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

Abstract

A pressing sensor according to the present invention comprises: a piezoelectric film that has output anisotropy; a plurality of detection electrodes that are disposed on a first main surface of the piezoelectric film and detect charges generated in the piezoelectric film; a ground electrode that is disposed on a second main surface of the piezoelectric film; a detection unit that detects, from the charges detected by the detection electrodes, voltage signals generated in the piezoelectric film; and a processing unit that processes the voltage signals detected by the detection unit. The processing unit detects a pressing point by: taking a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film; setting a polarization distribution on the first main surface of the piezoelectric film on the basis of the voltage signals; obtaining a first line segment that extends in the first direction and constitutes a boundary on which the polarization discontinuously changes between a positive value, a negative value, and the value 0; obtaining a second line segment that extends in the second direction and constitutes a boundary on which the polarization discontinuously changes between a positive value, a negative value, and the value 0; and obtaining a point of intersection between the first line segment and the second line segment.

Description

Pressure sensor, pressure point detection method, and pressure point detection program

[0001] The present invention relates to a technique for detecting pressure.

[0002] Conventionally, in products equipped with a typical pressure trackpad, the amount of displacement of the housing caused by the user's pressure operation is measured using a strain sensor, ultrasonic sensor, or capacitive touch panel (see, for example, Patent Document 1), thereby estimating the pressure applied to the operating surface and detecting the user's pressure operation.

[0003] JP 2017-78888 A

[0004] As such, a typical pressure trackpad measures the displacement of the housing caused by pressure. Therefore, to implement a pressure trackpad in a product, it is necessary to consider a housing structure that equalizes the displacement of the housing and the placement of the sensor element that measures the displacement of the housing. This results in high housing design costs and significant constraints on housing design.

[0005] Furthermore, due to the large restrictions on housing design, it becomes necessary to design each product individually, which places large restrictions on product cost and design.

[0006] An object of the present invention is to provide a technology that reduces the constraints on housing design when mounting a pressure sensor on a product.

[0007] 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 and having output anisotropy; a plurality of detection electrodes arranged on the first main surface of the piezoelectric film and detecting electric charges generated in the piezoelectric film; a ground electrode arranged on the second main surface of the piezoelectric film; a detection unit that detects voltage signals generated in the piezoelectric film from the electric charges detected by the detection electrodes; and a processing unit that processes the voltage signals 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 a distribution of polarization on the first main surface of the piezoelectric film based on the voltage signals, determines a first line segment extending in the first direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0 values, determines a second line segment extending in the second direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0 values, and detects a pressure point by determining the intersection of the first line segment and the second line segment.

[0008] The pressure point detection method of the present invention includes a pressure sensor comprising a piezoelectric film having a first main surface and a second main surface opposite to the first main surface and having output anisotropy; a plurality of detection electrodes arranged on the first main surface of the piezoelectric film to detect electric charges generated in the piezoelectric film; a ground electrode arranged on the second main surface of the piezoelectric film; a detection unit that detects voltage signals generated in the piezoelectric film from the electric charges detected by the detection electrodes; and a processing unit that processes the voltage signals 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 a distribution of polarization on the first main surface of the piezoelectric film based on the voltage signals, obtains a first line segment extending in the first direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0 values, obtains a second line segment extending in the second direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0 values, and detects the pressure point by obtaining an intersection of the first line segment and the second line segment.

[0009] The pressure point detection program of the present invention is mounted on a pressure sensor including: a piezoelectric film having a first main surface and a second main surface opposite to the first main surface and having output anisotropy; a plurality of detection electrodes arranged on the first main surface of the piezoelectric film and detecting electric charges generated in the piezoelectric film; a ground electrode arranged on the second main surface of the piezoelectric film; a detection unit that detects voltage signals generated in the piezoelectric film from the electric charges detected by the detection electrodes; and a processing unit that processes the voltage signals detected by the detection unit. The pressure point detection program causes the processing unit to perform the following operations: taking a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film; determining a polarization distribution on the first main surface of the piezoelectric film based on the voltage signals; determining a first line segment extending in the first direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; determining a second line segment extending in the second direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; and detecting an intersection of the first line segment and the second line segment.

[0010] According to the present invention, it is possible to reduce the constraints on the housing design when mounting a pressure sensor on a product.

[0011] FIG. 1 is a functional block diagram of the pressure sensor 1. FIG. 2 is an external perspective view of the piezoelectric sensor 11. FIG. 3 is a cross-sectional view of the piezoelectric sensor 11. FIG. 4 is a cross-sectional view of the piezoelectric film sensor 15. FIG. 5(A) is a conceptual diagram showing an example of deformation of the main surface 31 of the piezoelectric film sensor in response to pressure. FIG. 5(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in FIG. 5(A). FIG. 6(A) is a conceptual diagram showing another example of deformation of the main surface 31 of the piezoelectric film sensor in response to pressure. FIG. 6(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in FIG. 6(A). FIG. 7 is a flowchart showing pressure detection processing by a processing unit. FIG. 8 is a conceptual diagram for explaining pressure detection processing by a processing unit. FIG. 9(A) is a conceptual diagram showing an example of deformation of the main surface 31 of the piezoelectric film sensor in response to pressure. FIG. 9(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in FIG. 9(A). FIG. 10 is a flowchart showing pressure detection processing by a processing unit of a first modified example. FIG. 11 is a conceptual diagram for explaining pressure detection processing by a processing unit of a first modified example. FIG. 12(A) is a conceptual diagram showing an example of deformation of the main surface 31 of the piezoelectric film sensor in response to pressure. FIG. 12(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in FIG. 12(A). FIG. 13(A) is a conceptual diagram showing another example of deformation of the main surface 31 of the piezoelectric film sensor in response to pressure. FIG. 13(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in FIG. 13(A). FIG. 14 is a flowchart showing pressure detection processing by a processing unit of a second modified example. FIG. 15 is a flowchart showing processing of step s33 by a processing unit of a second modified example. Fig. 16 is a conceptual diagram for explaining the pressure detection process by the processing unit of the second modified example. Fig. 17 is a conceptual diagram for explaining the pressure detection process by the processing unit of the second modified example. Fig. 18 is a cross-sectional view of the piezoelectric sensor 11a. Fig. 19 is a cross-sectional view of the piezoelectric sensor 11b.

