Pressing sensor, pressing point detection method, and pressing point detection program

Abstract

The pressure sensor comprises: a piezoelectric film having anisotropic output; a plurality of detection electrodes disposed on a first main surface of the piezoelectric film for detecting charges generated on the piezoelectric film; a ground electrode disposed on a second main surface of the piezoelectric film; a detection unit for detecting a voltage signal generated on the piezoelectric film based on the charges detected by the detection electrodes; and a processing unit for processing the voltage signal detected by the detection unit. The processing unit takes a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film, determines the polarization distribution on the first main surface of the piezoelectric film based on the voltage signal, calculates a first line segment forming a boundary where polarization changes discontinuously between positive, negative, and zero values, and extends along the first direction, calculates a second line segment forming a boundary where polarization changes discontinuously between positive, negative, and zero values, and extends along the second direction, and calculates the intersection point of the first and second line segments, thereby detecting the pressure point.

Description

Technical Field

[0001] This invention relates to a technique for detecting pressure. Background Technology

[0002] In the past, products equipped with a general press touchpad were processed as follows: a strain sensor, an ultrasonic sensor, or a capacitive touchpad (see, for example, Patent Document 1) was used to measure the amount of displacement of the housing caused by the user's pressing operation, thereby estimating the pressure applied to the operating surface and detecting the user's pressing operation.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-78888 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In this case, a typical touchpad measures the displacement of the housing caused by pressing. Therefore, in order to install the touchpad in a product, it is necessary to study the housing structure to uniformize the displacement of the housing and the configuration of the sensor element that measures the displacement of the housing. As a result, the housing design is costly and subject to significant limitations.

[0008] Furthermore, due to the significant limitations in casing design, each product requires a separate design. This increases the constraints on product cost and design.

[0009] The purpose of this invention is to provide a technique that reduces the limitations of housing design when mounting a pressure sensor in a product.

[0010] Solution for solving the problem

[0011] The pressure sensor of the present invention comprises: a piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy; a plurality of detection electrodes disposed on the first main surface of the piezoelectric film for detecting charges generated on the piezoelectric film; a ground electrode disposed on the second main surface of the piezoelectric film; a detection unit for detecting a voltage signal generated on the piezoelectric film based on the charges detected by the detection electrodes; and a processing unit for processing the voltage signal detected by the detection unit, wherein... The processing unit takes a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film, determines the polarization distribution on the first main surface of the piezoelectric film based on the voltage signal, calculates a first line segment that forms the boundary where the polarization changes discontinuously between positive, negative and 0 values, and extends along the first direction, calculates a second line segment that forms the boundary where the polarization changes discontinuously between positive, negative and 0 values, and extends along the second direction, and calculates the intersection point of the first line segment and the second line segment, thereby detecting the pressing point.

[0012] The pressure point detection method of the present invention is a method for detecting pressure points by a processing unit in a pressure sensor. The pressure sensor comprises: a piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy; a plurality of detection electrodes disposed on the first main surface of the piezoelectric film, the plurality of detection electrodes detecting charges generated on the piezoelectric film; a ground electrode disposed on the second main surface of the piezoelectric film; a detection unit that detects a voltage signal generated on the piezoelectric film based on the charges detected by the detection electrodes; and a processing unit that processes the voltage signal detected by the detection unit. The measured voltage signal is processed. The processing unit takes a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film. Based on the voltage signal, it determines the polarization distribution on the first main surface of the piezoelectric film, calculates a first line segment that forms the boundary where the polarization changes discontinuously between positive, negative, and 0 values, and extends along the first direction. It then calculates a second line segment that forms the boundary where the polarization changes discontinuously between positive, negative, and 0 values, and extends along the second direction. Finally, it calculates the intersection of the first and second line segments, thereby detecting the pressing point.

[0013] The pressure point detection program of the present invention is mounted on a pressure sensor, the pressure sensor comprising: a piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy; a plurality of detection electrodes disposed on the first main surface of the piezoelectric film, the plurality of detection electrodes detecting charges generated on the piezoelectric film; a ground electrode disposed on the second main surface of the piezoelectric film; a detection unit that detects a voltage signal generated on the piezoelectric film based on the charges detected by the detection electrodes; and a processing unit that processes the voltage signal detected by the detection unit, wherein... The press point detection procedure causes the processing unit to perform the following processing: taking a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film, determining the polarization distribution on the first main surface of the piezoelectric film based on the voltage signal, finding a first line segment that forms the boundary where the polarization changes discontinuously between positive, negative, and 0 values, and extending along the first direction, finding a second line segment that forms the boundary where the polarization changes discontinuously between positive, negative, and 0 values, and extending along the second direction, finding the intersection point of the first line segment and the second line segment, thereby detecting the press point.

[0014] The effects of the invention

[0015] According to the present invention, the limitations of housing design when mounting a pressure sensor in a product can be reduced. Attached Figure Description

[0016] Figure 1 This is a functional block diagram of the pressure sensor 1.

[0017] Figure 2 This is a perspective view of the piezoelectric sensor 11.

[0018] Figure 3 This is a cross-sectional view of the piezoelectric sensor 11.

[0019] Figure 4 This is a cross-sectional view of the piezoelectric thin film sensor 15.

[0020] Figure 5 (A) is a conceptual diagram showing an example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 5 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 5 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0021] Figure 6 (A) is a conceptual diagram showing another example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 6 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 6 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0022] Figure 7 This is a flowchart showing the press detection process performed by the processing unit.

[0023] Figure 8 This is a conceptual diagram used to illustrate the press detection process performed by the processing unit.

[0024] Figure 9 (A) is a conceptual diagram showing an example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 9 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 9 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0025] Figure 10 This is a flowchart showing the press detection process performed by the processing unit of the first modified example.

[0026] Figure 11 This is a conceptual diagram used to illustrate the press detection process performed by the processing unit of the first modified example.

