capacitance Cs is fully charged, as shown in FIG. 12(a), disconnects the positive electrode of the measurement capacitance Cs from ground (S203). Whether the measurement capacitance Cs is fully charged can be determined by whether the voltage of the measurement capacitance Cs has reached the power supply voltage Vdd and stabilized, as in the above embodiment.

Next, the control unit 11 switches the switch element 12b to a conductive state, as shown in FIG. 12(b), and transfers the charge of the measurement capacitance Cs to the reference capacitance Cr (S204). The control unit 11 then waits for a period of time until this transfer is completed, and thereafter, as shown in FIG. 13(a), obtains the measurement value of the measurement unit 14 as the first voltage value Vx1 (S205). This completes the first control C1.

Then, as shown in FIG. 13(b), the control unit 11 switches the switch element 13 to the positive electrode side of the measurement capacitance Cs, and connects the positive electrode and negative electrode of the measurement capacitance Cs (S206). Then, as shown in FIG. 14(a), the control unit 11 switches the

switch elements

12b and 12c to the conductive state, and discharges the reference capacitance Cr and the measurement capacitance Cs (S207).

Then, the control unit 11 switches the

switch elements

12b and 12c to a non-conductive state, and further switches the switch element 12a to a conductive state as shown in FIG. 14(b) to connect the positive electrode of the measurement capacitance Cs to the power supply voltage Vdd (S208). Here, since the positive electrode and negative electrode of the measurement capacitance Cs are connected, the positive electrode and negative electrode of the measurement capacitance Cs are at the same potential. Therefore, the measurement capacitance Cs is not charged, and charging is performed on the parasitic capacitance other than the measurement capacitance Cs.

Then, the control unit 11 sets the switch element 12a to a non-conductive state to disconnect the positive electrode of the measurement capacitance Cs from the power supply voltage Vdd (S209), and then switches the switch element 12b to a conductive state to connect the positive electrode of the measurement capacitance Cs and the positive electrode of the reference capacitance Cr as shown in FIG. 15(a), thereby transferring charge to the reference capacitance Cr (S210). Here, since no charge has been accumulated in the measurement capacitance Cs as described above, the charge accumulated in the parasitic capacitance is transferred to the reference capacitance Cr. After the charge has been transferred, the control unit 11 obtains the measurement value of the measurement unit 14 as the first voltage value Vx1 as shown in FIG. 15(b) (S205). This completes the second control C2.

Then, the control unit 11 calculates the capacitance value of the measured capacitance Cs from the first voltage value Vx1 and the second voltage value Vx2 obtained in the first control C1 and the second control C2, respectively (S212).

The capacitance value of the measured capacitance Cs is calculated as follows:

First, as shown in FIG. 11(a), when the measured capacitance Cs is fully charged, the charge Qs of the measured capacitance Cs is expressed by the following formula, assuming that the capacitance value of the measured capacitance Cs is Cs1.

Qs = Cs1 x Vdd ... (6)

Furthermore, when the charge transfer is complete as shown in Figure 2(b), if the capacitance value with respect to the reference capacitance Cr is Cr, the following relationship holds:

　　Qs＝（Cr＋Cs1）×Vx1　…（7）

Therefore, the following relationship can be derived from equations (6) and (7):

However, as described above, this capacitance value Cs1 includes an error component due to parasitic capacitance. This error component Ce can be expressed by the following equation using the second voltage value Vx2 obtained by the operation of FIG. 15(b).

In other words, during the operation shown in Figures 14(a) to 15(b), the positive and negative electrodes of the measurement capacitance Cs are at the same potential, so the measurement capacitance Cs is invalidated, and only the reference capacitance Cr and the parasitic capacitance become the capacitance components. Therefore, the electrostatic capacitance value of the parasitic capacitance, i.e., the error component Ce, can be expressed by the above formula (9).

The capacitance value Cs of the measured capacitance Cs is the capacitance value Cs in equation (8) minus the error component Ce, and is calculated from equations (8) and (9) above using the following equation:

In equation (10), the capacitance value Cr and the power supply voltage Vdd are known, and the first voltage value Vx1 and the second voltage value Vx2 are obtained by the operations shown in Figures 13(a) and 15(b), so the capacitance value of the measured capacitance Cs can be calculated from equation (10) above.

FIGS. 17(a) and (b) are graphs showing simulation results of capacitance detected by the capacitance detection process of FIG. 7 (embodiment 1) and FIG. 16 (embodiment 2), respectively.

In this simulation, the capacitance value of the measured capacitance Cs was calculated by the processes in Figures 7 and 16 when the capacitance value of the measured capacitance Cs was changed. In Figures 17(a) and (b), the horizontal axis is the capacitance value set for the measured capacitance Cs, and the vertical axis is the capacitance value calculated by the processes.

As shown in Figures 17(a) and (b), the capacitance values calculated by the processes of the first and second embodiments are roughly equal to the capacitance values set for the measured capacitance Cs, and a linear approximation line was obtained from the plot of the simulation results. This confirms that these processes make it possible to obtain a capacitance value for the measured capacitance Cs in which the effects of parasitic capacitance are effectively suppressed.

<Effects of the Second Embodiment>
As shown in FIG. 13(a) and FIG. 15(b), the stable (saturated) voltage values (first voltage value Vx1, second voltage value Vx2) after the charge transfer are measured by the measuring unit 14, so that the capacitance value in a small range can be stably measured without using a high-precision AD converter. In addition, in the second control C2 shown in FIG. 16, the negative electrode and the positive electrode (wire with the same potential as the positive electrode) of the measurement capacitance Cs are connected in step S206, so that the measured second voltage value Vx2 is hardly influenced by the measurement capacitance Cs, but is mainly influenced by the reference capacitance Cr and the parasitic capacitance. In contrast, in the first control C1, the negative electrode of the measurement capacitance Cs is connected to the ground in step S201, so that the measured first voltage value Vx1 is influenced by the measurement capacitance Cs as well as the reference capacitance Cr and the parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance Cs from these two voltage values, the capacitance value without the influence of the parasitic capacitance can be calculated. Therefore, the electrostatic capacitance value of the measurement capacitance Cs can be measured with high accuracy.

