Pressing force sensor

Abstract

To provide a pressing force sensor which has a strain body having a small area and high sensitivity.SOLUTION: A pressing force sensor has: a housing having a cylindrical part provided with a first end surface; a strain body provided with a first surface and a second surface to be a surface opposite to the first surface; and a pair of strain gauges. An outer edge of the first end surface and the first surface have the same number of corners, that is, even numbers seen from a first direction perpendicular to the first surface. The second surface is bonded to the first end surface. The pair of the strain gauges are arranged opposite with a center of the second surface seen from the first direction on an arbitrary diagonal line of the second surface at an outer peripheral part of the second surface exposed in the cylindrical part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressing force sensor. [Background technology]

[0002] As an example of a pressing force sensor, a pulse wave sensor that detects pulse waves generated when the heart pumps blood is known. For example, a pulse wave sensor is provided with a pressure receiving plate that is supported so as to be flexible under the action of an external force, and a piezoelectric conversion means that converts the bending of the pressure receiving plate into an electric signal. This pulse wave sensor is formed in a dome shape with a convex curved surface on the outside of the circular pressure receiving plate that acts as a strain generator, and a pressure detection element is provided on the inner surface of the top of the pressure receiving plate as a piezoelectric conversion means (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-78689 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is preferable that a pressure sensor including the above-mentioned pulse wave sensor is small in size. However, if the area of ​​the strain element is simply reduced in order to reduce the size of the pressure sensor, the sensitivity will decrease.

[0005] The present invention has been made in view of the above-mentioned points, and has an object to provide a pressing force sensor having a small-area, highly sensitive strain generating body. [Means for solving the problem]

[0006] A pressing force sensor according to one embodiment of the present disclosure comprises a housing having a cylindrical portion with a first end surface, a strain gauge having a first surface and a second surface that is the surface opposite to the first surface, and a pair of strain gauges, wherein when viewed from a first direction perpendicular to the first surface, the outer edge of the first end surface and the first surface have the same number of corners, which is an even number, the second surface is joined to the first end surface, and the pair of strain gauges are arranged on an arbitrary diagonal line of the second surface at the outer periphery of the second surface exposed within the cylindrical portion, facing each other across the center of the second surface when viewed from the first direction. Effect of the Invention

[0007] According to the disclosed technique, it is possible to provide a pressing force sensor having a small-area, highly sensitive strain generating body. [Brief description of the drawings]

[0008] [Figure 1] 1 is a perspective view illustrating a pressing force sensor according to a first embodiment; [Diagram 2] 1 is an exploded perspective view illustrating a pressing force sensor according to a first embodiment; [Diagram 3] 1 is a cross-sectional view illustrating a pressing force sensor according to a first embodiment. [Figure 4] 4 is a bottom view illustrating a state in which a back cover is removed from the pressing force sensor according to the first embodiment. FIG. [Diagram 5] 3 is a bottom view illustrating a strain element and a strain gauge of the pressing force sensor according to the first embodiment. FIG. [Figure 6] FIG. 13 is a diagram showing the results of comparing the sensitivity of a circular flexure body with that of a square flexure body. [Figure 7] FIG. 13 is a diagram showing the results of comparing the areas of a circular flexure body and a square flexure body. [Figure 8] FIG. 1 is a diagram illustrating a bridge connection. [Figure 9] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Figure 10] 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. [Figure 11] 4 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. [Figure 12] 4 is a bottom view illustrating a strain element and a strain gauge of the pressing force sensor according to Modification 1 of the first embodiment. FIG. [Figure 13] 11 is a bottom view illustrating a strain element and a strain gauge of the pressing force sensor according to Modification 2 of the first embodiment. FIG. [Figure 14] 13 is a bottom view illustrating a strain element and a strain gauge of the pressing force sensor according to Modification 3 of the first embodiment. FIG. [Figure 15] 13 is a bottom view illustrating a strain element and a strain gauge of the pressing force sensor according to Modification 4 of the first embodiment. FIG. [Figure 16] 13 is a bottom view illustrating a strain element and a strain gauge of the pressing force sensor according to Modification 5 of the first embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] First embodiment FIG. 1 is a perspective view illustrating the pressing force sensor according to the first embodiment. FIG. 2 is an exploded perspective view illustrating the pressing force sensor according to the first embodiment. FIG. 3 is a cross-sectional view illustrating the pressing force sensor according to the first embodiment, showing a vertical cross section along line AA in FIG. 1. FIG. 4 is a bottom view illustrating a state in which a back cover is removed from the pressing force sensor according to the first embodiment. FIG. 5 is a bottom view illustrating a strain generating body and a strain gauge of the pressing force sensor according to the first embodiment.

