Calibration method for force measurement device, program, calibration device, and force measurement device

Abstract

[Problem] To calibrate a force measurement device so that a wide range of force can be accurately measured. [Solution] This calibration method comprises: a step for acquiring a plurality of data points; a step for assuming one of the plurality of data points as a virtual inflection point CP'; a step for calculating a first virtual function and a first determination coefficient R1 2 on the basis of a low-force data point where the magnitude of the force is less than or equal to a virtual inflection value Fk; a step for calculating a second virtual function and a second determination coefficient R2 2 on the basis of a high-force data point where the magnitude of the force is greater than or equal to the virtual inflection value Fk; a step for calculating a sum of the first determination coefficient and the second determination coefficient: R1 2 + R2 2; and a step for defining the virtual inflection value CP' where the sum of the first determination coefficient and the second determination coefficient: R1 2 + R2 2 reaches a maximum as an inflection value CP, defining the first virtual function as a first function f1, and defining the second virtual function as a second function f2 to calculate a Z direction sensitivity characteristic function.

Description

Calibration method, program, calibration device, and force measuring device

[0001] The present invention relates to a method for calibrating a force measuring device that measures force using changes in electrostatic capacitance, a program for causing a computer to execute this calibration method, a calibration device for calibrating a force measuring device, and the force measuring device.

[0002] A force measuring device that measures force using changes in capacitance has been known, as described in Patent Document 1. This force measuring device includes a force sensor in which a resin foam is sandwiched between two electrodes. When a force is applied to the force sensor, the foam of the force sensor deforms, and this deformation causes a change in capacitance between the two electrodes. This force measuring device measures the force by utilizing this deformation.

[0003] Patent No. 6280579

[0004] In the above force measuring device, the force applied to the force sensor is measured using a function that represents the relationship between the force applied to the force sensor and the rate of change in capacitance when that force is applied. Since this function represents the sensitivity of the force sensor to the applied force, it will be called the "sensitivity characteristic function."

[0005] The inventors have found that the sensitivity characteristic function varies depending on the magnitude of the force applied to the force sensor. In such cases, a sensitivity characteristic function that can accurately calculate a wide range of forces cannot be determined by simply fitting the calibration data to a predetermined function.

[0006] For example, a sensitivity characteristic function that fits well to small force data is difficult to fit to large force data. In other words, a sensitivity characteristic function that fits well to small force data cannot accurately calculate large forces. A sensitivity characteristic function that fits well to large force data is difficult to fit to small force data. In other words, a sensitivity characteristic function that fits well to large force data cannot accurately calculate small forces.

[0007] An object of the present invention is to calibrate a force measuring device that measures force based on changes in electrostatic capacitance so that it can accurately measure a wide range of forces.

[0008] Several aspects are described below as means for solving the problems. These aspects can be combined as needed. A calibration method according to one aspect of the present invention is a method for calibrating a force measuring device that measures force using a sensitivity characteristic function that represents the relationship between a force applied to a force sensor and the rate of change in the capacitance of the force sensor due to the force. The sensitivity characteristic function is expressed by a first function when the magnitude of the force is between 0 and an inflection value, and by a second function when the magnitude of the force is equal to or greater than the inflection value. The second function is connected to the first function at the inflection value but is a different function from the first function. A point on the sensitivity characteristic function at which the function representing the sensitivity characteristic function changes is defined as an inflection point. The inflection value refers to the magnitude of the force included in the inflection point. In other words, the inflection value refers to the magnitude of the force at which the function representing the sensitivity characteristic function changes.

[0009] In the above case, the calibration method includes the following steps: (a) applying forces of multiple magnitudes within a range from 0 to a force sensor greater than an inflection value and measuring the rate of change in capacitance of the force sensor when each force is applied, thereby obtaining multiple data points represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force; (b) assuming one of the multiple data points to be an inflection point and setting the magnitude of the force included in the assumed inflection point as a virtual inflection value; (c) calculating a first virtual function based on low-force data points of which the force magnitude is equal to or less than the virtual inflection value, and calculating a first coefficient of determination representing the degree of agreement between the low-force data points and the first virtual function; (d) calculating a second virtual function based on high-force data points of which the force magnitude is equal to or greater than the virtual inflection value, and calculating a second coefficient of determination representing the degree of agreement between the high-force data points and the second virtual function. The second virtual function is connected to the first virtual function by the virtual inflection value and is a function different from the first virtual function. (e) calculating the sum of the first determination coefficient and the second determination coefficient; (f) assuming another data point to be an inflection point and performing the above steps (c) to (e); and (g) determining the virtual inflection value included in the assumed inflection point when the sum of the first determination coefficient and the second determination coefficient is maximized as the inflection value, determining the first virtual function as the first function, and determining the second virtual function as the second function, thereby calculating a sensitivity characteristic function.

[0010] In the above-described method for calibrating a force measuring device, one of multiple data points used for calibration is assumed to be an inflection point at which the sensitivity characteristic function changes, a first virtual function is calculated based on a data point whose force magnitude is equal to or less than a virtual inflection value included in the assumed inflection point, and a first coefficient of determination representing the degree of agreement between the data point and the first virtual function is calculated. A second virtual function is calculated based on a data point whose force magnitude is equal to or greater than the virtual inflection value, and a second coefficient of determination representing the degree of agreement between the data point and the second virtual function is calculated. Furthermore, the sum of the first and second coefficients of determination is calculated. These processes are repeated by changing the assumed inflection point to another data point. As a result, multiple first virtual functions, second virtual functions, and sums of the first and second coefficients of determination are calculated.

[0011] The inflection point assumed when the sum of the first and second coefficients of determination is maximized is determined to be the inflection point where the sensitivity characteristic function changes, and the magnitude of the force included in this inflection point (i.e., the virtual inflection value) is determined to be the actual inflection value. The first virtual function calculated when the sum of the first and second coefficients of determination is maximized is determined to be the first function representing the sensitivity characteristic function when the magnitude of the force is equal to or less than the inflection value. The second virtual function calculated when the sum of the first and second coefficients of determination is maximized is determined to be the second function representing the sensitivity characteristic function when the magnitude of the force is equal to or greater than the inflection value.

[0012] In this way, by determining the virtual inflection value when the sum of the first and second coefficients of determination is maximum as the inflection value, determining the sensitivity characteristic function (first function) when the force magnitude is equal to or less than the inflection value based on the data points below the inflection point, and determining the sensitivity characteristic function (second function) when the force magnitude is equal to or greater than the inflection value based on the data points above the inflection point, it is possible to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces. As a result, a force measuring device that measures force based on changes in capacitance can be calibrated so that it can accurately measure a wide range of forces.

[0013] This is because, by separately calculating the first function and the second function as described above, the first function can be calculated as a function that well represents the data points below the inflection point, and the second function can be calculated as a function that well represents the data points above the inflection point. Also, by determining the virtual inflection value when the sum of the first determination coefficient and the second determination coefficient is maximum as the inflection value, it is possible to accurately determine at what point the sensitivity characteristic function changes.

[0014] In the above calibration method, the step of assuming an inflection point and a virtual inflection value may include the step of assuming, as an inflection point, a data point of which the magnitude of the force is close to the inflection value among the plurality of data points. This eliminates the need to assume all of the plurality of acquired data points as inflection points, thereby enabling faster calculation of the sensitivity characteristic function.

[0015] In the above calibration method, the sensitivity characteristic function may represent the relationship between a force applied in the thickness direction of the force sensor and the rate of change in capacitance due to the force. Since the sensitivity characteristic function for forces in the thickness direction is likely to change with the force, by calculating the sensitivity characteristic function using the above calibration method, the force measuring device can be calibrated so as to be able to accurately measure forces in a wide range in the thickness direction.

[0016] In the above calibration method, the first function and the first virtual function may be functions proportional to the magnitude of the force. When the magnitude of the force is equal to or less than the inflection value, the rate of change in capacitance changes in proportion to the magnitude of the force. Therefore, by setting the first function and the first virtual function representing the sensitivity characteristic function when the magnitude of the force is equal to or less than the inflection value as functions proportional to the magnitude of the force, an accurate sensitivity characteristic function can be calculated.

[0017] In the above calibration method, the second function and the second virtual function may be logarithmic functions of the force magnitude. When the force magnitude is equal to or less than the inflection value, the rate of change of the capacitance changes logarithmically with respect to the force magnitude. Therefore, by setting the second function and the second virtual function representing the sensitivity characteristic function when the force magnitude is equal to or greater than the inflection value to logarithmic functions of the force magnitude, an accurate sensitivity characteristic function can be calculated.

[0018] In the above calibration method, the step of calculating the second virtual function and the second coefficient of determination may include the following steps: (h) converting the second virtual function into a virtual proportional function. The virtual proportional function is a function in which the difference between the rate of change of capacitance and the rate of change of capacitance when the magnitude of the force is a virtual inflection value is proportional to the difference between the logarithm of the magnitude of the force and the logarithm of the virtual inflection value. (i) calculating the virtual proportional function based on the high-force data points; and (j) calculating the second virtual function from the calculated virtual proportional function.

[0019] When calculating a function based on data points, it is easier to calculate the function by converting the function into a proportional function and calculating the proportional function based on data points. Therefore, when the second function and the second virtual function are logarithmic functions, the second virtual function (second function) can be easily calculated by calculating the second virtual function using the above method.

[0020] A program according to another aspect of the present invention is a program for causing a computer to execute the above calibration method.

[0021] A calibration device according to yet another aspect of the present invention is a calibration device for calibrating the above-mentioned force measuring device. The calibration device includes an application unit and a calibration unit. The application unit applies a force to the force sensor. The calibration unit applies a force to the force sensor using the application unit, acquires data points represented by coordinate values ​​of the magnitude of the force applied to the force sensor and the rate of change in capacitance with respect to the force, and calculates a sensitivity characteristic function based on the acquired data points, thereby calibrating the force measuring device.

[0022] The calibration unit of the calibration device performs the following: (a) applies forces of multiple magnitudes to the force sensor within a range from 0 to a value greater than the inflection value using an application unit, and measures the rate of change in the capacitance of the force sensor when each force is applied, thereby obtaining multiple data points; (b) assuming one of the multiple data points to be an inflection point where the sensitivity characteristic function changes, and setting the magnitude of the force included in the assumed inflection point as a virtual inflection value; (c) calculating a first virtual function based on low-force data points of which the force magnitude is equal to or less than the virtual inflection value, and calculating a first coefficient of determination representing the degree of agreement between the low-force data points and the first virtual function; (d) calculating a second virtual function based on high-force data points of which the force magnitude is equal to or greater than the virtual inflection value, and calculating a second coefficient of determination representing the degree of agreement between the high-force data points and the second virtual function; (e) calculating the sum of the first and second coefficients of determination; and (f) performing steps (c) to (e) above, assuming another data point to be an inflection point. (g) A virtual inflection value included in the assumed inflection point when the sum of the first determination coefficient and the second determination coefficient is maximized is determined as the inflection value, the first virtual function is determined as the first function, and the second virtual function is determined as the second function, thereby calculating a sensitivity characteristic function.

[0023] This allows the calibration device to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces, thereby enabling the force measuring device that measures force based on changes in capacitance to be calibrated so that it can accurately measure a wide range of forces.

[0024] A force measuring device according to yet another aspect of the present invention includes a force sensor whose capacitance changes when force is applied, and a calculation unit that calculates the force using a sensitivity characteristic function that represents the relationship between the force applied to the force sensor and the rate of change in the capacitance of the force sensor due to the force.

[0025] In the above-described force measuring device, the sensitivity characteristic function is calculated as follows: (a) Applying forces of various magnitudes to the force sensor and measuring the rate of change in capacitance of the force sensor when each force is applied, thereby obtaining multiple data points represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force; (b) Designating one of the multiple data points as a first data point, and designating the magnitude of the force included in the first data point as a first force; (c) Designating one of the multiple data points whose force magnitude is smaller than the first force as a second data point, and calculating a first virtual function that passes through the first data point and the second data point. "Passing through the first data point and the second data point" includes not only cases where the first virtual function passes through the first data point and the first data point, but also cases where the first virtual function passes near the first data point and / or the second data point; (d) Designating one of the multiple data points whose force magnitude is larger than the first force as a third data point, and calculating a second virtual function that passes through the first data point and the third data point. "Passing through the first data point and the third data point" includes not only the case where the second virtual function passes through the first data point and the third data point, but also the case where the second virtual function passes near the first data point and / or near the third data point. (e) If the absolute value of the ratio of the difference between the differential value of the first virtual function on a line connecting the first data point and the second data point and the differential value of the second virtual function on a line connecting the first data point and the third data point is equal to or greater than a predetermined threshold, the first virtual function and the second virtual function are connected for calculation.

[0026] In the force measuring device, a first virtual function is calculated that passes through a first data point serving as a reference and a second data point whose force magnitude is smaller than a first force included in the first data point, among a plurality of data points represented by coordinate values ​​of the magnitude of a force applied to the force sensor and the rate of change in capacitance due to the force, and a second virtual function is calculated that passes through the first data point and a third data point whose force magnitude is larger than the first force. Then, when the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first and second data points and the differential value of the second virtual function on a line connecting the first and third data points is equal to or greater than a predetermined threshold, the first virtual function and the second virtual function are connected to calculate a sensitivity characteristic function.

[0027] If the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first data point and the second data point and the differential value of the second virtual function on a line connecting the first data point and the third data point and the differential value of the second virtual function on a line connecting the first data point and the third data point is equal to or greater than a predetermined threshold, this means that the function representing the sensitivity characteristic function at the first data point has changed significantly (from the first virtual function to the second virtual function or vice versa). In this case, by connecting the first virtual function and the significantly different second virtual function at the first data point, a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces can be calculated. As a result, the force measuring device described above can accurately measure a wide range of forces using a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces.

[0028] In the above force measuring device, the sensitivity characteristic function may include a plurality of functions connected at inflection points. This makes it possible to express a complex sensitivity characteristic function using a plurality of functions. In other words, even if the change in sensitivity of the force sensor to a wide range of forces is complex, it is possible to calculate a sensitivity characteristic function that accurately expresses the sensitivity of the force sensor to a wide range of forces.

[0029] When the sensitivity characteristic function includes multiple functions connected at inflection points, the multiple functions may be linear equations that change linearly with respect to the magnitude of the force applied to the force sensor, or may be nonlinear functions that change nonlinearly with respect to the magnitude of the force applied to the force sensor.