[0012] Hereinafter, several embodiments of the present invention will be described. In each embodiment, differences from the previous embodiments will be described. Similar effects due to similar configurations will not be mentioned for each embodiment.

[0013] [Embodiment] Fig. 1 is a functional block diagram of a pressure sensor 1. Fig. 2 is an external perspective view of a piezoelectric sensor 11. Fig. 3 is a cross-sectional view of the piezoelectric sensor 11. Fig. 4 is a cross-sectional view of a piezoelectric film sensor 15. The pressure sensor 1 includes a piezoelectric sensor 11, a detection unit 12, and a processing unit 13. The piezoelectric sensor 11 includes a piezoelectric film sensor 15 and a support 16. The piezoelectric film sensor 15 includes a piezoelectric film 21, adhesive materials 22 and 23, a plurality of detection electrodes 24, a ground electrode 25, and flexible substrates 26 and 27.

[0014] As shown in FIGS. 2 and 3, the piezoelectric film sensor 15 is supported by the support body 16 in a state where it is stretched in all directions parallel to the main surface 31 of the piezoelectric film sensor 15 .

[0015] The pressure sensor 1 is configured to detect pressure at one point on the main surface 31 of the piezoelectric film sensor 15 .

[0016] As shown in FIG. 4 , the piezoelectric film 21 has a first main surface 33 and a second main surface 34 opposite the first main surface 33, and has output anisotropy. The piezoelectric film 21 is formed, for example, from uniaxially stretched poly-L-lactic acid (PLLA). The detection electrode 24 is disposed on the first main surface 33 of the piezoelectric film 21 and detects electric charges 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. The 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.

[0017] The detection unit 12 detects a voltage signal generated in the piezoelectric film 21 from the charge detected by the detection electrode 24. The detection unit 12 has, 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 is composed of a CPU, memory, etc., and stores a program, and processes the voltage signal by executing the program.

[0018] In this specification, a predetermined direction parallel to the first main surface 33 of the piezoelectric film 21 according to the distribution of polarization on the first main surface 33 of the piezoelectric film 21 is defined as the x-axis direction. A direction parallel to the first main surface 33 of the piezoelectric film 21 and perpendicular to the x-axis direction is defined as the y-axis direction. A direction perpendicular to the first main 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 +x-axis direction, and the other side of the x-axis direction is defined as the left direction or −x-axis direction. One side of the y-axis direction is defined as the upward direction or +y-axis direction, and the other side of the y-axis direction is defined as the downward direction or −y-axis direction.

[0019] The processing unit 13 defines 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. The processing unit 13 then determines the orientation of a 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 will be described in detail below, the processing unit 13 determines a first line segment extending in the x-axis direction, forming a boundary where the polarization discontinuously changes between positive values, negative values, and zero. In other words, the first line segment is a line segment where the polarity of the polarization changes across the first line segment. The processing unit 13 then determines a second line segment extending in the y-axis direction, forming a boundary where the polarization discontinuously changes between positive values, negative values, and zero. In other words, the second line segment is a line segment where the polarity of the polarization changes across the second line segment. Then, the processing unit 13 detects the pressed point by finding the intersection of the first line segment and the second line segment.

[0020] 4 , the detection electrodes 24 are arranged in the x-axis direction and the y-axis direction on the piezoelectric film 21. The processing unit 13 determines cells arranged in the x-axis direction and the y-axis direction on the first main surface 33 of the piezoelectric film 21. When the first main surface 33 of the piezoelectric film 21 is viewed in plan, the cells correspond to the areas occupied by one detection electrode 24 on the first main surface 33 of the piezoelectric film 21. Based on the voltage signals corresponding to each detection electrode 24, the processing unit 13 determines the polarization of the piezoelectric film 21 for the cells corresponding to each detection electrode 24.

[0021] Alternatively, the processing unit 13 may estimate the polarization for more closely spaced or consecutive positions to determine the polarization distribution.

[0022] Fig. 5(A) is a conceptual diagram showing an example of deformation of the main surface 31 of the piezoelectric film sensor due to pressing force. Fig. 5(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in Fig. 5(A). Fig. 6(A) is a conceptual diagram showing another example of deformation of the main surface 31 of the piezoelectric film sensor due to pressing force. Fig. 6(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in Fig. 6(A).