[0027] Figure 12 (A) is a conceptual diagram showing an example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 12 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 12 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0028] Figure 13 (A) is a conceptual diagram showing another example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 13 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 13 A conceptual diagram of an example of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0029] Figure 14 This is a flowchart showing the press detection process performed by the processing unit of the second modified example.

[0030] Figure 15 This is a flowchart showing the processing of step s33 performed by the processing unit of the second variation.

[0031] Figure 16 This is a conceptual diagram illustrating the press detection process performed by the processing unit of the second modified example.

[0032] Figure 17This is a conceptual diagram illustrating the press detection process performed by the processing unit of the second modified example.

[0033] Figure 18 This is a cross-sectional view of the piezoelectric sensor 11a.

[0034] Figure 19 This is a cross-sectional view of piezoelectric sensor 11b. Detailed Implementation

[0035] Several embodiments of the present invention are shown below. In each embodiment, points that differ from those previously described are explained. The same effects obtained through the same structure will not be mentioned in every embodiment.

[0036] [Implementation Method]

[0037] Figure 1 This is a functional block diagram of the pressure sensor 1. Figure 2 This is a perspective view of the piezoelectric sensor 11. Figure 3 This is a cross-sectional view of the piezoelectric sensor 11. Figure 4 This is a cross-sectional view of the piezoelectric thin film sensor 15. The press sensor 1 includes a piezoelectric sensor 11, a detection unit 12, and a processing unit 13. The piezoelectric sensor 11 includes a piezoelectric thin film sensor 15 and a support body 16. The piezoelectric thin film sensor 15 includes a piezoelectric thin film 21, adhesive materials 22 and 23, multiple detection electrodes 24, a ground electrode 25, and flexible substrates 26 and 27.

[0038] like Figure 2 and Figure 3 As shown, the piezoelectric thin film sensor 15 is supported by the support body 16 in a stretched state in all directions parallel to the main surface 31 of the piezoelectric thin film sensor 15.

[0039] The pressure sensor 1 is configured to detect a pressure applied to a point on the main surface 31 of the piezoelectric thin film sensor 15.

[0040] like Figure 4 As shown, the piezoelectric film 21 has a first main surface 33 and a second main surface 34 opposite to the first main surface 33, and the piezoelectric film 21 has output anisotropy. The piezoelectric film 21 is formed, for example, from uniaxially stretched L-shaped polylactic acid (PLLA). A detection electrode 24 is disposed on the first main surface 33 of the piezoelectric film 21 to detect the charge generated in the piezoelectric film 21. The detection electrode 24 is formed on a flexible substrate 26 and attached to the first main surface 33 of the piezoelectric film 21 by an adhesive material 22. A ground electrode 25 is disposed on the second main surface 34 of the piezoelectric film 21. The ground electrode 25 is formed on a flexible substrate 27 and attached to the second main surface 34 of the piezoelectric film 21 by an adhesive material 23.

[0041] The detection unit 12 detects the voltage signal generated on the piezoelectric film 21 based on the charge detected by the detection electrode 24. The detection unit 12 includes, for example, a charge amplifier circuit, an amplification circuit, and an A / D conversion circuit. The processing unit 13 processes the voltage signal detected by the detection unit 12. The processing unit 13 consists of a CPU, a memory, etc., and stores a program; the voltage signal is processed by executing this program.

[0042] In this specification, the direction parallel to the first principal surface 33 of the piezoelectric film 21, corresponding to the polarization distribution on the first principal surface 33, is defined as the x-axis direction. The direction parallel to the first principal surface 33 of the piezoelectric film 21 and perpendicular to the x-axis direction is defined as the y-axis direction. The direction perpendicular to the first principal surface 33 of the piezoelectric film 21 is defined as the z-axis direction. One side of the x-axis direction is defined as the right direction or the +x-axis direction, and the other side of the x-axis direction is defined as the left direction or the -x-axis direction. One side of the y-axis direction is defined as the up direction or the +y-axis direction, and the other side of the y-axis direction is defined as the down direction or the -y-axis direction.

[0043] The processing unit 13 takes an x-axis direction (first direction) and a y-axis direction (second direction) perpendicular to the x-axis direction on the first main surface 33 of the piezoelectric film 21. Thus, the processing unit 13 determines the orientation of the coordinate system on the first main surface 33 of the piezoelectric film 21. The processing unit 13 determines the polarization distribution on the first main surface 33 of the piezoelectric film 21 based on the voltage signal. As detailed below, the processing unit 13 calculates a first line segment that forms a boundary where the polarization changes discontinuously between positive, negative, and zero values, and extends along the x-axis direction. In other words, the first line segment is a line segment where the polarity of the polarization changes with respect to the first line segment. The processing unit 13 calculates a second line segment that forms a boundary where the polarization changes discontinuously between positive, negative, and zero values, and extends along the y-axis direction. In other words, the second line segment is a line segment where the polarity of the polarization changes with respect to the second line segment. Furthermore, the processing unit 13 calculates the intersection point of the first and second line segments, thereby detecting the pressing point.

[0044] like Figure 4 As shown, the detection electrodes 24 are arranged on the piezoelectric thin film 21 along the x-axis and y-axis directions. The processing unit 13 defines the units arranged on the first main surface 33 of the piezoelectric thin film 21 along the x-axis and y-axis directions. Each unit corresponds to the area occupied by a detection electrode 24 on the first main surface 33 of the piezoelectric thin film 21 when viewed from above. Based on the voltage signal corresponding to each detection electrode 24, the processing unit 13 determines the polarization of the piezoelectric thin film 21 for each unit corresponding to each detection electrode 24.

[0045] In a modified example, the processing unit 13 may also estimate the polarization corresponding to positions arranged at narrower intervals or consecutive positions to determine the distribution of polarization.