Here, the control unit 11 calculates the capacitance value of the measurement capacitance Cs using the above formula (10) from the first voltage value Vx1 obtained by the first control C1, the second voltage value Vx2 obtained by the second control C2, the power supply voltage Vdd applied to the measurement capacitance Cs, and the capacitance value of the reference capacitance Cr. As a result, as described above, the effect of error components due to parasitic capacitance on the capacitance value of the measurement capacitance Cs can be suppressed, and the capacitance value of the measurement capacitance Cs can be obtained with high accuracy.

<Modification 1>
7, after the charge of the reference capacitance Cr is transferred to the measurement capacitance Cs (S204), the first voltage value Vx1 is acquired after a fixed period has elapsed until the transfer is completed and the measurement value of the measurement unit 14 becomes stable (saturated) (S205). In contrast, in the modified example 1, the first voltage value Vx1 is acquired while changing the waiting period Tw, as in the modified example 1 of the above-mentioned embodiment 1.

FIG. 18 is a flowchart showing the process for calculating the capacitance value of the measurement capacitance Cs in the first modification example.

18, as in FIG. 8, the control unit 11 acquires the first voltage value Vx1 (S205) while changing the waiting period Tw (S221) until the first voltage value Vx1 becomes saturated (stable) (S223: NO). That is, after the charge transfer is started in step S204 of FIG. 16, the waiting period Tw (S222) until the first voltage value Vx1 is acquired is changed, and the first voltage value Vx1 is acquired (S205). The control unit 11 acquires the measurement value of the measurement unit 14 at the point when the measurement value becomes saturated (stable) as the first voltage value Vx1 to be used in calculating the capacitance value (S212).

In this case, as in the case of FIG. 8, the waiting period Tw is gradually lengthened from the minimum value of the setting range. However, in this case, as in the case of FIG. 8, the method of changing the waiting period Tw is not limited to this, and it may be changed by other methods. Also, the determination in step S223 may be performed in the same manner as the determination in step S123 in FIG. 8.

Then, the control unit 11 performs the processes of steps S206 to S210 to obtain the second voltage value Vx2, as in FIG. 16. After starting the transfer of charge in step S210, the control unit 11 waits for the waiting period Tw to elapse when the determination in step S222 becomes YES (S224), and obtains the measurement value of the measurement unit 14 at the time when the waiting period Tw has elapsed as the second voltage value Vx2 (S211).

In this case, as in the case of FIG. 8, the waiting period Tw in step S224 may be set as a fixed period in relation to the capacitance value of the parasitic capacitance that can be normally assumed. In other words, the waiting period Tw in step S224 may be set to a period slightly longer than the period until the distribution of charge from the parasitic capacitance of the normally assumed capacitance value to the reference capacitance Cr is completed.

Then, the control unit 11 applies the acquired second voltage value Vx2 and the first voltage value Vx1 when the determination in step S223 is YES to the above formula (10) to calculate the capacitance value of the measured capacitance Cs. This causes the control unit 11 to end the process of FIG. 18.

<Effects of Modification Example 1>
18, the control unit 11 repeatedly executes the first control C1 (steps S201 to S205) while changing the waiting period Tw from the transfer of the charge in step S204 to the acquisition of the first voltage value Vx1 in step S205 (S221) until the first voltage value Vx1 is saturated (S223: NO), and calculates the capacitance value using the saturated first voltage value Vx1 (S212). Therefore, when the capacitance value of the measurement capacitance Cs is small and the measurement value of the measurement unit 14 is saturated and stabilized early, the first voltage value Vx1 can be quickly obtained by the short waiting period Tw. Therefore, the calculation process of the capacitance value of the measurement capacitance Cs can be performed quickly.

<Modification 2>
In this modification example 2, similarly to the modification example 2 of the first embodiment, the capacitance value of the reference capacitance Cr is changeable.

FIG. 19 shows the configuration of the capacitance measurement circuit 10 according to the second modification.

As shown in FIG. 19, the capacitance measurement circuit 10 according to the second modification includes, as in FIG. 9, four capacitors Cra to Crd, four switch elements 16a to 16d, and a capacitance selection unit 15 as a capacitance value change unit for changing the capacitance value of the reference capacitance Cr. The switch elements 16a to 16d can be changed to N-type FETs. When the switch elements 16a to 16d are made conductive by the capacitance selection unit 15, the capacitors Cra to Crd are each connected between the wiring between the

switch elements

12b and 12c and the ground.

Even with this configuration, the reference capacitance Cr in FIG. 10 is formed by the combined capacitance of the capacitors among the four capacitors Cra to Crd that are connected between this wiring and ground. Therefore, the capacitance value of the reference capacitance Cr can be changed depending on which of the switch elements 16a to 16d is turned on by the capacitance selection unit 15. This makes it possible to adjust the capacitance value of the reference capacitance Cr to a value appropriate for the dynamic range of the measurement capacitance Cs. Therefore, even if the dynamic range of the measurement capacitance Cs is changed, the capacitance value of the measurement capacitance Cs can be properly measured within that dynamic range.

<Embodiment 3>
In the third embodiment, a configuration example is shown in which the capacitance measurement circuit 10 of the first embodiment is applied to a load detection device. The load detection device detects a load using a capacitance type load sensor. This type of load detection device can be applied to various systems. The load sensor included in the load detection device may be called a "capacitive pressure sensor element," a "capacitive pressure detection sensor element," a "pressure sensitive switch element," or the like.

First, the configuration of the load sensor 20 will be described with reference to Figs. 20(a) to 23. For convenience, mutually orthogonal X, Y, and Z axes are indicated in Figs. 20(a) to 23. The Z-axis direction is the thickness direction of the load sensor 20.

Figure 20(a) is a perspective view that shows a schematic diagram of a base member 21 and a conductive elastic body 22 that is placed on the upper surface (the surface on the positive side of the Z axis) of the base member 21.

The base member 21 is an elastic, insulating, flat-plate member. The base member 21 has a rectangular shape in a plan view. The thickness of the base member 21 is constant. The thickness of the base member 21 is, for example, 0.01 mm to 2 mm. When the thickness of the base member 21 is small, the base member 21 is sometimes called a sheet member or a film member. The base member 21 is made of a non-conductive resin material or a non-conductive rubber material.