[0023] In Fig. 5(A), the piezoelectric film sensor, and therefore the piezoelectric film, is deformed globally by pressure, not just at the pressure point p. As shown in Fig. 5(B), the polarization of the piezoelectric film changes globally on the first main surface of the piezoelectric film in response to the deformation. In Fig. 6(A), the piezoelectric film sensor, and therefore the piezoelectric film, is deformed locally around the pressure point p by pressure. As shown in Fig. 6(B), the polarization of the piezoelectric film changes locally around the pressure point p in response to the deformation, and takes on a value of 0 away from the pressure point p.

[0024] As shown in Figures 5(B) and 6(B), the polarization in the upper left region of the pressed point p and the polarization in the lower right region of the pressed point p have the same positive and negative signs. The polarization in the lower left region of the pressed point p and the polarization in the upper right region of the pressed point p have the same positive and negative signs. The polarization in the upper left region of the pressed point p and the polarization in the lower left region of the pressed point p have opposite positive and negative signs. In Figures 5(B) and 6(B), the polarization in the upper left and lower right regions of the pressed point p is positive, and the polarization in the lower left and upper right regions of the pressed point p is negative.

[0025] Such a polarization distribution appears because the piezoelectric film has output anisotropy.

[0026] 5B and 6B, the polarization distribution is depicted by approximately regarding the polarization distribution at the detected discrete points as the polarization distribution at continuous points for the sake of convenience. Therefore, the boundary lines s1 and s2 where the polarization sign changes correspond to the boundary lines between adjacent cells or to a row of cells where the polarization is zero.

[0027] Fig. 7 is a flowchart showing the pressure detection process by the processing unit, and Fig. 8 is a conceptual diagram for explaining the pressure detection process by the processing unit.

[0028] 7 , first, the processing unit searches for a point on a first line segment extending in the x-axis direction on the first principal surface of the piezoelectric film, where the polarization forms a boundary where the polarization changes discontinuously between positive values, negative values, and zero, and designates the found point as a first starting point (s11). A point on the first principal surface of the piezoelectric film corresponds to a point on the first line segment if it satisfies the following condition: In other words, the polarization changes in the y-axis direction from a positive value to a negative value, a negative value to a positive value, a positive value to a zero value, a zero value to a positive value, a negative value to a zero value, or a zero value to a negative value, with a point in the x-axis direction adjacent to the point. The polarization changes in the y-axis direction discontinuously, i.e., abruptly, for example, greater than a predetermined threshold value, with a point in the x-axis direction adjacent to the point.

[0029] For example, the processing unit determines that position (i, j) corresponds to a point on the first line segment if position (i, j) satisfies sgn[P(i+k, j+1)]≠sgn[P(i+k, j-1)], |P(i+k, j+1)-P(i+k, j-1)|>α for k=0, 1, k=0, -1, or k=1, -1. In the expression (i, j), i represents the position of the cell in the x-axis direction, and j represents the position of the cell in the y-axis direction. P(i, j) represents the polarization at position (i, j). α represents a predetermined threshold that determines 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.

[0030] In addition, the method for determining whether a point on the first principal surface of the piezoelectric film is a point on the first line segment is adjusted so that the first line segment is a line segment that passes through the pressing point and extends in the x-axis direction.

[0031] For example, the processing unit may set the origin of the coordinate system at the center of gravity (geometric center of gravity) of the first main surface of the piezoelectric film, and repeatedly search for points on the first line segment by examining or scanning points on the first main surface of the piezoelectric film from the origin toward the bottom end and then the top end from the origin toward the left end and then the right end. Alternatively, the processing unit may repeatedly search for points on the first line segment by examining points on the first main surface of the piezoelectric film from the bottom end to the top end from the left end to the right end. The processing unit may also search for points on the first line segment by examining points on the first main surface of the piezoelectric film in a different order.

[0032] In FIG. 8, the processing unit searches for points on the first line segment by examining points on the first main surface of the piezoelectric film from the origin O toward the bottom end and then the top end, finds the first starting point a0, and ends the search for points on the first line segment.

[0033] Next, the processing unit searches for two end points of the first line segment by searching points on the first main surface of the piezoelectric film in the left and right directions from the first starting point, and obtains the first line segment by finding the two end points (s12).

[0034] For example, the processing unit determines that the position (i, j) is an end point of the first line segment if the position (i, j) is a point on the first line segment and is at the right end or the left end of the first main surface of the piezoelectric film. Also, the processing unit determines that the position (i, j) is an end point of the first line segment if the position (i, j) is a point on the first line segment and the next position (i+1, j) or position (i-1, j) is not a point on the first line segment.

[0035] In Figure 8, the processing unit searches for the two end points of the first line segment by examining points on the first main surface of the piezoelectric film from the first starting point a0 in the left and right directions, and finds the two end points a1 and a2 of the first line segment, thereby obtaining the first line segment A.

[0036] Next, the processing unit searches for a point on the first principal surface of the piezoelectric film on a second line segment extending in the y-axis direction, which forms a boundary where the polarization discontinuously changes between positive values, negative values, and zero, and designates the found point as a second starting point (s13). A point on the first principal surface of the piezoelectric film corresponds to a point on the second line segment if it satisfies the following condition: In other words, the polarization changes in the x-axis direction from a positive value to a negative value, a negative value to a positive value, a positive value to a zero value, a zero value to a positive value, a negative value to a zero value, or a zero value to a negative value, with a point in the y-axis direction near the point as a boundary. The polarization changes in the x-axis direction discontinuously, i.e., abruptly, for example, by a value greater than a predetermined threshold, with a point in the y-axis direction near the point as a boundary.

[0037] For example, the processing unit determines that position (i, j) corresponds to a point on the second line segment if 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, or k=1,-1.

[0038] The method for determining whether a point on the first principal surface of the piezoelectric film is on the second line segment is adjusted so that the second line segment is a line segment that passes through the pressing point and extends in the y-axis direction.

[0039] For example, the processing unit may search for points on the second line segment by examining points on the first main surface of the piezoelectric film from the origin toward the left end and then the right end, repeatedly from the origin toward the bottom end and then the top end. Alternatively, the processing unit may search for points on the second line segment by examining points on the first main surface of the piezoelectric film from the left end toward the right end, repeatedly from the bottom end toward the top end. The processing unit may search for points on the second line segment by examining points on the first main surface of the piezoelectric film in a different order.

[0040] In FIG. 8, the processing unit searches for points on the second line segment by examining points on the first main surface of the piezoelectric film from the origin O toward the left end, finds the second starting point b0, and ends the search for points on the second line segment.

[0041] Next, the processing unit searches for two end points of the second line segment by examining points on the first main surface of the piezoelectric film from the second starting point downward and upward, and finds the two end points to determine the second line segment (s14).

[0042] For example, the processing unit determines that the position (i, j) is an end point of the second line segment if the position (i, j) is a point on the second line segment and is at the upper end or the lower end of the first main surface of the piezoelectric film. Also, the processing unit determines that the position (i, j) is an end point of the second line segment if the position (i, j) is a point on the second line segment and the next position (i, j+1) or position (i, j-1) is not a point on the second line segment.

[0043] In Figure 8, the processing unit searches for the two end points of the second line segment by examining points on the first main surface of the piezoelectric film downward and upward from the second starting point b0, and finds the two end points b1 and b2 of the second line segment, thereby obtaining the second line segment B.

[0044] Next, the processing unit determines the intersection point between the first line segment and the second line segment (s15) and outputs the intersection point as the pressed point (s16). The first line segment and the second line segment are line segments that pass through the pressed point and extend in the x-axis and y-axis directions, respectively. Therefore, the intersection point between the first line segment and the second line segment coincides with the pressed point.

[0045] 8, the processing unit obtains the intersection point c between the first line segment A and the second line segment B, and outputs the intersection point c as the pressed point. As shown in FIG. 8, the intersection point c coincides with the pressed point p.

[0046] The processing unit repeats steps s11 to s16 at regular intervals, and in this manner, the pressure sensor 1 detects the pressed point.

[0047] In a modified example, the processing unit may determine the first line segment and the second line segment using another method, for example, the processing unit may determine the first line segment and the second line segment using various edge or line detection methods proposed in the image processing field.

[0048] In another modification, the processing unit may execute steps s11 and s12 after executing steps s13 and s14.

[0049] The first line segment and the second line segment are configured with one or more rows of cells depending on the detection method of the first line segment and the second line segment, and therefore the intersection of the first line segment and the second line segment is configured with a single cell or multiple cells depending on the detection method of the first line segment and the second line segment.

[0050] If the processing unit cannot find the first starting point, the second starting point, or the intersection point between the first line segment and the second line segment, it determines that the pressed point does not exist and does not output anything.

[0051] According to this embodiment, the only constraint on the housing design when mounting the pressure sensor on a product is that the main surface of the piezoelectric film sensor be most recessed at the point of pressure. This reduces the constraints on the housing design when mounting the pressure sensor on a product. This also increases the degree of freedom in product design.

[0052] Furthermore, because a typical pressure trackpad measures the displacement of a housing in principle, it is subject to the influence of gravity depending on the housing's orientation. Furthermore, if the housing's elasticity decreases due to aging or other factors, there is a possibility that the pressure sensor may erroneously detect a pressure even when the user is not applying pressure. According to this embodiment, the pressure sensor detects pressure by capturing the characteristics of the polarization distribution on the first principal surface of the piezoelectric film. The polarization distribution caused by pressure has different characteristics from the polarization distribution caused by the factors described above. This reduces the effect of gravity acting on the piezoelectric film sensor on the pressure sensor's detection of pressure. Furthermore, the likelihood of the pressure sensor erroneously detecting pressure is reduced.

[0053] Furthermore, the piezoelectric sensor has a simple structure consisting of a piezoelectric film sensor and a support. The processing unit detects a pressure at a single point by determining the intersection of the first line segment and the second line segment. Therefore, in this embodiment, a pressure at a single point can be detected with a simple structure.

[0054] [First Modification] The pressure sensor of the first modification differs from the pressure sensor 1 in the following respect: The processing unit obtains all of the first line segments and second line segments, and obtains all of the intersections between the first line segments and the second line segments.

[0055] The pressure sensor of the first modified example is configured to detect pressure at one or more points.

[0056] Fig. 9A is a conceptual diagram showing an example of deformation of the main surface 31 of the piezoelectric film sensor due to pressure, and Fig. 9B is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in Fig. 9A.

[0057] FIG. 9A shows the deformation of the main surface 31 of the piezoelectric film sensor viewed in the direction from the pressing point p1 toward the pressing point p2.

[0058] In Fig. 9A, the piezoelectric film sensor, and therefore the piezoelectric film, is locally deformed around two pressure points p1 and p2. As shown in Fig. 9B, the polarization of the piezoelectric film changes locally around the pressure points p1 and p2 in response to the deformation, and takes a value of 0 at locations away from the pressure points p1 and p2.