[0046] Figure 5 (A) is a conceptual diagram showing an example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 5 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 5 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A). Figure 6 (A) is a conceptual diagram showing another example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 6 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 6 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0047] exist Figure 5 In (A), the piezoelectric thin film sensor, i.e., the piezoelectric thin film, deforms not only at the pressing point p, but also as a whole due to pressure. For example... Figure 5 As shown in (B), the polarization of the piezoelectric film varies globally on the first principal surface of the piezoelectric film according to its deformation. Figure 6 In (A), the piezoelectric thin-film sensor, i.e., the piezoelectric thin film, deforms locally around the pressing point p due to pressure. For example... Figure 6 As shown in (B), the polarization of the piezoelectric film varies locally around the pressing point p according to its deformation, and takes a value of 0 in the region far from the pressing point p.

[0048] like Figure 5 (B) and Figure 6 As shown in (B), the polarization of the upper left region of pressure point p has the same positive and negative sign as the polarization of the lower right region of pressure point p. The polarization of the lower left region of pressure point p has the same positive and negative sign as the polarization of the upper right region of pressure point p. The polarization of the upper left region of pressure point p has opposite positive and negative signs as the polarization of the lower left region of pressure point p. Figure 5 (B) and Figure 6 In (B), the polarization of the upper left and lower right regions of the pressing point p is positive, and the polarization of the lower left and upper right regions of the pressing point p is negative.

[0049] This polarization distribution is due to the output anisotropy of the piezoelectric film.

[0050] In addition, in such Figure 5 (B) and Figure 6In the diagram showing the polarization distribution as in (B), for ease of explanation, the distribution of polarization detected corresponding to discrete points is approximated as the distribution of polarization corresponding to continuous points to depict the polarization distribution. Therefore, the boundary lines s1 and s2 where the positive and negative signs of polarization change are equivalent to the boundary lines of adjacent cells, or a series of cells with polarization of 0.

[0051] Figure 7 This is a flowchart showing the press detection process performed by the processing unit. Figure 8 This is a conceptual diagram used to illustrate the press detection process performed by the processing unit.

[0052] like Figure 7 As shown, firstly, the processing unit searches for points on a first line segment on the first main surface of the piezoelectric film and uses the found points as the first starting point. The first line segment is a line segment extending along the x-axis direction that forms the boundary where polarization changes discontinuously between positive, negative, and zero values ​​(s11). A point on the first main surface of the piezoelectric film is considered equivalent to a point on the first line segment if it satisfies the following conditions: The polarization changes from a positive value to a negative value, from a negative value to a positive value, from a positive value to a zero value, from a zero value to a positive value, from a negative value to a zero value, or from a zero value to a negative value, with points near the point in the x-axis direction as the boundary in the y-axis direction. The polarization changes discontinuously, i.e. abruptly, for example, significantly greater than a predetermined threshold, with points near the point in the x-axis direction as the boundary in the y-axis direction.

[0053] For example, if the position (i,j) satisfies sgn[P(i+k,j+1)]≠sgn[P(i+k,j-1)] and |P(i+k,j+1)-P(i+k,j-1)|>α for k=0,1, k=0,-1, or k=1,-1, the processing unit determines that the position (i,j) corresponds to a point on the first line segment. In the expression (i,j), i represents the position of the element in the x-axis direction, and j represents the position of the element in the y-axis direction. P(i,j) represents the polarization at position (i,j). α represents the threshold specified for determining the discontinuity of the change in polarization. sgn[x] is a sign function that returns 1 if x>0, 0 if x=0, and -1 if x<0.

[0054] Furthermore, the method for determining whether a point on the first main surface of the piezoelectric film is a point on the first line segment has been adjusted so that the first line segment is a line segment that passes through the pressing point and extends along the x-axis.

[0055] For example, the processing unit may take the origin of the coordinate system at the centroid (geometric centroid) of the first principal surface of the piezoelectric film, and repeatedly investigate or scan the points on the first principal surface of the piezoelectric film from the origin to the left and right to search for points on the first line segment. Alternatively, the processing unit may repeatedly investigate the points on the first principal surface of the piezoelectric film from the left to the right to search for points on the first line segment. The processing unit may also investigate the points on the first principal surface of the piezoelectric film in other orders to search for points on the first line segment.

[0056] exist Figure 8 In the middle, the processing unit searches for points on the first line segment, investigates points on the first main surface of the piezoelectric film from the origin O to the lower and upper ends, finds the first starting point a0, and ends the search for points on the first line segment.

[0057] Next, the processing unit investigates the points on the first main surface of the piezoelectric film from the first starting point in the left and right directions to search for the two end points of the first line segment, and finds the two end points to determine the first line segment (s12).

[0058] For example, if the processing unit determines that position (i,j) is the end point of the first line segment when position (i,j) is a point on the first line segment and is located at the right or left end of the first main surface of the piezoelectric film, then position (i,j) is the end point of the first line segment. Conversely, if the processing unit determines that position (i,j) is the end point of the first line segment when position (i,j) is a point on the first line segment, but the next position (i+1,j) or position (i-1,j) is not a point on the first line segment, then position (i,j) is the end point of the first line segment.

[0059] exist Figure 8 In the process, the processing unit searches for the two end points of the first line segment. Starting from the first starting point a0, it investigates the points on the first main surface of the piezoelectric film in the left and right directions. By finding the two end points a1 and a2 of the first line segment, the first line segment A is obtained.

[0060] Next, the processing unit searches for points on the second line segment on the first main surface of the piezoelectric film and uses the found points as the second starting points. The second line segment is a line segment extending along the y-axis that forms the boundary where the polarization changes discontinuously between positive, negative, and zero values ​​(s13). A point on the first main surface of the piezoelectric film is equivalent to a point on the second line segment if the following conditions are met: the polarization changes from a positive value to a negative value, from a negative value to a positive value, from a positive value to zero, from zero value to a positive value, from a negative value to zero, or from zero value to a negative value, with points near the point in the y-axis direction as the boundary in the x-axis direction. The polarization changes discontinuously, i.e. abruptly, for example, greater than a predetermined threshold, with points near the point in the y-axis direction as the boundary in the x-axis direction.