The resin material used for the base member 21 is, for example, at least one resin material selected from the group consisting of styrene-based resin, silicone-based resin (e.g., polydimethylpolysiloxane (PDMS)), acrylic-based resin, rotaxane-based resin, and urethane-based resin. The rubber material used for the base member 21 is, for example, at least one rubber material selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and natural rubber.

The conductive elastic bodies 22 are disposed on the upper surface (the surface on the positive side of the Z axis) of the base member 21. In FIG. 20(a), three conductive elastic bodies 22 are disposed on the upper surface of the base member 21. The conductive elastic bodies 22 are elastic, conductive members. Each conductive elastic body 22 has a long strip shape in the Y axis direction. The three conductive elastic bodies 22 are disposed side by side at a predetermined interval in the X axis direction. Wiring W2 electrically connected to the conductive elastic bodies 22 is provided at the end of each conductive elastic body 22 on the negative side of the Y axis.

The conductive elastic body 22 is formed on the upper surface of the base member 21 by a printing method such as screen printing, gravure printing, flexographic printing, offset printing, and gravure offset printing. These printing methods make it possible to form the conductive elastic body 22 on the upper surface of the base member 21 with a thickness of about 0.001 mm to 0.5 mm.

The conductive elastomer 22 is composed of a resin material with conductive filler dispersed therein, or a rubber material with conductive filler dispersed therein.

The resin material used for the conductive elastic body 22 is the same as the resin material used for the base member 21 described above, and is at least one resin material selected from the group consisting of, for example, styrene-based resins, silicone-based resins (polydimethylpolysiloxane (e.g., PDMS), etc.), acrylic-based resins, rotaxane-based resins, and urethane-based resins.

The rubber material used for the conductive elastomer 22 is the same as the rubber material used for the base member 21 described above, and is at least one type of rubber material selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and natural rubber.

The conductive filler used in the conductive elastomer 22 is at least one material selected from the group consisting of metal materials such as Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), In ₂ O ₃ (indium (III) oxide), and SnO ₂ (tin (IV) oxide), conductive polymer materials such as PEDOT:PSS (i.e., a composite of poly 3,4-ethylenedioxythiophene (PEDOT) and polystyrene sulfonate (PSS)), and conductive fibers such as metal-coated organic fibers and metal wires (in a fibrous state).

FIG. 20(b) is a perspective view that shows a schematic diagram of the structure of FIG. 20(a) with conductor wire 23 installed.

The conductor wires 23 are linear members and are arranged overlapping on the upper surface of the conductive elastic body 22 shown in FIG. 20(a). In this embodiment, three conductor wires 23 are arranged overlapping on the upper surfaces of the three conductive elastic bodies 22. The three conductor wires 23 are arranged side by side at a predetermined interval along the longitudinal direction (Y-axis direction) of the conductive elastic body 22 so as to intersect with the conductive elastic body 22. Each conductor wire 23 is arranged extending in the X-axis direction so as to straddle the three conductive elastic bodies 22.

The conductor wire 23 is, for example, a coated copper wire. The conductor wire 23 is composed of a linear conductive member 23a and a dielectric 23b formed on the surface of the conductive member 23a.

Figure 21(a) is a schematic perspective view showing the state in which thread 24 is installed in the structure of Figure 20(b).

After the conductor wires 23 are arranged as shown in FIG. 20(b), each conductor wire 23 is connected to the base member 21 by threads 24 so as to be movable in the longitudinal direction (X-axis direction) of the conductor wire 23. In the example shown in FIG. 21(a), 12 threads 24 connect the conductor wires 23 to the base member 21 at positions other than the positions where the conductive elastic body 22 and the conductor wire 23 overlap. The threads 24 are made of chemical fibers, natural fibers, or a mixture of these fibers.

Figure 21(b) is a perspective view that shows a schematic diagram of the structure in Figure 21(a) with a base member 25 installed.

The base member 25 is placed from above (the positive side of the Z axis) of the structure shown in FIG. 21(a). The base member 25 is an insulating member. The base member 25 is, for example, at least one resin material selected from the group consisting of polyethylene terephthalate, polycarbonate, polyimide, etc. The base member 25 may be made of the same material as the base member 21. The base member 25 has a flat plate shape parallel to the XY plane, and has the same size and shape as the base member 21 in a planar view. The thickness of the base member 25 in the Z axis direction is, for example, 0.01 mm to 2 mm.

The four outer periphery sides of base member 25 are connected to the four outer periphery sides of base member 21 with silicone rubber adhesive, thread, or the like. This fixes base member 25 to base member 21. Conductor wire 23 is sandwiched between conductive elastic body 22 and base member 25. In this way, load sensor 20 is completed as shown in Figure 21 (b). Load sensor 20 can be used in a state where it is turned over from the state shown in Figure 21 (b).

22(a) and 22(b) are schematic diagrams showing the cross section of the load sensor 20 when the load sensor 20 is cut along a plane parallel to the Y-Z plane at the center position in the X-axis direction of the conductive elastic body 22. FIG. 22(a) shows the cross section when no load is applied, and FIG. 22(b) shows the cross section when a load is applied.

As shown in Figures 22(a) and (b), the conductor wire 23 is composed of a conductive member 23a and a dielectric 23b formed on the conductive member 23a. The conductive member 23a is a linear member having electrical conductivity. The dielectric 23b covers the surface of the conductive member 23a. The conductive member 23a is composed of, for example, copper. The diameter of the conductive member 23a is, for example, about 60 μm.

The dielectric 23b has electrical insulation properties and is made of, for example, a resin material, a ceramic material, a metal oxide material, etc. The dielectric 23b may be at least one resin material selected from the group consisting of polypropylene resin, polyester resin (for example, polyethylene terephthalate resin), polyimide resin, polyphenylene sulfide resin, polyvinyl formal resin, polyurethane resin, polyamideimide resin, polyamide resin, etc., or at least one metal oxide material selected from the group consisting of Al ₂ O ₃ , Ta ₂ O ₅ , etc. The dielectric 23b is formed at least in the range of the conductor line 23 overlapping the conductive elastic body 22.