[0059] Fig. 10 is a flowchart showing the pressure detection process by the processing unit of the first modified example. Fig. 11 is a conceptual diagram for explaining the pressure detection process by the processing unit of the first modified example.

[0060] 10, first, the processing unit searches for and finds the first line segments (s21) by executing the same processes as steps s11 and s12 shown in Fig. 7. If the search for all the first line segments has not been completed (s22: no), the processing unit resumes the search for the first line segments.

[0061] More specifically, the processing unit starts searching for points on the first line segment from a predetermined point such as the origin. Next, the processing unit determines the first line segment from the points on the found first line segment. However, if the points on the found first line segment are on a first line segment that has already been found, it is not necessary to determine the first line segment from the points on the first line segment. Next, the processing unit searches for points on the first line segment and resumes searching for points on the first line segment from the point next to the point most recently searched. When the processing unit has finished searching for all points on the first main surface of the piezoelectric film, it ends the search for points on the first line segment.

[0062] 11, the processing unit starts searching for points on the first line segment from the origin O, finds a first starting point a01, and obtains a first line segment A1. Then, it resumes searching for points on the first line segment from the point next to the first starting point a01, finds a first starting point a02, and obtains a first line segment A2.

[0063] If all the first line segments have been searched (s22: yes), the processing unit searches for and finds the second line segments (s23) by executing the same processes as steps s13 and s14 shown in Fig. 7. If the search for all the second line segments has not been completed (s24: no), the processing unit resumes the search for the second line segments.

[0064] More specifically, after finishing searching for points on the first line segment, the processing unit starts searching for points on the second line segment from a predetermined point such as the origin. Next, the processing unit determines the second line segment from the point on the found second line segment. However, if the point on the found second line segment is on an already found second line segment, it is not necessary to determine the second line segment from the point on that second line segment. Next, the processing unit searches for points on the second line segment and resumes searching for points on the second line segment from the point next to the most recently searched point. When the processing unit has finished searching for all points on the first main surface of the piezoelectric film, it finishes searching for points on the second line segment.

[0065] 11, the processing unit starts searching for points on the second line segment from the origin O, finds a second starting point b01, and obtains a second line segment B1. Then, the processing unit resumes searching for points on the second line segment from the point next to the second starting point b01, finds a second starting point b02, and obtains a second line segment B2.

[0066] If all the second line segments have been searched (s24: yes), the processing unit determines all the intersections between the first line segments and the second line segments (s25) and outputs the intersections as pressed points (s26).

[0067] For example, the processing unit may find the intersections between the first line segments and the second line segments for all combinations of the first line segments and the second line segments.

[0068] In Figure 11, the processing unit obtains the intersections between the first line segment and the second line segment for combinations of the first line segment and the second line segment (A1, B1), (A1, B2), (A2, B1), and (A2, B2), thereby obtaining the intersection c1 between the first line segment A1 and the second line segment B1, and the intersection c2 between the first line segment A2 and the second line segment B2.

[0069] The processing unit repeats steps s21 to s26 at regular intervals, and in this manner, the pressure sensor of the first modified example detects the pressed point.

[0070] In a modified example, the processing unit may be given a maximum number of pressing points in advance, and when the processing unit finds the maximum number of first line segments, second line segments, or intersections, the processing unit may end the search for the first line segments, second line segments, or intersections and proceed to the next process.

[0071] In another modification, the processing unit may execute steps s21 and s22 after executing steps s23 and s24.

[0072] If the processing unit cannot find the first line segment, the second line segment, or the intersection point, it determines that the pressed point does not exist, and does not output anything.

[0073] According to the first modification, the piezoelectric sensor has a simple structure composed of a piezoelectric film sensor and a support, as described above. The processing unit detects all of the pressing points by determining all of the intersections between the first line segment and the second line segment. Therefore, in the first modification, the simple structure allows the detection of pressing at multiple points, not just one.

[0074] The pressure sensor of the second modification differs from the pressure sensor of the first modification in the following respect: The processing unit determines a rectangular region having opposite vertices at two intersections selected from the intersections of the first line segment and the second line segment, defined by a rectangle with sides parallel to the x-axis direction, and in which the polarization takes a value of 0.

[0075] The pressure sensor of the second modified example is configured to detect pressure at one or more points.

[0076] Fig. 12(A) is a conceptual diagram showing an example of deformation of the main surface 31 of the piezoelectric film sensor due to pressure. Fig. 12(B) is a conceptual diagram showing polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in Fig. 12(A). Fig. 13(A) is a conceptual diagram showing another example of deformation of the main surface 31 of the piezoelectric film sensor due to pressure. Fig. 13(B) is a conceptual diagram showing an example of polarization of the piezoelectric film when the main surface 31 of the piezoelectric film sensor is deformed as shown in Fig. 13(A).

[0077] 12(A) to 13(B), the pressed area is not regarded as a point having a minimum area, but is explicitly depicted as an area having a certain area. The pressed area is the part of the pressed surface that comes into contact with the pressing body when the pressing body presses the surface to be pressed. The pressing body is an object that performs the pressing, such as a finger.

[0078] FIG. 12A shows the deformation of the main surface 31 of the piezoelectric film sensor viewed in the direction from the pressed region r1 toward the pressed region r2.