[0061] For example, if the position (i,j) satisfies sgn[P(i+1,j+k)]≠sgn[P(i-1,j+k],|P(i+1,j+k)-P(i-1,j+k)|>α for k=0,1,k=0,-1 ork=1,-1, the processing unit determines that the position (i,j) is equivalent to a point on the second line segment.

[0062] Furthermore, the method for determining whether a point on the first main surface of the piezoelectric film is a point on the second line segment has been adjusted so that the second line segment is a line segment that passes through the pressing point and extends along the y-axis.

[0063] For example, the processing unit may repeatedly search for points on the second line segment by investigating points on the first main surface of the piezoelectric film from the origin to the bottom and top, and from the origin to the left and right. Alternatively, the processing unit may repeatedly search for points on the second line segment by investigating points on the first main surface of the piezoelectric film from the bottom to the top, and from the left to the right. The processing unit may also search for points on the second line segment by investigating points on the first main surface of the piezoelectric film in other orders.

[0064] exist Figure 8 In the middle, the processing unit searches for points on the second line segment, investigates the points on the first principal surface of the piezoelectric film from the origin O to the left, finds the second starting point b0, and ends the search for points on the second line segment.

[0065] Next, the processing unit searches for the two end points of the second line segment by investigating the points on the first main surface of the piezoelectric film in the downward and upward directions from the second starting point, and finds the two end points to determine the second line segment (s14).

[0066] For example, if the processing unit determines that position (i,j) is the end point of the second line segment when position (i,j) is a point on the second line segment and is located at the upper or lower end of the first main surface of the piezoelectric film, then position (i,j) is the end point of the second line segment. Conversely, if the processing unit determines that position (i,j) is a point on the second line segment but the next position (i,j+1) or position (i,j-1) is not a point on the second line segment, then position (i,j) is the end point of the second line segment.

[0067] exist Figure 8 In the middle, the processing unit searches for the two end points of the second line segment, and investigates the points on the first main surface of the piezoelectric film in the downward and upward directions from the second starting point b0. By finding the two end points b1 and b2 of the second line segment, the second line segment B is obtained.

[0068] Next, the processing unit calculates the intersection point of the first line segment and the second line segment (s15) and outputs this intersection point as the pressing point (s16). The first line segment and the second line segment are line segments that pass through the pressing point and extend along the x-axis and y-axis directions, respectively. Therefore, the intersection point of the first line segment and the second line segment coincides with the pressing point.

[0069] exist Figure 8 In the process, the processing unit obtains the intersection point c of the first line segment A and the second line segment B, and outputs the intersection point c as the pressing point. For example... Figure 8 As shown, the intersection point c coincides with the pressing point p.

[0070] The processing unit repeats steps s11 to s16 at constant intervals. In this way, the pressure sensor 1 detects the pressure point.

[0071] In a variation, the processing unit may also determine the first and second line segments using other methods. For example, the processing unit may use various edge or line detection methods proposed in the field of image processing to determine the first and second line segments.

[0072] In another variation, the processing unit may execute steps s11 and s12 after executing steps s13 and s14.

[0073] Furthermore, according to the detection method for the first and second line segments, the first and second line segments are composed of one or more columns of units. Therefore, according to the detection method for the first and second line segments, the intersection of the first and second line segments is composed of one or more units.

[0074] Furthermore, if the processing unit cannot find the first starting point, the second starting point, or the intersection of the first line segment and the second line segment, it determines that there is no pressing point and outputs nothing.

[0075] According to this embodiment, the limitation on the housing design when mounting the pressure sensor in the product is only that the main surface of the piezoelectric film sensor is most concave at the pressing point. Therefore, the limitations on the housing design when mounting the pressure sensor in the product can be reduced. In addition, the degree of freedom in product design is increased.

[0076] Furthermore, conventional touchpads measure the displacement of the housing in principle, and are therefore affected by gravity based on the housing's posture. Additionally, if the housing's elasticity decreases due to years of degradation, a false press may be detected even when no pressure is applied by the user. According to this embodiment, the pressure sensor detects a press by capturing the characteristics of the polarization distribution on the first main surface of the piezoelectric film. Moreover, the polarization distribution generated by a press has different characteristics than the polarization distribution generated by the aforementioned factors. Therefore, the influence of gravity applied to the piezoelectric film sensor on the pressure sensor's press detection is reduced. Furthermore, the possibility of the pressure sensor falsely detecting a press is reduced.

[0077] Furthermore, the piezoelectric sensor has a simple structure consisting of a piezoelectric thin-film sensor and a support. The processing unit detects the pressure at a point by determining the intersection of the first line segment and the second line segment. Therefore, in this embodiment, the pressure at a point can be detected with a simple structure.

[0078] [First variation]

[0079] The pressure sensor in the first modified example differs from pressure sensor 1 in the following aspects: the processing unit calculates all the first line segment and the second line segment, and calculates all the intersection points of the first line segment and the second line segment.

[0080] The pressure sensor in the first variation is configured to detect pressure at one or more points.

[0081] Figure 9 (A) is a conceptual diagram showing an example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 9 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 9 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0082] In addition, Figure 9 In (A), the deformation of the main surface 31 of the piezoelectric thin film sensor is observed along the direction from the pressing point p1 toward the pressing point p2.

[0083] exist Figure 9 In (A), the piezoelectric thin-film sensor, i.e., the piezoelectric thin film, is locally deformed around the two pressing points p1 and p2. For example... Figure 9 As shown in (B), the polarization of the piezoelectric film varies locally around the pressing points p1 and p2 according to its deformation, and takes a value of 0 in the region far away from the pressing points p1 and p2.