As shown in Figure 22(a), when no load is applied, the force applied between the conductive elastic body 22 and the conductor wire 23, and the force applied between the base member 25 and the conductor wire 23, are almost zero. From this state, when a load is applied to the surface of the base member 21 on the negative side of the Z axis, as shown in Figure 22(b), the conductive elastic body 22 and the base member 21 are deformed by the conductor wire 23.

As shown in FIG. 22(b), when a load is applied, the conductor wire 23 is brought closer to the conductive elastic body 22 so that it is wrapped in the conductive elastic body 22. As a result, the contact area between the conductor wire 23 and the conductive elastic body 22 increases. This causes a change in the capacitance between the conductive member 23a and the conductive elastic body 22. By detecting the capacitance between the conductive member 23a and the conductive elastic body 22, the load applied to this area is obtained.

FIG. 23 is a plan view that shows a schematic diagram of the internal configuration of the load sensor 20. For convenience, the thread 24 and the base member 25 are omitted from FIG. 23.

As shown in Figure 23, element parts A11, A12, A13, A21, A22, A23, A31, A32, and A33 whose capacitance changes depending on the load are formed at the positions where three conductive elastic bodies 22 and three conductor lines 23 intersect. Each element part includes a conductive elastic body 22 and a conductor line 23 near the intersection of the conductive elastic body 22 and the conductor line 23.

In each element portion, the conductor wire 23 constitutes one pole of the capacitance (e.g., an anode), and the conductive elastic body 22 constitutes the other pole of the capacitance (e.g., a cathode). That is, the conductive member 23a (see Figures 22(a) and (b)) in the conductor wire 23 constitutes one electrode of the load sensor 20 (capacitive load sensor), the conductive elastic body 22 constitutes the other electrode of the load sensor 20 (capacitive load sensor), and the dielectric 23b (see Figures 22(a) and (b)) included in the conductor wire 23 corresponds to the dielectric that determines the capacitance in the load sensor 20 (capacitive load sensor).

When a load is applied to each element in the Z-axis direction, the conductor wire 23 is enveloped in the conductive elastic body 22. This changes the contact area between the conductor wire 23 and the conductive elastic body 22, and the capacitance between the conductor wire 23 and the conductive elastic body 22 changes. The end of the conductor wire 23 on the negative side of the X-axis and the end of the wiring W2 installed on the conductive elastic body 22 on the negative side of the Y-axis are connected to the capacitance measurement circuit 10, which will be described later with reference to FIG. 24.

When a load is applied to element part A11, the contact area between the conductive member 23a of the conductor line 23 and the conductive elastic body 22 increases in element part A11 via the dielectric 23b. In this case, the load applied to element part A11 can be calculated by detecting the capacitance between the conductive elastic body 22 on the most negative side of the X-axis and the conductor line 23 on the most positive side of the Y-axis. Similarly, in other element parts, the load applied to the other element parts can be calculated by detecting the capacitance between the conductive elastic body 22 and the conductor line 23 that intersect in the other element parts.

FIG. 24 shows the configuration of the load detection device 1.

For convenience, FIG. 24 illustrates only the conductor wire 23 and the conductive elastic body 22 as components of the load sensor 20, and the conductive elastic body 22 is illustrated as a line.

The load detection device 1 includes the capacitance measurement circuit 10 according to the first embodiment and the load sensor 20 shown in FIG. 21(b). Here, the nine element parts A11 to A33 shown in FIG. 23 each correspond to a measurement capacitance Cs. The conductor wire 23 (conductive member 23a) of the element parts A11 to A33 corresponds to the positive electrode of the measurement capacitance Cs, and the conductive elastic body 22 of the element parts A11 to A33 corresponds to the negative electrode of the measurement capacitance Cs.

The capacitance measurement circuit 10 includes

element selection units

17 and 18 for switching the element unit to be measured among the nine element units A11 to A33 shown in FIG. 23. The element selection unit 17 includes switch elements 17a to 17c, and the element selection unit 18 includes switch elements 18a to 18d.

Switch elements 17a to 17c connect the wiring W2 drawn out from the conductive elastic body 22 to either the ground line L3 or the potential line L2. These switch elements 17a to 17c correspond to switch element 13 in FIG. 1. Switch element 18d connects the potential line L1 to one of switch elements 18a to 18c. Switch elements 18a to 18c connect the wiring W1 drawn out from the conductor line 23 (conductive member 23a) to either the output terminal of switch element 18d or the ground line L3.

The capacitance measurement circuit 10 also includes an equipotential generator 19 for generating a potential equal to that of the potential line L1. In the configuration of FIG. 1, one terminal of the switch element 17a is directly connected to the wiring between the

switch elements

12b and 12c in order to make the positive and negative electrodes of the measurement capacitance Cs equal in potential. In contrast, in FIG. 24, in addition to the switch element 17a,

other switch elements

17b and 17c, wiring W2, conductive elastic body 22, and other circuit parts are connected to the potential line L2 to which one terminal of the switch element 17a is connected, so the impedance of these circuit parts is higher than in the case of FIG. 1. For this reason, in the configuration of FIG. 24, an equipotential generator 19 is arranged to make the potential of the potential line L2 equal to that of the potential line L1.

FIG. 24 shows the states of switch elements 17a-17c, 18a-18d in first control C1 when measuring the capacitance value of element part A11. In this state, the conductor wires 23 (positive poles) of element parts A11-A13, which are the topmost of the nine element parts, are connected to potential line L1. As a result, the remaining six element parts are in a state of being disconnected in terms of the circuit. In addition, the same potential as that of potential line L1 is applied to the conductive elastic bodies 22 of element parts A12 and A13 by equipotential generator 19, so element parts A12 and A13 are disabled. Therefore, only element part A11 to be measured is connected to capacitance measurement circuit 10.

In this state, the control unit 11 executes the first control C1 in FIG. 7 to obtain the first voltage value Vx1. Next, in step S106 of the second control C2 in FIG. 7, the control unit 11 switches the switch element 17a to the potential line L2 side as shown in FIG. 25, and executes the processes of steps S107 to S110. As a result, the control unit 11 obtains the second voltage value Vx2. Then, the control unit 11 executes the process of step S111 to calculate the capacitance value of the element unit A11. Furthermore, the control unit 11 calculates the load applied to the element unit A11 from the calculated capacitance value. The load may be calculated by a processing unit other than the control unit 11 from the capacitance value calculated by the control unit 11. In this way, the process for the element unit A11 is completed.