[0030] In the above force measuring device, the sensitivity characteristic function may be represented by a first function when the magnitude of the force is between 0 and an inflection value, and may be represented by a second function that is connected to the first function at the inflection value and different from the first function when the magnitude of the force is equal to or greater than the inflection value. This makes it possible to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces, for example, when the sensitivity of the force sensor to forces changes at the inflection point.

[0031] In the above-described force measuring device, the sensitivity characteristic function may be calculated as follows: (f) A plurality of data points are obtained by applying forces of different magnitudes to the force sensor within a range from 0 to a value greater than the inflection value; (g) A first data point is assumed to be an inflection point at which the sensitivity characteristic function changes, and the first force is set as a virtual inflection value. (h) A first virtual function is calculated based on low-force data points of which the force magnitude is equal to or less than the virtual inflection value, and a first coefficient of determination representing the degree of agreement between the low-force data points and the first virtual function is calculated; (i) A second virtual function is calculated based on high-force data points of which the force magnitude is equal to or greater than the virtual inflection value, and a second coefficient of determination representing the degree of agreement between the high-force data points and the second virtual function is calculated. The second virtual function is connected to the first virtual function by the virtual inflection value and is different from the first virtual function; (j) The sum of the first and second coefficients of determination is calculated. (k) Assuming another data point to be an inflection point, perform steps (g) to (j) above. (l) Determine the virtual inflection value included in the assumed inflection point when the sum of the first determination coefficient and the second determination coefficient is maximized as the inflection value, determine the first virtual function as the first function, and determine the second virtual function as the second function.

[0032] This makes it possible to accurately measure a wide range of forces using a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces.

[0033] The force measuring device may further include a display unit that displays numerical data relating to the force applied to the force sensor, the numerical data being calculated by the calculation unit using the sensitivity characteristic function, thereby allowing the magnitude of the force applied to the force sensor to be confirmed as a numerical value.

[0034] In the above force measuring device, the display unit may display the direction of the force applied to the force sensor in addition to the numerical data related to the force, thereby allowing the user to confirm not only the magnitude of the force applied to the force sensor but also the direction in which the force is applied.

[0035] Force measuring devices that measure force by changes in capacitance can be calibrated to accurately measure a wide range of forces.

[0036] 1 is a diagram showing the overall configuration of a force measuring device; FIG. 1 is a cross-sectional view of a force sensor in the Y direction; FIG. 2 is a diagram showing the planar shapes of a first electrode, a second electrode, a fourth electrode, and a fifth electrode; FIG. 3 is a diagram showing the planar shapes of a third electrode and a sixth electrode; FIG. 4 is a diagram showing an example of a state in which a force is applied to a force sensor; FIG. 5 is a diagram showing the configuration of a first information processing device; FIG. 6 is a diagram showing an example of a Z-direction sensitivity characteristic function; FIG. 7 is a diagram showing the configuration of a calibration device; FIG. 8 is a flowchart showing the calibration operation of the force measuring device when calculating the Z-direction sensitivity characteristic function; FIG. 9 is a diagram showing an example of a second virtual function expressed on a semi-logarithmic graph;

[0037] 1. First Embodiment (1) Overall Configuration of Force Measuring Device The configuration of a force measuring device 1 of the first embodiment will be described using Fig. 1. Fig. 1 is a diagram showing the overall configuration of the force measuring device. Of the "forces" applied to the force sensor 10, forces in the planar directions of the force sensor 10 (X direction, Y direction) are sometimes called "shear forces." The force measuring device 1 includes the force sensor 10, a controller 2, and a first information processing device 3.

[0038] The force sensor 10 is a sensor for detecting force based on a change in capacitance caused by the application of force. The force sensor 10 is capable of measuring not only force in the thickness direction (Z direction) of the force sensor 10 but also shear force (force in a planar direction). In the force measuring device 1, a plurality of force sensors 10 are arranged side by side in the X-axis direction of the sensor arrangement member AR ( FIG. 8 ), and a plurality of force sensors 10 are arranged side by side in the Y-axis direction. This allows the force measuring device 1 to measure the position on the sensor arrangement member AR where a force is acting, as well as the direction and magnitude of the force acting on the force sensor 10 at that position.

[0039] The controller 2 has a drive circuit 21 and a sense circuit 23. The drive circuit 21 is a circuit for providing an AC voltage for driving each force sensor 10 of the force measuring device 1. The sense circuit 23 is a circuit for measuring the electrostatic capacitances (first capacitance C1 to fourth capacitance C4, which will be described later) formed in each force sensor 10.

[0040] The first information processing device 3 is connected to the controller 2. The first information processing device 3 calculates the magnitude, direction, etc. of the force applied to the force sensor 10 based on the capacitance of the force sensor 10 measured by the sense circuit 23.

[0041] (2) Force Sensor The detailed configuration of the force sensor 10 will be described below with reference to Figures 1 to 4. Figure 2 is a cross-sectional view of the force sensor in the Y direction. Figure 3 is a diagram showing the planar shapes of the first electrode, the second electrode, the fourth electrode, and the fifth electrode. Figure 4 is a diagram showing the planar shapes of the third electrode and the sixth electrode.

[0042] As shown in FIG. 2, the force sensor 10 includes a first surface layer L1, a first shield layer L2, a first insulating layer L3, a first conductive layer L4, a second shield layer L5, an insulating elastomer layer L6, a second conductive layer L7, a second insulating layer L8, a third insulating layer L9, a second surface layer L10, a third conductive layer L11, and a fourth conductive layer L12.

[0043] The first surface layer L1 is an insulating layer that serves as the first surface of the force measuring device 1. The first shield layer L2 is formed on the first surface layer L1. The first shield layer L2 is an insulating layer that protects the third conductive layer L11 from damage. The first shield layer L2 may be omitted.

[0044] The first insulating layer L3 is an insulating layer formed on the third conductive layer L11. The first insulating layer L3 is a layer of an insulating material such as polyethylene terephthalate (PET) resin, for example.

[0045] The first conductive layer L4 is provided on the first insulating layer L3. The first conductive layer L4 is provided with a first electrode 11 and a second electrode 12. That is, the first electrode 11 and the second electrode 12 are formed on the first insulating layer L3. The first electrode 11 and the second electrode 12 are made of a thin film having electrical conductivity.

[0046] 3, the first electrode 11 and the second electrode 12 have a rectangular shape extending in the X direction. The first electrode 11 and the second electrode 12 face each other with a first gap G1 in the Y direction. The first electrode 11 is connected to a first wiring 31a. The second electrode 12 is connected to a second wiring 31b. The first wiring 31a and the second wiring 31b are made of conductive thin films and extend in the Y direction.

[0047] 1 , the first electrode 11 and the second electrode 12 are connected to the drive circuit 21 by a first wiring 31 a and a second wiring 31 b, respectively. When measuring a force, the drive circuit 21 applies AC voltages to the first electrode 11 and the second electrode 12 at different timings. That is, the first electrode 11 and the second electrode 12 function as drive electrodes when the force sensor 10 measures a force.

[0048] The second shield layer L5 is formed on the first conductive layer L4. The second shield layer L5 is an insulating layer for protecting the first electrode 11, the second electrode 12, and the first wiring 31a formed on the first conductive layer L4 from breakdown. The second shield layer L5 may be omitted.

[0049] The insulating elastic layer L6 is disposed on the second shield layer L5. The insulating elastic layer L6 is a layer including an insulating elastic body 13. When a force is applied to the force sensor 10, the insulating elastic body 13 is elastically deformable in the direction of the force.

[0050] The second conductive layer L7 is provided under the second insulating layer L8. The second conductive layer L7 is provided with a third electrode 14. That is, the third electrode 14 is formed on the insulating elastic layer L6. The third electrode 14 is made of a conductive thin film.

[0051] 1 , the third electrode 14 has a rectangular shape extending in the X direction. The third electrode 14 is disposed so as to overlap a part of the first electrode 11 formed on the first conductive layer L4, the first gap G1, and a part of the second electrode 12. As a result, a first capacitance C1 and a second capacitance C2 are formed in the overlapping portion between the first electrode 11 and the third electrode 14 and the overlapping portion between the second electrode 12 and the third electrode 14, respectively.

[0052] 2, the third electrode 14 is preferably arranged so that an overlapping area A1 between the first electrode 11 and the third electrode 14 is equal to an overlapping area A2 between the second electrode 12 and the third electrode 14 when no force is applied to the force sensor 10. This makes the first capacitance C1 and the second capacitance C2 equal when no force is applied, making them easy to use as a reference.

[0053] 4, the third electrode 14 is connected to the sense circuit 23. The sense circuit 23 measures the first capacitance C1 and the second capacitance C2 based on the charge detected by the third electrode 14 when a voltage is applied to the first electrode 11 and when a voltage is applied to the second electrode 12. That is, the third electrode 14 functions as a detection electrode when the force sensor 10 measures a force in the Y direction.

[0054] The second insulating layer L8 is an insulating layer formed on the second conductive layer L7.

[0055] The third insulating layer L9 is an insulating layer formed on the fourth conductive layer L12. The second surface layer L10 is an insulating layer that becomes the second surface of the force measuring device 1.

[0056] The third conductive layer L11 is provided on the first shield layer L2. A seventh electrode 19 is formed on the third conductive layer L11 over the entire force sensor 10. The seventh electrode 19 is made of a conductive thin film. The seventh electrode 19 is connected to the ground potential. The seventh electrode 19 reduces noise in the force sensor 10.

[0057] The fourth conductive layer L12 is provided on the second insulating layer L8. An eighth electrode 20 is formed on the fourth conductive layer L12 over the entire force sensor 10. The eighth electrode 20 is made of a conductive thin film. The eighth electrode 20 is connected to a ground potential. The eighth electrode 20 reduces noise in the force sensor 10.

[0058] The force measurement principle of the above-described force sensor 10 is as follows. As shown in Figure 5, consider the case where a force in the positive Y direction is applied to the force sensor 10. Note that a force in the negative Y direction can also be measured based on the following principle. Figure 5 is a diagram showing an example of a state in which a force is applied to the force sensor.

[0059] When a force in the positive Y direction is applied to the force sensor 10, the insulating elastic body 13 elastically deforms in the positive Y direction. This elastic deformation of the insulating elastic body 13 in the positive Y direction causes the third electrode 14 to move in the positive Y direction relative to the first electrode 11 and the second electrode 12. As a result, the overlapping area A1 between the first electrode 11 and the third electrode 14 and the overlapping area A2 between the second electrode 12 and the third electrode 14 change compared to when no force is applied. Specifically, the overlapping area A1 between the first electrode 11 and the third electrode 14, which are arranged in the positive Y direction, becomes larger, and the overlapping area A2 between the second electrode 12 and the third electrode 14, which are arranged in the negative Y direction, becomes smaller.

[0060] A force in the positive Y direction increases the overlap area A1 between the first electrode 11 and the third electrode 14, thereby increasing the first capacitance C1, and decreases the overlap area A2 between the second electrode 12 and the third electrode 14, thereby decreasing the second capacitance C2. In this way, by detecting the increase in the first capacitance C1 and the decrease in the second capacitance C2, it is possible to detect that a force has been applied in the positive Y direction, i.e., the direction in which the force has been applied. For example, if the difference (C1-C2) between the first capacitance C1 and the second capacitance C2 is larger than when no force is applied, it can be determined that a force has been applied in the positive Y direction. On the other hand, if the difference between the first capacitance C1 and the second capacitance C2 is smaller than when no force is applied, it can be determined that a force has been applied in the negative Y direction.

[0061] The amount of deformation of the insulating elastic body 13 due to the application of force depends on the magnitude of the force. Therefore, the magnitude of the force can be measured from the rate of change of the first capacitance C1 and / or the second capacitance C2, or the magnitude of the absolute value of the difference between the first capacitance C1 and the second capacitance C2.

[0062] Furthermore, when a force is applied to the force sensor 10 in the vertical direction (Z direction), the insulating elastic body 13 deforms in the vertical direction, causing its thickness to change (decrease). This change in thickness changes the distance between the first electrode 11 and the second electrode 12 and the third electrode 14, causing the first capacitance C1 and the second capacitance C2 to change (increase). By capturing this change in capacitance, it is possible to detect that a force has been applied in the vertical direction and measure the magnitude of the detected vertical force.

[0063] The force sensor 10 can measure not only forces in the Y direction but also forces in a direction different from the Y direction (X direction). To measure forces in the X direction, the force sensor 10 further includes a fourth electrode 16, a fifth electrode 17, and a sixth electrode 18. The fourth electrode 16, the fifth electrode 17, and the sixth electrode 18 will be described below with reference to FIGS. 3 and 4. The cross section of the force sensor 10 in the X direction has the same configuration as the cross section in the Y direction shown in FIG. 2, except that the first electrode 11 and the second electrode 12 become the fourth electrode 16 and the fifth electrode 17, respectively, and the third electrode 14 becomes the sixth electrode 18. Therefore, a description thereof will be omitted here.

[0064] The fourth electrode 16 and the fifth electrode 17 are provided on the first conductive layer L4. The fourth electrode 16 and the second electrode 12 are composed of conductive thin films. As shown in FIG. 3 , the fourth electrode 16 and the fifth electrode 17 have a rectangular shape extending in the Y direction. The fourth electrode 16 and the fifth electrode 17 face each other with a second gap G2 in the X direction. The force sensor 10 of this embodiment has four fourth electrodes 16 and four fifth electrodes 17. In the force sensor 10, the fourth electrodes 16 and the fifth electrodes 17 are alternately arranged in the X direction. Specifically, one fourth electrode 16 is arranged between two fifth electrodes 17 aligned in the X direction, with the second gap G2 between them. One fifth electrode 17 is arranged between two fourth electrodes 16 aligned in the X direction, with the second gap G2 between them.

[0065] The fourth electrode 16 is connected to the first wiring 31a. The fifth electrode 17 is connected to the second wiring 31b. Specifically, the fourth electrode 16 arranged at the end in the positive X direction is directly connected to the first wiring 31a on the positive X direction side. Furthermore, four fourth electrodes 16 are connected at the end in the negative Y direction to the first electrodes 11 for the force sensor 10 adjacent in the Y direction. Because the first electrodes 11 are connected to the first wiring 31a on the positive X direction side, the four fourth electrodes 16 are connected to the first electrodes 11 and, therefore, are connected to the first wiring 31a on the positive X direction side.