[0079] In Fig. 12(A), the piezoelectric film sensor, and therefore the piezoelectric film, is locally deformed around the pressed areas r1 and r2. The deformation of the piezoelectric film in the pressed area r1 and the deformation of the piezoelectric film in the pressed area r2 are not separated but integrated. As shown in Fig. 12(B), the polarization of the piezoelectric film changes locally around the pressed areas r1 and r2 and takes a value of 0 away from the pressed areas r1 and r2. However, the polarization of the piezoelectric film takes a value of 0 within a rectangle having two sides that contact the pressed area r1 and two sides that contact the pressed area r2.

[0080] In Fig. 13(A), the piezoelectric film sensor, and therefore the piezoelectric film, is locally deformed around the pressed region r. As shown in Fig. 13(B), the polarization of the piezoelectric film changes locally around the pressed region r and takes a value of 0 away from the pressed region r. However, the polarization of the piezoelectric film takes a value of 0 within a rectangle circumscribing the pressed region r.

[0081] In FIG. 13(B), depending on the method for determining the first and second line segments and the dimensions of the pressed area r, the boundary lines s1 and s2 are detected as two separate first line segments or as a single relatively wide first line segment, and the boundary lines s3 and s4 are detected as two separate second line segments or as a single relatively wide second line segment.

[0082] Fig. 14 is a flowchart showing the pressure detection process by the processing unit of the second modified example. Fig. 15 is a flowchart showing the process of step s33 by the processing unit of the second modified example. Fig. 16 and Fig. 17 are conceptual diagrams for explaining the pressure detection process by the processing unit of the second modified example.

[0083] As shown in Fig. 14, the processing unit first performs the same processes as steps s21 to s26 shown in Fig. 10 to find all intersections between first line segments and second line segments (s31). Next, rectangular areas are found for all combinations of two selected intersections from the obtained intersections (s32). The rectangular areas are defined by rectangles with opposite vertices at the two selected intersections, with sides parallel to the x-axis and y-axis directions, and have a polarization of 0.

[0084] 16 and 17, the processing unit obtains an intersection c1 between a first line segment A1 and a second line segment B1, and an intersection c2 between a first line segment A2 and a second line segment B2. Next, the processing unit obtains a rectangular area d for the combination of intersections (c1, c2).

[0085] In this specification, the intersection of the first line segment and the second line segment does not include a point that is shared by the first line segment and the second line segment and whose distance from the end point of the first line segment or the second line segment is shorter than a predetermined threshold that defines the vicinity of the end point of the first line segment or the second line segment. Therefore, the processing unit determines that a point that is shared by the first line segment and the second line segment near the end point of the first line segment or the second line segment is not an intersection of the first line segment and the second line segment.

[0086] Next, the processing unit determines the pressed area based on the rectangular area (s33).

[0087] Specifically, as shown in FIG. 15 , if an inscribed area may exist (s41), the processing unit determines the inscribed area as a pressed area (s42). The inscribed area has the surface shape of the pressing body and is defined as an area inscribed in a rectangular area. The surface shape of the pressing body is the shape of the portion of the surface of the pressing body that comes into contact with the surface being pressed when the pressing body presses the surface being pressed. Therefore, the surface shape of the pressing body matches the shape of the pressed area defined by the pressing body. The surface shape of the pressing body is given to the processing unit in advance.

[0088] If the inscribed area does not exist (s41: no) but the first and second contact areas exist (s43: yes), the processing unit determines the first and second contact areas as pressed areas (s44). The first contact area is defined as an area that has the surface shape of the pressing body, is within the rectangular area, and is adjacent to two sides of the rectangular area that share one intersection. The second contact area is defined as an area that has the surface shape of the pressing body, does not overlap the first contact area, is within the rectangular area, and is adjacent to two sides of the rectangular area that share the other intersection.

[0089] In addition, when there may be multiple first or second contact areas, the processing unit may determine that the first first or second contact area that it finds is the pressed area, or it may impose additional conditions to narrow down the first or second contact area and determine that the single first or second contact area is the pressed area.

[0090] The processing unit can determine the existence of an inscribed area, a first abutment area, or a second abutment area by checking whether an area having the surface shape of the pressing body can be arranged so as to satisfy the definition of an inscribed area, a first abutment area, or a second abutment area.

[0091] 16 , the processing unit determines that an inscribed area cannot exist, but that first and second contact areas can exist, and obtains a first contact area e1 and a second contact area e2. The first contact area e1 has the surface shape of the pressing body, is within rectangular area d, and is in contact with two sides of the rectangular area that share intersection c1. The second contact area e2 has the surface shape of the pressing body, does not overlap with the first contact area e1, is within rectangular area d, and is in contact with two sides of the rectangular area that share intersection c2.

[0092] 17, the processing unit determines that an inscribed area may exist and obtains an inscribed area e. The inscribed area e has the surface shape of the pressing body and is inscribed in the rectangular area d.

[0093] If the first and second contact areas cannot exist (s43: no), the processing unit includes the rectangular area and the intersection at the opposite vertex of the rectangular area in the pressed area-related data. The pressed area-related data indicates that some pressing body is in contact with the rectangular area of ​​the data and in the vicinity of the intersection of the data.

[0094] If the processing unit has not finished checking all rectangular areas in search of the pressed area (s46: no), it continues to check the remaining rectangular areas in search of the pressed area.

[0095] As shown in Figures 14 and 15, when the processing unit searches for a pressed area and checks all rectangular areas (s46: yes), it outputs the obtained pressed area, pressed area related data, or both (s34).

[0096] The processing unit repeats steps s31 to s34 at regular intervals, and in this manner, the pressure sensor of the second modified example detects the pressed point.

[0097] In a modified example, when the surface shape of the pressing body is not given in advance, the processing unit outputs pressed area related data including the obtained rectangular area and the intersection point at the opposite vertex.

[0098] In another variation, the processing unit may be provided with a plurality of surface shapes of pressing bodies in advance. In this case, the processing unit may order the surface shapes of the plurality of pressing bodies. Then, if an inscribed region cannot exist for the surface shape of a previous pressing body, the processing unit may determine whether an inscribed region can exist for the surface shape of a next pressing body. Similarly, if the first and second contact regions cannot exist for the surface shape of a previous pressing body, the processing unit may determine whether the first and second contact regions can exist for the surface shape of a next pressing body.

[0099] In yet another modification, the processing unit may be given a maximum number of pressure points in advance, and if the processing unit determines that the maximum number of pressure points can be obtained during the processing, the processing unit may proceed to the next processing.

[0100] If the processor cannot find an intersection, it determines that the pressed point does not exist and outputs nothing. If the processor finds an intersection that is not at a vertex of a rectangular area, it outputs the intersection as the pressed point.

[0101] According to the second modification, pressure at a plurality of points can be detected even when the deformations of the main surface at the plurality of pressure points are not separated.

[0102] [Third Modification] The pressure sensor of the third modification differs from the pressure sensor 1 in the following respects: the pressure sensor of the third modification includes a piezoelectric sensor 11 a instead of the piezoelectric sensor 11 .

[0103] 18 is a cross-sectional view of the piezoelectric sensor 11a. The piezoelectric sensor 11a includes a piezoelectric film sensor 15, a flat elastic body 41, and a fixing device 42. The elastic body 41 has a first main surface 35 and a second main surface 36 opposite the first main surface 35. The fixing device 42 fixes the elastic body 44 at an end of the second main surface 36 of the elastic body 41. The piezoelectric film sensor 15 is disposed on the second main surface 36 of the elastic body 41.

[0104] The pressure sensor of the third modified example is configured to detect pressure applied to the first main surface 35 of the elastic body 41 at one point.

[0105] The elastic body 41 is formed of, for example, a glass plate. The fixing device 42 is, for example, the exterior of a product in which the pressure sensor is mounted. The piezoelectric film sensor 15 is attached to the second main surface 36 of the elastic body 41 by, for example, an adhesive or a pressure-sensitive adhesive.

[0106] The elastic body is fixed at the end of its second main surface and bends overall when pressed, with its thickness barely changing. The piezoelectric film sensor, and therefore the piezoelectric film, is disposed on the second main surface of the elastic body. Therefore, when the first main surface of the elastic body is pressed, the deformation of the piezoelectric film propagates throughout the entire piezoelectric film, and the polarization induced in the piezoelectric film extends throughout the entire piezoelectric film. Due to these characteristics, the pressure sensor of the third variant is suitable for detecting pressure at a single point.

[0107] According to this modification, the piezoelectric film sensor is disposed on the second main surface of the elastic body. This structure facilitates industrial manufacturing of the pressure sensor, ensuring mass production of the pressure sensor.

[0108] [Fourth Modification] The pressure sensor of the fourth modification differs from the pressure sensor 1 in the following respects: the pressure sensor of the fourth modification includes a piezoelectric sensor 11b instead of the piezoelectric sensor 11.

[0109] 19 is a cross-sectional view of the piezoelectric sensor 11b. The piezoelectric sensor 11b includes a piezoelectric film sensor 15, a hard bottom plate 43, and a flat elastic body 44. The elastic body 44 is disposed between the piezoelectric film sensor 15 and the bottom plate 43. The elastic body 44 is attached to the piezoelectric film sensor 15 and the bottom plate 43 with, for example, an adhesive or a pressure-sensitive adhesive. The elastic body 44 is made of a material such as rubber or sponge, and its thickness changes when pressed.

[0110] The pressure sensor of the fourth modified example is configured to detect pressure applied to the main surface 31 of the piezoelectric film sensor 15 .

[0111] According to this modification, the piezoelectric film sensor is disposed on the main surface of the elastic body. This structure facilitates industrial manufacturing of the pressure sensor, ensuring mass production of the pressure sensor.

[0112] Furthermore, by using the pressure detection process of the pressure sensor 1, the first modified example thereof, or the second modified example thereof, it is possible to detect pressure at one point or multiple points.

[0113] The configurations shown in the above embodiments may be replaced or combined as appropriate.

[0114] The above description of the embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications that are equivalent to the scope of the claims and fall within the scope thereof.

[0115] The present invention has the following configuration.

[0116] (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; a plurality of detection electrodes disposed on the first main surface of the piezoelectric film to detect electric charges generated in the piezoelectric film; a ground electrode disposed on the second main surface of the piezoelectric film; a detection unit that detects voltage signals generated in the piezoelectric film from the electric charges detected by the detection electrodes; and a processing unit that processes the voltage signals 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 a distribution of polarization on the first main surface of the piezoelectric film based on the voltage signals; determines a first line segment extending in the first direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; determines a second line segment extending in the second direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; and detects a pressure point by determining an intersection of the first line segment and the second line segment.

[0117] (2) The pressure sensor according to (1), wherein the processing unit determines all of the first line segments and the second line segments, and determines all of the intersections between the first line segments and the second line segments.