The control unit 11 controls the switch elements 17a to 17c and 18a to 18d to sequentially switch the element part to be measured. For example, when the element part A12 is the object to be measured, the control unit 11 connects the switch element 17b to the ground line L3 and connects the

switch elements

17a and 17c to the potential line L2 in step S101 of the first control C1 in FIG. 7. The control unit 11 also causes the switch elements 18a to 18d to maintain the state shown in FIG. 24. In this state, the control unit 11 executes the process from step S102 onwards in FIG. 7. In step S106, the switch element 17b is switched to the potential line L2 side, and the process from step S107 onwards is carried out. In this way, the control unit 11 calculates the capacitance value of the element part A12, and calculates the load applied to the element part A12 from the calculation result.

<Effects of the Third Embodiment>
According to the load detection device 1 of the third embodiment, since it includes the capacitance measurement circuit 10 of the first embodiment, it is possible to stably obtain a capacitance value according to the load even when the load applied to the element parts A11 to A33 is small and the capacitance is small. Also, since it includes the capacitance measurement circuit 10 of the first embodiment, it is possible to accurately obtain a capacitance value in which the influence of parasitic capacitance is suppressed. Therefore, it is possible to stably and accurately detect a small range of load.

The load sensor 20 also includes multiple element parts A11 to A33, and the capacitance measurement circuit 10 includes

element selection units

17 and 18 for switching between element parts to be measured. This allows the load to be detected over a wide range in which the multiple element parts A11 to A33 are arranged. By switching between element parts to be measured using the

element selection units

17 and 18, the capacitance value of each element part can be measured stably and accurately using processing similar to that shown in FIG. 7.

In the configuration of FIG. 24, compared to the configuration of FIG. 1, more switch elements 17a-17c, 18a-18d and wiring are arranged, and furthermore, an equipotential generating unit 19 is arranged, so that the parasitic capacitance increases. However, even in this case, the effect of the parasitic capacitance is suppressed by the above formula (5), so that the capacitance value of each element unit can be calculated with high accuracy, and the load applied to each element unit can be detected with high accuracy.

The process of calculating the capacitance value of each element part may be changed to the process shown in FIG. 8. This allows the process of calculating the capacitance value for each element part to be performed quickly, and the load detection process for all nine element parts to be performed quickly.

Furthermore, the configuration of modified example 2 shown in FIG. 9 may be applied to the configuration of FIG. 24. As a result, even if the load sensor 20 to be measured is changed and the dynamic range of the element unit is changed, the capacitance value of each element unit can be measured properly and the load of each element unit can be detected with high accuracy.

<Embodiment 4>
In the fourth embodiment, a configuration example in which the capacitance measuring circuit 10 of the second embodiment is applied to a load detection device is shown. The load detection device detects a load by a load sensor similar to that of the third embodiment.

FIG. 26 is a diagram showing the configuration of a load detection device 1 according to embodiment 4.

As in FIG. 24, for convenience, FIG. 26 illustrates only the conductor wire 23 and the conductive elastic body 22 as components of the load sensor 20, and the conductive elastic body 22 is illustrated as a line.

The load detection device 1 includes the capacitance measurement circuit 10 according to the second embodiment and the load sensor 20 shown in FIG. 21(b). As in the third embodiment, the nine element parts A11 to A33 shown in FIG. 23 each correspond to a measurement capacitance Cs. The conductor wire 23 (conductive member 23a) of the element parts A11 to A33 corresponds to the positive electrode of the measurement capacitance Cs, and the conductive elastic body 22 of the element parts A11 to A33 corresponds to the negative electrode of the measurement capacitance Cs.

The configuration of switch elements 17a to 17c and switch elements 18a to 18d is the same as in FIG. 24. Also, as in FIG. 24, an equal potential generator 19 is provided to make the potential of potential line L2 equal to the potential of potential line L1.

As in FIG. 24, FIG. 26 shows the states of the switch elements 17a-17c and 18a-18d in the first control C1 when measuring the capacitance value of the element part A11. In this case, as in FIG. 24, only the element part A11 to be measured is connected to the capacitance measurement circuit 10.

In this state, the control unit 11 executes the first control C1 in FIG. 16 to obtain the first voltage value Vx1. Next, in step S206 of the second control C2 in FIG. 16, the control unit 11 switches the switch element 17a to the potential line L2 side as shown in FIG. 27, and executes the processes of steps S207 to S211. As a result, the control unit 11 obtains the second voltage value Vx2. Then, the control unit 11 executes the process of step S212 to calculate the capacitance value of the element unit A11. Furthermore, the control unit 11 calculates the load applied to the element unit A11 from the calculated capacitance value. The load may be calculated by a processing unit other than the control unit 11 from the capacitance value calculated by the control unit 11. In this way, the process for the element unit A11 is completed.

switch elements

17a and 17c to the potential line L2 in step S201 of the first control C1 in FIG. 16. The control unit 11 also causes the switch elements 18a to 18d to maintain the state shown in FIG. 26. In this state, the control unit 11 executes the process from step S202 onwards in FIG. 16. In step S206, the switch element 17b is switched to the potential line L2 side, and the process from step S207 onwards is carried out. In this way, the control unit 11 calculates the electrostatic capacitance value of the element part A12, and calculates the load applied to the element part A12 from the calculation result.

<Effects of the Fourth Embodiment>
According to the load detection device 1 of the fourth embodiment, since it includes the capacitance measurement circuit 10 of the second embodiment, it is possible to stably obtain a capacitance value according to the load even when the load applied to the element parts A11 to A33 is small and the capacitance is small. Also, since it includes the capacitance measurement circuit 10 of the second embodiment, it is possible to accurately obtain a capacitance value in which the influence of parasitic capacitance is suppressed. Therefore, it is possible to stably and accurately detect a small range of load. Also, by switching the element part to be measured by the

element selection parts

17 and 18, it is possible to stably and accurately measure the capacitance value of each element part by the same process as that of FIG. 16.