[0066] Furthermore, the fifth electrode 17 arranged at the end in the negative X direction is directly connected to the second wiring 31b on the negative X direction side. Furthermore, four fifth electrodes 17 are connected to the second electrode 12 at the end in the positive Y direction. Since the second electrode 12 is connected to the second wiring 31b on the negative X direction side, the four fifth electrodes 17 are connected to the second electrode 12, and thereby connected to the second wiring 31b on the negative X direction side.

[0067] 1, the fourth electrode 16 and the fifth electrode 17 are connected to the drive circuit 21 by the first wiring 31a and the second wiring 31b, respectively. That is, the fourth electrode 16 and the fifth electrode 17 function as drive electrodes when the force sensor 10 measures force.

[0068] The sixth electrode 18 is provided on the second conductive layer L7. The sixth electrode 18 is made of a conductive thin film. As shown in FIG. 4 , the sixth electrode 18 has a rectangular shape extending in the Y direction. However, the length of the sixth electrode 18 is shorter than the fourth electrode 16 and the fifth electrode 17. As described above, since there are four pairs of the fourth electrode 16 and the fifth electrode 17, four sixth electrodes 18 are also provided lined up in the X direction corresponding to the four pairs.

[0069] Each sixth electrode 18 is disposed so as to overlap a portion of each fourth electrode 16 formed on the first conductive layer L4, each second gap G2, and a portion of each fifth electrode 17. As a result, a third capacitance C3 and a fourth capacitance C4 are formed in the overlapping portion between the fourth electrode 16 and the sixth electrode 18 and the overlapping portion between the fifth electrode 17 and the sixth electrode 18, respectively.

[0070] 4, the sixth electrodes 18 are connected to each other by third wiring 31c arranged on the second conductive layer L7. Also, as shown in Fig. 1, the sixth electrodes 18 are connected to the sense circuit 23 by the third wiring 31c. That is, the sixth electrodes 18 function as detection electrodes when the force sensor 10 measures a force in the X direction.

[0071] As described above, the third wiring 31c connects the plurality of sixth electrodes 18 in the force sensor 10 and connects each of the sixth electrodes to the sense circuit 23. Therefore, the third wiring 31c extends in the X direction throughout the force sensor 10.

[0072] The principle of measuring a force in the X direction in the force sensor 10 is the same as the principle of measuring a force in the Y direction described above, and therefore, a description of the principle will be omitted here.

[0073] (3) Materials The materials used in each force sensor 10 are described below. The surface layers (first surface layer L1, second surface layer L10) and insulating layers (first shield layer L2, second shield layer L5, second insulating layer L8, third insulating layer L9) of the force sensor 10 can be made of, for example, silicone resin. Other materials include thermoplastic resin, thermosetting resin, and ultraviolet-curing resin. Examples of thermoplastic resin and thermosetting resin include polyethylene terephthalate (PET) resin, acrylic resin, urethane resin, fluororesin, polyester resin, polycarbonate resin, polyacetal resin, polyamide resin, and olefin. Examples of ultraviolet-curing resin include acrylic resin and epoxy resin.

[0074] The first electrode 11, second electrode 12, third electrode 14, fourth electrode 16, fifth electrode 17, sixth electrode 18, seventh electrode 19, eighth electrode 20, first wiring 31a, second wiring 31b, and third wiring 31c of the force sensor 10 can be configured as, for example, a metal film, a conductive ceramic film, a conductive paste film, or a conductive polymer film. Metal films include, for example, gold, silver, copper, nickel, aluminum, titanium, and palladium films. Conductive ceramic films include, for example, indium tin oxide and zinc oxide films. Conductive paste films include thin films made of materials in which metal particles are dispersed in a resin binder. An example of a conductive paste film material is silver paste. Conductive polymer films include, for example, polyhexylthiophene, polydioctylfluorene, pentacene, and tetrabenzoporphyrin films.

[0075] Methods for forming electrodes and wiring (first electrode 11, second electrode 12, third electrode 14, fourth electrode 16, fifth electrode 17, sixth electrode 18, first wiring 31a, second wiring 31b, and third wiring 31c) having predetermined shapes include, for example, forming a conductive film over the entire layer and then patterning it by etching. Forming a conductive film over the entire layer can be achieved, for example, by laminating a rolled conductive film, plating, sputtering, vapor deposition, or ion plating. Furthermore, in the case of a conductive paste film, a method for directly forming a pattern using a printing method such as screen printing, gravure printing, or offset printing can be used. The thickness of the electrodes and wiring can be appropriately selected, for example, from the range of 0.1 μm to 5 mm.

[0076] The insulating elastic body 13 is made of, for example, a foam or gel. An example of a foam is a resin in which gas is finely dispersed and molded into a foamed or porous shape. Examples of foam materials include silicone, urethane, polyethylene, and polystyrene. The thickness of the insulating elastic body 13 is appropriately selected from the range of, for example, 2 μm to 5 mm.

[0077] The insulating elastic body 13 may contain conductive particles in a proportion that allows the insulating properties to be maintained. Examples of the conductive particle material include carbon black, gold, silver, and nickel. This reduces the distance between the conductive particles contained in the insulating elastic body 13 when the insulating elastic body 13 is pressed, causing a sudden increase in the capacitance between the first electrode 11, the second electrode 12, and the third electrode 14, thereby improving the force detection sensitivity. The average particle size of the conductive particles is preferably one-tenth or less of the thickness of the insulating elastic body 13.

[0078] (4) First Information Processing Device The first information processing device 3 will be described below with reference to Fig. 6. Fig. 6 is a diagram showing the configuration of the first information processing device. The first information processing device 3 is a computer system including a CPU, a storage device (RAM, ROM, SSD, HDD, etc.), various interfaces (input / output interface, etc.), and a display device (organic EL display, liquid crystal display, etc.). The first information processing device 3 is, for example, a mobile terminal (smartphone, tablet terminal, etc.) or a personal computer.

[0079] The first information processing device 3 has a calculation unit 31, a first storage unit 33, and a display unit 35. The calculation unit 31 is configured by a CPU and other components that constitute the first information processing device 3, and executes various information processes in the force measuring device 1. Specifically, the calculation unit 31 calculates the magnitude, direction, etc. of the force applied to the force sensor 10 based on the rate of change in the capacitance of the force sensor 10 measured by the sense circuit 23.

[0080] The calculation unit 31 calculates the magnitude of the force using a function that represents the relationship between the magnitude of the force applied to the force sensor 10 and the rate of change in the capacitance of the force sensor 10 due to the applied force. The relationship between the magnitude of the force applied to the force sensor 10 and the rate of change in the capacitance of the force sensor 10 due to the applied force represents the sensitivity of the force sensor 10. Therefore, the function that represents this relationship is referred to as a sensitivity characteristic function. The calculation unit 31 performs the above force calculation by executing a calculation program MP stored in the first storage unit 33.

[0081] The inventors discovered that the sensitivity characteristic function for calculating the magnitude of a force is a unique function. Specifically, the sensitivity characteristic function for a force in the thickness direction (Z direction) of the force sensor 10 (referred to as the Z-direction sensitivity characteristic function) shows a nonlinear change in the rate of change in capacitance with respect to the magnitude of the force. Furthermore, within the force measurement range of the force measuring device 1, the sensitivity characteristic function for a force in the planar directions (X direction and Y direction) of the force sensor 10 is a proportional function (a function representing a straight line passing through the origin) in which the rate of change in capacitance is proportional to the magnitude of the force.

[0082] More specifically, as shown in FIG. 7, it was found that the Z-direction sensitivity characteristic function changes at an inflection point CP. Specifically, the inflection point CP is defined as (Nc, r Ｎｃ ) and the coordinate point (Nc: force at the inflection point CP, r Ｎｃ : rate of change of capacitance when force is Nc), it was found that the Z-direction sensitivity characteristic function becomes a first function f1 of the force magnitude when the force is Nc or ​​less (force≦Nc), and becomes a second function f2 of the force magnitude when the force is Nc or ​​more (force ≧Nc). Figure 7 is a diagram showing an example of the Z-direction sensitivity characteristic function.

[0083] The first function f1 could be approximated by a proportional function in which the rate of change in capacitance is proportional to the magnitude of the force. That is, if x is the magnitude of the force and y is the rate of change in capacitance, the first function could be approximately expressed as y = a * x (a: positive constant) (x ≦ Nc). The first function f1 passes through the inflection point CP. On the other hand, the second function f2 passes through the inflection point CP (connected to the first function f1 at the inflection point CP) and could be approximated by a logarithmic function in which the rate of change in capacitance changes logarithmically with the magnitude of the force. That is, the second function f2 could be approximately expressed as y = b * ln(x) + c (b, c: constants) (x ≧ Nc).

[0084] Therefore, when calculating the Z-direction force of the force sensor 10, the calculation unit 31 calculates the magnitude of the force using the first function f1 (y = a * x) if the magnitude of the applied force is predicted to be less than the force of the inflection point CP (x ≦ Nc), and calculates the magnitude of the force using the second function f2 (y = b * ln(x) + c) if the magnitude of the applied force is predicted to be greater than the force of the inflection point CP (x ≧ Nc).

[0085] The first storage unit 33 is configured with a storage device and the like that constitutes the first information processing device 3, and stores various programs, various information (parameters) necessary for force measurement, and the like. Specifically, the first storage unit 33 stores the calculation program MP and parameter information PI. The parameter information PI stores parameters that define the sensitivity characteristic function. As parameters related to the Z-direction sensitivity characteristic function, the parameter information PI stores the coordinate point of the inflection point CP, the value of the constant a (i.e., the slope) of the first function expressed as y = a * x, and the values ​​of the constants b and c of the second function expressed as y = b * ln(x) + c. The coordinate point of the inflection point CP is defined by the magnitude Nc of the force at the inflection point CP as the x-coordinate value, and the rate of change r of the capacitance at this time. Ｎｃ That is, the inflection point CP is a coordinate point whose y-coordinate value is (Nc, r Ｎｃ ) and is expressed as a coordinate point.

[0086] The parameter information PI also stores parameters that define a sensitivity characteristic function in a planar direction. As described above, the sensitivity characteristic function in a planar direction is a proportional function. Therefore, the parameter information PI stores the slope of the proportional function that represents the sensitivity characteristic function in the X direction and the slope of the proportional function that represents the sensitivity characteristic function in the Y direction.

[0087] In this way, the parameter information PI stores parameters of a function representing the sensitivity characteristic function. Furthermore, in the calculation program MP, the Z-direction sensitivity characteristic function is defined as, for example, y = d * x, y = e * ln(x) + f, with d, e, and f being variables. The sensitivity characteristic function in the planar direction is similarly defined. When calculating a force, the calculation unit 31 executing the calculation program MP reads out the parameters stored in the parameter information PI and substitutes them for the variables (the above d, e, and f) representing the sensitivity characteristic function of the calculation program MP.

[0088] The parameters of the sensitivity characteristic function may differ for each force sensor 10. Therefore, parameter information PI is prepared for each force sensor 10. This allows accurate force calculation using a common calculation program MP for different force sensors 10. As a result, it is no longer necessary to create a calculation program MP for each force sensor 10.

[0089] The parameters included in the parameter information PI can be calculated by executing a calibration method described below using a calibration device 4 described below.

[0090] The display unit 35 is configured by a display device or the like that constitutes the first information processing device 3, and displays various information. The display unit 35 displays the calculation results of the force calculated by the calculation unit 31.

[0091] (5) Calibration Device The configuration of the calibration device 4 will be described below. The calibration device 4 is a device that calibrates the above-mentioned force measurement device 1. Specifically, the calibration device 4 calibrates the force measurement device 1 by calculating parameter information PI of a sensitivity characteristic function used when calculating a force in the force measurement device 1. As shown in Fig. 8, the calibration device 4 includes an applying unit 5 and a second information processing device 6. Fig. 8 is a diagram showing the configuration of the calibration device.

[0092] The force applying unit 5 applies a force to the force sensor 10 to be calibrated. The following describes a specific configuration of the force applying unit 5. The force applying unit 5 has a mounting table 51, a pressure actuator 53, a drive mechanism 55, a force sensor 57, and a presser 59.

[0093] The mounting table 51 is configured to mount the sensor placement member AR, on which the force sensor 10 to be calibrated is mounted. The mounting table 51 is configured to prevent the sensor placement member AR from moving on the mounting table 51 when a force is applied to the sensor placement member AR. This can be achieved, for example, by fixing the sensor placement member AR to the mounting table 51, increasing the coefficient of friction between the mounting table 51 and the sensor placement member AR, or the like.

[0094] The pressure actuator 53 has a movable part 53a that is movable in the Z direction. The drive mechanism 55 moves the pressure actuator 53 in planar directions (X direction and Y direction). The drive mechanism 55 can be configured, for example, by a motor and a mechanism that converts the rotation of the motor into movement in the planar direction.

[0095] One end of the force sensor 57 is connected to the movable part 53a of the pressure actuator 53. On the other hand, a presser 59 is attached to the other end of the force sensor 57. In other words, the force sensor 57 is disposed between the movable part 53a and the presser 59. The force sensor 57 measures the force applied to the force sensor 10 by the force application unit 5.

[0096] The presser 59 is attached to the other end of the force sensor 57 opposite to the end connected to the movable part 53a. The presser 59 is made of a material having a large coefficient of friction with respect to the sensor placement member AR. The presser 59 can be made of an elastic material such as NBR rubber, for example.

[0097] In the application unit 5 having the above-mentioned configuration, by moving the movable part 53a of the pressure actuator 53 in the Z direction, the pressure element 59 can be moved further in the Z direction from a state in contact with the surface of the sensor placement member AR and pressed in, thereby pressing the sensor placement member AR.

[0098] With the sensor placement member AR pressed by the presser 59, the drive mechanism 55 moves the pressure actuator 53 in the planar direction to move the presser 59 in the planar direction, thereby applying a force in the planar direction to the force sensor 10. Note that if the presser 59 is not moved in the planar direction while the force sensor 10 is pressed by the presser 59, a force can be applied only in the Z direction of the force sensor 10. The force applied by the application unit 5 in this manner is measured by the force sensor 57.

[0099] One end of the force sensor 57 is connected to the movable part 53a of the pressure actuator 53. On the other hand, a presser 59 is attached to the other end of the force sensor 57. The force sensor 57 measures the force applied to the force sensor 10 by the presser 59.

[0100] Returning to the explanation of the calibration device 4, the second information processing device 6 is a computer system configured with a CPU, a storage device (RAM, ROM, SSD, HDD, etc.), various interfaces (input / output interface, etc.), and a display device (organic EL display, liquid crystal display, etc.). The second information processing device 6 is, for example, a mobile terminal (smartphone, tablet terminal, etc.) or a personal computer. As shown in FIG. 8 , the second information processing device 6 has a calibration unit 61 and a second storage unit 63.

[0101] The calibration unit 61 is configured by the CPU and other components of the second information processing device 6, and executes processing to calibrate the force measuring device 1 equipped with the force sensor 10 to be calibrated. The calibration unit 61 calibrates the force measuring device 1 by executing the calibration program AP stored in the second storage unit 63.

[0102] Specifically, the calibration unit 61 calibrates the force measuring device 1 as follows. First, the calibration unit 61 controls the pressing actuator 53 and drive mechanism 55 of the application unit 5 to apply a force to the force sensor 10 and measures the applied force with the force sensor 57. The calibration unit 61 also acquires the capacitance when a force is applied to the force sensor 10 from the sense circuit 23, and calculates the rate of change in the capacitance of the force sensor 10 when a force is applied, based on this.

[0103] Thereafter, the calibration unit 61 calculates data points represented by coordinate values ​​of the magnitude of the force applied to the force sensor 10 and the rate of change in capacitance with respect to the force. The calibration unit 61 calibrates the force measuring device 1 by calculating parameter information PI of the sensitivity characteristic function based on the acquired data points.

[0104] The second storage unit 63 stores various programs and various information (parameters) necessary for calibrating the force measurement device 1. Specifically, the second storage unit 63 stores the calculation program MP and parameter information PI obtained as a result of the calibration of the force measurement device 1. After calibration using the force sensor 10 to be calibrated, the parameter information PI stored in the second storage unit 63 is stored in the first storage unit 33 of the first information processing device 3 of the force measurement device 1 equipped with the force sensor 10.

[0105] (6) Calibration Operation of Force Measuring Device 1 Using Calibration Device (6-1) Calibration Operation for Force in Z Direction of Force Sensor Below, we will explain the calibration operation of the force measuring device 1 using the above-mentioned calibration device 4. As explained above, the Z-direction sensitivity characteristic function for calculating the Z-direction force of the force sensor 10 is composed of two functions (first function and second function) that change at the inflection point CP. Such Z-direction sensitivity characteristic cannot be calculated by simple fitting with the data points used for calibration.

[0106] The calibration operation of the force measuring device 1 when calculating the Z-direction sensitivity characteristic function will be described below with reference to Fig. 9. Fig. 9 is a flowchart showing the calibration operation of the force measuring device when calculating the Z-direction sensitivity characteristic function. The calibration operation of the force measuring device 1 according to the flowchart of Fig. 9 can be realized by the calibration unit 61 of the second information processing device 6 of the calibration device 4 executing the calibration program AP stored in the second storage unit 63.

[0107] First, data points for calculating the Z-direction sensitivity characteristic function are acquired (step S11). Specifically, the calibration unit 61 uses the application unit 5 to apply forces of multiple magnitudes to the force sensor 10 within a range from 0 to a magnitude greater than the inflection value Nc (the magnitude of the force at the inflection point CP), and measures the rate of change in capacitance of the force sensor 10 when each force is applied, thereby acquiring multiple data points (coordinate points of (F, r) (F: magnitude of the force in the Z direction, r: rate of change in capacitance when the magnitude of the force in the Z direction is F)) represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force.

[0108] More specifically, the calibration unit 61 controls the pressing actuator 53 of the application unit 5 to move the presser 59 in the Z direction to press the force sensor 10, thereby applying a force in the Z direction to the force sensor 10. When pressing the force sensor 10, the calibration unit 61 measures the applied force using the force sensor 57, and adjusts the position of the presser 59 in the Z direction so that the measured force becomes the target force.

[0109] Next, the calibration unit 61 acquires the capacitance of the force sensor 10 when a force of a target magnitude is applied from the sense circuit 23 of the controller 2 of the force measuring device 1. Thereafter, the calibration unit 61 calculates the rate of change of the capacitance based on the acquired capacitance. Here, the rate of change of the capacitance is expressed as the ratio of the capacitance when no force is applied to the capacitance when a force is applied.

[0110] For example, if the first capacitance (the capacitance between the first electrode 11 and the third electrode 14 of the force sensor 10) when no force is applied is C10, the second capacitance (the capacitance between the second electrode 12 and the third electrode 14 of the force sensor 10) is C20, the first capacitance when a predetermined force is applied is C11, and the second capacitance when that force is applied is C21, then the rate of change in capacitance with respect to a force applied in the Z direction can be calculated specifically as (C11 + C21) / (C10 + C20) - 1.

[0111] When acquiring the data points, the calibration unit 61 calculates a force F that is greater than the inflection value Nc from 0. ｎ A plurality of types of force are applied within the range of (Fn>Nc), and the rate of change in capacitance when each force is applied is calculated as described above.１ , F ２ , ...F ｎ By applying n types of forces in the Z direction, the change rate of the capacitance r1, r2, ... rn for each force is calculated, and (F １ , r １ ), (F ２ , r ２ ), ... (F ｎ , r ｎ ) and multiple data points are acquired.

[0112] After acquiring a plurality of data points, the calibration unit 61 assumes one of the acquired data points as a virtual inflection point CP (referred to as a virtual inflection point CP'), and sets the magnitude of the force at the virtual inflection point CP' as a virtual inflection value (step S12). For example, the virtual inflection point CP' is defined as (F ｋ , r ｋ ) (k: an integer between 1 and n) and the data point. In this case, the virtual inflection value is F ｋ is.

[0113] In this case, the calibration unit 61 may designate all of the multiple data points as candidates for the virtual inflection point CP', or may designate data points whose force magnitude is predicted to be near the inflection value Nc as candidates for the virtual inflection point CP'. As will be described later, the calculation of the Z-direction sensitivity characteristic function involves repeatedly calculating a first virtual function and a second virtual function for one virtual inflection point CP' while changing the virtual inflection point CP'. Therefore, by designating data points whose force magnitude is predicted to be near the inflection value Nc as candidates for the virtual inflection point CP', it is not necessary to designate all of the acquired multiple data points as virtual inflection points CP' (i.e., the number of data points that are candidates for the virtual inflection point CP' can be reduced), thereby reducing the number of times the calculation of the first virtual function and the second virtual function is performed. As a result, the Z-direction sensitivity function can be calculated more quickly.

[0114] After assuming the virtual inflection point CP′, the calibration unit 61 calculates the virtual inflection point F from among the plurality of data points acquired in step S11. ｋ A first virtual function is calculated based on data points (referred to as low-force data points) that are equal to or less than the first virtual function, and a first coefficient of determination R １ ２is calculated (step S13).

[0115] The first virtual function corresponds to the first function f1, passes through the virtual inflection point CP', and is a proportional function to the magnitude of the force. Therefore, the first virtual function can be defined as y = α * x (x: magnitude of force, y: rate of change of capacitance, α: constant). The calibration unit 61 calculates the constant α of the first virtual function by fitting this first virtual function to the low-force data points. Specifically, the calibration unit 61 can calculate the constant α of the first virtual function by linear regression (e.g., the least squares method).

[0116] More specifically, the low force data points are defined as (F １ , r １ ), (F ２ , r ２ ), ... (F ｋ , r ｋ ), the constant α is (F １ *r １ +F ２ *r ２ +...F ｋ *r ｋ ) / (F １ ２ +F ２ ２ +...F ｋ ２ ) can be calculated using the formula:

[0117] In addition, the first coefficient of determination R １ ２ can be calculated using the following equation 1 for the constant α calculated above. ａｖ is the rate of change of capacitance at the low force data point, r １ , r ２ , ...r ｋ is the average value of

[0118] Next, the calibration unit 61 selects a data point among the plurality of data points where the magnitude of the force is the virtual inflection value F ｋ A second virtual function is calculated based on the data points (called high-force data points) that are equal to or greater than the above, and a second coefficient of determination R ２ ２ is calculated (step S14).

[0119] The second virtual function corresponds to the second function f2. That is, the second virtual function is connected to the first virtual function at a virtual inflection point CP′ (that is, the virtual inflection value F ｋ The second virtual function is a logarithmic function of the force magnitude (which passes through a virtual inflection point CP' and is connected to the first virtual function at y). Therefore, the second virtual function can be defined as y = β * ln(x) + γ (x: force magnitude, y: rate of change of capacitance, β and γ: constants). Direct fitting of such a second virtual function, which is a logarithmic function, to high-force data points is difficult due to the complex mathematical formula.

[0120] When the second virtual function is viewed in a ln(x)-y (i.e., semi-logarithmic) coordinate system, the second virtual function can be viewed as a straight line equation with a slope of β and an intercept of γ, as shown in FIG. 10. FIG. 10 is a diagram showing an example of the second virtual function expressed on a semi-logarithmic graph. The second virtual function is also expressed as a linear function of the coordinate point (ln(F ｋ ), r ｋ ) Therefore, the second virtual function is ｋ =β(ln(x)−ln(F ｋ )) can also be expressed as

[0121] That is, the second virtual function is a virtual inflection value F ｋ The rate of change of capacitance when ｋ ) and the difference (y-r ｋ ) is the logarithm of the force magnitude (ln(x)) and the virtual inflection value F ｋ Logarithm of (ln(F ｋ )) and the difference (ln(x) - ln(F ｋ )) and its slope is β. This proportional function is called a virtual proportional function.

[0122] The calibration unit 61 converts the second virtual function (y=β*ln(x)+γ) into the virtual proportional function (y−r ｋ =β(ln(x)−ln(F ｋ))) and calculate a virtual proportional function based on the high force data points. Then, a second virtual function is calculated from the calculated virtual proportional function. This method allows the second virtual function to be easily calculated in the same manner as the first virtual function, without using a complicated method such as using a complex mathematical formula. Specifically, the calibration unit 61 can calculate the constant β of the virtual proportional function by linear regression, just like the first virtual function. If β can be calculated as follows, the constant γ can be calculated by ｋ −β*ln(F ｋ ) can be calculated using the formula:

[0123] More specifically, the high force data points are defined as (F ｋ , r ｋ ), (F ｋ＋１ , r ｋ＋１ ), ... (F ｎ , r ｎ ), the constant β is {(ln(F ｋ )-ln(F ｋ ))*(r ｋ -r ｋ ) + (ln(F ｋ＋１ ) -ln(F ｋ ))*(r ｋ＋１ -r ｋ )+...(ln(F ｎ )-ln(F ｋ ))*(r ｎ -r ｋ )} / {(ln(F ｋ ) -ln(F ｋ )) ２ + (ln(F ｋ＋１ ) -ln(F ｋ )) ２ + ... (ln (F ｎ )-ln(F ｋ )) ２} can be calculated using the formula:

[0124] In addition, the second coefficient of determination R ２ ２ can be calculated using the following equation 2 for the constant β calculated above. ａｖ is the rate of change of capacitance at the high-force data point and r ｋ The difference between ｋ -r ｋ , ...r ｎ -rｋ is the average value of

[0125] The constant α of the first virtual function, the first coefficient of determination R １ ２ , constants β and γ of the second virtual function, and the second coefficient of determination R ２ ２ After calculating the coefficient of determination, the calibration unit 61 calculates the sum R １ ２ +R ２ ２ is calculated (step S15).

[0126] For a specific virtual inflection point CP′, the constant α of the first virtual function, the first coefficient of determination R １ ２ , constants β and γ of the second virtual function, and the second coefficient of determination R ２ ２ After calculating the first and second coefficients of determination, R １ ２ +R ２ ２ After calculating the above, the calibration unit 61 determines whether or not there are any candidate data points for the virtual inflection point CP' for which these have not been calculated (step S16).

[0127] If there is a data point that is a candidate for a specific virtual inflection point CP′ (step S16: Yes), the calibration unit 61 selects the next data point after the data point selected as the virtual inflection point CP′ in step S12, that is, (F ｋ＋１ , r ｋ＋１ ) is set as a new virtual inflection point CP′ (step S17), and the above steps S12 to S15 are executed to determine the constant α of the first virtual function and the first coefficient of determination R １ ２ , constants β and γ of the second virtual function, and the second coefficient of determination R ２ ２ , the sum of the first and second coefficients of determination R １ ２ +R ２ ２ Calculate.

[0128] On the other hand, all of the candidate data points are set as virtual inflection points CP′, and the constant α of the first virtual function and the first coefficient of determination R １２ , constants β and γ of the second virtual function, and the second coefficient of determination R ２ ２ , the sum of the first and second coefficients of determination R １ ２ +R ２ ２ When the result of step S16 is "No", the calibration unit 61 calculates the constant α of the first virtual function, the first coefficient of determination R １ ２ , constants β and γ of the second virtual function, and the second coefficient of determination R ２ ２ , the sum of the first and second coefficients of determination R １ ２ +R ２ ２ Based on this, the Z-direction sensitivity characteristic function is calculated (step S18).

[0129] Specifically, the sum R of the first and second determination coefficients calculated for each of the virtual inflection points CP′ is １ ２ +R ２ ２ Among them, the maximum value is the sum R １ ２ +R ２ ２ The calculated virtual inflection point CP' (for example, (F ｍ , r ｍ ) (m: an integer of 1 or more and n or less)) is set as an inflection point CP of the Z-direction sensitivity characteristic function, and the virtual inflection value F of this virtual inflection point CP′ is ｍ The inflection value Nc of the inflection point CP (i.e., Nc = F ｍ ) and the virtual inflection point CP' is (F ｍ , r ｍ ) The constant α of the first virtual function calculated when ｍ is the constant a of the first function (i.e., a = α ｍ ), and the virtual inflection point CP' is (F ｍ , r ｍ ) The constant β of the second virtual function calculated when ｍ , γ ｍ are respectively set to the constants b and c of the second function (i.e., b=β ｍ , c=γ ｍ )

[0130] In this way, the sum R of the first and second determination coefficients is １ ２ +R ２ ２ The virtual inflection value F when ｍ is determined as the inflection value Nc, the Z-direction sensitivity characteristic function (i.e., first function f1) when the force magnitude is equal to or less than the inflection value Nc is determined based on data points below the inflection point CP, and the sensitivity characteristic function (i.e., second function f2) when the force magnitude is equal to or greater than the inflection value Nc is determined based on data points above the inflection point CP, thereby making it possible to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor 10 to a wide range of forces in the Z direction. As a result, the force measuring device 1, which measures force based on changes in capacitance, can be calibrated so that it can accurately measure a wide range of forces.

[0131] This is because, by calculating the first function f1 and the second function f2 individually as described above, the first function f1 can be calculated as a function that well represents the data points below the inflection point CP, and the second function f2 can be calculated as a function that well represents the data points above the inflection point CP. １ ２ +R ２ ２ The virtual inflection value F when ｍ This is because by determining the inflection value Nc as the inflection value Nc, it is possible to accurately determine at what point the sensitivity characteristic function changes.

[0132] (6-2) Calibration Operation of Force Sensor for Force in Planar Direction Next, the calibration operation of the force measuring device 1 for forces in the planar direction (i.e., calculation of the sensitivity characteristic function in the planar direction) will be described. As described above, the sensitivity characteristic function in the planar direction is expressed by a proportional function. The sensitivity characteristic function in the planar direction expressed as a proportional function can be calculated by fitting with data points (for example, the linear regression described above). Specifically, the sensitivity characteristic function in the planar direction can be calculated according to the flowchart shown in FIG. 11. FIG. 11 is a flowchart showing the calibration operation of the force measuring device when calculating the sensitivity characteristic function in the planar direction.

[0133] First, data points for calculating the sensitivity characteristic function in the planar direction are acquired (step S21). Specifically, the calibration unit 61 controls the pressure actuator 53 of the application unit 5 to move the presser 59 in the Z direction to press the force sensor 10, while controlling the drive mechanism 55 to move the presser actuator 53 in the X direction or the Y direction, thereby applying a force in the planar direction (X direction or Y direction) of the force sensor 10. While pressing the force sensor 10, the calibration unit 61 measures the applied force using the force sensor 57, and adjusts the position of the presser 59 in the Z direction so that the measured force becomes the target force.

[0134] Next, the calibration unit 61 acquires the capacitance of the force sensor 10 when a force of a target magnitude is applied from the sense circuit 23 of the controller 2 of the force measuring device 1. Thereafter, the calibration unit 61 calculates the rate of change of the capacitance based on the acquired capacitance.

[0135] For example, if the third capacitance (the capacitance between the fourth electrode 16 and the sixth electrode 18 of the force sensor 10) when no force is applied is C30, the fourth capacitance (the capacitance between the fifth electrode 17 and the sixth electrode 18 of the force sensor 10) is C40, and the third capacitance when a predetermined force is applied in the X direction is C32, then the rate of change of the capacitance with respect to the force applied in the X direction can be calculated as {C32 / (C30+C40)}-1 / 2. When this rate of change is a positive value, a force in the positive X direction is being applied, and when it is a negative value, a force in the negative X direction is being applied.

[0136] On the other hand, if the first capacitance (the capacitance between the first electrode 11 and the third electrode 14 of the force sensor 10) when no force is applied is C10, the second capacitance (the capacitance between the second electrode 12 and the third electrode 14 of the force sensor 10) is C20, and the first capacitance when a predetermined force is applied in the Y direction is C12, then the rate of change of the capacitance with respect to the force applied in the Y direction can be calculated specifically as {C12 / (C10+C20)}-1 / 2. When this rate of change is a positive value, a force in the positive Y direction is being applied, and when it is a negative value, a force in the negative Y direction is being applied.

[0137] The calibration unit 61 applies a plurality of types of force in the planar direction and calculates the rate of change in capacitance when each force is applied as described above. Ｘ１ , F Ｘ２ , ...F Ｘｐ By applying p kinds of forces in the X direction, r Ｘ１ , r Ｘ２ , ...r Ｘｐ The rate of change of capacitance with respect to Ｘ１ , r Ｘ１ ), (F Ｘ２ , r Ｘ２ ), ... (F Ｘｐ , r Ｘｐ ) and multiple data points are obtained. Ｙ１ , F Ｙ２ , ...F Ｙｑ By applying q kinds of forces in the Y direction, the force Ｙ１ , r Ｙ２ , ...r Ｙｑ The rate of change of capacitance with respect to Ｙ１ , r Ｙ１ ), (F Ｙ２ , r Ｙ２ ), ... (F Ｙｎ , r Ｙｑ ) and multiple data points are acquired.

[0138] Next, the calibration unit 61 calculates a sensitivity characteristic function in the plane direction based on the multiple data points acquired in step S21 (step S22). For example, if the sensitivity characteristic function in the X direction is defined as y = δ * x (x: magnitude of force, y: rate of change of capacitance, δ: constant), the calibration unit 61 calculates (F Ｘ１ *r Ｘ１ +F Ｘ２ *r Ｘ２ +...F Ｘｐ *r Ｘｐ ) / (F Ｘ１ ２ +F Ｘ２ ２ +...F Ｘｐ ２ ) and the constant δ. For example, if the sensitivity characteristic function in the Y direction is defined as y = ε*x (x: magnitude of force, y: rate of change of capacitance, ε: constant), the calibration unit 61 can calculate the following: (F Ｙ１ *r Ｙ１+F Ｙ２ *r Ｙ２ +...F Ｙｑ *r Ｙｑ ) / (F Ｙ１ ２ +F Ｙ２ ２ +...F Ｙｑ ２ ) and the constant ε can be calculated.

[0139] The constants determined as described above are stored as parameter information PI in the second storage unit 63. Thereafter, this parameter information PI is stored in the first storage unit 33 of the first information processing device 3 of the force measurement device 1 equipped with the force sensor 10 to be calibrated. In this way, the calibration of the force measurement device 1 is realized.

[0140] (7) Force Measuring Operation Using Force Measuring Device 1 The following describes the force measuring operation using the above-described force measuring device 1. First, the calculation unit 31 of the first information processing device 3 acquires capacitances (a first capacitance between the first electrode 11 and the third electrode 14, a second capacitance between the second electrode 12 and the third electrode 14, a third capacitance between the fourth electrode 16 and the sixth electrode 18, and a fourth capacitance between the fifth electrode 17 and the sixth electrode 18) from the sense circuit 23 of the controller 2.

[0141] Next, based on the acquired capacitance, the calculation unit 31 calculates the rate of change of capacitance in each direction of the force sensor 10. Specifically, the rate of change of capacitance in the X direction can be calculated as {C32 / (C30+C40)}-1 / 2 (C30: third capacitance when no force is applied, C40: fourth capacitance when no force is applied, C32: third capacitance when force is applied in the X direction).

[0142] The rate of change of capacitance in the Y direction can be calculated as {C12 / (C10+C20)}-1 / 2 (C10: first capacitance when no force is applied, C20: second capacitance when no force is applied, C12: first capacitance when force is applied in the Y direction).

[0143] The rate of change of capacitance in the Z direction can be calculated, for example, as (C11 + C21) / (C10 + C20) - 1 (C10: first capacitance when no force is applied, C20: second capacitance when no force is applied, C11: first capacitance when force is applied in the Z direction, C21: second capacitance when force is applied in the Z direction).

[0144] Thereafter, the calculation unit 31 can calculate the magnitude of the force in the X direction by substituting the rate of change in the capacitance in the X direction for y in the X direction sensitivity characteristic function (y = δ * x), and can calculate the magnitude of the force in the Y direction by substituting the rate of change in the capacitance in the Y direction for y in the Y direction sensitivity characteristic function (y = ε * x).

[0145] On the other hand, the force in the Z direction is calculated according to the flowchart in Fig. 12. Fig. 12 is a flowchart showing the operation of calculating the force in the Z direction. First, the calculation unit 31 determines whether the magnitude of the force applied to the force sensor 10 is predicted to be equal to or greater than the inflection value Nc of the inflection point CP (step S31).

[0146] The calculation unit 31 may calculate a predicted value of the magnitude of the force in the Z direction by substituting the calculated rate of change of capacitance in the Z direction for y in a first function (y = a * x) of the Z direction sensitivity characteristic function, or may calculate a predicted value of the magnitude of the force in the Z direction by substituting the calculated rate of change of capacitance in the Z direction for y in a second function (y = b * ln(x) + c) of the Z direction sensitivity characteristic function. The calculation unit 31 may determine whether the calculated predicted value of the magnitude of the force in the Z direction is equal to or greater than the inflection value Nc.

[0147] In addition, the calculation unit 31 calculates the calculated rate of change in capacitance in the Z direction as the rate of change r of capacitance at the inflection point CP. Ｎｃ It may be possible to determine whether the predicted value of the magnitude of the force is equal to or greater than the inflection value Nc depending on whether the predicted value is equal to or greater than the inflection value Nc.

[0148] If the predicted value of the magnitude of the Z-direction force is smaller than the inflection value Nc ("No" in step S31), the calculation unit 31 calculates the magnitude of the Z-direction force by substituting the calculated rate of change of capacitance in the Z-direction for y in the first function f1 (y = a * x) of the Z-direction sensitivity characteristic function (step S32).

[0149] On the other hand, if the predicted value of the magnitude of the Z-direction force is equal to or greater than the inflection value Nc ("Yes" in step S31), the calculation unit 31 calculates the magnitude of the Z-direction force by substituting the calculated rate of change of capacitance in the Z-direction for y in the second function f2 (y = b * ln(x) + c) of the Z-direction sensitivity characteristic function (step S33).

[0150] The force calculated using the sensitivity characteristic function as described above is displayed on the display unit 35 of the first information processing device 3. For example, the display unit 35 displays four display areas (first display area W1, second display area W2, third display area W3, and fourth display area W4) as shown in Fig. 13. Fig. 13 is a diagram showing an example of the display of the force calculation results.

[0151] The first display area W1 displays the magnitude of the force in the X direction measured by the force sensors 10 arranged at each position on the sensor arrangement member AR. The second display area W2 displays the magnitude of the force in the Y direction measured by the force sensors 10 arranged at each position. The third display area W3 displays the magnitude of the force in the Z direction measured by the force sensors 10 arranged at each position. The fourth display area W4 displays the forces measured by the force sensors 10 arranged at each position as vectors. That is, the fourth display area W4 displays the direction of the force applied to each force sensor 10.

[0152] The unit of the magnitude of the force displayed in the first to third display areas W1 to W3 can be selected from units expressing force such as N, KPa, mmHg, etc.

[0153] Furthermore, the display unit 35 is not limited to displaying the calculated force value itself, but can also display various numerical data related to the calculated force. For example, statistical values ​​of the force magnitude, such as the maximum, minimum, and average values ​​of the force magnitude measured in a limited area of ​​the sensor placement member AR, can be displayed on the display unit 35. Furthermore, for example, the distribution of the force magnitude on the sensor placement member AR can be represented by color.

[0154] In this way, by displaying numerical data related to the force applied to the force sensor 10 on the display unit 35, it is possible to confirm the magnitude of the force applied to the force sensor 10 as a numerical value. Furthermore, by displaying the direction of the force applied to the force sensor 10 in addition to the numerical data related to the force, it is possible to confirm not only the magnitude of the force applied to the force sensor 10 but also the direction in which the force was applied.

[0155] 2. Second Embodiment (1) Overview In the first embodiment described above, the Z-direction sensitivity characteristic function changes at an inflection point CP, i.e., when the force is equal to or less than Nc (force≦Nc), it is expressed as a first function f1 of the force magnitude, and when the force is equal to or greater than Nc (force ≧Nc), it is expressed as a second function f2 of the force magnitude. However, the Z-direction sensitivity characteristic function can also be expressed by another function.

[0156] Specifically, the Z-direction sensitivity characteristic function can be expressed as a plurality of functions FU1, FU2, ... connected at a plurality of inflection points CP1, CP2, ... as shown in Fig. 14, for example. Fig. 14 is a diagram showing an example of a sensitivity characteristic function expressed by a plurality of functions. The above-mentioned plurality of functions may be linear equations that change linearly with respect to the magnitude of the force applied to the force sensor 10, or may be nonlinear functions that change nonlinearly with respect to the magnitude of the force applied to the force sensor 10. The nonlinear function may be, for example, a polylinear expression of the magnitude of the force applied to the force sensor 10, a logarithmic function of the force applied to the force sensor 10, or the like.

[0157] In this way, the Z-direction sensitivity characteristic function can also be expressed by a plurality of functions FU1, FU2, ... connected at each of a plurality of inflection points CP1, CP2, ... as shown in FIG. 14, or, for example, like the Z-direction sensitivity characteristic function described in the first embodiment, it can also be expressed as two functions (first function f1, second function f2) connected at one inflection point.

[0158] By expressing the Z-direction sensitivity characteristic function as a plurality of functions FU1, FU2, ... connected at a plurality of inflection points CP1, CP2, ... as shown in FIG. 14, the Z-direction sensitivity characteristic function, which changes in a complex manner with respect to the magnitude of force, can be approximated and expressed by a simple function such as a linear equation or a nonlinear function.

[0159] In the second embodiment, the parameter information PI stores information about a plurality of inflection points CP1, CP2, . . . (for example, coordinate values ​​of each inflection point) and expressions representing a plurality of functions FU1, FU2, .

[0160] Furthermore, the calculation unit 31 refers to the parameter information PI described above, determines between which of the multiple inflection points CP1, CP2, ... stored in the parameter information PI the magnitude of the force applied to the force sensor 10 lies, selects from the multiple functions FU1, FU2, ... stored in the parameter information PI a function that passes through two inflection points that sandwich the magnitude of the force applied to the force sensor 10, and substitutes the rate of change in the capacitance of the force sensor 10 into the selected function, thereby being able to calculate the Z-direction force of the force sensor 10.

[0161] The second embodiment is similar to the first embodiment except that the Z-direction sensitivity characteristic function may be expressed as a plurality of functions FU1, FU2, ... connected at a plurality of inflection points CP1, CP2, .... That is, the configurations of the force measuring device 1 and the calibration device 4 of the second embodiment are the same as those of the first embodiment. Therefore, a description of the force measuring device 1 and the calibration device 4 will be omitted here.

[0162] (2) Calibration Operation of the Force Sensor for Force in the Z Direction in the Second Embodiment The calibration operation of the force measuring device 1 when calculating the Z-direction sensitivity characteristic function in the second embodiment will be described below with reference to Fig. 15. Fig. 15 is a flowchart showing the calibration operation of the force measuring device when calculating the sensitivity characteristic function in the second embodiment.

[0163] First, data points for calculating the Z-direction sensitivity characteristic function are acquired (step S41). Specifically, the calibration unit 61 uses the application unit 5 to apply forces of multiple magnitudes to the force sensor 10 and measure the rate of change in capacitance of the force sensor 10 when each force is applied, thereby acquiring multiple data points (coordinate points of (F, r) (F: magnitude of force in the Z direction, r: rate of change in capacitance when the magnitude of the force in the Z direction is F)) represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force. A more specific method for acquiring the multiple data points is similar to the acquisition method in step S11 described in the first embodiment, and therefore will not be described here.

[0164] The force applied to the force sensor 10 in step S41 is preferably, for example, a force having a magnitude that includes the allowable range of forces that can be measured by the force sensor 10. Specifically, the force applied to the force sensor 10 is preferably a plurality of forces that fall within a range from a force that is smaller than the minimum force that can be measured by the force sensor 10 to a force that is larger than the maximum force that can be measured by the force sensor 10.

[0165] By executing step S41, for example, F １ , F ２ , ...F ｎ By applying n kinds of forces in the Z direction, r １ , r ２ , ...r ｎ The rate of change of capacitance with respect to １ , r １ ), (F ２ , r ２ ), ... (F ｎ , r ｎ ) are acquired. １ , F ２ , ...F ｎ is F １ <F ２ <...F ｎ That is, F １ , F ２ , ...F ｎ The forces increase in this order.

[0166] Furthermore, "n" in the second embodiment (the number of types of applied force) may be different from or the same as "n" in the first embodiment. １ , F ２ , ...F ｎ ) may be different from or the same as in the first embodiment.

[0167] In step S41, the multiple data points can be acquired at intervals of, for example, about 3% to 7% of the rated load (the maximum value of the force detection range). In other words, the interval between two data points can be about 3% to 7% of the rated load (the maximum value of the force detection range). However, this is not limited to this, and the interval at which the multiple data points are acquired can be determined appropriately based on, for example, how finely the Z-direction sensitivity characteristic function is divided and expressed.

[0168] After acquiring the plurality of data points, the calibration unit 61 selects one of the acquired plurality of data points as a first data point (step S42). For example, the first data point is (F ｋ , r ｋ ) (k: integer of 1 or more and n or less). The first force, which is the magnitude of the force included in this first data point, is F ｋ When steps S42 and subsequent steps are executed for the first time, k=1.

[0169] Next, among the multiple data points, the force magnitude is the first force (F ｋ ) is selected as the second data point (step S43). ｋ , r ｋ The magnitude of the force (F ｋ ) minus 3% to 7% of the rated load (maximum value of the force detection range) (F ｋ A data point that satisfies −u*Fmax (u: constant (0.03 to 0.07), Fmax: maximum value of the force detection range) can be selected as the second data point. For example, ｋ , r ｋ ) among the data points adjacent to the first force (F ｋ ) is the data point that is smaller than ｋ－１ , rｋ－１ ) can be the second data point.

[0170] When steps S42 and subsequent steps are executed for the first time, that is, when k=1, the origin (0, 0) is selected as the second data point.

[0171] The data point selected as the second data point may or may not be adjacent to the first data point. Furthermore, multiple data points can be used as the second data point. In the next step S44, a first virtual function passing through the first and second data points is calculated. If the first virtual function is a linear equation, the calculation can be performed using at least two data points, the first data point and at least one second data point. On the other hand, if the first virtual function is a nonlinear function, a more accurate function can be calculated by using multiple data points, the first data point and multiple second data points.

[0172] After selecting the first and second data points, the calibration unit 61 calculates a first virtual function that passes through the selected first and second data points (step S44). For example, the first virtual function is expressed as a straight line equation, i.e., y=a １ x + b １ (x: magnitude of force, y: rate of change of capacitance, a １ : slope, b １ : intercept), the first data point (F ｋ , r ｋ ) and one second data point (F ｋ－１ , r ｋ－１ ) and y = {(r ｋ -r ｋ－１ ) / (F ｋ -F ｋ－１ )*(x-F ｋ ) + r ｋ In other words, y = {(r ｋ -r ｋ－１ ) / (F ｋ -F ｋ－１ )*x+(F ｋ *r ｋ -1-F ｋ－１ *r ｋ ) / (F ｋ -F ｋ－１ ) (i.e., slope a １ = (r ｋ -rｋ－１ ) / (F ｋ -F ｋ－１ ), intercept b １ = (F ｋ *r ｋ－１ -F ｋ－１ *r ｋ ) / (F ｋ -F ｋ－１ )) and the first virtual function can be calculated.

[0173] On the other hand, when the first virtual function is defined as a nonlinear function, for example, the first data point (F ｋ , r ｋ ) and a plurality of second data points, a first virtual function can be calculated by a fitting method such as linear regression (e.g., least squares method).

[0174] After calculating the first virtual function, the calibration unit 61 calculates the force magnitude of the first force (F ｋ ) is selected as a third data point (step S45). ｋ , r ｋ The magnitude of the force (F ｋ ) plus a force of approximately 3% to 7% of the rated load (maximum value of the force detection range) (F ｋ +u*Fmax (u: constant (0.03 to 0.07), Fmax: maximum value of the force detection range)) can be selected as the third data point. ｋ , r ｋ ) among the data points adjacent to the first force (F ｋ ) is the data point that is larger than ｋ＋１ , r ｋ＋１ ) can be the second data point.

[0175] Similar to the second data point, the data point selected as the third data point may or may not be adjacent to the first data point, and multiple data points may be selected as the third data point.

[0176] After selecting the third data point, the calibration unit 61 calculates a second virtual function that passes through the first data point and the third data point (step S46). For example, the second virtual function is expressed as a straight line equation, i.e., y=a ２ x + b２ (x: magnitude of force, y: rate of change of capacitance, a ２ : slope, b ２ : intercept), the first data point (F ｋ , r ｋ ) and one second data point (F ｋ＋１ , r ｋ＋１ ) and y = {(r ｋ＋１ -r ｋ ) / (F ｋ＋１ -F ｋ )*(x-F ｋ＋１ ) + r ｋ＋１ In other words, y = {(r ｋ＋１ -r ｋ ) / (F ｋ＋１ -F ｋ )*x+(F ｋ＋１ *r ｋ -F ｋ *r ｋ＋１ ) / (F ｋ＋１ -F ｋ ) (i.e., slope a ２ = (r ｋ＋１ -r ｋ ) / (F ｋ＋１ -F ｋ ), intercept b ２ = (F ｋ＋１ *r ｋ -F ｋ *r ｋ＋１ ) / (F ｋ＋１ -F ｋ )) and the second virtual function can be calculated.

[0177] On the other hand, when the second virtual function is defined as a nonlinear function, for example, the first data point (F ｋ , r ｋ ) and a plurality of third data points, a second virtual function can be calculated by a fitting method such as linear regression (e.g., least squares method).

[0178] After calculating the first and second virtual functions, the calibration unit 61 determines whether the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first and second data points and the differential value of the second virtual function on a line connecting the first and third data points is equal to or greater than a predetermined threshold value (step S47). The predetermined threshold value in this case can be, for example, about 5%.

[0179] For example, the differential value of the first virtual function on the line connecting the first data point and the second data point is expressed as the magnitude F of the force at the first data point on the first virtual function. ｋ The rate of change r calculated by substituting ｋ ', the magnitude of the force F at the second data point in the first virtual function ｋ－１ The rate of change r calculated by substituting ｋ－１ ' is calculated, and a point (F ｋ , r ｋ ') and point (F ｋ－１ , r ｋ－１ The slope of the line connecting (r ｋ '-r ｋ－１ ') / (F ｋ -F ｋ－１ ) can be calculated as follows.

[0180] For example, the derivative of the second virtual function on the line connecting the first data point and the third data point is the magnitude of the force F at the second data point. ｋ The rate of change r calculated by substituting ｋ '', the force magnitude F at the third data point in the second virtual function ｋ＋１ The rate of change r calculated by substituting ｋ＋１ Calculate the point (F ｋ , r ｋ ') and point (F ｋ＋１ , r ｋ＋１ The slope of the line segment connecting ｋ＋１ ''-r ｋ '') / (F ｋ＋１ -F ｋ ) can be calculated as follows.

[0181] When the first virtual function and the second virtual function are linear equations, the differential value of the first virtual function in the line connecting the first data point and the second data point is the slope of the equation of the line representing the first virtual function (i.e., the above a １ ) The differential value of the second virtual function on the line connecting the first data point and the third data point can be calculated by the slope of the equation of the line representing the second virtual function (i.e., the above a ２ ) can be done.

[0182] If the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first data point and the second data point and the differential value of the second virtual function on a line connecting the first data point and the third data point and the differential value of the second virtual function on a line connecting the first data point and the third data point is equal to or greater than a predetermined threshold ("Yes" in step S47), it is determined that the function representing the Z-direction sensitivity characteristic function changes at the first data point. That is, it is determined that the currently selected first data point is an inflection point. In this case, the calibration unit 61 calculates the Z-direction sensitivity characteristic function by connecting the first virtual function and the second virtual function at the first data point (step S48).

[0183] The first data point is (F ｃ , r ｃ ), the magnitude of the force is F ｄ (F ｄ <F ｃ ) to F ｃ The first virtual function VFU1(x) is expressed as the Z-direction sensitivity function, and the magnitude of the force is F ｃ From F ｅ (F ｅ >F ｃ ) up to VFU2(x) is expressed as a Z-direction sensitivity function, the above "connecting the first virtual function and the second virtual function at the first data point" can be expressed as, for example, "F ｄ ≦x≦F ｃ In the case of VFU1(x), F ｃ ≦x≦F ｅ In this case, the Z-direction sensitivity characteristic function is defined as VFU2(x), . . .

[0184] On the other hand, if the absolute value of the ratio between the difference between the differential value of the first virtual function on the line connecting the first data point and the second data point and the differential value of the second virtual function on the line connecting the first data point and the third data point and the differential value of the second virtual function on the line connecting the first data point and the third data point is smaller than the predetermined threshold value ("No" in step S47), it is determined that the function representing the Z-direction sensitivity characteristic function does not change at the first data point. In this case, the calibration unit 61 maintains the first virtual function as the Z-direction sensitivity characteristic function (step S49).

[0185] Specifically, the force magnitude F at the first data point ｋ and the force magnitude F at the second data point ｋ－１ and the force magnitude F at the first data point ｋ and the force magnitude F at the third data point ｋ＋１ In other words, it is determined that the Z-direction sensitivity characteristic function is expressed by the first virtual function between F and F. ｋ－１ ~F ｋ＋１ In the range of (a), the Z-direction sensitivity characteristic function is determined to be expressed by a first virtual function.

[0186] In step S49, the magnitude of the force is F ｋ－１ ~F ｋ＋１ In the range, when it is determined that the Z-direction sensitivity characteristic function is expressed by the first virtual function, when the next loop of steps S42 to S49 is executed with k=k+1, in step S42 of the next loop, the actual data point acquired in step S41 is not used, but a point on the first virtual function, that is, the first virtual function (x) calculated in the previous loop is used as F. ｋ＋１ The rate of change in capacitance vr calculated by substituting ｋ＋１ is the y-coordinate (F ｋ＋１ , vr ｋ＋１ ) is selected as the first data point.

[0187] Also, in step S43 of the next loop, instead of the actual data point acquired in step S41, a point on the first virtual function, that is, the first virtual function (x) calculated in the previous loop, is used as the F ｋ The rate of change in capacitance vr calculated by substituting ｋis the y-coordinate (F ｋ , vr ｋ ) is selected as the second data point.

[0188] As mentioned above, the force magnitude F of the third data point ｋ＋１ After determining the Z-direction sensitivity characteristic function up to , if the above steps S42 to S49 have not been performed for all data points (magnitudes of forces included in) acquired in step S41 ("No" in step S50), k = k + 1 is set (step S51), and the above steps S41 to S49 are performed for the next first data point.

[0189] On the other hand, if steps S42 to S49 have been executed for all data points (the magnitudes of the forces included in them) acquired in step S41 ("Yes" in step S50), the calibration operation ends.

[0190] By performing the above steps S41 to S51, it is possible to calculate an accurate Z-direction sensitivity characteristic function including a plurality of functions connected at each of a plurality of inflection points, as shown in Fig. 14. For example, even if the Z-direction sensitivity characteristic function changes in a complex manner with respect to the magnitude of the force, it is possible to calculate a Z-direction sensitivity characteristic that accurately represents the complex change by connecting a plurality of relatively simple functions.

[0191] Furthermore, when the Z-direction sensitivity characteristic function is expressed by a plurality of functions connected at each of a plurality of inflection points, and particularly when all of the plurality of functions are defined as simple functions such as linear equations, the magnitude of the force corresponding to the rate of change in the capacitance of the force sensor 10 can be calculated by simple calculations with low computational load, such as the four basic arithmetic operations (addition, subtraction, multiplication, and division). Furthermore, the amount of data required to determine the function can be reduced, and the calculations for determining the function can be simplified.

[0192] On the other hand, when a plurality of functions are defined as nonlinear functions, it is possible to calculate a Z-direction sensitivity characteristic function that more accurately represents the relationship between the force applied to the force sensor 10 and the rate of change in capacitance.

[0193] The reason why the "predetermined threshold" used in the determination in step S47 above is set to 5% will be explained. Generally, for the multiple data points obtained by actual measurement in step S41, the slopes of the line segments connecting adjacent data points have a variation of about 40%. Therefore, in the calibration method of the second embodiment, by setting the "predetermined threshold" to 5%, it is possible to calculate a Z-direction sensitivity characteristic function having multiple straight lines connecting the multiple data points obtained by actual measurement.

[0194] Furthermore, when the Z-direction sensitivity characteristic function changes from the first function f1 to the second function f2 at the inflection point CP as in the first embodiment, there is generally a difference of about 10% to 20% between the differential value (slope) of the first function f1 and the differential value of the second function f2 at the inflection point CP. Therefore, in the calibration method of the second embodiment, by setting the "predetermined threshold" to 5%, step S47 can be set to "Yes" at the first data point corresponding to the inflection point CP, and the inflection point CP can be accurately determined.

[0195] The calibration method (method of calculating the Z-direction sensitivity characteristic function) in the second embodiment can also be considered to include the calibration method in the first embodiment. Specifically, until the first data point becomes the inflection point CP, the error between the first virtual function and the data point is small, so the answer in step S47 is "No." Therefore, the first virtual function corresponding to the first function f1 (from the origin) to the inflection point CP can be determined as the Z-direction sensitivity characteristic function. The first data point and the plurality of second data points in the second embodiment can be considered to correspond to the low-force data points in the first embodiment.

[0196] On the other hand, when the first data point corresponds to an inflection point CP, the difference between the differential value of the first virtual function and the differential value of the second virtual function is equal to or greater than a predetermined threshold (i.e., "Yes" in step S47). Therefore, after the inflection point CP, the second virtual function corresponding to the second function f2 can be determined as the Z-direction sensitivity characteristic function. After the inflection point CP, the second function f2 can also be approximately represented by multiple functions connected at multiple inflection points. The first data point and multiple third data points in the second embodiment can be considered to correspond to the high-force data points in the first embodiment.

[0197] 3. Other Embodiments Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. In particular, the multiple embodiments and modifications described in this specification can be combined as needed. (A) The processing order and / or processing content of each step in the flowcharts shown in Figures 9, 11, 12, and 15 can be modified as appropriate without departing from the spirit of the invention.

[0198] (B) The first information processing device 3 of the force measuring device 1 and the second information processing device 6 of the calibration device 4 may be the same device. For example, the calibration program AP may be stored in the first storage unit 33 of the first information processing device 3, and the calculation unit 31 may execute the calibration program AP, thereby making it possible to perform the calibration of the force measuring device 1 described above.

[0199] (C) For example, when the force applied in the planar direction is large and the sensitivity characteristic function in the planar direction also changes at an inflection point, the sensitivity characteristic function in the planar direction can be calculated in the same manner as the calculation method for the Z-direction sensitivity characteristic function described above.

[0200] (D) Depending on the configuration, characteristics, etc. of the force sensor 10, the first function f1 of the Z-direction sensitivity characteristic function can be a function other than a proportional function with respect to the magnitude of the force, and the second function f2 can be a function other than a logarithmic function with respect to the magnitude of the force.

[0201] (E) A sense circuit 23 can be connected to the first electrode 11 and the second electrode 12, causing the first electrode 11 and the second electrode 12 to function as detection electrodes, and a drive circuit 21 can be connected to the third electrode 14, causing the third electrode 14 to function as a drive electrode.

[0202] (F) A sense circuit 23 can be connected to the fourth electrode 16 and the fifth electrode 17, causing the fourth electrode 16 and the fifth electrode 17 to function as detection electrodes, and a drive circuit 21 can be connected to the sixth electrode 18, causing the sixth electrode 18 to function as a drive electrode.

[0203] (G) In the second embodiment described above, the criterion for determining whether to connect the first virtual function and the second virtual function at the first data point was whether the absolute value of the ratio between the difference between the differential value of the first virtual function on the line connecting the first data point and the second data point and the differential value of the second virtual function on the line connecting the first data point and the third data point was equal to or greater than a predetermined threshold. In this case, the predetermined threshold was a percentage such as 5%. However, the present invention is not limited to this.

[0204] The above-mentioned predetermined threshold value expressed as a percentage is not limited to 5%, but can be determined appropriately taking into consideration the performance of the force measuring device 1, measurement accuracy, etc.

[0205] For example, the criterion for determining whether to connect the first virtual function and the second virtual function at the first data point can be the magnitude of a value related to the difference between the differential value of the first virtual function in a line connecting the first data point and the second data point and the differential value of the second virtual function in a line connecting the first data point and the third data point.

[0206] For example, the criterion for determining whether to connect the first virtual function and the second virtual function at the first data point may be whether the absolute value of the difference between the differential value of the first virtual function on the line connecting the first and second data points and the differential value of the second virtual function on the line connecting the first and third data points is equal to or greater than a predetermined threshold. In this case, the predetermined threshold is a numerical value that is not a percentage, such as a predetermined percentage of the differential value of the first virtual function on the line connecting the first and second data points, or a predetermined percentage of the differential value of the second virtual function on the line connecting the first and second data points.

[0207] Alternatively, the criterion for determining whether to connect the first virtual function and the second virtual function at the first data point may be whether the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first and second data points and the differential value of the second virtual function on a line connecting the first and third data points is equal to or greater than a predetermined threshold value. In this case, the predetermined threshold value may be a percentage (e.g., 5%).

[0208] For example, "the absolute value of the ratio of the difference between the differential value of the first virtual function on the line connecting the first data point and the second data point and the differential value of the second virtual function on the line connecting the first data point and the third data point is equal to or greater than a predetermined threshold value" includes the following cases:

[0209] For example, the meaning of "absolute value is equal to or greater than a predetermined threshold" can include the case where the ratio of the difference between the differential value of the first virtual function on the line connecting the first data point and the second data point and the differential value of the second virtual function on the line connecting the first data point and the third data point is negative and is equal to or less than a negative threshold (e.g., -5%), and the case where the ratio is positive and is equal to or greater than a positive threshold (e.g., +5%).

[0210] Alternatively, the absolute values ​​of the thresholds for positive and negative differential value differences may be different, for example, the threshold for positive differential value differences may be +5% and the threshold for negative differential value differences may be -3%.

[0211] 4. Supplementary Note The above embodiment can also be explained as follows. (1) The calibration method is a method for calibrating a force measuring device (e.g., force measuring device 1) that measures force using a sensitivity characteristic function that represents the relationship between a force applied to a force sensor (e.g., force sensor 10) and the rate of change in the capacitance of the force sensor due to the force. The sensitivity characteristic function is represented by a first function (e.g., first function f1) when the magnitude of the force is between 0 and an inflection value (e.g., inflection value Nc), and is represented by a second function (e.g., second function f2) when the magnitude of the force is equal to or greater than the inflection value. The second function is connected to the first function at the inflection value but is a different function from the first function.

[0212] In the above case, the calibration method comprises the following steps. The following steps (a) to (g) do not limit the processing order of each step. (a) By applying forces of different magnitudes to the force sensor within a range from 0 to a value greater than the inflection value and measuring the rate of change in capacitance of the force sensor when each force is applied, a data point (e.g., (F １ , r １ ), (F ２ , r ２ ), ... (F ｎ , r ｎ (b) assuming one of the plurality of data points as an inflection point (for example, a virtual inflection point CP′) at which the sensitivity characteristic function changes, and calculating the magnitude of the force included in the assumed inflection point as a virtual inflection value (for example, a virtual inflection value F ｋ (c) determining a low-force data point (e.g., (F １ , r １ ), (F ２ , r ２ ), ... (F ｋ , r ｋ )), a first virtual function (e.g., a constant α) is calculated based on the low-force data points, and a first coefficient of determination (e.g., the first coefficient of determination R １ ２ (d) calculating a high-force data point (e.g., (F ｋ , r ｋ ), (F ｋ＋１ , r ｋ＋１ ), ... (F ｎ , r ｎ )), a second virtual function (e.g., constants β, γ) is calculated based on the second virtual function, and a second coefficient of determination (e.g., the second coefficient of determination R ２ ２ (e) calculating the sum of the first and second determination coefficients (e.g., R １ ２+R ２ ２ (f) assuming another data point as an inflection point and performing the above steps (c) to (e). (g) determining, as an inflection value, a virtual inflection value included in the assumed inflection point when the sum of the first determination coefficient and the second determination coefficient is maximized, and determining the first virtual function as the first function and the second virtual function as the second function, thereby calculating a sensitivity characteristic function.

[0213] In the above-described method for calibrating a force measuring device, one of multiple data points used for calibration is assumed to be an inflection point at which the sensitivity characteristic function changes, a first virtual function is calculated based on a data point whose force magnitude is equal to or less than a virtual inflection value included in the assumed inflection point, and a first coefficient of determination representing the degree of agreement between the data point and the first virtual function is calculated. A second virtual function is calculated based on a data point whose force magnitude is equal to or greater than the virtual inflection value, and a second coefficient of determination representing the degree of agreement between the data point and the second virtual function is calculated. Furthermore, the sum of the first and second coefficients of determination is calculated. These processes are repeated by changing the assumed inflection point to another data point. As a result, multiple first virtual functions, second virtual functions, and sums of the first and second coefficients of determination are calculated.

[0214] The inflection point assumed when the sum of the first and second coefficients of determination is maximized is determined to be the inflection point where the sensitivity characteristic function changes, and the magnitude of the force included in this inflection point (i.e., the virtual inflection value) is determined to be the actual inflection value. The first virtual function calculated when the sum of the first and second coefficients of determination is maximized is determined to be the first function representing the sensitivity characteristic function when the magnitude of the force is equal to or less than the inflection value. The second virtual function calculated when the sum of the first and second coefficients of determination is maximized is determined to be the second function representing the sensitivity characteristic function when the magnitude of the force is equal to or greater than the inflection value.

[0215] In this way, by determining the virtual inflection value when the sum of the first and second coefficients of determination is maximum as the inflection value, determining the sensitivity characteristic function (first function) when the force magnitude is equal to or less than the inflection value based on the data points below the inflection point, and determining the sensitivity characteristic function (second function) when the force magnitude is equal to or greater than the inflection value based on the data points above the inflection point, it is possible to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces. As a result, a force measuring device that measures force based on changes in capacitance can be calibrated so that it can accurately measure a wide range of forces.

[0216] This is because, by separately calculating the first function and the second function as described above, the first function can be calculated as a function that well represents the data points below the inflection point, and the second function can be calculated as a function that well represents the data points above the inflection point. Also, by determining the virtual inflection value when the sum of the first determination coefficient and the second determination coefficient is maximum as the inflection value, it is possible to accurately determine at what point the sensitivity characteristic function changes.

[0217] (2) In the calibration method of (1), the step of assuming an inflection point and a virtual inflection value may include a step of assuming, as an inflection point, a data point among the plurality of data points whose magnitude of the force is close to the inflection value. This eliminates the need to assume all of the plurality of acquired data points as inflection points, thereby enabling faster calculation of the sensitivity characteristic function.

[0218] (3) In the calibration method of (1) or (2) above, the sensitivity characteristic function may represent the relationship between a force applied in the thickness direction (e.g., Z direction) of the force sensor and the rate of change in capacitance due to the force. Since the sensitivity characteristic function for forces in the thickness direction is likely to change with the force, by calculating the sensitivity characteristic function using the calibration method described above, the force measuring device can be calibrated so as to be able to accurately measure forces in a wide range in the thickness direction.

[0219] (4) In any of the calibration methods (1) to (3) above, the first function and the first virtual function may be functions proportional to the magnitude of the force. When the magnitude of the force is equal to or less than the inflection value, the rate of change in capacitance changes in proportion to the magnitude of the force. Therefore, by setting the first function and the first virtual function representing the sensitivity characteristic function when the magnitude of the force is equal to or less than the inflection value as functions proportional to the magnitude of the force, an accurate sensitivity characteristic function can be calculated.

[0220] (5) In any of the calibration methods (1) to (4) above, the second function and the second virtual function may be logarithmic functions of the force magnitude. When the force magnitude is equal to or less than the inflection value, the rate of change in capacitance changes logarithmically with respect to the force magnitude. Therefore, by setting the second function and the second virtual function representing the sensitivity characteristic function when the force magnitude is equal to or greater than the inflection value as logarithmic functions of the force magnitude, an accurate sensitivity characteristic function can be calculated.

[0221] (6) In the calibration method of (5) above, the step of calculating the second virtual function and the second coefficient of determination may include the following steps. The following steps (h) to (j) do not limit the order of the steps: (h) converting the second virtual function into a virtual proportional function. The virtual proportional function is a function in which the difference between the rate of change of capacitance and the rate of change of capacitance when the magnitude of the force is a virtual inflection value is proportional to the difference between the logarithm of the magnitude of the force and the logarithm of the virtual inflection value. (i) calculating the virtual proportional function based on high-force data points; and (j) calculating a second virtual function from the calculated virtual proportional function.

[0222] When calculating a function based on data points, it is easier to calculate the function by converting the function into a proportional function and calculating the proportional function based on data points. Therefore, when the second function and the second virtual function are logarithmic functions, the second virtual function (second function) can be easily calculated by calculating the second virtual function using the above method.

[0223] (7) A program (for example, the calibration program AP) is a program that causes a computer (for example, the first information processing device 3 or the second information processing device 6) to execute the above-described calibration method.

[0224] (8) A calibration device (e.g., calibration device 4) is a calibration device that calibrates the above-mentioned force measuring device. The calibration device includes an application unit (e.g., application unit 5) and a calibration unit (e.g., calibration unit 61). The application unit applies a force to the force sensor. The calibration unit applies a force to the force sensor using the application unit, acquires data points represented by coordinate values ​​of the magnitude of the force applied to the force sensor and the rate of change in capacitance with respect to the force, and calculates a sensitivity characteristic function based on the acquired data points, thereby calibrating the force measuring device.

[0225] The calibration unit of the calibration device performs the following. The following steps (a) to (g) do not limit the order of the processes performed by the calibration unit. (a) Applying forces of multiple magnitudes within a range from 0 to a force sensor greater than an inflection value using an application unit, and measuring the rate of change in capacitance of the force sensor when each force is applied, thereby obtaining multiple data points. (b) Assume that one of the multiple data points is an inflection point where the sensitivity characteristic function changes, and set the magnitude of the force included in the assumed inflection point as a virtual inflection value. (c) Calculating a first virtual function based on low-force data points of which the force magnitude is equal to or less than the virtual inflection value, and calculating a first coefficient of determination representing the degree of agreement between the low-force data points and the first virtual function. (d) Calculating a second virtual function based on high-force data points of which the force magnitude is equal to or greater than the virtual inflection value, and calculating a second coefficient of determination representing the degree of agreement between the high-force data points and the second virtual function. (e) Calculating the sum of the first and second coefficients of determination. (f) Assuming another data point to be an inflection point, and then executing the above (c) to (e). (g) Deciding the virtual inflection value included in the assumed inflection point when the sum of the first determination coefficient and the second determination coefficient is maximized as the inflection value, determining the first virtual function as the first function, and determining the second virtual function as the second function, thereby calculating the sensitivity characteristic function.

[0226] This allows the calibration device to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces, thereby enabling the force measuring device that measures force based on changes in capacitance to be calibrated so that it can accurately measure a wide range of forces.

[0227] (9) The force measuring device includes a force sensor whose capacitance changes when force is applied, and a calculation unit (e.g., calculation unit 31) that calculates the force using a sensitivity characteristic function that represents the relationship between the force applied to the force sensor and the rate of change in the capacitance of the force sensor due to the force.