[0011] 1 to 5, a view of the object viewed from a first direction P indicated by an arrow is a plan view, and a view of the object viewed from the opposite direction to the first direction P is a bottom view. The first direction P is a direction perpendicular to a first surface 20a of a flexure body 20 described later. Viewing from the first direction P also includes a case where the object is viewed from a perspective.

[0012] 1 to 5, the pressing force sensor 1 has a housing 10, a strain generating body 20, and strain gauges 1001, 1002, 1003, and 1004. The pressing force sensor 1 may include a cable, a shielded cable, a flexible board, or the like, for inputting and outputting electrical signals from and to the outside. Alternatively, the pressing force sensor 1 may be configured to communicate with the outside by a method such as wireless communication without using a cable. Note that when there is no need to particularly distinguish between the strain gauges 1001, 1002, 1003, and 1004, they will be simply referred to as strain gauge 100.

[0013] The housing 10 has a cylindrical portion 11 and a back cover 12. The housing 10 is a portion that holds the strain element 20. The cylindrical portion 11 and the back cover 12 can be formed from, for example, metal, resin, or the like.

[0014] The cylindrical portion 11 has a first end surface 11a and a second end surface 11b that is the opposite surface to the first end surface 11a. The first end surface 11a and the second end surface 11b are, for example, parallel to each other. The first end surface 11a and the second end surface 11b have, for example, the same area. The outer edges of the first end surface 11a and the second end surface 11b are quadrangular when viewed from the first direction P. That is, the outer edges of the first end surface 11a and the second end surface 11b have four corners when viewed from the first direction P. The inner edges of the first end surface 11a and the second end surface 11b are quadrangular when viewed from the first direction P. That is, the inner edges of the first end surface 11a and the second end surface 11b have four corners when viewed from the first direction P.

[0015] The outer edges of the first end face 11a and the second end face 11b are, for example, squares. The inner edges of the first end face 11a and the second end face 11b are, for example, squares with one side shorter than the square that constitutes the outer edges. The first end face 11a and the second end face 11b are, for example, frame-shaped when viewed from the first direction P. The inner edges and outer edges of the first end face 11a and the second end face 11b may be quadrilaterals other than squares.

[0016] The outer edge of the first end face 11a and the outer edge of the second end face 11b are connected by four outer side faces. The inner edge of the first end face 11a and the inner edge of the second end face 11b are connected by four inner side faces. Each of the inner side faces and the outer side faces is a quadrangle. Each of the inner side faces and the outer side faces is, for example, a rectangle.

[0017] A back cover 12 is joined to the second end surface 11b. The second end surface 11b side of the cylindrical portion 11 is closed by the back cover 12. The second end surface 11b and the back cover 12 can be joined by, for example, an adhesive. The cylindrical portion 11 and the back cover 12 may be molded as a single unit. The back cover 12 can be provided as necessary. In other words, the case 10 does not need to have a back cover 12.

[0018] The flexure body 20 is flat. The flexure body 20 has a first surface 20a and a second surface 20b that is the surface opposite to the first surface 20a. The first surface 20a and the second surface 20b are, for example, parallel to each other. The first surface 20a and the second surface 20b have, for example, the same area. When viewed from the first direction P, the outer edge of the first end surface 11a and the first surface 20a have the same number of corners, which is an even number. Specifically, the flexure body 20 is quadrilateral when viewed from the first direction P. That is, the first surface 20a and the second surface 20b each have four corners when viewed from the first direction P.

[0019] The flexure body 20 may have a load portion 22 protruding from the first surface 20a at the center of the first surface 20a. The amount of protrusion of the load portion 22 with respect to the first surface 20a is, for example, about 0.1 mm. The flexure body 20 is flexible, and elastically deforms when a load is applied to the load portion 22. The thickness t of the flexure body 20 excluding the load portion 22 is constant. The thickness t of the flexure body 20 excluding the load portion 22 may be, for example, 0.03 mm or more and 0.3 mm or less.

[0020] The material of the flexure body 20 may be, for example, metal, ceramic, glass, etc. Examples of metals used as the material of the flexure body 20 include SUS (stainless steel), copper, aluminum, etc. The flexure body 20 may be formed, for example, by a press processing method or the like.

[0021] An outer edge portion of the second surface 20b of the flexure body 20 is joined to the first end surface 11a of the tubular portion 11. The first end surface 11a side of the tubular portion 11 is closed by the flexure body 20. The second surface 20b of the flexure body 20 and the first end surface 11a of the tubular portion 11 can be joined by, for example, an adhesive.

[0022] The outer edges of the first surface 20a and the second surface 20b of the flexure body 20 are located between the outer edge of the first end surface 11a of the tubular portion 11 and the inner edge of the first end surface 11a when viewed from the first direction P. The outer edges of the first surface 20a and the second surface 20b of the flexure body 20 may overlap with the outer edge of the first end surface 11a of the tubular portion 11 when viewed from the first direction P. The outer edge refers to the outermost edge of the target member, and the outer edge portion refers to a region with a certain width that includes the outer edge.

[0023] The strain gauge 100 is provided on the second surface 20b of the flexure body 20. Since the flexure body 20 is flat, the strain gauge 100 can be easily attached. In this embodiment, the pressing force sensor 1 has a pair of strain gauges 1001 and 1002 and another pair of strain gauges 1003 and 1004 on the second surface 20b of the flexure body 20.

[0024] A pair of strain gauges 1001 and 1002 are arranged on the outer periphery of the second surface 20b exposed inside the cylindrical portion 11, on any one diagonal line D of the second surface 20b, so as to face each other across the center of the second surface 20b when viewed from the first direction P. Here, the outer periphery of the second surface 20b refers to a region outside an imaginary circle C centered on the center of gravity of the second surface 20b. Also, the inner periphery of the second surface 20b refers to a region inside the imaginary circle C. The imaginary circle C is a circle having a diameter half the length of the diagonal line D. The length of the diagonal line D is, for example, about 13 mm or more and 17 mm or less.

[0025] As described below, the pair of strain gauges 1001 and 1002 each have a resistor 130 that serves as a sensing portion. In the strain gauges 1001 and 1002, it is preferable that at least a portion of each sensing portion contacts the diagonal line D.

[0026] The other pair of strain gauges 1003 and 1004 are disposed between the load portion 22 and the outer circumferential portion (i.e., between the load portion 22 and the imaginary circle C) of the second surface 20b exposed inside the tubular portion 11, as viewed from the first direction P, so as to face each other with the load portion 22 in between. In other words, the other pair of strain gauges 1003 and 1004 are disposed outside the load portion 22 in the inner circumferential portion of the second surface 20b, which is a region inside the imaginary circle C, as viewed from the first direction P.

[0027] Another pair of strain gauges 1003 and 1004 is disposed, for example, on a virtual line E perpendicular to the diagonal line D. In this embodiment, since the second surface 20b is a square, the virtual line E coincides with another diagonal line different from the diagonal line D.

[0028] The other pair of strain gauges 1003 and 1004 has a resistor 130 that serves as a sensitive portion, as described below. In the strain gauges 1003 and 1004, it is preferable that at least a portion of each sensitive portion contacts the imaginary line E.

[0029] The inventors performed a simulation of stress distribution for a circular flexure body with a diameter of 15 mm and a square flexure body with a diagonal length of 15 mm, assuming that the flexure body was joined to the end face of a cylindrical part of the same shape as the flexure body. Note that all conditions other than the shapes of the flexure body and the cylindrical part, such as the material and thickness of the flexure body, are the same.

[0030] As a result, it was found that when a pair of strain gauges is attached diagonally on the outer periphery of the second surface of a square flexure body, the stress is more concentrated and a higher strain can be obtained compared to when a pair of strain gauges is attached to the same position on a circular flexure body. Therefore, a structural analysis was performed to compare the sensitivity of both.

[0031] 6 is a diagram showing the results of comparing the sensitivity of a circular flexure body and a square flexure body. The square flexure body has the same shape as the flexure body 20 shown in FIGS. 1 to 5. The circular flexure body has a diameter the same length as the diagonal D, is the same thickness as the flexure body 20, and is made of the same material as the flexure body 20. The four strain gauges on the circular flexure body are attached in the same positions as the flexure body 20.

[0032] As shown in Fig. 6, when the sensitivity of a circular flexure body is taken as 100%, the sensitivity of a square flexure body is 115%. In other words, it was confirmed that the sensitivity was improved by 15% by using a square flexure body compared to the conventional case where a circular flexure body is used.

[0033] Fig. 7 is a diagram showing the results of comparing the areas of a circular and a square flexure body. As shown in Fig. 7, when the area of ​​the circular flexure body is taken as 100%, the area of ​​the square flexure body is 63.7%. In other words, by making the shape square, a highly sensitive flexure body with a small area can be realized compared to the conventional case where a circular flexure body is used. As a result, a small-sized and highly sensitive pressing force sensor can be realized.

[0034] It should be noted that the sensitivity is higher when the strain gauge is attached near the corner of a square as in FIG. 5 than when the strain gauge is attached between adjacent corners of the square.

[0035] In addition, when manufacturing the flexure body, many flexure bodies are made from a large metal plate, so by making the area of ​​the flexure body small, the number of flexure bodies that can be produced can be increased. As a result, the productivity of the flexure body can be improved and costs can be reduced. Simply making a circular flexure body with a small diameter in order to increase the number of flexure bodies that can be produced reduces sensitivity, but by making the flexure body rectangular, it is possible to obtain sufficient sensitivity while still reducing the size.

[0036] The pressing force sensor 1 is used, for example, as a vital sensor. When the pressing force sensor 1 is used as a vital sensor, it can detect, for example, pulse pressure, blood pressure, pulse rate, oxygen level, etc. When the pressing force sensor 1 is a pulse wave sensor that detects a pulse wave, which is a wave of pulse pressure, the pressing force sensor 1 is used by being fixed to the arm of a subject so that the load section 22 is in contact with the radial artery of the subject. When a load is applied to the load section 22 in accordance with the pulse wave of the subject and the strain body 20 is elastically deformed, the resistance value of the resistor of the strain gauge 100 changes.

[0037] The pressing force sensor 1 can detect a pulse wave based on a change in the resistance value of the resistor of the strain gauge 100 accompanying the deformation of the strain body 20. The pulse wave is output as a periodic change in voltage, for example, from a measurement circuit connected to the electrodes of the strain gauge 100. The strain gauges 1001 and 1002 on the outer periphery of the strain body 20 are distorted by receiving a compressive stress, and the strain gauges 1003 and 1004 on the inner periphery are distorted by receiving a tensile stress. Therefore, for example, a four-gauge method in which four strain gauges are fully bridge-connected as shown in FIG. 8 can be used to obtain a large output.

[0038] 8, strain gauges 1001, 1002, 1003, and 1004 are connected to form any one of the four sides of a bridge circuit. A DC voltage E is supplied between the connection part of strain gauge 1001 and strain gauge 1004 and the connection part of strain gauge 1003 and strain gauge 1002. As a result, an output voltage e0 can be obtained as the output of the bridge circuit from between the connection part of strain gauge 1001 and strain gauge 1003 and the connection part of strain gauge 1002 and strain gauge 1004.

[0039] The full bridge connection may be made inside or outside the cylindrical portion 11. If necessary, a wiring board for making the bridge connection may be disposed inside the cylindrical portion 11.

[0040] [Strain gauge 100] Fig. 9 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 10 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line BB in Fig. 9.

[0041] 9 and 10, the strain gauge 100 has a substrate 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. That is, the strain gauge 100 has the resistor 130 as a detection element. The cover layer 160 can be provided as necessary. For convenience, only the outer edge of the cover layer 160 is shown by a dashed line in FIG. 9 and FIG. 10. First, each part constituting the strain gauge 100 will be described in detail.

[0042] In the explanation of the strain gauge using Figs. 9 to 11, for convenience, the side of the base material 110 on which the resistor 130 is provided is referred to as the "upper side" of the strain gauge 100, and the side on which the resistor 130 is not provided is referred to as the "lower side". Also, the surface located on the upper side of each part is referred to as the "upper surface", and the surface located on the lower side of each part is referred to as the "lower surface". However, the strain gauge 100 can also be used upside down. Also, the strain gauge 100 can be arranged at any angle. Also, the planar view refers to viewing the object in a normal direction from the upper side to the lower side with respect to the upper surface 110a of the base material 110. And, the planar shape refers to the shape of the object when the object is viewed in the normal direction. The strain gauge 100 is attached to the second surface 20b of the strain gauge 20 so that the base material 110 faces the second surface 20b of the strain gauge 20.

[0043] The substrate 110 is a member that serves as a base layer for forming the resistor 130 and the like. The substrate 110 is flexible. There is no particular limitation on the thickness of the substrate 110, and it may be appropriately determined depending on the intended use of the strain gauge 100, etc. For example, the thickness of the substrate 110 may be about 5 μm to 500 μm. From the viewpoint of the transferability of strain from the second surface 20b of the strain generating body 20 to the sensing part and the dimensional stability against environmental changes, the thickness of the substrate 110 is preferably within the range of 5 μm to 200 μm. From the viewpoint of insulation, the thickness of the substrate 110 is preferably 10 μm or more.

[0044] The substrate 110 is formed from an insulating resin film such as, for example, PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a member having a thickness of about 500 μm or less and having flexibility.

[0045] When the base material 110 is formed from an insulating resin film, the insulating resin film may contain a filler, impurities, etc. For example, the base material 110 may be formed from an insulating resin film containing a filler such as silica or alumina.

[0046] Examples of materials other than resin for the base material 110 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3). In addition to the above-mentioned crystalline materials, amorphous glass or the like may be used as the material for the base material 110. Metals such as aluminum, aluminum alloy (duralumin), and titanium may also be used as the material for the base material 110. When a metal base material 110 is used, an insulating film is provided so as to cover the upper surface 110a.

[0047] The resistor 130 is a thin film formed in a predetermined pattern on the upper side of the substrate 110. In the strain gauge 100, the resistor 130 is a sensing part that receives strain and generates a resistance change. The resistor 130 may be formed directly on the upper surface 110a of the substrate 110, or may be formed on the upper surface 110a of the substrate 110 via another layer. For convenience, the resistor 130 is shown in FIG. 9 as a dense matte pattern.

[0048] The resistor 130 has a structure in which multiple elongated parts are arranged at regular intervals with their longitudinal direction in the same direction (the direction of the line BB in the example of FIG. 9), and the ends of adjacent elongated parts are alternately connected to form a zigzag fold as a whole. The longitudinal direction of the multiple elongated parts is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction perpendicular to the line BB in the example of FIG. 9).

[0049] One end in the longitudinal direction of the two elongated portions located at the outermost sides in the grid width direction is bent in the grid width direction to form terminal ends 130e1 and 130e2 of the resistor 130 in the grid width direction. The terminal ends 130e1 and 130e2 of the resistor 130 in the grid width direction are electrically connected to the electrode 150 via the wiring 140. In other words, the wiring 140 electrically connects the terminal ends 130e1 and 130e2 of the resistor 130 in the grid width direction to the electrodes 150.

[0050] The resistor 130 can be formed, for example, from a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 130 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0051] Here, the Cr mixed phase film is a film in which Cr, CrN, Cr2N, etc. are mixed. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0052] The thickness of the resistor 130 is not particularly limited and may be appropriately determined depending on the intended use of the strain gauge 100. For example, the thickness of the resistor 130 may be about 0.05 μm to 2 μm. In particular, when the thickness of the resistor 130 is 0.1 μm or more, the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr) is improved. Furthermore, when the thickness of the resistor 130 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 110 caused by the internal stress of the film constituting the resistor 130 are reduced.

[0053] Considering the need to prevent lateral sensitivity and to prevent disconnection, the width of resistor 130 is preferably 10 μm to 100 μm. More specifically, the width of resistor 130 is preferably 10 μm to 70 μm, and more preferably 10 μm to 50 μm.

[0054] For example, when the resistor 130 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha chromium) which is a stable crystal phase the main component. For example, when the resistor 130 is a Cr mixed-phase film, the resistor 130 can make α-Cr the main component, so that the gauge factor of the strain gauge 100 is 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be in the range of -1000 ppm / °C to +1000 ppm / °C. Here, the "main component" means a component that occupies 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving the gauge characteristics, the resistor 130 preferably contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, the resistor 130 more preferably contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0055] In addition, when the resistor 130 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr2N. By containing 20% ​​by weight or less of CrN and Cr2N in the Cr mixed-phase film, a decrease in the gauge factor of the strain gauge 100 can be suppressed.

[0056] In addition, the ratio of CrN and Cr2N in the Cr mixed phase film is preferably such that the ratio of Cr2N is 80% by weight or more and less than 90% by weight with respect to the total weight of CrN and Cr2N. More specifically, the ratio is more preferably such that the ratio of Cr2N is 90% by weight or more and less than 95% by weight with respect to the total weight of CrN and Cr2N. Cr2N has semiconductor properties. Therefore, by setting the ratio of Cr2N to 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant. Furthermore, by setting the ratio of Cr2N to 90% by weight or more and less than 95% by weight, the resistor 130 is less likely to become ceramic, and the resistor 130 is less likely to be brittle fractured.

[0057] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr mixed-phase film, the possibility of unstable N being generated can be reduced, resulting in a stable strain gauge. Here, "unstable N" refers to trace amounts of N2 or atomic N that may be present in the Cr mixed-phase film. This unstable N may escape to the outside of the film depending on the external environment (e.g., high-temperature environment). When unstable N escapes to the outside of the film, the film stress of the Cr mixed-phase film may change.

[0058] In the strain gauge 100, when a Cr mixed-phase film is used as the material of the resistor 130, it is possible to realize high sensitivity and miniaturization. For example, while the output of a conventional strain gauge was about 0.04 mV / 2 V, when a Cr mixed-phase film is used as the material of the resistor 130, an output of 0.3 mV / 2 V or more can be obtained. In addition, while the size (gauge length x gauge width) of a conventional strain gauge was about 3 mm x 3 mm, when a Cr mixed-phase film is used as the material of the resistor 130, the size (gauge length x gauge width) can be miniaturized to about 0.3 mm x 0.3 mm.

[0059] The wiring 140 is provided on the substrate 110. The wiring 140 is electrically connected to the resistor 130 and the electrode 150. The wiring 140 is not limited to being linear, and may be in any pattern. The wiring 140 may have any width and any length. For convenience, the wiring 140 is shown in FIG. 9 as having a matte pattern with a lower density than the resistor 130.

[0060] The electrodes 150 are provided on the substrate 110. The electrodes 150 are electrically connected to the resistor 130 via the wiring 140. The electrodes 150 are formed in a substantially rectangular shape wider than the wiring 140 in a plan view. The electrodes 150 are a pair of electrodes for outputting a change in the resistance value of the resistor 130 caused by distortion to the outside. For example, a lead wire for external connection is joined to the electrodes 150. A metal layer having low resistance such as copper or a metal layer having good solderability such as gold may be laminated on the upper surface of the electrode 150. Although the resistor 130, the wiring 140, and the electrode 150 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process. In FIG. 9, the electrodes 150 are shown with a matte pattern having the same density as the wiring 140 for convenience.

[0061] The cover layer 160 (protective layer) is provided on the upper surface 110a of the base material 110 as necessary so as to cover the resistor 130 and the wiring 140 and expose the electrodes 150. Examples of materials for the cover layer 160 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin, polyolefin resin). The cover layer 160 may contain a filler or a pigment. The thickness of the cover layer 160 is not particularly limited and can be appropriately selected depending on the purpose. For example, the thickness of the cover layer 160 can be about 2 μm to 30 μm. By providing the cover layer 160, it is possible to suppress mechanical damage and the like from occurring in the resistor 130. In addition, by providing the cover layer 160, it is possible to protect the resistor 130 from moisture and the like.

[0062] [Manufacturing method of strain gauge 100] In the strain gauge 100 according to this embodiment, a resistor 130, wiring 140, electrodes 150, and a cover layer 160 are formed on a substrate 110. Note that another layer (such as a functional layer described below) may be formed between the substrate 110 and the layers of these members.

[0063] A method for manufacturing the strain gauge 100 will be described below. To manufacture the strain gauge 100, first, a base material 110 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on an upper surface 110a of the base material 110. The metal layer A is a layer that is finally patterned to become the resistor 130, the wiring 140, and the electrodes 150. Therefore, the material and thickness of the metal layer A are the same as the material and thickness of the resistor 130, the wiring 140, and the electrodes 150 described above.

[0064] The metal layer A can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer A. Instead of magnetron sputtering, the metal layer A may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like. After the metal layer A is formed on the upper surface 110a of the base material 110, the metal layer A is patterned by a well-known photolithography method into a planar shape similar to that of the resistor 130, the wiring 140, and the electrode 150 in FIG. 9.

[0065] Alternatively, a base layer may be formed on the upper surface 110a of the base material 110, and then the metal layer A may be formed. For example, a functional layer of a predetermined thickness may be vacuum-formed by conventional sputtering on the upper surface 110a of the base material 110. By providing a base layer in this manner, the gauge characteristics of the strain gauge 100 can be stabilized.

[0066] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 130). The functional layer preferably further has a function of preventing oxidation of metal layer A due to oxygen or moisture contained in base material 110, and / or a function of improving adhesion between base material 110 and metal layer A. The functional layer may further have other functions.

[0067] The insulating resin film constituting the base material 110 may contain oxygen or moisture, and Cr may form a self-oxidized film. Therefore, particularly when the metal layer A contains Cr, it is preferable to form a functional layer having a function of preventing the oxidation of the metal layer A.

[0068] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth of the metal layer A, and to fabricate a metal layer A consisting of a stable crystal phase. As a result, the stability of the gauge characteristics of the strain gauge 100 is improved. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 100.

[0069] Examples of materials for the functional layer include one or more metals selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

[0070] 11 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG 11 shows the cross-sectional shape of the strain gauge 100 when a functional layer 120 is provided as an underlayer for the resistor 130, the wiring 140, and the electrodes 150.

[0071] The planar shape of the functional layer 120 may be patterned to be substantially the same as the planar shapes of the resistor 130, the wiring 140, and the electrode 150, for example. However, the planar shapes of the functional layer 120, the resistor 130, the wiring 140, and the electrode 150 may not be substantially the same. For example, when the functional layer 120 is formed from an insulating material, the functional layer 120 may be patterned to be different from the planar shapes of the resistor 130, the wiring 140, and the electrode 150. In this case, the functional layer 120 may be formed in a solid shape in the region where the resistor 130, the wiring 140, and the electrode 150 are formed, for example. Alternatively, the functional layer 120 may be formed in a solid shape on the entire upper surface of the substrate 110.

[0072] After forming the resistor 130, the wiring 140, and the electrodes 150, a cover layer 160 is formed on the upper surface 110a of the base material 110 as necessary. The cover layer 160 covers the resistor 130 and the wiring 140, but the electrodes 150 may be exposed from the cover layer 160. For example, the cover layer 160 can be formed by laminating a semi-cured thermosetting insulating resin film on the upper surface 110a of the base material 110 so as to cover the resistor 130 and the wiring 140 and expose the electrodes 150, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 100 is completed.

[0073] Modification of the First Embodiment In the modified example of the first embodiment, an example of a pressing force sensor in which the position of the strain gauge disposed on the inner periphery of the second surface of the flexure body and the shape of the flexure body are different from those in the first embodiment will be shown. Note that in the modified example of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0074] Fig. 12 is a bottom view illustrating a strain element and a strain gauge of a pressing force sensor according to Modification 1 of the first embodiment. Fig. 13 is a bottom view illustrating a strain element and a strain gauge of a pressing force sensor according to Modification 2 of the first embodiment.

[0075] 12 and 13, the positions of strain gauges 1003 and 1004 arranged on the inner periphery of the strain body 20 are different from those in Fig. 5. In Fig. 12, the strain gauges 1003 and 1004 are arranged at an angle of about 45 degrees with respect to the diagonal line D. In Fig. 13, in addition to the strain gauges 1001 and 1002, the strain gauges 1003 and 1004 are arranged on the diagonal line D.

[0076] In this way, the strain gauges 1003 and 1004 can be arranged at any position on the inner circumference of the flexure body 20. In both cases of Fig. 12 and Fig. 13, the flexure body 20 is rectangular, and a pair of strain gauges is attached on the diagonal line D and on the outer circumference of the second surface 20b. Therefore, compared with the case where a pair of strain gauges is attached at the same position on a circular flexure body, stress is more concentrated and a high strain can be obtained. As a result, compared with the conventional circular flexure body, a flexure body with a small area and high sensitivity can be realized. And a small and highly sensitive pressing force sensor can be realized. Of course, the strain gauges 1003 and 1004 may be arranged at positions other than those in Fig. 12 and Fig. 13 as long as they are on the inner circumference of the flexure body 20.

[0077] When a strain gauge is attached to a flexure body, the stiffness of the flexure body increases due to the thickness of the attached strain gauge, making the flexure body less likely to deform. For example, when four strain gauges are arranged on one diagonal line as in Fig. 13, the stiffness of the flexure body increases to a large extent, and the sensitivity is likely to decrease. Therefore, from the viewpoint of suppressing the decrease in sensitivity, the arrangement of strain gauges 1003 and 1004 in Fig. 12 is more preferable than that in Fig. 13, and Fig. 5, in which the four strain gauges are most dispersedly arranged, is most preferable.

[0078] Fig. 14 is a bottom view illustrating the strain gauge and strain gauge of the pressing force sensor according to the third modified example of the first embodiment. As shown in Fig. 14, the strain gauges 1003 and 1004 do not need to be arranged. In this case, the pressing force can be detected by the two-gauge method using the strain gauges 1001 and 1002. However, the output is reduced compared to the case of using the four-gauge method.

[0079] Fig. 15 is a bottom view illustrating a strain element and a strain gauge of a pressing force sensor according to Modification 4 of the first embodiment. Fig. 16 is a bottom view illustrating a strain element and a strain gauge of a pressing force sensor according to Modification 5 of the first embodiment.

[0080] 15 and 16, the shape of the flexure body is different from that of Fig. 5. In Fig. 15, the flexure body 20 is a regular hexagon when viewed from the first direction P, and four strain gauges are attached to the second surface 20b of the regular hexagonal flexure body 20 at the same positions as in Fig. 5. In Fig. 16, the flexure body 20 is a regular octagon when viewed from the first direction P, and four strain gauges are attached to the second surface 20b of the regular octagonal flexure body 20 at the same positions as in Fig. 5.

[0081] In this way, the flexure body 20 may be an even-numbered polygon other than a rectangle. In both cases of Fig. 15 and Fig. 16, the flexure body 20 is used by joining the outer edge of the end face to a cylindrical part having the same number of corners as the flexure body 20 when viewed from the first direction P. In both cases of Fig. 15 and Fig. 16, a pair of strain gauges is attached on the diagonal line D and on the outer periphery of the second surface 20b of the flexure body 20. Therefore, compared to the case where a pair of strain gauges is attached to the same position of a circular flexure body, stress is more concentrated and a high strain can be obtained. As a result, even in the case of an even-numbered polygon other than a rectangle, a flexure body with a small area and high sensitivity can be realized compared to the conventional circular flexure body. And, a small-sized and high-sensitivity pressing force sensor can be realized.

[0082] 15 and 16, the other pair of strain gauges 1003 and 1004 is preferably disposed on a virtual line E perpendicular to the diagonal line D. This makes it possible to suppress an increase in the stiffness of the strain element caused by the attachment of the strain gauges, and suppress a decrease in sensitivity, as described above. In the case of FIG. 16, the virtual line E coincides with another diagonal line different from the diagonal line D.

[0083] In addition, in an even-sided elastic body, the more the number of corners, the closer to a circle the body becomes. Therefore, the fewer the number of corners, the more it can contribute to a smaller area and higher sensitivity. In other words, from the viewpoint of a smaller area and higher sensitivity, a hexagonal shape is more preferable than an octagonal shape for the elastic body, and a square shape is the most suitable shape.

[0084] In addition, the even polygon shape of the flexure body is not limited to a regular even polygon. For example, a rectangular flexure body can be realized with a small area and high sensitivity compared to the conventional circular flexure body. As a result, a small and highly sensitive pressing force sensor can be realized.

[0085] Although preferred embodiments have been described above in detail, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0086] 1 pressing force sensor, 10 housing, 11 cylindrical portion, 11a first end surface, 11b second end surface, 12 back cover, 20 strain body, 20a first surface, 20b second surface, 22 load portion, 100, 1001, 1002, 1003, 1004 strain gauge, 110 substrate, 110a upper surface, 130 resistor, 140 wiring, 150 electrode, 160 cover layer, 130e1, 130e2 termination

Claims

1. a housing having a cylindrical portion with a first end surface; a strain generating body having a first surface and a second surface opposite to the first surface; a pair of strain gauges; When viewed from a first direction perpendicular to the first surface, an outer edge of the first end surface and the first surface have the same number of corners, which is an even number; the second surface is bonded to the first end surface, A pressure sensor in which a pair of the strain gauges are arranged on the outer periphery of the second surface exposed within the cylindrical portion, on any one diagonal line of the second surface, facing each other across the center of the second surface when viewed from the first direction.

2. The pressing force sensor according to claim 1 , wherein each of the pair of strain gauges has a sensitive portion, and at least a portion of each sensitive portion is in contact with the diagonal line.

3. The pressing force sensor according to claim 1 , wherein a load portion protruding from the first surface is provided at the center of the first surface.

4. The pressing force sensor according to claim 3, wherein another pair of strain gauges is arranged on the second surface between the load portion and the outer peripheral portion, when viewed from the first direction, so as to face each other across the load portion.

5. The pressing force sensor according to claim 4 , wherein the other pair of strain gauges are arranged on an imaginary line perpendicular to the diagonal line.

6. The pressing force sensor according to claim 5 , wherein each of the other pair of strain gauges has a sensitive portion, and at least a portion of each sensitive portion is in contact with the imaginary line.

7. The pressing force sensor according to claim 4 , wherein one pair of the strain gauges and another pair of the strain gauges are connected to form a full bridge circuit.

8. The pressing force sensor according to claim 1 , wherein the strain element is quadrangular when viewed from the first direction.

9. The pressing force sensor according to claim 1 , which is used as a vital sensor.

10. The pressure sensor according to claim 9 , wherein the vital sensor is a pulse wave sensor.

Images