In the configuration of FIG. 26, more switch elements 17a-17c, 18a-18d and wiring are arranged than in the configuration of FIG. 10, and an equipotential generator 19 is also arranged, so that the parasitic capacitance increases. However, even in this case, the effect of the parasitic capacitance is suppressed by the above formula (10), so that the capacitance value of each element can be calculated with high accuracy, and the load applied to each element can be detected with high accuracy.

The process of calculating the capacitance value of each element unit may be changed to the process shown in FIG. 18. This allows the process of calculating the capacitance value for each element unit to be performed quickly, and the load detection process for all nine element units to be performed quickly.

Furthermore, the configuration of modified example 2 shown in FIG. 19 may be applied to the configuration of FIG. 26. As a result, even if the load sensor 20 to be measured is changed and the dynamic range of the element unit is changed, the capacitance value of each element unit can be measured properly and the load of each element unit can be detected with high accuracy.

<Other changes>
In the above-mentioned first and second embodiments, the switch elements 12a to 12c are configured by P-type or N-type FETs, but the switch elements 12a to 12c may be configured by switch elements other than FETs. Similarly, the switch element 13 may be configured by various types of switch elements as long as the connection destination of the negative electrode of the measurement capacitance Cs can be switched between ground and the positive electrode. Similarly, in the configurations of Figs. 24 to 26, various types of switch elements may be used as the switch elements 17a to 17c and the switch elements 18a to 18d.

In the above embodiment 1, after the switch element 13 is switched in FIG. 4(b), the reference capacitance Cr is charged in FIG. 5(a) without being discharged. However, the reference capacitance Cr may be discharged once and then charged in FIG. 5(a). In this case, however, it takes longer for the reference capacitance Cr to be fully charged than when the reference capacitance Cr is charged without being discharged as described above. Therefore, in order to proceed with the process more quickly, it is preferable to charge the reference capacitance Cr without discharging it, as in FIG. 5(a). This is also true in the flow from the operation in FIG. 13(b) to the operation in FIG. 14(a) in embodiment 2.

In addition, in the third and fourth embodiments, as shown in FIGS. 24 to 26, an equal potential is applied to the positive and negative electrodes of element parts A12 and A13 other than the element part A11 to be measured, thereby disabling element parts A12 and A13. However, switch

elements

17b and 17c may be set so that the negative electrodes of these elements are connected to ground line L3. In this case as well, the capacitance of element parts A12 and A13 is included in the parasitic capacitance described above, and is therefore cancelled out by the above formulas (5) and (10). Therefore, the capacitance of element part A11 to be measured can be obtained with high accuracy.

24 to 26, the two conductor lines 23 (conductive members 23a) other than the conductor line 23 (conductive member 23a) constituting the positive electrode of the element portion A11 to be measured are connected to the ground line by the

switch elements

18b and 18c, but the

switch elements

18b and 18c may be connected to the output line side of the switch element 18d, and the element portion having these two conductor lines 23 (conductive member 23a) as the positive electrode may be set in a floating state. In this case, too, the parasitic capacitances other than those of the element portion A11 to be measured are canceled by the above equations (5) and (10), so that the capacitance of the element portion A11 to be measured can be obtained with high accuracy.

The configuration and switching form of the

element selection units

17 and 18 may be other configurations and switching forms as long as the negative electrode of the element part to be measured can be connected to ground or to a wiring having the same potential as the positive electrode of the element part to be measured, and the capacitance of element parts other than the one to be measured can be canceled together with other parasitic capacitances by the above formulas (5) and (10).

In addition, in the above-mentioned third and fourth embodiments, the conductor wire 23 is composed of a coated copper wire, but it is not limited to this, and may be composed of a linear conductive member made of a material other than copper and a dielectric that coats the conductive member. Also, the conductive member may be composed of a twisted wire.

In addition, in the above-mentioned third and fourth embodiments, the conductive elastic body 22 is provided only on the surface of the base member 21 on the positive side of the Z axis, but a conductive elastic body may also be provided on the surface of the base member 25 on the negative side of the Z axis. In this case, the conductive elastic body on the base member 25 side is configured similarly to the conductive elastic body 22 on the base member 21 side, and is arranged so as to overlap the conductive elastic body 22 with the conductor wire 23 in between in a plan view. The wiring drawn out from the conductive elastic body on the base member 25 side is connected to the wiring W2 drawn out from the conductive elastic body 22 facing in the Z axis direction. In this way, when conductive elastic bodies are provided above and below the conductor wire 23, the change in capacitance in the element unit is approximately doubled in response to the conductive elastic bodies above and below, and the detection sensitivity of the load applied to the element unit can be improved.

In addition, in the above third and fourth embodiments, the dielectric 23b is formed on the conductive member 23a so as to cover the outer periphery of the conductive member 23a, but instead, the dielectric 23b may be formed on the upper surface of the conductive elastic body 22. In this case, in response to the application of a load, the conductive member 23a sinks so as to be enveloped by the conductive elastic body 22 and the dielectric 23b, and the contact area between the conductive member 23a and the conductive elastic body 22 changes. As a result, the load applied to the element portion can be detected, similar to the above embodiments.

In addition, in the above embodiments 3 and 4, the load sensor 20 is configured so that nine element parts are arranged in a matrix of three rows and three columns, but the number and arrangement of element parts in the load sensor 20 are not limited to this. For example, the load sensor 20 may be configured so that 16 element parts are arranged in a matrix of four rows and four columns, or the load sensor 20 may be configured so that multiple element parts are arranged in only one column. Alternatively, the load sensor 20 may be configured to have only one element part.

In addition, in the above third and fourth embodiments, the element portion is formed by intersecting the conductive elastic body 22 and the conductor wire 23, but the configuration of the element portion is not limited to this. For example, the element portion may be formed by a configuration in which a semi-spherical conductive elastic body and a flat electrode sandwich a dielectric. In this case, the dielectric may be formed on the surface of the electrode facing the conductive elastic body, or on the surface of the semi-spherical conductive elastic body.