[0084] Figure 10 This is a flowchart showing the press detection process performed by the processing unit of the first modified example. Figure 11 This is a conceptual diagram used to illustrate the press detection process performed by the processing unit of the first modified example.

[0085] like Figure 10 As shown, firstly, the processing unit executes and Figure 7 The same process is used in steps s11 and s12 to search for and find the first line segment (s21). If the first line segment has not been completely searched (s22: "No"), the search for the first line segment is started again.

[0086] More specifically, the processing unit begins searching for points on the first line segment from a predetermined point, such as the origin. Then, it calculates the first line segment based on the found points. However, if a found point on a previously found first line segment lies on that segment, it is not necessary to calculate the first line segment from that point. Next, the search continues, starting again from the next point after the previously found point. The processing unit terminates the search for points on the first line segment after investigating all points on the first main surface of the piezoelectric film.

[0087] exist Figure 11 In the process, the processing unit starts searching for points on the first line segment from the origin O, finds the first starting point a01, and obtains the first line segment A1. Then, it starts searching for points on the first line segment again from the next point after the first starting point a01, finds the first starting point a02, and obtains the first line segment A2.

[0088] If the processing unit finds all first line segments (s22: "Yes"), it executes the... Figure 7 The same process is used in steps s13 and s14 to search for and find the second line segment (s23). If the second line segment has not been completely searched (s24: "No"), the search for the second line segment starts again.

[0089] More specifically, when the processing unit finishes searching for points on the first line segment, it begins searching for points on the second line segment from a predetermined point, such as the origin. Then, it calculates the second line segment based on the found points on the second line segment. However, if a found point on a second line segment lies on an already found second line segment, it is not necessary to calculate the second line segment based on that point. Next, it searches for points on the second line segment again, starting from the next point after the previously found point. The processing unit ends the search for points on the second line segment when it has investigated all points on the first main surface of the piezoelectric film.

[0090] exist Figure 11 In the process, the processing unit starts searching for points on the second line segment from the origin O, finds the second starting point b01, and obtains the second line segment B1. Then, it starts searching for points on the second line segment again from the next point after the second starting point b01, finds the second starting point b02, and obtains the second line segment B2.

[0091] If the processing unit finds all the second line segments (s24: "Yes"), it calculates all the intersection points of the first line segment and the second line segment (s25) and outputs the intersection points as the pressing points (s26).

[0092] For example, the processing unit can also calculate the intersection point of the first line segment and the second line segment for all combinations of the first line segment and the second line segment.

[0093] exist Figure 11In the process, the processing unit calculates the intersection point of the first line segment and the second line segment for the combination of the first line segment and the second line segment (A1, B1), (A1, B2), (A2, B1), (A2, B2), thereby obtaining the intersection point c1 of the first line segment A1 and the second line segment B1, and the intersection point c2 of the first line segment A2 and the second line segment B2.

[0094] The processing unit repeats steps s21 to s26 at constant intervals. In this way, the pressure sensor of the first modified example detects the pressure point.

[0095] In a modified example, the processing unit may pre-assign a maximum number of pressing points. Furthermore, if the maximum number of first line segments, second line segments, or intersections is found, the processing unit may end the search for the first line segment, second line segment, or intersection and proceed to the next step of processing.

[0096] In another variation, the processing unit may execute steps s21 and s22 after executing steps s23 and s24.

[0097] Furthermore, if the processing unit cannot find the first line segment, the second line segment, or the intersection, it determines that there is no pressing point and outputs nothing.

[0098] According to the first modification, as described above, the piezoelectric sensor has a simple structure consisting of a piezoelectric thin-film sensor and a support. The processing unit detects all pressing points by determining all intersections of the first line segment and the second line segment. Therefore, in the first modification, it is possible to detect not only pressing at one point but also pressing at multiple points with a simple structure.

[0099] [Second variation]

[0100] The pressure sensor of the second modification differs from the pressure sensor of the first modification in the following aspects. That is, the processing unit determines a rectangular region defined by the following rectangle and having a polarization value of 0: the rectangle has a pair of vertices at two intersection points selected from the intersection points of the first line segment and the second line segment, and has a side parallel to the x-axis direction.

[0101] The pressure sensor in the second variation is configured to detect pressure at one or more points.

[0102] Figure 12 (A) is a conceptual diagram showing an example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 12 (B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 12 A conceptual diagram of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A). Figure 13 (A) is a conceptual diagram showing another example of the deformation of the main surface 31 of the piezoelectric thin film sensor corresponding to pressing. Figure 13(B) is shown on the main surface 31 of the piezoelectric thin film sensor as shown in Figure 31. Figure 13 A conceptual diagram of an example of the polarization of a piezoelectric thin film under the condition of deformation, as shown in (A).

[0103] exist Figure 12 (A) to Figure 13 In (B), the pressing area is not considered as a point with a very small area, but rather as a region with a defined area. The pressing area is the part of the surface that is in contact with the pressing body when the pressing body presses against the surface to be pressed. The pressing body is an object such as a finger that is used for pressing.

[0104] In addition, Figure 12 In (A), the deformation of the main surface 31 of the piezoelectric thin film sensor is observed along the direction from the pressing area r1 toward the pressing area r2.

[0105] exist Figure 12 In (A), the piezoelectric thin-film sensor, i.e., the piezoelectric thin film, is locally deformed around the pressing regions r1 and r2. The deformation of the piezoelectric thin film at pressing region r1 is inseparable from the deformation of the piezoelectric thin film at pressing region r2, but rather they are integrated. Figure 12 As shown in (B), the polarization of the piezoelectric film varies locally around the pressing regions r1 and r2, and takes a value of 0 in the regions far from the pressing regions r1 and r2. However, the polarization of the piezoelectric film takes a value of 0 within a rectangle having two sides connected to the pressing region r1 and two sides connected to the pressing region r2.

[0106] exist Figure 13 In (A), the piezoelectric thin-film sensor, i.e., the piezoelectric thin film, is locally deformed around the pressing area r. For example... Figure 13 As shown in (B), the polarization of the piezoelectric film varies locally around the pressing region r, taking a value of 0 in areas far from the pressing region r. However, the polarization of the piezoelectric film takes a value of 0 within the rectangle circumscribed by the pressing region r.

[0107] In addition, Figure 13 In (B), depending on the method for determining the first and second line segments and the size of the pressing area r, the boundary lines s1 and s2 are detected as two independent first line segments or a single first line segment with a relatively wide width, and the boundary lines s3 and s4 are detected as two independent second line segments or a single second line segment with a relatively wide width.

[0108] Figure 14 This is a flowchart showing the press detection process performed by the processing unit of the second modified example. Figure 15 This is a flowchart showing the processing of step s33 performed by the processing unit of the second variation. Figure 16 and Figure 17This is a conceptual diagram illustrating the press detection process performed by the processing unit of the second modified example.

[0109] like Figure 14 As shown, firstly, the processing unit executes and Figure 10 The same process is applied to steps s21-s26 to find all intersection points of the first and second line segments (s31). Next, a rectangular region is found for all combinations of two intersection points selected from the obtained intersection points (s32). The rectangular region is defined by a rectangle with a polarization value of 0: the rectangle has a pair of vertices at the two selected intersection points and has sides parallel to the x-axis and y-axis directions, respectively.

[0110] exist Figure 16 and Figure 17 In the process, the processing unit obtains the intersection point c1 of the first line segment A1 and the second line segment B1, and the intersection point c2 of the first line segment A2 and the second line segment B2. Then, the processing unit obtains the rectangular region d based on the combination of intersection points (c1, c2).

[0111] Furthermore, in this specification, the intersection of the first line segment and the second line segment does not include points that are shorter than a specified threshold used to define the vicinity of the end points of the first and second line segments, and are points shared by both the first and second line segments. Therefore, the processing unit determines that points shared by the first and second line segments near the end points of the first or second line segment are not intersections of the first and second line segments.

[0112] Next, the processing unit determines the pressing area based on the rectangular area (s33).

[0113] Specifically, such as Figure 15 As shown, when an inner region exists (s41), the processing unit determines the inner region as a pressing region (s42). An inner region is defined as a region having the surface shape of a pressing body and being inscribed within a rectangular region. The surface shape of the pressing body is the shape of the portion of its surface that contacts the surface being pressed when the pressing body presses against it. Therefore, the surface shape of the pressing body matches the shape of the pressing region defined by that pressing body. The surface shape of the pressing body is provided to the processing unit beforehand.

[0114] If an inner region cannot exist (s41: "No"), but a first abutting region and a second abutting region can exist (s43: "Yes"), the processing unit determines the first abutting region and the second abutting region as pressing regions (s44). The first abutting region is defined as a region having the surface shape of a pressing body, located within a rectangular region, and connected to both sides of the rectangular region at a common intersection point. The second abutting region is defined as a region having the surface shape of a pressing body, located within a rectangular region without overlapping with the first abutting region, and connected to both sides of the rectangular region at another common intersection point.

[0115] Furthermore, when multiple first contact areas or second contact areas exist, the processing unit may determine the initially found first contact area or second contact area as a pressing area, or it may determine one first contact area or second contact area selected by additional conditions as a pressing area.

[0116] The processing unit can determine the existence of an inner region, a first abutting region, or a second abutting region by investigating whether the area with the surface shape of the pressing body can be configured to satisfy the definition of an inner region, a first abutting region, or a second abutting region.

[0117] exist Figure 16 In the process, the processing unit determines that an inner region is impossible, but a first abutting region and a second abutting region are possible, thus obtaining a first abutting region e1 and a second abutting region e2. The first abutting region e1 has the surface shape of a pressing body, is located within a rectangular region d, and connects to both sides of the common intersection point c1 of the rectangular region. The second abutting region e2 has the surface shape of a pressing body, is located within the rectangular region d in a manner that does not overlap with the first abutting region e1, and connects to both sides of the common intersection point c2 of the rectangular region.

[0118] exist Figure 17 In the process, the processing unit determines that an inner region can exist, and thus obtains an inner region e. The inner region e has the surface shape of the pressing body and is inscribed within the rectangular region d.

[0119] In cases where a first contact area and a second contact area are impossible (s43: "No"), the processing unit includes the rectangular area and the intersection point located at its opposite vertices in the press area association data. The press area association data indicates that a pressing body has made contact within the rectangular area of ​​the data and near the intersection point of the data.

[0120] If the processing unit has not searched the entire pressing area and investigated the entire rectangular area (s46: "No"), it continues to search the pressing area and investigate the remaining rectangular area.

[0121] like Figure 14 and Figure 15As shown, if the processing unit has searched the pressing area and investigated all rectangular areas (s46: "Yes"), it outputs the obtained pressing area, pressing area associated data, or both (s34).

[0122] The processing unit repeats steps s31 to s34 at constant intervals. In this way, the pressure sensor of the second modified example detects the pressure point.

[0123] In a modified example, without pre-assigning a surface shape to the pressing body, the processing unit outputs pressing area association data including the obtained rectangular region and the intersection of its opposite vertices.

[0124] In another variation, the processing unit may be pre-assigned multiple surface shapes to the pressing bodies. In this case, the processing unit may also sort the surface shapes of the multiple pressing bodies. Furthermore, the processing unit may determine whether an inscribed region can exist for the surface shape of the next pressing body if an inscribed region is impossible for the surface shape of the previous pressing body. Similarly, if a first abutting region and a second abutting region are impossible for the surface shape of the previous pressing body, the processing unit may determine whether a first abutting region and a second abutting region can exist for the surface shape of the next pressing body.

[0125] In another variation, the processing unit may be pre-assigned a maximum number of pressing points. Furthermore, if the processing unit determines during an intermediate processing stage that the maximum number of pressing points can be obtained, it may proceed to the next processing step.

[0126] Furthermore, if no intersection point is found, the processing unit determines that no pressing point exists and outputs nothing. Conversely, if the found intersection point is not located at a vertex of the rectangular area, the processing unit outputs that intersection point as a pressing point.

[0127] According to the second variation, even when the deformation of the main surface at multiple pressing points is not separated, it is possible to detect pressing at multiple points.

[0128] [Third variation]

[0129] The pressure sensor in the third modification differs from the pressure sensor 1 in that it has a piezoelectric sensor 11a instead of the piezoelectric sensor 11.

[0130] Figure 18This is a cross-sectional view of the piezoelectric sensor 11a. The piezoelectric sensor 11a includes a piezoelectric thin film sensor 15, a plate-shaped elastic body 41, and a fixing member 42. The elastic body 41 has a first main surface 35 and a second main surface 36 opposite to the first main surface 35. The fixing member 42 fixes the elastic body 41 at the end of the second main surface 36. The piezoelectric thin film sensor 15 is disposed on the second main surface 36 of the elastic body 41.

[0131] The pressure sensor in the third variation is configured to detect pressure applied to a point on the first main surface 35 of the elastomer 41.

[0132] The elastomer 41 is formed, for example, from a glass plate. The fastener 42 is, for example, the outer casing of a product on which a pressure sensor is mounted. The piezoelectric film sensor 15 is attached, for example, to the second main surface 36 of the elastomer 41 by an adhesive or bonding agent.

[0133] The elastomer is fixed at one end of its second main surface, allowing it to flex as a whole with its thickness hardly changing upon pressure. A piezoelectric thin-film sensor, i.e., a piezoelectric thin film, is disposed on the second main surface of the elastomer. Therefore, when the first main surface of the elastomer is pressed, the deformation of the piezoelectric thin film propagates throughout the entire piezoelectric thin film, and the polarization generated in the piezoelectric thin film affects the entire film. Due to these characteristics, the pressure sensor of the third variation is suitable for detecting pressure at a single point.

[0134] According to this variation, the piezoelectric thin-film sensor is disposed on the second principal surface of the elastomer. This construction facilitates the industrial manufacturing of the pressure sensor and ensures its mass production capability.

[0135] [Fourth variation]

[0136] The pressure sensor of the fourth modification differs from the pressure sensor 1 in that it has a piezoelectric sensor 11b instead of the piezoelectric sensor 11.

[0137] Figure 19 This is a cross-sectional view of the piezoelectric sensor 11b. The piezoelectric sensor 11b includes a piezoelectric thin-film sensor 15, a robust base plate 43, and a flat elastomer 44. The elastomer 44 is disposed between the piezoelectric thin-film sensor 15 and the base plate 43. The elastomer 44 is attached to the piezoelectric thin-film sensor 15 and the base plate 43, for example, by an adhesive or bonding agent. The elastomer 44 is formed of materials such as rubber or sponge, and its thickness varies with pressure.

[0138] The pressure sensor in the fourth variation is configured to detect pressure on the main surface 31 of the piezoelectric thin film sensor 15.

[0139] According to this variation, the piezoelectric thin-film sensor is disposed on the main surface of the elastomer. This construction facilitates the industrial manufacturing of the pressure sensor and ensures its mass production capability.

[0140] Furthermore, by using the pressure detection processing of the pressure sensor 1, its first variant, or its second variant, it is possible to detect pressure at one or more points.

[0141] The structures shown in the various embodiments described above can also be appropriately replaced or combined.

[0142] It should be understood that the description of the above embodiments is illustrative in all respects and not restrictive. The scope of the invention is not shown by the above embodiments, but by the claims. Furthermore, the scope of the invention is intended to include all modifications within the meaning and scope equivalent to the claims.

[0143] The present invention has the following structure.

[0144] (1) A pressure sensor, comprising:

[0145] A piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy;

[0146] Multiple detection electrodes are disposed on a first main surface of the piezoelectric thin film to detect the charge generated in the piezoelectric thin film;

[0147] A ground electrode is disposed on the second main surface of the piezoelectric thin film;

[0148] The detection unit detects the voltage signal generated on the piezoelectric film based on the charge detected by the detection electrode; and

[0149] The processing unit processes the voltage signal detected by the detection unit.

[0150] The processing unit performs the following processing:

[0151] On the first main surface of the piezoelectric film, a first direction and a second direction perpendicular to the first direction are taken.

[0152] The polarization distribution on the first principal surface of the piezoelectric film is determined based on the voltage signal.

[0153] Find the first line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the first direction.

[0154] Find the second line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the second direction.

[0155] Find the intersection point of the first line segment and the second line segment, and then detect the pressing point.

[0156] (2) In the pressure sensor described in (1),

[0157] The processing unit calculates all the first line segment and the second line segment, and calculates all the intersection points of the first line segment and the second line segment.

[0158] (3) In the pressure sensor described in (1) or (2),

[0159] The processing unit determines a rectangular region defined by the following rectangle, wherein the polarization is 0: the rectangle has a pair of vertices at two intersection points selected from the intersection points of the first line segment and the second line segment, and has an edge parallel to the first direction.

[0160] (4) The pressure sensor described in (1) includes:

[0161] A flat, elastic body having a first main surface and a second main surface opposite to the first main surface; and

[0162] A fastener that secures the elastic body at one end of the second main surface of the elastic body.

[0163] The piezoelectric film is disposed on the second main surface of the elastomer.

[0164] (5) The pressure sensor described in any one of (1) to (3) comprises:

[0165] Base plate; and

[0166] A flat, elastomer.

[0167] The elastomer is disposed between the piezoelectric film and the base plate.