[0228] In the force measuring device described above, the sensitivity characteristic function is calculated as follows: (a) Applying forces of various magnitudes to the force sensor and measuring the rate of change in capacitance of the force sensor when each force is applied, thereby obtaining multiple data points represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force (e.g., step S41). (b) Designating one of the multiple data points as a first data point, and designating the magnitude of the force included in the first data point as a first force (e.g., step S42). (c) Designating one of the multiple data points whose force magnitude is smaller than the first force as a second data point, and calculating a first virtual function that passes through the first data point and the second data point (e.g., steps S43 to S44). The phrase "passing through the first data point and the second data point" refers not only to cases where the first virtual function passes through both the first data point and the first data point, but also to cases where the first virtual function passes through the vicinity of the first data point and / or the vicinity of the second data point. (d) Among the multiple data points, a data point with a force magnitude greater than the first force is designated as a third data point, and a second virtual function passing through the first data point and the third data point is calculated (e.g., steps S45 to S46). "Passing through the first data point and the third data point" refers not only to the case where the second virtual function passes through the first data point and the third data point, but also to the case where the second virtual function passes near the first data point and / or the third data point. (e) If the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first data point and the second data point and the differential value of the second virtual function on a line connecting the first data point and the third data point is equal to or greater than a predetermined threshold, the first virtual function and the second virtual function are connected to calculate the second virtual function (e.g., steps S47 to S48).

[0229] In the force measuring device, a first virtual function is calculated that passes through a first data point serving as a reference and a second data point whose force magnitude is smaller than a first force included in the first data point, among a plurality of data points represented by coordinate values ​​of the magnitude of a force applied to the force sensor and the rate of change in capacitance due to the force, and a second virtual function is calculated that passes through the first data point and a third data point whose force magnitude is larger than the first force. Then, when the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first and second data points and the differential value of the second virtual function on a line connecting the first and third data points is equal to or greater than a predetermined threshold, the first virtual function and the second virtual function are connected to calculate a sensitivity characteristic function.

[0230] If the absolute value of the ratio between the difference between the differential value of the first virtual function on a line connecting the first data point and the second data point and the differential value of the second virtual function on a line connecting the first data point and the third data point and the differential value of the second virtual function on a line connecting the first data point and the third data point is equal to or greater than a predetermined threshold, this means that the function representing the sensitivity characteristic function at the first data point has changed (from the first virtual function to the second virtual function, or vice versa). In this case, by connecting the first virtual function and a different second virtual function at the first data point, a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces can be calculated. As a result, the force measuring device described above can accurately measure a wide range of forces using a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces.

[0231] (10) In the force measuring device of (9) above, the sensitivity characteristic function may include a plurality of functions connected at inflection points (e.g., inflection points CP, CP1, CP2, ...). This makes it possible to express a complex sensitivity characteristic function using a plurality of functions. In other words, even if the change in sensitivity of the force sensor to a wide range of forces is complex, it is possible to calculate a sensitivity characteristic function that accurately expresses the sensitivity of the force sensor to a wide range of forces.

[0232] When the sensitivity characteristic function includes multiple functions connected at inflection points, the multiple functions may be linear equations that change linearly with respect to the magnitude of the force applied to the force sensor, or may be nonlinear functions that change nonlinearly with respect to the magnitude of the force applied to the force sensor.

[0233] (11) In the force measuring device of (9) or (10) above, the sensitivity characteristic function may be expressed by a first function when the magnitude of the force is between 0 and an inflection value, and may be expressed by a second function that is connected to the first function at the inflection value and different from the first function when the magnitude of the force is equal to or greater than the inflection value. This makes it possible to calculate a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces, for example, when the sensitivity of the force sensor to forces changes at the inflection point.

[0234] (12) In the force measuring device of (11) above, the sensitivity characteristic function may be calculated as follows: (f) A plurality of data points are obtained by applying forces of different magnitudes to the force sensor within a range from 0 to a value greater than the inflection value. (g) A first data point is assumed to be an inflection point at which the sensitivity characteristic function changes, and the first force is set as a virtual inflection value. (h) A first virtual function is calculated based on low-force data points of which the force magnitude is equal to or less than the virtual inflection value, and a first coefficient of determination representing the degree of agreement between the low-force data points and the first virtual function is calculated. (i) A second virtual function is calculated based on high-force data points of which the force magnitude is equal to or greater than the virtual inflection value, and a second coefficient of determination representing the degree of agreement between the high-force data points and the second virtual function is calculated. The second virtual function is connected to the first virtual function by the virtual inflection value and is different from the first virtual function. (j) The sum of the first and second coefficients of determination is calculated. (k) Assuming another data point to be an inflection point, perform steps (g) to (j) above. (l) Determine the virtual inflection value included in the assumed inflection point when the sum of the first determination coefficient and the second determination coefficient is maximized as the inflection value, determine the first virtual function as the first function, and determine the second virtual function as the second function.

[0235] This makes it possible to accurately measure a wide range of forces using a sensitivity characteristic function that accurately represents the sensitivity of the force sensor to a wide range of forces.

[0236] (13) The force measuring device according to any one of (9) to (12) above may further include a display unit (for example, the display unit 35). The display unit displays numerical data relating to the force applied to the force sensor, calculated by the calculation unit using the sensitivity characteristic function. This allows the magnitude of the force applied to the force sensor to be confirmed as a numerical value.

[0237] (14) In the force measuring device of (13) above, the display unit may display the direction of the force applied to the force sensor in addition to the numerical data related to the force. This allows the user to confirm not only the magnitude of the force applied to the force sensor but also the direction in which the force is applied.

[0238] 1: Force measuring device 4: Calibration device 5: Application unit 10: Force sensor 31: Calculation unit 35: Display unit 61: Calibration unit AP: Calibration program F: Force magnitude r: Rate of change of capacitance CP, CP1, CP2: Inflection points Nc: Inflection value CP': Virtual inflection point F ｋ , F ｍ : Virtual inflection value R １ ２ : First coefficient of determination R ２ ２ : Second coefficient of determination f1: First function f2: Second function

Claims

1. A calibration method for calibrating a force measuring device that measures force using a sensitivity characteristic function that represents the relationship between a force applied to a force sensor and the rate of change in capacitance of the force sensor due to the force, wherein the sensitivity characteristic function is represented by a first function when the magnitude of the force is between 0 and an inflection value, and is represented by a second function that is connected to the first function at the inflection value and different from the first function when the magnitude of the force is equal to or greater than the inflection value, the calibration method comprising the steps of: applying forces of multiple magnitudes within a range from 0 to greater than the inflection value to the force sensor, and measuring the rate of change in capacitance of the force sensor when each force is applied, thereby obtaining multiple data points represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force; assuming one of the multiple data points to be an inflection point where the sensitivity characteristic function changes, and setting the magnitude of the force included in the assumed inflection point as a virtual inflection value, which is a virtual inflection value. calculating a first virtual function based on low-force data points among a plurality of data points, the magnitude of which is equal to or less than the virtual inflection value, and calculating a first coefficient of determination representing the degree of agreement between the low-force data points and the first virtual function; calculating a second virtual function connected to the first virtual function at the virtual inflection value and different from the first virtual function based on high-force data points among a plurality of data points, the magnitude of which is equal to or greater than the virtual inflection value, and calculating a second coefficient of determination representing the degree of agreement between the high-force data points and the second virtual function; calculating the sum of the first coefficient of determination and the second coefficient of determination; and assuming another data point to be the inflection point, calculating the first virtual function and the first coefficient of determination, calculating the second virtual function and the second coefficient of determination, and calculating the sum of the first coefficient of determination and the second coefficient of determination. determining, as the inflection value, a virtual inflection value included in a hypothetical inflection point when a sum of the first determination coefficient and the second determination coefficient is maximized; determining, as the inflection value, the first virtual function as the first function; and determining, as the second virtual function, the second function, thereby calculating the sensitivity characteristic function.

2. The calibration method according to claim 1, wherein the step of assuming the inflection point and the virtual inflection value includes a step of assuming, as the inflection point, a data point among a plurality of data points whose magnitude of force is in the vicinity of the inflection value.

3. The calibration method according to claim 1, wherein the sensitivity characteristic function represents the relationship between a force applied in the thickness direction of the force sensor and a rate of change in capacitance due to the force.

4. The calibration method according to claim 1, wherein the first function and the first virtual function are proportional functions of the magnitude of the force.

5. The calibration method according to claim 1, wherein the second function and the second virtual function are logarithmic functions of the magnitude of the force.

6. The calibration method according to claim 5, wherein the step of calculating the second virtual function and the second coefficient of determination includes the steps of: converting the second virtual function into a virtual proportional function in which a difference between a rate of change in capacitance and a rate of change in capacitance when the magnitude of the force is the virtual inflection value is proportional to a difference between a logarithm of the magnitude of the force and the logarithm of the virtual inflection value; calculating the virtual proportional function based on the high-force data points; and calculating the second virtual function from the calculated virtual proportional function.

7. A program that causes a computer to execute the calibration method according to any one of claims 1 to 6.

8. A calibration device for calibrating a force measuring device that measures force using a sensitivity characteristic function that represents the relationship between a force applied to a force sensor and the rate of change in capacitance of the force sensor due to the force, comprising: an application unit that applies a force to the force sensor; and a calibration unit that calibrates the force measuring device by applying a force to the force sensor using the application unit, acquiring data points represented by coordinate values ​​of the magnitude of the force applied to the force sensor and the rate of change in capacitance due to the force, and calculating the sensitivity characteristic function based on the acquired data points, wherein the sensitivity characteristic function is represented by a first function when the magnitude of the force is between 0 and an inflection value, and is represented by a second function that is connected to the first function at the inflection value and different from the first function when the magnitude of the force is equal to or greater than the inflection value; and the calibration unit acquires multiple data points by applying forces of multiple magnitudes within a range from 0 to a value greater than the inflection value to the force sensor and measuring the rate of change in capacitance of the force sensor when each force is applied, assuming one of a plurality of data points as an inflection point where the sensitivity characteristic function changes, and setting the magnitude of the force included in the assumed inflection point as a virtual inflection value that is a virtual inflection value; calculating a first virtual function based on low-force data points among the plurality of data points, the magnitude of the force being equal to or less than the virtual inflection value, and calculating a first coefficient of determination representing the degree of agreement between the low-force data point and the first virtual function; calculating a second virtual function connected to the first virtual function at the virtual inflection value and different from the first virtual function based on high-force data points among the plurality of data points, the magnitude of the force being equal to or greater than the virtual inflection value, and calculating a second coefficient of determination representing the degree of agreement between the high-force data point and the second virtual function; calculating the sum of the first coefficient of determination and the second coefficient of determination; assuming another data point as the inflection point, calculating the first virtual function and the first coefficient of determination, calculating the second virtual function and the second coefficient of determination, and calculating the sum of the first coefficient of determination and the second coefficient of determination; a virtual inflection value included in a hypothetical inflection point when a sum of the first determination coefficient and the second determination coefficient is maximized is determined as the inflection value, the first virtual function is determined as the first function, and the second virtual function is determined as the second function, thereby calculating the sensitivity characteristic function.

9. A device comprising: a force sensor whose capacitance changes when a force is applied; and a calculation unit that calculates a force using a sensitivity characteristic function that represents the relationship between the force applied to the force sensor and the rate of change in capacitance of the force sensor due to the force, wherein the sensitivity characteristic function is obtained by applying forces of multiple magnitudes to the force sensor and measuring the rate of change in capacitance of the force sensor when each force is applied, thereby obtaining multiple data points represented by coordinate values ​​of the magnitude of the applied force and the rate of change in capacitance due to the force; designating one of the multiple data points as a first data point and the magnitude of the force included in the first data point as a first force; designating a data point of the multiple data points whose force magnitude is smaller than the first force as a second data point, and calculating a first virtual function that passes through the first data point and the second data point; designating a data point of the multiple data points whose force magnitude is larger than the first force as a third data point, and calculating a second virtual function that passes through the first data point and the third data point; a differential value of the second virtual function on a line connecting the first data point and the third data point, and a differential value of the second virtual function on a line connecting the first data point and the third data point, the differential value of the second virtual function on a line connecting the first data point and the third data point is calculated by concatenating the first virtual function and the second virtual function when the absolute value of the ratio is equal to or greater than a predetermined threshold.

10. A force measuring device according to claim 9, wherein the sensitivity characteristic function includes a plurality of functions connected at inflection points where the function representing the sensitivity characteristic function changes.

11. A force measuring device as described in claim 9, wherein the sensitivity characteristic function is represented by a first function when the magnitude of the force is between 0 and an inflection value, which is the magnitude of the force included in the inflection point, and is represented by a second function that is connected to the first function at the inflection value and different from the first function when the magnitude of the force is equal to or greater than the inflection value.

12. The sensitivity characteristic function is obtained by applying forces of various magnitudes within a range from 0 to a force sensor that are greater than the inflection value, thereby obtaining the plurality of data points; assuming that the first data point is an inflection point at which the sensitivity characteristic function changes, and setting the first force as a virtual inflection value that is a virtual inflection value; calculating the first virtual function based on low-force data points of which the magnitude of the force is equal to or less than the virtual inflection value, among the plurality of data points; calculating a first coefficient of determination that represents the degree of agreement between the low-force data points and the first virtual function; calculating the second virtual function that is connected to the first virtual function at the virtual inflection value and different from the first virtual function, based on high-force data points of which the magnitude of the force is equal to or greater than the virtual inflection value, among the plurality of data points; and calculating a second coefficient of determination that represents the degree of agreement between the high-force data points and the second virtual function; and calculating the sum of the first coefficient of determination and the second coefficient of determination.

12. The force measuring device according to claim 11, wherein the force is calculated by assuming another data point as the inflection point, calculating the first virtual function and the first coefficient of determination, calculating the second virtual function and the second coefficient of determination, calculating a sum of the first coefficient of determination and the second coefficient of determination, determining a virtual inflection value included in the assumed inflection point when the sum of the first coefficient of determination and the second coefficient of determination is maximum as the inflection value, determining the first virtual function as the first function, and determining the second virtual function as the second function.

13. The force measuring device according to claim 9, further comprising a display unit that displays numerical data relating to the force applied to the force sensor, calculated by the calculation unit using the sensitivity characteristic function.

14. The force measuring device according to claim 13, wherein the display unit displays the direction of the force applied to the force sensor in addition to the numerical data relating to the force.

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