In addition, the measurement capacitance measured by the capacitance measurement circuit 10 according to the present invention is not limited to the element portion of the load sensor, but may be other measurement capacitance. For example, a capacitance element formed in an electrostatic touch panel or a semiconductor device, an electrolytic capacitor, a ceramic capacitor, etc. may be used as the measurement capacitance of the capacitance measurement circuit 10.

In addition, various modifications of the embodiments of the present invention are possible within the scope of the technical ideas set forth in the claims.

(Additional Note)
The above description of the embodiments discloses the following techniques.

(Technique 1)
a reference capacitance having a predetermined capacitance value;
a switching unit that switches between application and non-application of a voltage to the reference capacitance;
a transfer unit that transfers the charge stored in the reference capacitance to a measurement capacitance;
a connection part for connecting the negative electrode of the measurement capacitance to a ground or a wiring having the same potential as the positive electrode of the measurement capacitance;
A measurement unit that measures a voltage of the measurement capacitance;
a control unit that controls the switching unit, the transfer unit, and the connection unit,
The control unit is
a first control for causing the transfer unit to transfer charges while a negative electrode of the measurement capacitance is connected to the ground after a voltage is applied to the reference capacitance;
a second control for causing the transfer unit to transfer charges in a state in which a negative electrode of the measurement capacitance is connected to the wiring having the same potential as a positive electrode of the measurement capacitance after a voltage is applied to the reference capacitance;
and calculating a capacitance value of the measurement capacitor based on a voltage value measured by the measurement unit after the charge is transferred by the first control and the second control.
1. A capacitance measurement circuit comprising:

With this technology, the capacitance value of the measurement capacitance is calculated based on the voltage value after the charge is transferred from the reference capacitance, so that it is possible to stably measure capacitance values in a small range without using a high-precision AD converter. In addition, in the second control, the negative electrode of the measurement capacitance is connected to a wire with the same potential as the positive electrode of the measurement capacitance, so the measured voltage value is hardly affected by the measurement capacitance, but is mainly affected by the reference capacitance and parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to ground, so the measured voltage value is affected by the measurement capacitance as well as the reference capacitance and parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, it is possible to calculate a capacitance value that is not affected by parasitic capacitance. Therefore, the capacitance value of the measurement capacitance can be measured with high precision.

(Technique 2)
In the capacitance measurement circuit according to the first aspect of the present invention,
The control unit calculates a capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, a value Vdd of the voltage applied to the reference capacitance, and a capacitance value Cr of the reference capacitance by the following formula:
1. A capacitance measurement circuit comprising:

This technology can suppress the effect of error components due to parasitic capacitance on the capacitance value of the measurement capacitance Cs, and the capacitance value of the measurement capacitance Cs can be obtained with high accuracy.

(Technique 3)
a reference capacitance having a predetermined capacitance value;
A switching unit that switches between application and non-application of a voltage to the capacitance to be measured;
a transfer section that transfers the charge stored in the measurement capacitance to the reference capacitance;
a connection part for connecting the negative electrode of the measurement capacitance to a ground or a wiring having the same potential as the positive electrode of the measurement capacitance;
A measurement unit that measures a voltage of the measurement capacitance;
a control unit that controls the switching unit, the transfer unit, and the connection unit,
The control unit is
a first control for applying a voltage to the capacitance to be measured while the negative electrode of the capacitance to be measured is connected to the ground, and then causing the transfer unit to transfer charges;
a second control for applying a voltage to the capacitance to be measured while connecting the negative electrode of the capacitance to be measured to a wiring having the same potential as the positive electrode of the capacitance to be measured, and then causing the transfer unit to transfer charges;
and calculating a capacitance value of the measurement capacitor based on a voltage value measured by the measurement unit after the charge is transferred by the first control and the second control.
1. A capacitance measurement circuit comprising:

This technology calculates the capacitance value of the measurement capacitance based on the voltage value after the charge is transferred from the measurement capacitance, so that it is possible to stably measure capacitance values in a small range without using a highly accurate AD converter. In addition, in the second control, the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance and a voltage is applied to the measurement capacitance, so that almost no charge is accumulated in the measurement capacitance, but charges are accumulated in the parasitic capacitance. Therefore, the voltage value measured by the second control is hardly affected by the measurement capacitance, and is mainly affected by the reference capacitance and the parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to the ground and a voltage is applied to the measurement capacitance, so that charges are applied to the measurement capacitance as well as the parasitic capacitance. Therefore, the voltage value measured by the twelfth control is affected by the measurement capacitance as well as the reference capacitance and the parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, it is possible to calculate a capacitance value that is not affected by the parasitic capacitance. Therefore, the capacitance value of the measurement capacitance can be measured with high accuracy.

(Technique 4)
In the capacitance measurement circuit according to the third aspect,
The control unit calculates a capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, a value Vdd of the voltage applied to the measurement capacitance, and a capacitance value Cr of a reference capacitance, by the following formula:
1. A capacitance measurement circuit comprising:

This technology can suppress the effect of error components due to parasitic capacitance on the capacitance value of the measured capacitance, allowing the capacitance value of the measured capacitance to be obtained with high accuracy.

(Technique 5)
In the capacitance measurement circuit according to any one of the first to fourth aspects,
the control unit repeatedly executes the first control while changing a waiting period from the transfer of the electric charge to the acquisition of the voltage value until the voltage value becomes saturated, and calculates the capacitance value using the saturated voltage value.
1. A capacitance measurement circuit comprising:

　With this technology, if the capacitance value of the measurement capacitance is small and the measurement value of the measurement unit saturates and stabilizes early, the first voltage value Vx1 can be obtained quickly with a short waiting period. Therefore, the calculation process of the capacitance value of the measurement capacitance can be performed quickly.

(Technique 6)
In the capacitance measurement circuit according to technology 5,
The control unit extends the waiting period each time the first control is repeated.
1. A capacitance measurement circuit comprising:

This technology allows the standby period to gradually approach the length at which the first voltage value Vx1 saturates. This makes it possible to smoothly set a standby period appropriate for the capacitance to be measured.