[0118] (3) The pressure sensor according to (1) or (2), wherein the processing unit determines a rectangular area in which the polarization takes a value of 0, the rectangular area being defined by a rectangle having opposite vertices at two intersections selected from the intersections of the first line segment and the second line segment and having sides parallel to a first direction.

[0119] (4) A pressure sensor as described in (1), comprising: a flat elastic body having a first main surface and a second main surface opposite to the first main surface; and a fixing device that fixes the elastic body at an end of the second main surface of the elastic body, wherein the piezoelectric film is disposed on the second main surface of the elastic body.

[0120] (5) The pressure sensor according to any one of (1) to (3), further comprising: a bottom plate; and a flat elastic body, the elastic body being disposed between the piezoelectric film and the bottom plate.

[0121] (6) A pressure sensor including: a piezoelectric film having a first main surface and a second main surface opposite to the first main surface and having output anisotropy; a plurality of detection electrodes disposed on the first main surface of the piezoelectric film and detecting charges generated in the piezoelectric film; a ground electrode disposed on the second main surface of the piezoelectric film; a detection unit that detects voltage signals generated in the piezoelectric film from the charges detected by the detection electrodes; and a processing unit that processes the voltage signals 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 a distribution of polarization on the first main surface of the piezoelectric film based on the voltage signals; determines a first line segment extending in the first direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; determines a second line segment extending in the second direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; and detects a pressure point by determining an intersection of the first line segment and the second line segment.

[0122] (7) A pressure point detection program mounted on a pressure sensor including: a piezoelectric film having a first main surface and a second main surface opposite to the first main surface and having output anisotropy; a plurality of detection electrodes disposed on the first main surface of the piezoelectric film and detecting electric charges generated in the piezoelectric film; a ground electrode disposed on the second main surface of the piezoelectric film; a detection unit that detects voltage signals generated in the piezoelectric film from the electric charges detected by the detection electrodes; and a processing unit that processes the voltage signals detected by the detection unit, the program causing the processing unit to perform the following operations: taking a first direction and a second direction perpendicular to the first direction on the first main surface of the piezoelectric film; determining a distribution of polarization on the first main surface of the piezoelectric film based on the voltage signals; determining a first line segment extending in the first direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; determining a second line segment extending in the second direction, where the polarization forms a boundary that discontinuously changes between positive values, negative values, and 0; and detecting a pressure point by determining an intersection of the first line segment and the second line segment.

[0123] 1: Pressure sensor 11, 11a, 11b: Piezoelectric sensor 12: Detection unit 13: Processing unit 15: Piezoelectric film sensor 16: Support 21: Piezoelectric 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: Elastic body 42: Fixing tool 43: Bottom plate 44: Elastic body

Claims

1. A piezoelectric film having a first major surface and a second major surface opposite to the first major surface, and having output anisotropy, a plurality of detection electrodes disposed on the first major surface of the piezoelectric film for detecting charges generated in the piezoelectric film, a ground electrode disposed on the second major surface of the piezoelectric film, a detection unit for detecting a voltage signal generated in the piezoelectric film from 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 major surface of the piezoelectric film, determines the distribution of polarization on the first major surface of the piezoelectric film based on the voltage signal, forms a boundary where the polarization changes discontinuously among positive values, negative values, and zero values, obtains a first line segment extending in the first direction, forms a boundary where the polarization changes discontinuously among positive values, negative values, and zero values, obtains a second line segment extending in the second direction, and detects a pressing point by obtaining an intersection point between the first line segment and the second line segment, a pressing sensor.

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

3. The pressing sensor according to claim 1 or 2, wherein the processing unit has opposite vertices at two intersection points selected from the intersection points between the first line segment and the second line segment, is defined by a rectangle having sides parallel to the first direction, and obtains a rectangular region where the polarization takes a value of zero.

4. A flat elastic body having a first major surface and a second major surface opposite to the first major surface, and a fixture for fixing the elastic body at an end of the second major surface of the elastic body, wherein the piezoelectric film is disposed on the second major surface of the elastic body, the pressing sensor according to claim 1.

5. A bottom plate and a flat elastic body, wherein the elastic body is disposed between the piezoelectric film and the bottom plate, the pressing sensor according to any one of claims 1 to 3.

6. A piezoelectric film having a first main surface and a second main surface on the opposite side of the first main surface and having output anisotropy, a plurality of detection electrodes disposed on the first main surface of the piezoelectric film for detecting charges generated in 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 in the piezoelectric film from the charges detected by the detection electrodes, and a processing unit for processing the voltage signal detected by the detection unit. In the pressing sensor, 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, the polarization forms a boundary that changes discontinuously among positive values, negative values, and a value of 0, obtains a first line segment extending in the first direction, the polarization forms a boundary that changes discontinuously among positive values, negative values, and a value of 0, obtains a second line segment extending in the second direction, and detects a pressing point by obtaining an intersection point between the first line segment and the second line segment.

7. A pressing point detection program installed in a pressing sensor including a piezoelectric film having a first main surface and a second main surface on the opposite side of the first main surface and having output anisotropy, a plurality of detection electrodes disposed on the first main surface of the piezoelectric film for detecting charges generated in 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 in the piezoelectric film from 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, the polarization forms a boundary that changes discontinuously among positive values, negative values, and a value of 0, obtains a first line segment extending in the first direction, the polarization forms a boundary that changes discontinuously among positive values, negative values, and a value of 0, obtains a second line segment extending in the second direction, and causes the processing unit to detect a pressing point by obtaining an intersection point between the first line segment and the second line segment.

Images