[0168] (6) A method for detecting a pressure point, wherein a processing unit in a pressure sensor detects a pressure point, the pressure sensor comprising:

[0169] A piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy;

[0170] Multiple detection electrodes are disposed on a first main surface of the piezoelectric thin film to detect the charge generated in the piezoelectric thin film;

[0171] A ground electrode is disposed on the second main surface of the piezoelectric thin film;

[0172] The detection unit detects the voltage signal generated on the piezoelectric film based on the charge detected by the detection electrode; and

[0173] The processing unit processes the voltage signal detected by the detection unit.

[0174] The processing unit performs the following processing:

[0175] On the first main surface of the piezoelectric film, a first direction and a second direction perpendicular to the first direction are taken.

[0176] The polarization distribution on the first principal surface of the piezoelectric film is determined based on the voltage signal.

[0177] Find the first line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the first direction.

[0178] Find the second line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the second direction.

[0179] Find the intersection point of the first line segment and the second line segment, and then detect the pressing point.

[0180] (7) A pressure point detection program, mounted on a pressure sensor, the pressure sensor comprising:

[0181] A piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy;

[0182] Multiple detection electrodes are disposed on a first main surface of the piezoelectric thin film to detect the charge generated in the piezoelectric thin film;

[0183] A ground electrode is disposed on the second main surface of the piezoelectric thin film;

[0184] The detection unit detects the voltage signal generated on the piezoelectric film based on the charge detected by the detection electrode; and

[0185] The processing unit processes the voltage signal detected by the detection unit.

[0186] The pressure point detection procedure causes the processing unit to perform the following processing:

[0187] On the first main surface of the piezoelectric film, a first direction and a second direction perpendicular to the first direction are taken.

[0188] The polarization distribution on the first principal surface of the piezoelectric film is determined based on the voltage signal.

[0189] Find the first line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the first direction.

[0190] Find the second line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the second direction.

[0191] Find the intersection point of the first line segment and the second line segment, and then detect the pressing point.

[0192] Explanation of reference numerals in the attached figures

[0193] 1: Press sensor; 11, 11a, 11b: Piezoelectric sensor; 12: Detection unit; 13: Processing unit; 15: Piezoelectric thin film sensor; 16: Support body; 21: Piezoelectric thin film; 22: Adhesive material; 23: Adhesive material; 24: Detection electrode; 25: Ground electrode; 26: Flexible substrate; 27: Flexible substrate; 31: Main surface; 33: First main surface; 34: Second main surface; 35: First main surface; 36: Second main surface; 41: Elastomer; 42: Fixing member; 43: Base plate; 44: Elastomer.

Claims

1. A pressure sensor, comprising: A piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy; Multiple detection electrodes are disposed on a first main surface of the piezoelectric thin film to detect the charge generated in the piezoelectric thin film. A ground electrode is disposed on the second main surface of the piezoelectric thin film; The detection unit detects the voltage signal generated on the piezoelectric film based on the charge detected by the detection electrode. as well as The processing unit processes the voltage signal detected by the detection unit. The processing unit performs the following processing: On the first main surface of the piezoelectric film, a first direction and a second direction perpendicular to the first direction are taken. The polarization distribution on the first principal surface of the piezoelectric film is determined based on the voltage signal. Find the first line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the first direction. Find the second line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the second direction. Find the intersection point of the first line segment and the second line segment, and then detect the pressing point.

2. The pressure sensor according to claim 1, wherein, The processing unit calculates all the first line segment and the second line segment, and calculates all the intersection points of the first line segment and the second line segment.

3. The pressure sensor according to claim 1 or 2, wherein, The processing unit determines a rectangular region defined by the following rectangle, wherein the polarization is 0: the rectangle has a pair of vertices at two intersection points selected from the intersection points of the first line segment and the second line segment, and has an edge parallel to the first direction.

4. The pressure sensor according to claim 1, comprising: A flat, elastic body having a first main surface and a second main surface opposite to the first main surface; and A fastener that secures the elastic body at one end of the second main surface of the elastic body. The piezoelectric film is disposed on the second main surface of the elastomer.

5. The pressure sensor according to any one of claims 1 to 3, comprising: Base plate; and A flat, elastomer. The elastomer is disposed between the piezoelectric film and the base plate.

6. A method for detecting a pressure point, wherein a processing unit in a pressure sensor detects a pressure point, the pressure sensor comprising: A piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy; Multiple detection electrodes are disposed on a first main surface of the piezoelectric thin film to detect the charge generated in the piezoelectric thin film. A ground electrode is disposed on the second main surface of the piezoelectric thin film; The detection unit detects the voltage signal generated on the piezoelectric film based on the charge detected by the detection electrode. as well as The processing unit processes the voltage signal detected by the detection unit. The processing unit performs the following processing: On the first main surface of the piezoelectric film, a first direction and a second direction perpendicular to the first direction are taken. The polarization distribution on the first principal surface of the piezoelectric film is determined based on the voltage signal. Find the first line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the first direction. Find the second line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the second direction. Find the intersection point of the first line segment and the second line segment, and then detect the pressing point.

7. A pressure point detection program, mounted on a pressure sensor, the pressure sensor comprising: A piezoelectric film having a first main surface and a second main surface opposite to the first main surface, the piezoelectric film having output anisotropy; Multiple detection electrodes are disposed on a first main surface of the piezoelectric thin film to detect the charge generated in the piezoelectric thin film. A ground electrode is disposed on the second main surface of the piezoelectric thin film; The detection unit detects the voltage signal generated on the piezoelectric film based on the charge detected by the detection electrode. as well as The processing unit processes the voltage signal detected by the detection unit. The pressure point detection procedure causes the processing unit to perform the following processing: On the first main surface of the piezoelectric film, a first direction and a second direction perpendicular to the first direction are taken. The polarization distribution on the first principal surface of the piezoelectric film is determined based on the voltage signal. Find the first line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the first direction. Find the second line segment that forms the boundary where the polarization varies discontinuously between positive, negative, and zero values, and extends along the second direction. Find the intersection point of the first line segment and the second line segment, and then detect the pressing point.

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