(Technique 7)
In the capacitance measurement circuit according to any one of the first to sixth aspects of the present invention,
A capacitance value changing unit that changes the capacitance value of the reference capacitance,
1. A capacitance measurement circuit comprising:

This technology makes it possible to adjust the capacitance value of the reference capacitance to a value appropriate for the dynamic range of the measurement capacitance. Therefore, even if the dynamic range of the measurement capacitance is changed, the capacitance value of the measurement capacitance can be measured appropriately within that dynamic range.

(Technique 8)
In the load detection device described in Technology 7,
a load sensor having an element portion whose capacitance changes in response to a load;
The capacitance measurement circuit according to any one of the first to seventh aspects of the present invention is provided.
The control unit performs the first control, the second control, and the process of calculating the capacitance by using the element unit as the measurement capacitance.
A load detection device comprising:

According to this technology, since it includes a capacitance measurement circuit described in any one of technologies 1 to 7, it is possible to stably obtain a capacitance corresponding to the load even in a range where the load applied to the element portion is small and the capacitance is small. In addition, since it includes a capacitance measurement circuit described in any one of technologies 1 to 7, it is possible to accurately obtain a capacitance value in which the effects of parasitic capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

(Technique 9)
In the load detection device described in Technology 8,
The load sensor includes a plurality of the element units,
The capacitance measurement circuit includes an element selection unit that switches the element unit to be measured.
A load detection device comprising:

With this technology, the

element selection units

17 and 18 can be used to switch the element part to be measured, allowing the capacitance measurement circuit to stably and accurately measure the capacitance value of each element part.

REFERENCE SIGNS LIST 1 Load detection device 10 Capacitance measurement circuit 11 Control unit 20 Load sensor 10a Switch element (switching unit)
10b Switch element (transfer section)
13 Switch element (connection part)
14 Measurement unit 15 Capacitance selection unit (capacitance value change unit)
16a to 16d Switch elements (capacitance value change units)
17, 18 Element selection section 17a to 17c Switch elements (connection section)
Cra to Crd Capacitor (capacitance value change unit)
Cr: Reference capacitance Cs: Measurement capacitance A11 to A33: Element part (measurement capacitance)

Claims

a reference capacitance having a predetermined capacitance value;
a switching unit that switches between application and non-application of a voltage to the reference capacitance;
a transfer unit that transfers the charge stored in the reference capacitance to a measurement capacitance;
a connection part for connecting the negative electrode of the measurement capacitance to a ground or a wiring having the same potential as the positive electrode of the measurement capacitance;
A measurement unit that measures a voltage of the measurement capacitance;
a control unit that controls the switching unit, the transfer unit, and the connection unit,
The control unit is
a first control for causing the transfer unit to transfer charges while a negative electrode of the measurement capacitance is connected to the ground after a voltage is applied to the reference capacitance;
a second control for causing the transfer unit to transfer charges in a state in which a negative electrode of the measurement capacitance is connected to the wiring having the same potential as a positive electrode of the measurement capacitance after a voltage is applied to the reference capacitance;
and calculating a capacitance value of the measurement capacitor based on a voltage value measured by the measurement unit after the charge is transferred by the first control and the second control.
1. A capacitance measurement circuit comprising:
2. The capacitance measurement circuit according to claim 1,
the control unit repeatedly executes the first control while changing a waiting period from the transfer of the electric charge to the acquisition of the voltage value until the voltage value becomes saturated, and calculates the capacitance value using the saturated voltage value.
1. A capacitance measurement circuit comprising:
3. The capacitance measurement circuit according to claim 2,
The control unit extends the waiting period each time the first control is repeated.
1. A capacitance measurement circuit comprising:
2. The capacitance measurement circuit according to claim 1,
The control unit calculates a capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, a value Vdd of the voltage applied to the reference capacitance, and a capacitance value Cr of the reference capacitance by the following formula:
1. A capacitance measurement circuit comprising:
2. The capacitance measurement circuit according to claim 1,
A capacitance value changing unit that changes the capacitance value of the reference capacitance is further provided.
1. A capacitance measurement circuit comprising:
a reference capacitance having a predetermined capacitance value;
A switching unit that switches between application and non-application of a voltage to the capacitance to be measured;
a transfer section that transfers the charge stored in the measurement capacitance to the reference capacitance;
a connection part for connecting the negative electrode of the measurement capacitance to a ground or a wiring having the same potential as the positive electrode of the measurement capacitance;
A measurement unit that measures a voltage of the measurement capacitance;
a control unit that controls the switching unit, the transfer unit, and the connection unit,
The control unit is
a first control for applying a voltage to the capacitance to be measured while the negative electrode of the capacitance to be measured is connected to the ground, and then causing the transfer unit to transfer charges;
a second control for applying a voltage to the capacitance to be measured while connecting the negative electrode of the capacitance to be measured to a wiring having the same potential as the positive electrode of the capacitance to be measured, and then causing the transfer unit to transfer charges;
and calculating a capacitance value of the measurement capacitor based on a voltage value measured by the measurement unit after the charge is transferred by the first control and the second control.
1. A capacitance measurement circuit comprising:
7. The capacitance measurement circuit according to claim 6,
the control unit repeatedly executes the first control while changing a waiting period from the transfer of the electric charge to the acquisition of the voltage value until the voltage value becomes saturated, and calculates the capacitance value using the saturated voltage value.
1. A capacitance measurement circuit comprising:
8. The capacitance measurement circuit according to claim 7,
The control unit extends the waiting period each time the first control is repeated.
1. A capacitance measurement circuit comprising:
7. The capacitance measurement circuit according to claim 6,
The control unit calculates a capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, a value Vdd of the voltage applied to the measurement capacitance, and a capacitance value Cr of a reference capacitance, using the following formula:
1. A capacitance measurement circuit comprising:
7. The capacitance measurement circuit according to claim 6,
A capacitance value changing unit that changes the capacitance value of the reference capacitance is further provided.
1. A capacitance measurement circuit comprising:
a load sensor having an element portion whose capacitance changes in response to a load;
A capacitance measurement circuit according to any one of claims 1 to 10,
The control unit performs the first control, the second control, and the process of calculating the capacitance by using the element unit as the measurement capacitance.
A load detection device comprising:
The load detection device according to claim 11,
The load sensor includes a plurality of the element units,
The capacitance measurement circuit includes an element selection unit that switches the element unit to be measured.
A load detection device comprising: